Ultraflat Soliton Microcombs in Driven Quadratic-Kerr Nonlinear Microresonators

Year: 2025

Authors: Wu GZ., Wei YT., Li LF., Chen SH., Bu LL., Baronio F., Lin T., Zhu M., Trillo S., Ni ZH.

Autors Affiliation: Southeast Univ, Sch Phys, Nanjing 211189, Peoples R China; Southeast Univ, Frontiers Sci Ctr Mobile Informat Commun & Secur, Nanjing 211189, Peoples R China; Purple Mt Labs, Nanjing 211111, Peoples R China; Univ Brescia, Dept Informat Engn, Via Branze 38, I-25123 Brescia, Italy; INO CNR, Via Branze 38, I-25123 Brescia, Italy; Southeast Univ, Adv Photon Ctr, Sch Elect Sci & Engn, Nanjing 210096, Peoples R China; Southeast Univ, Natl Mobile Commun Res Lab, Nanjing 210096, Peoples R China; Univ Ferrara, Dept Engn, Via Saragat 1, I-44122 Ferrara, Italy.

Abstract: We predict the generation of ultraflat broadband soliton microcombs in a driven quadratic-Kerr nonlinear microring resonator via phase-matched second-harmonic generation. The unprecedented spectral flatness arises from a novel cavity mechanism of symmetric dispersive wave generation, enabled by opposite groupvelocity dispersions-anomalous at the fundamental frequency and normal at the second harmonic- without requiring higher-order dispersion engineering. This mechanism manifests itself as a characteristic long-rippled-wing bright soliton at the second harmonic, thereby generating the ultraflat spectrum. We develop analytical criteria for predicting the radiated frequencies, and show that, under proper control of relative cavity losses, the resulting combs exhibit nearly vanishing (similar to 0 dB) comb-line power variations over a broad spectral range, at variance with platicon microcombs that operate at normal dispersions. Our results offer a pathway to realize octave-spanning, highly efficient, coherent ultraflat combs without needing external phase or intensity modulators, enabling applications such as high-capacity telecommunications, precision metrology, and astrophysical spectrograph calibration.

Journal/Review: PHYSICAL REVIEW LETTERS

Volume: 135 (11)      Pages from: 113801-1  to: 113801-8

More Information: This work was supported by the National Natural Science Foundation of China (Grants No. 12374301, No. 11974075, and No. 62105061) , the Jiangsu Provincial Frontier Technology Research and Development Program (Grant No. BF2025065) , the National Key Research and Development Program of China (Grant No. 2021YFA1200700) , and the State Key Laboratory of Silicon and Advanced Semiconductor Materials (Grant No. SKL2023-04) . S. T. and F. B. acknowledge support from the Progetti di Ricerca di Interesse Nazionale (PRIN) (Project No. 2020X4T57A) and the PRIN funded by European Union – Next Generation EU, Mission 4, Component C2 (Project No. 20222NCTCY) .
KeyWords: Frequency Comb Generation; Walk-off; Pattern Selection
DOI: 10.1103/cf1p-k6v6