Threshold characteristics analysis of a uniformly side-pumped Yb3+-doped gain-guided and index-antiguided fiber laser

• A uniformly side-pumped scheme of GG–IAG fiber laser is proposed.
• Improved rate equations and expression of threshold pump power are obtained.
• Analyzed the influence of the fiber laser parameters on threshold pump power.
• Fiber length and doped concentration are both larger compared to end-pumped scheme.
• Obtained the relationship between fiber length range and fiber core radius.

The improved rate equations with additional leakage losses of signal light for a uniformly side-pumped Yb3+-doped gain-guided and index-antiguided fiber laser are established. An exact analytical expression of threshold pump power is obtained. Then the effects of Yb3+ concentration, fiber length, core radius and mirror reflectivity on threshold pump power are discussed in detail, separately. The method of designing the fiber parameters is described while maintaining single mode oscillation, such as R1=1, R2=0.75, a=85 μm, L=10 cm, N=5×1020 cm−3, and threshold power is 6.3 W. Compared with end-pumped scheme, the doped concentration and length of the fiber used in side-pumped scheme can be both larger. The analytical solution was easy to calculate and showed distinct results for the optimal design of the fiber laser.