High Sensitivity Polarimetric Optical Fiber Pressure Sensor Based on Tapered Polarization-Maintaining and Fiber Bragg Grating.

ABSTRACT

In this paper, we propose a high sensitivity polarimetric optical fiber pressure sensor (OFPS) using a polarization-diversity loop composed of a polarization beam splitter, polarization controllers, and a sensor head. The sensor head consists of 8-cm-long tapered panda-type polarization-maintaining fiber (PMF) and a fiber Bragg grating (FBG) directly spliced with PMF, and the sensor head is located inside a pressure chamber. A pressure-induced birefringence change due to the photoelastic effect can be greatly enhanced at the tapered section of PMF, thereby increasing the pressure sensitivity of the sensor head. The tapered PMF was fabricated using a fusion splicer, and the tapered length and center waist diameter of the tapered PMF segment were ~350 and ~56.82 µm, respectively. At the polarization-diversity loop, PMF is used as a birefringent element to create an interference spectrum due to polarization interference. A pressure-induced birefringence change of PMF results in a wavelength shift of the interference spectrum. Because the PMF birefringence also has a cross sensitivity to temperature, the FBG is utilized for the compensation of the temperature effect on it. The resonance wavelength of the FBG is sensitive to ambient temperature changes but insensitive to changes in pressure. This spectral response of the FBG can be used to compensate additional ambient temperature changes occurred at the sensor head. The pressure sensitivity of our sensor was measured as approximately -27.70 nm/MPa, and an adjusted R² value representing the sensor linearity was measured as ~0.9903 in a measurement range of 0-0.5 MPa. Our fabricated sensor exhibits the highest pressure sensitivity among previously reported polarimetric OFPS.