The window of an optical fiber at which material dispersion is very small. Note 1: In silica-based fibers, the minimum-dispersion window occurs at a wavelength of approximately 1. 3 m. Note 2: The minimum-dispersion window may be shifted toward the minimum-loss window, i.e., 1. 55 m, by the addition of dopants during manufacture. 2. In a single-mode fiber, the window or, in the case of doubly or quadruply clad fibers, windows, at which material and waveguide dispersion cancel one another, resulting in extremely wide bandwidth, i.e., extremely low dispersion, over a very narrow range of wavelengths. Synonym zero dispersion window.