Abstract: Apparatus and methods are provided for transmitting and/or for receiving data over a free-space optical link. An optical data transmitter generates duplicate digital data streams carrying a same digital data sequence with a relative temporal offset and mixes them onto two different polarization channels according to a preselected linear mixing rule. An optical data receiver demodulates first and second digital streams from the two polarization channels and unmixes the demodulated data, to produce first and second output digital data streams according to a preselected linear unmixing rule. The receiver applies a quality indicator to select between segments of the respective output digital data streams that correspond to the same transmitted data sequence.

Abstract: An apparatus comprises an optical data receiver to receive first and second data-modulated optical carriers in different wavelength bands via a free space optical link and to generate an output digital data stream from demodulated segments of the first and second data-modulated optical carriers. The optical data receiver is configured to make selections between temporally corresponding portions of the first and second data-modulated optical carriers for generating successive portions of the output digital data stream. The optical data receiver is configured to make one of the selections between two of the temporally corresponding portions of the first and second data-modulated optical carriers based on at least one value of a quality indicator obtained for at least one of two temporally corresponding portions.