Latest results from the POF-ALL EU Project: Toward Improved Capacity over Large-Core Plastic Optical Fibers
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BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
Latest results from the POF-ALL EU Project: Toward Improved Capacity over
Large-Core Plastic Optical Fibers
Roberto Gaudino (1), Alessandro Nocivelli (2), Hans Kragl (3), Olaf Ziemann (4), Norbert Weber (5), Dieter Jaeger (6), Ton Koonen
(7), Carlo Lezzi (8), Andreas Bluschke (9), Sebastian Randel (10)
1 : Politecnico di Torino, Italy, gaudino@polito.it
2 : Luceat, Italy
3: DieMount GmbH, Germany
4: Plastic Optical Fiber Application Center, Germany
5: Fraunhofer Institute, Germany
6: Universität Duisburg-Essen, Germany
7: Technische Universiteit Eindhoven, The Netherlands
8: Fastweb SpA, Italy
9: Teleconnect GmbH, Germany
10: Siemens AG, Corporate Technology, Information and Communications, Germany.
Abstract We present an overview of the EU STREP project POF-ALL, aimed at developing new low-cost high-speed
short reach optical transmission systems based on large-core (1mm) Plastic Optical Fibers (POF).
of its potential applications. This paper focuses mainly on
1. Introduction: POF-ALL project description
the first aspect.
The POF-ALL technical goal is to build transmission
The POF-ALL project (“Paving the Optical Future with
device working with large core POF at 100+ Mbit/s
Affordable Lightning-fast Links”) aims at developing a
symmetrically over distances of 200+ meters, and at 1+
technology to allow delivery of 100+ Mbit/s symmetrically
Gbit/s over 50+ meters. The use of large core POF, while
to residential users at costs far lower than existing
being advantageous in terms of installation, anyway poses
alternatives, thanks to the use of Plastic Optical Fiber
strong physical transmission impairments (due to the
(POF). POF-ALL is an EU FP6 STREP project; it started
higher attenuation and dispersion of POF with respect to
on January 2006 and will end in June 2008. POF-ALL is
GOF) that the project deals with in an integrated way by
targeted at the edge network, a term that indicates the last
optimizing components, devices and transmission
part of access networks towards the final users and is often
techniques. With “large core” POF we mean essentially
a synonym of premises or in-building network. The edge
thick 1mm POF in one of their different flavors, being
network, due to its capillarity, is the most expensive part of
step-index (SI), double-step-index (DSI) or graded-index
the access network. The project is tailored to large
(GI). We believe that the focus on large-core POF is not
residential buildings, which are most common in European
simply a technical detail, but a key point of the project. In
cities. POF-ALL shall prove that POF can radically ease
fact, the large diameter makes 1mm POF a completely
installation difficulties and reduce costs while providing
different medium compared to GOF in terms of ease of
ample bandwidth, making it the ideal alternative for edge
installation, and thus of applications. It has been shown
networks. POF ease installation difficulties compared to
that, regarding ease of mechanical connections, a “do-it-
glass optical fibers (GOF) thanks to its very large diameter
yourself” approach by unskilled people is feasible, also
and mechanical resilience to stresses and low bending
thanks to commercially available plug-less connectors, a
radius.
requirement that would be ideal for the in-house scenario.
The full POF-ALL project is focused on large 1mm In fact, POF connections can be performed using very
core fibers based on PMMA material, in either the simple tools.
traditional Step-Index version or in the recent Graded-
Two main technical directions are investigated in the
Index version. In the rest of the paper, we will use the
project:
acronym POF to indicate 1mm PMMA plastic optical
fiber. • Transmission at 100 Mbit/s (Fast-Ethernet) over
distances above 200 meters, using standard 1mm SI-
The goal of the project is twofold. From one side, a
POF, with a final target of 300 meters.
great technical effort is put in place in order to greatly
improve the POF transmission capacity and reach with • Transmission at high speed (1 Gbit/s and more) over
respect to current commercial solution. From another side, distance around 100 meters, using 1mm GI-POF
significant POF-ALL resources are spent in dissemination This paper presents the most recent technical results of the
and market analysis, to understand the potential marketing project. In particular, it describes the three approaches that
impact of POF, and to improve the general understanding are currently under development. In the first one, described
in the following Sect. 2, we are investigating multilevel
978-1-4244-1942-5/07/$25.00 ©2007 IEEE IEEE Catalog Number: CFP0791D-CDR
ISBN: 978-1-4244-1942-5
Page 1 of 6 Library of Congress: 2007909452
BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
baseband transmission to obtain 100 Mbit/s transmission
over 200+ meters. In the second approach, described in
Sect. 3, we investigate the use of techniques taken from the
RF world, such as Quadrature Amplitude Modulation
(QAM), again to achieve 100 Mbit/s over 200+ meters. In
these two approaches, the selected fiber type is commercial
1mm step-index POF. In Sect. 4, we show most recent
results on higher bit rate transmission (1 Gbit/s and more)
over shorter distances (50-100 meter) and graded-index
(but still large core) POF. Finally, in Sect. 5 we address a
recent trend inside the project that is the use of even more
advanced modulation formats, and in particular orthogonal
frequency division multiplexing (OFDM).
2. Baseband approach, 200 meters
In a first approach, we investigate the use of multilevel Figure 1: 8-PAM eye-diagram after 200 meter, 120 Mbit/s
baseband transmission to obtain 100 Mbit/s transmission line rate
over 200+ meter. Due to the strong modal dispersion in 1
mm SI-POF over this distance, the available bandwidth is We have recently demonstrated this architecture at 120
of the order of 18 MHz [1]. Thus, bandwidth efficient Mbit/s line rate (for a net data rate equal to 100 Mbit/s)
multilevel transmission is required. We opted for a over a full experimental prototype. The resulting
proprietary and optimized proprietary transmission transmission system was error-free after 200 meters,
protocol, based on direct baseband 8-PAM modulation showing the eye-diagram represented in Fig. 1, and had a
coupled with pre- and post- equalization. The system we BER=10-3 after 275 meters (and 2 inline connectors),
are proposing thus requires advanced digital signal which may be turned into error-free after FEC. We believe
processing (DSP) algorithms, and it is based on the that these are record results in the POF field, and may
following blocks: show new fields of application for large-core POF systems.
• Conversion of the input binary data stream into 8- Our system has been developed in order to be fully
PAM, with (optionally) the addition of FEC coding to compatible with Fast-Ethernet, and the actual interfacing
improve transmission resilience from Ethernet to our proprietary transmission protocol is
• Pre-compensation filtering on the 8-PAM signal. This currently under development, and will be ready in Fall
is performed by an 8-taps FIR filter having a high-pass 2007.
response that partially pre-compensate the bandwidth The advanced digital signal processing proposed here are
limitation of the POF channel, and by an ad-hoc currently prototyped using a high-level FPGA. The
algorithm to compensate the LED intrinsic missing step toward a potential commercial use would be
nonlinearity the development of a dedicated ASIC chip, a task that,
• Digital-to-analog conversion of the resulting signal, though not feasible inside the available POF-ALL budget,
and application to a green wavelength LED with appears as quite straightforward, since the overall
suitable driver hardware complexity of our algorithms is comparable with several
• At the receiver side, detection of the incoming optical types of ASIC that have been developed for wireless
signal using a high-performance PIN photodiode application. In the last part of the project, a cost analysis of
followed by a transimpedance amplifier and a (linear) an ASIC realization will be performed.
automatic gain control circuit
• Analog-to-digital conversion, followed by DSP-like 3- QAM-like approach, 200+ meters
clock recovery and blind adaptive equalization. We Quadrature amplitude modulation (QAM) is a promising
notice here that adaptive equalization, besides alternative to fit the 100 Mbit/s transmission speed into the
compensating the POF channel low-pass response, limited bandwidth of a 200+ meters 1 mm-core SI-POF
turns out to find the optimal sampling point inside the link. QAM techniques are widely used in e.g. wireless
eye-diagram, thus greatly helping in optimizing the LANs, DVB-C, and DOCSIS cable modems. They are
performance of the full system. readily available in low-cost chip sets, thanks to the
• Demodulation from 8-PAM to binary already established large market volumes of these
applications. QAM basically deploys two orthogonal
transmission channels to convey the in-phase (I) and
quadrature-phase (Q) data signal components.
Commercially available chip sets consist of quadrature
modulator/demodulator circuits, as well as a Baseband
Processor (BBP) which converts the serial binary input
978-1-4244-1942-5/07/$25.00 ©2007 IEEE IEEE Catalog Number: CFP0791D-CDR
ISBN: 978-1-4244-1942-5
Page 2 of 6 Library of Congress: 2007909452
BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
data stream into the multi-level I- and Q-signals. To
emulate QAM transmission on a POF link, three options
are currently under investigation inside the POF-ALL
project [2]:
1) Direct QAM (see Fig. 2.a ); the I- and Q-signals are
modulated on the orthogonal cosine and sine versions
of an electrical harmonic carrier. This is the approach
commonly used in today’s large volume applications
mentioned before. For a data rate of R bit/s, and a N-
QAM scheme, the resulting symbol rate is R / log2 N .
In double-sideband quadrature modulation, as rule of
thumb the carrier frequency fc needs to be placed at Fig. 3 Received QAM-256 signal constellation (simulated)
least above 0.7⋅ R / log2 N , and the resulting required 0
bandwidth of the full channel should be at least equal to -2
QAM-256
1.4⋅ R / log2 N . -4
PAM-16
2) Baseband/subcarrier emulated QAM (see Fig. 2.b ); the WS QAM-256
I-signal is carried in baseband and the Q-signal is -6
log(SER)
log(Pe)
PAM-8
QAM-16 QAM-64
modulated on a carrier fc such that the I- and Q-spectra -8
do not overlap. The bandwidth of the link thus needs to -10
PAM-4
be at least 2.1⋅ R / log2 N . WS QAM-16
WS QAM-64
-12
3) Wavelength-sliced emulated QAM (see Fig. 2c) ); the I-
and Q-signal are both carried in baseband on two -14
-30 -28 -26 -24 -22 -20
separate wavelength channels, which may be formed by PP0 [dBm]
0 (dBm)
e.g. two complementary sliced parts of a broad
Fig. 4 SER versus average RX optical power, for direct QAM,
spectrum light source such as a LED. This option
m-PAM, and wavelength-sliced QAM
requires a link bandwidth of at least 0.7⋅ R / log2 N.
Of these three options, the most interesting are the direct
QAM, because of the re-use of readily available QAM chip Also a comparative analysis has been made of the
sets, and the wavelength-sliced one, as it requires clearly symbol error rate (SER) curves versus average received
the least link bandwidth. optical power for direct x-points QAM (QAM-x), x-level
I
POF I
Pulse Amplitude Modulation (PAM-x), and wavelength-
LD PD
data
in BBP
X
Σ
X LPF
BBP
data
out
sliced x-points QAM (WS-QAM-x). The curves are
X X LPF
Q
fc π/2 π/2
Q depicted in Fig. 4 for a given data rate of 100 Mbit/s, and
fc
indicate that wavelength-sliced QAM is a promising
a) direct QAM approach as it offers good receiver sensitivity together with
I
LD
POF
PD
LPF
I the least bandwidth requirements. In an experimental
data data
in BBP
X
Σ
BPF X LPF
BBP out setup, we measured the EVM of a direct QAM system
Q
Q
fc fc realized over a 100 meters 1 mm core SI-POF link. The
directly modulated light source was either a 658 nm Fabry-
b) baseband/subcarrier emulated QAM
Perot laser diode emitting 5 mW, or a 520 nm LED
SLED POF PD
data
I
S
WDM WDM
S xtalk
I
data emitting 2 mW. The EVM curves obtained with these
in BBP elim. BBP out
Q
S slicer demux S
Q
sources for QAM-16, -64, and -256 formats and a symbol
rate of 7.0 MBaud (implying bit-rates of 28, 42 and 56
c) wavelength-sliced emulated QAM Mbit/s, respectively) are shown in Fig. 5, and are plotted
versus the carrier frequency fc. The rapidly deteriorating
Fig. 2 QAM emulation system options
EVM versus fc indicates that the link bandwidth of the
By means of system software simulations using VPI LED-based system is smaller than that of the laser-based
Transmission Maker, the direct QAM system concept has system; this is attributed to the larger mode volume excited
been assessed for a bit rate of 129 Mbit/s and modulation by the LED. The LED system performance is limited by
formats QAM-64 and QAM-256. Good signal constellation the link bandwidth, whereas the laser-based system
diagrams have been obtained after 100 meters of 1 mm SI- performance seems limited by system non-linearities. The
POF; Fig. 3 shows the diagram for QAM-256 and a carrier curves indicate also that for this 100 meters SI-POF link
frequency fc = 40 MHz. The relative Error Vector the EVM requirements for QAM-64 (i.e. EVM
BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
10
9
8
7
6
EVM (%)
QAM-16
5 QAM-64
QAM-256 QAM-256
4
QAM-16
3 LED QAM-64
2
Figure 6: Normalized small signal frequency response
1
LD of red edge emitting laser diode
0
0 20 40 60 80
Even faster than edge emitting lasers are red VCSELs.
carrier freq. (MHz)
Unfortunately the temperature behavior of recent devices is
Figure 5:Measured EVM versus carrier frequency for quite poor and does not seem to satisfy the requirement of
direct QAM system over 100 meters SI-POF datacom equipment. For instance, the output power
typically drops below 100 µW at a temperature above
50 °C.
System experiments over the POF link reached 60
As a more far-fetched alternative for the longer term,
Mbit/s using QAM-16 with the 520 nm LED, and more
the project is also considering LEDs as alternative, lower
than 150 Mbit/s using QAM-64 with the 658 nm Fabry-
cost optical sources. Especially green and blue devices,
Perot laser diode.
and adopted driving concepts are analyzed to establish
4. High speed approach, 1 Gbit/s over 100 meters Gigabit transmitter devices. On the receiver side different
concepts are investigated to achieve high data rates with
Not only a longer transmission distance, but also higher bit large-area receivers. One approach is the utilization of
rates are investigated within the POF-ALL project. In elaborated driving concepts. This includes special
photodiode structures as well as low-input impedance
particular, Workpackage WP2 focuses on Gbit/s
transimpedance amplifiers and voltage up-conversion to
transmission. Due to its exceedingly high modal
minimize capacitance and carrier drift-time. The other
dispersion, at this bit rate the SI-POF is not easily usable,
approach is the application of concentrating optics on
unless very advanced modulation techniques are used as small size photodiodes.
discussed in the following Section 5. The current chapter is
Final goal of this workpackage inside the POF-ALL
focused on Gbit/s transmission over approx. 100 meters project is a pre-production transceiver prototype capable of
using standard binary NRZ code. We thus selected a fiber 1.25 Gbit/s. The transceiver should fulfill not only
with appropriate bandwidth, but still with a large core technical guidelines, but also economical and
diameter of 1 mm. Examples for these fibers are new environmental ones like eye-safety, low-costs, long
graded-index (GI) fibers like the OM-Giga from Optimedia lifetime and the demands of mass-production. The project
[5] or multicore fibers. These fiber types only recently is currently very close to this goal, as can be seen in Figure
appeared on the market. As all of these fibers are PMMA- 7, which shows a photograph of the current prototype
based, they have a potential for low cost compared to the transceivers developed inside POF-ALL. Two different
more expensive perfluorinated plastic optical fibers, and at small form factor gigabit transceivers are assembled at the
the same time provide much more bandwidth than SI-POF. moment, one in the POF typical SMI style and one in a
Attenuation characteristic of the PMMA material requires SFF style with EM-RJ connector. First prototypes for these
the use of red light. The transmission system thus requires transceivers will be available within Fall 2007, while full-
high-speed red light sources (650 nm) at the transmitter fledged media converters featuring these transceivers will
side. Moreover, large area receivers (effective area in the 1 follow by the end of the year 2007.
mm range) are necessary. Both requests are very After developing the transceivers, we performed a
uncommon in optical data transmission, so the main focus complete characterization. First tests on a full transmission
in this approach is on evaluating different light sources, links are very promising (see for example Figure 8),
photodiodes and sophisticated driving concepts. In Fig. 6, showing a good eye diagram after 50 meters at 1.25 Gbit/s
the frequency response of a common red edge-emitting line rate, completely compatible with Gigabit Ethernet
laser designed for DVD player applications is shown. The standards in terms of jitter and eye-mask.
3-dB cut-off frequency is well above 1 GHz. This result
demonstrates that even cheap devices built for DVD
applications can be used for high-speed data transmission,
thus taking advantage of mass-production and consequent
low cost.
978-1-4244-1942-5/07/$25.00 ©2007 IEEE IEEE Catalog Number: CFP0791D-CDR
ISBN: 978-1-4244-1942-5
Page 4 of 6 Library of Congress: 2007909452
BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
Figure 7: Small form factor transceiver devices
currently manufactured within POF-ALL Figure 10: Transmission of 910 Mbit/s NRZ over
100 m SI-PMMA-POF with passive equalizing
Figure 10 shows the transmission of 910 Mbit/s in
NRZ-code over standard SI-POF only with some
equalizing. Even though the eye-opening is not yet good,
this experiments show, that for shorter links - e.g. 30 to
50 m - standard POF still can be used for gigabit
transmission without the necessity for complex coding
schemes.
Figure 8: Eye-diagram and Gigabit ETHERNET mask
5. Recent results on OFDM techniques
test of 50 m GI-PMMA-POF link A new approach that is currently investigated by two
In a laboratory setup even higher data rates up to partners (Siemens and Teleconnect) that recently joined
3 Gbit/s have been reached. Also transmission of analog POF-ALL is the use of Orthogonal Frequency Division
carriers up to 2.4 GHz, as used in DVB-C links (figure 9) Multiplexing (OFDM). A first very good result, presented
and WLAN transmission systems has been demonstrated. last year at this same conference [3], was the experimental
demonstration of 1 Gbit/s transmission over a 100 meters 1
mm core SI-POF link, a result obtained using a 650 nm
DVD-player laser diode and OFDM multi-tone techniques
with 80 subcarriers and QAM-256. Starting from these
excellent preliminary results, the use of OFDM over POF
system has been inserted in the POF-ALL workplan.
Recent interesting results from partner Teleconnect
demonstrated the option of using commercial OFDM chips
originally developed for xDSL system over POF. Best
result so far have been a reliable 100 Mbit/s transmission
over 200 meters 1 mm core SI-POF, using a modified
VDSL chipset. The (optimized) bit-per-tone allocation for
the 3478 tones used in this demonstrator is shown in
Figure 8. We remark here that this demonstrator is using
only commercially available chips and it is completely
Figure 9: Transmission of satellite IF up to 2.2 GHz compatible at the input to Fast-Ethernet, thus proving as a
over 30 m GI-PMMA-POF readily available solution for extended reach Ethernet over
POF.
A further approach is the use of passive equalizer
Even higher performance has been obtained using a
circuits to compensate the frequency response of the fiber.
laboratory setup, as shown in [3], where the record
transmission of approx. 1 Gbit/s over 100 meter of step-
index POF has been demonstrated.
6. Conclusions
We have shown the most recent technical results of the
POF-ALL project. Best results include 100 Mbit/s
transmission over 200 meters of standard SI-PMMA-POF,
and 1 Gbit/s transmission over 50 meters of GI-PMMA-
POF. The first result (100 Mbit/s) can find potential
application in edge-network application where a high-
978-1-4244-1942-5/07/$25.00 ©2007 IEEE IEEE Catalog Number: CFP0791D-CDR
ISBN: 978-1-4244-1942-5
Page 5 of 6 Library of Congress: 2007909452
BroadBand Europe 2007 Paper We3B1 – Gaudino
Antwerp, Belgium, 3-6 December 2007
Downstream Upstream
f [MHz]
0,0086 2,1649 4,3211 6,4774 8,6336 10,79 12,946 15,102 17,259 19,415 21,571 23,727 25,884 28,04 30,196
bits per tone
10
5
0
1 201 401 601 801 1001 1201 1401 1601 1801 2001 2201 2401 2601 2801 3001 3201 3401
tone
Figure 11: bit-per-tone allocation in the 200 meter demonstrator using VDSL chips
speed signal is to be delivered for instance from an active
switch placed in the basement of large residential building
to each individual apartment. The second result (1 Gbit/s References
over 50+ meters) can today be very interesting in very [1] D. Cárdenas et al. “A Media Converter Prototype
short reach links inside the apartment, such as for example for 10Mb/s Ethernet Transmission over 425m of
for the high-definition digital TV connections. Large Core Step Index Polymer Optical Fiber”,
We believe that one of the important technical outputs of IEEE Journal of Lightwave Tech., December
the project is to have shown that the ultimate POF capacity 2006.
in terms of reach and/or bit rates are much higher than [2] A.M.J. Koonen et al., Proc. of POF 2006, Seoul,
what it is typically perceived in the POF community. Sep. 11-14, 2006
Moreover, we believe we are the first consortium that has [3] S. Randel et al.: “1Gbit/s transmission with 5.3
proposed advanced modulation techniques applied to bit/s/Hz spectral efficiency in a 100m standard 1
optics, such as multilevel PAM, QAM or even OFDM, or mm SI POF link using adaptive multiple
advanced digital equalization techniques. We believe that subcarrier modulation”, 32th European
there is a rationale for all these techniques in the medium Conference on Optical Communication, ECOC
term, due to the steady increase of performance and 2006, Postdeadline paper.
decrease of cost of digital electronics. Thus, moving a part [4] B. Offenbeck et al., 15th International
of the complexity from the “optical domain” to the Conference on Polymer Optical Fiber, Seoul,
“electronic domain”, or at least finding the best September 2006
compromise between the two domains may become the [5] http://www.fiberfin.com/fiber/giga_pof.html
most effective solutions in the near future. This is a trend [6] R. Gaudino et al., “On the ultimate capacity of SI-
that is also seen today in the long-haul GOF sector. For POF links and the use of OFDM: recent results
instance, two Sessions at the forthcoming ECOC 2007 from the POF-ALL project”, 16th International
Conference in Berlin are focused on OFDM over optics, Conference on Polymer Optical Fiber, Turin,
while a plethora of papers are dedicated to many different Italy, September 2007
flavors of new modulation formats and digital signal
processing for equalization. From a more academic, but
still interesting viewpoint, we believe we have for the first
time formulated the Shannon Capacity of the SI-POF
channel [6].
During the last year of the project, which will formally end
in June 2008, besides continuing on the technical part, we
will strongly focus on market analysis, in order to see what
broadband access scenario would benefit most from POF-
ALL technologies. Significant interest in the proposed
technologies may arise in in-apartment very high speed
links. POF-ALL results may also be beneficial in other
sectors, such as in next-generation industrial automation
links, in future automotive networks, and in other specific
niche sectors.
Acknowledgments: This project is fully funded by EU
project FP6-IST STREP titled “POF-ALL”, contract n.
027549
978-1-4244-1942-5/07/$25.00 ©2007 IEEE IEEE Catalog Number: CFP0791D-CDR
ISBN: 978-1-4244-1942-5
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