The specification describes an improved optical fiber design in which the criteria for high performance in a Raman amplified optical system, such as moderate effective area, moderate dispersion, low dispersion slope, and selected zero dispersion wavelength, are simultaneously optimized. In preferred embodiments of the invention, the dispersion characteristics are deliberately made selectively dependent on the core radius. This allows manufacturing variability in the dispersion properties, introduced in the core-making process, to be mitigated during subsequent processing steps.