Determining the type of an optical fibre from measured delay-time differences between pulse signals of different wavelengths

摘要

Wavelength division multiplexing (WDM) optical communication apparatus is operated in a monitoring mode to determine the type of optical fiber used in the system. The invention applies to WDM systems which contain a source of amplified spontaneous emission (ASE) light such as an Erbium-doped fibre amplifier (EDFA)3. When in the monitoring mode, the output from the ASE source 3 of a transmitting unit 100-1 is switched 103 through a filter 104 so that two or more discrete wavelengths from the wavelength band normally used for transmission of data are transmitted to a receiver (Fig. 8) across a fibre. The same pulse is simultaneously transmitted on each of the two or more wavelengths. The receiver measures the difference between pulse reception times, T(the "delay-time difference). The transmitting unit also transmits a control signal OSC and measures the round-trip time for this signal, Tosc. The ratio T/Tosccan be used to determine the fibre type because the ratio is related to the dispersion per unit length of the fibre.