We explore the application of a single-step nanoimprinting technique using water-soluble Polyvinyl Alcohol (PVA) to fabricate tunable metasurfaces. These metasurfaces display multiplexed structural color and meta holography. The structured PVA achieved below 100 nm, accompanied by aspect ratios approaching 10. Under increasing relative humidity conditions, the PVA metaatom can expand by approximately 35.5%, allowing precise control of wavefronts. Here, we demonstrate the optical security metasurfaces for multiplexed encryption, capable of revealing, concealing, or eliminating information based on changes in relative humidity, both irreversibly and reversibly.
In this presentation, I will present the findings of a compact depth sensing system for LiDAR that is based on a metasurface. I will explain the underlying design concept of this metasurface, which utilizes structured light to expand the range of view angles for point cloud generation. Two separate cameras, capture the generated point cloud, and depth information is calculated using the stereo-matching method. Additionally, I will propose electrically adjustable metalens that can be easily incorporated into AR/VR systems and electronic systems. These metaphotonic devices offer potential applications in diverse fields such as mobile sensors, biometric security systems, autonomous driving, metaverse, and driver assistance.
Here, we demonstrated vivid structural coloration and polarization-sensitive color metasurfaces using bandgap-engineered a-Si:H, whose extinction coefficient is near zero at the entire visible spectrum. The scattering response of high-index nanostructures is numerically analyzed with multipole expansion, and we vitrify that the low-optical losses of bandgap-engineered a-Si:H significantly improve color coverage of metasurface, achieving comparable coverage with the Adobe RGB gamut. Also, we demonstrated the application of optical encryption with polarization-sensitive structural coloration, achieving near-zero reflection when optical information is encrypted. We believe that structural coloration with low-loss a-Si:H will be widely used with its advantageous benefits compared to chemical pigments.
In this presentation, I will introduce the result of a metasurface-based compact depth sensing system that can be applied to LiDAR. I will explain the design principle of this structured light metasurface which can spread the point cloud with a large field of view angles. This spread point cloud is captured by two distinct cameras, and depth information is computed by the stereo-matching method. And I will suggest electrically tunable metalens which can be easily integrated with not only AR/VR systems but also electronic systems. These metaphotonic devices have the potential to be applied to various fields such as mobile sensors, biometric security systems, autonomous driving, metaverse, and driver assistance.
Here, we developed two types of tunable PVA metaphotonic platforms, which are 1) PVA metasurface that simultaneously displays a far-field holographic image and reflective structural coloration under coherent and incoherent light, respectively, and 2) humidity-responsive structural coloration that enables to generate RGB color in a single pixel. Three types of PVA metasurfaces have been designed: 1) revisable holography/structural coloration with pure PVA structures, 2) relative-humidity sensitive optical decryption with PVA-hydrogenated amorphous silicon structures, and 3) revisable holography/structural coloration with Pt-coated PVA structures. Considering that the aforementioned PVA structures have been fabricated with low-coat single-step nanoimprinting methods, they will be widely applied for various tunable optical components by significantly reducing their production costs.
The article comments on a recently proposed innovative process that uses direct laser writing to achieve vivid, fine-tunable color at centimeter scale by leveraging the fabrication speed and the spatial resolution of pixelated F-P cavity structures.
The explosion in the amount of information that is being processed is prompting the need for new computing systems beyond existing electronic computers. Photonic computing is emerging as an attractive alternative due to performing calculations at the speed of light, the change for massive parallelism, and also extremely low energy consumption. We review the physical implementation of basic optical calculations, such as differentiation and integration, using metamaterials, and introduce the realization of all-optical artificial neural networks. We start with concise introductions of the mathematical principles behind such optical computation methods and present the advantages, current problems that need to be overcome, and the potential future directions in the field. We expect that our review will be useful for both novice and experienced researchers in the field of all-optical computing platforms using metamaterials.
Tunable optical devices powered by metasurfaces provide a new path for functional planar optics. Lenses with tunable focal lengths could play a key role in various fields with applications in imaging, displays, and augmented and virtual reality devices. Here, we present a method for computationally designing an RGB-achromatic bifocal metalens and experimentally realize it through a scalable one-step nanoimprinting technique using a TiO2 nanoparticle embedded resin combined with an electrically tunable liquid crystal cell.
Hydrogels such as PVA have yet to be fully exploited in metasurfaces due to their fairly low refractive index and fabrication feasibility. Here, we demonstrate one-step nanoimprinted PVA metasurfaces with resolutions reaching sub-100 nm, and aspect ratios approaching 10. We then demonstrate three distinct relative humidity dependent dual-mode optical security applications using the PVA metasurfaces. Through the swelling of the PVA when exposed to high humidity conditions and careful design of meta-atoms with different dimensions orientated at specific angles, multiplexed color prints and holograms can be selectively uncovered or destroyed.
Metasurfaces have attracted great attention due to their ability to manipulate the phase, amplitude, and polarization of light in a compact form. Tunable metasurfaces have been investigated recently through the integration with mechanically moving components and electrically tunable elements. Two interesting applications, in particular, are to vary the focal point of metalenses and to switch between holographic images. We present the recent progress on tunable metasurfaces focused on metalenses and metaholograms, including the basic working principles, advantages, and disadvantages of each working mechanism. We classify the tunable stimuli based on the light source and electrical bias, as well as others such as thermal and mechanical modulation. We conclude by summarizing the recent progress of metalenses and metaholograms, and providing our perspectives for the further development of tunable metasurfaces.
Mie scatterer resonantly scatters when wavelength of incident light is similar to the size of the scatterer. The scattering of Mie resonator can be analyzed using multipole decomposition; silicon nanostructure has multipole scattering modes in visible regime. When the Mie scatterers are arrayed, the scattering response can be greatly amplified. To properly design array of Mie scatterer, i.e. metasurface, the hybridization of radiation mode of scatterer and lattice effect, i.e. guided-mode resonance (GMR), must be understood. Herein, we would like to provide the scattering mechanisms behind the hybridization between individual scattering mode and lattice effect, and use them to realize gradient structural coloration by silicon-based metasurface. We believe that a solid understanding of the coupling between individual Mie resonators and the lattice resonances can be a strong basis for designing planar spectral filters.
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