Transmission ring or network each made of fiber optic transmission links

摘要

The transmission network has a ring structure provided by a number of optical transmission paths (R1,R2,R3,R4,S1,S2,Z1,Z2,Z3), each of which is selectively operated in one or other transmission direction. An optical isolator (I) is inserted in selected transmission paths for preventing light propagation in opposition to the selected transmission direction. Switching of the isolator transmission direction depends on the transmission direction of the selected transmission path. The isolator may use a pair of polarisation filters at 45 degrees to one another.