Optical module and method for manufacturing optical module
An optical module according to an embodiment includes a first optical component and a second optical component including a multicore fiber (MCF) and a spatial joining part. The first optical component includes a first uncoupled MCF having small optical coupling between cores and a first coupled MCF having a mode field diameter (MFD) larger than a MFD of the first uncoupled MCF. The second optical component includes a second uncoupled MCF having small optical coupling between cores and a second coupled MCF having a MFD larger than a MFD of the second uncoupled MCF. In the first coupled MCF and the second coupled MCF, crosstalk is periodically produced along the length direction of an MCF, and the total of the length of the first coupled MCF and the length of the second coupled MCF is a length L in which crosstalk is suppressed.
1. An optical module comprising:
a first optical component and a second optical component including a multicore fiber (MCF); and
a spatial joining part configured to optically couple the first optical component to the second optical component, wherein
the first optical component includes a first uncoupled MCF and a first coupled MCF, the first uncoupled MCF having small optical coupling between cores, the first coupled MCF being located between the first uncoupled MCF and the spatial joining part, the first coupled MCF having a mode field diameter (MFD) larger than a MFD of the first uncoupled MCF,
the second optical component includes a second uncoupled MCF and a second coupled MCF, the second uncoupled MCF having small optical coupling between cores, the second coupled MCF being located between the second uncoupled MCF and the spatial joining part, the second coupled MCF having an MFD larger than an MFD of the second uncoupled MCF,
in the first coupled MCF and the second coupled MCF, crosstalk is periodically produced along length directions of the MCFs, and
in the spatial joining part in which a large crosstalk is produced from the first coupled MCF, a total of a length of the first coupled MCF and a length of the second coupled MCF is length L in which the crosstalk is suppressed.
2. The optical module according to claim 1 , wherein
a core diameter of the first coupled MCF is larger than a core diameter of the first uncoupled MCF, and
a core diameter of the second coupled MCF is larger than a core diameter of the second uncoupled MCF.
3. The optical module according to claim 2 , wherein at least any one of the first coupled MCF and the second coupled MCF has a core expansion part in which a core diameter is further expanded.
4. The optical module according to claim 3 , wherein the core expansion part is provided at a position apart from the spatial joining part.
5. The optical module according to claim 2 , wherein at least any one of the first coupled MCF and the second coupled MCF has a diameter shrinking part in which an outer diameter is decreased.
6. The optical module according to claim 1 , wherein the first coupled MCF and the second coupled MCF have a diameter shrinking part in which an outer diameter is decreased as apart from the first uncoupled MCF and the second uncoupled MCF.
7. The optical module according to claim 1 , wherein a transmission distance of an MCF that is a seven-core optical fiber is z, coupling of a core mode of a center core of the MCF (coupling from a center core to a center core) is P 00 (z), coupling of a core mode of an outer core of the MCF (coupling of an outer core i to an outer core i) is P ii (z), and a coupling coefficient is k, and then P 00 (z) and P ii (z) are expressed by Expression (1) and Expression (2) below, respectively,
P
00
(
z
)
=
4
7
+
3
7
·
cos
(
2
7
·
k
·
z
)
(
1
)
P
i
i
(
z
)
=
c
4
+
s
4
3
6
+
1
4
+
c
2
s
2
1
8
·
cos
(
2
7
·
k
·
z
)
+
s
2
1
8
·
cos
{
(
3
-
7
)
·
k
·
z
}
+
s
2
9
·
cos
{
(
2
-
7
)
·
k
·
z
}
+
s
2
9
·
cos
(
7
·
k
·
z
)
+
c
2
1
8
·
cos
{
(
3
+
7
)
·
k
·
z
}
+
c
2
9
·
cos
{
(
2
+
7
)
·
k
·
z
}
+
c
2
9
·
cos
(
7
·
k
·
z
)
+
1
9
·
cos
(
3
·
k
·
z
)
+
2
9
·
cos
(
2
·
k
·
z
)
+
1
9
·
cos
(
k
·
z
)
,
and
(
2
)
in Expression (1) and Expression (2), a length L in which the crosstalk is suppressed is a length of the transmission distance z of an MCF in which coupling P 00 (z) of a core mode of a center core of the MCF and coupling P ii (z) of a core mode of an outer core of the MCF are both 0.8 or more.