Single-mode optical fiber

A single-mode optical fiber, comprising:

• a central core surrounded by an outer optical cladding, said central core having a radius (a) of between about 3.5 microns and 7.5 microns and a refractive-index difference (Dn1) 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 (rring1) of between about 24 microns and 35 microns and a refractive-index difference (Dninner) with said outer optical cladding of between about −6×10−3 and −2.7×10−3;
• a ring positioned between said inner depressed cladding and said outer optical cladding, said ring having an inner radius (rring1), an outer radius (rring2), a width (wring) of between about 1.8 microns and 3 microns, and a refractive-index difference (Dnring) 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 (rout) of between about 45 microns and 48 microns and a refractive-index difference (Dnout) with said outer optical cladding of between about −6×10−3 and −2×10−3;
• wherein said outer optical cladding has an outer radius of between about 61.5 microns and 63.5 microns;
• wherein said central core has a volume (Vcore), the ratio of said volume of said central core over said width of said ring (Vcore/wring) being between about 0.12 micron and 0.2 micron, the volume (Vcore) of said central core being defined as follows:
• Vcore
• =
• 2
• ⁢
• ⁢
• π
• ⁢
• 
• ∫
• 0
• a
• ⁢
• Dn
• ⁡
• (
• r
• )
• ⁢
• r
• ⁢
• ⅆ
• r
• 
• wherein,
• Dn(r)=ncore(r)−ninner;
• ncore(r) is the refractive index of the central core at the radius r;
• and
• ninner is the average refractive index of the inner depressed cladding;
• wherein said outer depressed cladding has a volume of between about 17 μm2 and 25 μm2, said volume (Vout) of said outer depressed cladding being defined as follows:
• Vout
• =
• 2
• ⁢
• ⁢
• π
• ⁢
• 
• ∫
• rring
• ⁢
• ⁢
• 2
• rout
• ⁢
• Dn
• ⁡
• (
• r
• )
• ⁢
• r
• ⁢
• ⅆ
• r
• 
• wherein,
• Dn(r)=nout(r)−ncl;
• nout(r) is the refractive index of the outer depressed cladding at the radius r;
• and
• ncl is the average refractive index of the outer optical cladding.

An optical preform, comprising:

• a central core surrounded by an outer optical cladding, said central core having a refractive-index difference (Dn1) 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 a refractive-index difference (Dninner) with said outer optical cladding of between about −6×10−3 and −2.7×10−3;
• a ring positioned between said inner depressed cladding and said outer optical cladding, said ring having a refractive-index difference (Dnring) 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 (i) a refractive-index difference with the inner depressed cladding (Dninner−Dnout) of between about −2×10−3 and 2×10−3 and (ii) a refractive-index difference (Dnout) with said outer optical cladding of between about −6×10−3 and −2×10−3;
• wherein the ratio of the cross-sectional area of the central core to the cross-sectional area of the outer optical cladding is between about 0.0047 and 0.044;
• wherein the ratio of the cross-sectional area of the inner depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.14 and 0.95;
• wherein the ratio of the cross-sectional area of the ring to the cross-sectional area of the outer optical cladding is between about 0.025 and 0.28;
• and
• wherein the ratio of the cross-sectional area of the outer depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.30 and 1.56.