The Study Of All-Normal-Dispersion Passively Mode-Locked Yb-doped Fiber Laser And Amplifier

In recent years, high power ultrashort pulse have important applications in laser cutting, chemistry and physics basic research, optical communication and so on. Large numbers of enterprises and universities competing to the research and development work about high power ultrashort pulses. Because of its good stability and excellent beam quality, the mode locked fiber laser is a good choice for the development of ultra short pulse. Ytterbium ion energy level structure is simple, the distance is far, and there is no radiative relaxation, so Ytterbium ions can obtain high doping concentration. It is often used as the gain medium of high power laser. The main work of this paper is focus on all-positive-dispersion passive lock-moded ytterbium doped fiber laser. Respectively using graphene saturable absorber and nonlinear polarization rotation, setting up two mode-locked fiber lasers, and amplificate the pulses with home-made double-clad active fiber. The main contents and results are summarized as follows:?1? Introduce the background of fiber laser and mode-locked fiber laser, analyze the formation process of mode-locked pulses. Introduce the research progress of passively mode-locked fiber laser. According to the background, the development direction of the pulse laser is shorter width, higher repetition frequency, smaller environmental impact and wide tunable range, which explains the study of passively mode-locked fiber laser is important.?2? Introduce Yb-doped fiber laser theory. Begin with the spectral characteristics of Yb³⁺, we analyze the Yb-doped fiber laser energy level structure, introduce the laser cavity and the theory laser generation, prepare for the mode-locked Yb-doped laser.?3? We use laser induced deposition to prepare graphene saturable absorber, and apply it into a mode-locked Yb-doped fiber laser to experimentally investigate different operational states. Bright pulses, dark-bright pulse pairs and their second-harmonic pulse, as well as dark pulses and their second, third-harmonic pulses have all been obeserved. In particular, it is the first time to our knowledge to report on the formation of dark-bright pulse pairs, dark pulses and their harmonic mode locking?HML? counterparts in graphene-based passively mode-locked Yb-doped fiber laser with ANDi cavity. We analyze the causes combining with numerical simulation.?4? Analyze the linear and nonlinear characteristics relationship of nonlinear polarization rotation device. According to the theor, we set up a NPR mode-locked Yb-doped fiber laser, and measure laser threshold, spectral width, pulse energy of output pulses. Meanwhile, it is the seed source for following pulse amplification experiments.?5? Using the MCVD technology and the vapor-liquid mixing solution, we fabricate a series of Yb³⁺-doped double-clad fibers. Using the NPR mode-locked laser as a seed source, the Yb³⁺-doped double-clad fibers as amplifying fibers, we amplificate the pulses under MOPA structure. In the amplification process, by modifying the size of the active fiber and amplifier configuration, we preferably suppressed stimulated Raman light and ASE.