Patent ID: 7027737

Claim:
A data transmission apparatus comprising: a stationary part; a rotary part that rotates around an axis relative to said stationary part; a data generator mounted on said rotary part; a data output on said stationary part at which data generated by said data generator are accessible; a circular light channel extending completely around said rotary part, formed by a first optically reflective half-channel in said stationary part and a second optically-reflective half-channel in said rotary part facing toward each other, each of said first and second half-channels having a parabolic cross-section with a focal point and a vertex, the respective foci and vertices being co-linear; a light detector disposed in a wall of said first half channel in optical communication with said light channel and in data-transmitting communication with said data output; a light emitter which emits two substantially non-diverging light beams modulated to represent said data, respectively propagating in opposite directions in said light channel toward said light detector, said light emitter being disposed in a wall of said second half channel in data-receiving communication with said data generator to receive said data therefrom, and in optical communication with said light channel; and a light barrier disposed in said light channel to block one of said two beams so that only one of said two beams is detected at a time by said light detector, except when said light emitter and said light detector are 180° apart.