EQUIPMENT AND METHOD FOR CHARACTERIZING BIDIRECTIONAL CROSSTALK
The present disclosure is a device that detects each loss occurrence point of an optical fiber under test by using at least one of a loss distribution of first backscattered light from a first core or a loss distribution of second backscattered light from a second core, calculates a mode coupling matrix T i at an i-th loss occurrence point of the optical fiber under test, calculates a fiber length L i of an i-th fiber section having a separation at the i-th loss occurrence point of the optical fiber under test, and calculates bidirectional crosstalk in the first core or the second core by using the calculated mode coupling matrix T i and fiber length L i and using a fiber loss factor α and power coupling coefficient h of the optical fiber under test measured in advance.
1 . A device, wherein
the device
detects a loss occurrence point of an optical fiber under test by using at least one of a loss distribution of first backscattered light from a first core included in the optical fiber under test when an optical pulse is injected into one end of the first core or a loss distribution of second backscattered light from a second core adjacent to the first core when an optical pulse is injected into one end of the second core,
calculates a mode coupling matrix T i at an i-th loss occurrence point of the optical fiber under test,
calculates a fiber length L i of an i-th fiber section having a separation at the i-th loss occurrence point of the optical fiber under test, and
calculates bidirectional crosstalk in the first core or the second core by using the calculated mode coupling matrix T i and fiber length L i and using a fiber loss factor α and power coupling coefficient h of the optical fiber under test measured in advance.
2 . The device according to claim 1 , wherein
the device
calculates backscattered light P n(bs) accumulated along an entire fiber length L of the second core, occasioned by injecting signal light into the one end of the first core, by using the mode coupling matrix T i at the i-th loss occurrence point, a mode coupling matrix M i indicating mode coupling in the i-th fiber section, and a matrix B indicating backscattering approximated by constants,
calculates signal light P n(out) output from the one end of the second core, occasioned by injecting signal light into the other end of the second core, and
calculates the bidirectional crosstalk in the second core by calculating a ratio between the backscattered light P n(bs) and the signal light P n(out) .
3 . The device according to claim 2 , wherein
the device
calculates the mode coupling matrix M i indicating the mode coupling in the i-th fiber section of the optical fiber under test by using the calculated fiber length L i and the fiber loss factor α and power coupling coefficient h of the optical fiber under test,
calculates a fiber length from a position of an inlet to a position z of a fiber section k and calculates a mode coupling matrix M k (z) indicating mode coupling from the inlet to the position z of the fiber section k of the optical fiber under test by using the calculated fiber length and the fiber loss factor α and power coupling coefficient h of the optical fiber under test, and
applies the calculated mode coupling matrices T i , M i , and M k (z), the matrix B indicating backscattering approximated by constants, and signal light P in(1) injected into the one end of the first core to the following equations to calculate backscattered light P n(bs) in the second core.
[
Math
.
C1
]
P
n
(
bs
)
=
∫
0
L
P
n
(
z
)
dz
(
C1
)
[
Math
.
C2
]
P
bs
(
1
)
(
z
)
=
[
P
m
(
z
)
P
n
(
z
)
]
T
=
M
1
T
1
M
2
T
2
…
T
k
-
2
M
k
-
1
T
k
-
1
M
k
(
z
)
BP
(
z
)
(
C2
)
[
Math
.
C3
]
P
(
z
)
=
M
k
(
z
)
T
k
-
1
M
k
-
1
T
k
-
2
…
T
2
M
2
T
1
M
1
P
in
(
1
)
.
(
C3
)
4 . The device according to claim 2 , wherein
the device
calculates the mode coupling matrix M i indicating the mode coupling in the i-th fiber section of the optical fiber under test by using the calculated fiber length L i and the fiber loss factor α and power coupling coefficient h of the optical fiber under test, and
applies the calculated mode coupling matrices T i and M i and signal light P in(2) injected into the other end of the second core to the following equation to calculate the signal light P n(out) in the second core.
[
Math
.
C4
]
P
out
=
[
P
m
(
out
)
P
n
(
out
)
]
T
=
M
1
T
1
M
2
T
2
…
T
N
-
2
M
N
-
1
T
N
-
1
M
N
P
in
(
2
)
.
(
C4
)
5 . The device according to claim 1 , wherein
the device
calculates first coupling efficiency η 11 at the i-th loss occurrence point of the optical fiber under test by using the loss distribution of the first backscattered light,
calculates second coupling efficiency η 22 at the i-th loss occurrence point of the optical fiber under test by using the loss distribution of the second backscattered light, and
calculates the mode coupling matrix T i at the i-th loss occurrence point of the optical fiber under test by using the calculated first coupling efficiency η 11 and second coupling efficiency η 22 .
6 . The device according to claim 1 , further comprising:
a test light generation unit for generating the optical pulse; and
a reception unit for receiving the first backscattered light and the second backscattered light.
7 . A method comprising:
measuring first backscattered light from a first core included in an optical fiber under test when an optical pulse is injected into one end of the first core;
measuring second backscattered light from a second core adjacent to the first core when an optical pulse is injected into one end of the second core;
detecting a loss occurrence point of the optical fiber under test by using at least one of a loss distribution of the first backscattered light or a loss distribution of the second backscattered light;
calculating a mode coupling matrix T i at an i-th loss occurrence point of the optical fiber under test;
calculating a fiber length L i of an i-th fiber section having a separation at the i-th loss occurrence point of the optical fiber under test; and
calculating bidirectional crosstalk in the first core or the second core by using the calculated mode coupling matrix T i and fiber length L i and using a fiber loss factor α and power coupling coefficient h of the optical fiber under test measured in advance.
8 . A non-transitory computer-readable storage medium storing a program for being implemented on a computer as the device according to claim 1 .