Partially inscribed Bragg gratings suppressing high-order modes in high-power large-mode-area fiber oscillators

In this paper, we present the principle and design of a novel type of fiber Bragg gratings (FBGs) that are only partially inscribed into the large-mode-area fibers for high-power laser systems. The partial Bragg gratings can induce extra losses for high-order modes to suppress laser emission in direct fiber oscillators. Numerical modeling indicates these partial FBGs can very effectively limit the high-order LP11 mode from lasing and maintain the fundamental LP01 mode operation under up to 5 kW pump power, even for fibers of extremely large mode areas with core diameters up to 50 μm. Therefore, such partial FBGs can be excellent modal quality control components for single-mode high-power laser systems constructed with fibers of very large mode areas.