Differential Phase-Shift Keying (DPSK) is considered a favored technology
for long-haul transmission systems due to its robustness compared to fiber propagation impairments.
However, careful consideration of the combined impact of optical noise, fiber chromatic dispersion
(CD) and Kerr nonlinearity is necessary when designing such systems. We assume a dispersion-managed
system with equally spaced inline EDFAs. For small signal powers, the signal is affected only by
fiber attenuation and additive ASE noise. For larger signal powers, additional degradations are due
to the combined effect of CD and Kerr nonlinearity on the signal. Additionally, degradations caused by
nonlinear phase noise may occur when the intensity noise of inline EDFAs is converted into phase
noise due to fiber nonlinearity.
The simulation setup is displayed in
A 10-Gb/s DPSK signal is transmitted over 12 spans of perfectly dispersion-compensated spans of
150 km SSMF. The gain-controlled inline EDFAs adjust the signal power back to the input signal
power level and add ASE noise. After optical filtering, the DPSK signal is decoded using a
Mach-Zehnder Interferometer (MZI) and detected using a balanced direct detection receiver.
The BER is estimated using a semi-stochastic approach that accounts for noise impairments and
degradations due to intersymbol interferences (ISI).
shows the dependence of BER on transmitted power for three cases: 1) Linear fiber transmission
(nonlinear fiber effects are switched off); 2) Nonlinear transmission for the signal and
linear transmission for the noise (achieved by separating the propagation of signal and
noise using multiple data representations); 3) Nonlinear fiber transmission for signal and noise.
shows the three received eye diagrams after transmission over 12x150 km SSMF for a launch power of
Keywords: Differential Phase-Shift Keying (DPSK), Nonlinear Phase Noise, Mach-Zehnder Interferometer (MZI), Balanced Detection, Long-Haul transmission
Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.