New Frontiers of Metamaterials: Design and Fabrication
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Metamaterials: Design and Fabrication Pratik Chaturvedi, Keng Hsu, Shu Zhang, and Nicholas Fang
Classes of Optical Metamaterials Recent Developments
Abstract Artificially engineered metamaterials have emerged with properties and functionalities previously unattainable in natural materials. The scientific breakthroughs made in this new class of electromagnetic materials are closely linked with progress in developing physics-driven design and novel parallel fabrication methods. For example, a smooth superlens has been demonstrated with 30-nm imaging resolution, or 1/12 of the corresponding wavelength, far below the diffraction limit. Similarly, a photoswitchable optical negative-index material has been printed, showing a remarkable tuning range of refractive index in the communication wavelength. New frontiers are being explored as intrinsic limitations challenge the scaling of microwave metamaterial designs to optical frequencies. These novel metamaterials promise an entire new generation of passive and active optical elements, such as paper-thin superlenses and modulators.
Introduction Over the past eight years, metamaterials have shown tremendous potential in many disciplines of science and technology. Their extraordinary properties and applications have placed them on many scientific-breakthrough lists, including Materials Today’s top 10 advances in material science over the past 50 years.1 The core concept of metamaterials is to scale up conventional continuum materials by using artificially designed and fabricated structural units. The units establish the required effective properties and functionalities in a material. For example, splitring resonators (SRRs) and wires can be units considered to be the constituent “atoms,” and combined units of the two can be considered “molecules” of the metamaterial. Such metamaterials can be tailored in shape and size, the lattice constant and interatomic interaction can be artificially tuned, and “defects” can be designed and placed at desired locations (Figure 1 inset). An engineered material with simultaneous negative electric permittivity (ε) and negative magnetic perme-
category of metamaterials. Figure 1 is an illustrative chart of progress made in scaling artificial magnetism, negative refraction, and other novel phenomena such as subdiffraction-limited imaging to optical frequencies. The relevant lattice sizes and fabrication techniques are also indicated. In general, scaling up in the frequency domain requires scaling down in the spatial domain. The intricate structures of these novel metamaterials and devices necessitate development of viable manufacturing and novel characterization technologies. The physics-driven design for desired properties and applications leads to new insights. In this review, we describe recent advances in new metamaterials design and fabrication techniques and discuss some new approaches for the future.
ability (µ) can exist without violating any physical law. These materials show promise for exotic electromagnetic phenomena. Although
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