A fail-safe optical T-coupler for coupling a local terminal having at least one light source and at least one photodetector to a segmented optical data bus comprises an optically transparent acousto-optic cell, a pair of collimating lenses for coupling adjacent segments of the data bus to opposite ends...http://www.google.de/patents/US4867517?utm_source=gb-gplus-sharePatent US4867517 - Fail-safe acousto-optic T-couplers for optical communication networks
