Holograms, the optical devices to reconstruct predesigned images, show many applications in our daily life. However, applications of hologram are still limited by the constituent materials and therefore their working range is trapped at a particular electromagnetic region. In recent years, the metasurfaces, an array of subwavelength antenna with varying sizes, show the abilities to manipulate the phase of incident electromagnetic wave from visible to microwave frequencies. Here, we present a reflective-type and high-efficiency meta-hologram fabricated by metasurface for visible wavelength. Using gold cross nanoantennas as building blocks to construct our meta-hologram devices with thickness ∼ λ/4, the reconstructed images of meta-hologram show polarization-controlled dual images with high contrast, functioning for both coherent and incoherent light sources within a broad spectral range and under a wide range of incidence angles. The flexibility demonstrated here for our meta-hologram paves the road to a wide range of applications related to holographic images at arbitrary electromagnetic wave region.

We report a phase-modulated multicolor meta-hologram (MCMH) that is polarization-dependent and capable of producing images in three primary colors. The MCMH structure is made of aluminum nanorods that are arranged in a two-dimensional array of pixels with surface plasmon resonances in red, green, and blue. The aluminum nanorod array is patterned on a 30 nm thick SiO2 spacer layer sputtered on top of a 130 nm thick aluminum mirror. With proper design of the structure, we obtain resonances of narrow bandwidths to allow for implementation of the multicolor scheme. Taking into account of the wavelength dependence of the diffraction angle, we can project images to specific locations with predetermined size and order. With tuning of aluminum nanorod size, we demonstrate that the image color can be continuously varied across the visible spectrum.

All forms of light manipulation rely on light-matter interaction, the primary mechanism of which is the modulation of its electromagnetic fields by the localized electromagnetic fields of atoms. One of the important factors that influence the strength of interaction is the polarization of the electromagnetic field. The generation and manipulation of light polarization have been traditionally accomplished with bulky optical components such as waveplates, polarizers, and polarization beam splitters that are optically thick. The miniaturization of these devices is highly desirable for the development of a new class of compact, flat, and broadband optical components that can be integrated together on a single photonics chip. Here we demonstrate, for the first time, a reflective metasurface polarization generator (MPG) capable of producing light beams of any polarizations all from a linearly polarized light source with a single optically thin chip. Six polarization light beams are achieved simultaneously including four linear polarizations along different directions and two circular polarizations, all conveniently separated into different reflection angles. With the Pancharatnam-Berry phase-modulation method, the MPG sample was fabricated with aluminum as the plasmonic metal instead of the conventional gold or silver, which allowed for its broadband operation covering the entire visible spectrum. The versatility and compactness of the MPG capable of transforming any incident wave into light beams of arbitrary polarizations over a broad spectral range are an important step forward in achieving a complete set of flat optics for integrated photonics with far-reaching applications.

We propose all-dielectric metasurfaces that can be actively re-configured using the phase-change material Ge 2 Sb 2 Te 5 (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase-change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near-field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta-devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.

The research and development of optical metasurfaces has been primarily driven by the curiosity for novel optical phenomena that are unattainable from materials that exist in nature and by the desire for miniaturization of optical devices. Metasurfaces constructed of artificial patterns of subwavelength depth make it possible to achieve flat, ultrathin optical devices of high performance. A wide variety of fabrication techniques have been developed to explore their unconventional functionalities which in many ways have revolutionized the means with which we control and manipulate electromagnetic waves. The relevant research community could benefit from an overview on recent progress in the fabrication and applications of the metasurfaces. This review article is intended to serve that purpose by reviewing the state-of-the-art fabrication methods and surveying their cutting-edge applications.