Optical fiber and optical transmission system
View Patent ↗An optical fiber includes a core, a first clad that is provided on an outer circumferential portion of the core and has a refractive index lower than that of the core, and a second clad that is provided on an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad. In the optical fiber, a mode field diameter at a wavelength of 1.55 μm is equal to or greater than 11.5 μm, a cutoff wavelength is equal to or less than 1.53 μm, a bending loss at a bending radius of 30 mm and a wavelength of 1.625 μm is equal to or less than 2.0 dB/100 turns, and a delay time of transmission light per unit length at a wavelength of 1.55 μm is equal to or less than 4.876 μs/km.
1. An optical fiber, comprising:
a core;
a first clad that is provided on an outer circumferential portion of the core and has a refractive index lower than that of the core; and
a second clad that is provided on an outer circumferential portion of the first clad and has a refractive index lower than that of the first clad,
wherein a mode field diameter at a wavelength of 1.55 μm is equal to or greater than 11.5 μm,
wherein a cutoff wavelength is equal to or less than 1.53 μm,
wherein a bending loss at a bending radius of 30 mm and a wavelength of 1.625 μm is equal to or less than 2.0 dB/100 turns,
wherein a delay time of transmission light per unit length at a wavelength of 1.55 μm is equal to or less than 4.876 μs/km,
wherein a radius of the core is equal to or greater than 1.0 μm and equal to or less than 4.3 μm, and
wherein a radius of the first clad satisfies Equations (1) and (2):
[
Equation
1
]
a
2
≥
2
{
(
1.43
a
1
-
1.45
)
2
-
(
Δ
1
+
1.43
a
1
-
1.45
)
2
}
-
0.50
a
1
-
0.37
(
1
)
[
Equation
2
]
5.56
-
3.94
log
(
1
+
Δ
1
0.19
+
0.69
a
1
-
2.00
)
≤
a
2
≤
7.68
+
(
1.14
-
2.51
a
1
)
log
(
1
+
Δ
1
0.81
a
1
-
0.77
)
(
2
)
where a 1 in Equations (1) and (2) represents the radius [μm] of the core, a 2 represents the radius [μm] of the first clad, and Δ 1 represents a relative refractive index difference [%] of the first clad from the core.
2. The optical fiber according to claim 1 , wherein the relative refractive index difference of the second clad from the first clad satisfies Equation (3):
[Equation 3]
Δ 2 ≥−0.033+(−7.490−0.187 a 1 3.407 Δ 1 −0.044 a 1 4.324 Δ 1 2 ) a 2 −1.876−0.014a 1 3.099 Δ 2 (3),
where Δ 2 represents the relative refractive index difference [%] of the second clad from the first clad.
3. The optical fiber according to claim 1 wherein, in a sectional view crossing a longitudinal direction, a plurality of low-delay cores including the core as a first core and the first clad provided on an outer circumferential portion of the first core are disposed on concentric circles at the center of the second clad.
4. The optical fiber according to claim 3 , wherein the core is disposed as a second core at the center of the second clad.
5. The optical fiber according to claim 1 , wherein, in a sectional view crossing a longitudinal direction, a low-delay core including the core as a first core and the first clad provided on an outer circumferential portion of the first core is disposed at the center of the second clad, and
wherein the core is disposed as a third core on a concentric circle at the center of the low-delay core.
6. The optical fiber according to claim 1 , wherein, in a sectional view crossing a longitudinal direction, a low-delay core including the core as a first core and the first clad provided on an outer circumferential portion of the first core is disposed at the center of the second clad, and
wherein the cores are packed most closely as fourth cores around the low-delay core.
7. An optical transmission system, comprising:
the optical fiber according to claim 1 ;
a transmitter that is connected to one end of the optical fiber; and
a receiver that is connected to the other end of the optical fiber.