Advanced modulation formats for optical interconnects

Abstract

The rapid growth of artificial intelligence, machine learning, cloud computing, and the Internet of Things has dramatically increased global internet traffic, driving an unprecedented demand for computing resources. As data centers scale to accommodate this surge, their energy consumption has become a pressing concern, necessitating the development of efficiency solutions across various aspects of their design, construction, and implementation. Geometrically optimized constellations of Stokes Vector Modulation (SVM) and Mode Vector Modulation (MVM) are encouraging energy-efficient advanced modulation formats suitable for data centers, offering trade-offs between spectral efficiency and energy consumption under various optical link constraints. At present, being largely theoretical, research into practical realizations of these constellations, due in part to their challenging symmetries, combined with their performance under real-world transmission effects such as modal dispersion and intermodal crosstalk, has remained limited. This thesis, which aims to address these questions, finds that with adequate optimization frameworks such as steepest ascent, fine-tuning of Mach- Zehnder Modulator driving voltages can significantly enhance the constellation symmetry of SVM and MVM, leading to the first experimental realization of the theoretically ideal four-point SVM simplex en route toward the generation of SVM/MVM constellations exhibiting higher cardinalities. Additionally, numerical simulations of (6,64)-MVM under realistic transmission conditions reveal that, despite severe impairment, when combined with adequate optical compensation techniques and digital signal processing, MVM exhibits substantial gains in terms of receiver sensitivity compared to conventional 4-PAM, achieving an aggregate bit rate of up to 672 Gbps when transmitted over three spatial lanes.