Dispersion-decreasing fibers are optical fibers where the magnitude of the (typically anomalous) chromatic dispersion decreases along the propagation direction. Such a behavior can be obtained e.g. by gradually changing the fiber diameter during the fiber pulling process, because the fiber diameter affects the waveguide dispersion of the fiber. Such tapered fibers can be made of standard single-mode fibers, but also of photonic crystal fibers.
A possible application of dispersion-decreasing fibers is adiabatic soliton compression, where one exploits the fact that a soliton pulse adapts its parameters (including the pulse duration) to the fiber parameters, provided that the variation of dispersion is sufficiently slow.
Due to the difficulty of fabricating and handling dispersion-decreasing fibers, such fibers are not widely used.