Asymmetric χ (2) -translated optical frequency combs assisted by avoided mode crossing in concentric ring resonators

• Published in: Optics express 2024-09, Vol.32 (19), p.32924
• Main Authors: Wu, Pengzhuo, Tang, Xingyu, Yang, Yatao, Wang, Yifan, Yan, Yongxian, Pan, Ziyu, Zhang, Xucheng, You, Mingjian, Liu, Zhenyu, Bao, Changjing, Ji, Xingchen, Li, Yi, Zhao, Qiancheng
• Format: Article
• Language: English
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.531644

χ -translated microcomb generation in microresonators that possess both χ and χ 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 and χ 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 -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 W to 7.4 m W , 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.