Switchable Dual-Wavelength and Passively Mode-Locked All-Normal-Dispersion Yb-Doped Fiber Lasers

A switchable dual-wavelength and passively mode- locked ytterbium-doped fiber laser (YDFL) in the all-normal-dispersion (ANDi) regime is reported and demonstrated for the first time. Using a phase-shifted long-period fiber grating (PS-LPFG) as an all-fiber format spectral filter in the laser cavity, a stable and switchable dual-wavelength mode-locked operation is achieved by nonlinear polarization evolution (NPE). The maximum output energy of the dual-wavelength pulse is 25.76 nJ at a repetition rate of 2.499 MHz. It opens a new possibility to achieve switchable multiwavelength and mode-locked laser output in the ANDi cavity in an all-fiber format.