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Proceedings ArticleDOI

480 km transmission of MDM 576-Gb/s 8QAM using a few-mode re-circulating loop

07 Nov 2013-pp 1-2

AbstractWe demonstrate successful 3-mode-division-multiplexed × 192-Gb/s dual-polarization 8QAM (total 576 Gb/s) transmission over 480 km of few-mode fiber (FMF). This distance was obtained using an all few-mode re-circulating loop containing a 60 km FMF span.

Summary (1 min read)

Introduction

  • This distance was obtained using an all few-mode re-circulating loop containing a 60 km FMF span.
  • After little more than a couple of years impressive progress has been made, including realization of the first Pb/s systems based on multi-core fibers [3,4].
  • After all the main reason that this technology is being investigated is to address the foreseen capacity crunch in longhaul transmission systems.
  • Using 3-mode fiber, each mode carrying a 192-Gb/s DP-8QAM optical modulated signal (total date rate 576 Gb/s), 480 km transmission is obtained.

A. Transmitter setup

  • THz were passively combined using a 1×8 polarization-maintaining coupler, and subsequently modulated using an IQ-modulator, driven by two digital-to-analog converters running at a 32GBaud symbol rate that address the in-phase and quadrature ports of the IQ-modulator (Fig. 1).
  • The electrical driving signal was formed by combining three pseudo-random binary sequences of length 215 which were shifted by 8191 and 16383 symbols with respect to each other before combining them and mapping them onto 8QAM symbols.
  • After modulation, polarization-multiplexing was emulated by splitting the signal into two equally powered tributaries, delaying one by 700 symbols for de-correlation, and combining them again using a polarization-beam combiner (PBC).
  • The 192-Gb/s DP-8QAM signal subsequently is split into three signals which are delayed by 2285 and 4415 symbols with respect to the original signal again for emulation of three different signals, and fed to the spot launching spatial multiplexer (Fig.1a) [9], which launches the signals into a 3-mode supporting FMF pigtail [10].

B. Re-circulating loop

  • The FMF pigtail was connected to a free-space 3dB coupler.
  • The input signal was coupled into the loop containing two few-mode (FM) EDFAs [11], and 60 km of FMF with the parameters listed in Tab.
  • The 60 km FMF span has a differential group delay between the LP01 and LP11 modes of around 9 symbols.
  • In SM re-circulating loops acousto-optic modulators (AOM) are used for switching, i.e. filling, re-circulating and emptying the loop.
  • Therefore a chopper (Fig. 1b) was used inside the free-space 3dB coupler which provides the same functionality, although careful control of timing is required.

C. Receiver

  • At the output of the re-circulating loop a 3D waveguide device (Fig.1c) was used to spatial de-multiplex the three signals.
  • Both digital sampling scopes were carefully synchronized beforehand to assure all signals are received time-aligned.
  • The performance shows a ~1.5dB penalty with respect to theory at the FEC-limit.
  • The authors showed successful transmission of MDM 576-Gb/s 8QAM over 480 km of FMF using an all-FMF component re-circulating loop.

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480 km Transmission of MDM 576-Gb/s 8QAM
using a Few-Mode Re-circulating Loop
V.A.J.M. Sleiffer
1*
, H. Chen
1
, Y. Jung
2
, M. Kuschnerov
3
, D.J. Richardson
2
, S.U. Alam
2
, Y. Sun
4
, L. Grüner-Nielsen
4
,
N. Pavarelli
5
, B. Snyder
5
, P. O´Brien
5
, A.D. Ellis
6
, A.M.J Koonen
1
and H. de Waardt
1
1
COBRA institute, Eindhoven University of Technology, Eindhoven, The Netherlands *v.a.j.m.sleiffer@tue.nl
2
Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, United Kingdom
3
Coriant R&D GmbH, St-Martin-Str. 76, 81541 Munich, Germany
4
OFS, Priorparken 680, 2605 Brøndby, Denmark
5
Tyndall National Institute, Cork, Ireland
6
Aston University, Aston Triangle, Birmingham, B47ET, United Kingdom
Abstract We demonstrate successful 3-mode-division-
multiplexed × 192-Gb/s dual-polarization 8QAM (total 576 Gb/s)
transmission over 480 km of few-mode fiber (FMF). This
distance was obtained using an all few-mode re-circulating loop
containing a 60 km FMF span.
I. INTRODUCTION
Space-division multiplexing (SDM) is rapidly emerging as
a feasible and powerful means to increase the capacity of
optical transmission systems by using the spatial dimension in
either multi-core [1-4] or multi-mode [5-8] fibers. After little
more than a couple of years impressive progress has been
made, including realization of the first Pb/s systems based on
multi-core fibers [3,4]. In this paper we focus on few-mode
fiber transmission.
Whilst the first steps in SDM research were mainly directed
towards proving technological feasibility, an important next
step is to demonstrate that the various approaches under
investigation are able to support large distance transmission.
After all the main reason that this technology is being
investigated is to address the foreseen capacity crunch in long-
haul transmission systems.
The first research on long-haul transmission using few-
mode fiber (FMF) technology consisted of either single-mode
(SM) fibers to re-circulate the signal with SM-EDFAs [6, 7],
or, in case of an all-FMF re-circulating loop, quadrature phase
shift keying (QPSK) as the modulation format [8]. In this paper
we show the first all-FMF re-circulating loop using a
higher-order modulation format: 8-level quadrature amplitude
modulation (8QAM). Using 3-mode fiber, each mode carrying
a 192-Gb/s DP-8QAM optical modulated signal (total date rate
576 Gb/s), 480 km transmission is obtained.
II. EXPERIMENTAL SETUP
A. Transmitter setup
At the transmitter side five lasers running at 193.0, 193.1,
193.4 (channel under test (CUT)), 193.8 and 193.9 THz were
passively combined using a 1×8 polarization-maintaining
coupler, and subsequently modulated using an IQ-modulator,
driven by two digital-to-analog converters running at a
32GBaud symbol rate that address the in-phase and quadrature
ports of the IQ-modulator (Fig. 1). The electrical driving signal
was formed by combining three pseudo-random binary
sequences of length 2
15
which were shifted by 8191 and 16383
symbols with respect to each other before combining them and
mapping them onto 8QAM symbols.
After modulation, polarization-multiplexing was emulated
by splitting the signal into two equally powered tributaries,
delaying one by 700 symbols for de-correlation, and combining
them again using a polarization-beam combiner (PBC).
The 192-Gb/s DP-8QAM signal subsequently is split into
three signals which are delayed by 2285 and 4415 symbols
with respect to the original signal again for emulation of three
different signals, and fed to the spot launching spatial
DAC
DAC
Tx
5
PBC
1
x
8
700
Symb.
2825
Symb.
4415
Symb.
Scope 1
0.4nm
Scope 2
0.4nm
0.4nm
LO
LO
FM-EDFA FM-EDFA
30km
30km
Input
beam
Output
beam
1 2
2
1
a
b
c
LO
1x4
Loop
Coherent
Rx 3
Coherent
Rx 1
Coherent
Rx 2
Timing control
Fig 1. Experimental setup of the 60 km containing all-FMF re-circulating loop. a) 3-spot launching spatial multiplexer [9], b) chopper used as switching
mechanism for the re-circulating loop, c) 3D waveguide device with 3 single-mode fiber outputs, used as a spatial de-multiplexer

multiplexer (Fig.1a) [9], which launches the signals into a
3-mode supporting FMF pigtail [10].
B. Re-circulating loop
The FMF pigtail was connected to a free-space 3dB
coupler. The input signal was coupled into the loop containing
two few-mode (FM) EDFAs [11], and 60 km of FMF with the
parameters listed in Tab. 1. The 60 km FMF span has a
differential group delay between the LP
01
and LP
11
modes of
around 9 symbols. At the input and output of the loop a
FM-EDFA was placed to compensate for the span and
coupling loss of the 3dB coupler.
In SM re-circulating loops acousto-optic modulators
(AOM) are used for switching, i.e. filling, re-circulating and
emptying the loop. However, FM-AOMs do not exist.
Therefore a chopper (Fig. 1b) was used inside the free-space
3dB coupler which provides the same functionality, although
careful control of timing is required. The free-space optics is
tuned such that the output of the loop is blocked when the input
is open, and vice versa. The chopper provides a signal which
was used to control the timing to trigger the scopes at the
receiver side after determining the loop time and hold off time.
C. Receiver
At the output of the re-circulating loop a 3D waveguide
device (Fig.1c) was used to spatial de-multiplex the three
signals. The 193.4 THz CUT was filtered out using 50-GHz
tunable filters and afterwards fed to three coherent receivers
connected to two digital sampling scopes: an 8 port 40-
Gsamples/s scope (20 GHz electrical bandwidth) and a 4 port
50-Gsamples/s scope (16 GHz electrical bandwidth). Both
digital sampling scopes were carefully synchronized
beforehand to assure all signals are received time-aligned.
Afterwards, offline 6x6 MIMO-DSP was employed to
reconstruct the sent signals [12].
III. RESULTS
Fig. 2a shows the back-to-back performance of the
192-Gb/s DP-8QAM signal when mode multiplexed and
de-multiplexed. The performance shows a ~1.5dB penalty with
respect to theory at the FEC-limit.
Fig. 2c shows the transmission distance versus bit-error
rate. After 480 km an average BER over all modes of ~1.3·10
-2
is reached. After 540 km this BER increased to 3·10
-2
, which is
above the assumed FEC-limit at 2.4·10
-2
[13]. The inset shows
the recovered constellations after 480 km.
Fig. 2b shows the optimization of the tap number after 2, 5
and 8 loops. As observed in Fig. 2d, from the impulse
responses after 120, 300 and 480 km transmission, the DGD
between the LP
01
and LP
11
mode in the 60km span is not fully
averaged out. This causes the number of peaks to grow in each
loop as well as the number of taps needed to compensate this
(Fig. 2b). For 480 km the optimum number of taps is ~321.
IV. CONCLUSION
We showed successful transmission of MDM 576-Gb/s
8QAM over 480 km of FMF using an all-FMF component
re-circulating loop. As best we are aware this is the first
demonstration of a higher-order modulation format signal
being transmitted over an all-FMF re-circulating loop.
ACKNOWLEDGMENT
This work was supported by the EU FP7-ICT MODE GAP
project under grant agreement 258033.
REFERENCES
[1] J. Sakaguchi et al., JLT 31 (4), pp. 554-562 (2013).
[2] H. Takahashi et al., Proc. ECOC ‘12, paper Th.3.C.3.
[3] H. Takara et al., Proc. ECOC ‘12, paper Th.3.C.1.
[4] D. Qian et al., Proc. Frontiers in Optics ‘12, paper FW6C.3.
[5] V.A.J.M. Sleiffer et al., Optics Express 20 (26), B428-B438 (2012)
[6] S. Randel et al., Proc. OFC ’12, paper PDP5C.5
[7] R. Ryf et al., Proc. OFC ‘13, paper PDP5A.1.
[8] E. Ip et al., Proc. OFC ‘13, paper PDP5A.2.
[9] H. Chen et al., Proc. OECC ’13, PD3-6
[10] L. Grüner-Nielsen et al., JLT 30 (23), pp. 3693-3698 (2012)
[11] Y. Jung et al., Optics Express 21 (8), pp. 10383-10392 (2013)
[12] V.A.J.M. Sleiffer et al., 10.1109/JLT.2013.2274194
[13] D.A. Morero et. al, Globecom (2011)
Tab. 1. 60 km FMF span (@ 1550nm)
Spool 1
Spool 2
Length [km]
30
30
MPI [dB]
-26
-25
DGD [ps/m]
-0.044
0.053
Disp. LP
01
[ps/(nm·km)]
19.8
19.8
Disp. LP
11
[ps/(nm·km)]
20
20
14 18 22 26 30
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
OSNR [dB/0.1nm]
Bit-Error Rate
Theory
Average BER
Mode 1
Mode 2
Mode 3
a
FEC-limit
d
-120 -80 -40 0 40 80 120
-60
-40
-20
0
Tap Number
Magnitude [dB]
2 Loops (120km)
5 Loops (300km)
8 Loops (480km)
Average BER
Mode 1
Mode 2
Mode 3
FEC-limit
100 200
300 400
10
-4
10
-3
10
-2
Number of Taps
Bit-Error Rate
2 Loops (120km)
5 Loops (300km)
8 Loops (480km)
b
0 100 200 300 400 500 600
10
-5
10
-4
10
-3
10
-2
Transmission Distance [km]
Bit-Error Rate
Citations
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01 Jan 2014
TL;DR: The final author version and the galley proof are versions of the publication after peer review that features the final layout of the paper including the volume, issue and page numbers.
Abstract: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.

3 citations


Cites background or methods from "480 km transmission of MDM 576-Gb/s..."

  • ...Spot-based mode couplers have been realized by bulky optics [52], [53], laser inscribed 3D waveguide devices [16], [56] and optical fiber lanterns....

    [...]

  • ...In principle, these solutions can be categorized under two groups: mode selective excitation by matching the FMF mode profile [20], [47], [49]– [51] and mixed-mode excitation by arranging launch spots [52]–[54] or coupled waveguides [55], [56] in a particular structure [57] to launch the appropriate orthogonal mixtures of fiber modes....

    [...]

  • ...This chapter introduces spot-based mode couplers, which are based on the publications [53], [56], [54] carried out during Ph....

    [...]

  • ...2 Coupler design A number of promising MDM transmission systems based on spot-based mode couplers have been demonstrated recently, where free space [52], [53], [56], [129], [130] and photonic lantern [16], [55], [66] based solutions were employed....

    [...]

  • ...1 3DW device This section is based on the publication [56] made during the Ph....

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Dissertation
10 May 2016
Abstract: Le trafic internet mondial etant toujours plus important, l’augmentation du debit transmis dans les fibres optiques de facon a diminuer le cout par bit est necessaire. Les technologies actuelles sur fibres monomodes approchent une limite fondamentale empechant une augmentation consequente du debit dans les fibres optiques. Une nouvelle technique appelee le multiplexage de mode spatial est une solution pour depasser cette limite. Plusieurs modes spatiaux, correspondant aux solutions des equations de propagation, sont multiplexes dans une fibre specifique pour multiplier le debit transmis par le nombre de modes utilises. Pour la mise en œuvre de cette technique, ma strategie est de separer les modes spatiaux de facon hybride, c'est-a-dire d’abord optiquement puis avec un traitement numerique relativement peu complexe. Dans cette approche, la diaphonie entre les modes non degeneres n’est pas compensee et doit donc etre minimisee sur toute la ligne de transmission pour une transmission de donnees de bonne qualite. Par l’utilisation d’un multiplexeur-demultiplexeur et d’une fibre pouvant propager six modes spatiaux et induisant peu de diaphonie, j’ai realise la transmission d’un signal monocanal de 6x100 Gbit/s dans une fibre de 40 km. Pour des transmissions plus longues que 80 km, un amplificateur est necessaire pour compenser les pertes de la fibre optique. J’ai donc concu un amplificateur a fibre dope Erbium pour cinq modes spatiaux induisant peu de diaphonie et avec un gain superieur a 15 dB pour tous les modes et realise la transmission d’un signal de 5x100 Gbit/s sur une distance de 80 km avec un traitement numerique relativement simple.

Cites background from "480 km transmission of MDM 576-Gb/s..."

  • ...Cela a permis la démonstration de transmissions de trois modes sur plusieurs centaines de kilomètres avec des éléments compatibles avec la transmission de tous les modes simultanément [109] [110]....

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References
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Journal ArticleDOI
TL;DR: The total demonstrated net capacity, taking into account 20% of FEC-overhead and 7.5% additional overhead (Ethernet and training sequences), is 57.6 Tb/s, corresponding to a spectral efficiency of 12 bits/s/Hz.
Abstract: Transmission of a 73.7 Tb/s (96x3x256-Gb/s) DP-16QAM mode-division-multiplexed signal over 119km of few-mode fiber transmission line incorporating an inline multi mode EDFA and a phase plate based mode (de-)multiplexer is demonstrated. Data-aided 6x6 MIMO digital signal processing was used to demodulate the signal. The total demonstrated net capacity, taking into account 20% of FEC-overhead and 7.5% additional overhead (Ethernet and training sequences), is 57.6 Tb/s, corresponding to a spectral efficiency of 12 bits/s/Hz.

140 citations


Journal ArticleDOI
TL;DR: A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.
Abstract: We successfully fabricate three-mode erbium doped fiber with a confined Er3+ doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative thickness of the ring-doped layer in the active fiber and pump launch conditions. A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.

40 citations


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The authors demonstrate successful 3-mode-divisionmultiplexed × 192-Gb/s dual-polarization 8QAM ( total 576 Gb/s ) transmission over 480 km of few-mode fiber ( FMF ).