21,756 research outputs found
The FLAME-slab method for electromagnetic wave scattering in aperiodic slabs
The proposed numerical method, "FLAME-slab," solves electromagnetic wave
scattering problems for aperiodic slab structures by exploiting short-range
regularities in these structures. The computational procedure involves special
difference schemes with high accuracy even on coarse grids. These schemes are
based on Trefftz approximations, utilizing functions that locally satisfy the
governing differential equations, as is done in the Flexible Local
Approximation Method (FLAME). Radiation boundary conditions are implemented via
Fourier expansions in the air surrounding the slab. When applied to ensembles
of slab structures with identical short-range features, such as amorphous or
quasicrystalline lattices, the method is significantly more efficient, both in
runtime and in memory consumption, than traditional approaches. This efficiency
is due to the fact that the Trefftz functions need to be computed only once for
the whole ensemble.Comment: Various typos were corrected. Minor inconsistencies throughout the
manuscript were fixed. In Section II B. Additional description regarding
choice of Trefftz cell, was added. In Section III A. Detailed description
about units (used in our calculation) was adde
Field representation for optical defect resonances in multilayer microcavities using quasi-normal modes
Quasi-normal modes are used to characterize transmission resonances in 1D optical defect cavities and the related field approximations. We specialize to resonances inside the bandgap of the periodic multilayer mirrors that enclose the defect cavities. Using a template with the most relevant QNMs a variational principle permits to represent the field and the spectral transmission close to resonances
A convergent Born series for solving the inhomogeneous Helmholtz equation in arbitrarily large media
We present a fast method for numerically solving the inhomogeneous Helmholtz
equation. Our iterative method is based on the Born series, which we modified
to achieve convergence for scattering media of arbitrary size and scattering
strength. Compared to pseudospectral time-domain simulations, our modified Born
approach is two orders of magnitude faster and nine orders of magnitude more
accurate in benchmark tests in 1-dimensional and 2-dimensional systems
Finite-Difference Time-Domain Study of Guided Modes in Nano-plasmonic Waveguides
A conformal dispersive finite-difference time-domain (FDTD) method is
developed for the study of one-dimensional (1-D) plasmonic waveguides formed by
an array of periodic infinite-long silver cylinders at optical frequencies. The
curved surfaces of circular and elliptical inclusions are modelled in
orthogonal FDTD grid using effective permittivities (EPs) and the material
frequency dispersion is taken into account using an auxiliary differential
equation (ADE) method. The proposed FDTD method does not introduce numerical
instability but it requires a fourth-order discretisation procedure. To the
authors' knowledge, it is the first time that the modelling of curved
structures using a conformal scheme is combined with the dispersive FDTD
method. The dispersion diagrams obtained using EPs and staircase approximations
are compared with those from the frequency domain embedding method. It is shown
that the dispersion diagram can be modified by adding additional elements or
changing geometry of inclusions. Numerical simulations of plasmonic waveguides
formed by seven elements show that row(s) of silver nanoscale cylinders can
guide the propagation of light due to the coupling of surface plasmons.Comment: 6 pages, 10 figures, accepted for publication, IEEE Trans. Antennas
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