An analytical model for the determination of optimal outputreflectivity and fiber length in erbium-doped fiber lasers

An analysis relating the output power of erbium-doped fiber lasers to the output mirror reflectivity r_out is performed, and a closed-form expression valid for r_out<0.95 is obtained. It shows that the laser output power is nearly independent of the output reflectivity when 0.5<r_out<0.95. The closed-form expression is used to study the dependence of the output power with laser wavelength and confirms the large tuning range (60 nm) already reported. However, it is shown that the tuning range is greatly increased (up to more than 100 nm) if r_out is chosen near 0.9. Finally, an approximate expression for the optimal fiber length needed to achieve maximum laser output is derived