Abstract: A fiber optic device for use in fiber optic transmission systems and components thereof includes a pass-through fiber and one or more lengths of circulating fiber connected to the pass-through fiber by respective optical switches for selectively routing an optical signal through the circulating fiber lengths as it propagates along the pass-through fiber. The circulating fiber lengths are either dispersion compensating fibers or fibers doped with a substance that will amplify or absorb the optical signal in the respective presence or absence of a pump signal. The invention thus allows various amounts of dispersion or gain (absorption) to be selectively switched into or out of use depending upon requirements at the time. For example, an amplifying component could serve as a pre- or power- or in-line amplifier device depending on the lesser or greater amount of gain fiber elected by switching.