Mid-infrared supercontinuum generation in step-index As₂S₃ fibers pumped by a nanosecond shortwave-infrared...

A supercontinuum (SC) source spanning from 2 to 4 μm is demonstrated in As₂S₃-chalcogenide fibers pumped by a nanosecond supercontinuum pump source in the normal dispersion region. In this experiment, two pieces of 3-m-long step-index As₂S₃ fiber with different core diameters of 7 μm and 9 μm are pumped by a 1.9-2.5 μm nanosecond supercontinuum source. The zero dispersion wavelengths are both beyond 6.6 μm, thus cascaded stimulated Raman scattering is believed to be the dominant mechanism responsible for spectral broadening. With a low peak pump power of ~2.9 kW, both of the output spectra have extended to 4 μm with enhanced power distribution in the MIR region. The maximum output power of the mid-infrared supercontinua is ~140 mW. To the best of our knowledge, it is the first supercontinuum extenting to 4 μm in an As₂S₃ fiber pumped by shortwave-infrared SC pluses in the normal dispersion region.