19,528 research outputs found
Optical surface waves in periodic layered medium grown by liquid phase epitaxy
Optical surface waves propagating along the surface of a multilayer stack have been observed. The multilayer stack is grown by liquid phase epitaxy. The transverse intensity distribution measured is found to agree with our theoretical calculation
Observation of confined propagation in Bragg waveguides
A new type of waveguiding in a slab dielectric bounded on one side by air and on the other by a periodic layered medium (grown by molecular beam epitaxy) has been demonstrated
A study of topologies and protocols for fiber optic local area network
The emergence of new applications requiring high data traffic necessitates the development of high speed local area networks. Optical fiber is selected as the transmission medium due to its inherent advantages over other possible media and the dual optical bus architecture is shown to be the most suitable topology. Asynchronous access protocols, including token, random, hybrid random/token, and virtual token schemes, are developed and analyzed. Exact expressions for insertion delay and utilization at light and heavy load are derived, and intermediate load behavior is investigated by simulation. A new tokenless adaptive scheme whose control depends only on the detection of activity on the channel is shown to outperform round-robin schemes under uneven loads and multipacket traffic and to perform optimally at light load. An approximate solution to the queueing delay for an oscillating polling scheme under chaining is obtained and results are compared with simulation. Solutions to the problem of building systems with a large number of stations are presented, including maximization of the number of optical couplers, and the use of passive star/bus topologies, bridges and gateways
Scintillation observations of satellite signals
Scintillation observations of satellite signal
Coherent control of microwave pulse storage in superconducting circuits
Coherent pulse control for quantum memory is viable in the optical domain but
nascent in microwave quantum circuits. We show how to realize coherent storage
and on-demand pulse retrieval entirely within a superconducting circuit by
exploiting and extending existing electromagnetically induced transparency
technology in superconducting quantum circuits. Our scheme employs a linear
array of superconducting artificial atoms coupled to a microwave transmission
line.Comment: 13 pages, 4 figures and some supplementary materia
Mapping Topographic Structure in White Matter Pathways with Level Set Trees
Fiber tractography on diffusion imaging data offers rich potential for
describing white matter pathways in the human brain, but characterizing the
spatial organization in these large and complex data sets remains a challenge.
We show that level set trees---which provide a concise representation of the
hierarchical mode structure of probability density functions---offer a
statistically-principled framework for visualizing and analyzing topography in
fiber streamlines. Using diffusion spectrum imaging data collected on
neurologically healthy controls (N=30), we mapped white matter pathways from
the cortex into the striatum using a deterministic tractography algorithm that
estimates fiber bundles as dimensionless streamlines. Level set trees were used
for interactive exploration of patterns in the endpoint distributions of the
mapped fiber tracks and an efficient segmentation of the tracks that has
empirical accuracy comparable to standard nonparametric clustering methods. We
show that level set trees can also be generalized to model pseudo-density
functions in order to analyze a broader array of data types, including entire
fiber streamlines. Finally, resampling methods show the reliability of the
level set tree as a descriptive measure of topographic structure, illustrating
its potential as a statistical descriptor in brain imaging analysis. These
results highlight the broad applicability of level set trees for visualizing
and analyzing high-dimensional data like fiber tractography output
Light Transmission Through Metallic-Mean Quasiperiodic Stacks with Oblique Incidence
The propagation of s- and p-polarized light through quasiperiodic
multilayers, consisting of layers with different refractive indices, is studied
by the transfer matrix method. In particular, we focus on the transmission
coefficient of the systems in dependency on the incidence angle and on the
ratio of the refractive indices. We obtain additional bands with almost
complete transmission in the quasiperiodic systems at frequencies in the range
of the photonic band gap of a system with a periodic alignment of the two
materials for both types of light polarization. With increasing incidence angle
these bands bend towards higher frequencies, where the curvature of the
transmission bands in the quasiperiodic stack depends on the metallic mean of
the construction rule. Additionally, in the quasiperiodic systems for
p-polarized light the bands show almost complete transmission near the
Brewster's angle in contrast to the results for s-polarized light. Further, we
present results for the influence of the refractive indices at the midgap
frequency of the periodic stack, where the quasiperiodicity was found to be
most effective.Comment: 10 pages, 7 figure
Tunable transmission and bistability in left-handed bandgap structures
We study the defect-induced nonlinear transmission of a periodic structure
created by alternating slabs of two materials with positive and negative
refractive index. We demonstrate bistable switching and tunable nonlinear
transmission in a novel type of bandgap that corresponds to the vanishing
average refractive index, and compare the observed effects for two types of the
bandgaps.Comment: 3 pages, 5 figures; significant change
Bistable diode action in left-handed periodic structures
We study nonlinear transmission of an asymmetric multilayer structure created
by alternating slabs of two materials with positive and negative refractive
index. We demonstrate that such a structure exhibits passive spatially
nonreciprocal transmission of electromagnetic waves, the analogue of the
electronic diode. We study the properties of this left-handed diode and confirm
its highly nonreciprocal and bistable transmittance by employing direct
simulations.Comment: 4 pages, 5 figure
Transverse Bragg-reflector injection lasers
A GaAs-GaAlAs injection laser has been tested that confines light in the lateral dimension (normal to junction plane) by a multilayer Bragg reflector. In the past, light has been confined as a result of the higher-index guiding region and resulting evanescent fields
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