The present invention is directed to optical transmission lines of the type that normally couple one or more utilization devices into a signal loop and more particularly, to a by-pass relay for connecting and disconnecting a utilization device from an optical transmission line while still maintaining the optical continuity of the line.
Optical transmission lines have come into recent use because of their ability to couple signals from one point to another with a minimum amount of interference.
In electrical systems, interference is generally caused by electromagnetic radiaton, cross-coupling of signals and/or noise. These interfering effects, of course, diminish the quality of the received signal. In digital systems, for example, computer systems, the requirement for coupling a central processing unit to one or more peripheral units located in different cabinets some distance from the central processing unit creates a requirement for coupling signals with interference eliminated totally, or minimized to the smallest of levels, otherwise computing errors will result.
In such systems, it is necessary that the peripheral units be capable of being logically connected or disconnected from the transmission line without disrupting the operation of the loop as it affects other peripheral devices.
From the foregoing, it appears natural that a transmission line that would have the best noise immunity would be implemented using fiber optics. Such being the case, the present invention directs itself to the problem that arises as regards the connecting and the disconnecting of the peripheral device into the optical transmission line. Optical transmission lines may consist of a single optical fiber or a bundle of optical fibers. The interconnections between remotely disposed stations is established utilizing schemes that are analogous to electrical systems. These stations may be interconnected by a loop or a line data bus which interconnection reduces the number of optical signal transmission lines that have to be used from, for example, the number that would be required if each individual station and/or peripheral device were connected directly to the central station or computer processing unit CPU by its own transmission path.