| 摘要 |
Upon transmission path monitoring, when a monitoring signal responded by one of optical repeaters provided in a main signal transmission path is superposed on an optical main signal and sent out to the main signal transmission path, the optical main signal is branched to optical fibers, that are optical transmission paths, provided separately from the main signal transmission path and each provided with optical repeaters corresponding to the optical repeaters provided in the main signal transmission path, an optical main signal is selected from a desired optical fiber to be monitored from among the optical transmission paths and the monitoring signal is extracted from the optical main signal selected, thereby checking the quality of the desired optical fiber.
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