APPARATUS AND METHOD FOR OBTAINING MODE FIELD DIAMETER OF OPTICAL FIBER
The mode field diameter acquisition device according to the present disclosure is a device for acquiring a mode field diameter of each spatial mode of an optical fiber having a core, through which a plurality of spatial modes can propagate, from a near field pattern, and includes a mode field diameter acquisition unit configured to acquire a mode field diameter of a freely-selected spatial mode using a near field pattern of the spatial mode, and a mathematical expression based on a variational expression of a propagation constant of the spatial mode.
1 . A mode field diameter acquisition device for acquiring a mode field diameter of each spatial mode of an optical fiber having a core, through which a plurality of spatial modes can propagate, from a near field pattern, the mode field diameter acquisition device comprising
a mode field diameter acquisition unit configured to acquire a mode field diameter of a freely-selected spatial mode using a near field pattern of the spatial mode, and a mathematical expression based on a variational expression of a propagation constant for the spatial mode.
2 . The mode field diameter acquisition device according to claim 1 , wherein the mode field diameter acquisition unit calculates a mode field diameter using Expression C1,
[
Math
.
C1
]
M
F
D
v
μ
=
2
2
[
∫
0
∞
ψ
v
μ
2
rdr
∫
0
∞
(
d
ψ
v
μ
/
dr
)
2
rdr
+
v
2
∫
0
∞
(
1
/
r
)
ψ
v
μ
2
dr
]
1
/
2
(
C1
)
where MFD represents a mode field diameter, ν and μ represent mode orders in an azimuthal direction and a radial direction of the spatial mode targeted for acquisition, ψ νμ represents an electric field distribution of the LP νμ mode depending on a radial coordinate, and r represents a coordinate in a radial direction.
3 . The mode field diameter acquisition device according to claim 1 , wherein the mode field diameter acquisition unit calculates a mode field diameter using Expression C2,
[
Math
.
C2
]
M
F
D
v
μ
=
2
2
v
+
2
μ
-
1
[
∫
0
∞
ψ
v
μ
2
rdr
∫
0
∞
(
d
ψ
v
μ
/
dr
)
2
rdr
+
v
2
∫
0
∞
(
1
/
r
)
ψ
v
μ
2
dr
]
1
/
2
(
C2
)
where MFD represents a mode field diameter, ν and μ represent mode orders in an azimuthal direction and a radial direction of the spatial mode targeted for acquisition, ψ νμ represents an electric field distribution of the LP νμ mode depending on a radial coordinate, and r represents a coordinate in a radial direction.
4 . The mode field diameter acquisition device according to claim 2 , wherein the mode field diameter acquisition unit calculates connection loss using Expression C3,
[
Math
.
C3
]
α
v
μ
=
10
ln
(
10
)
d
2
(
M
F
D
v
μ
/
2
)
2
(
C3
)
where d represents an axial deviation amount.
5 . The mode field diameter acquisition device according to claim 3 , wherein the mode field diameter acquisition unit calculates connection loss using Expression C4,
[
Math
.
C4
]
α
v
μ
=
10
ln
(
10
)
(
v
+
2
μ
-
1
)
d
2
(
M
F
D
v
μ
/
2
)
2
(
4
)
where d represents an axial deviation amount.
6 . The mode field diameter acquisition device according to claim 1 , further comprising a near field pattern acquisition unit configured to acquire the near field pattern.
7 . A mode field diameter acquisition method for acquiring a mode field diameter of each spatial mode of an optical fiber having a core, through which a plurality of spatial modes can propagate, from a near field pattern, the mode field diameter acquisition method comprising
a mode field diameter acquisition procedure for acquiring a mode field diameter of a freely-selected spatial mode using a near field pattern of the spatial mode, and a mathematical expression based on a variational expression of a propagation constant of the spatial mode.
8 . A non-transitory storage medium containing a program for implementation on a computer as each functional unit included in the mode field diameter acquisition device according to claim 1 .