A single-mode optical fiber includes a central core surrounded by an outer optical cladding. The optical fiber includes an inner depressed cladding, a ring, and an outer depressed cladding positioned between the central core and the outer optical cladding. The central core typically has a refractive-index difference (Dn1) with the outer optical cladding of between about −0.5×10−3 and 0.5×10−3. The ring typically has an inner radius (rring1) of between about 21 microns and 35 microns and a refractive-index difference with the outer optical cladding (Dnring) of between about −0.5×10−3 and 0.5×10−3. The outer depressed cladding typically has a volume (Vout) of between about 15 μm2 and 30 μm2. The ratio of the volume of the central core over the width of the ring (Vcore/wring) is typically between about 0.12 micron and 0.2 micron.