Monolithic all-fiber mid-infrared supercontinuum source based on a step-index two-mode As₂S₃ fiber

We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a two-mode As₂S₃ fiber in the normal dispersion regime. The As₂S₃ fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from 1.8 μm to 4.2 μm is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond 2.4 μm. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.