Negative Effective Refractive Index Research Articles

Isotropic three-dimensional left-handed metamaterials

We investigate three-dimensional left-handed and related meta-materials based on a fully symmetric multi-gap single-ring SRR design and crossing continuous wires. We demonstrate isotropic transmission properties of a SRR-only meta-material and the corresponding left-handed material which possesses a negative effective index of refraction due to simultaneously negative effective permeability and permittivity. Minor deviations from complete isotropy are due to the finite thickness of the meta-material.

Observation of negative refraction and negative phase velocity in left-handed metamaterials

We report the transmission characteristics of a two-dimensional (2D) composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement.

TOTAL AND NEGATIVE REFRACTION OF ELECTROMAGNETIC WAVES

Recently there has been a great deal of interest in an unusual category of material, that is, a material that exhibits negative refractive index or more generally negative group velocity. Perhaps the most immediate application of this type of material is in an area known as total and negative refraction, which may potentially lead to many novel optical devices. The reason that the phenomenon of total and negative refraction has become so interesting to the physics community is also due largely to the notion that this phenomenon would never occur in conventional materials with positive refractive index. It turns out that total and negative refraction can be realized even in natural crystalline materials or in artificial materials (e.g. photonic crystals) without negative (effective) refractive index. In this brief review, after providing a brief historic account for the research related to finding materials with negative group velocity and achieving negative refraction, we discuss the three primary approaches that have yielded experimental demonstrations of negative refraction, in an effort to clarify the underlying physics involved with each approach. A brief discussion on the subwavelength resolution application of the negative (effective) refractive index material is also given.

Multifocal flat lens with left-handed metamaterial

We show experimental results demonstrating multiple focal lengths at microwave frequencies in a flat lens constructed of left-handed metamaterial (LHM). In contrast to conventional lenses, which are constructed of materials with positive index and require a curved surface or inhomogeneous structures to focus light or other electromagnetic radiation, no curvature is needed with a LHM because of a negative effective index of refraction. Such a flat lens has the advantage of being capable of changing the focal length by simply changing the distance between the electromagnetic source and the lens.

Analysis of wave propagation in a two-dimensional photonic crystal with negative index of refraction: plane wave decomposition of the Bloch modes

This work presents a comprehensive analysis of electromagnetic wave propagation inside a two-dimensional photonic crystal in a spectral region in which the crystal behaves as an effective medium to which a negative effective index of refraction can be associated. It is obtained that the main plane wave component of the Bloch mode that propagates inside the photonic crystal has its wave vector k' out of the first Brillouin zone and it is parallel to the Poynting vector ( S' ? k'> 0 ), so light propagation in these composites is different from that reported for left-handed materials despite the fact that negative refraction can take place at the interface between air and both kinds of composites. However, wave coupling at the interfaces is well explained using the reduced wave vector ( k' ) in the first Brillouin zone, which is opposed to the energy flow, and agrees well with previous works dealing with negative refraction in photonic crystals.

Effective negative refractive index of graded granular composites with metallic magnetic particles

The effective refractive index of a granular composite with graded metallic magnetic particles randomly embedded in a host matrix is investigated. Based on differential effective dipole approximation (DEDA) and Clausius–Mossotti relation, we calculated the effective refractive index of the graded granular composite. It is found that there exists a frequency region, where the effective refractive index is negative. And the gradient profiles of permittivity and magnetic permeability inside particles can affect the effective negative refractive index significantly. The gradient profile of permittivity plays more important role in an enhancement of effective negative refractive index than that of magnetic permeability, whereas it is on the contrary in the adjustment of characteristic frequency, at which the effective negative refractive index reaches to a maximum. Therefore, in theoretical, it is possible to gain an enhancement of the effective negative refractive index and appropriate characteristic frequency by adjusting the gradient profiles of permittivity and magnetic permeability inside particles.

NEGATIVE REFRACTION AND SUBWAVELENGTH FOCUSING USING PHOTONIC CRYSTALS

In this article, we present an experimental and numerical study of novel optical properties of two-dimensional dielectric photonic crystals (PCs) which exhibit negative refraction. We investigate two mechanisms which utilize the band structure of the PC to generate a negative effective index of refraction (neff<0) and demonstrate the negative refraction experimentally. To the isotropic extend of neff, different PC slab structures are employed to focus the radiation of a point source. It is shown experimentally that the PC can generate an image of the source with subwavelength resolution in the vicinity of the PC interface. Using a different PC, one can also obtain a far field focusing. In the latter case, we explicitly show the flat lens behavior of the structure. These examples indicate that PC-based lenses can surpass limitations of conventional lenses and lead to novel optics applications.

Time-Domain Measurement of Negative Group Delay in Negative-Refractive-Index Transmission-Line Metamaterials

We have simulated and constructed a one-dimensional metamaterial composed of a periodically loaded transmission line that exhibits both negative and positive group velocities in a band of effective negative index of refraction. The negative group velocity or, equivalently, the negative group delay, is demonstrated theoretically and experimentally in the time domain using modulated Gaussian pulses. Due to this negative delay, we can show an output pulse peak emerging from the loaded transmission line prior to the input peak entering the line, i.e., the output pulse precedes the input pulse. The fact that this surprising behavior does not violate the requirements of relativistic causality is illustrated with time-domain simulations, which show that discontinuities in the pulse waveforms are traveling at exactly the speed of light in vacuum. The pulse-reshaping mechanism underlying this behavior is also illustrated using time-domain simulations.

Experimental and theoretical analysis of the self-focusing of light by a photonic crystal lens

We demonstrate the self-focusing of electromagnetic waves in the microwave regime by using a two-dimensional photonic crystal lens with rectangular shape. A detailed study of the band structure shows that the focusing is due to the refractivelike behavior of the photonic crystal with a negative effective index of refraction in the frequency range under study. In contrast to lenses based on homogeneous isotropic materials, it is shown that the symmetry of the mode and the direction of incidence play a fundamental role in the performance of the photonic crystal lens.

Periodically loaded transmission line with effective negative refractive index and negative group velocity

We present the design and implementation of a periodically loaded transmission line, which simultaneously exhibits negative refractive index (NRI) and negative group delay (and, hence, negative group velocity). This is achieved by loading the transmission line in series with capacitors and RLC resonators and in shunt with inductors. We discuss the dispersion characteristics of such a medium and identify the frequency bands of NRI and negative group delay. The structures are theoretically studied using S-parameters simulations on truncated loaded transmission lines of different lengths, and the predicted results are compared to the measured scattering parameters of such lines printed on circuit boards using coplanar waveguide technology.

All-angle negative refraction in a three-dimensionally periodic photonic crystal

We introduce a photonic crystal that has a large range of effective negative refractive index in three dimensions (3D) and demonstrate its negative-refraction property by numerical simulations. With slight modifications, our design is also amenable to layer-by-layer fabrication. This work should enable experimental observation of negative refraction and related phenomena in 3D at optical frequencies.

All-angle negative refraction without negative effective index

We describe an all-angle negative refraction effect that does not employ a negative effective index of refraction and involves photonic crystals. A few simple criteria sufficient to achieve this behavior are presented. To illustrate this phenomenon, a microsuperlens is designed and numerically demonstrated.