Theoretical And Experimental Studies Of Yb³⁺-doped Double-clad Fiber Lasers

Double-clad fiber lasers are promising high-power lasers, due to their excellent characteristics, including high beam quality, high efficiency and long service time. They have great potential for many applications, such as, communication systems, industrial, military and medical applications. This thesis is composed of five chapters, reporting theoretical and experimental studies of Yb³⁺-doped double-clad fiber lasers.Firstly, the development history, advantages and applications of double-clad fiber laser are briefly introduced.The principles and structure of Yb³⁺-doped double-clad fibers and different techniques of pump beam coupling are discussed in Chapter 2, based on the energy levels and spectral characteristics of the doped Yb³⁺ions.Based on the steady-state rate equations when the scattering loss is considered, the simplified analytic solutions of Yb³⁺-doped double-clad fiber lasers with forward pumping configuration, backward pumping configuration and two-end pumping configuration are deduced, respectively. The results of simplified analytic solutions are in good agreement with those of the numerical simulations.Yb³⁺-doped double-clad fiber laser with forward pumping configuration and backward pumping configuration have been constructed and demonstrated, by making good using of the facilities available in our lab. A 975nm laser diode was used as the pump source using the single-end pumping technique. The experimental results and theoretical ones from our analytic solutions match very well, and our simplified analytic solutions have been validated. Using backward pumping configuration and a reflection grating, a tunable Yb³⁺-doped double-clad fiber laser has been successfully demonstrated. The wavelength tuning range from 1047nm to 1118nm is achieved with output power greater than 23.7W.Finally, the thesis is summarized, with suggestions for the future work.