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In this paper, we present a detailed experimental and theoretical study, showing that a novel nonzero dispersion-shifted fiber with negative dispersion enhances the capabilities of metropolitan area optical systems, while at the same time, reducing the system cost by eliminating the need of dispersion compensation. The performance of this dispersion-optimized fiber was studied using different types of optical transmitters for both 1310-and 1550-nm wavelength windows and for both 2.5and 10-Gb/s bit rates. It is shown that this new fiber extends the nonregenerated distance up to 300 km when directly modulated distributed feedback (DFB) laser transmitters at 2.5 Gb/s are used. The negative dispersion characteristics of the fiber also enhance the transmission performance in metropolitan area networks with transmitters that use electroabsorption (EA) modulator integrated distributed feedback (DFB) lasers, which are biased for positive chirp. In the case of 10 Gb/s, externally modulated signals (using either EA-DFBs or external modulated lasers using Mach-Zehnder modulators), we predict that the maximum reach that can be accomplished without dispersion compensation is more than 200 km for both 100-and 200-GHz channel spacing. To our knowledge, this is the first demonstration of the capabilities of a nonzero dispersion-shifted fiber with negative dispersion for metropolitan applications.

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We describe an experimental realization of ultralong-haul (ULH) networks with dynamically reconfigurable transparent optical add-drop multiplexers (OADMs) and optical cross-connects (OXCs). A simple new approach to dispersion management in ULH dense-wavelength-division-multiplexing (DWDM) transparent optical networks is proposed and implemented, which enables excellent transmission performance while avoiding dispersion compensation on a connection-by-connection basis. We demonstrate "broadcast-and-select" node architectures that take full advantage of this method. Our implementation of signal leveling ensures minimum variations of path-averaged power among the wavelength-division-multiplexing (WDM) channels between the dynamic gain-equalizing nodes and results in uniform nonlinear and spontaneous-emission penalties across the WDM spectrum. We achieve 80 10.7-Gb/s DWDM networking over 4160 km (52 spans 80 km each) of all-Raman-amplified symmetric dispersion-managed fiber and 13 concatenated OADMs or 320 320 wavelength-port OXCs with 320-km node spacing. The WDM channels use 50-GHz grid in band and the simple nonreturn-to-zero (NRZ) modulation format. The measured values exhibit more than a 1.8-dB margin over the forwarderror correction threshold for 10 15 bit-error-rate operation. We compare these results with point-to-point transmission of 80 10-Gb/s NRZ WDM signals over 4160 km without OADM/ OXC and provide detailed characterization of penalties due to optical signal-to-noise-ratio degradation, filter concatenation, and crosstalk. Index Terms-Add-drop multiplexer, dispersion management, optical communication, optical cross-connect (OXC), Raman amplification, transparent optical networks. I. INTRODUCTION T RANSPARENT ultra-long-haul (ULH) network systems have gained strong importance in the past few years, as the longer transparent reach distance of optical circuit connection promises network cost reduction through elimination of costly optical-to-electrical-to-optical (O/E/O) data regenerators.