The key objective of the CENTURION project has been successfully accomplished, following the proposed workflow described in the signed agreement. Specifically:
• During WP1, the ER was trained on simulation methods in Matlab, FPGA programming in Quartus and VHDL, and was familiarized with the equipment and facilities of the IFISC and specifically the Nonlinear Photonics Lab.
• During WP2, the ER designed and implemented theoretical investigations and numerical recipes of the advanced concepts of reservoir computing (RC). After investigating all-optical(AO) and opto-electronic(OE) configurations, an AO configuration with single-nonlinear element and time-delayed optical feedback was selected to perform all planned tasks. This configuration guaranteed the fastest processing methodology of optical communication signals. Optical header recognition was easily executed even with an OE configuration. The SNR conditions set by the acquisition system defines the performance of the classification task for multi-bit header recognition. In several of our studies, a significant finding was consolidated. The RC methodology could apply not only to solve an optical header recognition problem for switching and routing, but to generically post-process optical data streams that suffer from distortions as they propagate in nonlinear media. This finding opened a new research path. Therefore, the project focused on post-processing optical communication signals which were nonlinearly distorted by fiber transmission. This is believed to have a great impact on the ways that we process ultra-fast signals, since it directly competes with the up-to-date DSP methodologies used in the latest optical communication protocols.
• During WP3, the ER built and exploited successfully a photonic-based RC to post-process distorted optical communication signals. The FPGA-based implementation for this task – introduced as a back-up plan, for a verstatile but much slower processing solution – was not needed. Our research showed that the PRC methodology to post-process optical communication signals is generic. It has been applied to short-reach (up to 50km) and long-haul (up to 4000km) fiber-optic communication systems, considering even different encoding techniques (NRZ and PAM-4). These systems have been numerically evaluated and experimentally demonstrated by the ER, the PI and their collaborators.
The results obtained for NRZ and PAM-4 encoding schemes with direct detection are fascinating. The photonic RC was able to process the distorted signals without requiring any analytical description of the physical effects – linear and nonlinear – that cause the distortion. For all studied systems, short-reach and long-haul, with encoding rates from 10Gb/s up to 112Gb/s, the RC post-processing has been beneficial, improving the communication distance by up to 75%. For the short-reach transmission systems, the achieved distances are well above the ones described in the newly established IEEE protocol for short-reach fiber transmission, even though the latter refers to the wavelength region of 1.3μm where chromatic dispersion is minimized. The distance range we achieve with photonic RC post-processing is comparable to state-of-the-art DSP solutions.
A number of future challenges for this type of hardware processing with ultrafast optical communication signals remain. The classification of data streams in multiplexed channels (in polarization or wavelength) is of great significance to target 400G short-reach transmission systems at 1550nm. Moreover, complementary multiplexing methods of the to-be-processed signals need to be explored to establish real-time operation.
The results of the project have been disseminated so far in 3 international conferences, 6 international workshops, 1 published and 1 submitted peer-reviewed journal publication and at least other 10 outreach activities (talks, seminars, tutorials, lab demonstrations).
