Dispersion and Equalization in Fiber Optic Communication Systems

The temporal spreading of light pulses in an optical fiber can impose a limit on the highest data rate transmitted by a fiber optic communication system. Such spreading arises from differential mode delay in multimode fibers and material dispersion in both single-mode and multimode fibers. 1 The fiber materials and geometry together with the type of light source determine the magnitude of each effect. In this paper, we report the measurement of the additional optical power required to compensate for the loss in sensitivity resulting from the need to equalize detected light pulses that experience mode-delay spread. The experiment was carried out to determine the feasibility and practicality of equalization in dispersion-limited fiber systems. In the experiment, light from a Burrus 2 -type gallium arsenide light-emitting diode (LED) digitally modulated at 48 Mb/s is coupled into a liquid-core fiber.3 Intersymbol interference in the detected pulse train is reduced with a transversal equalizer4 by forcing zero crossings in the pulse response at all sampling times but one. Error rate measure1867