Non-Contact Optical Respiratory Rate and Heart Rate Monitoring Sensor Based on the Six-Hole High Birefringence Fiber

In this paper, an optical respiratory and heart rate non-invasive monitoring sensor is set up and proven to work well. The core part of this sensor is an optical fiber Sagnac interferometer (SI), built up by a 3 dB coupler and a section of homemade Six Holes High Birefringence Fiber (SH-HiBiF). Because of the circular asymmetric structure in the fiber, the wavelength-domain spectroscopy of the SI will shift linearly with the lateral stress changes with a sensitivity of 1.72 nm/kPa. Thus, if a single-wavelength laser is injected into the fiber, the respiratory and heart rate signals can modulate the light intensity and finally be demodulated by a photoelectric detector (PD). The heartbeat signals acquired by the proposed sensor demonstrate a high consistency (up to 95%) with those obtained from conventional electrical sensors, as validated by Bland-Altman analysis. Furthermore, the proposed monitoring sensor can help confirm the diagnosis of premature atrial contraction (PAC) even if it is not in contact with the human body, which is more comfortable for the patients. The temperature cross-sensitivity of this monitoring sensor is relatively low because the raw material of the sensing part is pure fused silica. Performed experiments demonstrate the sensor's feasibility in further research in the biomedical field.