Fiber-Optic Sensor With Dual Peanut-Type Pull-Cone Structure for Monitoring of Pulse and Respiration

Pulse and respiration are important physiological signals that represent the health of the cardiovascular and respiratory systems, it is necessary for the development of advanced monitoring technology. In paper, a wearable fiber-optic sensor for pulse and respiration monitoring is proposed. The sensor has a double peanut-type pull-cone structure, and mainly consists of a section of middle-tapered multimode fiber (MMF) which is sandwiched by two sections of single-mode fibers (SMFs). Since the fused points between the SMF and MMF are respectively fabricated to peanut shapes, the multimode interference can be induced. The experiment results demonstrate that the intensity of sensor’s spectral interference peak is sensitive to bending, but not to temperature. The curvature sensitivities are 13.803 dB/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 2.054 dB/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in ranges of 0~1.138 m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 1.138~5.915 m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>, respectively. The temperature sensitivity of the sensor is less than 0.0027 dB/°C in temperature range of 20~50 °C, which makes it mostly unaffected by ambient temperature in measurements of pulse and respiration. As the sensor is used to analyze the physiological signals of different subjects, not only the pulse-related parameters such as pulse frequency, augmentation index (AIx), waveform eigenvalue K-value and blood viscosity (V) can be obtained from the analysis of pulse waveforms successfully, but also demonstrate that the sensor can effectively distinguish different respiratory states, which expanded the functional applications of the fiber-optic sensor in biomedicine field.