Current Developments in Lens Design and Optical Engineering XXV

In this work, detailed literature about the power allocation schemes in optical wireless communication has been presented and discussed. The main goal is to evaluate the gain ratio power allocation (GRPA) and normalized gain difference power allocation (NGDPA) schemes in a 4x4 multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) based visible light communication (VLC) system. The work will evaluate the GRPA and NGDPA according to the system's overall achievable sum-rate and the sum-rate gain. The proposed MIMO-VLC system can utilize up to 4 subscribers regardless of their current position within the system coverage area. The work will examine the received bit rate of each user in different positions within the system coverage area. Target to maintain the same bit rate for each user, especially when the user is at the border of the system coverage area. Finally, the study will discuss the results before and after applying the power allocation schemes GRPA and NGPDA.

The Transport of Intensity Equation (TIE) is a partial differential equation that describes the relationship between the phase and the axial intensity variation of an optical field. The essence of phase retrieval using the TIE is to solve the partial differential equation under appropriate boundary conditions. Ichikawa, Lomman, and Takeda (ILT) verified the TIE experimentally for the first time, solving the equation by the Fourier transform method, thus obtaining the quantitative phase distribution of a one-dimensional sample. In this paper a modification of the Ichikawa-Lohmann-Takeda (ILT) method is presented. We extent the method using cylindrical coordinates for phase retrieval. The main idea is to replace the grating used in the original ILT method for a concentric-circular grating in order to exploit the cirular symmetry. Typically, the method implemented by ILT results in the solution of the Poisson Equation. The latter is resolved through a process based on artificial neural networks. Experimentally the phase is compared using the Schack-Hartmann sensor versus the solution found by solving the circular TIE.

A transmission and receiving optical antenna is built-in-house by TASA and Taiwan domestic optical company CALIN. A Cassegrain type telescope is designed and manufactured with primary aperture 80 mm. It could provide the transmitted and received gain about 104 dB, and the obscuration loss about -3.8 dB in the link channel for free space optical laser communication. It could also be integrated in the CubeSat or in the optical communication terminal for small satellite missions. The root-mean-square wave front error for the optical antenna is less than 100 nm. The optical aberrations introduced on-axis WFE loss is estimated about -0.72 dB in the link budget. An eyepiece is designed to locate near the focus of telescope to collimate the output beam with beam size about 3.3~4.7 mm for propagating 50 cm distance in the follow-up communication module system. With the strong supporting domestic electro-optical industry, it is expected to help a lot on the development of the Taiwan space technology.

Eye fundus images are used in clinical diagnosis to detect retinal disorders. When retinal images are degraded by scattering due to opacities of the eye tissues, the precise detection of abnormalities is complicated depending on the grading of the opacity. This pathology not only limits vision to patients but also can impede visualization of the eye fundus. In this work will show that the choice of the color space as well as the choice of color channel will enhance the performance of processing retinal images to assess the vasculature and optic nerve head as well as to identify retinal lesions or pathologies. We will present a method that combines the use of Contrast Limited Adaptive Histogram Equalization (CLAHE) and a deconvolution process to enhance retinal images in different color spaces for more accurate feature detection.

In this work, circular Zernike polynomials are considered as periodic structures that, when they are illuminated by a coherent wave front, form self-images at the Talbot distance Zt. This distance depends on the radius of the circular grating and the wavelength with which it is illuminated, Z_t=(2r^2)/λ. This phenomenon is explained by the Fresnel diffraction integral. A numerical simulation is used for a better explanation of the Talbot effect with this kind of structures and a comparison is made between the experimental and simulated results. In conclusion, this mathematical analysis and numerical simulation approach provides a basis for understanding the Talbot effect in the realm of Zernike-based azimuthal periodic structures.

The design of this headlight is different from the common headlight designs on the market. We try to concentrate the energy on the upper edge of the light shape and the regulatory area and design the upper edge of the light shape to have several secondary strong points and similar to the upper edge of the light shape. The shape is wide and narrow at the bottom, and the one-dimensional cylindrical lens array structure is used to extend the light shape horizontally. The superposition of energy creates a light shape with high contrast and can simultaneously meet multiple regulatory requirements.

This paper investigates the design of an ophthalmic rigid contact lens (CL) using a Q-type aspheric surface. The traditional power-series polynomial is commonly used for aspheric surface design. Still the significant slope departure from a best-fit sphere leads to high tolerance sensitivity and an inflection point. To solve this problem, the Q-type polynomial with slope constraint proposed by Forbes is applied to the aspheric CL. The Q-type aspheric polynomial can reduce error budget for maximal manufacturing yield. The simulation results demonstrated that the spherical aberration is successfully reduced by the Q-type aspheric CL for better visual acuity in darkness.

This study aims to investigate the impact of Bulk Scattering Diffuser (BSD) on color variation in Mini-LED backlight modules under different optical parameters. To predict spectral distribution distortion of BSD in Mini-LED backlight module, a virtual Mini-LED backlight is built in the optical simulation software. The scattering behavior of BSD is also established by the calculation model based on Mie scattering theory. In simulations, the corresponding color coordinate of distorted spectrum is moved in the CIE 1931 color space owing to varying parameters of BSD. Finally, under the condition of highly color uniformity, through the comparison between the color coordinates and the MacAdam ellipse, the suitable manufacturing parameters of BSD are discussed.

A luminaire designed for tunnel lighting is proposed, featuring the ability to adjust the ratio between counter-beam and pro-beam lighting based on different contexts. This allows the luminaire to achieve the optimal lighting mode for the conditions within the tunnel at that time. When both side LEDs are activated, it operates in symmetric lighting mode. When a single-side LED is activated, it switches to either counter-beam or pro-beam lighting mode. The advantage of this luminaire lies in the use of a single freeform secondary lens and LEDs, making installation simpler. It ensures driver safety and is more energy-efficient than traditional tunnel lights.

A neural network based generative optimization algorithm was investigated for designing athermalized lens design. In particular, deep learning framework was developed by employing PyTorch and incorporated lens variable conversion techniques along with a differentiable ray tracing module. The framework, combining supervised optimization with unsupervised optimization, could generate diversified lens designs starting from reference lens system including aspheric surfaces. Our generative optimization algorithm could also be applied to the design of athermal lens systems that minimize thermal focus shift with temperature changes. In addition, using the developed algorithm and considering the first order thermal expansion coefficient of each lens, we were able to design an all-plastic athermal lens system composed of polycarbonate and polymethyl methacrylate materials. The RMS spot size averaged over all fields and Seidel aberration were minimized for thermally expanded lens systems at various temperatures. The developed framework is expected to help lens designers create optimal designs.

This paper announces the development of a new, cryogenic refractometer at Leviton Metrology Solutions in Boulder, CO known as the Differential High Accuracy Refraction Measuring Apparatus, or DHARMA, which is nearing completion. DHARMA has been developed in part to provide a commercially-available source of cryogenic, refractive index measurements of similar or better quality to those provided by the CHARMS facility at NASA’s Goddard Space Flight Center. It was also conceived to provide the same the state-of-the art capabilities as CHARMS but extending into the long wave infrared (LWIR) where there is a growing need for such measurements. DHARMA’s basic design is presented along with preliminary data for measurements of cryogenic, absolute, refractive index for several prisms previously measured using CHARMS.

The Screen Image Synthesis meter was proposed to make high-speed BSDF measurement and whole field measurement, but it lacks the spectrum information. We proposed a snapshot hyperspectral technology and applied it to the SIS meter to build up a SIS hyperspectrum meter. It released the full power of SIS system. Besides, the proposed method doesn’t need to add any other bulky optical element. The experiments demonstrated the measurement is trustable in both spectrum distribution and color coefficient temperature distribution.

Minimizing glare and ghost images in optical systems via stray light control constitutes a significant portion of design time and costs. Optical coatings are crucial for reducing stray light to improve the signal-to-noise ratio (SNR). However, existing tools for identifying problematic surfaces are often manual, prompting extensive coating application to avoid extended development, which increases optics cost. To facilitate stray light analysis and reduce cost, a standalone tool has been developed that inquires about stray light optical path irradiance and assesses components' contribution to noise using realistic illumination scenarios. Coatings can be selectively applied to problematic surfaces until the desired SNR is attained. This approach significantly reduces analysis time and costs. GPU and Cloud computing expedite computations while maintaining precision and integrating seamlessly with Ansys' advanced ray-tracing tools, avoiding assumptions or approximations. It utilizes complete non-sequential ray data within a semi-sequential framework. Use cases and SNR analysis to validate the tool will be presented.

In this paper, we present our investigation into the prevention of blue-light leakage in phosphor-converted white LEDs through a passive approach. Our study primarily focuses on the application and optimization of a specific thermochromic material known as crystal nano cellulose (CNC). We integrated CNC within the epoxy lens of white LEDs. Importantly, under normal operating conditions, CNC minimally affects the optical properties of the emitted white light. However, in instances of overheating where blue-light leakage occurs, the temperature rise induces a darkening effect in CNC. By incorporating CNC as a responsive material in the design of white LEDs, our study offers a practical and efficient solution to address the adverse effects of blue-light leakage resulting from overheating. This enhancement not only improves the safety and comfort for users but also serves as an early warning mechanism for the aging of phosphor-converted white LEDs.

Urine test strips aid in prompt health assessment through color changes, but visual interpretation can be misleading, particularly with strips having multiple functions. To tackle this, some companies and studies have created paper strip analyzers using CMOS sensors. However, issues like ambient light and shooting angles often cause detection failures. Therefore, this study proposes integrating a 6 to 13-channel color sensor as the core component of a urine test strip analysis system and optical waveguide technology for optical system design architecture. This design aims to capture more color information in urine, and the optical waveguide technology ensures uniform light guidance, providing real-time transmission and high-quality image data for urine analysis systems. Ultimately, our system will employ artificial intelligence and image recognition technology to analyze the urine test strip data, accurately identifying subtle changes and abnormalities in urine, and providing timely health asses

These days, nothing lasts very long, and things often change for the better, but there are sure things in our community, such as this annual event, which has been going on for 25 years. The first edition en 2000 of the Current Developments in Lens Design and Optical Systems Engineering conference took place during INTERNATIONAL SYMPOSIUM ON OPTICAL SCIENCE AND TECHNOLOGY, 30 July - 4 August à San Diego. Over 45 oral presentations and ten posters were presented. The chairs were Robert E. Fischer, Warren J. Smith, R. Barry Johnson, and William H. Swantner. The proceeding was numbered 4093 and 24 years later the number is 12666 (2023). This presentation looks back on the great moments of our conference, its speakers, the subjects that have come and gone, and those that have remained.

The field of lens design has changed in many ways over the last quarter-century. Not only have the design tools changed, but the types of systems being designed have also changed. In this presentation we look back on how in design problems have changed and how optical design tools have changed to support new types of design problem.

The extraordinary optical performance of today’s state-of-the-art lithographic imaging systems for chip making is almost beyond belief. With the very high 1.35 NA value in a deep UV immersion design, the distortion over a 32 mm diameter field is less than 1.0 nanometers and the wavefront quality is better than 1/100 waves over the field. This required great progress in lithographic designs over the last 25 years and some key design techniques and insights that have been learned will be discussed here.

Optical simulations have always been tightly linked to our computational abilities, from the days of raytracing by hand through today's high-powered tools. Simulations become viable when they reach high enough accuracy to compete with hardware tests, and usually save time and money. For NASA, the James Webb Space Telescope marked the transition from direct hardware testing to a simulation-led build, and pushed all of our simulation tools forward in the process. The transition to simulation-led projects continues apace with integrated multi-physics tools, digital twins, AI/ML assistance, and smarter system engineering. To some extent, we can see where these initial steps will lead and imagine the simulation capabilities of the future.

Depth of field (DoF) determines the focused object depth in an optical imaging system. An extended depth of field (EDoF) should provide a larger axial resolution without significantly sacrificing the spatial resolution of the image. An optical-computational technique that uses a Trefoil phase mask (PM) to encode the scene numerically and experimentally and a convolutional neural network (CNN) to restore the acquired encoded images is presented. The Peak Signal to Noise Ratio (PSNR) evaluates the image quality. Simulations, as well as experimental results, are compared.

Development and optimization of new designs for freeform spectacle lenses can be a slow and iterative process requiring time-consuming studies and expensive designer expertise. Deep neural networks, meanwhile, have demonstrated an impressive ability to approximate very complex mappings when trained on large datasets in application areas such as computer vision. Here we demonstrate the application to lens design by utilizing domain-specific design parameters in the forward model. With this we train a number of different surrogate models capable of rapidly approximating the forward model. With this we produce a direct inverse model that can rapidly estimate custom designs for a range of parameter choices. Results are given for multiple different classes of freeform spectacle designs.

Freeform surfaces (FFS) offer an opportunity to create smaller optical systems with diffraction limited performance over wider fields of view that traditional conic designs. In infrared designs, it offers broadband response as well as an opportunity to manage the pupil of the optical system, enabling the camera and objective lens to be cold, improving performance. The process of FFS telescope design remains challenging to manage the performance and mechanical interference issues presented by folding. Using a Generative Adversarial Network (GAN) we model a series of telescopes and then present the network with a series of input requirements and evaluate the outputs of the network against requirements for size and performance.

Vein pattern recognition is a biometric identification technology that relies on the unique vascular patterns for each people hand. In this paper, we propose a method for people recognition that uses a combination of wavelet invariant moments and convolutional neural networks (CNNs). Wavelet invariant moments are a set of features that are extracted from an image using wavelet transform. These features can be invariant to translation, rotation, and scaling, which makes them well-suited for people recognition. CNNs has been shown to be very effective for image classification tasks. In this paper, we proposed method is evaluated on a 6000 palmvein images from the PolyU Multispectral Palmprint Database. The results show that the proposed method achieves an accuracy of 99%, which is higher than the accuracy of existing methods.

With 140+ petabytes of historical data holdings, 3.8 million square kilometers of daily multi-spectral collection, integration of Synthetic Aperture Radar and newly launching assets every quarter, the opportunities to develop insight from sense making technologies at Maxar are ever growing. During this discussion, we will cover the challenges of collecting, organizing, and exploiting multi source electro-optical remote sensing systems at scale using modern machine learning architectures and techniques to derive actionable insights.

Freeform optics, generally defined as optics without an axis of rotational symmetry, can be very useful for increasing performance while reducing size, weight, and element count in optical systems. Examples will be presented, ranging from one-off astronomical telescopes to optics for high-volume consumer devices. Although they can enable systems that would not otherwise be possible, freeform optics present significant challenges to designers and manufacturers. These challenges include finding a common language for design and fabrication, fabrication techniques, and especially metrology techniques. Potential solutions to some of these challenges will be discussed.

The Nancy Grace Roman Space Telescope (“Roman”) was prioritized by the 2010 Decadal Survey in Astronomy & Astrophysics and is NASA’s next astrophysics flagship observatory. Launching no earlier than 2026, it will conduct several wide field and time domain surveys, as well as conduct an exoplanet census. Roman’s large field of view, agile survey capabilities, and excellent stability enable these objectives, yet present unique engineering and test challenges. Roman comprises a Spacecraft and the Integrated Payload Assembly (IPA), the latter of which includes the Optical Telescope Assembly (OTA), the primary science Wide Field Instrument, a technology demonstration Coronagraph Instrument, and the Instrument Carrier, which meters the OTA to each instrument. The Spacecraft supports the IPA and includes the Bus, Solar Array Sun Shield, Outer Barrel Assembly, and Deployable Aperture Cover. It provides all required power, attitude control, communications, data storage, and stable thermal control functions as well as shading and straylight protection across the entire field of regard. This paper presents the Observatory as it begins integration and test, as well as describes key test and verification activities.

Recently, optical imaging systems have shown improvement not only in spatial resolution but also in depth of focus. This is due to both the development of material science and the implementation of techniques that reduce the optical aberrations. Aberrations are present in the information captured by the system, i.e., wavefront, making their elimination difficult. Various techniques, both physical and numerical, have been proposed to reduce aberrations. Numerical techniques are the most affordable to implement. Digital holography emerges as a prominent and effective numerical technique for correcting optical aberrations. Numerical compensation of aberrations is achieved by implementing phase compensation algorithms to model the complex field of the image. This paper presents a theoretical-experimental study on aberration correction using digital holography. The experimental setup involves a Mach-Zehnder interferometer in an off-axis configuration coupled with an algorithm for 3-D reconstruction and quantification of object information.

Three unusual mirror systems are shown. One is a single concave reflective/diffractive surface corrected for spherical aberration for all conjugates. Another is a telescope design with a kilometer diameter f/1.0 primary mirror. The last is a relay with two spherical mirrors that is nearly impossible to find with a computer..

Liquid Mirror Telescopes have been shown to be a credible alternative to traditional telescopes for building low-cost observatories. Previous LMTs were based on the rotation of a pool of mercury which, from the rotation, takes the shape of a parabola. However, they cannot be tilted as traditional telescopes to observe at fields away from the zenith. Here we present a telescope concept where a magnetic fluid is shaped to a parabolic surface by combining wetting effects and magnetic fields. The off-axis aberrations of the telescope when observing off-axis are cancelled by a surface correction of the parabolic liquid surface by adding a magnetic field correction. The scientific instruments are at the focal plane and designed as to track the beam as the field changes.

The fabrication of curved compound eye camera systems is usually complex since it can involve multiple non-standard components to achieve the desired effect. In this paper we aim to provide a close alternative to these custom optical elements using off the shelf components or to provide a framework to design these system using standard fabrication techniques. We will first demonstrate how lens distortion can be leveraged to optically bend a standard planar micro-lens array, and how this bending correlates to a curved micro-lens array. We will then show lab results of curved compound eye camera made using an off-the-shelf fisheye lens and a standard micro-lens array and how the equivalent curved micro-lens array system would reproduces image in the real world and provide a comparison using image simulation from an optical design software and a scene recorded using a neural radiance field.

Novel negative thermal expansion ALLVAR Alloys enables another degree of freedom for the system design on top of normal variables such as glass and material selection and element geometry. This presentation discusses and demonstrates the ability for ALLVAR Alloys to athermalize existing lens designs by controlling the thermal expansion of a lens housing. Thermal defocus analysis is presented and compared to data collected on an ALLVAR Alloy 30 athermalized lens assembly.

We propose a novel manufacturing technology for monolithic polymer optics such as aspherical lenses. UV-replication is well known from wafer level optics. Here supporting glass wafers remain in the final lens. This severely limits the degrees of freedom of the optical design. In addition, material shrinkage, when the polymer is cured, limits reasonable sag heights of the lenses, so that only low-resolution imaging optics are possible. In our UV-replication approach, there is no glass substrate in the individual lenses and the shrinkage is compensated in the process to achieve minimum form error. This enables large sag heights and aspherical lens profiles on both sides of thin menisci as required in high-resolution imaging optics which so far can be realized by injection molding only. Combining this with a high degree of parallelization such as in wafer-level-optics is the key to a large-scale and economical production. We present details of our new technology at the example of realized demo systems for 3D-sensing applications using nano-optical structures, imaging use-cases in endoscopy and those ultimately targeting mobile phone camera modules.

Over the past decades, advances in metamaterial and metasurfaces inspired innovation in many imaging systems. We have proposed more than 5 years a workflow to introduce metasurfaces in optical design by using semi-analytical models. These models recover the output phase and polarization after propagation through the metasurface and can be used within optical design software. As such, metasurfaces can be optimized in optical systems by using built-in optimization processes while avoiding time-consuming electrodynamics computation. In this presentation, we will review the status of these works as well as updated results in term of modeling meta-molecules and stigmatic ray tracing using metasurface.

Most depth and lidar sensors rely on near-infrared (NIR) sources to produce depth images as Silicon CMOS sensors can achieve a high quantum efficiency for an unbeatable cost at such wavelengths. Advances in short wave infrared (SWIR) sensor technologies, such as Silicon-Germanium sensors, changes this paradigm and opens a new window for groundbreaking sensor designs. Here, we propose to use a Silicon Metalens flat optics and build upon our stacked sensor technologies to obtain a fully Silicon integrated stacked sensor at SWIR wavelengths. We will discuss the design of the stacked sensor and focus on the Silicon Metalens for multiple use-cases. We will show numerical simulations of the optical stack for eye-tracking application or wide-angle time of flight (TOF) and how we can obtain very compact form factor modules. Finally, we will demonstrate the results of our Silicon metalens prototype at 1550nm.

The Cryogenic High Accuracy Refraction Measuring System (CHARMS) at NASA’s Goddard Space Flight Center (GSFC) has undergone some recent upgrades enabling refractive index measurements without the use of either liquid nitrogen (LN2) or liquid helium (LHe) cryogens, once again achieving sample temperatures around 30 K. CHARMS has also enjoyed the replacement of its very old, LN2-cooled, InSb mid-wave infrared (MWIR) camera with a new state-of-the-art InSb camera cooled with a closed-cycle Stirling cooler enabling unattended operation. The new camera improves signal-to-noise in MWIR index measurements. We report on measurements of two each Si and Ge prisms from room temperature down to below 35 K which are the first to benefit from these two recent upgrades. We also report on upgrades to CHARMS still in work which will enable cryogenic index measurements in the long wavelength infrared (LWIR) to wavelengths as long as 15-20 µm for the first time.

When an intense laser interacts with a gas of atoms, high-order harmonics are generated. In the time domain, this radiation forms a train of extremely short light pulses, of the order of 100 attoseconds. Attosecond pulses allow the study of the dynamics of electrons in atoms and molecules, using pump-probe techniques. This presentation will highlight some of the key steps of the field of attosecond science.