Secondary Optics Research Articles

52‐4: Micro LED Display Light Extraction Efficiency Improvement by Secondary Optics on Substrate

Micro LED displays are widely acknowledged as forthcoming display innovations. However, due to the micro LED device size reductions, the light extraction efficiency of micro LED devices will be compromised. This paper extends the EQE equation and implement a LEE secondary optics (the secondary optics of light extraction efficiency) factor. The paper also presents few directions to enhance the normal angle light intensity for micro LED displays. Our sample preparations have confirmed that a white glue layer can bring about an improvement of over 100%, and a lens with a protection layer can also boost the normal angle light intensity by 45%. Considering the overall display performance including surface reflection, we simulated a condition that can improve the normal angle light intensity by over 70% in micro LED displays.

CPV System Optical Performance Evaluation by Means of Direct Experimental Measurement Procedure

The optics is the component that most affects the concentrating photovoltaic (CPV) system performance, depending above all on the concentration factor and optical efficiency. Hence, a basic aspect is the concentrated solar flux measure on the receiving area, the evaluation of which is principally realized by indirect measurement methods. First, a literature review on indirect and direct methods used for the evaluation of concentrated solar flux and optical parameters is presented in this paper. The experimental measurement procedure, which is able to evaluate the optical parameters and concentrated solar flux in CPV systems, is also presented. The main steps of this procedure are represented by experimental system setup, sensor selection for concentrated solar flux estimation, identification of all the factors affecting optical performances, and development of an experimental campaign and output analysis. In particular, the optical characterization results of a CPV system are obtained by means of in-depth experimental analysis using Triple-Junction (TJ) solar cells with areas of 5.5 × 5.5 mm2 and 10 × 10 mm2. Three different setups have been analyzed related to primary and secondary optics composition. The main aim of this paper is the determination of a direct measuring technique, rarely adopted in literature in comparison to the established techniques, that is able to evaluate experimentally the optical parameter values and that can be standardized for other CPV systems. In particular, equations that link the optical concentration factor (C) and efficiency (ηopt) with focal distance (h) represent the fundamental results. They can be used for similar point-focus configurations presenting the same TJ cell size and ranges of C, ηopt and h. Finally, the experimental results of the direct method are compared with those of an indirect method adopting the same CPV system and operational conditions.

Full-angle chip scale package of mini LEDs with a V-shape packaging structure.

The light distribution of light-emitting diodes (LEDs) generally resembles that of a Lambertian light source. When used as large-area light sources, the light distribution angle of LEDs must be modified through secondary optics design to achieve uniformity and minimize the number of light sources. However, secondary optical components pose several challenges such as demanding alignment accuracy, material aging, detachment, and lower reliability. Therefore, this paper proposes a primary optical design approach to achieve full-angle emission in LEDs without the need for lenses. The design employs a flip-chip as the light source and incorporates a V-shaped packaged structure, including a white wall layer, optical structure layers, and a V-shaped diffuse structure. With this design, the LEDs achieve full-angle emission without relying on lenses. Our experimental results demonstrated a peak intensity angle of 77.7°, a 20.3% decrease in the intensity of the central point ratio, and a full width at half maximum (FWHM) of the light distribution of 175.5°. This design is particularly suitable for thin, large-area, and flexible backlight light sources. Moreover, the absence of secondary optical components allows for a thinner light source module.

Thermal performance enhancement in a solar parabolic trough collector with optimized secondary optics

Thermal performance enhancement in a solar parabolic trough collector with optimized secondary optics

Surface lattice resonances for beaming and outcoupling green μ LEDs emission

Abstract Light-Emitting Diodes (LEDs) exhibit a typical Lambertian emission, raising the need for secondary optics to tailor their emission depending on specific applications. Here, we introduce plasmonic metasurfaces to InGaN green emitting quantum wells for LEDs to control their far-field emission directionality and enhance the collection efficiency. The proposed mechanism is based on surface lattice resonances (SLRs) and relies on the near-field coupling between the InGaN multiple quantum wells (MQWs) and periodic arrays of aluminum (Al) nanodisks. Fourier microscopy measurements reveal that the angular photoluminescence emission pattern depends on the lattice constant of the metasurfaces. We demonstrate that integrating Al metasurfaces in LED wafers can enhance the collected outcoupled light intensity by a factor of 5 compared to the same sample without metasurfaces. We have also performed numerical calculations of the far-field emission based on the reciprocity principle and obtained a very good agreement with the experimental data. The proposed approach controls the emission directionality without the need for secondary optics and it does not require post-etching of the GaN, which makes it a potential candidate to control and enhance the generated light from micro-LEDs.

Experimental investigation in a solar parabolic trough collector with optimized secondary optics

ABSTRACT In the present study, experimental investigation of parabolic trough collector is carried out as per ASHRAE 93-1986 standard. In this study, two different case of receiver involving conventional absorber as standard model and optimized secondary optics absorber as proposed model. The heat transfer fluid used for the analysis is distilled water. The important performance parameters such as temperature variation, thermal efficiency, exergy efficiency, and pump work are explored and illustrated. Based on the results, the heating time and cooling time constants obtained for the proposed model are 110 and 115 s, respectively, which shows that the proposed model stabilizes quickly than the standard model. It is observed from the result that the proposed model attained a maximum thermal and exergy efficiency of 73.2 and 48.77%, respectively, which is 14.19 and 9.5% higher than that of the standard model. The electricity generation costs obtained for the proposed model and the standard model are Rs. 3.74/kWh and Rs. 5.71/kWh, respectively.

Unveiling light collection and pump enhancement from quantum wells with plasmonic metasurfaces using power dependent measurements

Low light extraction efficiency (LEE) is the greatest limiting factor for the brightness of reduced-size light-emitting diodes (LEDs) as it limits their emission intensity. In addition, LEDs have a Lambertian emission, which requires secondary optics to control the emission directionality. Plasmonic metasurfaces can introduce a way of manipulating the generated light from LEDs to enhance their LEE and steer the emitted light by reshaping the far-field emission. Here, we fabricate resonant plasmonic metasurfaces on top of a typical blue emitting wafer consisting of InGaN/gallium nitride quantum wells developed for commercial LED devices. The metasurface is separated from the InGaN quantum wells by p-GaN and indium-tin-oxide (ITO) layers with a cumulative thickness of 110 nm. Since this distance value is close to the emission wavelength in the corresponding medium, enhanced near-fields of localized plasmonic resonances do not reach the active region. Despite this, we observe a strong influence of the metasurfaces on the far-field photoluminescence emission from the quantum wells as demonstrated by Fourier imaging. Power-dependent excitation measurements of the samples allow us to retrieve the pump and light collection enhancement factors provided by the plasmonic metasurfaces. We demonstrate that the plasmonic metasurfaces can provide a pump enhancement factor of up to 4.1 and a collection enhancement factor of up to 3.2. We have also performed simulations based on the reciprocity principle and achieved a good qualitative agreement with the experimental results.

Liquid spherical lens as an effective auxiliary optical unit for CPV/T system with remarkable hydrogen production efficiency

How to efficiently convert solar radiation into energy sources for easy storage and consumption is an urgent issue. Although concentrated photovoltaics can achieve high efficiency, it places higher demands on the optical system and heat management. Herein, a new design is presented where a liquid spherical lens acts as a secondary optical element of the concentrating solar system, refracting the light beam while participating in spectral beam splitting. The radiation energy unavailable for solar cells is harvested by the liquid spherical lens through spectral beam splitting which serves to raise the temperature of the electrolyte. Compared with the conventional concentrated photovoltaic coupled electrolytic hydrogen production system, the addition of a liquid spherical lens improves the solar cell heat dissipation while increasing the operating temperature of the electrolyzer, achieving higher solar-to-hydrogen efficiency. The system with this design obtains a solar-to-electricity efficiency of 31.7% as verified by indoor experiments. The solar-to-hydrogen efficiency of the system achieved an average value of 22.1% and a benchmark maximum value of 22.7% during 7 h of continuous operation. The solar-to-hydrogen efficiency is improved by at least 10% compared to the design that separates the secondary optics from the spectral beam-splitting filter. Compared with existing systems employing commercial CPV modules, the efficiency is improved by at least 6% benefiting from the rational distribution of the spectrum by the liquid spherical lens.

CALCULATION AND EXPERIMENTAL STUDIES OF THE LIGHTING TECHNICAL CHARACTERISTICS OF THE LED MODULE

The article describes the characteristics of LED modules made using the Chip-on-Board technology. An overview of LED modules from different manufacturers is carried out. Variants of using differently oriented mounting of flat mirror surfaces and their influence on the lighting characteristics of LED modules have been investigated. Theoretical research and modeling of the LED module and differently oriented mirror surfaces in the TracePro software package have been carried out. The development of universal LED luminaires is one of the urgent tasks of lighting engineering. The market for LED light sources is rapidly improving, more efficient sources appear, therefore the creation of modern lamps based on various optical systems is a popular direction in the development of electronics. Secondary optics options for the COB module and simulation results in TracePro are presented.

Characterization of spherical optics performance compared to other types of optical systems in a point-focus CPV system

In this paper the novelty is represented by comparison of optical and energy performances of spherical mirror, rarely used as primary optics in point-focus CPV systems, with those of refractive or parabolic reflective optics. First, concentration factor and optical efficiency are experimentally determined varying distance between Triple-Junction (TJ) cell and spherical mirror, also with secondary optics that increases acceptance angle reducing precision required to solar tracker. Successively, the TJ cell temperature and electrical power values are evaluated under maximum concentration obtaining daily electrical producibility of 98Wh at Fisciano (Italy). Producibility is evaluated for correct and incorrect solar tracking, showing after 750 s decrease of 38.0% and 50.3% respectively with and without secondary optics. Hence, equations linking optical parameters are obtained by experimental data collected for three months and are adoptable for similar point-focus configurations with same TJ cell dimensions and ranges of concentration factor and focal distance. Finally, spherical optics performances are theoretically compared with those of parabolic mirror and experimentally with those of Fresnel lens. Spherical optics is preferable to parabolic from technical-economic point of view because it is easier to produce. Moreover, spherical mirror allows concentration factor and optical efficiency values three times higher than Fresnel lens. The electric power unitary costs of both optics are near but spherical optics requires a CPV system area about three times smaller with same power output. Electrical power and temperature values reached by single TJ cell with spherical optics are respectively about 10 W and 30 °C higher than those of Fresnel lens.

Development and research of a virtual model of a ZOM-type lighting device based on LEDs

The research results of the sample characteristics of a light-signaling device type ZOM-75W-AV with an incandescent lamp power of 75 W manufactured by Bellight are presented in this article. Based on the experimental data obtained, a virtual 3D model of a light-signaling device based on LEDs was developed. The development of the lighting device virtual model in CAD KOMPAS-3D is carried out. The performance of the virtual 3D model is tested using the DIALux program. CreeXLamp XHP35 LEDs is used as a light source, LEDil lenses is used as secondary optics, Osram driver is used as a power source. Keywords light-signaling device, ZOM, LED, virtual model, characteristics, experimental studies

Deep learning-based single-shot autofocus method for digital microscopy.

Digital pathology is being transformed by artificial intelligence (AI)-based pathological diagnosis. One major challenge for correct AI diagnoses is to ensure the focus quality of captured images. Here, we propose a deep learning-based single-shot autofocus method for microscopy. We use a modified MobileNetV3, a lightweight network, to predict the defocus distance with a single-shot microscopy image acquired at an arbitrary image plane without secondary camera or additional optics. The defocus prediction takes only 9 ms with a focusing error of only ∼1/15 depth of field. We also provide implementation examples for the augmented reality microscope and the whole slide imaging (WSI) system. Our proposed technique can perform real-time and accurate autofocus which will not only support pathologists in their daily work, but also provide potential applications in the life sciences, material research, and industrial automatic detection.

Optical and Thermal Analysis of Secondary Optics in Light Emitting Diodes’ Packaging: Analysis of MR16 Lamp

Optical and thermal control are two main factors in package design process of lighting products, specifically light emitting diodes (LEDs). This research is aimed to study the role of secondary optics in opto-thermal characterization of LED packages. Novel thin total internal reflection (TIR) multifaceted reflector (MR) lens is modelled and optimized in Monte-Carlo ray-tracing simulations for MR16 package, regarded as one of the widely used LED lighting products. With criteria of designing an optical lens with 50% reduced thickness in comparison to commercially available lenses utilized in MR16 packages, nearly same light extraction efficiency and more uniform beam angles are achieved. Optical performance of the new lens is compared with the experimental results of the MR16 lamp with conventional lens. Only 2.3% reduction in maximum light intensity is obtained while lens size reduction was more than 25%. Based on the detailed CAD design, heat transfer simulations are performed comparing the lens thickness effect on heat dissipation of MR16 lamp. It was observed that using thinner lenses can reduce the lens and chip temperature, which can result in improved light quality and lifetime of both lens and light source.

Effect of non-uniformity on concentrator multi-junction solar cells equipped with refractive secondary optics under shading conditions

Non-uniformity is a relevant concern of concentrator photovoltaic systems (CPV) due to its impact on the performance of multi-junction (MJ) solar cells. This work is focused on a state-of-the-art investigation related to the effects of shading on the irradiance profiles and electrical performance of MJ cells. For doing this, three different CPV single-units with a concentration of ≈559x have been experimentally investigated indoors at the CPV laboratory of the University of Jaén. The units are made up of poly(methyl methacrylate) (PMMA) Fresnel lens and standard GaInP/GaInAs/Ge MJ cells. Also, single-lens-optical element (SILO-Pyramid) and refractive truncated pyramid (RTP) homogenizers have been considered. The results indicate that shading produces additional spatial and spectral non-uniformities, and that these are reduced by the use of homogenizers. In addition, the non-uniform spectral illumination has been identified as the main cause of the additional reduction of the performance of MJ solar cells. In this sense, the SILO-Pyramid provides the best results and shows a significantly stable spectral performance under shading conditions. For a no-homogenizer case, the maximum power shows a reduction of 86.3% for a shading factor of 80%, while it is only reduced by 83.2% and by 81.6%, respectively, for the RTP and SILO-Pyramid.

Experimental Comparison between Spherical and Refractive Optics in a Concentrating Photovoltaic System

Since there are not standard configurations of the Concentrating Photovoltaic (CPV) systems, several types of optics are designed and analyzed. In this paper, the optical performances of a spherical mirror and a commonly used Fresnel lens of the same diameter are compared, highlighting their impact on the CPV system energy performance. First, the absolute and percentual variation trends of optical concentration factor and optical efficiency as function of the distance between each optical system and receiver are analyzed. The concentration levels obtained by means of the spherical mirror are much higher than the Fresnel lens, with maximum values of optical efficiency equal to 72.8% and 24.1%, respectively. The analysis of the concentration reduction due to a solar-tracking failure has also allowed the estimation of the acceptance angle, thus observing that the spherical mirror requires a less accurate solar tracker with respect to the Fresnel lens, especially if a secondary optics is adopted. As for the energy comparison, the spherical mirror allows increase of the Triple-Junction (TJ) cell temperature up to about 65 °C higher than the environmental temperature and to reach an electrical power of about 15 W in correspondence of a concentrated solar radiation of 470 kW/m2. Finally, the deviation between the cumulative electric energy produced by the TJ cell in the cases of correct and incorrect solar tracking and for the configurations with and without secondary optics has been also evaluated for both the optics. The equations experimentally obtained in this paper represent a more accurate tool to describe the physical phenomenon in comparison with the equations theoretically obtained for similar CPV systems. The results can be used to design a real CPV system that adopts a Fresnel lens or a spherical mirror. The equations experimentally obtained in this paper represent a more accurate tool to describe the physical phenomenon in comparison with the equations theoretically obtained for similar CPV systems. The results can be used to design a real CPV system that adopts a Fresnel lens or a spherical mirror.

Optical performance enhancement in a solar parabolic trough collector with optimized secondary optics

ABSTRACT The maximum concentration ratio of the commercial parabolic trough collectors is limited to 42% of the theoretical limit of concentration. Recently, the secondary flat reflector geometry has been proposed to increase the concentration ratio of parabolic trough close to the theoretical limit. Using those secondary reflector geometry as a starting point, we optimize the reflector geometry for commercial LS-3 parabolic trough with additional secondary optics named flat linear refracted Fresnel lens and evaluate the performance using Monte-Carlo ray tracing method. In this paper, theoretical and optical performance analyses of the proposed system have been investigated. The analysis of parabolic trough with additional secondary optics revealed a potential reduction in shadow area of the secondary reflector on the absorber tube and the primary mirror to 0%. It is found that the new concentration ratio of 48.24 was observed for the proposed system, which is nearly 84.19% higher than the commercial LS-3 collector.

Implementation Of The Flat Beam Technology In Lighting devices Using A Flat Mirror Surface

The article discusses one of the ways to obtain a contrasting boundary between the illuminated and unlit areas of the object (illumination technology Flat Beam) in LED lighting systems using secondary optics in the form of a flat mirror surface. The results of studies of high-power LED light sources with different emitting surface areas and with three proposed options for fixing a flat mirror surface are presented. It is shown experimentally that the optical system for LED light sources in the form of a flat mirror surface allows changing the luminous intensity curve of LED light sources, converting it in a given plane from a cosine to a concentrated one. This is how the Flat Beam lighting technology is realized. Variants of the practical application of this lighting technology obtained by using a flat mirror surface with LEDs are also proposed.

Computer Modelling And Experimental Research of Led Optical Systems

The paper considers the problem of design of modern light devices (LDs) based on LEDs and their optical systems (OSs). LEDs optical systems provide developers with opportunities to implement a variety of modern lighting tasks. In the market of competing products, it is often necessary to calculate and produce LED optics for specific lighting problems. The main one is the formation of a given distribution of illumination over the surface of the object. In comparison with existing lens and reflective OSs, individual projects with their own developed elements can give the desired result. The most popular services in LED lighting are the development of LED optics according to the customer’s specifications, lighting of the simulated product, development of 3D models for further production. The main stage in its development is the calculation and modelling of the OS. The results of this process are largely determined by the complex of lighting, thermal and functional characteristics of LDs. The development of modern LED LDs is inextricably linked with the use of specialized software. The article describes a mathematical model of the geometry of an OS that allows researcher to specify its shape for further design and provides a fast and accurate lighting calculation. To model objects, triangulation grids are often used, which makes it possible to fine tune their shape. To simplify the process of forming smoothed 3D surfaces, an edge was introduced as an auxiliary element of a triangulation grid. It makes it possible to simplify the process of approximating smooth surfaces without increasing the density of this grid. The developed software allows you to build optical surface models, perform ray tracing and calculate photometric body (PB). The article describes the simulation of LED OSs by the example of secondary LED optics. Computer simulation and prototyping of LED modules (LEDMs) for road lighting was carried out. 3D-models, a PB and curves of luminous intensity of LEDMs are received. The thermal imager an experimental study of the luminous and thermal characteristics of these modules was carried out. The results of the experiment showed very good agreement with the calculated models.

Angular resolution in VCSEL radiant intensity distribution measurements

AbstractVertical cavity surface‐emitting lasers (VCSEL) are getting more and more popular for 3D sensing and time‐of‐flight technology in consumer and automotive applications. VCSEL arrays with hundreds of single emitters are often used. Measurement of the radiant intensity distribution is the key to performing a proper eye safety assessment and designing suitable secondary optics for these emitters.

Calibration of residual aberrations in exoplanet imagers with large numbers of degrees of freedom

Imaging faint objects, such as exoplanets or disks, around nearby stars is extremely challenging because host star images are dominated by the telescope diffraction pattern. Using a coronagraph is an efficient solution for removing diffraction but requires an incoming wavefront with good quality to maximize starlight rejection. On the ground, the most advanced exoplanet imagers use extreme adaptive optics (ExAO) systems that are based on a deformable mirror (DM) with a large number of actuators to efficiently compensate for high-order aberrations and provide diffraction-limited images. While several exoplanet imagers with DMs using ∼1500 actuators are now routinely operating on large telescopes to observe gas giant planets, future systems may require a tenfold increase in the number of degrees of freedom to look for rocky planets. In this paper, we explore wavefront correction with a secondary adaptive optics system that controls a very large number of degrees of freedom that are not corrected by the primary ExAO system. Using Marseille Imaging Testbed for High Contrast (MITHiC), we implement a second stage of adaptive optics with ZELDA, a Zernike wavefront sensor, and a spatial light modulator to compensate for the phase aberrations of the bench downstream residual aberrations from adaptive optics. We demonstrate that their correction up to 137 cycles per pupil with nanometric accuracy is possible, provided there is a simple distortion calibration of the pupil and a moderate wavefront low-pass filtering. We also use ZELDA for a fast compensation of ExAO residuals, showing its promising implementation as a second-stage correction for the observation of rocky planets around nearby stars. Finally, we present images with a classical Lyot coronagraph on MITHiC and validate our ability to reach its theoretical performance with our calibration.