Direct and simultaneous detection of temperature and strain using combined Brillouin and Raman backscatters in single mode fiber

A novel direct detection method for simultaneous distributed measurement of the temperature and strain along a single mode fiber based on the optical time-domain reflectometer technique is proposed. The Raman backscattering is sensitive to temperature but not to strain, thus the temperature distribution along the fiber can be determined. A twin-channel Fabry-Perot interferometer is designed; of which, the Brillouin channel is used to analyze the strain information within measurement range of 2000 με strain and 400 °C temperature. The frequency center, spectrum bandwidth and intensity changes of Brillouin backscattering are transformed into transmission changes after passing through the Fabry-Perot interferometer. With the look-up table of response functions of detected temperature, the strain profile along the fiber can be known. The Rayleigh channel is design to preset and measure the outgoing laser frequency relative to the Brillouin channel. By modulating the voltage added to the piezoelectric tube of the Fabry-Perot interferometer, the frequency offset of outgoing laser to the Brillouin channel can be preset; the temperature dynamic range can be extended.