Achieving Equally-Spaced Brillouin frequency combs based on optoelectronic oscillator

Abstract

An innovative approach has been proposed to achieve a precisely equidistant Brillouin Frequency Comb (BFC). Experimental validation was performed through the integration of a Brillouin fiber laser with an Optoelectronic Oscillator (OEO). By leveraging Brillouin gain, the transition from phase modulation to intensity modulation was successfully achieved, resulting in the generation of an equidistant Optical Frequency Comb (OFC) with intervals that strictly match the Brillouin frequency shift. Specifically exciting only the first-order Stokes light within the optical fiber notably enhanced the side-mode suppression ratio of microwave signals. In our experiments, the following achievements were realized: a 7-line Optical Frequency Comb (OFC) with a frequency spacing of 10.398 GHz and a flatness of 2.48 dB. At an offset frequency of 10 kHz, the corresponding phase noise of the microwave signal was measured at −101.534 dBc/Hz. Furthermore, by manipulating the optical and electrical gains of the OEO, the capability to realize OFCs with varying frequency spacings was demonstrated. The proposed OEO addresses the issue of BFCs, where the comb spacing is not strictly uniform, leading to their slow development in the fields of optical communications, precise measurements, and more.