Lab-on-Fiber Microfiber Knot Resonator for Respiratory Rate Sensing

Respiratory rate is an important indicator in respiratory monitoring. To achieve accurate measurement of respiratory rate, we have proposed a novel all-fiber sensor based on a lab-on-fiber microfiber knot resonator. The sensor is made of precisely knotted micro-optical fibers, which enhance its performance in detecting small changes in humidity caused by breathing. When the humidity changes, the refractive index of the humidity-sensitive polyvinyl alcohol film alters accordingly. Experimental results demonstrate a humidity sensitivity of 0.069 dB/%RH. With a response time of 412 ms and recovery time of 318 ms enable dynamic respiratory rate monitoring. The investigation of various heart rates and breathing patterns demonstrate that the sensor can accurately detect and distinguish changes in breathing patterns. The sensor’s continuous monitoring capability and the impact of airflow crosstalk have been thoroughly evaluated, demonstrating its remarkable stability and reliability. Owing to its high sensitivity, low power consumption and a high-quality factor, the sensor can accurately monitors breathing in harsh environments.