Widely tunable multi-wavelength passively mode-locked Yb-doped fiber laser operation in an all-normal-dispersion regime

We have demonstrated the generation of widely tunable spectral multi-wavelength all-normal-dispersion (ANDi) Yb-doped fiber laser based on nonlinear polarization evolution (NPE) as the passively mode-locking mechanism. An easy-controlling tunable passband filter fabricated through a phase-shift long-period grating (PS-LPG) is employed to tune and control the wavelength in the laser cavity. By combining the character of the emission cross section of Yb-doped fiber, the tunable spectral ranges of the dual- and triple-wavelength pulses output is up to ∼20 nm and ∼7 nm, respectively. To our knowledge, it's the widest of tuning spectral range in the both dual- and triple-wavelength ANDi Yb-doped fiber laser with controllable and all-fiber format filter. The proposed method may provide a simple way to obtain a broad spectral range with multi-wavelength output in fiber laser systems.