In a single-mode optical fiber, the rate of change of dispersion, with respect to wavelength, at the fiber's zero-dispersion wavelength. Note 1: In silica-based optical fibers, the zero-dispersion wavelength occurs at approximately 1. 3 m, but this wavelength may be shifted toward the minimum-loss window by the addition of dopants to the fibre material during manufacture. Note 2: Doubly and quadruply clad single-mode fibres have two zero-dispersion points, and thus two zero-dispersion slopes.