Investigation of Transmission Impairments of 40-Gbaud, Two-, Four-, and Eight-Level RZ-DPSK

The letter discusses the tolerance against transmission impairments, i.e., chromatic dispersion, filtering, and self-phase modulation over a 320-km transmission link of 40-Gbaud single-polarization return-to-zero (RZ) eight-level differential phase-shift keying (D8PSK) in comparison to those of RZ binary DPSK and RZ quadrature DPSK at the same baud rate.