Vertical Illumination Research Articles

High-speed, phase contrast retinal and blood flow imaging using an adaptive optics partially confocal multi-line ophthalmoscope.

High-speed, phase contrast retinal and blood flow imaging using an adaptive optics partially confocal multi-line ophthalmosocope (AO-pcMLO) is described. It allows for simultaneous confocal and phase contrast imaging with various directional multi-line illumination by using a single 2D camera and a digital micromirror device (DMD). Both vertical and horizontal line illumination directions were tested, for photoreceptor and vascular imaging. The phase contrast imaging provided improved visualization of retinal structures such as cone inner segments, vessel walls and red blood cells with images being acquired at frame rates up to 500 Hz. Blood flow velocities of small vessels (<40 µm in diameter) were measured using kymographs for capillaries and cross-correlation between subsequent images for arterioles or venules. Cardiac-related pulsatile patterns were observed with normal resting heart-beat rate, and instantaneous blood flow velocities from 0.7 to 20 mm/s were measured.

Design of Novel Photodetector Array in Optical Communication Systems and Optimization of Signal Processing Algorithm

This study aims to enhance the high-speed and high-power performance of photodetectors, focusing on the epitaxial layer structure of photodetector arrays. The epitaxial structure of the photodetector involves a P–I–N structure with InAlAs/InGaAs heterostructures. InAlAs is used as the P-region material, and a dual-waveguide photodetector array is designed with a core diameter of 20 μm. The optical coupling is achieved through normal incident vertical illumination. Additionally, a novel structure of a dual-core symmetrically connected photodetector array is proposed, altering the electrode structure and core arrangement to maintain consistent distances for the output signals from the cores to the device’s output terminal. In order to address the issue of minimum bit error rate in optical communication systems under conditions of optical noise and limited energy efficiency of received optical signals, a photodetector array signal processing algorithm is proposed. The experimentally designed dual-core symmetrically connected P–I–N photodetector array achieves a 3 dB bandwidth of 15.37 GHz at an average photocurrent of 5 mA. Furthermore, it maintains a 3 dB bandwidth of 11.67 GHz at a high-power operating state of 50 mA, with an alternating current (AC) saturation current of 56 mA and a saturated RF output power of 1.11 dBm at 11.67 GHz. In comparison, the improved dual-core traveling-wave photodetector array at 11.67 GHz only achieves an AC saturation current of 38 mA and a saturated RF output power of 2.66 dBm. The signal processing algorithm for the selected dual-core symmetrically connected P–I–N photodetector array demonstrates that employing a method of merging array elements reduces the system’s computational complexity with minimal impact on the system’s power consumption.

Comproportionation of CO2 and Cellulose to Formate Using a Floating Semiconductor-Enzyme Photoreforming Catalyst.

Formate production via both CO2 reduction and cellulose oxidation in a solar-driven process is achieved by a semi-artificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO2 |FDH) producing up to 1.16±0.04 mmolformate g -1 in 24 hours at 30 °C and 101 kPa under anaerobic conditions. Isotopic labeling experiments with 13 C-labeled substrates support the mechanism of stoichiometric formate formation through both redox half-reactions. TiO2 |FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmolformate per m2 irradiation area after 24 hours. This work demonstrates the synergistic solar-driven valorization of solid and gaseous waste streams using a biohybrid photoreforming catalyst in aqueous solution and will thus provide inspiration for the development of future semi-artificial waste-to-chemical conversion strategies.

Comproportionation of CO2 and Cellulose to Formate Using a Floating Semiconductor‐Enzyme Photoreforming Catalyst

AbstractFormate production via both CO2 reduction and cellulose oxidation in a solar‐driven process is achieved by a semi‐artificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO2|FDH) producing up to 1.16±0.04 mmolformate g −1 in 24 hours at 30 °C and 101 kPa under anaerobic conditions. Isotopic labeling experiments with 13C‐labeled substrates support the mechanism of stoichiometric formate formation through both redox half‐reactions. TiO2|FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmolformate per m2 irradiation area after 24 hours. This work demonstrates the synergistic solar‐driven valorization of solid and gaseous waste streams using a biohybrid photoreforming catalyst in aqueous solution and will thus provide inspiration for the development of future semi‐artificial waste‐to‐chemical conversion strategies.

DEVELOPMENT AND STUDY OF A MICROSPECTROMETER LAYOUT

The photoelectronic processes occurring in a vertically located double-barrier photode-tector under the influence of an external bias voltage are simulated depending on the char-acteristics of the penetrating waves. Under conditions of vertical illumination, to obtain the spectral dependence of the intensity of absorbed radiation, an algorithm was developed for selecting individual waves from the integral flux of the optical signal under conditions of changing the external bias voltage in steps of 1 mV. The algorithm takes into account the main cause-and-effect relationships between the absorption coefficient and design and technological parameters. It makes it possible to obtain the intensities of individual waves from the integral radiation flux in the optical range, where there is a change in the sign of the spectral characteristics and a linear dependence of the point of sign change on the ap-plied voltage. A general architecture, functional structure and remote control scheme for the monitor-ing system for hazardous substances have been developed, as well as corresponding pro-grams with the help of which the algorithm was operated in the LabVIEW environment. To run the algorithm, a prototype of a spectral analysis device was developed and prepared, in which an Arduino Mega board controlled by a microcontroller was used to analyze the output signal of the photodetector. The layout was tested using multi-colored LEDs. The spectral dependence of the inten-sity and its numerical data are obtained on the screen using a new principle. This method is novel and opens up prospects for further development of the field of micro-sized spectro-photometers. To identify mixtures by spectral analysis and estimate their quantity, the RDP (Remote Desktop) protocol of the remote system and the LABVIEW graphical programming envi-ronment were used. RDP was created by Microsoft to provide remote access to Windows servers and workstations.

Optimization of Daylighting Outdoor Availability in Urban Kampung

Liveability interprets as making residents comfortable in their built environment. As daylighting becomes a necessity for human beings, daylight availability can improve the liveability of dwelling habitats, especially in high-density urban areas. Relayouting the building block without reducing the usable floor area can improve daylight availability. Kampung Braga is an example of how a heavy slum area has a low liveability quality and classifies into impoverished slum settlements at the stake of being resettled. The spatial arrangement becomes necessary to enhance the community’s quality of life. This article aims to examine how the intervention through urban layout can affect daylight availability to improve the liveability for kampung Braga. This research uses simulation methods with climate-based daylight modelling (CBDM) software to simulate daylighting with a dynamic approach. Rhinoceros for modelling, Honeybee for vertical sky component (VSC) simulation, and DIVA for daylight availability simulation. Based on the simulation on three alternative urban layouts in line with spatial plan context, it is shown that intervention through urban layout and typology of kampung Braga has shown better VSC and daylight availability values than the existing conditions. It is necessary to pay attention to the context of the building around the site when designing a specific building typology. Modifying configuration, floor height, model, and orientation show a better VSC reception and vertical facade illumination. City stakeholders need to be aware of the low liveability of the urban kampung. Planning the right urban plan design can improve daylighting availability and increase the liveability of the urban kampung.

Kirigami-inspired automatically self-inclining bifacial solar cell arrays to enhance energy yield under both sunny and cloudy conditions

SummaryThe application of photovoltaics (PVs) is expanding in various locations ranging from industrial facilities to residential housing. The emphasized concept in the PVs field is shifting from “watt-per-cost” to “energy-yield-per-watt.” To attain a high energy yield, fixed modules are not well suited to capture both direct and omnidirectional light. To achieve a high energy yield under both light conditions, we propose a self-inclining bifacial solar cell array fabricated by integrating a photothermal actuator, which senses incident light by itself, and actuating solar cells that incline at the appropriate angle to maximize captured light. In the vertical illumination state, the specific power of the self-inclining bifacial two-cell array is 11% higher than a fixed-angle aligned array. In an outside environment with a large proportion of diffused light, the self-inclining bifacial two-cell array also shows higher performance. We expect this work to enable PVs to be applied without regard to weather conditions.

Self-sustained rolling of a liquid crystal elastomer rod under inclined light illumination

The self-sustained motion of active materials has the great application values in the fields of soft robots, medical devices, micro nano devices, etc., due to its advantage of directly harvesting energy from the environment. Recent experiment has discovered that a straight liquid crystal elastomer (LCE) rod on a horizontal surface can roll continuously under the vertical light illumination, but the start of rolling requires external disturbance. In this paper, we adopt an inclined light to manipulate the rolling of a straight LCE rod, and theoretically study its rolling behaviors to obtain the illumination angle range for triggering the self-sustained rolling. It is found that the rolling of straight LCE rod can be triggered from rest without external disturbance under the inclined light, which is different from the case of the vertical light illumination. In addition, the rolling velocity of the LCE rod can be easily controlled by the light intensity and illumination angle. These predictions are consistent with the existing experimental results. This study may guide the potential applications of the optically-responsive rod in soft robots, harvesting energy and active machinery.

Pupil dilation and constriction in the skate Leucoraja erinacea in a simulated natural light field.

The skate Leucoraja erinacea has an elaborately shaped pupil, whose characteristics and functions have received little attention. The goal of our study was to investigate the pupil response in relation to natural ambient light intensities. First, we took a recently developed sensory-ecological approach, which gave us a tool for creating a controlled light environment for behavioural work: during a field survey, we collected a series of calibrated natural habitat images from the perspective of the skates' eyes. From these images, we derived a vertical illumination profile using custom-written software for quantification of the environmental light field (ELF). After collecting and analysing these natural light field data, we created an illumination set-up in the laboratory, which closely simulated the natural vertical light gradient that skates experience in the wild and tested the light responsiveness - in particular the extent of dilation - of the skate pupil to controlled changes in this simulated light field. Additionally, we measured pupillary dilation and constriction speeds. Our results confirm that the skate pupil changes from nearly circular under low light to a series of small triangular apertures under bright light. A linear regression analysis showed a trend towards smaller skates having a smaller dynamic range of pupil area (dilation versus constriction ratio around 4-fold), and larger skates showing larger ranges (around 10- to 20-fold). Dilation took longer than constriction (between 30 and 45 min for dilation; less than 20 min for constriction), and there was considerable individual variation in dilation/constriction time. We discuss our findings in terms of the visual ecology of L. erinacea and consider the importance of accurately simulating natural light fields in the laboratory.

Multi-objective optimization method for reducing mutual interference in cockpit illumination.

The cockpit is a compact space comprised of various light-emitting devices. The light from different devices interferes and overlaps on the target surface. The light distribution requirements of different target surfaces are different. A suitable decision-making process is required to simultaneously meet the requirements of multiple target surfaces. A GPR-NSGA-II framework was proposed in the present study and a corresponding Gaussian process regression prediction model was established to predict and optimize multiple optical quality parameters in the cockpit. The luminous flux and beam angle of the typical luminaires were selected as controlled input parameters in a model case. The average illumination of targets that need lighting were set as constraints, and uniformity of illuminance of these surfaces and vertical illumination (direct light) of the eye position were set as the variables. An orthogonal experiment was conducted using the lighting model and a dataset was generated to validate the proposed framework. The results demonstrate that the solution set of luminescence parameters in cockpit illumination can be specified by GPR-NSGA-II framework.

Enhanced photogalvanic effect in the two-dimensional MgCl2/ZnBr2 vertical heterojunction by inhomogenous tensile stress

The photogalvanic effect (PGE) occurring in noncentrosymmetric materials enables the generation of a dc photocurrent at zero bias with a high polarization sensitivity, which makes it very attractive in photodetection. However, the magnitude of the PGE photocurrent is usually small, leading to a low photoresponsivity, and therefore hampers its practical application in photodetection. Here, we propose an approach to largely enhancing the PGE photocurrent by applying an inhomogenous mechanical stretch, based on quantum transport simulations. We model a two-dimensional photodetector consisting of the wide-bandgap MgCl$_2$/ZnBr$_2$ vertical van der Waals heterojunction with the noncentrosymmetric $C_{3v}$ symmetry. Polarization-sensitive PGE photocurrent is generated under the vertical illumination of linearly polarized light. By applying inhomogenous mechanical stretch on the lattice, the photocurrent can be largely increased by up to 3 orders of magnitude due to the significantly increased device asymmetry. Our results propose an effective way to enhance the PGE by inhomogenous mechanical strain, showing the potential of the MgCl$_2$/ZnBr$_2$ vertical heterojunction in the low-power UV photodetection.

주거 밀집지역 보안등의 조명환경 특성 현장 조사 및 분석

Excessive or inappropriate use of artificial lighting creates inconveniences in the everyday lives of people, such as discomfort, sleep disorder, and unsafe walking condition, etc. This study aims to investigate the relationship between nighttime lighting environment (e.g. the type of lightings and the manner in which\h they are installed, installation conditions, and characteristics of the sidewalks, etc.) and the light pollution caused by such trespassing light in densely-populated residential areas. For our study, one dong (a municipality) was selected among the most densely-populated areas in Seoul, and we measured and analyzed properties of the lightings, road condition, installation condition, and light pollution (vertical illumination in residential areas) for the entire security lightings located within that area (dong).

Perfect in-plane CrI3 spin-valve driven by photogalvanic effect

Out-of-plane spin tunneling through the two-dimensional (2D) van der Waals ${\mathrm{CrI}}_{3}$ multilayer has recently been deeply explored, and giant magnetoresistance has been achieved in various ${\mathrm{CrI}}_{3}$ magnetic tunneling junctions (MTJs) via the control of interlayer antiferromagnetic coupling by both magnetic and electric fields. In contrast, knowledge of the in-plane spin-transport properties of 2D ${\mathrm{CrI}}_{3}$ is currently very limited. Here, based on quantum transport simulations, we study the in-plane transport properties of the photocurrent in a ${\mathrm{CrI}}_{3}$ MTJ with a bilayer/monolayer/bilayer configuration. The photogalvanic effect (PGE) is induced under vertical illumination of elliptically polarized light, giving rise to a robust photocurrent in a broad visible range at zero bias. A perfect spin-valve effect can be achieved with a magnetoresistance of 100% for some photon energies with an appropriate light helicity. Moreover, the PGE photocurrent for the antiparallel configuration is enhanced, as compared to the parallel configuration due to the increased device asymmetry. Our results show that a PGE-driven ${\mathrm{CrI}}_{3}$ photodetector is a promising candidate for low-power 2D spintronic devices.

High-speed and high-power germanium photodetector with a lateral silicon nitride waveguide

Up to now, the light coupling schemes of germanium-on-silicon photodetectors (Ge-on-Si PDs) could be divided into three main categories: (1) vertical (or normal-incidence) illumination, which can be from the top or back of the wafer/chip, and waveguide-integrated coupling including (2) butt coupling and (3) evanescent coupling. In evanescent coupling the input waveguide can be positioned on top, at the bottom, or lateral to the absorber. Here, to the best of our knowledge, we propose the first concept of Ge-on-Si PD with double lateral silicon nitride ( Si 3 N 4 ) waveguides, which can serve as a novel waveguide-integrated coupling configuration: double lateral coupling. The Ge-on-Si PD with double lateral Si 3 N 4 waveguides features uniform optical field distribution in the Ge region, which is very beneficial to improving the operation speed for high input power. The proposed Ge-on-Si PD is comprehensively characterized by static and dynamic measurements. The typical internal responsivity is evaluated to be 0.52 A/W at an input power of 25 mW. The equivalent circuit model and theoretical 3 dB opto-electrical (OE) bandwidth investigation of Ge-on-Si PD with lateral coupling are implemented. Based on the small-signal (S21) radio-frequency measurements, under 4 mA photocurrent, a 60 GHz bandwidth operating at − 3 V bias voltage is demonstrated. When the photocurrent is up to 12 mA, the 3 dB OE bandwidth still has 36 GHz. With 1 mA photocurrent, the 70, 80, 90, and 100 Gbit/s non-return-to-zero (NRZ) and 100, 120, 140, and 150 Gbit/s four-level pulse amplitude modulation clear openings of eye diagrams are experimentally obtained without utilizing any offline digital signal processing at the receiver side. In order to verify the high-power handling performance in high-speed data transmission, we investigate the eye diagram variations with the increase of photocurrents. The clear open electrical eye diagrams of 60 Gbit/s NRZ under 20 mA photocurrent are also obtained. Overall, the proposed lateral Si 3 N 4 waveguide structure is flexibly extendable to a light coupling configuration of PDs, which makes it very attractive for developing high-performance silicon photonic integrated circuits in the future.

Enhanced photocatalytic performance of BiOBr/CQDs hierarchical nanostructures mixed with SiO2 nanospheres

Reinforcing light harvesting is an effective means to improve photocatalytic efficiency of semiconductors. In this study, carbon-quantum-dot-modified BiOBr mixed with SiO2 nanospheres (BiOBr/CQDs + SiO2) were prepared via stepwise chemical precipitation route. The characterizations of X-ray diffraction, field-emission scanning electron microscopy and energy-dispersive X-ray apparatus demonstrated that the as-prepared BiOBr/CQDs + SiO2 displayed nanosheets-building spherelike hierarchical nanostructures mixing with dispersive SiO2 nanospheres. Control photocatalytic degradation of orange II under natural sunlight illumination indicated that the presence of SiO2 nanospheres could further promote the photocatalytic behaviors of BiOBr/CQDs apart from CQDs. Diffuse reflection spectrum demonstrated that SiO2 nanospheres were capable of reflecting UV − Vis light near to 100%. The possible mechanism for the enhanced light-absorption surface of suspending hierarchical photocatalyst in presence of SiO2 nanospheres was proposed via light propagation over suspending SiO2 nanospheres under vertical light illumination. Our method for enhancing photocatalytic efficiency provided a general method to enhance light harvesting of every suspending two- or three-dimensional photocatalysts.

Microspectrophotometry of Wood Grain and Color

A reflecting microscope spectrophotometer was used for the colorimetry of wood using CIE (Commission Internationale de l’Éclairage) chromaticity coordinates. A microscope scanning stage and scanning with optical fibers were used to detect grain patterns. Ten exotic woods with a fine grain structure were tested because they are highly valued in the manufacture of musical instruments and furniture, and they had a wide range in color and grain structure. With lateral illumination (45°) of samples and a large measuring aperture, the results were comparable to those that might be obtained with a commercial colorimeter detecting diffuse Lambertian reflectance. With vertical illumination and coaxial photometry in a microscope, Fresnel reflectance was dominant. The best predictor of CIE x with lateral illumination was reflectance at 400 nm (r = - 0.916, P &lt; 0.0005) and the relationship persisted with vertical illumination (r = -0.67, P &lt; 0.025). Scanning across woods at 520 nm with a microscope scanning stage, there were relationships of CIE x with scanning peak height (r = 0.75 P &lt; 0.01). In scanning across 6 cm of wood with optical fibers, there was a relationship of the number of reflectance peaks (from wood grain between dark lines) with peak width (r = - 0.89, P &lt; 0.0005). Woods with a fine grain had numerous small peaks while woods with a coarse grain had a few wide peaks. Thus, there is a connection between the color and grain pattern of wood.

Mid-infrared photodetector based on 2D material metamaterial with negative index properties for a wide range of angles near vertical illumination

We present the vertically illuminated Si compatible mid-infrared photodetectors based on graphene that forms negative-index metamaterial. The coupling into a 2D layer at the angles near normal to the surface is negligible without the help of a metamaterial. We propose a low loss metamaterial, the dielectric structure with the nano/microholes through 2D materials that supports a resonance and enhances quantum efficiency in a wide range of incident angles.

Optical aberrations and modulation transfer function of a thermal lens for use in imaging.

The optical aberrations of the thermal lens formed in a liquid are reported for the first time as expressed in terms of the Zernike polynomials coefficients. Convection of the liquid in which the thermal lens is formed is shown to strongly modify the lens imaging properties, even for the case of vertical heating laser illumination, as studied herein. The time evolution of the optical properties of the thermal lens is investigated. The direction from which the heating laser beam illuminates the thermo-optical liquid, in which the thermal lens is formed, has been found to be crucial for the lens optical power, type, and level of aberrations observed and the way these lens properties change in time.

Enhanced photogalvanic effects in the two-dimensional [formula omitted] monolayer by vacancy- and substitution-doping

The photogalvanic effect (PGE) enables the generation of photocurrent at zero bias and without the need of the p-n junction, and also offer a high polarization sensitivity in a broadband range, showing potential applications in the low-power 2D optoelectronics, however the PGE photocurrent is generally small. Here we studied the PGE in the 2D WTe2 monolayer using the quantum transport simulations, and proposed the mechanism to effectively enhance the PGE photocurrent by substitution-doping and vacancy-defects. The PGE photocurrent can be generated in the 2D WTe2 monolayer under the vertical illumination of linearly polarized light. The photocurrent can be enhanced evidently by creating the vacancy or Ga-substitution doping, and moreover a higher polarization sensitivity can be obtained. This performance is attributed to the reduced symmetry due to the doping, which increases the device asymmetry and therefore enhance the photocurrent. Our results propose the mechanism to effectively enhance the PGE by substitution doping and also show the promising applications of the 2D WTe2 monolayer in optoelectronics including the photodetections.

Inverted p-down Design for High-Speed Photodetectors

We discuss the structural consideration of high-speed photodetectors used for optical communications, focusing on vertical illumination photodetectors suitable for device fabrication and optical coupling. We fabricate an avalanche photodiode that can handle 100-Gbit/s four-level pulse-amplitude modulation (50 Gbaud) signals, and pin photodiodes for 100-Gbaud operation; both are fabricated with our unique inverted p-side down (p-down) design.