摘要
空间相干激光通信技术是当前卫星互联网远距离高速通信的主要途径,针对当前零差相干通信体制中光学锁相环载波恢复技术存在的锁定范围小、系统复杂以及对激光器线宽和频率调谐带宽要求高的问题,研究了基于半导体激光器注入锁定技术的相干接收端载波恢复方法,并利用数字解调技术实现了信号的接收。发射端采用曼彻斯特码型二进制相移键控(BPSK)调制技术有效保留了发射光信号中的载波分量,在接收端通过半导体激光器注入锁定技术对调制光中的载波分量进行过滤和放大,并将其作为本振光与调制信号进行混频探测,利用数字解调算法实现了通信速率为5 Gbit/s的BPSK相干信号的解调,同时分析了注入功率、调制速率和调制深度的改变对载波恢复效果的影响。该方案可有效降低空间相干激光通信对本振光的性能及接收端采样速率的要求,极大简化了空间相干通信系统的复杂度。
Objective In a space-integrated ground information network,high-speed laser communication is a key technology for high-speed intersatellite data transmission.Owing to its high sensitivity and strong anti-interference capabilities,coherent laser communication has become an ideal choice for long-distance inter-satellite communication.However,traditional analog coherent demodulation technology requires a complex optical analog lock-in loop(OPLL)control system and places high demands on the performance of the local oscillator laser,which increases the complexity and cost of the system.To address these issues,a new carrier recovery method is explored in this study and combined with digital coherent demodulation technology to reduce the system complexity.Methods A carrier recovery method for a coherent receiver based on semiconductor laser injection locking technology is investigated,and digital demodulation technology is used to realize signal reception.Manchester-coded binary phase-shift keying(BPSK)modulation technology is used at the transmitter to effectively retain the carrier component in the transmitted optical signal.The carrier component in the modulated light is filtered and amplified via semiconductor laser injection locking technology at the receiver,which is frequency-shifted by 160 MHz using an acousto-optic modulator before entering the 90°optical hybrid.The frequency shift reduces the effect of low-frequency beat noise on the system.A balanced photodetector with alternating current coupling is used to detect the mixed signal,and an oscilloscope is employed to collect the signal.The collected signal is processed offline to obtain a demodulated encoded signal.Results and Discussions Experiments are conducted on carrier recovery based on injection-locking technology at the receiver end.The impacts of different modulation depths,signal rates,and injection ratios on the performance of the local oscillator light after injection locking are analyzed.A decrease in the modulation rate and increases in the modulation depth and injection power can increase the proportion of the signal components contained in the recovered carrier spectrum,thereby reducing the quality of carrier recovery.In practical applications,selecting an appropriate modulation depth and injection power is beneficial for improving the carrier recovery quality.The demodulation of BPSK coherent communication signals at 5 Gbit/s is achieved,and the impact of various parameters is compared using the error vector magnitude(EVM).For signals with the baud rate of 5 GHz,the baseband signal is successfully demodulated at modulation depths of 0.33,0.42,and 0.49.In these cases,increasing the modulation depth results in a gradual decrease in the EVM,indicating that a higher modulation depth is beneficial for reducing the EVM.However,for signals with the baud rate of 4 GHz,the EVM at the modulation depth of 0.42 is lower than that at 0.49.This is because in previous experiments,for signals with the modulation depth of 0.49 at 4 GHz,the depression near the carrier component is reduced,and the local oscillator light mixed with the signal components can not successfully demodulate the baseband signal.Therefore,the EVM can be used to measure the combined quality of the local oscillator light recovered by injection locking and the signal light.For signals at 3 GHz,owing to the small depression near the carrier component,the signal can not be demodulated even at the modulation depth of 0.33,and the change in the EVM is not significant at this time.Conclusions The proposed coherent communication system based on the semiconductor laser injection-locking carrier recovery technology combines the advantages of high-bandwidth optical locking and digital coherent tuning. A homodyne carrier signal can berecovered from the signal light using an optical method and effective mixed signals can be obtained using a distributed feedback (DFB)laser with a linewidth in the MHz range. Complex electronic feedback loops are not required, significantly reducing the systemcomplexity. As a result, the demodulation of BPSK coherent communication signals at 5 Gbit/s without BER is achieved. Thisresearch can provide a simple and effective technical method for the carrier recovery of local oscillator light and is expected to beapplied to high-precision coherent demodulation scenarios, including space coherent laser communication, lidar, and opticalcomputing.
作者
刘天睿
任伟杰
章郑豪
孙建锋
苏庆帅
魏芳
李权
杨康文
蔡海文
Liu Tianrui;Ren Weijie;Zhang Zhenghao;Sun Jianfeng;Su Qingshuai;Wei Fang;Li Quan;Yang Kangwen;Cai Haiwen(School of Optical-Electrical and Computer Engineering,University of Shanghai for Science and Technology,Shanghai 200093,China;Shanghai Satellite Internet Research Institute Co.,Ltd.,Shanghai 201204;Wangzhijiang Innovation Center for Laser,Aerospace Laser Technology and System Department,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;Zhangjiang Laboratory,Shanghai 201210)
出处
《中国激光》
CSCD
北大核心
2024年第23期72-81,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(62275253,U23A20379)
上海市自然科学基金(21ZR1472100)
中国科学院战略性先导科技专项(B类)(XDB43030400)。
关键词
星间相干激光通信技术
光学锁相环
注入锁定
载波恢复技术
intersatellite coherent laser communication technology
optical phase-locked loop
injection locking
carrier recovery technology
