<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
    <!-- Field: Doc-Info; Name: Generator; Value: GoFiler Complete; Version: 4.15b -->
    <!-- Field: Doc-Info; Name: VendorURI; Value: http://www.novaworks.co -->
    <!-- Field: Doc-Info; Name: Source; Value: appliedopto_10q%2D20160930.xfr; Date: 2016%2D11%2D08T17:48:24Z -->
    <!-- Field: Doc-Info; Name: Status; Value: 0x00000000 -->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrli="http://www.xbrl.org/2003/instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
    <link:roleRef roleURI="http://ao-inc.com/role/DocumentAndEntityInformation" xlink:href="aaoi-20160930.xsd#DocumentAndEntityInformation" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedBalanceSheets" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedBalanceSheets" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedStatementsOfOperations" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedStatementsOfOperations" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedStatementsOfStockholdersEquityDeficit" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedStatementsOfStockholdersEquityDeficit" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:href="aaoi-20160930.xsd#CondensedConsolidatedStatementsOfCashFlows" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/DescriptionOfBusiness" xlink:href="aaoi-20160930.xsd#DescriptionOfBusiness" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/SignificantAccountingPolicies" xlink:href="aaoi-20160930.xsd#SignificantAccountingPolicies" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/FairValueOfFinancialInstruments" xlink:href="aaoi-20160930.xsd#FairValueOfFinancialInstruments" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/EarningsPerShare" xlink:href="aaoi-20160930.xsd#EarningsPerShare" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Inventories" xlink:href="aaoi-20160930.xsd#Inventories" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/PropertyPlantAndEquipment" xlink:href="aaoi-20160930.xsd#PropertyPlantAndEquipment" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/IntangibleAssets" xlink:href="aaoi-20160930.xsd#IntangibleAssets" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/NotesPayableAndLong-termDebt" xlink:href="aaoi-20160930.xsd#NotesPayableAndLong-termDebt" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/AccruedLiabilites" xlink:href="aaoi-20160930.xsd#AccruedLiabilites" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/OtherIncomeAndExpense" xlink:href="aaoi-20160930.xsd#OtherIncomeAndExpense" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensation" xlink:href="aaoi-20160930.xsd#Share-basedCompensation" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/StockholdersEquity" xlink:href="aaoi-20160930.xsd#StockholdersEquity" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/GeographicInformation" xlink:href="aaoi-20160930.xsd#GeographicInformation" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/SubsequentEvents" xlink:href="aaoi-20160930.xsd#SubsequentEvents" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/DescriptionOfBusinessPolicies" xlink:href="aaoi-20160930.xsd#DescriptionOfBusinessPolicies" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/SignificantAccountingPoliciesPolicies" xlink:href="aaoi-20160930.xsd#SignificantAccountingPoliciesPolicies" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/FairValueOfFinancialInstrumentsTables" xlink:href="aaoi-20160930.xsd#FairValueOfFinancialInstrumentsTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/EarningsPerShareTables" xlink:href="aaoi-20160930.xsd#EarningsPerShareTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/InventoriesTables" xlink:href="aaoi-20160930.xsd#InventoriesTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/PropertyPlantAndEquipmentTables" xlink:href="aaoi-20160930.xsd#PropertyPlantAndEquipmentTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/IntangibleAssetsTables" xlink:href="aaoi-20160930.xsd#IntangibleAssetsTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/NotesPayableAndLong-termDebtTables" xlink:href="aaoi-20160930.xsd#NotesPayableAndLong-termDebtTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/AccruedLiabilitesTables" xlink:href="aaoi-20160930.xsd#AccruedLiabilitesTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/OtherIncomeAndExpenseTables" xlink:href="aaoi-20160930.xsd#OtherIncomeAndExpenseTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensationTables" xlink:href="aaoi-20160930.xsd#Share-basedCompensationTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/GeographicInformationTables" xlink:href="aaoi-20160930.xsd#GeographicInformationTables" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/SignificantAccountingPoliciesDetailsNarrative" xlink:href="aaoi-20160930.xsd#SignificantAccountingPoliciesDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/FairValueOfFinancialInstrumentsDetails" xlink:href="aaoi-20160930.xsd#FairValueOfFinancialInstrumentsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/EarningsPerShareDetails-epsCalculation" xlink:href="aaoi-20160930.xsd#EarningsPerShareDetails-epsCalculation" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/EarningsPerShareDetailsNarrative" xlink:href="aaoi-20160930.xsd#EarningsPerShareDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/InventoriesDetails" xlink:href="aaoi-20160930.xsd#InventoriesDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/InventoryDetailsNarrative" xlink:href="aaoi-20160930.xsd#InventoryDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/PropertyPlantAndEquipmentDetails" xlink:href="aaoi-20160930.xsd#PropertyPlantAndEquipmentDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/PropertyPlantAndEquipmentDetailsNarrative" xlink:href="aaoi-20160930.xsd#PropertyPlantAndEquipmentDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/IntangibleAssetsDetails" xlink:href="aaoi-20160930.xsd#IntangibleAssetsDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/IntangibleAssetsDetailsNarrative" xlink:href="aaoi-20160930.xsd#IntangibleAssetsDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetails" xlink:href="aaoi-20160930.xsd#NotesPayableAndLong-termDebtDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetails-DebtMaturities" xlink:href="aaoi-20160930.xsd#NotesPayableAndLong-termDebtDetails-DebtMaturities" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetailsNarrative" xlink:href="aaoi-20160930.xsd#NotesPayableAndLong-termDebtDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/AccruedLiabilitiesDetails" xlink:href="aaoi-20160930.xsd#AccruedLiabilitiesDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/OtherIncomeAndExpenseDetails" xlink:href="aaoi-20160930.xsd#OtherIncomeAndExpenseDetails" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/OtherIncomeAndExpenseDetailsNarrative" xlink:href="aaoi-20160930.xsd#OtherIncomeAndExpenseDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensationDetails-optionActivity" xlink:href="aaoi-20160930.xsd#Share-basedCompensationDetails-optionActivity" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensationDetails-restrictedStockUnits" xlink:href="aaoi-20160930.xsd#Share-basedCompensationDetails-restrictedStockUnits" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensationDetails-shareBasedCompensationExpense" xlink:href="aaoi-20160930.xsd#Share-basedCompensationDetails-shareBasedCompensationExpense" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/Share-basedCompensationDetailsNarrative" xlink:href="aaoi-20160930.xsd#Share-basedCompensationDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/StockholdersEquityDetailsNarrative" xlink:href="aaoi-20160930.xsd#StockholdersEquityDetailsNarrative" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/GeographicInformationDetails-Revenues" xlink:href="aaoi-20160930.xsd#GeographicInformationDetails-Revenues" xlink:type="simple" />
    <link:roleRef roleURI="http://ao-inc.com/role/GeographicInformationDetails-LongLivedAssets" xlink:href="aaoi-20160930.xsd#GeographicInformationDetails-LongLivedAssets" xlink:type="simple" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/DocumentAndEntityInformation" xlink:title="00000001 - Document - Document and Entity Information" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedBalanceSheets" xlink:title="00000002 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:title="00000003 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedStatementsOfOperations" xlink:title="00000004 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedStatementsOfComprehensiveIncomeLoss" xlink:title="00000005 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedStatementsOfStockholdersEquityDeficit" xlink:title="00000006 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaapAdditionalPaidInCapitalMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapAdditionalPaidInCapitalMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComprehensiveIncomeMember" xlink:label="loc_us-gaapComprehensiveIncomeMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapComprehensiveIncomeMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaapRetainedEarningsMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapRetainedEarningsMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharesOutstanding" xlink:label="loc_us-gaapSharesOutstanding_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharesOutstanding_60" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaapStockholdersEquity_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquity_60" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_60" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueStockOptionsExercised_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueStockOptionsExercised_60" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesShareBasedCompensation_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesShareBasedCompensation_60" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_60" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax" xlink:label="loc_us-gaapOtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax_60" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax" xlink:label="loc_us-gaapOtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossBeforeReclassificationAndTax_60" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss_60" xlink:type="arc" order="9" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:title="00000007 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/DescriptionOfBusiness" xlink:title="00000008 - Disclosure - 1. Description of Business" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/SignificantAccountingPolicies" xlink:title="00000009 - Disclosure - 2. Significant Accounting Policies" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/FairValueOfFinancialInstruments" xlink:title="00000010 - Disclosure - 3. Fair Value of Financial Instruments" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/EarningsPerShare" xlink:title="00000011 - Disclosure - 4. Earnings Per Share" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Inventories" xlink:title="00000012 - Disclosure - 5. Inventories" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/PropertyPlantAndEquipment" xlink:title="00000013 - Disclosure - 6. Property, Plant and Equipment" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/IntangibleAssets" xlink:title="00000014 - Disclosure - 7. Intangible Assets" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/NotesPayableAndLong-termDebt" xlink:title="00000015 - Disclosure - 8. Notes Payable and Long-Term Debt" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/AccruedLiabilites" xlink:title="00000016 - Disclosure - 9. Accrued Liabilites" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/OtherIncomeAndExpense" xlink:title="00000017 - Disclosure - 10. Other Income and Expense" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensation" xlink:title="00000018 - Disclosure - 11. Share-Based Compensation" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/StockholdersEquity" xlink:title="00000019 - Disclosure - 12. Stockholders' Equity" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/GeographicInformation" xlink:title="00000020 - Disclosure - 13. Geographic Information" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/SubsequentEvents" xlink:title="00000021 - Disclosure - 14. Subsequent Events" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/DescriptionOfBusinessPolicies" xlink:title="00000022 - Disclosure - 1. Description of Business (Policies)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/SignificantAccountingPoliciesPolicies" xlink:title="00000023 - Disclosure - 2. Significant Accounting Policies (Policies)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/FairValueOfFinancialInstrumentsTables" xlink:title="00000024 - Disclosure - 3. Fair Value of Financial Instruments (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/EarningsPerShareTables" xlink:title="00000025 - Disclosure - 4. Earnings Per Share (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/InventoriesTables" xlink:title="00000026 - Disclosure - 5. Inventories (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/PropertyPlantAndEquipmentTables" xlink:title="00000027 - Disclosure - 6. Property, Plant and Equipment (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/IntangibleAssetsTables" xlink:title="00000028 - Disclosure - 7. Intangible Assets (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/NotesPayableAndLong-termDebtTables" xlink:title="00000029 - Disclosure - 8. Notes Payable and Long-Term Debt (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/AccruedLiabilitesTables" xlink:title="00000030 - Disclosure - 9. Accrued Liabilites (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/OtherIncomeAndExpenseTables" xlink:title="00000031 - Disclosure - 10. Other Income and Expense (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensationTables" xlink:title="00000032 - Disclosure - 11. Share-Based Compensation (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/GeographicInformationTables" xlink:title="00000033 - Disclosure - 13. Geographic Information (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/SignificantAccountingPoliciesDetailsNarrative" xlink:title="00000034 - Disclosure - 2. Significant Accounting Policies (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/FairValueOfFinancialInstrumentsDetails" xlink:title="00000035 - Disclosure - 3. Fair Value of Financial Instruments (Details)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaapFairValueByMeasurementFrequencyAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapFairValueByMeasurementFrequencyAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaapFairValueMeasurementFrequencyDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFairValueByMeasurementFrequencyAxis" xlink:to="loc_us-gaapFairValueMeasurementFrequencyDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaapFairValueMeasurementFrequencyDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFairValueByMeasurementFrequencyAxis" xlink:to="loc_us-gaapFairValueMeasurementFrequencyDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaapFairValueMeasurementsRecurringMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementFrequencyDomain" xlink:to="loc_us-gaapFairValueMeasurementsRecurringMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaapFairValueInputsLevel1Member_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel1Member_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaapFairValueInputsLevel2Member_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel2Member_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaapFairValueInputsLevel3Member_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel3Member_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaapAssetsAbstract_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAssetsAbstract_90" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:label="loc_us-gaapCashAndCashEquivalentsFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAssetsAbstract_90" xlink:to="loc_us-gaapCashAndCashEquivalentsFairValueDisclosure_90" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_RestrictedCashFairValueDisclosure" xlink:label="loc_AAOIRestrictedCashFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAssetsAbstract_90" xlink:to="loc_AAOIRestrictedCashFairValueDisclosure_90" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaapInvestmentsFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAssetsAbstract_90" xlink:to="loc_us-gaapInvestmentsFairValueDisclosure_90" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaapAssetsFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAssetsAbstract_90" xlink:to="loc_us-gaapAssetsFairValueDisclosure_90" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaapLiabilitiesAbstract_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLiabilitiesAbstract_90" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LoansPayableFairValueDisclosure" xlink:label="loc_us-gaapLoansPayableFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLiabilitiesAbstract_90" xlink:to="loc_us-gaapLoansPayableFairValueDisclosure_90" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure" xlink:label="loc_us-gaapLiabilitiesFairValueDisclosure_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLiabilitiesAbstract_90" xlink:to="loc_us-gaapLiabilitiesFairValueDisclosure_90" xlink:type="arc" order="8" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/EarningsPerShareDetails-epsCalculation" xlink:title="00000036 - Disclosure - 4. Earnings Per Share (Details-EPS calculation)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/EarningsPerShareDetailsNarrative" xlink:title="00000037 - Disclosure - 4. Earnings Per Share (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/InventoriesDetails" xlink:title="00000038 - Disclosure - 5. Inventories (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/InventoryDetailsNarrative" xlink:title="00000039 - Disclosure - 5. Inventory (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/PropertyPlantAndEquipmentDetails" xlink:title="00000040 - Disclosure - 6. Property, Plant and Equipment (Details)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LandImprovementsMember" xlink:label="loc_us-gaapLandImprovementsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapLandImprovementsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:label="loc_us-gaapBuildingAndBuildingImprovementsMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapBuildingAndBuildingImprovementsMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MachineryAndEquipmentMember" xlink:label="loc_us-gaapMachineryAndEquipmentMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapMachineryAndEquipmentMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaapFurnitureAndFixturesMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapFurnitureAndFixturesMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaapComputerEquipmentMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapComputerEquipmentMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransportationEquipmentMember" xlink:label="loc_us-gaapTransportationEquipmentMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_us-gaapTransportationEquipmentMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaapPropertyPlantAndEquipmentGross_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentGross_150" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaapAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_150" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentOther" xlink:label="loc_us-gaapPropertyPlantAndEquipmentOther_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentOther_150" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConstructionInProgressGross" xlink:label="loc_us-gaapConstructionInProgressGross_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapConstructionInProgressGross_150" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Land" xlink:label="loc_us-gaapLand_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLand_150" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaapPropertyPlantAndEquipmentNet_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentNet_150" xlink:type="arc" order="6" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/PropertyPlantAndEquipmentDetailsNarrative" xlink:title="00000041 - Disclosure - 6. Property, Plant and Equipment (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/IntangibleAssetsDetails" xlink:title="00000042 - Disclosure - 7. Intangible Assets (Details)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaapPatentsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapPatentsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaapTrademarksMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapTrademarksMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsGross_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsGross_70" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsAccumulatedAmortization_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsAccumulatedAmortization_70" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaapIntangibleAssetsNetExcludingGoodwill_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapIntangibleAssetsNetExcludingGoodwill_70" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/IntangibleAssetsDetailsNarrative" xlink:title="00000043 - Disclosure - 7. Intangible Assets (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetails" xlink:title="00000044 - Disclosure - 8. Notes Payable and Long-Term Debt (Details)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaapDebtInstrumentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapDebtInstrumentAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditMember" xlink:label="loc_us-gaapLineOfCreditMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_us-gaapLineOfCreditMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaapCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapCreditFacilityAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving1Member" xlink:label="loc_AAOIRevolving1Member_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving1Member_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ConstructionLoanMember" xlink:label="loc_AAOIConstructionLoanMember_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIConstructionLoanMember_110" xlink:type="arc" order="111" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving2Member" xlink:label="loc_AAOIRevolving2Member_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving2Member_140" xlink:type="arc" order="142" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving3Member" xlink:label="loc_AAOIRevolving3Member_170" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving3Member_170" xlink:type="arc" order="172" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving4Member" xlink:label="loc_AAOIRevolving4Member_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving4Member_200" xlink:type="arc" order="202" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving5Member" xlink:label="loc_AAOIRevolving5Member_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving5Member_230" xlink:type="arc" order="232" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_Revolving6Member" xlink:label="loc_AAOIRevolving6Member_320" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolving6Member_320" xlink:type="arc" order="322" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaapLongtermDebtTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapLongtermDebtTypeAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_TermLoan1Member" xlink:label="loc_AAOITermLoan1Member_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOITermLoan1Member_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_TermLoan2Member" xlink:label="loc_AAOITermLoan2Member_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOITermLoan2Member_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_NotePayable1Member" xlink:label="loc_AAOINotePayable1Member_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOINotePayable1Member_260" xlink:type="arc" order="261" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_NotePayable2Member" xlink:label="loc_AAOINotePayable2Member_290" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOINotePayable2Member_290" xlink:type="arc" order="291" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermNotesAndLoans" xlink:label="loc_us-gaapLongTermNotesAndLoans_360" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLongTermNotesAndLoans_360" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaapLongTermDebtCurrent_360" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLongTermDebtCurrent_360" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="loc_us-gaapLongTermDebtNoncurrent_360" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLongTermDebtNoncurrent_360" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaapDebtInstrumentMaturityDate_360" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentMaturityDate_360" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateTerms" xlink:label="loc_us-gaapDebtInstrumentInterestRateTerms_360" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentInterestRateTerms_360" xlink:type="arc" order="6" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetails-DebtMaturities" xlink:title="00000045 - Disclosure - 8. Notes Payable and Long-Term Debt (Details - Debt maturities)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/NotesPayableAndLong-termDebtDetailsNarrative" xlink:title="00000046 - Disclosure - 8. Notes Payable and Long-Term Debt (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaapLineOfCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapLineOfCreditFacilityAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaapLineOfCreditFacilityLenderDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLineOfCreditFacilityAxis" xlink:to="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaapLineOfCreditFacilityLenderDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLineOfCreditFacilityAxis" xlink:to="loc_us-gaapLineOfCreditFacilityLenderDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_EastWestComericaMember" xlink:label="loc_AAOIEastWestComericaMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOIEastWestComericaMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_EastWestBankMember" xlink:label="loc_AAOIEastWestBankMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOIEastWestBankMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_CTBCBankTaipeiMember" xlink:label="loc_AAOICTBCBankTaipeiMember_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOICTBCBankTaipeiMember_110" xlink:type="arc" order="111" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ESunCommercialBankTaiwanMember" xlink:label="loc_AAOIESunCommercialBankTaiwanMember_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOIESunCommercialBankTaiwanMember_140" xlink:type="arc" order="141" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_MegaInternationalCommercialBankTaiwanMember" xlink:label="loc_AAOIMegaInternationalCommercialBankTaiwanMember_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOIMegaInternationalCommercialBankTaiwanMember_200" xlink:type="arc" order="201" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ChinaConstructionBankMember" xlink:label="loc_AAOIChinaConstructionBankMember_300" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLineOfCreditFacilityLenderDomain" xlink:to="loc_AAOIChinaConstructionBankMember_300" xlink:type="arc" order="301" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaapCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapCreditFacilityAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_RevolvingLinesOfCreditMember" xlink:label="loc_AAOIRevolvingLinesOfCreditMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIRevolvingLinesOfCreditMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_TermLoanMember" xlink:label="loc_AAOITermLoanMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOITermLoanMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_EquipmentLoanMember" xlink:label="loc_AAOIEquipmentLoanMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIEquipmentLoanMember_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ConstructionLoanMember" xlink:label="loc_AAOIConstructionLoanMember_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIConstructionLoanMember_90" xlink:type="arc" order="92" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_CreditFacility1Member" xlink:label="loc_AAOICreditFacility1Member_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOICreditFacility1Member_140" xlink:type="arc" order="142" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_CreditFacility2Member" xlink:label="loc_AAOICreditFacility2Member_170" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOICreditFacility2Member_170" xlink:type="arc" order="172" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ComprehensiveCreditLineAgreementMember" xlink:label="loc_AAOIComprehensiveCreditLineAgreementMember_240" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_AAOIComprehensiveCreditLineAgreementMember_240" xlink:type="arc" order="241" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CurrencyAxis" xlink:label="loc_us-gaapCurrencyAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapCurrencyAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_AllCurrenciesDomain" xlink:label="loc_currencyAllCurrenciesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCurrencyAxis" xlink:to="loc_currencyAllCurrenciesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_AllCurrenciesDomain" xlink:label="loc_currencyAllCurrenciesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCurrencyAxis" xlink:to="loc_currencyAllCurrenciesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_TWD" xlink:label="loc_currencyTWD_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currencyAllCurrenciesDomain" xlink:to="loc_currencyTWD_120" xlink:type="arc" order="122" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionTypeAxis" xlink:label="loc_us-gaapTransactionTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapTransactionTypeAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionDomain" xlink:label="loc_us-gaapTransactionDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTransactionTypeAxis" xlink:to="loc_us-gaapTransactionDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionDomain" xlink:label="loc_us-gaapTransactionDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTransactionTypeAxis" xlink:to="loc_us-gaapTransactionDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_CreditFacility1Member" xlink:label="loc_AAOICreditFacility1Member_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapTransactionDomain" xlink:to="loc_AAOICreditFacility1Member_200" xlink:type="arc" order="202" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaapCounterpartyNameAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapCounterpartyNameAxis" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaapRepurchaseAgreementCounterpartyNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCounterpartyNameAxis" xlink:to="loc_us-gaapRepurchaseAgreementCounterpartyNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaapRepurchaseAgreementCounterpartyNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCounterpartyNameAxis" xlink:to="loc_us-gaapRepurchaseAgreementCounterpartyNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ChaileaseMember" xlink:label="loc_AAOIChaileaseMember_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRepurchaseAgreementCounterpartyNameDomain" xlink:to="loc_AAOIChaileaseMember_260" xlink:type="arc" order="261" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaapLongtermDebtTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapLongtermDebtTypeAxis" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_FinanceLease1Member" xlink:label="loc_AAOIFinanceLease1Member_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOIFinanceLease1Member_260" xlink:type="arc" order="262" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_FinanceLease2Member" xlink:label="loc_AAOIFinanceLease2Member_280" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_AAOIFinanceLease2Member_280" xlink:type="arc" order="282" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="loc_us-gaapVariableRateAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapVariableRateAxis" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaapVariableRateDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapVariableRateAxis" xlink:to="loc_us-gaapVariableRateDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="loc_us-gaapVariableRateDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapVariableRateAxis" xlink:to="loc_us-gaapVariableRateDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:label="loc_us-gaapLondonInterbankOfferedRateLIBORMember_330" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapVariableRateDomain" xlink:to="loc_us-gaapLondonInterbankOfferedRateLIBORMember_330" xlink:type="arc" order="331" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentIssuanceDate1" xlink:label="loc_us-gaapDebtInstrumentIssuanceDate1_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentIssuanceDate1_350" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:label="loc_us-gaapDebtInstrumentDescriptionOfVariableRateBasis_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentDescriptionOfVariableRateBasis_350" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaapLineOfCreditFacilityMaximumBorrowingCapacity_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityMaximumBorrowingCapacity_350" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCredit" xlink:label="loc_us-gaapLineOfCredit_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLineOfCredit_350" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_CashRestrictedForConstructionInProgressFairValue" xlink:label="loc_AAOICashRestrictedForConstructionInProgressFairValue_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOICashRestrictedForConstructionInProgressFairValue_350" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="loc_us-gaapLineOfCreditFacilityExpirationDate1_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityExpirationDate1_350" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityInterestRateDescription" xlink:label="loc_us-gaapLineOfCreditFacilityInterestRateDescription_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityInterestRateDescription_350" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaapLongTermDebt_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLongTermDebt_350" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount" xlink:label="loc_us-gaapDebtInstrumentUnusedBorrowingCapacityAmount_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentUnusedBorrowingCapacityAmount_350" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BankAcceptancesExecutedAndOutstanding" xlink:label="loc_us-gaapBankAcceptancesExecutedAndOutstanding_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapBankAcceptancesExecutedAndOutstanding_350" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_RestrictedCashInvestmentsOrSecurityDepositAssociatedWithLoanFacilities" xlink:label="loc_AAOIRestrictedCashInvestmentsOrSecurityDepositAssociatedWithLoanFacilities_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOIRestrictedCashInvestmentsOrSecurityDepositAssociatedWithLoanFacilities_350" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaapDebtInstrumentInterestRateEffectivePercentage_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentInterestRateEffectivePercentage_350" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_GuaranteeDeposit" xlink:label="loc_AAOIGuaranteeDeposit_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOIGuaranteeDeposit_350" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentMaturityDateDescription" xlink:label="loc_us-gaapDebtInstrumentMaturityDateDescription_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentMaturityDateDescription_350" xlink:type="arc" order="16" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/AccruedLiabilitiesDetails" xlink:title="00000047 - Disclosure - 9. Accrued Liabilities (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/OtherIncomeAndExpenseDetails" xlink:title="00000048 - Disclosure - 10. Other Income and Expense (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/OtherIncomeAndExpenseDetailsNarrative" xlink:title="00000049 - Disclosure - 10. Other Income and Expense (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensationDetails-optionActivity" xlink:title="00000050 - Disclosure - 11. Share-Based Compensation (Details-Option activity)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_40" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_40" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_40" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_40" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_40" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_40" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_40" xlink:type="arc" order="19" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageSharePriceOnDateOfExercise" xlink:label="loc_AAOIWeightedAverageSharePriceOnDateOfExercise_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_AAOIWeightedAverageSharePriceOnDateOfExercise_40" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageFairValueAbstract" xlink:label="loc_AAOIWeightedAverageFairValueAbstract_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:type="arc" order="23" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="24" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="25" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExcerciseWeightedAverageGrantDateFairValue" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExcerciseWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExcerciseWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="26" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="27" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="28" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageFairValueVestedAndExpectedToVest" xlink:label="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIWeightedAverageFairValueAbstract_40" xlink:to="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest_40" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40" xlink:type="arc" order="33" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_40" xlink:type="arc" order="34" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_40" xlink:type="arc" order="35" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageRemainingContractualTerm1_40" xlink:type="arc" order="36" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_AggregateIntrinsicValueAbstract" xlink:label="loc_AAOIAggregateIntrinsicValueAbstract_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:type="arc" order="38" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_40" xlink:type="arc" order="39" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValueGranted" xlink:label="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValueGranted_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValueGranted_40" xlink:type="arc" order="40" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodTotalIntrinsicValue" xlink:label="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodTotalIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeitedInPeriodTotalIntrinsicValue_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpiredInPeriodTotalIntrinsicValue" xlink:label="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpiredInPeriodTotalIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpiredInPeriodTotalIntrinsicValue_40" xlink:type="arc" order="43" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_40" xlink:type="arc" order="45" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_40" xlink:type="arc" order="46" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensationDetails-restrictedStockUnits" xlink:title="00000051 - Disclosure - 11. Share-Based Compensation (Details-Restricted Stock Units)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_40" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExpirations" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExpirations_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExpirations_40" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue2" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue2_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue2_40" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageFairValueVestedAndExpectedToVest2" xlink:label="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest2_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest2_40" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageSharePriceOnDateOfRelease" xlink:label="loc_AAOIWeightedAverageSharePriceOnDateOfRelease_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_40" xlink:to="loc_AAOIWeightedAverageSharePriceOnDateOfRelease_40" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue1" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsExericsableWeightedAverageGrantDateFairValue1_40" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_WeightedAverageFairValueVestedAndExpectedToVest1" xlink:label="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_40" xlink:to="loc_AAOIWeightedAverageFairValueVestedAndExpectedToVest1_40" xlink:type="arc" order="19" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_AggregateIntrinsicValueAbstract" xlink:label="loc_AAOIAggregateIntrinsicValueAbstract_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding_40" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueGranted" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueGranted_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueGranted_40" xlink:type="arc" order="23" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueReleased" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueReleased_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueReleased_40" xlink:type="arc" order="24" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueCancelled" xlink:label="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueCancelled_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOISharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueCancelled_40" xlink:type="arc" order="25" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_AggregateIntrinsicValueOtherThanOptionsExercisable" xlink:label="loc_AAOIAggregateIntrinsicValueOtherThanOptionsExercisable_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOIAggregateIntrinsicValueOtherThanOptionsExercisable_40" xlink:type="arc" order="27" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue" xlink:label="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_AAOIAggregateIntrinsicValueAbstract_40" xlink:to="loc_AAOIShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedAndExpectedToVestExercisableAggregateIntrinsicValue_40" xlink:type="arc" order="28" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensationDetails-shareBasedCompensationExpense" xlink:title="00000052 - Disclosure - 11. Share-Based Compensation (Details-Share based compensation expense)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaapIncomeStatementLocationAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapIncomeStatementLocationAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaapCostOfSalesMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapCostOfSalesMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaapResearchAndDevelopmentExpenseMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapResearchAndDevelopmentExpenseMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaapSellingAndMarketingExpenseMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapSellingAndMarketingExpenseMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaapGeneralAndAdministrativeExpenseMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapGeneralAndAdministrativeExpenseMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaapShareBasedCompensation_290" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensation_290" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/Share-basedCompensationDetailsNarrative" xlink:title="00000053 - Disclosure - 11. Share-Based Compensation (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_50" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_50" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/StockholdersEquityDetailsNarrative" xlink:title="00000054 - Disclosure - 12. Stockholders Equity (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionTypeAxis" xlink:label="loc_us-gaapTransactionTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapTransactionTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionDomain" xlink:label="loc_us-gaapTransactionDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTransactionTypeAxis" xlink:to="loc_us-gaapTransactionDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TransactionDomain" xlink:label="loc_us-gaapTransactionDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTransactionTypeAxis" xlink:to="loc_us-gaapTransactionDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="aaoi-20160930.xsd#AAOI_ATMOfferingMember" xlink:label="loc_AAOIATMOfferingMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapTransactionDomain" xlink:to="loc_AAOIATMOfferingMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaapCommonStockSharesAuthorized_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockSharesAuthorized_50" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaapPreferredStockSharesAuthorized_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockSharesAuthorized_50" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_50" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueNewIssues_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueNewIssues_50" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaapSharePrice_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharePrice_50" xlink:type="arc" order="5" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/GeographicInformationDetails-Revenues" xlink:title="00000055 - Disclosure - 13. Geographic Information (Details - Revenues)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaapStatementGeographicalAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementGeographicalAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaapSegmentGeographicalDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementGeographicalAxis" xlink:to="loc_us-gaapSegmentGeographicalDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaapSegmentGeographicalDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementGeographicalAxis" xlink:to="loc_us-gaapSegmentGeographicalDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_US" xlink:label="loc_countryUS_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryUS_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_TW" xlink:label="loc_countryTW_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryTW_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_CN" xlink:label="loc_countryCN_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryCN_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueNet" xlink:label="loc_us-gaapSalesRevenueNet_170" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSalesRevenueNet_170" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://ao-inc.com/role/GeographicInformationDetails-LongLivedAssets" xlink:title="00000056 - Disclosure - 13. Geographic Information (Details - Long lived assets)">
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaapStatementGeographicalAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementGeographicalAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaapSegmentGeographicalDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementGeographicalAxis" xlink:to="loc_us-gaapSegmentGeographicalDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaapSegmentGeographicalDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementGeographicalAxis" xlink:to="loc_us-gaapSegmentGeographicalDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_US" xlink:label="loc_countryUS_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryUS_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_TW" xlink:label="loc_countryTW_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryTW_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_CN" xlink:label="loc_countryCN_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentGeographicalDomain" xlink:to="loc_countryCN_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncurrentAssets" xlink:label="loc_us-gaapNoncurrentAssets_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNoncurrentAssets_90" xlink:type="arc" order="1" />
    </link:definitionLink>
</link:linkbase>
