Retardation based modulation of polarization ellipticity angle for analog optical space communication

Optical space communication systems offer a number of advantages over traditional RF systems, including high information capacity, small beam divergence, low power dissipation, and immunity to RF interference, etc.. As the polarization state of light varies little while propagating in free space, it can thus be used to carry information in coherent optical space communication systems. We report a relatively simple polarization ellipticity angle (PEA) modulation scheme. The scheme is based on the modulation of retardation between the two orthogonal polarization states through the use of one electro-optical birefringence crystal. Theoretical analysis shows that the new scheme has linear modulation response and is insensitive to source phase noise. With this scheme, an analog signal can be directly decoded onto a light carrier, saving the cost of A/D conversion and coding