Highly efficient, ultrahigh-density inorganic micro-LED displays are gaining a strong position in the market for use in augmented reality glasses. When applied to electronic contact lenses with an eye-adaptive form factor, the micro-LED displays evolve into next generation augmented reality viewers. Here, we report 1-nm-thick epitaxial AlN passivation for 1.5-μm-diameter InGaN red micro-LEDs with high external quantum efficiency of 6.5% at the peak wavelength of 649 nm. The flexible form factor of the red micro-LEDs is achieved through the development of a near-complete device transfer. By overcoming the existing bottlenecks of red spectral efficiency and form factor of inorganic micro-LEDs, we believe this will pave the way for another revolution in the augmented reality and metaverse industries.

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. Abstracting the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system with a sensing capability for developing varifocal augmented reality glasses and naturally fit haptic gloves. Here, we design a shape memory alloy-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified shape memory alloy actuator. Despite its light weight (0.22 g), the actuator has a high power density of 1.7 kW/kg, an actuation strain of 300% under 80 g of external payload. We show how the actuator enables image depth control and an immersive tactile response in the form of augmented reality glasses and two-way communication haptic gloves whose thin form factor and high power density can hardly be achieved by conventional actuators.

Augmented reality glasses are considered as a next generation mobile platform after smartphones. For consumer market penetration, many improvements in hardware and software are needed. We will talk about some of the most important part, the fatigue-free displays and the energy-efficient pose and localization sensors.

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. Abstracting the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system for developing varifocal augmented reality (AR) glasses and naturally fit haptic gloves. Here, we design a shape memory alloy (SMA)-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified SMA actuator (CASA). Despite its light weight (0.22 g), the CASA has a high power density of 1.7 kW/kg and an actuation strain of 300%. We show how CASA enables image depth control and an immersive tactile response in the form of AR glasses and haptic gloves whose thin form factor and high power density can hardly be achieved by conventional actuators.

The eye-box expansion method using the merging of waveguide and HOE (holographic optical element) is presented. Using the waveguide with the refractive index of 1.7, the wide FoV (field of view) that is up to 60° is achieved. Full color and wide FoV are obtained using 2 waveguides. Projection optical system based on Scheimpflug principle is proposed and designed to compensate large-scale off-axis HOE aberrations. In order to enhance image quality, the projection system is precisely simulated and the grating pitch and alignment are calculated to increase the eye-box and uniformity.

The coherent backlight unit (C-BLU) using a diffractive optical element (DOE) for full-color flat-panel holographic display is proposed. The coherent backlight unit is composed of two diffractive optical elements (DOEs) that are imprinted on the same glass substrate. The illumination area of the backlight is 250 mm x 130 mm and the thickness is 2.2 mm, which is slim compared to other conventional coherent backlight units for holographic display systems. In experiments, the total efficiency is measured as 0.8% at red (638 nm), 3.9% at green (520nm), and 3.4% of blue (473 nm). As a result, we could get the 10 inch full color holographic display with 4k resolution.

The electrically tunable beam deflector have been researched and developed for lots of purpose. For the transmission type beam deflector, an indium‐tin‐oxide (ITO) has been developed with blazed grating patterns. The ITO layer was designed and generated on the lower substrate for transmission type beam deflector. A pixel pitch of ITO grating patterns is 6um, the electrode width is 3um with 3um spacing. With this small pixel pitch, the maximum diffraction angle is 2.541° at a wavelength of 532nm. A minimum cell gap is 2.5um for the enough 2π phase modulation with high birefringence liquid crystal which is delta n, 0.31. Total 720‐ ITO line which was patterned on the lower substrate is controlled individually by driving integrated circuit (IC) from driving module. Beam deflector driving module with driving IC is designed for continuous beam steering. Driving algorithm is developed and applied to the driving system for high angular resolution and continuous beam steering.

The novel design for the compact augmented reality (AR) glasses that utilize holographic optical element (HOE) as a combiner is presented. The wide field of view (FoV) that is larger than 90°, full color and high contrast ratio (CR) are achieved based on the single layer HOE, which has the thickness of 25 μm. In order to implement compactness of AR glasses using HOE combiner, the combination of optical lenses is proposed. In this design, a chromatic aberration and astigmatism, which are caused by highly off-axis projection of the image onto HOE, and the precise wavefront reproduction that maximize the efficiency of the HOE are taken into account simultaneously. The geometrical image distortion is corrected by implementation of image pre-distortion algorithm. The interpupillary distance (IPD) adjustment is applied to compensate small eye box. Based on the design, wearable prototype is introduced. Through the experiments both on benchtop and prototype, at the distance of 2 m, large image with diagonal of 150 inches is displayed.

We report the glasses-type device for augmented reality. By utilizing holographicdisplay method and designing compact optical system, we removed usual discomfort in existing AR apparatus, and developed the approach to the ideal display.

The new encoding methods are proposed and demonstrated for amplitude‐only computer‐generated hologram (CGH). Traditionally, the amplitude‐only encoding method proposed by Burch, has been used over 50 years, because it is the deterministic solution for generating an ideal hologram added by its conjugated hologram. Since the amplitude‐only hologram cannot represent negative values, the result of Burch's encoding should always be added by some values, so that none of data is less than zero. It means that the electric‐field of zero amplitude mapped into the medium gray level in a spatial light modulator (SLM). In ideal holographic display, it does not cause any problem on reconstructing holograms, but the medium gray level actually adds the noise at the practical holographic display. We introduce the encoding methods which can map the zero amplitude into the zero gray level. These encoding methods can increase the contrast ratio of an amplitude‐only hologram by reducing unnecessary scattering and stray lights.

Highly efficient transmission-type beam deflectors that have high angular resolution have been widely used for various applications. Continuously tunable beam deflectors have also been needed for many purposes. An indium-tin-oxide (ITO), widely used for transparent electrodes, was placed on the upper and lower glass substrate. The ITO layer on the lower substrate was patterned by the contact mask aligner for relatively wide input and output pad compared to main grating ITO patterns in the active area. These input and output pads on the lower substrate are connected to each driving integrated circuit (IC), which has 360 channels for continuous control. A small pixel pitch of grating patterns of 6 μm (the electrode width is 3 μm with a 3 μm spacing) was developed, and the maximum diffraction angle is calculated and measured at 2.541° with a wavelength of 532 nm. A minimal cell gap of 2.5 μm was applied for the full 2π phase modulation by using a high-birefringence liquid crystal. A driving module for continuous beam steering is also developed and applied to the beam deflector system. A diffraction efficiency of about 50.9% is observed at an angle of diffraction about 2.541°.

Holographic display is considered as the ultimate 3D technology. However, technical challenges in device capability and computation inhibit its commercialization. This talk addresses several approaches to overcome these challenges.

The measurement and assessment should be accompanied on any type of electronic displays. Especially, quantitative analysis is indispensable as the reference to catch the direction to proceed. In this paper, we will present the approach for quantification of the holographic display images. To do it, we achieved the holographic display system with spatial light modulator and Fourier lens, and adopted indices needed for evaluation, such as contrast ratio, cross talk, color dispersion, and uniformity. These indices have been generally employed in the field of classical 2D display and multi-view 3D display. However, there have been almost no tries to adopt them in that of holographic 3D display system due to the absence of concrete methodology up to now. We suggested a standard image, and identified that measured numbers could be used to select the better way of generating the holographic image. We believe that this quantitative approach for assessment of holographic images will help more accurate and systematic development in that field.

In this letter, we propose sub-terahertz (sub-THz) slow-wave circuits for coherent radiation sources through beam wave interaction mechanism. The circuits are prepared using microfabrication in advanced silicon (Si) technologies. Our approach is to split the circuit into multi levels allowing a low aspect ratio configuration and alleviating the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles in nanoscale accuracy for high frequency operation. The dispersion relation retrieved from the measurement, therefore, corresponds well to the theoretical estimation. In particular, the sub-THz radiation is successfully measured in pulsed operation through the vacuum-sealed integration of the slow-wave circuit with a 15-kV, 90-mA thermionic electron gun. This observation offers a promising opportunity for the development of terahertz radiation sources based on silicon micro- and nanofabrication technologies.

There have been significant recent developments in the growth of single‐crystal gallium nitride (GaN) on unconventional templates for large‐area blue or green light‐emitting diodes (LEDs) which, together with layer transfer onto foreign substrates, can enable flexible and stretchable lighting applications. Here, the heteroepitaxial growth of GaN on amorphous and single‐crystal substrates employing various interlayers and nucleation layers is reviewed, as well as the use of weak interfaces for layer‐transfer onto foreign substrates. Recent progress in low‐temperature GaN‐based red–green–blue (RGB) LEDs on glass substrates, which has exhibited a calculated efficiency of 11% compared with that from commertial LEDs, is discussed. Layer‐transfer techniques with various interlayers are also discussed. These heteroepitaxial GaN growth and layer‐transfer technologies are expected to lead to new lighting and display devices with high efficiency and full‐color tunability, which are suitable for large‐area, stretchable display and lighting applications.

Novel 3D display architecture and algorithm are proposed and demonstrated Full HD 3D image with reduced accommodation-vergence conflict using limited computing power and a conventional LCD panel. The proposed 3D display architecture is integrated with a commercial 5.5” Full HD LCD panel and the used algorithm needs remarkably lower computing power than a conventional CGH algorithm based on Fresnel transformation. The experimental results show the accommodation depth cue which provides a clear 3D image only on focus position.

We propose the effective viewing window enhancement method for a holographic display with an amplitude-only SLM by using algorithmic approach. The basic concept is the superposition principle of holography. The multiple computer generated holograms (CGH) can be displayed on the SLM, and multiple 3D images are reconstructed at different positions within a viewing window simultaneously. In the experiments, we have implemented the holographic display using an amplitude-only SLM, a field lens, and laser light sources. We can observe the holographic 3D image in the frustum formed by the field lens through the viewing window located in the Fourier plane of the hologram. To enhance the effective viewing window, we generate multiple CGHs with an observer's eye positions, and then overlap them to make the final CGH. Multiple 3D images can be reconstructed in different positions within the theoretical viewing window from the CGH displayed on SLM. This makes the enlargement of viewing zone that can observe the holographic images. The multiple holograms can be also made for enlargement of the viewing window along both horizontal and vertical direction (2D enlargement viewing zone). We confirmed that the experimental results and the simulation based on Rayleigh-Sommerfeld theory match well.

We demonstrate a binocular holographic display with an amplitude‐only spatial light modulator (SLM), which enables us to display a 3D scene with much higher frame rate than the case of a conventional stereoscopic 3D. Instead of dividing either frames or pixels for assigning the left and right images, we divide the space near pupils by modulating the phase of a computer generated hologram.

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.