Light Engine Research Articles

Apparatus and method for measuring individual color-matching functions

This article presents a compact visual colorimeter for the purpose of measuring color-matching functions (CMFs) of individual observers through psychophysical experiments. Constructed from 3D-printed parts, optical elements, and LED-based light engines, the colorimeter facilitates the juxtaposition of two fields to create a bipartite field. The system underwent characterization to evaluate factors that may impact color-matching experiments, such as LED-light stability, spatial homogeneity of the bipartite field, and potential stray-light leakage. The study aimed to assess the accuracy and performance of the system in measuring individual observer CMFs. Results indicate that the system is stable enough to measure both intra- and inter-observer variations in CMFs.

An Algebraic Approach to Light–Matter Interactions

AbstractA theoretical and computational framework for the study and engineering of light–matter interactions is reviewed in here. The framework rests on the invariance properties of electromagnetism, and is formalized in a Hilbert space whose conformally invariant scalar product provides connections to physical quantities, such as the energy or momentum of a given field, or the outcome of measurements. The light–matter interaction is modeled by the polychromatic scattering operator, which establishes a natural connection to a popular computational formalism, the transition matrix, or T‐matrix. This review contains a succinct yet comprehensive description of the main theoretical ideas, and illustrates some of the practical benefits of the approach.

Modelling and Numerical Evaluation of Photovoltaic Parameters of a Highly Efficient Perovskite Solar Cell Based on Methylammonium Tin Iodide.

Designing a high performance solar cell structure requires the understanding of material innovation, device engineering, charge behavior, operation characteristics and efficient photoconversion of light to generate electricity. This study offers a detailed numerical evaluation of the device physics in a highly efficient methylammonium-based perovskite solar cell (PSC) of the configuration, FTO/WO3/CH₃NH₃SnI₃/GO/Fe. Utilizing the SCAPS-1D device simulator, an impressive open-circuit voltage (Voc) of 1.3184 V, short-circuit current density (Jsc) of 35.10 mA/cm², Fill factor (FF) of 78.38%, and power conversion efficiency (PCE) of 36.24% were achieved. The model cell exhibits a robust photon capture of 100% quantum efficiency between 360 and 750 nm. The study also presents temperature-dependent band alignment diagram which posted a built-in potential (Vbi) of 0.62 eV. The Vbi at 400 K was found to be 0.58 eV indicating that the model cell exhibits a decent temperature tolerance, and can retain approximately 93% of its power at 400 K. Through Mott-Schottky capacitance analysis, deeper insights into the space-charge region are inferred, while recombination-generation investigations emphasize the significance of electronic properties in optimizing device performance. This paper, therefore, lays the foundation for future studies, offering clear pathways for device optimization and identifying key areas that require further investigation.

Breaking the in-coupling efficiency limit in waveguide-based AR displays with polarization volume gratings

Augmented reality (AR) displays, heralded as the next-generation platform for spatial computing, metaverse, and digital twins, empower users to perceive digital images overlaid with real-world environment, fostering a deeper level of human-digital interactions. With the rapid evolution of couplers, waveguide-based AR displays have streamlined the entire system, boasting a slim form factor and high optical performance. However, challenges persist in the waveguide combiner, including low optical efficiency and poor image uniformity, significantly hindering the long-term usage and user experience. In this paper, we first analyze the root causes of the low optical efficiency and poor uniformity in waveguide-based AR displays. We then discover and elucidate an anomalous polarization conversion phenomenon inherent to polarization volume gratings (PVGs) when the incident light direction does not satisfy the Bragg condition. This new property is effectively leveraged to circumvent the tradeoff between in-coupling efficiency and eyebox uniformity. Through feasibility demonstration experiments, we measure the light leakage in multiple PVGs with varying thicknesses using a laser source and a liquid-crystal-on-silicon light engine. The experiment corroborates the polarization conversion phenomenon, and the results align with simulation well. To explore the potential of such a polarization conversion phenomenon further, we design and simulate a waveguide display with a 50° field of view. Through achieving first-order polarization conversion in a PVG, the in-coupling efficiency and uniformity are improved by 2 times and 2.3 times, respectively, compared to conventional couplers. This groundbreaking discovery holds immense potential for revolutionizing next-generation waveguide-based AR displays, promising a higher efficiency and superior image uniformity.

Superhydrophobic performance of aluminum textured with a picosecond laser

Aluminum is a common and light engineering metal with high strength, good processability, corrosion resistance, high electrical conductivity, and strong recyclability, properties that allow its wide use in different fields. Strengthening the surface properties of aluminum materials can not only enable aluminum materials to be applied to complex environments but also extend their service life. In this study, two kinds of micro–nano structures—unidirectional micro-grooves and grid micro-grooves—were prepared on the surface of 1060 aluminum using picosecond-laser direct etching, so that its surface can attain superhydrophobic properties and enhance its application performance. The effect of the scanning interval of picosecond laser on the hydrophobic performance was investigated, and the findings indicate that the hydrophobic properties are most effective by using scanning interval of 20 μm. The scanning electron microscope (SEM) and atomic force microscope (AFM) analyses revealed the formation of a micro-nano structure resembling nanoflower particles on the laser-treated aluminum surface, which contributed to increased surface roughness. EDS analysis indicated an increase in carbon (C) content, likely due to the adsorption of organic molecules from the air, which further promoted hydrophobicity. X-ray diffraction spectrometry (XRD) and X-ray photoelectron spectroscopy (XPS) provided insights into the surface chemistry and the presence of various elements and compounds. The superhydrophobic aluminum surfaces demonstrated remarkable stability and self-cleaning capabilities, desirable traits for many practical applications. This study provides a simple and rapid method for preparing superhydrophobic materials on aluminum surfaces and has potential practical application value.This innovation paves the way for the development of high-performance aluminum materials suitable for a wide range of environments and uses.

Anisotropic optical property of ferroelectric Bi2O2X(X = S,Se,Te) monolayer and strain engineering

Based on the first-principles calculations, ferroelectric Bi2O2X(X = S,Se,Te) monolayers with unequivalent in-plane lattice constants are confirmed to be the ground state, which is consistent with the experiment result (Ghosh et al 2019 Nano Lett. 19 5703–09), and the anisotropic optical property is firstly investigated. We find that the polarizations of Bi2O2X monolayers points along the direction of a-axis, and Bi2O2Te monolayer process the largest polarization. Furthermore, both the biaxial and uniaxial strains are favor for the enhancement of polarization of Bi2O2X monolayers. It should be mentioned that the type of band gap will convert from indirect to direct for Bi2O2Te monolayer when the a-axial tensile strain is larger than 2%. At last, the optical absorption coefficient for Bi2O2X monolayers are calculated, and we obtain that Bi2O2Te monolayer has the strongest optical absorption within the range of visible light, the anisotropy and possible strain engineering to improve the optical absorption are discussed in detail. Our findings are significant in fields of optoelectronics and photovoltaics.

Customizable polarization-selective narrowband meta-filters using a printable UV-curing nanocomposite.

Low-cost nanocomposite metasurfaces have demonstrated attractive potential to replace the equivalent dielectric metasurfaces for light engineering. However, the resonance characteristics of embedded structures in nanocomposite metasurfaces have not been further analyzed beyond the effective refractive index. Herein, we have proposed customizable polarization-selective narrowband meta-filters using ultraviolet-curable (UV) nanocomposites. As an additional degree of freedom, near-field effects between highly concentrated doped nanoparticles can enhance the Mie resonance of the low aspect ratio (AR = 0.2) meta-units. The surface lattice resonances (SLRs) of meta-filters can be coupled with enhanced Mie resonances of individual meta-units to realize tunable narrowband (FWHM ∼0.007λ) reflections with intensities near unity. Meanwhile, the polarization-selective properties of the reflection peaks can be tuned by optimizing the asymmetric lattice. Such proposed new-generation customizable meta-filters will offer, to our knowledge, novel strategies for filtering specific near-infrared polarized fluorescence in the integrated imaging systems.

On the Secondary Flow System of an Aggressive Inter Compressor Duct

Abstract In contrast to the highly optimized rotating components, the inter compressor duct (ICD) is offering a high potential for further improvements. Due to a more aggressive design, the length of the whole engine can be reduced. Shorter and thus lighter engines are leading to further fuel savings for the next engine generation. The design of current ICDs is very conservative because of high uncertainties in design space. An extensive test campaign on two highly aggressive ICDs has been conducted at an annular cascade at German Aerospace Center (DLR) Cologne to explore these limitations. The test section consists of low-pressure compressor (LPC)-OGVs, struts, and high-pressure compressor (HPC)-inlet guide vanes (IGVs). To simulate the influence of the last rotor of the LPC and to vary the incidence of the OGV, a moveable swirler is placed in front of the OGV. This simplification results in differences compared to a real rotor outlet flow. Due to geometric constraints, the ability to move the swirler can only be achieved by adding partial gaps in the rear part of the swirler at hub and shroud. These gaps have a huge impact on the secondary flow structure of the swirler outflow and therefore on the inflow of the ICD. In this article, the secondary flow system of an aggressive ICD is analyzed in detail by the means of experimentally validated computational fluid dynamics (CFD) simulations. Special attention is given to the influence of the nonrotating swirler on the secondary flow system. Furthermore, a recommendation for future experimental setups with respect to the described effects is concluded.

Full-colour 3D holographic augmented-reality displays with metasurface waveguides

Emerging spatial computing systems seamlessly superimpose digital information on the physical environment observed by a user, enabling transformative experiences across various domains, such as entertainment, education, communication and training1–3. However, the widespread adoption of augmented-reality (AR) displays has been limited due to the bulky projection optics of their light engines and their inability to accurately portray three-dimensional (3D) depth cues for virtual content, among other factors4,5. Here we introduce a holographic AR system that overcomes these challenges using a unique combination of inverse-designed full-colour metasurface gratings, a compact dispersion-compensating waveguide geometry and artificial-intelligence-driven holography algorithms. These elements are co-designed to eliminate the need for bulky collimation optics between the spatial light modulator and the waveguide and to present vibrant, full-colour, 3D AR content in a compact device form factor. To deliver unprecedented visual quality with our prototype, we develop an innovative image formation model that combines a physically accurate waveguide model with learned components that are automatically calibrated using camera feedback. Our unique co-design of a nanophotonic metasurface waveguide and artificial-intelligence-driven holographic algorithms represents a significant advancement in creating visually compelling 3D AR experiences in a compact wearable device.

Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging (Laser Photonics Rev. 18(5)/2024)

Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging (Laser Photonics Rev. 18(5)/2024)

Multi-optimization of rod fastened rotor on the distribution of bending stiffness and unbalance

A rod fastened rotor (RFR), which contains serial disks, rods (or a rod), and a torque tube, is the main form of heavy duty gas turbines and light duty aero engines. The roughness of the interface is the main parameter affecting the bending stiffness of RFR, and the jumpiness of the disks is the intuitive representation of the unbalance of the rotor. In this paper, a multi-optimization algorithm, NSGA-Ⅱ, was used to improve the vibration behavior of the RFR-bearing system. First, the quantitative relation between the bending stiffness of the rotor and the roughness of the interface was set up by combining the Persson contact theory and the Greenwood–Williamson model, and the nondimensional bending stiffness (NS) was proposed as the optimization objective of roughness. Then, the optimization objective of the jumpiness of the disk, (A + B), was rendered based on the minimum unbalance force. Finally, the multi-optimization on the roughness and jumpiness of the RFR was carried out, and the vibration behavior was improved greatly. In addition, this multi-optimization method was applied to a practical RFR, and the experimental results showed that the vibration amplitude was reduced by about 82%. The work in this paper can provide the guidance for vibration reduction of the rotor system.

Reconsidering the spectral distribution of light: Do people perceive watts or photons?

The spectral distribution is a fundamental property of non-monochromatic optical radiation. It is commonly used in research and practical applications when studying how light interacts with matter and living organisms, including humans. In the field of lighting, mis-conceptions about the spectral distribution of light are responsible for unfounded claims, which pervade the scientific and technical communities. Starting from the definition of the spectral distribution, this paper describes the ambiguities and errors associated with a purely graphical analysis of the spectral distribution. It also emphasizes the importance of considering the particle nature of light in research involving both visual and non-visual effects, which implies using the spectral distribution expressed in the photon system of units, a system that has been seldom used in lighting research for historical reasons. The authors encourage lighting engineers and researchers to determine which system is best suited to their work and then proceed with the correct use of spectral distributions and of spectral weighting functions for applications involving optical radiation.

Experimental investigation on the potential of passive prechambers for use in 2S engines

Design improvement of Internal Combustion Engines (ICEs) is required by the continuous update of European exhaust emission standards and vehicle registration protocols. This has pushed research and industry efforts towards the development of Low Temperature Combustion (LTC) systems. Among various LTC technologies, the so called “jet ignition” is claimed to be well-suited for light engines, since it provides a more uniform and rapid combustion while ensuring the mixture ignition process. In this context, the adoption of prechambers was found well-suited for two-stroke engines, for which low-pressure direct injection technologies have been developed in the last decade to reduce the fuel short circuit phenomenon. The present paper experimentally investigates the use of different passive combustion prechambers in a Low-Pressure Direct Injection (LPDI) 2-stroke engine, with the main purpose to understand the relationship between prechamber geometrical parameters and engine performance. A 50-cc single cylinder LPDI motorcycle engine is chosen as the test case and it is re-arranged to run in jet ignition mode. The experimental analysis focuses on the evaluation of benefits provided by jet ignition combustion compared to the baseline LPDI propulsion unit at different engine operating points. Design criteria for prechambers development and the tuning process of engine combustion parameters (such as start of injection, ignition time and throttle valve opening) are described in detail. The results of experimental activity are finally shown and critically discussed, highlighting advantages and disadvantages of this application in terms of engine performance, efficiency and cycle-to-cycle variation.

Calibrating the Livengood–Wu integral knock model for differently sized methanol engines

Experimental test campaigns have begun to demonstrate the potential of methanol as an alternative fuel for heavy-duty spark-ignited engines. However, there is no consensus yet on the scope of this solution in terms of maximum power and engine size. A zero-dimensional combustion model is therefore being developed outside the scope of this work. Its main objective will be to predict key performance parameters such as power and efficiency as function of engine size. Due to the high loads typically encountered in heavy-duty engines, knock will be the main constraint to maximize the engine's potential. This work therefore aims to find an accurate knock model that can be implemented in the modelling framework. The Livengood–Wu knock integral model is being considered as a good candidate, as it is computationally inexpensive and thus allows for a large number of engine configurations to be modelled within a reasonable time. Due to a lack of autoignition delay times of methanol at conditions relevant to heavy-duty engines, a large database was created using chemical kinetics calculations. A neural network model was trained with the tabulated data for fast data retrieval. To validate whether the knock integral approach is robust enough to be applied to a wide range of engine sizes, a calibration constant was added to match the knock predictions to experimental data. Its value was calculated for three different engines, a light and heavy-duty SI engine and a large-bore dual-fuel engine. They highlight a remarkable difference in calibration constant across the different engines investigated.

The use of palm oil for light and heavy diesel engines and its environmental benefits for Helsinki

The use of palm oil for light and heavy diesel engines and its environmental benefits for Helsinki

Lighting design method of a football stadium considering visualization

This research is about implementation of visualization to evaluate and correct lighting state and characteristics of lighting engineering on computers in lighting design of football pitch considering shelter and tower. The visualization of architectural lighting and ornament with lamplights designs has not been studied in detail until now in the world, and the method of visualization design for achieving FIFA standards in asymmetric four-tower football stadium lighting is described in the light mode and under the brief introduction by the lighting simulation programs DIALux and Relux..

Results of an interlaboratory study on the working curve in vat photopolymerization

The working curve informs resin properties and print parameters for stereolithography, digital light processing, and other photopolymer additive manufacturing (PAM) technologies. First demonstrated in 1992, the working curve measurement of cure depth vs radiant exposure of light is now a foundational measurement in the field of PAM. Despite its widespread use in industry and academia, there is no formal method or procedure for performing the working curve measurement, raising questions about the utility of reported working curve parameters. Here, an interlaboratory study (ILS) is described in which 24 individual laboratories performed a working curve measurement on an aliquot from a single batch of PAM resin. The ILS reveals that there is enormous scatter in the working curve data and the key fit parameters derived from it. The measured depth of light penetration Dp varied by as much as 7x between participants, while the critical radiant exposure for gelation Ec varied by as much as 70x. This significant scatter is attributed to a lack of common procedure, variation in light engines, epistemic uncertainties from the Jacobs equation, and the use of measurement tools with insufficient precision. The ILS findings highlight an urgent need for procedural standardization and better hardware characterization in this rapidly growing field.

Light Engineering and Silicon Diffractive Optics Assisted Nonparaxial Terahertz Imaging

AbstractThe art of light engineering unveils a world of possibilities through the meticulous manipulation of photonic properties such as intensity, phase, and polarization. Precision control over these properties finds application in a variety of fields spanning communications, light–matter interactions, laser direct writing, and imaging. Terahertz (THz) range, nestled between microwaves and infrared light, stands out for its remarkable ability to propagate with minimal losses in numerous dielectric materials and compounds, making THz imaging a powerful tool for noninvasive control and inspection. In this study, a rational framework for the design and optimal assembly of nonparaxial THz imaging systems is established. The research is centered on lensless photonic systems composed solely of high‐resistivity silicon‐based nonparaxial elements such as the Fresnel zone plate, the Fibonacci lens, the Bessel axicon, and the Airy zone plate, all fabricated using laser ablation technology. Through a comprehensive examination through illumination engineering and scattered light collection from raster‐scanned samples in a single‐pixel detector scheme, the imaging systems are evaluated via diverse metrics including contrast, resolution, depth of field, and focus. These findings chart an exciting course toward the development of compact and user‐friendly THz imaging systems where sensors and optical elements seamlessly integrate into a single chip.

Chirality manipulation of ultrafast phase switches in a correlated CDW-Weyl semimetal

Light engineering of correlated states in topological materials provides a new avenue of achieving exotic topological phases inaccessible by conventional tuning methods. Here we demonstrate a light control of correlation gaps in a model charge-density-wave (CDW) and polaron insulator (TaSe4)2I recently predicted to be an axion insulator. Our ultrafast terahertz photocurrent spectroscopy reveals a two-step, non-thermal melting of polarons and electronic CDW gap via the fluence dependence of a longitudinal circular photogalvanic current. This helicity-dependent photocurrent reveals continuous ultrafast phase switches from the polaronic state to the CDW (axion) phase, and finally to a hidden Weyl phase as the pump fluence increases. Additional distinctive attributes aligning with the light-induced switches include: the mode-selective coupling of coherent phonons to the polaron and CDW modulation, and the emergence of a non-thermal chiral photocurrent above the pump threshold of CDW-related phonons. The demonstrated ultrafast chirality control of correlated topological states here holds large potentials for realizing axion electrodynamics and advancing quantum-computing applications.

A Study on the Challenges and Legal Issues arising from Chinese investment in Bangladesh Natural Resources and Infrastructure

This study focuses on the challenges and legal issues surrounding Chinese investment in Bangladesh's natural resources and infrastructure. It looks at the impact of Chinese investment on the country's resources and infrastructure, including any legal and regulatory issues that may arise. The study may examine how Bangladesh's laws and regulations protect the country's natural resources and infrastructure from foreign investment, and whether these laws are adequate to ensure that the country's resources are being used sustainable and in a manner that benefits the local communities. Additionally, the study may look at the role of international law and international organizations in mediating disputes between Bangladesh and Chinese investors. I have mentioned foreign investments in natural resources of Bangladesh e.g. natural gas, petroleum oil, coal and water resources. Until now, China only invests in a couple of sectors relating to natural resources. These investments are infrastructure projects e.g. power generation, construction, port establishment, agro-processed product, electrical and electronics, light engineering, roads, railways, power plants, and water treatment facilities, etc. This is a second generation Chinese BIT that incorporated general Characteristics of BITs of that era. Under this BIT, Regarding the dispute of expropriation, an ad hoc arbitral tribunal can be formed which would determine its own procedure, but the first negotiation shall take place between the parties to solve the dispute. Under these agreements, the disputes shall be settled by applying generally recognized principles of international law accepted by the parties.