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Doctorate thesis defense of Abir Hraghi

Doctorate thesis defense on January 23th 2017 at 10H00 AM ,in Amphi II, Sup’Com.

Entitled : Application of Mach-Zehnder Modulator for High Speed Optical Communication Network

Presented by : Abir Hraghi 



Rabah Attia

Professor, Ecole Polytechnique de Tunisie, Tunisia





Houria Rezig

Professor, ENIT, Tunisia


Habib Fathallah

Associate Professor, FSB, Tunisia



Didier Erasme

Professor, Télécom ParisTech, France


Thesis Director

Mourad Menif

Professor, SUP’COM, Tunisia



In this thesis, we report the study of the new optical transmission systems which are under investigation by the Institute of Electrical and Electronics Engineers (IEEE) and the International Telecommunication Union (ITU) communities in order to define new standards. We start by studying the performance of 160 Gbps signal based on dual carrier technique mixed with the DQPSK (DC-DQPSK). Then, we use the combination of the polarization multiplexing and the dual carrier with 16QAM modulation format to generate 400 Gbps signal. Besides, we implement the main multicarrier techniques which are Wavelength Division Multiplexing-Nyquist (WDM-Nyquist) and Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) in order to achieve 1 Tbps. We analyze the performance of the implemented optical systems (160 Gbps, 400 Gbps and 1 Tbps) by discussing their back-to-back receiver sensitivity, their Optical Signal-to-Noise Ratio (OSNR) requirement and their robustness to linear and nonlinear effects.

Aiming to achieve 1 Tbps optical bit rate system, we have shown that the generation of terabit superchannel requires an important number of subcarriers. Thus, an Optical Flat Comb Source (OFCS) is designed by using electro-optical modulators to generate a multicarrier source. Particularly, Mach-Zhender Modulators (MZMs) are adopted to provide an established technology that have been, for more than a decade, an integral part of the ever growing optical network infrastructure. An OFCS based on a Dual Arm Mach-Zehnder Modulator (DA-MZM) using two kinds of excitations (mono-tone and dual-tone excitation) is proposed. We extend the work to highlight the stability of the OFCS in terms of number of flat harmonics, subcarrier spacing, spectral ripple and power level of the flat spectral lines. We have used a modified simulated annealing-based optimization method to find the necessary ranges for which the comb source is ultraflat with less than 1 dB ripple. Using the mono-tone excitation technique, the number of the spectral lines is found to be equal to 32 with 1dB as spectral ripple. However, an asymmetric comb source is generated with a flat region of 32 spectral lines (1 dB spectral ripple) with minimum power level compared to the mono-tone excitation technique. In order to increase the number of the spectral lines in the flat region, we have used a cascade of two stages MZM (a dual arm MZM followed by a push pull MZM). This configuration enables the generation of 41 spectral lines with 1 dB as spectral ripple using a global optimization method. We have experimentally proven that the cascade of two MZM increases the number of carriers. The efficiency of the OFCS is demonstrated in the generation of 16QAM-OFDM-UDWDM system with direct detection for access network. The performance results of 3 filtered channels are presented in terms of Error Vector Magnitude (EVM) in back-to-back conditions and after propagation through 25 km and 100 km standard single mode fiber (SSMF).


Advanced optical modulation, Coherent detection, Mach-Zenhder Modulator, Wavelength Division Multiplexing (WDM), Optical Flat Comb Source (OFCS), WDM-Nyquit, CO-OFDM, superchannel….