All fiber human heart-rate sensor based on the evanescent field disturbance in no-core fiber

An all-fiber sensor for heart rate monitoring is proposed and demonstrated based on the disturbance of the evanescent field in the no-core fiber (NCF). The sensing structure is realized through splicing a piece of single mode fiber (SMF) at the ends of the NCF, respectively. When a broad-band light is injected into the structure, the vibration of the pulse signal applied to the sensing structure will lead to the disturbance of the evanescent field in the NCF and modulate the intensity of the optical output power. Therefore, when the sensing structure is placed at the wrist of a human, it can be used to monitor the heart rate. It is demonstrated that a standard electrocardiogram (ECG) signal can be obtained when 30-mm long NCF is used in monitoring the heart rate. According to the measured ECG signals, the proposed sensor can have a response to the heart pulse at different rates ranging from 60 beats per minute (bpm) to 120 bpm.