Glucose is an indispensable nutrient for metabolism in living organisms and is widely used in food, industry, and medical fields. Glucose is often added as a sweetener in food and often used in industry as a reducing agent for various products. In medical treatment, glucose is added to many drugs as a nutritional additive, and it is also an indicator that diabetics need to pay attention to at all time. Therefore, the market has a great demand for low-cost, high-sensitivity, fast, and convenient glucose sensors, and the industry has always attached great importance to the work of creating new glucose sensor devices. Therefore, we proposed a SnO₂ nanofibers/Au structure multimode-single-mode-multimode (MSM) fiber surface plasmon resonance (SPR) glucose sensor. SnO₂ nanofibers were fixed to a single-mode fiber core that had been plated with the Au film by electrospinning. When the glucose concentration increased at 5 vol% intervals, the corresponding resonance wavelengths had different degrees of redshifts. Comparing the two structures, as the glucose concentration range increased from 0 vol% to 60 vol%, the sensitivity increased from 228.7 nm/vol% in the Au structure to 337.3 nm/vol% in the SnO₂ nanofiber/Au structure. At the same time, the linear correlation between the resonant wavelength and the refractive index of the two structures was greater than 0.98. Moreover, the SnO₂ nanofibers/Au structure significantly improved the practical application performance of SPR sensors.

We report the numerical and experimental studies of the two-dimensional Brillouin gain spectrum (BGS) distribution deformation induced by the self-phase modulation in the Brillouin optical time domain reflectometry (BOTDR) with a 20.6 km sensing distance. The BGS distribution deformation is investigated by analyzing the evolution of the point spread function along the fiber in the two-dimensional model of the BOTDR. In the simulation and experimental results, the specific deformation degree of the BGS distribution induced by the self-phase modulation is related to the pump pulse profile, pump pulse peak power, BGS demodulation method, and detected scattered light component. By comprehensively analyzing the evolution of the point spread function induced by the self-phase modulation and using the image deconvolution, a typical BOTDR sensor with a 25 ns pump pulse reaches the 20 cm spatial resolution over the 20.6 km sensing fiber.

A large number of slopes appear along the line during railway construction, which will pose a threat to railway safety operation. Slope monitoring plays an important role in ensuring the safety of railway operation. Aiming at the difficulties of sensor multiplexing, low accuracy, and large disturbance by trains, this paper proposes a railway slope monitoring method based on integrated fusion detection of inclination and vibration. Instability and failure characteristics of the K3 slope in Shuohuang Railway and dynamic characteristics under the excitation of the train load are analyzed by the finite element method (FEM) analysis. Based on the above analysis, a slope monitoring system is established utilizing the self-developed dual-parameter fiber Bragg grating (FBG) sensor. The monitoring data of the past four years show that the slope is in a relatively stable state at present. The monitoring data are consistent with the results of the FEM. The feasibility of the damage identification method based on inclination and vibration characteristics is verified, which provides a new method for railway slope monitoring.

Fiber optic sensors have been gradually used in aerospace, petrochemical, electronic power, civil engineering, and biomedical fields because of their many advantages such as the anti-electromagnetic interference, corrosion resistance, light weight, small size, high accuracy, and easy reuse. In recent years, sensing and demodulation technologies based on microwave photonics have attracted widespread attention. Optical fiber sensing combined with microwave photonics has higher sensitivity and flexibility, which is important for the demodulation of interferometric signals. This article introduces and analyzes the principle, structure, and performance of the demodulation technology of fiber optic interferometric signals based on microwave photonics from the perspective of system structures, such as filters, oscillators, and interferometers, and discusses the future research and development directions.

This article proposes a line scanning chromatic confocal sensor to solve the problem of limited chromatic confocal measurement due to the small measurement range and low measurement efficiency in the industrial inspection process. To obtain an extensive dispersion range, the advantages of a simple single-axis structure are combined with the advantages of a large luminous flux of a biaxial structure. Considering large-scale measurement, our sensor uses off-axis rays to limit the illumination path and imaging path to the same optical path structure. At the same time, the field of view is expanded, and a symmetrical structure is adopted to provide a compact optical path and improve space utilization. The simulation and physical system test results shows that the sensor scanning line length is 12.5 mm, and the axial measurement range in the 450 nm to 750 nm band is better than 20 mm. The axial resolution of the detector is ±1 µm combined with the subpixel centroid extraction data processing method, and the maximum allowable tilt angle for specular reflection samples is ±7°. The thicknesses of transparent standard flat glass and the wet collagen membrane are measured. The maximum average error is 1.3 µm, and the relative error is within 0.7%. The constructed sensor is of great significance for rapidly measuring the three-dimensional profile, flatness, and thickness in the fields of transparent biological samples, optics, micromechanics, and semiconductors.

The illegal water injection into meat not only breaks the market equity, but also deteriorates the meat quality and produces harmful substances. In this work, we proposed a fiber Bragg grating (FBG) sensor that enabled fast, quantitative, and in-situ detection of the moisture content of water-injected meat. The FBG was written in the erbium-ytterbium (Er/Yb) co-doped fiber, which could perform the self-photothermal effect by injecting the near infrared laser into the fiber. As the heated fiber sensor probe was inserted into the meat sample, the temperature decreased due to the heat dissipation mediated by moisture. The intracore Bragg grating could monitor the temperature loss by recording the Bragg wavelength shift, which reflected the water content quantitatively. The results revealed that the sensor could complete the detection within 15 s. The sensor’s sensitivity to detect changes in the pork water content was theoretically calculated to be 0.090847%. The proposed sensor is expected to provide a novel approach for examination of the meat moisture.

Since the discovery of the extraordinary optical transmission phenomenon, nanohole arrays have attracted much attention and been widely applied in sensing. However, their typical fabrication process, utilizing photolithographic top-down manufacturing technologies, has intrinsic drawbacks including the high costs, time consumption, small footprint, and low throughput. This study presented a low-cost, high-throughput, and scalable method for fabricating centimeter-scale (1×2 cm²) nanohole arrays using the improved nanosphere lithography. The large-scale close-packed polystyrene monolayers obtained by the hemispherical-depression-assisted self-assembly method were employed as colloidal masks for the nanosphere lithography, and the nanohole diameter was tuned from 233 nm to 346 nm with a fixed period of 420 nm via plasma etching. The optical properties and sensing performance of the nanohole arrays were investigated, and two transmission dips were observed due to the resonant coupling of plasmonic modes. Both dips were found to be sensitive to the surrounding environment, and the maximum bulk refractive index sensitivity was up to 162.1 nm/RIU with a 233 nm hole diameter. This study offered a promising approach for fabricating large-scale highly ordered nanohole arrays with various periods and nanohole diameters that could be used for the development of low-cost and high-throughput on-chip plasmonic sensors.

In recent years, detecting and quantifying multiple gases have garnered widespread attention across various fields, particularly in volatile organic compound (VOC) detection, which holds significant importance for ecosystems and the medical field. The Raman spectroscopy has been widely used in multi-gas detection due to its advantages in fast response speed and non-destructive detection. This paper reviews the latest research progress of the multi-gas sensing technology in the Raman spectroscopy, focusing on using the hollow-core fiber to enhance the gas signal intensity. The basic principles of the fiber-enhanced Raman spectroscopy are introduced. The detailed discussion includes the system architecture, parameter configuration, and experimental results. Then, the latest advances in the coherent anti-Stokes Raman scattering multi-gas detection technology are reviewed. Finally, the challenges faced by the hollow-core fiber in practical applications are discussed.

Fabry-Pérot (FP) microcavities have attracted tremendous attention in recent years due to their favorable optical characteristics of the high quality (Q) factor and small mode volume. In this work, we presented a novel approach that utilized the soft lithography and imprinting technology to incorporate the convex micro-lens array structure into the FP (FP-lens) cavity. A strong mode-profile restriction of the micro-lens simultaneously reduced the mode volume and enhanced the Q factor, exhibiting high tolerance to non-parallelism of mirrors compared with that of the plane-plane FP (PP-FP) microcavities. In the experiment, the Q factor of the FP-lens cavity was measured to be 8.145×10⁴, which exhibited a 5.6-fold increase than that of the PP-FP cavity. Furthermore, we experimentally measured the refractive index sensing performance of the FP-lens cavity with the sensitivity of 594.7 nm/RIU and a detection limit of 4.26×10⁻⁷ RIU. On the basis of this superior sensing performance, the FP-lens cavity has the great potential for applications in biosensors.

A new type of human immunoglobulin G (IgG) sensors based on the surface plasmon resonance (SPR) in the low refractive index (RI) plastic optical fiber (POF) and an antibody immobilization method is presented. A 50-nm-thick gold film was formed on the polished D-shaped fiber surface by magnetron sputtering. The RI response of the POF sensor is 30 049.61 nm/RIU, which is 26.5 times higher than that of single mode fiber (SMF) SPR sensors. The proposed SPR biosensor can be developed by simple and rapid modification of the gold film with 11-mercapto undecanoic acid (MUA). Upon immobilization of the goat anti-human IgG antibody, the resonance wavelength shifts by 11.2 nm. The sensor can be used to specifically detect and quantify the human IgG at concentrations down to 245.4 ng/mL with the sensitivity of 1.327 7 nm per µg/mL, which offers an enhancement of 12.5-fold compared to that of the conventional SMF based SPR sensors. The proposed device may find the potential applications in the case of use at the point of care.

Cancer has been one of the most serious diseases, resulting in more than 10 million deaths every year. Fiber-optic sensors have great potential for diagnosing and treating cancer due to their flexibility, precise positioning, real-time monitoring, and minimally invasive characteristics. Compared to traditional central laboratory examination, fiber-optic biosensors can provide high sensitivity, miniaturization, and versatility, which feature the point-of-care diagnostic capability. Herein, we focus on recent advances in fiber-optic biosensors for cancer theranostics. It is primarily concerned with advancements in the design of various fiber sensing approaches, fiber cancer sensing, and therapy sensors. With fiber-optic biosensors, cancer marker detection, cancerous cell differentiation, ex vivo tumor model validation, and in vivo tumor detection can be achieved. And the medical fiber also can be used to provide photothermal therapy, photodynamic therapy, and combination therapy for solid tumors. Additionally, cancer sensing and therapy can be integrated into the fiber, which demonstrates the multiplexing capabilities of fiber-optic biosensors. Lastly, we systematically summarize the fiber biosensor applications from in vitro to in vivo, and conclude with the challenges in development and prospects.

Intelligent food packaging with the multisensory analysis is promising as the next generation technology of food packaging. The oxygen content in food packaging is one of the crucial parameters affecting the food quality and shelf life. Caviar is among the most nutritious and costly food sources. Here, a photonic oxygen-sensing system, based on the time-resolved phosphorescence spectroscopy of a platinum complex, is developed for non-contact, non-intrusive, and real-time vacuum packaging quality control, and implemented for caviar packaging. The sensor is embedded in protective polyethylene layers and excited with a short-pulsed light emitting diode (LED) source. Integration of a blue pulsed light source, a fast and amplified silicon photodiode controlled by the Spartan-6 field programmable gate array (FPGA), and a long lifetime platinum complex results in a photonics-based oxygen sensor with a fast response and high sensitivity to the vacuum packaging damage, which is suitable for caviar. It is revealed that applying the polyethylene layers protects the caviar from the platinum complex, leaching while not interfering with the sensor functionality. Characterizing the photonic system based on its sensitivity, repeatability, stability, and long-term operation demonstrates its capability for this application.

In this work, we present the investigation of the quantum dot color filter (QDCF) micro-light emitting diode (micro-LED) display. Green and red quantum dot photoresist (QDPR) materials are patterned into a pixelated array and precisely bonded with an all-blue micro-light emitting diode (micro-LED) substrate, forming a red, green, and blue (RGB) full color display through color conversion. A few factors that influence the achievable color gamut are further investigated. The resulting 1.1-inch 228-pixels per inch (ppi) display demo shows the good performance. The findings in this paper pave a way to the future industrialization of the micro-LED display.

In this paper, a new concept of forward-pumped random Raman fiber laser (RRFL)-based liquid refractive index sensing is proposed for the first time. For liquid refractive index sensing, the flat fiber end immersed in the liquid can act as the point reflector for generating random fiber lasing and also as the sensing head. Due to the high sensitivity of the output power of the RRFL to the reflectivity provided by the point reflector in the ultralow reflectivity regime, the proposed RRFL is capable of achieving liquid refractive index sensing by measuring the random lasing output power. We theoretically investigate the effects of the operating pump power and fiber length on the refractive index sensitivity for the proposed RRFL. As a proof-of-concept demonstration, we experimentally realize high-sensitivity half-open short-cavity RRFL-based liquid refractive index sensing with the maximum sensitivity and the sensing resolution of–39.88W/RIU and 2.5075×10⁻⁵ RIU, respectively. We also experimentally verify that the refractive index sensitivity can be enhanced with the shorter fiber length of the RRFL. This work extends the application of the random fiber laser as a new platform for highly-sensitive refractive index sensing in chemical, biomedical, and environmental monitoring applications, etc.

In view of the problem that the sensing characteristics of the multi-mode interferometric fiber sensors cannot be accurately analyzed, an analysis method based on the fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) is proposed and demonstrated theoretically and experimentally. The suitabilities of the rectangular window function with the narrow main lobe (high spectrum resolution) and low side lobe (high main mode energy leakage) and the Hanning window function with the wide main lobe (low spectrum resolution) and high side lobe (high energy concentration) in this kind of sensor analysis are discussed, respectively. This method can not only realize the sensing performance analysis of the various modes, but also overcome the inconsistency of the different interference wavelength (dip) sensing characteristics in the conventional analysis methods. At the same time, this method is also beneficial to solve the repetitive problem of such sensors.