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Global energy shortage necessitates enhancing environmentally friendly and energy-saving technologies. This study demonstrates a smart thermal emitter (STE) with high visual transparency and temperature-dependent emissivity to realize smart thermal management in buildings or automobiles. The STE consisting of layered transparent conductive oxide (TCO), zinc sulfide (ZnS), and thin vanadium dioxide (VO2) films was fabricated using the sputtering process. The STE exhibited high transmittance in the visible region owing to the extremely thin VO2 film and the large optical bandgaps of TCO and ZnS. The average transmittance in the wavelength range of 400–800 nm was 0.57. Owing to the metal–insulator transition of VO2, a metal–insulator–metal structure resonating in the infrared region was formed above 70 °C, which increased the thermal emissivity. The thermal emissivity values at 29 and 91 °C in the infrared region within 2.5–15 μm were 0.29 and 0.66, respectively. The appearance of the STE remained almost unchanged even when the emissivity increased with temperature because the refractive index spectra of VO2 in the visible range hardly change by the metal–insulator transition. In addition, W-doped VO2 allowed the STE to operate under summer temperatures (48 °C). This scalable fabrication process and high visual transparency have significant potential in practical applications, such as windows or exterior coatings, for smart thermal management. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings (FBGs) are widely used in high-radiation environments owing to their high sensitivity, stability, and resistance to electromagnetic interference. In this study, pure and Ge-doped silica core fibers were fabricated using chemical vapor deposition. Based on these fibers, two temperature sensors, FBG-Si and FBG-Ge, were developed using femtosecond laser direct writing combined with metalized armoring. The fibers and sensors were exposed to gamma radiation, and their stability, temperature accuracy, and refractive index were systematically evaluated. Electron paramagnetic resonance and radiation-induced loss were used to investigate the effects of gamma radiation on the fiber materials and temperature sensors at the atomic micro-scale. The results showed that the Bragg center wavelength (λB) of the FBGs linearly redshifted with increasing temperature under non-stressed conditions. After gamma irradiation, at a temperature, λB, redshifted further with increasing radiation dose. The FBG-Si sensor exhibited higher stability and smaller temperature errors than FBG-Ge. Both sensors exhibited a decrease in output power after irradiation. The performance degradation of the FBGs after irradiation is attributed to an increase in the number of color centers and defects within the grating, leading to higher transmission losses. As the radiation dose increased, the concentration of the color centers increased, leading to changes in the refractive index of the gratings. This ultimately resulted in a redshift in λB and caused temperature measurement errors. [ABSTRACT FROM AUTHOR]

We have demonstrated reconfigurable light states in an optical lattice utilizing the electro-optic Pockels effect in a LiNbO 3 slab through altering the transverse refractive index profile of the lattice by pseudo-random bit sequence (P R B S). By modifying the P R B S equivalent voltage range, different light states (ballistic, superdiffusive, diffusive, subdiffusive, and localized) are achieved within the completely disordered lattice. Furthermore, altering the maximum length size and number of periods of the P R B S creates lattices with different pseudo-random refractive index patterns. This provides a broader range of voltage control for switching from superdiffusive state to diffusive state than completely disorder lattice, allowing for precise voltage control over spatial profile for specific applications. This reconfigurable light states in this P R B S controlled lattice hold significant promise for various uses within a single integrated platform even after fabrication. [ABSTRACT FROM AUTHOR]

To date, the orientational birefringence and the photoelastic birefringence of alternating copolymers have not been studied in detail. We focused on N-substituted maleimide (RMI) and styrene (St) as alternating copolymers and analyzed the birefringence, refractive index, and glass transition temperature (Tg) of the alternating copolymers. It was found that the photoelastic coefficient and Tg exhibit a nonlinear relationship with the composition ratio of RMI and St. It is considered that the alternating copolymerization of RMI and St confirms that the conformation is inhibited by interacting with each other. A zero–zero-birefringence polymer that exhibits no birefringence was obtained by using N-ethylmaleimide and St and adjusting the composition ratio. This polymer showed a high Tg, low haze, and a low temperature dependence of birefringence. [ABSTRACT FROM AUTHOR]

Direct methods to manipulate internal heat conduction in solids remain nearly elusive. In this work, we propose a two-dimensional (2D) gradient thermal metamaterial lens designed to control the internal non-Fourier heat conduction. This gradient thermal metamaterial comprises cylindrical structures made of dermis immersed in a stratum background with an effective refractive index adhering to the hyperbolic secant profile rule. Subsequently, the effective refractive index of the thermal metamaterial is defined and numerically assessed using the extended plane wave expansion method. Thereafter, the non-Fourier heat conduction is analyzed numerically via the finite element method in the time-domain. Our findings indicate that the proposed gradient thermal metamaterial can focus the heat effectively and is akin to a flat thermal lens. The proposed flat thermal lens offers promising avenues for enhancing the material properties by laser-based technologies. [ABSTRACT FROM AUTHOR]

The water/ethanol system possesses complexities at the molecular level, which render its description a difficult task. For the elucidation of the system's hydrogen bonding features that are the key factors in its complex behavior, we conduct a Density Functional Theory analysis on relevant water/ethanol clusters inside implicit solvent cavities for the determination of the ethanol donor hydrogen bond strength. We record Attenuated Total Reflectance spectra of water/ethanol-OD solutions and utilize our density and refractive index measurements for post-processing. The application of the Badger–Bauer rule reveals a minimum in the strength of the ethanol donor hydrogen bond for a composition of xwater = 0.74. We attempt to analyze further this result by estimating the effect of the implicit solvent on the ethanol donor hydrogen bond strength, finding it to be incremental. A brief analysis of different cluster conformations is carried out to determine the cooperativity conditions that can potentially explain the observed minimum in the ethanol donor hydrogen bond strength. These observations are related to notions of microheterogeneity in water/alcohol mixtures and provide context toward a more elaborate picture of association in heteroclusters. [ABSTRACT FROM AUTHOR]

In this study, we establish comprehensive design guidelines to maximize single-mode transmission by efficient coupling between a III-nitride quantum-dot-in-nanowire light emitter and a photonic waveguide in the ultraviolet-visible (UV-Vis) spectral range. Considering feasible epitaxial growth, deposition, and fabrication techniques, this study performs detailed electromagnetic simulations to identify the design limits of viable material systems suitable for monolithic integration of vertical III-nitride nanowires on standard ridge waveguides. We show that unlike systems operating in the near-infrared wavelengths, light coupling and transmission in the UV-Vis range are significantly constrained by substrate leakage and backreflection. Such constraints arise from refractive index contrast of the associated waveguide and substrate materials suitable for epitaxial growth and device fabrication. For optimized dimensions of the nanowire and waveguide structures, the maximum unimodal transmission for practical monolithic systems is ∼ 14 % within the wavelength range of 300–500 nm. The theoretical transmission limit of the monolithic system is shown to be 35 % with a substrate of unity refractive index. It has been shown that the best strategy of maximizing coupling between the emission mode of the vertical nanowire and the propagation mode of the planar ridge waveguide is to increase the refractive index contrast between the waveguide and substrate material. Based on these key findings, we propose heterogeneously integrated hybrid structures, which significantly exceeds the unimodal transmission limits of standard monolithic systems attainable with III-nitride material systems in the UV-Vis wavelengths. [ABSTRACT FROM AUTHOR]

Nanostructures possessing plasmonic and magnetic properties can enhance the transverse magneto-optical Kerr effect (TMOKE) by exciting surface plasmon resonances (SPRs). This provides a promising platform for magneto-optical SPR sensors with significantly improved sensing performance. Here, we propose a high-performance magneto-optical SPR sensor, which consists of a bilayer Au/Co grating placed on a gold film. By tuning the structural parameters, a Fano-like TMOKE spectrum with a linewidth of only 0.0135 nm and an amplitude approaching the theoretical maximum is obtained. We attribute the optimal TMOKE signal achieved by the sensor to the critical coupling concept which is associated with the trade-off between scattering and intrinsic decay rates of the system. The optimized nanostructure sensor demonstrates a sensitivity of 1432 nm/RIU to refractive index fluctuations as small as 0.0001 in air, and all figures of merit (FOM) up to 105 RIU−1, making it suitable for gas sensor fabrication. [ABSTRACT FROM AUTHOR]

The 2D Bi2Te3 narrow bandgap semiconductor is an outstanding applicant for optoelectronics and thermoelectric devices. The doping of Se into Bi2Te3 makes metal-double chalcogenide more important. In the current investigation, the Se diffusion into the Bi2Te3 film by thermal annealing at different temperatures is probed through a temperature-dependent Raman study along with other characterizations. Upon annealing, the Se/Bi2Te3 films of ∼810 nm thickness resulted in significant changes to their structural, electronic, and optical behavior. The existence of a rhombohedral Bi2Te3 phase was confirmed by structural investigation. The improvement in crystallinity and decrease in lattice strain modified the optical behavior of the films. The morphology analysis showed a slight aggregation at the higher annealed stage. The uniform and homogeneous dispersal and the composition of elements in the film were verified through surface mapping and compositional analysis. The optical investigation revealed a drop in absorbance with increased transmittance. The direct optical bandgap increased from 0.53 ± 0.002 to 0.77 ± 0.002 eV, showing a blue shift. The non-linear refractive index decreased from 3.72 to 1.85 × 10−16 m2/W upon annealing. The temperature-dependent Raman analysis demonstrated a thermally induced significant vibrational change in the material with specific additional peaks at higher annealing. Such findings can be employed as a phase change material at very high temperatures. The obtained findings are very useful for optoelectronic applications. Surface wettability shows a reduction in hydrophilicity, thus inching toward a hydrophobic one with an increase in annealing temperatures. The enhancement in the photocurrent with the increment in the annealing temperature is more suitable for photovoltaic applications. [ABSTRACT FROM AUTHOR]

Vibrational sum frequency spectra provide information about interfaces that is sensitive to the orientation of molecules, their electronic environment, and the local electric fields. Here, we use molecular dynamics simulations in order to study a surfactant, para-cyanophenol, at the air–water interface. The volume fractions of water and the organic surfactant are considered at various points over the nanometer-scale region in a Lorentz–Lorenz model. We find that the calculated ratios of nonlinear susceptibility tensor elements are in agreement with experimental data only when this depth profile was considered. We also use these data to evaluate the ratio of the C–N hyperpolarizability tensor elements in the interfacial region. [ABSTRACT FROM AUTHOR]

A plasma refractive index sensor based on metal–insulator–metal waveguide-coupled analogy T-shaped with double-ring resonators was designed. The transmission characteristics of the waveguide were investigated using the finite-difference time-domain method with perfectly matched layer absorbing boundary conditions. By optimizing the structure parameters, the sensor obtained the maximum sensitivity (S) of 1110 nm/RIU and the maximum figure of merit of 1904. The results demonstrate that this new structure can generate dual Fano resonances and exhibit typical refractive index sensing functionality, which provides valuable insights into the design and optimization of plasma refractive index sensors. Additionally, by measuring the concentration of plasma solution and glucose solution, it has been proven that the structure has the prospect of practical application. [ABSTRACT FROM AUTHOR]

We have used surface plasmon resonant metal gratings to induce and probe the dielectric response (i.e., electro-optic modulation) of ionic liquids (ILs) at electrode interfaces. Here, the cross-plane electric field at the electrode surface modulates the refractive index of the IL due to the Pockels effect. This is observed as a shift in the resonant angle of the grating (i.e., Δϕ), which can be related to the change in the local index of refraction of the electrolyte (i.e., Δnlocal). The reflection modulation of the IL is compared against a polar (D2O) and a non-polar solvent (benzene) to confirm the electro-optic origin of resonance shift. The electrostatic accumulation of ions from the IL induces local index changes to the gratings over the extent of electrical double layer (EDL) thickness. Finite difference time domain simulations are used to relate the observed shifts in the plasmon resonance and change in reflection to the change in the local index of refraction of the electrolyte and the thickness of the EDL. Simultaneously using the wavelength and intensity shift of the resonance enables us to determine both the effective thickness and Δn of the double layer. We believe that this technique can be used more broadly, allowing the dynamics associated with the potential-induced ordering and rearrangement of ionic species in electrode–solution interfaces. [ABSTRACT FROM AUTHOR]

In this paper, design and fabrication of a dual-band near-zero index metamaterial (MTM) structure using copper on an epoxy resin fiber (FR-4) dielectric substrate is reported for refractive index sensing applications. The primary objective is to achieve dual-band operation spanning a 1–15 GHz frequency range, with a specific focus on achieving a broad bandwidth in the C-band. The resonance of the MTM structure was ascribed to the coupling of plane electromagnetic waves with surface plasmon polaritons on the structure, resulting in a quadrupole plasmon resonance mode. Furthermore, transmission characteristics of the fabricated MTM structure were experimentally measured and found to align closely with the simulated results obtained through the finite element method in COMSOL Multiphysics. The designed MTM structure demonstrates negative and near-zero permittivity at resonance frequencies, enabling left-handed and near-zero index behavior in dual microwave frequency bands. Under room temperature conditions, the MTM sensor exhibited sensitivities of 1 GHz/RIU and 3 GHz/RIU at resonance frequencies of 2.7 and 7.3 GHz, respectively. Consequently, the MTM structure exhibits significant potential for diverse applications, serving as a valuable component in sensors, detectors, and optoelectronic devices operating in the GHz region. [ABSTRACT FROM AUTHOR]

A new microwave metamaterial microstrip line (meta-MSL) is studied by integrating planar mushroom metamaterial structures into a conventional MSL. The meta-MSL is featured with an enhanced effective refractive index than the conventional, extracted from numerical demonstrations using the S-parameter method. The extraordinarily increased refractive index is found to be associated with weak dispersion and low dissipation loss, making the meta-MSL particularly beneficial to compact a microwave Wilkinson power divider (WPD). One metamaterial WPD (meta-WPD) is built using new meta-MSLs. Full-wave numerical calculations reveal that the new meta-WPD has low insertion losses, low reflections, and high isolations between the output ports, working as a good substitute for the conventional WPD. However, the new meta-WPD is exceptional in its small size, which is particularly useful in mobile and wireless applications where compact microwave components are in critical demand. [ABSTRACT FROM AUTHOR]

Optical biosensors with their sensitivity, compact design, and reliability stand out as versatile tools capable of detecting a wide range of analytes. Recently, nanophotonic structures supporting bound states in the continuum (BIC) modes have been actively studied, which is especially interesting for biosensing applications due to their high quality (Q) factor and strongly localized electric field, achieving favorable interaction between field and nanometer scale analyte on the sensing surface. Herein, we demonstrate an optical label-free sensing by accidental or Friedrich–Wintgen (FW) BIC supported on silicon nitride gratings. We compared the sensing performance in terms of bulk, and surface sensitivity, and figure of merit with FW-BIC in the leaky regime and with a symmetry-protected (SP) BIC, which are also supported by the studied platform. We exploit the fact that for FW-BIC a high-Q factor up to 498 comparable to that of SP-BIC (up to 425) retains for a much larger set of interrogation angles, providing excellent interrogation stability. We observed that FW-BIC has slightly higher bulk sensitivity than SP-BIC [186 and 158 nm/RIU (refractive index unit), respectively], but at the same time similar characteristics in terms of surface sensitivity and figure of merit. In addition, we show that both BIC resonances are significantly superior in all respects to the leaky regime due to better field confinement. Finally, the surface of sensing device was also functionalized to detect a cardiac biomarker, myoglobin, exhibiting the limit of detection of 49 ng/ml with clinically relevant level. [ABSTRACT FROM AUTHOR]

Here, we report the frequency-dependent spectrum of ice Ih in the range of 0.2–2 THz. We confirm the presence of a feature that blue-shifts from around 1.55–1.65 THz with a decreasing temperature from 260 to 160 K. There is also a change in the trend of the refractive index of ice corresponding to a dispersion, which is also around 1.6 THz. The features are reproduced in data acquired with three commercial terahertz time-domain spectrometers. Computer-simulated spectra assign the feature to lattice translations perpendicular to the 110 and 1 ̄ 10 planes of the ice Ih crystal. The feature's existence should be recognized in the terahertz measurements of frozen aqueous solution samples to avoid false interpretations. [ABSTRACT FROM AUTHOR]

The analytical expressions for the cross-spectral density matrix elements of the partially coherent elegant Laguerre–Gaussian (eLG) vortex beam propagating through anisotropic turbulent plasma were derived based on the extended Huygens-Fresnel principle and used to study the changes in the polarization degree and the coherence degree of the partially coherent eLG vortex beam in the turbulent plasma. The numerical results show that the polarization degree of a partially coherent eLG vortex beam reaches a specific value (which is equal to the degree of polarization in the source plane) after a long propagation distance in the turbulent plasma. Moreover, this value is independent of the beam order, topological charge, correlation coefficient, wavelength of the source plane, anisotropy parameter, refractive index fluctuation variance, and outer and inner scales of the turbulent plasma. The results also show that with increasing distance, the coherence degree first decreases from unity and then oscillates around zero. However, this oscillation gradually disappears after traveling a long distance. Our results intuitively present the beam polarization and coherence properties through anisotropic hypersonic turbulence, which can be useful for optical communication in hypersonic turbulent environments. [ABSTRACT FROM AUTHOR]

Modulation of the refractive index in a medium by external stimuli enables fast and reversible control of light propagation. This technology for controlling light has led to new discoveries in a wide range of research fields from physics to life sciences and has played a major role in the development of photonics devices. In this article, we focus on ultrasound as an external stimulus and have devised a method to control the refractive index of a medium using ultrasound. Our research group has previously discovered that a giant refractive-index gradient (Δn on the order of 10−2) was induced when water was irradiated with high-frequency (100 MHz range), high-intensity (on the order of MPa) ultrasound. Here, we report ray-tracing simulations in a medium with a refractive-index gradient induced by ultrasonic radiation. A numerical model of the refractive-index gradient was developed based on the experimental data, and ray-tracing simulations were performed using the Euler–Lagrange equation. The ray-tracing simulation results were close numerically to the profiles of the laser beam observed in the experiment when the laser beam was incident on the refractive-index-gradient medium. [ABSTRACT FROM AUTHOR]

Photocatalytic water-splitting represents a promising avenue for clean hydrogen production, necessitating an in-depth understanding of the photocatalytic reaction mechanism. The majority of the photocatalytic materials need cocatalysts to enhance the photo-oxidation or reduction reactions. However, the working mechanism, such as collecting charge carriers or reducing the reaction barrier, is not clear because they disperse inhomogeneously on a surface, and it is difficult to follow the local charge carrier behavior. This study employs the pattern-illumination time-resolved phase microscopy (PI-PM) method to unravel the spatial charge carrier behavior in photocatalytic systems, utilizing time-resolved microscopic image (refractive index change) sequences and their clustering analyses. This approach is robust for studying the change in local charge carrier behavior. We studied two major cocatalyst effects on photocatalysts: TiO2 with/without Pt and hematite with/without CoPi. The PI-PM method, supported by charge type clustering and the effects of scavengers, allowed for the analysis of local activity influenced by cocatalysts. This approach revealed that the introduction of cocatalysts alters the local distribution of charge carrier behavior and significantly impacts their decay rates. In TiO2 systems, the presence of Pt cocatalysts led to a local electron site on the micron scale, extending the lifetime to a few tens of microseconds from a few microseconds. Similarly, in hematite films with CoPi, we observed a notable accumulation of holes at cocatalyst sites, emphasizing the role of cocatalysts in enhancing photocatalytic efficiency. The study's findings highlight the complexity of charge carrier dynamics in photocatalytic processes and the significant influence of cocatalysts. [ABSTRACT FROM AUTHOR]

The plasmonic coupling between silver (Ag) and gold (Au) nanoparticles (NPs) under four polarization modes was examined: a longitudinal mode (L-mode), where the electric field of a linearly polarized incident light parallels the dimer axis, and three transverse modes (T-modes), where the electric field of the light is perpendicular to the dimer axis. The coupling was studied using the discrete dipole approximation followed by an in-house postprocessing code that determines the extinction (Qext), absorption (Qabs), and near-field (Qnf) spectra from the individual NPs as well as the whole system. In agreement with the literature results, the extinction/absorption spectra of the whole dimer have two peaks, one near the Ag localized surface plasmon resonance (LSPR) region and the other at the Au LSPR region, with the peak at Ag LSPR being reduced in all modes and the peak at Au LSPR being red-shifted and increased in the L-mode but not in the T-modes. It is further shown that the scattering at the Ag LSPR region is reduced and becomes less than the isolated Ag NPs, but the absorption at the Ag LSPR is increased and becomes greater than the isolated Ag NPs for the 50 nm Ag–Au heterodimer. This suggests that the scattering from Ag NPs is being reabsorbed by the neighboring Au NPs due to the interband electronic transition in Au at that wavelength range. The Qext from the individual NP in the heterodimer shows the presence of the Fano profile on the Au NP but not on the Ag NP. This phenomenon was further investigated by using a dielectric particle (DP) placed near the Ag or Au NPs. The Fano profile appears in the absorbing DP spectra placed near either Ag or Au NPs. However, the Fano profile is masked upon further increases in the refractive index value of the DP particle. This explains the absence of a Fano profile on the Ag NPs in the Ag–Au heterodimer. The large near-field enhancement on both Ag and Au NPs at the Au plasmonic wavelength in the L-mode for large NPs was investigated through a DP-Au system. The large enhancement was shown to arise from a large imaginary component of the DP refractive index and a small real component. Through examination of both the near- and far-field properties of the individual NPs as well as the whole system and examinations of DP-Ag and DP-Au systems, our study provides a new understanding of the couplings between Ag and Au NPs. [ABSTRACT FROM AUTHOR]

Ultrawide bandgap ZnGa2O4 (ZGO) thin films were grown on sapphire (0001) substrates at various growth temperatures with a perspective to investigate the electrical and optical characteristics required for high-power electronic applications. Due to the variation in the vapor pressure of Zn and Ga, severe loss of Zn was observed during pulsed laser deposition, which was solved by using a zinc-rich Zn0.98Ga0.02O target. A pure phase single-crystalline ZGO thin film was obtained at a deposition temperature of 750 °C and an oxygen pressure of 1 × 10−2 Torr. The out-of-plane epitaxial relationship between the sapphire and ZGO thin film was obtained from φ-scan. The x-ray rocking curve of the ZGO thin film grown at 750 °C exhibits a full width at half maximum of ∼0.098°, which indicates a good crystalline phase and quality of the thin film. Core-level x-ray photoelectron spectroscopy of ZGO grown at 750 °C indicated that Zn and Ga were in the 2+ and 3+ oxidation states, respectively, and the atomic ratio of Zn/Ga was estimated to be ∼0.48 from the fitted values of Zn-2p3/2 and Ga-2p3/2. The high-resolution transmission electron microscopy images revealed a sharp interface with the thickness of the ZGO film of ∼265 nm, and the signature of minor secondary phases was observed. The bandgap of the ZGO film at different growth temperatures was calculated from the ultraviolet-diffuse reflectance spectroscopy spectra, and its value was obtained to be ∼5.08 eV for the 750 °C grown sample. The refractive index (n) and the extinction coefficient (k) were determined to be ∼1.94 and 0.023 from the ellipsometric data, respectively, and the real dielectric function (ɛr) was estimated to be ∼6.8 at energy 5 eV. The ultrawide bandgap and dielectric function of ZGO recommend its possible potential applications in deep-ultraviolet optoelectronic devices and high-power electronics. [ABSTRACT FROM AUTHOR]

The precise detection of target substances through refractive-index sensing is essential in various fields such as environmental monitoring, food assessment, and optical applications. This study demonstrates a real-time refractive index sensor based on a liquid-infiltrated metal-insulator-metal island (MIMi) structure in a lithography-free manner. In the MIMi structure, the top layer of the metal islands is formed through solid-state dewetting, which serves as an etching mask to form nanopillars in the insulator layer. This allows for the infiltration of external substances, resulting in different structural colors depending on the refractive index. This design results in a redshift of the resonance peak as the infiltrated refractive index increases. Furthermore, by adjusting the area fraction of the metal-island layer and etching depth of the insulator layer, the resonance-peak position can be controlled within the visible range according to the target refractive index. The advantages of our design are the use of cost-effective materials and the ability to implement scalable fabrication. Our proposed method offers a convenient method to sense the target refractive index in real time. [ABSTRACT FROM AUTHOR]

In this work, we combine the concepts of magnetic circular dichroism, nanocavities, and magneto-optical hyperbolic metamaterials (MO-HMMs) to demonstrate an approach for sensing down to a few molecules. Our proposal comprises a multilayer MO-HMM with a square, two-dimensional arrangement of nanocavities. The magnetization of the system is considered in polar configuration, i.e., in the plane of polarization and perpendicular to the plane of the multilayer structure. This allows for magneto-optical chirality to be induced through the polar magneto-optical Kerr effect, which is exhibited by reflected light from the nanostructure. Numerical analyses under the magnetization saturation condition indicate that magnetic circular dichroism peaks can be used instead of reflectance dips to monitor refractive index changes in the analyte region. Significantly, we obtained a relatively high sensitivity value of S = 40 nm/RIU for the case where refractive index changes are limited to the volume inside nanocavities, i.e., in the limit of a few molecules (or ultralow concentrations), while a very large sensitivity of S = 532 nm/RIU is calculated for the analyte region distributed along the entire superstrate layer. [ABSTRACT FROM AUTHOR]

In this article, we investigate the structural relaxation of lithium silicate glass during isothermal physical aging by monitoring the temporal evolution of its refractive index and enthalpy following relatively large (10–40 °C) up- and down-jumps in temperature. The Kohlrausch–Williams–Watts function aptly describes the up- and down-jump data when analyzed separately. For temperature down-jumps, the glass exhibits a typical stretched exponential kinetic behavior with the non-exponentiality parameter β < 1, whereas up-jumps show a compressed exponential behavior (β > 1). We analyzed these datasets using the non-exponential and non-linear Tool–Narayanaswamy–Moynihan (TNM) model, aiming to provide a comprehensive description of the primary or α-relaxation of the glass. This model described both up- and down-jump datasets using a single value of β ≤ 1. However, the standard TNM model exhibited a progressively reduced capacity to describe the data for larger temperature jumps, which is likely a manifestation of the temperature dependence of the non-exponentiality or non-linearity of the relaxation process. We hypothesize that the compressed exponential relaxation kinetics observed for temperature up-jumps stems from a nucleation-growth-percolation-based evolution on the dynamically mobile regions within the structure, leading to a self-acceleration of the dynamics. On the other hand, temperature down-jumps result in self-retardation, as the slow-relaxing denser regions percolate in the structure to give rise to a stretched exponential behavior. [ABSTRACT FROM AUTHOR]

This paper aims to theoretically examine the phenomenon of modulation instability (MI) in the presence of a considerable nonlinear refractive index movement in a triad-core nonlinear coupler, including a bi-negative refractive material transmission medium. The formula for the instability gain is deduced with the help of the linear stability analysis. The significant role of cubic, quintic, septic, nonic, and stability of the front-to-reverse-transmitting wave nonlinearities in the phenomenon of MI in the nonlinear triad-core coupler is critically confirmed via MI gain spectra analysis. It is found that the cubic, quintic, septic, and nonic nonlinearities improve the MI in both dispersion regimes (normal and anomalous) by boosting the gain and width of the instability profile by taking account of reverse-to-front ratio power (f). On the other hand, quintic nonlinearity improves the MI in the cubic case by enhancing its width and gain in the normal and anomalous dispersion areas. Using 3D pictures, we analyze the dynamic behavior of the MI under an anomalous dispersion area and find that, in both normal and anomalous dispersion scenarios, the instability shape develops with septic and nonic nonlinearity. Furthermore, as the figures clearly show, neither the normal nor the anomalous dispersion scenario significantly changes due to septic and nonic nonlinearity alone. We aim to shed light on the role of contamination in saturation nonlinearity by examining soliton and MI, their production, and control in triad-core couplers, focusing on a Negative Index Meta Material (NIMM) transmission medium. [ABSTRACT FROM AUTHOR]

This mixed study presents the optical properties of gallium nitride material at different conditions and thicknesses over a very wide wavelength range for optical simulations. The availability of optical properties of gallium nitride over a very wide wavelength range facilitates the use of gallium nitride in different simulated optical devices such as laser diodes, LEDs, and other optical and electronic devices. Fitted equations, plotted figures, and MATLAB codes for refractive indices will be presented to reduce mistakes within simulations. [ABSTRACT FROM AUTHOR]

The experimental data of densities, ρ, speeds of sound, u, and refractive indices, nD, are reported for three binary mixtures of acetonitrile + aromatic hydrocarbons, namely: acetonitrile + n-butylbenzene, acetonitrile + sec-butylbenzene and acetonitrile + tert-butylbenzene, respectively, at T = (298.15, 303.15, 308.15, 313.15, and 318.15) K, on the entire composition ranges and under atmospheric pressure, p = 0.1 MPa. The values obtained from experimental measurements have been correlated by the Jouyban-Acree model with good accuracy. The excess molar volumes, V m E , excess speeds of sound, uE, excess isentropic compressibilities, κ S , excess molar isentropic compressibilities, K S , m E , refractive index deviations, ΔnD, and excess molar refractions, R m E , have been calculated from experimental data. For each of the studied mixtures, the excess or deviation properties have been correlated with the Redlich–Kister polynomial equation and the coefficients of correlations were reported. In this manuscript, Perturbed Chain Statistical Associating Fluid Theory Equation of State (PC-SAFT EoS) was used for modeling the density as predictive approach. On the other hand, PC-SAFT + two models were used for calculate the speed of sound of binary mixtures, and PC-SAFT + four mixing rules were used for compute the refractive index of binary mixtures. [ABSTRACT FROM AUTHOR]

The space-and time-averaged velocity profiles in gravel beds show some features that differentiates them from that established in smooth beds, but the obstruction posed by the gravel hampers the experimental measurements below the sediments. To overcome such difficulties, we coupled particle image velocimetry (PIV) with refractive index matching (RIM) by means of substituting the gravel with hydrogel spheres. We applied a superposition of models on the experimental velocity profile: the Darcy, the mixing, the logarithmic, and the wake law models. The resulting analytical profile is adherent to the experimental data in all the regions of the flow, from the bottom to the free surface. After including a second data set from literature, we carried out the dimensional analyses on the parameters in the profile, defining them as functions of the general characteristics of the flow and of the bed. In particular, the position of the inflection point, and thus the relative contribution of the mixing and the logarithmic layers on the overall profile, were found to be related to the permeability Reynolds number. [ABSTRACT FROM AUTHOR]

Purpose: Titanium dioxide (TiO2) has high opacity, high brightness and whiteness, owing to its high refractive index value. It is mainly used in the coating industry and continuous efforts have been made to replace some of the TiO2 in paint with new pigments. This study aims to replace part of TiO2 pigment with various percentages of BaSO4, CaCO3 and kaolin in styrene butyl acrylate-based paint formulations, without changing the properties of paints using only titanium dioxide. Design/methodology/approach: To determine the optimum use rate of new pigment mixing, opacity, gloss, scrub resistance and weather resistance properties have been investigated in the water-based paint formulation. The morphological properties of these samples were examined by scanning electron microscopy analysis. Findings: In the total color change (ΔE) measurements, it was observed that the sample coded 85Ti/15Ba produced extremely similar results to the situation when TiO2 was used alone. It was seen that the best results were obtained when 85Ti/15Ba was used instead of TiO2. Originality/value: Comparison research on the impact of replacing TiO2 with BaSO4, CaCO3 and kaolin on the performance characteristics of water-based styrene butyl acrylate-based paint formulations has not been done in the literature, according to the literature search. [ABSTRACT FROM AUTHOR]

The article describes a new method for determining the complex dielectric permittivity of films, whose thickness is much smaller than the terahertz (THz) radiation wavelength. This method is based on the simultaneous measurement of THz waveforms reflected by and transmitted through the sample-containing films (dual-mode configuration). We present analytical and numerical solutions of the Maxwell equations, which allow to precisely and easily determine the complex material parameters of the films for transverse electric (TE) and transverse magnetic (TM) polarization cases for the arbitrary incident angle of the THz beam. The proposed method reduces the noise contribution related to laser fluctuation, which improves the precision determination of the dielectric permittivity. [ABSTRACT FROM AUTHOR]

Recently, scientists have been interested in developing advanced techniques for technological applications using sustainable biochar (BC) materials. In this study, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, PEDOT/PSS, was doped with 5 wt.% and 10 wt.% of Activated biochar (A-BC) obtained from Chlorophyta (green Algae) using a microwave combustion process. XRD, FTIR, TGA, BET, and SEM were used to analyze the structural properties of PEDOT/PSS@BC. The XRD results demonstrate that A-BC impacts the amorphous nature of PEDOT/PSS, causing the doped composite to have a higher crystalline structure. While measuring dark current density-voltage, it was found that PEDOT/PSS@BC/n-Si showed better-rectifying characteristics compared to pristine PEDOT/PSS/n-Si, with a higher rectification ratio. When A-BC was used, the power conversion efficiency (PCE) was 13.02%, with a short circuit current density (Jsc) of 34.37 mA/cm2, open-circuit voltage (Voc) of 0.65 V, and fill factor (FF) of 58%. These findings demonstrated that using A-BC improved the characteristics of PEDOT/PSS/n-Si devices, and the increase in performance was affected by the concentration of A-BC. A-BC can act as an efficient electron acceptor, facilitating charge transfer and reducing recombination losses. [ABSTRACT FROM AUTHOR]

We have designed and modeled one dimensional narrow-gap aluminum nanogratings for plasmonic sensing of bulk and localized changes in the refractive index in the UV spectral region. The proposed configuration of the plasmonic sensors based on narrow-gap nanogratings allows normally light to be directly coupled into plasmonic waveguide modes in the gaps between the nanogratings, thereby alleviating the problem of employing bulky prism coupling mechanisms. The rigorous coupled wave analysis (RCWA) simulations were performed to optimize all the narrow-gap nanograting parameters such as the periodicity ' P ', the gap between the nanograting walls ' W ', and height ' H ' of the nanogratings such that the plasmonic sensors based on these nanogratings operated in the UV spectral region and had the highest values of sensing performance characteristics. The plasmon resonance related dips in the reflectance spectra of these narrow-groove nanogratings can be tuned in the far-UV and deep-UV wavelength ranges by varying the different structural parameters of these nanogratings. Furthermore, we have defined other performance parameters like FOM bulk * and FOM localized * to account for the depth of the plasmonic resonance dip along with the sensitivity (S) and figure of merit (FOM). These narrow-gap nanogratings have localized regions of high electromagnetic fields inside the gaps between the nanogratings, which results in enhanced sensitivity of the proposed structures. We have calculated the maximum bulk sensitivity (S) of 190 nm RIU−1 with the figure of merit (FOM bulk *) of 2.567 RIU−1 in the UV region. Similarly, the highest localized sensitivity (S s) of 18.2 nm nm−1 and a figure of merit (FOM localized *) of 0.15356 nm−1 was obtained for the narrow-gap aluminum nanograting based plasmonic sensor. The high sensitivity achieved in localized and bulk sensing enables this configuration to be developed into a compact and highly robust sensor for chemical and bio-sensing applications. [ABSTRACT FROM AUTHOR]

The influence of multi‐step sintering at high temperatures was used to meticulously characterize the crystallization, mechanical, and optical properties of a SiO2−Li2O−Al2O3−K2O−P2O5${\rm SiO}_2{-}{\rm Li}_2{\rm O}{-}{\rm Al}_2{\rm O}_3{-}{\rm K}_2{\rm O}{-}{\rm P}_2{\rm O}_5$ glass system with the addition of ZrO2${\rm ZrO}_2$ and Y2${\rm Y}_2$O3${\rm O}_3$. The research began with a novel base glass composition of 3.8 wt% Li2${\rm Li}_2$CO3${\rm CO}_3$, 4.2 wt% K2${\rm K}_2$CO3${\rm CO}_3$, 4.5 wt% Al2${\rm Al}_2$O3${\rm O}_3$, 35 wt% SiO2${\rm SiO}_2$, and 2.5 wt% (NH4)2${({\rm NH}_4)}_2$HPO4${\rm HPO}_4$, to which 47 wt% ZrO2${\rm ZrO}_2$ and 3 wt% Y2${\rm Y}_2$O3${\rm O}_3$ added. The initial glass powder was sintered in two steps at low temperatures. Either 500∘C$^\circ{\rm C}$ for 10 min or 500∘C$^\circ{\rm C}$ for 10 min then a raise to 650∘C$^\circ{\rm C}$ for 20 min was used in the first step. Then, the second step of sintering was done at 850∘C$^\circ{\rm C}$. Finally, after the pellet preparation, final calcination was conducted at 1450∘C$^\circ{\rm C}$. The resulting microstructure was a composite material with various grain components embedded within a glass matrix. The low first sintering temperature triggered the optimum crystal growth, and after the final calcination process, a new glass‐ceramic named ZrSiO4−ZrO2−Zr0.95Y0.066O1.985${\rm ZrSiO}_4{-}{\rm ZrO}_2{-}{\rm Zr}_{0.95}{\rm Y}_{0.066}{\rm O}_{1.985}$–LiAl(SiO3)2${\rm LiAl}{({\rm SiO}_3)}_2$ was synthesized. The synthesized ceramics demonstrated strong diametral tensile strength and excellent Vickers micro‐hardness values, a remarkable refractive index, and optical band gaps larger than 3.1 eV. Consequently, the process of multi‐step sintering at high temperatures clenches the impending manufacture of a novel composite ceramic having remarkable hardness and good optical properties that encourage several biological, technological, and industrial applications. [ABSTRACT FROM AUTHOR]

Research on the improvement of the photoelectric conversion efficiency of solar cells is always the focus. In this paper, an efficient anti-reflection micro/nanostructure is proposed to improve the conversion efficiency of the solar cell. Graded effective refractive index theory is used to achieve the anti-reflection effect while the simulation model is established by FDTD. A specific periodic nanostructure is obtained, which can achieve a good anti-reflection effect. According to the simulation model, the reflectivity of the solar cell is reduced by 0.85% and the transmittance is increased by 0.85% in the band range of 200 nm to 1000 nm. Specifically, high anti-reflection phenomena are obtained in the band range of ultraviolet and blue light, in which the reflectivity is reduced by 1.56% and the transmittance is increased by 1.55%. Based on the simulation results, the array nanostructure is produced by etching the self-assembled polystyrene (PS) microspheres. Finally, the required structure is formed on the silicon wafer by nanoimprinting and etching technology. The reflectivity of 2.8% is obtained on silicon, which can potentially increase the opto-electrical performance of the solar cell. [ABSTRACT FROM AUTHOR]

The experimental data base of scattering matrices of three well-characterized Martian dust analogues with narrow particle size distributions representative of Martian dust aerosols is used to check the the suitability of hexahedra model particles to reproduce the scattering behaviour of realistic polydisperse irregular particles at 488 and 640 nm. In general, the hexahedra model performs well. The scattering matrix elements as functions of the scattering angle can be reproduced with good accuracy for particle size distributions that contain small particles; however, the discrepancies increase with increasing particle size due to wavelength-scale surface roughness and internal structure found within large dust grains that are not accounted for by the smooth hexahedra model particles. We further perform sensitivity tests to study the effect of absorption, real part of the complex refractive index, and particle size distribution within the model to understand their contribution to the modelled scattering matrix elements. By using the best-fitting parameters from the sensitivity study, we have created a data base of optical properties that includes bulk extinction efficiencies, single-scattering albedos, asymmetry factors, extinction cross-sections, and phase matrices of the analogue samples from 200 to 2000 nm. The obtained values can be further used in radiative-transfer simulations. This work emphasizes the importance of accounting for the full scattering matrix as information on particle shape, size, and complex refractive index is lost when omitting polarization. [ABSTRACT FROM AUTHOR]

The synthesis of inverse vulcanized (IV) organic polysulfides under mild conditions offers an effective strategy to reduce energy costs and enhance safety. In this study, we present a tetrabutylammonium fluoride (TBAF)-catalyzed IV process that enables reactions at ambient temperatures. This protocol significantly expands the methodologies available for IV reactions and broadens the potential applications of the resulting polymers. By incorporating 5 wt% TBAF as a catalyst, this method allows the use of both activated and non-activated olefins in IV processes under mild conditions. The method is characterized by low energy consumption, a simple catalyst system, and the elimination of H2S by-products. The synthesized terpolymer of S8, ethylene glycol dimethacrylate (EGDMA), and N,N′-methylene diacrylamide (MBA) exhibits excellent optical transparency, a high refractive index (nav > 1.54), and exceptional ultraviolet (UV) blocking properties across the entire UV range (200–400 nm), while maintaining high transmission in the visible light spectrum. The reaction mechanism was further explored through experimental studies and density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

The optical transparency of silica glass significantly improves when subjected to compression at its melting temperature. Using a rare hydrostatic iso-pressure apparatus capable of reaching 0.98 GPa at 1800 °C with Ar gas as the pressure medium, we obtained centimeter-sized glass samples, allowing us to measure various properties. Both the density and refractive index increased with pressure, while the refractive index dispersion decreased monotonically. However, Rayleigh scattering intensity, and small ring structures show a minimum around 0.8 GPa. High-energy X-ray scattering analysis indicates that the short-range structure, around 4 Å, governs the monotonic trends in the averaged physical properties, such as density and refractive index. In contrast, non-monotonic changes are observed with the disappearance of intermediate-range order at around 8 Å. This simplification of structural ordering is crucial for achieving extreme transparency in silica glass. The effect of suppression of the 8 Å order is well explained by the predicted topological pruning phenomenon, where large voids and small unstable ring structures vanish, leading to the minimal light scattering under high pressure. Our experimental findings also reveal that the optimal pressure for achieving this transparency is much lower than previously predicted, which makes the process more feasible for mass-production applications. There is an urgent need to enhance silica glass transparency for optical fibers. This study achieves this by hot compression above the melting point. Measurements of density, refractive index, Rayleigh scattering, and ring structures reveal two pressure-dependent trends. High-energy X-ray scattering links these to structural changes at ~4 Å (short-range) and ~8 Å (intermediate-range). Notably, optimal enhancement occurs at pressures as low as 0.8 GPa, far below the 4 GPa predicted by molecular dynamics simulations, making the process practical for high-transparency silica glass fiber production. [ABSTRACT FROM AUTHOR]

The interlayer interactions in van der Waals (vdW) materials are imprinted in their low-frequency rigid-layer phonon spectra. Investigating the symmetries of these phonon modes offers a pathway to generate optical anisotropy in the terahertz range. Here, we employ polarization-sensitive terahertz time-domain spectroscopy to study a sample of clinochlore, a naturally abundant, large bandgap vdW mineral. Our measurements revealed a pronounced anisotropic feature in the complex refractive index spectrum near 1.13 THz, consistent with shear modes predicted by our density-functional perturbation theory that accounts for impurities in the mineral. Polarimetry analysis revealed that this shear phonon anisotropy reshapes the polarization state of transmitted terahertz waves, inducing both Faraday rotation and ellipticity. Furthermore, we applied Jones formalism to interpret the phononic symmetries and describe our observations in terms of its polarization eigenstates. These results highlight the potential of exploring vdW minerals as central building blocks for vdW heterostructures with compelling technological applications. [ABSTRACT FROM AUTHOR]

Guanine crystals with a high refractive index (1.85) are widely applied as optical materials in organisms. However, the synthesis of colored guanine crystalline plates doped with different kinds of commercial organic molecules still remains challenging. In this work, guanine crystalline microplatelets with different colors and pearlescent luster were synthesized by doping cationic or molecular dyes into guanine crystals. The synthesized dye-doped guanine crystals were pure β-form anhydrous guanine (β-AG) single crystalline microplatelets and exposed the (100) plane similar to those of biological guanine crystals. Dye-doped β-AG crystals exhibited various colors, such as red, yellow, green, blue and purple, and their aqueous dispersions exhibited bright pearlescent luster. We doped different organic molecules into the crystal lattices and obtained single crystalline β-AG microplatelets with superior pearlescent luster. It was observed that both cationic and neutral molecular dyes with small molar volume could be easily doped into guanine crystals, and the preferential exposure of the (100) plane of guanine crystalline microplatelets was not affected. Moreover, the diffuse reflection intensities of most dye-doped β-AG crystals were up to 80% in the near-infrared band. Overall, dye-doped β-AG microplatelets with brilliant colors, high reflectivity and pearlescent luster are multifunctional composite materials, which possess broad application prospects in the fields of displays, inks and pearlescent pigments. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents are an exciting class of designer solvents that are increasingly gaining popularity. Deep eutectic solvents based on amino acids are particularly interesting for biomedical applications due to their potential low toxicity. However, very few have been reported to date, and only one of these has been comprehensively studied, made from a combination of proline and glycerol. Here, we report for the first time a systematic investigation into amino acid-based deep eutectic solvents, with a particular focus on the structural features of amino acids that promote eutectic formation and their influence on viscosity, refractive index, surface tension and thermal behavior. Of the 22 amino acids (and related compounds) examined, only 3 (lysine, arginine and, as previously reported, proline) formed stable homogenous liquids in combination with glycerol or ethylene glycol. For these mixtures, it was found that the second component (glycerol or ethylene glycol) had a much more significant influence on the physical properties than the identity of the amino acid. Most significantly, it was found that far fewer amino acids readily formed deep eutectic solvents than has been generally assumed. This is the first work to systematically characterize deep eutectic solvents based on amino acids and, as such, paves the way for future biomedical applications of these solvents. [ABSTRACT FROM AUTHOR]

Six novel urethane-dimethacrylates with quaternary ammonium groups (QAUDMAs) were successfully synthesized from 2-(methacryloyloxy)ethyl-2-hydroxyethylmethylalkylammonium bromide (QAHAMA-n, where n was 8 and 10) and diisocyanate (isophorone diisocyanate (IPDI), 4,4′-methylenedicyclohexyl diisocyanate (CHMDI), and 4,4′-diphenylmethane diisocyanate (MDI)). Their chemical structures were confirmed through nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). The refractive index (RI) and density (dm) were also determined. The novel QAUDMAs were compounded with common dental dimethacrylates and subsequently photopolymerized. The resulting copolymers, comprising QAUDMA 40 wt.%, bisphenol A glycerolate dimethacrylate (Bis-GMA) 40 wt.%, and triethylene glycol dimethacrylate (TEGDMA) 20 wt.%, were tested for water sorption (WS) and solubility (SL). The WS and SL values decreased following these orderings based on the diisocyanate: IPDI > CHMDI > MDI for WS, and MDI > CHMDI > IPDI for SL. The WS values ranged from 11.50 to 13.82 µg/mm3, and were significantly lower than the recommended maximum for dental materials, 40 µg/mm3. The SL values that met the recommended maximum, 7.5 µg/mm3, ranged from 2.67 to 6.75 µg/mm3. Only the copolymer having the QAHAMA-8- and MDI-derived QAUDMA had the SL slightly exceeding 7.5 µg/mm3, at 7.89 µg/mm3. [ABSTRACT FROM AUTHOR]

This work presents a novel design for an asymmetric loop-terminated Mach–Zehnder interferometer (a-LT-MZI) based on a silicon-on-insulator (SOI) platform, tailored for refractive index (RI) sensing applications. A significant advantage of incorporating the Sagnac loop into the MZI configuration is its ability to reduce the interferometer's effective length by half, offering a more compact design. This makes it ideal for integration into miniaturized optical devices, enabling space-efficient configurations without compromising precision or performance. The proposed device, featuring a pathlength difference (∆L) of 24.35 µm demonstrates a sensitivity of 261 nm/RIU, which is further enhanced to 510 nm/RIU by incorporating a subwavelength (SWG) waveguide in the asymmetric sensing arm. This modification boosts light–matter interaction, resulting in a larger shift in the interference fringes and significantly improving the sensor's performance. [ABSTRACT FROM AUTHOR]

As a kind of important functional device, terahertz metamaterial absorbers (TMA) have been focused on by many researchers for their capacity to absorb electromagnetic waves and wide application fields. In this work, we designed a terahertz metamaterial absorber with narrow-band absorption for refractive index sensing, which consisted of a circular metal ring resonator and a square metal ring resonator. The simulation results show that the absorptivity of the proposed TMA reached over 68.8% and 93.27% at 1.926 and 4.413 THz, respectively. Moreover, the absorption mechanism was studied through the electromagnetic field energy distribution, and the influence of structural parameters on absorption performance was exhibited. In refractive index sensing, a high sensitivity (S) of 2.537 THz/RIU (refractive index unit, RIU) was achieved by utilizing the coupling of ring resonators. The maximal quality factor (Q-factor) and figure of merit (FOM) of the TMA were 234.73 and 147.67 RIU−1, respectively. Additionally, we established an RLC equivalent circuit model (ECM) for the TMA, and we further illustrated the performance of the TMA in refractive index sensing through fitting the sensitivity based on the ECM to the sensitivity of the TMA. Our study exhibits the considerable potential application for the field of terahertz sensing, and the ECM for refractive index sensing will be helpful for continual investigation. [ABSTRACT FROM AUTHOR]

Total internal reflection generally occurs at incident angles beyond the critical angle, confining electromagnetic waves in dielectrics with higher refractive indices. In this work, we present a metasurface-based solution to transform such total reflection into high-efficiency transmission. We demonstrate that a phase-gradient antireflection metasurface designed on the dielectric surface not only compensates for the transverse wave vectors of the incident and transmitted waves but also addresses the impendence mismatch between the two media, eventually achieving high-efficiency transmission with flexibly-controlled wavefronts beyond the critical angle. The design of this unique metasurface is enabled by applying the reciprocity principle to circumvent the traditional limitation of total internal reflection. The theory and functionalities of the phase-gradient antireflection metasurfaces are verified through both simulations and microwave experiments. Our work opens a new avenue for high-efficiency radiation manipulation beyond the critical angle, enabling rich applications such as high-efficiency waveguide-to-free-space couplers, high-radiation-efficiency quantum dots, and high-radiation-efficiency light-emitting diodes. [ABSTRACT FROM AUTHOR]

Bragg gratings are crucial components in passive photonic signal processing, with wide-ranging applications including biosensing, pulse compression, photonic computing, and addressing. However, the design of integrated waveguide Bragg gratings (WBGs) for arbitrary wavelengths presents significant challenges, especially when dealing with highly asymmetric layer stacks and large refractive index contrasts. Convenient approximations used for fiber Bragg gratings generally break down in these cases, resulting in nontrivial design challenges. In this work, we introduce a general simulation and design framework for WBGs, which combines coupled mode theory with three-dimensional finite-element method eigenfrequency computations. This approach allows for precise design and optimization of WBGs across a broad range of device layer stacks. The design flow is applicable to further layer stacks across nearly all wavelengths of interest, given that the coupling between the forward and backward propagating mode is dominant. [ABSTRACT FROM AUTHOR]

The actual techniques allowing the fabrication of waveguides in lithium niobate are not able to satisfy one of the demands of modern integrated photonics namely the well-controlled tunability of index contrast over a large range of values (from high-index contrast to low index contrast). This paper presents a simple and reliable method allowing well-controlled index contrast tunability between high-index contrast (Δne = 0.1) and low-index contrast (Δne = 0.035) while benefiting from the optical nonlinearity of LiNbO3 waveguides fabricated using HiVac-VPE technique. The study involves both planar and channel lithium niobate waveguides. The planar waveguides subjected to an annealing process for 1 to 5.5 h, are characterized before and after the thermal treatment, in order to determine the index contrast evolution and to analyze the changes of index profile shapes. Furthermore, it is found that the index profile after annealing is fitted by an exponential function different from Gaussian fit found in well-known Annealed Proton Exchange technique. Additionally, the index contrast dependence of the annealing time is also fitted by an exponential function. Channel waveguides, fabricated in the same condition, were designed for single-mode propagation at telecom wavelength. After characterization, the best of investigated annealed channel waveguides exhibits propagation losses around 1.5 ± 0.1 dB/cm. Therefore, the presented technique offers the opportunity for customization of photonics circuitry, scalability of integrated photonics platform, enhancement of non-linear optical efficiency at the single photon level for quantum information platforms. [ABSTRACT FROM AUTHOR]

Inorganic electrochromic materials (ECMs) hold great promise for display applications due to their superior stability. However, their limited color modulation range remains a significant challenge. In this study, we employ a simple and efficient anodization process to incorporate structural colors into ECMs, achieving full-color displays. The fabricated WO3–W films exhibit diverse structural colors and demonstrate broad color modulation capabilities during the electrochromic process with the main peaks/troughs in the reflectance spectra shifting by up to 240 nm. These broad color transitions are attributed to the variations in the optical parameters of the anodized WO3 layer, including a maximum refractive index change of 0.66 (550 nm reference wavelength) and a maximum thickness expansion of 18%. These variations, driven by the insertion of guest ions, can be precisely controlled by the applied reduction potential. Our research offers technological approaches and theoretical insights for the application of inorganic ECMs in the domain of colorful displays. [ABSTRACT FROM AUTHOR]

Cervical cancer belongs to the most dangerous types of cancers posing considerable threat to women's survival. It is most often diagnosed in the advanced stages as precancerous lesions are often symptom-free and difficult to identify. Microwave imaging, especially in terahertz (THz) range, is a convenient and noninvasive cancer detection tool. It enables characterization of biological tissues and discrimination between healthy and malignant ones. This study presents a novel triple-band biosensor based on metamaterials (MTMs). By leveraging unique properties of MTMs, the proposed biosensor operates as a perfect absorber. It exploits resonant modes in the THz spectrum to achieve remarkable sensitivity. Meticulous selection of the sensor geometry and dimensions enables efficient miniaturization. Meanwhile, utilization of frequency-domain data to detect refractive index changes improves resolution of cancerous tissue identification. Extensive numerical investigations corroborate its ability to carry out reliable early-stage cervical cancer diagnosis. This includes identification of the spatial extent of the malignant tissue. Excellent electrical properties of the sensor are accompanied by its compact size, which is highly desirable for non-invasive and portable applications. [ABSTRACT FROM AUTHOR]