Flexible misaligned fiber-optic sensor for respiration and heart rate monitoring

In this paper, a flexible fiber-optic sensor based on a misaligned structure is proposed for monitoring respiration and heartbeat signals. The sensor uses a misaligned splicing structure of single-mode fiber, enabling part of the core light to couple into the cladding and the outside, which significantly enhances its sensitivity to bending. Within the measurement range of 0–1.172 m⁻¹, the sensitivity reaches 44.751 dB/m⁻¹, enabling precise detection of small bending signals. To improve flexibility and wearing comfort, the sensor is coated with a PDMS layer, which allows direct attachment to the skin for respiration and heart rate monitoring. Experimental results show that the sensor can stably monitor respiration and heart signals at different postures and body locations, and it maintains excellent performance under different temperatures and in repeated tests after two months. The sensor has a simple structure, high sensitivity, strong stability, and good compatibility with the human body, showing great potential for applications in wearable health monitoring.