Transformation optics

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

Transformation optics approach to singular metasurfaces

Abstract: Metasurfaces can be formed by nanostructuring a metal surface at the subwavelength scale and are used for the control of radiation in varied ways. Extremely sharp points on the surface give rise to singular metasurfaces, which efficiently convert incident radiation into surface plasmons. These plasmons slowly approach the singular points, which act as energy sinks, thus leading to increased absorption for a wide frequency band. This continuous spectrum is the main characteristic of singular metasurfaces: while being periodic they are actually equivalent to a bulk structure in one extra dimension and for that reason they present a continuous rather than discrete set of modes.

Zero-order-free meta-holograms in a broadband visible range

Abstract: The unwanted zero-order light accompanied by the birth of diffractive optical elements and caused mainly by fabrication errors and wavelength variations is a key factor that deteriorates the performance of diffraction-related optical devices such as holograms, gratings, beam shapers, beam splitters, optical diffusers, and diffractive microlenses. Here, inspired by the unique characteristic of nano-polarizer-based metasurfaces for both positive and negative amplitude modulation of incident light, we propose a general design paradigm to eliminate zero-order diffraction without burdening the metasurface design and fabrication. The experimentally demonstrated meta-hologram, which projects a holographic image with a wide angle of 70°×70° in the far field, presents a very low zero-order intensity (only 0.7% of the total energy of the reconstructed image). More importantly, the zero-order-free meta-hologram has a large tolerance limit for wavelength variations (under a broadband illumination from 520 to 660 nm), which brings important technical advances. The strategy proposed could significantly relieve the fabrication difficulty of metasurfaces and be viable for various diffractive-optics-related applications including holography, laser beam shaping, optical data storage, vortex beam generation, and so on.

Colloidal superlattices for unnaturally high-index metamaterials at broadband optical frequencies.

Abstract: The recent advance in the assembly of metallic nanoparticles (NPs) has enabled sophisticated engineering of unprecedented light-matter interaction at the optical domain. In this work, I expand the design flexibility of NP optical metamaterial to push the upper limit of accessible refractive index to the unnaturally high regime. The precise control over the geometrical parameters of NP superlattice monolayer conferred the dramatic increase in electric resonance and related effective permittivity far beyond the naturally accessible regime. Simultaneously, effective permeability change, another key factor to achieving high refractive index, was effectively suppressed by reducing the thickness of NPs. By establishing this design rule, I have achieved unnaturally high refractive index (15.7 at the electric resonance and 7.3 at the quasi-static limit) at broadband optical frequencies (100 THz ~300 THz). I also combined this NP metamaterial with graphene to electrically control the high refractive index over the broad optical frequencies.

Perfect imaging with geodesic waveguides

Abstract: Transformation optics is used to prove that a spherical waveguide filled with an isotropic material with radial refractive index n=1/r has radially polarized modes (i.e. the electric field is only radial) with the same perfect focusing properties as the Maxwell fish-eye (MFE) lens. An approximate version of that device, comprising a thin waveguide with a homogeneous core, paves the way to experimentally attaining perfect imaging in the MFE lens.

Mu and epsilon near zero metamaterials for perfect coherence and new antenna designs.

Abstract: Wave interference is a fundamental physical phenomenon. Traditionally, the coherent effect of two identical point sources only takes place when the optical path is an integer number of wavelengths. In this paper, we show that mu and epsilon near zero (MENZ) metamaterials can be used to realize a perfectly constructive and isotropic interference. No matter how many point sources are embedded in the MENZ region, the wavefronts overlap perfectly. This translates into a total relaxation of the conventional condition for coherence enabled by the apparent infinite wavelength of the fields within MENZ metamaterials. Furthermore, we investigate crucial parameters such as the shape and size of the MENZ region. We demonstrate that flat sided geometries give rise to constructive interference beams serving as a powerful design mean. We also reveal the importance of relying on deeply sub-wavelength MENZ volumes as larger sizes increase the impedance and therefore reduce the output power of the device. The proposed concepts bear significance for current trends in antenna design which are inspired by the recent developments of electromagnetic metamaterials. Moreover, the perfect coherence effect can be appealing for power combiners, especially in the terahertz where sources are dim, as the irradiation intensity scales with the square of the number of embedded sources.