NUMERICAL SIMULATION
Numerical Model
The numerical model of the DP-16QAM transmission system illustrated in Fig. 3 is implemented with OptiSystem 18. For a single-channel transmission, a symbol rate of 14 GBaud is chosen to transmit at a high bit rate of 112 Gbit/s. Considering a ~4% ethernet overhead and ~7% forward error correction (FEC) overhead translates into about 100 Gbit/s net data rate. At the transmitter, a polarization beam splitter (PBS) separates the two polarization states of the output of a continuous-wave (CW) laser operating at a wavelength of 1550 nm and a narrow linewidth of 0.1 MHz. The laser power is swept from 7 dBm to 15 dBm. Using two identical LiNbO3 Mach-Zehnder Modulators (MZM), the and polarization respectively modulates symbols from two 16-QAM modulators fed by a data stream of 215 – 1 pseudo-random bit sequence (PRBS). A polarization beam combiner (PBC) then recombines the two polarization signals, after which the signal is transmitted over a standard single-mode fiber of up to 4,000 km (50 spans 80 km).