Fibre=optic cable bandwidth measuring device - has semiconductor laser modulated by noise diode connected to amplifier coupled to photodetector and spectrum analyser via cable

摘要

The device measures the bandwidth of a length of multimode fibre optic cable (30) typically 1-4 Km, and uses a diode laser (D1) whose output is modulated by noise provided by a noise generator (D2) in the form of an avalanche diode. The noise is amplified by four identical amplifiers (14) of 1.5 GHz bandwidth and 50 dB gain. The noise level generated is -47 dB. The receiver (20) has a photodiode (D3) coupled to a spectrum analyser (21). After the spectrum has been recorded the cable is reduced to a standard reference length of 5-10 m without disturbing the transmitter and the spectrum again measured and then compared with and subtracted point by point from the previous recording.