Orthogonal GHz harmonic dual-comb generation in monolithic fiber cavity for acquisition speed multiplication

Asynchronous dual-comb generated in single laser cavity offer potent tools for simplified coherent measurements, owing to the common mode rejection which spares the sophisticated locking systems. However, the limited dimensional inhomogeneity in monolithic cavity induces relatively small repetition-rate-difference, hindering high-speed measurements. Here, a monolithic linear fiber laser with integrated multifunctional device employing polarization multiplexing is proposed and demonstrated for dual-comb acquisition speed enhancement. By tuning the inherent polarization-dependent degrees of freedom within the device, optical intensity distribution between orthogonal polarizations can be finely manipulated, thus boosting controllable asynchronous harmonic mode-locking. The two sets of harmonic mode-locked pulses enable the multiplication of the equivalent repetition-rate-difference and produce more temporal interferograms via least common multiple principles. With a fundamental-repetition-rate of 383 MHz, harmonic-repetition-rate up to 2.3 GHz and acquisition speed over 244 kHz are obtained in experiments, faster by 2 orders of magnitudes than previous single-fiber-cavity dual-combs. Equivalent repetition-rate-difference up to 400 kHz is also achieved with shorter laser cavity. This orthogonally polarized GHz harmonic dual-comb laser offers insights for a novel dual-comb generation paradigm and provides a single-fiber-integrated solution for acquisition boosting in wide measurement applications.