Fiber-optic Fabry–Perot pressure sensor with the Vernier effect based on dynamic adjustment of the cavity length method

This paper proposes and validates a fiber-optic pressure sensor based on a Fabry–Perot interferometer, which enhances sensitivity through the Vernier effect generated by concatenating parallel cavities. The sensor consists of a sensing cavity and a reference cavity. The sensing cavity was fabricated by fusing a segment of short multimode fiber (MMF) to a single-mode fiber (SMF), followed by the fusion of a segment of capillary glass tubing (HST1) to the end of the MMF, and coating the end of HST1 with a polydimethylsiloxane film. The reference cavity was fused to the internal section of a capillary glass tube (HST2) by SMF, whereas dynamically adjusting its cavity length to induce the Vernier effect between the two cavities. The inclusion of the MMF enhances the interference fringe contrast in the reflectance spectrum. The sensor’s performance was characterized through both theoretical and experimental studies. The sensor demonstrated a sensitivity of −233.4nm/MPa within the 0–250 kPa range. At low temperatures, the temperature cross-sensitivity was as low as −5.3×10 −3 MPa/ ∘ C. This parallel-cavity Fabry–Perot pressure sensor, exhibiting the Vernier effect, offers several advantages, including high sensitivity, low cost, and simple fabrication, making it suitable for practical sensing applications.