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Overview

Nonlinear Effects in 10Gbit/s DPSK Long-Haul Transmission

Description

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. Assuming 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 due to nonlinear phase noise may occur when the intensity noise of inline EDFAs is converted into phase noise due to the fiber nonlinearity.

Typical Results

The simulation setup is displayed in Figure 1. A 10Gb/s DPSK signal is transmitted over 12 spans of perfectly dispersion compensated spans of 150km 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).
Figure 2 shows the dependence of BER on transmitted power for three cases: 1) Linear fiber transmission (nonlinear fiber effects are switched-off); 2) Nonlinear fiber transmission for the signal - linear fiber 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. Figure 3 shows the three received eye diagrams after transmission over 12x150km SSMF for a launch power of 6 dBm.

Keywords

Differential Phase-Shift Keying (DPSK), Nonlinear Phase Noise, Mach-Zehnder Interferometer (MZI), Balanced Detection, Long-Haul transmission