Polarization analysis of quantum-optical systems for space laser communications using a modified BB84 protocol

Subject of study . The polarization characteristics of a guidance system for quantum-optical space laser communication are studied. Aim of study . The aim of this study is to experimentally demonstrate the advantages of axisymmetric laser beams over the linearly polarized beams commonly used in the BB84 protocol for space-based quantum laser communication. Unlike linearly polarized beams, the structure of axisymmetric beams remains unchanged with variations in the propagation direction between ground-based and onboard laser terminals. Method . The radiation polarization and polarization losses of the outgoing beam produced by a quantum-optical guidance system were determined at various azimuth and zenith angles. Main results . The polarization state of the radiation at the output of the guidance system was experimentally characterized, and the associated polarization losses were investigated. Practical significance . The laser beams generated by the quantum-optical guidance system for ground-based space laser communication exhibited significant variations in the orientation of the polarization plane depending on the beam direction. Consequently, laser beams with axisymmetric polarization structures are more suitable for such systems. This paper examines the structures and parameters of the key polarization elements required for the generation and diagnostics of these beams.