114 research outputs found
A modal model for diffraction gratings
A description of an algorithm for a rather general modal grating calculation
is presented. Arbitrary profiles, depth, and permittivity are allowed. Gratings
built up from sub-gratings are allowed, as are coatings on the sidewalls of
lines, and arbitrary complex structure. Conical angles and good conductors are
supported
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 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)
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
Finite wavelength cloaking by plasmonic resonance
We consider cloaking by a coated cylindrical system using plasmonic
resonance, and extend previous quasistatic treatments to include the effect of
finite wavelength. We show that a probe cylinder can still be cloaked at finite
wavelengths, but the cloaking cylinder develops a non-zero scattering
cross-section. We show that this latter effect is dominated by a monopole term
in the case of an ideal (lossless) cloaking material, and by a dipole term in
the case of a realistic (lossy) material. It can be reduced but not eliminated
by variations of geometric or dielectric parameters of the cloaking cylinder
First-principles method for high- photonic crystal cavity mode calculations
We present a first-principles method to compute radiation properties of
ultra-high quality factor photonic crystal cavities. Our Frequency-domain
Approach for Radiation (FAR) can compute the far-field radiation pattern and
quality factor of cavity modes times more rapidly than conventional
finite-difference time domain calculations. It also provides a simple rule for
engineering the cavity's far-field radiation pattern
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
Paired modes of heterostructure cavities in photonic crystal waveguides with split band edges
We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate. © 2010 Optical Society of America
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