Comunicazioni Ottiche a Multiplazione Spaziale

Modern information society is largely enabled by information and communications technologies, whose foundation lies in a worldwide optical fiber network extending over billions of kilometers of fiber that interconnects countries and continents. By harnessing the enormous potential bandwidth of optical fibers, along with the utilization of both polarizations of light, advanced modulation techniques, and coherent detection, data rates up to 100 Tb/s can be achieved over standard single-mode fibers (SMFs), very close to the theoretical capacity of such fibers. With SMFs approaching their transmission capacity limits, the ongoing exponential growth in the demand for larger data rates calls for the development of novel optical transmission technologies. Multi-band wavelength-division multiplexing (WDM) and space-division multiplexing (SDM) have emerged as two of the most promising technologies to address the impending information capacity crunch driven by the ever-increasing demand for higher transmission capacities. Multi-band WDM leverages the entire available transmission bandwidth of optical fibers, extending well beyond the conventional low-loss spectral region of silica fibers, thereby offering a cost-effective solution to increase the capacity of existing fiber infrastructures. In principle, this approach enables a potential bandwidth increase by up to a factor of 12 compared to current fiber-optic systems, while still relying on the same optical infrastructure. However, the actual capacity increase is smaller then this twelve-fold increase in bandwidth due to system and physical limitations of optical fibers, such as optical amplification, fiber nonlinearities and higher fiber loss outside of the conventional band. In contrast, SDM requires the deployment of novel optical fibers capable of supporting multiple spatial channels within a single fiber cladding. Nevertheless, this approach is also compatible with the use of multi-band WDM. In fact, transmission capacities more than 100 times larger have already been demonstrated when combining multi-band WDM and SDM, highlighting its significantly greater potential as the leading solution for future fiber-optic systems. This thesis investigates multi-band WDM and SDM as the key enablers of next generation ultra-high-capacity transmission systems. Multiple aspects are addressed, including transmission experiments and fiber characterizations conducted both in laboratories settings and, most importantly, over field-deployed SDM fiber. Notably, petabit-per-second-class transmission is demonstrated over an installed fiber testbed in the city of L'Aquila, highlighting the feasibility of these technologies for real-world deployment.