用于大气相干激光通信的自适应光学应用基础研究

Free-space laser communication is an attractive alternative to radio-frequency links for long-range and high-speed communication, for its wider communication bandwidth, smaller antenna size, lower power consume and higher security. The coherent laser communication is attractive as its receiver is very sensitive and is immune to the background noise. However, the coherent laser communication is helpless when it is used in the atmospheric communication links. The atmospheric turbulence distorts the intensity, wavefront and the propagation direction of the transmission laser, which degrades the communication performance. There are many methods that can be used to overcome the disturbance caused by the atmospheric turbulence. Howerver, all of the methods have their own disadvantages. Under the condition, we propose that the adaptive optics can be used in the coherent laser communication system. The adaptive optics can correct the distorted wavefront and the scintillation caused by the atmospheric turbulence. The coherent laser communication can work well as if there is no atmospheric turbulence in the communication links. Our work will be conducted using theory analysis, computer simulation and experiment validation. We will study the principle that the adaptive optics improves the performance of the coherent communication. We will study the design of the adaptive optics under different turbulent conditions. We believe that the carefully designed adaptive optics can work best under the corresponding communication condition and can make the long-rang and high-speed communication successful.Our work would greatly contribute to the atmospheric laser communication of our country.

空间激光通信具有码率高、功耗低和保密性高等优点，是解决微波通信瓶颈、实现高速通信的有效手段。其中，相干激光通信因其具有接近散粒噪声极限的接收灵敏度、很强的抗噪声干扰性能，而备受青睐。然而，在大气通信链路中，相干激光通信遇到了困难。大气湍流引起传输激光光强、相位和传输方向随机变化，严重影响通信质量。抑制大气湍流的办法有多种，但在提高通信质量的同时，存在着各自的问题。在该背景下，本项目提出把自适应光学技术引入相干激光通信系统中，主动补偿大气湍流的随机扰动，恢复传输激光的相干性，以改善通信质量。项目将分别从理论分析、数值仿真和实验验证等方面，研究自适应光学改进大气相干激光通信效能的机理，研究在各种湍流条件下实现高质量通信的自适应光学系统设计方法。可以预见，通过本项目的深入研究，必将找到一种突破长距离、高码率大气激光通信技术瓶颈的途径，推动我国大气激光通信技术不断向前发展。

本项目把自适应光学技术引入大气相干激光通信系统中，主动补偿大气湍流的随机扰动，改善通信质量，使得空间激光通信的高码率、高保密性等优势得到有效发挥。项目通过理论分析和数值仿真，弄清楚了自适应光学技术对空间激光通信的作用，即自适应光学技术通过提高信号光和本振光的相位匹配精度（空间相干通信）或者提高光纤的耦合效率（对于光纤激光解调终端），扩大了星地激光通信链路的适用范围(把D/r0=1附近扩展到D/r0=10以上)，从而使得大气激光通信在常规的大气条件下可以实现。项目还搭建了实验平台，从实验上实现并演示了自适应光学系统对大气激光通信链路的有益作用。通过本项目的研究，为我国星地激光通信技术的演示验证奠定了研究基础。