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Modulation Format Conversion in Future Optical Networks

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Modulation Format Conversion in Future Optical Networks Modulation Format Conversion in Future Optical Networks Javier Cano Adalid Master Thesis Supervisors: Christophe Peucheret and Jorge Seoane Research Center COM Technical University of Denmark March, 2009 ii Abstract The signal generation and receiver schemes of different modulation formats such as on off keying (OOK) in either non‐return to zero (NRZ) or return to zero (RZ), correlative coding and phase‐shift keying (PSK) are described and numerically simulated. Their receiver sensitivities for back to back structure are numerically simulated at 40 Gb/s and compared. The results show how using balanced reception, DPSK has the benefit of approximately 3 dB. We demonstrate that duobinary modulation is characterized by a higher tolerance to the chromatic dispersion in comparison with NRZ. Conversion techniques between modulation formats are described. Different all optical format conversion based on the mentioned method are discussed. Finally, format conversion from RZ‐OOK to RZ‐DPSK based on HNLF nonlinearities is investigated in great detail and numerically simulated at 40 Gb/s. Some converter requirements such as powers, wavelengths, bandwidths, pulse widths and pulse shapes among other are studied. The results show that shorter pulse widths in control signal for the case of walk‐off presence provide worse conversion. Sensitivity of converted RZ‐DPSK is compared with a conventional 33RZ‐DPSK signal showing a penalty close to 4 dB. Finally, the effect of the control wavelength variation at the input of the converter is investigated when the probe signal corresponds with conventional 33%RZ, 50%RZ and 67%RZ duty cycle. iii Acknowledgements I would like to thank many people who have supported my Telecommunication degree studies and helped me to the process of writing this thesis. Firstly, I would like to thank my supervisors Chritophe Peucheret and Jorge Seoane for providing me this great opportunity of realizing this thesis in the field of the optical communications and for his help and patience. I extend many thanks to my friends and student roommates who made me more pleasant the realization of this thesis with their company (Carlos, Javi, Pablo and Antonio). I wish to thank Michal Pawlik for all his help my first days and for making me easier my accommodation in Department of Photonics. I am very grateful to Andrea, Antonio, Javi and Carlos for spending his time reading the thesis and trying to give me some advises. I could not forget all people I met during my period in Denmark who gave me unforgettable moments, especially Miguel, Maria, Josepin, Spanish invasion in general, and all my flat mates during my stay in Luntojtevej Skolaestraede. Lastly, but not less important, thanks to my family (my father Jose, my mother María Luisa and my sister Laura) who always has supported me in all my decisions and gave me the possibility to finish my degree abroad in Denmark. Thank you dad for all your advices, support and scoldings during all my student life. I know that if you had not encouraged me maybe I would have not ever studied this degree. Besides I want to thank the rest of the family as well. Many thanks to all the people I did not mention in these acknowledgements. It is not because you are not important for me but because of time reasons I have to finish here. iv List of Acronyms AMI Alternate Mark Inversion ASE Amplified Spontaneous Emission BER Bit‐Error Rate BPF Band Pass Filter CD Chromatic Dispersion CS‐RZ Carrier‐Suppressed Return‐to‐Zero CSRZ‐DPSK Carrier‐Suppressed Return‐to‐Zero Differential Phase‐Shift Keying CW Continuous Wave CROW Coupled Ring‐resonator Optical Waveguide DFG Difference Frequency Generation DGD Differential Group Delay DPSK Differential Phase‐Shift Keying DQPSK Differential Quadrature Phase‐Shift Keying DWDM Dense Wavelength‐Division Multiplexing EDFA Erbium‐Doped Fiber Amplifier ER Extinction Ratio FDI Fiber Delay Interferometer FWHM Full Width at Half Maximum FWM Four‐Wave Mixing FP‐LD Fabry‐Perot Laser Diodes GVD Group Velocity Dispersion HNLF Highly Nonlinear Fiber MAN Metropolitan Area Network MZI Mach‐Zehnder Interferometer MZDI Mach‐Zehnder Delay Interferometer MZM Mach‐Zehnder Modulator NLSE NonLinear Schrödinger Equation NRZ Non‐Return‐to‐Zero NRZ‐OOK Non‐Return‐to‐Zero On‐Off Keying OOK On‐Off Keying OSNR Optical Signal‐to‐Noise Ratio PMD Polarization Mode Dispersion PPLN Periodically Poled Lithium Niobate PRBS Pseudo‐Random Bit Sequence PRZ Pseudo‐Return‐to‐Zero v PSK Phase‐Shift Keying RZ Return‐to‐Zero RZ‐DPSK Return‐to‐Zero Differential Phase‐Shift Keying RZ‐OOK Return‐to‐Zero On‐Off Keying QPM Quasi Phase Matching SHG Second‐Harmonic Generation SOA Semiconductor Optical Amplifier SOP State of Polarization SPM Self‐Phase Modulation TE Transverse Electric TM Transverse Magnetic WAN Wide Area Network WDM Wavelength‐Division Multiplexing XGM Cross‐Gain Modulation XPM Cross‐Phase Modulation vi Table of contents Chapter 1 Introduction........................................................................................................................1 1.1.‐ Project Motivation................................................................................................ 1 1.2.‐ Thesis Structure .................................................................................................... 4 Chapter 2 Advanced Modulation Formats ..................................................................................5 2.1.‐ Classification of modulation formats ................................................................... 6 2.1.1.‐Intensity Modulation Formats ........................................................................ 7 2.1.1.1.‐ NRZ‐OOK.................................................................................................. 7 2.1.1.2.‐ RZ‐OOK .................................................................................................... 8 2.1.1.3.‐ CSRZ....................................................................................................... 11 2.1.2.‐ Correlative Coding and Partial‐Response Formats ...................................... 12 2.1.2.1.‐ Duobinary.............................................................................................. 12 2.1.3.‐ Differential Phase Modulation..................................................................... 14 2.1.3.1.‐ Binary DPSK ........................................................................................... 14 2.1.3.2.‐ DQPSK.................................................................................................... 18 2.2.‐ Numerical simulations. Sensitivity comparison.................................................. 21 2.3.‐ Summary............................................................................................................. 25 Chapter 3 All‐Optical Modulation Formats Conversion..................................................... 26 3.1.‐ General Overview. Employed techniques ......................................................... 27 3.1.1.‐ Semiconductor Optical Amplifier................................................................. 27 3.1.2.‐ Mach‐Zehnder Delay Interferometer .......................................................... 29 3.1.3.‐ Ring‐Resonator Optical waveguide.............................................................. 29 3.1.4.‐ Narrow‐Band Silicon Microring Resonator .................................................. 30 3.1.5.‐ Spectral Line‐by‐Line pulse shaping............................................................. 31 3.1.6.‐ Highly nonlinear fiber .................................................................................. 32 3.1.7.‐ PPLN waveguide........................................................................................... 34 3.2.‐ State of the art................................................................................................... 37 3.3.‐ OOK to OOK format conversion ......................................................................... 39 3.3.1.‐ Motivation.................................................................................................... 39 3.3.2.‐ Modulation format conversions .................................................................. 40 3.4.‐ OOK to Correlative Coding format conversion................................................... 54 vii 3.4.1.‐ Motivation.................................................................................................... 54 3.4.2.‐ Modulation format conversion.................................................................... 55 3.5.‐ OOK to DPSK format conversion ........................................................................ 55 3.5.1.‐ Motivation.................................................................................................... 55 3.5.2.‐ Modulation format conversions .................................................................. 56 3.6.‐ DPSK to Correlative Coding format conversion.................................................. 61 3.7.‐ DPSK to DPSK format conversion ....................................................................... 62 3.7.1.‐ Motivation.................................................................................................... 62 3.7.2.‐ Modulation Format conversions.................................................................. 62 3.8.‐ FSK to PSK format conversion............................................................................. 64 3.8.1.‐ Motivation...................................................................................................
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