Light　with　helical　phase　structures,　carrying　quantized　orbital　angular　momentum　(OAM),　has　many　applications　in　both　classical　and　quantum　optics,　such　as　high-capacity　optical　communications　and　quantum　information　processing.　Frequency　conversion　is　a　basic　technique　to　expand　the　frequency　range　of　the　fundamental　light.　The　frequency　conversion　of　OAM-carrying　light　gives　rise　to　new　physics　and　applications　such　as　up-conversion　detection　of　images　and　generation　of　high　dimensional　OAM　entanglements.　Quasi-phase　matching　(QPM)　nonlinear　crystals　are　good　candidates　for　frequency　conversion,　particularly　due　to　their　high-valued　effective　nonlinear　coefficients　and　no　walk-off　effect.　Here　we　report　the　first　experimental　second-harmonic　generation　(SHG)　of　an　OAM-carried　light　with　a　QPM　crystal,　where　a　UV　light　with　OAM　of　100.　is　generated.　OAM　conservation　is　verified　using　a　specially　designed　interferometer.　With　a　pump　beam　carrying　an　OAM　superposition　of　opposite　sign,　we　observe　interesting　interference　phenomena　in　the　SHG　light;　specifically,　a　photonics　gear-like　structure　is　obtained　that　gives　direct　evidence　of　OAM　conservation,　which　will　be　very　useful　for　ultra-sensitive　angular　measurements.　Besides,　we　also　develop　a　theory　to　reveal　the　underlying　physics　of　the　phenomena.　The　methods　and　theoretical　analysis　shown　here　are　also　applicable　to　other　frequency　conversion　processes,　such　as　sum　frequency　generation　and　difference-frequency　generation,　and　may　also　be　generalized　to　the　quantum　regime　for　single　photons.　(C)　2014　Optical　Society　of　America