有理数主动锁模掺铥脉冲激光器理论分析

发布时间：2019-04-26 17:47

【摘要】：2 μm波段脉冲激光在医疗、国防、机械加工和光通信等领域都有很大的应用前景。主动锁模光纤激光器利用的锁模方式一般是引入外界信号使激光器腔体内的参量达到周期性变化,但由于其调制器频率的限制,导致输出激光脉冲的重复频率受限,无法实现高重复频率的超短脉冲。有理数谐波锁模技术是对基于调制器锁模技术的改进方案。本文研究有理数主动锁模技术,建立了有理数主动锁模掺铥脉冲激光器的理论模型,通过理论仿真,分析组成锁模激光器的各参数对激光器输出脉冲特性的影响,期望在压窄输出激光脉冲宽度的基础上,提高脉冲的重复频率,从而解决调制频率的限制问题的方法,获得基于有理数主动锁模的2 μm波段超短激光脉冲。本文的主要工作为:1,建立了有理数主动锁模掺铥脉冲光纤激光器的数值仿真模型,仿真模型由掺铥光纤放大器模型、普通单模光纤中脉冲传输模型和调制器模型这三部分组成。详细分析了三个部分在2μ 波段有理数谐波脉冲激光的形成过程中的作用。2,分析了不同倍频情况下,2 μm波段脉冲激光时域波形和频域的稳定性。仿真结果表明,通过较小的调制频率即可输出高重复频率的锁模脉冲。激光器在时域上输出18倍频脉冲所用到的调制频率为fm= 3.6fc,即基频的3.6倍。并且在频域上分析激光器的稳定性,结果表明:有理数主动锁模技术的稳定性比普通主动锁模技术的稳定性差,并且随着阶数的增加稳定性随之而降低。3,研究了有理数主动锁模掺铥光纤激光器输出的超短脉冲功率、脉宽以及能量参数随有源光纤的长度、掺杂浓度、泵浦光功率及单模光纤的非线性等变化的特性。仿真结果表明,在一定的铥离子掺杂浓度范围内,输出功率随掺杂浓度的增加而线性增加,脉宽则随之变窄;在一定范围内增加掺铥光纤的长度能够提高激光器输出脉冲功率并有效降低脉宽;普通单模光纤的非线性效应主要影响输出脉冲的脉宽,通过优化光纤长度可获得最窄脉宽的脉冲激光输出;在适当范围内增加泵浦光功率和调制器的调制深度,均可提高输出激光脉冲的功率并有利于压窄脉宽。
[Abstract]:2 渭 m-band pulse laser has great application prospects in medical, national defense, mechanical processing and optical communication. Active mode-locked fiber lasers usually introduce external signals to make the parameters of the laser cavity change periodically. However, due to the limitation of the modulator frequency, the repetition rate of the output laser pulse is limited. Ultra-short pulses with high repetition rates cannot be achieved. Rational harmonic mode-locking technology is an improved scheme based on modulator mode-locking technology. In this paper, the rational number active mode-locking technology is studied, and the theoretical model of thulium-doped pulse laser with rational number active mode-locking is established. Through the theoretical simulation, the influence of the parameters of the mode-locked laser on the output pulse characteristics of the laser is analyzed. It is expected that on the basis of narrowing the pulse width of the output laser, the repetition rate of the pulse can be improved, so as to solve the problem of limiting the modulation frequency, and the ultra-short laser pulse of 2 渭 m band based on rational number active mode-locking can be obtained. The main work of this paper is as follows: 1. The numerical simulation model of rational number active mode-locked thulium-doped pulsed fiber laser is established. The simulation model is based on thulium-doped fiber amplifier model. The pulse transmission model and modulator model in ordinary single-mode fiber are composed of three parts. The role of three parts in the formation of 2 渭 band rational harmonic pulse laser is analyzed in detail. (2) the stability of 2 渭 m band pulse laser in time domain and frequency domain under different frequency doubling conditions is analyzed. The simulation results show that the mode-locked pulse with high repetition rate can be outputted with small modulation frequency. The modulation frequency used by the laser to output 18-fold frequency pulse in time domain is 3.6 times of fm= 3.6 fc, that is, 3.6 times of the fundamental frequency. The stability of the laser in frequency domain is analyzed. The results show that the stability of rational active mode locking technique is worse than that of ordinary active mode locking technique, and the stability decreases with the increase of order. The ultra-short pulse power, pulse width and energy parameters of an active mode-locked thulium-doped fiber laser with rational number vary with the length of active fiber, doping concentration, pump power and nonlinearity of single-mode fiber. The simulation results show that the output power increases linearly with the increase of doping concentration and the pulse width becomes narrower in the range of doping concentration of thulium ion. Increasing the length of thulium-doped fiber in a certain range can improve the output pulse power and reduce the pulse width effectively. The nonlinear effect of the ordinary single-mode fiber mainly affects the pulse width of the output pulse. The narrowest pulse width can be obtained by optimizing the length of the fiber. Increasing the pump power and the modulation depth of the modulator in a proper range can increase the power of the output laser pulse and facilitate the compression of narrow pulse width.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN248

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