Low-noise extraction of a single frequency comb line by fiber Brillouin amplification

We present a low-noise extraction of individual frequency lines from an optical frequency comb based on fiber Brillouin amplification. The phase and intensity noise properties of this extraction process are comprehensively investigated. The excess phase noise introduced by the extraction process under various conditions is studied in detail and found to be determined by environmental disturbances on the Brillouin gain fiber, which is reduced in our short-fiber, all-polarization-maintaining (PM) scheme. The simplicity and low phase noise characteristics of this approach demonstrate its capability in maintaining the coherence of a frequency comb line with ultra-narrow linewidth. Furthermore, the intensity noise of the extracted comb line is found to be strongly dependent on amplified spontaneous Brillouin scattering, further emphasizing the benefits of the all-PM design. These findings underscore the potential of this comb line extraction technique as a robust low-noise single-frequency laser generator or optical frequency synthesizer required in demanding fields such as cold atomic physics, optical communications, and optical clocks.