Evaluation of return-to-zero modulation for wavelength-division-multiplexed transmission over conventional single-mode fiber

Summary form only given. In spite of ancient lore suggesting that lightwave receivers have several dB better sensitivity for return-to-zero (RZ) modulated signals, deployed lightwave systems typically use non-return-to-zero (NRZ) modulation. In anticipation of increases in lightwave transmission bit rates beyond those conveniently manipulated by electronic devices, much effort has been devoted to all-optical techniques for lightwave signal processing. These techniques often require pulsed light rather than cw light and therefore RZ modulation may become important. However, nonlinearity plays a dominant role in many-channel wavelength-division multiplexed (WDM) systems, so one might speculate that RZ modulation, with its higher peak powers and larger bandwidths, may not be practical in high-performance WDM systems. If correct, this will reduce the attractiveness of many all-optical techniques. In previous experimental work, RZ and NRZ have been compared in the long, low-dispersion-fiber systems typically deployed undersea. Here, we compare RZ and NRZ in a WDM system employing the 1.3-/spl mu/m dispersion-zero fiber (SMF) currently deployed in many national terrestrial networks.