This PDF file contains the front matter associated with SPIE Proceedings Volume 12022, including the Title Page, Copyright information, Table of Contents and Conference Committee list.

InGaN-based blue light-emitting diodes (LEDs), with their high efficiency and brightness, are entering the display industry. However, a significant gap remains between the expectation of highly efficient light sources and their experimental realization into tiny pixels for ultrahigh-density displays for augmented reality (AR). Her, we report using tailored ion implantation (TIIP) to fabricate highly-efficient, electrically-driven pixelated InGaN microLEDs (μLEDs) at the mid-submicron scale (line/space of 0.5/0.5 μm. Moreover, we demonstrate high-density TFT and QD C/F integration technologies.

This paper focuses on micro LED R, G, B emitter technologies for low power wearable displays. Selection of materials, novel micro LED architectures, LED driving schemes, backplanes and their impact on LED performance trade-off will be presented to meet long battery life wearable display requirements. An objective comparison will be presented based on strengths and weaknesses of micro LED technologies for their fit and wide adoption in displays vs. status quo. Micro LED technologies are expected to gain significant adoption in a wide range of wearable display products in near future.

For decades it has been expected that near-eye displays such as augmented reality (AR) and virtual reality (VR) glasses and headsets will eventually take over conventional displays. Nevertheless, these technologies currently have barely penetrated everyday life. This hinderance can be explained by a lack of true next-generation near-eye display architectures that overcome the critical issues of stereoscopic wearables – notably vergence-accommodation conflict (VAC). The lack of such display architectures is directly related to the slow evolution and reorientation of image source industry. A major issue is the light transmission efficiency from an image-source towards the eyes of a viewer, directly impacted by the emission angle of light sources versus the need for collimated light. Collimation is a wasteful process, therefore, there is a limit to image brightness achievable with the currently available solid-state light sources. Inevitably, designers turn to more collimated light sources – lasers. While this approach yields improvements in size, it comes at the cost of image fidelity by introducing speckle patterns. Other alternatives (such as OLED microdisplays) are possible but are also not without issues. Thus, there needs to be a breakthrough in available image-sources for AR displays to reach at least a comparable image to what the 2D display counterparts can currently offer. Be it a full-color solid state uLED microdisplay, superluminescent LEDs, or developments in photonics by integration of RGB light sources into compact packages, the key-challenge is to leverage these advancements enabling a next-generation near-eye display architecture.

We demonstrated a high power UVC LED using a novel high-quality AlN template. The superior electrical performance is attributed to the decent quality-strain engineering with AlN/AlGaN epitaxy. Using p-type AlGaN SL instead of p-GaN as the contact layer, might reduce the UVC light absorption coefficient up to 90%, and improve the output power of the device up to 45%. The utilization of p-AlGaN layer and nPSS improved the light extraction efficiency via different mechanisms.

UV-C radiation for disinfection applications is used for decades. The major light source in most of these applications is the mercury containing UV-C low-pressure discharge lamp. Compared to this mature technology the UV-C LED is still new and in the introduction phase. LEDs enable new applications which cannot or have not been addressed by conventional lamps before. The radiant power, efficiency and price performance of today’s UV-C LEDs show a significant gap to the conventional lamp and a direct replacement of the current technology seems to be very challenging. In this paper we are trying to estimate the point of time by when UV-C LEDs are able to replace conventional UV-C lamps in different applications by performing a total cost of ownership calculation of the UV-C source at several time points in the future based on roadmaps for different performance parameters and considerations of the respective application efficiencies. A comparison of the applications upper air treatment, secondary air treatment, batten fixture surface treatment and municipal water treatment shows that in some applications a lamp replacement by LED is already realistic today. The significant difference of the application efficiency between LED and lamp-based systems lead to an earlier possible adoption of the LED technology than expected from a direct comparison of the performance parameters of the sources itself.

Ultraviolet Germicidal Irradiation (UVGI) is a proven method of disinfection for both bacterial and viral pathogens. Since the acceleration of the COVID-19 pandemic caused by SARS-CoV-2, the industry has witnessed significant technological innovation and an influx of UV-C LEDs, devices, and disinfectant enclosures. To ensure germicidal efficacy, UV-C LEDs and associated devices need accurate characterization of their optical power and irradiance. When UV-C sources are installed in enclosures and rooms, additional challenges arise that need to be evaluated to ensure germicidal efficacy is maintained. These challenges include 1) under- and over-dosing due to non-uniformity of UV-C dosage, 2) poorly understood room/chamber dynamics and reflectance, 3) shadowing, and 4) sensor, material, and source degradation. Here, we introduce a new detector portfolio that is calibrated at critical UV-C wavelengths, such as 265 nm, and enables real time UV-C Irradiance measurements at near-field and far-field. Temporal monitoring of irradiance allows for real time dosage calculation. Seasoned optical components ensure accurate detector performance and enable source output degradation monitoring. An adaptable API, network capability, and a dashboard facilitate simultaneous monitoring of multiple detectors and easy integration with existing installation infrastructure. With a proprietary cosine diffuser, these detectors include an exceptional f2 directional response making them ideal for deployment in rooms, enclosures, and HVAC systems.

With this work we propose a guideline for the development of efficient and effective UVC surface disinfection systems for SARS-CoV-2 based on LED technology. The work analyzes the optical and electrical characteristics of state of the art UVC LEDs. From the most recent scientific literature, optical simulations, and laboratory experiments we propose guidelines for the design of high efficiency LED based antiviral system for the treatment of contaminated surfaces. To validate the guidelines two different UVC-LED irradiation systems, for spherical and flat surfaces, have been designed, manufactured and tested. Results indicate a log-4 inactivation of SARS-CoV-2 in few minutes.

In this study, we developed highly efficient pixelated near-infrared organic light-emitting diodes (NIR-OLEDs) featuring self-emission and small form factor, which are expected to expand applications of light sensing. To realize new NIROLEDs in which active-matrix drive is possible by multiple fine pixels, we established a highly efficient NIR-OLED material and top-emitting NIR-OLEDs with fine pixels. Excellent characteristics including pixel pitch of 7.8 μm, peak wavelength of more than 900 nm, and external quantum efficiency of approximately 1% were successfully demonstrated. In addition, we confirmed the feasibility of highly efficient NIR-OLEDs with fine pixels, which is expected to contribute toward miniaturized sensing light sources with low power consumption, and hence improved value.

The advance of automated vehicles imposes increasing requirements on the sensor system of vehicles. Besides the ongoing development of perception algorithms, different hardware approaches exist in order to improve the detection of infrastructure and road users. In the far-field in front of the vehicle, the detection of infrastructure and road users relies on camera and LiDAR systems. However, the reliability of both systems is influenced by weather conditions, especially due to reflections from snow, rain, or fog and the camera by the ambient lighting as well. Optimized algorithms are implemented to improve the vision of both systems but limitations remain. RaDAR is proven to work more reliably in adverse weather conditions but struggles in providing sufficient data for detailed object classification. In combination with data fusion, the sensor systems can provide a partly redundant perception of the road and its users. This paper aims to provide a proof of concept for the improvement of the vision of camera systems in low light by using active NIR illumination. For this purpose, the spectral emission of visible and near-infrared sources is compared with the sensitivity of a camera. Considering regulatory emission limits, an optimal wavelength for additional NIR lighting is determined. Based on the determined wavelength we research the correlation between the output power of the sources and the camera’s perceived brightness and introduce possible applications for the additional NIR illumination

After Al-treating a gallium crucible, a noticeable improvement to device performance and epilayer surfaces could be seen. This improvement was compared to a device that had the highest reported mid-infrared radiance at time of publication. Using papers and previous growths, the improvement could be narrowed down to the Al-treatment of the gallium crucible. Surface preparation, growth conditions, and device structures tested were as close to identical for before and after Al-treatment.

As optoelectronic semiconductor research reaches a level of saturation, incorporation of unconventional processes and techniques often add to new phenomena and opportunities. In this manuscript, we share our perspective regarding the application of electrochemistry to GaN and related compound semiconductors. Two specific examples of using nanoporous structures, created by electrochemistry, for mini-/micro- LEDs and for vertical cavity surface emitting lasers (VCSELs) are discussed.

The shortage on radio spectrum forced to a high sophistication in spectrum efficiency. Optical wireless communication (OWC), rather than RF communication, may be a game changer, as the available optical spectrum is sheer unlimited. In addition, light can more easily be directed to the desired user (only). Narrowing the emitted light beams allows denser reuse, even within one room, and enables an increase in throughput. The authors report their experience from creating indoor OWC systems and verify these insights against throughput models. The trade-off between high throughput in only a narrow beam versus offering a wide coverage area is discussed. LEDs and free-form optics allow simple ways to direct a beam, which is more attractive than a phased-array as used in RF. The suitability of a Lambertian radiation patterns is challenged and compared to an optical system that is designed to provide constant irradiance. An example of a sectorized system comprising four segments with free-form optics is presented and its performance and characteristics are discussed, for a Lambertian and a directional detector

Vehicle Communication Systems consist of vehicles and roadside units that communicate with one another in order to exchange information, such as traffic information and safety warnings. Split intersections are an innovative solution for congested urban areas. In this case, a congested two-way-two-way intersection is made into two lighter intersections. It facilitates a smoother flow with less driver delay, by reducing the number of conflict points and improving the travel time. Based on Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I) and Infrastructure-to-Vehicle (I2V) communications, we propose a Visible Light Communication system that can safely manage vehicles crossing an intersection using Edge of Things facilities. The connected vehicles communicate with each other and with the infrastructure through visible light, by using headlights, street lamps, and traffic signals, In parallel, an intersection manager coordinates the traffic flow and interacts with the vehicles through internally installed Driver Agents. Request/response mechanisms and time/space relative pose concepts are used to control the flow of vehicles safely crossing the intersection. A communication scenario is established, and a “mesh/cellular” hybrid network configuration is proposed. Data is encoded, modulated and converted into light signals emitted by the transmitters. As receivers and decoders, optical sensors with light filtering properties, are used. Bidirectional communication between the infrastructure and the vehicles is tested, using the VLC request/response concept. Results show that the short-range mesh network ensures a secure communication from street lamp controllers to the edge computer through the neighbor traffic light controller with active cellular connection and enables peer-to-peer communication, to exchange information between VVLC ready connected cars.

This paper builds a model for the benchmarking and the selection of a suitable LED for wireless optical communication, in particular for indoor LiFi Infrared or visible light communication. It reviews LED measurements and theoretical models for such trade-off and applies these into communication bit-rate throughput expressions. While illumination LEDs are chosen for a large quantum efficiency, for communications also a large 3 dB bandwidth is preferred. In the LED, electron hole pairs recombine radiatively (thereby emitting a photon) or non-radiatively (causing a leakage current and reducing EQE). Non-radiative recombination also contributes to the response speed of the LED and increases its 3 dB bandwidth. On the other hand, a reduction in effective optical power may counterproductively lead to an inadequate signal-to-noise ratio. A trade-off is postulated empirically, in the form of a rule of thumb: “transmit power raised to the power alpha times bandwidth raised to the power one minus alpha” appears to be an LED constant. This semi-empirical model gives straight lines on a log-log scale. This paper searches for a theoretical justification for such a model, where current density acts as a parameter to make the trade-off. According to communication theory, the achievable bit rate grows approximately linearly with an increasing bandwidth but approximately logarithmically with the received energy per bit. However, this needs to be reviewed for a gentle low pass roll-off of the LED response, as it allows modulation far beyond the 3 dB bandwidth. These lead to a perspective on how to operate the LED: a system design faces the challenge to trade-off power versus bandwidth according to the physics LED properties, to optimize a communication throughput target.

III-N light-emitting-diodes (LEDs) are subject of intense investigations, thanks to their high efficiency and great reliability. The quality of the semiconductor material has a significant impact on the electro-optical performance of LEDs: for this reason, a detailed characterization of defect properties and the modeling of the impact of defects on device performance are of fundamental importance. This presentation addresses this issue, by discussing a set of recent case studies on the topic; specifically, we focus on the experimental characterization of defects, and on the modeling of their impact on the electro-optical characteristics of the devices.

This paper investigates the effect of the properties and position of defects on the performance and reliability of InGaN/GaN Multi Quantum Well (MQW) LED. To this aim, we analyzed color-coded structures featuring two quantum wells, emitting respectively at 405 nm and 495 nm. In order to evaluate the mechanisms that limit the reliability of the devices, a constant current stress at I=80 A/cm² and T=350K was carried out. From the degradation results, the electrical characteristics show an increment in the leakage current in the sub-turn on forward voltage regime compatible with a diffusion process. To interpret the measurement results, we implemented a simulation deck through Apsys Crosslight software, in order to model the effect that different trap concentrations and spatial locations have on the optical characteristics. The energy of the involved traps was derived by deep level optical spectroscopy analysis (DLOS). By comparing the simulation results with the experimental data, we observed that optical degradation is compatible with an increment of defect density in specific layers of the active region. Moreover, we found that the position of the traps (i.e. their proximity to the quantum wells or the EBL), modifies the band bending and influences the carrier density inside the wells, thus affecting the recombination rate and the peak emission wavelength. Therefore, we suggest that the optical degradation in MQW LED can be ascribed to a combined effect of defects with different spatial location.

Perovskite quantum dots (PQD) can be created using a ligand assisted reprecipitation method at room temperature with affordable equipment. These PQDs can exhibit much higher photoluminescence (PL) than bulk perovskite films of the same material. In this study, methylammonium lead bromide (MAPbBr3) quantum dots were created using energetically aligned capping ligands of trans-cinnamic acid (TCA) and 3,3-Diphenylpropylamine (DPPA). The bandgap of the PQDs was adjusted by varying the quantity of ligands added to the solution during the ligand assisted reprecipitation process. Prototype light emitting diodes (LEDs) were created using the PQD thin films.

Laser pumped phosphor (LPP) light sources are by now well established for generation of yellow or green light in digital projection applications. But also white light sources that are compliant with the requirement of car headlights are already on the market. Lately, high luminance white light sources in the wide field of specialty lighting are of growing interest. Since requirements for color temperature, luminance and color homogeneity are different for each application, a thorough understanding of factors that influence those properties is required. We discuss various optical concepts and show how a specific material design of luminescent ceramics allows for direct generation of white light in a simple optical setup. Different applications require different color coordinates and luminance levels. We present a range of white ceramic converters and show the impact of material selection to address those needs. In particular, we present data on the strong interaction between color coordinates and irradiance limit. Besides material selection, operating conditions need to be considered. We study the impact of laser parameters such as wavelength, power and spot size on color coordinates and efficacy. The cooling of the static ceramic converter and its impact on peak irradiance is investigated as well. In summary, this study provides a comprehensive guideline for material selection and optical design of high luminance white light sources.

State-of-the-art RGB microdisplays use quantum-dot color converters (CC), which suffer from photostability issues and low blue-light absorption. Inorganic MQW based CC offer higher blue-light absorption and better photostability. However, their practical use for microdisplays has not been implemented yet because of their low light extraction efficiency (LEE) inherent to their high refractive indices. In this paper, we investigate the use of photonic crystals (PhC) with different optogeometrical parameters to fully optimize AlGaInP/InGaP MQW CC for blue-to-red and green-to-red color conversions in microdisplays. A 600nm-thick CC was successfully bonded on a transparent substrate using oxide-mediated molecular bonding. By using optimized photonic-crystal designs, we obtained a large LEE enhancement (x 9) within ultra-short extraction lengths (~2μm), which shows quasi-perfect light outcoupling and compatibility with pixel lateral sizes under 5μm. Experimental results are in agreement with 3D-FDTD simulations, showing that those unique characteristics are paired with highly directional emission. A phenomenological model derived from the standard coupled-mode theory has been proposed and used to determine the mean coupling strengths between the guided Bloch modes and radiated modes. We believe that the design guidelines set in this work could pave the way for the use of inorganic MQW CC to achieve monolithic integration for full-color microdisplay applications.

Various high temperature phosphor materials, such as glass phosphor, ceramic phosphor, and crystal phosphor have been under stage of development targeting high power white light generation, which are suitable for various high power, small etendue applications. Stationary phosphor plates are getting into commercial projectors for some lower power projectors mostly limited by the power density limits of the phosphor materials. This paper presents a compact rotating, tilted, planar mirror, such that the output focused laser spot can be made to follow an elliptical path on the phosphor plate, increasing the effective area of the focused spot, and resulting in a higher limit of output optical power of the system. The key to such optical design is that the output of the system maintains the same small etendue of a single focused spot, and not the etendue of the circular path, for efficient coupling of the output to the projection optics. The maximum power capacity is very dependent on heat sinking especially the top surface of the phosphor plate. With the current heat sinking methodology, the maximum power is 89 W focused into a spot size in the range of 0.5 mm, which will further be determined accurately. The estimated power density ranges from about 300 to 600 W/sq. mm. along an elliptical path with axes measures 4.23 mm and 6.23 mm at 7,200 RPM. This has an improvement of power density limit many times compared to the phosphor specification of 45W/sq. mm. Further increase of power density limit is expected with further heat sinking developments. It is believed that the heat transmission between the top and the bottom of the phosphor plate would plan an important role in the power capacity. Phosphor plates with smaller thickness are being prepared for further investigation.

White light is obtained from converting blue light from an LED source with yellow light emission from phosphor such as YAG-Ce. Phosphors are incorporated in glass or a resin matrix to use with blue LED sources. A novel and a versatile method using a pulsed CO₂ laser is presented which helps in rapid fabrication and reducing complexity of fabrication of phosphor glass composites on glass surface. Mixture of YAG-Ce phosphor and recycled borosilicate glass powder is deposited on borosilicate glass substrate using a settling method. The thickness and composition of the deposited layer can be easily controlled by altering the quantity and weight ratio of the mixture, thus making it easier to control the resultant color temperature of the sample. Localized surface melting of the glass is obtained by irradiating the samples with a pulsed CO₂ laser. This creates an adhesion of the mixture to the substrate surface when cooled while encapsulating phosphor in a glass matrix. Phosphor to glass weight ratio as high as 50% can be easily obtained by this method. Phosphor is not exposed to high temperatures for an elongated period to cause thermal degradation, thus avoiding the need to develop special low melting point glass materials. The effects of different parameters such as composition and temperature are presented. This method allows the use of a CO₂ laser to accomplish multiple functions like fabricating microstructures and polishing in a single step to manipulate the light output.

Germicidal irradiation with a dose of UV-C light is an effective method for disinfecting surfaces, water, and air. New commercial devices are abandoning mercury gas-arc lamps in favor of UV-C LEDs, but UV-C LEDs are less efficient. This requires optical designs that use lenses to deliver UV-C light with high irradiance values to the target. This paper presents metallic optical reflectors (MORs), made with stamping processes, as a new lens for UV-C LEDs. Designs are described, tested, and validated for applications in SMD packages and chip-on- board (COB) modules. Aspherical mirror surface in MORs narrow the beam and achieve viewing angles as small as 15° FWHM with high efficiency. Simulations and tests conducted with a gonio-spectroradiometer agree sufficiently well so that the optical model can be used to design germicidal irradiation systems for surfaces or air in upper-room applications.

In the present work, a purple laser diode of 405 nm is employed for the excitation of different types of phosphors for the purpose of building a white light source. Three different types of phosphor materials were synthesized – a blue phosphor (BAM), a green phosphor (GYAG) and a red phosphor based on nitride. These samples were synthesized in the form of silicone pellets, having different thicknesses and different concentrations in the silicone matrix. In this study, two different approaches were followed. First, the three different samples were stacked together in various combinations to study the colorimetric parameters of the emitted converted light, particularly the correlated color temperature (CCT) and the color rendering index (CRI). In the second approach, the three types of phosphors were merged in the same silicone pellet. Pellets with different thickness and ratio of the three phosphors were prepared, and their CCT and CRI parameters were measured under laser excitation. In the first case, a CCT of 2264 K and a CRI of 74 were achieved while with the second approach, an average temperature of 4500 K and a CRI of 85 were reached. While the difference between the CRI values for both cases is not big, the CCT value of the mixed samples is twice as high as the value of the stacked pellets, something attributed to simultaneous excitation of phosphors in mixed samples while, when stacked, each material is irradiated in a specific order.

UV LED lifetime measurement is a challenging yet essential task required for component comparison and product development. Typical batch test systems utilize specialized integrating spheres suitable for UV light measurements and require periodic opto-electrical measurements at specific junction temperatures, which are time-consuming, labor intensive, and costly. Measurement uncertainties can be introduced due to imprecise positioning and manual operation. Typically, measurements using the integrated sphere provide the absolute intensity integrated over the solid angles, providing non-directional radiometric output. While such measurements provide the basis to set lifetime trends, ageing characteristics can be directional, varying with LED emission angles, playing an important role in determining device lifetimes depending on specific applications. We propose the design of a fully-automated lifetime test system, equipped with robotics, driven using artificial intelligence tools suitable for production scale testing of UV LEDs. This system allows for rapid, repeatable, relative optical measurements without the use of an integrating sphere, hence reducing capital and labor costs. The system is equipped with location sensors and learning algorithms which permit precise positional control across the three dimensions making it versatile for use with different types of LED optics at varying heights. It enables radiometric output measurements in a pre-determined angular grid around the LED, providing output degradation data as a function of emission angle in near field without the need for a goniometric apparatus. The system is designed to be easily scaled to accommodate larger arrays, enabling a flexible and cost-effective solution.

Ultraviolet sources are of great interest to many research areas and their applications. From UV disinfection to UV spectroscopy, UV sources with different emission power and wavelengths are needed. Commercially available UV lamps may be arc-discharge, incandescent, or fluorescent lamps; however, their cost may reach thousands of US dollars. Furthermore, they do not always fulfill the needs of the application. For example, arc-discharge or incandescent lamps have a wide emission spectrum forcing the use of different expensive filters for the applications needing a narrower emission bandwidth. Moreover, high emission power could not be desirable to biomedical research and applications due to associated damage with ultraviolet light. LEDs may solve the aforementioned issues; however, a single LED is clearly not a solution if a broad spectrum is needed. In this work, we present the design and characterization of a homemade LED-based UV source with variable emission in terms of power and wavelength. The source is constructed with five different LEDs in the UVA interval, covering an spectral range from 355 to 395 nm. An Arduino unit controls the source, allowing the user to select the emission of only one or the sum of a set of LEDs with desired wavelengths, extending the bandwidth. Finally, we present an analysis of the advantages and disadvantages of the proposed source for different optical applications.