133 research outputs found
Group velocity of dielectric waveguide modes
The group velocity and dispersion of surface-wave nodes propagating along a circular dielectric rod are computed and presented graphically in normalised form. The group velocity as each mode approaches the cutoff frequency is calculated approximately
Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays
We analyze wave propagation in coupled planar waveguides, pointing specific
attention to modal cross-talk and out-of-plane scattering in quasi-planar
photonics. An algorithm capable of accurate numerical computation of wave
coupling in arrays of planar structures is developed and illustrated on several
examples of plasmonic and volumetric waveguides. An analytical approach to
reduce or completely eliminate scattering and modal cross-talk in planar
waveguides with anisotropic materials is also presented
Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides
This paper shows how to analyze plasmonic metal-insulator-metal waveguides
using the full modal structure of these guides. The analysis applies to all
frequencies, particularly including the near infrared and visible spectrum, and
to a wide range of sizes, including nanometallic structures. We use the
approach here specifically to analyze waveguide junctions. We show that the
full modal structure of the metal-insulator-metal (MIM) waveguides--which
consists of real and complex discrete eigenvalue spectra, as well as the
continuous spectrum--forms a complete basis set. We provide the derivation of
these modes using the techniques developed for Sturm-Liouville and generalized
eigenvalue equations. We demonstrate the need to include all parts of the
spectrum to have a complete set of basis vectors to describe scattering within
MIM waveguides with the mode-matching technique. We numerically compare the
mode-matching formulation with finite-difference frequency-domain analysis and
find very good agreement between the two for modal scattering at symmetric MIM
waveguide junctions. We touch upon the similarities between the underlying
mathematical structure of the MIM waveguide and the PT symmetric quantum
mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM
waveguide supports forms a canonical example against which other more
complicated geometries can be compared. Our work here encompasses the microwave
results, but extends also to waveguides with real metals even at infrared and
optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed,
figures slightly modifie
An Absolute Measurement of the Cosmic Microwave Background Radiation Temperature at 10.7 GHz
A balloon-borne experiment has measured the absolute temperature of the
cosmic microwave background radiation (CMBR) at 10.7 GHz to be Tcmbr = 2.730 +-
.014 K. The error is the quadratic sum of several systematic errors, with
statistical error of less than 0.1 mK. The instrument comprises a cooled
corrugated horn antenna coupled to a total-power radiometer. A cryogenic
mechanical waveguide switch alternately connects the radiometer to the horn and
to an internal reference load. The small measured temperature difference (<= 20
mK) between the sky signal and the reference load in conjunction with the use
of a cold front end keeps systematic instrumental corrections small.
Atmospheric and window emission are minimized by flying the instrument at 24 km
altitude. A large outer ground screen and smaller inner screen shield the
instrument from stray radiation from the ground and the balloon. In-flight
tests constrain the magnitude of ground radiation contamination, and low level
interference is monitored through observations in several narrow frequency
bands.Comment: 14 pages, 1 figure, submitted to ApJ
AMiBA: Broadband Heterodyne CMB Interferometry
The Y. T. Lee Array for Microwave Background (AMiBA) has reported the first
science results on the detection of galaxy clusters via the Sunyaev Zel'dovich
effect. The science objectives required small reflectors in order to sample
large scale structures (20') while interferometry provided modest resolutions
(2'). With these constraints, we designed for the best sensitivity by utilizing
the maximum possible continuum bandwidth matched to the atmospheric window at
86-102GHz, with dual polarizations. A novel wide-band analog correlator was
designed that is easily expandable for more interferometer elements. MMIC
technology was used throughout as much as possible in order to miniaturize the
components and to enhance mass production. These designs will find application
in other upcoming astronomy projects. AMiBA is now in operations since 2006,
and we are in the process to expand the array from 7 to 13 elements.Comment: 10 pages, 6 figures, ApJ in press; a version with high resolution
figures available at
http://www.asiaa.sinica.edu.tw/~keiichi/upfiles/AMiBA7/mtc_highreso.pd
CMB Telescopes and Optical Systems
The cosmic microwave background radiation (CMB) is now firmly established as
a fundamental and essential probe of the geometry, constituents, and birth of
the Universe. The CMB is a potent observable because it can be measured with
precision and accuracy. Just as importantly, theoretical models of the Universe
can predict the characteristics of the CMB to high accuracy, and those
predictions can be directly compared to observations. There are multiple
aspects associated with making a precise measurement. In this review, we focus
on optical components for the instrumentation used to measure the CMB
polarization and temperature anisotropy. We begin with an overview of general
considerations for CMB observations and discuss common concepts used in the
community. We next consider a variety of alternatives available for a designer
of a CMB telescope. Our discussion is guided by the ground and balloon-based
instruments that have been implemented over the years. In the same vein, we
compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the
South Pole Telescope (SPT). CMB interferometers are presented briefly. We
conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and
Planck, to demonstrate a remarkable evolution in design, sensitivity,
resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1:
Telescopes and Instrumentatio
Optical guided dispersions and subwavelength transmissions in dispersive plasmonic circular holes
The light transmission through a dispersive plasmonic circular hole is
numerically investigated with an emphasis on its subwavelength guidance. For a
better understanding of the effect of the hole diameter on the guided
dispersion characteristics, the guided modes, including both the surface
plasmon polariton mode and the circular waveguide mode, are studied for several
hole diameters, especially when the metal cladding has a plasmonic frequency
dependency. A brief comparison is also made with the guided dispersion
characteristics of a dispersive plasmonic gap [K. Y. Kim, et al., Opt. Express
14, 320-330 (2006)], which is a planar version of the present structure, and a
circular waveguide with perfect electric conductor cladding. Finally, the modal
behavior of the first three TM-like principal modes with varied hole diameters
is examined for the same operating mode.Comment: 20 pages, 5 figures, 1 tabl
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