Coherent optical communication systems are fundamentally of interest because of the high achievable antenna gains, enormous potential information rates, privacy and security of the link, and other advantages relating to particular link geometries. In this work, direct detection at a visible wavelength is being investigated with three kinds of receivers: (1) a photon bucket (large aperture receiver), (2) a four element array with electronic processing (linear addition and nonlinear weighted addition), and (3) a four element array with optical processing (linear addition).