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Register a new userGeneralized field-transforming metamaterials
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In this paper we introduce a generalized concept of field-transforming metamaterials, which perform field transformations defined as linear relations between the original and transformed fields. These artificial media change the fields in a prescribed fashion in the volume occupied by the medium. We show what electromagnetic properties of transforming medium are required. The coefficients of these linear functions can be arbitrary scalar functions of position and frequency, which makes the approach quite general and opens a possibility to realize various unusual devices.
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Using detailed simulations we investigate the magnetic response of metamaterials consisting of pairs of parallel slabs or combinations of slabs with wires (including the fishnet design) as the length-scale of the structures is reduced from mm to nm. We observe the expected saturation of the magnetic resonance frequency when the structure length-scale goes to the sub-micron regime, as well as weakening of the effective permeability resonance and reduction of the spectral width of the negative permeability region. All these results are explained by using an equivalent resistor-inductor-capacitor (RLC) circuit model, taking into account the current-connected kinetic energy of the electrons inside the metallic parts through an equivalent inductance, added to the magnetic field inductance in the unit-cell. Using this model we derive simple optimization rules for achieving optical negative permeability metamaterials of improved performance. Finally, we analyze the magnetic response of the fishnet design and we explain its superior performance regarding the high attainable magnetic resonance frequency, as well as its inferior performance regarding the width of the negative permeability region.
Exact solutions are obtained for all the modes of wave propagation along an anisotropic cylindrical waveguide. Closed-form expressions for the energy flow on the waveguide are also derived. For extremely anisotropic waveguide where the transverse permittivity is negative while the longitudinal permittivity is positive, only transverse magnetic (TM) and hybrid modes will propagate on the waveguide. At any given frequency the waveguide supports an infinite number of eigenmodes. Among the TM modes, at most only one mode is forward wave. The rest of them are backward waves which can have very large effective index. At a critical radius, the waveguide supports degenerate forward- and backward-wave modes with zero group velocity. These waveguides can be used as phase shifters and filters, and as optical buffers to slow down and trap light.
It is shown theoretically that a nonchiral, two-dimensional array of metallic spheres exhibits optical activity as manifested in calculations of circular dichroism. The metallic spheres occupy the sites of a rectangular lattice and for off-normal incidence they show a strong circular-dichroism effect around the surface plasmon frequencies. The optical activity is a result of the rectangular symmetry of the lattice which gives rise to different polarizations modes of the crystal along the two orthogonal primitive lattice vectors. These two polarization modes result in a net polar vector, which forms a chiral triad with the wavevector and the vector normal to the plane of spheres. The formation of this chiral triad is responsible for the observed circular dichroism, although the structure itself is intrinsically nonchiral.
We theoretically prove that electromagnetic beams propagating through a nonlinear cubic metamaterial can exhibit a power flow whose direction reverses its sign along the transverse profile. This effect is peculiar of the hitherto unexplored extreme nonlinear regime where the nonlinear response is comparable or even greater than the linear contribution, a condition achievable even at relatively small intensities. We propose a possible metamaterial structure able to support the extreme conditions where the polarization cubic nonlinear contribution does not act as a mere perturbation of the linear part.
Starting from positive and negative helicity Maxwell equations expressed in Riemann-Silberstein vectors, we derive the ten usual and ten additional Poincar{e} invariants, the latter being related to the electromagnetic spin, i.e., the intrinsic rotation, or state of polarization, of the electromagnetic fields. Some of these invariants have apparently not been discussed in the literature before.
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