Bidirectional mode-locked fiber laser based on nonlinear multimode interference

Bidirectional mode-locked lasers are an ideal light source for dual-comb technique for their system compactness and common noise cancellation. Here, we report an all-fiber bidirectional mode-locked laser based on nonlinear multimode interference. Asynchronous pulse trains in different directions with a repetition rate difference of 7 Hz are obtained. Besides, we record the pulse trains and spectra at different pump powers. In our experiment, the counter-propagating pulse (CPP) trains can operate in different states, such as the counterclockwise (CCW) direction works in single pulse while the clockwise (CW) direction works in multi-pulse or harmonic mode-locking. We believe that the work will provide a new platform for studying the dynamic characteristics of bidirectional mode-locked lasers.