12.1  INTRODUCTION

Optical fiber components can be broadly classified as passive and active. Electrical
powering is not required for passive components, which include multiplexers and
demultiplexers, fixed-wavelength filters, interleavers, fixed optical add/drop multiplexers,
dispersion compensators, couplers, splitters, pump combiners, isolators, and
circulators. Active components include optical amplifiers, tunable wavelength filters,
tunable dispersion compensators, wavelength converters, optical switches, external
modulators, transmitters, and receivers. Optical sources (laser diodes) at different
wavelengths, optical detectors, and optical fiber form the major components in any
fiber optic communication system. Besides these, other components are required to
amplify the signals in the optical domain and to compensate for accumulated dispersion.
Many of these also contain fiber optic components such as optical taps,
wavelength-division multiplexers and demultiplexers, and optical isolators.
Various technologies have been developed to achieve many of these functions:

1. Fiber-based: includes, for example, optical fiber amplifiers, fiber dispersion
   compensators, fiber Bragg gratings, and fused fiber components.
2. Integrated optics–based: includes, for example, arrayed waveguide devices,
   semiconductor optical amplifiers, and high-speed modulators.
3. Microoptics and thin film–based: includes, for example, filters, and multiplexers

Various fiber optic components are listed and compared with corresponding bulk
optical devices in Table 12.1.

We discussed optical amplifiers and dispersion compensators based on fibers
and fiber Bragg grating–based dispersion compensators and wavelength-selective
reflectors earlier. In this chapter we discuss other important components that are
used in fiber optic communication systems. For a recent review of various fiber optic
components, see, e.g., Pal (2006).