Optimizing fiber dispersion for DWDM systems

Nonlinear optical distortions can be a primary system limitation in long, amplified, dense wavelength-division multiplexed (DWDM) transmission systems. Because of their low threshold, the most problematic nonlinearities are those caused by the optical Kerr effect, which includes four-wave mixing (FWM), self-phase modulation (SPM), and cross-phase modulation (XPM) between different wavelengths. Because these effects depend either directly or indirectly on fiber dispersion, system impairments can be reduced by dispersion-management techniques. In this paper, we evaluate the effect of fiber dispersion and dispersion compensation on system penalties. Using the split-step Fourier transform numerical simulation of the nonlinear Schrodinger equation, we analyze a 16-wavelength DWDM system with the following parameters: 100-GHz nominal spacing, 17, 20 and 23 dBm total input power, 90-km amplifier spacing, 720-km system length, 2.6 (mw km)^-1 nonlinear index, 0.21 dB/km fiber loss. The input signal is a chirpless, 16-bit, pseudorandom pulse stream with 100-ps FWHM, super-Gaussian pulses. The receiver is a 50-GHz pass band optical filter followed by a 7-GHz lowpass, tenth degree Bessel, electrical filter. Low-level system noise is added to allow any SPM- or XPM-induced gain to be evident, but additional amplifier noise is neglected in order to focus on optical fiber physics. The simulator calculates eye opening and system penalties for each channel