Optimization of Single-Sideband DCS-RZ Format for Long-Haul 43-Gb/s/channel Ultradense WDM Systems

The optimization of the single-sideband (SSB) duobinary carrier-suppressed (DCS) return-to-zero (RZ) format for long-haul ultradense wavelength-division multiplexing (UDWDM) systems with a 43-Gb/s/channel and a channel spacing of 50 GHz is investigated numerically. It is shown that the optimized SSB-DCS-RZ format with an electrical transmitter bandwidth of 0.35 of the bit rate has about 1 dB of $Q$ -factor improvement relative to the conventional SSB-DCS-RZ format (an electrical transmitter bandwidth of 0.25 of the bit rate) due to the reduction of noise bandwidth, smaller linear crosstalk, and better tolerance to the intra-channel fiber nonlinear effects. No substantially different UDWDM system performance is observed when varying the duty cycle of the DCS-RZ signal with optimized SSB filters settings. The UDWDM transmission performance of SSB-DCS-RZ formats is compared with the bandwidth-limited (BL)-duobinary formats. It is shown that generally, the SSB-DCS-RZ formats have poorer $Q$-factor and tolerance to the total residual dispersion but much higher tolerance to the in-line dispersion compensation and intra-channel nonlinear effects than the BL-duobinary formats.