44 research outputs found
Judiciously distributing laser emitters to shape the desired far field patterns
The far-field pattern of a simple one-dimensional laser array of emitters
radiating into free space is considered. In the path of investigating the
inverse problem for their near fields leading to a target beam form,
surprisingly we found that the result is successful when the matrix of the
corresponding linear system is not well-scaled. The essence of our numerical
observations is captured by an elegant inequality defining the functional range
of the optical distance between two neighboring emitters. Our finding can
restrict substantially the parametric space of integrated photonic systems and
simplify significantly the subsequent optimizations
Electromagnetic cloaking of cylindrical objects by multilayer or uniform dielectric claddings
We show that dielectric or even perfectly conducting cylinders can be cloaked
by a uniform or a layered dielectric cladding, without the need of any exotic
or magnetic material parameters. In particular, we start by presenting a simple
analytical concept that can accurately describe the cloaking effect obtained
with conical silver plates in the visible spectrum. The modeled structure has
been originally presented in [S. A. Tretyakov, P. Alitalo, O. Luukkonen, C. R.
Simovski, Phys. Rev. Lett., vol. 103, p. 103905, 2009], where its operation as
a cloak in the optical frequencies was studied only numerically. We model
rigorously this configuration as a multi-layer dielectric cover surrounding the
cloaked object, with excellent agreement to the simulation results of the
actual device. The concept of using uniform or multilayer dielectric covers,
with relative permittivities larger than unity, is then successfully extended
to cloaking of impenetrable objects such as conducting cylinders.Comment: 14 pages, 9 figure
On Modeling Perfectly Conducting Sharp Corners With Magnetically Inert Dielectrics Of Extreme Complex Permittivities
The idea of replacing an edgy perfectly conducting boundary by the
corresponding interface filled with a dielectric material of extreme complex
permittivities, is examined in the present work. A semi-analytical solution to
the corresponding boundary value problems is obtained and the merit of the
modeling has been checked. Certain conclusions for the effect of the
constituent material parameters and the geometric features of the configuration
on the model effectiveness, are drawn and discussed.Comment: 8 pages, 17 figures, research journa
Multistage Kondo effect as a manifestation of dynamical symmetries in the single- and two-electron tunneling
The concept of dynamical symmetries is used for formulation of the
renormalization group approach to the Kondo effect in the Anderson model with
repulsive and attractive interaction . It is shown that the generic local
symmetry of the Anderson Hamiltonian is determined by the SU(4) Lie group. The
Anderson Hamiltonian is rewritten in terms of the Gell-Mann matrices of the
4-th rank, which form the set of group generators and the basis for
construction of irreducible vector operators describing the excitation spectra
in the charge and spin sectors. The multistage Kondo sceening is described in
terms of the local SU(4) dynamical symmetry. It is shown that the similarity
between the conventional Kondo cotunneling effect for spin 1/2 in the positive
model and the Kondo resonance for pair tunneling in the negative model
is a direct manifestation of implicit SU(4) symmetry of the Anderson/Kondo
model.Comment: 13 pages, 5 figure
PT-Symmetric planar devices for field transformation and imaging
The powerful tools of transformation optics (TO) allow an effective distortion of a region of
space by carefully engineering the material inhomogeneity and anisotropy, and have been
successfully applied in recent years to control electromagnetic fields in many different scenarios,
e.g., to realize invisibility cloaks and planar lenses. For various field transformations, it is not
necessary to use volumetric inhomogeneous materials, and suitably designed ultrathin
metasurfaces with tailored spatial or spectral responses may be able to realize similar
functionalities within smaller footprints and more robust mechanisms. Here, inspired by the
concept of metamaterial TO lenses, we discuss field transformations enabled by parity-time (PT)
symmetric metasurfaces, which can emulate negative refraction. We first analyze a simple
realization based on homogeneous and local metasurfaces to achieve negative refraction and
imaging, and we then extend our results to arbitrary PT-symmetric two-port networks to realize
aberration-free planar imagin
PT-Symmetric planar devices for field transformation and imaging
The powerful tools of transformation optics (TO) allow an effective distortion of a region of
space by carefully engineering the material inhomogeneity and anisotropy, and have been
successfully applied in recent years to control electromagnetic fields in many different scenarios,
e.g., to realize invisibility cloaks and planar lenses. For various field transformations, it is not
necessary to use volumetric inhomogeneous materials, and suitably designed ultrathin
metasurfaces with tailored spatial or spectral responses may be able to realize similar
functionalities within smaller footprints and more robust mechanisms. Here, inspired by the
concept of metamaterial TO lenses, we discuss field transformations enabled by parity-time (PT)
symmetric metasurfaces, which can emulate negative refraction. We first analyze a simple
realization based on homogeneous and local metasurfaces to achieve negative refraction and
imaging, and we then extend our results to arbitrary PT-symmetric two-port networks to realize
aberration-free planar imagin