GIMF-Based SA for Generation of High Pulse Energy Ultrafast Solitons in a Mode-Locked Linear-Cavity Fiber Laser

A mode-locked high pulse energy fiber laser with a linear cavity by using an all-fiber structured graded index multimode fiber (GIMF) based saturable absorber (SA) is presented. The saturable absorption effect of the SA is based on the nonlinear multimode interference (NL-MMI). This is the first time the GIMF-based SA has been used in a mode-locked all-fiber laser with a linear cavity. The stable fundamental mode-locking operation can still be maintained at the maximum pump power. The output solitons have the center wavelength, spectral width, pulse duration, and repetition rate of 1571 nm, 4 nm, 675 fs, and 11.69 MHz, respectively. The maximum average output power reached is 61.4 mW, corresponding to the pulse energy up to 4.72 nJ and the pulse peak power of 7.79 kW. The proposed GIMF-based SA opens a promising way for a practical fiber-integrated mode-locker for large pulse energy fiber laser technology.