MULTICORE OPTICAL FIBER AND DESIGN METHOD
There are provided a multi-core optical fiber including four step-index type cores with a standard cladding diameter and having excellent mass productivity, quality, and yield while meeting desired specifications, and a design method thereof. A multi-core optical fiber according to the present disclosure includes: four cores arranged in a square lattice shape along a longitudinal direction, each of the four cores having a step-index type refractive index distribution with a radius a; and a cladding region having a lower refractive index than that of each core and a diameter of 125±1 μm and provided on an outer peripheral portion of each core, where an absolute value of a relative refractive index difference between each core and the cladding region is Δ. The four cores are arranged so that a relationship between a minimum distance (OCT) from the center of each core to an outer periphery of the cladding region, a minimum value Λ of spacing between the cores, and the MFD at a wavelength of 1310 nm satisfies Formula C1, and the radius a of each core and the relative refractive index difference Δ between the core and the cladding region are set. [ Formula C 1 ] OCT ≥ 3.73 MFD + 3.43 Λ ≤ - 5.28 MFD + 83.54 ( C1 )
1 . A multi-core optical fiber comprising:
four cores, each of the four cores having a step-index type refractive index distribution with a radius a; and
a cladding region having a lower refractive index than that of each core, a diameter of 125±1 μm and an absolute value of a relative refractive index difference between each core and the cladding region being Δ, and provided on an outer peripheral portion of each core, wherein
a mode field diameter (MFD) at a wavelength of 1310 nm is 8.2 to 9.6 μm,
a cutoff wavelength is 1260 nm or less, and
the four cores are arranged, the radius a of each core is set, and the relative refractive index difference Δ between each core and the cladding region are set so that a relationship between a minimum distance (OCT) from a center of each core to an outer periphery of the cladding region, a minimum value Λ of spacing between the cores, and the MFD at a wavelength of 1310 nm satisfies Formula C1.
[
Formula
C
1
]
O
C
T
≥
3
.73
MFD
+
3
.43
(
C
1
)
Λ
≤
-
5
.28
MFD
+
8
3
.54
2 . The multi-core optical fiber according to claim 1 , wherein a relationship between a total value XT of crosstalk of a unit length at a wavelength of 1625 nm and the MFD at a wavelength of 1310 nm satisfies Formula C2, the crosstalk being received by any core of the cores from other cores.
[
Formula
C
2
]
X
T
≥
27.
MFD
-
2
5
1.8
(
C
2
)
3 . The multi-core optical fiber according to claim 1 , wherein a relationship between a total value XT of crosstalk of a unit length at a wavelength of 1360 nm and the MFD at a wavelength of 1310 nm satisfies Formula C3, the crosstalk being received by any core of the cores from other cores.
[
Formula
C
3
]
X
T
≥
3
3.7
MFD
-
3
4
2.3
(
C
3
)
4 . A multi-core optical fiber comprising:
four cores, each of the four cores having a step-index type refractive index distribution with a radius a; and
a cladding region having a lower refractive index than that of each core, a diameter of 125±1 μm and an absolute value of a relative refractive index difference between each core and the cladding region being Δ, and provided on an outer peripheral portion of each core, wherein
a mode field diameter MFD at a wavelength of 1550 nm is 9 to 12 μm,
a cutoff wavelength is 1530 nm or less, and
the four cores are arranged, the radius a of each core is set, and the relative refractive index difference Δ between each core and the cladding region are set so that a relationship between a minimum distance (OCT) from a center of each core to an outer periphery of the cladding region, a minimum value Λ of spacing between the cores, and the MFD at a wavelength of 1550 nm satisfies Formula C4.
[
Formula
C
4
]
O
C
T
≥
2.82
MFD
+
3.7
(
C
4
)
Λ
≤
-
3
.99
MFD
+
8
3
.15
5 . The multi-core optical fiber according to claim 4 , wherein a relationship between a total value XT of crosstalk of a unit length at a wavelength of 1625 nm and the MFD at a wavelength of 1550 nm satisfies Formula C5, the crosstalk being received by any core of the cores from other cores.
[
Formula
C
5
]
X
T
≥
2
4.6
MFD
-
2
94.8
(
C5
)
6 . The multi-core optical fiber according to claim 4 , wherein a relationship between a total value XT of crosstalk of a unit length at a wavelength of 1565 nm and the MFD at a wavelength of 1550 nm satisfies Formula C6, the crosstalk being received by any core of the cores from other cores.
[
Formula
C
6
]
X
T
≥
2
6.
MFD
-
315.8
(
C6
)