This PDF file contains the front matter associated with SPIE Proceedings Volume 11062, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

A novel technique is presented for full-color reconstruction of large-scale computer-generated holograms (CGHs). In this method, three printed CGHs are transferred to three volume CGHs with the wavelength corresponding to RGB colors, and then stacked to superimpose the RGB images. This CGH is not only portable but also the image is sharp and vivid as compared with that by RGB color-filters. A little position shift, caused in the reconstructed color images because of aberration by the thick glass substrate, can be compensated in calculation of the original CGHs. However, fabricated hologram was about 5 cm in the size so far, because it is difficult to create larger CGHs. In this paper, we also present techniques to create large stacked full-color volume CGHs by using scanning-copy. The fabricated full-color CGHs are demonstrated to verify the techniques.

Recently, a very efficient mask-based technique for CGH, called the switch-back technique, has been proposed to perform silhouette light-shielding efficiently. In this algorithm, the fields behind polygons are shielded by binary mask patterns, called silhouette masks, which are generated by orthogonal projection of the polygon shape. Thus, the mask plane is parallel to the hologram but not parallel to the polygon. As a result, there are many small gaps between neighboring masks. Background fields that should be shielded by the masks sometimes leak out from the gaps. Viewers perceive the gaps as many cracks in the surfaces of the reconstructed object. To get over the problem, exacter algorithm than silhouette lightshielding, called surface light-shielding, has been proposed using rotational transform of wave-fields, but it was too timeconsuming to apply it for large-scale CGHs. In this report, we propose a novel occlusion processing technique using improved surface light-shielding to calculate large-scale CGHs without any cracks. Actual large-scale CGHs are demonstrated to confirm validity of the algorithm.

In this paper the designs of secondary lenses for LED of reflective and refractive types are proposed for extended sources. The lens surface profile for desired illumination pattern on a screen can be obtained by solving first-order differential equations based on the Snell’s law and the energy conservation. Intensity distributions on a target screen were received by ray tracing using Zemax software. High efficiency ultra-slim lenses with illumination areas exceeding the distance between the LED chip and screen by more than six times are demonstrated for different chip sizes. Aspheric lenticular and two-dimensional microlens arrays are designed using wave-optics and ray-tracing methods. Possibility of development of high resolution and wide viewing angle 3D display based on free-form backlight unit is discussed.

An electrically tunable filter based on a plasmonic phase retarder and liquid crystal cells is reported. The plasmonic phase retarder consists of a periodic array of deep-subwavelength metallic nanostructures. A first entrance polarizer prepares the incident light in a polarization state oriented at 45° from the nanowires orientation. A strong phase retardation between TM and TE polarizations is induced by the plasmon resonances. A polarization analyzer based on liquid crystal cells allows to project the transmitted light onto a polarization state whose orientation depends on the applied voltage. Using this approach, a range of 8V is enough to span more than 50% of the area covered by standard RGB filters in CIE color coordinates with a single filter. In order to ensure the applicability to large area production, UV nanoimprint lithography (UV-NIL) and thin film coatings have been used to fabricate the plasmonic phase retarder. The nanoimprint master consists in a periodic binary grating with a sub-wavelength period below 200nm in order to avoid diffraction effects in the visible range and maximize the angular stability. The grating master is imprinted and coated with a silver thin film and encapsulated. The evaporation is performed with an angle, so that a self-shadowing effects prevents full coverage of the surface. The resulting structure consists in a periodic array of silver nanowires of total width 50nm, with a cross section forming an inverted U-shape. This particular shape shows a high degree of tunability of the plasmon resonance position given the constraints of a sub-wavelength periodicity. Multiple interfering resonances are observed so that the nominal transmission can reach >70%. Placed between a polarizer oriented at 45° from the nanowires orientation and a liquid crystal cell, the transmission spectrum of the plasmonic phase retarder can be tuned with the applied voltage. For a low voltage, the polarization transmitted through the liquid crystal cell is oriented along the gratings lines. For higher voltage, the light transmitted through the liquid crystal cell is oriented across the grating lines and the resulting spectrum has a dip in transmission, which is the signature of a plasmon resonance. At a voltage of 8V, a full rotation of the polarization by 180° has been applied. Different colors can be obtained within this range, including orange, magenta, purple, blue, turquoise, green and yellow with the same tunable filter. Other designs have been investigated in order to obtain more saturated blue, green or red using this approach.

Dielectric and plasmonic metasurfaces provide excellent control over the shaping of optical wavefronts via the manipulation of polarisation, phase and amplitude of the light. Taking advantage of their subwavelength thicknesses, metasurfaces have shown to be a very promising technology in a variety of applications including beam steering and focusing, polarisation and angular momentum control, enhancement of nonlinear effects, as well as holographic information encoding for 3D displays. Recently, the emergence of virtual reality and augmented reality technologies have led to the constant demand of effective techniques for the 2D visualisation of 3D objects. Normal mapping, for example, is widely used in computer graphics to create shading effects and recreate 3D-like features of surface textures, such as regular patterns, bumps or ripples. Here, we report on the development of the concept of surface normal mapping for the representation of 3D objects and shading effects with optical metasurfaces. In this work, the metasurface is designed to implement diffuse reflection and uses the concept of normal mapping to control its scattering properties. As a proof of principle, a flat diffuse metasurface imitating lighting and shading effects of a 3D cube was fabricated and characterised under incoherent illumination. The “3D image” is displayed directly on the illuminated metasurface and its shading varies in response to the change in illumination angle. The metasurface performs in a broad range of the visible spectrum, including the three main RGB wavelengths. The 3D images created via normal mapping based on optical metasurfaces provide an effective technology for 3D security features and anti-counterfeiting. This type of metasurfaces can also be useful in the design of efficient optical diffusers for display technology and etalons for metrology.

In this work, we demonstrate for the first time to our knowledge, a green light wavelength demultiplexer device, based on multi Slot waveguide (SW) structures. Gallium Nitride (GaN) surrounding Silica (SiO₂) were chosen for confining the light inside the SW region and found to be suitable for operation within the visible light spectrum. The proposed device as well as his geometry, aims and optimized to demultiplex wavelength in the green light range with wavelengths of 500, 510, 520 and 530 nm. The device is composed of six SW units and six S-bands (SB). A full vectorial beam propagation method (FV-BPM) and coupling mode theory used to study and analyze the demultiplexer device. The proposed device obtains losses better than 0.1275 dB, crosstalk as well as –21.135 dB and full width at half maximum (FWHM) smaller than 9.5 nm, in an overall compact size of only 104 μm. The proposed device has the ability to increase the data bit rate in visible light communication (VLC) system that works with wavelength division multiplexing (WDM) technology.

NewSight Reality’s (NSR’s) novel, patent pending AR Transparent Optical Module (TOM) that addresses many limitations of today’s AR devices like size, weight, light and energy efficiency, transparency with the ability to be embedded within ophthalmic lens is disclosed. NSR’s’ transformational design replaces the light engine and optical engine with a single multilayer hermetically sealed transparent module. TOM comprises a proprietary transparent Light Engine (that uses a TOLED, OLED or iLED) and a proprietary Micro-Lens Array (MLA) Optical Engine to project digital information from an image source to the eye of a user. The proprietary near eye display is see-through and preferably utilizes pixels and subpixels 5 microns or less in size. The micro-lens array is a proprietary design that collimates light from the pixels and projects a retinal image with a resolution of 1-2 arc minutes. TOM is hermetically sealed with a flexible multilayer coating that makes it resistant to sweat and environmental conditions. One of the main advantages of TOM is that it is a single thin, lightweight module. The innovation can have a thickness ranging between 1.0mm and 2.0 mm, weight of ~ 2 grams, transparency greater than 80% with light efficiency reaching the pupil of the eye that is very high due to near eye location of TOM. This enables low power and long battery life. TOM can be curved to the front surface base curve of an ophthalmic lens and can be integrated into an eyewear lens for monocular or binocular AR/MR eyewear. Optical Modeling using Zemax ray tracing confirms that this technical approach can result in highly efficient, high image quality AR.

As manufacturing capabilities have developed, the potential to create complex geometries for optical elements of a variety of materials has become a reality. Under these conditions, freeform optical components have become more prevalent in the industry, and have allowed a new class of optical systems to be engineered. In the past, freeforms have commonly been described parametrically for optimization, which in some cases limits their flexibility and utility. In this paper we demonstrate a novel freeform design methodology which uses a grid-based sag definition to serve as an alternative to polynomial coefficient optimization. The OpticStudio TrueFreeForm model allows direct optimization of sag values at grid points across the surface to enable spatially-selective surface sag optimization. Here, a case study is presented on the effectiveness of TrueFreeForm optimization in the design of freeform optical surfaces for use in modern augmented reality/virtual reality (AR/VR) optical systems. We demonstrate the flexibility and advantages of grid sag optimization and discuss key implementation considerations in the context of a freeform wedge prism system as might be found in an AR headset. In particular we demonstrate, via sub-aperture grid sag optimization, the integration of an eye-tracking subsystem into the AR wedge prism. An average MTF of 0.446 at 40 lp/mm is achieved in the user pupil imaging portion of the eye-tracking system, while introducing no degradation in the nominal performance of the AR visual display system.

We present the first light source module that is realized with RGB superluminescent LEDs in a compact 14-pin butterfly housing for speckle-free display applications. The module provides a free-space output with collimated RGB beams that are colinearly aligned having 10 mW output power per color.

For applications in the field of XR, devices based on light guiding are one beneficial approach to combine the virtual image with the light impinging from the real-world environment. Usually, lightguide devices like AR glasses are quite complex, due to the required management of a large field of view and light of different wavelengths. Due to this complexity, numerous parameters must be considered in order to design a functional device which provides a sufficient image quality and optical performance. In the talk we are going to present a systematic approach to design lightguide devices including different types of grating structures used for in- and out-coupling of the light. We will show, that this systematic approach, which is enabled by the fast physical optics technology of VirtualLab Fusion software, allows to combine the benefits of functional and parametric design and optimization strategies. Typical design tasks are discussed in detail, e.g. the trade-off between uniformity and system efficiency. In the talk, the design approach and the capabilities of the Field Tracing technology of VirtualLab Fusion are demonstrated based on various examples.

We present an underexplored variation of the classical optical freeform prism design that incorporates 3 optical surfaces. This optical architecture can make use of one, two, or three freeform surfaces. Our initial prototype uses a single freeform surface along with a sphere and a at surface to simplify manufacturing complexity. There are two key contributions in this paper that to our knowledge have not been achieved previously: 1) the design of a thin, 4 mm to 1 mm gradient thickness, curved freeform lightguide (nearly 4x thinner than the original freeform prism), and 2) lightguide fabrication utilizing ophthalmic machines. This particular optical design makes combined use of total internal reflections and partial reflections. The advantages of this optical architecture include the curved optical surfaces that eliminate the optical collimator requirement in at lightguides, a relatively large eyebox, and a manufacturing approach that reuses the standard ophthalmic process for fabricating the eyeside and worldside optical surfaces. The limitations of the optical design are low efficiency (~ 5%), multiple image artifacts, and lack of optical see-through.

Lightguides in combination with gratings seem to be a promising candidate for the development of AR/MR glasses. The research and development of this technique is done in numerous companies and institutes and there is still a lot of room for new ideas and innovations. The design and the modeling of such lightguides is very different to lens design and requires new techniques in modeling. Though ray tracing gives insight also in the case of lightguides, an analysis which includes all relevant effects must be based on a physical-optics approach which is fast and user-friendly. With the Fast Physical Optics technique in our software VirtualLab Fusion we provide such a modeling approach. We include the polarization of the in-coupled light, fully vectorial grating analysis, coherence, interference and diffraction effects in the analysis carried out in one software platform, with a fully non-sequential consideration of the lightpaths through the lightguide. In the talk we briefly explain the underlying modeling concepts and demonstrate analysis results for a specific FOV with respect to merit functions like uniformity in the eyebox, uniformity and MTF over the FOV for an example design done in VirtualLab Fusion. We address computation speed and distributed computing.

This paper is a review of the main waveguide combiner architectures that have been implemented in industry and academia to produce Augmented Reality (AR) and Optical See-Through (OST) Mixed Reality (MR) Head Mounted Displays (HMDs). We review their features and limitations and show product examples. We review also the design constrains and the main optical simulation techniques used to model and predict the overall performances of such optical waveguide combiners.

Lightguide structures are widely applied in different applications, and, nowadays, the are drawing special interest in the field of near-to-eye display systems. Such systems are typically realized with either planar or curved lightguides together with gratings for coupling light out of or into the lightguides. For the application in display, the field of view (FOV) supported by the lightguide parts becomes an important issue for the system design. In this work, we analyze the behavior of typical gratings for lightguide coupling, especially with the angular dependency taken into consideration. It will be shown that to obtain uniformity and relatively high efficiency over large FOV is a challenging task. With the evolutionary algorithm, we firstly optimize the coupling grating structure to obtain balance between uniformity and average efficiency over the desired FOV. Furthermore, by taking the image generation unit into account, we present a systematic design concept for the lightguide coupling grating. In such a manner, the constrain on the uniformity of the grating diffraction efficiency can be released to certain degree, which brings additional freedom and possibilities into the design.

DigiLens Switchable Bragg Grating (SBG) waveguide technology for transportation AR HUD consumer products enables switchable, tunable and digitally reconfigurable color HUDs with a field of view, brightness and form factor surpassing those of competing technologies. DigiLens waveguide gratings are printed into a proprietary polymer and liquid crystal mixture that can provide any required combination of diffraction efficiency and angular bandwidth in a thin waveguide with high transparency and very low haze. DigiLens waveguides can be laminated to integrate multiple optical functions into a thin transparent device. Our current reference designs for dashboard mounted and wearable ARHUDs will be presented.

In this paper the multi-view 3D display system which includes the modules of capturing three-dimensional objects, image processing (creation of 3D image files) and display screen for the 3D image displaying based on integral imaging technology is developed. Large display screens using multi-projectors are created. Multi-projector system is used for improving the performance, such as viewing resolution, viewing angle, etc. Preliminary experimental results obtained using Full HD multi-projectors are discussed. 3D display based on mobile devices is also developed. 3D image files are created using 2D + depth files and 2D images captured at different view angles. Images on smartphones Sony 4K (resolution 3840 x 2160) and Samsung and LG (resolution 2560 x 1440) are demonstrated.

Automatic License Plate Recognition (ALPR) is a technology designed to automatically read vehicle license plates. Traditional ALPR systems first detect the License Plate (LP), then apply the Optical Character Recognition (OCR) pipeline, which includes LP image pre-processing, character segmentation, character classification and post-processing. An ALPR system developed with such approaches often fails to provide acceptable results due to numerous challenging situations, which significantly increase the appearance variability of LPs as well as the characters to be classified. Recently, Convolutional Neural Network (CNN) models have proved efficient for ALPR problems. However, many of these CNN-based methods yet exhibit vulnerabilities to properly localize the region of the characters’ sequence and therefore provide an incorrect segmentation. Herein, this paper presents a novel real-time ALPR system that uses the concept of saliency map within the CNN model. The key contribution is at the segmentation step where the characters are located by means of the saliency map, which helps to refine the character classification step. The proposed ALPR pipeline consists of the two modules: 1) LPlocalization-CNN to detect the LP and 2) Saliency-Map-CNN to segment the characters in the LP. Experiments are conducted on a private and two public datasets and the proposed method is compared to the state-of-the-art methods. Results show that it performs well with respect to both accuracy and computation time, and hence clearly demonstrate the usefulness of the proposed system for the real-world ALPR applications.

This research deals with an approach of holistic optimization for optical systems in one open software environment. Studying the available methods of optical design and optimization packages, we understand that all existing approaches have drawbacks and/or missing elements. Hence, we chose to focus on: (i) develop an open optical design software from scratch, (ii) a multi-objective approach that considers not only the image quality, but also the post image processing, (iii) broad exploration of the holistic design space to find the best possible trade-off solutions . In any optical design software process ow, we first need the lens data from the user. Next we trace the rays along the optical system to calculate the OPD map at the exit pupil. Notably, the efficiency and precision of any optical design software depends on the number of rays traced. Here we improved the performance of the design software by using interpolation schemes. We implemented bilinear, cubic, spline interpolation schemes and compared the results. Based on the OPD analysis we estimate the performance of the optical system by calculating the FFT and Huygens PSF, MTF, spot diagram, OPD diagram and Zernike coefficients. Here we also address the sampling problems of the FFT PSF and study the relationship between the sampling of OPD and PSF. In contrast to commercial design software we disclose and extend the underlying algorithms and show the impact on the results. As a main feature we employ image processing libraries to enhance the image inside the optimization iteration. Hence, we build an end to end optical design software in which we allow tolerances to certain optical imaging aberrations and still retrieve the same processed image performance. The final software is an open source and is available to all and anyone can contribute to improve it in future. In summary post processing of the image is an integral part of the optimization of the optical system and therefore allows for an overall simpler but powerful optical system.

Fourier ptychography (FP) has emerged as a powerful tool to improve spatial resolution. In order to apply FP technique to long-distance imaging for example remote sensing, many factors have to be overcome, such as diffraction, noise, turbulence and so on. In this paper, we mainly aims at studying the influence of atmospheric turbulence on FP technique, and using iterative algorithms to restore high-legible image and eliminating the residual errors, so it will meet or reach the diffraction limit of imaging system. The optical imaging systems which work in atmospheric circumstance will face the problem of imaging through atmospheric turbulence, which causing the blurring of image and badly impact the imaging capability of optical systems. We combine the FP with the theory of adaptive optics to achieve the effective recovery of the long-range target, which is subject to the effect of atmospheric turbulence. In this work, we firstly introduce a Fourier Series (FS) atmospheric phase screen generator to simulate the atmospheric-induced wave front phase distortions and represent the wave front phase as a two dimensional periodic function. Both the spatial and temporal correlations between wave-front phase screens separated by time and/or angle are properly modeled. And using the adaptive optics， we complete the correction of the atmospheric turbulence in large distance imaging through the developed algorithm. Then we propose using laser arrays coupled with coherent illumination as an effective method of improving spatial resolution in long distance images. We emulate a laser arrays realized by optical fiber conduction and also show that appropriate phase retrieval based reconstruction algorithm which can be used to effectively recover the lost high resolution details from the multiple low resolution acquired images. Finally we analyze the effects of the atmospheric turbulence on the reconstructed image quality. The results prove that under the influence of atmospheric turbulence at outer scale of 1-m, inner scale of 0.1-m, Fourier ptychographic reconstruction can obtain good image quality for object 200 meters far away. The spatial resolution is increased six-fold.

In the field of 3D display technologies for a long-time accommodation-based depth cues have been dismissed. On one hand they are treated as weak depth cues, but on other hand their inclusion has been technologically challenging. Either way, accommodation depth cues are essential in ensuring natural image perception; they add realism to the 3D scene and help overcoming technologically inhibiting effects of vergence-accommodation conflict. In this work we examine implementation and associated considerations of optical diffuser technology via spatial volume demultiplexer chip (SVDC) within a stereoscopic Augmented Reality (AR) wearable display. The role of SVDC is to demultiplex series of two-dimensional image depth planes into a perceivably three-dimensional scene with said focus depth cues. The SVDC chip is designed to be entirely solid-state solution, requiring only voltage driving signal for the image demultiplexing action. In case of using an SVDC for multi-plane display architecture, the image source is a rear image projection unit ensuring high refresh-rate stream of required 2D image depth planes. The SVDC technology is scalable, it facilitates improved light efficiency due to controlled internal reflections which allows for diverse optical design in AR as well as VR settings. Provided is indicative evaluation and comparison of different optical image combiner solutions in respect to using a SVDC display architecture for near-eye stereoscopic AR display systems. Considered designs of optical image combiners include flat beam splitter with a refractive eyepiece, “bird-bath” optics, and single curved (free-form) reflective image combiner.

Conventional display metrics¹ are currently used to evaluate the performance of augmented reality (AR) displays: the maximum luminance it can reach, the image uniformity, the contrast ratio and others. However, these metrics initially defined for non-transmissive displays, do not consider the impact of the see-through environment² as it exists in AR applications. These measurements (usually obtained in a dark laboratory) are used to quantify the performance of AR display devices, but do not necessary relates to the perceived quality of images rendered by such devices, due to the non-linearity of human perception. Upon this, the projected image (Fig. 1) is an overlay upon the see-through environment. The intensity balance between these two “layers” becomes critical as the perceived scene (Fig. 2) is resulting from color mixing. Here, we want to highlight the fact that the brightness (perceived intensity) and color uniformity² of the projected image becomes less important whereas the contrast ratio between the image and the environment becomes very critical. Other metrics are also less significant once the outside scene is added such as pixel sharpness² (MTF) and the generated halo effects. These metrics are still important to evaluate the display performance for comparison purpose, but higher thresholds should be permitted for an AR display. The performance requirements must be adjusted in accordance to the AR application itself and not as it is done for conventional displays.

Manufacturing of the physical prototypes of the mixed reality devices may be very cost ineffective, so authors propose using the virtual prototyping approach to estimate the visual perception quality of newly developed approaches aimed on reduction of the visual perception conflicts and particularly the restoration of the light-optical characteristics of the real environment. In the current article the virtual prototyping method is used to analyze the visual perception conflict in the real mixed reality devices equipped with light-optical environment restoration technology. Two approaches to the restore the real-world illumination are analyzed: detection of directly visible light sources with neural networks and analysis of the shadows cast by the real-world objects. An image with the real known illumination conditions is also synthesized that is considered as the perfect results of the restoration of the illumination conditions. By comparing the simulation results authors show the visual quality of each of the elaborated methods along with possible sources of the visual perception conflict that should be the aim of the further research. Visual perception for cases of optical see-through and video seethough mixed reality systems is presented.

Current LED based structured illumination projectors use commercial objective lenses to project the pattern, leading to an increased size of the projector. We present a compact, pseudo-random pattern generator with an enhanced field of view (FOV) of 60° × 60° to project structured light for machine vision applications. The miniaturization of optics is achieved by utilizing the multi-aperture approach. Currently such multi-aperture projection optics have an FOV of about 20°. Enlarging the FOV of microlenses results in higher geometric aberrations. Aberration correction for wide FOV is done by distributing the optical power over several microoptical surfaces, as in traditional optical systems, leading to a design of stacked microoptics. The correction of dominant aberrations like astigmatism is done by employing anamorphic microlenses. Further enhancement of the FOV is achieved by continuously varying the FOV of the individual lenslets over the microlens array (MLA). Thus, every channel of the array projects light to a different region of the image plane, resulting in a symmetric and continuous filling of the FOV across the image field. Consequently, anamorphic irregular or 'chirped' MLAs with lenslets of varying focal length and orientation depending upon its location in the MLA are designed. This also requires the projection optics to be illuminated with a field dependent incidence for which a two lens condenser optic is designed. A regular condenser lens array couples the light into the channels similar to the scheme for Köhler illumination, while the stacked microoptics along with a bulk field lens image the slide object on to the projection plane. A corresponding prototype with stacked and chirped microoptics with buried apertures and slide structures is realized using advanced reflow technology and characterization of such an arrayed pattern projector is presented.

Surface inspection of non-transparent objects is a common task in the field of industrial quality control. For specular reflective surfaces, deflectometry methods can be used. For diffuse reflecting surfaces, the back reflected light has the shape of a cone due to diffuse scattering. This work describes, how the ideas from digital phase reconstruction microscopy can be modified to obtain height profiles of such object surfaces. The approach is evaluated with textile samples and the task to determine their degree of pilling after a specific preparation procedure. The method is applied in further cases of objects which suffer from some reflections or shadows and the results of this attempt are provided as well.

Ultra-precision angle measurement sensors have been developed for a large number of high-performance commercial, industrial and military applications. The sensors are designed to answer the general questions “where am I?” or “where is that?” in indoor and outdoor environments. These angle measurement sensors are composed of ultra-precision optical modules, specialized coding masks, analog optical detectors and digital processing. We call the general technology “Angle Coding” and the particular products Accu-Arc sensors. In comparison to all previous systems, Accu-Arc sensors are composed of small, lightweight, monolithic optical components that have a wide field of view and an intrinsically rugged package, have no moving parts, use low complexity electronics enabling low power and high speed, and use modern ultra-precision optical fabrication and assembly techniques for the lowest possible production costs combined with the highest possible performance.

Far-field dot pattern generation is analyzed for a Gaussian beam source that illuminates a sinusoidal phase grating which is placed at a certain distance behind the beam waist. We obtain a bigger field of view with more numbers of points using a Gaussian beam in comparison to a plane wave illumination because of the initial curvature of the Gaussian beam. Light propagation modeling through the sinusoidal grating is carried out using different approximations for a thin and thick phase grating. Using thin element approximation (TEA), the complex field is carried out with low computational effort and accuracy. We compare TEA with more accurate methods, such as FFT-BPM and FDTD methods. For thin phase gratings, TEA can be used but for thick gratings, FDTD method is the only valid option. For thick phase gratings, the effect of reflection from phase grating on the field modulation increases and we use FDTD method to find the correct far field pattern distribution.

Lensless phase-retrieval system with phase modulation of free propagation wavefront is proposed. Contrary to the traditional super-resolution phase-retrieval, the method in this paper requires a single observation only and uses advanced SR-SPAR iterative technique. Successful object imaging relies on modulation of the object wavefront with a random phase-mask, which generates enlarged intensity patterns, allowing us to extract more information than it is possible without such a mask. The achieved high-quality super-resolution phase-imaging is demonstrated by simulation-tests produced with the parameters corresponding to the physical prototype of the considered optical system.

Ghost Imaging is a fairly recently emerged imaging concept, which in its earliest forms was based on correlating the output of two photodetectors – a high-resolution pinhole detector scanning the light field that has not interacted with the object being imaged, and a bucket detector measuring light that has interacted with said object. While it was originally believed to be an effect with a purely quantum nature, as the first experiments were based on entangled photons, it was later understood to be generalizable to situations with much higher photon densities [Shapiro, 2008]. The revelation that using computer-generated light patterns can enable one to forgo the pinhole detector entirely led to the onset of Computational Ghost Imaging (CGI). Effectively, then, CGI uses an imaging scheme reversed from what is generally used in most applications, using a multi-pixel projector to form light patterns and measuring the object-distorted patterns with a single-pixel detector. The resolution of the acquired image is determined on the resolution of the used light patterns. The major advantage of such a scheme is that in recent years, ultrafast single pixel light detectors have been developed, giving CGI great potential for use in 3D-vision applications. While initially randomized patterns were used in CGI, it was shown that it is far more efficient to use patterns that form an orthogonal basis, most commonly utilizing the Hadamard matrices, whereby the amount of measurements needed to form a good image of the scene of interest dropped significantly [Shibuya, 2015]. Using patterns based on the Hadamard matrices, however, introduces a dependency of the final quality of the registered image on the properties of the Hadamard matrix used to form the patterns. For instance, the Hadamard matrix required to achieve patterns of a given resolution may simply not exist, or the composition of the Hadamard matrix may introduce anomalies such as a certain pixel standing out of the final image. In addition to the effects the pattern characteristics have on the final image, the image may also be distorted by the way the image is retrieved from patterns and the respective measurement results from the single-pixel detectors. Namely, for CGI, mainly 2 strategies can be taken for the assembly. One involves weighted addition, and the other assembles an equation system which is then solved. The two methods can lead to identical results, as they do in Differential Computational Ghost Imaging (DCGI), but don’t necessarily do so [Ferri, 2010]. We show, based on simulations, how one can utilize the different order Hadamard matrices in conjunction to one another as well as the Hadamard matrix properties to achieve patterns of a desired resolution in terms of final pixel count, and in which cases the image assembly methods are identical. Furthermore, limitations for further increasing the resolution accessibility will be shown. These results have the potential to directly reduce the number of measurements needed to acquire an image of a certain resolution, and can thus be of great value in CGI applications, ranging from 3D-vision in autonomous cars to optical cryptography.

Image restoration is a process used to remove blur (from different sources like object motion or aberrations) from images by either non-blind or blind-deconvolution. The metrics commonly used to quantify the restoration process are peak signal-to-noise ratio (PSNR) and structural similarity index measure (SSIM). Often only a small sample of test images are used (like Lena or the camera guy). In optical design research PSNR and SSIM are not normally used, here image quality metrics based on linear system theory (e.g. modulation transfer function, MTF) are used to quantify optical errors like spherical or chromatic aberration. In this article we investigate how different image restoration algorithms can be quantified by applying image quality metrics. We start with synthetic image data that is used in camera test stands (e.g. Siemens star etc.), apply two different spatially variant degradation algorithms, and restore the original image by a direct method (Wiener filtering within sub-images), and by an iterative method (alternating direction method of multipliers, ADMM). Afterwards we compare the quality metrics (like MTF curves) for the original, the degraded and the restored image. As a first result we show that restoration algorithms sometimes fail in dealing with non-natural scenes, e.g. slanted-edge targets. Further, these first results indicate a correlation between degradation and restoration, i.e. the restoration algorithms are not capable of removing the optically relevant errors introduced by the degradation, a fact neither visible nor available from the PSNR values. We discuss the relevance in the context of the automotive industry, where image restoration may yield distinct advantages for camera-based applications, but testing methods rely on the used image quality metrics.

Imaging in deep infrared and terahertz region of the electromagnetic spectrum is difficult due to the unavailability of large sensor arrays. This can be mitigated by using single pixel detectors or radiometers along with a spatial light modulator. A framework for design and analysis of such imaging radiometer systems is presented. Remote exploration systems in space, deep ocean or disaster situations have limited power and computational resources. This puts a cap on the measurement budget of such systems. Apart from being power limited the exploration system must act on its own without external help. A three step sampling procedure involving image segmentation and compressive sampling is proposed which assigns the measurement budget based on coarse reconstructions of the scene. The sampling procedure is simulated using the framework and the effect of various system parameters on the final data output is analyzed. Simulations are performed to illustrate the capability of the framework to design such imaging systems and to study the trade offs between the optical, electrical and software domain.

Wave-front coding is a mile-stone technique that can be used to greatly extend the DOF (depth of field) of incoherent imaging system. Besides the phase mask design, the digital restoration is very crucial to obtain clear image with largely extended DOF. Richardson-Lucy (RL) algorithm is a kind of nonlinear image restoration method which is based on Poisson noise model and maximum likelihood estimation. Because RL algorithm can generate high quality restoration result and own the capability to realize super-resolution construction, it has been widely applied in the field of astronomy, macroscopic imaging and et.al. However, classical RL algorithm converges very slowly and have to be run many times to achieve an acceptable restoration result when it is applied to wave-front coded imaging system whose point spread function has quite a large support region. Our previously published results demonstrate that at least 60 times iterations are needed for each color channel, which severely prohibits real-time implementation of classical RL algorithm.. Therefore in this manuscript, an improved vector extrapolation based RL algorithm is designed by embedding the modified exponent into the framework of traditional vector extrapolation based RL algorithm. Not only a bigger iteration step indicating a bigger acceleration ratio is obtained, but also the noise amplification is effectively prohibited. Experimental results demonstrate that with the same number of iterations, the restored image corresponding to the improved vector extrapolation based RL algorithm has a better visual quality. At the same time, the structural similarity index (SSIM) is used as a criterion to determine the optimum iterations for each color channel and optimum combinations of algorithm parameters, based on which total iterations for color images are reduced approxiamately 78.9% and visually satisfactory restoration results can be obtained without denoising the restored image further. It could be considered that the work reported in this manuscript paves the way for realization of the embedded processing based real-time wave-front coded imaging in the future.

The blur of the optical system can cause inevitable degradation of acquired images. In this paper we present a novel method to measure the spatially-varying blur of the camera lens. We obtained the Discrete Cosine Transform (DCT) coefficients of the blur kernels by applying DCT single-pixel imaging to all the camera pixels. The spatially-varying blur kernels are then reconstructed by applying inverse DCT to the acquired coefficients. Experimental results show that the proposed method can acquire a more accurate blur kernel compared to the traditional Gaussian kernel.

In general, optical designers employ combinations of multiple lenses with extraordinary dispersion materials to correct chromatic aberrations, which usually leads to considerable volume and weight. In this paper, a tailored design scheme that exploits state-of-the-art digital aberration correction algorithms in addition to traditional optics design is investigated. In particular, the proposed method is applied to the design of refractive telescopes by shifting the burden of correcting chromatic aberrations to software. By tailoring the point spread function in primary optical design for one specified wavelength and then enforcing multi-wavelength information transfer in a post-processing step, the uncorrected chromatic aberrations are well mitigated. Accordingly, a telescope of f-8, 1,400mm focal length, and 0.14° field of view is designed with only two lens elements. The image quality of the designed telescope is evaluated by comparing it to the equivalent designs with multiple lenses in a traditional optical design manner, which validates the effectiveness of our design scheme.

Various optical schemes of single-component lenses with a remote pupil and a telecentric beam path, as well as a method of their calculation based on the theory of third-order aberrations, are presented. For illustration, the results of the aberration calculation of lenses of this type are given.

This paper proposes a procedure for automatized fine-focusing of particles’ image in digital microscopy. First, analytical formulas for a calculation of axial defocus are derived using the complex amplitude propagation. Afterwards, the formulas are used for a design of an iterative algorithm for the fine-focusing. Uncertainty analysis and error simulations are then presented. In the final part of the paper, the method is verified by a simple experimental setup. The proposed strategy can find utilisation in many practical applications of automatized processes, not only in digital microscopy.

The relevance of this topic is due to the rapid development of virtual and augmented reality systems. The problem lies in the formation of natural conditions for lighting objects of the virtual world in real space. To solve a light sources determination problem and recovering its optical parameters were proposed the fully-convolutional neural network, which allows catching the 'behavior of light' features. The output of FCNN is a segmented image with light levels and its strength. Naturally, the fully-convolutional neural network is well suited for image segmentation, so as an encoder was taken the architecture of VGG-16 with layers that pools and convolves an input image to 1x1 pixel and wisely classifies it to one of a class which characterizes its strength. As image dataset was synthesized by Integra developed realistic scene rendering software 'Lumicept', which has on its boat powerful tools for modeling and passing the behavior of light, so there is no doubt of wrong behavior or visualization of light rays and its secondary lighting, that guarantees proper optical parameters and its classification. Lumicept renders the image and its multi-color mask, where each color corresponds to it's optical strengthens. More 'cold' colors mean less intensive illumination when 'hot' colors correspond for the light sources, in digit equivalent that values ranging from 0 to 500 nits (or candela per square meter), where 0 is not lit at all area and 500 is a value of a light brightness of a typical room lamp. These images were used to feed CNN to dense layer, where the network learn features to recognize and as output upsamples to a segmentation image. To say more closely about an upsample layer, this is a kind of a function that brings a low-resolution image to a high-one by duplicating each pixel twice, this is called the nearest neighbor approach. Now FCNN decision can be used in tasks of definition of lighted areas of an accommodation, restoring brightness parameters, taking features of shadows, analyzing its secondary illumination and classifies it to one of a brightness level, which nowadays is one of a major task in augmented reality systems to place a synthesized object to our environment to match the specified optical parameters and lighting of a room, also speaking about determination of a light, the CNN encoder can determine the type of illumination, by this, is meant ceiling ones or wall light sources. Neural network training was conducted on 221 train images and 29 validation images with learning rate 1E-2 and 200 epochs, after training the loss was 0,2. As a test was used an ‘intersection over union’ method, that compares the ground truth area of an input image and output image, comparing its pixels and giving the result of accuracy. The mean IoU is 0.7, almost rightly classifying the first class with a value of 90 percents of accordance and the last class with a probability of 30 percents. Lately, the FCNN will be trained on more images and will be trained to determine light sources location.

The article deals with the features of the design of helmet displays. Features of individual elements and requirements for some of them. One of the most important aberrations that should be taken into account when designing such systems, un centered distortion, some moments of modeling distortion and ways of its compensation are also considered.

In this study, we demonstrate a novel wax-patterned paper-polymer centrifugal optical system for performing multiple biomedical tests. The system consists of a detector (photodiode, LED), a diagnostic disc (paper, plastic) and a DC motor, allowing monitoring of changes in real time absorbance. Here, a wax printer was used to form hydrophobic channels on paper. The diagnostic disc can be prepared by attaching wax-patterned paper to a plastic disc. After the diagnostic disc is mounted on the dc motor, the fluid first wets the wax-patterned paper by centrifugal force, slowly moves by capillary action, and the reaction proceeds in the reaction zone with enzyme and color indicator. Microfluidic devices prepared in the wax-patterned paper have several attractive features such as low cost, ease of use, disposability and portability. In addition, the centrifugal disk-based platform can provide a solution for high-efficiency analysis that can process multiple reactions in parallel and monitor reactions in real time. To demonstrate the usability of this system, we performed realtime monitoring of glucose, an important indicator of blood glucose. The detection results could be delivered with the calibration curve within 10 seconds and no complex image analysis was required. The developed wax-patterned paperpolymer centrifugal optical system is promising for clinical multianalyte point-of-care testing due to its ease of manufacture, ease of operation, low cost and high sensitivity.

We developed the acetylcholinesterase detection system using paper hybrid centrifugal fluidic disc platform. A new method of metering using paper was applied to disk platforms. After the solution is applied to the paper, a certain amount of solution flows to the detection zone according to the rotation speed and rotation time of the disc. Detection zones contain various concentrations of pesticide and material for colorimetric detection. Therefore, the buffer-injected through the inlet is distributed in the same amount in 6 detection zones to activate the pre-contained enzyme. The disk platform was configured to obtain a calibrated curve for the concentration of acetylcholinesterase. Pesticides inhibit acetylcholinesterase and cause a cholinergic overdose. Blood pesticide detection is a method of measuring acetylcholinesterase activity. Therefore, a calibration curve that is detected in the same environment is needed to diagnose the activity of the enzyme due to pesticide poisoning of blood. The assay consists of acetylthiocholine and ELLMAN reagent. Acetylcholinesterase decomposes acetylthiocholine into thiocholine and ELLMAN reagent develops yellow color by the product. The color change of the detection zone was obtained through scanner after 2 minutes of buffer injection. In this study, the concentration of the enzyme was detected by metering through paper without any elaborate plastic processing or chemical treatment of the channel. The platform can provide a suitable standard for detecting suspected blood and pesticide substances on the same disk platform.

Magneto-optical devices are actively used to identify and verify magnetic images. We propose magneto-optical plasmonic nanostructures as sensitive material for detecting magnetic images and magnetic information. We show the increase in magneto-optical responce by utilizing plasmonic principals compared with structures of pure magneto-optical material.

In lighting design, freefrom optical element plays a key role due to its considerable degree of freedom. In spite of many methods to design freefrom optical system, the prototype of the system is still important, for describing freefom optics with mathematical equations or optimizing in optical design software. In this paper, we analyze several illumination systems in order to verify that different forms of lens could achieve similar light distribution curves (LDCs). In section 3, an approach to realize IESNA Type I lighting with the help of optimization in Zemax is proposed based on calculating reference LDC. The result shows that the efficiency of the system is 84.27% and the optimized LDC is very near to the desired one.

Augmented reality (AR) systems have many different applications from consumer electronics devices to military devices. Head-mounted displays have been extensively investigated during the last years. Modern technologies make it possible to manufacture more and more complex devices, and the symbol generators used in such systems continue to improve. FLCOS, AMOLED, and other microdisplays are usually used as a source of image in such type of the systems. Seethrough augmented reality systems can also work with a smartphone. Devices with ever greater resolution and smaller size appear on the market providing small response time and high brightness. While designing the optical architecture for HMD, one usually considers how it works with certain source of image. We have considered several AR optical architectures with flat and curved mirrors as a combiner, and how they work with sources of different type, size, resolution, etc. Thus, the object of the research is to design several optical schemes for augmented reality see-through head-mounted displays working with different sources of image.

In this paper an optical element (image rotating cell) consisting of a single piece isotropic material with three internally reflecting faces for image rotation by the angle 90 degrees is proposed. The principle of operation is based on the geometrical phase effect (Berry phase). It is shown that the rotator made of polymer as well as silica glasses is not affected by the chromatic dispersion in a visible range.

One of the main problems of MR devices is a physically correct representation of luminance distribution for virtual objects and its shadows in the real world. In other words, reconstruction of the luminance distribution over the scene is one of the key parameters that allow solving the problem of "seamless" interaction between the virtual and real worlds and serves as the primary means for improving the quality of perception when we use the augmented reality system. By using neuro networks, it becomes possible to estimate the number of light sources, their positions and radiation goniodiagrams. Authors use the fast and high-quality photorealistic image synthesis to synthesize the virtual image of the real world under the restored illumination conditions. Having both real world image and synthesized real world image at restored illumination conditions it becomes possible to estimate the error of the roughly estimated light source positions to correct it. It is possible by application of the special shading analysis method. The first step requires two kind of information: reconstructed geometry of surrounding space and HDR image, with luminance data. One of the main issues is that there are two kinds of illumination: primary illumination, from light sources, and secondary illumination or background illumination, from non-luminous objects. The task is to remove background illumination and define primary illumination. After restoration illumination condition, a virtual object could be properly added to visible image of real environment.

Transport of Intensity Equation (TIE) is a simple and efficient method for phase retrieval by solving the equation between the intensity axial derivative and phase. In this method, the estimation of the axial derivative of intensity is very crucial. Simply, we use two defocused intensity images to estimate the axial derivative by finite difference method. However, the result is still unsatisfactory even though the optimal defocused distance is adopted. The reason lies in that the intensity’s axial change is not linear in the propagation of light. Simply using the finite difference between the two defocused images will ignore higher order axial derivatives. In other words, the estimation of the axial derivative of intensity will contain nonlinear errors. To solve this problem, we propose an extrapolation-based method to estimate the axial derivative of intensity using multiple intensity images. With Taylor expansion and a series of combination and eliminations on these images, high order terms of axial derivative errors are removed. As a result, the nonlinear errors in estimation of the axial derivative will be reduced. The performance of our proposed method for different types of phases under different illumination conditions is investigated. Compared with normal TIE, our method can obtain a much more accurate phase profile.

This paper serves as an introduction to the EDO19 conference “Digital Optical Technologies” dedicated specifically to digital optics for AR/VR and MR Head Mounted Display (HMD) systems, in all their incarnations: Display, Imaging and Sensors. We will introduce the field of AR/VR/MR optics historically, and review the most important criteria for AR/VR/MR optical design: matching the performances of the optics to the ones of the human visual system. This can be done for all Digital Optical Elements reviewed throughout this conference: free space optics, waveguide optics (waveguide combiners), diffractive, holographic and metasurface optical elements, tunable, switchable and reconfigurable optics, and novel computational techniques for display and imaging.