Patent ID: 8798424

Claim:
A single-mode optical fiber, comprising: a central core surrounded by an outer optical cladding, said central core having a radius (a) and a refractive-index difference (Dn 1 ) with said outer optical cladding of between about −0.5×10 −3 and 0.5×10 −3 ; an inner depressed cladding positioned between said central core and said outer optical cladding, said inner depressed cladding having an outer radius (r ring1 ) and a refractive-index difference (Dn inner ) with said outer optical cladding; a ring positioned between said inner depressed cladding and said outer optical cladding, said ring having an inner radius (r ring1 ) of between about 21 microns and 35 microns, an outer radius (r ring2 ), a width (w ring ), and a refractive-index difference (Dn ring ) with said outer optical cladding of between about −0.5×10 −3 and 0.5×10 −3 ; and an outer depressed cladding positioned between said ring and said outer optical cladding, said outer optical cladding having an outer radius (r out ) and a refractive-index difference (Dn out ) with said outer optical cladding; wherein said central core has a volume (V core ), the ratio of said volume of said central core over said width of said ring (V core /w ring ) being between about 0.12 micron and 0.2 micron, the volume (V core ) of said central core being defined as follows: Vcore = 2 ⁢ ⁢ π ⁢  ∫ 0 a ⁢ Dn ⁡ ( r ) ⁢ r ⁢ ⅆ r  wherein, Dn(r)=n core (r)−n inner ; n core (r) is the refractive index of the central core at the radius r; and n inner is the average refractive index of the inner depressed cladding; wherein said outer depressed cladding has a volume of between about 15 μm 2 and 30 μm 2 , said volume (V out ) of said outer depressed cladding being defined as follows: Vout = 2 ⁢ ⁢ π ⁢  ∫ rring ⁢ ⁢ 2 rout ⁢ Dn ⁡ ( r ) ⁢ r ⁢ ⅆ r  wherein, Dn(r)=n out (r)−n cl ; n out (r) is the refractive index of the outer depressed cladding at the radius r; and n cl is the average refractive index of the outer optical cladding.