34,656 research outputs found
Digital nonlinearity compensation in high-capacity optical communication systems considering signal spectral broadening effect
Nyquist-spaced transmission and digital signal processing have proved effective in maximising the spectral efficiency and reach of optical communication systems. In these systems, Kerr nonlinearity determines the performance limits, and leads to spectral broadening of the signals propagating in the fibre. Although digital nonlinearity compensation was validated to be promising for mitigating Kerr nonlinearities, the impact of spectral broadening on nonlinearity compensation has never been quantified. In this paper, the performance of multi-channel digital back-propagation (MC-DBP) for compensating fibre nonlinearities in Nyquist-spaced optical communication systems is investigated, when the effect of signal spectral broadening is considered. It is found that accounting for the spectral broadening effect is crucial for achieving the best performance of DBP in both single-channel and multi-channel communication systems, independent of modulation formats used. For multi-channel systems, the degradation of DBP performance due to neglecting the spectral broadening effect in the compensation is more significant for outer channels. Our work also quantified the minimum bandwidths of optical receivers and signal processing devices to ensure the optimal compensation of deterministic nonlinear distortions
Nonlinear pulse shaping in fibres for pulse generation and optical processing
The development of new all-optical technologies for data processing and signal manipulation is a field of growing importance with a strong potential for numerous applications in diverse areas of modern science. Nonlinear phenomena occurring in optical fibres have many attractive features and great, but not yet fully explored, potential in signal processing. Here, we review recent progress on the use of fibre nonlinearities for the generation and shaping of optical pulses and on the applications of advanced pulse shapes in all-optical signal processing. Amongst other topics, we will discuss ultrahigh repetition rate pulse sources, the generation of parabolic shaped pulses in active and passive fibres, the generation of pulses with triangular temporal profiles, and coherent supercontinuum sources. The signal processing applications will span optical regeneration, linear distortion compensation, optical decision at the receiver in optical communication systems, spectral and temporal signal doubling, and frequency conversion
Chromatic Dispersion Compensation in electrical domain via Signal Pre-distortion using a dual-drive Mach-Zehnder Modulator
In recent years, evolution of technology has contributed a major role in the field of optical communication systems. There is an ever growing demand for transmitting signals at higher data rates and compensating the transmission impairments simultaneously. Speed of the signal transmission down the optical fiber is limited by transmission impairments that are characterized as linear or nonlinear losses. In my thesis, I lay a special emphasis on linear loss especially chromatic dispersion and it\u27s effect on an optical signal down the fiber and study the compensation techniques in an electrical domain challenging the methods employed in an optical domain. In this digital world, there is an increase in the evolution of electrical components such as high speed memory units and low power consumption models. Electrical domain provides advantages in terms of processing the signal in a cost effective way and achieving the similar results with respect to the optical domain. In addition to the analysis, my investigation includes the effect of noise present in optical fiber communication systems and limitations of electrical components in achieving the compensation
A survey on fiber nonlinearity compensation for 400 Gbps and beyond optical communication systems
Optical communication systems represent the backbone of modern communication
networks. Since their deployment, different fiber technologies have been used
to deal with optical fiber impairments such as dispersion-shifted fibers and
dispersion-compensation fibers. In recent years, thanks to the introduction of
coherent detection based systems, fiber impairments can be mitigated using
digital signal processing (DSP) algorithms. Coherent systems are used in the
current 100 Gbps wavelength-division multiplexing (WDM) standard technology.
They allow the increase of spectral efficiency by using multi-level modulation
formats, and are combined with DSP techniques to combat the linear fiber
distortions. In addition to linear impairments, the next generation 400 Gbps/1
Tbps WDM systems are also more affected by the fiber nonlinearity due to the
Kerr effect. At high input power, the fiber nonlinear effects become more
important and their compensation is required to improve the transmission
performance. Several approaches have been proposed to deal with the fiber
nonlinearity. In this paper, after a brief description of the Kerr-induced
nonlinear effects, a survey on the fiber nonlinearity compensation (NLC)
techniques is provided. We focus on the well-known NLC techniques and discuss
their performance, as well as their implementation and complexity. An extension
of the inter-subcarrier nonlinear interference canceler approach is also
proposed. A performance evaluation of the well-known NLC techniques and the
proposed approach is provided in the context of Nyquist and super-Nyquist
superchannel systems.Comment: Accepted in the IEEE Communications Surveys and Tutorial
Volterra-assisted Optical Phase Conjugation: a Hybrid Optical-Digital Scheme For Fiber Nonlinearity Compensation
Mitigation of optical fiber nonlinearity is an active research field in the
area of optical communications, due to the resulting marked improvement in
transmission performance. Following the resurgence of optical coherent
detection, digital nonlinearity compensation (NLC) schemes such as digital
backpropagation (DBP) and Volterra equalization have received much attention.
Alternatively, optical NLC, and specifically optical phase conjugation (OPC),
has been proposed to relax the digital signal processing complexity. In this
work, a novel hybrid optical-digital NLC scheme combining OPC and a Volterra
equalizer is proposed, termed Volterra-Assisted OPC (VAO). It has a twofold
advantage: it overcomes the OPC limitation in asymmetric links and
substantially enhances the performance of Volterra equalizers. The proposed
scheme is shown to outperform both OPC and Volterra equalization alone by up to
4.2 dB in a 1000 km EDFA-amplified fiber link. Moreover, VAO is also
demonstrated to be very robust when applied to long-transmission distances,
with a 2.5 dB gain over OPC-only systems at 3000 km. VAO combines the
advantages of both optical and digital NLC offering a promising trade-off
between performance and complexity for future high-speed optical communication
systems
Revisiting Multi-Step Nonlinearity Compensation with Machine Learning
For the efficient compensation of fiber nonlinearity, one of the guiding
principles appears to be: fewer steps are better and more efficient. We
challenge this assumption and show that carefully designed multi-step
approaches can lead to better performance-complexity trade-offs than their
few-step counterparts.Comment: 4 pages, 3 figures, This is a preprint of a paper submitted to the
2019 European Conference on Optical Communicatio
Stochastic Digital Backpropagation with Residual Memory Compensation
Stochastic digital backpropagation (SDBP) is an extension of digital
backpropagation (DBP) and is based on the maximum a posteriori principle. SDBP
takes into account noise from the optical amplifiers in addition to handling
deterministic linear and nonlinear impairments. The decisions in SDBP are taken
on a symbol-by-symbol (SBS) basis, ignoring any residual memory, which may be
present due to non-optimal processing in SDBP. In this paper, we extend SDBP to
account for memory between symbols. In particular, two different methods are
proposed: a Viterbi algorithm (VA) and a decision directed approach. Symbol
error rate (SER) for memory-based SDBP is significantly lower than the
previously proposed SBS-SDBP. For inline dispersion-managed links, the VA-SDBP
has up to 10 and 14 times lower SER than DBP for QPSK and 16-QAM, respectively.Comment: 7 pages, accepted to publication in 'Journal of Lightwave Technology
(JLT)
Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments
We experimentally investigate mutual information and generalized mutual
information for coherent optical transmission systems. The impact of the
assumed channel distribution on the achievable rate is investigated for
distributions in up to four dimensions. Single channel and wavelength division
multiplexing (WDM) transmission over transmission links with and without inline
dispersion compensation are studied. We show that for conventional WDM systems
without inline dispersion compensation, a circularly symmetric complex Gaussian
distribution is a good approximation of the channel. For other channels, such
as with inline dispersion compensation, this is no longer true and gains in the
achievable information rate are obtained by considering more sophisticated
four-dimensional (4D) distributions. We also show that for nonlinear channels,
gains in the achievable information rate can also be achieved by estimating the
mean values of the received constellation in four dimensions. The highest gain
for such channels is seen for a 4D correlated Gaussian distribution
Time-Frequency Packing for High Capacity Coherent Optical Links
We consider realistic long-haul optical links, with linear and nonlinear
impairments, and investigate the application of time-frequency packing with
low-order constellations as a possible solution to increase the spectral
efficiency. A detailed comparison with available techniques from the literature
will be also performed. We will see that this technique represents a feasible
solution to overcome the relevant theoretical and technological issues related
to this spectral efficiency increase and could be more effective than the
simple adoption of high-order modulation formats.Comment: 10 pages, 9 figures. arXiv admin note: text overlap with
arXiv:1406.5685 by other author
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