Spatial mode modulation of laser beams for optical communication

A new channel for optical communication is described, in which the energy distribution among the spatial modes of a laser beam is modulated. The number and strength of the modes directly influences the spatial coherence of a beam, which can then be detected with a simple interferometer. The transmitter is an electric-optic device that allows one or two modes to propagate depending on the logic state. The distribution of the energy among the allowed modes is independent of the overall intensity, thereby giving another depth of multiplexing in addition to common schemes such as intensify and frequency modulation, polarization, and wavelength-division multiplexing, etc. We present an optical interconnection scheme by which the intensity carries the data and the spatial coherence conveys the address information on the same beam.