Multidimensional Constellation Shaping for Coherent Optical Communication Systems

Abstract: To overcome the increasing demands for Internet traffic, exploiting the available degrees of freedom in optical communication systems is necessary. In this thesis, we study how constellation shaping can be achieved in various dimensions and how various shaping schemes affect the whole performance in real systems. This thesis investigates the performance of constellation shaping methods including geometric shaping and probabilistic shaping in coherent fiber-optic systems. To study geometric shaping, we explore multidimensional lattice-based constellations. These constellations provide a regular structure with fast and low-complexity encoding and decoding. We show the possibility of transmitting and detecting constellations with a size of more than 10^{28} points, which can be done without a look-up table to store the constellation points. Moreover, we experimentally realize our proposed multidimensional modulation formats in long-haul optical communication systems. Finally, we investigate the performance of probabilistically shaped quadrature amplitude modulation and compare it with uniform cross quadrature amplitude modulation in the presence of transmitter impairments, and with uniform quadrature amplitude modulation in links where higher-order modulation formats co-propagate with on-off keying wavelength channels.