| In this dissertation, the three scientific puzzles in the application fields of big power fiber laser for common rare-earth-ions doped optical fibers have been studied, including the problems between big core diameter and good laser beam quality, high coupling efficiency, and photo-darkening. Firstly, we design the waveguide structures for ytterbium-doped PCF and erbium-doped PCF, construct the hydrodynamics model for silica PCF high-temperature melt, develope the fabrication process route for PCF. Then, the ytterbium-doped PCF, erbium-doped PCF and double-cladding fiber gratings were manufactured. The laser experiments of the two kinds of PCF were earried out, and their performances were also analyzed. Finally, the ultra-mode-area ytterbium-doped optical fiber (YDF) was prepared and its laser beam quality was also studied. The mechanism of photo-darkening was construed, and the photo-darkening characteristics of different materials were also investigated, and the relevant countermeasures to reduce the photo-darkening were put forward.The research contents and results are formulated in the following.(1) The waveguide structures of rare-earth-ion doped PCF have been investigated. It is shown that the single-mode operation performance with large core for PCF can be acquired, the conditions are that the ratio of air hole diameter to lattice constant in the triangular array is smaller than or equal to 0.30, and lattice constant is smaller or equal to 15 times of transmission wavelength (λ). The cladding numerical aperture (NA) as high as 0.7 can be achieved at the condition that the radial size of large air-holes in the outer-cladding is larger than or equal to three times ofλand the bridge width is smaller than or equal to 0.5 times ofλThe double-cladding ytterbium-doped PCF with a core diameter of 43μm has been realized successfully, and tests demonstrate that the fiber could operate at the single-mode and the NA of inner-cladding reached 0.65, which can tackle the problems of large core and single-mode operation, and the high coupling efficiency. (2) The fabrication process technologies have been profoundly made research. The hydrodynamics model for silica PCF high-temperature melt has been constructed, and the influence disciplinarians of different parameters on the process sensitivity degree have been investigated, the preferable drawing conditions are that the furnace temperature is 2123K, the load speed of PCF perform is faster than 3mm/min, the fiber drawing speed is faster than 200m/min, and the pressure margin between outside and inner of capillary should be less than 300 pa. To the conventional solution-doping process deficiencies of rare-earth ions, the novelty all-gas-phase doping process for rare-earth-ions has been invented, the fabrication process route for rare-earth-doped PCF has been presented, and the ytterbium-doped PCF and erbium-doped PCF have been fabricated successfully.(3) The laser performances of double-cladding ytterbium-doped PCF have been studied. The all-fiber ytterbium-doped PCF laser has been constructed with self-make ytterbium-doped PCF and fiber grating. With the 915nm laser diode pumping, the output laser power at the center wavelength of 1080.2 nm is 3.96 watts, the slope efficiency is 79.6%, and the laser beam quality M2 is 1.2. The spectrum absorption characteristics of the double-cladding ytterbium-doped PCF are different from the common double-cladding ytterbium-doped optical fiber (DCYDF), its absorption coefficients at 915nm and 976nm wavelength are higher than that of the common DCYDF, the width of its absorption peak at 915nm wavelength is bigger than that of the common DCYDF, and the wavelength of its absorption valley is shifted 10nm to the longer wavelength. The reason may be that the ytterbium-ion energy levels are disturbed to some extent by the electric fields of the compounded air-silica glass network. This results in the novelty performance of Stark splitting, which influences the transition behavior of ytterbium-ions from 2F7/2 to 2F5/2.Therefore, the absorption spectra are widened and heightened, and the absorption valley shifts to the longer wavelength.(4) The research of erbium-doped optical fiber and its laser amplifying performances has been made. It is discovered that raising the doping domain of erbium-ions can efficiently increase the overlap factor and improve the amplifying efficiency. The laser amplifying experiments and bending loss tests of erbium-doped optical fibers show that the erbium-doped PCF has comparatively higher gain, better gain flatness and anti-bending ability than the common erbium-doped optical fiber. These results are attributed to the bigger overlap factor and better confining ability of fundamental mode light field for air-silica compounded structured materials.(5) The ultra-large mode-area ytterbium-doped optical fiber has been investigated. The novelty structure DCYDF with a core-diameter of 100μm has been designed and fabricated successfully. The lasers experiments show that the ultra-large mode-area ytterbium-doped optical fiber with Frustrated Total Internal Reflection structure can remarkably improve the laser beam quality. With this fiber, the average laser beam quality factor M2 in the directions of x and y are 2.977 and 2.583, which is 40% smaller than that of the common large-core YDFs.(6) The photo-darkening characteristics of YDFs have been investigated. On the basis of analyzing the photo-darkening mechanisms, the YDFs with different material prescriptions have been fabricated. The aging tests of pumping laser and laser experiments of output power stability have been carried out with these YDFs, the results show that the kinds of YDFs with high doping concentration of ytterium-ions are inclined to photo-darkening, and the aluminum-ions and phosphorus-ions co-doping agents can reduce the photo-darkening of the same-concentration YDFs.
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