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Multilevel transmission and equalization for polymer optical fiber systems [Elektronische Ressource] / Florian Breyer

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174 Pages
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Published 01 January 2010
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¨ ¨TECHNISCHE UNIVERSITAT MUNCHEN
Lehrstuhl fu¨r Nachrichtentechnik
Multilevel Transmission and Equalization
for Polymer Optical Fiber Systems
Florian Breyer
Vollst¨andiger Abdruck der von der Fakult¨at fu¨r Elektrotechnik und Informationstechnik
der Technischen Universit¨at Mu¨nchen zur Erlangung des akademischen Grades eines
Doktor–Ingenieurs
genehmigten Dissertation.
Vorsitzender: Univ.–Prof. Dr.–Ing. habil. G. Rigoll
Pru¨fer der Dissertation: 1. Univ.–Prof. Dr.–Ing. N. Hanik
2. Prof. ir. T. Koonen,
Technische Universiteit Eindhoven, Niederlande
Die Dissertation wurde am 15.04.2010 bei der Technischen Universit¨at Mu¨nchen eingere-
icht und durch die Fakult¨at fu¨r Elektrotechnik und Informationstechnik am 02.12.2010
angenommen.iii
Preface
This thesis was written during my time as a research and teaching assistant at the Insti-
tute for Communications Engineering at the Technische Universit¨at Mu¨nchen and as an
external researcher at Corporate Technology - Information&Technology at Siemens AG
within a collaboration project.
First, I would like to thank my supervisor Professor Dr. Norbert Hanik, Prof. Dr. An-
dreas Kirst¨adter and Dr. Bernhard Spinnler for setting up this project in 2005, and
giving me the opportunity to work towards my doctoral degree in the academic as well
as in the industrial environment. Especially, I am deeply grateful to Prof. Dr. Norbert
Hanik for his guidance, support and the perfect working atmosphere within the optical
research group at the Institute. I am also very grateful to Prof. Ton Koonen for acting
as co-supervisor.
To my colleagues at Siemens, I would like to thank Dr. Sebastian Randel for his guid-
ance, advice, the fruitful numerous technical discussions during my time at Siemens and
for acting as co-supervisor. Many thanks and a mark of respect to my research partner
Dr. Jeffrey Lee, who has done an excellent job on his Ph.D. project. I think we have
achieved great collaborative work together and have learned so much from each other. I
will definitely miss the nearly uncountable hours together in the lab. Further, I would
like to thank Dr. Joachim Walewski for involving me in his research of visible light com-
munications. A special thanks to Dr. Daniel Cardenas for introducing me to the world
of FPGA programming.
Manyfriendsandcolleaguescontributedtomakingtheyearsenjoyable. Iwouldlikethank
allofthemwhoareresponsibleforthegoodatmosphereattheInstitute,especiallymycol-
leagues from the optical research group Stephan Hellerbrand, Bernhard G¨obel, Leonardo
Coelho, Oscar Gaete and Beril Inan. Another special thanks to Manfred Ju¨rgens for the
support and the production of several mechanical components for my project.
Finally, I would like to thank my family for their unique support and encouragement they
provided me throughout the years, especially my brother Michael for proof-reading this
thesis. Last but not least, thanks to Rebecca for her love, support, proof-reading and the
patience of waiting so many times in the evenings.
Florian BreyerMu¨nchen, April 2010v
Contents
1 Introduction 1
2 Polymer Optical Fiber Systems 5
2.1 Polymer Optical Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1 PMMA SI-POF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.2 PMMA GI-POF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.3 PF-GI-POF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2 Light Sources for PMMA-based POF Systems . . . . . . . . . . . . . . . . 13
3 Fiber Model for the SI-POF 17
3.1 Modeling of Light Propagation in SI-POFs . . . . . . . . . . . . . . . . . . 17
3.2 Transmission impairments in SI-POFs . . . . . . . . . . . . . . . . . . . . 21
3.2.1 Mode-dependent attenuation . . . . . . . . . . . . . . . . . . . . . . 21
3.2.2 Modal dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2.3 Mode coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Derivation of the time-dependent power flow equation . . . . . . . . . . . . 25
3.4 Solution of the time-dependent power-flow equation . . . . . . . . . . . . . 28
3.5 Channel model performance . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.5.1 Fiber parameters and launching condition . . . . . . . . . . . . . . 31
3.5.2 Numerical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 32vi Contents
3.5.3 Validation with Experimental Results . . . . . . . . . . . . . . . . . 36
3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4 Baseband Transmission over Polymer Optical Fibers 41
4.1 The IM/DD channel model . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2 The capacity of the SI-POF IM/DD channel . . . . . . . . . . . . . . . . . 46
4.2.1 Derivation of the channel capacity of the SI-POF IM/DD channel . 46
4.2.2 Numerical results for the Channel capacity . . . . . . . . . . . . . . 50
4.3 Modulation Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4 Electronic Dispersion Compensation. . . . . . . . . . . . . . . . . . . . . . 60
4.4.1 Symbol-spaced adaptive Equalizers . . . . . . . . . . . . . . . . . . 60
4.4.2 Fractionally-spaced adaptive Equalizers . . . . . . . . . . . . . . . . 63
4.5 Equalizer Coefficient Adaptation Schemes . . . . . . . . . . . . . . . . . . 64
4.5.1 Least-Mean-Square (LMS) Algorithm . . . . . . . . . . . . . . . . . 65
4.5.2 Blind Adaptation using the Stop-and-Go algorithm . . . . . . . . . 66
4.6 Performance bounds of FFE and DFE . . . . . . . . . . . . . . . . . . . . 67
4.6.1 MMSE calculation for FFE and DFE . . . . . . . . . . . . . . . . . 67
4.6.2 BER performance bounds of FFE and DFE . . . . . . . . . . . . . 69
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5 POF Transmission Experiments 73
5.1 SI-POF Systems with Laser launch and receiver equalization . . . . . . . . 74
5.1.1 1.25 Gbit/s Transmission with On-Off-Keying . . . . . . . . . . . . 74
5.1.2 2 Gbit/s Transmission with On-Off-Keying . . . . . . . . . . . . . . 81
5.2 SI-POF Systems with LED launch and receiver equalization . . . . . . . . 84
5.2.1 500 Mbit/s Transmission with PAM-4 modulation . . . . . . . . . . 84Contents vii
5.2.2 1.25 Gbit/s Transmission using PAM-4 modulation . . . . . . . . . 88
5.3 PF-GI-POF Systems with VCSEL launch . . . . . . . . . . . . . . . . . . 93
5.3.1 10 Gbit/s Transmission using PAM-4 modulation . . . . . . . . . . 94
5.3.2 Comparison of OOK and PAM-4 for 10 Gbit/s over PF-GI-POF . . 98
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
6 Real-Time Implementation Aspects of GigE over SI-POF 107
6.1 Prototyping Platform - FPGA DSP board . . . . . . . . . . . . . . . . . . 108
6.2 Analog Frontend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
6.3 DSP implementation inside the FPGA . . . . . . . . . . . . . . . . . . . . 113
6.3.1 Line Coding for PAM-4 modulation . . . . . . . . . . . . . . . . . . 113
6.3.2 Parallelization of FFE equalizer . . . . . . . . . . . . . . . . . . . . 116
6.3.3 Clock Recovery using Goertzel algorithm . . . . . . . . . . . . . . . 122
6.3.4 Forward Error Correction insertion . . . . . . . . . . . . . . . . . . 126
6.4 Gigabit Ethernet POF Media Converter . . . . . . . . . . . . . . . . . . . 128
6.5 Complexity Analysis of the Gigabit Ethernet POF Media Converter . . . . 130
6.6 BER performance of the Real-Time demonstrator . . . . . . . . . . . . . . 132
6.6.1 BER performance measurement setup . . . . . . . . . . . . . . . . . 132
6.6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
6.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
7 Conclusions and Recommendations 135
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
7.2 Achievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
7.3 Recommendations for future research . . . . . . . . . . . . . . . . . . . . . 139
A Crank-Nicolson scheme 141viii Contents
B 8B10B line-code for 1000Base-X 143
C Abbreviations and Symbols 149
Bibliography 157ix
Zusammenfassung
Diese Arbeit behandelt die Anwendung mehrstufiger Modulationsformate mit
Empf¨angerentzerrung fu¨r optische Polymerfaser (POF) Systeme. Die Standard 1 mm
Stufenindex POF wird dabei detailliert untersucht. Fu¨r diese Faser wird ein Kanal-
modell entwickelt, das die drei wichtigsten Mehrmoden-Fasereffekte beinhaltet, n¨amlich
die moden-abha¨ngige D¨ampfung, die Modendispersion und die Modenkopplung. In
diesen POF Systemen kann nur Intensita¨tsmodulation angewendet werden. Deshalb
wird eine Mehrstufen-Modulation mit empfa¨ngerseitiger Entzerrung kombiniert, um die
Bandbreitenbeschra¨nkung aufgrund von Modendispersion und den aktiven Komponen-
ten zu kompensieren. Diese Kombination wird sowohl in theoretischen Betrachtungen
der maximalen Entzerrerleistungsfa¨higkeit als auch in zahlreichen Experimenten unter-
¨sucht. Es wird gezeigt, dass die Ubertragung einer Rekord-Bitrate von bis zu 2 Gbit/s
u¨ber 100 m SI-POF durch Verwendung einer Laserdiode als optisches Sendeelement und
der Kombination aus Mehrstufenmodulation und Entzerrung mo¨glich ist. Abschließend
¨wird die Implementierung eines Medienkonverters zur Gigabit Ethernet Ubertragung
vorgestellt, der mit einer LED als Sendeelement arbeitet und auf einer FPGA-Plattform
basiert, die folgende Signalverarbeitungsalgorithmen ausfu¨hrt: PAM-4 Modulation, li-
neare Empf¨angerentzerrung, Fehlerkorrektur und Taktru¨ckgewinnung.
Abstract
This work deals with equalized multilevel transmission schemes for polymer optical fiber
(POF) systems. In particular, the standard 1 mm core diameter step-index PMMA-
based POF (SI-POF) is investigated. A fiber model is developed, which includes the
three major fiber effects, such as mode-dependent attenuation, modal dispersion, and
mode coupling. As only intensity modulation can be applied, multi-level modulation is
combined with receiver equalization schemes to overcome the bandwidth limitations due
to modal dispersion and the active components. This combination is evaluated in terms
of theoretical equalizer bounds and various experiments. It is shown that record bit-rates
of up to 2 Gbit/s over 100 m SI-POF can be achieved by the use of this combination and
a laser diode. Finally a full working Gigabit Ethernet media converter is implemented
on a FPGA platform using a red LED, PAM-4 modulation, linear receiver equalization,
forward error correction, and clock recovery.