Chromatic dispersion is measured in units of ps/(nmkm): picoseconds (10 -12 seconds) of light pulse spread per nanometer (10-9 meters) of laser spectral width and per kilometer of fiber length (103 meters). They are simply reporting values from the external standards. Table 151-13 uses the worst case S0 and ZDW given in Table 151-14, and calculates the worst case positive and negative dispersion using the worst case TX wavelengths given in Table 151-7 and footnote (b), and the worst case fiber length. In a dispersive prism, material dispersion (a wavelength -dependent refractive index) causes different colors to refract at different angles, splitting white light into a spectrum. Single-mode fibers, used in high-speed optical networks, are subject to. Dispersion distorts signals and limits the data rate of digital signals sent over fiber optic cable. Normally, dispersion in fiber optic cable includes modal dispersion, chromatic dispersion and polarization mode dispersion.