Research On High-Power Y_b～(3+)-doped Double-Clad Fiber Laser

Fiber laser has become a focus of research in the field of optoelectronics worldwide since the double-clad fiber was invented in 1988. Owe to its excellent performance and abroad of applications, fiber laser becomes the third generation of laser technological representation. In this paper, Yb³⁺-doped Double Clad Fiber Lasers (Yb³⁺-DCFLs) have been studied in experimentally and theoretically. The main subjects are as the following:(1) Brief review of the history, development and application of Yb³⁺-DCFLs. And it point out the practical significance of the research of double-clad fiber lasers.(2) The basic theory of fiber laser is introduced:the energy level and spectrum characteristics of Yb³⁺ are detailed; Then the Fabry-perot (F-P) cavity and fiber gratings resonator are discussed; Moreover, the rate equations of theory Yb³⁺-DCFLs are constituted, by using this theory, the expression of output power and slope efficiency are obtained as well as numerical analysis for Yb³⁺-DCFLs is carried out .(3) The structure of single clad fiber and double clad fiber with their transmit characteristics are introduced. Furthermore, we analysis the effect of difference inner-cladding structures on the absorption efficiency of pump light, and the fiber length has a significantly impact on output power.(4) The structures and characteristics of high power diode laser bar are reviewed. Pumping methods of end-pumping and side-pumping, together with their advantages and disadvantages are summarized as well.(5) After analyze the changing of Gaussian beam, it is studied that the fundamental Gaussian bean through two lens-coupling system, the general law in deciding the parameters of coupling system is deduced. A special coupling system is designed accordingly to our experiment, and the coupling efficiency of 79% was achieved.(6) The output characteristics of Yb³⁺-DCFLs base on F-P cavity and fiber gratings resonator are studied in our experiments, the output power is obtained from the laser with D-shape double clad fiber are more than 25w and 27w respectively; and the total optical-to-optical efficiency are up to 63% and 67% accordingly. There are some problems in the experiments, then some improvement suggestions are presented.