Bidirectional mode-locked all-normal dispersion fiber laser

The bidirectional mode-locked oscillator is an emerging light source architecture suitable for dual-comb applications. Therein, bidirectional mode-locked fiber lasers (MLFLs) are particularly promising for their cost effectiveness, system compactness, and environmental robustness. However, the pulse energy has been limited to tens of picojoules, restricting practical dual-comb applications, especially in the nonlinear regime. In this paper, we break the pulse energy limit by devising the first bidirectional all-normal dispersion MLFL with an artificial saturable absorber (ASA). Bidirectional dissipative solitons are generated with > 5 -THz bandwidths and > 1 -nJ pulse energies. Free-running laser performance is extensively characterized, and the physical mechanism for bidirectional ASA mode-locking is studied. Last but not least, a proof-of-concept dual-comb spectroscopy measurement is demonstrated. Our work paves the way for a new class of bidirectional MLFLs benefiting dual-comb applications in both linear and nonlinear regimes.