Optical Principles Research Articles

Improved numerical modeling of photovoltaic double skin façades with spectral considerations: Methods and investigations

Photovoltaic double skin façades are crucial tools for mitigating the escalating energy consumption in buildings. However, current simulation studies often neglect the variation in solar spectra and focus on only limited operational modes, resulting in incomplete and less accurate modeling. In response to these limitations, this study proposes an improved numerical model incorporating temporal spectral variations and non-uniform surface temperatures, which comprehensively encompasses all operational modes of photovoltaic double skin facades. Real-time solar spectra are acquired using specialized software and remote sensing data, while the transportation and conversion of radiation energy will be solely solved at individual wavelength steps, providing the model with spectrum resolution. Built on the fundamental principles of optics, thermodynamics, and hydromechanics, the proposed two-dimensional numerical model consistently demonstrates desirable accuracy across various airflow paths and mechanical ventilation conditions. Based on the proposed model, the feasibility of the previously proposed parameter-based control strategy is proved, which offers potential energy savings of 25.9–341.6 MJ compared to the radical strategy and 67.5–170.7 MJ compared to the conservative strategy. The photovoltaic efficiency drop due to spectral mismatch is also quantified as about 15–35 %. These results highlight the potential of the proposed model as an efficient tool for future research.

Long-range fourier ptychographic imaging of the object in multidimensional motion

Fourier Ptychographic (FP) is a cutting-edge technique for achieving high resolution in long-range imaging, holding significant research value. However, most of the research on FP has been limited to high-resolution imaging of stationary objects, considerably narrowing the scope of its applications. In real-world scenarios, the object may move in three dimensions and rotate during the image acquisition process. To address such scenarios, this paper proposes a method for achieving FP of the object in multidimensional motion using a single camera. Starting from the principles of Fourier optics and diffraction, the paper calculates the effects of an object's movement in different dimensions on the light field. The Fourier-Mellin algorithm is to be applied to deduce changes in the light field from captured intensity images and align all collected data under a chosen reference light field. During image reconstruction, we propose an additional phase retrieval algorithm that integrates total variation regularization to address aperture offset issues. The paper validates the proposed method's effectiveness through simulations and experiments. FP is successfully applied to objects in multidimensional motion. The method also doubles the imaging system's resolution.

Physics-aware cross-domain fusion aids learning-driven computer-generated holography

The rapid advancement of computer-generated holography has bridged deep learning with traditional optical principles in recent years. However, a critical challenge in this evolution is the efficient and accurate conversion from the amplitude to phase domain for high-quality phase-only hologram (POH) generation. Existing computational models often struggle to address the inherent complexities of optical phenomena, compromising the conversion process. In this study, we present the cross-domain fusion network (CDFN), an architecture designed to tackle the complexities involved in POH generation. The CDFN employs a multi-stage (MS) mechanism to progressively learn the translation from amplitude to phase domain, complemented by the deep supervision (DS) strategy of middle features to enhance task-relevant feature learning from the initial stages. Additionally, we propose an infinite phase mapper (IPM), a phase-mapping function that circumvents the limitations of conventional activation functions and encapsulates the physical essence of holography. Through simulations, our proposed method successfully reconstructs high-quality 2K color images from the DIV2K dataset, achieving an average PSNR of 31.68 dB and SSIM of 0.944. Furthermore, we realize high-quality color image reconstruction in optical experiments. The experimental results highlight the computational intelligence and optical fidelity achieved by our proposed physics-aware cross-domain fusion.

Machine learning-based optimization of photogrammetric JRC accuracy

To improve the accuracy of photogrammetric joint roughness coefficient (JRC) estimation, this study proposes two optimization models based on ground sample distance (GSD), point density, and the root mean square error (RMSE) of checkpoints. First, an algorithm that automatically generates spatial positions for equipment based on the convergence strategy was developed, using principles of Structure from Motion and Multi-View Stereo (SfM-MVS) and the shooting parameter selection algorithm (SPSA). Second, a portable positioning plate containing ground control points and checkpoints was designed based on optical principles, and a moving camera capture strategy guided by SPSA was proposed. Combining SPSA, portable positioning plate, and moving camera capture strategy, a photogrammetric experiment for small-scale rock samples in the field was conducted, collecting 48 datasets with different shooting parameters. Subsequently, a dataset incorporating GSD, point density, RMSE, and three JRC estimation metrics was established, revealing their correlations and sensitivities. Using seven machine learning algorithms, optimization models for photogrammetric JRC accuracy were developed, with Linear Multidimensional Regression and Gaussian Process Regression models improving JRC accuracy by an average of 85.73%. Finally, the applicability and limitations of the newly proposed method were further discussed.

An Unstructured Mesh Coordinate Transformation‐Based FDTD Method

ABSTRACTWe propose a novel unstructured mesh finite‐difference time‐domain (FDTD) method for solving electromagnetics problems with complicated geometries. The method, which solves the TE‐mode reduced form of Maxwell's equations, can handle both material interfaces and anisotropic material. Using the transformation optics principle, which describes how fields and material tensors change under coordinate transformations, we locally transform each cell in the mesh to a reference unit‐square computational domain where the usual FDTD update is performed. This comes at a cost: employing unstructured grids and coordinate transformations requires more complicated data structures, a mesh orientation process, and potentially introduces an anisotropic material tensor at every mesh cell. Nonetheless, we find that the method maintains the same desirable properties of the classic FDTD method (explicit, divergence‐free B‐field, nondissapative, and second‐order accuracy) while also gaining conforming material interfaces and boundaries in complicated geometry. Even further, we prove that the method is stable under a Courant condition and a fairly nonrestrictive mesh condition, hence defeating the late‐time stability issue plaguing prior nonorthogonal FDTD methods. To verify the method, we conduct convergence studies on three electromagnetic cavity problems with known exact solutions. For these numerical studies, we find that the method maintains second‐order convergence and stability.

Analysis of fringe field effects on measurement errors for Q-scanning-based emittance diagnosis system

As a widely recognized emittance measurement technique, the Q-scanning method typically plays a crucial role in the commissioning process of accelerator-based beam injectors. The Q-magnet, being a pivotal component, significantly influences the measurement capability, thus warranting detailed examination in this study. By reassessing the measurement outcomes of the Q-magnet, the impact of fringe fields on emittance measurement precision is thoroughly scrutinized within this framework. Subsequently, corrections to the transfer matrices of the Q-scanning system under different excitation currents are implemented by revisiting fundamental beam optic principles. Moreover, virtual measurements via both theoretical calculations and beam dynamics simulations are conducted to validate these corrections, utilizing the setup of an existing beam injector established at Huazhong University of Science and Technology. Both the theoretical and experimental results indicate that the measurement accuracy of the Q-scanning technique can be improved by correcting the fringe field effects.

Investigation of square-root higher-order topological insulator based on honeycomb-Kagome lattice of graphene plasmonic crystals

Abstract In this paper, we construct a composite lattice that integrates a breathing Kagome lattice with a honeycomb lattice, and a Honeycomb-Kagome model based on graphene plasmonic is studied. Through simulation, it is proved that the band distribution of the square-root higher-order topological insulator model based on graphene plasmonic crystal coincides with that of the Hamiltonian. Our findings reveal that the square-root higher-order topological insulator combination model based on graphene plasmonic has multiple corner states. Furthermore, we examine the robustness of these corner states against defects. The research results offer potential application prospects for nano-scale plasmonic topological laser devices, and topological waveguides.

Fabrication of slanted gratings with high refractive index starting from master nanoimprint mold.

Recently, nanoimprinting has attracted a new round of attention in the industry due to the boom in demand for augmented reality/virtual reality (AR/VR), metalens and microlens, and even semiconductors. Slanted gratings have great application prospects in AR/VR displays because of their high efficiency in light coupling. UV-Nanoimprint lithography (UV-NIL) has been identified as one of the most feasible routes for mass manufacture of high refractive index (RI) slanted gratings. This paper presents a fabrication of high RI slanted gratings based on UV-NIL. A comprehensive study on the optical principles of slanted gratings is conducted, followed by simulation-based optimization of the grating parameters. The key element for applying nanoimprint to fabricate slanted gratings is the master mold, which is acquired by a tilted angle etching of metal gratings as an etching mask on silicon wafers with F-based plasma. The influence of experimental parameters, such as the etching power and etching mask thickness on the morphology of the slanted gratings on the master mold are investigated. The working mold was simply duplicated from the master mold by UV-NIL with a low surface energy working mold material. The high RI slanted gratings were achieved by imprinting a UV-curable resin with high RI. Finally, experimental verification was performed to assess the optical performance of the slanted gratings.

Real-Time Resolution Enhancement of Confocal Laser Scanning Microscopy via Deep Learning

Confocal laser scanning microscopy is one of the most widely used tools for high-resolution imaging of biological cells. However, the imaging resolution of conventional confocal technology is limited by diffraction, and more complex optical principles and expensive optical-mechanical structures are usually required to improve the resolution. This study proposed a deep residual neural network algorithm that can effectively improve the imaging resolution of the confocal microscopy in real time. The reliability and real-time performance of the algorithm were verified through imaging experiments on different biological structures, and an imaging resolution of less than 120 nm was achieved in a more cost-effective manner. This study contributes to the real-time improvement of the imaging resolution of confocal microscopy and expands the application scenarios of confocal microscopy in biological imaging.

Research on the NI-MLA Method for Enhancing the Spot Position Detection Accuracy of Quadrant Detectors Under Atmospheric Turbulence

The distorted spots induced by atmospheric turbulence significantly degrade the spot position detection accuracy of the quadrant detector (QD). In this paper, we utilize angular measurement and homogenization characteristics of non-imaging microlens array (NI-MLA) systems, effectively reducing the distortion degree of the spots received on the QD target surface, thereby significantly enhancing the spot detection accuracy of the QD. First, based on the principles of geometric optics and Fourier optics, it is proved that the NI-MLA system possesses the angular measurement characteristic (AMC) within the paraxial region while deriving and verifying the focal length of the system. Then, the QD computation curve characteristics of the system under non-turbulence are explored. This study further elucidates the mathematical principle of the NI-MLA system for mitigating the spot position detection random error of QD (SPDRE-QD) and discusses in depth the relationship between the NI-MLA system’s capability to mitigate the SPDRE-QD and the system’s parameters under various turbulence intensities. Finally, it is experimentally verified that the root-mean-square error (RMSE) of the QD computation values using the NI-MLA system are reduced by a significant improvement of at least 2.44 times and up to 17.36 times compared with that of the conventional optical system of QD (COS-QD) under turbulence conditions ranging from weak to strong.

A Review: Laser Interference Lithography for Diffraction Gratings and Their Applications in Encoders and Spectrometers

The unique diffractive properties of gratings have made them essential in a wide range of applications, including spectral analysis, precision measurement, optical data storage, laser technology, and biomedical imaging. With advancements in micro- and nanotechnologies, the demand for more precise and efficient grating fabrication has increased. This review discusses the latest advancements in grating manufacturing techniques, particularly highlighting laser interference lithography, which excels in sub-beam generation through wavefront and amplitude division. Techniques such as Lloyd’s mirror configurations produce stable interference fringe fields for grating patterning in a single exposure. Orthogonal and non-orthogonal, two-axis Lloyd’s mirror interferometers have advanced the fabrication of two-dimensional gratings and large-area gratings, respectively, while laser interference combined with concave lenses enables the creation of concave gratings. Grating interferometry, utilizing optical interference principles, allows for highly precise measurements of minute displacements at the nanometer to sub-nanometer scale. This review also examines the application of grating interferometry in high-precision, absolute, and multi-degree-of-freedom measurement systems. Progress in grating fabrication has significantly advanced spectrometer technology, with integrated structures such as concave gratings, Fresnel gratings, and grating–microlens arrays driving the miniaturization of spectrometers and expanding their use in compact analytical instruments.

Inspiration from Visual Ecology for Advancing Multifunctional Robotic Vision Systems: Bio-inspired Electronic Eyes and Neuromorphic Image Sensors.

In robotics, particularly for autonomous navigation and human-robot collaboration, the significance of unconventional imaging techniques and efficient data processing capabilities is paramount. The unstructured environments encountered by robots, coupled with complex missions assigned to them, present numerous challenges necessitating diverse visual functionalities, and consequently, the development of multifunctional robotic vision systems has become indispensable. Meanwhile, rich diversity inherent in animal vision systems, honed over evolutionary epochs to meet their survival demands across varied habitats, serves as a profound source of inspirations. Here, recent advancements in multifunctional robotic vision systems drawing inspiration from natural ocular structures and their visual perception mechanisms are delineated. First, unique imaging functionalities of natural eyes across terrestrial, aerial, and aquatic habitats and visual signal processing mechanism of humans are explored. Then, designs and functionalities of bio-inspired electronic eyes are explored, engineered to mimic key components and underlying optical principles of natural eyes. Furthermore, neuromorphic image sensors are discussed, emulating functional properties of synapses, neurons, and retinas and thereby enhancing accuracy and efficiency of robotic vision tasks. Next, integration examples of electronic eyes with mobile robotic/biological systems are introduced. Finally, a forward-looking outlook on the development of bio-inspired electronic eyes and neuromorphic image sensors is provided.

VenSpec-H spectrometer on the ESA EnVision mission: Design, modeling, analysis

VenSpec is a spectrometer suite on board ESA's EnVision mission to planet Venus, due for launch in November 2031. VenSpec consists of three spectrometers, VenSpec-M, VenSpec-U and VenSpec-H. VenSpec-H stands for Venus Spectrometer with High resolution. It operates in the near-infrared wavelength range between 1.15 and 2.5 μm and it aims at mapping the near surface atmosphere during the night and the atmosphere above the cloud deck during the day. More specific, VenSpec-H will measure gases related to volcanism and surface changes on Venus. It will perform its measurements by means of nadir observations.In this paper an overview is given of the main design requirements, followed by a description of the design activities performed during the feasibility study (phase A) and the preliminary definition (phase B1) of the instrument, including mathematical modeling and analysis, and prototyping. Focus is put on the optical working principle of the instrument, where an echelle grating, used as diffractive element, is combined with an inventive combination of filters for spectral band selection.The design and development of VenSpec-H is done in a consortium under Belgian management and with important contributions from Belgian, Swiss, Spanish, and Dutch research institutes, universities, and industrial partners.

Study on stress singularities in cylindrical shells with an arbitrary oriented crack using digital gradient sensing technique

In this paper, the transmitted digital gradient sensing (DGS) technique is applied to analyze stress singularity at the tip of an arbitrary oriented crack in a cylindrical shell. A thoretical model of the opitcal path near the tip of the inclined crack in a cylindrical shell under mixed-mode fracture is proposed based on the geometric optical imaging principle. An optical governing equation of DGS technique is established to relate the mixed-mode stress intensity fractors (SIFs) at the crack tip to the shell geometry parameters and the inclined crack sizes, and the angular deflection contours are theoretically plotted using this govering equation. Uniaxial tensile tests are carried out on polymethyl methacrylate (PMMA) cylindrical shells containing an edge crack with different inclined angles, and the optimal calculation area for the exaction of SIFs is determined from linear elasitic fracture mechanics. The effects of shell radius, shell thick, crack length, and crack angle on the mixed-mode SIFs are studied, respectively. These results show that the DGS technique is effective and accurate to evalute the stress singulary around an arbitrary oriented cracks in cylindrical shells.

Comparative analysis of three jaw motion tracking systems: A study on precision and trueness.

The purpose of this study was to assess the precision and trueness of three jaw motion tracking systems, the KaVo ARCUSdigma system, SDiMatriX system, and Modjaw system, in recording mandibular movements based on optical and ultrasonic principles. Twenty-five healthy subjects were selected for the present study to measure protrosive movement and left and right lateral movements using the three jaw motion tracking systems. Each subject's mandibular movement was recorded twice with a 1-week interval. Five parameters-sagittal condylar inclination (SCI) angle, incisal guide angle, Bennett angle, lateral condylar inclination angle, and Fischer's angle-were acquired for further analysis. The precision of the jaw motion tracking systems was evaluated by comparing the results of two measurements of the same parameter. Simultaneously, cone beam computed tomography (CBCT) was utilized during the initial data acquisition and was aligned with intercuspal position (ICP) and edge-to-edge occlusion intraoral scan data. Bone landmarks were used to calculate bilateral SCI as a reference for comparison with the SCI values from each jaw motion tracking system. An independent-sample t-test was conducted to compare parameter differences, with statistical significance set at a p-value below 0.05. There were no significant differences among the three jaw motion tracking systems regarding the corrected values of SCI, incisal guide angle, Bennett angle, lateral condylar inclination angle, and Fischer's angle during the 1-week interval (p>0.05). The values of bilateral SCI obtained by CBCT were 48.57±6.74 (L) and 48.35±5.28 (R), respectively. No significant differences were found between the reference SCI and those parameters measured by the KaVo ARCUSdigma system and the Modjaw system (p>0.05), while the results obtained from the SDiMatriX system indicated a significant difference compared to the reference SCI (p<0.05). The three jaw motion tracking systems exhibited favorable results in terms of precision. Regarding trueness, both the KaVo ARCUSdigma system and the Modjaw system demonstrated a satisfactory levels suitable for applications in digital prosthodontics within clinical settings. However, further refinement is needed to enhance the trueness of the SDiMatriX system.

Fundamentals of Determination of the Biological Tissue Refractive Index by Ellipsoidal Reflector Method

This paper presents the theoretical fundamentals, prerequisites for creation, and peculiarities of modeling a new method for determining the refractive index of biological tissues. The method uses a mirror ellipsoid of revolution as an optical element to ensure total internal reflection phenomena. This paper thoroughly analyzes the differences in the refractive index of healthy and pathological tissues on a biometric diagnostic basis. The analysis is used to model the measurement setup’s parameters. This paper also considers various methods of determining the refractive index of biological tissues based on different principles of physical optics, such as interferometry, refractometry, ellipsometry, and goniophotometry. It systematizes typical optical elements of total internal reflection that can be used in goniophotometry. It justifies the selection of the element base for the goniometric installation based on the ellipsoidal reflector method. A simulation of the installation operation was carried out for various parameters of the ellipsoidal reflector, ensuring the measurement of the biological tissue refractive index from 1.33 to 1.7. This paper also proposes a constructive solution for manufacturing an ellipsoidal reflector of the required configuration.

Organic Crystals and Optical Functions in Biology: Knowns and Unknowns.

Organic crystals are widely used by animals to manipulate light for producing structural colors and for improving vision. To date only seven crystal types are known to be used, and among them β-guanine crystals are by far the most widespread. The fact that almost all these crystals have unusually high refractive indices (RIs) is consistent with their light manipulation function. Here, the physical, structural, and optical principles of how light interacts with the polarizable free-electron-rich environment of these quasiaromatic molecules are addressed. How the organization of these molecules into crystalline arrays introduces optical anisotropy and finally how organisms control crystal morphology and superstructural organization to optimize functions in light reflection and scattering are also discussed. Many open questions remain in this fascinating field, some of which arise out of this in-depth analysis of the interaction of light with crystal arrays. More types of organic crystals will probably be discovered, as well as other organisms that use these crystals to manipulate light. The insights gained from biological systems can also be harnessed for improving synthetic light-manipulating materials.

Optical design and analysis of a high-speed triple galvanometer laser 3D scanning system

In this paper, a triple galvanometer laser three-dimensions (3D) scanning system (TGLSS) was proposed. The system consisted of three galvanometers and two parabolic mirrors, with rapid movement of the laser focus in 3D space by rotations of the three galvanometers. The optical principle of the TGLSS was analyzed, and the method of designing TGLSS by geometrical optics and Abbe’s sine condition was given in detail. Scanning range and focusing quality were analyzed by optical simulations. An experiment was carried out to verify the feasibility of TGLSS. The implications of TGLSS for reflective dynamic focusing device (RDFD)-based laser system and their impact on technologically relevant applications were discussed. The great potential for enhancing the speed of advanced laser processing in 3D space was offered by TGLSS.

Recent improvements in the novel approach to the fast detection of surface contaminations

Here, we present the idea behind a novel measurement system and the recent improvements in detecting surface contaminations using a tunable, very fast three-core quantum cascade laser (QCL) system. It is developed as a potential replacement for the old established double-wheel sampling system currently used to detect surface threats caused by hazardous, non-volatile chemical substances. The novel system design is based on an optical measurement principle, allowing standoff detection and identification, thus rendering ground contact unnecessary. One of the leading military requirements for a CBRN reconnaissance vehicle is a high marching speed; hence, this new system is designed to have an ultra-short acquisition time and an adequate spectral bandwidth for measurements in the mid-infrared (MIR). This innovative approach may replace the more cumbersome indirect detection techniques. We discuss the main advantages and evaluate possible application scenarios that we expect from this setup. Active IR backscatter spectroscopy generally permits the contactless identification of hazardous chemical substances on surfaces. Here, the design was optimized around an approximate measuring distance of decimeters. Using a monoaxial setup, the autofocus is less demanding than alternative approaches and even allows for rapid measurements of rough surfaces. We built the improved measurement system based on novel QCL modules that integrate micro-opto-electro-mechanical grating scanners (MOEMS) in an external cavity. These elaborate laser modules provide almost one kilohertz (kHz) spectral scan speeds and typically cover a spectral range of 200–300 cm-1, respectively. Furthermore, such modules achieve measurement times of as short as one millisecond per spectrum. The full spectral coverage of the system is realized by coupling several of such modules.

Incorrectly Focused Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) Laser Beam Leads to Massive Destructive Effects in Small-Aperture (Pinhole) Intraocular Lenses.

Pinhole intraocular lenses (IOLs) were developed to improve reading by compensating for loss of accommodative function. The IC-8® Apthera™ is a small-aperture presbyopia-correcting IOL that combines the proven principle of small-aperture optics with an aspheric monofocal lens to deliver a continuous range of vision for patients withcataractsfrom distance to near vision. Posterior capsule opacification is the most common sequela after cataract surgery. It is effectively treated by laser capsulotomy. However, if the laser beam is incorrectly focused, the IOL can be permanently damaged (pits/shots). In this experimental study, yttrium-aluminum-garnet (YAG) pits were purposefully created. Defects were analyzed and compared between the periphery of the ring in the clear area of the hydrophobic acrylic lens and at the carbon black (CB)-polyvinylidene fluoride (PVDF) filtering component (FilterRing™) of the pinhole lens. All defects were made using identical settings/energy levels (2.6mJ). The damage induced to the IC-8® Apthera™ IOL was examined by low-magnification images, light microscopy, scanning electron microscopy, and micro-computed tomography (micro-CT). YAG defects in the carbon black filter ring were much more severe than those in the clear zone due to the high absorption of the carbon black. Massive defects and destruction of the lens with tearing out of fragments and particles were observed. The missing volume calculated from the micro-CT reconstruction was 0.266 mm3, which is 1.6% of the entire IOL volume, or more than 1000 times the volume damaged in the largest shot in the periphery. Based on the results, we highly recommend using the lowest possible energy levels, posterior offset setting, and circular pattern for maximum safety when performing laser capsulotomy with pinhole implants. Care should be taken to avoid creating irreversible iatrogenic defects that may affect overall quality. The safest area for performing capsulotomy seems to be the periphery of the ring segment. Video available for this article.