7 - Dispersion and our attempts to prevent it

Abstract

This chapter discuses the spreading effect called dispersion of optic fibers. Dispersion causes the pulses to spread out and they blend together and the information can lost. This degree of dispersion can be made acceptable by decreasing the transmission frequency, thus allowing larger gaps between the pulses. This type of dispersion is called intermodal dispersion. The chapter also approaches the problem of intermodal dispersion in two ways: one could redesign the fiber to encourage the modes to travel at the same speed along the fiber or eliminate all the modes except one. The first strategy is called graded index optic fiber. Chromatic dispersion is the combined effect of two other dispersions: material dispersion and waveguide dispersion. Both result in a change in transmission speed, the first is due to the atomic structure of the material and the second is due to the propagation characteristics of the fiber.