Research On Erbium-doped Fiber Laser Based On Phase-shifted Fiber Grating

With the development of laser technology, erbium-doped fiber lasers get widespread attention due to its wide gain window, low insertion loss and so on. At present they have been utilized in the optical communications, light sensing, laser processing, precision interferometry, holography and many other important areas of applications.In this dissertation, a novel erbium-doped fiber laser is proposed. It consists of a ring cavity and a filter which is composed of a uniform fiber Bragg grating and a phase-shifted fiber grating. Laser with high performance is achieved by designing transmission parameters of the gratings accurately.The main research works are listed as below.(1)The erbium-doped fiber laser is analyzed theoretically in detail. The three basic transition processes and the energy-level systems are described. As a result, the gain formula, the spectrum broadening formula and the rate equations of erbium-doped fiber are obtained. The stimulated absorption cross-section and stimulated emission cross-section of erbium-doped fiber are analyzed. The characteristics of the ring cavity and mode selection methods are introduced briefly. The rate equations of traveling wave are discussed based on ring cavity structure. These offer the foundation of simulating models theoretically.(2)The transmission characteristics of uniform fiber grating are analyzed by using the coupled-mode theory and the transmission characteristics of phase-shifted fiber grating by using the transfer matrix theory. The influences on the grating spectral characteristics of different grating parameters are investigated. The transmission characteristics of the filter is improved by using apodized gratings.(3)The time-domain model and frequency-domain model are both established. Then the system is simulated by inputting different parameters. The output parameters are obtained including wavelength, power, width and efficiency of the laser. The results are discussed in the conditions of different fiber lengths, different pump power and different output ratios. Some suggestions are proposed at last.A reasonable conclusion is obtained from the above work. It offers a good guide to make fiber lasers.