Wearable optical fiber sensor in no-core fiber for heart rate monitoring

Wearable heart rate (HR) sensors have gained remarkable progress in human vital signal monitoring and promoted the improvement of accurate medicine monitoring. The flexibility and stability are significant for wearable sensors, that determine the wearing comfort and signal accuracy. Here, a no-core fiber (NCF) based optical fiber sensor for precise continuous HR monitoring is presented. Two symmetric tapers are used to combine single mode fiber (SMF) and NCF, as well as improves the sensor’s robustness. The sensor probe exhibits a high bending sensitivity, reaching −10.346 dB/m⁻¹ within a curvature range of 1.36–2.30 m⁻¹, which is capable of detecting subtle bending signals with high accuracy. The sensor probe is integrated into a textile, an intensity demodulation system is created, pulse wave signal feature extraction and low-pass filtering signal processing algorithm are adopted, heartbeat signals are effectively real-time monitored for different positions (standing, sitting, and lying down) and different body parts (wrist, chest, and neck). The performance in comparison with commercial sensor demonstrates that the PCC is 0.958. With advantages of simple fabrication, high sensitivity, robustness, high stability, and wide applicability, the sensor holds a significant potential for human health monitoring.