10x224-Gb/s POLMUX-16QAM transmission over 656 km of
large-Aeff PSCF with a special efficiency of 5.6 b/s/Hz
Citation for published version (APA):
Sleiffer, V. A. J. M., Alfiad, M. S., Borne, van den, D., Kuschnerov, M., Veljanovski, V., Hirano, M., Yamamoto,
Y., Sasaki, T., Jansen, S. L., Wuth, T., & Waardt, de, H. (2011). 10x224-Gb/s POLMUX-16QAM transmission
over 656 km of large-Aeff PSCF with a special efficiency of 5.6 b/s/Hz.
IEEE Photonics Technology Letters
,
23
(20), 1427-1429. https://doi.org/10.1109/LPT.2011.2162722
DOI:
10.1109/LPT.2011.2162722
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IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 20, OCTOBER 15, 2011 1427
10 224-Gb/s POLMUX-16QAM Transmission
Over 656 km of Large-
PSCF With a Spectral
Efficiency of 5.6 b/s/Hz
V. A. J. M. Sleiffer, Student Member, IEEE,M.S.Alfiad, Student Member, IEEE, D. van den Borne, Member, IEEE,
M. Kuschnerov, Member, IEEE, V. Veljanovski, M. Hirano, Y. Yamamoto, T. Sasaki, S. L. Jansen, Member, IEEE,
T. Wuth, Member, IEEE, and H. de Waardt, Member, IEEE
Abstract—The authors demonstrate the successful transmission
of 10 channels w ith 224-Gb/s POLMUX-16QAM modulation
(28 GBaud) on a 37.5-GHz wavelength grid. Using large-
pure-silica-core fibers they show a 656-km transmission distance
with a spectral efficiency of 5.6 b/s/Hz. They report a back-to-back
performance penalty of 3.5 d B compared to theoretical limits
at the forward-error correction (FEC) limit (bit-error rate of
3.8
10 ), and a margin of 0.5 dB in Q-factor with respect to the
FEC limit after 656 km of transmission.
Index Terms—Coherent detection, polarization multip lexing
(POLMUX), quadrature amplitude modulation (QAM).
I. INTRODUCTIO N
T
HE rapid increase in popularity of bandwidth-consumin g
applications such as internet video, cloud storage and so -
cial networking requires large volumes of data to be transmitted
over long distances. This has fueled the historically exponential
growth of data traffic volumes in the worldwide telecommunica-
tion network, and based on current trends it is likely to continue
to drive an unsurpassed need for transmission capacity over
the next decade. The industry-wide drive to develop the optical
components, subsystems an d systems required to upgrade long-
haul and ultra long-haul networks to 100 G line rates is a key
development to facilitate the need for more capacity in core net-
works. Pola rization-multip lexed quadrature ph a se shif t keying
(POLMUX-QPSK) [1] has emerged in recent years as t he most
suitable modulatio n format for 100 G line rates, as it is compat-
ible with th e standardized 50-GHz channel spacing. This allows
for a spectral efficiency of 2.0 b/s/Hz, scaling C-band transmis-
sion systems to a total capacity of betw een 8 and 10 Tb/s.
Manuscript received April 04, 2011; revised July 06, 2011; accepted July 16,
2011. Date of publication July 22, 2011; date of current version September 21,
2011.
V.A.J.M.Sleiffer,M.S.Alfiad, and H. de Waardt are with the COBRA In-
stitute, Eindhoven University of Technology, 5612A Z Eind ho v en, The Nether-
lands (e-mail: v.a.j.m.sleiffer@tue.nl; m.s.alfiad@ieee.org; h.d.waardt@tue.nl).
D. van den Borne, M. Kuschnerov, V. Veljanovski, S. L. Jansen,
and T. Wuth are with Nokia Siemens Networks, 81541 Munich, Ger-
many (e-mail: dirk.vandenborne@nsn.com; maxim.kuschnerov@nsn.com;
vladimir.veljanovski@nsn.com; sander.jansen@nsn.com; torsten.wuth@nsn.
com).
M. Hirano, Y. Yam amoto, and T. Sasaki are with S umitom o Electric
Industries, Ltd., Yokohama 244-8588, Japan (e-mail: masahirano@sei.co.jp;
yamamoto-yoshinori@sei.co.jp; sasaki-takashi@sei.co.jp).
Color versions of one or m ore of the figures in this letter ar e available online
at http://ieeexplore.i eee.org.
Dig
ital Object Identifier 10.1109/LPT.2011.2162722
With 100 G transport solution now well established and
first commercial deployments o ngo ing , there is strong need to
understand ho w long-haul transmission systems can evolve to
400 G line rates. Increasing the spectral e fficiency by using
higher-order modulation formats is the most effective metho d
to realize higher transmission capacities at a com parable
or lower cost per transmitt ed bit. Transponder techn olo gies
developed for 100 G line rates such as the optical compo-
nents for dual-polarization QPSK modu lation can be largely
reused when scaling to d enser modulation formats. Based
on such technolog ies several transmission experiments h ave
been reported using 16-level quadrature amp litude modulation
(POLMUX-16QAM) [2], [3], or even denser constellations
such as POLMUX-32QAM [4], POLMUX-64QAM [5], [6]
or POLMU X -1 28Q AM [7]. However, this research show ed
as well that the increase in optical signal-to-noise (OSNR)
threshold coupled with a decreased nonlinear threshold makes
it tremendously challenging to transport such formats over
long-haul distances.
The strongly reduced transmission ma rgin for dense constel-
lations limit s the spectral efficiency that can be used for long-
haul transmission [8], m akin g it very hard to transport 400 G
within a 50-GHz W DM grid [4]. This underlin es the need for
an optim ized infrastructur e to improv e the feasible transmis-
sion distance of next-generation transport systems while main-
taining the maxim um possible spectral efficiency. One solu-
tion is the use of flexi-grid technology, which allows a flex-
ible scaling o f channel spacing across the transmission band [9],
[10]. This permits 40 0 G line rates to use a spectral band broader
than 50 GHz, and enables a trade-off between transmission dis-
tance and spectral efficiency depending on network topology
and physical layer i nfrastructure. D ual-carrier modulation, with
both carriers being 200 G POLMUX-16QAM m odulated, is
a particularly pr omising approach to realize 400 G line rates,
as this all ows for the use of components with a lower optical
and/or electrical bandwidth. For this purpose we investigated
in this letter the transmission of 224 -Gb/s POLMU X-16QAM
on a 37.5-GHz grid over 656 km of large-
pure-silica-core
fiber [11]. This allows for a 5.6 b/s/Hz spectral efficiency, and
demonstrates the feasib ili ty of next-generation 400 G transport
using flexi-r a te technology on an optimized fiber infrastructure.
II. E
XPERIMENTAL SETUP
Fig.
1 depicts the setup used in the t ransmission experiment.
At t
he transmitter (Fig. 1 (a)), two combs of 5 lasers w ith a
1041-1135/$26.00 © 2011 IEEE
1428 IEEE PHOTONICS TECHNO LOGY LETTERS, V OL. 23, NO. 20, OCTOBER 15, 20 11
Fig. 1. Experim e ntal setup. (a) Transmitter ( Tx ). (b) Generation of electrical 4-PAM dri vin g signal. (c) Spe ctrum and recovered back-to-back constellations for
both polarizations. (d) Recirculating loop setup.
wavelength spacing of 75 GHz are coupled together using a
passive coupler. The two combs consist of a mix of ECL an d
DFB lasers, and the relative wavelength spacing between both
combs is 37.5 GHz. The output signals of both combs are subse-
quently 112-Gb/s 16-QAM modulated with two I Q-m od ulators,
with a
of 2.2 V. Two outputs of a pulse pattern generator
(PPG), generating
PRBS sequences at a 28-Gbaud symbol
rate, are first cleaned up using t wo D flip-flops (DFF). Each of
the DFF outputs is subsequently split, amplified and delayed for
de-correlation (Fig. 1(b)). One of the paths is 6 d B attenuated
and afterwards the two paths are com bined to create an elec-
trical 4-PAM signal [3]. Two 4-PAM signals are used to drive
the In-ph ase and Quadrature inputs of the IQ-m odu lators. An
additional attenuation of 6 dB has been used to reduce the im-
pact of the reflections from the IQ-modulator and amplifiers,
resulting in 4-PAM signal with a voltage swing of
[2]. The 112-Gb/s 16-QAM m odu lated signals are first ampli-
fied separately and subsequently multiplexed using a flexi-grid
wavelength selective switch (WSS, Waveshaper 4000S) with
37.5-GHz channel spacing. The resulting optical spectrum is
shown in Fig. 1(c). The combined signal is subsequently fed
into a polarization-m ultiplexing (POLM UX) stage. In this stage
the incoming optical signal is split up i n two equally power ed
tributaries, one delayed for de-correlation, and subsequently re-
combined using a polarization beam combiner (PBC), resulting
in 2 24-Gb /s POLMUX-1 6QAM m odulation.
The transmission link consists of a recirculating loop
(Fig. 1(d)) with four spans of 82-km large-
pure-silica-core
fiber. The average loss of the fiber is 0.161 dB/km, the chro-
matic dispersion coefficient is 21.0 ps/nm/km a t a wavelength
of 1550 nm, and the d ispersion slope equals 0.061
.
Theaverageeffectiveareaofthelarge-
fiber is 133 ,
which results in a nonlinear coefficient of 0.6
.The
average total loss of each of the 82-km spans is 14 dB, which
is a combination of the fiber loss and the splice losses between
standard single-mode fiber and the large-
fiber. The span
loss is compensated for by hybrid EDFA /R aman amplification
using backward-pumping with an average ON/OFF Raman
gain of 6.5 dB at the maximum pump power. The Raman gain
is reduced due to the core size of the large-
fiber, but the
low fiber loss at the Raman pump wavelengths (0.20 dB/km at
1450 nm) ensures that a sufficiently high Raman gain is still
obtained at moderate pump level (6 50 mW ).
After transmission, the chan nels of interest are filtered out
using a de-multiplexing filter with a 100-GHz bandwidth and
subsequently fed to a polarization-diversity 90
optical h ybrid.
The s ig nal is mixed with a local oscillato r (LO) with 100-kHz
linewidth, which selects the channel under test by coherent
channel selection (tuned within
60 MHz of the channel
wavelength). The four outputs of the 90
optical hybrid are
converted to the electrical domain using balanced photodiodes,
and subsequently dig iti zed using a 50-Gsamples/s real- time
digital sampling scope (D SA72004B). A sequence of one mil-
lion samples, corresponding to 4.48 million bits is subsequently
used for offline digital signal processing. Per measurement
point, the average BER of two 224-Gb/s POLMUX-16QAM
channels, selected by the de-multiplexing filter, are presented
in the results section. The average BER is calculated from
eight shots, fo ur shots of both channels separately, at different
time instances. Offline digital signal processing is used to
demodulate the resulting samples as described in [2]. During
the measurements no cycle slips were observed, and therefore
no differential decoding was used.
III. R
ESULTS
The back-to-back measured BER of the 224-Gb/s POLMUX-
16QAM modulated sig nal, single channel and mu ltiplex ed on
a 37.5-GHz grid, as a functio n of the OSNR is shown in Fig.
2. At a BER of
, the requ ired OSNR for single channel
224-Gb/s POLMUX-16QAM modulation is 2 5.4 dB . A 5.1-dB
penalty with respect to the theoretical O SN R requirement of a
224-Gb/s POLMUX-16QAM modulated signal is observed. At
the FEC-thresh o ld at a BER of
thedifferencebe-
tween the measured and theoretical required OSNR is reduced
to 3.5 dB (19.0 dB versus 22.5 d B). In the WDM co nfiguration
the required OSNR for a BER of
is equal to 27.1 dB. The
1.7-dB OSNR penalty between the single channel and WDM
configuration is resulting from the linear crosstalk between the
WDM signals, due to the tig ht channel spacing [3].
Fig. 3 shows the measured average BER as a function of the
launch power for the center two 224-Gb/s POLMUX-16QAM
channels (channels 5 and 6) after transmission over 656 km of
SLEIFFER et al .:10 224-Gb/s POLMUX-16QAM TRANSMISSIO N OVE R 656 km OF LAR GE- PSCF 1429
Fig. 2. Measured back-to-back BER curves for 224-Gb/s POLMU X-16QAM.
Fig. 3. Launch power variation versus average BER for the center two
224-Gb/s POLMUX-16QAM channels after 656 km of transmission.
Fig. 4. Average BER results for the center two 224-Gb/s POLMUX-16QAM
channels versus transmission distance.
large- pure-silica-core fiber. The o ptimal launch power is
1 dBm per 224-Gb/s POLMUX-16QAM channel, which con-
firms the significant benefit of large core fiber to improve the
nonlinear tolerance of high spectrally efficient modulation f or-
mats such as POLMUX-16Q AM modulatio n. Fig. 4 shows the
measured BER as a function of transmission distance for the
center two 224-Gb/s POLMUX-1 6QA M modulated ch annels,
and at the launch power of
1 dBm per channel. After 656 km
of large-
pure-silica-core fiber (2 recirculating loops) an av-
erage BER of
is measured. This translates into a
margin of approximately 0.6 dB i n Q-factor with respect to an
FEC-limit of
. A fter 3 recirculating loops (98 4 km)
the measured BER has degraded to
.
Fig. 5 shows the measured BER for each of the ten 224-Gb/s
WDM channels after 656 km transm ission and at the optimum
launch power. For each of the measurements, the ECL-lasers
are tuned from t he center channel to the channel un der test t o
ensure a low enough laser linewidth for carrier phase estima-
tion. The transmission results depicted in Fig. 5 confirm that all
the 224-Gb/s channels have nearly the same performance, and
Fig. 5. BER results for the ten 224-Gb/s POLMUX-16QAM c hannels after
656 km of tra nsmission.
the worst measured channel has a margin of 0.5 dB in Q-factor
(BER of
) with respect to the FEC-limit.
IV. C
ONCLUSION
We have shown tran smission of ten 224-Gb/s POLMUX-
16QAM modulated channels on a 37.5-GHz flexible grid, re-
sultinginaspectralefficiency of 5.6 b /s/Hz. A total capacity
of 2 Tb/s has been transmitted over 656 k m of large-
pure-
silica-core fiber with a margin of 0.5 dB in Q-factor w ith respect
to the FEC-limit for the worst channel.
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