Generation of Multiwavelength Noise-Like Square-Pulses in a Fiber Laser

The generation of multiwavelength square pulses is demonstrated in a passively mode-locked figure-eight fiber laser. The multiwavelength square pulses were found to be structured by superposing the square pulses centered at different wavelengths, whose pulse duration broadens with the increasing pump power. The square pulse was confirmed as the noise-like pulse by using an autocorrelator. By properly rotating the PCs, the dual- or triple-wavelength square pulse could be achieved. The obtained results provide a new viewpoint for understanding the formation mechanism of the multiwavelength pulses with noise-like square profiles in fiber lasers.