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We assessed the problem of low mixing efficiency caused by unstable signal polarization because of a moving reflector in a laser communication terminal with a periscopic scanner. A real-time polarization compensation method based on rotating waveplates is presented, which keeps the receiving signal light polarization at 45° linear polarized and improves system mixing efficiency. A geometric model of the laser communication terminal was first established, its polarization transmission characteristics were analyzed by three-dimensional polarization tracks, and a system polarization transmission matrix was calculated. The relationship between scan angle and polarization of the output signal was simulated. The connections between a polarization-compensating λ/4 waveplate and the λ/2 waveplate rotation angle and scan angle were established. These findings will pave the way for real-time polarization control technology for coherent free-space laser communications.

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In this study, the scintillation effects along a 7 km space laser communication path in an urban area were examined, including the relationship between the scintillation and bit error rate and the variation of the scintillation index with changes in the transmitting and receiving apertures. It was concluded that multi-aperture transmitting technology can effectively reduce the scintillation caused by atmospheric turbulence. For the investigated urban link, the scintillation index could meet the communication requirements for adjusting the receiving aperture. These results will facilitate space laser communication improvement and turbulence suppression along horizontal urban paths.