xpecting the delivery of Tbps light sources, and by 2010, we expect to see lasers operating in the petabits per second (Pbps) range. (With speeds in the Pbps range, the time between bursts is the same time that light takes to travel one-eighth the width of a human hair.) WDM furnishes separate channels for each service at the full rate. The idea is not to aggregate smaller channels into one larger channel but to provide a very high-speed channel that can terminate on today's switches and routers that, in fact, support 2.5Gbps and 10Gbps interfaces. WDM systems are generally divided into two market segments: dense (DWDM) and coarse (CWDM). While the definitions often overlap, generally a DWDM sys- tem supports more than 8 wavelengths and is used in long-haul transport networks. Both the WDM and DWDM terminology are used to describe this network element. DWDM systems today support in the range of 1 to 192 wavelengths, but every year, new systems are introduced that support increasing numbers of wavelengths. CWDM was specifically developed for metro area applications. It supports fewer wavelengths than DWDM, but it uses less expensive lasers, making it cost- effective for metro deployments, cable TV, and enterprise networks. While both DWDM and CWDM are based on the same principle of accommodating multiple wavelengths on a single fiber, they differ in terms of the type of light source used, the spacing between wavelengths, the total number of channels supported, the dis- tance over which they operate, and the type of amplifiers used. And it is important to note that at this time, DWDM and CWDM systems are not interoperable; they are incompatible when operating on the same network, but because CWDM is less expensive, it is often used. This remains an issue that needs to be resolved. The potential exists for transmitting thousands of channels-potentially as many as 15,000 wavelengths on a single fiber-with developments such as Bell Labs' chirped-pulse WDM. The idea of chirped pulse involves a specialized mode- locked 