Fault detector technique for fibre optic transmission line controllers

摘要

The fault detector technique has a receiver unit (44) extracting (56,58) a control wavelength from the available wavelengths. Extracted signals are passed to a detector (60) and amplifier (62) and the signal level compared (64) to a threshold (64). An alarm is raised if the light level is too low showing a fault. Signals are also passed to a demodulator. The demodulator has a fault detector, which raises a second alarm if demodulation faults are found.