Highly localized FBG fabricated by femtosecond laser single-pulse filaments

Abstract

A highly localized fiber Bragg grating (FBG) fabrication method has been proposed. The method utilizes the principle of introducing spherical aberration by a quartz glass plate to achieve a uniform filamentary modulation region induced by a single femtosecond laser pulse in a single-mode fiber. The focusing spot of the femtosecond laser passing through quartz glass plates with different thicknesses has been simulated. Combined with the results of femtosecond laser single-pulse fabrication, the effect of spherical aberration introduced by the quartz glass plate on the filament morphology has been analyzed. Based on this method, highly localized FBG arrays have been inscribed using the femtosecond laser point-by-point inscription technology. When the periods of the FBG arrays are the same, this method can effectively improve the reflectivity of FBGs without increasing the insertion loss. The method of modulating the filament morphology by adjusting the thickness of the glass plate offers a more efficient means for the fabrication of FBGs, and the high-integration FBG arrays have extensive application prospects in sensing and communication.