| 摘要 |
An optical distribution network using optical fibers connects a central office terminal to a number of optical network units which service respective subscribers. In order to monitor the onset and pace of signal degradation in the individual fibers of the network, an optical carrier signal is modulated with an amplitude-varied signal including at least two different amplitude levels that are above a selected amplitude threshold. At least one of the amplitude levels is chosen so that a portion of the signal having the chosen amplitude will not be reliably detected when a fiber in the path between the central office terminal and a destination optical network unit fails to meet a specified threshold power margin. Specifically, the amplitude-varied optical signal is transmitted from the central office terminal to each optical network unit, and a version or replica of the signal is returned by each optical network unit to the central office terminal, where a monitoring device attempts to detect the signal portions in the returned replica signals having the chosen amplitude. Non-detection of some or all of the signal portions having the chosen amplitude indicates that the power margin of a fiber link has fallen below the threshold.
|
