A lensless full-color holographic Maxwellian near-eye display using a single amplitude-type spatial light modulator is proposed in this Letter. The color holographic image is directly projected onto the retina without any eyepiece. The color crosstalk is clearly separated from the signal in the space owing to the encoded spherical wave and carrier wave. An aperture numerical filter and a real polarized filter are used at the pupil plane to accurately stop the crosstalk light. A high-quality dynamic speckless color holographic image was produced in the mid-air within a specific depth range. The horizontal eyebox expansion is achieved simply through multiple spherical wave encoding and verified through an optical experiment. The proposed display is compact and promising as the augmented reality near-eye display.

A holographic super multi-view (SMV) Maxwellian display based on flexible wavefront modulation is proposed for the first time, to the best of our knowledge. It solves the issue that the previous holographic Maxwellian displays could not provide depth cues for monocular vision. Different from the previous methods, two or more parallax images are multiplied by quadric phase distributions and converged to the viewpoints existing in the pupil to provide 3-D vision. A time division method is proposed to eliminate the cross talk caused by the coherence of different spherical waves. Experiments demonstrate that the proposed method can accurately reconstruct images at different depth without cross talk. The proposed method inherits the previous holographic Maxwellian display's advantages of flexible viewpoint position adjustment and large depth of field (DOF). Superior to geometric optics based SMV displays, the proposed system is compact without lens aberration since only a single spatial light modulator (SLM) is needed without any additional optical elements.

Holographic retinal projection display (RPD) can project images directly onto the retina without any lens by encoding a convergent spherical wave phase with the target images. Conventional amplitude-type holographic RPD suffers from strong zero-order light and conjugate. In this paper, a lensless phase-only holographic RPD based on error diffusion algorithm is demonstrated. It is found that direct error diffusion of the complex Fresnel hologram leads to low image quality. Thus, a post-addition phase method is proposed based on angular spectrum diffraction. The spherical wave phase is multiplied after error diffusion process, and acts as an imaging lens. In this way, the error diffusion functions better due to reduced phase difference between adjacent pixels, and a virtual image with improved quality is produced. The viewpoint is easily deflected just by changing the post-added spherical phase. A full-color holographic RPD with adjustable eyebox is demonstrated experimentally with time-multiplexing technique.

Multi-plane reconstruction is essential for realizing a holographic three-dimensional (3D) display. One fundamental issue in conventional multi-plane Gerchberg-Saxton (GS) algorithm is the inter-plane crosstalk, mainly caused by the neglect of other planes’ interference in the process of amplitude replacement at each object plane. In this paper, we proposed the time-multiplexing stochastic gradient descent (TM-SGD) optimization algorithm to reduce the multi-plane reconstruction crosstalk. First, the global optimization feature of stochastic gradient descent (SGD) was utilized to reduce the inter-plane crosstalk. However, the crosstalk optimization effect would degrade as the number of object planes increases, due to the imbalance between input and output information. Thus, we further introduced the time-multiplexing strategy into both the iteration and reconstruction process of multi-plane SGD to increase input information. In TM-SGD, multiple sub-holograms are obtained through multi-loop iteration and then sequentially refreshed on spatial light modulator (SLM). The optimization condition between the holograms and the object planes converts from one-to-many to many-to-many, improving the optimization of inter-plane crosstalk. During the persistence of vision, multiple sub-hologram jointly reconstruct the crosstalk-free multi-plane images. Through simulation and experiment, we confirmed that TM-SGD could effectively reduce the inter-plane crosstalk and improve image quality.The proposed TM-SGD-based holographic display has wide applications in tomographic 3D visualization for biology, medical science, and engineering design, which need to reconstruct multiple independent tomographic images without inter-plane crosstalk.

Augmented reality (AR) near-eye displays (NEDs) are emerging as the next-generation display platform. The existing AR NED only present one single video channel at a time, same as traditional media such as TVs and smartphones. In this Letter, to the best of our knowledge, we propose for the first time a multi-channel holographic retinal projection display (RPD), which can provide multi-channel image sources simultaneously, thus greatly increasing the information content. Due to the superposition capacity of a hologram, multiple images are projected to different viewpoints simultaneously through multiple spherical wave encoding, so that the viewer can switch among playing channels very fast through eye rotation. A full-color dynamic multi-channel holographic near-eye display is demonstrated in the optical experiment. The proposed method provides a good prospect that the future AR glasses can play dozens of video channels in parallel, and the user can switch among channels freely and efficiently just through a simple eye rotation.