Capacity increase in optical fiber links

The capability to increase the capacity of installed fiber optic links went through a paradigm shift over fifteen years ago. Originally, increasing the speed of single wavelength transmission was the most sensible upgrade path when electrical regeneration was required at each node. This later gave way to long reach, optically amplified transmission where both the line rate and DWDM channel count could be increased. This later paradigm made it more favorable for carriers to invest in fiber optic infrastructure. We are at a fascinating time when we can foresee the ultimate limit to capacity increases on fiber as we know it. Possible directions for future fiber technology are noted.