Drop discriminating network alarm system utilizing a single sensing fiber

摘要

A method is provided for detecting movement indicative of intrusion events on optical drop fibers of a network where the individual drop fiber can be identified to locate the event. The method uses a monitor system at the network end and multiplexing the monitor signal along the individual fibers to the respective terminals. At each of the terminals, the monitor signal is returned unchanged or in modified form along the same or different fibers to the network end. At the network end the received monitor signals is analyzed for changes in said monitor signals indicative of movement. Which one or more of the drop fibers has triggered the alarm is determined by modifying the monitor signal in wavelength or polarization, or by applying a modulation at the source and/or at multiplexing and/or at returning so that the monitor signal of one drop fiber has a difference from the monitor signal of another drop fiber.

主权项

1. A method for detecting intrusion into optical cables of a network, wherein the network comprises:
a plurality of drop cables each having a first end at a network end and a second end connected to respective ones of a plurality of terminals at respective end users; each cable including at least one data transmission fiber and at least one monitoring fiber; a multiplexing system for separating signals on an input fiber to each of the plurality of drop cables for supply to the respective terminals; the method comprising: providing a monitor system at the network end having a monitor signal output from a monitor signal source; multiplexing the monitor signal output for supply along said monitoring fibers of the plurality of drop cables to the respective terminals as a monitor signal; at each of the terminals, returning the monitor signal along said monitoring fibers to the network end; at the network end analyzing received monitor signals after transmission along said monitoring fibers for changes in characteristics of said monitor signals which changes are indicative of movement of said monitoring fibers for detecting an intrusion event on one or more of the drop cables; and determining which one or more of the drop cables has said movement thereof by modifying the monitor signal at one or more of said monitor signal source, said multiplexing and said returning; so that the monitor signal of one drop cables has a difference from the monitor signal of another drop cable; and detecting the difference to determine said one or more of the drop cables which has said movement.