Uncoupled-core multicore optical fiber with reduced cross talk

1 . An uncoupled-core multicore optical fiber comprising:

at least two core portions, each core portion comprising:

a core having a radius r 1 and a relative refractive index Δ 1 relative to pure silica, the core being doped with at least one of sodium, potassium, and rubidium; and

a depressed-index cladding having a radius r 2 and a relative refractive index Δ 2 relative to pure silica such that Δ 2 <Δ 1 , the depressed-index cladding surrounding and directly contacting the core, a volume V 2 of the depressed-index cladding being about 5.0% Δ-micron 2 to about 37.0% Δ-micron 2 ; and

a common cladding having a radius r 3 and a relative refractive index Δ 3 relative to pure silica such that Δ 2 <Δ 3 <Δ 1 , the common cladding surrounding and directly contacting the depressed-index cladding,

wherein:

a cable cutoff wavelength of each core portion is about 1530 nm or less,

an effective area of each core portion is about 100 micron 2 to about 135 micron 2 at a wavelength of 1550 nm,

each core portion comprises an attenuation at a wavelength of 1550 nm of about 0.165 dB/km or less,

a center-to-center spacing between centerlines of adjacent core portions is about 48 microns to about 60 microns,

co-propagating cross talk between the at least two core portions is about −40 dB or less per 100 km of optical fiber for a bend diameter of 140 mm, and

counter-propagating cross talk between the at least two core portions is about −45 dB or less per 100 km of optical fiber.

2 . The uncoupled-core multicore optical fiber of claim 1 , wherein co-propagating cross talk between the at least two core portions is about −50 dB or less per 100 km of optical fiber for a bend diameter of 140 mm.

3 . The uncoupled-core multicore optical fiber of claim 2 , wherein co-propagating cross talk between the at least two core portions is about −60 dB or less per 100 km of optical fiber.

4 . The uncoupled-core multicore optical fiber of claim 1 , wherein the at least two core portions consists of only two core portions.

5 . The uncoupled-core multicore optical fiber of claim 1 , wherein the centerline of each of the at least two core portions is positioned along an axis A.

6 . The uncoupled-core multicore optical fiber of claim 5 , wherein the axis A extends through a central axis of the multicore optical fiber.

7 . The uncoupled-core multicore optical fiber of claim 1 , wherein the effective area of each core portion is about 110 micron 2 to about 130 micron 2 at a wavelength of 1550 nm.

8 . The uncoupled-core multicore optical fiber of claim 1 , wherein the attenuation of each core portion at a wavelength of 1550 nm is about 0.160 dB/km or less.

9 . The uncoupled-core multicore optical fiber of claim 1 , wherein the relative refractive index Δ 1 is about −0.20% to about 0.20%.

10 . The uncoupled-core multicore optical fiber of claim 1 , wherein an average concentration of alkali in the core is about 20 ppm to about 500 ppm.

11 . The uncoupled-core multicore optical fiber of claim 10 , wherein the average concentration of alkali in the core is about 5 ppm to about 300 ppm.

12 . The uncoupled-core multicore optical fiber of claim 1 , wherein each core portion has a dispersion at 1550 nm of less than about 22 ps/nm/km.

13 . The uncoupled-core multicore optical fiber of claim 1 , wherein each core portion has a dispersion at 1550 nm of less than about 21 ps/nm/km.

14 . An uncoupled-core multicore optical fiber comprising:

at least two core portions, each core portion comprising:

a core having a radius r 1 and a relative refractive index Δ 1 relative to pure silica,

wherein each portion comprises an attenuation at a wavelength of 1550 nm of less than about 0.150 dB/km,

wherein co-propagating cross talk between the at least two core portions is about −40 dB or less per 100 km of optical fiber for a bend diameter of 140 mm, and

wherein counter-propagating cross talk between the at least two core portions is about −45 dB or less per 100 km of optical fiber.

15 . The uncoupled-core multicore optical fiber of claim 14 , wherein:

the core is doped with at least one of sodium, potassium, and rubidium,

the optical fiber further comprises:

a depressed-index cladding having a radius r 2 and a relative refractive index Δ 2 relative to pure silica such that Δ 2 <Δ 1 , the depressed-index cladding surrounding and directly contacting the core, a volume V 2 of the depressed-index cladding being about 5.0% Δ-micron 2 to about 37.0% Δ-micron 2 , and

a common cladding having a radius r 3 and a relative refractive index Δ 3 relative to pure silica such that Δ 2 <Δ 3 <Δ 1 , the common cladding surrounding and directly contacting the depressed-index cladding,

a cable cutoff wavelength of each core portion is about 1530 nm or less,

an effective area of each core portion is about 100 micron 2 to about 135 micron 2 at a wavelength of 1550 nm, and

a center-to-center spacing between centerlines of adjacent core portions is about 48 microns to about 60 microns.

16 . The uncoupled-core multicore optical fiber of claim 14 , wherein co-propagating cross talk between the at least two core portions is about −50 dB or less per 100 km of optical fiber for a bend diameter of 140 mm.

17 . The uncoupled-core multicore optical fiber of claim 14 , wherein counter-propagating cross talk between the at least two core portions is about −50 dB or less per 100 km of optical fiber.