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Free-space optical communication systems exploit the properties of light beams to transfer information through a free-space link. Indeed such systems provide an exciting alternative for communication. Here we introduce information transfer through free-space using a laser beam having its phase encoded with multiple orthogonal aberration modes. We use Zernike polynomials, which form a complete basis set, to represent the aberration modes. The user information is converted to co-efficients of the Zernike modes which are summed digitally to obtain the resultant phase profile. A single phase modulating device then reads the resultant phase to shape the wavefront of the beam to be transmitted. The receiving station estimates the co-efficients of all modes in the beam from a single measurement of a wavefront sensor, to retrieve the user information. We demonstrate data transfer using multiple modes, each with multiple strengths, and external perturbation compensation using the completeness property of the modes.

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In this paper, we report a peculiar movement of the beam cross sections associated with both the diffracted and undiffracted laser beams from a liquid crystal spatial light modulator (LCSLM). The beam movement becomes noticeable when the beam position is monitored continuously for several hours. We perform experiments to show that the beam movement is non-mechanical in nature and is connected with the power on/off instants of the LCSLM as well as the heat conductivity of the mounting slab which acts as the rigid support to the LCSLM panel. We also present a detailed analysis of the experimental findings to ascertain the possible cause of the beam fluctuations.