Study Of Yb-doped Double-clad Fibers

The Yb³⁺-doped double-clad fiber (YDCF) has many characteristics,such as the broad absorption and emitting area, high quantum efficiency and so on. The fiber laser with the gain fiber is Yb³⁺-doped double-clad fiber laser (YDCFL), which has the merits with high power, high efficiency, good beam quality and compact. Therefore, so it has many applications, such as precise laser processing, laser radar system, light communication and some military systems. Because the YDCF is one of the key components in the high power laser, YDCF has been largely researched, and it has been quickly developed recently.The merits, the applications, the recently progress and the development of the research of the YDCF have been summarized in this paper. Because the YDCF is used in the fiber laser, the characteristics and the recently progress of the YDCFL have been summarized, also. The main contents are listed as follows:1. The structures and the absorption of the double-clad fiber have been introduced. By using theories of the geometry optics and the fiber optics, the effects of the different structures of the inner cladding of the double-clad fiber in the fiber laser have been analyzed, and the theory model has been set up and new structure of the inner cladding has been designed.2. The preparing technique of the Yb³⁺-doped double-clad fiber has been studied. By analyzing the key technique of developing double-clad fiber in high power fiber laser, the high concentration doped technique has been researched. And by optimizing the key technique and the process, we have found the effective way of realizing the higher concentration in the double-clad fiber. By researching the technique of the large core diameter and controlling the refractive index of the core, we can decrease effectively the numerical aperture of the core. By researching the relation between the temperature of the tectorium and doped concentration, and optimizing the temperature and time of the drying, we fabricated successfully the large mode area Yb³⁺-doped double-clad fiber with excellent characteristics. The Yb³⁺-doped fiber is fabricated, which is doped concentration over 6000ppm, and absorption 7.5dB/m at the wavelength of 976nm, core diameter up to 30μm. The experiments of the fiber laser has been done by using the Yb³⁺-doped fiber, and the output laser is power up to 404W, and the slope efficiency 67.8%.3. A study of Ytterbium-doped double-clad fiber absorption characteristics is presented. Through the method of fiber-cutting and the technology of clad-mode peeling, the core absorption coefficient of Ytterbium-doped double-clad fiber is measured precisely. The error between the measurement result and the real absorption coefficient is less than 5%. With the white light the attenuation spectrum and effective absorption coefficient of Ytterbium-doped double-clad fiber is studied experimentally in detail. The results of the experiment is explained and analyzed qualitatively.