Cascaded Fabry-Perot interferometric air bubble strain sensor for finger motions

Strain sensors have important applications in health monitoring. Herein, a cascaded air bubble strain sensor based on Fabry-Perot interference is designed and analyzed. By using single-mode optical fibers, cascaded air bubbles are fabricated as the sensing elements. The external environment alters the wall thickness of the air bubbles and, consequently, the interference spectra. The sensor can detect strains in the range of 0–1200 με with a sensitivity of 11.07 pm/με. Considering the temperature cross-sensitivity, the sensor is placed in a thermostatic heating platform and heated to 100 °C. The temperature cross-sensitivity is 0.2 µε/°C. To demonstrate the practicality, the sensor is fixed on fingers to sense the bending motion of joints. Experimental results confirm high strain sensitivity and low temperature cross-sensitivity. As the sensor also offers good repeatability and stability for strain sensing, it has immense potential in applications such as finger rehabilitation training and gesture recognition. © 2025 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.