<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-06-17</periodOfReport>

    <issuer>
        <issuerCik>0001227025</issuerCik>
        <issuerName>NEOPHOTONICS CORP</issuerName>
        <issuerTradingSymbol>NPTN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001183755</rptOwnerCik>
            <rptOwnerName>CARANO BANDEL L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O OAK INVESTMENT PARTNERS</rptOwnerStreet1>
            <rptOwnerStreet2>901 MAIN AVENUE, SUITE 600</rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001131676</rptOwnerCik>
            <rptOwnerName>OAK INVESTMENT PARTNERS X LTD PARTNERSHIP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE. 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001143824</rptOwnerCik>
            <rptOwnerName>OAK X AFFILIATES FUND LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001095761</rptOwnerCik>
            <rptOwnerName>OAK INVESTMENT PARTNERS IX L P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE. 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001112201</rptOwnerCik>
            <rptOwnerName>OAK IX AFFILIATES FUND LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001112125</rptOwnerCik>
            <rptOwnerName>OAK IX AFFILIATES FUND A LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001299239</rptOwnerCik>
            <rptOwnerName>Oak Investment Partners XI L P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>901 MAIN AVENUE, SUITE. 600</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NORWALK</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06851</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.75</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-06-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7407</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2021-06-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7407</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7407</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The option shall vest ratably at a rate of 1/24th of the total number of shares granted on each monthly anniversary of the grant date, so long as the optionee remains a member of the Board of Directors of the Company.</footnote>
        <footnote id="F2">This option was issued pursuant to the 2010 Equity Incentive Plan and in accordance with the Company's Non-Employee Director Compensation Policy.</footnote>
        <footnote id="F3">Includes Director Option to purchase 4,697 shares of Common Stock, which is held by Mr. Carano on behalf of Oak Investment Partners IX, Limited Partnership (&quot;Oak IX, L.P.&quot;); Director Option to purchase 50 shares of Common Stock, which is held by Mr. Carano on behalf of Oak IX Affiliates Fund, Limited Partnership (&quot;Oak IX Affiliates, L.P.&quot;); Director Option to purchase 113 shares of Common Stock, which is held by Mr. Carano on behalf of Oak IX Affiliates Fund-A, Limited Partnership (&quot;Oak IX Affiliates-A, L.P.&quot;); 1,912 shares of Common Stock, which is held by Mr. Carano on behalf of Oak Investment Partners X, Limited Partnership (&quot;Oak X, L.P.&quot;); Director Option to purchase 31 shares of Common Stock, which is held by Mr. Carano on behalf of Oak X Affiliates Fund, Limited Partnership (&quot;Oak X Affiliates, L.P.&quot;); and 604 shares of Common Stock, which is held by Mr. Carano on behalf of Oak Investment Partners XI, Limited Partnership (&quot;Oak XI, L.P.&quot;).</footnote>
    </footnotes>

    <remarks>Remarks

Bandel L. Carano is a Director NeoPhotonics Corporation.  Mr. Carano is a Managing Member of Oak Associates IX, L.L.C., the General Partner of Oak IX, L.P.; a Managing Member of Oak IX Affiliates, L.L.C., the General Partner of Oak IX Affiliates, L.P. and Oak IX Affiliates-A, L.P.; Oak Associates X, L.L.C., the General Partner of Oak X, L.P.; a Managing Member of Oak X Affiliates, L.L.C., the General Partner of Oak X Affiliates, L.P.; and Oak Associates XI, L.L.C., the General Partner of Oak XI, L.P.
Each Reporting Person disclaims the existence of a &quot;group&quot; and disclaims beneficial ownership of any securities (except to the extent of such Reporting Person's pecuniary interest in such securities) other than any securities reported herein as being directly owned by such Reporting Person, and this report shall not be deemed an admission that such Reporting Person is the beneficial owner of any such securities for purposes of Section 16 or for any other purpose.</remarks>

    <ownerSignature>
        <signatureName>Bandel L. Carano</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak Associates X, L.L.C., the General Partner of Oak Investment Partners X, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak X Affiliates, L.L.C., the General Partner of Oak X Affiliates Fund, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak Associates IX, L.L.C., the General Partner of Oak Investment Partners IX, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak IX Affiliates, L.L.C., the General Partner of Oak IX Affiliates Fund, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak IX Affiliates, L.L.C., the General Partner of Oak IX Affiliates Fund-A, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Bandel L. Carano, Managing Member of Oak Associates XI, L.L.C., the General Partner of Oak Investment Partners XI, Limited Partnership</signatureName>
        <signatureDate>2011-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
