This device for measuring Brillouin scattering includes a single laser source (11), a modulator (12) placed on the path of the light emitted by the source (11) and designed to generate a pumping signal and a test signal which are injected to one end (13) of the fibre (10), a mirror (15) arranged at the other end (14) of the fibre in order to reflect the said signals, and an electronic unit (16) for producing time encoding of these signals in order to offset them in time relative to one another so that they cross at a point in the fibre after reflection at the end (14). A detector (20) connected to a detection fibre (18) that is coupled to the fibre (10) by a coupler (19) allows opto-electrical conversion of the two signals and determination of the value of the Brillouin scattering in the fibre.; Determination of physical parameters external to the fibre, such as temperature, on the basis of the value of the Brillouin scattering in this fibre.