Transformation optics

About: Transformation optics is a research topic. Over the lifetime, 2687 publications have been published within this topic receiving 102378 citations.

Nonlinear responses in optical metamaterials: theory and experiment

Abstract: We employed both theoretical calculations and experiments to study the nonlinear responses in optical metamaterials. The spectra of second-harmonic generations measured on a fishnet metamaterial are in quantitative agreements with calculations based on full-wave numerical simulations combined with field integrations, both exhibiting ~80 times enhancements at the magnetic resonance frequency. Our calculations explained several interesting features observed experimentally, and suggested an optimal metamaterial structure to yield the strongest nonlinear signals.

Three-Dimensional Anisotropic Zero-Index Lenses

Abstract: We propose, design, and experimentally demonstrate three-dimensional 3-D anisotropic zero-index lenses, which can improve the directivity of traditional antennas. We show that a 3-D anisotropic zero-index lens with eu → 0 is efficient to transverse magnetic (TM) modes and can decrease the beam width of the main lobe in the E-plane; while a 3-D anisotropic zero-index lens with μu → 0 is efficient to transverse electric (TE) modes and can reduce the beam width of the main lobe in the H-plane, in which u represents the propagating direction. If such two lenses are packed together, the directivity of both E- and H-planes is significantly improved. To verify this unique property, we design and fabricate four 3-D anisotropic zero-index lenses using metamaterials in the microwave frequency and perform the experiments in the anechoic chamber. Experimental results demonstrate that the beam widths of both E- and H-plane gain patterns are greatly reduced, which have good agreements to the full-wave simulations.

Design and demonstration of temporal cloaks with and without the time gap

Abstract: We introduce a Fourier analysis method to design temporal cloaks for hiding events in time domain. The cloaks are constructed with two linear time-invariant filters with different transfer functions, which can create a temporal gap and then closed it orderly, making any events occurring during the gap not detectable outside. We further reveal that even a no-gap temporal cloak can also hide events. All the analytical results are verified by fast Fourier transformation simulations.

Low-loss directional cloaks without superluminal velocity or magnetic response.

Abstract: The possibility of making an optically large (many wavelengths in diameter) object appear invisible has been a subject of many recent studies. Exact invisibility scenarios for large (relative to the wavelength) objects involve (meta)materials with superluminal phase velocity [refractive index (RI) less than unity] and/or magnetic response. We introduce a new approximation applicable to certain device geometries in the eikonal limit: piecewise-uniform scaling of the RI. This transformation preserves the ray trajectories but leads to a uniform phase delay. We show how to take advantage of phase delays to achieve a limited (directional and wavelength-dependent) form of invisibility that does not require loss-ridden (meta)materials with superluminal phase velocities.

Permeability Measurement of Metamaterials with Split-Ring-Resonators Using Free-Space Calibration-Independent Methods

Abstract: A calibration-independent microwave method is proposed for complex permeability extraction of metamaterial structures composed of periodic split-ring resonators. For the retrieval process, uncalibrated (raw) complex scattering parameter measurements of three measurement configurations in free-space are utilized. Two metric functions are derived for retrieval of complex permeability of homogeneous metamaterial slabs even when their lengths are unknown. The method is validated by retrieving the magnetic properties of some homogeneous SRR metamaterial slabs with a pre-assigned magnetic resonant frequency.