Repeaterless bidirectional 4 × 2.5 Gb/s WDM fiber transmission experiment

We report the demonstration of a successful duplex 20 Gb/s transmission system experiment over a single dispersion shifted fiber using two 4×2.5 Gb/s channels with a 1 nm spacing centered at the 1557 and 1538 nm wavelengths, respectively. For both upstream and downstream directions, we measured straight bit error rate (BER) performance with a 41 dB optical power budget at the BER of 10^-9. For a channel wavelength operating close to the zero dispersion wavelength, we derive an analytical expression for the signal-to-noise degradation due to four-wave-mixing products at a preamplifier receiver. Good agreement between experimental data and theoretical results is obtained.