Low dispersion single-mode fiber transmission - The question of practical versus theoretical maximum transmission bandwidth

We consider the question of the maximum transmission bandwidth in single-mode fibers from the theoretical as well as practical point of view. First, we show that there is an optimal input pulsewidth which gives minimum output pulsewidth and, therefore, determines the theoretical maximum transmission bandwidth. Both the first- and second-order dispersion terms are taken into account in calculating the optimal input pulsewidth, the optimal (minimum) output pulsewidth, and the corresponding maximum information rate for given fiber and source parameters. Next, we consider increasing the maximum transmission bandwidth by shifting the fiber's dispersion minimum to the desired wavelength, utilizing the doping and waveguide dispersion shifts. For long concatenated single-mode fibers, we also consider dispersion minimization using optical pulse equalization by purposely connecting fibers with positive and negative dispersion characteristics in series. Lastly, we consider polarization mode dispersion due to birefringence associated with fiber core ellipticity and asymmetrical stress. Based on these dispersion considerations, practical numerical examples are given, and a comparison between the chromatic dispersion and the polarization mode dispersion is made. The practical limit to the maximum transmission bandwidth in single-mode fibers is discussed.