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Design guidelines for flexible low-cost metro WDM systems over various fiber types

Today's Metro networks are facing the challenge to transport different services like 2.5 Gbit/s and 10 Gbit/s SDH, Gigabit and 10G Ethernet, and different data formats at costs as low as possible. Particularly due to cost and associated performance reasons wavelength-division multiplex (WDM) transmission systems are an attractive candidate for the Metro area e.g. offering different services over different wavelengths. However, for cost-reduction it is mandatory to avoid expensive components like optical amplifiers (OAs) and dispersion compensating modules (DCMs) whenever possible. This leads to a limited extension of the transparent reach due to e.g. transmitter and receiver characteristics, fiber dispersion, and fiber nonlinearity. It is the object of this paper to investigate the potential of Metro WDM systems and to derive design guidelines without use of OAs and DCMs. Based on computer simulations different fiber infrastructures like Standard Single-Mode Fiber (SSMF, ITU-G.652), positive and negative dispersion Non-Zero Dispersion Shifted Fibers (NZDSF) are analyzed with respect to 2.5 Gbit/s and 10 Gbit/s data rate per channel with low-cost direct and chirp-free external modulation at both data rates. Non-Return-to-Zero- (NRZ-) intensity-modulation is assumed as standard modulation format. At 10 Gbit/s single channel transmission external modulation over pure SSMF results in transmission length of about 50km. Only for high-input powers fiber nonlinearity partly compensates the fiber dispersion and allows an increase in reach up to 90km. For WDM transmission the performance is limited by Self-Phase Modulation (SPM) and Cross-Phase Modulation (XPM) allowing 40x10 Gbit/s uncompensated low-cost transmission over 50km of existing SSMF.