A cascade splicing-based multimode fiber-tapered single-mode fiber structure for pressure sensing

Pressure sensing holds immense significance in the realm of fiber optic sensors, particularly in the context of industrial and environmental safety monitoring. In this paper, we propose and experimentally validate an optical fiber structural sensor based on Mach-Zehnder interferometer (MZI) for pressure measurement. The sensor adopts a cascaded spliced single-mode-multimode-tapered single-mode fiber (SMF-MMFTapered SMF, SMTS) structure, taking advantage of the mode mismatch effect between different fiber types and the high sensitivity of the evanescent field surrounding the tapered single-mode fiber. A segment of multimode fiber (MMF) is incorporated as the mode coupler to enhance the multimode interference (MMI). Experimental results demonstrated the sensor's robustness to pressure and temperature changes, with measurement sensitivities of the interference wavelengths Dip A and Dip B at 5.751 nm/KPa and 1.394 nm/KPa, respectively, within the pressure range of 0 ∼ 4410 Pa. The sensor also exhibited a response of 1.113 nm/°C and 0.857 nm/°C in the temperature range of 27.5 °C ∼ 41 °C. The sensor indicates a low temperature crosstalk of only 0.194 KPa/°C. By applying temperature compensation to correct pressure measurements, the accuracy of pressure sensing can be significantly improved. The sensor offers distinct advantages, including high sensitivity, low temperature crosstalk, compact structure, and simple fabrication, making it a promising candidate for applications in biochemistry and industrial production.