Femtosecond mode-lock fiber laser with GIMF-SIMF-GIMF structure as the saturable absorber

Abstract

A femtosecond mode-lock all-fiber laser based on the nonlinear multimode interference (NL-MMI) effect is demonstrated. The saturable absorber (SA) in this laser is a graded-index multimode fiber-step index multimode fibergraded-index multimode fiber (GIMF-SIMF-GIMF) structure. The laser can work in mode-lock or soliton mode-lock two states. Through finely turning the polarization controller (PC), the laser will change the operation state. When the laser is running in the mode-locked state, the pump threshold is 51.4 mW. The center wavelength of the mode-lock pulse is 1559.71 nm with a spectral bandwidth of 10.73 nm, 354 fs duration and the fundamental repetition rate of 10.8 MHz. When the laser working in the soliton mode-lock state, the pump threshold is 54.1 mW. The center wavelength of the soliton pulse is 1561.85 nm, and the spectral bandwidth is 4.01 nm. The lasers have environmental stability. After a slight disturbance, the laser can stabilize itself to the mode-locked state.