FMCW激光雷达信号处理与研究

发布时间：2018-06-09 14:45

本文选题：激光雷达 + 调频连续波　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：调频连续波（FMCW）激光雷达具有高精度、高效率、非接触无需靶标、大尺寸无盲区等优点，能够在多种场合工作，是测量近距离大尺寸目标的重要方法之一。本文通过对FMCW激光雷达中的关键技术要点的研究，建立了线性调频连续波激光雷达测距系统，对系统信号进行了分析与处理，来提高绝对距离测量的精度，，根据系统要求，对关键器件进行了选取，搭建了实验平台。 FMCW绝对距离测量是依赖于激光器线性调频的，而实际中激光器频率调谐很难做到严格线性，这会引起差拍干涉频率展宽，从而引入较大的测量误差，本文根据FMCW测距技术的基本原理，研究了基于频率采样的方法来校正激光调谐非线性，采用马赫泽德干涉仪作为校正时钟，对原测量信号进行外部时钟采样，由于校正信号路和测量信号路含有相同的非线性，通过同步采样消除了非线性成分。由于系统采用全光纤器件设计，不同频率的激光在光纤中走过的光程也不一样，而测量路在自由空间中的光程随频率的变化可以忽略，测量路与校正路的色散量不能抵消，带来色散误差，本文对系统中可能存在的色散问题进行了分析论证，并且通过建模对色散误差进行了仿真模拟。FMCW技术的本质是干涉测量，实际中由于光纤的弯曲、应力变化或者环境影响都有可能导致参与干涉的测量臂和参考臂的两束光的偏振态发生改变，引起干涉信号的幅度衰落，甚至衰落为零，干涉现象完全消失，本文对这种偏振衰落问题对FMCW的影响进行了分析。在外部时钟采样中，由于校正信号路光学频率间隔的变化以及在AD采样或者校正信号到时钟信号的转换过程中引入的采样时延会导致外部时钟产生误差，从而导致采样误差。本文对采样误差以及采样误差引起的色散进行了分析讨论。基于FMCW理论，选取1550nm波段连续可调谐外腔式激光器作为光源，采用全光纤器件搭建光路，利用平衡探测器探测差拍信号，最后用高速采集卡获取数据。编写了Labview测量软件，对光纤端面以及自由空间中的量块进行测距实验，并且使用高精度导轨和双频激光干涉仪对测距结果进行标定，实验结果表明基于频率采样的方法很好的校正了激光器扫频的非线性，测距稳定性很高，但是光纤色散以及采样误差对测距精度的影响较大，只有通过对色散和采样误差进行算法或者光路延迟补偿才能获得更高的精度。
[Abstract]:FM CW FMCW laser radar has the advantages of high precision, high efficiency, no target in contact, no blind area in large size and so on. It is one of the important methods for measuring large and short range targets. Based on the study of the key technical points in FMCW lidar, a linear frequency modulation continuous wave laser radar ranging system is established in this paper. The signal of the system is analyzed and processed to improve the accuracy of absolute range measurement, according to the requirements of the system. The key devices are selected and the experimental platform is built. The absolute distance measurement of FMCW depends on the linear frequency modulation of the laser, but the frequency tuning of the laser is difficult to achieve strict linearity in practice, which will lead to the broadening of the beat interference frequency. According to the basic principle of FMCW ranging technology, the method based on frequency sampling to correct the laser tuning nonlinearity is studied in this paper. The Mahezard interferometer is used as the correction clock. For the external clock sampling of the original measurement signal, the nonlinear component is eliminated by synchronous sampling because the correction signal circuit and the measurement signal circuit contain the same nonlinearity. Because the system is designed with all optical fiber devices, the optical path of laser with different frequencies is different in the optical fiber, and the change of the optical path of the measurement path in free space with the frequency can be ignored, and the dispersion between the measuring path and the correction path cannot be offset. This paper analyzes and demonstrates the possible dispersion problem in the system, and simulates the dispersion error by modeling. The essence of the dispersion error is interference measurement. In practice, because of the bending of optical fiber, The change of stress or environmental influence may lead to the change of the polarization state of the two beams of light involved in the interferometer and the reference arm, which will cause the amplitude fading of the interference signal, or even decline to zero, and the interference phenomenon will disappear completely. The influence of this polarization fading problem on FMCW is analyzed in this paper. In the external clock sampling, because of the change of the optical frequency interval of the correction signal path and the sampling delay introduced in the AD sampling or the conversion process of the correction signal to the clock signal, the external clock will produce errors, which will lead to the sampling error. In this paper, the sampling error and the dispersion caused by the sampling error are analyzed and discussed. Based on the theory of FMCW, the continuous tunable external cavity laser in 1550nm band is selected as the light source, and all optical fiber devices are used to build the optical circuit. The balance detector is used to detect the beat signal, and the high speed data acquisition card is used to obtain the data. LabVIEW measurement software is developed to measure the optical fiber end surface and the measuring block in free space. The distance measurement results are calibrated by using high precision guideway and dual-frequency laser interferometer. The experimental results show that the method based on frequency sampling corrects the nonlinearity of laser frequency sweep and has high ranging stability, but fiber dispersion and sampling error have great influence on ranging accuracy. A higher precision can be obtained only through the algorithm of dispersion and sampling error or the compensation of optical path delay.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN957.51

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