103 research outputs found
A New Fast and Blind Cross-Polarization Modulation Digital Compensator
No full textWe propose a novel blind feed-forward compensator of cross-polarization modulation for PDM-QPSK signals. Simulations show an improvement of 1 dB in Q-factor in a 112Gbit/s 2000km SMF dispersion-managed link
DQPSK: when is a narrow filter receiver is good enough?
No full textIn this paper, we investigate experimentally and via
simulation the pros and cons of a narrow filter receiver for differential
quadrature phase-shift keying based on a single optical filter
and eschewing the conventional asymmetrical Mach–Zehnder interferometer
structure. We quantify the performance differences
between the two receivers, allowing system designers and operators
to determine when the less complex narrow filter receiver
might be the appropriate choice.We numerically optimize the 3-dB
bandwidth and center frequency of the narrow filter and show
it is more robust to carrier frequency detuning than the conventional
solution. We show that the narrow filter receiver is more
tolerant to chromatic dispersion (CD) than the conventional one,
and equally tolerant to first-order polarization-mode dispersion.
We show the impact of the 3-dB bandwidth on the receiver performance
when CD accumulates. Finally, we show via experiments
and simulations that the 3 dB advantage of the conventional receiver
vanishes when the nonlinear impairments are fiber nonlinearities;
comparing the two receivers at the optimum launch power
for a 25x80 km system, the difference in optical SNR margin is
reduced to 1.6 dB. Experiments are conducted at 42 Gb/s using
a commercially available narrow filter for reception
Low Complexity Compensation of SOA Nonlinearity for Single-Channel PSK and OOK
No full textCarrier density fluctuations in semiconductor optical
amplifiers (SOAs) impose penalties on phase-shift keying (PSK)
signals due to nonlinear phase noise (NLPN), and on-off keying
(OOK) signals due to self-gain modulation. In this paper, we propose
a simple scheme to equalize the impairments induced by SOA
nonlinearities, derived from the small signal analysis of carrier
density fluctuations. We demonstrate via simulation almost complete
cancelation of the NLPN added by a saturated SOA on a
differential PSK signal. We demonstrate via both simulations and
experiment the effectiveness of the method for mitigation of nonlinear
distortions imposed by SOAs on an OOK signal
SOA Intensity Noise Suppression: MulticanonicalMonte Carlo Simulator of Extremely Low BER
No full textWe present a thorough numerical study of intensity
noise mitigation of spectrum sliced wavelength-division multiplexing
(SS-WDM) systems employing a nonlinear semiconductor
optical amplifier (SOA) before the modulator. Our simulator of
the SS-WDM link, embedded inside a Multicanonical Monte Carlo
(MMC) platform, estimates the tails of the probability density
functions of the received signals down to probabilities smaller
than 10^-6. We introduce a new, simple, and efficient technique
to handle intersymbol interference (ISI) in MMC simulations.
We address the impact of optical postfiltering on SOA noise suppression
performance. While previous research experimentally
observed the SOA-induced noise cleaning in SS-WDM systems,
this is the first complete simulator able to correctly predict the
ensuing BER improvement. We measure the BER at different
bit-rates and validate predicted BERs with and without post
filtering
Statistical Characterization of Bit Patterning in SOAs: BER Prediction and Experimental Validation
No full textWe present a novel simulation tool for optical systems employing in-line nonlinear
SOAs, able to correctly estimate the bit error rate even in the presence of significant SOA-induced
intersymbol interference
Bit Patterning in SOAs: Statistical Characterization through Multicanonical Monte Carlo Simulations
No full textWe present a simulation tool based on the Multicanonical
Monte Carlo (MMC) method to characterize the
statistical properties of bit patterning in semiconductor optical
amplifiers (SOAs). Our tool estimates the conditional probability
density functions (PDFs) of marks and spaces of the received
signal. We introduce an experimental technique to directly measure
the conditional PDFs of the received marks and spaces using
a high bandwidth sampling scope. We demonstrate that predictions
from our simulation tool match the experimental data. We
measure the bit error rate (BER) of a SOA-based preamplified
receiver, where the SOA operates in the nonlinear regime, and
demonstrate that our simulation tool can predict the measured
BER
Nonlinear Cross-Polarization Mitigation Algorithm
No full textThe present document relates to optical transmission
systems. In particular, the present document relates
to methods and systems for the mitigation of Cross-
Polarization Modulation (XPOLM) in optical transmission
systems. A coherent optical receiver (200) adapted to
receive an optical signal transmitted over an optical transmission
channel exhibiting XPOLM is described. The received
optical signal comprises a first polarization component
and a second polarization component. The first
and second polarization components comprise sequences
of Mary phase shift keying, referred to as MPSK, symbols,
respectively, M being an integer, with M > 2. The
coherent optical receiver (200) comprises a conversion
and processing unit (201, 202) adapted to generate a set
of digital signals based on the received optical signal; a
polarization de-multiplexing unit (203) adapted to demultiplex
the set of digital signals into a first two dimensional,
referred to as complex, component in a first polarization
axis and a second complex component in a
second polarization axis; and an XPOLM compensation
unit (204) adapted to transform the first and second complex
components into the Stokes space, thereby yielding
a set of Stokes parameters; determine a rotation of the
first and second polarization axes based on the set of
Stokes parameters; and determine XPOLM compensated
first and second complex components by transforming
the first and second complex components in accordance
to the determined rotation of the first and second polarization
axes
A Fresh Look at Multicanonical Monte Carlo from a Telecom Perspective
No full textis a new form of adaptive importance sampling (IS). Thanks to its blind adaptation algorithm, it does not require an in-depth system knowledge for exploitation as does traditional IS. Hence MMC is a practical, handy tool to estimate via simulation the probability of rare events in complex telecom systems, such as the symbol error rate or the outage probability. In this paper, we present the analytical connections between MMC and IS, and describe the recursive algorithm via which MMC seeks an optimal “flat-histogram ” warping. We also provide practical guidelines on how MMC can be successfully applied in telecom to achieve accelerations of simulation time by many orders of magnitude with respect to standard Monte Carlo. Index Terms—Simulation, Monte Carlo methods, importance sampling, adaptive algorithm
Receiver-based fiber-optic link monitor
No full textA digital processor (DP) is configured to obtain a temporal sequence of digital phase distortion measurements of a first optical signal received by a coherent optical receiver (COR) from an optical fiber link, where the first optical signal co-propagates with a second, power-modulated, optical signal in different frequency channels. The DP is configured to estimate a cross-correlation between the temporal sequence of digital measurements and a temporal sequence of powers of the second optical signal for a plurality of relative time shifts between the sequences, and to identify a location along the optical fiber link based on a magnitude of the cross-correlation exceeding a threshold for a particular time shift
A first principles study of defects in titanium: interaction of twin boundaries with dislocations and oxygen interstitials
No full textInteraction between gliding dislocations and twin boundaries affects the plastic deformation of hcp metals such as titanium. In addition, oxygen greatly affects both strength and twinning in titanium. Predictive models of strength and twinning rely on understanding of the underlying atomic scale mechanisms which are best captured through computer simulations. While recent first-principles methods predict dislocation core structures and boundary geometries and energies, modeling a dislocation near a boundary requires new techniques to treat the long range strain field of the dislocation near a boundary. Using flexible boundary conditions with a new method to compute the lattice Green’s function for crystals containing a planar interface, we present a general method to study line defects interacting with interfaces with a tractable number of atoms. This method is general in the sense that it can consider long range atomic interactions and reconstructions near the interface. We use the interfacial lattice Green’s function to model a screw dislocation interaction with Ti (10-12) twin boundary for the first electronic structure prediction of a dislocation in a boundary. We predict the dislocation core geometry in the twin boundary and compare with the core structure in bulk titanium. The first principles nature of this study makes it possible to consider interactions with solutes. The interaction energy of an oxygen interstitial with the Ti (10-12) is also computed. While we applied our method to a systematic study of defects interactions in titanium, the method is general and opens up the possibility of investigating line defects/interface interactions with chemistry changes in arbitrary systems.Item withdrawn by Mark Zulauf ([email protected]) on 2011-10-11T21:29:24Z
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