초록 ▼

An optical time domain reflectometry apparatus has a laser and light modulator for producing coherent light pulses, each having two sections of higher intensity separated by a gap of lower or substantially zero intensity. As the light pulses propagate along the optical fibre, light is continuously R

An optical time domain reflectometry apparatus has a laser and light modulator for producing coherent light pulses, each having two sections of higher intensity separated by a gap of lower or substantially zero intensity. As the light pulses propagate along the optical fibre, light is continuously Rayleigh backscattered by inhomogeneities of the optical fibre. A photodetector generates backscatter signals representing the intensity of light Rayleigh backscattered in the optical fibre as each light pulse travels along the optical fibre. The PC uses these backscatter signals to derive a difference signal representing a change dI in intensity between signals generated from two successive pulses. The PC then calculates the Root Mean Square (RMS) of the difference signal averaged over the interval between the two sections of the light pulses. Next, the PC averages the backscatter signal generated from the first of the pulses over the same interval and normalises the RMS difference signal using the averaged signal to obtain a compensated difference signal that depends only on differences in the rate of change of phase of light of the light pulses as they travelled along the waveguide. This is repeated at different wavelengths to allow the compensated difference signal to be adjusted to represent the magnitude of the differences.

대표청구항 ▼

The invention claimed is: 1. An apparatus for detecting a disturbance in the propagation of light in an optical waveguide comprising:a light source for sending a light pulse along the waveguide, the light pulse being substantially coherent and varying in intensity over its duration to provide two se

The invention claimed is: 1. An apparatus for detecting a disturbance in the propagation of light in an optical waveguide comprising:a light source for sending a light pulse along the waveguide, the light pulse being substantially coherent and varying in intensity over its duration to provide two sections of higher intensity separated from one another by a section of lower or substantially zero intensity;a photodetector for generating a signal representing a time distributed intensity of light backscattered in the waveguide as the light pulse travels along the waveguide; anda processor in communication with the photodetector,wherein the light source sends two such light pulses along the waveguide,wherein the photodetector generates first and second such signals, one for each of the light pulses, andwherein the processor derives a difference signal indicative of differences between the first and second signals.