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Here, we analyzed the effect of a donor molecule (Rh6G) on the random laser emission of an acceptor molecule (Rh640 perchlorate) coated on the surface of a polymer optical fiber. Due to the energy transfer mechanism, the random lasing threshold of Rh640 perchlorate was found to be reduced in the presence of Rh6G. Also, the emission spectrum of Rh640 perchlorate was blue-shifted with the addition of Rh6G. Meanwhile, there is an enhancement in the lasing threshold of Rh6G in the presence of Rh640 perchlorate. The present study demonstrates that by properly adjusting the concentrations of both donor and acceptor molecules, we can obtain a dual-color random laser emission from polymer optical fiber. [ABSTRACT FROM AUTHOR]

A new galvanic cell design of a self‐powered and 3D‐printable soft sensor showing health monitoring, object recognition, and contactless hand gesture recognition, is reported. The soft sensor consists of a 3D‐printed poly(acrylic acid) (PAA) hydrogel electrolyte layer, a soft anode layer, and a soft cathode layer. The anode layer is a 3D‐printed and Cu2+ cross‐linked poly(N,N‐dimethylacrylamide‐co‐3‐alanine‐2‐hydroxypropylmethacrylate) (PDA) hydrogel dispersed with Cu metal particles (PDA/Cu2+/Cu hydrogel), while the cathode layer is a bottom thin layer of the PAA hydrogel containing MnO2 (PAA/MnO2). Using graphite films as the soft electrodes, the soft sensor is finally assembled. The soft sensor has high force and temperature sensitivities. It gives different electric current responses under stretching, bending, pressing, and impact loading. The soft sensor is demonstrated to be useful in detecting human motion and physiological activities, e.g., breath. Based on the force and contactless temperature sensitivities, the soft sensor is used to recognize human hand gestures and plastic balls with different diameters. This 3D printable soft sensor with self‐powering, contactless motion capturing, and multi‐pimulus sensing capabilities illustrates a new pathway to make soft sensory devices for healthcare and human‐machine interaction applications. [ABSTRACT FROM AUTHOR]

The mode coupling in a graded-index polymer photonic crystal fiber (GI PPCF) with a solid core has been investigated using the Langevin equation. Based on the computer-simulated Langevin force, the Langevin equation is numerically integrated. The numerical solutions of the Langevin equation align with those of the time-independent power flow equation (TI PFE). We showed that by solving the Langevin equation, which is a stochastic differential equation, one can successfully treat a mode coupling in GI PPCFs, which is an intrinsically stochastic process. We demonstrated that, in terms of effectiveness, the Langevin equation is preferable compared to the TI PFE. The GI PPCF achieves the equilibrium mode distribution (EMD) at a coupling length that is even shorter than the conventional GI plastic optical fiber (POF). The application of multimode GI PCFs in communications and optical fiber sensor systems will benefit from these findings. [ABSTRACT FROM AUTHOR]

This preclinical study was conducted to investigate the efficacy of interstitial PDT (i-PDT) for malignant gliomas arising deep within the brain, which are difficult to remove. C6 glioma cells were implanted into the basal ganglia of rats, and 3 weeks later, the second-generation photosensitizer talaporfin sodium (TPS) was administered intraperitoneally. Ninety minutes after administration, a prototype fine plastic optical fiber was punctured into the tumor tissue, and semiconductor laser light was irradiated into the tumor from a 2-mm cylindrical light-emitting source under various conditions. The brain was removed 24 h after the i-PDT and analyzed pathologically. The optical fiber was able to puncture the tumor center in all cases, enabling i-PDT to be performed. Histological analysis showed that tumor necrosis was induced in areas close to the light source, correlating with the irradiation energy dose, whereas apoptosis was induced at some distance from the light source. Irradiation using high energy levels resulted in tissue swelling from strong tumor necrosis, and irradiation at 75 J/cm2 was most suitable for inducing apoptosis. An experimental system of i-PDT using TPS was established using malignant glioma cells transplanted into the rat brain. Tumor cell death, which correlated with the light propagation, was induced in tumor tissue. [ABSTRACT FROM AUTHOR]

2-Furaldehyde (2-FAL) is one of the main by-products of the degradation of hemicellulose, which is the solid material of the oil–paper insulating system of oil-filled transformers. For this reason, it has been suggested as a marker of the degradation of the insulating system; sensing devices for 2-FAL analysis in a wide concentration range are of high interest in these systems. An optical sensor system is proposed; this consists of a chemical chip, able to capture 2-FAL from the insulating oil, coupled with a surface plasmon resonance (SPR) probe, both realized on multimode plastic optical fibers (POFs). The SPR platform exploits gold nanofilm or, alternatively, a double layer of gold and silicon oxide to modulate the sensor sensitivity. The capturing chip is always based on the same molecularly imprinted polymer (MIP) as a receptor specific for 2-FAL. The system with the SPR probe based on a gold nanolayer had a higher sensitivity and a lower detection limit of fractions of μg L−1. Instead, the SPR probe, based on a double layer (gold and silicon oxide), has a lower sensitivity with a worse detection limit, and it is suitable for the detection of 2-FAL at concentrations of 0.01–1 mg L−1. [ABSTRACT FROM AUTHOR]

An optical fiber relative humidity (RH) sensor based on tapered no-core fiber (TNCF) coated with Ti 3 C 2 T x MXene is proposed. The fluoride etching method is used to prepare Ti 3 C 2 T x , which is used as the humidity sensitive material with a multi-layer structure, large specific surface area and rich hydrophilic groups, and optical deposition method is used to integrate Ti 3 C 2 T x with TNCF. The diameter of TNCF between two sections of SMF is reduced to 11.6 μ m to enhance RH sensitivity. The refractive index (RI) of Ti 3 C 2 T x changes as a result of variations in RH, and this ultimately causes a shift in the transmission spectrum. The sensitivity of the device is −77 pm/%RH in the range of 33 %RH to 75 %RH. In the region of 75 %RH to 91 %RH, the sensitivity increases to 685 pm/%RH, the linear correlation coefficients of the two regions are 0.9521 and 0.9940, respectively. On average, the response time is approximately 3.5 s and the recovery time is about 12.7 s. The sensor may be utilized in possible domains, including biological, chemical, and food processing. Its benefits include a simple construction, cheap cost, high reversibility, and stability. [ABSTRACT FROM AUTHOR]

AbstractA high-sensitivity temperature sensor based upon an optical fiber Fabry-Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) is reported that employed a single mode fiber (SMF) and a hollow core fiber (HCF) to enhance the sensitivity. The sensing characteristics were investigated from 20 °C to 40 °C. The experimental results demonstrate that the sensor is sensitive to temperature due to the high thermal optical coefficient (TOC) and high thermal expansion coefficient (TEC) of PDMS, achieving a high sensitivity of 2.155 nm/°C. The designed sensor shows great potential for high-precision temperature sensing applications due to its high sensitivity, compact structure, and simple preparation. [ABSTRACT FROM AUTHOR]

In this study, a surface plasmon resonance (SPR) sensor based on modified plastic optical fibers (POFs) was combined with a specific molecularly imprinted polymer (MIP), used as a synthetic receptor, for glyphosate (GLY) determination in aqueous solutions. Since GLY is a non-selective herbicide associated with severe environmental and health problems, detecting glyphosate in environmental and biological samples remains challenging. The selective interaction between the MIP layer and GLY is monitored by exploiting the SPR phenomenon at the POF's gold surface. Experimental results show that in about ten minutes and by dropping microliter volume samples, the presented optical–chemical sensor can quantify up to three orders of magnitude of GLY concentrations, from nanomolar to micromolar, due to a thin MIP layer over the SPR surface. The developed optical–chemical sensor presents a detection limit of about 1 nM and can be used for onsite GLY measurements. Moreover, the experimental analysis demonstrated the high selectivity of the proposed POF-based chemical sensor. [ABSTRACT FROM AUTHOR]

Lead concentration in water has generally been detected using laboratory methods, which are expensive, time-consuming, and less efficient. Lead detection in water has been improved using bending multimode Plastic Optical Fiber (POF). The study involved bending varied in radius of 2.2 cm and 0.7 cm compared with straight POF while detecting the different lead concentrations in water. The chemical etching modified the POF to generate a sensing section using the evanescent wave technique. The results indicated that the output voltage and concentration have a logarithmic trendline relation with the highest R² = 0,996 in the 2.2 cm bending configuration graph. Based on sensor characterization, detection using a bending configuration with r = 0.7 cm achieves the highest sensitivity, 0.172 mV/ppm, but the highest loss, 14.067 dB, compared with a larger radius, r = 2.2 cm, and straight configuration. The highly sensitive bending POF is potentially utilized as an effective simplicity operation sensor without reagents for detecting lead in water. [ABSTRACT FROM AUTHOR]

Cortisol is a clinically validated stress biomarker that takes part in many physiological and psychological functions related to the body's response to stress factors. In particular, it has emerged as a pivotal tool for understanding stress levels and overall well-being. Usually, in clinics, cortisol levels are monitored in blood or urine, but significant changes are also registered in sweat and saliva. In this work, a surface plasmon resonance probe based on a D-shaped plastic optical fiber was functionalized with a glucocorticoid receptor exploited as a highly efficient bioreceptor specific to cortisol. The developed plastic optical fiber biosensor was tested for cortisol detection in buffer and artificial saliva. The biosensor response showed very good selectivity towards other hormones and a detection limit of about 59 fM and 96 fM in phosphate saline buffer and artificial saliva, respectively. The obtained detection limit, with a rapid detection time (about 5 min) and a low-cost sensor system, paved the way for determining the cortisol concentration in saliva samples without any extraction process or sample pretreatment via a point-of-care test. [ABSTRACT FROM AUTHOR]

In this study, a polymer-based surface plasmon resonance (SPR) sensor for refractive index measurements was designed and manufactured via inkjet 3D printing; then, it was optically characterized. Next, it was investigated how the surface finish of the 3D printed optical waveguide affects the sensor performance, i.e., its sensitivity. More in detail, it was studied how the surface roughness changes with the placement of the 3D printed items on the building platform. To achieve this purpose, a Phase I distribution-free quality monitoring analysis of the selected manufacturing process was implemented for a small pilot production run. The aim was to check the stability of surface roughness versus the placement of the 3D printed parts on the building platform. The 3D printed sensor's surface roughness was assessed through a profilometry study. In particular, the surface roughness was determined for the core of the optical waveguide used to excite the SPR phenomena. Furthermore, the SPR sensors were optically characterized to find the existing relationship between their sensitivity and the considered quality of surface finish. In particular, by varying the surface roughness of the used waveguide, the light scattering in the waveguide changes, and the SPR sensitivity changes too, similarly to the light-diffusing fibers covered by gold nanofilms where the guided light is scattered through a plurality of voids distributed in the core. The procedure followed to investigate the sensor roughness, and establishing their performance enabled the optimal operative range for their application in practice to be identified. Finally, a better knowledge of the 3D printing manufacturing process has been achieved to improve quality of surface finish. [ABSTRACT FROM AUTHOR]

An optical–chemical sensor based on two modified plastic optical fibers (POFs) and a molecularly imprinted polymer (MIP) is realized and tested for the detection of 2-furaldehyde (2-FAL). The 2-FAL measurement is a scientific topic of great interest in different application fields, such as human health and life status monitoring in power transformers. The proposed sensor is realized by using two POFs as segmented waveguides (SW) coupled through a micro-trench milled between the fibers and then filled with a specific MIP for the 2-FAL detection. The experimental results show that the developed intensity-based sensor system is highly selective and sensitive to 2-FAL detection in aqueous solutions, with a limit of detection of about 0.04 mg L−1. The proposed sensing approach is simple and low-cost, and it shows performance comparable to that of plasmonic MIP-based sensors present in the literature for 2-FAL detection. [ABSTRACT FROM AUTHOR]

A highly sensitivity balloon-like fiber interferometer based on ethanol coating is presented in this paper. The Mach–Zehnder interferometer is formed by bending a single-mode fiber to a balloon-like structure and nested in the Teflon tube. Then, an ethanol solution was filled into the tube of the balloon-like fiber interferometer by the capillary effect. Due to the high sensitivity of the refractive index (RI) of ethanol solutions to temperature, when the external temperature varies, the optical path difference changes. The change in temperature can be detected by the shift in the interference spectrum. Limited by the size of the balloon-like structure, three kinds of these structures with different sensitive lengths were prepared to select the best parameters. The sensitive lengths were 10, 15 and 20 mm, respectively, and the RI detection performance of each structure in 10~26% NaCl solutions was investigated experimentally. The results show that when the sensitive length is 20 mm, the RI sensitivity of the sensor is the highest, which is 212.88 nm/RIU. Ultimately, the sensitive length filled with ethanol is 20 mm. The experimental results show that the temperature sensitivity of the structure is 1.145 nm/°C in the range of 28.1 °C~35 °C, which is 10.3 times higher than that of an unfilled balloon-like structure (0.111 nm/°C). The system has the advantages of low cost and easy fabrication, which can potentially be used in high-precision temperature monitoring processes. [ABSTRACT FROM AUTHOR]

As the global aging population increases, the demand for rehabilitation of elderly hand conditions has attracted increased attention in the field of wearable sensors. Owing to their distinctive anti-electromagnetic interference properties, high sensitivity, and excellent biocompatibility, optical fiber sensors exhibit substantial potential for applications in monitoring finger movements, physiological parameters, and tactile responses during rehabilitation. This review provides a brief introduction to the principles and technologies of various fiber sensors, including the Fiber Bragg Grating sensor, self-luminescent stretchable optical fiber sensor, and optic fiber Fabry–Perot sensor. In addition, specific applications are discussed within the rehabilitation field. Furthermore, challenges inherent to current optical fiber sensing technology, such as enhancing the sensitivity and flexibility of the sensors, reducing their cost, and refining system integration, are also addressed. Due to technological developments and greater efforts by researchers, it is likely that wearable optical fiber sensors will become commercially available and extensively utilized for rehabilitation. [ABSTRACT FROM AUTHOR]

In order to solve the problem of flexible sliding tactile composite sensing in the actual grasp of intelligent robot fingers, this paper proposes a research on a convex fiber grating tactile sliding sensor based on mechanical fingers. Based on the sensing principle of fiber Bragg grating, 3D printing technology was used to encapsulate the FBG sensor array with elastic 50 A resin, a double-layer "hemispherical cuboid" distributed sensing unit was designed, and the FBG slippery tactile sensor was actually pasted on the surface of the mechanical finger for static and dynamic experiments. The experimental results show that the slippery tactile sensor designed in this paper has a good linear relationship with temperature and strain. The temperature sensitivities of the polymer-packaged FBGs are K T 1 = 13.04 pm/°C and K T 2 = 12.91 pm/°C, and they have a pressure sensitivity of 40.4 pm/N and 31.2 pm/N, respectively. The FBG sliding tactile sensor not only realizes the identification of the sliding signal generation point and the end point but also completes the classification and identification of sandpaper, cardboard, and polypropylene plastic, and it has a high degree of fit with the robot finger, which has certain application value for the intelligent robot sliding tactile signal perception. [ABSTRACT FROM AUTHOR]

In this research, we proposed and numerically investigated a D-shaped dual-core photonic crystal fiber (PCF) refractive index (RI) sensor based on surface plasmon resonance (SPR), and a plasma material indium tin oxide (ITO) is deposited on the polished surface of a D-shaped PCF to produce the SPR effect. The proposed PCF sensor incorporates a dual-core structure and innovatively introduces an elliptical air hole, which increases the coupling of the SPR effect, resulting in a notable improvement in sensor performance. This enhancement enables the sensor to efficiently detect variations in the RI of the analyte. Utilizing the finite element method (FEM), we analyzed the influencing characteristics of sensor performance, meticulously investigating and optimizing various structural parameters. In the RI sensing range spanning from 1.18 to 1.33, the designed PCF sensor exhibits an outstanding maximum wavelength sensitivity of 29,300 nm/RIU, along with the highest achievable amplitude sensitivity of 261.01 RIU−1. Upon analyzing the light signal modulated by the sensor, the findings unequivocally demonstrate that the proposed sensor displays outstanding sensitivity to changes in the analyte's RI via the SPR effect. This responsiveness enables effective and precise real-time detection. The proposed sensor is characterized by exceptional sensing performance, strong economic feasibility, and low manufacturing intricacy. Consequently, the proposed sensor can be used to detect medical oxygen, anesthetics, methane gas, glucose, fluorine-containing organics, etc., and it holds a diverse array of promising applications spanning industrial detection, biochemical analysis, and medical diagnostics. [ABSTRACT FROM AUTHOR]

In this paper, we propose and numerically characterize the optical characteristics of a dual eccentric-core D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) refractive index (RI) sensor. The dual eccentric-core structure can leak more power to plasma film to excite SPR phenomenon than conventional structures. We investigate the influences induce by diameter of air holes, distance between air holes and thickness of gold film. The results show that our sensor has the wavelength sensitivities (WS) of 44,000 nm/RIU for odd mode and 39,000 nm/RIU for even mode. Moreover, the sensor has the detection range of RI from 1.00 to 1.37, the maximum figure-of-merit (FOM) of 325/RIU, maximum resolution of 2.27 × 10−6 RIU for analyte RI change of 0.1 nm, and the minimum full-width at half-maximum (FWHM) of 56 nm. The sensor has wide application prospects in methane, blood plasma, and methanol detecting. [ABSTRACT FROM AUTHOR]

An ultrahigh sensitivity surface plasmon resonance sensor based on double-side polished photonic crystal fiber is designed, and the gold film with a zigzag cross section is used as the plasmonic material. We study the refractive index sensing characteristics of the proposed sensor by numerical simulation. The results show that compared with the flat gold film structure, the zigzag gold film structure effectively improves the sensing performance, and the sensitivity and resolution of the sensor are significantly enhanced. The maximum wavelength sensitivity and resolution of the proposed sensor can reach 20,000 nm/RIU and 5.00 × 10−6 RIU, respectively. The working wavelength range of the sensor is between 590 and 1200 nm, and the refractive index range that can be used for detection is 1.350 RIU-1.400 RIU. This can be applied to precise detection of extracellular vesicles, breast cancer cell, and red blood cells. The proposed sensor has significant advantages such as stable structure, ultrahigh sensitivity, fast response, small size, and saving noble metal. It has great application potential in biomedical testing and medical equipment. [ABSTRACT FROM AUTHOR]

A highly sensitive D-shaped microfluidic channel (MFC) incorporated in a single-mode fiber (SMF) equipped with a tungsten trioxide ( W O 3 ) layer coated with gold (Au) or silver (Ag) on the base of the MFC is designed and investigated utilizing a finite element method (FEM) to obtain the sensing performance of the optical fiber surface plasmon resonance (SPR) structure. The proposed sensor is appropriate for both bimetallic layers and analytes. With the sizeable cladding diameter of SMF, the fluidic channel size can be changed following demand, making fabrication more accessible and applicable. The hollow D-section above the core deposited a bimetallic structure of silver (Ag) or gold (Au) as plasmonic materials, followed by a tungsten trioxide ( W O 3 ) nanolayer. This optical fiber biochemical monitors the changes in the refractive index (RI) by measuring the transmission spectral shifts of the fiber at their resonance wavelengths. The W O 3 layer protects the plasmonic material from oxidation and effectively enhances the surface plasmon wave (SPW) while interacting with free electrons. Upon achieving the optimum structural parameters, the numerical investigation results showed that the maximum wavelength sensitivity of 6.0 μ m//RIU and 5.0 μ m//RIU for Au/ W O 3 and Ag/ W O 3 were obtained, with the coefficient of performance of 50.12 R I U - 1 and 134.84 R I U - 1 , respectively, for ultra-wide sensing ranges from 1.28 to 1.38. Also, the simulation outcomes revealed that the tungsten trioxide-coated with Ag or Au layers significantly enhanced the sensor. Finally, the numerical results of this study showed that the proposed sensor has substantial possibilities for large sensing RI applications such as biology and chemistry analytes, and it is also valid for other lower RI analyte sensing requirements as a consequence of its features such as high sensitivity, simple design, cost-effective design, and promising linear sensing performance. [ABSTRACT FROM AUTHOR]

The plastic scintillation optical fiber (PSOF) detector, characterized by its large contact area with measurement targets, effectively detects and quantifies radiation in diverse radiation-contaminated areas and liquid environments. While it is extensively utilized for measuring alpha, beta, gamma, and neutron radiations, comprehensive documentation on the spectrum measurement and energy calibration methods for gamma nuclides has not been reported. Accurate energy calibration is crucial for the precise quantification of radiation doses from various sources. The pulse-height spectrum produced by the PSOF detector does not display a Compton maximum because of the significant Gaussian energy broadening. Additionally, this spectrum compresses as the distance increases between the radiation source and the light measurement device. In this study, the energy spectrum of a PSOF for gamma nuclides was characterized by energy calibrations using Compton edge (CE). The CE channel in the measurement spectrum of the PSOF detector for three gamma nuclides was identified using the first-order differentiation method. This technique was successfully applied to spectra measured at various radiation source positions to determine the attenuation coefficients. The proposed energy calibration method allows for the conversion of pulse-height spectra obtained from alpha, beta, and neutron radiation measured with PSOF detectors into energy spectra. [ABSTRACT FROM AUTHOR]

Among the conventional inks used for inkjet printing, metals, oxides, or polymers have been deposited in order to form functional coatings. Gold is one of the most used metals for electrode fabrication in the gas sensor field due to its inert behavior when exposed to reactive gases and conductive properties. However, only a few commercial gold inks are commercially available, and the combination of excessive price, a high minimum purchase quantity, and an unknown composition renders the actual products unappealing. To meet these shortcomings, gold inks were formulated with different solvents in order to reach sufficient properties for the inkjet printing process, such as surface tension and viscosity. On the one hand, gold ink was developed using a gold nanoparticle (AuNP) solution as the metal. This ink was optimized from nanoparticle synthesis, with the ink formulation obtaining a 32 mN·m−1 surface tension and 11.2 mPa·s viscosity in order to be inkjet-printed onto polyimide foil. On the other hand, a particle-free ink, called a precursor based of ink, was also developed. In this case, ink was made by solubilizing gold salt in aqueous medium in order to reach jettable properties. Surface tension was measured at 32 mN·m−1 while viscosity was 14.0 mPa·s. Then, printing and deposition parameters were optimized in order to obtain a highly conductive gold coating. The measured resistivity was 2 × 10−7 Ω·m which is close to the bulk gold conductive value. These coatings could be used for the fabrication of various devices in different working fields. [ABSTRACT FROM AUTHOR]

In this paper, a new sensor is proposed to efficiently gather crucial information on corrosion phenomena and their progression within steel components. Fabricated with plastic optical fibers (POF), the sensor can detect corrosion-induced physical changes in the appearance of monitoring points within the steel material. Additionally, the new sensor incorporates an innovative structure that efficiently utilizes bi-directional optical transmission in the POF, simplifying the installation procedure and reducing the total cost of the POF cables by as much as 50% when monitoring multiple points. Furthermore, an extremely compact dummy sensor with the length of 5 mm and a diameter of 2.2 mm for corrosion-depth detection was introduced, and its functionality was validated through experiments. This paper outlines the concept and fundamental structure of the proposed sensor; analyzes the results of various experiments; and discusses its effectiveness, prospects, and economic advantages. [ABSTRACT FROM AUTHOR]

To measure vibration signals, a low-frequency fiber Bragg grating (FBG) acceleration sensor featuring a flexible hinge with a spring support and symmetric compensation structure has been designed. Based on the mechanical model of the sensor's structure, the expressions for sensitivity and resonant frequency of the sensor are derived. The structural parameters of the sensor are optimized, and a simulation analysis is conducted using ANSYS 19.2 software. According to the results of simulation analysis and size optimization, the sensor prototype is constructed. Subsequently, its amplitude-frequency response, sensitivity, and temperature characteristics are investigated through vibration experiments. The experimental results show that the resonant frequency of the sensor is 73 Hz, the operating frequency range is 0~60 Hz, and the sensitivity measures 24.24 pm/g. This design meets the requirements for measuring vibration signals at low frequencies. [ABSTRACT FROM AUTHOR]

This article presents a technique for reducing the stabilization length of steady-state modes in step-index plastic optical fibers (POFs), which is significant for sensor networks, Internet of Things, signal processing, and data fusion in sensor systems. The results obtained with the com- putational tool developed suggest that the D-shape created in the POF effectively reduces the stabi- lization length of the modes and, by extension, minimizes the dispersion effects of the modes by filtering out high-order modes. Applying the analysis to commercial POFs, the authors experimen- tally verified a reduction in the stabilization length of modes from 27 to 10 m and from 20 m to 5 m. Reducing the mode stabilization length minimizes the bit error rate (BER) in short-length SI-POF- based optical links operating at 250 Mbp/s. A reduction from 7.6 × 10−7 to 3.7 × 10−10 was achieved. [ABSTRACT FROM AUTHOR]

Recently, Subwavelength Grating Waveguides (SWG WG) attract a lot of attention for sensing applications because it offers better sensitivity than conventional WGs. The sensitivity of SWG WG is greatly improved due to the interaction between the analyte and guiding mode in the SWG segments. In this study, a highly sensitive sensor based on a silicon SWG slot waveguide (SWGSW) is proposed for detecting low-concentration fluoride contaminations in water. The gap called as "slot" between the silicon slab along with cladding and the spaces between the segmented silicon rail waveguide is filled with fluoride ion-contaminated water samples as analyte for strong light–matter interaction between guiding modes of the SWG structure, resulting in greater sensitivity of the proposed sensor. The sensitivity of the proposed structure is estimated by numerical simulations as S = 615.38 nm/RIU which is comparable to the existing reported optical sensor structures based on optical waveguide and optical fibre with a smaller footprint. Additionally, the effect of variation of geometrical parameters on the transmission resonances of the proposed structure is also analyzed for the optimization of a SWG WG structure. The obtained results will be helpful to realize and design highly sensitive sensors based on the SOI platform. [ABSTRACT FROM AUTHOR]

For accurate bio-sample identification, we present a unique optimized surface plasmon resonance sensor based on an X-shaped exposed-core photonic crystal fiber. Applications are made easier by the placement of the target analyte and plasmonic material on the fiber's exterior surface. The sensor has four separate silica channels that reach from the core to the metallic outer surface creating X-shape. These channels were intentionally placed to provide the highest sensitivity while maintaining the sensor's ability to be manufactured. Within a refractive index range of 1.33 to 1.40, our optimized sensor demonstrates improved detecting abilities, including a wavelength sensitivity of 8000 nm/RIU and amplitude sensitivity of - 1175.12 R I U - 1 . The suggested sensor also exhibits exceptional performance parameters, such as a resolution of 1.25 × 10 - 5 , a maximum signal-to-noise ratio (SNR) of 2.041 dB, a figure of merit (FOM) of 160.0 R I U - 1 , a detection accuracy (DA) of 0.02 nm−1, and minimum full width half maxima (FWHM) of 50 nm. When examining variations in the optical properties of the PCF due to different RIs of normal and cancer cells using finite element analysis, we achieve amplitude sensitivities of - 844.91, - 418 and - 1221.8 R I U - 1 for HeLa, Basal and MDA-MB-231 cell lines, respectively. [ABSTRACT FROM AUTHOR]

To investigate the therapeutic potential of photodynamic therapy (PDT) for malignant gliomas arising in unresectable sites, we investigated the effect of tumor tissue damage by interstitial PDT (i-PDT) using talaporfin sodium (TPS) in a mouse glioma model in which C6 glioma cells were implanted subcutaneously. A kinetic study of TPS demonstrated that a dose of 10 mg/kg and 90 min after administration was appropriate dose and timing for i-PDT. Performing i-PDT using a small-diameter plastic optical fiber demonstrated that an irradiation energy density of 100 J/cm2 or higher was required to achieve therapeutic effects over the entire tumor tissue. The tissue damage induced apoptosis in the area close to the light source, whereas vascular effects, such as fibrin thrombus formation occurred in the area slightly distant from the light source. Furthermore, when irradiating at the same energy density, irradiation at a lower power density for a longer period of time was more effective than irradiation at a higher power density for a shorter time. When performing i-PDT, it is important to consider the rate of delivery of the irradiation light into the tumor tissue and to set irradiation conditions that achieve an optimal balance between cytotoxic and vascular effects. [ABSTRACT FROM AUTHOR]

A novel photonic crystal fiber (PCF) sensor for refractive index detection based on polydimethylsiloxane (PDMS) is presented in this research, as well as designs for single-channel and dual-channel structures for this PDMS-PCF sensor. The proposed structures can be used to develop sensors with biocompatible polymers. The performance of the single-channel PDMS-PCF sensor was studied, and it was found that adjusting parameters such as pore diameter, lattice constant, distance between the D-shaped structure and the fiber core, and the radius of gold nanoparticles can optimize the sensor's performance. The findings indicate that the detection range of the single-channel photonic crystal is 1.21–1.27. The maximum wavelength sensitivity is 10,000 nm/RIU with a resolution of 1 × 10 − 5 RIU, which is gained when the refractive index is set to 1.27. Based on the results of the single-channel PCF, a dual-channel PDMS-PCF sensor is designed. The refractive index detection range of the proposed sensor is 1.2–1.28. The proposed sensor has a maximum wavelength sensitivity of 13,000 nm/RIU and a maximum resolution of 7.69 × 10 − 6 RIU at a refractive index of 1.28. The designed PDMS-PCF holds tremendous potential for applications in the analysis and detection of substances in the human body in the future. [ABSTRACT FROM AUTHOR]

This study explores the development of an innovative Fabry-Perot Interferometer (FPI) designed for temperature sensing and environmental monitoring. The device is constructed by embedding optical fibers within a 3D-printed resin scaffold, forming a structure with an open Fabry-Perot cavity. Intended as an integral component of Cyber-Physical-Social Systems (CPSS), this FPI structure aims to enhance the system's capacity to sense changes in external environmental conditions. Within the CPSS context, the FPI offers several advantages, including simple manufacturing processes, low production costs, and high sensitivity. These benefits contribute to providing precise environmental feedback to the system, which is essential in implementing effective security and privacy protection strategies. Experimental evaluations have shown that the FPI exhibits a high linear sensitivity of 14.330 nm/°C within a temperature range of 34.9°C-38.5°C, confirming its potential for application in CPSS for temperature monitoring and environmental sensing. [ABSTRACT FROM AUTHOR]

Nanoparticle- (NP-) doped optical fibres show the potential to increase the signal-to-noise ratio and thus the sensitivity of optical fibre strain detection for structural health monitoring. In this paper, our previous experimental/simulation study is extended to a design study for strain monitoring. 100 nm spherical gold NPs were randomly seeded in the optical fibre core to increase the intensity of backscattered light. Backscattered light spectra were obtained in different wavelength ranges around the infrared C-band and for different gauge lengths. Spectral shift values were obtained by cross-correlation of the spectra before and after strain change. The results showed that the strain accuracy has a positive correlation with the relative spectral sensitivity and that the strain precision decreases with increasing noise. Based on the simulated results, a formula for the sensitivity of the NP-doped optical fibre sensor was obtained using an aerospace case study to provide realistic strain values. An improved method is proposed to increase the accuracy of strain detection based on increasing the relative spectral sensitivity, and the results showed that the error was reduced by about 50%, but at the expense of a reduced strain measurement range and more sensitivity to noise. These results contribute to the better application of NP-doped optical fibres for strain monitoring. [ABSTRACT FROM AUTHOR]

Using the no-core fiber (NCF)–seven-core fiber (SCF) interference structure, two curvature sensors of Michelson interference type and Mach–Zehnder interference (MZI) type are proposed, respectively. The curvature sensor based on Michelson interference shows wavelength-modulation characteristics, the sensitivity is about −22.76 nm/m−1 with a linearity of 0.9823, the temperature sensitivity is only 0.054 nm/°C, and the effect of temperature on curvature can be negligible. The MZI sensor based on an enlarged taper-embedded cascaded structure is an intensity-modulated sensor. The sensitivities are −63.6271 dB m/m−1 and 93.3293 dBm/m−1 for the forward and reverse curvature, respectively, and the linearities are 0.9987 and 0.9930, respectively. But the strain sensitivity (8.357 × 10−4 dBm/με) of the MZI sensor is so tiny, which can avoid the strain cross effect. The two sensors can be used in the detection of the curvature at different (temperature/strain) conditions. [ABSTRACT FROM AUTHOR]

The cladding of PMMA based polymer optical fibers (POFs) is doped by Rhodamine 6G (Rh6G) in the solution composed of water and methanol. Methanol is added in order to lower the doping temperature compared to that of pure water. Results show that addition of methanol, like raising temperature, can effectively accelerate the doping process. It is also found that there is a critical doping temperature for the solution of given methanol content. Above that temperature, the doping process dramatically impairs the fiber and the fiber loss increases too much for further application. In addition, Microscope observation of cross-sections of doped fibers indicate that Rh6G only diffuses into the cladding. Concentration measurement of Rh6G in the cladding and the core of doped fibers confirms that there is almost no Rh6G in the core. In short, this study reveals that the doping process of PMMA based POFs can be accelerated by adding methanol into water at the same temperature. Most importantly, the solution of methanol and water may be able to dissolve those dopants that are insoluble in pure water, making the aqueous solution based doping method suitable for more dopants. [ABSTRACT FROM AUTHOR]

We propose a spectral filter based on a plastic optical fiber with micro-holes as a low-cost, robust, and highly reproducible spectral filter. The spectral filter is explored for two configurations: a fiber extended in a straight line and a fiber optic loop mirror scheme configuration. The transmission traces indicate a spectral blue shift in peak transmission, at 587 nm, 567 nm, 556 nm, and 536 nm for zero, one, two, and three holes in the fiber, respectively. The filter exhibits a bandpass period of approximately 120 nm. Additionally, we conduct a comparison of the transmission with holes separated by distances of 1 cm and 500 μm. The results demonstrate that the distance between holes does not alter the spectral transmission of the filter. In the case of the fiber loop mirror configuration, we observe that the bandpass can be adjusted, suggesting the presence of multimode interference. Exploring variations in the refractive index within the holes by filling them with glucose solutions at various concentrations, we determine that the filtering band and spectral shape remain unaltered, ensuring the stable and robust operation of our spectral filter. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Conventional methods for pathogen detection in water rely on time-consuming enrichment steps followed by biochemical identification strategies, which require assay times ranging from 24 hours to a week. However, in recent years, significant efforts have been made to develop biosensing technologies enabling rapid and close-to-real-time detection of waterborne pathogens. In previous studies, we developed a plastic optical fiber (POF) immunosensor using an optoelectronic configuration consisting of a U-Shape probe connected to an LED and a photodetector. Bacterial detection was evaluated with the immunosensor immersed in a bacterial suspension in water with a known concentration. Here, we report on the sensitivity of a new optoelectronic configuration consisting of two POF U-shaped probes, one as the reference and the other as the immunosensor, for the detection of Escherichia coli. In addition, another methos of detection was tested where the sensors were calibrated in the air, before being immersed in a bacterial suspension and then read in the air. This modification improved sensor sensitivity and resulted in a faster detection time. After the immunocapture, the sensors were DAPI-stained and submitted to confocal microscopy. The histograms obtained confirmed that the responses of the immunosensors were due to the bacteria. This new sensor detected the presence of E. coli at 104 CFU/mL in less than 20 min. Currently, sub-20 min is faster than previous studies using fiber-optic based biosensors. We report on an inexpensive and faster detection technology when compared with conventional methods. [ABSTRACT FROM AUTHOR]

A dual-channel surface plasmon resonance (SPR) sensor, based upon a multimode-single mode-multimode-single mode- multimode (MSMSM) fiber structure, is reported for the simultaneous measurement of temperature and refractive index. One channel is coated with an indium tin oxide-silver layer for refractive index sensing, and the channel is coated with Au and cyclohexane layer for temperature sensing. The experiments show that the sensor provides high sensitivity with values of 3379 nm/RIU across the refractive index range from 1.333 to 1.3699 and −3.163 nm/°C from 40 °C to 90 °C. The cross-sensitivity problem is resolved by the dual-wavelength matrix method. Moreover, the proposed sensor has good stability, low cost, and a compact structure and may be employed in biology, chemistry, and environmental testing. [ABSTRACT FROM AUTHOR]

Graphene quantum dot (GQD) is a new type of carbon nanometer material. In addition to the excellent properties of graphene, it is superior due to the quantum limit effect and edge effect. Because of its advantages such as water solution, strong fluorescent, small size, and low biological toxicity, it has important application potential in various fields, especially in sensors and biomedical areas, which are mainly used as optical electrical sensors as well as in biological imaging and tumor therapy. In addition, GQDs have very important characteristics, such as optical and electrical properties. There are many preparation methods, divided into top-down and bottom-up methods, which have different advantages and disadvantages, respectively. In addition, the modification methods include heterogeneous doping, surface heterogeneity, etc. There are still many challenges in developing GQDs. For example, the synthesis steps are still hard to conduct, but as the inquiry continues to deepen, GQDs will be revolutionary materials in the future. In this work, the literature concerning research progress on GQDs has been reviewed and summarized, while the key challenges of their application have been pointed out, which may bring new insights to the application of GQDs. [ABSTRACT FROM AUTHOR]

A composite fiber Fabry-Perot interferometer (FPI) -based optical fiber temperature sensor is theoretically proposed and practically demonstrated in this work, in which the composite FPI is formed by covering the end face of single-mode fiber with ultraviolet (UV) adhesive and nano-TiO 2 coating using the dip-coating method. With the superior thermo-optic characteristic of UV adhesive and the UV absorption of nano-TiO 2 , the sensitivity of the composite FPI temperature sensor can be effectively enhanced by UV irradiation. After five times of TiO 2 dip-coating processes, the composite FPI has a higher temperature sensitivity of 75.3 pm/°C (R2 = 0.9754) under 365 nm UV light, in which the measurement range is from 25 °C to 130 °C and the detection accuracy is 0.66 °C. The proposed sensor has a simple structure and preparation process, competitive sensitivity, high linearity, and satisfactory repeatability and stability, which can be an appropriate candidate to realize high-precision temperature sensing in industrial, chemical, biological, and environmental applications. [ABSTRACT FROM AUTHOR]

Here, the direct incorporation of photochromic WO3 nanoparticles is investigated in a matrix of polymethyl methacrylate (PMMA) by bulk radical polymerization for the fabrication of plastic optical fibers (POFs). All the prepared composites, from preforms to 1D single fibers and 2D fabrics, are thoroughly investigated, leading to insight into their thermal, morphological, and photochromic properties (coloring/bleaching amplitudes and kinetics). It is found that the preforms exhibit partially irreversible photochromic behavior, whereas the single fibers proved to be effectively reversibly photochromic through a degradation of transmission signal upon UV irradiation and a full recovery under dark conditions. The as‐prepared PMMA plastic fibers, both undoped and doped, show good homogeneity without any imperfections or contamination. The WO3 nanoparticles play a dual role as intrinsic and extrinsic absorption centres leading to higher transmission losses. Finally, a hand‐made textile woven with a bundle of doped fibers is presented. The proposed 1D single fibers and 2D fabrics demonstrate their great potential as novel hybrid inorganic–organic materials in the domain of flexible UV‐sensors and photochromic smart textile with improved color stability and lifetime. [ABSTRACT FROM AUTHOR]

The timely and cost-effective identification of the onset of corrosion and its progress would be critical for effectively maintaining structural integrity. Consequently, a series of fundamental experiments were conducted to capture the corrosion process on a steel plate using a new type of plastic optical fiber (POF) sensor. Electrolytic corrosion experiments were performed on a 5 mm thick steel plate immersed in an aqueous solution. The POF sensor installed on the upper side of the plate and directed downward detected the upward progression of the corrosion zone that formed on the underside of the plate. The results showed that the POF sensors could detect the onset of the upward-progressing corrosion front as it passed the 1 and 2 mm marks related to the thickness of the corroded zone. The POF sensors were designed to optically identify corrosion; therefore, the data obtained by these sensors could be processed using a newly developed graphic application software for smartphones and also identified by the naked eye. This method offered an easy and cost-effective solution for verifying the corrosion state of structural components. [ABSTRACT FROM AUTHOR]

Background: Simultaneous positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners and inserts are valuable tools for accurate diagnosis, treatment planning, and monitoring due to their complementary information. However, the integration of a PET system into an MRI scanner presents technical challenges for a distortion‐free operation. Purpose: We aim to develop a PET insert dedicated to breast imaging in combination with the 3T PET/MRI scanner Biograph mMR (Siemens Healthineers) as well as a brain PET insert for the 7T MRI scanner MAGNETOM Terra (Siemens Healthineers). For this development, we selected as a basis the C13500 series PET modules (Hamamatsu Photonics K.K.) as they offer an all‐in‐one solution with a scalable, modular design for compact integration with state‐of‐the‐art performance. The original PET modules were not designed to be operated with an MRI scanner, therefore we implemented several modifications such as signal transmission via plastic optical fiber, radio frequency (RF) shielding of the front‐end electronics, and filter for the power supply lines. In this work, we evaluated the mutual MRI compatibility between the modified PET modules and the 3T and 7T MRI scanner. Methods: We used a proof‐of‐concept setup with two detectors to comprehensively evaluate a potential distortion of the performance of the modified PET modules whilst exposing them to a variety of MR sequences up to the peak operation conditions of the Biograph mMR. A method using the periodicity of the sequences to identify distortions of the PET events in the phase of RF pulse transmission was introduced. Vice versa, the potential distortion of the Biograph mMR was evaluated by vendor proprietary MRI compatibility test sequences. Afterwards, these studies were extended to the MAGNETOM Terra. Results: No distortions were introduced by gradient field switching (field strength up to 20 mT/m at a slew rate of 66.0 T/ms−1). However, RF pulse transmission induced a reduction of the single event rate from 33.0 kcounts/s to 32.0 kcounts/s and a degradation of the coincidence resolution time from 251 to 299 ps. Further, the proposed method revealed artifacts in the energy and timing histograms. Finally, by using the front‐end filters it was possible to prevent any RF pulse induced distortion of event rate, energy, or time stamps even for a 700° flip angle (45.5 μT) sequence. The evaluations to assess potential distortions of the MRI scanner showed that carefully designed RF shielding boxes for the PET modules were required to prevent distortion of the RF spectra. The increase in B0 field inhomogeneity of 0.254 ppm and local changes of the B1 field of 12.5% introduced by the PET modules did not qualitatively affect the MR imaging with a spin echo and MPRAGE sequence for the Biograph mMR and the MAGNETOM Terra, respectively. Conclusion: Our study demonstrates the feasibility of using a modified version of the PET modules in combination with 3T and 7T MRI scanners. Building upon the encouraging MRI compatibility results from our proof‐of‐concept detectors, we will proceed to develop PET inserts for breast and brain imaging using these modules. [ABSTRACT FROM AUTHOR]

This article compares the performance of U and coil-shaped fiber optic sensors for the detection of fluoride in water. Low-cost and simple-to-use U-shape and coil-shape evanescent wave fiber optic sensors have been designed and developed for in-situ detection of fluoride in water. The sensitivities of coil and U-shaped sensors are found to be 0.1418 O.D./ppm and 0.1409 O.D./ppm, respectively, with linear regression coefficients (R2) of 98.25% and 98.20%. [ABSTRACT FROM AUTHOR]

This document is a review of recent advancements in Fiber Bragg Grating (FBG) sensing technology. It explores the fabrication techniques, applications, and future trends of FBGs and optical fiber sensors. The review includes summaries of specific research articles that focus on topics such as enhancing FBG sensors, using smaller-diameter optical fibers, and developing FBG force sensors. The articles highlight the potential advantages and advancements in these areas of FBG sensing technology. The review serves as a guide to the evolving field of FBGs and optical fiber sensor technologies, showcasing their potential for precision measurement and real-time monitoring. [Extracted from the article]

This paper presents a temperature-insensitive optical fiber strain sensor composed of single-mode fiber (SMF), no core fiber (NCF), and few-mode fiber (FMF). The NCF is fused to two FMFs with core-offset, exciting higher-order modes and generating mode interference. Experimental results demonstrate that the strain sensitivity of the optical fiber sensor can reach − 19.19 pm/με in a strain range from 0 to 600 με. Moreover, within a temperature range from 30℃ to 70℃, the strain-temperature crosstalk of the proposed sensor is remarkably low at 0.104 με/℃. This sensor is easy to fabricate, cost-effective, reusable, and shows promising applications in food processing, civil engineering, aerospace, and other fields. [ABSTRACT FROM AUTHOR]

Fly ash-based light-transmitting concrete (FLTC) is an innovative and energy-efficient construction material known for its superior characteristics. FLTC is a high-quality translucent concrete that offers excellent mechanical properties, and effective light transmission. This research study aimed to evaluate the performance of FLTC by incorporating plastic optical fibers (POF) and replacing a portion of the cement with fly ash. The investigation focused on assessing the mechanical properties and light transmittance capabilities of FLTC. Seven different concrete mixes of M20 grade were prepared, varying the volume of POF from 0.5% to 4% and replacing 25% of the cement with fly ash. After 28 days of curing, tests were conducted to measure compressive strength, splitting tensile strength, and light transmittance. The mechanical properties of FLTC demonstrated improvement with increasing POF volume ratios, while the light transmittance notably increased with higher POF volume ratios. FLTC achieved a remarkable light transmittance of up to 5.48% for specimens containing 4% POF volume ratio and 0.75 mm POF diameter, while still maintaining good mechanical properties. Additionally, FLTC exhibited an increase in compressive strength by 27.3 MPa, a tensile strength increases of 17.8%, and an upv value (ultrasonic pulse velocity) of 3.41 km/s. [ABSTRACT FROM AUTHOR]

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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]