Fiber-Optic Pressure Sensor Based on PDMS Polymer Diaphragm-Formed Vacuum Microcavity With Low Temperature–Pressure Cross-Sensitivity

Temperature–pressure cross-sensitivity is a thorny issue that affects the measurement accuracy of polymer diaphragm pressure sensors. To alleviate the aforementioned issue, we demonstrate a novel optical Fabry–Perot interferometer (FPI) pressure sensor based on polydimethylsiloxane (PDMS) polymer diaphragm-formed vacuum microcavity. A technique of liquid encapsulation with vacuum pump oil is innovatively proposed. The vacuum Fabry–Perot (FP) microcavity is fabricated by assembling a capillary filled with vacuum pump oil and a fiber-tip FP cavity formed by the PDMS polymer diaphragm in a vacuum environment. The structural dimension of the sensor and the initial pressure in the vacuum microcavity can be precisely and conveniently controlled. The optimal parameters of the sensor are determined through finite element method (FEM) to help achieve low temperature–pressure cross-sensitivity. From the experimental results, the proposed FP pressure sensor with a polymer diaphragm thickness of $33.1 ~\mu \text{m}$ exhibits a wavelength pressure sensitivity as high as 1.58 nm/kPa in the range of 0–2 kPa and a temperature–pressure cross-sensitivity as low as 0.10 kPa/°C, which proves that the temperature crosstalk is effectively suppressed. Moreover, the proposed sensor has several advantageous characteristics including cost-effectiveness, reliable repeatability, long-term stability, and mass-producible, which makes it suitable for monitoring small-range static hydrostatic pressure precisely over a dynamic temperature range.