Abstract

Optical frequency combs (OFCs) covering multiple spectral windows are of great interest as broadband coherent light sources. Pushing into high powers for traditional single OFCs as well as nonlinear frequency translated OFCs led to the narrowing of their bandwidths. Here, we present a hybrid integrated solution on the gallium phosphide-on-insulator (GaP-OI) platform to generate high-power two-color Kerr frequency combs at both the short-wave infrared (SWIR) and the mid-infrared (MIR) spectra. The design consists of a GaP-OI resonator with a partially etched gap for frequency comb generation at the two colors and a modal phase-matched strip waveguide for a second-harmonic generation (SHG). The resonator has a 3.25 µm wide anomalous dispersion window, which is enabled by mode hybridization and higher-order modes waveguide dispersion. The pump light at 1550 nm wavelength is frequency doubled from the 3100 nm wavelength light source, with a normalized SHG conversion efficiency of  ${793}\% \;{{\rm W}^{- 1}}\;{{\rm cm}^{- 2}}$. We also propose the ring-bus coupler design to efficiently deliver optical power into the resonator while suppressing the leakage out of the resonator. The simulated two-color combs show a bandwidth of 87 nm above the ${-}{30}\;{\rm dBm}$ power level at the SWIR spectrum and a bandwidth of  749 nm above the same power level at the MIR spectrum. Our proposed two-color OFC generation scheme levitates the ceiling in terms of high power and broad bandwidth simultaneously on a single platform, paving the way toward monolithic solutions to integrated broadband coherent sources.

© 2023 Optica Publishing Group

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