1,989 research outputs found
Coherent Optical DFT-Spread OFDM
We consider application of the discrete Fourier transform-spread orthogonal
frequency-division multiplexing (DFT-spread OFDM) technique to high-speed fiber
optic communications. The DFT-spread OFDM is a form of single-carrier technique
that possesses almost all advantages of the multicarrier OFDM technique (such
as high spectral efficiency, flexible bandwidth allocation, low sampling rate
and low-complexity equalization). In particular, we consider the optical
DFT-spread OFDM system with polarization division multiplexing (PDM) that
employs a tone-by-tone linear minimum mean square error (MMSE) equalizer. We
show that such a system offers a much lower peak-to-average power ratio (PAPR)
performance as well as better bit error rate (BER) performance compared with
the optical OFDM system that employs amplitude clipping.Comment: This idea was originally submitted at Nov. 28th, 2009. After many
times of rejection and resubmission, it was finally accepted by the journal
of Advances in Optical Technologie
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
An Overview on Application of Machine Learning Techniques in Optical Networks
Today's telecommunication networks have become sources of enormous amounts of
widely heterogeneous data. This information can be retrieved from network
traffic traces, network alarms, signal quality indicators, users' behavioral
data, etc. Advanced mathematical tools are required to extract meaningful
information from these data and take decisions pertaining to the proper
functioning of the networks from the network-generated data. Among these
mathematical tools, Machine Learning (ML) is regarded as one of the most
promising methodological approaches to perform network-data analysis and enable
automated network self-configuration and fault management. The adoption of ML
techniques in the field of optical communication networks is motivated by the
unprecedented growth of network complexity faced by optical networks in the
last few years. Such complexity increase is due to the introduction of a huge
number of adjustable and interdependent system parameters (e.g., routing
configurations, modulation format, symbol rate, coding schemes, etc.) that are
enabled by the usage of coherent transmission/reception technologies, advanced
digital signal processing and compensation of nonlinear effects in optical
fiber propagation. In this paper we provide an overview of the application of
ML to optical communications and networking. We classify and survey relevant
literature dealing with the topic, and we also provide an introductory tutorial
on ML for researchers and practitioners interested in this field. Although a
good number of research papers have recently appeared, the application of ML to
optical networks is still in its infancy: to stimulate further work in this
area, we conclude the paper proposing new possible research directions
Chromatic dispersion monitoring for high-speed WDM systems using two-photon absorption in a semiconductor microcavity
This paper presents a theoretical and experimental investigation into the use of a two-photon absorption (TPA) photodetector for use in chromatic dispersion (CD) monitoring in high-speed, WDM network. In order to overcome the inefficiency associated with the nonlinear optical-to-electrical TPA process, a microcavity structure is employed. An interesting feature of such a solution is the fact that the microcavity enhances only a narrow wavelength range determined by device design and angle at which the signal enters the device. Thus, a single device can be used to monitor a number of different wavelength channels without the need for additional external filters. When using a nonlinear photodetector, the photocurrent generated for Gaussian pulses is inversely related to the pulsewidth. However, when using a microcavity structure, the cavity bandwidth also needs to be considered, as does the shape of the optical pulses incident on the device. Simulation results are presented for a variety of cavity bandwidths, pulse shapes and durations, and spacing between adjacent wavelength channels. These results are verified experimental using a microcavity with a bandwidth of 260 GHz (2.1 nm) at normal incident angle, with the incident signal comprising of two wavelength channels separated by 1.25 THz (10 nm), each operating at an aggregate data rate of 160 Gb/s. The results demonstrate the applicability of the presented technique to monitor accumulated dispersion fluctuations in a range of 3 ps/nm for 160 Gb/s RZ data channel
Controlling Rayleigh-Backscattering-Induced Distortion in Radio over Fiber Systems for Radioastronomic Applications
Radio over Fiber (RoF) Systems exploiting a direct modulation of the laser
source are presently utilized within important Radioastronomic scenarios. Due
to the particular operating conditions of some of these realizations, the
phenomena which typically generate nonlinearities in RoF links for
telecommunications applications can be here regarded as substantially harmless.
However, these same operating conditions can make the RoF systems vulnerable to
different kinds of nonlinear effects, related to the influence of the Rayleigh
Backscattered signal on the transmitted one. A rigorous description of the
phenomenon is performed, and an effective countermeasure to the problem is
proposed and demonstrated, both theoretically and experimentally.Comment: Accepted for publication in IEEE/OSA Journal of Lightwave Technolog
Phase-coherent lightwave communications with frequency combs
Fiber-optical networks are a crucial telecommunication infrastructure in
society. Wavelength division multiplexing allows for transmitting parallel data
streams over the fiber bandwidth, and coherent detection enables the use of
sophisticated modulation formats and electronic compensation of signal
impairments. In the future, optical frequency combs may replace multiple lasers
used for the different wavelength channels. We demonstrate two novel signal
processing schemes that take advantage of the broadband phase coherence of
optical frequency combs. This approach allows for a more efficient estimation
and compensation of optical phase noise in coherent communication systems,
which can significantly simplify the signal processing or increase the
transmission performance. With further advances in space division multiplexing
and chip-scale frequency comb sources, these findings pave the way for compact
energy-efficient optical transceivers.Comment: 17 pages, 9 figure
Nonlinear Impairment Compensation for Polarization-Division Multiplexed WDM Transmission Using Digital Backward Propagation
It is shown experimentally that impairments induced by dispersion and Kerr nonlinearity can be compensated digitally for polarization-division multiplexed wavelength division multiplexing (WDM) transmission. The method of digital backward propagation based on solving the Manakov equation can be used to efficiently compensate for the nonlinear interactions between orthogonally polarized channels
- âŠ