Leveraging the orthogonality of Zernike modes for robust free-space optical communication

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. Free-space optical communication holds potential to achieve high information-transfer, but current schemes are affected by turbulence and aberrations. Here, encoding information in the phase using Zernike polynomial modes is demonstrated experimentally, while simulations suggest operation over 1 km in the presence of turbulence is feasible.