Asymmetric χ(2)-Translated Optical Frequency Combs Assisted by Avoided Mode Crossing in Concentric Ring Resonators

χ (2) -translated microcomb generation in microresonators that possess both χ (2) and χ (3) nonlinear responses opens the door for ultra-broadband integrated comb sources. The interplay between the second- and third-order nonlinearities within a fixed coupling coefficient fertilizes complicated cavity dynamics which is of paramount scientific and technological potential. However, this coupling coefficient can be drastically wavelength-dependent, which is lack of consideration in previous studies. Here, we extend the range of coupling strengths to a full description and propose a new approach to delineate the spectral response of the interactions between the χ (2) and χ (3) nonlinearities. Critically, the underpinned physics is enabled by avoided mode crossing (AMX) in concentric double-ring microresonators. We demonstrate that the evolution of the anti-symmetric mode at fundamental wavelengths disrupts spectral symmetry, leading to asymmetric χ (2) -translated optical frequency combs at second-harmonic wavelengths. Simultaneous generation of skewed two-color optical frequency combs is numerically realized in an exemplary gallium phosphide-on-insulator platform with a coupling constant from 133.3 m -1 W -1/2 to 7.4 m -1 W -1/2 , showing reasonable agreement with our theoretical model. Our findings provide a novel approach to shaping the optical frequency comb, which may facilitate potential applications in self-referencing and frequency metrology with desired comb spectral shapes.