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Optical 2R regenerator based on passive
saturable absorber for 40Gbit/s WDM
long-haul transmissions
0.65
D. Rouvillain, P. Brindel, F. Segnineau, L. Pierre,
0. Leclerc, H. Choumane, G. Aubin and J.L. Oudar
0.55
A semiconductor saturable absorber based on ion-irradiatedquantumwell vertical cavity
is implemented in a 40 Gbit/s dispersion-managed
R7. loop, yielding a Q-factor of 13 dH and 11.3dH at 7600km
distance in single-channel and in WDM environment with five
200 GHa-spaced 40 Gbit/s channels, respectively.
E
t
'
0.45
0.3:
0.45
0.65
0.55
X, m
Fig. 4 Triangular tmjectory (oJi1.rdynamics change)
Table 1: Performance of NN and PID controllers
Co"lrc,ller
Neural nehvork controller 1
m2 [kgl
Traiectones [RMS ermrrl
Circle I Sauare I Tnanele
10
I0
100
I0.02340I0.02085 0.02584
Conclusion: This Letter has presented an NN controller employing a
modified recurrent
for trajectory control of a robot. Using the NN
to learn the inverse model of the robot, the scheme does not require a
priori knowledge or asspmptions about its dynamics. The results of
computer simulations have shown that advantages of the proposed NN
controller include fasi convergence of the tracking error and smooth
control actions. The ability of the controller to reject Large dishlrbances has also been demonstrated in simulation. Comparison with a
PID controller has revealed the suverior verformance of the orowxed
neural control system. '
One answer to capacity demand in long-haul transmission systems
relies on the multiplication of 10 Gbitjs WDM channels but with the
consirdim uf mninrised specrral efficiency. In that respect, dispersion
management (DM) was proven to be a very efficient technique to
achieve such dense WDM long-haul transmissions with ultra-high
capacities [I]. An alternative for upgrading the total capacity of longhaul systems while reducing complexity and cost consists in increase in
channel line-rate (i.e. 40 Gbitjs), as recently reported [Z]. However, the
maximum achievable transmission distance is seen to decrease with
increasing channel bit rate as a consequence of ever-growing propagation impairments [3]. For this reason, means of propagation control
such as optical regeneration (OR) seems to be required to significantly
increase the transmission distance orland improve the margins of such
40 Gbitis systems. From a practical viewpoint, such regeneration
schemes should combine performance improvement with low
implementation costs.
In this Letter, we report the first experimental demonstration of a
1.55 pin quantum well saturable absorber (SA)-based regeneration
scheme in a 40 Gbitjs dispersion-managed RZ long-haul transmission.
The regeneration capabilities of such a passive 2R regenerator are also
investigated in a 40 Gbitjs WDM environment.
The ideal SA principle of operation is the following. When illuminated with an optical signal with peak power below some threshold
(Px.,), the photonic absorption of the SA is high and the device is
opaque to the signal. Above P,?<,,the SA transmitlance rapidly increases
and saturates to an asymptotic value near unity (passive loss being
overlooked). Under this condition, ASE noise and other low-power
components arc attenuated by the SA while '1' pulses pass though
unchanged. As B consequence, such SA device needs to be associated
with narrowband optical filters and nonlinear propagation to provide
efficient amplitude control of the incoming '1'. Such SAifilter combination improves OSNR and provides fully-passive 2R regeneration, as
experimentally demonstrated at 20 Gbitjs [4]. In the view of extending
such regenerative properties to 40 Gbitjs DM transmissions, a recent
work proposes and numerically demonstrates an improvement of such
an SA-based regenerator by insertion of a compression fibre in between
the SA device and the optical bandpass filter, as shown in Fig. I [ 5 ] .
Such a SA-based 2R combination is experimentally studied here.
Acknowledgment: The author wishes to express his thanks for financial suppon being provided by the Scientific and Technical Research
Council of Turkey (TUBITAK) in cawing out this study.
0 IEE 2002
27 June 2002
Electmnics L C I ~ W S Online NO: znnzn76~
DO/: 10.1n49/e~:znnzn769
S . Yildirim (Robotic Research Labomloty Mechanical Engineering
Division, Engineering Facully, Erciyes University, Kayseri 38039,
Turkey)
optical 2R regenerator
.~~~
R&W"CW
'Bipedal robot control using recurrent hybrid neural
network', Neural New. World 1999.9,(l-2), pp. 57-73
2 YILDLRIM. S.: 'Neural nehwrkfor control ofbipeds', Elt.ctmn. Lett., 1999,
1
YILDIRIM, S.:
35, pp. 20662065
3
YTLDIRIM. S., and UZMAY, i.: 'Stltistical analysis ofvehicle's vibration due
to mad roughness using radial basis neural network', Appl. AH^ Intell. 1,
2001, 15, (4). pp. 419427
ELECTRONICS LETERS
72th September 2002
!
Chirp
Fig. 1 Experimental loop serupfor 40 Gbitjs long-haul transmissions with
architecture of SA-hosed opticol 2R regenerator
The semiconductor saturable absorber we used is a metal organic
vapour phase epitaxy-grown (MOVPE) structure with nine
InGaAsPllnP quantum wells, inserted in a vertical cavity The device
Vol. 38 No. 19
1113
~
is fully passive and requires no Peltier cooler, nor bias voltage. It is to
be used in reflection made, thus yielding intrinsic polarisationinsensitive opcration. Device characterisation conducted at 40 GHz
showed a switching contrast in excess of 2.5 dB in the 1548 to
1561 nm wavelength range with a I / e response time shorter than 5 ps.
Investigations of the achial regenerative properties of the 2R
SA-based scheme are conducted by means of a 40Gbitls WDM
long-haul loop transmission. Input 40 Gbitjs RZ data stre,
results
from the time-multiplexing of 10 GHz Dulses of 8 PS FWHM emitted
from a GS-DFB laser at-1555.75nm wavelength-and coded with a
Z2' - I PRBS sequence. At the receiver side, bit error rate (BER)
measurements are performed an all four 10 Gbit/s mbutaries after
demultiplexing 40 Gbitjs data through a oolarisation-insensitive EAM
TcraLightBof local dispersion of 8 and -16 ps .nm-' .km-', respectively, at 1550nm wavelength. Such dispersion map results from
numerical investigations targeting optimal DM maps for 40 Gbit/s
WDM systems with reduced channel spacing.
.
. Actual realisation of
such spans was reported in [6], yielding a very good flatness of the link
dispersion over a wide 1470-1630nm range, with a value between -1
and Ops.nm-' .km-'.
Cumulated chromatic dispersion at 1555.75 nm
and average polarisation mode dispersion were measured to be
1.9 ps . nm-' and 0.06 ps .km-"', respectively. Span input power is
set to be 2 dBm using in-line 980 nm EDFA with 4.5 dB noise figure.
into the loop in either spectral side of the regenerated channel (see
Fig. 1) to emulate a realistic WDM transmission. Indeed, these extra
channels play a disturbing role during the 240 km propagation but are
extracted from the loop by the Demux stage in front of the SA
(see Fig. 2). Channel separation is 200 GHz (1.6 nm) and span input
power war increased to 6 dBm (-IdBm/channel).
----*--AS WOM)
SA controls signal-to-noise ratios hut not on the position of the pulses
in time. In the N x 40 Chills WDM loor, confieuration. system
performance is found to he similar to that miasured yn single-channel
(13dB at 1300km distance), as a consequem: of the optimised
dispersion map. When implementing the SA-bared 2R regenerator,
performance of the regenerated centred channel reaches Q = 13 dB at
2200 km distance and 11.3 dB after 7600 !an proptigation. Comparison
of this result with the previous one obtained in single channel illu:;trates
SA regenerative capabilities to improve the system performance in a
realistic WDM environment and demonstrates its regenerative effectiveness on 40 Gbit/s RZ signals. The impact of the concatenation of
DemuxjMux stages on such regenerated 40 Gl,it/s WDM system
performance remains to he investigated. The Q-factors are measured
at 40 Ghit/s line rate without fonvard-error correction (FEC)-associated
overhead. However. when accounting- far such overhead-induced
penalty of around 0.3 dB, system performance measured wirh the
SA-based regenerator
remained fullv
with FEC caoabilities
. compatible
.
to yield error-free 40 Gbitjs system operation over 7600 !an
Conclusions: The experimental investigation of a novel opti(:al 2R
regeneration scheme based on a fully passive ultrafast saturable
absorber requiring no bias voltage nor Peltier cooler is reported. An
intrinsically polarisation-insensitive SA device is associated with a
compression fibre and a narrowband optical filter, to perform passive
optical 2R regeneration over 40 Gbit/s dispersion-managed RZ pulses.
Loop implementation of the passive 2R regenerator with 240 km
periodicity yields a measured Q-factor of 13 dB sit 7600 km distance,
showing a near fivefold improvement with respect to non-SA-regenerated transmission. Complementary investigations of the actual
regenerative capabilities of the 2R scheme in a WDM transmission
environment have been successfully carried out, yielding a Q-factor of
11.3 dB at 7600 km distance, this being a clear improvement with
respect to the non-regenerated case. Such low-cost 2R regeneration
apparatus based on a fully passive saturable absorber potentially
opens the way for actual 40 Gbit/s WDM submarine systems.
AS (single channel)
+no AS no filter
0 IEE 2002
Electronics Letters Online No: 20020715
DOI: 10.1049/e1:20020715
+no AS +filter
0
2000
4000
6000
distance, km
8000
10000
Fig. 2 Exprimenrol Q g k t o r evolution againrl ~iansmissioadistance
The SA-based optical 2R regenerator is inserted in thc loop at the
chlrp-free point after a demultiplcxer of I nm filtering bandwidth for a
wavelength-by-wavelength processing. Launched input power into the
SA device, total insertion loss 8 dB (circulator included), is 15 dBm,
while the SA device yields a mean saturation power of 6 dBm. The
pulse compression stage comprises a 2 km span of standard NZ-DSF
fibre with 50 pm2 effective area and 3 ps . nm-' . !an-' chromatic
dispersion. Such fibre characteristics require the implementation of a
second EDFA for launching 15.5 dBm input power that could easily be
removed when considering best-suited highly nonlinear (HNL) fibre
instead. The narrowband optical filter used in the 2R scheme is of
0.9 nm handwidth.
Fig. 2 shows the experimental Q-factor taken as that measured on the
worst 10 Gbitls tributaw against distance. In single-channel configuration, Q-factors of 13 dB(BiR<5.10-6) and I LYdB (BER< IO-')
are
measured after 1300 and 1650 km bansmission, respectively, without
the SA-based 2R scheme and associated EDFAs. Onl; a sligh; improvement could be obtained with a Q-factor of 13 dB after 1600 !an when
implementing an optical filter of 0.9 nm bandwidth into the loop. When
inserting the SA-based 2R regenerator. a clear imDrovement in the
system performance is observed, yielding a Q-factor of 13 dB at
7600 h distance. It should be noted that the main system limitation
at such distances in single-channel transmission stems from timing jitter
accumulation and not amplitude fluctuations. Passive regeneration by
1114
-
D. Rouvillain, P. Brindel, F. Seguineau, L. Picrre and 0. Leclerc
(Alcatel Research & Innovation, Route de Nozay 91460 Morcoussis,
FrCJlZce)
E-mail: [email protected]
H. Choumane, G. Auhin and J.L. Oudar (LPN-CNRS UPR 20, site
d'Alcatel. Route de Nozay, 91460 Marcoussis, France)
References
1 VAREILLE. G., IULIEN. B , PITEL. P , and MARCEROU, J~F.: '3.65 Tbitjs
(365 x 11.6 Gbitjs) transmission experiment over 6850 km using
Inset: WDM optical s p e c n m at end of loop
~
4 June 2002
22.2 GHz channel spacing in NRZ format'. ECOC'2001, Amsterdam,
The Netherlands, 2001, Paper PD.M.1.7
2
BiGO, S., IDLER, W., ANTONA, J ~ C . , CHARLET. G., SIMMDNEAU C.,
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ECOC'2001, Amsterdam, The Netherland, 2001: Paper PD.M.I.1
3
4
CAI. J.X., NISSOY M., DAVIDSON, C.R., CAI. Y., PILIPETSKII. A . N , LI, H ,
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USA, 2002, Paper PD FC4
LECLERC, O., BRINDEL, ,!I
BARRf, S., AUBIN. G., MANGEWEY, J.,
CHOUMANE. H., and OUDAR, ILL.: '20 Gbit/s polanzatian-inseniitive
quantum well saturable absorber for 1.5 pm long-haul transmissions'.
ECOC 2000, Munich, Germany, September 2000, Paper PD 3 . 5
5 MATSUMOTO, M., and LECLERC, 0.: 'Analysis of a 2R optical regenerator
utilising self-phase modulation in a highly nonlinear fibre', Electron.
Lett., 2002.38, (12), pp. 576S77
6 DE MONTMORILLON. L.-A., BEAUMONT, F., GORLIER M., NOUCHI. P.,
FLEURY, L., SILLARD, P.,
J.-P.,
DANY.
MERESSE.
SALLES, V,
SAUZEAU, T., L A B A m , C ,
and LECLERC, 0.: 'Optimized
TeraLightTM/Revcne TeraLightO dispersion-managed link for
40 Gbit/s dense WDM ultra long-haul minsmission system'.
ECOC'OI. Amsterdam, The Netherlands, October 2001, Paper Poster
We.P.44
ELECTRONICS LETTERS
B.,
12th September 2002
Vol. 38 No. 19
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