Backreflection of the residual pump power into the cavity, and optimization of the fiber length, may significantly improve the efficiency of a strongly pumped fiber laser. A rate equation model is introduced and studied. Examples for Yb3+-doped fiber lasers, with DBR mirrors at either end, show that employing such a geometry results in higher efficiency with shorter optimal fiber length. Approximate analytical and quasi-analytical expressions are shown to be in excellent agreement with the exact numerical solution of the rate equations.
Ido Kelson and Amos Hardy, "Optimization of Strongly Pumped Fiber Lasers," J. Lightwave Technol. 17, 891- (1999)