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High-power Fiber Laser Key Technologies And Systems

Posted on:2008-05-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:S G FuFull Text:PDF
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Because double-clad fiber lasers possess both the good qualities of tradition solid lasers and fiber lasers, they have great potential in research and applied fields. In the paper, we focus on theoretical and experimental research on Yb3+-doped double-clad fiber lasers. Main works are abstracted as follows:1. Through the velocity rate equation, the explicit expressions of the output characteristics and the cavity parameters of the Yb3+-doped double-clad fiber lasers(YDFL) are obtained. The distribution of the power of pump laser and the relation between the output power and the pump power were analyzed by the method of numerical simulation. We further studied the influence to the maximum output power, threshold power, slope efficiency and output wavelength by the wavelength of pump and signal laser, fiber length and reflectance of both the front and back cavity mirrors of the Yb3+-doped double-clad fiber laser.2. A passive Q-switched large-mode-area Yb-doped fiber laser is demonstrated using a GaAs wafer as the saturable absorber. A high Ytterbium-doped fiber with a core diameter of 30μm and a numerical aperture of 0.07 was used to increase the laser gain volume, permitting greater energy storage and higher output power than conventional fibers. The maximum average output power is 7.2 W at 1080 nm wavelength, with the shortest pulse duration of 580 ns and the highest peak power of 170 W when the laser was pumped with a 25 W diode laser operating at 976 nm. The repetition rate increases with the pump power linearly and the highest repetition rate of 78 KHz has been obtained in the experiment.3. Using phase-mask method, low reflectivity FBGs are successfully fabricated into large-area-mode double-clad fiber directly. Using scanning phase mask technique, high reflectivity large-size FBGs with the reflective peak of more than 20 dB are fabricated successfully in hydrogen-loaded light-sensitive fibers4. A simple switchable multi-wavelength double-clad fiber laser using a multi-mode fiber Bragg grating (MMFG) as wavelength selective component is demonstrated. The MMFG is fabricated directly in the active double-clad fiber, resulting in low splicing loss and compact configuration. By properly adjusting the polarization controller in the cavity, the double-clad fiber laser can stably operate at different multi-wavelength states at room temperature. At lower pump level, the laser can be switched between single- and dual-wavelength operations while at higher pump level the laser can switch between dual- and triple-wavelength operations. The slope efficiency of system is 41% with the maximum output power of 6.2 W5. To produce strong tilted fiber Bragg gratings (TFBGs)we adopted a concatenating technique in the UV-inscription process. We were able to fabricate a 40-mm-long 45°TFBG by concatenating multi-section grating. The characteristics of the TFBGs are investigated also. Based on the 45°TFBG, a polarized fiber laser is demonstrated. Using a TFBG as the polarizer of the fiber laser, the polarize laser is achieved with more than 30 dB polarization-extinction ratio.
Keywords/Search Tags:Double-clad fiber, Yb3+-doped double clad fiber, fiber grating, passively Q-switching, tunable fiber laser, Yb3+-doped photonics fiber laser, switchable multi-wavelength fiber laser, tilted fiber Bragg grating, polarization dependence loss
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