We report a gallium phosphide-on-insulator (GaP-OI) photonic platform fabricated by an intermediate-layer bonding process aiming to increase the manufacture scalability in a low-cost manner. This is enabled by the “etch-n-transfer” sequence, which results in inverted rib waveguide structures. The shallow-etched 1.8 µm-wide waveguide has a propagation loss of 23.5 dB/cm at 1550 nm wavelength. Supercontinuum generation based on the self-phase modulation effect is observed when the waveguides are pumped by femtosecond pulses. The nonlinear refractive index of GaP, n2, is extracted to be 1.9 × 10−17 m2/W, demonstrating the great promise of the GaP-OI platform in third-order nonlinear applications.

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.

We propose and theoretically investigate the coupled concentric ring resonators on a thickness-constrained GaP on insulator (GaP-OI) integrated photonic platform. Achieving anomalous dispersion is fulfilled by mode hybridization in the coupled structure on a 200 nm thick GaP-OI resonator which originally only exhibits normal dispersion for the fundamental mode. The anomalous dispersion profile for the anti-symmetric mode is flattened and broadened in favor of Kerr frequency comb generation by optimizing the waveguide width and the coupling gap size synergistically. We show the flexibility of this design methodology by simultaneously flattening the dispersion profile while anchoring the dispersion peak location at 1550 nm. The optimized design has a flat anomalous dispersion span of 460 nm with a small peak of 160 ps/km/nm, 1.69 times lower than a traditional rectangular waveguide. The engineered dispersion profile enables a broadband Kerr frequency comb generation that has a 3 dB bandwidth of 67 nm and a 20 dB bandwidth of over 250 nm at both 1550 and 1650 nm pump wavelengths. The proposed design proves useful to achieve broad and flat anomalous dispersion on thickness-constrained materials, paving the way towards low-loss GaP-OI frequency comb resonators.