A Research Of High-precision Phase Difference Measurement

In recent years, laser has been widely used in the fields of industry, agriculture, medical, national defence construction and scientific experiments because of its characters of high coherence, high monochromaticity, high spectral brightness and highly directional. Laser ranging is a specific application of laser technology in the fields of military, engineering, sports and topographic mapping. To obtain the phase difference is the key of the research on phase laser ranging. The phase measurement error of the range finder may directly lead to the range error. Therefore, how to get a reliable phase difference value is worthy of researching. This thesis makes a comprehensive analysis on phase difference measurement technique and the principal results are as follows:1. Combined with specific project and requirement indexes for high-precision laser ranging, the thesis makes a comparison of various phase difference measurement programs and algorithms. Lastly, the algorithm based on the discrete Fourier transform (DFT) is choosed.2. The thesis analies the algorithm for phase difference measurement based on the discrete Fourier transform (DFT) in detail, including its principle and error. In order to improve the algorithm for phase difference measurement based on DFT, a detection scheme which including window function and spectrum correction is designed. By comparing the performance of different types of window functions and analyzing the principle of different spectrum correction methods, the thesis finally chooses the Hanning window and Ratio spectrum correction method, and then discusses the principle and implementation steps of this scheme.3. After the improved algorithm is tested and emulated, the thesis summaries the experimental results. It is proved that, the improved algorithm can significantly improve the accuracy of the phase difference measurement than the traditional detection method based on DFT.