Research On Yb～(3+)-doped Double-clad Fiber Lasers

Because rare-earth doped fiber lasers have many applications in optical communication, sensing, measuring and industrial fabrication for their compact structures, wonderful heat-sinking capability and highly conversion efficiency, they are studied more and more as source fiber devices. With the wide spectra, high conversion efficiency and high output power, double-clad Yb³⁺-doped fiber lasers (YDFL) will play more and more important role in future.There are the research progress and prosperous future of the double-clad YDFL in this thesis. Not only in theory but also in practice, the influence to output characteristic by the parameters of double-clad YDFL is studied. It is also introduced that the working principle, fabrication process and spectra characteristics of the double-clad fiber Bragg gratings (FBG). We show the latest status of cladding pump technology, and analyze three kinds of coupling methods in detail. We also study the double-clad YDFL in the ways of multiple wavelengthes, selecting frequency by double-clad FBQ and high power in practice. Main works are abstracted as follows:1. Theoretical research on double-clad fiber lasersThrough a new model, we got the explicit expressions of the output characteristics and the cavity parameters of the double-clad fiber lasers. The distribution of the power of pump laser and the relation between the output power and the pump power were analyzed by the method of numerical simulation. We further studied the influence to the maximum output power, threshold power, slope efficiency and output wavelength by the wavelength of pump and signal laser, fiber length and reflectance of both the front and back cavity mirrors of the double-clad YDFL. Then we got the theoretical foundation of the later experiments.By revising the original simplified model, we got the explicit results on the basis of the traits of FBG.2. The fabrication and theoretical research of FBGBy using coupled-mode theory, we analyzed the conversion between different modes in the FBG and the scheme of selecting frequency, worked out the expression of the parameters of FBQ numerically simulated the FBG in practice and discussed the results. With the phase-mask method, we made FBG in double-clad Yb³⁺-doped fibers with different inner sections, reflectance, and output wavelength, then analyzed the results theoretically.