Optimization of large-mode-area active fiber

The gain fiber is the important indicators to determine the output power and beam quality of fiber laser. The paper focused on the large-mode-area fiber (LMA) bending effect on fundamental mode (FM) area and mode field distortion by numerical analysis, the FM area and gain coefficient of LMA fiber with different refractive index (RI) and doped distributions were solved by finite-element method. The Gaussian hybrid refractive index distribution and doping profile were proposed firstly. It can effectively improve the gain coefficient and suppression coefficient of high-order modes (HOMs). Moreover, the bending against of the fiber can be strengthen, the design can balance the contradiction the mode area and bending resistance. Based on the numerical calculation, the gain fiber with Gaussian hybrid RI distribution and doping profile were designed, the fiber diameter was 65 m. At the wavelength of 1.064 m, the FM area can be 1.17103 m2, the FM relative gain coefficient and relative suppressing coefficient can reach 0.58 and 0.208 8, the output and beam quality of the fiber laser can be improved effectively.