TABLE OF CONTENTS A powerful aspect of an optical communication link is that many different wavelengths selected from the spectral regions ranging from the O-band through the L-band can be sent along a single fiber simultaneously. The technology of combining a number of wavelengths onto the same fiber is known as wavelength division multiplexing, or WDM. Conceptually, the WDM scheme is the same as frequency division multiplexing (FDM) used in microwave radio and satellite systems. Just as in FDM, the wavelengths (or optical frequencies) in WDM must be spaced properly to avoid interference between adjacent channels. The key system features of WDM are the following:
Capacity upgrade. The classical application of WDM has been to upgrade the capacity of existing point-to-point fiber optic transmission links. If each wavelength supports an independent network channel of a few gigabits per second, then WDM can increase the capacity of a fiber system dramatically with each additional wavelength channel.
Transparency. An important aspect of WDM is that each optical channel can carry any transmission format. Thus, by using different wavelengths, fast or slow asynchronous and synchronous digital data and analog information can be sent simultaneously, and independently, over the same fiber without the need for a common signal structure.
Wavelength routing. Instead of using electronic means to switch optical signals at a node, a wavelength-routing network can provide a pure optical end-to-end connection between users. This is done by means of lightpaths that are routed and switched at...
