Patent ID: 7304725
Filing Date: 2007-12-04
Classification: G01M,H04B

Abstract:
1. Optical time domain reflectometry apparatus, for sensing a parameter to be measured in a region of interest, which apparatus comprises: an optical fibre; source means operable to launch optical radiation into the optical fibre at a probe wavelength; and detection means operable to produce electrical output signals in response to optical radiation backscattered from the optical fibre; characterised in that the optical fibre comprises a first section, into which the optical radiation at the probe wavelength is launched, and a second section deployed in the region of interest, the first section having a higher intensity threshold for the onset of non-linear effects than the second section, the said source means being operable to launch optical radiation at the probe wavelength into the first section at an intensity lower than the non-linear effects intensity threshold of the first section but higher than the non-linear effects intensity threshold of the second section, the attenuation characteristics of the first section being chosen such that the intensity of the optical radiation at the probe wavelength reaching the second section is below the threshold for the onset of non-linear effects of the second section.