自适应非保偏—保偏光纤激光转换技术研究

发布时间：2018-07-18 21:31

【摘要】：高功率、高亮度的线偏光纤激光在非线性频率变换、引力波探测、激光通信、长距离传感、光束合成等领域有着广泛的应用。目前,获得高功率高亮度的线偏激光主要采用基于保偏光纤以及偏振相关器件的保偏光纤激光器。在保偏光纤激光器中,受激布里渊散射、受激拉曼散射等非线性效应和模式不稳定阈值要比同等条件下非保偏光纤激光器阈值低,保偏器件工艺复杂,价格昂贵,保偏光纤的切割、熔接等工艺难度较大。因此,一般而言,保偏光纤激光器输出功率比非保偏光纤激光器的输出功率低。为了获得更高功率的线偏振光纤激光,本文提出了自适应非保偏—保偏激光转换的技术方案,将非线偏振激光直接转为高消光比的线偏振激光。论文对基于偏振控制器和锁相控制原理的非保偏—保偏激光转换的技术展开了详细的理论和实验研究,主要内容包括:首先,介绍了保偏光纤激光器的发展现状和功率限制因素,指出了自适应偏振转换技术实现高功率保偏激光的可行性;回顾了国内外研究人员在偏振控制领域的研究成果,总结了偏振控制技术在传感、通信、光束合成等领域的发展现状。其次,提出并设计了基于偏振控制器的自适应非保偏—保偏激光转换控制系统,开展了详细的理论和实验研究。理论上给出控制系统的基本结构和工作原理,建立了基于偏振控制器的偏振转换系统的理论模型。基于随机并行梯度下降算法,数值模拟了算法的增益系数和扰动精度、偏振控制器的控制精度和步进增益以及激光器稳定性等因素对偏振转换效果的影响。结果表明,通过优化随机并行梯度下降算法的参数以及偏振控制器的参数可以获得高消光比的线偏振光。在理论研究的基础上,搭建了基于偏振控制器的自适应转换系统。根据系统的响应特性,改进了控制程序,分别进行了低功率种子光条件下和高功率放大器条件下的自适应偏振转换。实验结果表明:无论是非保偏的种子源还是高功率放大后的非保偏激光均可以利用偏振转换技术实现高消光比的偏振转换,此外,利用此结构可以对输出光束进行任意角度的转换输出。然后,提出并研究了基于偏振锁相的自适应转换控制系统。理论上,给出了控制系统的基本结构和工作原理,建立了基于偏振锁相的偏振转换系统的理论模型,分析了系统的重叠误差、倾斜误差,闭环时的锁相残差以及合成光束的光强不同等因素对偏振转换效果的影响。结果表明,系统重叠误差与倾斜误差通过在合成处的不重合与光能泄漏影响系统的转换效率,重叠误差会影响输出的偏振度,但倾斜误差并不影响输出的偏振度。在锁相残差较小的情况下可忽略两路光强不同对偏振度与转换效率造成的影响,因此,锁相残差是影响系统合成效率与偏振度的关键因素。实验上,分别搭建了全光纤结构与空间结构的基于锁相控制的实验平台。在全光纤偏振转换系统中,将非保偏的激光的消光比从5dB提高到了17.2dB。在空间结构系统中,最终获得了偏振度为93.5%的高消光比激光。最后,提出了直接将高功率宽谱非保偏激光器输出激光转换为线偏振激光的方案。分析了方案的可行性,研究了在宽谱光源的条件下利用基于偏振锁相的自适应转换系统进行偏振转换的可行性,并设计了初步的系统结构。本文通过理论和实验研究提出了基于偏振控制和偏振锁相非保偏—保偏光转换技术方案的可行性,为实现高功率线偏振激光提供了一定的参考。
[Abstract]:High power, high brightness line biased fiber laser is widely used in nonlinear frequency conversion, gravitational wave detection, laser communication, long distance sensing, beam synthesis and other fields. At present, the polarization laser based on polarization maintaining fiber and polarization dependent optical fiber laser is mainly used to obtain high power and high brightness. In the device, the stimulated Brillouin scattering, the stimulated Raman scattering and other nonlinear effects and the mode instability threshold are lower than the non conservative fiber laser under the same condition, the process is complicated and the price is expensive, the cutting of polarization maintaining fiber and the fusion are more difficult. In general, the output power of the polarization maintaining fiber laser is not guaranteed to be biased. The output power of fiber laser is low. In order to obtain higher power line polarization optical fiber laser, this paper proposes an adaptive non polarization preserving polarization laser conversion technology. The non linearly polarized laser is directly converted to a linear polarization laser with high extinction ratio. The paper is a non conservative polarization laser conversion based on the polarization controller and the phase lock control principle. The detailed theoretical and experimental research is carried out. The main contents are as follows: first, the development status and power limiting factors of the polarization maintaining fiber laser are introduced. The feasibility of the adaptive polarization conversion technology to realize high power polarization maintaining laser is pointed out, and the research results of researchers at home and abroad in the field of polarization control are reviewed and summarized. The development status of polarization control technology in sensing, communication, beam synthesis and other fields. Secondly, an adaptive non conservative partial polarization maintaining laser conversion control system based on polarization controller is proposed and designed. The detailed theoretical and experimental research is carried out. The basic structure and working principle of the control system are given in theory, and the polarization control based on polarization control is established. The theoretical model of the polarization conversion system. Based on the stochastic parallel gradient descent algorithm, the influence of the gain and disturbance accuracy of the algorithm, the control precision and the step gain of the polarization controller and the stability of the laser on the polarization conversion effect are numerically simulated. The results show that the parameter of the random parallel gradient descent algorithm is optimized. The parameters of the polarization controller can obtain the linear polarized light with high extinction ratio. On the basis of the theoretical study, an adaptive conversion system based on the polarization controller is built. According to the response characteristics of the system, the control program is improved, and the adaptive polarization rotation under the condition of low power seed light and high power amplifier is carried out respectively. The experimental results show that the polarization conversion of high extinction ratio can be achieved by the polarization conversion technology, both of the non conservative seed source and the non conservative laser after the high power amplification. In addition, the output beam can be converted at any angle by using this structure. Then, the adaptive rotation based on polarization phase locking is proposed and studied. In theory, the basic structure and working principle of the control system are given, and the theoretical model of polarization conversion system based on polarization locked phase is set up. The influence of the overlap error, the tilt error, the phase locked residual of the closed loop and the different light intensity of the synthetic beam on the polarization conversion effect is analyzed. The overlapping error and the tilt error affect the conversion efficiency of the system by the non coincidence and light leakage at the synthetic place, and the overlap error will affect the degree of polarization of the output, but the tilt error does not affect the degree of polarization of the output. The influence of the intensity and conversion efficiency of two different light intensity can be ignored in the case of the small phase locked residual difference. Phase locked residual is the key factor affecting the efficiency and degree of polarization of the system. In the experiment, the experimental platform based on phase locked control of all fiber structure and space structure is set up respectively. In all fiber polarization conversion system, the extinction ratio of the unbiased laser is increased from 5dB to 17.2dB. in the spatial structure system, and the polarization is finally obtained. A high extinction ratio laser with a degree of 93.5% is presented. Finally, a scheme to convert the output laser of a high power wide spectrum non conservative laser to a linearly polarized laser is proposed. The feasibility of the scheme is analyzed. The feasibility of the polarization conversion based on the polarization locked phase adaptive conversion system under the condition of wide spectrum light source is studied and the preliminary design is made. In this paper, the feasibility of the scheme based on polarization control and polarization locked polarization - Polarization - preserving - polarization conversion is proposed through theoretical and experimental research, which provides a certain reference for high power linear polarization laser.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

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