Measuring Brillouin backscatter from an optical fibre using digitisation

摘要

A method for measuring Brillouin backscattering from an optical fibre used for optical time domain reflectometry (OTDR). The method comprises mixing backscattered light received from the optical fibre 18 and having a Brillouin frequency fB(t) with coherent light at a frequency f1 in an optical detector 22 to produce an electrical signal with a difference frequency AF(t) = fB(t) - f1, and directly digitising the electrical signal using an analog-to-digital converter 30 to generate a sequence of samples representing the electrical signal, the samples then being processed to determine one or more properties of the Brillouin spectral line. The difference frequency may be further reduced by an additional frequency mixing stage to allow digitisation at a lower sampling rate.