Mode-locked Er-doped fiber laser based on nonlinear multimode interference

We demonstrated an all fiber passively mode-locked fiber laser by using one single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure as a saturable absorber (SA) based on the nonlinear multimode interference. The proposed SA with the modulation depth of 9.58%, saturation intensity of 36.50 MW cm(-2) and nonsaturable loss of similar to 21% was inserted into an Er-doped fiber laser cavity. Then the conventional soliton laser at 1566 nm was realized at a pump threshold of 180 mW. The output pulses had a pulse duration and repetition rate of 520 fs and 33.7 MHz, respectively. And the maximum pulse energy was 256 pJ. Our results further indicated that the SMF-GIMF-SMF structure can be used as an effective SA for ultrashort pulse generation.