In this paper, we analyze the image quality reconstructed by holographic display depending on spatial coherency and temporal coherency of the light source in holographic display system. The simulation was conducted by changing both spatial coherency and temporal coherency independently using proper modeling of coherency. A holographic display setup was composed to verify simulation results. LED and LD were respectively used as a light source for holographic display, and the quality of reconstructed images reproduced by using LED or LD was compared. The scheme of near-eye holographic display adopting LED as a light source which generates low speckle noise but narrow depth range was proposed. The proposed scheme of near-eye holographic display system was verified experimentally.
With the virtue of rapid progress in optics, sensors, and computer science, we are witnessing that commercial products or prototypes for augmented reality (AR) are penetrating into the consumer markets. AR is spotlighted as expected to provide much more immersive and realistic experience than ordinary displays. However, there are several barriers to be overcome for successful commercialization of AR. Here, we explore challenging and important topics for AR such as image combiners, enhancement of display performance, and focus cue reproduction. Image combiners are essential to integrate virtual images with real-world. Display performance (e.g. field of view and resolution) is important for more immersive experience and focus cue reproduction may mitigate visual fatigue caused by vergence-accommodation conflict. We also demonstrate emerging technologies to overcome these issues: index-matched anisotropic crystal lens (IMACL), retinal projection displays, and 3D display with focus cues. For image combiners, a novel optical element called IMACL provides relatively wide field of view. Retinal projection displays may enhance field of view and resolution of AR displays. Focus cues could be reconstructed via multi-layer displays and holographic displays. Experimental results of our prototypes are explained.
Augmented reality is recently attracting a lot of attention as one of the most spotlighted next-generation technologies. In order to get toward realization of ideal augmented reality, we need to integrate 3D virtual information into real world. This integration should not be noticed by users blurring the boundary between the virtual and real worlds. Thus, ultimate device for augmented reality can reconstruct and superimpose 3D virtual information on the real world so that they are not distinguishable, which is referred to as see-through 3D technology. Here, we introduce our previous researches to combine see-through displays and 3D technologies using emerging optical combiners: holographic optical elements and index matched optical elements. Holographic optical elements are volume gratings that have angular and wavelength selectivity. Index matched optical elements are partially reflective elements using a compensation element for index matching. Using these optical combiners, we could implement see-through 3D displays based on typical methodologies including integral imaging, digital holographic displays, multi-layer displays, and retinal projection. Some of these methods are expected to be optimized and customized for head-mounted or wearable displays. We conclude with demonstration and analysis of fundamental researches for head-mounted see-through 3D displays.
A method for realizing a three-dimensional see-through augmented reality in Fourier holographic display is proposed. A holographic optical element (HOE) with the function of Fourier lens is adopted in the system. The Fourier hologram configuration causes the real scene located behind the lens to be distorted. In the proposed method, since the HOE is transparent and it functions as the lens just for Bragg matched condition, there is not any distortion when people observe the real scene through the lens HOE (LHOE). Furthermore, two optical characteristics of the recording material are measured for confirming the feasibility of using LHOE in the proposed see-through augmented reality holographic display. The results are verified experimentally.