We study perspectives of nanowire metamaterials for negative-refraction waveguides, highperformance polarizers, and polarization-sensitive biosensors. We demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of our approach via three-dimensional numerical simulations. Finally, we illustrate the developed approach on the examples of nanowire-based high energy-density waveguides and non-magnetic negative index imaging systems with far-field resolution of one-sixth of vacuum wavelength.The anisotropy of effective dielectric permittivity is widely used in optical, infrared (IR), THz and GHz sensing, spectroscopy, and microscopy 1,2,3,4 . Strongly anisotropic optical materials can be utilized in nonmagnetic, non-resonant optical media with negative index of refraction, and have the potential to perform subdiffraction imaging and to compress the radiation to subwavelength areas 2,5,6,7 . The performance of these polarization-sensitive applications can be related to the relative difference of the dielectric constant along the different directions. In the majority of natural anisotropic crystals this parameter is below 30% 8 . While it may be sufficient for some applications, a number of exciting phenomena ranging from high-performance polarization control 4 to subwavelength light guiding 2,5,6 to planar imaging 7 require different components of a permittivity tensor to be of different signs.In this Letter we study the perspectives of using nanowire composites as meta-materials with extreme optical anisotropy. We demonstrate that even 10% stretching/compression of the nanowire structures may dramatically affect the electromagnetic properties of these systems and change the sign of components of the permittivity tensor. We present an analytical description of wave propagation in anisotropic nanowire composites -Generalized Maxwell-Garnett approach (GMG), and verify our technique via three-dimensional (3D) numerical simulations. Finally, we illustrate our approach on the examples of several nanowire-based systems for light compression below the diffraction limit and negative refractionimaging with far-field resolution of λ 0 /6 (with λ 0 being free-space wavelength).The use of metallic wire mesh as anisotropic lowfrequency plasma has been proposed in 9 and experimentally realized for normal light incidence in 4,10 . However, the applicability of these nanowire-based materials for any non-trivial geometry involving oblique light incidence or wave-guiding is still considered to be questionable due to strong nonlocal interactions 11 , that may potentially result in positive components of the permittivity tensor. Furthermore, the majority of existing effective-medium theories (EMTs) 11,12,13,14 are limited to the optical response of nanowires that are isotropically distributed in the host material. The predicted respo...
We develop an approach to use nanostructured plasmonic materials as a non-magnetic negative-refractive index system at optical and near-infrared frequencies. In contrast to conventional negative refraction materials, our design does not require periodicity and thus is highly tolerant to fabrication defects. Moreover, since the proposed materials are intrinsically non-magnetic, their performance is not limited to proximity of a resonance so that the resulting structure has relatively low loss. We develop the analytical description of the relevant electromagnetic phenomena and justify our analytic results via numerical solutions of Maxwell equations.
Curriculum developers are interested in how to leverage various instructional tools -like whiteboards, Mathematica notebooks, and tangible models -to maximize learning. Instructional tools mediate student learning and different tools support learning differently. We are interested in understanding how the features of instructional tools influence student engagement during classroom activities and how to design activities to match tools with instructional goals. In this paper, we explore these questions by examining an instructional activity designed to help advanced undergraduate physics students understand and visualize the electrostatic potential. During the activity, students use three different tools: a whiteboard, a pre-programmed Mathematica notebook, and a 3D surface model of the electric potential. We discuss how the tools may be used to address the the instructional goals of the activity. We illustrate this discussion with examples from classroom video. I. RESEARCH QUESTIONS & METHODSedited by Ding, Traxler, and Cao; Peer-reviewed,
We present a detailed study of optical properties of recently introduced nonmagnetic, nonperiodic planar materials with negative refractive index and demonstrate the possibility of achieving far-field resolution below the free-space diffraction limit in these systems.The optical materials where the phase velocity of propagating waves is opposite to the group velocity, also known as left-handed or negative refraction index materials (NIMs) have a potential to revolutionize science and applications related to nano-and micro-scale photonics [1,2]. Several fundamentally different approaches are being investigated for future optical NIM devices. The original NIM design [3], requiring the materials with simultaneously negative dielectric permittivity and magnetic permeability, requires use of resonance to achieve non-trivial magnetic response. The optical performance of these resonant systems suffers from strong resonant losses [3], limiting the practical size of ε−µ-structures to a fraction of a free-space wavelength [4]. Another widely-used NIM design relies on second-or higher-bands of photonic crystals to achieve the opposite directions of phase and group velocities [5]. However, the realization of optical photonic crystals requires extreme precision in fabrication of nanostructured composites, and the performance of these systems is strongly affected by microstructure disorder, unavoidable at fabrication step.Another approach to build a material with negative refractive index has been recently introduced in [6]. In contrast to ε−µ-or photonic crystal-based systems, described above, our design does not require magnetism or periodicity to achieve left-handed response. Instead, the negative refraction is realized in planar waveguide geometry with strongly anisotropic dielectric core (see Fig. 1). The electromagnetic wave propagating in the strongly anisotropic waveguide can be represented as a linear combination of the waveguide modes. Each such mode is defined by its polarization and a mode-specific dispersion relation. Transverse-magnetic (TM) modes are of interest for negative-refraction planar waveguides. The dispersion relation for a TM mode can be written in the free-space-like form:where k y and k z are the propagating components of the mode wavevector, ε is the dielectric permittivity along the optical axis of core materials, ω is the frequency, c is the speed of light in the vacuum, and the mode-specific parameter ν is controlled by a mode structure and the dielectric permittivity of the core in the direction perpendicular to its optical axis [6]. The effective refractive index of the mode is determined by εν ± = n . Similar to the free-space NIMs [6], the positive sign is selected in the case of simultaneously positive propagating constants, while simultaneously negative ε and ν represent n<0 case [6,7]. Fig. 1 Schematics of the anisotropy-based NIM system [7].Here we present a detailed study of the imaging properties of planar waveguides with strongly anisotropic dielectric core. To solve the Maxwell equat...
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