Respiration Monitoring Using Antiresonant Reflecting Guidance in Selectively Infiltrated Hollow Core Photonic Crystal Fiber

In this article, a respiration sensor based on anti-resonant reflecting effect is proposed and successfully manufactured. The sensor consists of a Section of hollow core photonic crystal fiber (PCF) spliced between single mode fibers. One of the cladding air holes is filled with liquid to create the anti-resonant effect. The moisture from human breath can condense on the outer surface of the hollow core PCF, which affects the anti-resonant reflecting guidance property of the waveguide. The breath pattern can be monitored by tracing the change in transmitted intensities. A wearable solution is provided by attaching the sensor head to a facial mask, and breath dynamic characteristics are collected and converted to electronic signals. The sensor device is used to monitor the breath condition of different volunteers during a variety of physiological activities. The sensor presents a rapid response time of 47 ms and recovery time of 63 ms. The peak expiratory flow (PEF) of the breathing process can also be measured with the sensor, since which has a linear relationship with the output voltage. On the other hand, the sensor is capable of measuring temperature change simultaneously. The resonant wavelength exhibits blueshift as temperature rises, and the temperature sensitivity is about −0.16 nm/°C. The sensor is lightweight, cost effective, and is suitable for monitoring patients during certain medical procedures, such as magnetic resonance imaging scan, where electronic sensors are not suitable.