Vectorial Polarization‐Resolved Annular Plasmonic Antenna for Efficient Second Harmonic Generation and Near‐Infrared Upconverted Photodetection

Abstract A vectorial polarization–resolved annular plasmonic antenna (APA) is presented that enables efficient second harmonic generation (SHG) and polarization‐controlled upconverted photodetection based on a metallo‐dielectric configuration. The antenna consists of concentric nanoring slits patterned on a silver film and integrated with an exfoliated InSe flake. When illuminated by a radially polarized (RP) vector beam, surface plasmon polaritons (SPPs) are launched from the slit edges and converge at the antenna center, resulting in an ≈80‐fold local field enhancement. This field concentration facilitates strong SHG emission from the central InSe region, as clearly visualized by far‐field SHG spatial imaging. In contrast, no SPP focusing is observed under azimuthally polarized (AP) excitation. The InSe‐coupled annular antenna is futher manifested as an efficient vectorial polarization‐resolved photodetector, where the upconverted photocurrent exhibited a modulation ratio up to ≈10 3 between RP and AP excitation. These findings highlight a versatile plasmonic device architecture that couples vector beam control with near‐field light concentration and electrical readout, offering promising routes for multifunctional photonic applications in nonlinear optics, polarization‐resolved sensing, and optoelectronic switching.