Oxyfluoride Core Silica-Based Optical Fiber with Intrinsically Low Nonlinearities for High Energy Laser Applications

A few-moded silica-based optical fiber fabricated from core materials that possess intrinsically low optical nonlinearities is reported. Specifically, the 8-μm core, 125-μm cladding diameter silicate fiber was composed of a strontium aluminosilicate oxyfluoride core with a fused silica cladding and was fabricated using the molten core method. Relative to conventional optical fibers, reductions of ∼6.3 dB in Brillouin gain coefficient (g_B ), ∼0.9 dB in Raman gain coefficient (g_R), and ∼2.2 dB in thermo-optic coefficient were realized as was a 'silica-like' nonlinear refractive index (n₂) with a value of ∼3 × 10^-20 m²/W. The role of each core material constituent on parameters that drive optical nonlinearities is discussed to provide a materials solution route for low nonlinearity fiber systems. Materially addressing optical nonlinearities represent a simpler and more effective approach to mitigating power-scaling limits in high energy fiber laser systems compared to the geometric approaches employed using microstructured fibers.