Aydin S. Evren

Bio: Aydin S. Evren is an academic researcher from Ankara University. The author has contributed to research in topics: Luneburg lens & Cloaking. The author has an hindex of 2, co-authored 3 publications receiving 10 citations.

Analytical, Numerical, and Experimental Investigation of a Luneburg Lens System for Directional Cloaking

Abstract: Scientific and Technological Research Council of Turkey (TUBITAK) Turkish Academy of Sciences

Directional Cloaking by Quadruple Luneburg Lens System

Abstract: In this study, we propose a method based on graded-index medium in order to cloak scatterer objects. We use discretized Luneburg lenses as a graded-index medium and the proposed structure consists of four discretized Luneburg lenses, i.e., it is can be considered as a quadruple Luneburg lens system. Numerical investigations for directional cloaking are performed by using finite-difference time-domain methods. It is shown that an object can be cloaked inside the dark zone of created by Luneburg lenses and the proposed structure can provide cloaking at optical wavelengths.

Hyperbolic Secant Graded Index Photonic Crystal Flat Lens for Subwavelength Focusing of Light

Abstract: In this paper, we propose a graded index (GRIN) medium to obtain subwavelength focusing of light in high and low normalized frequency regimes by using all-dielectric materials. Distributed profile of hyperbolic secant GRIN structure is approximated by using two-dimensional (2D) photonics crystals (PCs). The focusing of light is quantitatively and systematically analyzed at low frequencies. It is clearly shown that the efficiency of focusing phenomenon changes as in terms of full-width at half-maximum (FHWM) and focal point distances according to structure length and other important parameters. Light focusing at subwavelength dimension has the capability of achieving unique contributions to lasing, optical imaging and microscopy, nanolithography, data storage and optical precision measurements. Moreover, an experimental verification of the numerical analyses is demonstrated in the microwave regime and corresponding results will be shared in the conference.

Paraxial ray optics cloaking

Abstract: Despite much interest and progress in optical spatial cloaking, a three-dimensional (3D), transmitting, continuously multidirectional cloak in the visible regime has not yet been demonstrated. Here we experimentally demonstrate such a cloak using ray optics, albeit with some edge effects. Our device requires no new materials, uses isotropic off-the-shelf optics, scales easily to cloak arbitrarily large objects, and is as broadband as the choice of optical material, all of which have been challenges for current cloaking schemes. In addition, we provide a concise formalism that quantifies and produces perfect optical cloaks in the small-angle (`paraxial') limit.

Structural Luneburg lens for broadband cloaking and wave guiding.

Abstract: In this paper, we explore the concept of structural Luneburg lens (SLL) as a design framework for performing dynamic structural tailoring to obtain a structural wave cloak and a structural waveguide. The SLL is a graded refractive index lens, which is realized by using a variable thickness structure defined in a thin plate. Due to the thickness variation of the plate, the refractive index decreases radially from the centre to the outer surface of the lens. By taking advantage of the unique capabilities of SLL for flexural wave focusing and collimation, we develop a structural wave cloak and waveguide based on SLLs. The SLL design enables the integration of functional devices into thin-walled structures while preserving the structural characteristics. Analytical, numerical, and experimental studies are carried out to characterize the performance of the SLL cloak and the SLL waveguide. The results demonstrate that these SLL devices exhibit excellent performance for structural wave cloaking and waveguiding over a broadband operating frequency range.

Analytical, Numerical, and Experimental Investigation of a Luneburg Lens System for Directional Cloaking

Abstract: Scientific and Technological Research Council of Turkey (TUBITAK) Turkish Academy of Sciences

Demonstration of carpet cloaking by an anisotropic zero refractive index medium.

Abstract: In this Letter, we numerically and experimentally demonstrate the carpet cloaking effect by a rectangular lattice two-dimensional photonic crystal (PC) exhibiting a semi-Dirac cone (SDC) dispersion phenomenon. The proposed SDC PC with an anisotropic zero refractive index medium operates as an optical carpet cloak for a perfect electric conductor surface bump. The experimental verification of the cloak is realized at microwave frequencies at around 12.1 GHz via dielectric rods. A good agreement between experimental measurements and numerical calculations is observed. Finally, features such as rendering larger objects invisible are possible with the proposed idea.