Probing Changes in Pressure With Subpascal Resolution Using an Optical Fiber Fabry–Perot Interferometer

Abstract

This article reports a novel optical fiber extrinsic Fabry–Perot interferometer (EFPI) for probing pressure changes with subpascal (~0.1 Pa, $\sim 1.45\times 10^{-5}$ psi) resolution. The principal idea of the sensor is to employ a traditional C-shaped Bourdon tube as a mechanical transducer that is coupled to a highly sensitive EFPI device. The cavity of the EFPI device is formed between a gold-coated mirror, mounted to a concave section of the Bourdon tube, and the endface of an optical fiber mounted at the base section of the Bourdon tube. Based on this design, the pressure-induced deflections of the Bourdon tube are directly correlated with the changes in cavity length of the EFPI, which can be determined by analyzing the interference signals. An experiment based on probing hydrostatic pressure changes induced by the addition of single water droplets to a test chamber was performed to quantify the measurement resolution of the proposed sensor because an apparatus for producing exceedingly small, stable, and reproducible pressure changes does not exist. Compared with conventional optical fiber pressure sensors, the proposed pressure sensor requires a simple fabrication process and can be used to measure pressure changes with high sensitivity ( $\sim 23.5~\mu \text{m}$ /kPa, cavity length change/pressure change). Moreover, the sensitivity and resolution of the pressure sensor can be flexibly adjusted using Bourdon tubes designed for different dynamic ranges (e.g., 0–70 MPa, 0–10152 psi). It is believed that the proposed novel pressure sensor has the potential to find a wide range of applications that require precise instrumentation.