Bi-Directional Mode-Locked Thulium Fiber Laser as a Single-Cavity Dual-Comb Source

We demonstrate the use of a bi-directional mode-locked thulium doped fiber ring laser as a single cavity free-running dual-comb source. We consider the effect of group-velocity dispersion on the repetition rate difference between the two combs and demonstrate a tunable repetition rate difference from 48-229 Hz. Dual-comb spectroscopy of atmospheric H
₂
O near 1.87 μm is performed over a 1.47-m air path in laboratory with a peak single-shot signal-to-noise ratio of 27.5.