Metrics for negative-refractive-index materials

Frequency optimization of permeability metamaterial for enhanced resolution

We analyze and optimize the performance of unconventional negative permeability (μ) metamaterial and demonstrate its ability to focus and restore the decaying Fourier harmonics (FH) in microwave regime operating frequencies. We show that multiple real μr' and imaginary μr'' values of μ_r at same or multiple operating frequencies for a resonant type of -μ metamaterial could not exhibit finest resolution at the region of interest (ROI), unless and until the distance of the source plane with respect to metamaterial and ROI could be re-optimized in accordance with μr' and μr'' of μ_r. Using the variable parameters to enhance the resolution limit of -μ metamaterial, we optimize the metamaterial's configuration for maximum propagation field absorption and regeneration of decaying FH at ROI. The optimization of the test bed that contains the source plane, -μ metamaterial, and ROI followed by the regeneration of the decaying FH from the source plane at the surface of the material, yielded a high image resolution at ROI.

Rogue wave train generation in a metamaterial induced by cubic-quintic nonlinearities and second-order dispersion

We investigate the behavior of the electromagnetic wave that propagates in a metamaterial for negative index regime. Second-order dispersion and cubic-quintic nonlinearities are taken into account. The behavior obtained for negative index regime is compared to that observed for absorption regime. The collective coordinates technique is used to characterize the light pulse intensity profile at some frequency ranges. Five frequency ranges have been pointed out. The perfect combination of second-order dispersion and cubic nonlinearity leads to a robust soliton at each frequency range for negative index regime. The soliton peak power progressively decreases for absorption regime. Further, this peak power also decreases with frequency. We show that absorption regime can induce rogue wave trains generation at a specific frequency range. However, this rogue wave trains generation is maintained when the quintic nonlinearity comes into play for negative index regime and amplified for absorption regime at a specific frequency range. It clearly appears that rogue wave behavior strongly depends on the frequency and the regime considered. Furthermore, the stability conditions of the electromagnetic wave have also been discussed at frequency ranges considered for both negative index and absorption regimes.

Electromagnetic field energy density in homogeneous negative index materials

An exact separation of both electric and magnetic energies into stored and lost energies is shown to be possible in the special case when the wave impedance is independent of frequency. A general expression for the electromagnetic energy density in such a dispersive medium having a negative refractive index is shown to be accurate in comparison with numerical results. Using an example metamaterial response that provides a negative refractive index, it is shown that negative time-averaged stored energy can occur. The physical meaning of this negative energy is explained as the energy temporarily borrowed by the field from the material. This observation for negative index materials is of interest when approaching properties for a perfect lens. In the broader context, the observation of negative stored energy is of consequence in the study of dispersive materials.

Two-dimensional point spread matrix of layered metal-dielectric imaging elements

We describe the change of the spatial distribution of the state of polarization occurring during two-dimensional (2D) imaging through a multilayer and in particular through a layered metallic flat lens. Linear or circular polarization of incident light is not preserved due to the difference in the amplitude transfer functions for the TM and TE polarizations. In effect, the transfer function and the point spread function (PSF) that characterize 2D imaging through a multilayer both have a matrix form, and cross-polarization coupling is observed for spatially modulated beams with a linear or circular incident polarization. The PSF in a matrix form is used to characterize the resolution of the superlens for different polarization states. We demonstrate how the 2D PSF may be used to design a simple diffractive nanoelement consisting of two radial slits. The structure assures the separation of nondiffracting radial beams originating from two slits in the mask and exhibits an interesting property of a backward power flow in between the two rings.

Subwavelength imaging with nonmagnetic anisotropic bilayers

A nonmagnetic compensating bilayer imaging system having two uniaxially anisotropic layers is described. Evanescent fields in vacuum are converted to propagating waves in the bilayer, and one layer compensates the phase progression of the other. In this way, subwavelength imaging performance is possible with substantial flexibility in operating wavelength. Conditions for enhanced resolution and sensitivity to the material parameters are examined with a view to fabrication.

Imaging performance of an isotropic negative dielectric constant slab

The influence of material and thickness on the subwavelength imaging performance of a negative dielectric constant slab is studied. Resonance in the plane-wave transfer function produces a high spatial frequency ripple that could be useful in fabricating periodic structures. A cost function based on the plane-wave transfer function provides a useful metric to evaluate the planar slab lens performance, and using this, the optimal slab dielectric constant can be determined.

Perfect-lens-material condition from adjacent absorptive and gain resonances

We suggest, based on the principle of causality and for a material exhibiting adjacent absorptive and gain resonances, that there can be an intervening frequency where perfect imaging is in theory possible. At this frequency, both the dielectric constant and the permeability are negative, leading to a negative refractive index, and there is no loss. In such a material exhibiting a double resonance, the gain must be at the higher frequency. Through appropriate tuning of the refractive index, all propagating and evanescent fields from the object could then in principle be reconstructed at the image plane, subject to practical implementation limits.

Compensating losses in negative-index metamaterials by optical parametric amplification

Optical parametric amplification controlled by the auxiliary electromagnetic field enables transparency, amplification, and oscillation with no cavity in strongly absorbing negative-index metamaterials. The opposite directions of the wave vector and the Poynting vector in such materials result in extraordinary optical properties, including "backward" phase matching and the generation of entangled pairs of left- and right-handed counterpropagating photons.

Generation and control of optical vortices using left-handed materials

Optical vortices are shown to be generated in the near-field through interference between a propagating wave and the amplified evanescent field in a slab of lossy left-handed material. While small loss adversely impacts the sub-wavelength performance in the lens application, the vortex character shown relies on some degree of imperfection. These vortices can be controlled by means of gain/loss and the incident field.

Resolution of negative-index slabs

Different definitions of the resolution of negative-index-material (NIM) slabs and classical optical lenses with magnification 1 are presented and evaluated for both cases. Several numerical codes--based on domain and boundary discretizations and working in the time and frequency domains--are applied and compared. It is shown that superresolution depends very much on the definition of resolution and that it may be obtained not only for NIM slabs but also for highly refracting classical lenses when the distances of the image and source points from the surface of the lens or slab are shorter than the wavelength.

Poynting vector analysis of a superlens

A power analysis of the lossy negative refractive index or left-handed slab lens is described. The presence of vortices in the image plane is revealed with small loss or gain, and these are attributed to the influence of field growth in the evanescent spectrum.