Distributed temperature sensor using optical reflectometry

A distributed temperature sensor comprising a laser diode adapted to launch pulses of optical radiation into an optical fibre arranged to be located in thermal contact with an object, and a single optical filter coupled to a light detector to detect optical radiation backscattered from the fibre, wherein pulses of optical radiation are launched by the laser diode into the optical fibre and optical radiation backscattered from the fibre is detected by passing the backscattered radiation through the single optical filter whereby a first signal from Raman scattering is recorded at the anti-Stokes Raman wavelength from a pulse launched by the laser diode in a laser mode and a second signal from Rayleigh scattering is recorded at the anti-Stokes Raman wavelength from a pulse launched by the laser diode in a light emitting diode mode, and a comparison is made of the two signals, wherein the light detector counts photons passing through the single optical filter, wherein the photon count provides an indication of temperature and the arrival time of the signals allows identification of the position of that temperature along the length of the optical fibre.

A temperature sensing method in which pulses of optical radiation are launched by a laser diode into an optical fibre and optical radiation backscattered from the fibre is detected, the method comprising passing the backscattered radiation through a single optical filter whereby a first signal from Raman scattering is recorded at the Stokes Raman wavelength from a pulse launched by the laser diode in a laser mode and a second signal from Rayleigh scattering is recorded at the Stokes Raman wavelength from a pulse launched by the laser diode in a light emitting diode mode, and a comparison is made of the two signals, wherein said detecting is performed using a light detector to count photons passing through the single optical filter, wherein the photon count provides an indication of temperature and the arrival time of the signals allows identification of the position of that temperature along the length of the optical fibre.