SIDE-TONE OTDR FOR IN-SERVICE OPTICAL CABLE MONITORING

摘要

An OTDR provides both in-service and out-of-service measurement information for an optical transmission system with multiple repeaters (34, 44). The repeaters include an optical high-loss loop back (hllb) path and an OTDR path. The OTDR (30) is coupled to the input lines of the optical transmission system via an optical coupler so that both traffic signals and test signals from the OTDR (30) can be transmitted simultaneously. When the OTDR (30) is provided in-service measurement information, test signals in the form of side-tone pulses are transmitted on the transmission system. The OTDR (30) filters out the traffic signal from the return signal. The HLLB path (40) through the amplifier pairs of each repeater is distinguishable in the filtered return signal. When the OTDR (30) is providing out-of-service measurement information, the level of the side-tone pulses is increased because interference with the traffic signal is no longer a concern.