laser, which rapidly emits very wide pulses of light. Because each part of a fiber interacts differently with varying frequencies of light, the result of chirped- pulse WDM is unequal dispersion. The pulse is stretched out when it enters the fiber, and data can be put on the discrete frequencies that emerge. You can think of this process in terms of a horse race: When a race starts, horses emerge together from the gate, but because each horse keeps a separate pace, spaces soon develop between the horses. This is the same type of stretching out that happens to the laser light in chirped-pulse WDM. If we couple the potential for 15,000 wavelengths on one fiber with each of those wavelengths supporting Pbps, we have an explosion of bandwidth that is like noth- ing we have known before. As fantastic as all this sounds, we're likely to see even greater achievements; after all, we are still in the very early stages of knowledge about what we can achieve with optical networking. Before any real progress can be made, the realm of microphotonics, or integrated photonic circuits, must mature. Chapter 11 Optical Networking DWDM Developments and Considerations As the number of wavelengths increases and the difference between the wave- lengths gets smaller, the need for wavelength stability becomes greater to ensure that the optical carriers do not bump into each other. Getting this stability requires either a stock of boards for each wavelength (maintained by network operators) or tunable lasers. If you have 320 wavelengths, you need 320 separate boards, each tuned to the appropriate wavelength. For redundancy purposes, you need a backup for each of those boards. And you need this at each location where you have a wavelength division multiplexer. You can see that a tunable laser that could adopt the behavior of a specific frequency as needed would greatly reduce the operating cost and the costs of spare parts and inventory. DWDM is beginning to be able to address network survivability requirements. It is also now capable of 