Theoretical and experimental investigation on the gain filtering effect in the high-power fiber oscillator using confined-doped fiber

In this work, a confined-doped fiber oscillator model considering the spatial hole-burning effect is established to help understand the underlying physical mechanism of the gain filtering effect. The influences of the relative doping ratio on the gain filtering effect are systematically analyzed in a fiber oscillator under different power levels, which reveals the possibility of achieving near pure fundamental mode laser operation by carefully designing the relative doping ratio of the confined-doped fiber. Simultaneously, the comparison experiment adopting homemade large-mode-area confined-doped fiber and fully-doped fiber is conducted to verify the gain filtering effect of confined-doped fiber in high-power oscillators. This work could provide a practical reference for optimizing the design of the confined-doped fiber laser systems for high-power high-brightness laser operation.