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14/09/2017

Doctorate thesis defense of Abderrahmen TRICHILI




Doctorate thesis defense on September 14th 2017 at 14H00 ,in Amphi Ibn Khaldoun, Sup’Com 2.


Entitled :Spatial Mode Control in Fibers for High Bit Rate Optical Communications

Presented by :Abderrahmen TRICHILI





Committee


President

Hichem Besbes

Professor, SUP’COM, Tunisia.

 

 

 

Reviewers

Mohamed-Slim Alouini

Professor, KAUST, Kingdom of Saudi Arabia

 

Rabah Attia

Professor, Ecole Polytechnique de Tunisie, Tunisia

 

Examiner

Marco Santagiustina

Professor, Università degli Studi di Padova, Italy.

   

Thesis Director

Mourad Zghal

Professor, SUP’COM, Tunisia.

 

Abstract


Over the last few years, there has been a considerable interest in using the spatial structure of the light as an additional degree of freedom for data transmission in optical communication networks. With the emergence of mode division multiplexing (MDM), it is possible to overcome the steadily increasing bandwidth demand issues. By implementing MDM, multiple optical modes having different shapes are injected simultaneously over the same optical fiber or on the same free space link and the overall transmission capacity of the communication systems will increase. MDM is accompanied with major challenges which are mainly the generation, multiplexing and de-multiplexing of high-order modes and therefore controlling the encountered linear and nonlinear effects when propagating over optical fibers and atmospheric turbulence when the medium is a free space link.


In this thesis, we deal with the different challenges related to the practical implementation of MDM. As a first step, we perform the design of a low-loss fiber based coupler for linearly polarized mode multiplexing. As a second step, we propose an experimental method to generate and detect Bessel Gaussian modes with high fidelity. We then experimentally demonstrate a technique for de-multiplexing Laguerre Gaussian (LG) modes allowing the detection of one mode from a densely packed set and the approach can be extended for other mode basis. With the objective of harnessing light in few mode fibers with different characteristics, we perform a rigorous modeling for the supercontinuum generation in a few mode photonic crystal fiber and we identify the impact of the various nonlinear effects involved in the process. For fiber optic communications, we numerically and analytically study phase sensitive and phase insensitive amplification and nonlinear mode conversion by means of intermodal four wave mixing occurring between waves belonging to different modes. Effect of random linear mode coupling is included in the analysis. The final part is dedicated to the demonstration of information transmission experiments using 100 LG spatial modes, with non-zero radial components and orbital angular momentum, on three distinct wavelengths. As a proof-of-principle, we employ different encoding schemes to transmit information with high fidelity in a free space link using spatial light modulators and CCD cameras. In an additional information encoding experiment, we investigate the impact of atmospheric turbulence on the propagation of multiple LG modes. The accomplished results presented in this thesis offer a route to high-bit-rate mode division multiplexing in optical fiber as well as free space communication systems.


Keywords


Mode division multiplexing, high order modes, few mode fibers, free space optics, propagation effects.