Nonregenerated 547-km, 2.5-Gbit/s transmission at 1550 nm over standard fibre using direct modulation

Return-to-zero format and low biasing currents are shown to improve significantly the robustness of directly-modulated 2.5-Gbit/s DFB lasers towards chromatic dispersion. As a result, 547 km of standard fibre are spanned without any dispersion compensation device.