Greatly enhanced spatial detection of optical backscatter for sensor applications

Abstract

Abstract A pseudo random bit sequence is amplitude modulated onto a light source (2) (other types of modulation are discussed in the specification) and this modulated beam is transmitted down an optical fibre (3) or any material and the detected backscatted signal is multiplied (9) with a digitally delayed reference version of the transmitted sequence. By varying the delay between the transmitted and the reference pseudo random sequence spatial information can be recovered with improved signal to noise ratios compared to conventional Optical Time Domain Reflectometry. This enables improvements in the detected signal to noise ratio of the backscatter allowing reduced signal averaging times or reduced peak transmitted power. This technique can be used to produce enhanced optical sensors, sensing any external parameter on which the backscatter is dependent using video, and coherent detection. Enhanced fibre loss measurement techniques and enhanced fibre discontinuity measurement techniques are described. Distributed temperature sensors are described using Billouin and Raman backscatter. Because of enhanced detection the spatial resolution for a given signal averaging time can be reduced. The measurement of the amplitude, spectra, phase and polarisation of the scatter can also be used to characterise the properties of the material and the influence of any external parameters which influence the properties of the materials producing the backscatter. The measurement of backscatter can therefore be used to measure any external measurand which influences the amplitude, frequency, phase and polarisation of the backscatter.

Inventors

• 👤 Jeremy Kenneth Arthur Everard

Bibliographic Details