optical layer throughout the telecommuni- cations network and enable service operators to exploit the bandwidth capacity that is inherent in optical fiber but that has gone largely untapped until now. At the same time, the widespread introduction of this technology could lead to a long-haul bandwidth glut and price disruptions,4 and set expectations for price points at the metro access/metro core that may or may not be achievable. Vendors of DWDM systems and technology include Nortel, Cisco, Alcatel, Ciena, Lucent, JDS Uniphase, E-Tek, Photonic Inte- grated Research Inc., Kymata, Lightwave Microsystems, Bookham, Silkroad, and Nanovation to list a few. Many U.S. carriers have settled on DWDM at STM-16/OC-48 rates as their technology of choice for gaining more capacity at the long-haul level, but OC-192 (and soon OC-768 [40- Gbps]) systems are also in play. Sixteen-channel DWDM has been deployed throughout the carrier infrastructure, and 32-channel systems and above are also entering the field. This chapter examines DWDM technology and its applicability, or lack thereof, to the metro access/metro core segment. We will focus on the eco- Dense Wavelength Division Multiplexing (DWDM) Systems nomics of this candidate solution. Some of the underlying technologies for WDM/DWDM were discussed in Chapter 2, "Optics Primer." Here, we make only a brief reference to phased-array technology and claim that it is per- haps the most applicable technology to the metro access environment. The basic elements of a WDM system, including the transponders, are dia- grammed in Figure 5-1. Transponders Transponders Figure 5-1 WDM system and Fiber transponders 40-120 km 0.22 dB/km Optical Amplifiers (~4 THz Bandwidth) Wavelength Wavelength Multiplexer Demultiplexer (e.g., B1 Monitoring) Optical Electrical Electrical 1310 nm Performance Optical Transceiver Monitoring Transmitter Short Reach Intermediate Reach Loopback Long Reach Optical Electrical Electrical 1310 nm Performance Optical Transceiver Monitoring Receiver Controller Chapter 5 5.