Noise characteristics of a polarization-duplex dual-comb fiber laser based on a single gain fiber

Abstract

We demonstrate gain-sharing polarization-duplex dual-comb laser. Here, a nonlinear amplifying loop mirror (NALM) with a single gain fiber is used to achieve simultaneous mode-locking for the generation of the two frequency combs with slightly different repetition rates. Our system provides stable mode-locking and a good overlap of frequency comb spectra. The repetition rate difference is about 100 kHz and has high stability: we determined a standard deviation of 0.75 Hz, and the Allan deviation is 0.073 Hz at an integration time of 1 s for this free-running system. In the case of simultaneous mode-locking, our system shows a relative intensity noise (RIN) characteristic that has, to the best our knowledge, not yet been reported for dual-comb lasers. On the other hand, the phase noise characteristic of our mode-locked dual-comb laser is similar to the characteristic obtained when one beam path is blocked and the laser is used for single frequency-comb generation.