A Knee-Flexion Angle Optical Fiber Sensor Based on Spherical Fused Triple-Clad Fiber

A knee-flexion angle sensor based on spherical fused triple-clad fiber (TCF) is proposed and demonstrated. The optical path difference between the core and cladding modes in the angle sensor changes as the knee joint flexion angle changes, resulting in deviations in the interference spectrum. We conducted comparison experiments on various TCF lengths. When the TCF length is 3 cm, the maximum sensor’s angle detection range is from $0~^{\circ }$ to $110~^{\circ }$ . The angle sensitivity of the sensor is −0.35 nm/°, and the linear regression coefficient (R2) is 99.6 %, respectively. Furthermore, in the temperature range of 30- $90~^{\circ }$ C, the maximum temperature sensitivity is 0.08 nm/°C, and the R2 is 99.8 %. The sensor has the advantage of being compact, easy to manufacture, and highly repeatable, making it suitable for real-time human health monitoring and rehabilitation.