High-sensitivity distributed optical fiber sensor for simultaneous hydrostatic pressure and temperature measurement based on birefringent frequency-scanning -OTDR

A highly sensitive distributed optical fiber sensor (DOFS) for simultaneous hydrostatic pressure and temperature measurement is proposed and experimentally demonstrated. By taking advantage of the high sensitivity of frequency scanning phase -sensitive optical time domain reflectometry (phi-OTDR), both the frequency shift of Rayleigh scattering and birefringence along polarization maintaining fiber (PMF) can be demodulated with high accuracy. In the experiment, a standard panda PMF is utilized as sensing fiber, and the sensitivity of Rayleigh backscattering to hydrostatic pressure and temperature are 0.9323 GHz/MPa and -1.507 GHz/K, respectively. By contrast, the conventional DOFS based on Brillouin scattering only shows a hydrostatic pressure and temperature sensitivity of -0.74 MHz/MPa and 1 MHz/K, respectively. Meanwhile, that of birefringence is estimated to be 0.0976 GHz/MPa and -0.0522 GHz/K, respectively. Due to the large sensitivity difference of pressure and temperature, the crosstalk between pressure and temperature can be well resolved. Simultaneous measurement of hydrostatic pressure and temperature is carried out, and the frequency shift of uncertainties of Rayleigh scattering and birefringence 0.59 MHz and 0.68 MHz, respectively, corresponding to a hydrostatic pressure accuracy of 10 kPa and temperature accuracy 66.5 mK.