title: Sub-symbol-rate sampling for PDM-QPSK signals in super-Nyquist WDM systems using quadrature poly-binary shaping.
abstract: We compare the performance of sub-symbol-rate sampling for polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) signals in super-Nyquist wavelength division multiplexing (WDM) system by using quadrature duo-binary (QDB) and quadrature four-level poly-binary (4PB) shaping together with maximum likelihood sequence estimation (MLSE). PDM-16QAM is adopted in the simulation to be compared with PDM-QPSK. The numerical simulations show that, for a software defined communication system, the level number of quadrature poly-binary modulation should be adjusted to achieve the optimal performance according to channel spacing, required OSNR and sampling rate restrictions of optics. In the experiment, we demonstrate 3-channel 12-Gbaud PDM-QPSK transmission with 10-GHz channel spacing and only 8.4-GSa/s ADC sampling rate at lowest. By using QDB or 4PB shaping with 3tap-MLSE, the sampling rate can be reduced to the signal baud rate (1 samples per symbol) without penalty.
authors.forename: Cheng
authors.initials: C
authors.lastname: Xu
authors.forename: Guanjun
authors.initials: G
authors.lastname: Gao
authors.forename: Sai
authors.initials: S
authors.lastname: Chen
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.forename: Ming
authors.initials: M
authors.lastname: Luo
authors.forename: Rong
authors.initials: R
authors.lastname: Hu
authors.forename: Qi
authors.initials: Q
authors.lastname: Yang