The received power was measured at the end of the transmission line before the power was coupled either into the optical demultiplexer in the precompensation scheme or into the input of
Trang 140 Gb/s and 4 40 Gb/s TDM/WDM
Standard Fiber Transmission
C M Weinert, R Ludwig, W Pieper, H G Weber, D Breuer, K Petermann, and F K¨uppers
Abstract— We investigate the possibilities of 40 and 4 22 40
Gb/s time division multiplexing wavelength division multiplexing
(TDM/WDM) return-to-zero (RZ) transmission over embedded
standard single-mode fibers (SMF) at a transmission wavelength
of 1.55 m both experimentally and theoretically Dispersion
of the SMF is compensated by a dispersion compensating fiber
(DCF) Transmission over a span of 150 km of SMF in the
single-channel case and of 100 km SMF in the multisingle-channel case are
reported Numerical calculations are employed to investigate the
possibility of cascading the spans both for single-channel and
multichannel transmission For single-channel transmission, it
is shown that optimum performance is achieved with
postcom-pensation of the DCF The input power at the SMF and DCF
input have to be chosen carefully For four channel transmission,
the performance is mainly limited by residual dispersion in the
outermost wavelength channels It is shown numerically that
improvement is achieved by employing the newest type DCF
which also compensates the dispersion slope of the SMF For
a WDM channel separation of 2 nm no significant additional
degradation due to cross-phase modulation (XPM) or four-wave
mixing is observed.
Index Terms—Fiber transmission, optical communication,
op-tical dispersion management, time division multiplexing (TDM)
transmission, wavelength division multiplexing (WDM)
transmis-sion.
I INTRODUCTION
NEW challenges to modern telecommunications such as an
expanded internet and broadband distributive and
inter-active services demand for growing transmission capacities
Increasing the bandwidth can be either done by providing
more channels in a wavelength division mutliplexing (WDM)
system or by enhancing the bit rate of already existing channels
using time division multiplexing (TDM) or by a combination
of both Capacity upgrading by TDM offers some advantages
for network operators in view of economic efficiency This
is due to reduced network management efforts and because
already installed single-band erbium-doped fiber amplifiers
(EDFA’s) do not have to be replaced by broad-band amplifiers
as used in the latest generation of WDM systems
Manuscript received February 16, 1999; revised July 19, 1999.
C M Weinert, R Ludwig, W Pieper, and H G Weber are with
Heinrich-Hertz-Institut f¨ur Nachrichtentechnik Berlin GmbH, Berlin D-10587 Germany
(e-mail: weinert@hhi.de).
D Breuer and K Petermann are with the Institut f¨ur
Hochfrequen-ztechnik, Technische Universit¨at Berlin, Berlin D10587 Germany (e-mail:
breuer@sun6hft.ee.TU-Berlin.de).
F K¨uppers is with Deutsche Telekom, Technologiezentrum Darmstadt
D-64307 Germany (e-mail: franko.kueppers@telekom.de).
Publisher Item Identifier S 0733-8724(99)08023-8.
Whereas 10 Gb/s TDM systems are already commercially available, even in WDM configurations with up to 32 channels,
40 Gb/s TDM transmission is still subject to research and development A lot of work has already been done including impressive laboratory demonstrations like 40 Gb/s soliton transmission over 70 000 km in a dispersion shifted fiber (DSF) loop [1], 8 40 Gb/s [2] and 4 40 Gb/s [3] TDM/WDM transmission over standard single-mode fiber (SMF), and 30 40 Gb/s WDM transmission over 85 km
of nonzero dispersion fiber (NZDF) [4] In this work we will concentrate on transmission over SMF which is still the basis
of most fiber optic networks all over the world
Fundamental investigations have demonstrated the useful-ness of SMF for single-channel 40 Gb/s transmission experi-mentally [5], also compared to DSF and NZDF [6] Numerical [7] and theoretical [8] studies gave first ideas about the design
of an appropriate passive dispersion management scheme for upgrading the existing SMF fiber basis Also the choice of the appropriate modulation format [return-to-zero (RZ) instead of nonreturn-to-zero (NRZ)] has been clarified [9], [10] The increasing interest of network operators in 40 Gb/s TDM transmission is demonstrated by recent field trials which have taken place in Japan (NTT) [11], [12] and Europe (British Telecom [13] and Deutsche Telekom [14]) In particular, the field trials of Deutsche Telekom focussed on practical problems a network operator will face when high speed optical systems are operated on a fiber base which was not intended for carrying 40 Gb/s single-channel signals when installed more than ten years ago One problem is polarization mode dispersion (PMD) but system manufacturers have realized this and first solutions like an automatic PMD compensation
in 40 Gb/s optical transmission systems are proposed [15] The present state of 40 Gb/s SMF transmission (theory, numerical simulation, laboratory experiments and field trials for single-channel multispan transmission and first laboratory experiments for multichannel single-span transmission) let it appear advisable to do the next step forward toward mul-tichannel multispan transmission which will be investigated here based on our previous work The focus will be on chromatic dispersion management schemes taking into account the newest types of dispersion compensating fibers
II THEORY
Neglecting effects of polarization and scattering effects like stimulated Raman scattering and stimulated Brillouin scattering, propagation of optical pulses in fibers is described
0733–8724/99$10.00 1999 IEEE
Trang 2chromatic dispersion The dispersion parameters and
result from expansion of ( ) around the center frequency
and describe dispersion effects up to third order Fiber
dispersion is usually given by the dispersion and the
dispersion slope For high bitrate transmission
chromatic dispersion is one of the main limiting factors
because dispersion induced pulse broadening decreases the
signal to noise ratio The increase in pulse width can be
estimated from the analytical expression of broadening of
isolated Gaussian pulses which is also a good approximation
for sech2 pulses [16] Since chromatic dispersion of the SMF
is large at 1.55 m ( ps(nmkm) 1) it is necessary to
compensate dispersion As discussed in Section I we will treat
compensation schemes with DCF’s The DCF has a negative
and can therefore compensate the dispersion of the SMF
However, the particular DCF used in the transmission
exper-iments (hereafter denoted DCF1) can only partly compensate
the slope of dispersion This means that zero dispersion
can be achieved for one wavelength channel only whereas at
other wavelength channels a residual dispersion remains This
residual dispersion severely limits the bandwidth of WDM
transmission Fiber loss is described by (given in dB/km) in
the third term on the right hand side of (1)
The last term on the right hand-side of (1) describes fiber
nonlinearity It is proportional to the pulse intensity , as
defined in (2), is the nonlinear coefficient related to the
nonlinear refractive index , the effective fiber core area ,
and the velocity of light The nonlinear effects included
in the NLSE are self-phase modulation (SPM), cross-phase
modulation (XPM), and four-wave mixing (FWM) Single
channel transmission is affected by SPM only whereas in
multichannel transmission the combined effects of SPM, XPM,
and FWM lead to signal degradation Since SPM affects the
optical wave via its interaction with chromatic dispersion
partial cancellation of the nonlinear fiber degradation can
be achieved by using appropriate dispersion schemes [18]
FWM, on the other hand, is expected to be negligible because
the large dispersion value in each span prevents the phase
matching condition which is necessary for FWM to become
effective [17]
The NLSE will be solved numerically using the well known
split-step fast Fourier transform (FFT) algorithm [16]
Simu-lations were done for a PRBS of length using sech2
pulses of 4 ps FWHM The amplifier noise was modeled as
white noise created by a Gaussian random generator and added
to the optical field amplitude at the output of each amplifier
87.5 GHz for multichannel transmission The photodiode is modeled as a square law detector followed by an electrical low pass filter
In Table I, we list the parameters for the fiber span including two different DCF’s DCF1 was used in the experiment DCF2
is a new fiber which became available very recently Therefore
it was only used in the numerical simulation DCF2 nearly perfectly compensates both and
The calculated quantities which we compare with experi-ment, are the pulse width of the RZ pulses and the eye closure penalty The pulse width is determined by averaging over the individual pulse widths of the bit sequence The eye closure penalty is evaluated from the eye closure at the receiver for the complete transmission path as compared to back-to-back eye closure
III EXPERIMENTAL
A Single-Channel 40 Gb/s Transmission
The schematic of the experimental set-up is depicted in Fig 1 The data transmitter comprises a tunable mode-locked laser, operating at 10 GHz repetition rate [19] The pulse train is intensity modulated with a pseudorandom bit sequence (PRBS) of length or using an external modulator The 10 Gb/s optical data signal is sequentially bit interleaved
by a fiber delay-line multiplexer In the multiplexer, the bit sequences were shifted against each other by
bit periods ( = 2, 4) in order to ensure a PRBS,
40 Gb/s single-polarization (no polarization multiplexing) data signal The pulsewidth of the transform-limited pulses is
4 ps with a sech2 pulse shape The 40 Gb/s signal is then transmitted over 150 km SMF The overall link dispersion
is compensated to zero for the signal wavelength of
nm by using 27 km of DCF1 (see Table I) The DCF
is placed either at the transmitter (precompensation) or at the receiver (postcompensation) The optical power launched into the DCF is always low (<5 dBm) to ensure operation in the linear transmission regime At the receiver a SLALOM-based configuration is used as an optical demultiplexer [20] Fig 2 shows measured bit error rates for two word lengths and for the two different compensation schemes An error-free transmission (BER = 10 9) was achieved with receiver sensitivities of 27 dBm for PRBS For PRBS there was an additional penalty of 1 dB for both compensation schemes which we attributed to the system electronics The measurements of the four TDM channels showed identical
Trang 3Fig 1 Experimental setup for transmission of one WDM channel.
(a)
(b) Fig 2 Measured bit error rates for the transmission of one WDM channel.
(a) Precompensation and (b) postcompensation.
results Therefore, in Fig 2 only one channel is depicted
The receiver sensitivity in Fig 3 refers to 40 Gb/s The
received power was measured at the end of the transmission
line before the power was coupled either into the optical
demultiplexer in the precompensation scheme or into the
input of the postcompensation scheme In the precompensation
scheme the launched signal power into the SMF was 11 dBm
In the postcompensation scheme a signal power of 14 dBm
Fig 3 Bit error measurements using the postcompensation scheme in the one channel experiment.
was launched into the fiber In the following we describe measurements with PRBS = only in order to compare these results with calculations in the subsequent sections Fig 3 shows bit error ratio measurements with various optical input powers into the 150 km SMF in the postcompensation scheme Similar measurements were also performed in the precompensation scheme From these results we evaluated the system penalty versus the input power, which is discussed and compared with theoretical results in Section IV
B 4 40 Gb/s TDM/WDM Transmission
The experimental setup is shown in Fig 4 The four WDM channels to were generated by two modelocked semi-conductor lasers (FWHM 1.3 ps) and with the use of spectral slicing technique based on an arrayed waveguide grating (AWG) The AWG has a channel spacing of 2 nm and a FWHM of 0.9 nm Using this technique, optical pulses (FWHM 4.0 ps) at four different wavelengths to with a wavelength spacing of 2 nm were obtained The four pulse trains were coupled together into one intensity modulator
10 Gb/s data signals was then multiplexed four times by the same fiber delay-line multiplexer as described in Section III-A
Trang 4Fig 4 Experimental setup for transmission of four WDM channels.
Fig 5 Optical spectra of the four WDM channels each with 40 Gb/s Also,
the measured pulse widths at the input of the demultiplexer are shown.
Finally, we obtained four 40 Gb/s OTDM single-polarization
WDM channels at wavelengths to All four WDM
channels carry the same data pattern Without dispersion, the
interchannel interference would be maximum because the data
then travel synchronously The large local dispersion causes a
walk-off between the pulses of different wavelength channels
and thus the interchannel interaction is reduced and averaged
out We therefore expect no change when using nonidentical
modulation in the WDM channels
The 4 40 Gb/s data signal was then transmitted over 100
km of SMF The dispersion compensating fiber (17.5 km of
DCF1) was placed at the receiver Behind the DCF a tunable
optical filter (FWHM 2 nm) was used to select one of
the four 40 Gb/s WDM channels Note, that no individual
dispersion compensation of the WDM channels was applied
Fig 5 shows the optical spectra of all four WDM channels
at the output of the transmission line The width (FWHM) of
the optical pulses at the input of the demultiplexer (SLALOM)
varied between 4.5 and 8 ps depending on how close a channel
was with respect to the optimum wavelength for dispersion
compensation This optimum wavelength was chosen to be
at about 1551 nm A comparison of the measured pulse
Fig 6 Measured bit error rates for the four WDM channels.
width with the calculated pulse broadening over the fiber span verified the total fiber dispersion and its slope The selected channel was then demultiplexed in the time domain as already described in Fig 1 The SLALOM demultiplexer has
a small polarization dependence which may lead to reduced contrast ratio for separation of the different TDM channels Therefore, for each WDM channel, polarization was adjusted for minimum BER before the BER curve was measured measurement Fig 6 shows the BER-measurements on each of the four WDM channels The measurements of the four TDM channels showed identical results Therefore, in Fig 6 only one channel is depicted The received power was measured
at the output of the 100 km transmission line The data presented were taken for a PRBS of length to allow for a comparison with simulations However, the performance exhibited small dependence ( 1 dB) for pattern lengths up
to similar to the results in Fig 2 From the error ratio performance of the system, both before and after the transmission, we can see that the transmission penalty (BER
10 9) is about 3 dB This penalty was attributed to the dependence of the demultiplexer on the pulse width The demultiplexer had an optimum performance for pulse width less than 4 ps Similar to the investigations in Section III-A, the penalty was investigated versus the optical power at the input of the SMF As compared to single-channel transmission
no additional penalty due to nonlinear effects was obtained for four channel transmission with a total fiber coupled input power up to 20 dBm
IV NUMERICAL SIMULATION ANDDISCUSSION
A Single-Channel Single-Span Transmission
For the theoretical analysis the setup depicted in Fig 1 was assumed According to Fig 1 the 40 Gb/s signal was transmitted over 150 km SMF At the transmission wavelength
of 1548 nm the accumulated SMF dispersion was completely compensated by the 27 km of DCF1 (see Table I) which was either placed at the receiver (postcompensation) or at the transmitter (precompensation) The input pulse width of the sech2pulses was 4.3 ps In the numerical calculations a PRBS pattern of length was chosen to allow a comparison
Trang 5be-Fig 7 System penalty for 150-km SMF transmission against average fiber
(SMF) input power for pre- and postcompensation scheme.
tween the experimental and theoretical results As shown in the
experimental part it was verified that a pattern length of
did not cause a significant change Both compensation schemes
pre- and postcompensation were investigated Fig 7 shows
the penalty against the average fiber input power for the two
different compensation schemes assuming complete dispersion
compensation For the experimental data the penalty was
extracted from the BER curve for postcompensation as shown
in Fig 3 with respect to back-to-back for a BER of 10 9
A similar BER extraction was used for precompensation As
shown in Fig 7 a good agreement between experimental and
theoretical data is achieved An EDFA noise figure of 6 dB was
assumed At low fiber input powers, the system performance
is hampered due to a low signal-to-noise ratio (SNR) and at
high input powers, the system performance is degraded due
to the increasing impact of nonlinear self-phase modulation
In the postcompensation scheme the system penalty increases
strongly for fiber input powers exceeding 16 dBm, whereas
in the precompensation scheme the penalty increases already
at power levels exceeding 13 dBm In the linear regime for
low fiber input powers there is no difference between pre- and
postcompensation
Fig 8 shows the eye-diagrams for both compensation
schemes after 150-km SMF transmission at an average fiber
input power of 16 dBm To show the principle difference of
the two compensation schemes and to avoid burdening the
interpretation by amplifier noise, we used the eye-diagrams
of the theoretical study neglecting the amplifier noise The
eye-diagrams in Fig 8 show that signal distortions in the
precompensation scheme arise mainly due to strong
bit-pattern dependent variations of the pulse peak power In
the postcompensation scheme, however, the signal distortions
at 16 dBm are significantly lower and a penalty of about
2 dB is achieved A mixed compensation scheme with 1/3
precompensation and 2/3 postcompensation and vice versa
was also investigated No improvement of a split compensation
scheme was achieved in this case Since for NZDF a significant
difference in the spectra for pre- and postcompensation has
already been observed [21] we also monitored the spectrum
after 150 km SMF transmission for both transmission schemes
However, in contrast to NZDF the spectra were almost
(a)
(b) Fig 8 Theoretical eye-diagrams after 150 km SMF fiber at 16 dBm for pre-and postcompensation (a) Precompensation pre-and (b) postcompensation.
identical We attribute this to the high local dispersion of the SMF Due to the high chromatic dispersion of the SMF a large phase mismatch between the different frequency components occurs This leads to a reduced influence of SPM in the SMF compared to the influence of SPM in the NZDF
The system behavior in the precompensation scheme may
be explained as follows: in the precompensation scheme the data signal is at first transmitted over the DCF Due to the reduced power in this fiber the signal is mainly affected by chromatic dispersion This causes severe pattern dependent dispersive waveform distortions If this signal is now launched into the SMF the nonlinearity in this fiber causes strong signal distortions of the already perturbed pattern This leads to large variations in the peak power at the end of the transmission line Simulation showed that these distortions are not caused
by higher order dispersion ( )
To investigate the optimum compensation ratio and the dis-persion tolerance for 40 Gb/s RZ single-channel transmission Fig 9 shows the penalty versus the residual link dispersion for SMF transmission for the postcompensation scheme for two different input powers For both fiber input powers 10 and 16 dBm the optimal system performance occurred for complete dispersion compensation The penalty shows a symmetrical behavior around zero average dispersion like in a linear transmission scheme indicating that at high power levels no optimization due to under-compensation is feasible A similar
Trang 6Fig 9 Penalty against residual dispersion for 150 km SMF transmission for
the postcompensation scheme for different fiber input powers.
Fig 10 Investigated compensation schemes for cascaded span transmission.
behavior has been reported for RZ transmission at 10 Gb/s [9]
The dispersion tolerance for 1 dB penalty at an input power of
10 dBm is about 15 ps/nm corresponding to a SMF length
of about 1 km
B Single-Channel Cascaded Span Transmission
To investigate the potential of cascading single-channel
40 Gb/s transmission over multiple spans we performed
nu-merical calculations using different dispersion compensation
schemes In this study we considered a postcompensation, a
symmetrical compensation, and an alternating compensation
scheme as depicted in Fig 10 Particularly for 10 Gb/s RZ
transmission the symmetrical and alternating schemes showed
superior performance compared to pure postcompensation
[22] Precompensation was not considered, since already in
single-span transmission it was less effective than
postcom-pensation The amplifier spacing was reduced to 100 km In all
compensation schemes DCF1 was considered to be operated in
the linear regime Fig 11 shows the calculated penalty against
Fig 11 Penalty after 300-km SMF transmission against fiber input power for post-, symmetrical, and alternating compensation scheme.
the average fiber input power for the three compensation schemes for three spans corresponding to 300 km SMF For low input power all schemes show almost identical behavior The performance is limited by the amplified spontaneous emission noise For higher input powers there is only a differ-ence of about 0.5 dB between the post- and the alternating-compensation scheme The penalty is about 1.3 to 1.8 dB for a fiber input power of 12 dBm In the symmetrical compensation scheme, however, the penalty increases significantly at power levels exceeding 9 dBm The eye closes due to variation of the peak power like in the pure precompensation scheme in single-span transmission We attribute the superior performance of the post- and alternating compensation scheme to the fact that in both compensation schemes the first fiber part is of SMF fiber (like in pure postcompensation), whereas in the symmetrical scheme the first fiber part is of DCF type (precompensation)
C Multichannel Cascaded Span 40 Gb/s Transmission
We first show the calculated results for the 4 40 Gb/s transmission over 100 km of SMF with postcompensation by 17.5 km SMF [3] In order to compare the measured results with experiment, we first look at the pulse broadening in the four channels at 1547, 1549, 1551, and 1553 nm which will be labeled channels 1, 2, 3, and 4, respectively For the average SMF input power of 10 mW and using the values for the fiber nonlinearity and for the dispersion (DCF1) as given in Table I the calculated values of the pulse width (FWHM) are 8.5, 6.2, 4.5, and 6.2 ps, respectively, which compare very well with the measured pulse widths given in Fig 6 For the calculation the dispersion zero was placed at 1551 nm The eye-diagrams
of the four channels are shown in Fig 12 Because of the dispersion zero at 1551 nm channels 2 and 4 are very similar whereas channel 1 shows the largest eye closure penalty due to the large pulse broadening The pulse broadening of the four channels are mainly due to residual dispersion This can be shown by a simple estimate of pulse broadening of channel 1 which is 4nm away from the dispersion zero Using the values given in Table I the sum of the residual dispersion in channel
1 amounts to ps/nm Using the well known pulse broadening formula [16], the pulse broadens from
Trang 7Fig 12 Calculated eye-diagrams for channel 1 to 4 of the 4 2 40 Gb/s
single-span transmission The FWHM of the pulses averaged over the 2 7 0 1
bits is given as parameter.
to 8.8 ps at the end of the fiber span which is close to the
measured pulse width
The effects of FWM were tested numerically by launching
power into three channels only and monitoring the effect of
FWM in the fourth channel The simulations showed that
no noticable FWM products appear in the fourth channel
This was expected because of the phase mismatch due to the
dispersion map and because of large channel spacing
We also investigated possible signal degradation due to
XPM numerically by comparing the eye-diagram of channel
2 of the 4 40 Gb/s system with the eye-diagram of a
single channel at the same wavelength We chose identical
bit patterns and parallel polarization for all channels The large
local dispersion leads to a walk-off between pulses in different
channels Consequently we see no difference in XPM crosstalk
if the bit strings are delayed or changed between the channels
Comparison of the average pulse width and the eye closure
penalty showed no difference between the four channel and
the single-channel case
In order to test the cascadability of 4 40 Gb/s transmission
we perform numerical simulations of the repeated span with
100 km SMF postcompensated by 17.5 km DCF1 However,
we now minimize residual dispersion in the outer wavelength
channels by choosing the dispersion zero at 1549 nm and the
four channels at 1546, 1548, 1550, and 1552 nm In Fig 13,
we depict the eye-diagrams for the inner channel at 1548 nm
and the outer channel at 1546 nm for one and three cascaded
spans The eye-diagrams of the channels at 1550 and 1552 nm
are not shown since they are essentially the same as the ones
at 1548 and 1546 nm, respectively This reflects the symmetry
with respect to the dispersion zero
From Fig 13, it is seen that the outer channel 1 at 1546 nm
shows the largest degradation This degradation of the eye
comes from pulse broadening which limits transmission to
two or maximum three cascades As seen from comparison
(a)
(b) Fig 13 Calculated eye-diagrams for the 4 2 40 Gb/s transmission span
cascaded one to four times: (a) for channel 1 at 1546 nm and (b) for channel
2 at 1548 nm.
Fig 14 Calculated eye closure penalty versus SMF input power for channel
1 (1546 nm) after three cascaded spans solid: line—compensation with DCF1 used in the single-span experiment, dashed line—compensation with DCF2, and dotted line—compensation with DCF1 plus individual channel dispersion compensation at the receiver.
with the inner channel, this broadening is caused by the residual dispersion due to the imperfect compensation of the dispersion slope In order to verify this, we show in Fig 14 the calculated eye closure penalties for the outer channel 1 after 3 cascades with the experimentally used DCF1 (solid line) and for compensation with DCF2 (dashed line) which nearly completely compensates both and It is found that both curves are similar in shape with a minimum in the range between 3–10 dBm per channel However, the curve for the experimental DCF1 is shifted by about 3dB to higher penalty values compared to compensation by DCF2
It is also interesting to compare perfect dispersion com-pensation of DCF2 with the combined effects of incomplete
Trang 8As for the single-span transmission we investigated the
effects of XPM and FWM There are found minor pulse
broad-ening effects due to XPM whereas FWM remains negligible
We also numerically investigated the effects of incomplete
dispersion compensation by slight reduction of the DCF length
(undercompensation) The channels which have to be
im-proved are the outermost wavelength channels Shortening
the DCF in general improves the low wavelength channel
but degrades the high wavelength channel Therefore, no
net improvement is achieved for multiwavelength channel
transmission by undercompensation with the DCF
V CONCLUSION
In conclusion, we reported recent achievements in fiber
optic 40 Gb/s TDM/WDM transmission Theory and results
of numerical and experimental investigations were presented
and discussed starting with a single-channel single-span (150
km SMF) configuration for which pre- and postcompensation
schemes were compared with the result that postcompensation
allows for higher input powers The number of channels was
increased to four with a channel spacing of 2 nm For 100
km SMF no additional penalty compared to single-channel
transmission could be observed For single-channel multispan
(3 100 km SMF) transmission the different
compensa-tion schemes showed almost identical behavior at low signal
power levels For higher power levels post- and alternating
compensation schemes showed superior system performance
whereas pre- and symmetrical compensation suffers from the
high nonlinear distortions in the DCF Finally we investigated
numerically a 4 40 Gb/s WDM/TDM transmission over
3 100 km SMF and found that system behavior is
domi-nated by the residual chromatic dispersion of the individual
WDM channels Because of the residual chromatic
disper-sion in the outer channels undercompensation schemes which
are advantageous for single-channel transmission fail for the
multichannel transmission Nonlinear channel interaction like
XPM and FWM were of minor importance which is due to
the high local dispersion of a dispersion compensated SMF
transmission line Using the newest type of DCF which offers
an appropriate dispersion slope to compensate for chromatic
dispersion exactly over a broad wavelength range, every single
channel of the WDM system behaves like a single-channel
system with exact compensation Similar good results for
individual channel compensation at the end of the cascaded
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C M Weinert, photograph and biography not available at the time of
publication.
R Ludwig, photograph and biography not available at the time of publication.
W Pieper, photograph and biography not available at the time of publication.
H G Weber, photograph and biography not available at the time of
publication.
D Breuer, photograph and biography not available at the time of publication.
K Petermann, photograph and biography not available at the time of
publication.
F K ¨uppers, photograph and biography not available at the time of
publi-cation.