Holographic displays have gained unprecedented attention as next-generation virtual and augmented reality applications with recent achievements in the realization of a high-contrast image through computer-generated holograms (CGHs). However, these holograms show a high energy concentration in a limited angular spectrum, whereas the holograms with uniformly distributed angular spectrum suffer from a severe speckle noise in the reconstructed images. In this study, we claim that these two physical phenomena attributed to the existing CGHs significantly limit the support of accommodation cues, which is known as one of the biggest advantages of holographic displays. To support the statement, we analyze and evaluate various CGH algorithms with contrast gradients - a change of contrast over the change of the focal diopter of the eye - simulated based on the optical configuration of the display system and human visual perception models. We first introduce two approaches to improve monocular accommodation response in holographic viewing experience; optical and computational approaches to provide holographic images with sufficient contrast gradients. We design and conduct user experiments with our prototype of holographic near-eye displays, validating the deficient support of accommodation cues in the existing CGH algorithms and demonstrating the feasibility of the proposed solutions with significant improvements on accommodative gains.

Since 1960s, digital holography (DH) has been developed significantly as an exquisite optical sensing technique with its computational interpretation. Recent advances in the image sensor and the coherent light source have suggested the possibility of using DH in portable form that can be utilized in industrial fields. Field of view (FOV) should be sufficiently wide and the system be simple for successful landing of DH on the industrial market. To embody the possibility, in this paper, we present a method for implementing off-axis reflective DH using a single diffraction grating. Beam splitter and mirror in the conventional off-axis DH are replaced with a single diffraction grating. This replacement enables the implementation of simple interferometer while maintaining the performance of the holography. In addition, we apply the multiplexed illumination method to enhance space-bandwidth product of off-axis hologram. Using the wavelength dependence of the diffraction grating, the FOV can be doubled without additional optical element. We demonstrate the proposed method by three holographic imaging experiments with two laser diodes. The prototype provides lateral resolution of 19.69$\mu$m with the FOV of 6.85 mm × 8.72 mm. The FOV is 1.9 times wider than the image sensor area of 6.85 mm × 4.59 mm. Overall size of the prototype is 12 cm × 17 cm × 5 cm, showing the suitability of implementation to the various industrial fields.