Mid-infrared supercontinuum generation in chalcogenide fibers with high laser damage threshold

Laser damage thresholds (Ith) at 1.03 µm, as well as third-order nonlinear refractive indices (n2) and two photon absorption coefficients (β) at 1.55 µm of a number of Ge-As-S glasses were measured and systematically studied. The glass with the composition Ge_0.12As_0.24S_0.64 showed a high Ith and the maximum figure of merit (fm= n2/(β·λ)), and therefore was selected as the core material for the fabrication of a step-index fiber. A compatible glass with the composition Ge_0.18As_0.1S_0.72 was chosen as the cladding material. Based on the dispersion calculations, the fiber with a core diameter of ∼7-10 µm was designed. The designed fiber was fabricated by a multiple step rod-in-tube method. When the fiber with a core diameter of ∼9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, the mid-infrared supercontinuum (SC) covering 1.3-8.1 µm was generated. These results demonstrate the good potential of Ge-As-S chalcogenide fibers for producing high-brightness broadband mid-infrared SC light sources.