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A proof of principle biosensor for the Brucella abortus recognition onsite is presented. The system is based on a plasmonic optical fiber probe functionalized with an oriented antibody layer immobilized on a short polyethyleneglycol (PEG) interface through carbodiimide chemistry and protein G as an intermediate layer. The biosensor is inserted in a holder built in 3D printing technology, obtaining a custom holder useful for housing the sample to be measured and the equipment. The removable sensor chip is a low-cost Surface Plasmon Resonance (SPR) platform based on D-shaped plastic optical fibers (POFs), built-in in 3D printed connectors, used here for the first time to detect bacteria via a bio-receptor layer specific for its membrane protein. The performances of the biosensor in Brucella abortus recognition are tested by using two different SPR-POF probes combined with the same bio-receptor layer. The best sensor configuration has presented a sensitivity at low concentrations of one order of magnitude greater than the other. A limit of detection (LoD) of 2.8 bacteria/mL is achieved well competitive with other systems but without the need for amplification or special sample treatments. Specificity has been tested using Salmonella bacteria, and reproducibility, regenerability and stability are moreover evaluated. These experimental results pave the way for building an efficient and specific biosensor system for Brucella abortus detection onsite and in a few minutes. Moreover, the proposed POF-based SPR biosensor device, with respect to the already available technologies, could be a Point-of-care-test (POCT), simple to use, small-size and portable, low-cost, don't necessary of a microfluidic system, and can be connected to the Internet (IoT). [ABSTRACT FROM AUTHOR]

As the focus tilts toward online detection methodologies for transformer oil aging, bypassing challenges associated with traditional offline methods, such as sample contamination and misinterpretation, fiber optic sensors are gaining traction due to their compact nature, cost-effectiveness, and resilience to electromagnetic disturbances that are typical in high-voltage environments. This study delves into the sensitivity analysis of intensity-modulated plastic optical fiber sensors. The investigation encompasses key determinants such as the influence of optical source wavelengths, noise response dynamics, ramifications of varying sensing lengths, and repeatability assessments. Our findings highlight that elongating sensing length detrimentally affects both linearity response and repeatability, largely attributed to a diminished resistance to noise. Additionally, the choice of the optical source wavelength proved to be a critical variable in assessing sensor sensitivity. [ABSTRACT FROM AUTHOR]

Robotic systems and the human body consist of numerous joint structures, all of which require precise angle adjustments. At present, encoder, strain gauge, and electrical resistance-based sensors are commonly used for angle measurement. However, these sensors have limitations when used in underwater or in environments with strong electromagnetic waves. Therefore, we have developed an angle sensor based on step-index profile plastic optical fiber (SI-POF), which is cost-effective and highly durable, in this study in order to overcome the limitations of existing angle measurement sensors. To this end, the amount of light loss according to the gab and angle changes that occur when the POF angle sensor is applied to the robot arm was experimentally measured, and based on the results, a simulation of the amount of light loss when the two losses occurred at the same time was conducted. In addition, the performance of the POF angle sensor was evaluated by measuring sensitivity and resolution, and comparative verification with a commonly used encoder was conducted to verify the reliability of sensors in extreme environments, such as those with electromagnetic fields and those that are underwater. Through this, the reliability and practicality of the POF angle sensor were confirmed. The results obtained in this study suggest that POF-based angle sensors can contribute to the development of the biomimetic robot industry as well as ordinary robots, especially in environments where existing sensors are difficult to apply, such as areas with underwater or electromagnetic interference (EMI). [ABSTRACT FROM AUTHOR]

Here, we improved the performance characteristics of surface plasmon resonance (SPR)-based optical sensors by using new two-dimensional materials in the structure of these sensors. We studied three types of two-dimensional materials: graphene, molybdenum disulfide (MoS2), and black phosphorus (BP). We also applied the angular interrogation method and employed numerical studies within MATLAB simulations. We investigated the characteristics of a simple configuration, including the type of prism, the thickness of the gold layer, and the number of layers of two-dimensional materials. We compared reflectance, sensitivity, detection accuracy (DA), and figure of merit (FoM) for various materials. We also studied the sensitivity of the sensor in relation to the refractive index of the sensing medium. We observed that the sensitivity reaches a peak at specific refractive index values. The best value for sensitivity is measured at 9778.9 RIU−1, with a detection accuracy of 32 deg−1 and FoM = 15,375 (deg·RIU)−1 for a black phosphorus-based structure. One distinctive feature of this study is investigating the effects of changing the resolution in simulations, which is considered one of the main factors in obtaining more accurate answers and achieving higher sensitivity. [ABSTRACT FROM AUTHOR]

A negative curvature hollow core fiber (NCHCF) refractive index (RI) sensor based on localized surface plasmon resonance (LSPR) is proposed. The gold nanowires are deposited in four cladding tubes in the y-direction, with the core region serving as the analyte channel. The full vector finite element method (FEM) is used to analyze the influence of various structural parameters on this sensor, and the structural parameters are optimized and selected. Ultimately, an average sensitivity of 9356.59 nm/RIU is accomplished within a spacious refractive index detection scope of RI = 1.28–1.43. The sensor attained a maximum sensitivity of 10,220 nm/RIU at RI = 1.36. In the bargain, there is an excellent linear correlation between the resonance wavelength and the refractive index of the analyte, with a value of 0.99901 and a factor of merit (FOM) range of 119.9563–155.9432 RIU−1, achieving a resolution of 10−6 RIU. The sensor has potential applications in various fields such as environmental protection, food safety, and medical diagnostics due to its high sensitivity, spacious detection scope, and positive linear response. [ABSTRACT FROM AUTHOR]

In this study, a sensor probe based on surface plasmon resonance (SPR) concept is proposed and examined for the detection of tuberculosis. The sensor probe includes a D-shaped photonic crystal fiber (PCF) micro-elliptical channel, gold (Au), and 2D materials like MOS2 and MXene. The finite element method (FEM) is utilized to compute the confinement loss and performance parameters for a healthy and tuberculosis-infected biomolecules. The effect of MoS2 on gold is to strengthen the coupling between the core mode and the surface plasmon polariton (SPP) mode of the fiber. In addition, the monolayer of MXene is functionalized as a bio-recognition element (BRE) above the MoS2 layer. The influence of inserting MoS2 and MXene on the sensor probe is examined in depth. Using MoS2 and MXene layers, the maximum wavelength sensitivity of the PCF structure is increased to 45,000 nm/RIU. Maximum figure of merit (FOM) for the sensor is 265 RIU−1, and it has a high refractive index (RI) resolution of 2.22 × 10−6 RIU. The acquired results indicate that the proposed probe has superior sensing capabilities compared to the biosensors used in recent investigations. Finally, the proposed 2D material-based D-shaped PCF sensor probe with functionalized MXene has a high value of sensitivity and FOM, making it a good platform for detecting tuberculosis-infected biomolecules having refractive index between 1.343 and 1.351 RIU. [ABSTRACT FROM AUTHOR]

Evanescent wave optical fibre sensors have attracted a lot of attention for the detection of chemical species due to their sensitivity, selectivity, and repeatability. In addition, plastic optical fibre sensors are inexpensive, simple to fabricate, and not only act as sensors, but the same fibre can also be used to transport sensor signals. The fibre sensor's sensitivity can be increased by removing the fibre cladding partially or fully. Also, different geometries have been reported to enhance the sensitivity of fibre sensors even more. In this paper, we report a U-shaped optical fibre sensor that utilises evanescent wave absorption as its primary mechanism for determining phosphate concentration in water. The U-shaped geometry offers enhanced sensitivity as compared to straight geometry. The developed U-shaped plastic optical fibre probe demonstrates impressive linear performance, which is evident in its remarkable regression coefficient of 98.48% and sensitivity of 0.0991 O.D./ppm. Due to their distinct features, plastic optical fibre sensors pave the way for improved water quality monitoring and analysis, which presents a vital contribution to both the industrial and environmental domains. [ABSTRACT FROM AUTHOR]

In this study, we propose a piezoelectric ceramic sensor-based health monitoring method to monitor the stress state of diagonally braced H-shaped steel structures. Loading experiments were carried out on diagonally braced H-shaped steel under different working conditions. Subsequently, the amplitude and energy of piezoelectric signals under these two working conditions were compared and analyzed, and finite element analysis was performed using ABAQUS software to verify the results. The experimental results showed that with an increase in the web height or load, the time-domain waveform energy index of the H-shaped steel increased. Under different working conditions, such as a diagonally braced H-shaped steel member with a web height of 10 cm, when the pressure value was less than 10 N/mm2, the energy index increased by approximately 15.98% for every 1 N/mm2 increase in the pressure. When the pressure value was greater than 10 N/mm2 and less than 15 N/mm2, the energy index increased by approximately 1% for every 1 N/mm2 increase in pressure. Further, the energy index increased by approximately 8.4% for every 1 cm increase in the height of the web. Simultaneously, it can be seen from the results of the finite element analysis that the stress and strain at the induction position of the piezoelectric ceramic sensor increased with an increase in the external pressure. The study of structural health monitoring for diagonally braced H-shaped steel structures holds significant importance in ensuring the safety and reliability of these structures, achieving predictive maintenance, evaluating structural performance and energy efficiency, and optimizing structural maintenance. [ABSTRACT FROM AUTHOR]

Fiber optic surface plasmon resonance (SPR) sensors are widely used in sensing applications in the fields of physics, chemistry and biology. This paper presents a numerical simulation of a D-shaped fiber optic SPR based refractive index sensor designed with a silver, gold, molybdenum disulfide, and graphene coated structure with and without gratings, for the first time. A FEM-based software is used to carry out the simulation studies. Aiming to obtain the highest performance, gold/silver layers are coated with MoS2 and graphene. Sensor parameters are computed and optimum values are discovered for these parameters; grating periods, gap size between gratings, residual cladding thickness, gratings numbers, and thickness of coating layers. 11,775 nm /RIU as the maximum sensitivity in the range of 1.33–1.4 RI is reached. Results demonstrate that the proposed multilayer and grated structure yields a 98.7% higher sensitivity value with reference to the simulation of a regular D-shaped Ag-coated fiber SPR sensor, which makes it promising for chemical, biochemical, and other applications of the future with the delicate sensing ability. [ABSTRACT FROM AUTHOR]

Behavior of a new step-index optical fiber having a Reuleaux-triangular-shaped core cross-section has been examined numerically. Two cases involving straight and bent optical fibers have been mainly discussed. Using James' equal-area formula, cut-off conditions of this proposed fiber have been given. Reuleaux-triangular-cored fiber can have a larger modal field area than circular-cored fiber with the same parameters when the normalized frequency is less than a certain value. As to a bent Reuleaux-triangular-cored fiber, bending orientation angle of this fiber is the most important factor determining the mode field distribution, except for the normalized frequency and bending radius. Compared with circular-cored optical fiber, the reduction of modal field area of this new fiber caused by bending can be reduced by 8.16%, and the bending loss can be reduced by 22.16%. Thus, the Reuleaux-triangular-cored fiber may be used as a bending sensor. [ABSTRACT FROM AUTHOR]

Using the dip-coating technique, a photo-anode based on a plastic optical fiber (POF) was coated with a mixture of titanium oxide nanoparticles (TiO2:Ti4O7). The semiconductor-coated material was prepared so that UV radiation fed into the fiber would escape along its path, photo-exciting the electrically polarized semiconductor film and producing oxidant species capable of degrading pollutant chemicals in aqueous solution. The photoelectrode was developed to evaluate the potential degradation of organic pollutants in aqueous solutions, and for this purpose, methyl red was used to assess the photo-anode performance under photocatalysis, electrocatalysis, and photo-electrocatalysis processes. The results revealed that, as expected from the specific properties of TiO2 and Ti4O7, the TiO2:Ti4O7-coated POF substrates showed a synergistic effect when UV light and electrical polarization are applied. The main purpose of using POFs instead of conventional SiO2 fibers is that the former implies substantially lower cost and mechanical flexibility, which will result in the future novel photo-electrochemical arrangements for water treatment. [ABSTRACT FROM AUTHOR]

In the past decade, the applications of dielectric barrier discharge (DBD) plasma technologies have been expanding, and one of the most exciting and rapidly growing applications is in biology and medicine. Most biomedical studies with DBD plasma systems are performed in vitro, which include cells grown on the surface of plastic well plates, or in vivo, which include animal research models (e.g. mice, pigs). Since many DBD systems use the biological target as the secondary electrode for direct plasma generation and treatment, they are sensitive to the surface properties of the target, and thus can be altered based on the in vitro or in vivo system used. This could consequently affect biological response from plasma treatment. Therefore, in this study, we investigated the DBD plasma behavior both in vitro (i.e. 96-well flat bottom plates, 96-well U-bottom plates, and 24-well flat bottom plates), and in vivo (i.e. mouse skin). Intensified charge coupled device (ICCD) imaging was performed and the plasma discharges were visually distinguishable between the different systems. The geometry of the wells did not affect DBD plasma generation for low application distances (≤ 2 mm), but differentially affected plasma uniformity on the bottom of the well at greater distances. Since DBD plasma treatment in vitro is rarely performed in dry wells for plasma medicine experiments, the effect of well wetness was also investigated. In all in vitro cases, the uniformity of the DBD plasma was affected when comparing wet versus dry wells, with the plasma in the wide-bottom wells appearing the most similar to plasma generated on mouse skin. Interestingly, based on quantification of ICCD images, the DBD plasma intensity per surface area demonstrated an exponential one-phase decay with increasing application distance, regardless of the in vitro or in vivo system. This trend is similar to that of the energy per pulse of plasma, which is used to determine the total plasma treatment energy for biological systems. Optical emission spectroscopy performed on the plasma revealed similar trends in radical species generation between the plastic well plates and mouse skin. Therefore, taken together, DBD plasma intensity per surface area may be a valuable parameter to be used as a simple method for in situ monitoring during biological treatment and active plasma treatment control, which can be applied for in vitro and in vivo systems. [ABSTRACT FROM AUTHOR]

Plastic lens arrays (PLAs) have the advantages of a light weight and a compact size. However, their optical performance is often degraded by warpage, caused by the accumulation of residual stress during the injection molding process. Accordingly, the present study employs mold flow analysis simulations and a Taguchi‐Gray relational analysis (GRA) framework to optimize the processing parameters of the injection compression molding (ICM) process. The analyses focus specifically on the effects of the mold temperature, melt temperature, injection velocity, packing pressure, packing time, and compression gap on the optical path difference (OPD) and lens center displacement (LCD) of the fabricated lens array. The results confirm that the optimized processing parameters significantly improve the OPD, LCD, birefringence, and imaging properties of the PLA compared to those of a PLA fabricated using standard molding conditions. [ABSTRACT FROM AUTHOR]

An optical fiber sensor for the simultaneous measurement of microdisplacement and temperature based on balloon-shaped single-mode fibers cascaded with a fiber Bragg grating with two core-offset joints is proposed. The interference between the core mode and cladding mode is caused by the stimulation of the cladding mode by the core-offset joints' structure. The cladding of the core has a distinct refractive index, which causes optical path differences and interference. The balloon-shaped structure realizes mode selection by bending. As the displacement increases, the radius of the balloon-shaped interferometer changes, resulting in a change in the interference fringes of the interferometer, while the Bragg wavelength of the fiber grating remains unchanged. Temperature changes will cause the interference fringes of the interferometer and the Bragg wavelength of the fiber grating to shift. The proposed optical fiber sensor allows for the simultaneous measurement of microdisplacement and temperature. The results of the experiment indicate that the sensitivity of the interferometer to microdisplacement is 0.306 nm/µm in the sensing range of 0 to 200 μm and that the temperature sensitivity is 0.165 nm/°C, respectively. The proposed curvature sensor has the advantages of a compact structure, extensive spectrum of dynamic measurement, high sensitivity, and simple preparation, and has a wide range of potential applications in the fields of structural safety monitoring, aviation industry, and resource exploration. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance-based arc-shaped photonic crystal fiber high-sensitivity refractive index (RI) sensor is proposed. An open arc-shaped analyte channel is produced at the top of the fiber to facilitate RI detection of the analyte, and a gold film is coated inside the arc-shaped structure to stimulate mode coupling. The performance of the sensor is analyzed by using the finite element method (FEM). The results have demonstrated that the sensor can detect a sensing range of 1.35-1.42 with maximum RI sensitivity of 24900 nm/RIU and resolution of 4:01×10-6 RIU. Furthermore, the highest figure of merit (FOM) of 661.71 RIU-1 is obtained. Additionally, the effects of air hole size and air hole distance on sensitivity are investigated. Finally, the proposed sensor characterizes great potential in biomedical, chemical, and other fields due to its excellent performance. [ABSTRACT FROM AUTHOR]

The paper considers the advantages and disadvantages of existing methods for temperature compensation of data from fiber-optic sensors based on fiber Bragg gratings as part of an embedded system for simultaneous testing of deformation and temperature of polymer composite materials. It is shown that when external temperature testing is impossible, it is most expedient to implement the method of two optical fibers with different sensitivity to at least one of these parameters due to different dopants. Technological issues related to the formation of a spatial topology and the provision of an effective survey of the embedded optical system for monitoring polymer composite materials by the two-fiber method are considered. The results of theoretical research of a linear model of temperature compensation, a model that takes into account the influence of cross sensitivity, as well as a quadratic model of temperature compensation of optical testing data are presented. It has been established that the linear model is the simplest, however, when using it, one should take into account the error associated with the inaccuracy of the approximation of optical inspection data by a linear function. At the same time, it is shown that in order to improve the quality and reliability of the results of optical testing, it is advisable to use a quadratic model of temperature compensation, which provides an error level comparable to the error of the fiber-optic sensor survey device. The results obtained can be used to develop methods for the simultaneous testing of samples, as well as monolithic and three-layer structures from structural layered polymer composite materials with limiting molding conditions (temperature less than 180°C, specific pressure lower than 0.7 MPa), as in the process of bench and other tests, and, in the future, in real operating conditions. [ABSTRACT FROM AUTHOR]

As a new global pollutant, microplastics have been widely a concern in recent years. The traditional microplastic detection technology has the disadvantages of weak signal, high cost, and complicated operation. Therefore, this paper designs and builds a set of spatial heterodyne microscopic differential Raman spectroscopy (SHMDRS) system for microplastic detection. The system combines the spatial heterodyne system (SHS) with the microscopic differential Raman system (MDRS). The system was simulated and designed by ZEMAX software, and the SHMDRS system was built on the experimental platform. The 531.742‐ and 532.567‐nm dual‐wavelength lasers were used as the excitation light source. Four kinds of microplastic samples, namely, PS, PC, PP, and HDPE, were tested to verify the feasibility of the system. Under the integration time of 10 s and the laser power of 200 mW, the microplastic samples were detected by the SHMDRS system and dispersive spectrometer, respectively. The signal‐to‐noise ratio (SNR) of Raman spectra of different systems was compared and calculated. The differential Raman spectra of four kinds of microplastic samples were obtained by dual‐wavelength laser, and the pure Raman spectra of four kinds of microplastic samples were restored by multiple constrained iterative algorithm. The results show that the spectral resolution of the SHMDRS system is 2.809 cm−1, and the spectral range is 255.47–2023.21 cm−1. The SNRs of the Raman spectra obtained by the SHMDRS system are better than those of the dispersive spectrometer, and the differential Raman spectroscopy can effectively remove the interference of the fluorescence background. This method has a good development prospect. [ABSTRACT FROM AUTHOR]

The presented literature review was prepared by a team of authors united by the Program and Organizing Committees of the "Optical Reflectometry, Metrology, and Sensing" (ORMS) conference in 2023. It is intended to assess the state and prospects in this area for the coming years. The review covers the following topics: distributed acoustic sensors, fiber-optic measurement systems based on Brillouin scattering, research methods based on the principles of optical reflectometry in the frequency domain, and low-coherence approaches to distributed temperature and strain monitoring. [ABSTRACT FROM AUTHOR]

In this article, an optical bio-chemical sensor based on D-shaped optical fiber is presented for ethanol detection application. The gold and graphene nanolayers are coated for inducing the SPR over an optical fiber flat surface. The molecularly imprinted polymer (MIP) thin film is also coated over the gold film to enhance the molecular interaction between the sensing fluid and the sensing surface. The ethanol concentration is detected with reference to the 0% concentration and increased to 90% in a sample solution. The shift in resonance wavelength detects the concentration of the ethanol in the fluid sample due to the change in RI. The result shows a very good agreement between the concentration of ethanol in fluid and the resonance wavelength (RW) shift. The maximum obtained average sensitivity is 2.5 nm/concentration (every 10%) or 714 nm/RIU with Au/MIP thin film and 1137 nm/RIU for graphene/Au/MIP thin film. Based on the result and optical properties of the proposed sensor, it might be used as a real-time alcohol detector. This sensor can protect foods and drinks from the imbalance of chemicals and preservatives. [ABSTRACT FROM AUTHOR]

We proposed an active differential intensity (DI) fiber coupled plasmon waveguide resonance (CPWR) sensor based on the mode competition effect in the C-band, aiming to enhance the sensitivity. The sensing head is a fiber probe with a sensing layer of ITO/Au/ITO/TiO2 film, enabling the excitation of CPWR in the C-band. The narrow CPWR spectrum allows DI interrogation by tracking the intensity of light at two wavelengths. The fiber probe is inserted into a dual-wavelength fiber laser to adjust the intra-cavity loss at the two lasing wavelengths. By using the differential modulation of the reflectivity from the refractive index variations, the mode competition effect is triggered. The powers at two lasing wavelengths change oppositely, enlarging the power difference and then resulting in enhanced sensitivity. The average sensitivity is up to 5702 dB/RIUs, which is 10 times higher than that of conventional DI interrogation. The sensitivity enhancement mechanism based on the mode competition effect provides a new technical approach for enhancing the sensitivity of DI SPR sensors. [ABSTRACT FROM AUTHOR]

Graphene, as a novel thermoelectric (TE) material, has received growing attention because of its unique microstructure and excellent thermoelectric properties. In this paper, graphene fibers (GFs) are synthesized by a facile microfluidic spinning technique using a green reducing agent (vitamin C). The GFs have the merits of high electrical conductivity (2448 S/m), high flexibility, and light weight. Further, a flexible temperature sensor based on GF and platinum (Pt) with a sensitivity of 29.9 μV/°C is proposed, and the thermal voltage output of the sensor can reach 3.45 mV at a temperature gradient of 120 °C. The sensor has good scalability in length, and its sensitivity can increase with the number of p-n thermocouples. It has good cyclic stability, repeatability, resistance to bending interference, and stability, showing great promise for applications in real-time detection of human body temperature. [ABSTRACT FROM AUTHOR]

Recently, rapid progress has been achieved in the field of nanomaterial preparation and investigation. Many nanomaterials have been employed in optical chemical sensors and biosensors. This review is focused on fiber-optic nanosensors for chemical sensing based on silica and plastic optical fibers. Four types of fiber-optic chemical nanosensors, namely fiber nanotip sensors, fiber nanoarray sensors, fiber-optic surface plasmon resonance sensors, and fiber-optic nanomaterial-based sensors, are discussed in the paper. The preparation, materials, and sensing characteristics of the selected fiber-optic nanosensors are employed to show the performance of such nanosensors for chemical sensing. Examples of fiber-optic nanobiosensors are also included in the paper to document the broad sensing performance of fiber-optic nanosensors. The employment of fiber-nanotips and nanoarrays for surface-enhanced Raman scattering and nanosensors employing both electrical and optical principles and "Lab-on-fiber" sensors are also included in the paper. The paper deals with fiber-optic nanosensors based on quantum dots, nanotubes, nanorods, and nanosheets of graphene materials, MoS2, and MXenes. [ABSTRACT FROM AUTHOR]

This project addresses the lack of a real-time, low-cost sensor to detect salt levels in water. The authors aim to develop an optical fiber sensor for water salinity detection. The sensor employs the principles of absorption spectroscopy using a broadband light source and spectrometer to detect changes in the optical spectrum of the sensor in the presence of varying concentrations of sodium chloride ions. A D-shaped sensor is fabricated by modifying the circular structure of a plastic optical fiber. Functionalized carbon nanotubes are drop casted over the D-shaped sensing region. Both uncoated and CNT-coated POF sensors are exposed to different concentrations of sodium chloride in water, and the spectral response is recorded. The results show that the sensors exhibited a strong correlation in their intensity response towards varying concentrations of sodium chloride salt ranging from 0 to 25%. The uncoated sensor had a sensitivity of 31A.U./% salt, and the CNT-coated Sensor had a sensitivity of 114 A.U/% salt. The functionalized CNT layer increased the sensitivity of the POF sensor by approximately 4 times. The outcome of this research provides a cost-effective and reliable method for water salinity detection in industrial and environmental applications. [ABSTRACT FROM AUTHOR]

Utilizing the modified transfer matrix method, under transverse electric polarization, asymmetric optical bistability is achieved by designing one-dimensional photonic crystals (PCs) with two Bragg reflector segments containing traditional dielectrics and asymmetric defect multilayers consisting of a magnetized ferrite and nonlinear Kerr dielectric. When the incident wave frequency equals the resonance frequency, owing to the breaking of symmetry in the defect layers and the Voigt magneto-optical effect generating in the magnetized ferrite layers together with the Kerr effect existing in the Kerr dielectric layers, the asymmetric optical modulations are presented as the bistable state in the forward propagation and the multistable state in the backward propagation. Also, the diverse energy localization distributions of the electric field in the proposed PCs from the two incident directions are graphically illustrated. Furthermore, the optical bistable switch-up and switch-down thresholds of the proposed resonator can be tailored flexibly by the external magnetic field, the incident angle, the thicknesses of different dielectrics, and the nonlinear coefficient of Kerr dielectric. This work provides a constructive proposal for the design of light modulators, such as the optical isolator, the optical triode, the all-optical diode, and the sensor. [ABSTRACT FROM AUTHOR]

A structure for simultaneous measurement of refractive index (RI) and temperature (T) is proposed based on photonic crystal (PhC) beam structures. The sensor structure consists of three parallel 1D PhC cavities, in which the middle cavity 1 has a wide linewidth, and cavity 2 and cavity 3 on both sides have a narrow linewidth. By changing the RI of the analyte and the T of the ambient, we explored the linear relationship between the two parameters and resonant wavelengths, respectively. For cavity 2 with air mode, the RI and T sensitivities are 377.2 nm/RIU and 101 pm/K, respectively. For cavity 3 with dielectric mode, the RI and T sensitivities are 194 nm/RIU and 261 pm/K, respectively. In addition, we also discussed the crosstalk between two adjacent cavities at different RI and T, and all crosstalk values are lower than −7 dB and −6 dB for RI and T, respectively. Compared with previous sensor structures, the proposed sensor structure could be used in simultaneous RI and T sensing with higher sensitivity and lower crosstalk values. [ABSTRACT FROM AUTHOR]

Background: Justification of imaging procedures such as cone beam computed tomography (CBCT) in radiotherapy makes no doubt. However, the CBCT composite dose is rarely reported or optimized, even though the repeated CBCT cumulative dose can be up to 3% of the prescription dose. This study aimed to evaluate the performance and utility of a new plastic scintillating optical fiber dosimeter for CBCT dosimetric quality assurance (QA) applications before a potential application in patient composite CBCT dosimetry. Methods: The dosimeter, made of 1 mm diameter plastic fiber, was installed under a linear accelerator treatment table and linked to photodetectors. The fiber impact on the fluence and dose delivered was respectively assessed with an electronic portal imaging device (EPID) and EBT3 Gafchromic® film. The presence of artifacts was visually evaluated on kV images. The dosimeter performances were determined for various acquisition parameters by comparison with ionization chamber values. Results: The maximum impact of the fiber on the fluence measured by the EPID was −1.2% for the 6 MV flattening filter-free beam. However, the fiber did not alter the film dose profile when measured for all the beams tested. The fiber was not visible at energies ≥ 80 kV and was merely visible on the CBCT images. When the rate of images per second or mA was changed, the maximum relative difference between the device and the ionization chamber CTDIs was <5%. Changing collimation led to a −7.2% maximum relative difference with an absolute dose difference that was insignificant (−0.3 mGy). Changing kV was associated with a −8.7% maximum relative difference, as published in the literature. Conclusions: The dosimeter may be a promising device for CBCT recurrent dosimetry quality control or dose optimization. According to these results, further developments are in progress in order to adapt the solution to the measurement of patient composite CBCT doses. [ABSTRACT FROM AUTHOR]

Optical fiber Fabry-Pérot (FP) interferometer sensors have long been the focus of researchers in sensing applications because of their simple light path, low cost, compact size and convenient manufacturing methods. A miniature and highly sensitive optic fiber temperature sensor using an ultraviolet glue-filled FP cavity in a hollow capillary fiber is proposed. The sensor is fabricated by fusion splicing a single-mode fiber with a hollow capillary fiber, which is filled with ultraviolet glue to form a FP cavity. The sensor has a good linear response in the temperature testing and high-temperature sensitivity, which can be increased with the length of the FP cavity. The experimental results show that the temperature sensitivity reaches 1.174 nm/°C with a high linear response in the range of 30–60 °C. In addition, this sensor is insensitive to pressure and can be highly suitable for real-time water temperature monitoring for ocean research. The proposed ultraviolet glue-filled structure has the advantages of easy fabrication, high-temperature sensitivity, low cost and an arbitrary length of capillary, which has broad application prospects for marine survey technology, biological diagnostics and environmental monitoring. [ABSTRACT FROM AUTHOR]

Noncontact measurement techniques in structural dynamics field have progressed significantly in the past few decades. Vision-based measurement techniques are unique in that they have the ability to achieve full-field measurement and possess the typical advantages associated with noncontact measurement techniques. Recently, vision-based techniques have also been applied to streaming of videos for structural dynamic displacement measurement. The most recent trends in vision-based measurements include target tracing, digital image correlation, and target-less approaches. There are, however, some shortcomings of the vision-based techniques such as susceptibilities to image noise, prevailing light conditions, and limit in measurement resolution. To reduce these shortcomings, a method known as video motion magnification (MM) can be used to amplify small structural motions. Using the phase-based motion magnification (PBMM) and subpixel edge detection methods, the full-field dynamic displacements of the structure can be obtained. The deep convolutional long short-term memory (ConvLSTM) network is applied to aid in the selection of the frequency band for magnification in the PBMM algorithm. To achieve higher measurement accuracy, the displacement results with and without MM are combined with the finite impulse response (FIR) filter which can reduce the error caused by the PBMM procedure. In the tests, plastic optical fiber (POF) displacement sensors are introduced and used as reference measurements to compare the dynamic displacement results from the proposed vision-based method. Compared with the measured displacements with POF sensors, the proposed method offers high level of accuracy for full-field displacement measurement. [ABSTRACT FROM AUTHOR]

Flexible screen-printing technology combined with the use of a nano/material coating for improving electrode functionalities boosted the manufacturing of highly sensitive electrochemical sensors addressing the need for fast and easy-to-handle tests in different application fields. However, due to the large-scale production and disposable and single-use nature of these devices, their environmental footprint should be taken into careful consideration. Herein, the innovative reuse of post-consumer polyethene terephthalate (PET) plastics as an alternative substrate coupled with biochar as an environmentally friendly and cost-effective modifier is described as a sustainable alternative for the production of robust electrochemical sensors. The good printability of reused plastics with graphite inks despite the chemical heterogeneity, different crystallinity, and surface roughness was demonstrated using atomic force microscopy and attenuated total reflection Fourier transform infrared spectroscopy. Functionalization with brewers' spent grain biochar enabled the fabrication of highly performing electrochemical sensors for nitrite detection in water having a limit of detection and a limit of quantification of 3.3 nM and 10.3 nM, respectively, with a linear range spanning from 0.01 to 500 μM, and good reproducibility (RSD% 8%). The innovative intervention of the biochar-multilayer system markedly enhanced the electron transfer process at the electrode interface while simultaneously serving as an absorptive material for the investigated analyte. This work lays a foundation for repurposing end-of-life plastics for the electronics industry and presents a customizable reuse strategy aimed to keep the value of plastics in the economy and reduce waste and leakage into the natural environment. [ABSTRACT FROM AUTHOR]

This article reviews recent research progress on the annealing effects on polymer optical fibers (POFs), which are of great importance for inscription, stability and sensing applications of fiber Bragg gratings (FBGs) in POFs due to their unique properties related to polymer molecular chains. In this review, the principle of annealing to reduce frozen-in stress in POFs drawing and different annealing timings are firstly summarized. Then, the annealing methods for POFs are introduced under several different conditions (temperature, humidity, strain, stress and solution). Afterwards, the principle of FBGs and several inscription techniques are reported. Subsequently, the annealing effects on the properties of POFs and polymer optical fiber Bragg gratings (POFBGs) quality are discussed. Finally, the influence of annealing on POFBG sensitivity is summarized. Overall, this paper provides a comprehensive overview of annealing techniques and their impact on both POFs and POFBGs. We hope that it will highlight the important progress made in this field. [ABSTRACT FROM AUTHOR]

An ultracompact optical fiber Fabry–Perot interferometric sensor is proposed and demonstrated for high‐temperature measurement. The device is simply a section of single‐mode fiber with angled end face of 45°, the reflected light from the angled fiber end face is directed sequentially to the fiber core–cladding and cladding–air interfaces, respectively, and reflected back, and finally returned to the fiber core after being reflected by the angled fiber end face again. As a result, a Fabry–Perot interferometer is constructed. Because of the thermal‐expansion and thermal‐optical effect of the fiber material, the optical path difference between the core–cladding and cladding–air surfaces is changed with temperature, hence the device is well suitable for temperature measurement. In particular, the fiber device has good high‐temperature sustainability up to 1100°C, which makes it attractive for high‐temperature measurement in a narrow or hard‐to‐reach spatial environment. [ABSTRACT FROM AUTHOR]

Twist sensors have emerged as crucial tools in the field of structural health monitoring, playing a significant role in monitoring and ensuring the integrity of critical infrastructure such as dams, tunnels, bridges, pipelines, and buildings. We proposed and demonstrated an all-fiber in-line twist sensor which was based on a capillary fiber spliced between two single-mode fibers with a transverse offset. Through a series of experiments, the sensor's performance was evaluated and quantified. The results showcased remarkable twist sensitivities in both clockwise and anticlockwise directions. With a transverse offset of 8.0 µm, the sensor exhibited twist sensitivities of −0.077 dB/° and 0.043 dB/° in the clockwise and anticlockwise directions, respectively, in the measured twist range from 0 to 90°. Furthermore, it was also demonstrated that the sensor was temperature insensitive at the chosen wavelength of 1520 nm, which can assist in increasing measurement accuracy. Our sensor's low cost, simplicity of manufacture, and improved performance will push forward its adoption in future engineering applications such as structural health monitoring in dams, tunnels, and buildings. [ABSTRACT FROM AUTHOR]

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Optical fibre sensors are an essential subset of optical fibre technology, designed specifically for sensing and measuring several physical parameters. These sensors offer unique advantages over traditional sensors, making them gradually more valuable in a wide range of applications. They can detect extremely small variations in the physical parameters they are designed to measure, such as analytes in the case of biosensing. This high sensitivity allows them to detect subtle variations in temperature, pressure, strain, the refractive index of analytes, vibration, and other environmental factors with exceptional accuracy. Moreover, these sensors enable remote sensing capabilities. Since light signals are used to carry information, the sensing elements can be placed at distant or inaccessible sites and still communicate the data back to the central monitoring system without signal degradation. In recent times, different attractive configurations and approaches have been proposed to enhance the sensitivity of the optical fibre-based sensor and are briefly explained in this review. However, we believe that the choice of optical fibre sensor configuration should be designated based on the specific application. As these sensors continue to evolve and improve, they will play an increasingly vital role in critical monitoring and control applications across various industries. [ABSTRACT FROM AUTHOR]

In this work, two different lossy mode resonance (LMR) platforms based on plastic optical fibers (POFs) are developed and tested in a biochemical sensing scenario. The LMR platforms are based on the combination of two metal oxides (MOs), i.e., zirconium oxide (ZrO2) and titanium oxide (TiO2), and deposited on the exposed core of D-shaped POF chips. More specifically, two experimental sensor configurations were obtained by swapping the mutual position of the Mos films over to the core of the D-shaped POF probe. The POF–LMR sensors were first characterized as refractometers, proving the bulk sensitivities. Then, both the POF–LMR platforms were functionalized using molecularly imprinted nanoparticles (nanoMIPs) specific for human transferrin (HTR) in order to carry out binding tests. The achieved results report a bulk sensitivity equal to about 148 nm/RIU in the best sensor configuration, namely the POF-TiO2-ZrO2. In contrast, both optical configurations combined with nanoMIPs showed an ultra-low detection limit (fM), demonstrating excellent efficiency of the used receptor (nanoMIPs) and paving the way to disposable POF–LMR biochemical sensors that are easy-to-use, low-cost, and highly sensitive. [ABSTRACT FROM AUTHOR]

Detection of air bubbles in fluidic channels plays a fundamental role in all that medical equipment where liquids flow inside patients' blood vessels or bodies. In this work, we propose a multi-parameter sensing system for simultaneous recognition of the fluid, on the basis of its refractive index and of the air bubble transit. The selected optofluidic platform has been designed and studied to be integrated into automatic pumps for the administration of commercial liquid. The sensor includes a laser beam that crosses twice a plastic cuvette, provided with a back mirror, and a position-sensitive detector. The identification of fluids is carried out by measuring the displacement of the output beam on the detector active surface and the detection of single air bubbles can be performed with the same instrumental scheme, exploiting a specific signal analysis. When a bubble, traveling along the cuvette, crosses the readout light beam, radiation is strongly scattered and a characteristic fingerprint shape of the photo-detected signals versus time is clearly observed. Experimental testing proves that air bubbles can be successfully detected and counted. Their traveling speed can be estimated while simultaneously monitoring the refractive index of the fluid. [ABSTRACT FROM AUTHOR]

In this study, a new approach using optical fiber sensor based on a single fiber Bragg grating (FBG) is proposed to overcome the cost and complexity limitations. The reflected frequency of the half-etched region is shifted by utilizing a half-etched uniform FBG as the sensing element. The proposed sensor is evaluated using the refractive index measurement technique, and its validity is demonstrated by subjecting it to temperature variations. A sensitivity of − 524.48 MHz/°C is exhibited by the proposed sensor over a dynamic range of about 25 °C to 70 °C. It is demonstrated that the proposed sensor is highly sensitive, cost-effective, and reduces the complexity of the manufacturing and measurement process. This novel approach has significant potential for applications in various fields, including biomedical sensing, environmental monitoring, and industrial process control. [ABSTRACT FROM AUTHOR]

This research aims to develop a high sensitive temperature sensor to get around challenges like cost and complexity as well as to improve sensitivity in the megahertz band. Depending on the optical heterodyne technique, a new approach is proposed to construct an optical fiber sensor for measuring temperature. Two types of the narrow band pass filters (BPF) are employed in this approach as sensing elements. Both BPFs are Fabry–Perot filters, which are made from quartz and crystron material. The thermo-optics coefficients of filters materials are approximate. In the proposed sensor, a wideband optical source is equally split and then launched to sensing elements. A 3-dB coupler combines the output of the thermo-sensitive BPFs. A combined signal from these two BPF, which centered at 1552.22 nm and 1552.187 nm, is detected by a photodiode and the beat frequency can be defined to attain a high-resolution. The temperature sensing strategy is explored to evaluate the proposed approach. The results show that the proposed sensing system has the beat frequency varied from 4 to 12.5 GHz over temperature range from 0 to 100 °C. The sensor has sensitivity of 85.9 MHz/oC with fast response to temperature change and reducing the cost of manufacturing and measuring of the optical fiber sensors. [ABSTRACT FROM AUTHOR]

This study fabricated an ultra-high refractive index (RI) sensor based on tapered no-core fiber (NCF) involving a simple inexpensive process. A splice section of NCF in the middle of single mode fiber was tapered to small diameters. The sensor was sensitive to the surrounding RI with a large measurement range of 1.3330–1.4437. The RI sensitivity differed with varying wavelengths, with a value of 41 916 nm/RIU at approximately 1550 nm, for the RI ranges of 1.4407–1.4437. It yielded a low temperature sensitivity of 8 pm °C−1, which indicates an ultra-low temperature cross-sensitivity. The proposed fiber optic RI sensor can be used in many fields such as medicine and biochemical applications. [ABSTRACT FROM AUTHOR]

Optical biosensors based on grating-coupled surface plasmon resonance (GCSPR) technology are an important research topic in the field of bio-photonics. This paper presents a high-performance and high-sensitivity nanostructured bimetallic GCSPR sensor based on two-dimensional materials. When designing the sensor, the sensitivity, full width at half peak (FWHM) and dip strength of the absorption peak (DS) were considered comprehensively, and the comprehensive evaluation parameter FOM+ is defined by making improvements on the basis of figure of merit (FOM). The performance of the sensor can be judged more comprehensively. The performance of the sensor was further improved by optimizing the structure of the sensor. An ultra-thin gold layer was added on the surface of the silver-based GCSPR sensor, which solves the problem of the easy oxidation of silver metal. We tried to coat graphene oxide two-dimensional nanomaterials on the surface of the bimetallic sensor, and the sensitivity and FOM+ of the sensor reached 350 deg/RIU and 473.23, respectively. This is a great improvement compared with the GCSPR sensor in a previous study, and it can be improved at least 74.7%. This sensor can measure a variety of biological molecules and biological cells with high sensitivity and performance by detecting the change in the refractive index of the solution to be measured. [ABSTRACT FROM AUTHOR]

In this paper, an optical fiber humidity sensor based on acrylate AB adhesive film is studied, and two methods—a bubbling method and a dual pressure assisted method—for preparing thin films are proposed. The forms will make the thin film lighter and make the sensor more sensitive. Using a glass tube to connect the acrylate AB adhesive film to the single mode optical fiber, the humidity sensor is obtained. Through humidity response experiments, the sensor's sensitivity reaches 167.5 pm/% RH, and the response time reaches 4.8 s/% RH. At the same time, the experiments show that the sensor has good repeatability and stability. Finally, the influence of temperature on the working process is analyzed, and we provide a method for improvement through FBG. [ABSTRACT FROM AUTHOR]

We have developed a radioluminescence-based survey meter for use in industries in which there is involvement in naturally occurring radioactive material (NORM), also in support of those needing to detect other weak emitters of radiation. The functionality of the system confronts particular shortcomings of the handheld survey meters that are currently being made use of. The device couples a LYSO:Ce scintillator with a photodetector via a polymer optical fibre waveguide, allowing for "intrinsically safe" inspection within pipework, separators, valves and other such component pieces. The small-diameter optical fibre probe is electrically passive, immune to electromagnetic interference, and chemically inert. The readout circuit is entirely incorporated within a handheld casing housing a silicon photomultiplier (SiPM) detection circuit and a microprocessor circuit connected to an LCD display. A 15 m long flexible PMMA optical fibre waveguide is butt coupled to an ABS plastic probe that retains the LYSO:Ce scintillator. Initial tests have included the use of lab-based mixed gamma-ray sources, measurements being made in concert with a reference conventional GM survey-meter. Characterization, via NORM sources at a decontamination facility, has shown useful sensitivity, covering the dose-rate range 0.10- to 28 µSv h−1 (R-squared 0.966), extending to 80 µSv/h as demonstrated in use of a Cs-137 source. The system is shown to provide an effective tool for detection of radioactivity within hard to access locations, in particular for sources emitting at low radiation levels, down to values that approach background. [ABSTRACT FROM AUTHOR]

Interferometric optical fiber sensors have become the preferred choice for ethanol vapor detection because of their high sensitivity and figure of merit. However, the response time of interferometric fiber optic ethanol vapor sensors is very long. To address this issue, we experimentally investigated an ethanol vapor sensor based on a nematic liquid crystal (NLC) film embedded optical fiber Sagnac interferometer. The high birefringent NLC film, which worked as the sensing media of ethanol vapor for its absorption of ethanol vapor, was penetrated into the Sagnac ring to generate the spectral interference. The results showed that the measurement sensitivity of ethanol gas concentration reached 2.22 pm ppm−1. The detection range was about 1210 ppm–10 000 ppm. Most importantly, the response time of the proposed sensor is only 15 s. The designed sensor, which showed the advantages of fast response, high sensitivity, and stability, could be a competitive candidate for ethanol vapor sensing. [ABSTRACT FROM AUTHOR]

In this work, a simple, controllable and mass-produced microcrack technique for stretchable strain sensors is presented. Specifically, the conductive layer (hydroxylated MWCNTs) and the flexible substrate (Ecoflex) of fiber strain flexible sensors are modified based on proton irradiation defect engineering. The evolution of defects in sensitive materials and the density of microcracks in flexible substrates are controlled by controlling the irradiation fluence during the irradiation process. In particular, when the irradiation fluence is 1 × 1014 p cm−2, the gauge factor (GF) of the fiber strain sensor is as high as 1274.8, and the response time and recovery time are reduced by 49.4% and 45.1%, respectively. At the same time, the microcracked structure does not fracture easily under a large strain, the maximum strain being 800%. In addition, fiber strain flexible sensors can also be used to detect biomechanical signals in different scenarios. This simple and efficient microcrack technique opens up a new prospect for the fabrication of high-performance stretchable strain sensors. [ABSTRACT FROM AUTHOR]