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Experimental Research Of High-energy Fiber Laser Based On Nonlinear Polarization Evolution Or New Saturable Absorber

Posted on:2016-11-25Degree:MasterType:Thesis
Country:ChinaCandidate:X L WangFull Text:PDF
GTID:2348330488972820Subject:Optical Engineering
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Fiber lasers have the advantages of high stability, excellent heat-dissipation, compact structure and good beam quality. In recent years, they have developed rapidly, becoming a research hotspot. Erbium doped fiber laser, because of its special application in the field of communication, gets development and studied firstly. As far, it has been very mature. Then, the study of 1 ?m ytterbium doped fiber laser(YDFL) and 2 ?m thulium doped fiber laser(TDFL) near infrared wavelengths are researched on. For the requirements of the current research and market development, we systematically research on the YDFL and TDFL in this paper. Based on the nonlinear polarization evolution(NPE) and new saturable absorbers in the all fiber ring cavity respectively, experimental studies of the high-pulse-energy Q-switched or mode-locked lasers have been made. The main research contents are divided into the following sections:1. In the study of YDFLs, stable mode-lockings are realized based on the NPE respectively with space structure and all-fiber structure. In the oscillators of space structure, stable mode-locking is realized with the maximum output power of 181 m W, the repetition rate of 49.21 MHz and pulse duration of 3 ps. Then, rotating the birefringent filter plate frame, the mode-locked spectra can be continuously tuned from 1015 nm- 1045 nm. In the tuning process, the mode-locking is stable. At the pump power of 500 m W, by properly rotating the birefringent filter and wave plate, stable second harmonic mode-locking with repetition rate of 99.64 MHz can be obtained. Compared with the fundamental mode-locking, the output power decreased obviously. In the oscillators of all-fiber structure, mode-locked states and output-powers at different output ratios of 5%, 10%, 20%, 30% and 50% are studied. The stable mode-locked operation with 7-m-long cavity is realized. In this mode-locking, we compared the mode-locked spectra with filter and without filter, concluding the result that the filter plays an indispensable role in mode-locked fiber laser in all-normal dispersion region. In order to obtain high energy mode-locked pulse, the cavity length is changed to as long as 347 m. The mode lockings are realized at different output couplers. The maximum single pulse energy of 263 n J is obtained at the output ratio of 50%, with the high effiency of 33%, repetition rate of 614 KHz and pulse duration of 10 ns, which is the highest single pulse energy obtained in all fiber YDFL oscillators to our best knowledge.2. The different properties of single wall carbon nanotubes and graphene oxide as the Q switcher in the all fiber YDFLs with ring cavity are systematically studied. Based on SWCNT SA(Single Walled Carbon Nanatube, Saturable Absorber), the Q-switched pulses are obtained with the pulse width of 1.0 ?s, the repetition rate of 66.24 KHz, central wavelength of 1032 nm and the average output power of 2.69 m W at the maximum pump power of 125 m W. Compared with the previous all fiber Q-switched fiber lasers, the stable mode locking is achieved with a rather low threshold of 38 m W and a maximum single pulse energy of 40.6 n J which is the best result in the relevant reports. Based on GOSA(Graphene Oxide Saturable Absorber), the maximum single pulse energy of 69.4 n J output is obtained, which is the largest single pulse energy in Q-switched Yb-doped all fiber lasers based GOSA. Under the same condition, when the GOSA is removed, the self Q-switched operation can be obtained by adjusting the polarization controller. Compared to the self Q-switched phenomenon, the state of Q-switching based on graphene oxide is more stable.3. In the Thulium doped fiber lasers, we optimize the all-fiber ring resonators by respectively trying the output couplers of 10% and 50% ratios. At the pumping power of 1.95 W, continuous-wave laser with the maximum output power of 61 m W is obtained. Based on new saturable absorber material: topological insulator- Bi2Te3, in the form of a sandwich structure inserting in the cavity, we realize a stable mode locking at repetition rate of 7.794 MHz under 1.85 W of pump power. The maximum mode locked output power is 26 m W, corresponding to a single-pulse-energy of 3.34 n J.
Keywords/Search Tags:All fiber, Nonlinear Polarization Evolution, Single walled carbon nanatube, Graphene oxide saturable absorber, Topological insulator saturable absorber, High energy pulse
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