Femtosecond laser welding of silica glass fiber for robust Bragg grating sensing in high temperature environment

Femtosecond laser welding was extended to telecom optical silica fiber (SMF28) by focusing through quartz substrates and ferrules to form all-glass weld seams along a thin contact line. Different quartz material welding was demonstrated such as fiber-to-plate and fiber-to-ferrule welding. Strong weld seams up to (<30μm) wide were generated in the geometries without inducing photochemical or thermal degrading degradation of a fiber Bragg grating (FBG) positioned only 62.5 μm from the weld zone. Welding was optimized by thermal modeling of the heat-affected zone and by real-time monitoring of the FBG thermo-optical shift during laser scanning. Four-point bending confirmed a high mechanical strength while thermal annealing showed stable mechanical and FBG responses were available up to 1000˚C. Femtosecond laser writing and welding thus demonstrated a flexible means for photonics fabrication and packaging of FBGs, enabling reliable, high frequency vibration sensing suited for application.