Timely detection of highly infectious pathogens is essential for preventing and controlling public health risks. However, most traditional testing instruments require multiple tedious steps and ultimately testing in hospitals and third-party laboratories. The sample transfer process significantly prolongs the time to obtain test results. To tackle this aspect, a portable fiber optic surface plasmon resonance (FO-SPR) device was developed for the real-time detection of infectious pathogens. The portable device innovatively integrated a compact FO-SPR sensing component, a signal acquisition and processing system, and an embedded power supply unit. A gold-plated fiber is used as the FO-SPR sensing probe. Compared with traditional SPR sensing systems, the device is smaller size, lighter weight, and higher convenience. To enhance the detection capacity of pathogens, a monolayer graphene was coated on the sensing region of the FO-SPR sensing probe. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was used to evaluate the performance of the portable device. The device can accurately detect the SARS-CoV-2 spike S1 protein in phosphate-buffered saline (PBS) and artificial saliva within just 20 min, and the device successfully detected cultured SARS-CoV-2 virus. Furthermore, the FO-SPR probe has long-term stability, remaining stable for up to 8 days. It could distinguish between the SARS-CoV-2 spike protein and the MERS-CoV spike protein. Hence, this FO-SPR device provides reliable, rapid, and portable access to test results. It provides a promising point-of-care testing (POCT) tool for on-site screening of infectious pathogens.

A highly sensitive hybrid structure sensor based on suspended-core fiber (SCF) is proposed for vector curvature and temperature measurement. The sensor is prepared by self-assembly of SCF-based cascaded Fabry-Perot interferometer (cFPI), single-mode fiber (SMF), and fiber Bragg grating (FBG). In view of the asymmetry of the cFPI, theoretical analysis of the beam transmission and spectral characteristics is implemented when the beam is incident from different directions. The two sensing fibers in the triangular distribution sensor will not be located on the neutral plane at the same time, which makes it possible to measure bending in any orientation. The Vernier effect formed by the cFPI enlarges the curvature and temperature sensitivity to −1064.5 pm/m ⁻¹ and 50.7 pm/°C, respectively, without affecting the measurement range. The spectrum shows the opposite spectral response when the sensor bending direction difference is 180°. The sensor overcomes the bottleneck of bending sensitive blind spots in dual-fiber sensing. In addition, the sensor maintains a smaller size and more flexible preparation, which is conducive to its application in artificial intelligence, medical detection.

In this letter, we propose a novel bamboo-shaped interference sensor based on multistage photonic-band gap microstructured fiber (PBG-MF) and single-mode fiber (SMF) to build the cascaded Fabry-Perot interferometer (FPI). Due to the honeycomb space inside the PBG-MF, a higher extinction ratio (ER) is obtained in the reflection spectrum of the interferometer, which is conducive to improving the detection limit (DL) and resolution of the sensor. The bending direction can be identified by the structure proposed in this letter. Maximum curvature sensitivity is 991 pm/m ^-1 in the convex direction. Maximum curvature sensitivity is -1118 pm/m ^-1 in the concave direction. The sensor has the advantages of small size, high sensitivity, and high package stability. It is particularly suitable for ultra-short distance curvature sensing, such as the joints of the human body.

The resonant response of the hollow microcapillary resonator (HMCR) assembled with liquid-metal core edge-coupled with microfiber coupler (MFC) was theoretically and experimentally investigated. Primarily, for the first time, the analogy electromagnetically induced transparency (EIT) phenomenon and Fano resonance was proposed and discovered in this coupling system. Different from the traditional method, the discrepancy in temperature characteristics of waveguide super-mode and whispering gallery mode (WGM) leads to the evolution of EIT and Fano resonances. This feature has great application value for fiber optic sensors, filters, and switches due to its sharp and asymmetric lineshape. Secondly, the temperature response characteristics were improved by assembling a liquid metal core inside the HMCR. Benefitting from the high thermal expansion-coefficient material, this solution reduces externally imposed energy consumption during the tuning process. In addition to all that, to realize the multi-parameter tuning characteristics, a fiber Bragg grating (FBG) unit was constructed to perform strain tuning. This research has significant implications for sensor measurement, optical filters, optical switches, and optical modulators.

A novel fiber Fabry-Perot interferometer (FPI) vector curvature sensor based on Vernier effect is proposed and demonstrated. The triangular-distributed sensing structure is fabricated by self-assembly of FPI and single-mode fiber (SMF). When the device is bent in any orientation, a direction-dependent wavelength shift of the interference pattern is produced because the sensing fiber always deviates from the neutral plane. In order to overcome the trade-off between high sensitivity and large dynamic range, we connect the reference fiber and the sensing fiber to produce the Vernier effect. Without affecting the measurement range of the sensing structure, the sensitivity of the self-assembled sensor based on Vernier effect is amplified by 5 times and 3.6 times respectively by using different FPIs as sensing arm. The experimental results show that the sensing structure has good stability and repeatability. Compared with the substrate packaging, the fiber FPI sensing structure based on self-assembly can realize miniaturization, which is conducive to the application of the sensor in medical detection and artificial intelligence.