Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Since its discovery, the asymmetric Fano resonance has been a characteristic feature of interacting quantum systems. The shape of this resonance is distinctively different from that of conventional symmetric resonance curves. Recently, the Fano resonance has been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. The steep dispersion of the Fano resonance profile promises applications in sensors, lasing, switching, and nonlinear and slow-light devices.

The Fano resonance in plasmonic nanostructures and metamaterials

We present an introduction to surface-enhanced Raman scattering (SERS) which reviews the basic experimental facts and the essential features of the mechanisms which have been proposed to account for the observations. We then review very recent fundamental developments which include: SERS from single particles and single molecules; SERS from fractal clusters and surfaces; and new insights into the chemical enhancement mechanism of SERS.

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Surface-enhanced Raman scattering

Plasmons in strongly coupled metallic nanostructures.

Magic stairs, a staircase loop, is a kind of optical illusion. Such cognitive paradox is an inherent defect when two-dimensional (2D) images represent high-dimensional information. For this demand, we demonstrate an intelligent depth-sensing system prototype applicable for diverse scenes, a switchable stereo vision system that adopts a 60 × 60 achromatic meta-lens array to measure depth over a 30-cm range with the support of deep learning. This system combines a light field camera and a structured light system to adapt to all light levels. The design, application, and experimental verification of the intelligent depth-sensing meta-device are reported in this talk. 

A meta-device for magic stairs (Conference Presentation)

Using plasmonic nanostructures to manipulate the scattered light from the SPP waves will be experimental demonstrated. The surface plasmon waves can be scattered and modified by various plasmonic structures composed of gold nanobumps. The height and intensity profile of the focusing patterns are precisely controlled in three-dimensional space by the curved arrangement of nanobumps. The modulation of the projecting height of the focusing pattern is reached as high as 10 micron-meters. The intensity profile of focusing pattern can be approached to a diffraction-limited spot. The projecting image constructed by focusing spot from designing nanobumps arrangement is achieved in three-dimensional space.

Three dimensional light manipulation for full-color nano-projector

본 발명은 유전체 층 및 나노막대 어레이를 포함하는 광학 구성품을 제공하고; 상기 나노막대 어레이는 상기 유전체 층의 표면 상에 형성되고 또한 측면 방향 및 수직 방향을 따라 연장된다. 상기 나노막대 어레이는 상기 유전체 층을 따라 연장되는 복수의 나노막대들을 포함한다. 상기 나노막대들은 서로의 사이에 간격을 가지고, 또한 각은 2 개의 인접하는 나노막대들에 의해 정의된다. 범프는 상기 나노막대의 2 개의 끝단들 각각에 형성된다.

광대역 메타-광학 장치

In this paper, a nano-liquid/liquid waveguide coupling based on evanescent tunneling effect is demonstrated. For the first time, the feature size in the fluidic beyond the diffraction limit with changes as small as 1 nm can be imaged in the microchannel. The evanescent coupling length can be tuned by the flow rates and the fluids materials flexible than semiconductor ones. This implies that single molecule imaging can be achieved with the developed near field interaction technique.

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Nano-liquid/liquid waveguide coupling by evanescent tunneling effect for biomolecule imaging applications

Toroidal dipole is created by currents flowing on a surface of a doughnut-shaped structure along its meridians first considered by Zel'dovich in 1957 [1]. Toroidal metamaterials were first theoretically proposed in 2007 [2]. In 2010, the toroidal metamaterials consisted by four three-dimensional resonant split rings show toroidal response in microwave region [3]. In this paper, we study the optical responses by integrating four U-shaped split-ring resonators (SRRs) together. The resonances of the four U-shaped SRRs array with magnetic field of incident light passing through the resonant rings was numerically investigated by using commercial software COMSOL 3.5a based on finite-element method (FEM). The permittivity of gold was described by the Lorentz-Drude model [4]. The size of a single U-shaped SRR is 250nm (arms) x 300nm (bottom) and 50nm line width wire loop. Simulation results shows toroidal and magnetic dipole resonance at free space wavelength 2520nm and 2620nm respectively. Incident light induced magnetic dipoles point in the same direction produced magnetic resonance. In contrast, four magnetic dipoles form a head-to-tail configuration which concentrates toroidal resonance.

Din Ping Tsai

Papers

A meta-device for magic stairs (Conference Presentation)

Three dimensional light manipulation for full-color nano-projector

광대역 메타-광학 장치

Nano-liquid/liquid waveguide coupling by evanescent tunneling effect for biomolecule imaging applications

Plasmonic toroidal metamaterials at optical frequencies