Mid-Infrared Single-Mode Ge-As-S Fiber for High Power Laser Delivery

Traditional single-mode As-S fiber is limited in the transmission of high power mid-infrared laser by its low threshold of laser-induced damage. A single-mode chalcogenide (ChG) fiber based on Ge-As-S glasses has been prepared via a novel extrusion method for the first time, the transmission performance and thermal damage of the fiber during the power delivery have been studied in details. The fiber can sustain a laser power of 6.2 W at wavelength of 3.8–4.7 μm, i.e., power density of 1.97 MW/cm
²
under atmosphere surrounding without any obvious damage on the fiber surfaces. This is in sharp contrast with the power transmission under 1 W at a wavelength longer than 4 μm for typical single-mode As-S fiber. By measuring the fiber surface temperature and estimating the temperature distribution in the fiber through calculations, the kinetics of fiber thermal damage has been investigated, and it is estimated that the fiber can transmit more than 10 W of laser power at wavelength of 3.8–4.7 μm. In addition, by comparing the self-focusing effect of traditional As-S fiber and Ge-As-S fiber, it is found that the critical power of Ge-As-S fiber is larger than that of As-S fiber, and the difference becomes even larger with increasing wavelength.