Intracavity-loss controlled wavelength-tunable bidirectional mode-locked erbium-doped fiber laser.

Bidirectional wavelength-tunable mode-locked fiber lasers have demands for many applications. In our experiment, two frequency combs from a single bidirectional carbon nanotube mode-locked erbium-doped fiber laser are obtained. Continuous wavelength tuning is demonstrated in the bidirectional ultrafast erbium-doped fiber laser for the first time. We utilized the microfiber assisted differential loss-control effect on both directions to tune operation wavelength and it presents different wavelength tuning performances in two directions. Correspondingly, the repetition rate difference can be tuned from 98.6 Hz to 32 Hz by applying strain on microfiber within 23 µm stretching length. In addition, a minor repetition rate difference variation of 4.5 Hz is achieved. Such technique may provide possibility to expand wavelength range of dual-comb spectroscopy and broad its application fields.