Abstract

We demonstrate the first saturable absorber made of a chalcogenide multimode fiber assembly, and its use within a resonant fiber cavity to trigger mode-locking. The saturable absorber operates from nonlinear multimode interference in a singlemode-multimode-singlemode fiber structure with lateral offsets at both input and output interfaces. It has a modulation depth of 10% and a peak power saturation intensity $< $ 55 MW/cm $^2$ . It acts simultaneously as a tunable bandpass filter with a continuous tunability of 61 nm. The saturable absorber triggers a pulsed regime in a fiber laser cavity, leading to mode-locking in a tunable wavelength range of 1834 nm to 1895 nm. The mode-locked fiber laser can be set to generate a pulse train with conventional single pulse pattern or resembling pulse pattern. The all-fiber saturable absorber is a promising component for the fabrication of mode-locked fiber lasers operating in the mid-infrared wavelength range.

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