Filter bandwidth and subcarrier spacing tolerance of single-carrier 32 Gbaud PDM-QPSK

We demonstrate optical and electrical filter requirements that enable tight (<;50GHz) channel spacing for 32 Gbaud PDM-QPSK with all-EDFA loop transmission. Performance in both linear and nonlinear regimes is quantified for 37.5 GHz spacing (3.4 b/s/Hz).