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Chapter 1
INTRODUCTION
The most advanced submarine systems currently operating are
based or Dense Wavelength Division Multiplexing (DWDM) of channels at 10
Gbit/s. This means that the system capacity isNx 10 Gbit/s, whereNis the number of
optical carriers (channels), each at a separate wavelength and modulated at 10 Gbit/s.
The introduction of a larger bit rate (e.g. 40 Gbit/s) is not expected in deployed links
for a few years. However, the first WDM transmissions at a 40 Gbit/s channel rate
were reported in research laboratories over transatlantic distances . Subsequently, they
were extended to transpacific distances but did not exhibit adequate margins forindustrial implementation.
Despite using the most advanced Forward Error Correction (FEC) techniques,
the performance, measured in terms of Q-factor, was not sufficient in the laboratory
to ensure that the minimum Q factor required by the customer would be met after
factoring in all the expected repair and industrial penaltiesAlcatel Research and
Innovation has therefore achieved a world first, by demonstrating the transmission of
40 channels at 40 Gbit/s over a transpacific distance with industrial margins .One of
the key technological factors in achieving this result was updating the modulation
format to Alternate-Polarization Return-to-Zero Differential Phase Shift Keying
(APol RZ-DPSK). Furthermore, repeaters based on Raman amplification are used
instead of the conventional Erbium-Doped Fiber Amplifiers (EDFA) to limit the
accumulation of noise. These amplifiers require a specific fiber arrangement to
efficiently reduce propagation impairments at 40 Gbit/s.
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Chapter 2
MODULATION FORMAT
The modulation format designates the approach used to apply the
incoming digital information to each of the optical carriers. The most straightforward
way to do so at B bit/s (e.g. 40 Gbit/s) is by Amplitude Shift Keying (ASK), that is,
by switching the laser output light intensity ON or OFF, depending on whether the
symbol to be transmitted is a mark (1) or a space (0), at a rate equal to the
information frequency B GHz (e.g. 40 GHz).This operation is often achieved by
applying the electrical signal to an electro optical amplitude modulator fed with laser
light. It produces so-called Non- Return-to-Zero(NRZ) data. Figure depicts thecomputed waveform of an eight-bit binary sequence with corresponding intensity,
phase and eye-diagram, modulated with NRZ format, as well as with all the other
formats discussed later. The associated optical spectra are drawn, as well as
schematics of the most conventional ways of generating the formats.
The Return- Zero (RZ) format has often been viewed as a promising
ASK alternative to NRZ. Using RZ, any 1 symbol is represented by pulse, which
can be of variable duration. This into the NRZ electro-optical amplitude modulator.
Whereas ASK formats are used exclusively in products at 10 bit/s, Differential Phase
Shift Keying (DPSK) offers better performance at 40 Gbit/s. In this case, information
is carried by the phase itself. DPSK data is generated by passing laser light into an
electro-optical device which modulates the optical phase. Often this device is
concatenated with a pulse carver (identical to an RZ modulator but driven by a clock)
to make RZ-DPSK optical data. Whether DPSK or RZ-DPSK, a trick has to be used
at the receiver end, since the photodiodes used to convert the optical data into
electrical data are essentially intensity-sensitive.
The most common trick is differential detection, that is, comparison
of the phase of a given bit with that of the following bit, before the photodiode (hence
the D which completes PSK in DPSK or in RZ-DPSK). This operation is performed
in a passive fiber interferometer in which one arm is one bit longer than the other.
Note that differential detection scrambles the optical data, which can therefore only be
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recovered if passed into a pre-coder at the transmitter side. Besides, the interferometer
has the advantage of having two output arms carrying complementary outputs of the
intensity-converted signal. By departing from conventional receivers with ASK, and
having two photodiodes operating in parallel (their photocurrents being subtracted in
the end), it is possible to enhance the robustness to noise (and hence the system
margin) by a helpful ~3 dB. In other words, if the optical power level at each fiber
input were reduced by ~3 Db with respect to the power specifications for ASK
formats, the system performance would still fall within customer requirements.
Additionally, the optical level could be increased with respect to the
power specifications for ASK formats because both the DPSK and RZ-DPSK formats
have excellent intrinsic resistance to power-dependent propagation impairments
(known as intra-channel nonlinear effects). In our experiment, we further increase this
resistance, using the fact that light is preferably modeled as a vector with two
transverse polarization components. By alternating the polarization of adjacent bits
into a dedicated modulator driven at half the information frequency B, to make
Alternate Polarization DPSK (APol RZ-DPSK) data, we show that the system
margins can be increased by another 3 dB. Note that this APol technique requires the
passive fiber interferometer in the receiver to have one arm longer than the other by
two bits instead of one. All these features make APol-RZDSPK one of the most
promising modulation formats for 40 Gbit/s submarine systems.
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Fig. 2.1 Typical Characteristics of Four Modulation systems
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Chapter 3
WAVELENGTH-DIVISION MULTIPLEXING
In fibre-optic communications, wavelength-division multiplexing
(WDM) is a technology which multiplexes multiple optical carriersignals on a single
optical fibreby using different wavelengths (colours) of laser light to carry different
signals. This allows for a multiplication in capacity, in addition to making it possible
to performbidirectional communications over one strand of fibre. "The true potential
of optical fibre is fully exploited when multiple beams of light at different frequencies
are transmitted on the same fibre. This is a form of frequency division multiplexing
(FDM) but is commonly called wavelength division multiplexing.
The term wavelength-division multiplexing is commonly applied to an
optical carrier (which is typically described by its wavelength), whereas frequency-
division multiplexing typically applies to a radio carrier (which is more often
described by frequency). However, since wavelength and frequency are inversely
proportional, and since radio and light are both forms ofelectromagnetic radiation, the
two terms are equal.
3.1 WDM SYSTEMS:
A WDM system uses a multiplexerat the transmitter to join the signals
together, and a demultiplexerat the receiver to split them apart. With the right type of
fibre it is possible to have a device that does both simultaneously. The first WDM
systems only combined two signals. Modern systems can handle up to 160 signals and
can thus expand a basic 10 Gbit/s fibre system to a theoretical total capacity of over
1.6 Tbit/s over a single fibre pair. WDM systems are popular with telecomm
unications companiesbecause they allow them to expand the capacity of the network
without laying more fibre.
By using WDM and optical amplifiers, they can accommodate several
generations of technology development in their optical infrastructure without having
to overhaul the backbone network. Capacity of a given link can be expanded by
simply upgrading the multiplexers and demultiplexers at each end.This is often done
by using optical-to-electrical-to-optical translation at the very edge of the transport
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network, thus permitting interoperation with existing equipment with optical
interfaces.
Most WDM systems operate on single mode fibre optical cables,
which have a core diameter of 9 m. Certain forms of WDM can also be used in
multi-mode fibre cables (also known as premises cables) which have core diameters
of 50 or 62.5 m. Early WDM systems were expensive and complicated to run.
However, recent standardization and better understanding of the dynamics of WDM
systems have made WDM much cheaper to deploy. Optical receivers, in contrast to
laser sources, tend to be wideband devices. Therefore the demultiplexer must provide
the wavelength selectivity of the receiver in the WDM system.
WDM systems are divided in different wavelength patterns,
conventional, dense WDM. Conventional WDM systems provide up to 16 channels
in the 3rd transmission window (C-band) of silica fibres around 1550 nm with a
channel spacing of 100 GHz. DWDM uses the same transmission window but with
less channel spacing enabling up to 31 channels with 50 GHz spacing, 62 channels
with 25 GHz spacing sometimes called ultra dense WDM. New amplification options
(Raman amplification) enable the extension of the usable wavelengths to the L-band,
more or less doubling these numbers.
WDM, DWDM are based on the same concept of using multiple
wavelengths of light on a single fibre, but differ in the spacing of the wavelengths,
number of channels, and the ability to amplify the multiplexed signals in the optical
space. EDFA provide an efficient wideband amplification for the C-band, Raman
amplification adds a mechanism for amplification in the L-band.
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3.2 BASIC OPERATION OF WDM
WDM enables the utilization of a significant portion of the
available fiber bandwidth by allowing many independent signals to be transmitted
simultaneously on one fiber, with each signal located at a different wavelength.
Routing and detection of these signals can be accomplished independently, with the
wavelength determining the communication path by acting as the signature address of
the origin, destination or routing. Components are therefore required that are
wavelength selective, allowing for the transmission, recovery, or routing of specific
wavelengths.
In a simple WDM system , each laser must emit light at a different
wavelength, with all the lasers light multiplexed together onto a single optical fiber.
After being transmitted through a high-bandwidth optical fiber, the combined optical
signals must be demultiplexed at the receiving end by distributing the total optical
power to each output port and then requiring that each receiver selectively recover
only one wavelength by using a tunable optical filter. Each laser is modulated at a
given speed, and the total aggregate capacity being transmitted along the high-
bandwidth fiber is the sum total of the bit rates of the individual lasers.
An example of the system capacity enhancement is the situation in
which ten 2.5-Gbps signals can be transmitted on one fiber, producing a system
capacity of 25 Gbps. This wavelength-parallelism circumvents the problem of typical
optoelectronic devices, which do not have bandwidths exceeding a few gigahertz
unless they are exotic and expensive. The speed requirements for the individual
optoelectronic components are, therefore, relaxed, even though a significant amount
of total fiber bandwidth is still being utilized.
Cha
pter
4
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Fig.3.1 Diagram of a simple WDM system
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DWDM SYSTEM
Dense Wavelength Division Multiplexing refers originally to optical
signals multiplexed within the 1550-nm band so as to leverage the capabilities of
EDFAs, which are effective for wavelengths between approximately 1525 nm - 1565
nm (C band), or 1570 nm - 1610 nm (L band). EDFAs can amplify any optical signal
in their operating range, regardless of the modulated bit rate. In terms of multi-
wavelength signals, so long as the EDFA has enough pump energy available to it, it
can amplify as many optical signals as can be multiplexed into its amplification band
(though signal densities are limited by choice of modulation format). EDFAs
therefore allow a single-channel optical link to be upgraded in bit rate by replacing
only equipment at the ends of the link, while retaining the existing EDFA or series of
EDFAs along a long haul route. Furthermore, single-wavelength links using EDFAs
can similarly be upgraded to WDM links at reasonable cost.
The EDFAs cost is thus leveraged across as many channels as can be
Multiplexed into 1550 nm band..Optical networks use Dense Wavelength
Multiplexing as the underlying carrier. The most important components of any
DWDM system are transmitters, receivers, Erbium-doped fiber Amplifiers, DWDM
multiplexors and DWDM demultiplexor.
.
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Fig. 4.1 The Structure of DWDM System
4.1 DWDM SYSTEMS
At this stage, a basic DWDM system contains several main components:
1. A DWDM terminal multiplexer. The terminal multiplexer actually contains one
wavelength converting transponder for each wavelength signal it will carry. The
wavelength converting transponders receive the input optical signal , convert that
signal into the electrical domain, and retransmit the signal using a 1550-nm band
laser. (Early DWDM systems contained 4 or 8 wavelength converting
transponders in the mid 1990s. By 2000 or so, commercial systems capable of
carrying 128 signals were available.) The terminal mux also contains an optical
multiplexer, which takes the various 1550-nm band signals and places them onto a
single SMF-28 fibre. The terminal multiplexer may or may not also support a
local EDFA for power amplification of the multi-wavelength optical signal.
2. An intermediate optical terminal, or Optical Add-drop multiplexer
This is a remote amplification site that amplifies the multi-
wavelength signal that may have traversed up to 140 km or more before reaching
the remote site. In more sophisticated systems (which are no longer point-to-
point), several signals out of the multiwavelength signal may be removed and
dropped locally.
3. A DWDM terminal demultiplexer.
The terminal demultiplexer breaks the multi-wavelength signal back into
individual signals and outputs them on separate fibres to detect. Originally, this
demultiplexing was performed entirely passively.
WDM wavelengths are positioned in a grid having exactly 100 GHz
(about 0.8nm) spacing in optical frequency, with a reference frequency fixed at
193.10 THz (1552.52nm). The main grid is placed inside the optical fibre amplifier
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bandwidth, but can be extended to wider bandwidths. Today's DWDM systems use 50
GHz or even 25 GHz channel spacing for up to 160 channel operation.
DWDM systems have to maintain more stable wavelength or frequency than those
needed for CWDM because of the closer spacing of the wavelengths. Precision
temperature control of laser transmitter is required in DWDM systems to prevent
"drift" off a very narrow frequency window of the order of a few GHz.
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Chapter 5
REPEATER DESIGN
To compensate for fiber loss, the optical signal must be returned to its
initial value as often as possible. To achieve this, repeaters are inserted periodically
along the link (typically 150 to 200 over a transpacific submarine distance). In all
deployed optical systems, the repeaters rely on EDFA technology. By contrast, in our
experiment they are based on Raman amplification technology. EDFA technology
provides optical amplification in a short section of specially-designed fiber, and can
therefore be viewed as lumped when compared with the typical repeater span length
of over 50 km. In contrast, Raman amplification technology uses the transmission
fiber as the amplification medium, and should therefore be considered as distributed.
At each Raman repeater, a strong continuous wave is launched (generally backwards)
into the transmission fiber. Through the effect of stimulated Raman scattering, this
wave serves as a pump to amplify the WDM channels propagating in the opposite
direction, provided that its wavelength is approximately 100 nm smaller than the
wavelength region where gain is needed.This technique can improve the Optical
Signal-to-Noise (OSNR) because of its distributed nature.
A better insight into this phenomenon can be obtained by computing
the relative change in signal power along a link with a 66 km repeater span length, as
shown in Figure 2. When using all-Raman amplification, the power decay resulting
from fiber loss is stopped at about 20 km before the next repeater. At this point, the
power level is P higher than at the input of a regular EDFA. This minimum power
level in the repeater span Pmin mainly sets the amount of noise generated by the
overall amplification process. Therefore, deploying Raman amplifiers effectively
reduces the repeater span loss by several dB (smaller than but in the range of P), or
effectively increases the OSNR by the same amount. However, at the same time, the
average power along the line is higher than with EDFA. This means that the benefits
in terms of OSNR cannot be fully exploited for extra margins, since the power at each
fiber input must be reduced to avoid breaching the upper power limit set by nonlinear
impairments.
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A better insight into Raman versus erbium performance is
provided in the next section. Other detrimental effects, such as double Rayleigh
backscattering, should also be taken into account when assessing the true system
margins provided by Raman amplification. Stimulated Raman scattering provides
gain only over a limited wavelength region, and gain uniformity is generally obtained
by inserting several pumps at different wavelengths simultaneously into the
transmission fiber.
In our experiment, we use four pumps at 1439.5 nm, 1450 nm, 1461
nm and 1493 nm, providing gain to the 32 nm-wide multiplex, all sent backwards in
each repeater span. More generally, the compatibility of Raman amplification with
large bandwidths (larger than EDFAs) is probably where its greatest potential lies.
However, the need for large bandwidths is not expected to drive the market for the
next few years. Moreover, this compatibility should be balanced against one of the
major drawbacks of Raman repeaters, namely their electrical power consumption.
Electrical power is a scarce resource in submarine systems because it is supplied over
the cable itself.
Fig. 5.1 Schematic of distributed Raman amplification, as compared with lumped
erbium amplification
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Chapter 6
FIBER ARRANGEMENT
Since Raman repeaters use the transmission fiber as the
amplification medium, careful consideration needs to be given to adapting the fiber
parametersfor optimal system performance. Fiber types differ mainly in terms of their
loss and effective area (which describes the energy confinement within the fiber and
hence its sensitivity to nonlinear effects), as well as their Polarization Mode
Dispersion (PMD) and chromatic dispersion properties. PMD originates from minute
imperfections in fiber manufacturing which alter the material composition or the local
fiber geometry, causing anisotropy.Because of this anisotropy, the two polarization
components of light travel at different velocities, causing unwanted waveform
distortions. The effect of PMD is especially detrimental at high bit rates (e.g. 40
Gbit/s). We assume that the transmission fiber and all the system components exhibit
low PMD, so that transpacific distances are achievable. This is a difficult target to
meet at an industrial level with existing technologies.
Chromatic dispersion is a phenomenon caused by different spectralcomponents not traveling at the same speed. It distorts the waveforms and therefore
requires compensation. Almost all deployed submarine links are based on Non-Zero-
Dispersion Shifted Fiber (NZDSF). In this type of fiber, the strong wavelength
dependence of the chromatic dispersion characteristics makes it difficult to
compensate the dispersion uniformly across all WDM channels, which is required to
achieve uniform performance versus wavelength. This is especially true at 40 Gbit/s
where the sensitivity to dispersion is greater than at 10 Gbit/s.
Here we consider a different fiber scheme involving two types of
fiber with positive (+D) and negative (-D) dispersion characteristics. These have been
considered for the longest and most stringent 10 Gbit/s submarine systems, and
appear to be better suited to a 40 Gbit/s channel rate than NZDSF. The typical loss
and effective area for +D fiber are 0.185 dB/km and 110 m2, respectively, compared
with 0.23 dB/km and 30 m2, respectively, for the D fiber. The total lengths of +D
and D fiber are dictated by the need to compensate for the overall dispersion.
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This still leaves various possibilities for concatenating the +D/D
fibers, which we study next as a function of the amplifier configuration. We compare
four fiber/amplifier configurations,as shown inFigure 3. Configuration (a) is the most
common configuration involving EDFA repeaters. Configuration (b) is the replica of
configuration (a), but combines a Raman preamplifier and an EDFA in the repeaters,
whereas configuration (c) uses only Raman repeaters. Finally, configuration (d)
differs from configuration (c) in that the transmission fiber consists of three fiber
sections (+D/-D/+D) rather than two. We compare the relative performance of all four
configurations by evaluating the maximum reachable distance Dmax versus the
repeater spanlength. Dmax is obtained when the lower optical power limit given by
the tolerance to noise coincides with the higher optical power limit given by the
accumulation of non-linear impairments .
For an accurate evaluation, we have taken into account a realistic
insertion loss for all the critical components of the repeaters. In particular, a gain
equalizing filter is needed at every amplifier to contain the power excursion versus
wavelength along the link. In our simulations, we assume a maximum insertion loss
of the gainequalizing filter, which is 1.2 dB higher with EDFA-based repeaters than
with those based on all-Raman. This accounts for the fact that EDFA gain is generally
less uniform than Raman amplifier gain. We have also taken into account the
relatively high 0.3 dB per splice loss of the D-fiber.
Figure 4 is a plot ofDmax, normalized to the maximum
distance that can be achieved with the optimum 40 km span length in the EDFA
configuration (a).In most cases, configurations using some form of Raman
amplification perform better than those based solely on EDFAs, but the advantage
does not translate into more than a 20% increase in the maximum reach Dmax.
Besides, with a conventional two-section +D/-D fiber configuration, a hybrid
EDFA/Raman configuration (b) slightly out performs the all-Raman configuration
(c), especially when the repeater span length exceeds 40 km.
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However, the winning configuration (d) uses only Raman amplifiers,
but with three +D/- D/+D sections of fiber. Whereas a three section scheme would be
of limited interest with EDFAs, it enhances the benefits of Raman amplification by
ensuring that the maximum optical power level is found at the beginning and at the
end of each repeater span in the fiber type (+D), which has a larger effective area and
is therefore the least sensitive to nonlinear impairments. Note that the greatest benefits
are obtained with an optimal repeater span length of ~60-80 km, significantly larger
than the optimal 40 km span length with configuration (a) based on EDFAs.
Fig. 6.1 Impact of amplification scheme and span length on system performance
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Chapter 7
WDM LABORATORY EXPERIMENT
Figure 5 shows the setup for the laboratory experiment conducted atAlcatel Research and Innovation to emulate an Nx 40 Gbit/s submarine system. The
WDM transmitter consists of 40 laser diodes with wavelengths ranging from 1569.54
nm to 1602.32 nm. Because of the cost issues, not all the lasers are modulated with
independent information; instead, in each band they are combined into two sets of 200
GHz spaced channels, corresponding to odd and even channels, through 1 x 20 array-
waveguide multiplexers. These sets are modulated independently using the APol RZ-
DPSK format by 223-1 bit-long pseudo-random bit sequences at 40 Gbit/s with 7%
overhead data (i.e. at 43 Gbit/s). The overhead emulates the presence of Forward
Error Correction (FEC), a digital technique used to correct errors in the received data
stream, and which is now part of all WDM transmission systems. Odd and even
channels are then interleaved, boosted into an EDFA and fed to our recirculating loop
through a switch SW1 and a 3 dB coupler.
A loop is a convenient way to emulate transmission over long distances
without resorting to the required quantity of fiber and repeaters. It incorporates a
switch SW2, which, like SW1, is controlled by delay generators, triggering the
measuring equipment synchronously with the loop. Initially, the loop is filled with a
flow of data traveling clockwise after closing SW1 while keeping SW2 open. Then
SW2 is closed and SW1 opened at time t0, which initiates circulation of the loaded
data. A fraction of the light from this data is continuously extracted via the loop
coupler and detected by the receiver. The transmission quality is evaluated by
comparing the received data sequence with the initial one. The number of bit errors
over the number of transmitted bits yields the Bit Error Ratio (BER).
The BER is measured only within a small gating window starting at time t>
t0 to select only data that has traveled a given number n of round trips (i.e. a given
distance), nbeing derived from the loop trip time and tt0. The recirculating loop
consists of seven 65 km fiber spans (near the optimum ofFigure 4), plus one 55 km
span, giving a total distance of 510 km. Each span incorporates three sections of +D/
-D/+D fiber using the (d) fiber configuration. Spans are separated by repeaters based
on Raman amplification. They all incorporate a gain-equalizing filter, but further
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power equalization is performed in the laboratory by a dedicated dynamic device. To
compensate for its loss and for all the other loop-specific losses, a Raman amplifier is
inserted at the end of the loop, based on a dedicated fiber section. At the receiver end,
the signal is sent into a preamplifier EDFA.
The chromatic dispersion is finely tuned before the photodiode so as to meet
the receiver requirements. Channel selection is performed by a tunable optical filter
emulating a wave- length demultiplexer. The two complementary outputs of the
demodulator are input to a 43 Gbit/s balanced receiver. The BERs of all 40 channels
were recorded after 18 loops and 22 loops, corresponding to distances of 9180 km and
11 220 km, respectively. The BERs were then numerically converted into Q-factors,
which are plotted for both distances in Figure 6. at 9180 km, the Q-factors of all the
channels are better than 11.5 dB.
A third-generation FEC would achieve better than 10-13 BER after correction
when the Q-factor is higher than the 8.5 dB limit (4 x 10-3 BER). Thus, 11.5 dB is 3
dB above the FEC limit, and should be compatible with industrial margin
requirements. When the transmission distance is increased to 11 220 km (a record
distance for 40 Gbit/s systems), the performance of the worst channel (9.9 dB) is still
1.4 dB above the FEC limit.
Fig. 7.1 Experimental setup: 18 loops of 510 km emulate a 9180 km transpacificdistance
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Chapter 8
CONCLUSION
The growing demand for broadband services is generating additional traffic
in optical networks, which will be reflected in submarine WDM systems. In the not
too distant future, such systems will likely move to a 40 Gbit/s channel rate. In this
article, the authors have highlighted some of the technologies that could enable a 40
Gbit/s channel rate to be introduced. Raman technology may bring some benefits to
system performance, but whether these benefits are worth the development of the
associated disruptive repeater design remains a matter of debate. It has been shown
that the result of this debate should influence the fiber arrangement between two
repeaters, and that the effect of polarization mode dispersion should be contained.
However, adapting the modulation format to the requirements of 40 Gbit/s operation
is the direction that will bring us closest to the actual implementation of 40 Gbit/s
systems. In this respect, the APol-RZ-DPSK format must be short-listed as one of the
most promising formats. Based on these elements, Alcatel Research and Innovation
has demonstrated, in a world first, that 40 Gbit/scould be transmitted over both
transatlantic and transpacific distances with industrial margins. This experiment has
confirmed Alcatels leading position in optical transmission research.
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REFERENCES
[1] H. Sugahara et al: 6,050 km transmission of 32 x 42.7 Gbit/s DWDM signals
using Raman-amplified quadruplehybrid span configuration, Proceedings of the
Optical Fiber Communications Conference 2002, paper FC6, Anaheim, 18-22 March
2002.
[2] J.-X. Cai et al: Transmission of thirtyeight 40 Gbit/s channels (>1.5 Tbit/s) over
transoceanic distance, Proceedings of the Optical FiberCommunications Conference
2002, paper FC4, Anaheim, 18-22 March 2002.
[3] C. Rasmussen et al: DWDM 40G transmission over trans-pacific distance
(10,000 km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified
100 km UltraWaveTM fiber spans, Proceedings of the Optical Fiber
Communications Conference 2003, paper PD18, Atlanta.
[4] T. Tsuritani et al: 70 GHz spaced 40 x 42.7 Gbit/s transmission over 8700 km
using CS-RZ DPSK signal
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Seminar Report 2007 40Gbit/s in WDM Submarine Transmission
ACKNOWLEDGEMENT
I express my sincere gratitude to the entire faculty of Electronics &
Communication Dept. of Govt. College of Engg., Kannur for their support and
guidance provided for this seminar.
I am highly indebted to our respected guide Mr.B.S. Shajeemohan, Asst.
Prof. Dept. of Electronics & Communication for his excellent guidance and
cooperation.
I am also grateful to Mr. Rishidas, Asst. Prof. Dept. of Electronics &
Communication for his support.
I also extend my thanks to Mr. Dinesh Babu, Asst. Prof. Dept. of Electronics
& Communication for his useful suggestions.
I would also like to thank all my friends and my family, who were the sourceof constant encouragement.
Above all I thank the Almighty for His grace.
DHANYA. P.T
Dept. of ECE Govt. College of Engg., Kannur
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Seminar Report 2007 40Gbit/s in WDM Submarine Transmission
ABSTRACT
The most advanced submarine systems currently operating are based or Dense
Wavelength Division Multiplexing (DWDM) of channels at 10 Gbit/s. This means
that the system capacity is Nx 10 Gbit/s, where N is the number of optical carriers
(channels), each at a separate wavelength and modulated at 10 Gbit/s. The
introduction of a larger bit rate (e.g. 40 Gbit/s) is not expected in deployed links for a
few years. However, the first WDM transmissions at a 40 Gbit/s channel rate were
reported in research laboratories over transatlantic distances . Subsequently, they were
extended to transpacific distances but did not exhibit adequate margins for industrial
implementation.
Dept. of ECE Govt. College of Engg., Kannur
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Seminar Report 2007 40Gbit/s in WDM Submarine Transmission
CONTENTS
1. INTRODUCTION 1
MODULATION FORMAT 2
2. WAVELENGTH-DIVISION MULTIPLEXING 5
3.1 WDM SYSTEMS 5
3.2 BASIC OPERATION OF WDM 7
3. DWDM SYSTEM 8
4.1 DWDM SYSTEMS 9
4. REPEATER DESIGN 11
5. FIBER ARRANGEMENT 13
6. WDM LABORATORY EXPERIMENT 16
CONCLUSION 18
7. REFERENCES 19