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21 mars 2018

[Thèse / PhD position] On baseband nonlinear distortion mitigation in coherent optical OFDM systems with a semiconductor optical amplifier cascade

Catégorie : Doctorant

Host Research Unit: Lab-STICC, CNRS UMR 6285 (www.labsticc.fr)

Host University: Ecole Nationale d’Ingénieurs de Brest (ENIB), Brest, France

Partner Institutions: Université de Bretagne Occidentale (Brest, France); Hong-Kong Polytechnic University

Starting date: October 2018

Funding: Doctoral contract (around 1684 € gross/month)

Research areas/key words: optical communication, optical amplification, digital signal processing, nonlinear systems, predistortion techniques, macro-modeling.


Context and aims

As pointed out by a number of recent studies Semiconductor Optical Amplifiers (SOA) might become a pertinent alternative to Erbium-Doped Fiber Amplifiers (EDFA) for some application scenarios, due to their attractive features such as large optical bandwidth, small size and possibility of integration at limited cost. In particular, the practical feasibility of a SOA-based metro-access infrastructure has been demonstrated, with the simultaneous operation of multiple services using advanced modulation formats such as QAM or PSK, including Polarization Division Multiplexing (PDM). These studies consider not only the conventional stand-alone SOA scenario but also the cascaded setup which enables high-capacity paths in the order of Tbit/s. Single carrier modulation formats are mainly considered in the literature dealing with SOA-based amplification in optical networks. But, over the past decade orthogonal frequency-division multiplexing (OFDM) and its variants have been recognized as promising techniques to support high data rate in next-gen optical communications, due to some important advantages like simple compensation of linear channel impairments, dynamic bandwidth allocation capability in a multiuser context, and powerful digital signal processor (DSP)-based implementation. However, the typical non-constant envelope property makes OFDM-like signals sensitive to channel nonlinear impairments. As a result of their fast gain dynamics and nonlinear intrinsic properties, SOAs may thus impact the system performance for such signals.

Various memory-polynomial Digital Baseband PreDistorsion (DPD) schemes have recently been investigated at the Lab-STICC for linearizing a Coherent Optical OFDM transmitter employing an SOA as a power booster. Extensive simulations, based on a precise SOA physical model, and early experiments showed that a significant bit-error-rate performance gain can hence be achieved.

However, these results have been established by considering a relatively simple scenario (SOA stand-alone setup, single polarization, limited electrical bandwidth) and with a number of simplifying assumptions; thus, a complementary research effort is required towards high-speed and efficient SOA-based CO-OFDM transmissions. In particular, the investigations might include the following points:

Balanced contributions between theoretical studies and experiments will be targeted throughout the project, with a systematic experimental validation of the proposed algorithms thanks to the facilities made available by the partners. Special care will be taken to the dissemination of research results, with a systematic aim of publication in international refereed journals and international conferences.

The study will be conducted within a multidisciplinary international partnership involving Lab-STICC/ENIB (Prof. S. Azou, Dr. P. Morel), Lab-STICC/UBO (Prof. N. Tanguy, Dr. M. Telescu) and the Hong-Kong Polytechnic University (Prof. Chao Lu). During the project, the recruited PhD student will do a stay at Hong-Kong so as to access top-level research facilities for carrying out study on optical communications.

Required degree and skills

Application details and contact information

The application should contain a CV, a cover letter, recent university records and reference letters. Please note that as part of selection, short-listed candidates will be invited for interview shortly after the deadline.

Apply before April 30 th 2018

Address all applications to:

Prof. Stéphane Azou
Email: azou@enib.fr
Tél.: (+33)


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