Measurement of Distributed Temperature and Strain Using Raman OTDR with a Fiber Line Including Fiber Bragg Grating Sensors

In this study, we propose a novel fiber optic sensor to show the measurement feasibility of distributed temperature and strains in a single sensing fiber line. Distributed temperature can be measured using optical time domain reflectometry (OTDR) with a Raman anti-Stokes light in the sensing fiber line. Moreover, the strain can be measured by fiber Bragg gratings (FBGs) in the same sensing fiber line. The anti-Stokes Raman back-scattering lights from both ends of the sensing fiber, which consists of a 4 km single mode optical fiber, are acquired and inserted into a newly formulated equation to calculate the temperature. Furthermore, the center wavelengths from the FBGs in the sensing fiber are detected by an optical spectrum analyzer; these are converted to strain values. The initial wavelengths of the FBGs are selected to avoid a cross-talk with the wavelength of the Raman pulsed pump light. Wavelength shifts from a tension test were found to be 0.1 nm, 0.17 nm, 0.29 nm, and 0.00 nm, with corresponding strain values of 85.76 mu is an element of, 145.55 mu is an element of, 247.86 mu is an element of, and 0.00 mu is an element of, respectively. In addition, a 50 m portion of the sensing fiber from 30. to 70. at 10. intervals was used to measure the distributed temperature. In all tests, the temperature measurement accuracy of the proposed sensor was less than 0.50 degrees C