Optimal Refractive Index Research Articles

Tunability of Sb2Se3 phase change material for multi-domain optoelectronics

Phase change materials play an essential role in the development of tuneable optics by overcoming the limitations possessed by conventional optics due to their static behaviour. Due to their non-volatile nature, chalcogenide materials attained attention beyond other phase change materials. Antimony-based chalcogenides are promising due to low absorption loss, optimal refractive index change, and compatibility with silicon integration. This study optimises near-stoichiometric sputtered Sb2Se3 thin films and investigates their compositional, physical, and optical properties change by thermal, optical, and electrical stimuli. We further extend the investigation to the induced intermediate states in the Sb2Se3 thin film for multi-bit operation for tunable photonics and phase-change memory with a current switching ratio of 104 during a phase transition. The findings are integral to the realisation of high-capacity optical switches and routers, displays with larger colour distribution, and photonic memories with high computational capabilities.

Nano Application of Oil Concentration Detection Using Double-Tooth Ring Plasma Sensing

Based on the unique properties of optical Fano resonance and plasmonic-waveguide coupling systems, this paper explores a novel refractive index concentration sensor structure. The sensor structure is composed of a metal–insulator–metal (MIM) waveguide and two identically shaped and sized double-tooth ring couplers (DTR). The performance structure of the nanoscale refractive index sensor with DTR cavity was comprehensively assessed using the finite element method (FEM). Due to the impact of various geometric parameters on the sensing characteristics, including the rotation angles, the widths between the double-tooth rings, and the gaps between the cavity and the waveguide, we identified an optimal novel refractive index sensor structure that boasts the best performance indices. Finally, the DTR cavity sensor achieved a sensitivity of 4137 nm/RIU and Figure of merit (FOM) of 59.1. Given the high complexity and sensitivity of the overall structure, this nanoscale refractive index sensor can be applied to the detection of oil concentration in industrial oil–water mixtures, yielding highly precise results.

Effects of MgF2 anti-reflection coating on optical losses in metal halide perovskite solar cells

The importance of light management for perovskite solar cells (PSCs) has recently been emphasized because their power conversion efficiency approaches their theoretical thermodynamic limits. Among optical strategies, anti-reflection (AR) coating is the most widely used method to reduce reflectance loss and thus increase light-harvesting efficiency. Monolayer MgF2 is a well-known AR material because of its optimal refractive index, simple fabrication process, and physical and chemical durabilities. Nevertheless, quantitative estimates of the improvement achieved by the MgF2 AR layer are lacking. In this study, we conducted theoretical and experimental evaluations to assess the AR effect of MgF2 on the performance of formamidinium lead-triiodide PSCs. A sinusoidal tendency to enhance the short-circuit current density (J SC) was observed depending on the thickness, which was attributed to the interference of the incident light. A transfer matrix method-based simulation was conducted to calculate the optical losses, demonstrating the critical impact of reflectance loss on the J SC improvement. The predicted J SCs values, depending on the perovskite thickness and the incident angle, are also presented. The combined use of experimental and theoretical approaches offers notable advantages, including accurate interpretation of photocurrent generation, detailed optical analysis of the experimental results, and device performance predictions under unexplored conditions.

Stoke's shift and quantum efficiency enhancement in fluorescent coumarin aldehyde (HMCA) dye-conjugated chitosan matrix for optoelectronic applications

A greenish-yellow emissive fluorescent coumarin aldehyde conjugated chitosan matrix was prepared by performing a Schiff base reaction between 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (HMCA) and chitosan. The newly formed imine linkage was confirmed by the appearance of an absorption band at 1641 cm−1 in the IR spectrum and also supported by the solid-state 13C-NMR with cross polarisation magic angle spinning (CPMAS) method. The molecular weight of the HMCA-conjugated chitosan matrix was augmented with an increase in the HMCA concentration. The SEM images unveiled crystallite aggregates in the chitosan matrix and the improved crystallinity was witnessed in the PXRD result. The chemically conjugated chitosan film unveiled a larger Stoke's shift value of 183–224 nm which was just 50–130 nm in pure HMCA. The conjugate material could overcome the self-absorption issue associated with the coumarin aldehyde. The coumarin aldehyde exhibited dual emission at 390 nm and 440 nm but it was shifted to 520 nm with single emission upon reaction with chitosan. The observed redshift could be assigned for the formation of static excimer that resulted from the chitosan backbone containing pendant chromophore (coumarin dye) which could interact with another neighbouring chromophoric group of the same chain or different chain creating a ground-state stable dimer. The emission of conjugate material shifted from blue to greenish yellow region with a higher quantum yield of 30.21 % compared to 8.57 % of HMCA alone. The calculated indirect band gap of 2.25–2.34 and the optimum refractive index suggested the potential optoelectronic applications of HMCA-conjugated chitosan as an OLED Material.

Analyzing the ZnO and CH3NH3PbI3 as Emitter Layer for Silicon Based Heterojunction Solar Cells

Today, it has become an important task to modify existing traditional silicon-based solar cell factory to produce high-efficiency silicon-based heterojunction solar cells, at a lower cost. Therefore, the aim of this paper is to analyze CH3NH3PbI3 and ZnO materials as an emitter layer for p-type silicon wafer-based heterojunction solar cells. CH3NH3PbI3 and ZnO can be synthesized using the cheap Sol-Gel method and can form n-type semiconductor. We propose to combine these two materials since CH3NH3PbI3 is a great light absorber and ZnO has an optimal complex refractive index which can be used as antireflection material. The photoelectric parameters of n-CH3NH3PbI3/p-Si, n-ZnO/p-Si, and n-Si/p-Si solar cells have been studied in the range of 20–200 nm of emitter layer thickness. It has been found that the short circuit current for CH3NH3PbI3/p-Si and n-ZnO/p-Si solar cells is almost the same when the emitter layer thickness is in the range of 20–100 nm. Additionally, when the emitter layer thickness is greater than 100 nm, the short circuit current of CH3NH3PbI3/p-Si exceeds that of n-ZnO/p-Si. The optimal emitter layer thickness for n-CH3NH3PbI3/p-Si and n-ZnO/p-Si was found equal to 80 nm. Using this value, the short-circuit current and the fill factor were estimated around 18.27 mA/cm2 and 0.77 for n-CH3NH3PbI3/p-Si and 18.06 mA/cm2 and 0.73 for n-ZnO/p-Si. Results show that the efficiency of n-CH3NH3PbI3/p-Si and n-ZnO/p-Si solar cells with an emitter layer thickness of 80 nm are 1.314 and 1.298 times greater than efficiency of traditional n-Si/p-Si for the same sizes. These findings will help perovskites materials to be more appealing in the PV industry and accelerate their development to become a viable alternative in the renewable energy sector.

Design and Optimization of Liquid Crystal RIS-Based Visible Light Communication Receivers

In the design of reconfigurable intelligent surfaces (RISs)-aided visible light communication (VLC) systems, most studies have focused on the deployment of mirror arrays and metasurfaces on walls to influence signal propagation and enhance communication performance. This paper provides a new research direction in the design and performance optimization of RIS-aided VLC systems whereby voltage-controlled tunable liquid crystals (LCs) are deployed as part of the VLC receiver. The purpose of the LC RIS is to provide incident light steering and intensity amplification in order to improve the received signal strength and the corresponding achievable data rate. More specifically, an LC RIS-based VLC receiver design is proposed and its operating principles and the channel model for a VLC system with such a receiver are provided. Since the refractive index of the LC RIS plays a critical role in the wave-guiding and light amplification capabilities of this novel receiver, a rate maximization problem is considered to achieve the optimal refractive index and the required voltage to obtain the best light amplification and data rate performances. This communication design problem is a non-convex optimization problem for which a metaheuristic approach is developed based on the sine-cosine algorithm. Simulation results are used to confirm the considerable data rate improvement by the proposed LC RIS-based VLC receiver and optimization algorithm when compared to a VLC receiver without the LC RIS and a baseline scheme, respectively.

Ultrasensitive total internal reflection sensor with rotatory biased weak measurement

A modified weak measurement scheme, rotatory biased weak measurement, is proposed to significantly improve the sensitivity and resolution of the total internal reflection sensor. This method introduces an additional phase in the post-selected procedure and generates an extinction point in the spectrum distribution. The biased post-selection makes smaller coupling strength available, which leads to an enhancement of phase sensitivity and refractive index sensitivity. In rotatory biased weak measurement, an enhanced refractive index sensitivity of 13605 nm/RIU is achieved compared to 1644 nm/RIU in standard weak measurement. The performance of total internal reflection sensors with different sensitivity is analyzed, and it is shown the optimal refractive index resolution of sensors increases with sensitivity. An optimal refractive index resolution of 4×10−7 RIU on a total reflection structure is demonstrated, which is far beyond the state-of-the-art resolution of 3×10−6 RIU of total internal reflection sensors. The rabbit anti-mouse IgG and mouse IgG binding reaction experiments demonstrate that our system has a high response to the concentration of IgG in a wide range and the limit of detection is 15 ng/mL. This work provides a total internal reflection sensor with the advantages of simple structure, low cost, and high resolution at the same time.

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO2/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO2 sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO2 and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO2 and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO2/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO2/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO2/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.

Synthetic aperture rainbow refractometry.

This work proposed a synthetic aperture rainbow refractometry (SARR) by synthesizing rainbow signals of the same droplet with dual-wavelength laser beams, in order to increase the aperture of rainbow refractometry. In this way, the SARR can apply to long distance and small droplets measurement. An achromatic imaging system, which simultaneously records while separating the two rainbow signals in two channels of a color image, is elaborately designed. A data processing algorithm is developed to retrieve the optimal droplet refractive index and size. Numerical simulations of different droplet sizes from 10 μm to 200 μm certify the viability of the SARR. Proof-of-concept experiments of micron-sized ethanol droplets are performed with 1650 mm measurement distance. Results show that the SARR can accurately measure droplet refractive index and size with uncertainties of 2.3 × 10-4 and 2μm, respectively. The feasibility and accuracy of the proposed SARR are successfully demonstrated, paving the way for rainbow refractometry applied to large-scale industrial applications.

IMPACT OF TEXTURING SILICON COATED WITH A SINGLE ANTIREFLECTIVE LAYER

This paper focuses on anti-reflective coatings on monocrystalline silicon solar cells and the impact of front surface texturing. The reference wavelength of silicon is =700 nm, with its optimum refractive index (n = 3.7838) and a surface reflectivity of 33%. The calculations were made on the basis of layer thickness values and refractive indices that allow the phase and amplitude conditions chosen to be respected, namely (MgF2) (SiOxNy), (SiOx), and (SiNx:H). Numerical simulations have shown low reflectivitys at the surface of the planar cell coated with a single layer, but texturing on this same alloy allows a significant reduction in reflectivity. However, the comparison of the results of silicon coated with a simple anti-reflection layer on a plane surface and the textured one gives us important differences such as: 7,05% for MgF2 /Si, 4,6% SiOx/Si, 0,6% for SiOxNy/Si and 0,4% for SiNx:H/Si.

Studies on nano crystalline copper doped Nickel Zinc ferrites for optoelectronic applications

Investigation of optical and dielectric properties of nanocrystalline Ni0.65Zn0.35 Cu x Fe(2-2x/3) O4 (for x = 0.00–0.05 in steps of 0.01) ferrites synthesized using hydrothermal route is successfully carried out. Two distinct analytical spectroscopic methods with Dichloro – 5,6-Dicyano – 1,4-Benzo quinone (DDQ) and Bromo Phenol Blue (BPB) are adopted to observe the UV–visible absorption spectroscopy in the dispersed solutions of all samples. The formation of ion pair complex in the presence of BPB results in two distinct absorption edges in the visible region, around 440 nm and 580 nm in the present ferrite samples. Application of Tauc's formalism gives rise to two optical band gap values Eg1 and Eg2 in the range of 2.12–2.40 eV and 3.583–3.674 eV, respectively. The formation of charge transfer complex with all sample solutions in presence of DDQ reagent results in sharp absorption edges in the UV-region around 306 nm wavelength. An initial rise followed by continuous drop in band gap values ranging from 3.814 to 3.824 eV is observed from Tauc's plots. The optimum refractive index (n) values calculated for the three types of band gap values using empirical relations display the optical absorption potentiality of Ni–Cu–Zn nano ferrites in both Visible and UV – regions. Variation of band gap values is ascribed to the lattice strain effect, quantum confinement and narrowing band gap effects. Real part of dielectric constant (ε′), dielectric loss factor (tanδ) and ac-conductivity(σac) are studied for all samples at room temperature with in the frequency range of 42 Hz to 5 MHz. The values of ε′ and tanδ are observed to decrease with increase in frequency, while that of σac are found to increase with increase in frequency. Improved dielectric properties, existence of optical band-gap values observed in the present Ni–Cu–Zn ferrites promote these materials for their utility in optoelectronic devices and high frequency applications.

Enhancement of holographic performance and stability of photopolymer materials by introducing epoxy resin and dyes

The use of a composite photopolymer system together with a photoinitiator have a significant effect on the optical properties of a volume phase holographic grating. This paper reports on the performance of a low refractive index monomer combined with a high refractive index epoxy resin. Performance improvements include the compatibility between the cross-linked network structure of the matrix and the recording medium. The effects of the exposure conditions and the internal composition of the materials on holographic performance were investigated. The results showed that the optimal refractive index modulation depends on the ratio of the epoxy resin and the pre-polymerization temperature. The use of Irgacure 784 as a photoinitiator gave better performance than Rose Bengal (RB) in terms of diffraction efficiency (∼92.5 %), transmittance (∼98 %) and slight shrinkage (0.314 %) was observed. The use of a dual-photoinitiator gave improvements in the radical generation rate and the stability, permitted recordings at an exposure energy of 50 mJ/cm2 and afforded high sensitivity (3.9 × 10-2 cm2/J) as a result of the synergy between the two photoinitiators. In other words, due to the highly reactive Irgacure 784 and the inhibiting polymerization characteristics of RB, enhancement of holographic performance and good stability were realized. It was shown in the photocuring and aging experiments that the photopolymer possessed anti-aging properties. The photopolymer can record multiplexed images at 532 nm and polarization holograms, demonstrating that it has the capability to perform high-density data recording.

Improving the refractive index by engineering PbS/PVA nano polymer composite for optoelectronic applications

High refractive index polymer nanocomposites are of major interest since they are potential candidates in solar cell applications and optoelectronics. Lead sulfide (PbS) nanoparticles were synthesized using a straightforward chemical route. Polyvinyl alcohol (PVA) films with different concentrations of doped PbS nanoparticles (0%, 1%, 2%, 3%, 6%, and 10%) have been prepared by casting technique. The structural properties of PbS nanoparticles and filled PVA films were investigated using XRD, the optical and FTIR analyses were performed for the prepared films. This paper verifies that the optical parameters, including the refractive index, of the PVA polymer, are enhanced by loading PbS nanoparticles in its matrix, The optical bandgap was extensively decreased from 3.08 eV for the blank PVA film to 1.97 eV for 10% PbS/PVA. The 3% dopant sample reveals the optimum refractive index value which, making it a candidate for many future applications.

The Equations and Optical Parameters of Antireflective Multilayers: A Literature Review

In this paper, the study is focused on the anti-reflection coatings on silicon solar cells and monocrystalline solar cells. The impact of optical parameters such as refractive index on the reflectivity as well as the impact of the as well as the impact of the diffusion length of the carriers was studied. The calculations performed according to the transfer matrices on the stacking of layers through the diopters have allowed establishing simulations for antireflective multilayer coatings. In our study, the reference wavelength was chosen equal to l= 700 nm, which gives us an optimal refractive index of silicon (n = 3.7838) corresponding to a reflectivity at the surface of 33%. To reduce this high reflectivity, the coating of the surface is a technique used to improve the transmission of the incident luminous flux in the active material and light flux in the active material which is silicon.

Development of a label-free dual-grating waveguide coupler biosensor

This study developed a novel dual-grating waveguide coupler biosensor (DGB) which comprised two optical gratings and a waveguide layer, wherein the first grating coupled light into the waveguide layer, and the second grating coupled light out of the waveguide layer. The DGB used the combined light input and output coupling effects of the first and second gratings of the biosensor to improve the normalized refractive index sensitivity and detection capability. In addition, the double-sided grating waveguide (DSG) structure was used to increase the biosensor coupling angle range and coupling position range, improving device setup error tolerance and reducing detection device cost. The results showed that the DGB had a refractive index resolution of 1.82 × 10−6 RIU and a normalized refractive index sensitivity of 48.55 RIU−1, which was twice that of a single-grating waveguide coupler biosensor (SGB). N-(2,4-dinitrophenyl)-ε-amino-n-caproic acid (DNP) and anti-DNP immunoassay results showed that the limit of detection (LOD) was 2.73 × 10−8 g/ml. Compared with other biosensors, the dual-grating waveguide coupler biosensor proposed in this study has a better optimal refractive index resolution and an excellent LOD.

Structure and mid-infrared optical properties of spin-coated polyethylene films developed for integrated photonics applications

Polyethylene is a promising polymer for mid-infrared integrated optics due to its broad transparency and optimal refractive index. However, simple fabrication protocols that preserve its optical characteristics are needed to foster a wide range of applications and unlock its full potential. This work presents investigations of the optical and structural properties of spin-coated linear low-density polyethylene films fabricated under humidity-controlled conditions. The film thickness on polymer concentration dependence shows a non-linear behavior, in agreement with previously reported theoretical models and allowing predictive concentration-dependent thickness deposition with high repeatability. The surface roughness is on the nanometer-scale for all investigated concentrations between 1% and 10%. The crystallinity of the films was studied with the Raman spectroscopy technique. Mid-infrared ellipsometry measurements show a broad transparency range as expected for bulk material. Layer exposure to solvents revealed good stability of the films, indicating that the fabricated layers can outlast further fabrication steps. These investigations confirm the excellent properties of spin-coated thin films fabricated with our novel method, creating new opportunities for the use in photonic integrated circuits

Electronic, magnetic, and optical properties of bulk and (1 1 1)-surfaces of CoMnZnSi quaternary Heusler alloy

The structural stability, electronic structure, and magnetic and optical properties of CoMnZnSi quaternary Heusler alloy (QHA) in the bulk and (111)-slab forms have been investigated by performing density functional theory (DFT) calculations. Formation and cohesive energies, and elastic constants confirm that the bulk CoMnZnSi is chemically and mechanically stable at an equilibrium lattice parameter of 5.81 Å. The calculated elastic constants also indicate that this QHA has ductile and anisotropic features. We investigate and discuss the bonding behavior from charge density distribution and density of states. These calculations in the bulk phase show a perfect half-metallic behavior with an integer value of magnetic moment (4 µB) and a large spin-flip gap of 0.39 eV. On the other hand, the Co (111) and Si (111)-slabs exhibit semi-metallic nature at the Fermi level. These results indicate that CoMnZnSi qualifies for spintronic applications. In the bulk and Co (111), Zn (111), and Si (111)-surfaces, the magnetic moment of Co and Mn atoms are ferromagnetically aligned, while the ferrimagnetic alignment of Co with Mn has been found in Mn (111)-surface. We also investigate the optimal conductivity, dielectric functions, reflectivity, absorption coefficient, refractive index, and loss function to understand the underlying optical properties of this alloy.

Study on the sensitivity enhancement of fiber SPR sensor by gold nanorods

Purpose This paper aims to study the sensitivity enhancement effect of the gold nanorod on fiber surface plasmon resonance (SPR) sensor. It proposes modeling the sensing effects of fiber SPR sensor decorated with metal nanoparticles. By using simulation and experiment, the sensitivity enhancement effect of the gold nanorod was studied and demonstrated. Design/methodology/approach The paper opted for an exploratory study using simulation approach of finite-difference time-domain. Specifically, the effect of ratios and aspect ratios of gold nanorod on sensing performance are investigated theoretically. Based on the mathematical models, the validation experiments by using the gold nanorod with the aspect ratios of 5.1 were done to verify the sensitivity enhancement effect of the gold nanorod. Findings In conclusion, it is evident that with the increases of the aspect ratios, the sensing sensitivity of the refractive index increases first, then gradually stabilizes or decreases. After parameter optimization, the ratios and aspect ratios of gold nanorod are chosen to be 8 nm and 12.5, respectively, which makes the optimal refractive index sensitivity of 4465.53 nm/RIU be realized. In addition, the validation experiments by using the gold nanorod with the aspect ratios of 5.1 verify the sensitivity enhancement effect of the gold nanorods. Originality/value This paper proposes and demonstrates a new method for the sensitivity enhancement of fiber SPR sensor. After parameter optimization, the maximum sensitivity of 4465.53 nm/RIU was achieved by using 8 nm gold nanorods with the aspect ratios of 12.5. To verify the sensitivity enhancement of the gold nanorods, the authors also did the validation experiments. The testing results indicated that after the decoration of the gold nanorods, the sensitivity of the sensing probe increases from 2190.57 nm/RIU to 2693.24 nm/RIU, which demonstrates the sensitivity enhancement effect of the gold nanorods.

Organic Thin-Film Characteristics Modulated by Deposition Substrate Rotation Speed and the Effect on Organic Light-Emitting Diodes.

In this paper, we report on the effects of the substrate thermal evaporation process rotation speed on the electroluminescence (EL) characteristics of organic light-emitting diodes (OLEDs). In general OLED research, rotational and angle tilted deposition are widely used to maintain uniformity. However, there have been few reports on the effects of this deposition method on film characteristics. We analyzed these effects and found that the film density and its refractive index showed remarkable changes as a function of substrate rotational speed during tilted deposition. The EL characteristics of the transport layer of fluorescent OLEDs were also significantly affected. We derived the OLED optimal thickness and refractive index from our calculations.

Lipo-PEG nano-ocular formulation successfully encapsulates hydrophilic fluconazole and traverses corneal and non-corneal path to reach posterior eye segment

The present study describes a special lipid-polyethylene glycol matrix solid lipid nanoparticles (SLNs; 138 nm; −2.07 mV) for ocular delivery. Success of this matrix to encapsulate (entrapment efficiency − 62.09%) a hydrophilic drug, fluconazole (FCZ-SLNs), with no burst release (67% release in 24 h) usually observed with most water-soluble drugs, is described presently. The system showed 164.64% higher flux than the marketed drops (Zocon®) through porcine cornea. Encapsulation within SLNs and slow release did not compromise efficacy of FCZ-SLNs. Latter showed in vitro and in vivo antifungal effects, including antibiofilm effects comparable to free FCZ solution. Developed system was safe and stable (even to sterilisation by autoclaving); and showed optimal viscosity, refractive index and osmotic pressure. These SLNs could reach up to retina following application as drops. The mechanism of transport via corneal and non-corneal transcellular pathways is described by fluorescent and TEM images of mice eye cross sections. Particles streamed through the vitreous, crossed inner limiting membrane and reached the outer retinal layers.