Triangular Gratings Research Articles

Optimization on the design of nano-patterned ZnS:Cu LED surface using FDTD simulation

Communication technology is one of the most important parts of human history and is fast developing. Visible Light Communication (VLC) can be categorized as a Light Fidelity (Li-Fi) communication that uses visible light through a Light Emitting Diode (LED) to transfer data and information. Even though LEDs are considered as very good light sources, they also have problems with effectiveness, which is influenced by their surface structures. The LEDs must also be able to focus the transmitted data and greatly reduce the signal-to-noise ratio. One of the problems encountered with LEDs is the presence of Total Internal Reflection (TIR) due to the large difference in refractive index between the LED and air, which causes photons to be trapped in the LED. Some trapped photons' energy may change into heat, thus reducing the LED's Light Extraction Efficiency (LEE). Using nanopatterns on the surface of LEDs is one way to reduce TIR on LEDs and enhance photon extraction from LEDs. Many parameters can influence the performance of nanopatterns on LEDs, so modelling efforts are needed before fabrication to save time and cost. Ansys Lumerical FDTD can be used to simulate and model the effects of nanopatterns on LED surfaces on LEE and beam focusing effect. In this study, simulations were carried out using Ansys Lumerical FDTD with variations in nanopattern shape parameters in the form of grating, blaze grating, triangular grating, and hemisphere. Apart from that, variations were also made to the height and width parameters of the grating to see the effect of these parameters on the efficiency of the LED. The FDTD simulation codes were validated using the Ansys database. The optimization results show that the most optimum shape is the grating nanopattern with a width of 216 nm and a height of 300 nm, which produces a peak wavelength of 480 nm in the far field pattern and has the highest increase in the LEE of 300 times in ±15° and 5500 times in ±5°. The huge spike in LEE enhancement at ±5° indicates that the nanopattern caused a focusing effect. The simulation results were compared using previous experimental data of Fabricated ZnS:Cu LED. It is shown that the simulation results are in line with the experimental data. The result shows that the simulation is very useful in designing the nano-patterned ZnS:Cu LED surface to achieve the best performance in the LEE and LED focusing effect for a specific application such as the VLC.

Nanoscale grating-based perovskite solar cell with improved efficiency

MAPbI3 perovskite-based solar cell (PSC) has attracted much attention due to its high absorption rate. The top flat electrode degrades the behavior of PSC due to limiting the light reached to the absorber layer, which reduces the efficiency. In this study, the influence of texturing the top FTO electrode surface with a triangular saw-tooth grating on both the optical and electrical performance is reported. The interference effects are also considered in this work by modeling the PSC structure as a Fabry–Perot resonator. In this regard, the finite difference time domain method is utilized to precisely simulate the optical characteristics of the nano-structural design. Also, the optical behavior of PSC is studied at different triangular grating (TG) structures and dimensions at which the light absorption is maximized. Furthermore, the effect of absorber thickness and defect density on the optoelectronic performance is investigated. We configured the conversion efficiency (η) of the proposed PSC structure by using the bulk and Langevin recombination mechanisms. The proposed grating structure enhances the light coupling, and hence the light absorption and the generated current density are increased. For absorber thickness of 350 nm, we reported a maximum conversion efficiency (η) of 19.5% for the proposed triangular grating (TG) structure with an enhancement of 19.6% compared to the structure with a flat FTO layer. As the defect density is increased from 1012 cm−3 to 1018 cm−3, the efficiency of the optimum TG PSC is reduced from 19.5% to 10.1%, respectively. The simulation results, therefore, contribute to the understanding of the PSC-based MAPbI3 design and can be used to improve its physical behavior.

Exploiting graded triangular gratings for optimal nano-focusing: A novel approach to enhance SERS efficiency

Plasmonic graded nano-gratings enable rainbow trapping of multiple resonant modes over a wide wavelength spectrum, useful for multi-channel Surface Enhanced Raman Spectroscopy (SERS) of molecular species. However, rectangular nano-gratings have limitations in achieving efficient rainbow trapping and localizing a wide spectrum of plasmonic modes due to their stepwise geometry, which induces high dissipation of surface plasmon polaritons into the substrate. An alternative platform of graded triangular nano-gratings enables increased localization and more efficient adiabatic transformation between neighboring grooves. Varying groove angles, depths, and periods in the tapered geometry allow for smooth adjustment of the surface plasmon polariton propagation constant, reducing losses and maximizing nano-focusing inside the groove tips. To overcome the limitation of low aspect ratio in wet-etching silicon, we employed a multi-step process of reactive ion etching of a SiO2 barrier layer to generate aperture width, followed by anisotropic wet-etching. The resulting graded triangular nano-gratings showed excellent SERS enhancement along three laser wavelength excitations. The enhancement factors of 638 and 785 nm wavelengths are 8.5 × 109 and 9 × 108, respectively, for the detection of 1 µM Rhodamine 6G. In addition, graded triangular nano-gratings show similar enhancement factors for other species, specifically the lipid DPEE-PEG, at the 532 nm laser excitation wavelength with an excellent SERS enhancement factor of 1.5 × 109. Owing to the ability of the graded triangular gratings to elicit pronounced SERS responses across three distinct laser excitations, they unequivocally qualify as “rainbow trapping” structures. Wider apertures, lower ohmic losses, and the ability to tune the groove angle beyond conventional etching methods bode well for graded triangular gratings as a superior platform for miniature sensors.

Geometrical Optimization of 2D MoS2-Ag Rectangular and Triangular Grating for Enhanced Solar Cell Efficiency

Geometrical Optimization of 2D MoS2-Ag Rectangular and Triangular Grating for Enhanced Solar Cell Efficiency

Optimizing Algorithm for Existing Fiber-Optic Displacement Sensor Performance.

This paper describes the optimal design of a miniature fiber-optic linear displacement sensor. It is characterized by its ability to measure displacements along a millimetric range with sub-micrometric resolution. The sensor consists of a triangular reflective grating and two fiber-optic probes. The measurement principle of the sensor is presented. The design of the sensor's triangular grating has been geometrically optimized by considering the step angle of the grating to enhance the sensor's resolution. The optimization method revealed a global optimum at which the highest resolution is obtained.

The Effects of Temperature Variation with Surface Triangle Grating on Silicon Thin-Film Solar Cell Array Efficiency

AbstractThis paper examines the effect of temperature variation on the surface triangular grating of the surface plasmon polariton (SPP) on the effectiveness of the entire array of silicon thin-film solar cells. Thin-film solar cells’ optical and electrical characteristics are examined using the electromagnetic and semiconductor models. The 3D Multiphysics simulator is used to present this study. The MATLAB/SIMULINK model based on mathematical formulas is developed to simulate the entire array of solar cells with thin films. This approach is suggested for quickly simulating the thin-film array. The presented model was applied on thin-film solar cells with and without SPP depending on the complete cell parameters from the COMSOL Multiphysics model. The triangle’s SPPs accomplish a 14.76% efficiency increase of 1.07% over a solar cell without SPPs.

Design of High Performance Triangular Fiber Bragg Grating Temperature Sensor using OptiSystem and OptiGrating Software

This paper presents on the design of high performance triangular Fiber Bragg Grating (FBG) as temperature sensor. This triangular FBG is designed and simulated using OptiGrating Software. The Triangular FBG design is exported to OptiSystem Software. In the OptiSystem software, the overall triangular FBG temperature sensor system is designed and simulated. It found that the triangular FBG has higher temperature sensitivity which is 37.5pm/°C than the standard FBG which is around 13pm/°C. It also has high linearity of 99.2% which specifies the consistency of wavelength shift as the temperature is increased. It also has higher resolution due to its sharp peak and smaller bandwidth.

Morphological Design of the Photonic Crystals Influence on Improving the Optoelectronic Properties of a-SiGe:H Thin Film Solar Cell

Abstract: With their nano-engineered feature, Photonic Crystals (PhCs) allow the best control of the propagation and absorption of light in an increased way. In our work, we applied the Rigorous Coupled Wave Analysis (RCWA) method to calculate the diffraction efficiency, field distribution, for a specific incidence angle and absorption energy in a periodic structures using unpatterned, 1DPhC, half circle and triangular grating structures with both a-Si:H, a-SiGe:H thin film semiconductor materials with different gratings of PhCs to improve optical absorption, taking into account the J-V solar cell characteristics. According to our simulation, the ideal result was in the case of triangular grating with a-SiGe:H semiconductor material so for the presence of Germanium, which enhances light absorption by reducing the band gap energy. The optical light absorption was more than 85.7% by increase the lattice parameter from 0.3µm to 0.5µm. Moreover, we found a solar cell efficiency enhancement of 16.6%, with a total improvement of 7.74%; as compared with unpatterned grating. Concerning the incidence angle effect, the better one is ranged between 50° and 70° with a peak absorption ratio of 99%. Keywords: Photonic crystals, RCWA, Incidence angle, Triangular grating, Solar cell.

Fringe visibility in X-ray interferometer using dual triangular phase gratings

In recent years, the X-ray interferometer using dual phase gratings has been extensively studied. The large periodic fringes produced by the X-ray interferometer using dual phase gratings can be directly detected by ordinary detectors. At the same time, the X-ray interferometer using dual phase gratings can reduce the radiation dose of the sample without using absorption gratings. Meanwhile, a high fringe visibility is always preferred to achieve a high signal-to-noise ratio for X-ray grating interferometry. However, recent studies have reported that experimental fringe visibility in X-ray interferometer using dual rectangular phase gratings is relatively low. Therefore, it is necessary to further increase the fringe visibility in X-ray interferometry using dual phase gratings. This work focuses on the analysis of fringe visibility in X-ray interferometer using dual triangular phase gratings. Based on the fringe intensity distribution formula of X-ray dual phase grating interferometer, the fringe visibility of the dual triangular phase grating interferometer is investigated as a function of the grating spacing under monochromatic and polychromatic illumination, respectively. For comparison, the fringe visibility of the dual rectangular phase grating interferometer is also studied under the same condition. The results show that the maximum fringe visibility of the dual triangular phase grating interferometer increases with the phase shift increasing regardless of monochromatic or polychromatic illumination. Under monochromatic illumination, the maximum fringe visibility of dual 5π/2 triangular phase gratings is about 21% higher than that of dual rectangular phase gratings. Under polychromatic illumination, the fringe visibility of dual 5π/2 triangular phase gratings is at least 23% higher than that of dual rectangular phase gratings. Under polychromatic illumination, the greater the deviation of X-ray average energy from the grating design energy, the greater the decrease of maximum fringe visibility of the dual phase grating interferometer is. In addition, with the increase of the focal size of X-ray source, the maximum fringe visibility of the dual phase grating interferometer decreases, under polychromatic illumination. We hope that those results can be used as guidelines for designing and optimizing X-ray interferometer using dual triangular phase gratings.

Simulation Study of Sub-Period Super-Resolution X-ray Phase Imaging with Triangular Phase Grating

X-ray phase contrast image has higher sensitivity to materials with light elements than the conventional absorption contrast. Phase image measurement technique using diffraction gratings can be used in the laboratory. Furthermore, X-ray phase microscope using the diffraction gratings has been also developed. However, phase measurement with diffraction gratings has a drawback that the spatial resolution is limited to the grating period. To overcome this problem, a scanning system using a triangular phase grating has recently been proposed, which is expected to archive a large field of view and a high spatial resolution. This study aims to investigate the feasibility of the system and a deep understanding of the optical system by simulation.

Broadband radiation pressure on a small period diffractive film.

The p-polarization component of radiation pressure force from an unpolarized blackbody light source is predicted by the use of a Maxwell equation solver for a right triangular prism grating of period 2 μm and refractive index 3.5. The transmitted and reflected angular scattering distributions are found to qualitatively agree with diffraction theory: At relatively short wavelengths the transmitted light is concentrated near the refraction angle, and reflected light is concentrated near the reflection angle. Owing to diffraction and multiple internal reflections, however, the spectral irradiance of transmitted and reflected light was found to significantly vary with wavelength. We found that the high value of the refractive index produced a large fraction of reflected light, thereby reducing the net transverse component of radiation pressure force. These results suggest that low index transmission gratings, anti-reflection coatings, optimized metasurface films, or reflection gratings should be explored for future solar sailing missions.

Blazed gratings with both controllable blaze angle and anti-blaze angle fabricated by using a twice oblique ion beam etching method.

A twice oblique ion beam etching method is proposed to fabricate triangular blazed gratings that have controllable both blaze angle and anti-blaze angle. The anti-blaze angle is controlled by first obliquely etching the photoresist mask to obtain an asymmetrical trapezoidal grating, one sidewall of which then evolves into the anti-blaze facet in the second etch step. The blaze angle is controlled by obliquely etching the asymmetrical trapezoidal grating to obtain a triangular blazed grating. We show the key process steps of the method by fabricating a blazed grating with the blaze angle of 20.9° and the anti-blaze angle of 89.0°. The method is verified not only to increase the anti-blaze angle to near 90°, but also have a good tolerance against over-etching.

Multi-Wavelength Super-Resolution Imaging by Structured Illumination of Bloch Surface Waves

Multi-wavelength imaging ability is important for bio-imaging, to obtain multi-modal information of biological activities. We propose a multi-wavelength super-resolution imaging method, employing the Bloch surface waves (BSWs) supported by one-dimensional photonic crystal as subwavelength structured illumination fields. Here 488 nm (blue), 532 nm (green), and 632.8 nm (red) are chosen as the illumination wavelengths, and a two-dimensional equilateral triangular grating is designed to couple the incident plane waves to the BSWs in the all-dielectric photonic crystal. The triangular grating ensures a more uniform resolution improvement along with whole lateral directions and provides better imaging quality compared with lattice grating. In our demonstration, the resolution improvements are above 2.4 fold for the three wavelengths, and lateral resolutions are below 120 nm in the Rayleigh criterion. Moreover, as the illumination device is composed of a periodic planar structure, the larger field of view is achievable. The proposed method could achieve multi-wavelength wide-field super-resolution surface imaging while maintaining high speed, good imaging quality and bio-compatibility.

Reflection Mechanism of Dielectric Corner Reflectors: The Role of the Diffraction of Evanescent Waves and the Goos-Hänchen Shift.

Nano- and microstructures have been developed for asymmetric light transmission (ALT) filters operating in a wide wavelength range. One of the most straightforward structures with ALT properties is a dielectric corner reflector (DCR) comprising a one-dimensional grating of a triangular shape on one surface. The DCR possesses strong reflection only for one-way light illumination due to multiple total internal reflections (TIRs) inside the triangular grating. For triangular structures being much larger than the wavelength of light, the reflection properties are expected to be fully described by geometrical optics. However, geometrical optics do not account for the Goos–Hänchen (GH) shift, which is caused by the evanescent wave of the TIR. In this work, the reflection mechanism of DCRs is elucidated using the finite element method and a quantitative model built by considering the GH shift. The reduction in reflection of the DCR is dominated by diffraction of the evanescent wave at the corner of the triangular structure. Our model is based on simple mathematics and can optimize the DCR geometry for applications addressing a wide wavelength range such as radiative cooling.

Оптимизация технологии изготовления дифракционных Si-решеток треугольного профиля для мягкого рентгеновского и экстремального ультрафиолетового излучения

Anisotropic wet etching of vicinal single-crystallyne Si (111)4° wafers was used to obtain blazed gratings with high efficiency for soft X-ray (SXR) and extreme ultraviolet (EUV) applications. An improved experimental technology for the fabrication of triangular Si gratings, both medium frequency (250 and 500 mm-1) and high-frequency 2500 mm-1, is presented. The stages of a Cr mask formation for grooves etching, removing Si protrusions in order to smooth the profile, and polishing the surface to reduce nanoroughness are optimized. This work describes the method for simultaneous (in one process) obtaining a smoothed triangular profile of the Si grating and a polished surface of grooves by wet etching.

A theoretical study of grating effects on the performance of surface plasmon resonance sensing surface

The purpose of this paper is to conduct a theoretical analysis of the performance of a Surface Plasmon Resonance (SPR) sensing surface based on and the attenuated total reflection (ATR) phenomenon. Initially, the proposed structure comprises a prism, a thin gold layer, and an analyte. The effect of rectangular and triangular gratings on the SPR sensing surface’s sensitivity is evaluated. The finite element method (FEM) simulation results indicate that the presence of gratings significantly increases the sensitivity of the structure to the point where the maximum sensitivity of 62.5 (deg/RIU) has been achieved for both gratings when the width and height are 5 nm and 15 nm, respectively.

Surface Plasmon Enhanced Light Emitting Diodes Based on Triangular Grating

Surface Plasmon Enhanced Light Emitting Diodes Based on Triangular Grating

Optical capture capability enhancement by right-angled triangular visible absorber

Polarization-insensitive thin-film absorber is proposed by right-angled triangular grating. Combining the electric field distribution under two polarizations, the physical mechanism of absorption is analyzed using the finite element method. The presented results show that the average absorption efficiency exceeds 90.10% with a spectral range of 300-680 nm, and the incident angle can reach 50°. Compared with reference planar and triangular structures, the thin-film visible absorber presented has better absorption characteristics. Furthermore, compared with the reported visible absorber by rectangular grating, the visible absorber designed in this work has enhanced absorption spectrum bandwidth of 380 nm and wide angle of 50°. It is believed that the novel absorber has great potential in the field of visible light absorber.

Asymmetric light transmission based on a 1D triangular metal grating

Here, we present a 1D isosceles triangle silver grating on the dielectric substrate. The grating performs asymmetric light transmission (ALT) characteristics for the light with both transverse magnetic (TM) and transverse electric (TE) polarization states over a waveband in the vicinity of 1.55 µm. By checking the efficiency of each diffraction order and the distribution of the electromagnetic field, we found that the ALT characteristics originate from the high transmitted or reflected diffraction channels excited by forward and backward direction incidence. The grating shows the ALT characteristics in a waveband where incident wavelengths are less and more than the period, so that the grating may be a candidate for the wideband ALT devices. It is worth stressing that the contrast ratio (CR) at a specific wavelength can exceed more than 29 dB (the incident angle is 5.6897°; the incident wavelength is 1.7759 µm) under oblique incidence.

Surface-plasmon-enhanced LED based on multilayer gratings and core-shell Ag/SiO2 nanoparticles

This paper proposes a novel GaN-based LED with nano-grating structure based on surface plasmons. This structure mainly contains n-GaN, multiple quantum wells and p-GaN, Ag–SiO2 grating, core–shell Ag/SiO2 nanoparticle and ITO triangular grating. The basic principle of the light emitting characteristics of LED is described in detail. The COMSOL software is used to analyse properties and optimise parameters based on the finite element method. The radiated intensity, absorbed intensity and electric field distribution are obtained. The results indicate that this structure has a higher luminous efficiency with the luminous intensity increased to about 58.59 times compared with the ordinary structure and about 3.94 times compared with the reference structure, and can enhance the internal quantum efficiency and the external quantum efficiency of the LED simultaneously.