As the market interest in augmented reality (AR) displays increases, research on compact and lightweight optical system design using holographic optical elements (HOE) is also actively conducted. HOE plays an essential role in augmented reality optics as an image combiner that provides users with combined real and virtual scenes due to its advantages of transparency and high selectivity of light. However, an optical system using HOE has an issue in which aberrations such as astigmatism occur. Compensating the aberrations and securing wide eye-box and viewing angle to provide users with a convenient and immersive viewing experience remain a challenge for AR optics using HOEs. This paper presents studies conducted to correct aberrations, expand the eye-box and broaden the viewing angle for the AR optical systems using HOEs, such as head-up displays (HUDs) and near-eye displays. In the case of the HUD, we propose a method to correct the aberrations. In the proposed method, two freeform mirror shapes are designed using a commercial raytracing software to minimize the aberrations by the HOE attached to a flat windshield. Combined with the image pre-compensation, the proposed system provides aberration-free consistent images over its entire eye-box. In the case of near-eye displays, the eye-box expansion technique using multiplexed HOE is introduced.
Various technologies to realize the augmented reality (AR) devices have been proposed. Holographic optical element (HOE) is among the most appealing optical components for the optical combiner of AR devices. With the compact size and bendable material, HOE can be applied to AR systems with various form factors. Since HOE has high angular selectivity, the light from the real scene remains nearly intact, making HOE the most promising technology for see-through AR displays. However, several issues of HOE still remain to be resolved, such as narrow field of view or eye box, and severe aberration. In this invited paper, we present the basic characteristics and issues of HOE and introduce how we can resolve the issues.
We first discuss the key factors of augmented reality (AR) and virtual reality (VR) displays. Various requirements for immersive experiences are categorized as six factors that must be considered when designing the AR/VR head-mounted displays (HMDs). These factors have a strong correlation with other factors and should maintain a moderate balance between them. Based on recent researches we second introduce various technologies for AR/VR. By comparing the pros and cons of each method, we discuss the progression of AR/VR devices that can provide more affordable HMD devices for the public.
Holographic near-eye displays (NEDs) have large potential for augmented reality (AR) devices as they modulate the wavefront of light. They can provide observers with comfortable three-dimensional (3D) views with focus-cues, and little optical aberrations since the unwanted phase delay added by optical systems can be compensated by wavefront modulation. With the advent of ultra-high-definition (UHD) spatial light modulator (SLM), a degree of freedom in designing holographic NEDs has been further expanded. Here, we introduce several holographic NEDs using UHD SLM. The holographic NED using an HOE is introduced for the optical see-through display. Besides, the holographic NED with enlarged eye-box using point-source array and eye-tracking method will be presented. Finally, the holographic NED of which optical aberration is compensated by Zernike’s polynomial adaptation will be introduced.
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