The pore water pressure sensor based on Sagnac interferometer with polarization-maintaining photonic crystal fiber for the geotechnical engineering

The pore water pressure sensors with the six-hole suspended-core polarization-maintaining photonic crystal fiber (SC-PM-PCF) and commercial polarization-maintaining photonic crystal fiber (PM-PCF) are designed based Sagnac interferometer and calibrated in the laboratory. According to the theoretical analysis and calibration results, the transmission spectrum is very sensitive to the pore water pressure. It is found that the wavelength of the spectrum has a good linear relationship with variances of the surrounding pore water pressure, and the coefficient of wavelength-pressure of the commercial PM-PCF is 304.41 kPa/nm with the length of 35 cm as the sensing element while the coefficient of the SC-PM-PCF is 254.75 kPa/nm with the length of 100 cm. Finally, the two PM-PCF sensors are applied and compared with the conventional Pore water Pressure Transducers (PPTs) in a physical model test. It is found that measurements of the PM-PCF sensors are in good agreement with the results measured by the conventional PPTs.