Synchronously-tunable bidirectional mode-locked fiber laser based on Lyot filtering effect

We report a widely tunable mode-locking in a bidirectional fiber laser, where the wavelength tuning is achieved by a birefringent filter. The central wavelength of the CW pulse can be tuned within 1549.5 nm-1572.7 nm, synchronously, the central wavelength of the CCW pulse changes within 1548.3 nm-1573.1 nm. The relative wavelength difference of the bidirectional pulses is controllable within a certain range, which supports the switching of the laser output between asynchronous and synchronous pulses. The bidirectional output pulses do not exhibit significant variations both in spectral shapes and central wavelengths in 20 min. In addition, we record a novel output with bidirectional soliton-type switchability. Our work achieves a wide range of CW and CCW pulses with tunable center wavelengths simultaneously based on the bidirectional laser and Lyot filtering effect, which may facilitate the design of dual-wavelength fiber lasers and satisfy different application requirements.