A type of diffraction grating comprising groves etched into a transparent material such as glass. As the elements of light in the incident spectrum strike the grooves at a certain angle, they are diffracted and, therefore, separated to various degrees, with blue light diffracted the least and red light the most. This approach is used effectively in fiber optic transmission systems (FOTS) employing wavelength division multiplexing (WDM). See also diffraction, diffraction grating, FOTS, and WDM.