149,860 research outputs found
Conical quadreflex antenna analytical study
A method for evaluating the performance of a four-reflection or quadreflex antenna is reported. Geometrical optics was used initially to determine the ideal feed pattern required to produce uniform illumination on the aperture of the conical reflector and the reverse problem of quickly finding the aperture illumination given an arbitrary feed pattern. The knowledge of the aperture illumination makes it possible to compute the antenna efficiency, which is useful for comparing antenna performance during tradeoff studies. Scattering calculations, using physical optics techniques, were then used to more accurately determine the performance of a specific design
Design Considerations for Large Detector Arrays on Submillimeter-wave Telescopes
The emerging technology of large (~ 10,000 pixel) submillimeter-wave
bolometer arrays presents a novel optical design problem---how can such arrays
be fed by diffraction-limited telescope optics where the primary mirror is less
than 100,000 wavelengths in diameter? Standard Cassegrain designs for
radiotelescope optics exhibit focal surface curvature so large that detectors
cannot be placed more than 25 beam diameters from the central ray. The problem
is worse for Ritchey-Cretien designs, because these minimize coma while
increasing field curvature. Classical aberrations, including coma, are usually
dominated by diffraction in submillimeter-wave single dish telescopes. The
telescope designer must consider (1) diffraction, (2) aberration, (3) curvature
of field, (4) cross-polarization, (5) internal reflections, (6) the effect of
blockages, (7) means of beam chopping on- and off-source, (8) gravitational and
thermal deformations of the primary mirror, (9) the physical mounting of large
detector packages, and (10) the effect of gravity and (11) vibration on those
detectors. Simultaneous optimization of these considerations in the case of
large detector arrays leads to telescopes that differ considerably from
standard radiotelescope designs. Offset optics provide flexibility for mounting
detectors, while eliminating blockage and internal reflections. Aberrations and
cross-polarization can be the same as on-axis designs having the same diameter
and focal length. Trade-offs include the complication of primary mirror
homology and an increase in overall cost. A dramatic increase in usable field
of view can be achieved using shaped optics. Solutions having one to six
mirrors will be discussed, including a possible six-mirror design for the
proposed South Pole 10m telescope.Comment: in proceedings "Radio Telescopes" SPIE Astronomical Telescopes and
Instrumentation, 30 March 2000, Munich. SPIE code 4015-46. 12 pages 4 figures
Revised to fix typos, figur
The design and evaluation of grazing incidence relay optics
X-ray astronomy, both solar and celestial, has many needs for high spatial resolution observations which have to be performed with electronic detectors. If the resolution is not to be detector limited, plate scales in excess of 25 microns arc/sec, corresponding to focal lengths greater than 5 m, are required. In situations where the physical size is restricted, the problem can be solved by the use of grazing incidence relay optics. A system was developed which employs externally polished hyperboloid-hyperboloid surfaces to be used in conjunction with a Wolter-Schwarzschild primary. The secondary is located in front of the primary focus and provides a magnification of 4, while the system has a plate scale of 28 microns arc/sec and a length of 1.9 m. The design, tolerance specification, fabrication and performance at visible and X-ray wavelengths of this optical system are described
Optical Nanotransmission Lines: Synthesis of Planar Left-Handed Metamaterials in the Infrared and Visible Regimes
Following our recent theoretical development of the concept of
nano-inductors, nano-capacitors and nano-resistors at optical frequencies and
the possibility of synthesizing more complex nano-scale circuits, here we
theoretically investigate in detail the problem of optical
nano-transmission-lines (NTL) that can be envisioned by properly joining
together arrays of these basic nano-scale circuit elements. We show how, in the
limit in which these basic circuit elements are closely packed together, the
NTLs can be regarded as stacks of plasmonic and non-plasmonic planar slabs,
which may be designed to effectively exhibit the properties of planar
metamaterials with forward (right-handed) or backward (left-handed) operation.
With the proper design, negative refraction and left-handed propagation are
shown to be possible in these planar plasmonic guided-wave structures,
providing possibilities for sub-wavelength focusing and imaging in planar
optics, and laterally-confined waveguiding at IR and visible frequencies. The
effective material parameters for such NTLs are derived, and the connection and
analogy between these optical NTLs and the double-negative and double-positive
metamaterials are also explored. Physical insights and justification for the
results are also presented.Comment: 26 pages, 12 figures, accepted for publication in JOSA B, scheduled
to appear March 200
Robust topology optimization of three-dimensional photonic-crystal band-gap structures
We perform full 3D topology optimization (in which "every voxel" of the unit
cell is a degree of freedom) of photonic-crystal structures in order to find
optimal omnidirectional band gaps for various symmetry groups, including fcc
(including diamond), bcc, and simple-cubic lattices. Even without imposing the
constraints of any fabrication process, the resulting optimal gaps are only
slightly larger than previous hand designs, suggesting that current photonic
crystals are nearly optimal in this respect. However, optimization can discover
new structures, e.g. a new fcc structure with the same symmetry but slightly
larger gap than the well known inverse opal, which may offer new degrees of
freedom to future fabrication technologies. Furthermore, our band-gap
optimization is an illustration of a computational approach to 3D dispersion
engineering which is applicable to many other problems in optics, based on a
novel semidefinite-program formulation for nonconvex eigenvalue optimization
combined with other techniques such as a simple approach to impose symmetry
constraints. We also demonstrate a technique for \emph{robust} topology
optimization, in which some uncertainty is included in each voxel and we
optimize the worst-case gap, and we show that the resulting band gaps have
increased robustness to systematic fabrication errors.Comment: 17 pages, 9 figures, submitted to Optics Expres
Cloaking and anamorphism for light and mass diffusion
We first review classical results on cloaking and mirage effects for
electromagnetic waves. We then show that transformation optics allows the
masking of objects or produces mirages in diffusive regimes. In order to
achieve this, we consider the equation for diffusive photon density in
transformed coordinates, which is valid for diffusive light in scattering
media. More precisely, generalizing transformations for star domains introduced
in [Diatta and Guenneau, J. Opt. 13, 024012, 2011] for matter waves, we
numerically demonstrate that infinite conducting objects of different shapes
scatter diffusive light in exactly the same way. We also propose a design of
external light-diffusion cloak with spatially varying sign-shifting parameters
that hides a finite size scatterer outside the cloak. We next analyse
non-physical parameter in the transformed Fick's equation derived in [Guenneau
and Puvirajesinghe, R. Soc. Interface 10, 20130106, 2013], and propose to use a
non-linear transform that overcomes this problem. We finally investigate other
form invariant transformed diffusion-like equations in the time domain, and
touch upon conformal mappings and non-Euclidean cloaking applied to diffusion
processes.Comment: 42 pages, Latex, 14 figures. V2: Major changes : some formulas
corrected, some extra cases added, overall length extended from 21 pages (V1)
to 42 pages (present version V2). The last version will appear at Journal of
Optic
Topology optimization of freeform large-area metasurfaces
We demonstrate optimization of optical metasurfaces over --
degrees of freedom in two and three dimensions, 100--1000+ wavelengths
() in diameter, with 100+ parameters per . In particular,
we show how topology optimization, with one degree of freedom per
high-resolution "pixel," can be extended to large areas with the help of a
locally periodic approximation that was previously only used for a few
parameters per . In this way, we can computationally discover
completely unexpected metasurface designs for challenging multi-frequency,
multi-angle problems, including designs for fully coupled multi-layer
structures with arbitrary per-layer patterns. Unlike typical metasurface
designs based on subwavelength unit cells, our approach can discover both sub-
and supra-wavelength patterns and can obtain both the near and far fields
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