High Refractive Index Research Articles

Anthocyanins of Delonix Regia Floral Petals: A Novel Approach on Fluorescence Enhancement, Forster Resonance Energy Transfer Mechanism and Photostability Studies for Optoelectronic Applications.

In this work, we focused on extracting the anthocyanin dye in acetone, butanol, ethanol, and water solvents from Delonix regia flowers by a simple maceration extraction process. The identification of functional group analysis, vibrational studies, energy transfer mechanisms, optoelectronic properties, photostability studies, FRET-assisted potential light emissions and photometric properties of the anthocyanin dyes are successively investigated. FTIR spectroscopy and vibrational studies have confirmed the existence of polyphenolic groups in 2-phenyl chromenylium (anthocyanin) dyes. The optoelectronic results show the least direct bandgap (2.04eV), indirect bandgap (1.55eV), Urbach energy (0.380eV), high refractive index (1.20), dielectric constant (2.794), and high optical conductivity (1.954 × 103 S/m) for the anthocyanin dye extracted found in water solvent. The photoluminescence properties such as Stoke's shift, high quantum yield, and lifetime results show that anthocyanin dyes are promising candidates for red-LEDs and optical materials. The absorption and emission spectra of the anthocyanin dyes follow the mirror image rule and the Franck-Condon factor exists between vibrational energy levels corresponding to all the electronic transitions. The excellent correspondence between the absorption and emission spectra reinforces that the anthocyanins are efficient (46%) FRET probes. Further, photometric properties such as CIE, CRI, CCT and colour purity results of anthocyanins in all studied solvents revealed that this material exhibits orange to red shades (x = 0.48 → 0.54 and y = 0.36 →0.45) and is well suitable for have great potential in the manufacturing of Organic-LEDs and other optoelectronic device applications.

Bio‐Inspired Crystalline Core‐Shell Guanine Spherulites

AbstractSpherical particles with diameters within the wavelength of visible light, known as spherulites, manipulate light uniquely due to their spatial organization and their structural birefringence. Most of the known crystalline spherulites are branched, and composed of metals, alloys, and semi‐crystalline polymers. Recently, a different spherulite architecture was discovered in the vision systems of decapod crustaceans ‐ core‐shell spherulites composed of highly birefringent (Δn ∼ 30%) organic single‐crystal platelets, with exceptional optical properties. These metastructures, which efficiently scatter light even in dense aqueous environments, have no synthetic equivalence and serve as a natural proof‐of‐concept as well as synthetic inspiration for thin scattering media. Here, we present the synthesis of core‐shell spherulites composed of guanine crystal platelets (Δn ∼ 25%) in a two‐step emulsification process in which we use a water/oil/water emulsion and induced pH changes to promote interfacial crystallization. Carboxylic acids neutralize the dissolved guanine salts to form spherulites composed of single, radially stacked, β‐guanine platelets, which are oriented tangentially to the spherulite surface. Using Mie theory calculations and forward scattering measurements from single spherulites, we find that due to the single‐crystal properties and orientation, the synthetic spherulites possess a high tangential refractive index, similarly to biogenic particles.This article is protected by copyright. All rights reserved

Ar transport and blister growth kinetics in titania-doped germania-based optical coatings

Blistering is a phenomenon sometimes observed in sputtered-deposited thin films but seldom investigated in detail. Here, we consider the case of titania-doped germania (TGO)/silica multilayers deposited by ion beam sputtering. TGO is a candidate as high refractive index material in the Bragg mirrors for the next iteration of gravitational waves detectors. It needs to be annealed at 600 ∘C for 100 h in order to reach the desired relaxation state. However under some growth conditions, in 52-layer TGO/silica stacks, blistering occurs upon annealing at a temperature near 500 ∘C, which corresponds to the temperature where Ar desorbs from TGO. In order to better understand the blistering phenomenon, we measure the Ar transport in single layers of TGO and silica. In the case of < 1 µm-thick TGO layers, the Ar desorption is mainly limited by detrapping. The transport model also correctly predicts the evolution of the total amount of Ar in a 8.5 µm stack of TGO and silica layers annealed at 450 ∘C, but in that case, the process is mainly limited by diffusion. Since Ar diffusion is an order of magnitude slower in TGO compared to silica, we observe a correspondingly strong accumulation of Ar in TGO. The Ar transport model is used to explain some regimes of the blisters growth, and we find indications that Ar accumulation is a driver for their growth in general, but the blisters nucleation remains a complex phenomenon influenced by several other factors including stress, substrate roughness, and impurities.

Synthesis of Structure-Adjustable R-Au/Pt-CdS Nanohybrids with Strong Plasmon Coupling and Improved Photothermal Conversion Performance

Noble metal nanomaterials with a localized surface plasmon resonance effect exhibit outstanding advantages in areas such as photothermal therapy and photocatalysis. As a unique plasmonic metal nanostructure, gold nanobipyramids have been attracting much interest due to their strong specific local electric field intensity, large optical cross sections, and high refractive index sensitivity. In this study, we propose a novel three-component hetero-nanostructure composed of rough gold nanobipyramids (R-Au NBPs), Pt, and CdS. Initially, purified gold nanobipyramids are regrown to form R-Au NBPs that have a certain degree of roughness. These R-Au NBP substrates with a rough surface provide more hotspots and strengthen the intensity of localized electric fields. Subsequently, Pt and CdS nanoparticles are selectively deposited onto the surface of R-Au NBPs. Pt nanoparticles can provide more active sites. Each component of this hetero-nanostructure directly contacts others, creating multiple electron transfer channels. This novel design allows for tunable localized plasmon resonance wavelengths ranging from the visible to near-infrared regions. These factors contribute to the final superior photothermal conversion performance of the R-Au/Pt-CdS nanohybrids. Under the irradiation of near-infrared light (1064 nm), the photothermal conversion efficiency of R-Au/Pt-CdS reached 38.88%, which is 4.49, 1.5, and 1.22 times higher than that of Au NBPs, R-Au NBPs, and R-Au NBPs/Pt, respectively.

Characterization and the physical properties of nano-sized Bi2O3/polymer for energy and high-refractive index applications

The present work focuses on developing nanocomposites for optoelectronics and energy storage devices leveraging the unique physicochemical features of bismuth (III) oxide (Bi2O3) using a polyvinyl pyrrolidone/polyvinyl alcohol matrix (PV(A/P)). Bi2O3 nanofillers (NF) and Bi2O3/PV(A/P) nanocomposite (NC) films were prepared by facile chemical solution approaches. The X-ray (XRD) data and a transmission electron image revealed that the NF exhibits a monoclinic phase, resembling slightly deformed agglomerated spheres. In the FTIR spectrum, different stretching vibrations of Bi-O-Bi bonds were found, along with their complexation and interaction with the reactive groups in the matrix. The SEM revealed a uniform distribution of Bi2O3 NF loading up to 1.5 wt% on the sample’s surface. Thermal analyses (TGA and DSC thermograms) were used to study the thermal stability, melting, and decomposition temperatures of the NC films. The dielectric features were studied under frequencies between 2 × 103 and 8 × 106 Hz and heating from 293 to 393 K. The dielectric constant and energy density were increased with Bi2O3 NF content. This implies that we can utilize the prepared NC for the fabrication of energy storage devices. The influences of the Bi2O3 NF doping level on the transmittance, band gap, Urbach energy, refractive index, conductivity, and other physical parameters were discussed. The modifications induced in the dielectric/optical parameters make the prepared NC films the best candidates for applications requiring a high refractive index, such as optical coatings and integrated photonic devices.

3D Laser Writing of Low-Loss Cross-Section-Variable Type-I Optical Waveguide Passive/Active Integrated Devices in Single Crystals.

Optical waveguides fabricated in single crystals offer crucial passive/active optical components for photonic integrated circuits. Single crystals possess inherent advantages over their amorphous counterpart, such as lower optical losses in visible-to-mid-infrared band, larger peak emission cross-section, higher doping concentration. However, the writing of Type-I positive refractive index modified waveguides in single crystals using femtosecond laser technology presents significant challenges. Herein, we introduce a novel femtosecond laser direct writing technique that combines slit-shaping with an immersion oil objective to fabricate low-loss Type-I waveguides in single crystals. This approach allows for precise control of waveguide shape, size, mode-field and refractive index distribution, with a spatial resolution as high as 700nm and a high positive refractive index variation on the order of 10-2, introducing new degrees of freedom to design and fabricate passive/active optical waveguide devices. As a proof-of-concept, we successfully produced a 7mm-long circular-shaped gain waveguide (∼10µm in diameter) in an Er3+-doped YAG single crystal, exhibiting a propagation loss as low as 0.23dB/cm, a net gain of ∼3dB and a polarization-insensitive character. The newly-developed technique is theoretically applicable to arbitrary single crystals, holding promising potential for various applications in integrated optics, optical communication, and photonic quantum circuits. This article is protected by copyright. All rights reserved.

A GaN-based SOI plasmonic nanolaser design with high-output power

Abstract Due to its unique optical and electrical properties, gallium nitride (GaN) exhibits great promise for nanolaser cavities. &amp;#xD;These characteristics include high electron mobility, wide bandgap energy, and a high refractive index. Moreover, GaN exhibits remarkable thermal stability, making it appropriate for high-power laser applications. The choice of active medium material can significantly impact the laser's performance, including its wavelength, output power, and efficiency. This work designed and numerically demonstrated a GaN -WG built-in SiO_2 substrate with an input and output Si-waveguide nanolaser. These nanolasers lase multi-output wavelengths in both directions &amp;#xD;(forward and backward) at 1680 and 1750 nm, respectively. The pump power is 800 nm. The GaN- waveguide material, when used in nanolaser cavity design, gives many different advantages like concentration of the Gaussian envelope and improved polarization depending on rate (PDR). Increasing lasing efficiency by 76.6 % in the forward direction and 96.7% in the backward direction. Get a low lasing threshold of approximately 200 μW in the forward direction and 180 μW backward direction. Finally, improved the output laser power in both directions (460 μW and 600 μW) in the forward and backward directions, respectively.&amp;#xD;

Efficient fabrication of high quality SU-8 photoresist based microsphere lasers via emulsion

Abstract SU-8 photoresist is a highly important material in the field of microfabrication and photonics owing to its low cost, excellent chemical and mechanical durability, high refractive index and transparency in the visible range. As a result, SU-8 photoresist has been employed as a cavity matrix for microsphere lasers. However, the current fabrication technique of SU-8 based microsphere lasers is complex and time-consuming. Here, we demonstrate a novel, cost-effective fabrication method for dye-doped SU-8 microspheres with diameters ranging from about 15 to 100 µm. These microspheres exhibit efficient lasing emission under optical pulse excitation. Lasing thresholds of 20 to 30 µJ·mm-2 and quality factors ranging from 1500 to 3000 are achieved. The size dependence of lasing characteristics indicates that the lasing mechanism is due to whispering gallery mode. Interestingly, these microsphere lasers can work in water, presenting promising application prospects in the fields of biological and chemical sensors.

All Dielectric High Q-Factor Metasurface Refractive Index Sensor Based on Dual Fano Resonances in THz Region

All Dielectric High Q-Factor Metasurface Refractive Index Sensor Based on Dual Fano Resonances in THz Region

Silicon nanocrystal slab optical waveguide by multi-energy ion implantation: linear and nonlinear optical properties

Silicon nanocrystals (Si-nc) have gained attention in optics and photonics research areas in recent years due to their advanced optical nonlinear properties. However, a nonlinear integrated optical platform that allows the fabrication of photonic devices with different Si-nc composition is yet under investigation. In this work, we experimentally demonstrated a nonlinear optical waveguide based on ion implantation that offers advantages in terms of material composition, low propagation losses, and enhanced nonlinear optical properties, such as a high nonlinear refractive index. In this work we present the fabrication of Si-nc containing waveguiding structures, and a study of their linear and nonlinear optical properties. Our nonlinear integrated optical platform presents a two-photon absorption coefficient β = 3.17x10-6 cm·W-1 and a nonlinear refractive index n2 = 1.19x10-10 cm2·W-1, which shows potential applications in all-optical signal processing devices, such as single-photon sources.

Study on structure and properties of La2O3–TiO2–B2O3 system glass

High refractive index La2O3–TiO2–B2O3 (LTB) system glasses have been successfully prepared by traditional melt-quenching method. Based on XPS results, we acquire details regarding the Ti oxidation state, coordination environments of boron and titanium, and the ratio of bridging to non-bridging oxygens within the glass. The predominant structural units identified in the glass matrix include [BO4], [BO3] and [TiO5] polyhedra, alongside a fraction of [TiO4] and [TiO6] polyhedra. The incorporation of TiO2 results in a reduction of the [BO4] tetrahedral groups and an increase of bridging oxygens and non-bridging oxygens bonds with Ti within the glass structure. 20 % of Ti(Ⅳ) ions in the glass are reduced to Ti(Ⅲ) ions. The addition of TiO2 content leads to an increase in Vickers hardness and refractive index of the glass, with [TiO5] polyhedra notably enhancing the refractive index. However, the increase in TiO2 content correspondingly decreases glass transmittance due to the charge transfer between Ti4+ or Ti3+and O2−.

Optical trapping-enhanced probes designed by a deep learning approach

Realizing optical trapping enhancement is crucial in biomedicine, fundamental physics, and precision measurement. Taking the metamaterials with artificially engineered permittivity as photonic force probes in optical tweezers will offer unprecedented opportunities for optical trap enhancement. However, it usually involves multi-parameter optimization and requires lengthy calculations; thereby few studies remain despite decades of research on optical tweezers. Here, we introduce a deep learning (DL) model to attack this problem. The DL model can efficiently predict the maximum axial optical stiffness of Si/Si3N4 (SSN) multilayer metamaterial nanoparticles and reduce the design duration by about one order of magnitude. We experimentally demonstrate that the designed SSN nanoparticles show more than twofold and fivefold improvement in the lateral (k x and k y ) and the axial (k z ) optical trap stiffness on the high refractive index amorphous TiO2 microsphere. Incorporating the DL model in optical manipulation systems will expedite the design and optimization processes, providing a means for developing various photonic force probes with specialized functional behaviors.

Measurement of rotated Janus particle’s position and orientation in the optical trap

Optical tweezers are precise tools for translating and rotating micrometer-sized particles and are used widely in biology and physics. In a linearly polarized optical trap, Janus particles comprising two hemispheres with different refractive indexes can be rotated about the beam axis following the polarization direction. In previous research, the position and orientation of a Janus particle relative to the polarization direction were simulated using the T-matrix method, whereas this paper is focused on accurate experimental measurements. The position and orientation of a Janus particle are extracted by image processing, and the polarization direction is controlled by a motor-driven half-wave plate (HWP). The particle’s orientation and the polarization direction are related via the HWP’s rotation angle. However, rotating the HWP not only rotates the polarization direction but also causes the trap center to fluctuate positionally because of the inevitable misalignment between the HWP’s rotation axis and the optical axis. Both the trap center and the polarization direction affect the particle’s position, but the influence of the former is removed with the aid of a homogeneous microsphere. The experimental results show that the Janus particle rotates following the polarization direction to keep the interface between its two hemispheres always parallel to the polarization direction. Also, the particle’s centroid moves in a circular orbit around the trap center to hold the trap center in the hemisphere with the higher refractive index. The experimental results agree with the previous simulation results and are of use for future applications.

Size Control and Antioxidant Properties of Sulfur-Rich Polymer Colloids from Interfacial Polymerization.

High sulfur content polymeric materials, known for their intriguing properties such as high refractive indices and high electrochemical capacities, have garnered significant interest in recent years for their applications in optics, antifouling surfaces, triboelectrics, and electrochemistry. Despite the high interest, most high sulfur-content polymers reported to date are either bulk materials or thin films, and there is a general lack of research into sulfur-rich polymer colloids. Water-dispersed, sulfur-rich particles are anticipated to broaden the range of applications for sulfur-containing materials. In this study, we present the preparation and size control parameters of an aqueous dispersion of sulfur-rich polymers with the sulfur content of dispersed particles exceeding 75wt.%. Employing polymeric stabilizers with varying hydrophilic-lipophilic balance (HLB), along with changing the rank of inorganic polysulfides, allowed for the control of particle size in the range of 360nm to 1.8µm. The sulfur-rich colloid demonstrated antioxidant properties in water, demonstrating the potential for the use of sulfur-rich polymeric materials readily removable, heterogeneous radical scavengers. This article is protected by copyright. All rights reserved.

Numerical simulation on high quality anapole resonator with large electric field concentration in all-dielectric metasurface

In the field of nanophotonics, the manipulation of light using high refractive index dielectric materials has garnered significant attention in recent years. This occurs because dielectric materials with a high refractive index demonstrate lower losses in comparison to metallic plasmonic materials. Furthermore, the interference between internal toroidal dipole moment and electric dipole moment leads to destructive interference in the radiation field, resulting in the formation of an anapole state and localization of energy in the near-field. In this work, we initially excite the anapole state in a silicon nanodisk with a periodic nanostructured disk. By introducing a cross slit and adjusting the structural parameters, the anapole state is further optimized, and achieving highly concentrated near-field energy within the cross air slit of the silicon nanodisk. Specially designed, with a full width at halfmaximum (FWHM) of the transmitted spectrum of only 0.09 nm, and a Q factor of up to 9745, close to 104. Additionally, the structure can produce up to 571 times the electric field enhancement. The remarkable performance of a high Q factor and localized near-field energy holds great potential for various applications, including enhancing nonlinear effects, surface enhanced Raman scattering (SERS) and designing nanolasers.

First-principles study of the structural, mechanical, electronic, optical, and elastic properties of non-toxic XGeBr3 (X=K, Rb, and Cs) perovskite for optoelectronic and radiation sensing applications

In this study, a comprehensive analysis of the structural, electronic, optical, and elastic properties of cubic perovskite structure XGeBr3(X=K,Rb,andCs) was carried out using GGA-PBE functional based density functional theory in CASTEP code. The simulated values of the lattice parameter were increased with the changing of X from K to Cs (a = 5.51 Å, 5.54 Å, and 5.59 Å respectively). All the compounds possessed direct band gaps and acquired values for the structures KGeBr3, RbGeBr3 and CsGeBr3 were 0.525 eV, 0.599 eV, and 0.708 eV, respectively. Furthermore, the atomic orbital's contribution to the formation of band structure was clarified thoroughly. The thermodynamic, as well as the mechanical stability, has been accomplished with the assurance of negative formation energy and Born-Huang approximation. In addition, a larger shearing modulus attained by CsGeBr3 manifests its strength. Moreover, all structures bear the proof of having ductility and existing central force inside the structures. Finally, the calculated anisotropic index notifies that all structures exhibit anisotropy with the trend of CsGeBr3 < RbGeBr3 < KGeBr3. This is also authenticated through the 3D anisotropy contour plot generated by utilizing ELATE software, which is for the first time in regard to the comparative scenario among them. With the investigation of the optical characteristics of the compounds XGeBr3, intriguing features such as broad absorption spectrum, high dielectric function and refractive index at zero photon's energy, and high conductivity have been affirmed accompanying the marginal value of loss function as well as reflectivity that elevates the probability of being employed in optoelectronic applications along with different absorber layers of tandem solar cells. In addition, these compounds could be used as radiation detectors since they have broad absorption at extreme ultraviolet rays.

Multiband highly sensitive metamaterial-based THz absorber for edible oil adulteration sensing

A terahertz (THz) wave technology is very appealing for applications in detection in biomedicine, biological spectroscopy, material characterization, detection, imaging, sensing, and other convenient applications. Metamaterials (MMs) are artificial structures that have structures in a regular periodic arrangement and don’t exist in nature. By utilizing a proposed terahertz metamaterial absorber, a broad spectrum of adulterated lubricants can be detected. It is an efficient detection process that enables the development of a THz detection approach by making use of the metamaterial as a sensor. The proposed terahertz absorber is analyzed and optimized using the CST Microwave Studio 2019 software. The article proposed a multiband THz metamaterial absorber with a unit size of 70 µm. According to the demonstrated results, we can achieve five narrow absorption peaks with perfect absorption within the frequency range between (0.2–4.2) Terahertz. Also, the result shows that, the average absorbance of 99.07% at the resonance frequencies of 0.56, 1.42, 2.676, 3.14, and 3.89 THz. The E (electric) and H (magnetic)-field distributions on the resonator at different resonance frequencies were also analyzed as well as. The recommended metamaterial absorber has a good sensing capability at different resonant frequencies, with refractive index sensitivities of 80 GHz/RIU, 240 GHz/RIU, 480 GHz/RIU, 480 GHz/RIU, and 520 GHz/RIU obtained by modifying the refractive index of the sample holder or the analytic layer, respectively. As a result, the proposed detector has a high refractive index sensitivity, high Q-factor, and high FOM, making it suitable for detecting oil adulteration.

Harnessing the synergy of ZrO2 and SiO2 dielectric micro-/nanoparticles in polymer-based photonic films for robust passive daytime radiative cooling

Polymer-based materials emerge as promising building blocks for passive daytime radiative cooling (PDRC) due to their affordability and ease of production. Enhancing these polymers with inorganic particle doping has shown to boost their mechanical properties and light scattering ability, a result of the increased refractive index contrast with air. However, the incorporation of a single type of inorganic particle often falls short in optimizing overall performance. Herein, we introduce a novel approach by simultaneously integrating high refractive index zirconium dioxide (ZrO2) and wide band gap silicon dioxide (SiO2) dielectric particles into polydimethylsiloxane (PDMS) matrix. This dual-particle strategy synergistically improves the radiative cooling capabilities of the resulting photonic film. Remarkably, with a thickness of 1,000 μm, it achieves an impressive 96.7% reflection of solar irradiance, while maintaining a high emissivity of 95.2% in the atmospheric window. Under solar intensity of ∼836.7 W/m2, it delivers an average cooling power of 82.42 W/m2, achieving a substantial sub-ambient temperature drop of up to 8.26 °C. We further explored its effectiveness in enhancing freshwater collection efficiency, leveraging its radiative cooling properties. Furthermore, the photonic film also exhibits versatile properties including flexibility, hydrophobicity, thermal stability, color scalability, and weather resistance, thus enhancing its suitability for various practical applications.

Fast, Precise, High Contrast Laser Writing for Photonic Chips with Phase Aberrations

AbstractIntegrated photonic chips have significant potential in telecommunications, classic computing, quantum systems, and topological photonics. Direct laser writing offers unique capability for creating three‐dimensional photonic devices in an optical glass chip with quick prototyping. However, it is a challenge for existing laser writing schemes to create index‐modified structures in glass that precisely match the laser focal shape while also achieving high refractive index contrasts and high scanning speeds. Here, we introduce a refractive index modification scheme that combines the advantages of non‐thermal and thermal regime fabrication methods. We also propose a waveguide formation model that is verified through a thorough study on the effects of phase aberrations. The presented new photonic chip fabrication scheme uses a novel focal intensity distribution, where pulse energy is relocated to the bottom of a laser focus by manipulating primary and higher order spherical aberrations. The technique can produce index modifications with high scanning speed (can be 20 mm/s or higher), high index contrast (ranging from 0.009 to 0.021), and high precision to fabricate with arbitrary cross‐sections. This method has potential to expand the capabilities of photonic chips in applications that require small‐scale, high precision, or high contrast refractive index control.

Crystalline germanium high-Q microresonators for mid-IR

High-quality-factor optical microresonators have become an appealing object for numerous applications. However, the mid-infrared band experiences a lack of applicable materials for nonlinear photonics. Crystalline germanium demonstrates attractive material properties such as high nonlinear refractive index, large transparency window including the mid-IR band, particularly long wave multiphonon absorption limit. Nevertheless, the reported optical losses in germanium microresonators might not allow the potential of the Ge-based devices to be revealed. In this study, we report the fabrication of germanium microresonators with radii of 1.35 and 1.5 mm, exhibiting exceptional quality factors (Q-factors) exceeding 20 million, approaching the absorption-limited values at a wavelength of 2.68 µm. These Q-factors are a hundred times higher than previously reported, to the best of our knowledge. We measured the two-photon absorption coefficient combined with free-carrier absorption leveraging the high-Q of the resonators (obtained βTPA = (0.71 ± 0.12) · 10−8 m/W at 2.68 µm). This research underscores the potential of whispering gallery mode microresonators as valuable tools for measuring absorption coefficients at different wavelengths, providing a comprehensive analysis of various loss mechanisms. Furthermore, the exceptional Q-factors observed in germanium microresonators open intriguing opportunities for the advancement of germanium-based photonics within the mid-infrared spectral band.