Second harmonic generation of optical spin-orbit interactions in hybrid plasmonic nanocircuits.

The manipulation of nonlinear spin-orbit interaction at the nanoscale is crucial for advancing information processing in integrated nanophotonics. However, the weak spin-orbit interaction (SOI) in conventional waveguide materials significantly limits the efficiency of nonlinear optical processes. In this work, we design a hybrid plasmonic waveguide composed of a gold film and a Y-branch CdSe nanowire, which addresses the aforementioned limitations. The designed hybrid structure enables efficient directional emission of second-harmonic generation (SHG) via control of the polarization of the excitation light. The transversely emitted SHG can be visualized for directly imaging the SOI. Our work not only provides a way to enhances the efficiency of the nonlinear SOI but also a promising platform for further advances in integrated photonics and nonlinear optics.