Three-dimensional focusing of broadband microwave beams by a layered photonic structure.

Experiment and analysis confirm that a finite layered structure involving glass layers with broad strip metallizations can be characterized by broadband negative refractionlike behavior in three dimensions. The structure is further characterized as capable of 2:1 broadband focusing of near field radiation, with verified experimental focusing bandwidth of 1:5:1. This represents a significant improvement over the two-dimensional and narrow band focusing operation of current implementations of left-handed media. An electronic reconfigurable version is identified together with potential applications.

Negative refraction and focusing of circularly polarized waves in optically active media.

Analysis indicates that certain types of optically active media are capable of producing negative refraction and focusing of circularly polarized waves. It is established that a slab of such material acts just as Veselago's hypothetical left-handed media lens, providing subwavelength resolution as Sir Pendry's ideal lens, but for circularly polarized waves.

Optical properties of an ideal homogeneous causal left-handed material slab.

The optical properties of a homogeneous slab of material characterized by causal permittivity epsilon (f) , and permeability mu (f) are investigated through finite difference time domain simulations. Lorentzian epsilon (f) and mu (f) are used to produce values of interest in the resulting index n (f) , namely, n<0 , 0

Characteristics of waves guided by a grounded "left-handed" material slab of finite extent.

The properties of waves guided by a plane-parallel finite slab of material having an ideal, homogeneous, and causal permittivity epsilon (f) , and permeability mu (f) , are investigated analytically and numerically through simulations done via a finite difference time domain (FDTD) code. Lorentzian functional forms are chosen for epsilon (f) and mu (f) . Wave guidance is examined for frequency ranges where the material in the slab is in the left-handed material (LHM) regime, i.e., the real parts of epsilon (f) and mu (f) are negative. It is shown that for reasonably thin slabs, and unlike ordinary materials, there is a unique power recirculation or feedback mechanism wherein the fields in the vicinity of the slab exchange power across the free-space/LHM slab interface. Within the LHM slab, the power travels backwards towards the source. This results in significant but bounded energy accumulation near the edge of the slab closest to the source. The energy exchange across the slab interface is necessary in order to sustain the resulting backward wave in the slab. Slabs thicker than a wavelength are also analyzed, leading to a reversal of the power loop description. The agreement between analytical and numerical results is excellent. They confirm the guided wave physics of a LHM slab.

Electromagnetic waves focused by a negative-index planar lens.

We demonstrate that negative refraction occurs for both cw and pulsed electromagnetic waves when traversing from a "right-handed" (index > 0) to a "left-handed" (index < 0) material (LHM) which has causal dispersive intrinsic properties. We also demonstrate that a divergent line source spaced a distance H in front of a planar LHM slab and excited by either an impulse cw or a Gaussian frequency pulse is imaged at a distance H away, inside the LHM, and at H to the other side of the slab. The image size is approximately lambda consistent with limitations dictated by wave optics. We find no evidence of evanescent mode amplification. The studies were performed using numerical experiments with finite difference time domain solutions and incorporating a causal Lorentzian form for the frequency-dependent material properties.

Calculations and measurements of wire and/or split-ring negative index media.

Broadband calculations (70 MHz-20 GHz) and measurements (2-15 GHz) were performed on planar stacks of two-dimensional double-split rings arrays interspersed with arrays of thin wires. Recent work on similar composite structures infers a negative index of refraction (n<0) over a narrow frequency range. We have performed finite-difference time-domain (FDTD) calculations on various combinations of ring geometries, wire arrays, and stack spacings. Excellent agreement was obtained between FDTD simulations and our measured transmission spectra. Examining the FDTD time progression of fields we find regions of both negative and positive indices as well as an inverse Doppler effect.