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Mode-locked Tm fiber laser using SMF-SIMF-GIMF-SMF fiber structure as a saturable absorber.

We demonstrate a mode-locked all-fiber Tm laser using a single mode-step index multimode-graded-index multimode-single mode fiber structure as a saturable absorber based on the nonlinear multimodal interference. Stable fundamentally mode-locking operation was obtained at a pump threshold of 180mW. The output soliton pulses had a center wavelength, spectral width, pulse duration, and repetition rate of 1888 nm, 3.6 nm, 1.4 ps, and19.82 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator with many potential applications in eye-safe ultrafast photonics.