Abstract: Data communication between spaced locations is effected by interface assemblies for each location mounted in a light path. Each interface assembly includes light sensitive and/or light emitting elements for extracting and/or adding light portions to a column of light passing along the path. In one form, a typical interface unit includes back-to-back light sensitive devices and light emitting devices on opposite sides of a planar board with light transparent apertures interspersed with these transmit/receive units in a matrix configuration. The transparent apertures are arranged to pass light originating from another location and intended for still another location along the light path without disturbance. The interfacing assemblies effectively space share the coupling light column so that data communications can be established concurrently between any of the locations particularly when the light column path is formed as a closed loop.