Yb-doped Double-clad Fiber Laser

The double-clad fiber lasers (DCFLs) develop very fast in recent years for its advantages include good beam quality, high efficiency, compact structure and easy to run in high power. The fiber lasers have been widely applied in the fields of laser processing, optical communication, medical treatment and military etc. The theory and technology research of laser Diode (LD) pumped Yb³⁺-doped double-clad fiber laser (Yb³⁺-DCFL) is the currently ultimate branch in the laser techniques field. In the dissertation, theoretical and experimental investigation of Yb³⁺-DCFL are presented. The main subjects are as the follow:1. The double-clad fiber is introduced briefly, and the development of the researches, main applications and the development way in the field of fiber laser worldwide are summarized, and the significance of this research subject is pointed out.2. The principle of Yb³⁺-DCFLs are discussed; The energy level, spectrum characteristics and characteristics of stimulated emission of Yb³⁺ are detailed, which indicate its superiority to emit laser. The technology of cavity, end-pumped, side-pumped and taper-pumped of double clad fiber laser are introduced and dissertated.3. Power govern equations of DCFL are constituted. The characteristics of output wavelength, threshold power and slope efficiency of fiber laser are analyzed. By using the govern equations, output characteristics of Yb³⁺-DCFLs are analyzed theoretically and the expressions of output power, the threshold and the slope efficiency have been given. The output characteristic of Yb³⁺-DCFL was numerically studied with MATLAB. The power distribution of pumping light and laser light in fiber, threshold, fiber length, slope efficiency, ratio of output mirror, modes of pump on the characteristic of the fiber laser are investigated. These discussions provided a theoretical basis to the optimum design of double-clad fiber laser.4. The experiment of Yb³⁺-doped double-clad fiber laser with Fabry-Perot cavity is carried out. The maximum output power obtained from Yb³⁺-DCFL is 3.13W. The slope efficiency and optical to optical are up to 68.32% and 63.36%. The experimental results and some problems in the experiments are explained, then some idea and suggestions are presented.