零差相干空间激光通信中灵敏度退化机理分析与近散弹噪声极限探测技术

Optical coherent detection is attractive for space laser communication links because of its better sensitivity、less vulnerability to bankground 、flexible modulation，especiallly it is well known the homodyne Binary Phase Shift Keying（BPSK） receivers can theoretically obtain maximum sensitivity under shot-noise limited condition,so becomes the focus on space laser communication with highrates and long distance.The realistic model for the performance determination of the homodyne PSK receiver with a Costas loop for long-haul communication is proposed；the receiver sensitivity,linewidths requirements,hybrid efficiency and the power penalties taking into account the laser phase noise ,ASE noise,shot noise of corresponding photodiodes is deliberated; the impact on polarizing、atmosphere turbulence、optical tracking error、Doppler frequency shift is investigated. Whatmore,PSK optical homodyne receiver is developed；phase synchroniczation between the input signal and the lacal oscillator laser was achieved using a Costas-type phase-locked loop；pre-processing of the optical signals to be synchronized was done with a basically lossless six-port 90 degree hybrid；Each one of front ends was implemented by means of a transimpedance preamplifier and by two InGaAs photodiodes operating in a balanced manner.At last,homodyne receiver based on BPSK wil be demodulated with sensitivity of －43dBm at bit rate of 10Gbps under initial frequency offset of ±8GHz simulated as Doppler Shifts due to ralative movement，which will be demonstrated the possibility of future large capacity space communications by the optial link and is expected for the next generation space date relay satellite systems.

零差相干探测具有灵敏度高、调制灵活、抗干扰能力强等突出技术优势，使其在高速率、远距离空间信息传输领域具有重要应用潜力。然而，若使空间相干激光通信系统的实际探测灵敏度接近散弹噪声极限，不仅需要解决零差相干探测的本振与信号激光器的位相的可靠锁定和跟踪等核心问题、而且还需充分考虑多普勒频移、空间混频效率等外界因素的不利影响。本项目拟在深入分析高灵敏度零差相干探测、高效率空间混频效率等机理的基础上，重点攻关基于COSTAS环的高稳定零差锁相技术，宽范围、高精度频率捕获技术与多普勒补偿技术等关键技术；搭建空间相干激光通信模拟试验系统，并对重要性能指标进行测试和验证。最终实现通信速率为10Gbps、灵敏度达到－42dBm的优异性能指标。为即将在GEO-LEO星际、GEO-地面等远距离、高速率空间信息传输奠定坚实的技术基础，将给空间信息传输带来跨越式发展。

随着国家对高速率、远距离的信息传输越来越重视，零差相干探测作为理想的技术解决途径有很高的研究价值，为探索零差相干探测的极限性能，有必要着重进行研究。本项目拟在空间约束环境条件下开展近散弹噪声极限的零差相干探测理论分析和关键技术研究。首先对零差相干接收系统及其内部关键器件进行理论建模及软件仿真，通过分析系统的各部分性能仿真，推导影响探测灵敏度的主要参数；之后对窄线宽 DFB 激光发射技术、高效率空间相干光混频技术和高精度、高稳定的光学锁相技术等关键技术进行攻关，对各单元技术的研究逐步优化系统探测灵敏度，其中结合高效率光混频和高精度光锁相，可使系统探测灵敏度提高约3dB；最后搭建空间相干激光通信试验系统，对发射分系统、相干接收分系统等进行实验研究，并进行系统的性能测试与评估，试验结果表明，系统的探测灵敏度可达-40.72dBm（通信速率10Gbps），结合分光比能量优化引入的3dB，总探测灵敏度达到-43dB，满足合同要求。本项目的研究成果为后续高速率、远距离空间激光通信的发展提供了理论依据。