University of Alberta SINGLE SIDEBAND MODULATION FOR DIGITAL FIBER OPTIC COMMUNICATION SYSTEMS Michael James Sieben O A thesis submitted to the College of Graduate Studies and Research in partial fuifiilment of the requirernents for the degree of Doctor of Phiiosophy Department of Electrical and Computer Engineering Edmonton, Alberta Fail 1998 National Library Bibliothèque nationale I*I of Canada du Canada Acquisitions and Acquisitions et BibliographicServices servicesbibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON KIA ON4 Ottawa ON KIA ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Librq of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriiute or seU reproduire, prêter, distribuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic formats. la forme de rnicrofiche/nlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts from it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. ABSTRACT This thesis investigates the potential of optical single sideband signahg at 10 Gb/s for increasing the transmission distance of digital iightwave communication systems. The prirnary bit rate/distance Limitation in digital fiber optic systems operating on standard single mode fiber at the 1.55 pm wavelength is chrornatic dispersion. Optical single sideband modulation offers an alternative to reducing the impact of chromatic dispersion in these optical systems. A number of novel approaches for transmitting a digital optical single sideband signal in a self-homodyne detection system were developed. Two appraaches showed to be beneficiai and practicaiiy implernentable. The fint approach was based on driving each arm of a dual arm drive Mach-Zehnder modulator with a combination of a baseband digital signal and the Hilber. transform of that signal respectively to create an optical single sideband signai. The second ap~roachwas based on driving each arm of a dual arm dnve Mach-Zehnder modulator in the conventional push-pull manner while driving a subsequent phase modulator with the Hilbert transform of that signai to create an optical single sideband signal. In tem of reducing the effects of chrornatic dispersion, transmitting the signal in a single sideband format has two advantages over a double sideband format. First, the optical bandwidth of the transmitted single sideband signal is approximately haif of a conventional double sideband signal. Second, an optical single sideband signal can be self- homodyne detected and the majority of the phase information preserved since no spectmm back folding occurs upon detection thus allowing the received signal to be partiaily equalized in the electricai domain. Simulation results showed that 10 Gbfs data could be transrnitted at the 1.55 jun wavelength on standard single mode fiber over distances beyond 1ûûû km with post- detection electrical dispersion compensation. Experirnental results showed transmission of IO Gb/s up to 320 km. Critical parameters in the experhent included frequency modulation to amplitude modulation noise due to the laser source Linewidth interacting with the chromatic dispersion in the fiber and the nonideal frequency response of a number of the electrical components used at the transmitter and receiver including the signaling source and the equalizer. To rny wife. Esther ACKNO WLEDGMENTS The author th& his pnmary supervisors, Dr. Jan Conradi at Corning Inc. and David Dodds at the University of Saskatchewan, for their guidance and instruction throughout the course of this work. Their advice and assistance throughout the course work, research and in the preparation of this thesis are gratehilly appreciated The author also thanks Dr. Jim McMullin for assuming the role of supervisor at the University of Aiberta when Dr. Conradi retumed to industry in January of 1998. The author also th& the additional members of his examining committee Dr. Robert Jopson, Dr. Ioanis Nikolaidis, Dr. Abdul Elazzabi and Dr. Igor Filanovsky for their tirne and effort. The author also thanks Sheldon Walldin of Telecommunication Research Labs (Tli Labs) for initiating the design of the fiber optic digital communication simuiation program, for his help and advice in assembling the initial experimental circuits, and for many additional helpful theoretical discussions. The author also thanks David Clegg of TR Labs for his tremendous help and speedy response in assembling many of the power supplies, Lasers and other equipment used in the experiments. The author aiso thanks Jason Larnont, Raymond Semeniuk and Antony Roth of TR Labs for their help during the assembly of the experimental circuits. The author also thanks his colieagues, Rajkumar Nagaranjan, David Moore, Ping Wan, Geoff Hayward, Gary Hassell, Alan Hnatiw, Dave Boertjes, Tom Young, Sing Cheng, Heng Foo, Ray DeCorby and Bob Davies for many interesting and stimulating discussions. They dong with the rest of the students and staff at TR Labs have created an exceUent research environment. The author also thanks Norte1 for dowing additional research to be carried out at their Skyline lab in Ottawa Special thanks goes out to Terry Taraschuk and Yuanmin Cai for their tremendous help a. the Norte1 site. The author also thanks the other Nortel employees that helped out at the Nortel site. The author also thanks Siecor of Saskatoon, Saskatchewan and Photonetics of Wakefield, Massachusetts for temporary loan of 150 km of standard single mode fiber and a tunable narrow linewidth laser respectively. Finally, the author thanks his family, fnends. coaches and teammates for their interest in his work and encouragement to continue. This research was supported in part by TR Labs, the Province of Alberta, the University of Alberta, Nortel and the Natural Sciences and Engineering Research Council of Canada (NSERC). TABLE OF CONTENTS 1. INTRODUCrION ........................................................................... 1 1.1 Fiber Optic Applications .............................................................. -1 1.2 Thesis Objectives...................................................................... -4 1.3 Thesis Organization ................................................................... -5 2 . BACKGROUND TO CKROMATIC DISPERSION ................................... -6 2.1 Dispersion and Attenuation .......................................................... -6 2.2 Previous Approaches to Lirnit the Effects of Chromatic Dispersion ............. 12 2.2.1 Opticai Methods ................................................................. 12 2.2.2 Post Detection Methods ....................................................... -22 2.2.3 Transmission Format Methods ............................................... -25 3 . THEORY OF OPTICAL SINGLE SIDEBAND ......................................... 28 3.1 Benefits of Optical Single Sideband ................................................ -28 3.2 Prior Art in Optical Single Sideband Systems ...................................... 30 3.3 Theoretical Developrnent of New Optical Single Sideband Systerns............ -37 3.4 Hilbert Transfomis of Broadband Baseband Signais .............................. 48 3.5 Cornparison of Optical Single Sideband and Composite Single Sideband Techniques .................................................................. 58 3.6 Optical Single Sideband and Duobinary Signaling ................................. 62 4 . SIMULATION OF DIGITAL OPTICAL SINGLE SIDEBAND S YSTEMS ........ 64 4.1 Simulated System Models and Parameters .......................................... 64 4.2 Noise Modeling ....................................................................... -75 4.2.1 Normal Detection with Gaussian Noise ...................................... 76 4.2.2 Nomal Detection with Square-Root Operation and nonGaussian Noise .............................................................................. 82 4.3 Simulation Results .................................................................... -85 4.3.1 Cornparison of Designs 1, 2 and 3 ........................................... -85 4.3.2 Variations on the Hilbert Transforrn Filter ................................... 93 4.3.3 Variations on the Modulation Depth and Bias Angle .......................-97 4.3.4 Cornparison of Single and Double Sideband Systems...................... 106 4.3.5 Variations on the Pattern Length .............................................. 111 4.3.6 Comparison of Normal Single Sideband with Composite Single Sideband ............................ ... ........................................ 112 4.3.7 Cornparison of Design 2 with and without Square-Root Function ........ IL5 4.3.8 Single Sideband with Non-Zero Source Linewidth ......................... 119 4.3.9 Modeled Microstrip Equalizer ................................................ -122 5. DIGITAL OPTICAL SINGLE SIDEBAND EXPERIMENTAL RESULTS ........ -125 5.1 Introduction to the Experïrnents ..................................................... -125 5.2 Optical Spectnim Analyzers ........................................................... 126 5.3 Experiments