Stereoscopic display techniques used in virtual reality (VR) and augmented reality (AR) do not satisfy the physiological requirements for human vision, leading to issues such as fatigue and motion sickness. Electroholography based on computer-generated hologram (CGH) is an ideal technique for a three-dimensional display. However, there are limitations of both the field of view (FOV), which is the size of the reconstructed image, and the viewing zone, which is the range of the reconstructed image that can be observed. Expanding both FOV and the viewing zone is desirable, but there is a trade-off between them. For the reasons mentioned above, holographic head-mounted display (HMD) systems have been proposed. Since HMD systems are used in a fixed position, the narrow viewing zone does not significantly affect the observation of the reconstructed image. Thus, we need to prioritize the expansion of FOV. We developed a practical holographic HMD system that includes a concave mirror to expand the FOV. Concave mirrors can reduce chromatic aberration when making full-color images because the convergence of light is independent of wavelength. Our holographic HMD system can also support three degrees of freedom (3DoF) by including a motion sensor to obtain the user’s attitude angle. To support 3DoF, we carry out phase-compensation as a fast calculation algorithm. This enabled CGH calculations to be more efficient for modifying the user’s attitude angle and was realized real-time calculation of 3DoF.
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