All-fiber counter-propagating all-normal-dispersion (CANDi) laser for coherently averaged dual-comb spectroscopy

This study introduces a novel all-fiber counter-propagating all-normal-dispersion (CANDi) laser. By leveraging the birefringence of polarization-maintaining fibers and a fiber polarization beam splitter, a compact and stable all-fiber structure is constructed, effectively replacing traditional free-space components, significantly reducing cavity loss, and optimizing noise characteristics. Experimental results show that this laser not only retains the advantages of conventional CANDi lasers but also achieves a new stable bi-directional dual-wavelength locking state, demonstrating excellent self-starting performance in both single-wavelength and dual-wavelength modes. As a proof-of-concept demonstration in dual-comb spectroscopy, the laser successfully measured the transmission spectrum of a high-Q microcavity at the 1070 nm band in a free-running single-wavelength mode-locked state, and demonstrated excellent dual-comb measurement performance. This verifies its great potential in high-sensitivity spectroscopic sensing. The emergence of this all-fiber CANDi laser provides a simple, fast, and high-bandwidth solution for acquiring high-resolution dual-comb spectroscopy information without active stabilization. Its application prospects in the field of fiber-optic sensing are broad, and it is expected to play a key role in high-precision and high-sensitivity molecular detection and environmental monitoring.