Evaluation of optically back-scattered signals for path dependent measurement e.g. temp. profile of back-scattering medium

摘要

The signal evaluation involves light which is introduced into a back-scattering medium (1) e.g. a quartz glass fibre, from at least one end. The light from a source (3) is amplitude modulated and frequency swept. Depending on its light density spectrum the light is prefiltered (6,8) to reduce the density of backscattered light in the spectral Raman band. The light is coupled into the back-scattering medium and into at least one reference channel (RK) and coupled out wavelength selectively. The coupled out frequency ranges are band pass filtered (10.1,10.2) and a notch filter used to evaluate light at the mean wavelength of the light source for both measurement channels (k1,k2). The received signals from two measurement channels and the reference channel light is opto-electronically converted and evaluated by a network analyser (4). The resulting signals are passed through a window function (5.1) and Fourier transformed (5.2) using the reference channel light for normalisation (5.4) where the path dependent properties are eliminated and the corrected measurement channel signals are set in relation to each other.