A singlemode optical fiber that has been designed to reduce chromatic dispersion. The fiber core is fabricated in several layers with different refractive indices running in parallel throughout its length. Zero-dispersion-shifted fiber has zero chromatic dispersion at 1550 nm. It is no longer manufactured, because it causes interference in WDM transmission. Nonzero-dispersion-shifted fiber is designed for WDM. It has zero dispersion near 1500 nm and beyond 1600 nm, which provides lower dispersion in the 1550 nm range. See graded-index fiber, step index fiber and dispersion.