Abstract: A compensating optical fiber length having a negative chromatic dispersion slope, the compensating optical fiber having a core region surrounded by a cladding region, the cladding region defining a first ring of holes, which substantially defines, around the core region an annulus with an inner radius r1 and an outer radius r2, and at least one second ring of holes that surrounds the first ring of holes, the holes running along the compensating optical fiber longitudinally and being spaced apart from each other substantially according to a predefined pitch ?, wherein a) r1??/n?r2 where n is the refractive index of the material making up the core region of the compensating optical fiber length; b) the holes of the first and the at least one second ring are substantially of the same diameter d; and c) the ratio d/? substantially satisfies the following relationship (A) 0.8?d/?<1.