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Abstract: This paper explores the influence of colour and surface topography on refractive index measurement by reflection, with particular reference to offset lithography printed coated paper. Previous work has studied the influence of coated paper porosity on the distribution of ink components throughout a printed offset ink film, using the technique of gloss goniophotometry and refractive index measurement. Porous papers were shown to have a fast removal of ink oils, which lead to a surface concentration of organic pigment and consequent depletion of resin binder. The resulting surface was optically rough and gave a less glossy ink film. The theory for gloss goniophotometer refractive index measurement is based upon polarised light reflectance at the interface between two smooth, non-absorbing isotropic media. A printed coated paper is not ideally suited to optical studies, as it is coloured, rough, non-homogeneous and contains particles which are capable of scattering light. This work was therefore carried out to determine the influence of colour and roughness on the measurement of effective refractive index. It is established that the effect of colour on measurement of refractive index is negligible when measured at an angle of 75°. The issue of roughness has not been resolved theoretically, with conflicting references on its effect on the measured RI. However, experimental work in the literature suggests that the effect of roughness on the measured RI is only marginally dependent upon the scale of the roughness. [Copyright &y& Elsevier]

Ultrafast laser photoinscription and laser-based refractive index engineering develop towards a unique way for three-dimensional optical design inside bulk materials for the conception of embedded photonic applications. The specific optical functions for the light guiding elements, notably their single mode characteristics and the accessible spectral domains, depend on the achieved refractive index contrast in the material transparency window and on the characteristic dimensions of the optical modification. We give here an overview of several laser processing options, developed to increase the effective index area and contrast using pulse engineering methods in space and time, and optical design involving focal shaping, tubular concepts, evanescently coupled waveguide arrays, or structured waveguides. [ABSTRACT FROM AUTHOR]

Changes in the composition of an offset lithographic ink film have been studied as a function of the substrate porosity. Using optical and topographical characterisation techniques, evidence is presented that the surface composition of the ink film varies with the rate of ink vehicle removal. In the case of microporous substrates there is fast removal of ink oils which leads to concentration of organic pigment, consequent depletion of resin binder and hence less glossy ink films. The resulting surface is therefore optically rough. In contrast, substrates that give slower removal of the ink vehicle generate a high gloss due to comparatively optically smooth ink film which has a lower pigment concentration at the surface. In Part II further evidence in support of this mechanism is presented using surface analytical spectroscopic techniques. [Copyright &y& Elsevier]

Abstract: Complex refractive index of strongly depolarizing starch acetate is investigated as a function of bulk package density, which is compulsory parameter in analysis of light scattering from nanoscale starch acetate pigments and fillers. The measurements were made using a laser-goniometer and spectrophotometer to gain data for refractive index analysis according to the Brewster’s law and Fresnel equations. The real part of refractive index was verified by microscopic immersion method. [Copyright &y& Elsevier]

• The first investigation combining phononic crystal lens and origami structure. • Introducing an unilateral gradient on the Miura-ori to form a phononic crystal lens. • The folding angle-dependent refractive index brings flexibility and adjustability. As an art of paper folding, origami has inspired designs of diverse tailorable mechanical structures within physics and engineering communities. In this letter, by introducing a unilateral gradient on the Miura-ori crease pattern, we realize a gradient-index (GRIN) origami phononic crystal (PC) lens. The width distribution of a pair of adjacent panels is designed to allow the graded Miura-ori PC lens to have a refractive index variation highest at the center axis and a hyperbolic secant gradient distribution along a direction transverse to the direction of the Lamb wave propagation. The folding angle-dependent gradient refractive index distribution gradually bends and focuses the incident waves at different frequencies toward the center axis. Both numerical modeling and experimental verification are conducted to validate the focusing of the plane wave on the graded Miura-ori PC lens. [ABSTRACT FROM AUTHOR]

We argue that the ‘ L -aspartic acid nickel chloride’ crystal reported by the authors of the title paper (Optics Communications, 291 (2013) 304–308) is actually the well-known diaqua( L -aspartato)nickel(II) hydrate crystal. [ABSTRACT FROM AUTHOR]

With excellent mechanical and optical properties, sapphire substrate becomes a very important industrial material especially for LED manufacturing. Its quality control requires two tasks, double-sided surface profiling and defect detection. In this paper, a 3D surface scanning system is proposed as a platform for sapphire substrate inspection. During the scanning process, the height information of both upper and lower surfaces is measured by a chromatic confocal probe. For lateral positioning feedback, an in-house developed sensor, namely, image grating, is introduced in this paper. For these inspection processes, there are three challenges: 1) the motion error in the vertical direction, 2) simultaneous measurement of both upper and lower surfaces, and 3) lateral positioning error in a large scanning area. To address these challenges, three key technologies were developed: 1) real-time motion error compensation based on a fringe interferometer, 2) a double-sided measurement for transparent specimen without the pre-knowledge of its refractive index, and 3) planar image grating pair for accurate 2D displacement feedback. The experimental results showed that the proposed measurement system was able to achieve 50 nm accuracy of the standard deviation when measuring the step height of gauge blocks. When the system measured 4-inch double-sided polished sapphire substrate, the measurement repeatability of TTV (Total Thickness Variation) was within 60 nm; and that of warpage was within 10 nm. As a side product, refractive index can also be measured using the proposed system, and experimental results showed respectable consistency. • A motion error compensation system is proposed based on film interferometry. • By setting up a pair of image gratings, lateral positioning errors and 2D Abbe error can be minimised. • The proposed technology is able to achieve nanometer repeatability in measuring thickness variation and warpage. • This system is able to simultaneously measure transparent specimens without having to know the refractive index. • The proposed system can also be used for general surface topography measurement purposes. [ABSTRACT FROM AUTHOR]

In this paper, we present spectroscopic ellipsometry measurements of five selected bulk chalcogenide glasses (Ge 28 Sb 6 Se 66 , Ge 19 Sb 17 Se 64 , Ge 12 Sb 25 Se 63 , Ge 28 Sb 12 Se 60 and As 40 Se 60) for broad wavelength range (0.3–15 μm) at the temperatures from room temperature up to glass transition temperature (with reserve). Temperature dependence of bandgap energy obtained from Tauc-Lorentz oscillator together with temperature dependence of refractive index for selected wavelengths (1.55, 3.4, 7.0 and 10.6 μm) where the studied materials are transparent are presented together with thermo-optic coefficients d E g /d T and d n /d T for these wavelengths. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is used primarily as an opacifier in solid dosage forms and is present in the majority of tablet and capsule dosage forms on the market. The IQ* TiO2 Working Group has previously shown that titanium dioxide has unique properties which are necessary for its function in these formulations and noted that, as the potential replacements lack the semi-conductor properties, high refractive index and whiteness of E171, it might be hard to replicate these properties with alternative materials. In this paper we detail the results of readiness surveys and practical assessments that have been conducted with alternative materials by IQ member companies. A range of technical challenges and regulatory hurdles were identified which mean that, in the short term, it may be difficult to replace titanium dioxide with the currently available alternative materials while readily achieving the same drug product quality attributes, especially for some of the marketed formulations that titanium dioxide is currently used for. We note the higher technical complexity, due to the variability, color fading and identified scale up risk, of E171 free film coatings and the likely impact on development costs and timelines. We also highlight several regulatory hurdles that would have to be overcome if a titanium dioxide replacement was required for some markets but was not mandated by others. [ABSTRACT FROM AUTHOR]

Gradient refractive index materials (GRINs) are rapidly evolving in optical achromats and compact imaging systems. And GRINs with multi-band imaging mean higher integration for advanced optical imaging systems. In this paper, GRINs covering mid-wave infrared (MWIR) and long-wave infrared (LWIR) were prepared by thermal diffusion method based on Ge 20 Se 80-x Te x glasses. Similar glass transition temperatures (ΔT g = 1 °C) and coefficients of thermal expansion (ΔCTE = 5.47 ppm/K) permit efficient bonding and diffusion processes between the glasses. The GRINs were visualized by infrared imagers, and the axial diffusion results were accurately characterized by Raman spectroscopy and energy dispersive spectrometer (EDS). The refractive index difference (Δn) of the GRINs reaches 0.23 and the diffusion depth reaches 3.53 mm. Diffusion coefficients and activation energy were calculated and discussed. Dispersion property is initially evaluated by Abbe number and partial dispersion. [ABSTRACT FROM AUTHOR]

This paper concerns the analysis of a passive, broadband approximate cloaking scheme for the Helmholtz equation in R d for d = 2 or d = 3. Using ideas from transformation optics, we construct an approximate cloak by "blowing up" a small ball of radius ϵ > 0 to one of radius 1. In the anisotropic cloaking layer resulting from the "blow-up" change of variables, we incorporate a Drude-Lorentz-type model for the index of refraction, and we assume that the cloaked object is a soft (perfectly conducting) obstacle. We first show that (for any fixed ϵ) there are no real transmission eigenvalues associated with the inhomogeneity representing the cloak, which implies that the cloaking devices we have created will not yield perfect cloaking at any frequency, even for a single incident time harmonic wave. Secondly, we establish estimates on the scattered field due to an arbitrary time harmonic incident wave. These estimates show that, as ϵ approaches 0, the L 2 -norm of the scattered field outside the cloak, and its far field pattern, approach 0 uniformly over any bounded band of frequencies. In other words: our scheme leads to broadband approximate cloaking for arbitrary incident time harmonic waves. [ABSTRACT FROM AUTHOR]

To this day, the inter-core crosstalk and intra-core crosstalk are potential factors limiting optical fiber transmission over long distances and serious degradation of signal quality in communication systems of multi-core few-mode fibers. To this end, this work proposes a heterogeneous sixteen-core four-mode fiber with two types of refractive index profiles is proposed in this paper, which consists of a graded-index core and a step-index core. After optimization, the four modes can transmit independently and steadily at 1550 nm, and the effective refractive index difference between adjacent modes is more than 1 × 10−3. Under the optimal fiber parameters, the inter-core crosstalk results can be obtained from the research results and are less than −69 dB/km, which reflects the significant effect of the proposed fiber in reducing the inter-core crosstalk. The proposed fiber is the first to use the combination of step-index core and graded-index core so that the inter-core crosstalk of heterogeneous fibers is successfully suppressed at a low level, while providing new ideas and solutions for future research on novel low-crosstalk multi-core few-mode fibers that can be applied to terrestrial and undersea communication systems. • This paper presents a novel sixteen-core four-mode fiber with two types of refractive index profiles. • The inter-core crosstalk of all LP modes is lower than −69 dB/km at 1550 nm. • The effective mode field area and dispersion of the same mode in adjacent cores have small differences. • The number of channels in the sixteen-core fiber reaches 96 and the relative space efficiency is as high as 24. [ABSTRACT FROM AUTHOR]

In this paper, we investigate soliton solutions and other exact solutions of the highly dispersive perturbed nonlinear Schrödinger equation having Kudryashov's arbitrary form with sextic-power law of refractive index and generalized non-local laws. Studying is conducted by applying the modified extended direct algebraic method, which offers several types of solutions. The extracted solutions including (combo bright-dark, singular, dark, bright) solitons, exponential solutions, rational solutions and singular periodic solutions. The extracted solutions confirmed the effectiveness and strength of the current technology. To illustrate the properties of some solutions, graphic representations of those solutions are given. This study contributes to the understanding of nonlinear wave phenomena and showcases the applicability of the modified extended direct algebraic method in obtaining exact solutions for complex nonlinear equations. The optical solitons produced in respect to this form have never been explored by the proposed technique before, and the results have never been published. [ABSTRACT FROM AUTHOR]

• This paper introduces the control of metasurface on single dimension, double dimension and three-dimensional degree of freedom of electromagnetic wave to realize information encryption, and other dimensions such as spatial frequency control and some common computational imaging encryption algorithms, and analyzes the advantages and disadvantages of these encryption methods. • Compared with traditional optical encryption devices, metasurface encryption has the advantages of compact, high resolution and high security factor, and has a good development prospect. • Information security is particularly important in the information age. Traditional optical encryption devices rely on the phase accumulation effect of diffractive elements in space, and usually need to gradually change the refractive index and thickness of the medium to achieve it. Information security is particularly important in the information age. Traditional optical encryption devices rely on phase, amplitude, and even polarization modulation, with the phase typically produced by the phase accumulation effect of diffractive elements in space, which requires a gradual change in the medium's refractive index and thickness to achieve. This also causes the shortcomings of traditional optical encryption devices such as large volume, high design complexity and poor resolution, which is not conducive to miniaturization. Metasurface, as a two-dimensional form of metamaterials, has artificial sub-wavelength structure, which can flexibly manipulate the phase, amplitude, wavelength and orbital angular momentum of electromagnetic waves by changing the shape, size, spin and arrangement of meta -atoms. Due to the design flexibility of the metasurface and its arbitrary wavefront operation, more and more research is linking it to efficient and reliable encryption devices in the future. This paper introduces the control of metasurface on single dimension, double dimension and three-dimensional degree of freedom of electromagnetic wave to realize information encryption, and other dimensions such as spatial frequency control and some common computational imaging encryption algorithms, and analyzes the advantages and disadvantages of these encryption methods. Compared with traditional optical encryption devices, metasurface encryption has the advantages of compact, high resolution and high security factor, and has a good development prospect. [ABSTRACT FROM AUTHOR]

Biosensors are of great significance for human health and safety monitoring, especially the sensor based on Surface Plasmon Resonance (SPR), widely used in biomolecular detection. Improving its sensitivity has always been the focus of research. In this paper, SPR in grating structures was primarily investigated and then a SPR-based nanoscale metal grating sensor was proposed. With Finite Difference Time Domain (FDTD) simulation, optimization of the sensor's duty ratio, thickness of the Gold (Au) layer, and periodic parameters was conducted. Then sensitivity and quality factor of the sensor are analyzed to obtain the optimal sensor parameters. With a grating period of 0.64 μ m , Au layer thickness of 30 nm, and sensor's fill factor of 0.625, the sensor achieves a sensitivity of 0.417 μ m /refractive index unit (RIU), demonstrating optimal performance. Additionally, Abaqus tensile simulations were performed on the grating imprinting section, validating the uniformity and consistency of strain in the Polydimethylsiloxane (PDMS) substrate-Au film grating structure during stretching. Finally, a combination mold based on acrylic material is designed, effectively addressing the challenging demolding characteristics of cured PDMS material, offering an efficient manufacturing approach for PDMS substrate fabrication. The SPR-based nanoscale grating multimodal sensor designed in this paper exhibits high sensitivity and potential cost-effectiveness in protein molecule detection and flexible stress-strain sensing applications, revealing promising broad prospects for practical utilization. • Simulations and experiments on multimodal sensing devices based on surface plasmon resonance of nanometal gratings is conducted, optimizing the duty ratio, Au layer thickness, and period parameters of the sensor, and exploring the optimal design parameters of the sensing device. • Low refractive index detection in the range of 1–1.05 is achieved, which indicates high sensitivity and potential cost-effectiveness, together with potential applications in various chemical and biomedical fields. • The simulation verifies the stability of the sensing performance of the sensing device under stretching conditions and a combination mold based on acrylic material is designed, effectively solving the difficult peeling characteristics of the cured PDMS material. [ABSTRACT FROM AUTHOR]

• A scheme for detecting a small variation rate of the refractive index based on orbital angular momentum interferometry is proposed and demonstrated in this paper. • A nonuniform RI variation rate is measurable by using the proposed scheme with a resolution of 3.46 × 10−7 s−1 in this work. • It is proved by experiments that the measurement error of variation rate of the refractive index of using the OAM beam is smaller than that using the Gaussian beam. • It is proved by numerical simulations and experiments that the measurement error of variation rate of the refractive index decreases with increasing topological charge of OAM beam. A scheme for detecting a small variation rate of the refractive index (RI) based on orbital angular momentum (OAM) interferometry and time–frequency analysis is proposed and demonstrated in this paper. Two vortex beams carrying OAM of opposite signs are used for interference to produce a petal-like intensity distribution. The RI variation of the sample leads to a time-varying phase delay between the reference and measurement paths and causes a rotation of the petal-like pattern. The rotation angular velocity of the petal-like pattern is proportional to the variation rate of RI, and the normalized cross correlation method is used to estimate it. Then, a time–frequency analysis method is employed to study the time evolution of the variation rate of RI. Four kinds of RI models with different variation rates are simulated, the results are consistent with expectations. Experiments for detecting the RI variation rate of water are also carried out, the results are generally in agreement with the theoretical values and confirm that a nonuniform RI variation rate is measurable. An RI variation rate resolution of 3.46 × 10−7 s−1 is obtained. It is proven that the measurement error of using the OAM beam is smaller than that using the Gaussian beam, and the measurement error decreases with increasing topological charge of OAM beam. The direction of RI changes can be distinguished. The proposed measurement method is simple in structure, and extends a new approach to detect the relation between the RI and other physical parameters. [ABSTRACT FROM AUTHOR]

Chalcogenide glass is widely recognized as an excellent nonlinear optical material. Enhancing its nonlinear optical properties through metal doping has emerged as a prominent research avenue in the field of chalcogenide glass. In this paper, silver (Ag) doped Ge 28 Sb 12 Se 60 (GSS) chalcogenide glass films with different concentrations were prepared by co-evaporation method. The nonlinear absorption coefficients (β) of different samples were investigated by open-aperture top-hat Z-scan experiments and pump-probe experiments, and the nonlinear refractive index (γ) values were determined using the Tichy-Ticha relation. The results showed that the nonlinear absorption of GSS thin films can be improved by Ag doping. The nonlinear absorption coefficient β exhibits the maximum enhancement of about 2.5 times at 8.3% concentration, with the maximum β reaching 1.83×10−6 m/W. The nonlinear absorption mechanism observed in the thin films can be attributed to free carrier absorption, and the free carrier lifetime is positively correlated with the Ag doping concentration. Within the selected Ag concentration range, the nonlinear refractive index (γ) of Ag doped chalcogenide glass films continues to increase, reaching about 3 times at 30.7% concentration, with the maximum γ being 4.643×10−17 m2/W. Additionally, the third-order nonlinear polarizability (χ (3)) values can be increased from 1.014×10−11 esu to 3.314×10−11 esu with increasing Ag concentration. The research results in present paper are of great significance for further exploration of the optical nonlinear enhancement properties and carrier recombination dynamics in chalcogenide glass. • The nonlinear absorption coefficient β reaches a maximum enhancement of about 2.5 times at 8.3% Ag concentration. • The nonlinear refraction of Ag doped GSS films increases with Ag concentration and reaches about 3 times at 30.7%. • The nonlinear absorption response mechanism and nonlinear dynamic process of Ag doped GSS films are revealed. [ABSTRACT FROM AUTHOR]

The use of optically active ions doped into photonic media containing noble metals is an intriguing area of photoluminescence (PL) research. In this paper, we present a new approach using nickel ions doped into photonic glass ceramics (GCs) containing Au metal NCs. We exploit the unique PL properties of Ni2+ embedded in ZnAl 2 O 4 nanocrystals (NCs). Under the same conditions, the Au-ZAO duplex samples exhibit 2–3 times higher near-infrared (NIR) emission intensity and higher absorption intensity compared to the samples without Au metal. We provide direct evidence of energy harvesting around NCs through numerical simulations. The significant NIR PL properties of Ni2+ in Au-ZAO GCs can be explained by the significant dielectric coefficient difference between the Au metal, the surrounding medium, and the ZAO NCs. Furthermore, the intense and broad emission spectra of our samples cover the entire second biological NIR region, which makes them particularly useful for biomedical applications. [ABSTRACT FROM AUTHOR]

Dust plays a key role in many Earth system processes and is ubiquitous in the Martian atmosphere. Various intensive field campaigns, laboratory analyses, space-based remote sensing missions, and global modeling efforts aim to characterize dust optical properties. This is a bountiful time for dust scientists, and yet the interpretation of retrievals and comparison to models remains complicated by various conflicting assumptions that are part of each algorithm. For example, the conversion of satellite radiance measurements into products like aerosol optical depth for model evaluation depends upon aerosol properties like particle size and shape that are often prescribed and not part of the retrieval. Conversely, the model calculation of aerosol optical depth often uses different assumptions. The goal of this review is to first document algorithmic assumptions by various satellite retrieval products and models, and identify where there is consistency and where there are differences. In general, the differences documented in this paper reflect uncertainties resulting from incomplete observational characterization of dust aerosols and limitations in our understanding. Second, we note what observations might reduce uncertainties in our knowledge and bring greater consistency to retrievals and models, allowing for a more rigorous and harmonious comparison. The lack of comprehensive and realistic shape models for dust is an outstanding issue, such that closure between forward modeling from particle refractive index, shape, and size and observed optical properties cannot be achieved. Limitations in the computational methods that must be applied to model scattering from complex shapes also makes accurate optical modeling for dust challenging. Field observations indicate the persistence of coarse and giant dust particles at higher altitudes and farther downwind from their source than previously expected. Remote sensing retrieval algorithms based on observations at visible wavelengths have limited sensitivity to these particles and generally do not consider them, although a recent product based on longwave radiances is encouraging. Current measurements of the refractive index of bulk dust and fundamental dust minerology components such as hematite vary widely, inhibiting attempts to represent the variability in dust optical properties and forcing, as expected from different major dust source regions on Earth that have varying mineralogical composition. Some remote sensing retrieval algorithms allow for limited refractive index variability in their inversion solutions through mixing with other fine mode aerosol models, or optimizing the single scattering albedo, but Earth system models surveyed for this paper assume a globally uniform, size-invariant refractive index. Although no Martian dust samples have yet been returned to Earth, remote sensing observations indicate that Martian dust is globally homogenous in composition, and a single spectral refractive index assumption has been widely adopted to represent Martian dust. The lack of comprehensive, statistically representative measurements of dust particle microphysical properties (size distribution, morphology, complex index of refraction spectra, internal structure heterogeneity), and the resulting optical properties, limits our ability to verify the fidelity of these assumptions. A chain of measurements is needed, ranging from characterizing individual dust mineralogy components (e.g., pure hematite and goethite) to in situ sampling of complex atmospheric aerosol mixtures. Such results could be applied to both remote sensing retrievals that characterize the optical properties of the total aerosol burden in the atmosphere from total radiance measurements, and to global models that represent the total aerosol burden in the atmosphere by building it up from the balance of individual aerosol sources and sinks. • Algorithmic assumptions by various satellite retrieval products and models • No closure between forward modeled and observed dust optical properties. • Retrieval algorithms using visible channels have low sensitivity to large particles. • Field observations indicate the persistence of coarse and giant dust particles. • Retrieval algorithms and global models make different refractive index assumptions. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed study of the effect of WO 3 and Ni films in the presence of BP and BlueP-MDC nanomaterial layers on the sensitivity of a surface plasmon resonance (SPR) following the change in refractive index of the detection medium. Our nanostructure is based on the Kretschmann multilayer configuration composed of a BK7 prism, an Ag metallic film deposited on ZnO and a hybrid multilayer composed of WO 3 /Ni/2D-nanomaterials. In the first part, the study aims to optimize the effect of the thicknesses of the layers of the nanomaterials of the structure on the surface plasmon resonance. We obtain an angular sensitivity of the order of 480 deg/RIU for a figure of merit of 177.11 RIU−1 at the wavelength of 633 nm. These values are respectively 300% and 342% higher than those of a conventional SPR sensor (BK7/Ag/SM). After modeling the SPR biosensor studied in this paper, we showed how the plasmon resonance and sensitivity of the SPR sensor are affected by the refractive index of liquid biochemical elements. The proposed SPR structure can be used in highly sensitive urinary glucose detection and medical analysis applications. [Display omitted] • Engineering and optimization of the SPR device highly sensitive for biomedical processing and detection. • The optimized nanostructure shows the highest sensitivity 480 deg/RIU. • Highest sensitivity enhancement 300% for SPR biosensor. • This study demonstrated high FoM of 177.11 RIU-1 with an enhancement of 342%. • Detection of glucose concentration in human urine samples to test the glucose levels of people with diabetes. [ABSTRACT FROM AUTHOR]

Scintillation material presents a variety of applications used in radiation environments such as dosimetry, spectrometry, and radiography facility. Neutron radiography is a non-destructive testing (NDT) method that uses a proper scintillator such as LiI/ZnS for neutron detection. This paper investigated the effect of neutron-induced point defects on the optical properties of this scintillator used in TRR's neutron radiography system. The combination of Monte Carlo and atomistic modeling methods was utilized in this regard. The results showed that the induced point defects lead to a more than 10 and 22% reduction in the refractive index and reflectivity of the LiI scintillator at optical wavelength respectively. Moreover, the refractive index of the ZnS scintillator decreases more than 6.4 % by Zn interstitial, Zn vacancy, and S vacancy and increases 8.9 % by S interstitial at optical wavelength. [ABSTRACT FROM AUTHOR]

SiO 2 -based ceramic cores are widely used in the preparation of gas turbine engine hollow blades due to their excellent chemical stability and easy removal after casting. In this paper, ZrSiO 4 reinforced SiO 2 -based ceramics were fabricated using digital light processing (DLP) technology. The results showed that the addition of ZrSiO 4 reduced the cure depth due to its high UV light absorptivity and refractive index. When the content of ZrSiO 4 increased to 15 wt%, the cristobalite content reached the maximum, and radial shrinkage reached the minimum of 1.4%. ZrSiO 4 grains could hinder the propagation of cracks, enhancing the room-temperature flexural strength. At 1550 °C, fracturing across SiO 2 grains in SiO 2 -based ceramics led to the great improvement of high-temperature flexural strength. When the content of ZrSiO 4 reached 15 wt%, the flexural strength at room temperature and high temperature was 11.5 MPa and 36.7 MPa, respectively. Therefore, the SiO 2 -based ceramics prepared using DLP technology have good room temperature and high temperature properties, and are expected to be used for hollow blade casting. [ABSTRACT FROM AUTHOR]

Low haze and anti-reflective glass has high potential applications in automobile and optoelectronic fields. Etching is a novel and effective method to fabricate gradient refractive index anti-reflective layer on glass surface. However, the gradient layer on glass surface prepared by the etching method usually characterizes rough porous structure, and the structural defect results in high haze and low abrasion resistance to restrict its applications. In this paper, a hydrothermal etching method has been explored to prepare anti-reflective glass. It has demonstrated to be a new and facile method successfully to tailor the porous nanostructure of gradient refractive index layer and largely decrease the haze of the glass, by adding complex compound in the etching solution. Compared with the etching solution containing NaOH, adding the complex compound of C 6 H 5 Na 3 O 7 in the etching solution has the advantage to overcome the defects. The grain diameter of the graded porous anti-reflective film decreases from ~63 nm to ~18 nm, the etched film thickness increases from 0.44 μm to 1.55 μm, the haze decreases drastically from 23.76% to 1.00%, the reflectivity decreases from 5.88% to 1.08% and the abrasion resistance greatly increases. However, when changing the complex compound from C 6 H 5 Na 3 O 7 to Na 2 HPO 4 , the haze is 23.44% and has no effect on decreasing haze. Structural characterizations show that the grain size in the porous gradient layer can be easily tailored by changing the ion radius of complex anion in the etching solution, and the optical properties can be controlled. The paper provides new insights into the nanostructures and the preparation approach of anti-reflective glass. [ABSTRACT FROM AUTHOR]

This paper presents a high-sensitivity dual-open microchannel PCF-SPR refractometric sensor that was numerically analyzed using the Finite Element Method (FEM). A dual-open microchannel was created on both sides of the fiber to facilitate analyte infiltration and improve its detection performance. The microchannel of PCF was coated with gold plasmonic material to achieve practical sensing. The results revealed that the refractive index sensing range of the proposed refractometric sensor is between 1.37 and 1.43, with a highest amplitude sensitivity of 3743.64 RIU−1 and a wavelength sensitivity of 33000 nm/RIU. Additionally, it offers a maximum resolution of 5.56 × 10−6 RIU. All structure parameters, such as air-hole length, pitch, open-channel radius, and gold thickness, are optimized. The proposed sensor is a significant improvement in the detection of multiple analytes in bio-sensing applications. • This paper presents a high-sensitivity dual-open microchannel PCF-SPR refractometric sensor. • The refractive index sensing range of the proposed refractometric sensor is between 1.37 and 1.43. • High amplitude and wavelenght sensitivities of 3743.64 RIU−1 and 33000 nm/RIU respectively. Maximum resolution is 5.56 × 10−6 RIU. • The proposed sensor is an important improvement in the detection of multiple analytes in bio-sensing applications. [ABSTRACT FROM AUTHOR]

• The JM is multi-function, has high quality factors, and works in THz. • The JM can realize two different logic gates on the positive and negative scales. • The JM can realize the sensing of three different physical quantities. • The JM provides a new way for the detection of human organs by angle sensing. • The JM provides a new idea for glucose and bacterium detections by RI sensing. In this paper, a Janus metastructure (JM) is given, which can realize the multi-function of different logic gates and detection of multiple physical quantities such as magnetic field, angle, and refractive index on the positive and negative scales. Furthermore, the multiscale sensing is also controlled by the logic gate. By varying the two different magnetic fields applied to the specific medium layers, the sharp absorption peak (AP), which is modulated by the external magnetic fields, is obtained in the terahertz (THz) range. The emergence of AP follows NOR logic and AND logic gates, on the positive and negative scale respectively. The results demonstrate that the frequency point (FP) of AP will fluctuate in response to the changes in the detection of physical quantities. Consequently, it is possible to accomplish physical quantities sensing functionalities by determining the FP of AP. The JM, proposed in this paper, provides a new research idea and has a more promising future. Its detection ranges of refractive index, tiny angular changes and magnetic field are 0.61 ∼ 0.65 T or 1.185 ∼ 1.2 T, 1.4 ∼ 1.9 degrees or 2.9 ∼ 3 degrees, and 1.05 ∼ 1.45 or 2.1 ∼ 2.5, which can be widely used in biomedical and physical fields. [ABSTRACT FROM AUTHOR]

• A new method to invert the complex refraction index (CRI) and particle morphology of non-spherical aerosols based on the full Stokes parameters of non-spherical aerosols is proposed. • The method has fewer limitations, and does not need to assume a function to describe the aerosol size distribution. It can invert the CRI and particle morphology for unknown non-spherical aerosol particles accurately. • A new Stokes parameters measurement system for non-spherical aerosol particles is designed. The full Stokes parameters and backscattering matrix of dust aerosols particles are measured and inverted. • The light scattering parameters calculated by the full Stokes parameters can be used for fine classification of particles of different morphology. The complex refraction index (CRI) and particle morphology of aerosols are the most important microphysical parameters of aerosols. They are related to the light scattering parameters of aerosols closely. However, the variation of polarization state of light scattering parameters of non-spherical particles is very sensitive to the CRI and particle morphology. In order to accurately obtain the CRI and particle morphology of non-spherical aerosols, a new method of inversion the CRI and particle morphology for non-spherical aerosols using the full Stokes parameters of non-spherical aerosols is proposed. In this paper, a new Stokes parameters measurement system for non-spherical aerosol is designed. The backscattering (180°) full Stokes parameters of the typical non-spherical aerosol (dust aerosol particle population) are measured. The CRI value of dust aerosols estimated using this method is consistent with those of the references. The feasibility of our retrieval method is confirmed. In this paper, the relationship between the dust aerosol CRI and the change of particle size during the dust settling process is investigated. The results show that the average CRI of dust aerosol does not vary with the particle size distribution in settling process. At the same time, the linear depolarization ratio and the ellipticity of backscattered polarized light of the dust aerosol particles are calculated using the full Stokes parameters. It is found that the non-spherical aerosol linear depolarization ratio and the ellipticity of backscattering polarized light are very sensitive to particle morphology. They can be used for fine classification of particles of different morphology in the dust aerosol particle population. [ABSTRACT FROM AUTHOR]

• The developed NbB 2 -based ceramic absorber coating exhibits solar absorptance of 0.950 and emissivity of 0.15 at 82 °C. • Spectroscopic ellipsometry analysis shows gradation in refractive index in the coating structure from top layer to the substrate. • The developed coating exhibit good wide-angle selectivity up to 48°. • The coatings exhibited good thermal stability up to 200 h at 500 °C in vacuum. The development of any new ceramic absorber demands the evaluation of different performance-limiting properties. In a recently published paper from our research group, we reported the development of NbB 2 -based new tandem absorber. In our efforts to investigate further potentiality for concentrated solar power applications, this study reports the optical and angular dependent reflectance properties of the NbB 2 /Nb(BNO)/Al 2 O 3 spectrally selective absorber. The optical properties (extinction coefficient and refractive index) and the dielectric constants of the coatings were determined using spectroscopic ellipsometry analysis. Such analysis together with SCOUT simulation of the reflectance spectrum, confirms the refractive index gradient from the substrate to the top layer. The angular-dependent reflectance measurement demonstrates good solar absorptance (from 8 to 48°). More importantly, the coatings exhibited good thermal stability up to 200 h in vacuum at 500 °C. Extensive transmission electron microscopy analysis reveals the traces of oxygen in the layers. The moderate decrease in absorptance can be rationalised due to the compaction and formation of an oxide layer. Based on the obtained results and earlier published studies, the potential of the NbB 2 -based coatings as solar selective absorber for concentrated solar power applications is established. [ABSTRACT FROM AUTHOR]

• FDTD and theoretical calculation show that the absorber has three absorption modes, which indicates that the absorber has wavelength selectivity. • The patterned graphene of this absorber is not complicated, easy to make, and has high application value. • The absorber can be tuned from three aspects: the fermi level of Graphene, the relaxation time and the refractive index of the dielectric layer. At the same time, there is a good linear relationship between the refractive index of the dielectric layer and the wavelength of the absorption peak, which is convenient for tuning. • The absorber has high sensitivity and a figure of merit, and is not sensitive to changes in the incidence angle of light, making it a promising application in the field of sensors. In this paper, propose a highly sensitive absorber that utilizes graphene-based patterns to achieve perfect absorption on three different spectral bands. This absorber is designed as a traditional metamaterial structure, optimized to achieve perfect absorption. With the participation of surface plasmon resonance, the absorber achieved absorption rates of 99.14 %, 98.21 %, and 99.32 % at resonance wavelengths of 2933.53 nm, 2956.05 nm, and 3360.45 nm, respectively. Considering factors such as impedance matching and electric field, provide a comprehensive physical explanation for the generation of these absorption peaks. In addition, demonstrated how can modify the wavelength of the absorption peak by adjusting the Fermi energy, and fine tune the absorption rate of a fixed wavelength by manipulating the relaxation time, thereby demonstrating the versatility of our design. In addition, this research explored the complex relationship between the Fermi level and the resonant wavelength and studied the influence of the refractive index of the dielectric layer on the resonant wavelength. It is worth noting that this relationship can be expressed as a strict linear function. As the external refractive index changes, calculated the sensitivity of the absorber, with a peak sensitivity of 768.75 nm/RIU (refractive index unit). This high sensitivity corresponds to a quality factor of 93.31 for the absorption peak. At the same time, our absorber also has good insensitivity to incident angles. In summary, due to its outstanding performance characteristics, this research proposed absorber has broad application prospects in fields such as optoelectronic detection and high sensitivity sensors. [ABSTRACT FROM AUTHOR]

—This paper investigates a dual-side, dual-mode reflective cross-polarization converter for biosensing applications. The converter consists of a polyimide substrate with a modified dumbbell-shaped resonator on one surface and its complementary slot on another. The overall volume is 8.25μm × 8.25μm × 2.47 μm with dual-band operation of 6.39268–7.311692 THz and 9.783001–23.53473 THz for PCR≥80 % for front signal incidence and two full widths at half maximum (FWHM) bands i.e. 11.71594–12.26761 THz & 19.12042–19.87691 THz for back signal incidence. The periodicity is ∼λ o /6, and substrate thickness is ∼λ o /19 at 6.39268 THz. This device has performance stability for incident angle (θ)≤30o. The performance of this device can be tuned from dual-band operation to single-band by varying the chemical potential of the graphene strip for signal incidence from both sides. This device can classify cancer or tuberculosis-infected cells concerning healthy cells by using the variations in their corresponding refractive indices that lead to changes in the band edge frequencies. This device can differentiate between infected and healthy cells or different refractive indices with a high sensitivity of ∼5 THz/RIU. This device has merits of dual side sensing, wide operating bandwidth, multiple frequencies for sensing purposes, and high sensitivity over previously reported sensors. • Bi-directional Cross polarization converter with incident angle (θ) stability for θ≤30o, thickness and 8.25×8.25×2.47µm3. • Front signal has PCR≥80% for ∼6.39-7.32 THz & ∼9.78-23.53 THz. • Back signal has PCR≥50% for ∼11.72-12.27 THz & ∼19.12-19.88 THz. Graphene chemical potential reconfigures this to single band. • Can be used as Biosensor to detect cancer, tumour, malaria, tuberculosis, Leukemia with high sensitivity of ∼5 THz/RIU. • Proposed refractive index sensing method utilizes fL or fH instead of fr, resulting in more accurate sensing. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a high-sensitive glucose sensor using the tilted fiber Bragg gratings (TFBGs). The TFBGs with different tilt angle has been fabricated by phase mask scanning method with an argon ion double-frequency 244 nm laser. As tilt angle increases, the bandwidth of the cladding mode excited by TFBGs gradually expands and cladding mode region shifts towards shorter wavelengths. The higher-order cladding modes appeared at the shorter wavelength side demonstrate a larger separation in the spectrum. TFBGs with different tilt angles for glucose concentration measurement have been investigated experimentally. When the concentration of glucose solution increases, the surrounding refractive index changing make the cut-off mode resonance shift to a longer wavelength. In addition, the tilt angle of TFBGs does affect the glucose sensitivity, that the larger tilt angle is, the higher sensitivity could achieve. In this work, a maximum glucose sensitivity of 80.91 pm/(mg/ml) could be obtained for TFBGs with tilt angle of 10°. The proposed TFBGs with superiorities of high glucose sensitivity and wider detection range, makes it potential for glucose detection in the field of chemical and biomedical sensing. • A high-sensitive glucose sensor based on tilted fiber Bragg gratings (TFBGs) is proposed, with detailed spectral analysis. • The cut-off mode resonance shows a red-shift with glucose concentration increasing, proving the potential in glucose detection. • The glucose sensitivity of TFBGs varies with tilt angle, which could achieve 80.91 pm/(mg/ml) with 10° TFBGs. [ABSTRACT FROM AUTHOR]

This paper proposes a metamaterial absorption device (MAD) based on Block Dirac semimetal (BDS), which exhibits five band perfect absorption in 5.96 THz, 7.86 THz, 9.84 THz, 11.91 THz, 12.22 THz, the absorption rates of M 1 -M 5 are 0.987, 0.998, 0.997, 0.996, 0.999 and Q-factors are 54.36, 131.06, 61.61, 99.75, 102.58, respectively. The MAD has a three-layer structure consisting of substrate gold, silica, and top layer BDS, where BDS is designed as a cylindrical and circular microstructure. And polarization insensitivity due to the symmetry of the design. According to calculations, the MAD conforms to the impedance matching theory. In the analysis of the electric field diagram, it was revealed that the absorption of electromagnetic waves comes from LSPR and guided mode resonance effects. Based on the characteristics of BDS, this device can be tuned with changes in BDS Fermi energy, while also possessing certain physical tuning capabilities. When exploring the refractive index sensitivity of the device, we found that it has a high refractive index sensitivity. Among them, the sensitivity of M 1 -M 5 is 2000 GHz/RIU, 570 GHz/RIU, 3970 GHz/RIU, 3000 GHz/RIU, and 1000 GHz/RIU, respectively Overall, this device has strong application prospects in sensing fields such as biomedicine. [Display omitted] • Multi-band perfect absorption. • High Q-factor mode and refractive index sensitivity. • Physical and chemical tuning performance. • Electromagnetic coupling caused by LSPR and guided-mode resonance. [ABSTRACT FROM AUTHOR]

In this paper, we design a novel H-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor, which is composed of a dual-sided U-shaped groove and an Ag–MoS 2 coating. The proposed sensor exhibits an asymmetrical structure with birefringence, which provides a possible way to detect the refractive index (RI) of analytes with dual-polarization. Based on the finite element method (FEM) simulations, the influences of the structural parameters on the sensing performances are discussed. For y -polarization, the proposed sensor detects the changes of RI from 1.37 to 1.41 with a maximum wavelength sensitivity of 11,700 nm/RIU, while for x -polarization, RI changes from 1.29 to 1.35 with a maximum sensitivity of 7800 nm/RIU. Thus, a PCF-SPR sensor with dual-polarization and wide RI detection range is achieved, which holds significant promise for applications in biology, medicine, and food safety. • A novel H-shaped PCF-SPR sensor for dual-polarization based on the finite element method is proposed. • Wide refractive index detection range is achieved. • MoS 2 layer is used for enhancing the wavelength sensitivity and preventing oxidation. • Maximum wavelength sensitivities are 11,700 nm/RIU for y-pol, and 7800 nm/RIU for x-pol. [ABSTRACT FROM AUTHOR]

In this paper, a pseudo-elliptical-ring-core polarization-maintaining few-mode fiber structure assisted by concentric circular stress-applying region is proposed. Numerical simulation results show that the structure can stably support 14 transmission modes. By introducing two elliptical stress regions with low refractive index inside the core, and a circular stress region with concentric core between the fiber core and cladding, the effective refractive index difference between higher-order modes is significantly improved. In the C + L band, the minimum refractive index difference between adjacent modes is not less than 2 × 10−4. At 1550 nm, the effective refractive index difference between the two fundamental modes reaches 4.8 × 10−4. The mode dispersions are less than |-33| ps/nm/km, and the maximum bending loss is in the order of 10−7 dB/m (bending radius ≥2.5 cm). This work may pave the way for the development of short-distance large-capacity optical fibers. • The min Δ n eff between adjacent modes is not limited by the separation degree of the two fundamental modes. • The Δ n eff between two fundamental modes reaches 4.8 × 10−4 at 1550 nm. • Concentric circular stress region equalizes the separation degree of the lower and higher order degenerate modes. • In the whole C + L band, the Δ n eff between each guided mode is not less than 2 × 10−4. [ABSTRACT FROM AUTHOR]

On-chip refractive index (RI) sensors, which use resonant shifts of micro-cavities to detect environment change, have the advantages of high sensitivity, real-time detection, and compact footprints. However, the cross-sensitivity of the temperature variation severely interferes with sensing results. In this paper, we present a dual-mode microring resonator (MRR) with a cladding layer of polyhexamethylene biguanide hydrochloride (PHMB) for relative humidity (RH) sensing to overcome the limitation. Specifically, the influences of the RH-induced RI change of the PHMB cladding and temperature variations on the effective RIs of TE 0 and TE 1 modes can be decoupled based on the transmission spectral measurements. Using this method, we have demonstrated the temperature-compensated RH sensing which achieved a maximum sensitivity of −54.7 pm/%RH and a limit of detection of 0.8 %RH under the room temperature condition. Besides, a computational model based on the sensing response of the device was proposed and verified, which demonstrated that the structure can accurately measure changes in RH and temperature simultaneously. Our methodology has the potential to become a new reference for developing on-chip RI sensors with temperature compensation. • The device fabricated by using the multi-project foundry service can achieve temperature self-compensation while detecting RH. • The device can achieve a maximum RH sensitivity of −54.7 pm/%RH under the fixed room temperature of 24℃. • The experimental cross-sensitivity characteristics between RH and temperature are consistent with the computational model. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs), constructed from organic ligands that are rich in conjugated π bonds, have been gaining significant attention for gas sensing. This paper reports the synthesis of Nb-H 2 BIPA-TC, an octahedral MOF, starting from niobium as the metal centre and benzoimidephenanthroline tetracarboxylic acid (H 4 BIPA-TC) as the ligand. The Nb-H 2 BIPA-TC-MOF was grown under light irradiation on the surface of a lithium niobate waveguide substrate and assessed for its ability to sense acidic and basic gases. The Nb-H 2 BIPA-TC-MOF formed an octahedral crystal structure after being grown for only 20 min. The obtained film was optically transparent and featured low light attenuation (< 1.28 dB mm−1). Owing to the Lewis acid-base nature of the Nb-H 2 BIPA-TC-MOF, the designed sensor exhibited a specific 'turn on-off' sensing response to H 2 S, SO 2 , and ethylenediamine (EDA) gases. The host-guest interaction between the gas-sensitive Nb-H 2 BIPA-TC -MOF and different analyte gases induced different degrees of 'on-off' switching in its refractive index. The designed MOF showed a significant and reproducible 'turn on-off' response to H 2 S and EDA gases in the 0.1–100 ppm concentration range. The designed MOF responded to these two gases for at least 28 days with a 10–23 % reduction in the sensing response per 7 days. Owing to its low immunity to relative humidity, the designed MOF can be employed under low humidity conditions for the detection of H 2 S/SO 2 and EDA. • An octahedral Nb-H 2 BIPA-TC-MOF was fabricated using UV light irradiation approach. • The designed Nb-MOF exhibited a specific 'turn on-off' response to H 2 S/SO 2 and EDA. • The host-guest interaction induced different degrees of the 'on-off' switch in RI. • The designed Nb-H 2 BIPA-TC-MOF is reproduced and suite for low humidity condition. [ABSTRACT FROM AUTHOR]

Efficient and accurate calculation of Mie scattering parameters for aerosol particles holds significant scientific value and practical implications across various fields such as climate change and environmental science. Traditional multilayer Mie scattering computations are challenged in effectively handling particles that exhibit radial refractive index gradients, leading to low computation speed and accuracy. This paper proposes a novel method driven by deep learning, named RIMie, to offer accuracy and efficient Mie parameters prediction, addressing major challenges in computational efficiency and accuracy. This study provides an efficient and accurate deep learning strategy for calculating Mie scattering parameters of complex aerosol particles, markedly outperforming existing methods. • Novel approach predicts complex particle Mie scattering. • LSTM network boosts accuracy and efficiency in scattering prediction. • Optimizes quantification method for aerosol particle scattering. • Offers significant implications for improving climate modeling accuracy. [ABSTRACT FROM AUTHOR]

• Dual quasi-bound states in the continuum with high sensitivity and high-quality factor are excited in a photonic crystal slab. • By constructing a sensing matrix, the cross sensitivity between temperature and refractive index is eliminated. • The demodulation deviations of temperature and refractive index are analyzed and calculated. • Compared with other dual-parameter sensors, the proposed sensor has lower demodulation deviations. In this paper, a silicon photonic crystal slab driven by dual symmetry breaking-induced quasi-bound states in the continuum (quasi-BICs) is theoretically proposed for high-performance refractive index and temperature sensing. The suspended photonic crystal slab structure and the small inclination angle α of trapezoidal nanoholes enhance the sensitivities and Q -factors of quasi-BICs, respectively. The effects of geometric parameters and polarization angle of light source on quasi-BICs are analyzed. Numerical results show the Q -factors of dual quasi-BICs (QBIC1 and QBIC2), which are dominated by electric quadrupole (EQ) and magnetic dipole (MD), are close to 106 and 105, respectively. The refractive index sensitivities of QBIC1 and QBIC2 exceed 700 nm/refractive index unit (RIU). In addition, the demodulation deviation caused by the resolution of the sensor is calculated by analyzing the two-dimensional sensing matrix. The simultaneous enhancement of Q -factor and sensitivity creates favorable conditions for reducing the demodulation deviation. The maximum demodulation deviations of refractive index and temperature of the designed sensor are 3.1 × 10−6 RIU and 0.1 K, respectively. Our work shows the potential of quasi-BICs for developing high-performance dual-parameter and multi-parameter detection. [ABSTRACT FROM AUTHOR]

Dual-core tapered fibers sustain two distinguished polarization axes and in each polarization axis, two supermodes interfere with each other to form a sinusoidal pattern in the transmission spectrum. By monitoring the wavelength shift of troughs in the transmission spectrum of each polarization axis when physical parameters in the surrounding environment change, multiparameter sensing can be achieved. In this paper, the factors for enhancing measurement sensitivity and accuracy of dual-core tapered fiber-based sensors, including taper length, taper diameter, and distance between two cores, are investigated theoretically: long sensor length, small core diameter and small distance between two cores (large superposed area) in the dual-core geometrical structure lead to a high-sensitivity and high-accuracy measurement to the variations of the surrounding environment. Theoretical analysis also shows that the sensitivity of transverse strain is much larger than that of longitudinal strain with a large distinguished difference between the two axes. Based on the theoretical deduction, 5 cm long dual-core tapered silica fibers with a core diameter of 10 μ m and different core distances are fabricated, and the transmission spectra in two distinguished polarization axes are utilized for monitoring the variations of refractive index and strain simultaneously. High measurement sensitivities are obtained with sensitivities of 2263.5 nm/RIU, − 1. 72 pm/ μ ε from the transmission spectrum of one principal polarization axis of the dual-core fiber and 2167.1 nm/RIU and − 2. 25 pm/ μ ε from the transmission spectrum of the second polarization axis. Dual-core silica fiber tapers are simple, compact fiber sensors with high-sensitivity and high-accuracy dual-parameter measurement capabilities. • Effect of dual-core geometric structure on sensitivity is studied theoretically. • Effect of dual-core geometric structure on sensitivity is studied experimentally. • High-sensitivity and high-accuracy measurement is achieved. [ABSTRACT FROM AUTHOR]

• High-Q Dual-Resonance Metasurface : We propose a novel square nanoblock octamer all-dielectric metasurface capable of generating dual-resonance modes with exceptional Q-factors in the mid-infrared spectrum. • Physical Mechanism Analysis: Through multipole decomposition and electromagnetic field distribution analysis, we elucidate the physical mechanisms underlying the dual-resonance modes, which are dominated by toroidal dipole (TD) and magnetic quadrupole (MQ), respectively. • Exceptional Sensing Performance: Our result demonstrates outstanding refractive index sensing performance, achieving a maximum sensitivity of 3666 nm/RIU and a figure of merit (FoM) of 55,302 RIU-1. • Gas Sensing Capabilities: By incorporating gas-sensitive films, our metasurface serves as highly sensitive gas sensors capable of detecting hydrogen and methane with sensitivities of −1.304 nm/% and −0.484 nm/% for hydrogen, and −2.366 nm/% and −8.917 nm/% for methane, respectively. • Significance: Our research contributes to the development of high-performance mid-infrared refractive index, hydrogen, and methane sensor devices, with potential applications in various fields including environmental monitoring, medical diagnostics, and industrial safety. The attainment of dual-resonance boasting high Q-factors in the mid-infrared spectrum stands as a captivating domain of inquiry. In this paper, a square nanoblock octamer all-dielectric metasurface is proposed. It generates dual-band responses in the mid-infrared band, exhibiting exceptional Q-factors of up to 15,149 and 120,856 respectively. The data evince a remarkable alignment between the Q-factor derived from fitting the Fano resonances and that computed through FWHM. Multipole decomposition and electromagnetic field distributions indicate dual-resonance modes are controlled by toroidal dipole (TD) and magnetic dipole (MD). The maximum sensitivity to the refractive index is 3666 nm/RIU, the maximum FoM is 55,302 RIU−1, and the polarization is insensitive. Gas sensors can be developed by filling the metasurface structure with hydrogen and methane-sensitive films. This sensor has a maximum sensitivity of −1.304 nm/% for hydrogen and −8.917 nm/% for methane. This research provides an important and effective approach to achieving high-performance mid-infrared refractive index, hydrogen, and methane sensor devices. [ABSTRACT FROM AUTHOR]

• The fundamentals, classification and fabrication of optical fiber sensors with dispersion turning point are reviewed. • Three main methods for DTP implementation in optical fiber sensors are introduced. • The aim is to provide effective methods for superior performance of turning point-enhanced optical fiber RI sensors. • The potential strategy of turning point effect for biosensing applications is assessed. Optical fiber sensor operating at the dispersion turning point (DTP) has become a promising building block for future development in biosensing application due to its ultrahigh sensitivity. In this paper, we comprehensively review the fundamentals of various optical fiber sensors under the turning point condition, together with the basic definition, classification, design, fabrication and applications. Three main methods for DTP implementation are introduced and highlighted: i) phase matching condition in long period grating, ii) refractive index (RI) matching to the effective refractive index of the waveguide in modal interferometer, and iii) mode coupling via diameter regulation in modal interferometer, optical microfiber coupler and polarization interferometer. The aim here is to provide reliable and effective methods to achieve the superior performance on turning point-enhanced optical fiber RI sensors, accelerating the development of transduction technology for the research of novel biomedical sensors. [ABSTRACT FROM AUTHOR]

A tri-band terahertz (THz) absorber for sensing the adulteration percentage in mustard oil is proposed in this paper. It consists of a gold based metallic resonating geometry and metallic ground plane on the top and bottom layers of the dielectric material respectively. It has three absorption peaks with peak absorptivity of 99.74%, 99.96% & 99.94% and Full Width at Half Maxima (FWHM) of 0.57, 0.862 & 1.112 THz at 4.6296, 8.295 & 12.6309 THz respectively. The proposed absorber's unit cell volume has an overall volume of 10 μ m × 10 μ m × 1. 61 μ m (0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L is wavelength at lowest operating frequency i.e. 4.6296 THz). It has polarization insensitive absorption performance under normal incidence and incident angle (θ ∘) stability up to 50° for A ≥ 90%. The proposed structure is simulated through by using CST & HFSS. The results are validated by developing an equivalent circuit model (ECM). The results of CST, HFSS and ECM are found to be in good agreement. A sensitivity varying from ∼ 0.23 THz/RIU to ∼ 1.62 THz/RIU is achieved for Refractive Index (RI) sensing case, whereas a high sensitivity in the range of ∼ 0.4 THz/RIU to ∼ 2 THz/RIU is achieved for mustard oil adulteration sensing case by mounting the absorber's top surface with a polyimide based container filled with an analyte (either refractive index material or mustard oil). During the validation, a maximum ∼ 0.16% error in mustard oil adulteration estimation is achieved. The proposed sensor has advantages of simple & ultra compact dimensions, high sensitivity and minimal error in impurity concentration estimation with respect to other absorber-based sensors. • Unit cell volume 0.15432 λ L × 0. 15432 λ L × 0. 024846 λ L where λ L = λ at 4.6296 THz • Peak absorption of ∼ 99.9% at 4.6296, 8.295 and 12.6309 THz • Polarization independent and Incident angle (θ °) stability up to 50°for A ⩾ 90% • Used as Mustard oil adulteration sensor with maximum sensitivity of ∼ 2 THz/RIU. • Maximum 0.16% error in estimation of unknown refractive indices (avg. calc. RI) [Display omitted] [ABSTRACT FROM AUTHOR]

A complete lattice Boltzmann model combined with immersed boundary method (LB-IBM) is developed to address radiative heat transfer problem in irregularly shaped media. This method investigates radiative heat transfer in two-dimensional uniform/gradient refractive index media with various geometric shapes. The thermal effects generated by irregular boundaries are represented in the form of thermal density and interpolated onto adjacent lattices in the lattice Boltzmann model (LBM). Then, the four-point discrete delta function is used as the interface scheme of the immersed boundary method. Therefore, the standard LBM can effectively solve radiation problems in irregular geometries. The accuracy of the LB-IBM is validated through a comparative analysis with the results predicted by the finite volume method, embedded boundary method, and other numerical methods. Moreover, this paper promotes the application of LBM in radiative heat transfer in irregularly shaped media by providing a straightforward and efficient mesoscopic tool. This lays the foundation for establishing a framework of LBM for unified treatment of convection, conduction and thermal radiation. [ABSTRACT FROM AUTHOR]

In this paper, a polyethylene oxide/polyvinylpyrrolidone blend (PEO/PVP; 70/ 30 wt%) was manufactured via the solution casting process. The influence of varying content of Ti 3 C 2 MXene on the structural, optical, and photocatalytic performance of PEO/PVP mixture against MB dye is studied. The absorbance of PEO/PVP was increased at the visible range after adding Ti 3 C 2 , which is attributed to the plasmon resonance in MXene. With increasing MXene ratios inside PEO/PVP, optical conductivity, optical dielectric constant, direct and indirect bandgaps, and refractive index are found to decrease. Furthermore, the effect of MXene on some dispersion parameters was estimated. The photocatalytic performance of a 1 cm2 sheet of PEO/PVP blend against MB dye degradation was found to be influenced by MXene content. The degradation % of MB dye after 120 min increased from 48 % for pure blend to 51, 52, 54, and 61.6 % after incorporating 0.5, 1, 2, and 5 wt% of MXene, respectively. The rate constant of the photocatalytic degradation (k) value was enhanced from 0.0054 for pure PEO/PVP to 0.0057, 0.0058, 0.0063, and 0.008 after adding 0.5, 1, 2, and 5 wt% of MXene respectively, indicating MXene enhanced the degradation rate. The findings endorsed MXene to change structural, optical parameters and the photocatalytic performance of the PEO/PVP blend to be suitable for many applications. • Different PEO/PVP blends reinforced with different Ti 3 C 2 MXene ratios were prepared. • Anomalous variation in crystallite size and interplanar spacing of PEO/PVP with increasing MXene ratio was observed. • MXene integration decreased optical conductivity, optical dielectric constant, bandgaps, and refractive index of PEO/PVP. • The photocatalytic performance of PEO/PVP against MB dye was enhanced by increasing MXene content. [ABSTRACT FROM AUTHOR]

[Display omitted] • Differential system based on microfiber interferometer and FBG for detecting propofol. • The molecularly imprinted polymer combined polydopamine film enchance sensitivity. • This system has high sensitivity, good specificity, and good stability. • This system simplifies demodulation method and reduces the cost of. In this paper, a high performance differential sensing system combining microfiber interferometer (MFI) and fiber Bragg gratings (FBGs) based on molecularly imprinted polymer (MIP) film is proposed for specific propofol concentration detection. Surface refractive index changes are translated into interference wavelength shift resulting in the change of grating power difference, which helps simplify demodulation equipment. Beta‐cyclodextrin (β‐CD) assisted MIP film enables optic‐fiber system to have specific recognition of propofol. Experimental results show that the sensing system has an obvious response to propofol in the concentration range of 0.001–10 mM, and a sensitivity of 6.04 nm/mM and the optimal sensitivity of differential modulation is 10.89 dB/mM in the concentration range of 0.001–0.05 mM. The sensing system also has excellent stability and specificity in artificial urine environment. The proposed sensing system not only provides a new method for the determination of propofol concentration, broadens the application field of optical sensor, and provides a new platform for application in biomedicine fields. [ABSTRACT FROM AUTHOR]

High sensitive bovine serum albumin (BSA) detection is the basis for biosensing experiments. This paper experimentally optimized the microfiber Mach-Zehnder interferometer (MZI) based on taper geometries including taper waist diameter, tapered area length, taper angle, and taper asymmetry. Based on refractive index (RI) sensitivity as the primary criterion and free spectra range (FSR), extinction ratio as secondary factors, an ultrahigh sensitive label-free microfiber with controllable optimized structure was obtained, which exhibited ultrahigh RI sensitivity of 11140.87 nm/ RIU. In the subsequent BSA concentration measurement, experiments demonstrated a high BSA sensitivity of 3.79 nm/(mg/mL) and a low BSA detection limit of 0.0052 mg/mL. Besides, the proposed sensor also had exceptional performance in terms of BSA response time, stability, and repeatability. The superior performance of this biosensor in BSA response proved its potential for biosensing applications. [Display omitted] • An ultra-sensitive BSA biosensor is demonstrated by optimizing the taper geometries of microfiber. • The fabrication of structurally optimized microfiber is controllable by adjusting the parameter. • A BSA sensitivity of 4.22 nm/(mg/mL) with the detection limit of 0.0047 mg/mL is achieved. • The performance of biosensor is excellent in the dynamic response, stability, and repeatability of BSA response. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed a graphene-based tunable plasmonic sensor in the far-infrared region. Our structure consists of patterned graphene disks on a SiO 2 gap dielectric structure. On a SiO 2 substrate, a monolayer of graphene is placed. On top of that, with a gap dielectric structure, graphene is disk patterned, forming a 2D metastructure. At the resonance wavelength where the dominating electric dipole due to plasmonic resonance is suppressed, the scattering is enhanced due to the magnetic dipole and magnetic quadrupole. The parameter tuning of the proposed device can tune this scattering. We have shown a dominating tunable magnetic quadrupolar scattering at some geometrical parameters. Moreover, graphene has a tunable chemical potential, allowing us to tune the resonance wavelength up to 30 µm. We have shown two tuning schemes to this range with the advantage of a double graphene structure. Along with the interplay of the multipole analysis of these plasmonic resonances, we have shown practical application to sensing. A chemical solvent sensor for detecting hazardous solvents like benzene and nitrobenzene has been proposed, considering the experimental dispersion of these compounds. The chemical solvent sensor has shown a maximum sensitivity of 1307.716 nm/RIU. We also have shown a potential application for high-sensitivity sensing where the refractive index changes only a fraction compared to the base parameter of the air environment, reporting a maximum sensitivity of 4830.95 nm/RIU. [ABSTRACT FROM AUTHOR]

• A Nano-cavity based multispectral plasmonic refractive index sensor was investigated. • Considering the sensitivity and proximity to the telecommunication window, the structure is designed. • Higher bulk and surface sensitivity for detection of biological analytes • A higher bulk sensitivity of 958.3 nm/RIU for the mode III. • Electric field enhancement and Surface charge distribution was evaluated. In this paper, a Nano-cavity based multispectral plasmonic refractive index sensor for prostate-specific antigen (PSA) detection was investigated. The proposed structure includes two cavities in the form of a T and E shape inside a metal layer. The validity of the findings was verified through the use of the 3D finite difference time domain (FDTD) method. The identification of biomolecules is difficult for conventional biosensors in which there is a very limited amount of analyte, other metrics should be used. In most cases, there is enough analyte to completely cover the sensing surface. Here, in addition to bulk sensitivity, the surface sensitivity was analyzed. The proposed structure has three resonance modes. According to our findings, the designed structure has a bulk sensitivity of 958.3 nm/RIU for the third mode (mode III), 550 nm/RIU for the second mode (mod II), and 637.1 for the first mode (mode I). Having three resonance modes makes this structure a suitable option for use in multispectral applications. The surface sensitivity of 429.4, 457.6, and 465.5 nm/RIU was obtained for surface layer thicknesses of 3.5 nm, 5 nm, and 6.5 nm, respectively. Our results show the proposed structure has good potential in different biological applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a detailed study of the temperature effect (0 − 100 ° C), on the plasmonic resonance and sensitivity of a surface plasmon resonance (SPR) to the medium detection refraction index change. We examine this SPR based on the Kretschmann multilayer configuration constituted by a BK7 prism, an Ag/Au bimetallic layer deposited on TiO 2 /SiO 2 and a BlueP/MoS 2 heterostructure monolayer. First, a simple numerical calculation is provided to analyze the temperature effect on the plasmonic resonance. The model take into account the dependence on temperature of the refractive index of different materials composing the investigated structures. The main idea is to show how the sensitivity of the SPR based sensor is influenced according to operating temperature which is critical parameter when considering bio-sensing applications. [Display omitted] • Study of the temperature effects on the BK7/TiO 2 /SiO 2 /Ag/Au/BlueP-MoS 2 /Sensing-medium biosensor. • Linear shift of plasmon resonance as a function of simultaneously measured temperature and refractive index. • The temperature coefficient sensitivity reaches as high as -1020.41 ppm/°C. • Obtained a sensitivity of 345.42deg/RIU, a value 139.9% higher than the conventional design. • The sensor is able to detect the analyte for a large variation of the refractive index, even at low temperatures. [ABSTRACT FROM AUTHOR]

This paper reports the double-line waveguides in Er,Yb:YAG prepared by femtosecond laser (fs-laser) writing at 1030 nm, 450 fs pulse and 100 kHz repetition rate. When light propagates at 632.8 nm along transverse electric (TE) and transverse magnetic (TM) polarization, efficient single-mode guidance is demonstrated in the double-line structures. The minimum transmission loss is as low as 0.98 dB/cm in waveguide with space of 18 μm. The structural modifications in damaged tracks and strain-affected regions were characterized by confocal micro-Raman spectroscopy, and the refractive index variations were analyzed. The corresponding fluorescence emissions of Er3+ and Yb3+ are investigated in the Er,Yb:YAG double-line structure. [ABSTRACT FROM AUTHOR]

It is more than important to sensitively take the temperature in industrial production and experimental study. In this paper, the high-sensitivity temperature sensor based on high birefringent photonic crystal fiber is proposed. To increase the sensitivity, polydimethylsiloxane (PDMS) was filled into the internal elliptical air hole of the photonic crystal fiber (PCF) to propose the PDMS/silica hybrid PCF structures. Temperature is measured by the quantitative change in birefringence of the refractive index of the PDMS material with temperature. We designed it as a detection loop and obtain the temperature detection sensitivity of up to 8.01 nm/°C in the range of −20 °C–20 °C, which was 6.5 times higher compared to the sensitivity obtained by filling with ethanol. This enables the designed PCF temperature sensor to be used for real-time and accurate temperature monitoring in the fields of bio-detection, chemistry, pharmaceuticals, etc. • A birefringent photonic crystal fiber structure is proposed, which has great application potential in temperature detection. • The temperature detection sensitivity was improved 6.5 times than that of filling ethanol. • In the designed optical fiber loop, the temperature range can be adjusted by adjusting the length of the optical fiber. [ABSTRACT FROM AUTHOR]