The remarkable potential of metasurface holography promises revolutionary advancements for imaging, chip-integrated augmented/virtual reality (AR/VR) technology, and flat optical displays. The choice of constituent element geometry constrains many potential applications purveyed through polarization-independent optical response. The limited capabilities and degree of freedoms in commonly used meta-atoms restrict the design flexibility to break the conventional trade-off between polarization-insensitivity and bandwidth. Here, we propose a geometric phase-enabled novel design strategy to break this conventional trade-off. The proposed strategy ensures the realization of broad-band polarization-insensitivity through a simplified design procedure. An identical output wavefront manipulation is achieved by adjusting the phase delay freedom of geometric phase engineering under different incident polarization conditions. For proof of concept, a metahologram device is fabricated by an optimized complementary metal-oxide-semiconductor (CMOS)-compatible material of hydrogenated amorphous silicon (a-Si:H). This metahologram device reproduces the required hologram with high image fidelity and efficiency under different polarization scenarios of white light incidence. Due to the simple design strategy, low computational cost, and easy fabrication, the proposed technique can be an excellent candidate for realizing polarization-insensitive metahologram devices.

Broad-Band Polarization-Insensitive Metasurface Holography with a Single-Phase Map.

Secure packaging and transportation of light-sensitive chemical and biomedical test tubes are crucial for environmental protection and public health. Benefiting from the compact form factor and high efficiency of optical metasurfaces, we propose a broad-band polarization-insensitive flexible metasurface for the security of sensitive packages in the transport industry. We employ both the propagation and the geometric phase of novel TiO2 resin-based anisotropic nanoresonators to demonstrate a flexible and broad-band polarization-insensitive metasurface in the visible domain. The ultraviolet nanoimprint lithographic technique (UV-NIL) is used to fabricate high-index TiO2 nanoparticle-embedded-resin (nano-PER) structures that are patterned on a flexible substrate. This novel approach provides swift single-step fabrication without secondary fabrication steps such as deposition and etching. Moreover, replicating and transforming patterns over flexible substrates make the proposed technique highly suitable for large-throughput commercial manufacturing. As the proposed metahologram manifests high transmission efficiency in the visible domain, such flexible metaholographic platforms could find several exciting applications in bendable/curved displays, wearable devices, and holographic labeling for interactive displays.

Single-Step Fabricable Flexible Metadisplays for Sensitive Chemical/Biomedical Packaging Security and Beyond.

Futuristic holographic displays will essentially require broadband chiro‐optical effects for medical imaging, virtual reality, smart security, and optical encryption. However, conventional metasurfaces cannot provide such on‐chip realization of broadband chiro‐optical effects. Moreover, the simultaneous conversion of amplitude, polarization, and phase (APP) at optical wavelengths to introduce giant chirality has not been realized yet. In this paper, a planar all‐dielectric metasurface is proposed incorporating extra degrees of freedom to comprehend the conversion of APP with broadband chiro‐optical effects in terms of giant asymmetric transmission with maximum efficiency of ≈77% at the wavelength of 567 nm. The underlying mechanism behind induced chiro‐optical effects is also investigated using higher‐order multipolar dielectric resonances. Moreover, experimental validation is performed using the reproduced polarization‐encrypted meta‐holograms at broadband visible wavelengths. This work expands the scope of meta‐nanophotonics with potential applications in bioimaging and polarization‐encrypted displays for healthcare and smart security applications.

Broadband Chiro‐Optical Effects for Futuristic Meta‐Holographic Displays

Multi‐functional metasurfaces have attracted great attention due to the significant possibilities to realize highly integrated and ultra‐compact meta‐devices. Merging nano‐printing and holographic information multiplexing is one of the effective ways to achieve multi‐functionality, and such a merger can increase the information encoding capacity. However, the current approaches rely on stacking layers and interleaving, where multiple resonators effectively combine different functionalities on the cost of efficiency, design complexity, and challenging fabrication. To address such challenges, a single meta‐nanoresonator‐based tri‐functional metasurface is proposed by combining the geometric phase‐based spin‐decoupling and Malus's law intensity modulation. The proposed strategy effectively improves information capacity owing to the orientation degeneracy of spin‐decoupling rather than layer stacking or super‐cell designs. To validate the proposed strategy, a metasurface demonstrating two helicity‐dependent holographic outputs is presented in far‐field, whereas a continuous nano‐printing image is in near‐field. It is also employed on CMOS‐compatible and cost‐effective hydrogen amorphous silicon providing transparent responses for the whole visible band. As a result, the proposed metasurface has high transmission efficiency in the visible regime and verifies the design strategy without adding extra complexities to conventional nano‐pillar geometry. Therefore, the proposed metasurface opens new avenues in multi‐functional meta‐devices design and has promising applications in anti‐counterfeiting, optical storage and displays.

Single‐Cell‐Driven Tri‐Channel Encryption Meta‐Displays

Metasurface holography, the reconstruction of holographic images by modulating the spatial amplitude and phase of light using metasurfaces, has emerged as a next-generation display technology. However, conventional fabrication techniques used to realize metaholograms are limited by their small patterning areas, high manufacturing costs, and low throughput, which hinder their practical use. Herein, we demonstrate a high efficiency hologram using a one-step nanomanufacturing method with a titanium dioxide nanoparticle-embedded-resin, allowing for high-throughput and low-cost fabrication. At a single wavelength, a record high 96.4% theoretical efficiency is demonstrated with an experimentally measured conversion efficiency of 90.6% and zero-order diffraction of 7.3% producing an ultrahigh-efficiency, twin-image free hologram, that can even be directly observed under ambient light conditions. Moreover, we design a broadband meta-atom with an average efficiency of 76.0% and experimentally demonstrate a metahologram with an average efficiency of 62.4% at visible wavelengths from 450 to 650 nm. 

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Metasurface Holography Reaching the Highest Efficiency Limit in the Visible via One‐Step Nanoparticle‐Embedded‐Resin Printing

Abstract Taking inspiration from beautiful colors in nature, structural colors produced from nanostructured metasurfaces have shown great promise as a platform for bright, highly saturated, and high-resolution colors. Both plasmonic and dielectric materials have been employed to produce static colors that fulfil the required criteria for high-performance color printing, however, for practical applications in dynamic situations, a form of tunability is desirable. Combinations of the additive color palette of red, green, and blue enable the expression of further colors beyond the three primary colors, while the simultaneous intensity modulation allows access to the full color gamut. Here, we demonstrate an electrically tunable metasurface that can represent saturated red, green, and blue pixels that can be dynamically and continuously controlled between on and off states using liquid crystals. We use this to experimentally realize ultrahigh-resolution color printing, active multicolor cryptographic applications, and tunable pixels toward high-performance full-color reflective displays. 

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Liquid crystal-powered Mie resonators for electrically tunable photorealistic color gradients and dark blacks

/pdf/liquid-crystal-powered-mie-resonators-for-electrically-10rkwe6k.pdf

Using a single substrate, we demonstrate a simple two-dimensional (2-D) phase grating cell with an octothorp electrode. Owing to the large spatial phase difference in any direction, the proposed grating cell has a high haze value in the opaque state (76.7%); Moreover, it has the advantages of a one-dimensional (1-D) phase grating cell, such as high fabricability, fast response time, and low operating voltage. Furthermore, the proposed grating cell has a faster response time than the 2-D grating cell (comparable to a 1-D grating cell). All the electro-optic parameters have been calculated using a commercial modeling tool. Consequently, we expect our proposed grating cell to find applications in virtual reality (VR)/augmented reality (AR) systems or window displays with fast response times. 

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A simulation of diffractive liquid crystal smart window for privacy application

We demonstrate using a diffractive smart window with homogeneous-aligned (HA) liquid crystals (LCs) owing to the large spatial phase difference in all directions in the opaque state. The proposed grating cell had a high haze value (88.57%), which was 1.16 times higher than the previously reported vertically aligned (VA) grating cells because the proposed grating cell had a higher twist angle than what the VA grating cell had. Our proposed HA grating cell can be used in various smart window applications. 

https://www.tandfonline.com/doi/pdf/10.1080/15980316.2023.2203365?needAccess=true&role=button

Diffractive liquid crystal device for privacy window with a low operating voltage

We studied the effectiveness of the conductor-backed design on implementing the liquid-crystal phase shifter (LCPS) over the floating-electrode-free (FE-free) design at 28 GHz. We compared and analyzed the LC driving characteristics under the same cell gap thickness (= 50 μm), characteristic impedance (= 50 Ω), and the physical length. This work can be thought of as a comparison between the in-plane-switching mode and quasi-electronically controlled birefringence mode of the liquid-crystal display. We verified that the conductor-backed design is adequate for designing the LCPS in terms of the driving voltage, response time, and tuning range. These analyzed results will help design more efficient passive phase shifter using LCs.

Comparative Analysis of Liquid-Crystal Driving between the Grounded-Coplanar Waveguide and the Floating-Electrode-Free Coplanar Waveguide in Liquid-Crystal Phase Shifters

W. Kim

Papers

Liquid crystal-powered Mie resonators for electrically tunable photorealistic color gradients and dark blacks

Liquid crystal-powered Mie resonators for electrically tunable photorealistic color gradients and dark blacks

A simulation of diffractive liquid crystal smart window for privacy application

Diffractive liquid crystal device for privacy window with a low operating voltage

Comparative Analysis of Liquid-Crystal Driving between the Grounded-Coplanar Waveguide and the Floating-Electrode-Free Coplanar Waveguide in Liquid-Crystal Phase Shifters