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.