Theoretical Study Of Yb-Doped Double-Clad Fiber Laser

Compared with traditional solid state laser, fiber laser has many merits, such as high efficiency good beam quality compact and good heat dissipation. Yb³⁺ doped fiber laser has been attracted greatly because of simple energy structure, no excited state absorption, and wide tunable range. Different from general fiber, double clad fiber has an inner clad at the outside of fiber core. In double clad fiber laser, Pump light propagates in inner clad and is absorbed by doped fiber core. Laser can be produced in doped fiber core. Because of large geometrical size and numerical aperture (NA) of inner clad, high pump power can be coupled into the double clad fiber so that high output laser power can be yielded.In this paper, Yb³⁺ doped double clad fiber laser is studied in theory. The main work is as follows:The first chapter has introduced the backgrounds of the fiber laser which include the history of the fiber laser; The development of the researches, main applications and the development way in the field of double-clad fiber laser worldwide are summarized and the significance of this research subject is pointed out.The basic theory and the structure of double-clad fiber laser is researched. According as the constitute of double-clad fiber laser, we discuss the structure and characteristic of double-clad fiber, the cavity and the coupling technology.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. Power govern equations of DCFL are constituted.According to rate equations of fiber laser, the output characteristic of Yb³⁺-DCFL was numerically studied with MATLAB. The power distributions of pump and laser, the effects of output coupling reflectivity, scattering loss coefficient and wavelength of pump light on the characteristics of fiber laser are studied by shooting method .The results can help us design double clad fiber laser.