A new type of structure of optical fiber pressure sensor based on polarization modulation

Abstract

In this study, a new type of structure of optical fiber pressure sensor (OFPS) based on polarization modulation is proposed, which selects a high-birefringence fiber (HBF) as the sensing unit to measure the pressure in the fluid medium. The PM-1550-01 fiber produced by NTK Photonics Inc. is evaluated as the sample in our subject. Firstly, the regularities of birefringence variation on the PM-1550-01 followed by the external pressure load and the ambient temperature are analyzed by the finite element method (FEM). The results show that the pressure sensitivity is 2.05 × 10−6 RIU/MPa in the pressure range of 0–100 MPa, and the temperature sensitivity is 7.27 × 10−10 RIU/°C in the temperature range of 0–100 °C. Thus, the pressure-temperature cross-sensitivity is only 0.355 kPa/°C in theory. Secondly, the expression of the output light intensity of the introduced OFPS is deduced based on the principles of polarization interference and phase modulation. Combined with simulation results, the measurement ranges of the sensor can be set and adjusted by the length of the sensing unit. Finally, the proposed OFPS is fabricated and external pressure tests within the range of 0–50 MPa are completed. The results show that the pressure sensitivity is approximately 0.145 dB/MPa in the pressure range of 0–44 MPa. There is a fine consistency between the experimental data and simulation results. In addition, the proposed OFPS has many other advantages, such as small size, simple fabrication process and large measurement range, which make it appropriate to be applied in high-pressure measurement in hostile conditions, e.g., downhole and ocean-bottom.