All-fiber normal-dispersion mode-locked laser with gain filter

An all-fiber normal-dispersion mode locked laser is presented. No additional spectral filter components are involved in the cavity. Spectral filtering is achieved through gain narrowing by three segments of gain fibers with different lengths. The performances of the fiber lasers with and without gain narrowing are discussed. A stable mode locked pulse train is observed in the cavity with gain filtering with pulse duration of 72 ps. The gain filtering effect is discussed theoretically.