Chromatic dispersion
Chromatic dispersion turns up in 2 fields: photonics, fiber optics. Here is what it means to the people in each one.
Chromatic dispersion in photonics
The change of refractive index with wavelength, which separates colors in prisms and spreads pulses in time.
Every optical material has an index that varies with wavelength, so different colors bend and travel differently. Spatially it causes prism splitting and chromatic aberration in lenses; in time it spreads pulses, described by group delay, GVD and higher orders. In fibers it combines material and waveguide contributions and is quoted as D in ps per nm per km, about 17 at 1550 nm in standard singlemode fiber.
"Chromatic dispersion in that singlet throws the 400 nm focus half a millimeter short of the 800, swap in an achromat."
Chromatic dispersion in fiber optics
Pulse spreading caused by different wavelengths in a light source traveling at slightly different speeds in fiber.
Every laser emits a small spread of wavelengths, and because glass index and waveguide effects vary with wavelength, those colors arrive at slightly different times. Standard singlemode fiber has zero dispersion near 1310 nm and about 17 ps/nm/km at 1550 nm. Over long 10G spans it limits reach unless compensated with dispersion-compensating fiber or modules, and coherent transceivers correct it digitally.
"Link's 120 km of plain G.652 at 10G with no DCM, so chromatic dispersion is going to eat that budget before loss does."