The invention proposes an optical fiber presenting a reference index profile
having more than six steps. At a wavelength of 1550 nm it presents chromatic dispersion
that is positive, and a ratio of the square of effective area over chromatic dispersion
slope that is greater than 100,000 m4.nm2.km/ps. The
invention makes it possible to improve the propagation characteristics of prior
art fibers by optimizing index profile. It can be implemented using conventional
techniques for building up preforms by VAD or by MCVD.