| 摘要 |
In an optical time domain reflectometry method and apparatus in which optical radiation at a preselected wavelength ( lambda 0) is launched into a fibre, deployed through a region of interest, and back-scattered optical radiation in first and second preselected spectral bands, centred on respective first ( lambda 0) and second ( lambda -1) wavelengths, is used to produce output signals dependent upon the values being sensed, the preselected wavelength ( lambda 0) is selected in accordance with a predetermined attenuation characteristic of said fibre such that an average attenuation value, which is the average of the respective attenuation losses at said first ( lambda 0) and second ( lambda -1) wavelengths, is substantially minimised. <IMAGE> |
