Holographic three-dimensional display is an important display technique because it can provide all depth information of a real or virtual scene without any special eyewear. In recent years, with the development of computer and optoelectronic technology, computer-generated holograms have attracted extensive attention and developed as the most promising method to realize holographic display. However, some bottlenecks still restrict the development of computer-generated holograms, such as heavy computation burden, low image quality, and the complicated system of color holographic display. To overcome these problems, numerous algorithms have been investigated with the aim of color dynamic holographic three-dimensional display. In this review, we will explain the essence of various computer-generated hologram algorithms and provide some insights for future research.

Metasurface holograms harness multiple degrees of freedom of light to enhance information channel capacity. Traditionally, wavelength multiplexing holography with high-capacity information channel was only achievable through 3D volume holograms using Bragg diffraction. Here, we demonstrate ultranarrow-linewidth wavelength-vortex multiplexing holography in metasurface holograms. By applying elementary dispersion engineering, we develop a sparse k -vector–filtering aperture array in momentum space, enabling sharp wavelength selectivity combined with orbital angular momentum selectivity. Further leveraging transformer neural networks for the design of phase-only holograms, we showcase the reconstruction of up to 118 independent images from a single hologram, achieving a simulated ultranarrow linewidth of 2 nanometers within the visible range. We apply these developed metasurface holograms for holographic visual cryptography, attaining unprecedented security levels with an information rate over 2500 times higher than traditional methods. Our results open exciting avenues for the application of metasurface holograms in various fields, including 3D displays, holographic encryption, and optical artificial intelligence.

Secret sharing is a promising technology for information encryption by splitting the secret information into different shares. However, the traditional scheme suffers from information leakage in decryption process since the amount of available information channels is limited. Herein, we propose and demonstrate an optical secret sharing framework based on the multi-dimensional multiplexing liquid crystal (LC) holograms. The LC holograms are used as spatially separated shares to carry secret images. The polarization of the incident light and the distance between different shares are served as secret keys, which can significantly improve the information security and capacity. Besides, the decryption condition is also restricted by the applied external voltage due to the variant diffraction efficiency, which further increases the information security. In implementation, an artificial neural network (ANN) model is developed to carefully design the phase distribution of each LC hologram. With the advantage of high security, high capacity and simple configuration, our optical secret sharing framework has great potentials in optical encryption and dynamic holographic display.

In this paper, we propose a fast calculation method using look-up table and wavefront-recording plane. Wavefront-recording plane method consists of two steps: the first step is the calculation of a wavefront-recording plane which is placed between the object and the hologram. In the second step, we obtain the hologram by executing diffraction calculation from the wavefront-recording plane to the hologram plane. The first step of the previous wavefront-recording plane method is time consuming. In order to obtain further acceleration to the first step, we propose high compressed look-up table method based on wavefront-recording plane. We perform numerical simulations and optical experiments to verify the proposed method. Numerical simulation results show that the calculation time reduces dramatically in comparison with previous wavefront-recording plane method and the memory usage is very small. The optical experimental results are in accord with the numerical simulation results. It is expected that proposed method can greatly reduce the computational complexity and could be widely applied in the holographic field in the future.

A curved multiplexing method based on the curved computer-generated hologram (CCGH) is proposed theoretically and demonstrated experimentally to increase field of view (FOV) and spatial bandwidth. Point source method is used to calculate the CCGH. Curved multiplexing method can be used to reconstruct different 3D objects at the same position by bending a composed hologram which is synthesized of several CCGHs with different central angles. Numerical simulations and optical experiments demonstrate that the method is feasible. It could have a good prospect by combining with the curved display screen and flexible display materials.

In this paper, we propose an accurate high-compressed look-up-table method that uses less memory to generate the hologram. In precomputation, we separate the longitudinal modulation factors and only calculate the basic horizontal and vertical factors. Therefore, we obtain other horizontal and vertical modulation factors of object points by simply shifting the basic horizontal and vertical modulation factors while computing holograms. We perform numerical simulations and optical experiments to verify the proposed method. Numerical simulation results show that the proposed method has the least memory usage, the fastest computation time and no distortion. The optical experimental results are in accord with the numerical simulation results. The proposed method is simple and effective to calculate computer-generated holograms for color dynamic holographic display with high speed, less memory usage and high accuracy that could be applied in the holographic field in the future.