139 research outputs found
Coherent modulation up to 100 GBd 16QAM using silicon-organic hybrid (SOH) devices
We demonstrate the generation of higher-order modulation formats using
silicon-based inphase/quadrature (IQ) modulators at symbol rates of up to 100
GBd. Our devices exploit the advantages of silicon-organic hybrid (SOH)
integration, which combines silicon-on-insulator waveguides with highly
efficient organic electro-optic (EO) cladding materials to enable small drive
voltages and sub-millimeter device lengths. In our experiments, we use an SOH
IQ modulator with a {\pi}-voltage of 1.6 V to generate 100 GBd 16QAM signals.
This is the first time that the 100 GBd mark is reached with an IQ modulator
realized on a semiconductor substrate, leading to a single-polarization line
rate of 400 Gbit/s. The peak-to-peak drive voltages amount to 1.5 Vpp,
corresponding to an electrical energy dissipation in the modulator of only 25
fJ/bit
Electrically packaged silicon-organic hybrid (SOH) I/Q-modulator for 64 GBd operation
Silicon-organic hybrid (SOH) electro-optic (EO) modulators combine small
footprint with low operating voltage and hence low power dissipation, thus
lending themselves to on-chip integration of large-scale device arrays. Here we
demonstrate an electrical packaging concept that enables high-density
radio-frequency (RF) interfaces between on-chip SOH devices and external
circuits. The concept combines high-resolution
printed-circuit boards with technically simple metal wire bonds and is amenable
to packaging of device arrays with small on-chip bond pad pitches. In a set of
experiments, we characterize the performance of the underlying RF building
blocks and we demonstrate the viability of the overall concept by generation of
high-speed optical communication signals. Achieving line rates (symbols rates)
of 128 Gbit/s (64 GBd) using quadrature-phase-shiftkeying (QPSK) modulation and
of 160 Gbit/s (40 GBd) using 16-state quadrature-amplitudemodulation (16QAM),
we believe that our demonstration represents an important step in bringing SOH
modulators from proof-of-concept experiments to deployment in commercial
environments
A verified equivalent-circuit model for slotwaveguide modulators
We formulate and experimentally validate an equivalent-circuit model based on
distributed elements to describe the electric and electro-optic (EO) properties
of travellingwave silicon-organic hybrid (SOH) slot-waveguide modulators. The
model allows to reliably predict the small-signal EO frequency response of the
modulators exploiting purely electrical measurements of the frequency-dependent
RF transmission characteristics. We experimentally verify the validity of our
model, and we formulate design guidelines for an optimum trade-off between
optical loss due to free-carrier absorption (FCA), electro-optic bandwidth, and
{\pi}-voltage of SOH slot-waveguide modulators
Comb-based WDM transmission at 10 Tbit/s using a DC-driven quantum-dash mode-locked laser diode
Chip-scale frequency comb generators have the potential to become key
building blocks of compact wavelength-division multiplexing (WDM) transceivers
in future metropolitan or campus-area networks. Among the various comb
generator concepts, quantum-dash (QD) mode-locked laser diodes (MLLD) stand out
as a particularly promising option, combining small footprint with simple
operation by a DC current and offering flat broadband comb spectra. However,
the data transmission performance achieved with QD-MLLD was so far limited by
strong phase noise of the individual comb tones, restricting experiments to
rather simple modulation formats such as quadrature phase shift keying (QPSK)
or requiring hard-ware-based compensation schemes. Here we demonstrate that
these limitations can be over-come by digital symbol-wise phase tracking
algorithms, avoiding any hardware-based phase-noise compensation. We
demonstrate 16QAM dual-polarization WDM transmission on 38 channels at an
aggregate net data rate of 10.68 Tbit/s over 75 km of standard single-mode
fiber. To the best of our knowledge, this corresponds to the highest data rate
achieved through a DC-driven chip-scale comb generator without any
hardware-based phase-noise reduction schemes
Mitgliedschaft in Gewerkschaften: Inklusions- und Exklusionstendenzen in der Organisation von Arbeitnehmerinteressen in Europa
"Die Gewerkschaften stehen heute in vielen europäischen Ländern vor beträchtlichen Mitgliederproblemen. Jedoch variiert der gewerkschaftliche Organisationsgrad zwischen einem eher niedrigen Niveau in Süd- und Osteuropa und einem höheren Niveau in Nordeuropa. Außerdem zeigen sich im internationalen Vergleich erhebliche Unterschiede zwischen sozialen Gruppen. Zu welchem Grad gelingt es den Gewerkschaften noch, ihre Klientel einzubinden und zumindest als Mitglieder zu mobilisieren? Dieser Frage wird mit Hilfe von deskriptiven Analysen des European Social Surveys von 2002/03 für West- und Ost-Deutschland sowie weiteren 18 europäischen Ländern nachgegangen. Es werden zentrale Muster der Inklusion bzw. Exklusion von Arbeitnehmerinteressen aufgezeigt und mögliche Erklärungen der (Nicht-)Mitgliedschaft in Gewerkschaften erörtert. Neben den sozialstrukturellen Ursachen für geringere Organisationsgrade von Frauen, Arbeitslosen und atypisch Beschäftigten, werden zentrale institutionelle Faktoren herausgearbeitet, die selektive Anreize für eine Gewerkschaftsmitgliedschaft schaffen und den betrieblichen Zugang für Gewerkschaften erleichtern. Die theoretische Fruchtbarkeit eines In-/ Exklusionsansatzes zeigt sich besonders in der mangelnden Repräsentation der Interessen von atypisch Beschäftigten und Arbeitslosen sowie solchen in peripheren (unorganisierten) Arbeitsplätzen." (Autorenreferat)"In many European countries trade unions face considerable membership problems. Union density varies between a mostly low level in Southern and Eastern European societies and high levels in Nordic countries. Moreover, there are considerable cross-national differences between social groups. To what degree do trade unions integrate their clientele and are they capable of mobilizing members? We study this question by using descriptive statistics from the European Social Survey of 2002/03 for (Western and Eastern) Germany and for 18 other European countries. We discuss crucial patterns of inclusion and exclusion in the organization of labour interests and possible explanatory factors for (non-)membership. In addition to social structural causes for low union density of women, the unemployed and atypical employed, we review several institutional factors that provide selective incentives for membership and foster union access to workplaces. The inclusion/exclusion perspective proves particularly valuable for the analysis of low representation of the unemployed and atypical employed as well for those working in peripheral (unorganized) workplaces." (author's abstract
Non-sliced Optical Arbitrary Waveform Measurement (OAWM) Using a Silicon Photonic Receiver Chip
Comb-based optical arbitrary waveform measurement (OAWM) techniques can
overcome the bandwidth limitations of conventional coherent detection schemes
and may have disruptive impact on a wide range of scientific and industrial
applications. Over the previous years, different OAWM schemes have been
demonstrated, showing the performance and the application potential of the
concept in laboratory experiments. However, these demonstrations still relied
on discrete fiber-optic components or on combinations of discrete coherent
receivers with integrated optical slicing filters that require complex tuning
procedures to achieve the desired performance. In this paper, we demonstrate
the first wavelength-agnostic OAWM front-end that is integrated on a compact
silicon photonic chip and that neither requires slicing filters nor active
controls. Our OAWM system comprises four IQ receivers, which are accurately
calibrated using a femtosecond mode-locked laser and which offer a total
acquisition bandwidth of 170 GHz. Using sinusoidal test signals, we measure a
signal-to-noise-and-distortion ratio (SINAD) of 30 dB for the reconstructed
signal, which corresponds to an effective number of bits (ENOB) of 4.7 bit,
where the underlying electronic analog-to-digital converters (ADC) turn out to
be the main limitation. The performance of the OAWM system is further
demonstrated by receiving 64QAM data signals at symbol rates of up to 100 GBd,
achieving constellation signal-to-noise ratios (CSNR) that are on par with
those obtained for conventional coherent receivers. In a theoretical
scalability analysis, we show that increasing the channel count of non-sliced
OAWM systems can improve both the acquisition bandwidth and the signal quality.
We believe that our work represents a key step towards out-of-lab use of highly
compact OAWM systems that rely on chip-scale integrated optical front-ends
IMPACT OF AORTIC VALVE CALCIFICATION SEVERITY ON FIVE-YEAR RESULTS OF PATIENTS UNDERGOING TRANSCATHETER AORTIC VALVE REPLACEMENT
Efficient free-space read-out of WGM lasers using circular micromirrors
Lasing from whispering-gallery mode (WGM) resonators occurs omnidirectional in azimuthal plane. Most applications of WGM resonators require spectral analysis with off-chip detectors, where in-plane emission and beam divergence hinder efficient detection. We demonstrate redirecting WGM laser emission from all azimuthal angles using a circular micromirror placed around the cavity. By collecting reflections off the micromirror via free-space optics, read-out intensity improved by one order of magnitude. Blocking vertically emitted spontaneous emission and recording reflections off the micromirror only, signal-to-noise ratio improved from 4.6 dB to 15 dB. Our read-out concept may be applied to arbitrary WGM cavity geometries without deteriorating the cavity`s quality factor
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