Holographic optical elements for head-up display and near-eye display

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.