Optical fiber comprising an optical core surrounded by an optical cladding, wherein the optical cladding is formed of an inner intermediate optical cladding adjacent to the optical core and of an outer optical cladding, wherein the optical core has a refractive-index profile Δn(r) of trapezoid-like shape, as a function of a radial distance r from the center of the optical core, the optical core having a center part of radius R1 and a transition part ranges from the radius R1 to a radius R2, such that R2 > R1, said refractive-index profile being defined by: - a surface integral A core defined as follows: A core = 2 ∫ 0 R 2 Δ n r . dr - a transition slope S defined as follows: S = Δ n 2 − Δ n 1 R 2 − R 1 with: Δn1, the refractive-index difference of the center part of the optical core with respect to the outer optical cladding; Δn2, the refractive-index difference of a cladding part, adjacent to the optical core, with respect to the outer optical cladding; and wherein: - the surface integral A core is between 180×10 -3 and 270×10 -3 μm; - the radius R2 is between 6.8 and 11.5 μm; - the transition slope S is between 1.7×10 -3 and 12×10 -3 μm -1 ; - the center part of the optical core comprises a region of depressed refractive index, called inner depressed core, ranging from the center of the optical core to radius R0 and having a refractive-index difference with respect to the outer optical cladding Δn0 such that Δn1 > Δn0 ≥ (Δn1-6×10 -3 ), said inner depressed core having a surface integral A 0 and assuming a surface integral A trap as the surface integral of depressless core's refractive-index profile, said surface integrals A 0 and A trap being defined as follows: A 0 = 2 ∫ 0 R0 Δ n1 − Δ n r dr A trap = 2 Δ n1 ⋅ R1 + ∫ R1 R2 Δ n r dr with a ratio A 0 /A trap lower than or equal to 0.1. - a surface integral A core defined as follows: A core = 2 ∫ 0 R 2 Δ n r . dr - a transition slope S defined as follows: S = Δ n 2 − Δ n 1 R 2 − R 1 with: Δn1, the refractive-index difference of the center part of the optical core with respect to the outer optical cladding; Δn2, the refractive-index difference of a cladding part, adjacent to the optical core, with respect to the outer optical cladding; Δn1, the refractive-index difference of the center part of the optical core with respect to the outer optical cladding; Δn2, the refractive-index difference of a cladding part, adjacent to the optical core, with respect to the outer optical cladding; - the surface integral A core is between 180×10 -3 and 270×10 -3 μm; - the radius R2 is between 6.8 and 11.5 μm; - the transition slope S is between 1.7×10 -3 and 12×10 -3 μm -1 ; - the center part of the optical core comprises a region of depressed refractive index, called inner depressed core, ranging from the center of the optical core to radius R0 and having a refractive-index difference with respect to the outer optical cladding Δn0 such that Δn1 > Δn0 ≥ (Δn1-6×10 -3 ), said inner depressed core having a surface integral A 0 and assuming a surface integral A trap as the surface integral of depressless core's refractive-index profile, said surface integrals A 0 and A trap being defined as follows: A 0 = 2 ∫ 0 R0 Δ n1 − Δ n r dr A trap = 2 Δ n1 ⋅ R1 + ∫ R1 R2 Δ n r dr <EOS>