Metasurface holography: from fundamentals to applications

Abstract: Holography has emerged as a vital approach to fully engineer the wavefronts of light since its invention dating back to the last century. However, the typically large pixel size, small field of view and limited space-bandwidth impose limitations in the on-demand high-performance applications, especially for three-dimensional displays and large-capacity data storage. Meanwhile, metasurfaces have shown great potential in controlling the propagation of light through the well-tailored scattering behavior of the constituent ultrathin planar elements with a high spatial resolution, making them suitable for holographic beam-shaping elements. Here, we review recent developments in the field of metasurface holography, from the classification of metasurfaces to the design strategies for both free-space and surface waves. By employing the concepts of holographic multiplexing, multiple information channels, such as wavelength, polarization state, spatial position and nonlinear frequency conversion, can be employed using metasurfaces. Meanwhile, the switchable metasurface holography by the integration of functional materials stimulates a gradual transition from passive to active elements. Importantly, the holography principle has become a universal and simple approach to solving inverse engineering problems for electromagnetic waves, thus allowing various related techniques to be achieved.

• The paper demonstrates how metasurfaces enhance holographic imaging by precisely controlling light amplitude, phase, and polarization to overcome conventional limitations.
• It classifies metasurfaces into distinct types and details design methodologies using digital synthesis and multiplexing to achieve superior image resolution.
• The study explores active control via phase-change and 2D materials, paving the way for reconfigurable holographic devices and future photonic innovations.

Metasurface Holography: A Comprehensive Review

The paper "Metasurface holography: from fundamentals to applications," authored by Lingling Huang, Shuang Zhang, and Thomas Zentgraf, provides a detailed review of the advancements in metasurface holography, drawing connections from its fundamental principles to practical applications. This paper comprehensively addresses how metasurfaces have transformed the field of holography by overcoming the limitations of traditional holographic methods, which include large pixel sizes, small fields of view, and limited space-bandwidth products.

Metasurfaces are two-dimensional structures that offer unprecedented control over light through subwavelength thickness elements, making them ideal for applications in holography. The research presented in this review underscores the burgeoning capabilities of metasurfaces to engineer the amplitude, phase, and polarization of light, thus enabling the realization of high-resolution and low-noise holographic images.

Key Contributions and Advancements in Metasurface Holography

1. Principles of Metasurface Holography:
   • The paper elaborates on previous holographic concepts and integrates these with the novel engineering of metasurfaces to improve image reconstruction. With precise control over scattering amplitudes and phases at the nanoscale, metasurfaces address the limitations inherent in conventional holography, providing a clearer pathway to holographic solutions, including those designed to tackle inverse electromagnetic wave problems.
2. Classification of Metasurfaces:
   • Metasurfaces are categorized into four primary types based on their materials and operational mechanisms: plasmonic, all-dielectric, geometric based on Pancharatnam-Berry (PB) phase, and Huygens' metasurfaces. Each category offers different advantages in terms of production efficiency, high-quality factors, and broadband operational capabilities.
3. Design Procedures:
   • The paper discusses practical methodologies for designing and fabricating metasurface holograms, incorporating digital synthesis and computational holography techniques. It emphasizes the importance of phase control strategies in hologram design to achieve optimal image resolutions.
4. Holographic Multiplexing:
   • A critical focus of this work is the exploration of holographic multiplexing techniques, which expand the storage capacity and efficiency of holographic systems. Techniques range from color holography employing spatial multiplexing and PB phases to polarization multiplexing, which exploits the birefringent properties of metasurfaces to encode and reproduce multiple holographic images.
5. Applications in Nonlinear and Surface Wave Holography:
   • The review dives into the field of nonlinear holography that arises from metasurfaces’ ability to enhance nonlinear optical processes. It highlights breakthroughs in nonlinear frequency conversions and spin-dependent nonlinear metasurface holography. Furthermore, metasurfaces extend holography techniques into the manipulation of surface plasmon polaritons, enabling novel applications in near-field control and plasmonic circuits.
6. Dynamic and Active Control:
   • Through the integration of active materials, such as phase-change materials and 2D materials, metasurfaces possess active control capabilities, which can be toggled to dynamically adjust the holographic images, paving the way for reconfigurable and adaptive optical devices.

Implications and Future Directions

The research within this domain not only significantly enhances the functionalities and efficiencies of holographic devices but also opens doors to future innovations in photonic and optoelectronic technologies. The prospect of entirely tunable, reconfigurable holographic devices holds promise for advancements in areas such as dynamic imaging systems, data storage, and secure optical communications.

As the frontier of metasurface holography continues to advance, further investigation into more efficient fabrication techniques and robust active elements will be crucial. Continued exploration may also lead to disruptive innovations in applications beyond optical holography, including acoustic and quantum systems.

This review acts as a pivotal reference for researchers in the field, providing foundational knowledge and inspiring further study into the vast potentials of metasurface holography. As technology evolves, metasurfaces are poised to redefine the interaction between light and materials, cementing their role in the future of optical sciences.