The present invention relates to an in-cable monomode optical fiber comprising an optical core surrounded by optical cladding, said optical core presenting an index profile constituted by a stepped central part, surrounded by an intermediate zone of refractive index less than that of said central part, itself surrounded by an annular zone having refractive index less than that of said central part and greater than that of said intermediate zone, said fiber having, for a wavelength of 1550 nm, a chromatic dispersion slope in the range 0 to 0.1 ps/nm2·km, said fiber being characterized in that it further presents the following features for a wavelength of 1550 nm: an effective surface area greater than or equal to 60 &mgr;m2, a chromatic dispersion in the range 3 ps/(nm·km) to 14 ps/(nm·km), and a ratio between the effective surface area and the chromatic dispersion slope greater than 900 &mgr;m2·nm2·km/ps.