All-polarization-maintaining dual-comb Er-fiber laser with combined figure-8 and figure-9 architectures

We propose and demonstrate, for the first time to the best of our knowledge, an all-polarization-maintaining (all-PM) dual-comb Er-fiber laser based on combined figure-8 and figure-9 architectures. The opposite signs of the non-reciprocal phase shifts required for figure-8 and figure-9 architectures in the shared nonlinear amplifying loop mirror (NALM) are achieved using a single non-reciprocal phase shifter (NRPS) that operates in two orthogonal polarizations. The capability of common mode noise cancellation, environmental stability, long-term reliability, and the tunable range of the repetition rate difference Δf between two combs has been investigated and characterized. In addition, the dual-comb spectroscopy measurement with our dual-comb fiber laser is demonstrated to resolve the transmission spectrum of a flat-top DWDM (dense wavelength division multiplexer) demultiplexer, with a passband of ∼50 GHz at 1564.5 nm. Our experimental results indicate that the combined-architecture all-PM fiber laser, with its large tunable range of 100 kHz in Δf , shows significant potential for dual-comb applications in precise and rapid metrology outside the laboratory.