Tri-Comb and Quad-Comb Generation Based on a Multi-Dimensional Multiplexed Mode-Locked Laser

By introducing an additional comb beyond its dual-comb predecessor, tri-comb consisting of three combs with different mode spacing has shown its unique potential in several metrology areas such as nonlinear spectroscopy, frequency, and distance measurement. However, tri-comb generation based on three frequency-stabilized comb lasers would be overly complicated and costly for many potential applications. Previous studies had realized dual-comb generation from a single-cavity laser by leveraging multiplexing in one of the waveguiding dimensions of the optical pulses. Such sources with built-in passive mutual coherence could greatly reduce system complexity. Yet, squeezing more combs into one multiplexing dimension becomes increasingly difficult without significant sacrifice in performance, which could jeopardize the usefulness of such a scheme. In this paper, it is proposed and demonstrated that multi-comb generation could be realized by tapping into the multidimensional joint parameter space. Up to four wavelength/polarization multiplexed, asynchronous ultrashort pulse sequences can be generated with good stability from an all-fiber, mode-locked ring-cavity laser. This could offer an attractive alternative solution as the low-complexity light sources for field-deployable multi-comb metrology applications.