Active Optical Components are used to manipulate light through a variety of electrical methods, including adaptive reflection, variable diffusion, or tunable focusing. Common optical passive components in optical communications include: fiber optic connectors, fiber optic couplers. The active devices described in this chapter include variable optical attenuators, tunable optical filters, dynamic gain equalizers, optical add/drop multiplexers, polarization controllers, and dispersion compensators. In contrast. An optical transmission system essentially consists of three components.