624 research outputs found
Densely Integrated Photonic Devices based on Microring Resonators in Access Networks
The application of optical fibers has led to virtually lossless point to point data links in the core network with practically unlimited bandwidth. In response to increasing bandwidth demands of consumers the optical techniques employed in these networks are now gradually extended towards the consumers premises. At the access network level, where equipment is shared by a few users at the most, cost is the major issue. In addition the demand of optical transparency at the nodes and hubs, excluding conversion between the optical and electrical domains, results in a high degree of complexity of the devices. Fortunately, through the use of flexible WDM bandwidth allocation schemes that provide bandwidth where needed, and cheap mass-produced densely integrated optical components, the cost can be reduced significantly. Promising building blocks in these components are Microring Resonators (MRs) built using high refractive index waveguides which can be used to create densely integrated wavelength filters as well as more complex functionality.\ud
In this work we present a 1x4 reconfigurable optical add-drop multiplexer (rOADM) as well as a 1x4x4 reconfigurable wavelength router in variants operating in the second and third telecom window. The devices, which can be used at bit rates up to 40 Gbit/s, have a footprint less than 2 mm2 and are based on thermally tunable vertically coupled microring resonators fabricated in the high contrast (Δn≈0.55) Si3N4/SiO2 materials system. In addition to the presented devices a new polarization diversity scheme is proposed that solves the issue of polarization dependence behavior of microring resonators without the need of doubling the optical circuit
Prototype Detector for Ultrahigh Energy Neutrino Detection
Necessary technical experience is being gained from successful construction
and deployment of current prototype detectors to search for UHE neutrinos in
Antarctica, Lake Baikal in Russia, and the Mediterranean. The prototype
detectors have also the important central purpose of determining whether or not
UHE neutrinos do in fact exist in nature by observation of at least a few UHE
neutrino-induced leptons with properties that are not consistent with expected
backgrounds. We discuss here the criteria for a prototype detector to
accomplish that purpose in a convincing way even if the UHE neutrino flux is
substantially lower than predicted at present.Comment: 18 pages, 8 figures, submitted to Astroparticle Physic
Henri Temianka Correspondence; (mrsklein)
This collection contains material pertaining to the life, career, and activities of Henri Temianka, violin virtuoso, conductor, music teacher, and author. Materials include correspondence, concert programs and flyers, music scores, photographs, and books.https://digitalcommons.chapman.edu/temianka_correspondence/3870/thumbnail.jp
Henri Temianka Correspondence; (aklein)
This collection contains material pertaining to the life, career, and activities of Henri Temianka, violin virtuoso, conductor, music teacher, and author. Materials include correspondence, concert programs and flyers, music scores, photographs, and books.https://digitalcommons.chapman.edu/temianka_correspondence/3707/thumbnail.jp
Magnetic Reconnection May Control the Ion-Scale Spectral Break of Solar Wind Turbulence
The power spectral density of magnetic fluctuations in the solar wind
exhibits several power-law-like frequency ranges with a well defined break
between approximately 0.1 and 1 Hz in the spacecraft frame. The exact
dependence of this break scale on solar wind parameters has been extensively
studied but is not yet fully understood. Recent studies have suggested that
reconnection may induce a break in the spectrum at a "disruption scale"
, which may be larger than the fundamental ion kinetic scales,
producing an unusually steep spectrum just below the break. We present a
statistical investigation of the dependence of the break scale on the proton
gyroradius , ion inertial length , ion sound radius ,
proton-cyclotron resonance scale and disruption scale as a
function of . We find that the steepest spectral indices of
the dissipation range occur when is in the range of 0.1-1 and the
break scale is only slightly larger than the ion sound scale (a situation
occurring 41% of the time at 1 AU), in qualitative agreement with the
reconnection model. In this range the break scale shows remarkably good
correlation with . Our findings suggest that, at least at low
, reconnection may play an important role in the development of the
dissipation range turbulent cascade and causes unusually steep (steeper than
-3) spectral indices.Comment: Accepted in ApJ
On the Conservation of Cross Helicity and Wave Action in Solar-Wind Models with Non-WKB Alfven Wave Reflection
The interaction between Alfven-wave turbulence and the background solar wind
affects the cross helicity in two ways. Non-WKB reflection converts
outward-propagating Alfven waves into inward-propagating Alfven waves and vice
versa, and the turbulence transfers momentum to the background flow. When both
effects are accounted for, the total cross helicity is conserved. In the
special case that the background density and flow speed are independent of
time, the equations of cross-helicity conservation and total-energy
conservation can be combined to recover a well-known equation derived by
Heinemann and Olbert that has been interpreted as a non-WKB generalization of
wave-action conservation. This latter equation (in contrast to cross-helicity
and energy conservation) does not hold when the background varies in time.Comment: 9 pages, 1 figure, in press at Ap
A Modified Version of Taylor's Hypothesis for Solar Probe Plus Observations
The Solar Probe Plus (SPP) spacecraft will explore the near-Sun environment,
reaching heliocentric distances less than . Near Earth,
spacecraft measurements of fluctuating velocities and magnetic fields taken in
the time domain are translated into information about the spatial structure of
the solar wind via Taylor's "frozen turbulence" hypothesis. Near the perihelion
of SPP, however, the solar-wind speed is comparable to the Alfv\'en speed, and
Taylor's hypothesis in its usual form does not apply. In this paper, we show
that, under certain assumptions, a modified version of Taylor's hypothesis can
be recovered in the near-Sun region. We consider only the transverse,
non-compressive component of the fluctuations at length scales exceeding the
proton gyroradius, and we describe these fluctuations using an approximate
theoretical framework developed by Heinemann and Olbert. We show that
fluctuations propagating away from the Sun in the plasma frame obey a relation
analogous to Taylor's hypothesis when and , where is the component of the spacecraft velocity
perpendicular to the mean magnetic field and () is the
Elsasser variable corresponding to transverse, non-compressive fluctuations
propagating away from (towards) the Sun in the plasma frame. Observations and
simulations suggest that, in the near-Sun solar wind, the above inequalities
are satisfied and fluctuations account for most of the fluctuation
energy. The modified form of Taylor's hypothesis that we derive may thus make
it possible to characterize the spatial structure of the energetically dominant
component of the turbulence encountered by SPP.Comment: 5 pages, 1 figure, accepted in ApJ Lette
Reconfigurable optical add-drop multiplexer using microring resonators
We report a reconfigurable four-channel optical add-drop multiplexer for use in access networks. The optical add-drop multiplexer (OADM) is based on vertically coupled thermally tunable Si/sub 3/N/sub 4/--SiO/sub 2/ microring resonators (MRs) and has been realized on a footprint of 0.25 mm/sup 2/. Individual MRs in the OADM can be tuned across the full free-spectral range of 4.18 nm and have a 3-dB bandwidth of 50 GHz
Optical network components based on microring resonators
In the last years much effort has been made to arrive at optical integrated circuits with high complexity and advanced functionality for application in optical networks. For this aim high index contrast structures, like optical microresonators, are employed that allow for a large number of functional elements within a given chip area: VLSI photonics. Experimental results of work performed at MESA+ will be reported including a microresonator-based, ultra-compact reconfigurable optical add-drop multiplexer operating at 40 Gbit/s and fabricated in SiON technology. In addition a discussion will be given of new challenges and possible solutions
High index contrast photonics components for optical data communication
Microresonator-based high index contrast integrated optical components show promising performance for the demands of near-future optical networks. Experimental results of an ultra-compact reconfigurable OADM at 40 Gbit/s are presented in detail
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