Papers by Keyword: Negative Refraction

Abstract: An asymmetrical chiral metamaterial at microwave frequency is constructed by using four double-layered L-shaped strips which are rotated by 90⁰ with respect to their adjacent metal strip. These different size strips allows another degree of freedom in the equalizing the orthogonal components of the electric fields at the output interface with 90^o phase difference when the x-polarized wave excites the structure. The proposed structure exhibits the properties of chiral medium such as optical activity and circular dichroism. The L shaped chiral objects can be etched on double side substrate. The effect of structure on different electromagnetic parameter like chirality, optical activity and reflection characteristics are analyzed. Due to the strong chirality the structure posses negative refractive index for either left circularly or right circularly polarized wave. In this paper, a numerical study in the frequency domain of the electromagnetic-wave propagation through these types of structures is achieved by using the commercial software Computer Simulation Technology (CST) microwave studio.

Abstract: Metamaterials composed of metallic strips on both side of the substrate are analyzed at microwave frequencies. The rectangular shaped metallic foils are rotated by 90^o with respect to their adjacent metal strip on each side of the substrate. The twist angle between the cross strips on opposite sides of substrate is 40^o. The proposed structure exhibits the properties of chiral medium such as optical activity and circular dichroism due to their cross coupling between the electric and magnetic fields. The rectangular shaped chiral objects can be easily fabricated on double side substrate. Both transmission and reflection resonances are illustrated. The chiral configuration of this metamaterial structure is analyzed in commercial software Computer Simulation Technology (CST) microwave studio and negative refractive index is observed. Moreover, other electromagnetic structural parameters such as chirality, optical activity and polarization effect are discussed.

Abstract: An all-dielectric fishnet metamaterial (DFM) composed of multilayer dielectric structure with periodically patterned holes is proposed to generate left-handed behavior in optical frequency region. Different from the metallic fishnet negative index metamaterial realized by coupling the neighbouring functional layers along the propagation direction, this DFM owes its simultaneous negative permeability and permittivity to the hybrid coupled resonances in the same layer. Based on this configration, a wide-band and polarization-independent negative refraction with maximum figure of merit as large as 13.85 is obtained by a silicon-based DFM at 450 nm wavelength. Simple and easy to fabricate, this concept is believed to provide an alternative route to realize high-performance negative index metamateirals at optical frequencies.

Abstract: In this paper, we investigate numerically the negative refraction properties of a closed-ring pair (CRP) structure metamaterial under parallel incidence. The surface currents and magnetic-field distribution are demonstrated to the physical mechanism of the negative refraction of the CRP. It is found that the electric response is attributed to the plasma oscillation of electrons and resulting in negative permittvity. However, the magnetic response origins from the antsymmetric resonant mode, which is excited by the edges of up and down of the CRP structure. In addition, the electric field distribution based on wedge-shaped and parallelogram-shaped models and the backward wave propagation from the phase changes in the moving picture are shown to further confirm the negative refraction.

Abstract: Anomalous optical transmission phenomena have ever been discovered in various metamaterials, which can be modulated more easily in Photonic crystals (PhCs). Compared with the regular PhCs composed of round rods closely packed in air, the equal frequency contours (EFC) of honeycomb lattice PhCs constituted by trigonal rods are more rounded and more suitable to realize the all-angle left-handed negative refraction (AALNR) in the low band region. Due to the hex EFC distribution, the regular PhC can be applied in the optical collimator design. In the higher band regions, the more complicated refraction behaviors can be excited based on the intricate undulation of one band or the overlap of different bands in PhCs. These unique features will provide us with more understanding of electromagnetic wave propagation in PhCs and give important guideline for the design of new type optical devices.

Abstract: Negative refraction is a fantastic optical property and attracts more and more attentions. As first proposed, materials with negative permittivity and negative permeability simultaneously exhibit negative refraction. Recently, negative refraction was found in the indefinite medium based on the strong anisotropy of permittivity. In this paper, the theory of the negative refraction in the anisotropic materials and the research progress in recent years were reviewed.

Abstract: We numerically investigate the imaging properties of the two dimensional square photonic crystal. It is found that the dependence of the image-to-interface distance on the object-to-interface distance is almost linear. We can manipulate the near field location of the image through the object-to-interface distance. When the object is located 1μm away from the interface, the image locates at the output interface which can be used to realize the near field optical display.

Abstract: Using of the multiple scattering methods, we characterize the positive and negative multi-refraction and transmission properties of a solid-based phononic crystal composed of coated solid inclusions in view of its applications in tunable multimode filtering. The geometrical parameters are chosen so that a left-handed longitudinal wave mode and a right-handed transverse wave mode, are simultaneously obtained in this three-component phononic crystal. When multimode Gaussian beams are placed transmitting through the phononic crystal slab, both positive and negative refractions are observed. We then study the individual propagation behavior of different modes. The angle dependent transmission beams with different energy distributions are found at the other side of the slab. Transmitted transverse waves coming from different directions incidence finally walk together into four oriented beams. Meanwhile, longitudinal wave incidence with different directions behaves simply as negative refraction in the slab. A far-field longitudinal wave image can be achieved being excited by a longitudinal wave point source. The three-component phononic crystal slab thus can be served as an alternate in tunable multimode filtering devices.

Abstract: Light focusing characteristics of a negative refractive lens fabricated out of a silicon-on-insulator photonic crystal (PC) slab are investigated theoretically and experimentally. It focuses in the near infrared, but the focal spot is degraded by a lens aberration. To reduce the aberration, we designed a composite PC that gives rise to a narrower focal spot. In addition, two unique functions of this lens are demonstrated: refocusing outside of the PC and parallel focusing, enabling image transfer and real image formation, respectively. These results prove the feasibility of an in-plane free space optical network based on negative refraction.

Abstract: Study of the refraction and rightness effects in 2D Archimedean lattice photonic crystals is presented. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Besides the familiar Archimedean lattices like square, triangular, honeycomb and Kagome ones, we consider also, the less known 32,4,3,4 (ladybug) and 3,4,6,4 (honeycombring) structures. This involves the calculations of band structures, band-gap maps, equifrequency contours, FDTD simulations of electromagnetic propagation through the structures, as well as an experimental verification of negative refraction at microwaves.