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Mid-infrared supercontinuum generation in telecommunication multimode fiber by nanosecond 2.054 μm laser pulses

We demonstrated a broadband mid-infrared (mid-IR) supercontinuum (SC) directly generated in telecommunication multimode fiber (MMF) pumped by 2.054 μm nanosecond laser pulses. The characteristics of mid-IR SC, including the output spectrum, pulse energy, and optic-to-optic conversion efficiency, were exhaustively investigated at different pump powers and fiber lengths. The nonlinear processes for SC generation in fiber were analyzed, and the frequency shift of the modulation instability (MI) was theoretically calculated, which was close to the experimental data. The output SC pulse shapes were measured in different output powers, and no split was found. The SC laser beam was nearly diffraction limited with an M2  =1.15 in 2.1 μm measured by the traveling knife-edge method, and the laser beam spot was monitored by an infrared vidicon camera.