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/nr2 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) 0.8d/<1.
