Deep learning-based ballistocardiography reconstruction algorithm on the optical fiber sensor.

Ballistocardiography (BCG) is a vibration signal related to cardiac activity, which can be obtained in a non-invasive way by optical fiber sensors. In this paper, we propose a modified generative adversarial network (GAN) to reconstruct BCG signals by solving signal fading problems in a Mach-Zehnder interferometer (MZI). Based on this algorithm, additional modulators and demodulators are not needed in the MZI, which reduces the cost and hardware complexity. The correlation between reconstructed BCG and reference BCG is 0.952 in test data. To further test the model performance, we collect special BCG signals including sinus arrhythmia data and post-exercise cardiac activities data, and analyze the reconstructed results. In conclusion, a BCG reconstruction algorithm is presented to solve the signal fading problem in the optical fiber interferometer innovatively, which greatly simplifies the BCG monitoring system.

Few-Mode Fiber Characterization System Based on the Spatially and Spectrally Imaging Technique.

With the widespread use of few-mode fibers, mode characteristics testing becomes essential. In this paper, current few-mode fiber testing techniques are discussed, and the S2 imaging technique is chosen and demonstrated to be capable of few-mode fiber characterization in principle. As a result, the few-mode fiber characterization system with the S2 imaging technique is built and used to obtain accurate mode dispersion of two-mode fibers (a commonly used few-mode fiber) of different lengths. Then, various filters are applied to extract the fundamental and high-order modes to acquire mode coupling components (discrete and distributed mode coupling). The proposed system spectrally characterizes the few-mode fiber by resolving the interference information from the superimposed optical field spatially and has a simple structure and easy operation, which will provide parameter guidance for FMF designing and the FMF sensing experiment optimizing.

Ballistocardiography monitoring system based on optical fiber interferometer aided with heartbeat segmentation algorithm.

An optical fiber interferometer-based ballistocardiography (BCG) monitoring system aided with the IJK complex detection algorithm is proposed in this paper. A new phase modulation method based on a moving-coil transducer is developed to address the problem of signal fading in the optical fiber interferometer and keep the system in quadrature by the closed loop controller. As a result, a stable BCG signal without baseline drift can be obtained. This BCG monitor based on optical fiber interferometer using phase modulation method owns the advantages of compact, low-cost, portable, and user-friendly. In addition, an end-to-end modified U-net is developed to conduct pixel-wise classification in the BCG signal. This network can achieve high accuracy and shows its capability to segment IJK complex and body movement in the BCG signal. In conclusion, the proposed BCG monitoring system with IJK complex segmentation algorithm is potential and promising in healthcare applications.

Photo-induced bleaching and thermally stimulated recovery of BAC-P in Bi-doped phosphosilicate fibers.

The first results of the study on photobleaching and thermally induced recovery in Bi-doped phosphosilicate fiber have been presented. It was revealed that the rate of bleaching of phosphor-related Bi active center (BAC-P) becomes slower with the decrease of photon energy. The quadratic dependence of the bleaching rate of BAC-P on laser power is obtained under 532 nm laser irradiation. The effect of temperature on the bleaching dynamics of BAC-P is also investigated under 532 nm radiation, suggesting a thermally aggravated bleaching process upon heating at certain temperatures (≥300∘C). Furthermore, the thermal recovery of bleached Bi-doped silica-based fiber (BDF) is investigated and a 13% increase of luminescence is achieved upon thermal quenching for 5 min at 400ºC. The underlying mechanism of photobleaching and thermo-stimulated recovery process of BAC-P is also discussed.

Non-invasive human vital signs monitoring based on twin-core optical fiber sensors.

Twin-core fiber (TCF)-based sensor was proposed for non-invasive vital sign monitoring, including respiration and heartbeat. The TCF was homemade and the corresponding sensor was fabricated by sandwiching single-mode fiber (SMF) on both ends. The offset distance between SMF and TCF was optimized while the length of TCF was identified from preliminary vital sign measurement results. Then, the TCF-based sensor was attached under a mattress to realize non-invasive vital sign monitoring. Both respiration and heartbeat signal can be obtained simultaneously, which is consistent with the reference signals. For further application, post-exercise physiological activitity characterization were realized based on this vital sign monitoring system. In discussion, mode coupling in TCF was analyzed and utilized for curvature sensing with achieved sensitivity as high as 18 nm/m-1, which supported its excellent performance for vital signs monitoring. In conclusion, the TCF-based vital signs monitors can be a promising candidate for healthcare and biomedical applications.

Torsion sensor based on inter-core mode coupling in seven-core fiber.

We proposed a novel torsion sensor based on inter-core mode coupling in seven-core fiber (SCF). The torsion sensor is fabricated by tapering a commercially available SCF spliced with two single mode fibers. Waist diameter and length of the taper structure were experimentally optimized to achieve good transmission spectrum. Based on this structure, the torsion measurement was conducted, and the experimental results demonstrated that the transmission spectrum shows a red shift with the fiber twist. The torsion sensitivity increases with the twisting angle, which can achieve as high as 1.00 nm/°. The direction of wavelength shift was observed to be opposite when twisting the tapered SCF in clockwise and counter-clockwise direction, demonstrating its capability to discriminate the rotation orientation. Moreover, all the measurements were repeated in attempts to confirm its stable performance as well as high accuracy. Mode coupling dynamics and theory of optical anisotropy in twisted fiber are adopted to discuss the sensitivity performance, which agrees well with experimental results. The novel torsion sensor could provide a promising candidate for the applications requiring accurate rotation.