Jaebum Cho

Holographic display for see-through augmented reality using mirror-lens holographic optical element

A holographic display system for realizing a three-dimensional optical see-through augmented reality (AR) is proposed. A multi-functional holographic optical element (HOE), which simultaneously performs the optical functions of a mirror and a lens, is adopted in the system. In the proposed method, a mirror that is used to guide the light source into a reflection type spatial light modulator (SLM) and a lens that functions as Fourier transforming optics are recorded on a single holographic recording material by utilizing an angular multiplexing technique of volume hologram. The HOE is transparent and performs the optical functions just for Bragg matched condition. Therefore, the real-world scenes that are usually distorted by a Fourier lens or an SLM in the conventional holographic display can be observed without visual disturbance by using the proposed mirror-lens HOE (MLHOE). Furthermore, to achieve an optimized optical recording condition of the MLHOE, the optical characteristics of the holographic material are measured. The proposed holographic AR display system is verified experimentally.

Additive light field displays: realization of augmented reality with holographic optical elements

We propose a see-through additive light field display as a novel type of compressive light field display. We utilize holographic optical elements (HOEs) as transparent additive layers. The HOE layers are almost free from diffraction unlike spatial light modulator layers, which makes this additive light field display more advantageous when modifying the number of layers, thickness, and pixel density compared with conventional compressive displays. Meanwhile, the additive light field display maintains advantages of compressive light field displays. The proposed additive light field display shows bright and full-color volumetric images in high definition. In addition, users can view real-world scenes beyond the displays. Hence, we expect that our method can contribute to the realization of augmented reality. Here, we describe implementation of a prototype additive light field display with two additive layers, evaluate the performance of transparent HOE layers, describe several results of display experiments, discuss the diffraction effect of spatial light modulators, and analyze the ability of the additive light field display to express uncorrelated light fields.

miR-34a inhibits differentiation of human adipose tissue-derived stem cells by regulating cell cycle and senescence induction.

MicroRNAs (miRNAs) are critical in the maintenance, differentiation, and lineage commitment of stem cells. Stem cells have the unique property to differentiate into tissue-specific cell types (lineage commitment) during cell division (self-renewal). In this study, we investigated whether miR-34a, a cell cycle-regulating microRNA, could control the stem cell properties of adipose tissue-derived stem cells (ADSCs). First, we found that the expression level of miR-34a was increased as the cell passage number was increased. This finding, however, was inversely correlated with our finding that the overexpression of miR-34a induced the decrease of cell proliferation. In addition, miR-34a overexpression decreased the expression of various cell cycle regulators such as CDKs (-2, -4, -6) and cyclins (-E, -D), but not p21 and p53. The cell cycle analysis showed accumulation of dividing cells at S phase by miR-34a, which was reversible by co-treatment with anti-miR-34a. The potential of adipogenesis and osteogenesis of ADSCs was also decreased by miR-34a overexpression, which was recovered by co-treatment with anti-miR-34a. The surface expression of stem cell markers including CD44 was also down-regulated by miR-34a overexpression as similar to that elicited by cell cycle inhibitors. miR-34a also caused a significant decrease in mRNA expression of stem cell transcription factors as well as STAT-3 expression and phosphorylation. Cytokine profiling revealed that miR-34a significantly modulated IL-6 and -8 production, which was strongly related to cellular senescence. These data suggest the importance of miR-34a for the fate of ADSCs toward senescence rather than differentiation.

Accelerated synthesis algorithm of polygon computer-generated holograms

For the real-time computation of computer-generated holograms (CGHs), various accelerated algorithms have been actively investigated. This paper proposes a novel concept of sparse computation of polygon CGH, which is inspired by an observation of the sparsity in the angular spectrum of a unit triangular polygon and present the accelerated algorithm using the intrinsic sparsity in the polygon CGH pattern for the enhancement of computational efficiency effectively. It is shown with numerical results that computation efficiency can be greatly improved without degrading the quality of holographic image.

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.

Fast reconfiguration algorithm of computer generated holograms for adaptive view direction change in holographic three-dimensional display

Reconfiguration is a computational algorithm of adaptively updating computer generated holograms (CGHs) for the positional change of an observers viewing window with low computational load by efficiently using pre-calculated elementary CGHs. A fast reconfiguration algorithm of CGHs for three-dimensional mesh objects is proposed. Remarkable improvement is achieved in the computation speed of CGHs, which is at least 20-times faster than repetitive re-computation of CGHs. The image quality of reconfigured CGHs is analyzed.

Computational multi-projection display

A computational multi-projection display is proposed by employing a multi-projection system combining with compressive light field displays. By modulating the intensity of light rays from a spatial light modulator inside a single projector, the proposed system can offer several compact views to observer. Since light rays are spread to all directions, the system can provide flexible positioning of viewpoints without stacking projectors in vertical direction. Also, if the system is constructed properly, it is possible to generate view images with inter-pupillary gap and satisfy the super multi-view condition. We explain the principle of the proposed system and verify its feasibility with simulations and experimental results.

Viewing angle enhancement of an integral imaging display using Bragg mismatched reconstruction of holographic optical elements

Holographic-optical-element (HOE)-based integral imaging display can be applied to augmented reality. However, a narrow viewing angle is a bottleneck for commercialization. Here, we propose a method to enhance the viewing angle of the integral imaging display using Bragg mismatched reconstruction of HOEs. The viewing angle of the integral imaging display can be enlarged with two probe waves, which form two different viewing zones. The effect of Bragg mismatched reconstruction is analyzed with simulation and experiment. In order to show feasibility of the proposed method, a display experiment is demonstrated.

Double bi-material cantilever structures for complex surface plasmon modulation

A complex modulation structure of surface plasmon polaritons using double bi-material cantilevers is proposed. It is shown with numerical analysis that the thermally controlled mechanical actuation of double bi-material cantilevers can modulate the amplitude and phase of surface plasmon polaritons across a full complex modulation range independently and simultaneously. The complex modulation structures designed for visible wavelengths are presented and their multi-wavelength integration is discussed.

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