Non-Uniform Constellations for Polarization Division Multiplexed CO-OFDM Systems

In this paper we propose a transmission scheme for Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) systems with Multiple Input Multiple Output (MIMO) processing. Our proposal consists of the concatenation of two techniques, Non-Uniform Constellations (NUC) in the mapper, and Spatial Multiplexing (SM) in the implementation of Polarization-Division Multiplexed (PDM) systems. The main target of the proposed scheme is to reduce the overall performance loss introduced by Polarization Mode Dispersion (PMD) and Polarization Dependent Loss (PDL) in PDM-CO-OFDM systems. This approach will be compared to techniques traditionally used in CO-OFDM links as Golden codes and Silver codes as well as traditional SM. The full transmission chain has been modelled using Matlab. Simulations have been run to check the performance improvement achievable by our proposal showing a gain of up to 0.82 dB in the carrier to noise compared to traditional schemes, with no additional hardware complexity at the receiver side.