111 research outputs found
Multistability at arbitrary low optical intensities in a metallo-dielectric layered structure
We show that a nonlinear metallo-dielectric layered slab of subwavelength
thickness and very small average dielectric permittivity displays optical
multistable behavior at arbitrary low optical intensities. This is due to the
fact that, in the presence of the small linear permittivity, one of the
multiple electromagnetic slab states exists no matter how small is the
transmitted optical intensity. We prove that multiple states at ultra-low
optical intensities can be reached only by simultaneously operating on the
incident optical intensity and incidence angle. By performing full wave
simulations, we prove that the predicted phenomenology is feasible and very
robust.Comment: 4 pages, 4 figure
|\epsilon|-Near-Zero materials in the near-infrared
We consider a mixture of metal coated quantum dots dispersed in a polymer
matrix and, using a modified version of the standard Maxwell-Garnett mixing
rule, we prove that the mixture parameters (particles radius, quantum dots
gain, etc.) can be chosen so that the effective medium permittivity has an
absolute value very close to zero in the near-infrared, i.e. |Re(epsilon)|<<1
and |Im (epsilon)|<<1 at the same near-infrared wavelength. Resorting to
full-wave simulations, we investigate the accuracy of the effective medium
predictions and we relate their discrepancy with rigorous numerical results to
the fact that |epsilon|<<1 is a critical requirement. We show that a simple
method for reducing this discrepancy, and hence for achieving a prescribed
value of |\epsilon|, consists in a subsequent fine-tuning of the nanoparticles
volume filling fraction.Comment: 3 pages, 3 figure
Collision and fusion of counterpropagating micron-sized optical beams in non-uniformly biased photorefractive crystals
We theoretically investigate collision of optical beams travelling in
opposite directions through a centrosymmetric photorefractive crystal biased by
a spatially non-uniform voltage. We analytically predict the fusion of
counterpropagating solitons in conditions in which the applied voltage is
rapidly modulated along the propagation axis, so that self-bending is
suppressed by the "restoring symmetry" mechanism. Moreover, when the applied
voltage is slowly modulated, we predict that the modified self-bending allows
conditions in which the two beams fuse together, forming a curved light-channel
splice.Comment: 12 page
Two-peaked and flat-top perfect bright solitons in epsilon-near-zero nonlinear metamaterials: novel Kerr self-trapping mechanisms
We analytically investigate transverse magnetic (TM) spatial bright solitons,
as exact solutions of Maxwell's equations, propagating through nonlinear
metamaterials whose linear dielectric permittivity is very close to zero and
whose effective nonlinear Kerr parameters can be tailored to achieve values not
available in standard materials. Exploiting the fact that, in the considered
medium, linear and nonlinear polarization can be comparable at feasible and
realistic optical intensities, we identify two novel self-trapping mechanisms
able to support two-peaked and flat-top solitons, respectively. Specifically,
these two novel mechanisms are based on the occurrence of critical points at
which the effective nonlinear permittivity vanishes, the two mechanisms
differing in the way the compensation between linear and nonlinear polarization
is achieved through the non-standard values of the nonlinear parameters.Comment: 7 pages, 4 figure
Azimuthally polarized spatial dark solitons: exact solutions of Maxwell's equations in a Kerr medium
Spatial Kerr solitons, typically associated with the standard paraxial
nonlinear Schroedinger equation, are shown to exist to all nonparaxial orders,
as exact solutions of Maxwell's equations in the presence of vectorial Kerr
effect. More precisely, we prove the existence of azimuthally polarized,
spatial, dark soliton solutions of Maxwell's equations, while exact linearly
polarized (2+1)-D solitons do not exist. Our ab initio approach predicts the
existence of dark solitons up to an upper value of the maximum field amplitude,
corresponding to a minimum soliton width of about one fourth of the wavelength.Comment: 4 pages, 4 figure
Optimisation of the Detection Sensitivity of Plasmonic Nanoantenna Based Sensors for Mid-infrared Spectroscopy
AbstractIn this paper we report on the optimisation of the optical characteristics of 2D-arrays of plasmonic gold nanoantennas (NA) that can be used as high sensitivity mid-infrared spectroscopic sensor for the detection of chemical/biological substances by using the Surface Enhanced Infrared Absorption (SEIRA) technique. This approach allows to detect the presence of a substance adsorbed on the NA by measuring its optical absorption under the conditions for which the maximum of the reflectivity response of the 2D-array occurs at the same wavelength of the substance maximum absorption peak. In particular, by acting on the 2D-array periodicity, NA shape, size and thickness, numerical simulations of the 2D-array detection response, based on Finite Element Method (FEM), demonstrate that is possible to obtain an increase in the detection sensitivity of more than three orders of magnitude with respect to that one achievable if the same substance is deposited on an unstructured planar metal surface, independently from the wavelength at which the substance absorption occurs. Moreover, we present the results of an analysis of the dependence of the 2D-array maximum reflectivity and peak wavelength on the geometrical parameters characterising the NA and the 2D-array
Singularity-driven Second and Third Harmonic Generation in a {\epsilon}-near-zero nanolayer
We show a new path to {\epsilon}~0 materials without resorting to metal-based
metamaterial composites. A medium that can be modeled using Lorentz oscillators
usually displays {\epsilon}=0 crossing points, e.g. {\epsilon}=0 at
{\lambda}~7{\mu}m and 20{\mu}m for SiO2 and CaF2, respectively. We show that a
Lorentz medium yields a singularity-driven enhancement of the electric field
followed by dramatic lowering of thresholds for a plethora of nonlinear optical
phenomena. We illustrate the remarkable enhancement of second and third
harmonic generation in a layer of {\epsilon}~0 material 20nm thick, and discuss
the role of nonlinear surface sources
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