1,721,072 research outputs found
Numerical investigation on graphene based mantle cloaking of a PEC cylinder
Full text linkA specific coating for the achievement of the mantle cloaking of a metallic cylinder in the Terahertz frequencies is investigated. The coat is realized starting from a dielectric layer covering the cylinder, over which a certain number of modulated strips of graphene are laid. Properly set the values of the available parameters (chemical potential of graphene μc, dielectric constant, dielectric thickness h, number of modulated strips n and variation of width of each strip w(z)), a combination of the values that allows to reach the cloaking of the object is obtained. In order to quantify the cloaking at the desired frequency f0, the Maximum Radar Cross Section is computed and compared to the various structures
Kapitza homogenization of deep gratings for designing dielectric metamaterials
No full textWe theoretically investigate the homogenization of the dielectric response to transverse electric waves of a transverse grating characterized by the Kapitza condition; i.e., the permittivity is rapidly modulated with a modulation depth scaling as the large wavelength-to-modulation-period ratio. We show that the resulting effective dielectric permittivity, in addition to the standard average of the underlying dielectric profile, has a further contribution arising from the fast and deep dielectric modulation. Such a contribution turns out to be comparable with the other one and hence can provide an additional method for designing dielectric metamaterials. As an example, we discuss an effective metal-to-dielectric transition produced by the Kapitza contribution obtained by changing the grating depth, a remarkable result for applications involving epsilon-near-zero metamaterial design. (C) 2013 Optical Society of Americ
Graphene-nonlinearity unleashing at lasing threshold in graphene-assisted cavities
No full textWe investigate the nonlinear optical features of a graphene sheet embedded in an active cavity and we show that, when tuned near its lasing threshold, the cavity is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multivalued features. As opposed to standard situations where the small thickness of the graphene sheet hampers its remarkable nonlinear optical properties to be exploited, in our scheme the strong nonlinear optical regime is mainly triggered by the very intrinsic planar localization of graphene nonlinearity. The proposed strategy for exploiting graphene nonlinearity through its unleashing could open novel routes for conceiving ultraefficient nonlinear photonic devices
Effective medium theory for kapitza stratified media: Diffractionless propagation
No full textWe show that in the presence of a rapidly modulated dielectric permittivity with a large modulation depth (Kapitza medium) a novel and robust regime of diffractionless electromagnetic propagation occurs. This happens when the mean value to depth ratio of the dielectric profile is comparable to the small ratio between the modulation period and the wavelength. We show that the standard effective medium theory is inadequate to describe the proposed regime and that its occurrence is not substantially hampered by medium losses. We check the feasibility of the proposed regime by means of a large modulation depth metal-dielectric layered medium whose electromagnetic behavior is analytically investigated. DOI: 10.1103/PhysRevLett.110.14390
Harnessing quadratic optical response of two-dimensional materials through active microcavities
No full textWe propose a method for efficiently harnessing the quadratic optical response of two-dimensional graphenelike materials by theoretically investigating second-harmonic generation from a current biased sheet placed within a planar active microcavity. We show that, by tuning the cavity to resonate at the second-harmonic frequency, a highly efficient frequency doubling process is achieved (several orders of magnitude more efficient than the free-standing sheet). The efficiency of the process is not due to phase matching, which is forbidden by the localization of the nonlinear quadratic response on the two-dimensional atomic layered material, but stems from the interplay between the two-dimensional planar geometry of the nonlinear medium and the field oscillation within the active cavity near its threshold. The suggested method can easily be extended to different wave interactions and nonlinearities, and therefore it can represent a basic tool for efficiently exploiting nonlinear optical properties of two-dimensional materials
Nonlocal homogenization theory in metamaterials: Effective electromagnetic spatial dispersion and artificial chirality
No full textWe develop, from first principles, a general and compact formalism for predicting the electromagnetic response of a metamaterial with nonmagnetic inclusions in the long-wavelength limit, including spatial dispersion up to the second order. Specifically, by resorting to a suitable multiscale technique, we show that the effective medium permittivity tensor and the first- and second-order tensors describing spatial dispersion can be evaluated by averaging suitable spatially rapidly varying fields, each satisfying electrostatic-like equations within the metamaterial unit cell. For metamaterials with negligible second-order spatial dispersion, we exploit the equivalence of first-order spatial dispersion and reciprocal bianisotropic electromagnetic response to deduce a simple expression for the metamaterial chirality tensor. Such an expression allows us to systematically analyze the effect of the composite spatial symmetry properties on electromagnetic chirality. We find that even if a metamaterial is geometrically achiral, i.e., it is indistinguishable from its mirror image, it shows pseudo-chiral-omega electromagnetic chirality if the rotation needed to restore the dielectric profile after the reflection is either a 0 degrees or 90 degrees rotation around an axis orthogonal to the reflection plane. These two symmetric situations encompass two-dimensional and one-dimensional metamaterials with chiral response. As an example admitting full analytical description, we discuss one-dimensional metamaterials whose single chirality parameter is shown to be directly related to the metamaterial dielectric profile by quadratures
Kapitza dielectric metamaterials
No full textWe theoretically investigate the homogenization of the dielectric response of Kapitza dielectric metamaterials, i.e. materials hosting a subwavelength periodic grating whose depth scales as the large wavelength to modulation period ratio. We show that the standard effective medium theory is inadequate to describe the propagation in the considered metamaterials and, most importantly, a novel regime of diffractionless propagation occurs for transverse magnetic waves
Transverse power flow reversing of guided waves in extreme nonlinear metamaterials
No full textWe 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
Reflection solitons supported by competing nonlinear gratings
No full textWe analytically investigate solitons counterpropagating in a longitudinally modulated Kerr medium by means of the Hirota bilinear approach. We show that Hirota solvability (partial integrability of the system) physically corresponds to the exact mutual cancellation of the effects of all the underlying nonlinear gratings. This cancellation is achieved in two different situation: either through a suitable choice of the field profile or by means of a peculiar tailoring of the nonlinear modulation. In the first situation we obtain both bright and dark one-soliton solutions whose intensity ratio between forward and backward propagating beams is set by the nonlinear modulation. In the second situation, we derive two-soliton solutions obtained by nonlinearly dressing two independent linear grating eigenmodes sharing the same propagation constant
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