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chi20190522上海光机所范薇557595In high-power laser systems, in order to make the quality of the beam in the transmission process meet the requirements of the near-field and far field, it is necessary to modulate the spatial distribution of the front-end injected light to improve the final output quality. As a proactive device, the liquid crystal spatial light modulator is an indispensable part of the beam shaping field. Accurate modulation of the phase, intensity and polarization of the incident beam is achieved by manipulating the anisotropic medium inside the liquid crystal light valve by an electric field. In the addressing mode, each pixel unit of the spatial light modulator is independently controlled by the electrical signal or the optical signal, and control the external field on the liquid crystal layer to modulate the amplitude and phase information of the readout light. For an optically addressed spatial light modulator, the liquid crystal light valve is applied with the driving voltage, and the photoconductive layer receives write light with the varying spatial intensity, thereby changing the electric field distribution of the liquid crystal layer. Compared with the electrical addressing mode, the optical addressing mode does not require a pixel electrode, thereby reducing the fabrication difficulty of the device, avoiding the electrode diffraction effect, having a higher fill factor, and having the advantages of low cost and high compactness. Based on the above advantages, optically addressed spatial light modulators have an irreplaceable role in modern laser beam steering technology. In our group about optical addressed spatial light modulator design and performance testing, we found that the setting of the driving condition parameters affects the modulation capability and modulation accuracy of the modulator. It is very significant to analyze the correlation between them to improve the performance of the modulator. Therefore, this article focuses on the following aspects: (1) The realization principle of liquid crystal spatial light modulator is analyzed based on the anisotropy of liquid crystal, refractive index ellipsoid and electro-optic characteristics. The difference between the amplitude and phase modulation of the modulator on the incident light is analyzed by the JONES matrix of liquid crystal molecular layer. The principle of pure phase modulation is explained. The advantages and disadvantages of several common phase modulation measurement methods are compared. At the same time, the theoretical analysis of the implementation principle of the vertical polarization measurement method used in this paper is carried out.. (2) The performance parameters of the phase-only optically addressed spatial light modulator is analyzed and optimized, which including: i. The phase change curves obtained by the combination of the equivalent circuit of the liquid crystal light valve and the voltage response curve of the liquid crystal cell have the same distribution as the experimental measurement values, and the maximum error rate of the two is within 4%. The corresponding relationship is obtained between the driving voltage frequency or write light intensity and the phase change of the liquid crystal light valve, respectively. Finally the optically addressed spatial light modulator has a modulation capacity of 1 λ under suitable driving conditions. ii. A phase modulation system with both a wave-front sensor and a charge coupler device was built. The test results show that the system has a spatial resolution of 200 μm for the binary grayscale modulation. Based on the system, a feedback wave-front modulation can be realized. iii. The working stability of the optically addressed phase-only spatial light modulator is analyzed and optimized based on the equivalent circuit of the optically addressed spatial light modulator and the experiment for stability measurement. The results show that the voltage waveform on the liquid crystal layer of the light valve causes the phase fluctuation of the readout light modulated by the optically addressed spatial light modulator, and the voltage frequency and write light intensity jointly affect the modulator’s phase change capability and phase fluctuation. iv. By testing the phase change curves of the optically addressed spatial light modulator, it is found that when the voltage period is less than 5% of the response time, the phase fluctuation rate corresponds to the maximum phase change of the phase modulation curve is reduced to 0.35%, but the phase modulation capability is only 0.8λ at this time. By optimizing the driving condition parameters of the optically addressed spatial light modulator, a phase modulation capability of 1λ is obtained, and the phase fluctuation rate corresponding to the maximum phase change of the phase modulation curve is 1%.2019atalunwen21961512482815Spatial light modulator, Phase change, Spatial resolution, Voltage waveform, Phase fluctuationResearch on Phase-only Optical Addressed Spatial Light Modulator for Wave-front Control in High Power Laser Systems高功率激光系统中用于波前控制的相位型光寻址空间光调制器高功率激光系统中,为了使光束在传输过程中的质量满足近场远场的要求, 需要对前端注入光的空间分布进行调制,以提高最终的输出质量。液晶空间光调 制器作为主动型器件,是光束整形领域不可或缺的部分。通过外场操纵液晶光阀 内部的各项异性介质实现对入射光束相位、强度、偏振的精确调制。在寻址模式 下,空间光调制器的每个像素单元独立地受到电信号或光信号的控制,改变液晶 层加载的外场,实现对读出光复振幅信息的调制。对于光寻址空间光调制器,液 晶光阀被施加驱动电压,由光电导层接收空间强度变化的写入光,从而改变液晶 层的电场分布。相比于电寻址模式,光寻址模式不需要像素电极,从而降低了器 件的制作难度,避免了电极衍射效应,具有更高的填充因子,且具有成本低、紧 凑性高等优势。基于以上优点,光寻址空间光调制器在现代激光光束控制技术中 具有无可替代的作用。在我们组关于光寻址空间光调制器设计及性能测试的过程 中发现,驱动条件参数的设置影响调制器的调制能力及调制精度,分析研究其间 的对应关系对提升调制器的性能有非常重要的意义。因此,本文围绕以下几个方 面展开: (1) 基于液晶的各项异性、折射率椭球及电光特性,分析液晶空间光调制器的实 现原理;由液晶分子层的 JONES 矩阵,分析液晶对入射光束振幅和相位的 调制差异,解释了纯相位调制实现的原理。比较了常见的几种相位调制测量 方法的优缺点,同时对本文中使用的垂直偏振测量法的实现原理进行了理论 分析。 (2) 分析测试了纯相位光寻址空间光调制器的性能参数,并且进行了性能的优化, 具体包括: i. 液晶光阀等效电路与液晶盒电压响应曲线结合拟合得到的相位改变量曲线 与实验测量值具有一致的分布,且二者最大误差率在4%以内,通过分析得 到了写入光强度及驱动电压频率分别与液晶光阀相位改变量的对应关系, 最终使得光寻址空间光调制器在合适的驱动条件下具有1 λ 的调制能力。 ii. 搭建了兼具波前传感器与电荷耦合器的相位调制系统。测试结果表明,系统 对二值图调制结果具有200μm的空间分辨率,基于该系统能够实现反馈波前调制的能力。 iii. 在光寻址空间光调制器的电路仿真及稳定性测试的实验基础之上,分析、 优化纯相位光寻址空间光调制器的稳定性。结果表明,光阀液晶层的电压 脉冲波形会引起光寻址空间光调制器对读出光的相位调制波动,而驱动电 压频率与写入光强度同时影响相位调制波动幅度及相位调制量。 iv. 测试分析了光寻址空间光调制器的相位改变量曲线。结果表明,当驱动电压 周期低于响应时间的5%时,最大相位改变量对应的相位波动率减小为 0.35%,但此时相位调制能力仅为0.8 λ。通过优化光寻址空间光调制器驱动 条件参数,获得了1 λ 的相位调制能力,同时最大相位改变量对应的相位 波动率为1%。空间光调制器,相位改变量,空间分辨率,电压波形,相位波动中国科学院上海光学精密机械研究所裴丽丽光学工程硕士
中文题目: 高功率激光系统中用于波前控制的相位型光寻址空间光调制器
外文题目: Research on Phase-only Optical Addressed Spatial Light Modulator for Wave-front Control in High Power Laser Systems
作者: 裴丽丽
导师姓名: 范薇
学位授予机构: 中国科学院上海光学精密机械研究所
答辩时间: 20190522
中文关键词:
空间光调制器,相位改变量,空间分辨率,电压波形,相位波动
英文关键词:
Spatial light modulator, Phase change, Spatial resolution, Voltage waveform, Phase fluctuation
中文摘要:
英文摘要:
文献类型:学位论文
学位级别: 硕士
正文语种: chi
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