Theoretical And Experimental Study On High-Power Ytterbium-Doped Double-Clad Fiber Laser

High power fiber laser is a novel laser technology that combined of the LD modules , pumping techniques , double-clad fiber(DCF) fabricating technology and fiber grating techniques. And it has attracted many scholar's attention in laser field. Base on the work already studied, the dissertation focuses on theoretical and experimental study of high-power ytterbium-doped double-clad fiber laser . The research work in detail is shown as follow:1,The energy level structure of ytterbium and producing mechanism of Raman Effect are discussed. From the steady states rate equations, the Stimulated Raman Theory of high-power ytterbium-doped double-clad fiber laser is analyzed. Base on this and the program that we have, corresponding mathematics model has been established. At the same time, some new solutions of differential eguations with boundary conditions have been studied. In the process of resolving differential eguations, we combine with two methods to make different variables converge early or late, and get the results steadily. According to the characteristic of the differential eguations, reverse integration is adopted, so the calculating time is shortened greatly. And the settling of overflow when the differential eguations are integral makes the feedback be effective.2,Through the mathematics model, the output characteristic of high-power ytterbium-doped double-clad fiber laser with Raman Effect is simulated, and the action of increasing fiber core area, shortening fiber length, reducing Yb3+-doped concentration, increasing signal laser wavelength for reducing Raman Effect has been analyzed. The critical pump power and output power characteristic of fiber laser is discussed when pumping is different(single pump, bidirectional pump). Especially the change of Raman Effect is studied chiefly when cavity mirror reflectivity is changing. The conclusion is useful for the optimization of high-power ytterbium-doped double-clad fiber laser to decrease the effect of Raman Effect.3,The output power characteristic and laser distributing along the fiber in high power fiber laser with Raman Effect are took into account in multi-point pump model for the first time in this paper. All these can conduct the experiment of DCFLs in multi-point pump model.4,Making use of the program we wrote, we have modifed our fiber laser system theoretically using experimental parameters, and provide some theoretical basis for the optimization of our experiment ahead.5,Base on mixed mode Gussian-Like theory, the principle of coupling system for high power fiber laser is studied, and some improving advice of minishing diffraction loss of the coupling system is provided for the first time. A collimation-protect connector is designed and machined, and it has been used for LD pig tail and coupling system successfully. Then, experimental coupling system is designed and machined. The analysis of experimental coupling system has been done, and some useful suggestion of optimization for the system is brought forward staring the experimental result. It is proved experimentally that the coupling system designed by ourselves is helpful. So the next experiment can be continued favorably. 6,The capability parameter of LD, dichroic mirrors is measured, and the principia and characteristic of every part of fiber laser is described in detail. We truss the double-clad fiber laser experiment system with the coupling system designed by ourselves, roundly describle the output characteristic and process of a linear cavity end-pumping fiber laser experiment, and with different dichroic mirrors and fiber length we have done lots of experimental work, get some useful conclusions, gain a lot of helpful experimental experience. At last, we discuss the problem and phenomena found in the experiment with interrelated theories deeply, provide some advice to improve our fiber laser system. Ground on the coupling system we designed and using D type inner-clad fiber, we get signal output power by 1.6W when the pump power incident on the fiber is 3.7W.