Fiber Bragg grating in large-mode-area fiber for high power fiber laser applications

Fiber Bragg gratings (FBGs) are indispensable components in the design of monolithic high-power fiber lasers. As the laser power scales up, the adoption of larger-mode-area fibers with high V numbers poses new challenges for FBG design and fabrication. In this paper, we present the simulation, fabrication, and measurement of the FBGs inscribed on large-mode-area fibers. The simulation used the T-matrix approach to calculate the spectral response of the FBG that matched well with the measured spectra. The observed fringes in the reflection spectrum are explained by the interference between the low-order modes that were also confirmed with the simulation. Some unique features of the FBG and their potential applications are discussed.