多普勒测风雷达激光稳频与锁相技术研究
文献类型：学位论文
| 作者 | 卞正兰 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 瞿荣辉 |
| 关键词 | 多普勒测风雷达 PDH稳频 OPLL 反馈控制 光电自准直测角 |
| 其他题名 | Study of Laser Frequency Stabilizing and Phase Locking Technology Applied in the Doppler Wind Lidar |
| 中文摘要 | 多普勒测风雷达是迄今为止唯一能够获得直接三维风场廓线的卫星遥感设备，被认为是在大气激光遥感领域内最具有应用价值和最值得推广应用的新概念技术之一，为各国政府所重视。研制的星载直接探测多普勒测风雷达，其发射光源为基于种子注入技术的Nd:YAG激光器的三倍频输出，波长355nm。根据种子注入原理，种子激光器的频率漂移直接决定了发射光源的频率稳定性，进而直接影响雷达的风场探测性能。在仅考虑种子激光器的频率漂移引入的风速测量误差时，要求种子激光器的频率抖动必须小于1MHz，才能达到优于0.5m/s的测风精度。对于星载应用的多普勒测风雷达，由于卫星与散射体之间相对运动也会引入多普勒频移，探测系统会将此项频移误认为是风速变化引起的多普勒频移量，从而造成风速测量误差。因此星载直接探测多普勒测风雷达要求种子光源同时具有3GHz的调谐范围，以及200KHz的最小调谐精度，实现对该类误差的精确补偿。 针对上述应用需求，本论文旨在研究同时具备高频率稳定性和宽调谐范围的种子光源。所采用的方案是首先采用Pound-Drever-Hall（PDH）稳频方法，将一台Nd:YAG激光器锁定在经双层温控系统控制的FPI（Fabry-Poret Interferometer）共振频率处，稳定其输出激光频率；其次将此稳频激光器作为主激光器，利用OPLL（Optical Phase Locked Loop）技术，将作为从激光器的另外一台Nd:YAG激光器锁定在该主激光器上，实现从激光器对主激光器的频率跟踪；最后通过调节本地参考振荡器的频率，改变主从激光器间频率偏差，此时从激光器便同时具备了高的频率稳定性及宽的调谐范围。因此本论文重点研究了PDH稳频技术和OPLL技术，主要内容如下： 1、对于PDH稳频技术： 深入研究了PDH稳频原理和反馈控制理论，建立了PDH反馈控制系统数学模型，并在此基础上，分析了稳频精度的各种影响因素，以及反馈环路中各部分噪声的传递过程，提出了PDH稳频系统的具体设计要求。 采用具有控制灵活和精度较高的数模混合方案，研制了一套结构紧凑，操作灵活的1064nm固体激光器自动稳频系统。高集成度的DSP(Digital Signal Processor)作为稳频控制系统的心脏，直接数字频率合成器（DDS）产生激光器高频相位调制信号，模拟混频器解调激光器的频率漂移信息。于2.5小时内，稳频激光器的相对频率漂移不超过±17KHz，其均方根误差（RMS）为5KHz，绝对频率稳定度优于200KHz。当稳频系统稳定工作时，主动对FPI施加6Hz的固定扰动，系统能够在30ms内迅速恢复稳定，具有较强的抗干扰特性。 2、对于OPLL技术： 深入研究了OPLL的工作原理，以及环路各组成部分的工作特性，建立了基于数字鉴频鉴相器（DPFD）的OPLL反馈控制系统数学模型，并在此基础上，分析了环路中各部分噪声的传递过程，以及各组件参数的选择对系统相位噪声的影响，提出了偏频锁定（Offset Locked）系统的具体设计要求。 采用高集成度的DPFD鉴别主从激光器间频率偏差，避免了昂贵的微波振荡源及复杂的微波电子学设计。研制了一套结构简单，稳定性好的数字偏频锁定系统。主从激光器间频率偏差在3GHz范围内可调，调谐步进可设为200KHz的任意整数倍。主从激光器锁频精度在1分钟内优于22Hz，3小时内不超过550Hz，其3小时拍频数据的阿伦方差于系统锁定后32s时达到最小值，为 ，满足星载直接探测多普勒测风雷达的应用需求。 3、本论文的另外一部分工作是基于单线阵CCD的二维光电自准直仪的研制。设计分划丝形状为N型字符，以提高自准直仪的测角精度，并且辨别被测反射镜的角度变化方向。分划板有效口径φ22mm，刻线夹角为18°，刻线顶角外接圆直径为25mm，两条平行刻线间距为7.725mm；采用傅里叶相移算法，使得系统在CCD图像畸变的情况下仍然具有较高的测角精度；采用LED曝光时间的脉宽调节（PWM）方法，避免CCD图像因照明光强的波动引起的信噪比不稳定，从而提高测角精度和测角范围。研制的基于单线阵CCD二维光电自准直仪在1m的测量距离内，测角范围±420"，测量精度优于±1"。 |
| 英文摘要 | Doppler wind lidar (DWL) is the only satellite remote sensing equipment which is able to obtain the direct three-dimensional wind field profile so far. It is considered to be one of the new concepts deserving promotion and application in the field of the atmospheric laser remote sensing, and receives more and more attentions from various countries governments. The detection performance of the direct detection DWL is directly influenced by the emission laser which is the third harmonic of an injection-seeded Nd:YAG laser. When only considering the wind speed measurement error introduced by the frequency drifts of the seed laser, the seed laser frequency drifts with less than 1MHz is required to make sure the wind speed measuring accuracy up to 0.5m/s. For the space-borne DWL, the detection performance will be affected by the relative motion between the satellite and scatterers; therefore the space-borne direct detection DWL also requires the seed laser to possess a tuning range of 3GHz and minimum tuning accuracy of 200 KHz. Based on those application requirements, a seed laser with both high frequency stability and wide tuning range is studied. The realized method is that firstly the Pound-Drever-Hall (PDH) frequency stabilization technology is used to lock the frequency of a Nd:YAG laser on the resonant frequency of the FPI (Fabry-Perot Interferometer); secondly this tabilized laser is employed as the ML (master laser), then the OPLL (Optical Phase Locked Loop) technology is applied to lock the frequency offset between another Nd:YAG laser as SL (Slave Laser) and this ML; Therefore the SL has the characteristics of both high frequency stability and wide tuning range. The main work of this thesis is summarized as follows: 1、 PDH frequency stabilization technology The detail design requirements for the PDH frequency stabilization system is proposed based on setting up the theoretical model of the PDH feedback control system and analysing the various factors affecting the frequency stabilization accuracy and the transfer process of the noise caused by the parts of the feedback loop; An automatic frequency stabilization system with compact structure and flexible operation is developed by the method of the analog-digital mixed system. The high integrate chip of DSP (Digital Signal Processor) is chosen as the heart of the frequency stabilizing system, the direct digital frequency synthesizer (DDS) is chosen to generate the radio frequency modulating signal, and the analog mixer is chosen to demodulate the laser frequency drifts. At last, the measured laser frequency drifts of less than ±17KHz during 2.5 hours, and the absolute frequency stability of better than 200 KHz are obtained. It takes about 30ms for the system to get back into stabilization when a regular disturbance with the frequency of 6Hz was put on the FPI. 2、 OPLL technology The detail design requirements for the OPLL system is proposed based on setting up the theoretical model of the OPLL feedback control system based on DPFD (Digital Phase Frequency Detector) and analysing the transfer process of the noise caused by the loop components. A robust offset locked system with compact structure is designed by choosing the DPFD to detect the frequency difference between the ML and SL. The results of the experiment show that the tunable range of the SL is up to 3 GHz; the tuning step length is arbitrary integral multiple of 200 KHz; the locking accuracy is better than 22Hz in one minute, and no more than 550Hz during 3 hours; The minimum Allan deviation of is obtained when the sample time is 32s. 3、 The development of two-dimensional photoelectric autocollimator based on single linear CCD is another part of this thesis. The reticle of N type character is desgined to improve the accuracy of angle measurement and identify the direction of the measured mirror rotation. The angle of the reticle is 18°in the effective reticle aperture which is Φ22mm, the circumcircle diameter of the reticle is 25mm, and the two parallel groove distance is 7.725mm; The Fourier Phase Shift algorithm is introduced to ensure the high angle measuring accuracy when the CCD image is distorted; The PWM method for the exposure time of the LED is used to avoid the instability of the SNR (signal to noise ratio) caused by the fluctuations of the illumination light intensity. At last the measuring range of ±420" in the distance of 1m, and the accuracy of less than ±1" are obtained. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15708]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 卞正兰. 多普勒测风雷达激光稳频与锁相技术研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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