Multicore optical fiber, method of designing multicore optical fiber, and optical transmission method
View Patent ↗It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 125±1 μm for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index Δ1 relative to the core of the first cladding region and a specific refractive index Δ2 relative to the core of a second cladding region including four cores and the first cladding region.
1. A multicore optical fiber having only four cores having a radius a1 disposed in a longitudinal direction in square lattice shape, wherein the multicore optical fiber further comprises:
first cladding regions disposed around each of the cores and having a radius a2 with a refractive index lower than a refractive index of the cores, a specific relative refractive index difference to the cores αeing A1; and
a second cladding region disposed on an outer periphery of the first cladding regions and having a refractive index higher than the refractive index of the first cladding regions and lower than the refractive index of the cores, a specific relative refractive index difference to the core being Δ2,
wherein an outer diameter of the second cladding region is 125±1 μm,
bending loss at a wavelength of 1625 nm and a bending radius of 30 mm is 0.1 dB/100 turns or less, and
a cutoff wavelength is 1530 nm or less.
2. The multicore optical fiber according to claim 1 , further comprising a region having a width w and having a same refractive index as the refractive index of the second cladding region between each of the cores and the first cladding region.
3. The multicore optical fiber according to claim 2 , wherein the width w is 0 μm<w≤1.3 μm.
4. The multicore optical fiber according to claim 1 , wherein a relationship between the Δ1 and a total value XT (dB/km) of inter-core crosstalk per km satisfies Formula C1,
[Formula C1]
Δ 1 ≤4.93×10 −5 XT− 0.00127 (C1).
5. The multicore optical fiber according to claim 1 , wherein a relationship between the a1 and the Δ1 satisfies Formula C2,
[Formula C2]
a 1 ≥−28041Δ 1 2 −560.65Δ 1 +3.1369 (C2).
6. The multicore optical fiber according to claim 1 , wherein a relationship between the Δ2 and a total value XT (dB/km) of inter-core crosstalk per km satisfies Formula C3,
[Formula C3]
Δ 2 ≥−1.14×10 −5 XT− 0.00509 (C3).
7. The multicore optical fiber according to claim 1 , wherein
a ratio a2/a1 between the a1 and the a2 is 1.0 or more and 3.0 or less,
a relationship between the Δ1, the a2/a1, and an effective cross-sectional area Aeff at a wavelength of 1550 nm satisfies Formula C4 and
a relationship between the Δ2, the a2/a1, and the Aeff satisfies Formula C5,
[Formula C4]
Δ 1 ≤(1.9×10 −5 A eff 2 −0.00033 A eff +0.0163) a 2 /a 1 +(−8.0×10 −6 A eff 2 +0.00139 A eff −0.0705) (C4)
[Formula C5]
Δ 2 ≤(5.0×10 −7 A eff 2 +6.5×10 −6 A eff −0.00108) a 2 /a 1 +(−2.9×10 −7 A eff 2 +5.58×10 −5 A eff −0.00594)
and
Δ 2 ≤(5.0×10 −7 A eff 2 −9.5×10 −5 A eff +0.0056) a 2 /a 1 +(−1.6×10 −6 A eff 2 +0.00031 A eff −0.0208) (C5).
8. The multicore optical fiber according to claim 5 , wherein the Δ1 and the Δ2 satisfy Formula C6,
[Formula C6]
−0.7%≤Δ 1 ≤−0.49%
−0.4%≤Δ 2 ≤−0.27% (C6).
9. The multicore optical fiber according to claim 7 , wherein the Δ1 and the Δ2 satisfy Formula C6,
[Formula C6]
−0.7%≤Δ 1 ≤−0.49%
−0.4%≤Δ 2 ≤−0.27% (C6).