Tunable optical negative-index metamaterials employing anisotropic liquid crystals
TL;DR: In this paper, a full-wave analysis technique based on the finite element-boundary integral method is developed and used to rigorously treat the scattering from periodically structured metamaterials incorporating anisotropic liquid crystals (LCs) and dispersive materials.
Abstract: A full-wave analysis technique based on the finite element-boundary integral method is developed and used to rigorously treat the scattering from periodically structured metamaterials incorporating anisotropic liquid crystals (LCs) and dispersive materials. Reconfiguration of the negative-index metamaterials is achieved by controlling the magnetic resonance via tuning permittivity of the embedded anisotropic LCs. Numerical results show that the refractive index of the metamaterials can be reconfigured by tuning the director orientation of anisotropic LCs or by using temperature-dependent LCs. The design configurations and their characteristics in the near- and the mid-infrared ranges are presented.
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TL;DR: This Review summarizes research on photonic, terahertz and microwave electromagnetic metamaterials and metadevices with functionalities attained through the exploitation of phase-change media, semiconductors, graphene, carbon nanotubes and liquid crystals.
Abstract: Metamaterials, artificial electromagnetic media that are structured on the subwavelength scale, were initially suggested for the negative-index 'superlens'. Later metamaterials became a paradigm for engineering electromagnetic space and controlling propagation of waves: the field of transformation optics was born. The research agenda is now shifting towards achieving tunable, switchable, nonlinear and sensing functionalities. It is therefore timely to discuss the emerging field of metadevices where we define the devices as having unique and useful functionalities that are realized by structuring of functional matter on the subwavelength scale. In this Review we summarize research on photonic, terahertz and microwave electromagnetic metamaterials and metadevices with functionalities attained through the exploitation of phase-change media, semiconductors, graphene, carbon nanotubes and liquid crystals. The Review also encompasses microelectromechanical metadevices, metadevices engaging the nonlinear and quantum response of superconductors, electrostatic and optomechanical forces and nonlinear metadevices incorporating lumped nonlinear components.
1,741 citations
TL;DR: Non-volatile, bidirectional, all-optical switching in a phase-change metamaterial delivers high-contrast transmission and reflection modulation at near- to mid-infrared wavelengths in device structures down to ≈1/27 of a wavelength thick.
Abstract: Today's telecommunications networks are still largely optically opaque - consisting of electronic nodes connected by point-to-point optical links, relying on a series of optical-electrical conversions. Moving to all-optical switching will allow increased bit rates and low latency movement of data, providing greater routing agility, reducing energy requirements and simplifying network structures. This promise, and indeed the fact that the fundamental capacity limits of existing infrastructure are being reached, has sparked renewed interest in the extension of telecommunications bands to longer infrared wavelengths (where lower intrinsic losses in fibre media are possible) and intense efforts to develop techniques based on space-division multiplexing (in which many distinguishable data paths are established through the same fibre strand using either multiple cores or a multimode core) to substantially increase capacity. Future network architectures will require a new generation of highly integrated devices capable of functions such as all-optical switching and mode (de)multiplexing. We report here on the proof-of-principle demonstration of a non-volatile all-optical switch that combines the chalcogenide glass phase-change medium widely used in rewritable optical disks with nanostructured plasmonic metamaterials to yield a high-contrast, large area, reversible switching solution that may be optimised to function across a broad infrared band.
419 citations
TL;DR: In this paper, a review of the optical nonlinearities of liquid crystals is presented, and a thorough review of a wide range of nonlinear optical processes and phenomena enabled by these unique properties.
324 citations
TL;DR: The terahertz metamaterials are artificial composites that acquire their electromagnetic properties from embedded subwavelength metallic structures and can be engineered to take on arbitrary values, including those not appearing in nature.
Abstract: Metamaterials are artificial composites that acquire their electromagnetic properties from embedded subwavelength metallic structures. In theory, the effective electromagnetic properties of metamaterials at any frequency can be engineered to take on arbitrary values, including those not appearing in nature. As a result, this new class of materials can dramatically add a degree of freedom to the control of electromagnetic waves. The emergence of metamaterials fortunately coincides with the intense emerging interest in terahertz radiation (T-rays), for which efficient forms of electromagnetic manipulation are sought. Considering the scarcity of naturally existing materials that can control terahertz, metamaterials become ideal substitutes that promise advances in terahertz research. Ultimately, terahertz metamaterials will lead to scientific and technological advantages in a number of areas. This article covers the principles of metamaterials and reviews the latest trends in terahertz metamaterial research from the fabrication and characterization to the implementation.
308 citations
TL;DR: In this paper, the authors review the recent progress in tunable and reconfigurable metasurfaces and metadevices through different active materials deployed together with the different control mechanisms including electrical, thermal, optical, mechanical, and magnetic, and provide the perspective for their future development for applications.
Abstract: Metasurfaces, two-dimensional equivalents of metamaterials, are engineered surfaces consisting of deep subwavelength features that have full control of the electromagnetic waves. Metasurfaces are not only being applied to the current devices throughout the electromagnetic spectrum from microwave to optics but also inspiring many new thrilling applications such as programmable on-demand optics and photonics in future. In order to overcome the limits imposed by passive metasurfaces, extensive researches have been put on utilizing different materials and mechanisms to design active metasurfaces. In this paper, we review the recent progress in tunable and reconfigurable metasurfaces and metadevices through the different active materials deployed together with the different control mechanisms including electrical, thermal, optical, mechanical, and magnetic, and provide the perspective for their future development for applications.
286 citations
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TL;DR: In this paper, the optical constants for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV.
Abstract: The optical constants $n$ and $k$ were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 \AA{}. Three optical measurements were inverted to obtain the film thickness $d$ as well as $n$ and $k$. The estimated error in $d$ was \ifmmode\pm\else\textpm\fi{} 2 \AA{}, and that in $n$, $k$ was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 \AA{} were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.
17,509 citations
TL;DR: In this article, the authors analyzed the reflection and transmission coefficients calculated from transfer matrix simulations on finite lengths of electromagnetic metamaterials, to determine the effective permittivity and permeability.
Abstract: We analyze the reflection and transmission coefficients calculated from transfer matrix simulations on finite lengths of electromagnetic metamaterials, to determine the effective permittivity ~«! and permeability ~m! .W e perform this analysis on structures composed of periodic arrangements of wires, split ring resonators ~SRRs!, and both wires and SRRs. We find the recovered frequency-dependent« and m are entirely consistent with analytic expressions predicted by effective medium arguments. Of particular relevance are that a wire medium exhibits a frequency region in which the real part of « is negative, and SRRs produce a frequency region in which the real part of m is negative. In the combination structure, at frequencies where both the recovered real parts of « and m are simultaneously negative, the real part of the index of refraction is also found to be unambiguously negative.
2,689 citations
TL;DR: In this article, the authors used the extended Cauchy equations to link the visible refractive indices to infrared, where the refractive index measurements are more difficult, and extrapolated results almost strike through the measured data.
Abstract: The refractive indices of E7 liquid-crystal mixture were measured at six visible and two infrared (λ=1.55 and 10.6μm) wavelengths at different temperatures, using Abbe and wedged cell refractometer methods, respectively. The experimental data of the visible wavelengths fit the extended Cauchy equations well. Using the extended Cauchy equations, we can extrapolate the refractive indices of E7 to IR. The extrapolated results almost strike through the measured data. Thus, the extended Cauchy equations can be used to link the visible refractive indices to infrared, where the refractive index measurements are more difficult.
332 citations