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Theoretical And Experimental Research On Optical Fiber Phase-Conjugator

Posted on:2004-03-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:T ZhouFull Text:PDF
GTID:1118360092485949Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Multi-mode optical fiber phase-conjugator is used as one possible method to improve beam quality of high-power LD-pumped solid-state laser for its merits of high fidelity, all-solidity, convenience and flexibility. Up to now, using optical fiber phase-conjugator, more than 92% fidelity but maximum reflectivity of just 60% had been reported. Therefore, it is useful to make further study on heightener of reflectivity and applying in laser system with narrow pulse-width less than 30ns and high repetition rate more than 100Hz for space -communication and laser-detect.In this paper, a new theoretical model is established for optical fiber pumped by broadband laser. Using the new model, we have analyzed the influence of longitudinal-mode number, bandwidth and line-width of pumping source on SBS reflectivity, and pointed out the monochromaticity of pumping laser has obvious affect on optical fiber conjugator. Furthermore, the variation of SBS performance parameters, such as threshold and reflectivity, with parameters of pumping laser and multi-mode optical fiber has been researched by analysis of the numerical solution. Experiments have also been operated in LD-pumped solid-state laser system with high-repetition more than 100Hz and narrow pulse-width between 15ns and 47ns. The experimental results agree with calculated results by the theoretical model.Applying 200 m quartz fibers in the LD-pumped laser system with double-pass configuration, 57% SBS reflectivity, near 92% SBS fidelity and 85% relative stability have been obtained. And high beam quality of phase-conjugated laser close to that of oscillator has been achieved. Furthermore, the fiber phase-conjugator has been used in LD-pumped solid-state laser system with four-pass configuration to suppress the self-oscillating (SO) phenomena caused by amplified spontaneous emitting (ASE) in laser amplifier. When using 200 m fiber, the energy of SO has been successfully decreased from 12mJ to below the precision of energy-detector. Thus, 21mJ of single pulse energy has been obtained. In the case of 10% reflectivity, less than 3.7ns with 8.6:1 pulse-compression ratio has been observed. As our acknowledgement, that is the first reported.In addition, a new type of phase conjugator using tapered fiber is designed, which combined the higher reflectivity of small core-diameter fiber and higher damage threshold of large core-diameter fiber. The theoretical analysis has also been carried out in Section IV. Applying it in double-pass system, the maximum SBS reflectivity arrives at 85% and relative stability arrives at 90%, which is more than that of common optical fiber phase-conjugator.As a method to obtain higher SBS reflectivity by improving the monochromaticity of laser system, the LD end-pumped pulse-microchip laser operated on high-repetition and single-frequency has also been researched. In section V, we revised the previous theoretical model for passive-Q-switched laser using Cr4+:Nd3+:YAG by introducing the space dependence between the photons and inversion populations in microchip resonator. Using the revised model, the influence of pumping LD parameters on microchip laser with plane-plane resonator has been studied by numerical analysis.By experimental approach, high stable 1064nm laser pulses with pulse-width 6ns, more than 100kHz repetition rate have been obtained in Cr4+:Nd3+:YAG microchip with 6mm*lmm. The experimental results prove that the revised theoretical model is more suitable than previous model to describe microchip laser. By pre-pumping technique, controllable repetition rate from IHz to 1kHz has been achieved in Cr4+:Nd3+:YAG microchip. Furthermore, gain-switching pulse operation on Nd:YVO4 with 20mm*1mm has been experimental searched, and 1064nm laser with 80ns pulse-width has been obtained.
Keywords/Search Tags:Optical Fiber, Phase-conjugation, MOPA, DPL, Microchip, high-repetition
PDF Full Text Request
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