Optical free space communication apparatus using polarization

An optical communications system comprising:

• a first terminal operable to transmit and receive optical signals, said first terminal including a first half-wave plate (HWP) polarizer responsive to a first linearly polarized optical beam having a first wavelength and rotating the first linearly polarized optical beam to a first linear direction, a first beam splitter responsive to and passing the first linearly polarized beam, and a first circular polarizing element responsive to the first linearly polarized optical beam from the first beam splitter and circularly polarizing the first beam for transmission, said first circular polarizing element being switchable between two orthogonal switching states, said first terminal further including a second beam splitter, a first acquisition sensor and a first communications sensor;
• and
• a second terminal operable to transmit and receive optical signals, said second terminal including a second HWP polarizer responsive to a second linearly polarized optical beam having the first wavelength and rotating the second linearly polarized optical beam in the first linear direction, a third beam splitter responsive to and passing the second linearly polarized beam, and a second circular polarizing element responsive to the second linearly polarized optical beam from the third beam splitter and circularly polarizing the second beam for transmission, said second circular polarizing element being switchable between the two orthogonal switching states, said second terminal further including a fourth beam splitter, a second acquisition sensor and a second communications sensor, wherein the first terminal receives the second circularly polarized beam from the second terminal, said first circular polarizing element linearly polarizing the received circularly polarized second optical beam in a second linear direction that is orthogonal to the first linear direction and said first beam splitter directing the second linearly polarized optical beam to the second beam splitter, and wherein the second terminal receives the first circularly polarized optical beam from the first terminal, said second circular polarizing element linearly polarizing the received circularly polarized first optical beam in the second linear direction and said third beam splitter directing the first linearly polarized optical beam to the fourth beam splitter.