1,585 research outputs found
Chains of coupled square dielectric optical microcavities
Chains of coupled square dielectric cavities are investigated in a 2-D setting, by means of a quasi-analytical eigenmode expansion method. Resonant transfer of optical power can be achieved along quite arbitrary, moderately long rectangular paths (up to 9 coupled cavities are considered), even with individual standing-wave resonators of limited quality. We introduce an ab-initio coupled mode model, based on a simple superposition of slab mode profiles as a template for the field of individual cavities. Although no loss mechanisms are built in, the model can still help to interprete the results of the former numerical experiments
Calculation of fully anisotropic liquid crystal waveguide modes
The accurate analysis of optical waveguides is an important issue when designing devices for optical communication. Waveguides combined with liquid crystals have great potential because they allow waveguide tuning over a wide range using low voltages. In this paper, we present calculations that combine an advanced algorithm for calculating liquid crystal behavior and a finite-element mode solver that is able to incorporate the full anisotropy of the materials. Calculation examples demonstrate the validity of our program
Eigenmodes of index-modulated layers with lateral PMLs
Maxwell equations are solved in a layer comprising a finite number of
homogeneous isotropic dielectric regions ended by anisotropic perfectly matched
layers (PMLs). The boundary-value problem is solved and the dispersion relation
inside the PML is derived. The general expression of the eigenvalues equation
for an arbitrary number of regions in each layer is obtained, and both
polarization modes are considered. The modal functions of a single layer ended
by PMLs are found, and their orthogonality relation is derived. The present
method is useful to simulate scattering problems from dielectric objects as
well as propagation in planar slab waveguides. Its potential to deal with more
complex problems such as the scattering from an object with arbitrary cross
section in open space using the multilayer modal method is briefly discussed.Comment: 17 pages, 4 figure
The finite element solution of inhomogeneous anisotropic and lossy dielectric waveguides
This thesis presents a new variational finite element formulation and its implementation for the analysis of microwave and optical waveguide problem with arbitrarily- shaped cross section, inhomogeneous, transverse-anisotropic, and lossy dielectrics. In this approach, the spurious, nonphysical solutions, which ordinarily appear interspersed with the correct results of earlier vectorial finite element methods and thus have been the most serious problem in finite element analysis of waveguides, are totally eliminated. In this formulation either the propagation constant or the frequency may be treated as eigenvalues of the resulting generalized eigenvalue problem. This formulation also has the capability to find complex modes of lossless waveguides. Furthermore, the numerical efficiency of the solution is maximized since this formulation uses the most economical representation of a problem, in terms of only two vector components. This is achieved without losing the sparsity of the matrices of the resultant eigenvalue equation, which only depends on the topology of mesh used. This property is very important for solving large-size problems by efficient sparse matrix algorithms. In this work, a basic vector wave equation which involves only transverse components of magnetic field is straightforwardly derived from Maxwell equations. This differential equation incorporates the divergence condition V.B = 0 and leads to a canonical form of the resultant eigenvalue equation. The Local Potential Method is used to obtain the variational formulation. When implementing the finite element method, the Rayleigh-Ritz procedure is used to find stationary values of the functional to get the resulting generalized matrix eigenvalue equation. To show the validity and applicability of the method, a series of examples of microwave and optical waveguides including inhomogeneity, anisotropy and loss are studied. These examples show good accuracy and complete absence of spurious modes, demonstrating the effectiveness of the new formulation developed
Transmission properties in waveguides: An optical streamline analysis
A novel approach to study transmission through waveguides in terms of optical
streamlines is presented. This theoretical framework combines the computational
performance of beam propagation methods with the possibility to monitor the
passage of light through the guiding medium by means of these sampler paths. In
this way, not only the optical flow along the waveguide can be followed in
detail, but also a fair estimate of the transmitted light (intensity) can be
accounted for by counting streamline arrivals with starting points
statistically distributed according to the input pulse. Furthermore, this
approach allows to elucidate the mechanism leading to energy losses, namely a
vortical dynamics, which can be advantageously exploited in optimal waveguide
design.Comment: 8 pages, 4 figure
Proposal for compact solid-state III-V single-plasmon sources
We propose a compact single-plasmon source operating at near-infrared
wavelengths on an integrated III-V semiconductor platform, with a thin ridge
waveguide serving as the plasmon channel. By attaching an ultra-small cavity to
the channel, it is shown that both the plasmon generation efficiency ({\beta})
and the spontaneous-decay rate into the channel can be significantly enhanced.
An analytical model derived with the Lorentz reciprocity theorem captures the
main physics involved in the design of the source and yields results in good
agreement with fully-vectorial simulations of the device. At resonance, it is
predicted that the ultra-small cavity increases the {\beta}-factor by 70% and
boosts the spontaneous decay rate by a factor 20. The proposed design could
pave the way towards integrated and scalable plasmonic quantum networks.
Comparison of the present design with other fully-dielectric competing
approaches is addressed.Comment: 8 pages, 4 figure
Conductor losses calculation in two-dimensional simulations of H-plane rectangular waveguides
This paper presents a novel numerical approach to simulate H-plane rectangular-waveguide microwave circuits considering a reduced quasi-2D simulation domain with benefits for computational cost and time. With the aim to evaluate the attenuation of the full height 3D component, we propose a modified expression for the waveguide top/bottom wall conductivity. Numerical 2D simulations are validated against results from full wave 3-D commercial electromagnetic simulator. After a benchmark on a simple straight waveguide model, the method has been successfully applied to an asymmetric un-balanced power splitter, where an accurate power loss prediction is mandatory. Simulation time and memory consumption can be reduced by a factor ten and seven respectively, in comparison with complete 3D geometries. Finally, we show that, also for quasi-2D E-bend waveguide, a case where the translational H-plane symmetry is broken, the error on conductor losses computation is mitigated by our approach since the method remains still valid in a first approximation
Poor-man's model of hollow-core anti-resonant fibers
We investigate various methods for extending the simple analytical capillary
model to describe the dispersion and loss of anti-resonant hollow-core fibers
without the need of detailed finite-element simulations across the desired
wavelength range. This poor-man's model can with a single fitting parameter
quite accurately mimic dispersion and loss resonances and anti-resonances from
full finite-element simulations. Due to the analytical basis of the model it is
easy to explore variations in core size and cladding wall thickness, and should
therefore provide a valuable tool for numerical simulations of the ultrafast
nonlinear dynamics of gas-filled hollow-core fibers.Comment: In preparatio
Reduction of the radar cross section of arbitrarily shaped cavity structures
The problem of the reduction of the radar cross section (RCS) of open-ended cavities was studied. The issues investigated were reduction through lossy coating materials on the inner cavity wall and reduction through shaping of the cavity. A method was presented to calculate the RCS of any arbitrarily shaped structure in order to study the shaping problem. The limitations of this method were also addressed. The modal attenuation was studied in a multilayered coated waveguide. It was shown that by employing two layers of coating, it was possible to achieve an increase in both the magnitude of attenuation and the frequency band of effectiveness. The numerical method used in finding the roots of the characteristic equation breaks down when the coating thickness is very lossy and large in terms of wavelength. A new method of computing the RCS of an arbitrary cavity was applied to study the effects of longitudinal bending on RCS reduction. The ray and modal descriptions for the fields in a parallel plate waveguide were compared. To extend the range of validity of the Shooting and Bouncing Ray (SBR) method, the simple ray picture must be modified to account for the beam blurring
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