Research on the influence mechanism of angular misalignment on the transmission performance in inter-satellite coherent laser communication

Abstract

Space laser communication technology offers several advantages, including high speed, large capacity, and robust anti-interference capabilities. In comparison to traditional direct detection laser communication, coherent laser communication technology exhibits enhanced sensitivity, spectral efficiency, and the capacity for multiple debugging formats. Consequently, it is becoming the dominant development direction in the field of high-speed and long-distance space laser communication between satellites. The relative motion of the satellite platform gives rise to angle misalignments in the transmitting and receiving terminals, resulting in alignment mismatch losses and phase errors. This, in turn, leads to a reduction in the signal-to-noise ratio (SNR) and an increase in the bit error rate (BER). In light of the aforementioned issues, this study establishes a mathematical model of the relationship between angle misalignment and BER in coherent laser communication. Additionally, a 10 Gbps Polarization Multiplexed Quadrature Phase Shift Keying (PM-QPSK) inter-satellite coherent laser communication experimental system is bulit. The use of fast steering mirror (FSM) serves to simulate inter-satellite angle misalignment. The influence of angular misalignment on various communication parameters, including received optical power, error vector magnitude (EVM), constellation diagram, and BER, is investigated. The experimental results demonstrate that when the transmitter and receiver are in a collimated state, the received optical power is −30 dBm, the EVM is 7.33%, the BER is 2.5E-13, and the constellation diagram is within acceptable limits. As the angular misalignment between the transmitter and receiver is increased gradually to 320 μrad, the received optical power decreases by 12 dB to −42 dBm, the EVM decreases to 15.73%, the BER increases by approximately three orders of magnitude, and the constellation diagram deteriorates. This study offers a reference point for the measurement and compensation of angular misalignment in coherent laser communication, and provides significant guidance for the design of inter-satellite coherent laser communication terminals.