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.