Investigation into the Feasibility of Designing a Fail Safe Optical Data Link.

Abstract

Abstract : This report describes the development of a fail safe optical data link terminal and the construction of a serial fiber optic data bus system which uses several of these terminals. Such a system consists of a master terminal containing a CPU, and LED source, and a photodiode detector; and several remote send/receive terminals, each containing an electro-optic modulator and a photodiode detector. Multimode monofibers are the transmission media, and data can be impressed or tapped off at each remote terminal. The main thrust of this contract was to develop a serial data bus system which continues to operate if power fails at one or more remote terminals. After consideration of several types of terminals, an angle collimation terminal and a mirror terminal were constructed. Both were designed to be compatible with Corning low loss multimode glass fibers (NA = .15) and both used about 85-micrometer thick LiTaO3 crystals to control light flow by the electro-optic effect. Because of its superior optical insertion loss (5.7 dB) and modulation depth (51% with 100 V applied), the mirror terminal was selected for system implementation. From three additional mirror terminals constructed, the best two were chosen for the system and permanently butt coupled to fiber terminations. The two terminals and a master terminal were then assembled into a complete system and tested. Overall performance met or approached system objectives and the fail safe nature of the system was clearly shown. (Author)