Byounghyo Lee

Analysis and Implementation of Hologram Lenses for See-Through Head-Mounted Display

We introduce an approach to implementation of see-through head-mounted displays using hologram lenses, which are categorized by holographic optical elements. The hologram lenses magnify displayed images and superimpose the magnified images on the real-world simultaneously, which allows system configuration to be compact. Here, we investigate imaging properties and optical issues of hologram lenses using the spectral analysis of light field. Also, the astigmatism of hologram lenses is analyzed and its compensation method is proposed and verified. We conclude by describing display results and a practical application of the proposed method.

See-through optical combiner for augmented reality head-mounted display: index-matched anisotropic crystal lens

A novel see-through optical device to combine the real world and the virtual image is proposed which is called an index-matched anisotropic crystal lens (IMACL). The convex lens made of anisotropic crystal is enveloped with the isotropic material having same refractive index with the extraordinary refractive index of the anisotropic crystal. This optical device functions as the transparent glass or lens according to the polarization state of the incident light. With the novel optical property, IMACL can be utilized in the see-through near eye display, or head-mounted display for augmented reality. The optical property of the proposed optical device is analyzed and aberration by the anisotropic property of the index-matched anisotropic crystal lens is described with the simulation. The concept of the head-mounted display using IMACL is introduced and various optical performances such as field of view, form factor and transmittance are analyzed. The prototype is implemented to verify the proposed system and experimental results show the mixture between the virtual image and real world scene.

Foveated Retinal Optimization for See-through Near-Eye Multi-Layer Displays (Invited Paper)

In order to implement 3-D displays with focus cues, several technologies, including multi-layer displays, have been introduced and studied. In multi-layer displays, a volumetric 3-D scene is represented by 2-D layer images via optimization process. Although this methodology has been thoroughly explored and discussed in optical aspect, the optimization method has not been fully analyzed. In this paper, we deal with pupil movement that may prevent efficient synthesis of layer images. We propose a novel optimization method called foveated retinal optimization, which considers the foveated visual acuity of human. Exploiting the characteristic of human vision, our method has tolerance for pupil movement without gaze tracking while maintaining image definition and accurate focus cues. We demonstrate and verify our method in terms of contrast, visual metric, and experimental results. In experiment, we implement a see-through near-eye display that consists of two display modules, a light guide, and a holographic lens. The holographic lens enables us to design a more compact prototype as performing the roles of an image combiner and floating lens, simultaneously. Our system achieves

Integration of relay optics in LED-based reflective off-axis digital holographic microscopy

38^\circ \times 19^\circ

Distortion analysis of index matched anisotropic crystal lens with the ray tracing model

field of view, continuous focus cues, low aberration, small form factor, and clear see-through property.

See-through light field displays for augmented reality

Digital holography is widely known as one of the techniques reconstructing a depth profile of the object. For digital holography (DH), the light source that has a long coherence length such as laser or laser diode is generally recommended. Recently, digital holographic microscopy (DHM) utilizing light emitting diode (LED) as a light source has attracted attention. However, it has to satisfy certain conditions for LED be utilized in off-axis DHM as it has small coherence length. Due to this fact, the hologram cannot be captured from the other side of a beam splitter. Therefore, we propose an LED-based off-axis reflective DHM that combines a 4-f system that optically relays the field to the sensor plane of charge-coupled device (CCD). We analyze the reason why the sample plane has to be relayed by 4-f system. We provide experimental results to verify the necessity of relay optics in LED-based reflective off-axis DHM.

A head-mounted compressive three-dimensional display system with polarization-dependent focus switching

In this paper, we propose the index matched anisotropic crystal lens. The proposed optical element acts as a transparent glass in extraordinary polarized light and a lens in ordinary polarized light. The conceptual diagram and principle of the index matched anisotropic crystal lens are presented and the ray tracing simulation is performed to verify and analyze the functionality and the distortion of the real world scene. The index matched anisotropic crystal lens is implemented with calcite and the index matching liquid. The preliminary system to show the feasibility of the proposed optical element is implemented. The lens mode and the transparent mode are presented and the distortion along the incident direction of the light is also analyzed by the experiment. It is expected that the index matched anisotropic crystal lens can be a good candidate for the head-up display and head-mounted display.

Multi-layer see-through near-eye display using index-matched anisotropy crystal lens

Augmented reality (AR) is a fascinating technology that receives considerable attention of public and industries. Here, we introduce an optical tool, holographic optical element (HOE), which can be applied for AR applications. HOEs are holographic volume gratings, which have transparency and distinctive optical characteristics. HOEs can perform the roles of optical elements by transforming an incident wavefront to a predefined wavefront via diffraction [Close 1975]. Since HOEs are usually recorded in thin film such as photopolymers, they have various advantages in weight, cost, and thickness. Thus, there have been several applications using HOEs, including see-through light field displays [Hong et al. 2014] and head-mounted displays [Kasai et al. 2001].

One-Shot Light Field Fourier Ptychographic Microscopy for Complex Imaging

A head-mounted compressive three-dimensional (3D) display system is proposed by combining polarization beam splitter (PBS), fast switching polarization rotator and micro display with high pixel density. According to the polarization state of the image controlled by polarization rotator, optical path of image in the PBS can be divided into transmitted and reflected components. Since optical paths of each image are spatially separated, it is possible to independently focus both images at different depth positions. Transmitted p-polarized and reflected s-polarized images can be focused by convex lens and mirror, respectively. When the focal lengths of the convex lens and mirror are properly determined, two image planes can be located in intended positions. The geometrical relationship is easily modulated by replacement of the components. The fast switching of polarization realizes the real-time operation of multi-focal image planes with a single display panel. Since it is possible to conserve the device characteristic of single panel, the high image quality, reliability and uniformity can be retained. For generating 3D images, layer images for compressive light field display between two image planes are calculated. Since the display panel with high pixel density is adopted, high quality 3D images are reconstructed. In addition, image degradation by diffraction between physically stacked display panels can be mitigated. Simple optical configuration of the proposed system is implemented and the feasibility of the proposed method is verified through experiments.

Foveated Retinal Optimization for See-Through Near-Eye Multi-Layer Displays

In this paper, we propose the multi-layer see-through near eye display using index-matched anisotropic crystal lens (IMACL). Using the polarization multiplexing property of the IMACL and angular multiplexing property of the diffuser holographic optical elements (DHOE), the novel multi-layer see-through near eye display is realized. We show the principle of the proposed system and verify the proposed system with experiments.