Multicore optical fiber

The multicore optical fiber according to claim 1, wherein each of the core portions has, as optical characteristics thereof, a cable cutoff wavelength λcc of 1530 nm or less, a mode field diameter of 8.8 to 11.2 μm at a wavelength of 1550 nm, and a bending loss of 0.5 dB or less at a wavelength of 1625 nm per turn at a radius of curvature of 30 mm;

• wherein each of the core portions comprises a first core portion having a refractive index higher than that of the cladding region;
• a second core portion, disposed about the first core portion, having a refractive index different from that of the first core portion;
• and a trench layer, disposed so as to surround the second core portion, having a refractive index lower than that of the cladding region;
• and
• wherein, letting a be the radius of the first core portion, Ra be the ratio of the outer diameter of the first core portion to the outer diameter of the second core portion, Rb be the ratio of the outer diameter of the second core portion to the outer diameter of the trench layer, Δ1 be the relative refractive index difference of the first core portion with respect to the second core portion, Δ3 be the relative refractive index difference of the trench layer with respect to the second core portion, and Δ4 be the relative refractive index difference of the cladding region with respect to the second core portion, the multicore optical fiber satisfies the following expressions (4) to (9):
• 4.01 [μm]≦a≦5.15 [μm] (4)
• 0.627≦Ra≦0.970 (5)
• 0.470≦Rb (6)
• 0.154[%]≦Δ1≦0.395[%] (7)
• −0.529[%]≦Δ3≦0.0[%] (8)
• −0.029[%]−≦Δ4≦0.123[%] (9).

3:

• The multicore optical fiber according to claim 2, wherein, letting Λ be the core pitch, Rth [mm] be the permissible maximum radius of curvature, and XTS be the average value of the permissible maximum crosstalk distribution after propagation over the fiber length LF [km], the multicore optical fibers satisfies the following expression (10):
• Λ
• ≥
• ln
• 
• (
• R
• th
• ·
• L
• F
• XT
• S
• )
• +
• 5.5498
• 0.7655
• ,
• (
• 10
• )
• wherein the average value XTμ of the crosstalk distribution after propagation over the fiber length LF [km] at a wavelength of 1565 nm is XTS or less.

4:

• The multicore optical fiber according to claim 2, wherein, letting Λ be the core pitch, Rth [km] be the permissible maximum radius of curvature and XTS be the average value of the permissible maximum crosstalk distribution after propagation over the fiber length LF [km], the multicore optical fibers satisfies the following expression (11):
• Λ
• ≥
• ln
• 
• (
• R
• th
• ·
• L
• F
• XT
• S
• )
• +
• 5.4554
• 0.7229
• ,
• (
• 11
• )
• wherein the average value XTμ of the crosstalk distribution after propagation over the fiber length LF [km] at a wavelength of 1625 nm is XTS or less.

9:

• A multicore optical fiber comprising a plurality of cores extending along a predetermined axis while being arranged like a hexagonal lattice on a cross section perpendicular to the axis and a cladding region surrounding each of the plurality of cores, the multicore optical fiber having a core pitch of 40.2 μm or more and, as optical characteristics of each core portion constituting at least a part of the associated one of the plurality of cores, a cable cutoff wavelength λcc of 1530 nm or less, a mode field diameter of 9.5 to 10.5 μm at a wavelength of 1550 nm, a bending loss of 0.5 dB or less at a wavelength of 1625 nm per turn at a radius of curvature of 30 mm, and a core-to-core crosstalk of −30 dB or less at a probability of 99.99% or higher at a wavelength of 1625 nm after propagation over 100 km;
• wherein each of the core portions comprises a first core portion having a refractive index higher than that of the cladding region;
• a second core portion, disposed about the first core portion, having a refractive index different from that of the first core portion;
• and a trench layer, disposed so as to surround the second core portion, having a refractive index lower than that of the cladding region;
• wherein, letting a be the radius of the first core portion, Ra be the ratio of the outer diameter of the first core portion to the outer diameter of the second core portion, Rb be the ratio of the outer diameter of the second core portion to the outer diameter of the trench layer, Δ1 be the relative refractive index difference of the first core portion with respect to the second core portion, Δ3 be the relative refractive index difference of the trench layer with respect to the second core portion, and Δ4 be the relative refractive index difference of the cladding region with respect to the second core portion, the multicore optical fiber satisfies the following expressions (12) to (17):
• 4.42 [μm]≦a≦5.15 [μm] (12)
• 0.627≦Ra≦0.811 (13)
• 0.470≦Rb≦0.899 (14)
• 0.295[%]≦Δ1≦0.395[%] (15)
• −0.529[%]≦Δ3≦−0.173[%] (16)
• −0.029[%]≦Δ4≦0.123[%] (17), and
• wherein, letting Λ be the core pitch, the multicore optical fiber satisfies the following expressions (18) to (23):
• a
• ≥
• 1.314
• ·
• 10
• 1
• -
• 1.988
• ·
• 10
• -
• 1
• 
• Λ
• 
• [
• µm
• ]
• (
• 18
• )
• Ra
• ≤
• 4.062
• ·
• 10
• -
• 2
• 
• Λ
• -
• 1.007
• (
• 19
• )
• Rb
• ≤
• 1
• 5.254
• -
• 7.847
• ·
• 10
• -
• 2
• 
• Λ
• (
• 20
• )
• Δ
• 
• 
• 1
• ≥
• 1.099
• -
• 1.799
• ·
• 10
• -
• 2
• 
• Λ
• 
• [
• %
• ]
• (
• 21
• )
• Δ
• 
• 
• 3
• ≤
• 4.350
• ·
• 10
• -
• 2
• 
• Λ
• -
• 2.236
• 
• [
• %
• ]
• (
• 22
• )
• Δ
• 
• 
• 4
• ≤
• 2.928
• 
• 
• Λ
• 2
• -
• 2.108
• ·
• 10
• 2
• 
• 
• Λ
• +
• 3.808
• ·
• 10
• 3
• -
• 0.9439
• 
• 
• Λ
• +
• 2.937
• ·
• 10
• 1
• 1.440
• 
• 
• Λ
• -
• 50.74
• 
• [
• %
• ]
• .
• (
• 23
• )