Converting from a broadband to a narrowband thermal emission spectrum with minimal loss of energy is important in the creation of efficient environmental sensors and biosensors as well as ...thermo-photovoltaic power generation systems. Here, we demonstrate such thermal emission control by manipulating photonic modes with photonic crystals as well as material absorption with quantum-well intersubband transitions. We show that the emission peak intensity for our device can be more than four times greater than that of a blackbody sample under the same input power and thermal management conditions due to an increase in the temperature compared to the blackbody reference, and the emission bandwidth and angular spread are narrowed by a factor of 30 and 8, respectively. These results indicate that the energy saved by thermal emission control can be recycled and concentrated to enhance the narrow peak emission intensity.
Although perfectly matched layers (PMLs) have been widely used to truncate numerical simulations of electromagnetism and other wave equations, we point out important cases in which a PML fails to be ...reflectionless even in the limit of infinite resolution. In particular, the underlying coordinate-stretching idea behind PML breaks down in photonic crystals and in other structures where the material is not an analytic function in the direction perpendicular to the boundary, leading to substantial reflections. The alternative is an adiabatic absorber, in which reflections are made negligible by gradually increasing the material absorption at the boundaries, similar to a common strategy to combat discretization reflections in PMLs. We demonstrate the fundamental connection between such reflections and the smoothness of the absorption profile via coupled-mode theory, and show how to obtain higher-order and even exponential vanishing of the reflection with absorber thickness (although further work remains in optimizing the constant factor).
This paper describes Meep, a popular free implementation of the finite-difference time-domain (FDTD) method for simulating electromagnetism. In particular, we focus on aspects of implementing a ...full-featured FDTD package that go beyond standard textbook descriptions of the algorithm, or ways in which Meep differs from typical FDTD implementations. These include pervasive interpolation and accurate modeling of subpixel features, advanced signal processing, support for nonlinear materials via Padé approximants, and flexible scripting capabilities.
Program title: Meep
Catalogue identifier: AEFU_v1_0
Program summary URL::
http://cpc.cs.qub.ac.uk/summaries/AEFU_v1_0.html
Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland
Licensing provisions: GNU GPL
No. of lines in distributed program, including test data, etc.: 151 821
No. of bytes in distributed program, including test data, etc.: 1 925 774
Distribution format: tar.gz
Programming language: C++
Computer: Any computer with a Unix-like system and a C++ compiler; optionally exploits additional free software packages: GNU Guile 1, libctl interface library 2, HDF5 3, MPI message-passing interface 4, and Harminv filter-diagonalization 5. Developed on 2.8 GHz Intel Core 2 Duo.
Operating system: Any Unix-like system; developed under Debian GNU/Linux 5.0.2.
RAM: Problem dependent (roughly 100 bytes per pixel/voxel)
Classification: 10
External routines: Optionally exploits additional free software packages: GNU Guile 1, libctl interface library 2, HDF5 3, MPI message-passing interface 4, and Harminv filter-diagonalization 5 (which requires LAPACK and BLAS linear-algebra software 6).
Nature of problem: Classical electrodynamics
Solution method: Finite-difference time-domain (FDTD) method
Running time: Problem dependent (typically about 10 ns per pixel per timestep)
References:
1 GNU Guile,
http://www.gnu.org/software/guile
2 Libctl,
http://ab-initio.mit.edu/libctl
3 M. Folk, R.E. McGrath, N. Yeager, HDF: An update and future directions, in: Proc. 1999 Geoscience and Remote Sensing Symposium (IGARSS), Hamburg, Germany, vol. 1, IEEE Press, 1999, pp. 273–275.
4 T.M. Forum, MPI: A Message Passing Interface, in: Supercomputing 93, Portland, OR, 1993, pp. 878–883.
5 Harminv,
http://ab-initio.mit.edu/harminv.
6 LAPACK,
http://www.netlib.org/lapack/lug.
We investigate the design of taper structures for coupling to slow-light modes of various photonic-crystal waveguides while taking into account parameter uncertainties inherent in practical ...fabrication. Our short-length (11 periods) robust tapers designed for ? = 1.55?m and a slow-light group velocity of c/34 have a total loss of < 20 dB even in the presence of nanometer-scale surface roughness, which outperform the corresponding non-robust designs by an order of magnitude. We discover a posteriori that the robust designs have smooth profiles that can be parameterized by a few-term (intrinsically smooth) sine series which helps the optimization to further boost the performance slightly. We ground these numerical results in an analytical foundation by deriving the scaling relationships between taper length, taper smoothness, and group velocity with the help of an exact equivalence with Fourier analysis.
We demonstrate that a holey photonic-crystal fiber with chalcogenide-glass index contrast can be designed to have a complete gap at a propagation constant beta = 0 that also extends into the non-zero ...beta region. This type of bandgap (previously identified only at index contrasts unattainable in glasses) opens up a regime for guiding zero-group-velocity modes not possible in holey fibers with the more common finger-like gaps originating from beta-->infinity. Such modes could be used to enhance nonlinear and other material interactions, such as for hollow-core fibers in gas-sensor applications.
We experimentally demonstrate that the addition of partial lattice disorder to a thin-film microcrystalline silicon photonic crystal results in the controlled spectral broadening of its absorption ...peaks to form quasi resonances: increasing light trapping over a wide bandwidth while also reducing sensitivity to the angle of incident radiation. Accurate finite-difference time-domain simulations are used to design the active-layer photonic crystal so as to maximize the number of its absorption resonances over the broadband interval where microcrystalline silicon is weakly absorbing before lattice disorder augmented with fabrication-induced imperfections is applied to further boost performance. Such a design strategy may find practical use for increasing the efficiency of thin-film silicon photovoltaics.
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