Dispersion-flattened concentric structure for microcomb bandwidth broadening in GaP-OI resonators

Abstract

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.

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.…”