US Patent 11444691 Optical free space communication apparatus using polarization

An optical communications system including two communications terminals in communication with each other using optical signals having the same wavelength. Both terminals include a half-wave plate polarizer for rotating linearly polarized optical signals and a quarter-wave plate polarizer for circularly polarizing the optical signals. The quarter-wave plate polarizers are oriented 90° relative to each other so that circularly polarized optical signals sent from one terminal to the other terminal are linearly polarized 90° relative to a transmission polarization orientation to be separable from the transmitted optical signals by a beam splitter.