Theory Analysis Of Multi-Point Pump Er³⁺/Yb³⁺ Co-Doped Double-Clad Fiber Laser

Double-clad fiber laser has been getting more and more attention these years because of its special structure and the outstanding function of the rare earth ions doped. Especially, multi-point pump double-clad fiber has been researched for its advantages, such as extending the pump power effectively, improving the heat dissipation of the fiber and optimizing the output characteristics.We mainly researched the output characteristics of the Er3+/Yb3+ co-doped fiber laser under the multi-point pump. Firstly, some basic principles of fiber lasers are introduced briefly, including the key technique of double-clad fiber lasers, the characteristics, the development as well as the applications. Secondly, we analyzed the energy system of the laser and the rate equation in steady state. Thirdly, we introduced the effect of dosage concentrations changing of Er3+/Yb3+to the laser that is to put Yb3+ into Er3+ by suppressing the phenomenon of reducing the transformation efficiency caused by concentration quenching. We found that it is feasible to decreasing the transfer efficiency by putting Yb3+ into Er3+ to avoid the drop to transformation efficiency due to concentration quenching. Finally, based on the rate equation, numerical analysis of the 980nm Er3+/Yb3+ co-doped double-clad fiber laser has been preformed in Matlab software. According to the output characteristics of the multi-point pump Er3+/Yb3+ co-doped fiber laser, we calculated the influence of pump number on the transformation efficiency with the same fiber length. Then optimal design is implemented.According to the simulation results, several conclusions are drawn as follow:1. Compared with the single-point pump laser, the distribution of pump power in multi-point pump laser is more even along the fiber.2. The output power varies with the number of the multi-point pump. Before the fiber laser is saturated, the larger the points number is, more output power we could gain.3. The output power is affected by the reflectivity of mirrors on both ends. The larger the front mirror reflectivity or the smaller the back mirror reflectivity, the more output power could be gained.4. To the laser with a certain fiber length, the number of pump power must be considered to obtain output efficiency and to avoid more loss of pump power. We found that the efficiency of the laser would be high if the length of the fiber is 100m and the pump power obeys homogeneous distribution and the pump point is no more than 5. When the length and the power are stated, different distributions of pump power have little influence in the efficiency of the laser, but the laser's efficiency will be improved once the output pump power close to the output.