Fiber core mode leakage induced by refractive index variation in high-power fiber laser
Yan Ping, Wang Xuejiao, Huang Yusheng, Fu Chen, Sun Junyi, Xiao Qirong, Li Dan †, Gong Mali
       

(color online) (a) Gain spectrum (power) of the first-order cladding modes at the fiber end; (b) gain spectrum (power) of the second-order cladding modes at the fiber end.