WDM TRANSMISSION TECHNOLOGIES FOR DISPERSION-SHIFTED FIBERS

Dense WDM techniques that exploit the enormous bandwidth of dispersion -shifted fibers (DSFs) while avoiding the impairments due to nonlinear effects are described. First, the nature of four-wave mixing (FWM), t he dominant impairment factor in WDM transmission systems, is investig ated using DSF installed in the field and laboratory experiments. This provides useful information for the practical design of WDM networks based on DSF. Second, practical techniques to reduce FWM impairment, u nequal channel allocation and off-lambda-zero channel allocation (equa l channel allocation in the novel 1580 nm band) along with gain-shifte d erbium-doped fiber amplifiers for the 1570 to 1600 nm band, is descr ibed. Comparisons between off-lambda-zero and unequal channel allocati on are provided in terms of the maximum transmission distance for vari ous numbers of channels. Two schemes to immunize WDM systems against g roup velocity dispersion, span-by-span dispersion compensation and opt ical duobinary format, are presented. The combination of unequal chann el allocation with off-lambda-zero channel allocation as well as the c ombination of two bands: the conventional 1550 nm band and the novel 1 580 nm band are proven to be very useful in expanding the usable bandw idth of DSFs.