Fault detection system for an amplified optical transmission system

摘要

A fault detection circuit and method of detecting catastrophic faults for example from a total line outage due to a transmission waveguide being inadvertently cut, includes tapping a sample of the amplified transmission multichannel signal light for analysis. The tapped light is then fed to a periodic filter such as a Mach Zehnder interferometer or a Fabry Perot etalon having a free spectral range and phase at one output that coincides with the channel central wavelengths of the transmission system. Another output of the periodic filter provides an output response that is phase shifted by 180 degrees. Two output signals from the two output two output signals are then compared, in one embodiment by using a photodiode bridge. When one output of the periodic filter has a substantially different signal energy than the other, it is assumed that no faults occur. Conversely when the two outputs are substantially similar, it is assumed that a catastrophic fault has occurred.