$L$ -Band Noise-Like Pulse Generation in a Bidirectional Mode-Locked Fiber Laser

We report on the generation of L-band noise-like pulses (NLPs) in a bidirectional mode-locked fiber laser. Benefiting from the absence of the isolator and the in-band absorption of the erbium-doped fiber, mode-locked pulses at the waveband over 1600 nm are delivered from this bidirectional oscillator. With appropriate settings, conventional solitons can evolve into NPLs in both clockwise and counter clockwise directions, which are validated by the sideband-free spectral shape and the distinguishable autocorrelation trace. In addition, it is experimentally found that the L-band NLP tends toward splitting due to the enhanced soliton collapse effect and the peak power clamping effect at the waveband around 1605 nm. Consequently, second-sixth harmonic mode locking of the NLP is, respectively, observed for the bidirectional operation. To the best of our knowledge, it is the first investigation of L-band NLPs in a bidirectional mode-locked fiber laser.