Angle Of Incident Light Research Articles

Enhanced blue-green response of nanoarray AlGaAs photocathodes for underwater low-light detection.

Underwater optical communication and low-light detection are usually realized via blue-green laser sources and blue-green light-sensitive detectors. Negative-electron-affinity AlGaAs photocathode is an ideal photosensitive material for ocean exploration due to its adjustable spectrum range, long working lifetime, and easy epitaxy of materials. However, compared with other photocathodes, the main problem of AlGaAs photocathode is its low quantum efficiency. Based on Spicer's three-step photoemission model, nanoarray structures are designed on the surface of AlGaAs photocathode to improve its quantum efficiency from two aspects of optical absorption and photoelectron transport. Through simulation, it is concluded that the cylinder with diameter of 120 nm and height of 600 nm is the best nanoarray structure, and its absorptance is always greater than 90% in the 445∼532 nm range. Moreover, the absorptance and quantum efficiency of the cylinder nanoarray AlGaAs photocathode are less affected by the incident angle. When the angle of incident light reaches 70°, the minimum absorptance and quantum efficiency are still 64.6% and 24.9%. In addition, the square or hexagonal arrangement pattern of the nanoarray has little effect on the absorptance, however, a reduction in the overall emission layer thickness will decrease the absorptance near 532 nm.

Dual-Function Meta-Grating Based on Tunable Fano Resonance for Reflective Filter and Sensor Applications.

Localized surface plasmon resonance (LSPR)-based sensors exhibit enormous potential in the areas of medical diagnosis, food safety regulation and environmental monitoring. However, the broadband spectral lineshape of LSPR hampers the observation of wavelength shifts in sensing processes, thus preventing its widespread applications in sensors. Here, we describe an improved plasmonic sensor based on Fano resonances between LSPR and the Rayleigh anomaly (RA) in a metal-insulator-metal (MIM) meta-grating, which is composed of silver nanoshell array, an isolation grating mask and a continuous gold film. The MIM configuration offers more freedom to control the optical properties of LSPR, RA and the Fano resonance between them. Strong couplings between LSPR and RA formed a series of narrowband reflection peaks (with a linewidth of ~20 nm in full width at half maximum (FWHM) and a reflectivity nearing 100%) within an LSPR-based broadband extinction window in the experiment, making the meta-grating promising for applications of high-efficiency reflective filters. A Fano resonance that is well optimized between LSPR and RA by carefully adjusting the angles of incident light can switch such a nano-device to an improved biological/chemical sensor with a figure of merit (FOM) larger than 57 and capability of detecting the local refractive index changes caused by the bonding of target molecules on the surface of the nano-device. The figure of merit of the hybrid sensor in the detection of target molecules is 6 and 15 times higher than that of the simple RA- and LSPR-based sensors, respectively.

Semitransparent Organic Position Sensitive Detector with Thin Ag Electrode Toward the Angle Detection of Incident Light Using Stacked‐Type Device

A semitransparent organic position sensitive detector (PSD) that takes advantage of the translucent feature of organic semiconductors is developed. It is fabricated by controlling the thickness of the Ag thin film used as the common electrode to create a translucent electrode. The linearity accuracy of the sensor is evaluated to be 2.7% for the incident light from the indium tin oxide side and 3.6% for the incident light from the Ag side. When two semitransparent devices are stacked and vertically incident, a linearity of about 6.0% is obtained, even for the device placed on the lower side. Furthermore, it is demonstrated that the incident angle of light can be detected by stacking two semitransparent devices. When the incident angle of light varies from 0° to 30°, the maximum difference from the actual incident angle is 6.5°. This work is anticipated to be useful for developing angular detection devices based on organic PSD.

Fabrication of transparent and hazy cellulosic light-management film for enhancing photon utilization in photocatalytic membrane process

Given the high demand of photocatalytic membrane filtration processes on both mass transport and light-utilization, this work introduces a novel transparent and highly porous cellulose film (P-RCF) that can serve as a light management layer to enhance the photon utilization of photocatalytic membrane processes. The built-in micron-sized pores act not only as channels for mass transport (filtration resistance ∼5 × 1010/m) but also as forward scatterers to endow the film with a high transmission haze (∼77%) without impairing its transmittance (∼90%). A g-C3N4 membrane with attached P-RCF (P-RCF@C3N4) exhibited enhanced photocatalytic activity for both tetracycline (TC) oxidation and Cr(VI) reduction. Moreover, by adjusting the incident light angle from 0° to 50°, the observed TC degradation kinetics on P-RCF@C3N4 became more stable than those on the bare g-C3N4 membrane, exhibiting incident-angle-independent properties. This enhanced photocatalytic performance can be attributed to the synergistic effect of refractive-index matching and light scattering within our transparent film, which reduces light reflection and traps the light inside at the photoactive layer, resulting in extended light propagation and utilization. This study provides a novel and versatile strategy for developing light management techniques for advanced photocatalytic membrane systems.

Single-step detection of toxic airborne metallic nanoparticles using Goos–Hänchen effect in photonic Bragg grating structures

A real-time photonic crystal sensor is suggested for the detection of airborne heavy metal nanoparticles (HMNPs). The sensor consists of a sandwiched sampling cell between two stacks of alternating TiO2 and Si-Ge layers, forming the core of the device. The sensor’s performance is based on monitoring changes in both the intensity and phase of a probe beam as it propagates through the core. By analyzing the fluctuations in intensity, central frequency, and full width at half maximum (FWHM) of the resonant mode within the transmittance spectrum bandgap, or by monitoring the phase changes at the angle of maximum transmittance that may result in a remarkable Goos–Hänchen (GH) shift in transmittance, the sensor can identify the pollutant nanoparticles. Tuning the thicknesses of the slabs and the number of unit cells in the photonic crystal can dynamically shift the resonant mode and bandgap edges, allowing for easy adjustment of the sensor’s responsivity. Furthermore, the optical response of the sensor can be tuned through external parameters such as the incident angle of the probe light or an externally applied electric field. Additionally, the sensor exhibits sensitivity not only to changes in the extent of the sample but also to the shape of the present HMNPs. These characteristics make the proposed configuration cost-effective, user-friendly, and suitable for HMNPs detection without the need for complex sample preparation, data analyses or additional tools/accessories.

On predicting annual output energy of 4-terminal perovskite/silicon tandem PV cells for building integrated photovoltaic application using machine learning

Building integrated photovoltaic (BIPV), based on tandem PV cells, is considered a new alternative for combining solar energy with buildings. Accurately predicting the BIPV-harvested annual output energy (Eout,annual) is crucial for evaluating the BIPV performance. Machine learning (ML) is a potential candidate for solving such a problem without the time-consuming process of experimental investigations. This contribution proposes an artificial neural network (ANN) to predict the Eout,annual of 4-terminal perovskite/silicon (psk/Si) PV cells under realistic environmental conditions. The input variables of the proposed model consist of the input solar irradiance (Pin), incident light's angle (Ain), the PV module's temperature (Tmod), the psk absorber's thickness (Thpsk), and the psk absorber's bandgap (Bpsk). The input data were received from the simulated results. This work also evaluates the degree of importance of each input variable and optimizes the architecture of the ANN using the surrogate algorithm before predictions. The optimized ANN-3 (three hidden layers) model shows superior performance indicators, including a mean squared error of MSE = 0.02283, correlation coefficient R = 0.99999, and Willmott's index of agreement Iw = 0.99999. Consequently, the predicted highest Eout,annual at Bpsk of 1.71 eV is 297.73, 115.01, 193.98, and 97.6 kWh/m2 for the rooftop, east, south, and west facades, respectively.

Tunable Multiple Surface Plasmonic Bending Beams into Single One by Changing Incident Light Wavelength

Controllable surface plasmonic bending beams (SPBs) with propagating along bending curves have a wide range of applications in the fields of fiber sensors, optical trapping, and micro-nano manipulations. In terms of designing and optimizing controllable SPB generators, there is great significance in realizing conversion between multiple SPBs and single SPB without rebuilding metasurface structures. In this study, a SPB generator, composed of an X-shaped nanohole array, is proposed to realize conversion between multiple SPBs and a single one by changing the incident light wavelength. The Fabry–Pérot (F–P) resonance effect of SPPs in nanoholes and localized surface plasmonic (LSP) resonance of the nanohole are utilized to explain this conversion. It turns out that the relationship between the electric field intensities of SPBs and the polarization angle of incident light satisfies the sine distribution, which is consistent with dipole radiation theory. In addition, we also find that the electric field intensities of SPBs rely on the width, length, and angle of the X-shaped nanohole. These findings could help in designing and optimizing controllable and multi-functions SPBs converters.

Performance improvement of yellow flip-chip mini-LEDs via full-angle distributed Bragg reflector

Miniaturized light-emitting diodes (mini-LEDs) have gained much attention for liquid crystal displays back-light and self-emissive displays. However, the unsatisfactory performance of InGaN long-wavelength mini-LEDs hinders their practical applications. Herein, we develop a full-angle distributed Bragg reflector (DBR) and investigate its impact on the performance of yellow flip-chip mini-LEDs. The full-angle DBR consists of different stacks of Ti3O5/SiO2 layers that are optimized for multiple central wavelengths. Compared to conventional single-DBR stacks, such full-angle DBR enables wider reflectance bandwidth and less dependence of reflectance on the light incident angle from 0° to 50°. Specifically, full-angle DBR features high reflectance beyond 99% from 447 to 580 nm at an incident angle of 50°. Full-angle DBR is found to enhance the electric field intensity at the top of devices, indicating that light extraction efficiency is promoted. As a result, yellow flip-chip mini-LEDs with full-angle DBR show higher light output power than those without DBR at the same currents. Our work paves a way to improve the performance of small-size emitters with long wavelength.

The Sensitivity of a Hexagonal Au Nanohole Array under Different Incident Angles

Surface plasmon resonance sensors have been widely used in various fields for label-free and real-time detection of biochemical species due to their high sensitivity to the refractive index change of the surrounding environment. The common practices to achieve the improvement of sensitivity are to adjust the size and morphology of the sensor structure. This strategy is tedious and, to some extent, limits the applications of surface plasmon resonance sensors. Instead, the effect of the incident angle of excited light on the sensitivity of a hexagonal Au nanohole array sensor with a period of 630 nm and a hole diameter of 320 nm is theoretically investigated in this work. By exploring the peak shift of reflectance spectra of the sensor when facing a refractive index change in (1) the bulk environment and (2) the surface environment adjacent to the sensor, we can obtain the bulk sensitivity and surface sensitivity. The results show that the bulk sensitivity and surface sensitivity of the Au nanohole array sensor can be improved by 80% and 150%, respectively, by simply increasing the incident angle from 0° to 40°. The two sensitivities both remain nearly unchanged when the incident angle further changes from 40° to 50°. This work provides new understanding of the performance improvement and advanced sensing applications of surface plasmon resonance sensors.

Nonlinear optical bistability based on epsilon-near-zero mode in near-infrared band.

We propose a simple thin-layer structure based on epsilon-near-zero mode field enhancement to achieve optical bistability in the near-infrared band. The high transmittance provided by the thin-layer structure and the electric field energy limited in the ultra-thin epsilon-near-zero material means that the interaction between the input light and the epsilon-near-zero material can be greatly enhanced, creating favorable conditions for the realization of optical bistability in near-infrared band. The optical bistability hysteresis curve is closely related to the incident angle of light and the thickness of epsilon-near-zero material. This structure is relatively simple and easy to prepare, so we believe that this scheme will have a positive effect on the practicality of optical bistability devices in all-optical devices and networks.

14‐2: Angle‐insensitive meta‐surface color filters designed by integrating genetic algorithm with artificial neural network

Next‐generation displays require tiny pixel sizes and are applied to AR/VR and holograms. Conventional color filters have limitations in miniaturization and shows poor reliability from heat, light and other environment. Meta‐surface color filters (MCFs) are one of the solutions to replace conventional color filters, suitable for high‐resolution displays. Structural design parameters are adjusted to determine the filtering properties of the MCFs. In addition, the metal based meta‐surface shows better durability cause of the intrinsic characteristics of the material. However, if the structure is complicated, there require many case‐ studies for verification, which increases trial and error. In addition, resonance by phase matching between structures changes according to the angle of incident light. In this study, we suggest a method to reduce the trial and error required in designing structure. Also, the design parameters of the MCFs of the desired color was extracted through an AI model capable of reverse design. Furthermore, we propose a novel MCFs that shows characteristics independent to the angle of incident light through a coaxial hole and disk array structure.

Development of an angle detection system for channeling implantation to the c-axis of SiC using birefringence phenomenon

We developed an angle detection system for channeling ion implantation in 4H-SiC using the birefringence phenomenon. Our optical method detects the c-axis direction in 4H-SiC due to its uniaxial optical properties. The system, consisting of a laser, polarizer, gonio stage, and analyzer, is simple and cost-effective. We conducted experiments on both on-axis and off-axis 4H-SiC (0001) samples, presenting angular dependence results around the [1–100] and [11–20] rotations. Despite the need for consideration of light incident angles, the performance was comparable to Rutherford backscattering spectrometry. These findings suggest the potential application of our system in channeling implantation to the c-axis of 4H-SiC.

A machine learning-based prediction of crystal orientations for multicrystalline materials

We established a rapid, low-cost, and accurate technique to measure crystallographic orientations in multicrystalline materials by optical images and machine learning. A long short-term memory neural network was trained with pairs of light reflection patterns and the correct orientations of each grain, successfully predicting orientation with an error median of 8.61°. The model was improved by diverse data taken from various incident light angles and by data augmentation. When trained on different incident angles, the model was capable of estimating different orientations. This is related to the geometrical configuration of the incident light angles and surface facets of the crystal. The failure in certain orientations is thought to be complemented by supplementary data taken from different incident angles. Combining data from multiple incident angles, we acquired an error median of 4.35°. Data augmentation was successfully performed, reducing error by an additional 35%. This technique can provide the crystallographic orientations of a 15 × 15 cm2 sized wafer in less than 8 min, while baseline techniques such as electron backscatter diffraction and Laue scanner may take more than 10 h. The rapid and accurate measurement can accelerate data collection for full-sized ingots, helping us gain a comprehensive understanding of crystal growth. We believe that our technique will contribute to controlling crystalline structure for the fabrication of high-performance materials.

Efficient solar absorber based on VO2-W-SiO2 hybrid metamaterials

The broad spectrum near unity solar absorber shows important significance in the solar energy conversion. In this work, a polarization independent broadband and wide-angle metamaterials solar absorber consisted of VO2 periodic arrays and alternately stacked SiO2/W layers is designed. To explore the absorption of solar radiation and proper geometric parameters, numerical studies are carried out on the proposed structure. And the absorption of the designed structure is above 90% in the spectra range of 300-2000 nm with an average absorption of 95%. Moreover, the proposed structure possesses excellent solar absorptivity and insensitivity to the incident angle and polarization of sunlight. The average integrated absorption remains 90% with the light incident angle of 50°. Hence, the proposed broadband solar absorber has potentially valuable applications in thermophotovoltaic conversion, thermal emitters, solar cell, and so on.

Low-Threshold Optical Bistability Based on Photonic Crystal Fabry–Perot Cavity with Three-Dimensional Dirac Semimetal

In this paper, we investigate theoretically the tunable low threshold optical bistability (OB) in the terahertz range based on photonic crystals’ Fabry–Perot (FP) cavity with a three-dimensional Dirac semimetal (3D DSM). On the one hand, a 3D DSM with a high nonlinear refractive index coefficient creates conditions for the generation of OB. Additionally, the finite film thickness of 3D DSMs leads to significantly a enhanced interaction volume compared to graphene, which allows easier preparation and has stable properties. On the other hand, the resonance of the FP cavity plays a positive role in promoting the tunable low-threshold OB. It was found that the OB threshold and hysteresis curve can be continuously adjusted by manipulating the Fermi energy and relaxation times of a 3D DSM. Additionally, the bistable curve of the composite structure is also closely related to the angle of incident light. Through parameter optimization, OB with a threshold approaching 105 V/m can be obtained. The photonic crystal’s FP cavity with a 3D DSM structure provides a feasible way to achieve low-threshold OB and a building block for future integrated all-optical devices.

Out-of-Plane Electronics on Flexible Substrates Using Inorganic Nanowires Grown on High-Aspect-Ratio Printed Gold Micropillars.

Out-of-plane or3Delectronics on flexible substrates are an interesting direction that can enable novel solutions such as efficient bioelectricity generation and artificial retina. However, the development of devices with such architectures is limited by the lack of suitable fabrication techniques. Additive manufacturing (AM) can but often fail to provide high-resolution, sub-micrometer 3D architectures. Herein, the optimization of a drop-on-demand (DoD), high-resolution electrohydrodynamic (EHD)-based jet printing method for generating 3D gold (Au) micropillars is reported. Libraries of Au micropillar electrode arrays (MEAs) reaching a maximum height of 196µm and a maximum aspect ratio of 52 are printed. Further, by combining AM with the hydrothermal growth method, a seedless synthesis of zinc oxide (ZnO) nanowires (NWs) on the printed Au MEAs is demonstrated. The developed hybrid approach leads to hierarchical light-sensitive NW-connected networks exhibiting favorable ultraviolet (UV) sensing as demonstrated via fabricating flexible photodetectors (PDs). The 3D PDs exhibit an excellent omnidirectional light-absorption ability and thus, maintain high photocurrents over wide light incidence angles (±90°). Lastly, the PDs are tested under both concave and convex bending at 40mm, showing excellent mechanical flexibility.

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.