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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]

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]

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]

This paper reports a double-sided polished microstructured fiber based on the refractive index that simultaneously measures the refractive index and temperature. Two polished planes were introduced into the cladding. A gold film and polydimethylsiloxane are deposited on one side of the plane for temperature measurements, and graphene layers are coated on the surface of the silver film on the other side for refractive index measurements. The finite element method is used to characterize the sensing characteristics of the sensor. The results show that when the liquid refractive index is from 1.36 to 1.4 and the temperature from 70 °C to 110 °C, the maximum sensitivity of the sensor is 15,000 nm/RIU and 8.8 nm/°C, respectively. The double-sided polished structure facilitates the development of multi-parameter measurement sensors for various applications. [ABSTRACT FROM AUTHOR]

An all fiber Mach–Zehnder interferometric (MZI) sensor for measuring temperature and refractive index (RI) is proposed and experimentally demonstrated. The proposed sensor is fabricated with a coreless–few mode–coreless fiber structure. Variations in ambient temperature and RI cause changes in phase differences between the fundamental mode and the higher-order modes, leading to shifts in interference spectrum. The two resonance dips shifts within the wavelength spectrum are used to investigate the temperature and RI characteristics of the sensor. Experimental results show that the two dips have different responses to temperature and RI, indicating that the sensor can realize simultaneous measurement of temperature and RI; the maximum sensing sensitivities are 0.0739 nm/°C and −25.29 nm/RIU, respectively. The proposed sensor has potential applications in physical, biological, and chemical sensing owing to its low cost, good linearity, and simple fabrication. [ABSTRACT FROM AUTHOR]

In this work, a double-slab structure is proposed, in which one slab is made of near-zero-real-part-of-impedance metamaterial (NZRPIM), and the other slab is made of ordinary transparent material. We shall demonstrate that, when a beam of electromagnetic wave is normally incident into the double-slab structure, the transmission may be enhanced significantly due to existence of a cross term induced by coherent superposition between forward and backward waves arising in the NZRPIM slab, thus the corresponding transmission peak may be strongly affected by the other slab and fluid arising between the two slabs, which is instructive significance for the design and application of high sensitivity refractive index sensor based on electromagnetic wave intensity detection. Our work may provide a new possible way to design and manufacture sensors by using NZRPIM. [ABSTRACT FROM AUTHOR]

Temperature measurement and control has an extremely important role in both scientific research and manufacturing. Capacitive liquid crystal (LC) temperature sensors can monitor the temperature using the linear variation of the capacitance of LC cell with temperature, but the sensitivity and other properties need to be improved. In order to improve the performance of capacitive LC temperature sensor, we propose to mix twisted nematic LC (1M10600-100) with ferromagnetic nanoparticles γ-Fe2O3 to prepare LC temperature sensor in this paper. The relationship between the capacitance change rate of different concentrations of nano-doped LC materials at 0.1–20 V and different temperatures was tested, the sensitivity of the sensor was calculated, and the mechanism of the effect of doped nanoparticles on the performance of the device was analyzed. The experimental results show that the sensitivity of the capacitive temperature sensor made of nano-doped LC with the concentration of 0.03 wt% is as high as 9.5 pF/°C at 12 V, which is about 14.87% higher than the undoped device, and its recovery and stability remain almost unchanged. The Pearson correlation coefficient only changes by 0.02%. The results of this paper provide some guidance for the improvement of the performance of capacitive LC temperature sensors, and the development of high-sensitivity temperature sensors based on LC materials. [ABSTRACT FROM AUTHOR]

A Fabry-Perot air chamber was prepared at the splicing point of two single-mode fibers by the heating-expansion of liquid glycerin. The morphology of the Fabry-Perot air chamber was optimized by the splicing parameters (drawing process, discharging location, time and intensity) and the fibers' end-face (plane or arc). The in-line Fabry-Perot interferometer was employed to determine the tensile strain from 0 to 1.2 N. A sensitivity of 3.628 nm/N and the resolution of ∼0.005 N were experimentally demonstrated. The reported Fabry-Perot strain sensor is easy to fabricate, low cost, and flexible to connect with other fibers. [ABSTRACT FROM AUTHOR]

A sensitivity refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shaped high birefringence photonic crystal fibre (PCF) is presented and studied by the finite element method (FEM). Through the designing of air holes arrangement in PCF, the birefringence of optical fibre is improved and the SPR effect of y-polarized core mode is directionally excited. The designed D-shaped PCF with gold film in the damaged air holes enhances the interaction of the evanescent field with the external medium. Simulation results indicate that the sensor has a sensing range from 1.30 to 1.37, and the average spectral sensitivity is 10348.3 nm/RIU. The maximum spectral sensitivity of 19,288 nm/RIU and a high resolution of 5.18 × 10−6 RIU can be obtained at 1.37. This high sensitivity sensor has broad application prospects in life science and other research fields. [ABSTRACT FROM AUTHOR]

A high sensitivity surface plasmon resonance (SPR) based temperature and magnetic field sensor in a dual-core D-shaped photonic crystal fiber (PCF) with two types of holes is reported. The flat surface of the dual-core D-shaped PCF is coated with ethanol as the temperature-sensitive material. A large diameter hole coated with a gold ring is filled with a magnetic fluid as a magnetic field-sensitive material. Using the finite element method (FEM), the electric field distribution mode is simulated, and the loss spectra of the temperature sensing channel (channel I) and magnetic field sensing channel (channel II) are calculated. The influence of the types of metal films and rings, large hole diameter, small hole diameter, and gold film and gold ring thicknesses on the sensor performance are discussed. The results showed that the reported sensor is able to measure temperature and magnetic field independently and simultaneously due to its dual channels. The influence of temperature on magnetic field measurements is reduced by reducing the hole diameter. The results show that the temperature sensitivity is 1.151 nm/°C and the correlation coefficient is 0.9954 from 20 to 70 °C. The magnetic field intensity sensitivity is 0.0779 nm/Oe from 25 to 200 Oe and 0.0212 nm/Oe from 200 to 275 Oe with correlation coefficients of 0.9937 and 0.9989 across these ranges. This high sensitivity D-shaped PCF sensor will promote the development of high-performance dual-parameter devices. [ABSTRACT FROM AUTHOR]

A new experimental approach to the complex study of electrocaloric, pyroelectric, and thermal effects associated with the bulk and local electrical conductivity of ferroelectrics and related materials is proposed. The key to this approach is the analysis of the dynamics of the sample temperature response to an arbitrary external action, including long-term electrical impacts. The metrological justification of the experimental technique is based on direct non-contact high-speed monitoring of the sample temperature using an IR photodiode sensor designed by Ioffe Institute. Its efficiency is confirmed by numerous experimental data on electrocaloric properties of ferroelectrics, relaxors, and relaxors-based multilayer structures. [ABSTRACT FROM AUTHOR]

In the current review, recent advances in the field of surface plasmon resonance (SPR)-based plastic optical fiber (POF) sensors are summarized. The review focused on the different types of sensors and their uses. The performance of POF sensors with different geometries, i.e. U-bent, D-shaped, side-polished, and tapered geometries, is explored using SPR/localized SPR (LSPR) techniques in biochemical and medical applications. The coating materials used in SPR-POF sensor fabrication are highlighted, and the possibility of using simple, low-cost structures to produce a high sensitivity POF sensor is presented. Appropriate materials, such as aptamer, Pd/Au, molecularly imprinted polymer (MIP), and graphene, are selected for POF fabrication in different application fields. The SPR-based D-shaped POF sensor with Pd/Au coating materials, which is used for biochemical sensing applications, has relatively good sensitivity. Meanwhile, the SPR-based D-shaped POF sensor with Au+MIP coating materials is a good choice for the detection of furfural and dibenzyl disulfide analytes in transformer oil. For LSPR-based POF, U-bent configuration is suitable for biochemical sensing [ABSTRACT FROM AUTHOR]

In this study, extensive research has been carried out to determine the optimum geometry resulting in the highest sensitivity for the tapered fibre-optic sensors in a broad geometrical range. A staircase concatenation method was introduced to investigate the effect of the taper angle and diameter on the sensor's sensitivity. The results show that the sensor's sensitivity increases by reducing the taper diameter. Moreover, the effect of the tapering angle on the sensitivity has an optimum point. As a result, there is an optimum taper curvature for exponential-linear profiles, which results in the highest sensitivity. Indeed, it was revealed that the sensitivity changes versus taper diameter and angle could be justified considering the coupled power to different modes of the tapered fibre as well as the ratio of the power outside the fibre taper to the total power for different modes. [ABSTRACT FROM AUTHOR]

Driven by the exceptionally high mechanical properties of carbon nanotubes (CNTs), over the years an extensive research effort has been devoted to the reinforcement of high-performance polymer fibres with CNTs. However, to date, improvements in the strength of these fibres have been rather modest even for relatively high CNT contents. After a brief review of CNT reinforced polymer fibres, here, analytical and numerical finite element models will be used to show that these experimental findings are to be expected based on the intrinsic mechanical properties of these polymer fibres and CNTs, their aspect ratio and interfacial characteristics. Results show that for realistic CNT contents and aspect ratios, the extraordinary strength of CNTs cannot be easily fully exploited in high-performance polymer fibres like Dyneema®or Kevlar®. Even if CNTs are perfectly aligned, bonded and dispersed, the low intrinsic shear strength of these highly anisotropic polymer fibres limits effective stress transfer and nanotube reinforcement. [ABSTRACT FROM AUTHOR]

An optical fiber Mach–Zehnder interferometer based on double S-tapers is proposed for strain sensing. The double S-taper strain sensor is formed by two steps. The fiber is pulled during arc discharging, and a second arc discharge is performed while the fixtures are misaligned to form a S-taper. The transmission spectra were collected with different structural parameters, including the axial offset, taper region diameter, and transition region length. The transmission spectra of each group of parameters are compared and analyzed. This work is meaningful for further research on double S-taper strain sensors. When the axial offset is 60 μm, the S2-taper region diameter is 54 μm, the transition region length is 0.7 cm, the strain experiment is tested from 0 με to 800 με, and the strain sensitivity is 6.63 pm/με. In addition, the stability, reversibility, and temperature sensitivity were experimentally characterized. [ABSTRACT FROM AUTHOR]

The effect of the temperature on refractive index (RI) sensors based on U and Coil-shaped plastic optical fiber (POF) was investigated. For this purpose, four POF-RI sensor probes were produced, and RI changes caused by ethanol changes in solutions were detected. Two of the produced probes were U-shaped, while the other two were Coil-shaped. For the first time in the literature, the effect of both the geometry of the U and Coil-shaped POF-RI sensors on the sensor parameters and the effect of the medium temperature have been analyzed together. As a result of the experiments conducted at 25°C, the best RI change detection sensitivity, linearity, and resolution values were determined as 821%/RIU, 0.9974 (R2), 5.18 × 10−4. In addition, temperature dependence loss (TDL) and temperature dependence RI deviation (TDR) were measured at different temperatures (25–40°C) in the 1.3346–1.45 RI range, and the effect of temperature change on POF-RI sensor probes was characterized. [ABSTRACT FROM AUTHOR]

This paper shows the status of the ethernet-based communication solutions, focused on optical links, for the automotive industry. First, the implementation of a product compatible with the 1000BASE-RHC according to the IEEE Std 802.3bv is presented, which is the first able to transmit 1 Gbps over POF (Plastic Optical Fiber) for automotive. Second, a new architecture to achieve up to 25 Gbps for automotive is described. The proposed Multi-Gigabit system leverages existing technologies, as VCSELs (Vertical-cavity surface-emitting laser), multi-mode fibers and photodiodes already developed for the data centers industry. [ABSTRACT FROM AUTHOR]

A new method to improve the sensitivity of a fiber-based dissolved oxygen sensor by enhancing the evanescent field on the surface of optic fiber has been proposed and verified. The finite difference beam propagation method was used to simulate the transmission of light into the fiber. According to the simulation results, the evanescent field intensities of the step type fiber and tapered fiber were analyzed. Subsequently, a tapered fiber and step type fiber were fabricated. The layer-by-layer self-assembly process was used to place the fluorescent dye onto the surface of fiber. The reversibility, stability, response time, and temperature characteristics of the tapered fiber sensor were characterized. The experimental results show that the sensor has good repeatability, stability and temperature stability, with a response time of approximately 88 s for a change in dissolved oxygen concentration from 0 to 15 mg/L. The experimental measurements showed that the sensitivity of the tapered fiber dissolved oxygen sensor is 1.3-fold higher for dissolved oxygen concentrations from 0 to 15 mg/L compared to the step type fiber device. [ABSTRACT FROM AUTHOR]

This paper investigates the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures. More specifically, the results of a series of laboratory experiments aimed at assessing the suitability and accuracy of DOFS for crack monitoring in reinforced concrete members subjected to external loading are reported. The experiments consisted on three-point bending tests of concrete beams, where a polyamide-coated optical fiber sensor was bonded directly onto the surface of an unaltered reinforcement bar and protected by a layer of silicone. The strain measurements obtained by the DOFS system exhibited an accuracy equivalent to that provided by traditional electrical foil gauges. Moreover, the analysis of the high spatial resolution strain profiles provided by the DOFS enabled the effective detection of crack formation. Furthermore, the comparison of the reinforcement strain profiles with measurements from a digital image correlation system revealed that determining the location of cracks and tracking the evolution of the crack width over time were both feasible, with most errors being below ±3 cm and ±20 µm, for the crack location and crack width, respectively. [ABSTRACT FROM AUTHOR]

A reflective seawater salinity and temperature sensor based on surface plasmon resonance (SPR) effect with multimode single-mode (MS) fiber structure has been proposed and demonstrated. Firstly, the sensing mechanism of the optical fiber SPR sensor was analyzed. Next, the influence of the type of metal, the thickness of the metal film, and the length of sensing area upon the SPR spectrum were simulated and compared. Based on these measurements, a reflective and highly-sensitive refractive index sensor was fabricated and experimentally demonstrated. Finally, a dual-parameter SPR sensor for the simultaneous measurement of seawater salinity and temperature was proposed by coating polydimethylsiloxane (PDMS) on half of the sensor as a temperature sensitive material, whose sensitivities were demonstrated to be 0.31 nm/‰ and -2.02 nm/°C, respectively. The proposed sensor not only resolves the cross-sensitivity problem between salinity and temperature, but also provides a simple structure with low cost and high sensitivity. [ABSTRACT FROM AUTHOR]

In this work, single- and double-pass configurations of ytterbium-doped optical fiber amplifiers (YDFAs) have been investigated. This low quantum defect rare-earth dopant and their performance near 1 µm region has been comprehensively investigated on the basis of gain and noise figure in relation with input signal power and input pump power. The obtained results showed that at an input pump power of 100 mW, the gain was proportionally increased with ytterbium-doped fiber (YDF) length for both proposed configurations, but double-pass regime scored higher gain. This is due to the double-propagation of the forwarded and amplified spontaneous emission (ASE) signal into the active medium and hence will maximize the attainable gain near the 1 µm wavelength region. At YDF length of 5 m, the double-pass technique showed better amplification performance at a lower input signal power of −20 dB compared to the higher input signal power of 0 dB. The maximum gain and optical signal-to-noise ratio (OSNR) attained by double-pass configuration were 24.6 dB and 53.4 dB, respectively. Double-pass amplification at input signal power of −20 dB has increased the gain by 11.2 dB in comparison with the single-pass technique. [ABSTRACT FROM AUTHOR]

An all-fibre splicing Fabry–Perot interferometer (FPI) sensor is successfully demonstrated for measurements of pressure, refractive index (RI) and temperature. The sensor structure is fabricated via fusing a tiny segment of hollow-core fibre (HCF) with single-mode fibre (SMF), and a micro-hole is micromachined on the HCF using a 193 nm excimer laser. Thus, the open micro-HCF can sense changes in air pressure and liquid RI. In contrast, the micro-SMF can only be used to measure temperature changes. The proposed sensor can be used for the measurements of air pressure, liquid RI and temperature. Experimental results show that the pressure resolution and liquid RI resolution of the sensor are 0.012 MPa and 10−5 RIU, respectively, and the temperature resolution is superior to be 0.08°C. The all-fibre sensor with the merits of small dimensions, easy fabrication and low cost can be used in harsh and small volume environments. [ABSTRACT FROM AUTHOR]

The vital capacity is the maximum amount of air a person can expel from the lungs and its measurement helps to diagnose and calculate degree of recovery from lung diseases. In this study, a sensor is developed to measure the vital capacity of human lung. It is developed based on the optical fibre sensing technique. The vital capacity is estimated noninvasively by measuring the volume of air exhaled by the lung into a spherical balloon. The expansion of the balloon is measured by intensity modulated optical fibre sensor and then the vital capacity is estimated. The result from the sensor is compared with a standard reference device. [ABSTRACT FROM AUTHOR]

In an effort to optimize axially compressed members of a wooden structure, composite 2-D lattice structures were designed and manufactured with wood-plastic composites as the panel and glass fiber reinforced plastic as the core by using a simple insert-glue method. The compressive behavior of composite 2-D lattice structures made of cores with different diameters and inclination angles was investigated. Analytical models were employed to predict the theoretical load capacity, equivalent compressive strength, and failure types of lattice structures. Reinforcing hoops were then made at the two ends of cores according to its force characteristics and failure type. [ABSTRACT FROM AUTHOR]

A D-shaped optical-fiber refractive index sensor based on surface plasmon resonance is reported. Rigorous coupled-wave analysis was used to simulate the numerical modeling. The influences of different metal grating parameters on the coupling efficiency were studied and an optimal phase match was obtained. The results show that wavelength sensitivity of the proposed optical fiber sensor is as high as 0.925 μm/RIU for refractive index values from 1.35 to 1.43 with a high linearity value of 0.997. The reported structure may promote the development of high-performance biochemical sensing devices. [ABSTRACT FROM AUTHOR]

By employing the Langevin equation, we have examined a mode coupling in low and high NA step index plastic optical fibres. The numerical integration of the Langevin equation is based on the computer-simulated Langevin force. The solution matches the experimental data reported previously. We have shown that by solving the Langevin equation (stochastic differential equation) one can treat a mode coupling in multimode low and high NA step index plastic optical fibres, which is the result of fibre's intrinsic random perturbations. [ABSTRACT FROM AUTHOR]

A novel polymer waveguide for surface plasmon resonance (SPR) sensing is theoretically proposed and experimentally demonstrated. The waveguide sensor simply consists of a polymer and a thin gold film on a silica layer. According to the multilayer transfer-matrix theory and the multiple reflection theory, a formula describing the reflectivity of total light power is deduced and analyzed, which is related to the dielectric constant of both the waveguide and the metal, the thickness of the metal film, and the length of the sensing area. By the addition of liquids with refractive indices ranging from 1.40 to 1.47 in the sensing area, the proposed polymer waveguide-based surface plasmon resonance sensor exhibited an experimental sensitivity of 1489 dB/RIU. With a refractive index range between 1.45 and 1.47 beyond the measurement range of typical SPR fiber based sensors, the reported device operates with very high sensitivity. The proposed portable, compact, and simple polymer waveguide-based surface plasmon resonance sensor shows potential for low cost and on-chip multiple channel sensing for practical applications. [ABSTRACT FROM AUTHOR]

An in-line optical fiber Mach-Zehnder interferometer (MZI) sensor with high fringe visibility is reported. The sensor is formed by splicing a short section of four-core fiber (FCF) between two coupling sections. The coupling section is fabricated by cascading very short segment of few mode fiber, multimode fiber (MMF), and large core diameter MMF together. A maximum fringe visibility of approximately 30 dB is obtained in the transmission spectrum. The temperature and curvature sensing response were also experimentally investigated. The temperature sensitivities are 61 pm/°C and 49 pm/°C for dip A and dip B ranging from 30 °C to 80 °C, respectively. The curvature sensitivities for dip A and dip B are 20.77 nm/m−1 and 12.89 nm/m−1 in the range of 0.2983 m−1 to 0.7916 m−1, as well as 9.99 nm/m−1 and 5.38 nm/m−1 from the range of 0.7916 m−1 to 1.039 m−1, respectively. The proposed MZI sensor has the advantage of easy fabrication, compactness, higher fringe visibility, and low cost. [ABSTRACT FROM AUTHOR]

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is −88.2RIU−1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of −0.311°C−1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments. [ABSTRACT FROM AUTHOR]

This paper explores high sensitivity fiber optic sensors based on lossy mode resonance (LMR). The sensitivity enhancement is achieved by simultaneously optimizing the diameter of the fiber core and the length of sensing region. The influence of these factors on the sensor sensitivity was analyzed by simulation using the transfer matrix method (TMM) and verified by experiments. The simulation results show that the sensor has high sensitivity and a narrow full width at half maxima when the sensing area is 10 mm. The sensitivity was as high as 3261 nm/refractive index units (RIU) when the core diameter is 200 μm. The experimental results have the same trend as the simulations, with a maximum value of 3100 nm/RIU. The resolution of the sensor may be as high as 1.29 × 10−8 RIU using a spectrometer with a resolution of 0.04 pm. The sensor was also shown to be relatively precise and stable. Since no systematic study concerning the influence of combining the sensing area length and fiber diameter on the sensor performance index yet has been published, this paper provides a reference for future characterization of high-sensitivity and high-precision optical fiber LMR sensors. [ABSTRACT FROM AUTHOR]

A D-type optical fiber surface plasmon resonance (SPR) sensor based on gold film and Au nanoshells is described. The sensor has a smaller full width at half maximum (FWHM) and a higher quality factor. The influence of the coupling effect between the Au nanoshells and gold film with different internal and external diameter ratios on the sensor was investigated by the finite element method. The simulation results show that the coupling effect between the SPR of the gold film and the localized surface plasmon resonance (LSPR) of the Au nanoshells effectively improved the electric field strength of the sensing region. The refractive index measurements show that the sensitivity of the D-type fiber/gold film/Au nanoshell (50/40 AuNS) SPR sensor is 3064 nm/RIU, which is 993 nm/RIU higher than for the D-type fiber/gold film SPR sensor. The D-type fiber/gold film/Au nanoshell (50/40 AuNS) SPR sensor also provides good linearity with a value of 99.4%. The sensor reported in this paper can be used for reference in the development of high performance biosensors. [ABSTRACT FROM AUTHOR]

Among numerous types of health-monitoring and damage-sensing sensors that can be integrated into composites, electrically conductive sensors offer a simple, cost-effective, and durable option for structural health monitoring in fiber reinforced composites. In this study, a novel approach is introduced to create electrical conductive networks in glass fiber reinforced composites. For this purpose, hollow micro-channels are generated using vaporization of sacrificial components (VaSCs) which are subsequently filled with CNT-epoxy conductive fillers to induce conductive pathways within the composite. The presence of vascular conductive pathways was not found to hinder the structural integrity of the composites. The use of such conductive pathways for in situ strain monitoring of composites was investigated. The strain sensitivity of the prepared conductive pathways in the composite were found more than twice that of conventional strain sensors, rendering such conductive pathways a promising alternative for in-situ strain monitoring of continuous fiber-reinforced composites. [ABSTRACT FROM AUTHOR]

Data exchange between wavelength restricted networks is a vital component of a communication link especially a data centre and the long-haul fibre network. Using VCSEL transmitters, we experimentally demonstrate an all passive bidirectional wavelength conversion based on electrical-to-optical-to-electrical driven transmitters whose transmission wavelengths are not restricted. In this study, a downstream 1550 nm VCSEL modulated at 8.5 Gbps is transmitted over 24 km SMF and its electrical data signal used to drive an 850 nm transmitter and transmitted over 50 m MM fibre. An upstream illustration by modulating an 850 nm VCSEL with 8.5 Gbps and driving a 1550 nm is similarly performed to represent a bidirectional wavelength conversion and quality of signal analysed at the 10−9 BER level. A 1.6 dB average penalty is incurred in this set-up due to the inter-modal dispersion experienced by the multimode-mode signals in the 850 nm wavelengths. This work provides a convenient, cheaper and efficient technique for integrating the short- and long-haul transmitted signals in backbone fibre-links. [ABSTRACT FROM AUTHOR]

The influence of core radius on refractive index sensitivity of long period fiber grating (LPFG) sensor has been studied theoretically for the first time, and a new method to fabricate LPFG sensor with high sensitivity is proposed. The structure and parameters of the optical fiber, the period of the gratings, and the coupling order of the cladding modes are all held consistent in the process of studying the change of the core radius. The resonant wavelength of LPFG sensor shifts with changes in the external environment, which is simulated by the transfer matrix method. The sensitivity of LPFG sensor is enhanced by more than 200 times when the core radius increases from 3.1 to 5.1 μm. The results show that LPFG sensors with larger core radii have higher sensitivity. Selecting a fiber with a large core radius to fabricate LPFG sensors is proposed as a method to improve the sensitivity of these devices. This new simple and effective method is expected to be widely used in the manufacture of high sensitivity LPFG sensors in the future. [ABSTRACT FROM AUTHOR]

In this paper, we report the design and characterization of an optical fibre cholesterol biosensor by using sol–gel immobilization technique. The cholesterol enzyme is encapsulated inside of the sol–gel film onto an end of a plastic optical fibre. Two film deposition methods (Dip-Coating and Immersion) were studied. The morphology analysis and sensing properties permit us to determine the best film deposition to sense cholesterol concentration. The range of measured is 4.4–5.2 mM in real time and our results were validated by comparing them with other previously published results. The biosensor is portable, simple cheap, and easy to use. [ABSTRACT FROM PUBLISHER]

A novel set-up for remote sensing the turbidity of a solution using plastic optical fibres together with a mirror is proposed. The authors have estimated turbidity of a liquid in terms of the nephelometric turbidity unit – NTU, a standard unit that relates the solution appearance with its turbidity for two proposed set-ups. Its performance was also investigated using clay sample measurements over a concentration range of 0–10 g/L. The proposed set-ups are useful for detection of suspended particles in a solution even in small quantities due to its high sensitivity, simplicity and robustness. [ABSTRACT FROM PUBLISHER]

This article reports a numerical investigation on the transmission performance of multilevel systems operating in building links encompassing step-index plastic optical fibers. For such an aim, a simplified model for the multimode fiber propagation is introduced. A sub-carrier multiplexing technique is also simulated to demonstrate the distribution of broadcasting television channels by adopting such fibers. The reported results show that a unique building network based on step-index plastic optical fibers is suitable to carry both Ethernet and broadcast TV signals in all rooms. [ABSTRACT FROM AUTHOR]

Low-cost multimode glass and plastic optical fibers are attractive for high-capacity indoor telecom networks. Many existing buildings already have glass multimode fibers installed for local area network applications. Future indoor applications will use combinations of glass multimode fibers with plastic optical fibers that have low losses in the 850-nm–1,310-nm range. This article examines real-world link losses when randomly interconnecting glass and plastic fiber segments having factory-installed connectors. Potential interconnection issues include large variations in connector losses among randomly selected fiber segments, asymmetric link losses in bidirectional links, and variations in bandwidths among different types of fibers. [ABSTRACT FROM AUTHOR]

Two types of 4 × 4 plastic optical fiber star couplers incorporated with a polymer waveguide as the optical power distributor are proposed, and their high performances are demonstrated. The characteristics of the proposed star coupler are investigated based on ray optics, and its power distribution performance is evaluated in terms of the flatness of the coupling ratio and the amount of the excess loss. Under the best conditions, the flatness of the coupling ratio and the excess loss of the fabricated device have been obtained as 2.0 dB and 2.5 dB, respectively. [ABSTRACT FROM AUTHOR]

In this study, as a preliminary work on the realisation of an optical/electrical acupuncture needle, we have attempted to impart electrical conductivity to a plastic optical fibre (POF) by coating a thin gold layer on its surface. First, we investigated the adhesion between the gold and two different substrates, poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)), which were used as the core and the cladding of POF, respectively. To enhance the interfacial adhesion between the gold layer and the substrates, the following two different approaches were applied: low-power plasma treatment and physical surface roughening. A 50 nm-thick gold layer was deposited by ion sputtering onto both the substrates and also onto the 0.5 mm-diameter POF. The variation of wettability and adhesion according to the plasma conditions were investigated through water contact angle measurement and cross-hatch cut testing. Despite the decreased contact angles of the substrates after Ar or O2 plasma treatment, both polymers exhibited very poor adhesion to the gold layer. However, substrates roughened by sandblasting showed 3B class adhesion to gold in the cross-hatch tape test results. The POF that was gold-sputtered after sandblasting showed an electrical conductivity of 1.35 × 103 S cm-1 without any significant optical loss. This fabrication technique may be used for developing a medical needle capable of simultaneously applying electrical and optical stimulus. [ABSTRACT FROM AUTHOR]

Besides serving as transmission links, optical fibers have been used also to realize several types of photonic devices, namely optical amplifiers, lasers, and broadband sources. Finally, a paper by Sofia Latas et al. investigates different ways of controlling the soliton explosions in passively mode-locked fiber lasers through management of the system parameters, namely the fiber dispersion, spectral filtering, linear, and nonlinear gains. One of these papers, by Yuri Barmenkov et al. (https://doi.org/10.1080/01468030.2020.1826608), reports on the basic spectroscopic properties of a home-made holmium-aluminum-germanium co-doped silica fiber, designed for laser applications. [Extracted from the article]

The double aim of the present article is to give a brief description of our research group's main results achieved in recent years and to provide a comprehensive analysis of light propagation properties in multi-step index (MSI) fibers based on the geometric optics method. Therefore, in the initial part we present our research team and its main lines of research on plastic optical fibers (POF). Afterward, the discussion focuses on a new theory we have developed for the propagation in MSI fibers. First of all, we derive the ray invariants β and l , which allow us to instantly determine the direction of the ray at any position along its trajectory, and we discuss the characteristics of the ray path, setting the classification of rays into bound, refracting and tunneling categories. Then, we calculate the ray-path parameters, namely the path length L p , the ray half period z p and the ray transit time t . Furthermore, we analyze the ray temporal dispersion. Specifically, we take a practical case in which the width of each layer is maintained constant, allowing, in contrast, for the respective refractive indices to take any value, and we derive closed expressions for the ray dispersion. Finally, we investigate the light power acceptance properties of an MSI fiber, calculating the effectiveness of both diffuse and collimated light sources in launching bound rays and the coupling losses with lateral and longitudinal misalignments. [ABSTRACT FROM AUTHOR]

Acrylic plastic optical fibers containing the laser dye Rhodamine B chloride have been drawn from unclad doped acrylic preforms. Different samples of these doped plastic optical fibers were illuminated laterally with a He-Ne laser centered at 543.4nm and the fluorescence was induced. Experimental results show evidence that the fluorescence peak position and absorption coefficient are determined by the fiber length and dye concentration. A rate of (5.55 ± 0.32) nm/cm of the fluorescence red shift and (0.41 ± 0.02)/cm at λ = 600 nm of the absorption coefficient was obtained by one sample doped at 0.0001 mol%. [ABSTRACT FROM AUTHOR]