| 摘要 |
The optical time domain reflectrometry (OTDR)/backscatter trace of an optical fibre is obtained used a light emitting diode (LED) (19) as the source in place of the more conventional laser diode. The LED 19 is driven to produce a pulsed output which is applied to one end of the optical fibre 20 via a 3dB fibre coupler 21. Photons output from the fibre are coupled to a detector 22 such as an avalanche photodiode operating in a photon counting mode. The detector output is integrated (13, Fig. 1) and used to provide an OTDR/backscatter trace on an oscilloscope or chart (18, Fig. 1). For a 1.3 mu m LED, a germanium avalanche photodiode detector cooled to temperature of the order of liquid nitrogen temperatures is required, but at shorter wavelengths an uncooled silicon photodiode suffices. The apparatus may be used as a fault finder for use in the field. It is simple to operate and safer and cheaper than one employing a laser diode as the source. <IMAGE> |
