Comprehensive noise analysis for counter-propagating all-normal dispersion (CANDi) fiber laser

Counter-propagating all-normal dispersion (CANDi) fiber laser, an emerging single-cavity dual-comb laser (SCDCL) architecture with unprecedented pulse energy, is particularly promising for various nonlinear dual-comb applications. However, its noise characteristics and the underlying physical mechanisms have never been systematically investigated. To unleash the full potential of CANDi laser and also provide a general reference for the community of SCDCL, a systematic noise analysis of CANDi laser is performed based on the combination of experimental characterization and numerical simulation. In particular, the factors determining the relative intensity noise (RIN) floor and the harmonic noise peaks are investigated. The laser RIN floor is found to be pump RIN limited and the pump-to-laser RIN transfer function is identified to be dependent on both pumping direction and mode-locking position, which sheds light on general solutions for making SCDCLs more robust against pump RIN. Two distinct dual-comb crosstalk mechanisms (reflection and gain competition) have been discovered, and gain competition has been identified to be the cause of the harmonic noise peaks. The influence of such crosstalk and effective ways of mitigation has been discussed, which stimulates further innovation of SCDCL architectures. Our study not only provides a much deeper understanding of CANDi laser characteristics but also serves as a valuable general reference for the whole SDCDL community, which facilitates the development of low-cost and highly stable lasers and promotes the practical applications of dual-comb metrology.