60 research outputs found
Supermodes of Hexagonal Lattice Waveguide Arrays
We present a semi-analytical formulation for calculating the supermodes and
corresponding Bloch factors of light in hexagonal lattice photonic crystal
waveguide arrays. We then use this formulation to easily calculate dispersion
curves and predict propagation in systems too large to calculate using standard
numerical methods.Comment: Accepted by J. Opt. Soc. Am. B, DocID:160522.
http://www.opticsinfobase.org/abstract.cfm?msid=16052
Absorption enhancing proximity effects in aperiodic nanowire arrays
Aperiodic Nanowire (NW) arrays have higher absorption than equivalent
periodic arrays, making them of interest for photovoltaic applications. An
inevitable property of aperiodic arrays is the clustering of some NWs into
closer proximity than in the equivalent periodic array. We focus on the modes
of such clusters and show that the reduced symmetry associated with cluster
formation allows external coupling into modes which are dark in periodic
arrays, thus increasing absorption. To exploit such modes fully, arrays must
include tightly clustered NWs that are unlikely to arise from fabrication
variations but must be created intentionally.Comment: Accepted by Optics Expres
Efficient butt-coupling of surface plasmons on a silver-air interface
Butt-coupling of light into a surface plasmon is a simple and compact coupling method with a range of potential uses in photonic circuitry. Although butt-coupling has been successfully implemented in many coupling configurations, the coupling effectiveness is not fully understood. Here, we present a semi-analytical study which models the coupling efficiency of an incident beam into a surface plasmon on silver in the presence of loss using an projection method in one dimension. We find that the coupling efficiencies for silver between the wavelengths of 0:38-1:6 µm reach 77-88% with optimum incident beam parameters
Efficient end-fire coupling of surface plasmons in a metal waveguide
We present a semi-analytical study exploring the end-fire coupling of an incident beam into a surface plasmon mode propagating on a metal–dielectric interface. An energy-conserving projection method is used to solve for the resultant reflected and transmitted fields for a given incident beam, thereby determining the efficiency of the surface plasmon coupling. The coupling efficiency is found to be periodic with waveguide width due to the presence of a coupled, transversely propagating surface plasmon. Optimization of the incident beam parameters, such as beam width, position, and wavelength, leads to numerically observed maximum efficiencies of approximately 80% when the beam width roughly matches the width of the surface plasmon.This research was supported by the Australian Research
Council (ARC) Centre of Excellence for Ultrahigh Bandwidth
Devices for Optical Systems (CE110001018)
Anderson Localization of Classical Waves in Weakly Scattering Metamaterials
We study the propagation and localization of classical waves in
one-dimensional disordered structures composed of alternating layers of left-
and right-handed materials (mixed stacks) and compare them to the structures
composed of different layers of the same material (homogeneous stacks). For
weakly scattering layers, we have developed an effective analytical approach
and have calculated the transmission length within a wide region of the input
parameters. When both refractive index and layer thickness of a mixed stack are
random, the transmission length in the long-wave range of the localized regime
exhibits a quadratic power wavelength dependence with the coefficients
different for mixed and homogeneous stacks. Moreover, the transmission length
of a mixed stack differs from reciprocal of the Lyapunov exponent of the
corresponding infinite stack. In both the ballistic regime of a mixed stack and
in the near long-wave region of a homogeneous stack, the transmission length of
a realization is a strongly fluctuating quantity. In the far long-wave part of
the ballistic region, the homogeneous stack becomes effectively uniform and the
transmission length fluctuations are weaker. The crossover region from the
localization to the ballistic regime is relatively narrow for both mixed and
homogeneous stacks. In mixed stacks with only refractive-index disorder,
Anderson localization at long wavelengths is substantially suppressed, with the
localization length growing with the wavelength much faster than for
homogeneous stacks. The crossover region becomes essentially wider and
transmission resonances appear only in much longer stacks. All theoretical
predictions are in an excellent agreement with the results of numerical
simulations.Comment: 19 pages, 16 figures, submitted to PR
Double-heterostructure cavities: from theory to design
We derive a frequency-domain-based approach for radiation (FAR) from
double-heterostructure cavity (DHC) modes. We use this to compute the quality
factors and radiation patterns of DHC modes. The semi-analytic nature of our
method enables us to provide a general relationship between the radiation
pattern of the cavity and its geometry. We use this to provide general designs
for ultrahigh quality factor DHCs with radiation patterns that are engineered
to emit vertically
Optimizing Photovoltaic Charge Generation of Nanowire Arrays: A Simple Semi-Analytic Approach
Nanowire arrays exhibit efficient light coupling and strong light trapping,
making them well suited to solar cell applications. The processes that
contribute to their absorption are interrelated and highly dispersive, so the
only current method of optimizing the absorption is by intensive numerical
calculations. We present an efficient alternative which depends solely on the
wavelength-dependent refractive indices of the constituent materials. We choose
each array parameter such that the number of modes propagating away from the
absorber is minimized while the number of resonant modes within the absorber is
maximized. From this we develop a semi-analytic method that quantitatively
identifies the small range of parameters where arrays achieve maximum short
circuit currents. This provides a fast route to optimizing NW array cell
efficiencies by greatly reducing the geometries to study with full device
models. Our approach is general and applies to a variety of materials and to a
large range of array thicknesses.Comment: Accepted by ACS Photonic
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