A METHOD OF MEASURING ON AN OPTICAL FIBRE

摘要

In a method of measuring on an optical fibre (2), a pulse is launched into the fibre, and the temporal course (8, 9) of the echo of this pulse is measured. Then, a signal level representing the background noise present in the fibre is subtracted in a subsequent signal processing of the echo signal. The signal level representing the present background noise is calculated on the basis of the instantaneous value (20) of the background noise which it assumes during the measurement of the echo signal. In a first embodiment the background noise is measured at a wavelength different from the wavelength of the emitted pulse. In a second embodiment wherein several successive pulses (25, 26) are launched into the fibre, optical power (27) is launched into the fibre at a wavelength other than the pulse wavelength during the intervals between said pulses.