This PDF file contains the front matter associated with SPIE Proceedings Volume 11708, including the Title Page, Copyright information and Table of Content

Various technologies to realize the augmented reality (AR) devices have been proposed. Holographic optical element (HOE) is among the most appealing optical components for the optical combiner of AR devices. With the compact size and bendable material, HOE can be applied to AR systems with various form factors. Since HOE has high angular selectivity, the light from the real scene remains nearly intact, making HOE the most promising technology for see-through AR displays. However, several issues of HOE still remain to be resolved, such as narrow field of view or eye box, and severe aberration. In this invited paper, we present the basic characteristics and issues of HOE and introduce how we can resolve the issues.

Liquid crystal-based reflective polarization volume gratings (PVGs), also known as a linear Bragg–Berry phase optical element or a member of volume Bragg gratings (VBGs), is a functional planar structure with a patterned orientation of optical axis. Due to the strong polarization selectivity, nearly 100% diffraction efficiency, large diffraction angle, and simple fabrication process, PVGs have found potential applications in novel photonic devices and emerging near-eye displays. In this work, we start from the operation principles and liquid crystal configurations to discuss the optical properties, including diffraction efficiency, angular and spectral response, and polarization state of the diffracted light. Specifically, we emphasize promising applications of PVGs for near-eye displays and novel photonic devices. Through analyzing the functionalities of PVGs with simulations, PVG-based novel devices are proposed. We further develop polarization volume lenses (PVLs) with high diffraction efficiency, low f/#, and large diffraction angles. Previously reported planar lenses are of thin form factor but with on-axis imaging and large f/#. By patterning PVGs with parabolic phase, the obtained PVLs exhibit a small f/#, high diffraction efficiency, and large off-axis diffraction angle. The PVLs offer a new design for near-eye systems, especially for augmented reality (AR) displays. Based on PVLs, we propose a new multi-focal-plane AR system with a polarization multiplexing method to eliminate the vergence-accommodation conflict.

A new type of smectic liquid crystal based display technology is introduced. Thanks to commensurate liquid crystal molecular switching, even very viscous smectic liquid crystals provide sub-millisecond optical response time with decent applied voltage. This new type of display technology is called as SSD (Smectic Single Domain) liquid crystal technology. An SSD-LC panel shows applied electric field polarity dependent response. Moreover, its dynamic response gives in-plane only retardation switching with vertically applied electric field to the smectic liquid crystal layer. Sub-millisecond optical response with in-plane only retardation switching would provide almost viewing angle, color shift free image.

We introduce an original approach for an extended Head Up Display solution. This configuration is based on the projection of images directly on the windshield of a vehicle, allowing the display of various information around the user viewing axis, as a peripheral dashboard. We highlight that this solution is only effective if we can manage both directivity and diffusivity of the reflected light. We introduce for that purpose two technological options. A pragmatic one allows us to evaluate at short term the HUD behavior. Another proposes an original approach with a manufacturing process based on the etching of a deep cube corner cavity in a composite silicon wafer that incorporates a diffuser surface. We demonstrate both technological options and give some perspectives for future works.

An autoencoder neural network is proposed for real-time phase-only CGH generation. As an unsupervised learning method, the input and output of the autoencoder are both the original images, which dispenses with calculating corresponding holograms. It could automatically learn the encoding of phase-only holograms during the training period. Once the training is completed, the phase-only hologram of any two-dimensional image can be quickly generated. The calculation time is 1-2 orders of magnitude faster than the traditional iterative algorithms and the reconstructed image quality is improved.

We developed a high definition holographic display with two different approaches. First approach is to adjust a wellknown display technology using a liquid crystal as an optical modulator. While merit of display technology is a large panel size, the challenge is to define a small pixel pitch and to reduce a crosstalk effect of a liquid crystal. Second approach is to adapt a silicon technology with a new optical modulator, Ge₂Sb₂Te₅. Although we can easily define a small pixel pitch, we have to confront a small panel size. We will explain our solutions to overcome these issues.

Spatial light modulator is the key component for dynamic computer generated hologram (CGH) and phase type liquid crystal on silicon (LCoS) device is among the most commercialized. Due to the consideration on efficiency or the requirement from system architecture in the holographic displays, the reconstruction illumination could obliquely incident on the LCoS, which will cause distortion of signal window, hence the image within the signal window. Therefore, the target image needs pre-distortion before the calculation and optimization for the corresponding phase pattern on LCoS in order to obtain the originally desired pattern. This paper illustrates the mechanism of image distortion and provides quantitative analysis for arbitrary azimuthal and radial angle of reconstruction illumination on LCoS device. The required correction is also derived with the corresponding experiment showing the effectiveness of the proposed scheme.

We propose an integral imaging tabletop three-dimensional (3D) display system. The system uses a dynamic tilted barrier array combined with a high-brightness two-dimensional display panel and lens array to provide tabletop 3D images with a complete 360° viewing zone. Besides, we propose a high-efficient elemental image array (EIA) generation method based on the backward ray-tracing technique for the integral imaging tabletop 3D display system. The EIA can be obtained in one rendering step by calculating the backward rays from all viewpoints to the corresponding pixels of the EIA. The experimental results verify the feasibility of the integral imaging tabletop 3D display system and the high-efficient EIA generation method.

Camera-Monitor-Systems (CMS) for mirror replacements such as rear-view are becoming increasingly important for vehicles. Such systems must meet high safety requirements like non-erroneous reproduction and short latency. Supervision today only covers interface data and power supply. It is assumed that the display convert the digital data properly to optical output without any failure. This was our motivation to go further: We have successfully developed and evaluated advanced optical safeguarding methods of displays using photodiodes or a camera. Several photodiodes are mounted below the cover glass and acquire the light emission of the display through waveguide effect. The photodiodes measure the weighted integral of many pixels, so a “sensitivity map” was created using reference images. A target value for each photodiode is calculated from the RGB input data and correlated with the actual measurement. The ultimate method is to capture the display output using a camera and to compare the reproduced image with the target content. The camera image must be corrected for various effects such as distortions, Moiré, gamma and reflections of ambient light. As the reproduced GUI is known, several ROIs are defined and supervised modularly e.g. the video image is segmented and its histograms are compared with the original CMS camera data. Our methods provide a significant step towards “light-to-light” monitoring of CMS from camera input to display output. This enables functional safety for commercial monitors of remote operators for Level 5 autonomous cars in case of failures.

Multiview display is a popular method to deliver three-dimensional (3D) images by generating a perspective directional view. However, there are some limitations such as a low resolution, lack of motion parallax, and a narrow viewing angle. In this paper, we propose a method to implement a multi-view display system that provides a 3D image in high resolution. The original setup is composed of a stereoscopic 3D display panel and a head tracking camera. The directional view image of a 3D object is captured by a camera array and shown on a stereoscopic 3D display. A user interface is designed to control the hardware. An Intel RealSense sr300 camera is used to track the observer's viewing angle. The images are captured rotationally through a movable camera array in a 30-degree span. There are 71 and 3 views in the horizontal and vertical direction, respectively. The directional view information is displayed according to the observer's viewing direction as well as the head position. The observer can realize a high-resolution 3D image with smooth motion parallax. Most importantly, the proposed system interactively displays the exact view direction according to the user’s viewing angle which feels more natural to the observer.

We introduce our recent work on the occlusion-capable near-to-eye display. Our implementation uses only a single digital micromirror device (DMD) both for the real scene masking and virtual image display. The real scene imaging onto the DMD and the mixed scene projection toward the eye are achieved using a single optics of polarization-based double-path configuration. These single DMD and the shared optics feature contributes to the reduction of the overall system volume. In the presentation, we explain the principle and introduces our recent experimental results demonstrating 60Hz display of color virtual images with per-pixel occlusion in over 90% maximum occlusion ratio.

Reducing the size of Virtual Reality head-mounted displays is of main interest to improve the comfort of users, which is a particularly complex design problem due to the very large field of view needed to feel the immersion. Such reduction can be achieve via folded polarization “pancake” optics, but at the expense of a very low transmission efficiency and poor contrast. High compactness without those drawbacks can be achieved by multichannel optics, whose design for high performance is carried out at LIMBAK intensively introducing freeform optical surfaces, adding variable magnification to maximize the VR display resolution where it is to be normally gazed, and applying two-dimensional distortion software corrections to each channel. This presentation will cover the recent advances in these systems, the growing variety of geometries, the benefits obtained when including gaze-tracking and the resolution boosts obtained by the application of pixel interlacing strategies.

Although head-up displays (HUDs) have already been installed in some commercial vehicles, their application to augmented reality (AR) is limited owing to the resulting narrow field of view (FoV) and fixed virtual-image distance. The matching of depth between AR information and real objects across wide FoVs is a key feature of AR HUDs to provide a safe driving experience. Meanwhile, current approaches based on the integration of two-plane virtual images and computer-generated holography suffer from problems such as partial depth control and high computational complexity, respectively, which makes them unsuitable for application in fast-moving vehicles. To bridge this gap, here, we propose a light-field-based 3D display technology with eye-tracking. We begin by matching the HUD optics with the light-field display view formation. First, we design mirrors to deliver high-quality virtual images with an FoV of 10 × 5° for a total eyebox size of 140 × 120 mm and compensate for the curved windshield shape. Next, we define the procedure to translate the driver eye position, obtained via eye-tracking, to the plane of the light-field display views. We further implement a lenticular-lens design and the corresponding sub-pixel-allocation-based rendering, for which we construct a simplified model to substitute for the freeform mirror optics. Finally, we present a prototyped device that affords the desired image quality, 3D image depth up to 100 m, and crosstalk level of <1.5%. Our findings indicate that such 3D HUDs can form the mainstream technology for AR HUDs.

Metal halide perovskites (MHPs) have emerged as promising candidates for next-generation display because of their advantages on luminescent properties and external quantum efficiency exceeding 20 % in less than 5 years since the first efficient EL operation. However, the short operational lifetime of PeLEDs is limiting their practical application. Especially, the ion migration in perovskite under intense electric field is known to destroy the crystal structure and cause device failure. Here, we suggest new strategies to overcome the lifetime limitation of PeLEDs. First, we introduced the proton-transfer-induced 3D/2D hybrid structure with extremely suppressed ion migration and low defect density, showing extremely suppressed luminance overshoot and >20 times longer operational lifetime. Also, we could further prolong the lifetime of PeLEDs by using ideal mixed-cation system and suppressing the electric-field-induced catastrophic failure by inducing self-assembled core/shell structure.

Lots of attentions owing to its superior properties such as narrow electroluminescence (EL) spectra, tunable emission colors, high luminance, and simple fabrication process. Typically, in a QLED, quantum dots (QD) layer is sandwiched by organic materials as hole transporting layer (HTL) and inorganic zinc oxide (ZnO) nanoparticles as electron transporting layer (ETL), respectively. Because the electron mobility of ZnO is typical higher than the hole mobility of organic material, it results in carrier unbalance and reduces the efficiency. Hence, it is important to improve the hole transporting ability to achieve charge balance condition for higher efficiency. In this study, we have fabricated green QLEDs with two different HTL materials. By using HTL with high mobility and suitable energy level, voltage decreased from 11.1 V to 5.8 V at 10 mA/cm2, together with enhancement of current efficiency from 21.8 cd/A to 58.1 cd/A, and external quantum efficiency from 5.94% to 16.0%, corresponding to 2.6-times improvement.

Micro-light-emitting-diode (μLED) displays with low power consumption are highly desirable for the mobile devices powered by batteries. However, since the smaller LED chip size corresponds to lower optical efficiency, this advantage is compromised. In this paper, we develop a model to evaluate the power consumption of micro-LED displays based on ambient contrast ratio. Then, the optimal μLED chip sizes to achieve the lowest power consumption for smartphones, laptop computers, and TVs, are obtained. Furthermore, we propose to employ different RGB chip sizes in μLED displays. In comparison with the optimal results with uniform LED chip size, our new design offers an additional 12% average power saving for real image contents.

In this study, we report a bistriazoles derivative to be the wide bandgap host for blue emitters. In particular, this bistriazoles derivative possesses a wide bandgap of 4.0 eV and bipolar carrier transportation behavior. In addition, its bipolar behavior is classified to the rare case of electron-favorable bipolar carrier transportation, which was identified by the time-of-flight measurement and unipolar device. The electron mobility is little faster than hole one, which benefits the adjustment of carrier balance in the emitting layer. Employing to be the host of blue phosphorescent OLED, the device exhibits a high-efficiency performance with a 30.2%EQE.

Recently, a new emission mode, triplet-triplet annihilation up conversion (TTAUC), of OLED was proposed with the mechanism as follows: when the carriers recombine at the sensitizer layer with a lower energy bandgap, the generated triplet excitons of sensitizer transfer to the triplet-triplet annihilation (TTA) emitter and emit a higher energy photon. In our experiment, we used tris(8-hydroxyquinolinato)aluminum (Alq3) as sensitizer, 9,10-Bis(2-naphthyl)anthraces (ADN) as TTA emitter and 1,1'-(2,5-Dimethyl-1,4-phenylene)dipyrene (DMPPP) as triplet diffusion singlet blocking (TDSB) layer. To improve the efficiency of TTAUC-OLED, 4,4’ -Bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi), was doped in ADN host. With 6% of DPAVBi doping, no obvious change was observed in electrical characteristics, indicating electron traps from dopant is limited. Maximum EQE achieved EQE= 4.66% in the optimized device.

Multi-view displays reproduce more than one view of an object. Classical 3D displays allow only a single user. Today’s multi-view displays are flat and reproduce two or more images. They base on e.g. parallax barrier, lenticular lenses, light field displays and projection with reduced effective resolution. Another method is projection on rotating mirrors. This approach requires highest frame rates (~5,000 Hz), so only prototypes without color and grey are realized so far. Our approach base on a rotating (prototype 60 rps) periscope-like mirror system (with magnification) in the center of a 360° circular display. For prototyping, we used large high-resolution flat displays. One simple method is to use a fixed position on a single display for every corresponding view. To avoid motion blur and ghosting one mirror is equipped with a vertical slit screen to block light from neighboring areas. We implemented eye tracking for efficient rendering in real time and reproduce only relevant views according the corresponding angular position of the viewer’s eyes. So a standard high resolution display can be used to generate thousands of different perspectives (at full color and 60 Hz). Possible applications of our multi-view display are collaborative work for e.g. several designers, which can see the object from very different locations and interactively improve design, (science) museums and entertainment.

Recently, Quantum-dot light-emitting diode (QLED) has attracted much attention due to narrow electroluminescence (EL) spectra, low driving voltage, tunable emission colors and simple fabrication. In conventional QLED structure, inorganic zinc oxide (ZnO) nanoparticles was usually used as electron transporting layer material by spin-coating. However, defects in solution-processed ZnO film may quench quantum dot (QD) emission and increase the driving voltage. In this study, we fabricated ZnO by sputtering process with the inverted structure. Compared to the QLED with solution-processed ZnO as the ETL, driving voltage of the device with sputtered-ZnO as the ETL significantly decreased from 7.04 V to 2.95 at current density of 20 mA/cm2, while the current efficiency remained at 11.46 and 11.70 cd/A at current density of 80 mA/cm2.

We have proposed a wide-viewing area autostereoscopic displays using eye tracking system in order to expand the viewing zone of glasses-free stereoscopic displays using a parallax barrier. It was possible to keep the stereoscopic vision by arranging parallax images at geometrically optimal positions based on the viewer's position detected by eye tracking even if the viewer moved. However, due to the expansion of the viewing zone, when the viewer observes a display at a large angle for the normal direction of the display, the influence of the refraction of light rays by the material between the parallax barrier and the display becomes large and the optimum position to arrange parallax images changes. As a result, the crosstalk occurs and the stereoscopic vision was lost in the areas of large angles. In order to overcome this problem, we propose the image processing method considering the influence of refraction to extremely increase the viewing zone angle. Considering the influence of the refraction, we evaluate the position of the subpixel actually observed by the viewer. Based on the evaluation, we correct the position of the parallax images. To verify the effectiveness of the proposed method, we measured crosstalk at the OVD. When we use the proposed method, the viewing zone angle with a crosstalk rate of 10% or less for the entire display could be expanded to ±30° compared to viewing zone angle ±12.8 without proposed method.

We have previously proposed the retinal projection type super multi-view 3D-HMD which provides the viewer with 3D images by inducing the stimulus of the accommodation of the viewer’s eye using the blurring of the multiple projected retinal image. However, in the previous HMD using a mechanical shutter, since we could not flexibly design the function of the shutter, we could not project the ideal multiple retinal image. To overcome this problem, we propose the improved 3D-HMD with the variable function shutter using a DMD as an optical shutter. In the proposed 3D-HMD, multiple parallax images are displayed by time division, and these images are converged on respective points by the holographic lens. However, the parallax image converges not only on the correct convergent point but also on unnecessary convergent points due to using the multiple exposure holographic lens. Therefore, to pass only one convergent light corresponding to the correct parallax image, we used the DMD shutter synchronized to the display device. To verify the effectiveness of using a DMD as a shutter, we made the prototype 3D-HMD and confirmed that the blur of the image by the prototype 3D-HMD can induce the accommodation. Since the high-speed optical shutter using a DMD realizes the function as a shutter by changing the pinhole image on the DMD, we can flexibly design the number and the alignment of convergent points in the proposed 3D-HMD. Therefore, in the proposed 3D-HMD, we can project the ideal multiple projection retinal image by using the DMD shutter.

Although phosphorescent and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLED) exhibit high efficiency and long lifetime for red and green emission, blue OLED is still a bottleneck. In mass production, triplet-triplet emission (TTA) OLED is the main stream for reasonable lifetime together with limited efficiency. To improve the efficiency of blue TTA-OLED, a bilayer emitting layer (EML) was employed. Compared to single-EML device, external quantum efficiency of the bilayer OLED increased from 9.4% to 13.0%, which mainly resulted from the increase of delayed emission from 15.0% to 37% with enhanced TTA process.

Augmented Reality (AR) is now subject to a great technological acceleration. Different actors of the field develop many different projection technics. However, with each projection technic comes display strategies to improve the comfort and immersion of the user and the quality of the image displayed. Some recent works propose to use new principle of projection based on unconventional optics to create new products aiming to reduce many of the current problems related with the conventional projection principle of AR devices. CEA Leti recently proposed a disruptive optical concept for AR display[1], which is based on the interaction of a grating of monomode linear waveguides with pixelated holograms. This work uses simulations to analyze optical issues associated with this new optical concept. The main topic covered is the study of the SNR depending on the resolution criteria chosen.

Spatial light modulators (SLM) based on liquid crystal on silicon (LCOS) are widely used for phase-related applications. The inherent aberrations such as curvature and liquid crystal thickness variation that are caused by the fabrication process may need to be compensated. Measuring the pixel dependent phase response, by means of a Twyman-Green interferometer at 640 nm, enables high precision calculation of compensation functions, leading to a wavefront flatness in the order of λ/11 (peak-to-peak). In this work we present the performance of the measurement setup, the 2D phase response of multiple LCOS panels and the results of active compensation of major aberration effects.