Angle Of Incident Light Research Articles

Enhanced sensitivity of a surface plasmon resonance biosensor utilizing Au/ITO hyperbolic metamaterial

A surface plasmon resonance (SPR) sensor unitizing hyperbolic metamaterial (HMM) composing by a few pairs of Au and ITO layers was proposed. The sensing performance of Au/ITO-HMM sensor was demonstrated to be tuned by the metal filling fraction and the incidence angle of light by simulation. Electric field and penetration depth distributions at the sensing interface were calculated to explain the physical mechanism of sensitivity enhancement. With the light incident angle of 75° and 66°, we experimentally demonstrated that the proposed SPR sensor could achieve the average sensitivity of 3341 nm/RIU and 14242 nm/RIU, respectively. The proposed Au/ITO-HMM-SPR sensor with ultra-high sensitivity can be found potential application in the biochemical sensing with much lowered concentration.

Near-perfect wide-band absorbers based onone-dimensional photonic crystal structures in1-20 THz frequencies.

This paper investigates the absorption behavior of one-dimensional (1D) photonic crystal (PhC) structures in the 1-20THz region. The structures are analyzed by the transfer matrix method to achieve accurate results quickly with ordinary simulation facilities. The simulation results indicate a strong dependence of the absorber performance on the thickness and material of the PhC layers, as well as the frequency and angle of incident light. The combination of silica and titanium (Ti) materials as dielectric and metal layers presents a great choice for broadband high-absorption applications so that this structure can absorb, on average, more than 80% of the normal incident radiation in the studied frequency range. Additionally, this absorber has the lowest dependence on incident light with the angle varying from 0° to 80° compared to identical absorbers with silver, aluminum, gold, chromium, nickel, and tungsten metals. The excellent absorption feature of the Ti-based absorber compared to the other absorbers is attributed to the lower permittivity of Ti (in both real and imaginary parts) in comparison with the other metals. In addition to owning simple and fabrication-friendly structures, 1D PhCs can pave the way to achieve various absorption spectra proportional to the needs of photonics, communications, and aerospace applications.

SPECTRA: A Novel Compact System for Surface Plasmon Resonance Measurements.

Surface plasmon resonance (SPR) is a common and useful measurement technique to perform fast and sensitive optical detection. SPR instrumentations usually comprise optical systems of mirrors and lenses which are quite expensive and impractical for point-of-care applications. In this work, we presented a novel and compact SPR device called SPECTRA, designed as a spectrophotometer add-on with a grating coupling configuration. The device is conceived as a marketable solution to perform quick SPR measurements in grating configuration without the requirement of complex instrumentation. The device can be customized either in a vertical structure to reach lower incident light angles, or in a horizontal configuration, which is suitable for SPR analysis using liquid solutions. The SPECTRA performance was evaluated through SPR measurements in typical applications. The vertical SPECTRA system was employed to detect different functionalization molecules on gold 720 nm-period grating devices. Meanwhile, the horizontal SPECTRA configuration was exploited to carry out fluid-dynamic measurements using a microfluidic cell with glycerol solutions at increasing concentrations to account for different refractive indexes. The experimental tests confirmed that the SPECTRA design is suitable for SPR measurements, demonstrating its capability to detect the presence of analytes and changes in surface properties both in static and dynamic set-ups.

Strategically constructed high-reflectivity multiple-stack distributed Bragg reflectors for efficient GaN-based flip-chip mini-LEDs

Full-angle distributed Bragg reflectors (DBRs) consisting of numerous sub-DBRs with discrete central wavelengths have been developed to enhance performance of GaN-based flip-chip mini light-emitting diodes (FC mini-LEDs). However, relatively low reflectivity of full-angle DBRs at large angle incidence restricts further enhancement in performance of FC mini-LEDs. Here, we introduce a reflectivity optimization strategy for constructing high-reflectivity multiple-stack DBRs by rationally engineering the number of sub-DBRs and adjusting central wavelength distribution of sub-DBRs. Based on the reflectivity optimization strategy, we devise a Ti3O5/SiO2 quintuple-stack DBR which is composed of five sub-DBRs. Our quintuple-stack DBR maintains a high reflectivity (>97.5%) over a wide range of incident angles of light. Notably, compared with the full-angle DBR, our quintuple-stack DBR exhibits higher reflectivity at large angle incidence and thinner multilayer thickness. Furthermore, we demonstrate two types of GaN-based blue FC mini-LEDs with indium-tin oxide (ITO)/quintuple-stack DBR and ITO/full-angle DBR p-type ohmic contacts. Benefiting from superior reflection performance, blue FC mini-LED with ITO/quintuple-stack DBR achieves an enhancement of ∼5.8% in light output power at 10 mA, in comparison with blue FC mini-LED with ITO/full-angle DBR. Our work signifies an advancement towards high-reflectivity DBRs, which enables higher-performance FC mini-LEDs.

Enhancement of absorption in a CH3NH3PbI3-based photonic crystal in the presence of the monolayer MoS2

Using the transfer matrix approach, we investigate theoretically the absorbance, transmittance, and reflectance through one-dimensional CH3NH3PbI3 perovskite-based photonic crystal at room temperature. In our proposed structure, a monolayer MoS2 film is embedded between two CH3NH3PbI3 layers. We found that, the presence of monolayer MoS2 film increases the absorbance in longer wavelengths (lambda > 600begin{array}{*{20}c} , , {rm nm} end{array} ). With increasing the number of periods, absorbance increases in most wavelengths of the incident light. It was shown that, by controlling the number of periods, the absorbance coefficient can be tuned according to the wavelength and angle of incident light. Furthermore, for incident light with longer wavelength, the absorbance, transmittance as well as reflectance versus thickness of the perovskite layer have an oscillatory behavior, and with increasing the number of periods this oscillatory behavior becomes more obvious and prominent. For the incident light in the infrared region, by increasing the number of periods the absorbance as opposed to the transmittance increases for different incidence angles. While, the reflectance coefficient first shows oscillatory behavior by increasing the number of periods, then with a further increase in the number of periods it reaches a constant value. The proposed structure can be useful for optoelectronic and optical devices. Such as improving the efficiency of solar cells based on the hybrid inorganic–organic perovskites and infrared sensor system.

Optical Characterization of ALD-Coated Nanoporous Alumina Structures: Effect of Sample Geometry or Coated Layer Material

Optical characterization of nanoporous alumina-based structures (NPA-bSs), obtained by ALD deposition of a thin conformal SiO2 layer on two alumina nanosupports with different geometrical parameters (pore size and interpore distance), was performed by two noninvasive and nondestructive techniques such as spectroscopic ellipsometry (SE) and photoluminescence (Ph) spectra. SE measurements allow us to estimate the refraction index and extinction coefficient for the studied samples and their dependence with wavelength for the 250–1700 nm interval, showing the effect of sample geometry and cover-layer material (SiO2, TiO2, or Fe2O3), which significantly affect the oscillatory character of both parameters, as well as changes associated with the light incidence angle, which are attributed to surface impurities and inhomogeneity. Photoluminescence curves exhibit a similar shape independently of sample pore-size/porosity, but they seem to affect intensity values. This analysis shows the potential application of these NPA-bSs platforms to nanophotonics, optical sensing, or biosensing.

Novel cholesteric liquid crystal films creating angle insensitive reflective colors

AbstractWe have developed novel cholesteric liquid crystal (Ch‐LC) films creating angle insensitive reflective colors. The wavy alignment formed by rapid change of the helical twisting power (HTP) enables the suppression of color shift with different incident angles of light. These films open the door to create various decorative films for innovative applications.

Tunable multichannel Fibonacci one-dimensional terahertz photonic crystal filter

This paper proposes a multichannel terahertz optical filter based on a one-dimensional photonic crystal with a third-order Fibonacci structure, including a bulk Dirac semimetal. The tuning of the optical properties of the proposed structure has been theoretically studied as a function of the Dirac semimetals' Fermi energy. Furthermore, the effects of the Fibonacci structure's periodic number and light's incident angle on optical channels were investigated. The results reveal that changes in the Fermi energy and incident angle remarkably affect the frequency and transmission of the optical channels. Additionally, the number of optical channels increases by increasing the periodic number of the Fibonacci structure.

Concentrating behavior of elastic fresnel lens solar concentrator in tensile deformation caused zoom

The focal length of the Fresnel lens changing with the light incident angle will decrease Fresnel lens solar concentrators' energy efficiency and daily working hours, which seriously hinders its commercial application. Existing solutions, mainly including single-axis tracking, two-dimensional tracking, and passive tracking have their limitations and fail to realize the maximum application potential of the Fresnel lens. This paper proposes a novel elastic Fresnel lens solar concentrator, whose focal length can be regulated by tensile deformation. The mechanical and optical coupling simulations are conducted to reveal its concentrating behavior during tensile deformation. An exemplary elastic Fresnel lens with an aperture width of 200 mm and an original focal length of 360 mm is designed and studied. The simulation results illustrate that the optimal base thickness of the elastic Fresnel lens is 1 mm when its prism thickness is 2 mm. Under the optimal thickness parameters combination, the elastic Fresnel lens has an effective elongation rate r about 15%, which increases the focal length by 163 mm and 47% to the original focal length. The focus width only increases from 16 mm to about 20 mm when adjusting the focal length from 360 mm to 523 mm. Besides, the step-zoom strategy increases the exemplified elastic Fresnel lens’ acceptable angle from 30° to 45°. The tensile deformation caused zoom method increases the working hours of Fresnel lens by 1.5 times, demonstrating the effectiveness of this method.

Valley-optical absorption in planar transition metal dichalcogenide superlattices

In this study, we investigate the optical absorption of a planar superlattice comprising alternatively arranged two-dimensional Transition Metal DiChalcogenide semiconductors. Within a semi-classical model and using the Dirac-like equation in the presence of light interaction as a perturbation, we obtained the governing Hamiltonian. Using this Hamiltonian, we derived a fully analytical relationship for the absorption coefficient of the structure. By calculating the effective mass for different bands and using the Drude-Lorentz model, our approach is able to determine the oscillator strength and the effective refractive index of the structure. We found that the spin–orbit coupling has important effect on the absorption coefficient and energy bands where it reduces the absorption coefficient of the structure from typical value of 11.54 ({10}^{5}{mathrm{cm}}^{-1})–5.937({10}^{5}{mathrm{cm}}^{-1}), also the valence band experiences a significant blue shift, while the conduction band shows minor changes due to spin orbit coupling. Moreover, the role of incident light angle and light polarization were studied in details at different valleys of K and {K}^{^{prime}}. The most important finding is that by changing the polarization of incident light, it is possible to increase the absorption coefficients of K and {K}^{^{prime}} valleys by up to 30 times. For light propagation direction close to perpendicular to the plane of the superlattice, the right-circular polarization is absorbed only by K valley in contrast to the left-circular polarization, which is absorbed by the {K}^{^{prime}} valley. Our model might be used to design newly developed 2D optovalleytronic devices.

Investigations on electromagnetic wave scattering simulation from rough surface: Some instructions for surface roughness measurement based on machine vison

There are many experimental variables in the research of surface roughness measurement based on machine vision technology, such as light incident angle, light wavelength, workpiece material, surface features. It is, however, time-consuming and also labour-intensive to conduct experiments considering all these variables. In this work, we proposed to conduct Electromagnetic Wave Scattering Simulation considering these variables using finite element method (FEM) in order to give instructions for actual imaging design. The simulation process is more theoretically robust, more efficient and cost-effective rather than actual experiments with empirical models. In the simulation process, a simulation model is designed first. In this model, the light incident angles θ include 15°, 30°, 45°, 60° and 75°; the light wavelengths λ include 400 nm, 550 nm and 700 nm corresponding to blue, green and red; the workpiece materials include stainless steel (SUS), copper (Cu), aluminium (Al), and silicon carbide (SiC). Then, a series of rough surface with different surface roughness values are obtained by defining cosine functions and non-Gaussian surfaces. The simulation results show that given material, when 0≤Ra ≤ 0.1 μm, the performance of small θ is obviously better than that of large θ. When 0.1≤Ra ≤ 1 μm, large θ is better (θ ≥ 60°). This derives to obtain better measurement accuracy.

An IoT-based smart optical platform for colorimetric analyzing multiple samples of biomarkers

In this work, we have designed, implemented, and characterized an IoT-enabled optical platform that serves as a highly efficient colorimetric analyzer for disposable rapid diagnostic test kits. We have taken color images of the test chip using an external camera module connected to an IoT-enabled single-board mini-computer, which are then analyzed using an image processing algorithm. To prevent image burning and to reduce the impact of ambient lighting, we have proposed a unique light-diffusing model and have maintained a strategic distance within the white acrylic imaging enclosure of the platform. In order to ensure even and uniform distribution of light on the sample within the platform, we have carried out a study with the incorporation of a highly bright single LED, an LED array, and attaching a PDMS-made light diffuser on the LED array at varying light incident angles on custom-made single-channel test kits containing blood hematocrit. Finally, based on the optimized lighting conditions, we have successfully applied the proposed platform for the detection of blood hematocrit, β-hCG, and SARS-CoV-2 antigen, and were able to identify their different levels of concentration. Since the device is portable in size and cost-effective to implement, it can also be used for analyzing other biomarkers in resource-limited communities for point-of-care (POC) applications.

Design of Full Stokes Vector Polarimetry Based on Metasurfaces for Wide-Angle Incident Light

Polarization measurement plays an important role in optical detection, communication, and imaging systems. Compact polarimetry with a wide angle of incident light will break the restrictions of the limited incident angle and improve its practicality. In this paper, a full Stokes vector polarimetry with a wide incident angle of ±20°, based on a two-dimensional metasurface, is proposed. According to the simulation results, the maximum measurement error of the Stokes vector at 20° oblique incidence is 0.09. The light transmittance of the proposed structure is higher than 83%. Moreover, the tilt angle of the incident light can be determined with a calculation error lower than 0.5°, according to the focusing position of the transmitted light on the focal plane. The operating wavelength of the proposed polarimetry is set to 530 nm of green light, which makes it a potential application in visible light communication and underwater optical systems.

Tunable Single-Mode Output by Optical-Mode Selection

The ability to manipulate and select optical modes effectively and accurately is strongly desired to enable single-mode operation. Here, we report an optical system consisting of two directly coupled metal-cladded optical resonators that can realize a single-mode peak through control of the tuning between the resonant wavelengths of the two optical resonators. Additionally, the wavelength of the single-mode peak can be chosen via adjusting the angle of incident light. Furthermore, the linewidth and power of the single-mode output can be controlled completely by the thickness of the resonator guide layer and the angle of incident light. This optical system provides a way to realize optical information processing without the need for complex structures and specific materials.

All-optical polarization tuning based on an intensity-dependent nonlinear metasurface

Active control of light polarization at the nanoscale is essential for integrated photonic devices. Here, an all-optical approach is proposed to tune the polarization state of near-infrared light using a nonlinear metasurface. Based on the large intensity-dependent refractive index change of epsilon-near-zero (ENZ) materials, a phase difference between two orthogonal electric fields at ENZ wavelength can be continuously tuned in a range larger than 0.61π by varying the incident light power. The polarization state of the reflected light can thus be actively tuned from linear to circular state via an all-optical approach. Notably, abundant polarization states can be obtained by altering the polarization angle of incident light. The proposed all-optical approach is promising for tunable photonic functionalities of practical applications.

A Janus Logic Gate with Sensing Function

AbstractA layered metastructure (LM) formed by a quasi‐periodic arrangement of graphene and isotropic dielectric mediums, which can realize the functions of the tunable logic gate and refractive index (RI) sensing based on spin Hall effect (SHE), is theoretically studied. The asymmetric arrangement of the mediums and the increased angle of the incident electromagnetic waves (EWs) equip the LM with Janus feature. Through the modulation of the graphene chemical potential, the sharp absorption peak (AP) in the terahertz (THz) range can be obtained, and then the AP can be used to implement NOT logic and OR logic respectively corresponding to the forward and backward scales. By locating the incident angle of light corresponding to the SHE displacement peak, the linear measurement relationship between RI and SHE angle can be realized, and the widest RI measurement range is 1–1.4 with the angles changing from 21.88° to 61.84°. Additionally, a good linear range can be achieved, owning the optimum sensitivity (S) up to 153.5° RIU−1. The RI sensing still strictly follows the logic functions of the forward NOT and backward OR via adjusting the chemical potential of graphene and discriminating the peak value of SHE displacement.

High-efficiency silicon metasurface mirror on a sapphire substrate

For a possible implementation of high-efficiency Si-nanosphere metasurface mirrors functioning at telecom wavelengths in future gravitational wave detectors, exact dimensional and configuration parameters of the total system, including substrate and protective coating, have to be determined a priori. The reflectivity of such multi-layer metasurfaces with embedded Si nanoparticles and their potential limitations need to be investigated. Here we present the results on how the substrate and protective layer influence optical properties and demonstrate how dimensional and material characteristics of the structure alter light reflectivity. Additionally, we consider the impact of manufacturing imperfections, such as fluctuations of Si nanoparticle sizes and their exact placement, on the metasurface reflectivity. Finally, we demonstrate how high reflectivity of the system can be preserved under variations of the protective layer thickness, incident angle of light, and its polarization.

Optimized Design and Simulation of Optical Section in Electro-Reflective Modulators Based on Photonic Crystals Integrated with Multi-Quantum-Well Structures

In the design of photonic integrated circuits (PICs), the optical connections of the PIC surface, along with the electronic components of the chips, are significant issues. One of the optoelectronics components that utilizes these surface connections are electro-reflective modulators, consisting of an optical section and an electronic section. In this paper, a novel scheme of two-dimensional photonic crystals (PhCs) is presented for the optical and reflective sections of this device. This design is two-dimensional; thus, it has less volume than the current bulky structures. The finite element method is utilized to simulate and optimize the scheme of PhCs and gold layer parameters. Furthermore, optimization of design parameters is accomplished through the Nelder–Mead method. Moreover, the modeling and simulation of the proposed hybrid PhCs has been investigated according to the structural parameters with tolerance. These tolerances, related to the nanorods’ radius and lattice constants, are considered to justify and vindicate the fabrication technology limitations and conditions. In the “on” state of the modulator, the light transmission ratio is 98% for a 903 nm wavelength with a 45° angle of deflection and incident light, nd the bandwidth is 20 nm. For an 897 nm wavelength with a 41° angle, the transmission ratio is 95%, and the bandwidth is 7 nm.

Plasmonic Mode Analysis on Asymmetric ITO/Au/ITO Hyperbolic Metamaterials Using Prism-Coupled Spectroscopic Ellipsometry

Various trilayers (ITO-Au-ITO) of a constant total thickness of 43 nm, with different bottom and top ITO film thicknesses, have been prepared by magnetron sputtering. The effects of the relative position of the inserted gold layer on the trilayers’ plasmonic properties have been systemically investigated. To study their optical reflectance changes caused by the surface plasmon resonance, total internal reflection ellipsometry (TIRE) has been employed. Two reflectance minima, corresponding to the pseudo-Brewster (PB) and bulk plasmon polariton (BPP), are observed from the reflectance spectra. The impacts of the light incident angles on the behaviors of these modes have been monitored. The measured reflectivity spectra match well with the simulated reflectivity spectra based on the Fresnel formalism. For the ITOt/Au/ITOb = 5/3/35 sample, where the Au layer is positioned closest to the sampling liquid, the BPP mode becomes the sharpest (based on the amplitude and half-width) as compared to other samples, indicating that the closer the ITOt/Au interface is to the sampling liquid, the stronger the observable plasmonic resonance effect is. Furthermore, it is found that the dip position of this BPP mode is independent of the angle of incidence but is sensitive to the refractive index of the sampling liquid. Our results show that the dip position shifts to a shorter wavelength with increasing refractive index of the sampling liquid. This means that the trilayer can act as a refractive index sensor. By linear regression, the obtained sensing accuracy is up to 552 nm/RIU. This facilitates the potential application of this trilayer structure as a surface plasmon-enhanced refractive index sensor.

InGaN nanowire array photocathode with high electron harvesting capability

With the rise of III-V semiconductor materials, InGaN materials began to be widely concerned. Nanowire arrays have excellent light trapping ability and generate a large number of photogenerated electrons. However, the adjacent nanowires will absorb these electrons twice, so the quantum efficiency cannot perfectly measure the emission performance of the nanowire array photocathode. We introduce the collection efficiency to evaluate the photoemission performance. It is based on this background that we study the photoemission performance of InGaN nanowire array under the assistance of height, incident light Angle and applied electric field. Finite-difference time-domain (FDTD) method is used to compare the quantum efficiency and collection efficiency of InGaN nanowire. We find that when the height of the nanowire is 600 nm, the angle of incident light is 65°, and the electric field strength is 0.6V/μm, InGaN nanowire arrays have the highest collection efficiency, with the collection efficiency up to 34% and the collection ratio up to 71%. The collection efficiency is 66% higher than that without external electric field. Therefore, the research in this paper can provide a theoretical reference for the preparation and performance improvement of InGaN nanowire array photocathode.