Modal-interfered-based fiber-optic wearable curvature sensor for rapid joint-movement monitoring

In this paper, a novel fiber-optic wearable sensor, to our knowledge, is proposed and completed experimentally based on core-mismatched multimode fibers with core-offset splicing. The spectral characteristics are simulated and analyzed with varied offset and lengths, and the comprehensive tests in terms of curvature and temperature responses are performed under the optimal offset. The experimental results show that the wavelength responses of curvature are directly related to the length of the offset-multimode-fiber, and the maximum reaches -25.41nm/m^-1 with a temperature sensitivity of 50.47 pm/°C. Furthermore, the intensity-demodulated-based real-time monitoring setup is built, and the encapsulated sensor is applied to rapid joint movement scenarios of the knee, elbow, and finger, respectively. The tested results show that a large bending angle (close to 90°) can be achieved with a real-time response (∼0.2s) and a high signal-to-noise ratio.