Tunable and Switchable Multiwavelength Passively Mode-Locked Fiber Laser Based on SESAM and Inline Birefringence Comb Filter

A tunable and switchable multiwavelength passively mode-locked fiber laser by using a semiconductor saturable absorber mirror (SESAM) and an inline birefringence fiber filter is proposed and demonstrated. By properly rotating the polarization controllers (PCs), up to 7-wavelength mode-locked pulses in 3-dB bandwidth with 3.65-nm channel spacing are obtained. The wavelength switchable operation is determined by the characteristics of the comb filter used in the experiment. Taking advantage of an intensity-dependent loss mechanism caused by the nonlinear polarization rotation (NPR) effect, the mode competition is efficiently suppressed. In addition, the lasing locations of multiwavelength mode-locked pulses can be flexibly tuned via the wavelength-dependent loss mechanism.