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Fundamentals of the Nonlinear Optical Channel

Periodic Reporting for period 2 - FUN-NOTCH (Fundamentals of the Nonlinear Optical Channel)

Reporting period: 2019-07-01 to 2020-12-31

Fiber optics can carry very large amounts of data at very high speeds. Indeed, nearly all the global Internet traffic is transported by optical fibers. However, the current traffic demands growing by a factor larger than 10 every decade, and thus, it is unclear if these fibers can continue carrying all the data across the globe. Maintaining the transport of digital information across the world at high speeds and reliably is of vital importance for society, specially now that more and more services heavily depend on digital systems. To meet capacity demands, fiber optical communication systems are being operated at high powers, bringing these systems into the nonlinear regime of the optical fibers. This regime is not well understood from an information and communication theory point of view. The overall objective of this project is to unveil the fundamental limits behind data transmission of fiber optics in the highly nonlinear regime.
The work is divided into 5 work packages (WPs). The research carried out in the project so far has been focused on mathematical modeling (WP1 and WP2) as well as to design new transceiver structures (WP4). Multiple experimental validations have also already performed (WP5) and results on soliton-based communications have been obtained in WP3. In terms of scientific outcome the project has generated 30 publications (16 journals and 14 conference articles). The specific results are as follows:

In WP1 and WP2, a new mathematical model has been developed. In WP3, we have mainly focused on the analysis of maximum transmission rates (or bounds thereof) of soliton-based communication systems. In WP4, we have made multiple contributions to the areas of channel coding and signal shaping. We pioneered the use of low-complexity (finite-blocklength) probabilstic shaping based on the idea of enumerative sphere shaping. We also developed new algorithms that combine soft and hard decisions from the optical channel. These algorithms have the potential to be used in next-generation ultra-high speed optical transponders. Finally, we have experimentally validated all the three new transceiver designs described above (from WP4) in the context of WP5.
All the work described above goes beyond the state of the art and is demonstrated by the fact that these works have been published in highly prestigious journals (Nature Communications, the IEEE Transactions on Communications, and the IEEE Journal of Lightwave Technology). The results in this project have also been presented at the most important conferences in the fiber optical research: The Optical Networking and Communication Conference & Exhibition and the European Conference on Optical Communication. Our work has also received the Best Paper Award at the 2018 Asia Communications and Photonics Conference for our work on WP4.

The expected results until the end of the project are to continue developing new channel models and transceivers as well as validating these in optical experiments. Now that we have made progress on the channel modeling aspects of the problem, we also expect to start producing more results in the information-theoretic aspects of the project (WP3).
New channel model using perturbation on dispersion term