Metasurface Holograms for Holographic Imaging

Abstract

that of the input beam) of amplitude holograms is very low, since much of the incident power is reflected or scattered. Fortunately, the interference intensity pattern can also be translated into phase variations to generate a phase hologram, [6] which is usually preferred because it has a higher diffraction efficiency and can substantially increase the brightness of the reconstructed images. The phase profile in traditional phase-only hologram is controlled by etching different depths into a transparent substrate. Two-level binary phase holograms have been widely used because of their ease of fabrication, but they have a theoretical diffraction efficiency of only 40.5% and suffer the twinimage issue. Multilevel-phase holograms promise high diffraction efficiency and avoid the twin-image problem, but require expensive and complicated grayscale, variable-dose, or multistep lithography processes. [7] Later on, computer-generated holography (CGH) [8,9] was proposed to numerically calculate the phase and amplitude distributions at the hologram plane, which are then encoded into spatial light modulators (SLMs) [10,11] or specific optical elements such as dielectric gratings [12] and dielectric optical antennas. [13] However, since conventional phase holograms rely on light propagation over distances much longer than the wavelength in order to accumulate enough phase variation for effective wavefront shaping, the optical elements for building the phase hologram will have large unitcell size and film thickness due to the limited refractive indices of natural materials. The smallest achievable hologram pixel size usually is as large as several micrometers (several times of the wavelength for visible light), which makes the hologram suffer the highorder diffraction, twin-image issue, and limited resolution. [14] Therefore, compact holograms with subwavelength features in both the thickness and the pixel size are highly demanded, which will not only improve the quality of holographic imaging reconstruction but also reduce the hologram footprint for nanophotonic integration.One significant breakthrough to bring new capabilities in confining light to subwavelength scale is plasmonics, [15,16] where the coupling between electromagnetic waves and collective electron oscillations at metal-dielectric interfaces is studied. Due to the strong interaction with the incident light, plasmonic metamaterials provide more freedom in controlling light at visible and near-infrared frequencies due to their arbitrarily designed permittivity and permeability. [17][18][19] However, the fabrication challenges at nanoscale and the absorption loss of bulk metamaterials at optical frequencies are usually As a revolutionary three-dimensional (3D) optical imaging technique, optical holography has attracted wide attention for its capability of recording both the amplitude and phase information of light scattered from objects. Holograms are designed to transform an incident wave into a desired arbitrary wavefront in the far field, which requires ultim...

Progresses in the practical metasurface for holography and lens

“…However, in the case of a metahologram, which indicates the holography produced by a metasurface, the problems regarding large pixel pitch vanish thanks to its subwavelength periodic length. This is because each meta-atom contains information of the phase or amplitude of light [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In this section, we discuss how light reacts with meta-atoms and review some of the representative metahologram studies together.…”

“…The prefix meta-means to transcend the following suffix, which implies that one can think of the optical metasurface as something that surpasses the normal surface. Metasurfaces are different from normal surfaces because light reacts abnormally at their boundary in an unexpected manner [1][2][3][4][5][6][7][8][9][10][11][12][13]. Practically, they are composed of artificial subwavelength structures that utilize lightmatter interactions for specific purposes.…”

Stimuli‐Responsive Naphthalene Diimide as Invisible Ink: A Rewritable Fluorescent Platform for Anti‐Counterfeiting

“…From practical point of view, it is highly desirable that stimuliresponsive materials can be employed to fabricate ordered solid-state thin films, rather than powder or solutions that ultimately lead to the development of smart sensors. [10] During past decades, a wide variety of anti-counterfeiting technologies, including plasmonic labels, [11,12] radio frequency identification (RFID), [13,14] holography, [15][16][17] bar/QR codes, [18][19][20] have been developed to combat the unauthorized counterfeiting. However, most of these anti-counterfeiting technologies suffer from disadvantages such as they can be easily replicate/ cracked.…”

Reversible Image Contrast Manipulation with Thermally Tunable Dielectric Metasurfaces

“…Today, increasing the resolution of miniaturized displays is an important technological challenge for small gadgets. Currently, most imaging systems are based on recording or reproducing the spatial distribution of intensity of light at the detector or screen, where higher resolutions can be achieved by reducing the pixel sizes of displays. The further need for improving the resolution in images and displays, together with higher compactness, has motivated scientists to exploit novel alternatives, such as metasurfaces, allowing substantial improvements to the current technologies.…”