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The metaverse has captured significant attention as it provides a virtual realm that cannot be experienced in the physical world. Programmable optical holograms, integral components of the metaverse, allow users to access diverse information without needing external equipment. Meta-devices composed of artificially customized nano-antennas are excellent candidates for programmable optical holograms due to their compact footprint and flexible electromagnetic manipulation. Programmable optical meta-holograms can dynamically alter reconstructed images in real-time by directly modulating the optical properties of the metasurface or by modifying the incident light. Information can be encoded across multiple channels and freely selected through switchable functionality. These advantages will broaden the range of virtual scenarios in the metaverse, facilitating further development and practical applications. This review concentrates on recent advancements in the fundamentals and applications of programmable optical meta-holograms. We aim to provide readers with general knowledge and potential inspiration for applying programmable optical meta-holograms, both intrinsic and external ways, into the metaverse for better performance. An outlook and perspective on the challenges and prospects in these rapidly growing research areas are provided.

In this paper, a novel method is proposed to achieve two distinct information channels by simultaneously manipulating both the transmitted cross- and co-polarized components of a 1-bit coding metasurface under linearly polarized incidence. Compared to previously demonstrated incidence-switchable or position multiplexed holograms, our proposed coding meta-hologram can simultaneously project two independent holographic images without inevitable change of the incidence state and can at the same time also avoid crosstalk between different channels. Moreover, the orientation of the double-layered split ring (SR) apertures is specially designed to be 45° or 135° to achieve identical multiplexed functionality for both -polarized and -polarized incidences. The proof-of-concept experimental demonstrations present total transmittance efficiency above 30% for the dual linearly polarized incidences at 15 GHz, and good imaging performances with 53.98%/48.18% imaging efficiency, 1.55%/1.46% RMSE, and 29.9/28.72 peak signal-to-noise ratio for the cross-/co-polarized channels under -polarized incidence, and 47.27%/45.75% imaging efficienc , 1.55%/1.43% RMSE, and 18.74/25.93 peak signal-to-noise ratio under -polarized incidence, demonstrating great potential of the proposed multiplexed coding meta-hologram in practical applications such as data storage and information processing.

The research and development of methods using of the specialized diffractive microstructure sensors embedded in the pattern of computer-generated holograms (CGH) manufactured on circular and X-Y laser writing systems is discussed. These microstructures consist of two parts: one of which is written before the CGH in the field of future hologram and the second one is written during the long-term writing of the CGH. The shift between the first and second part of the microstructure is the trace of the writing errors and allows one to determine and calculate the error of CGH fabrication along both orthogonal coordinates. The developed method is based on the principle of diffraction-based overlay with 1D and 2D built-in diffractive microstructure-sensors. Mathematical modeling and results of experimental test writings of such diffractive microstructure sensors are described. The efficiency of using these types of build-in sensors for the writing errors estimation for CGHs is demonstrated.

Herein, we have discussed three major methods which have been generally employed for the generation of optical beams with orbital angular momentum (OAM). These methods include the practice of diffractive optics elements (DOEs), metasurfaces (MSs), and photonic integrated circuits (PICs) for the production of in-plane and out-of-plane OAM. This topic has been significantly evolved as a result; these three methods have been further implemented efficiently by different novel approaches which are discussed as well. Furthermore, development in the OAM detection techniques has also been presented. We have tried our best to bring novel and up-to-date information to the readers on this interesting and widely investigated topic.

Polarization is a basic characteristic of electromagnetic waves that conveys much optical information owing to its many states. The polarization state is manipulated and controlled for optical information security, optical encryption, and optical communication. Metasurface devices provide a new way to manipulate wave-fronts of light. A single ultrathin metasurface device can generate and modulate several differently polarized light fields, and thus carries optical information in several different channels. Terahertz (THz) waves have become widely used as carrier waves for wireless communication. Compact and functional metasurface devices are in high demand for THz elements and systems. This paper proposes a tri-layer metallic THz metasurface for multi-channel polarization generation and phase modulation with a high efficiency of approximately 80%. An azimuthally polarized THz vectorial beam generator is realized and characterized for use as a THz polarization analyzer. The incident polarization angle can be observed graphically with high accuracy. Moreover, a vectorial hologram with eight channels for different linear polarization states is demonstrated experimentally. The information in different holograms can be hidden by choosing the polarization channel for detection. This work contributes to achieving multi-functional metasurface in the THz band and can benefit THz communication and optical information security.

Efficiently generating 3D holograms is one of the most challenging research topics in the field of holography. This work introduces a method for generating multi‐depth phase‐only holograms using a fully convolutional neural network (FCN). The method primarily involves a forward–backward‐diffraction framework to compute multi‐depth diffraction fields, along with a layer‐by‐layer replacement method (L2RM) to handle occlusion relationships. The diffraction fields computed by the former are fed into the carefully designed FCN, which leverages its powerful non‐linear fitting capability to generate multi‐depth holograms of 3D scenes. The latter can smooth the boundaries of different layers in scene reconstruction by complementing information of occluded objects, thus enhancing the reconstruction quality of holograms. The proposed method can generate a multi‐depth 3D hologram with a PSNR of 31.8 dB in just 90 ms for a resolution of 2160 × 3840 on the NVIDIA Tesla A100 40G tensor core GPU. Additionally, numerical and experimental results indicate that the generated holograms accurately reconstruct clear 3D scenes with correct occlusion relationships and provide excellent depth focusing. This work introduces the forward–backward‐diffraction framework for computing multi‐depth diffraction fields and the layer‐by‐layer replacement method for handling occlusion relationships. When combined with a fully convolutional neural network, it generates multi‐depth holograms with excellent depth focusing and corrects occlusion relationships. The reconstructed scene exhibits minimal speckle noise and few edge artifacts.

Meta-holographic encryption is a potentially important technique for information security. Despite rapid progresses in multi-tasked meta-holograms, the number of information channels available in metasurfaces is limited, making meta-holographic encryption vulnerable to some attacking algorithms. Herein, we demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices. These two matrices are imposed to the incident light and the metasurface, respectively. While the all-dielectric metasurface is static, the phase matrix of incident light provides additional degrees of freedom to precisely control the eventual functions at will. With a single Si metasurface, arbitrary holographic images and videos have been transported and decrypted. We hope that this work paves a more promising way to optical information encryption and authentication. Here, the authors demonstrate a re-programmable metasurface that can produce arbitrary holographic images for optical encryption. The encrypted information is divided into two matrices and defined to the incident laser to produce arbitrary holographic images.

Reprogrammable metasurfaces, which establish a fascinating bridge between physical and information domains, can dynamically control electromagnetic (EM) waves in real time and thus have attracted great attentions from researchers around the world. To control EM waves with an arbitrary polarization state, it is desirable that a complete set of basis states be controlled independently since incident EM waves with an arbitrary polarization state can be decomposed as a linear sum of these basis states. In this work, we present the concept of complete-basis-reprogrammable coding metasurface (CBR-CM) in reflective manners, which can achieve independently dynamic controls over the reflection phases while maintaining the same amplitude for left-handed circularly polarized (LCP) waves and right-handed circularly polarized (RCP) waves. Since LCP and RCP waves together constitute a complete basis set of planar EM waves, dynamically-controlled holograms can be generated under arbitrarily polarized wave incidence. The dynamically reconfigurable meta-particle is implemented to demonstrate the CBR-CM’s robust capability of controlling the longitudinal and transverse positions of holograms under LCP and RCP waves independently. It’s expected that the proposed CBR-CM opens up ways of realizing more sophisticated and advanced devices with multiple independent information channels, which may provide technical assistance for digital EM environment reproduction.

The emergence of holographic technologies is challenging the traditional concert format within the music events industry. Research on attendee satisfaction of holographic performances remains scarce resulting in uncertainty of future industry application. Utilizing qualitative manual thematic analysis as well as quantitative mean analysis, this article investigates attendee satisfaction at the ABBA Voyage concert in London. Furthermore, the acceptance of holographic technology was investigated through questioning attendees' intention of future attendance of holographic performances. 147 valid survey responses revealed a high average satisfaction rate. Three dominating themes of attendance motivation were also identified: (1) nostalgia, (2) socialization and (3) novelty. Nevertheless, survey responses revealed a dependence of the acceptance of holograms on the specific artist, specifically mentioning issues concerning morality and production type. Consequentially, a co-dependence between push and pull factors is proposed with the artist as a key pull factor and the three attendance motivations as a set of push factors.

Allowing subwavelength-scale-digitization of optical wavefronts to achieve complete control of light at interfaces, metasurfaces are particularly suited for the realization of planar phase-holograms that promise new applications in high-capacity information technologies. Similarly, the use of orbital angular momentum of light as a new degree of freedom for information processing can further improve the bandwidth of optical communications. However, due to the lack of orbital angular momentum selectivity in the design of conventional holograms, their utilization as an information carrier for holography has never been implemented. Here we demonstrate metasurface orbital angular momentum holography by utilizing strong orbital angular momentum selectivity offered by meta-holograms consisting of GaN nanopillars with discrete spatial frequency distributions. The reported orbital angular momentum-multiplexing allows lensless reconstruction of a range of distinctive orbital angular momentum-dependent holographic images. The results pave the way to the realization of ultrahigh-capacity holographic devices harnessing the previously inaccessible orbital angular momentum multiplexing. Conventional hologram designs lack orbital angular momentum selectivity. Here, the authors design metasurface holograms consisting of GaN nanopillars with discrete spatial frequency distributions allowing the reconstruction of distinctive orbital angular momentumdependent holographic images.