Experimental Investigation of the Wavelength Tunability in All-Normal-Dispersion Ytterbium-Doped Mode-Locked Fiber Lasers

The wavelength tunability of all-normal-dispersion (ANDi) ytterbium (Yb)-doped mode-locked fiber laser is experimentally investigated, where the laser is mode-locked by nonlinear polarization rotation and the wavelength is adjusted by an intracavity tunable filter. The influences of pump power, gain fiber length, and cavity length (i.e., repetition rate) on the mode-locking wavelength and output spectrum are investigated. It is found that the tunable range of mode-locking wavelength depends on the length of the Yb-doped fiber, as well as the cavity loss, and is independent of the cavity length. Mode-locking in a longer wavelength regime can be obtained by increasing the gain fiber length, although the length depends on the cavity loss. Moreover, the effects of pump power, central wavelength, Yb-doped fiber length, and cavity length on other output parameters are discussed. The variation range of pump power to keep the mode-locking status is also analyzed. We find that the pump power range for keeping the mode-locking status decreases, and the typical output pulsewidth increases dramatically as the repetition rate decreases. Guidelines for designingANDi Yb-doped mode-locked fiber lasers are proposed.