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Nonlinear Compensation in Hybrid Raman/EDFA Amplified Optical Systems

Periodic Reporting for period 1 - CHAOS (Nonlinear Compensation in Hybrid Raman/EDFA Amplified Optical Systems)

Reporting period: 2015-04-01 to 2017-03-31

Over the past 25 years, optical fiber communications have heralded a revolution in the high-speed transmission information of information accross the globe, in perfect synergy with the advent of world-changing concepts such as the world-wide-web, big data transmission and processing, video communication or high-definition on-demand entertainment. The capacity of fiber optic communication systems has experienced a steady and rapid growth over the years, adapting to the ever growing requirements of society. In recent years, worries have arisen regarding the theoretical capacity limits for fiber-optic technology, and several methods have been proposed to overcome the barrier posed by the nonlinear Shannon limit.

This project combines several of the most promising (both in terms of potential cost and performance) solutions to this problem, developing new methods for nonlinear effect compensation in systems with advanced optical amplification relying on the most efficient transmission formats. A novel amplification scheme that uses fibre Bragg grating (FBG) to form an ultra-long Raman fibre laser (URFL) along the transmission span allows to achieve second order pumping of the signal with a single pump wavelength only. Contrary to conventional 2nd/dual order Raman amplification, in URFL the gain profile can be modified, and in fact enhanced by selecting appropriate FBGs. This
unique amplification method minimises the variation of the effective gain-loss coefficient along the propagation forming a quasi-lossless
transmission medium. This amplification can realise full potential of coherent detection without the need of installing new fibres. Digital coherent detection offers additional degree of freedom to transmit the information with an optical phase. This allows higher capacity transmission without increasing receivers’ complexity as both the phase and polarization of the signal can be recovered with digital signal processing (DSP). Additionally digital backpropagation (DBP) can compensate for both, linear and nonlinear impairments by solving an inverse nonlinear Schrödinger equation (NLSE) and effectively reduce the impact of nonlinear phase noise (NLPN).

To summarise, this project develops the algorithms and methods for nonlinearity compensation in novel URFL optical transmission system and reduce the computational complexity of the DSP code. It brings nonlinear compensation with DBP one step closer to a commercial implementation, and explores other methods for nonlinear compensation, such as Optical Phase Conjugation, in combination with advanced distributed amplification schemes.
The project has successfully managed to propose, model and test experimentally a number of potential solutions for nonlinearity compensation in systems with advanced distributed Raman amplification. We have identified the importance of managing signal power evolution through the use of distributed amplification for optimal performance, and the relevance of adequately taking into account such signal power profiles in nonlinearity compensation, whether it is relying on digital backpropagation, nonlinear Fourier transform or optical phase conjugation. In the case of mid-link optical phase conjugation, we have demonstrated the possibility of improving system performance by adopting the signal power evolution that minimises asymmetry between the original and conjugate sections of the transmitted link. All these results have been adequately disseminated in 19 scientific publications in journals and relevant conferences, as well as a number of invited talks at different institutions.
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The main outcome of the project that is beyond state of art includes nonlinear compensation improvement in the use of optical phase conjugation with optimized signal power evolution profiles obtainable through distributed Raman amplification. The research covered advanced higher order Raman amplification schemes and presented both simulation and experimental results using advanced modulation formats.
Important advances beyond the state of the art have also been obtained in the use of DBP in systems with distributed Raman amplification.

This progress is exemplified in the 19 journal and conference papers published up to date as well as 10 invited talks for a scientific and general public that are listed below.


INVITED TALKS

1. P. Rosa, G. Rizzelli, J. D. Ania-Castañón “Advanced Raman architecture for high capacity optical networks and nonlinear mitigation using optical phase conjugation,” National Institute of Telecommunication, Poland, 2016
2. P. Rosa, G. Rizzelli, J. D. Ania-Castañón “Advanced Raman architecture for high capacity optical networks and nonlinear mitigation using optical phase conjugation,” Gdansk University of Technology, Poland, 2016
3. P. Rosa and J. D. Ania-Castañón ""Caso de éxito: Proyecto MSCA-IF-EF-ST “CHAOS,” invited talk in Taller preparación propuestas Marie Skłodowska-Curie Individual Fellowships 2016, CSIC, Spain, 2016
4. P. Rosa, G. Rizzelli, J. D. Ania-Castañón “Nonlinear compensation in optical fibres using an Optical Phase Conjugation”, in Proc. “Boundary Value Problems, Functional Equations and Applications BFA”, Poland 2016
5. P. Rosa “How to write a successful proposal for European Fellowships under Horizon 2020 programme: Marie Skłodowska-Curie”, plenary talk in “Boundary Value Problems, Functional Equations and Applications BFA”, Poland 2016
6. P. Rosa, G. Rizzelli, and J. D. Ania-Castañón “Symmetry Optimisation for Optical Phase Conjugation in Raman-Amplified Communication Systems” invited talk in OPTOEL, Spain, 2015
7. P. Rosa, G. Rizzelli, J. D. Ania-Castañón “Nonlinear compensation with advanced Raman amplification and optical phase conjugation”, invited talk in Reunión de Jóvenes Investigadores SINFOTON, Spain, 2015
8. P. Rosa, G. Rizzelli, J. D. Ania-Castañón “Raman amplification for nonlinear impairment compensation using optical phase conjugation”, invited talk in Optical Technologies for Society, Spain, 2015
9. P. Rosa “How to write a successful proposal for European Fellowships under Horizon 2020 programme: Marie Skłodowska-Curie,” Pedagogical University of Cracow, 2015
10. P. Rosa, G. Rizzelli, J. D. Ania-Castañón, Optimisation of Random Distributed Feedback Raman amplifier for high capacity transmission,” Pedagogical University of Cracow, 2015"
OPC configuration
Signal asymmetry in the fibre
Asymmetry comparison