Abstract
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 (1300–1600 nm). 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 113 nm × 250 nm, 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 1 µm 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 such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.
Highlights
The development of broadband and efficient optical frequency up-converters integrated with nanophotonics systems is highly desired for a range of applications, including biosensing[1], imaging[2,3], and photonic circuitry[4,5,6]
We show that efficient second harmonic generation (SHG)/sum frequency generation (SFG) (>1500 times that of bare waveguides on glass) can be realized in hybrid plasmonic waveguides via effective phase matching enabled by the excitation of higher-order modes in the waveguides
When input light is focused at the end of a waveguide, scattering of free-space photons at points of structural symmetry breaking allows for satisfaction of momentum conservation and excitation of the hybrid plasmonic transverse magnetic (TM) modes in the waveguide[12,36]
Summary
The development of broadband and efficient optical frequency up-converters integrated with nanophotonics systems is highly desired for a range of applications, including biosensing[1], imaging[2,3], and photonic circuitry[4,5,6]. These devices can be realized by second harmonic generation (SHG), the process in which two low-energy photons of the same frequency are converted. Li et al Light: Science & Applications (2020)9:180 efficiencies in photonic devices such as waveguides[9] and microring resonators[10,11]. A promising way to overcome these limitations is to exploit hybrid plasmonic systems, which integrate a metal with nonlinear nanomaterials and allow effective interplay between the subwavelength light confinement and large nonlinear susceptibility[17,18,19,20,21].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
