Research On Absorption Efficiency Of Double Cladding Fiber Laser

In this thesis, the basic principal, wide application and recent development of fiber laser are introduced first. Then double cladding fiber laser ,as its important branch, is described. Though it is superior to normal fiber laser with high power output, the absorption efficiency of double cladding fiber laser is fairly low. So researchers pay close attention to various new technologies to improve the absorption efficiency.Based on analysis on the reasons of ineffective pump behaviors, several improvement methods are concluded. Raising core radius and doped concentration, bending fibers and optimizing cross section shapes have already been used in applications. Then two different kinds of analytical methods are described in detail. Based on geometrical optics method and mode analysis method, the absorption efficiency on circular symmetry, offset , rectangular and elliptical double cladding fiber laser are calculated and analyzed. The results show that the elliptical cross section is the best one of the four. Besides, other fiber parameters which can improve the absorption efficiency are also discussed.Finally the advantages and disadvantages of the two kind methods are concluded. Each of them has its scope of application.