Several NFT-based optical transmission systems were studied in the project. For these systems, we assumed a zero gain-loss, and so the only source of transmission corruption considered was the in-line optical noise. We proposed the asymptotic analytical theory describing the noise action on nonlinear modes and signal-noise interference phenomena. Then, the leading order results of the approximate theory for the NFT noise were checked against the same data obtained with the use of massive Monte-Carlo simulations.
(i) The case of “conventional” nonlinear spectrum modulation. With the outcomes obtained, we were then able to define the limitations of our analytical approach. We showed that the effective nonlinear noise emerging in the NF domain deviates significantly from the progenitor Gaussian noise in the optical domain. We found that the complex NF noise covariance normalised to the propagation distance demonstrates a non-monotonic dependence on the latter and deviates noticeably from its linear limits. In addition, we investigated the impact of solitons or, in other words, eigenvalues on the capacity and performance of an optical transmission system.
(ii) For the b-modulated systems, we derived the completely new results regarding the stochastic corruption affecting the data encoded into the b-coefficient. For this advanced NFT system, we performed the similar checks as in (i), and found a very good correspondence between the theory for the nonlinear noise correlators and the results of Monte-Carlo simulations.
(iii) For the NFT transmission system employing two polarisations, we developed the fast NFT and inverse NFT signal processing routines in collaboration with the Delft Technical University (Prof. Sander Wahls).
(iv) The profound knowledge of the noise properties inside the NFT domain allows us to design special-tailored equalisers. We proposed two types of advanced equalisers based on the machine learning/artificial intelligence. The application of these advanced tools effectively removes nonlinear and noise-induced signal impairments at the receiver resulting in better system performance. These approaches were proposed for the experimental evaluation. However, due to the novelty and complexity of the proposed method, so far, no complete experimental confirmation of the theoretical results has been obtained, and this is the subject of the on-going studies.
Overall, The Fellow presented the project outcomes on 5 international scientific conferences, several seminars, 2 workshops and published in 7 peer-reviewed conference proceedings. In addition to the dissemination activities in the scientific community, all results were shared with the general public using social media (Twitter, ResearchGate). Moreover, The Fellow took part in such events as Unifest, BigBang Fair and Chinese Summer school to promote engineering and specifically nonlinear photonic among children.
