Opto Electronics

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Advanced Optical Modulation Formats in High-speed Lightwave System by

Sen Zhang

Submitted to the Department of Electrical Engineering and Computer Science and the Faculty of the Graduate School of the University of Kansas in partial fulfillment of the requirements for the degree of Master of Science

_________________________________ Professor in Charge

_________________________________

_________________________________ Committee Members

________________________ Date thesis accepted

Dedicated to my dear parents and sister

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ACKNOWLEDGEMENTS
I would like to thank my advisor Professor Ronqing Hui, for his guidance in this thesis, and his support and valuable suggestions during my graduate study at the University of Kansas. He has taught me a lot, not limited in academic area. Also I would like to thank Professor Chris Allen and Professor John Gauch for their advices for my thesis and tutoring in my graduate study. I would also like to thank two PhD students, Biao Fu and Yueting Wan, in our laboratory. Without their support, my graduate study in the Lightwave Telecommunications Laboratory will not be smooth and great. I would like to thank my friends, Minnan Fei and Yuan Zhang, for their spiritual support through my study abroad. I appreciate their help and encouragement so much. There are so many people I would like to thank. When I think of them, I would like to say “thank you” from the bottom of my heart.

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ABSTRACT
In the next generation of lightwave systems, high speed datarate like 10Gb/s or 40Gb/s per channel is very attractive. In addition, to pack more channels into one single fiber, channel spacing is decreased from 200GHz to 50GHz or even smaller. The direct side-effect is that linear and nonlinear degrading effects will be severe in such high-speed lightwave systems. An optimal modulation format which is more tolerant to linear and nonlinear impairments is needed urgently. In this thesis, we will detail and compare several different modulation formats in high speed datarate lightwave systems. Five modulation formats are under research: NRZ-OOK, RZ-OOK, CS-RZ, NRZ-DPSK, and RZ-DPSK. First of all, system performance of modulation formats over several existing transmission fibers are compared in both 10Gb/s and 40Gb/s WDM systems. We found that the dominant degrading effect is dependent on datarate; also the choice of optimal fiber is dependent on modulation formats and datarate. Then, a simplified first-order rule concerning of SPM effect is extracted from series of numerical simulations of several modulation formats; in addition, RZ-DPSK is found to be the most tolerant to SPM degrading effect among the investigated modulation formats. Last, we show a 40Gb/s experimental testbed. Based on this testbed, CS-RZ and NRZ have been realized. These researches in both numerical methods and experiments give us an insight view of advanced modulation formats and provide a foundation for future research.

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TABLE OF CONTENTS
1. 2. INTRODUCTION............................................................................................... 1 SIGNAL PROPAGATION IN OPTICAL FIBERS ........................................ 5 2.1. 2.2. OVERVIEW ..................................................................................................... 5 LINEAR AND NON-LINEAR EFFECTS IN FIBER ................................................. 8

2.2.1. Optical Loss .............................................................................................. 8 2.2.2. Chromatic Dispersion............................................................................. 10 2.2.3. SPM & XPM ........................................................................................... 12 2.2.4. SRS & SBS............................................................................................... 13 2.2.5. FWM...
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