High-power two-color Kerr frequency comb generation on the gallium phosphide-on-insulator platform at SWIR and MIR spectra

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%W−1cm−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 −30dBm 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.

Investigation of χ (2)-Translated Optical Frequency Combs Tunability in Gallium Phosphide-on- Insulator Resonators

“…This study is a vital complement to previous experimental work [13], in which modeling and controlling of the χ (2) -based frequency translation were missing. Distinguished from other works of GaP-OI integrated nonlinear devices which solely focused on either second- [17], [18], [20] or third-order [14], [21] nonlinearity, this work emphasizes the frequency translation that links the χ (3) process and the χ (2) process, paving the way towards realizing highly efficient two-color frequency combs [15]. What's more, we improved the CLLE model so that it can not only work with the modal phase-matching condition [22] but also the cyclic phase-matching condition which is commonly encountered in ring resonators, extending the application scope of the framework for the nonlinear coupling between the χ (2) and χ (3) processes.…”

“…Among them, gallium phosphide (GaP) stands out due to its intriguing nonlinear and linear optical properties [13]. GaP has a conspicuous third-order nonlinearity with n2 = 1.9×10 -17 m 2 W -1 [14] and an intrinsic second-order nonlinearity with d36 = 41 pm/V at 1550 nm [15]. Besides, two-photon absorption can be neglected above 1.1 μm, which renders high power pump in the entire telecommunication bands possible.…”