Threshold characteristics analysis of a forward pumped Nd3+-doped gain-guided and index alternate-guided fiber laser

Abstract

Gain guided and index alternate-guided (GGIA-G) fiber is suggested by our group recently. In order to grasp more laser performance of the GGIA-G fiber, the threshold characteristics of the fiber laser is analyzed in this work. Firstly, the improved rate equations of the forward pumped GGIA-G fiber laser are established and solved. Secondly, the threshold pump power of the GG-IG fiber, GG-IAG fiber and GGIA-G fiber are compared, and the effects of parameters including Nd3+ concentration N, fiber length L, fiber core radius a, refractive index difference Δn and output mirror reflectivity R2 on the threshold pump power Pth are discussed in detail, separately. Finally, the method of designing the fiber parameters for single mode laser operation is given out. When R1s=1.0, R2s =0.8, a=50 μm, N=1.0×1020 cm−3, L2: L=0.2 and Δn=-0.005, the allowed fiber length range for single mode laser operation is about 4.1 cm∼9.0 cm. The related research results will be helpful to the better application of the GGIA-G fiber.