Overview

There are strong economic motivations to increase the number of modulated wavelength channels that can be accommodated by a fiber-based telecom system. Not only does the designer avoid the cost of adding new cable, but it is possible to dramatically increase the bandwidth per existing channel.

This requires, of course, the creation of new hardware and system management tools that can squeeze more optical channels into each fiber and then find them at the other end, separate them, and deal with them individually. This implies constantly improving the capabilities of filters, lasers, amplifiers, multiplexers, and other components that must "handle the photons with care." From the system management point of view, standards must evolve along with the hardware so that transmission penalties are minimized, bandwidth is maintained, and growth paths are not shut off.

As a result of the press of technologies that support the concentration and ultimate division of wavelengths, we have included this chapter to specifically address wavelength separation. It addresses antiresonant reflecting optical waveguides (ARROWs), waveguides, gratings, multiplex and demultiplex components, filters of various types, and so on. Throughout, we have tried to include practical issues, such as controlling the performance of these components in the real environments where they will be used, with particular attention to the thermal environments that are encountered in the field. We have included most of the popular filter systems, including those that use fiber Bragg gratings, conventional gratings, and waveguide methods.

Gratings, particularly those created within fibers, such as fiber...