A chromatic dispersion compensating and dispersion slope compensating optical fiber comprises a central core having an index difference Δn 1 with an outer optical cladding, a first buried inner cladding having an index difference Δn 2 with the outer cladding, a ring having an index difference Δn 3 with the outer cladding and a second buried inner cladding having an index difference Δn 4 with the outer cladding. The index difference between the first buried inner cladding and the outer cladding Δn 2 is less than or equal to -13.5.10 -3 and the index difference between the second buried inner cladding and the outer cladding Δn 4 is less than or equal to -3.10 -3 . The fiber has, for a wavelength of 1550 nm, a chromatic dispersion less than or equal to -50 ps/nm/km and a ratio of the chromatic dispersion over the chromatic dispersion slope DOS less than or equal to 70 nm. The second deeply buried inner cladding allows obtaining a low DOS value whilst maintaining acceptable optical characteristics.