Second harmonic generation and sum frequency generation (SHG and SFG) provide effective means to realize coherent light at desired frequencies when lasing is not easily
achievable. They have found applications from sensing to quantum optics and are of
particular interest for integrated photonics at communication wavelengths. Decreasing the
footprints of nonlinear components while maintaining their high up-conversion efficiency
remains a challenge in the miniaturization of integrated photonics. Here we explore
lithographically defined AlGaInP nano (micro)structures/ Al2O3/Ag as a versatile platform
to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both
narrow- and broadband infrared (IR) wavelength regimes (1300–1600nm). The effective
excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows
efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113nm×250nm, with a mode area on the deep subwavelength scale (λ2/135) at fundamental wavelengths.
Remarkably, we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides. This together with mode analysis highlights the origin of the improved
SHG/SFG efficiency. We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1µm diameter AlGaInP disks/Al2O3/Ag with a conversion efficiency of 14.8%MW−1 which is five times the SHG value using the narrowband IR source. In both configurations, the hybrid plasmonic structures exhibit >1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts. Our results manifest the potential of developing suchnanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications