Toward free-running operation of dual-comb fiber lasers for methane sensing.

The phase information provided by the beat note between frequency combs and two continuous-wave lasers is used to extrapolate the phase evolution of comb modes found in a spectral region obtained via nonlinear broadening. This thereafter enables using interferogram self-correction to fully retrieve the coherence of a dual-comb beat note between two independent fiber lasers. This approach allows the $ f - 2f $f-2f self-referencing of both combs, which is a significant simplification. Broadband near-infrared methane spectroscopy has been conducted to demonstrate the simplified system's preserved performance.