On-demand dual-comb generation in a single-cavity via a real-time intelligent spectral seeker

The repetition frequency difference in the dual-comb light source is critical for balancing measurement accuracy and refresh rate in high-precision ranging and spectroscopy. The single cavity dual-wavelength mode-locked fiber laser (MLFL) based on a birefringent filtering mechanism can produce the dual-comb regime (DCR) through dedicated cavity designs and careful tuning of birefringent filter characteristics (e.g., central wavelength, spectral separation, and modulation depth). However, achieving automatic, on-demand tuning of the repetition frequency difference of DCR in the MLFL is challenging. In this work, we demonstrate, on-demand DCR generation with a specified repetition frequency difference in an MLFL usinging a spectral seeker. A programmable optical filter combined with time-stretch dispersive Fourier transform enables real-time spectral acquisition with absolute wavelength accuracy. Subsequently, reinforcement learning tunes the polarization state of the electric polarization controller inside the cavity in real time to optimize the birefringent filter, thereby generating the DCR with the target emission wavelength corresponding to a desired repetition frequency difference. Thus, on-demand DCR generation is achieved by controlling the emission wavelength of one of the dual combs, which spans from 1528 nm to 1539 nm, thereby adjusting the repetition frequency difference from 162 Hz to 212 Hz. Furthermore, the mean time for automatic DCR generation (i.e., from free-running state to the desired DCR) is 0.407s, which is ∼6 times faster than the state of the art. The intelligent MLFL continuously operates under the DCR for over 12 hours, exhibiting outstanding stability. The demonstrated on-demand DCR generation with real-time control represents a magnificent step towards utilizing the single cavity dual-comb source in diverse applications, such as high-precision ranging and spectroscopy.