Search Results (180)

Highly saturated structural colors are crucial for the micro-nanophotonic displays. However, achieving Schrödinger’s red pixels remains a challenge due to the difficulty in suppressing higher-order resonances in the blue-green wavelength band. In this paper, we utilize the TuRBO algorithm for global physical parameter optimization of periodic ${\mathrm{Sb}}_2{\mathrm{S}}_3$ nanopillar metasurface structures to realize the high-saturation red. Based on the intrinsic dispersion characteristics of ${\mathrm{Sb}}_2{\mathrm{S}}_3$ characterized by high extinction coefficients in the blue-green wavelength band, the high-saturation Schrödinger’s red that surpasses the Adobe RGB boundary has been produced successfully. The calculated results show that after 45 iterations, the structure achieves gradient refractive index matching, aligning the intrinsic dispersion of ${\mathrm{Sb}}_2{\mathrm{S}}_3$ with the ideal reflection spectrum of Schrödinger’s red pixels, thereby effectively suppressing higher-order resonances in the blue-green wavelength band. Ultimately, an ultra-high saturation red is achieved with CIE coordinates of (0.6507, 0.3043) in the CIE chromaticity space. Full article

While the recently developed tissue clearing protocols pathoDISCO and activeDISCO significantly accelerate the clearing of large tissue specimens through active chemical dehydration using 2,2-dimethoxypropane, the final step of refractive index (RI) matching with viscous organic solvents as dibenzyl ether (DBE) remains restricted by slow passive diffusion. To overcome this bottleneck, we applied 40 kHz ultrasound using a standard, cost-effective laboratory bath to significantly enhance the diffusion kinetics of the clearing medium into large specimens. Our investigation on multi-centimeter-sized porcine muscle and human earlobe samples demonstrates that 40 kHz acoustic oscillations generated by a standard ultrasound cleaning device not only accelerate the clearing process but also yield superior and stable long-term optical transparency. We also tested 1 MHz high-frequency ultrasound but it offered no kinetic advantages and tended to induce tissue micro-fractures, an artifact we have not observed at 40 kHz at comparable energy levels. We therefore propose that standard 40 kHz ultrasound baths, ubiquitous in laboratories for cleaning purposes, represent an ideal and accessible tool for optimizing solvent-based tissue clearing. Full article

We propose an absorber composed of graphene and vanadium dioxide (VO₂). The phase transition of VO₂ enables dynamic switching of the absorption response between a single broadband state and three narrowband states. The results indicate that when VO₂ changes to the metallic state, the absorber exhibits triple narrow band absorption. When VO₂ is in the dielectric phase, the absorber demonstrates single broadband absorption. The absorption can be regulated through the Fermi energy level (E_F) of graphene. Furthermore, the proposed absorber exhibits polarization-independent characteristics and maintains stable absorption performance under wide-angle oblique incidence. The absorber also has high refractive index sensitivity. Impedance matching theory is employed to investigate the physical mechanism governing the absorber. The tuning principle of the device was analyzed and verified successfully by using an equivalent circuit model (ECM). Full article

Total internal reflection (TIR) loss is a critical bottleneck limiting light extraction in AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs), primarily due to the large refractive-index contrast at the light-emitting interface. Here, pyramid-shaped dielectric metasurfaces are designed and fabricated at the sapphire/air interface of flip-chip AlGaN-based DUV LEDs using a scalable nanoimprinting process. The metasurface functions as a light outcoupling layer that modifies the interfacial momentum-matching condition and redistributes photon propagation directions. Experimental results and theoretical simulations show that metasurfaces with different feature sizes enhance light extraction through distinct mechanisms. The subwavelength pyramid nanoarray perturbs the local optical field and provides additional in-plane momentum components, facilitating the coupling of high-angle photons into radiative channels, whereas the larger pyramid void structure mainly promotes photon extraction through geometrical redirection, tilted output interfaces, and dry-etching-induced rough surface scattering. As a result, an average light output power (LOP) enhancement of over 8% is achieved for AlGaN-based DUV LEDs emitting at approximately 275 nm. This work demonstrates a low-cost, scalable, and effective strategy for enhancing the LEE of DUV LEDs, with promising potential for high-efficiency ultraviolet optoelectronic application. Full article

Background: Eosinophilic esophagitis (EoE) is a chronic immune-mediated disease that is increasingly recognized as a systemic inflammatory condition. Its potential association with subsequent coded ocular diagnoses has not been well characterized in large-scale longitudinal studies. Methods: We conducted a retrospective cohort study using the TriNetX Global Collaborative Network, which aggregates de-identified electronic health records from multiple international healthcare systems. Adults aged ≥18 years with at least two clinical encounters between 2005 and 2024 were included. Patients with EoE (ICD-10-CM K20.0) were identified as the exposure cohort, while individuals undergoing routine health examinations without EoE served as controls. Those with prior ocular disease, malignancy, or death were excluded. Propensity score matching (1:1) was used to balance demographics, body mass index, comorbidities, medication use, and socioeconomic factors. The primary outcomes were coded ocular diagnostic categories identified using ICD-10-CM codes. To reduce the likelihood of including pre-existing conditions, ocular disease events diagnosed within 3 months after the index date were excluded from the analysis. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated. Sensitivity analyses incorporated alternative exposure definitions, washout periods, and follow-up durations, with additional stratification by age, sex, and race. Results: After matching, 64,613 patients were included in each cohort. EoE diagnostic coding was associated with a higher subsequent occurrence of several coded ocular diagnostic categories, including visual disturbance and blindness (HR = 1.521; 95% CI: 1.383–1.673), disorders of refraction and accommodation (HR = 1.324; 95% CI: 1.188–1.474), lacrimal system disorders (HR = 1.504; 95% CI: 1.274–1.775), cataract (HR = 1.637; 95% CI: 1.384–1.935), glaucoma (HR = 1.463; 95% CI: 1.157–1.849), and disorders of the vitreous body and globe (HR = 1.903; 95% CI: 1.510–2.399). These findings should be interpreted cautiously because several outcomes, such as visual disturbance, disorders of refraction and accommodation, and ocular pain, were broad diagnostic categories and may be susceptible to detection or coding practices. Conclusions: In this large-scale EHR-based cohort study, EoE diagnostic coding was associated with a higher subsequent occurrence of several coded ocular diagnostic categories. These findings should be interpreted as exploratory associations rather than evidence of direct causal or mechanistic relationships, particularly for broad or detection-prone outcomes such as visual disturbance, disorders of refraction and accommodation, and ocular pain. Full article

The fading of painted relics is a widespread deterioration phenomenon in ancient painted cultural relics, yet its underlying mechanism has long been attributed solely to pigment oxidation. Directed at colored drawings with complex surface microstructures, such as pottery paintings, wall murals and architectural paintings, here we challenge this view by demonstrating that light scattering induced by sub-micron pores within the paint layer plays a dominant role, especially Mie scattering when pore sizes approach visible light wavelengths (400–700 nm). In order to minimize the damage to the genuine painted relics, a large number of simulated experiments were conducted first. Using porous polyacrylamide (PAM) membranes and nylon 6 filter membranes as model systems, we show that pore-induced scattering reduces the optical path length for light absorption, leading to a significant decrease in color saturation and brightness. By filling the pores with non-volatile colorless ionic liquids ([BMIM]PF₆) (n = 1.41) or glycerol (n = 1.47)—both possessing refractive indices close to those of the pigments—the scattering is effectively suppressed, and the original color is restored. The filling treatment reduces the color difference (ΔE*ab) by 30%–50% and the surface reflectivity by 20%–40%. Mercury intrusion porosimetry and fluorescence spectroscopy confirm that pore elimination and optical path lengthening are responsible for the color recovery. The proposed mechanism and restoration strategy were successfully validated on authentic painted brick fragments from the Western Qing Tombs (Hebei, China), where severely faded green and red patterns reappeared after ionic liquid treatment. This study provides a new interface-regulation paradigm for the conservation of painted cultural heritage, shifting the focus from irreversible chemical remediation to reversible physical restoration and offers a generalizable platform for controlling light scattering in porous optical materials. Full article

Background: Whether congenital cataract-related visual deprivation and subsequent rehabilitation are associated with retinal structural and vascular network differences remains unclear. This study evaluated superficial retinal vascular network descriptors and retinal nerve fiber layer (RNFL) thickness in children after bilateral congenital cataract extraction and secondary intraocular lens implantation. Methods: Age-matched children served as controls. Participants underwent spectral-domain optical coherence tomography (OCT) and 6 × 6 mm optical coherence tomography angiography (OCTA). Metrics were magnification-corrected, and comparisons used generalized estimating equation models adjusted for age, eye side, axial length, and spherical equivalent. Results: Eighteen pseudophakic children (36 eyes; median age, 8 years) and 17 controls (34 eyes; median age, 9 years) were included. In adjusted models, macular mean vessel diameter was higher in pseudophakic eyes (β = 11.16 µm; p = 0.003), as was macular mean tortuosity (β = 0.032; p = 0.001). Branchpoint density was lower in direction but not independently significant (p = 0.125). Choroidal thickness, choroidal vascularity index, and foveal avascular zone area did not differ significantly. Temporal RNFL thickness was greater in pseudophakic eyes (β = 13.37 µm; p = 0.007); other RNFL parameters were not significant. Conclusions: These findings suggest exploratory differences in superficial vascular network morphology and temporal RNFL thickness. However, because the groups differed clinically in best-corrected visual acuity, refractive status, and axial length, residual confounding cannot be excluded despite magnification correction and adjusted modeling. Full article

A simplified design framework for narrowband terahertz thermal emitters based on a resonant Salisbury-type structure is investigated numerically. The structure consists of a metallic backreflector, a dielectric spacer, and a thin resonant layer with a Lorentz-type dielectric response. Using the transfer matrix method, we show that matching the intrinsic resonance of the resonant layer with an interference resonance of the Salisbury structure enables selective enhancement of a single emissivity peak without requiring time-consuming full-wave optimization at the initial design stage. The influence of spacer thickness, refractive index, and resonance strength on the spectral response is analysed, providing simple guidelines for tuning the emission frequency and suppressing parasitic peaks. A realistic implementation based on a graphene metamaterial layer on a silicon spacer is also investigated using finite-element simulations to demonstrate the applicability of the proposed design concept. The obtained emissivity and thermal emission spectra show that the approach can be used for the efficient design of spectrally selective terahertz thermal emitters in the 10–40 THz range. Full article

We propose a novel silicon-based THz Mach–Zehnder interferometer (MZI) biosensor integrated with a polarization splitter and rotator (PSR). An optimized PSR is positioned at the input of the MZI, enabling arbitrary polarization inputs to be converted into the same TE mode, which eliminates the dependence of conventional MZI sensors on the input light polarization. The PSR structural parameters are optimized using 3D-FDTD simulations to achieve phase matching, and the calculation results show that efficient TM–TE-polarization conversion occurs along a coupling length of 22.9 mm. Furthermore, the PSR achieves a maximum TE-mode extinction ratio of −30.1 dB and a polarization conversion efficiency of 82.33% in the 0.44 to 0.45 THz range, effectively maintaining the polarization consistency of light entering the MZI. Meanwhile, the characteristic frequency shows a regular blue shift with increasing external refractive index, and the final results demonstrate that the designed MZI biosensor achieves a high sensitivity of 13,215.81 nm/RIU near the center frequency of 0.45 THz. All results presented in this work are obtained through numerical simulations, and experimental validation as well as analyte-concentration-dependent refractive index characterization will be addressed in future studies. To sum up, we propose a high-sensitivity terahertz MZI biosensor featuring a PSR with an on-chip integration scheme, which supports arbitrary polarization inputs and offers a highly integrated solution for specific detection in biomedicine. Full article

The integration density of photonic integrated circuits is fundamentally limited by evanescent field overlap and subsequent inter-channel crosstalk. Layered transition metal dichalcogenides (TMDCs) bypass these confinement constraints through intrinsic optical birefringence and high refractive indices. Here, we report the near-infrared optical constants and waveguide dispersion of molybdenum diselenide (MoSe₂). Ellipsometry performed on centimeter-scale crystals yields an in-plane refractive index of 4.1–4.7 over 1000–2000 nm, with an extinction coefficient close to the sensitivity limit of the fit away from strong excitonic resonances. To validate the anisotropic dielectric tensor at the device scale, scattering-type scanning near-field optical microscopy (s-SNOM) was utilized to map the propagation of transverse-magnetic modes in 235 nm thick exfoliated flakes. Spatial Fourier analysis of the edge-scattered near-field interference yields effective mode indices that precisely match the modeled dispersion. Using the verified dielectric tensor, finite-element simulations demonstrate that single-mode MoSe₂ waveguides optically outperform equivalent tungsten disulfide (WS₂) benchmarks. The enhanced evanescent field suppression in the claddings of MoSe₂ waveguide increases the coupling length by a factor of 3.5, reducing the required routing pitch and enabling a 12.5% direct increase in on-chip integration density. The results identify MoSe₂ as a high-index anisotropic platform for compact waveguiding in the near-infrared. Full article

Flow over permeable beds is important in sediment transport and mixing processes, yet detailed velocity and stress measurements remain difficult to obtain, particularly close to the sediment–water interface (SWI). In this work, we use refractive-index-matched PIV to study turbulent open-channel flow over and within a permeable bed composed of monodisperse borosilicate glass beads. Measurements are reported for three low-$R{e}_K$ cases, $R{e}_K=0.224$, $R{e}_K=0.335$, and $R{e}_K=0.360$, to resolve the mean velocity structure and the associated viscous, turbulent, Reynolds, and dispersive stress distributions. The results show that both the mean velocity and the turbulence intensity decrease rapidly below the SWI, indicating strong damping within the porous bed. Above the bed, the flow retains a boundary-layer structure, and increasing $R{e}_K$ enhances the turbulence intensity without changing the overall regime. The results indicate a shift from turbulent transport above the bed to viscous control within the porous layer, while dispersive stresses peak near the interface. Overall, the SWI controls momentum exchange within a thin region and the porous bed suppresses turbulence penetration into the subsurface. Full article

The development of phase change materials (PCMs) for window applications with both high optical transparency and effective temperature regulation is crucial for passive energy saving. However, liquid leakage during phase transition and enhanced interfacial light scattering often cause fluctuations in optical transmittance and deterioration of image clarity. To address these challenges, a highly transparent phase change composite was constructed via a microencapsulation strategy. Submicron core–shell microcapsules were fabricated using n-octadecane as the core and silica as the shell, enabling effective encapsulation of the liquid PCM component. The resulting microcapsules exhibited a high melting enthalpy of 155.3 J g⁻¹. They were subsequently homogeneously dispersed within a refractive-index-matched polymer matrix, mitigating light scattering during phase transition by reducing interfacial refractive index mismatch. The composite exhibited favorable thermal energy storage capability and transmittance performance, with a visible light transmittance of 83.75% and a transmittance fluctuation of only ~5% before and after phase transition. After 100 thermal cycles, the optical attenuation remained as low as 0.35%, demonstrating excellent cycling stability. This work provides a new strategy for balancing optical transparency and phase change function, with potential applications in smart windows and flexible electronics. Full article

With the increasing application of novel glass materials in the field of optics, traditional empirical and trial-and-error approaches to glass development are gradually becoming insufficient to meet escalating performance demands. In this study, we propose a neural network-based machine learning method for the design of advanced fluoride glass materials. Predictive models for density and refractive index were first developed based on online fluoride glass datasets. Moreover, SHapley Additive exPlanations (SHAP) analysis was adopted to uncover the quantitative composition-property relationship. Then, the well-trained model was employed for inverse design, identifying specific compositions that fulfill desired properties in terms of density and refractive index. Finally, several recommended compositions were experimentally validated and the measured density and refractive index matched well with the corresponding input values, thereby confirming the effectiveness of the proposed method in designing new fluoride glass materials. Full article

The use of additive manufacturing for rapid prototyping of near-infrared and terahertz components provides seamless and error-free production. This article discusses the additive manufacturing and post-processing of axicons and their performance evaluation using attenuation and near-field-measurements based fundamental techniques. The axicons are manufactured using the materials cyclic olefin copolymer (TOPAS) and polymethyl methacrylate (PMMA), for their respective use in terahertz and near-infrared applications. The optical and terahertz components manufactured using traditional 3D-printing processes, e.g., fused filament fabrication or stereolithography apparatus exhibit high surface roughness in the range of 15 ± 2.5 µm, resulting in undesired propagation and scattering in the near infrared wavelengths. This research work proposes an economical post-processing technique for additively manufactured terahertz and near-infrared axicons for applications in multispectral characterization, e.g., bio-sensing. The authors used an enhanced method of dip-coating, which involves interval dipping and intermittent hardening to achieve better surface finish. An emphasis is placed on interval dipping and intermittent hardening, which lead to excellent transparency in case of additively-manufactured near-infrared axicons. The dip-coated samples exhibit surface roughness below 10 nm. With the use of heated resin material as the coating layer, due to reduced viscosity, the resin material distributes uniformly over the surface of the 3D-printed terahertz and near-infrared axicons. The authors also observed that the DOF length deviation between unprocessed and enhanced dip-coated axicons remains within the measurement error estimation from analytical calculations. In addition to the improved surface finish and transparency, the coatings are also closely matched in refractive index to the axicon material. Such post-processed axicons pave the way for producing a wide array of systems in the fields of communication, imaging, and bio-sensing. Full article

The aim of this review is to explore the improvement in diffraction efficiency, photosensitivity and pressure sensitivity in holographic materials containing glycerol. Glycerol is a well-known, non-toxic, water-soluble polyol compound. Glycerol polymers have attracted increased attention recently due to the diversity of the available compositions. Glycerol provides access to a range of monomers for subsequent polymerizations. Various glycerol containing polymers, including polyvinyl alcohol films, polyesters, polyethers and polycarbonates, have been investigated for different applications. It was discovered in 2009 that the addition of glycerol to the composition of water-soluble holographic photopolymers facilitates the faster formation of holograms due to greater photosensitivity. It was also discovered that the presence of glycerol in holographic photopolymers makes them highly pressure-sensitive. A new family of holographic photopolymer materials, containing glycerol and capable of recording holograms with bright reflections, was reported. The novel photopolymers are composed of glycerol, a polymeric binder, a crosslinking monomer, an initiation system, and sensitising dyes. No wet-processing of holograms is necessary. Each holographic photopolymer film contains bis-acrylamide (BA) monomer in polyvinyl alcohol matrix, triethanolamine and methylene blue dye solution, glycerol and water. It was shown that the new holographic material is capable of reaching a refractive index modulation matching that of the well-known acrylamide photopolymer material, but more quickly. The new holographic photopolymer materials are cheap and environmentally friendly. The use of glycerol to improve diffraction efficiency, photosensitivity and pressure sensitivity in holographic recording layers continues to expand. This review describes the development and applications of glycerol-containing photopolymer materials. An environmentally friendly diacetone-based photopolymer was developed. The positive effect of glycerol on N-vinylpyrrolidone photopolymer was investigated. Finally, potential opportunities for future research in the area of glycerol-containing photopolymers are outlined. Full article