Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Optical detection techniques

The Research of Space Object Optical Coherent Detection

Author LiBangXu
Tutor YuanXiuHua
School Huazhong University of Science and Technology
Course Optical Engineering
Keywords Coherent detection Lidar Atmospheric turbulence Space target Wavefront compensation
Type Master's thesis
Year 2009
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Space object detection is currently an essential part in space activities , with the threat of spacecraft 1-10cm of space target detection is a top priority . This type of space for target detection , we designed a spatial unity transceiver coherent detection optical target detection system . The detection system uses a laser radar transmitter / receiver in the form of coherent detection scheme and closed-loop detection wavefront distortion compensation system . Throughout this article all around the system for research and analysis, is committed to improving the whole system coherent detection performance. ( A ) broad access to various domestic and international literature and information on the status of space target detection and current state of technology for a comprehensive introduction. Through analysis and comparison , to design a transceiver unity of space object detection systems that use weak coherent technology for detecting the received signal , using closed-loop control wavefront compensation by the turbulence caused by the wavefront distortion . ( 2 ) goals for space exploration, deduced Lidar equation . The radar equation atmospheric loss , far-field divergence angle of the laser , the receiving antenna aperture , spatial target distance and spatial target attitude angle and other parameters were analyzed, and the parameters obtained by numerical simulation on the impact of the theoretical value of the received power . ( 3 ) coherent detection of the laser radar systems, analysis derived coherent heterodyne detection efficiency theoretical expression , and then come to the heterodyne signal to noise ratio is proportional to the relationship between efficiency . Atmospheric turbulence and by analysis of backscattered light , the light reception signal obtained theoretical expression . Focuses on analysis of the system parameters and atmospheric turbulence ( using wavefront Zernike polynomials analog ) Poor efficiency of external impact . To make maximum heterodyne efficiency , we obtained by numerical simulation of system parameters optimization. ( 4 ) analysis and comparison of the various existing wavefront compensation technique is proposed coherent detection can significantly improve the performance of the gradient descent algorithm based compensation system, and theoretically proved that the gradient descent compensation algorithm convergence . Random perturbation gradient prediction for parallel algorithms and general gradient prediction algorithms convergence performance comparison . By numerical calculation, the convergence speed of the system , complexity and wavefront compensation error analysis .

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