为研究混频器中信号光分光比对相干零差接收机性能的影响,建模分析了90°空间光混频器的信号光分光比对接收机锁相性能和通信性能的影响。数值模拟结果表明,信号光Q路分光比k<0.5时,可提高通信性能,增加探测灵敏度;k=0.5时,环路锁相时间最短,锁频范围最大;k>0.5时,分光比存在最优值使锁相残余相位误差最小。根据分析结果设计了一种基于旋转半波片的分光比自适应调整系统,利用软件仿真研究了系统在不同分光比时的通信和锁相性能。结果表明,激光波长为1550 nm,线宽为5 kHz,通信速率为10 Gbit/s时,通过旋转半波片使Q路的分光比在0.1~0.6之间自适应调整,就能改变系统的锁相性能和探测灵敏度。当k=0.1时,探测灵敏度提高了2.56 dB;当k=0.5时,锁相支路可实现的频差锁定范围为133 MHz;当k=0.6时,锁相残余相位误差最小。仿真结果验证了该系统的可行性,同时为自适应调整分光比的90°混频器实用化提供了参考。

In order to investigate the effect of signal light splitting ratio on the performance of coherent homodyne receiver, the effect of signal light splitting ratio of 90° spatial optical hybrid on the phase-locked performance of the receiver and the communication performance is modeled and analyzed. From our numerical simulation results, we know that the communication performance and detection sensitivity are improved with the signal light splitting ratio of Q branch k<0.5, and the loop locked-in time is the shortest and frequency-locked range is maximum when k=0.5. In the case of k>0.5, we can obtain an optimal value of k to minimize the residual phase error. Based on the above analysis, we design an adaptive adjustment system with signal light splitting ratio based on a half-wave plate using softare simulations, and its communication and phase-locked performances are analyzed at different splitting ratios. Those results show that under conditions of 1550 nm laser wavelength, 5 kHz linewidth and 10 Gbit/s communication rate, the phase-locked performance and detection sensitivity can be adjusted when k varies in the range of 0.1-0.6 by rotating half-wave plate. The detection sensitivity is improved by 2.56 dB with k=0.1, and for k=0.5, the frequency deviation lock range of the phase-locked branch is 133 MHz. What's more, the residual phase error is the smallest when k=0.6. Those results illustrate the system is feasible and also provide a reference for the application adjustment of the 90° hybrid with adaptive splitting ratio.