Ultra‐Flat Broadband Low‐Noise Frequency Comb in a Fiber Fabry‐Perot Resonator

Abstract

A low‐noise microcomb with a flat and broadband spectrum is highly desired for various applications, including spectroscopy, sensing, and communications. However, both dissipative Kerr solitons (DKSs) and platicons have limitations in spectrum flatness due to their sech‐shaped profile or peaks of dispersive waves. In this study, an ultra‐flat and broadband microcomb are presented in a fiber Fabry‐Perot (F‐P) resonator. By optimizing the group velocity dispersion (GVD) and third‐order dispersion (TOD), an ultra‐flat low‐noise comb spectrum is obtained with a −1 dB bandwidth of up to 58 nm and a −30 dB bandwidth of 190 nm. Additionally, a method to control the contribution of the stimulated Raman scattering (SRS) effect by adjusting the desynchronization frequency to meet the phase‐matching condition is proposed. With the contribution from SRS, the −30 dB bandwidth is further extended to 230 nm with more than 7700 comb lines. Furthermore, a detailed investigation is conducted on the interaction among GVD, TOD, SRS, and Kerr nonlinearity, revealing the generation mechanism of such an ultra‐flat broadband comb spectrum. The work will provide valuable insights for the advancement of dispersion‐engineered resonators and further stimulate the study of the effects of SRS in fiber and integrated resonators are anticipated.