1,720,991 research outputs found
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
Modeling Nonlinearity in Coherent Transmissions with Dominant Interpulse-Four-Wave-Mixing
No full textBy extending a well-established time-domain perturbation approach to dual-polarization propagation, we provide an analytical framework to predict the nonlinear interference (NLI) variance, i.e., the variance induced by nonlinearity on the sampled field, and the nonlinear threshold (NLT) in coherent transmissions with dominant intrachannel four-wave-mixing (IFWM). Such a framework applies to non dispersion managed (NDM) very long-haul coherent optical systems at nowadays typical baudrates of tens of Gigabaud, as well as to dispersion-managed (DM) systems at even higher baudrates, whenever IFWM is not removed by nonlinear equalization and is thus the dominant nonlinearity. The NLI variance formula has two fitting parameters which can be calibrated from simulations. From the NLI variance formula, analytical expressions of the NLT for both DM and NDM systems are derived and checked against recent NLT Monte-Carlo simulations
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
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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
Experimental characterization of Gaussian-distributed nonlinear distortions
No full textWe show that in dispersion-uncompensated 100G systems Kerr nonlinearity is akin to
additive Gaussian noise. Its variance grows as a power of propagation distance, and represents 1/3
of total noise variance at optimal channel power
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