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INnovatiVE cohereNt detecTIon Optical access Networks

Periodic Reporting for period 1 - INVENTION (INnovatiVE cohereNt detecTIon Optical access Networks)

Reporting period: 2016-04-01 to 2018-03-31

In the called “information age”, digital communications play an essential role on the economy and sustainable growth of the society. Access
networks are essential part of the communication infrastructure as bridge between end-users and core networks. Their design must make possible
the provision of real-time high-bandwidth access to Internet, essential for advanced communication services as immersive video and ubiquitous
cloud computing. It is clearly foreseen that the only long-term solution to the problem involves optical fiber as transmission medium, the so called
optical access networks. Passive optical network (PON) is the most widely employed technology because of the cost reduction it entails, but the
capacity of actual time-division multiplexed PONs will be exhausted eventually as more bandwidth-hungry applications become available in the
near future. Telecommunications carriers face the challenge of meeting the unprecedented bandwidth demand by end users at the same time the
capital and operating expenditures requirements are reduced.
INVENTION project targets the development of cost-effective and high capacity communication architectures for their employment on optical
access/metro networks. The proposed concept will be based on the employment of coherent detection with low-cost and simplified optical receiver
architectures, making sure that the proposed approaches meet the cost requirements of these optical networks. The proposed concepts will be
implemented by a suitable combination of optical signal processing techniques and digital-signal-processing (DSP) algorithms, keeping the
required DSP at realizable levels. The final scope of INVENTION is the proposal of mid-term and long-term solutions for the achievement of the
objectives included in the digital agenda 2020 for the ICT strategy.
The work performed during INVENTION has focused on the study of modulation formats and their complexity for short-reach optical communications and the development of digital signal processing algorithms for the recovery of information signals in optical coherent systems. Apart from the development of conventional algorithms in these kind of systems (signal conditioning, clock recovery, carrier and phase recovery, and diverse types of equalization), during INVENTION simplification of some of the algorithms involved and innovative impairment mitigation techniques have been studied and developed.
The technical work has been disseminated in several publications (Optics Express, Optics Letters and Journal of Lightwave Technology), and shared with the scientific community through the participation in several conferences such as the European Conference on Optical Communication and Optical Fiber Communication Conference and Exhibition.
Thanks to INVENTION, Dr. Christian Sánchez received during the project training from Prof. Andrew Ellis, and other colleagues at Aston addressing various topics, such as: project management, intellectual property, technical writing, financial and research data management, as well as career and personal development planning. His leading, work team and communication skills were strengthened through the various activities he got on board during INVENTION:
• Outreach activities aimed to technical and general audiences.
• Leading of a group of people at the Aston Institute of Photonics Technology (AIPT) for the development of a commonly shared digital-signal processing platform within AIPT.
• Contributing with and leading the writing of proposals, involving internationally renowned partners.
• Supervision of a Master student's final dissemination work, and helping with the supervision of PhD students.
• Leading inventor on one patent regarding a novel digital impairment mitigation technique.
• Participation in international collaborative projects (INSPACE).
• Comparison studies of modulation formats were performed, showing the advantages with one respect to other in terms of complexity and performance.
• Contribution to the development of mathematical models accounting for the propagation of signals in few-mode fibers.
• Results using simplified carrier frequency and phase recovery algorithms with enhanced frequency-offset tolerance were obtained.
• A novel fiber nonlinearity mitigation technique (four-wave mixing-aware constellation modulation technique (FACT)) has been developed, in which the signal is adapted at the transmitter to enhance its tolerance to the accumulated nonlinear interference in a distortion-less way. Though it shares some common features with other digital nonlinearity mitigation techniques, it combines in some distinctive elements which make this technique different to previously proposed methods, and might represent a paradigm change on how the fiber nonlinearity effects are combated.