Soft optical fiber curvature sensor for finger joint angle proprioception

Soft optical fiber curvature sensor for finger joint angle proprioception was proposed, which was composed of a protective silicone layer, an optical fiber curvature sensor and two wearable fingertips. The key element of the sensor is an in-line Mach-Zehnder interference structure with a seven-core fiber and two single-mode fiber ball. The optical path difference between core mode and surrounding core modes of the sensor could be varied with the changes of curvature, which will cause the shift of interference spectrum. Experimental results show that when the curvature change in the range of 0 similar to 1 m(-1), the curvature sensitivity of the sensor was 2.744 nm/m(-1), and the linearity was 0.9967. Through the verification test of sensing equipment, the based Mach-Zehnder interference soft optical fiber curvature sensing approach is effective for the measurement of the bending shape of the joint angle model. The Mach-Zehnder interference sensor proposed in this paper has a more compact structure, simple manufacturing process and high reliability, which would find potential applications in the sports medicine rehabilitation or robotic monitoring fields.