U.S. patent application number 14/834448 was filed with the patent office on 2016-01-21 for connection structure for multi-core fiber and optical-fiber-bundle structure, connection structure for multi-core fibers, method for exciting rare-earth-doped multi-core fibers, and multi-core-optical-fiber amplifier.
The applicant listed for this patent is FURUKAWA ELECTRIC CO., LTD.. Invention is credited to Katsunori IMAMURA, Koichi MAEDA, Tsunetoshi SAITO, Yukihiro TSUCHIDA, Kengo WATANABE.
Application Number | 20160020573 14/834448 |
Document ID | / |
Family ID | 51428252 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160020573 |
Kind Code |
A1 |
WATANABE; Kengo ; et
al. |
January 21, 2016 |
CONNECTION STRUCTURE FOR MULTI-CORE FIBER AND OPTICAL-FIBER-BUNDLE
STRUCTURE, CONNECTION STRUCTURE FOR MULTI-CORE FIBERS, METHOD FOR
EXCITING RARE-EARTH-DOPED MULTI-CORE FIBERS, AND
MULTI-CORE-OPTICAL-FIBER AMPLIFIER
Abstract
An optical-fiber-bundle structure is connected to one end of a
multi-core fiber. The multi-core fiber has a tapered section formed
therein. The outside diameter of the multi-core fiber and the core
pitch thereof decrease in the tapered section. It is possible for
the multi-core fiber to have an increasing core pitch on the
connection-side thereof which connects to the optical-fiber-bundle
structure; hence, it is possible to use an easy-to-use
large-diameter optical fiber as the optical fiber to be provided in
the optical-fiber-bundle structure. When connecting another
multi-core fiber to the other end of the multi-core fiber, it is
possible to match the outer diameters thereof; hence, when fusion
splicing to one another, it is unlikely for a positional shift of
the cores to occur.
Inventors: |
WATANABE; Kengo; (Tokyo,
JP) ; SAITO; Tsunetoshi; (Tokyo, JP) ;
TSUCHIDA; Yukihiro; (Tokyo, JP) ; MAEDA; Koichi;
(Tokyo, JP) ; IMAMURA; Katsunori; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FURUKAWA ELECTRIC CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
51428252 |
Appl. No.: |
14/834448 |
Filed: |
August 25, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2014/054652 |
Feb 26, 2014 |
|
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14834448 |
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61769375 |
Feb 26, 2013 |
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Current U.S.
Class: |
359/341.3 ;
385/95 |
Current CPC
Class: |
H01S 3/06783 20130101;
G02B 6/2856 20130101; G02B 6/2552 20130101; H01S 3/1608 20130101;
H01S 3/094042 20130101; H01S 3/06745 20130101; H01S 3/06737
20130101; G02B 6/02042 20130101; H01S 3/094003 20130101; G02B 6/40
20130101 |
International
Class: |
H01S 3/067 20060101
H01S003/067; H01S 3/094 20060101 H01S003/094; G02B 6/40 20060101
G02B006/40; G02B 6/255 20060101 G02B006/255 |
Claims
1. A connection structure for a multi-core fiber and an
optical-fiber-bundle structure wherein: the optical-fiber-bundle
structure comprises a plurality of signal light optical fibers that
transmit signal lights that are arranged at predetermined
intervals; the multi-core fiber comprises cores, which are
optically connected to the signal light optical fibers that
transmit signal lights at a first end thereof on the connection
side that is connected with the optical-fiber-bundle structure, and
a cladding having a refractive index lower than that of the cores
and covering the cores; and the multi-core fiber is a tapered fiber
having a tapered section in which the outer diameter thereof
varies, the outer diameter and the core pitch at the first end of
the multi-core fiber being wider than the outer diameter and the
core pitch at a second end of the multi-core fiber, which is on the
opposite side of the connection part that is connected with the
optical-fiber-bundle structure.
2. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 1, wherein: the
multi-core fiber is further connected to a second multi-core fiber;
and the core of the second multi-core fiber is optically connected
with the core of the multi-core fiber.
3. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 2, wherein: the
second end of the multi-core fiber approximately matches with the
outer diameter of an opposing end of the second multi-core fiber;
and the outer diameter of at least one of the second end of the
multi-core fiber and the opposing end of the second multi-core
fiber is reduced by etching without any changes in the core
pitch
4. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 2, wherein: the
optical-fiber-bundle structure further comprises a pump light
optical fiber that transmits pump light; and the second multi-core
fiber is a rare-earth-doped multi-core fiber.
5. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 4, wherein: the
pump light optical fiber that transmits pump light is a multi-mode
fiber and the core of the pump light optical fiber that transmits
pump light is connected to the cladding of the first end of the
multi-core fiber.
6. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 4, wherein: the
pump light optical fiber that transmits pump light is arranged at
the center of the optical-fiber-bundle structure and the signal
light optical fibers that transmit signal lights are arranged on
the outer circumference of the pump light optical fiber that
transmits pump light.
7. The connection structure for a multi-core fiber and an
optical-fiber-bundle structure according to claim 6, wherein: the
diameter of the pump light optical fiber that transmits pump light
is larger than the diameter of the signal light optical fiber that
transmits signal light that transmit signal light.
8. A connection structure for multi-core fibers, wherein: a first
multi-core fiber having a plurality of cores is connected with a
second multi-core fiber having an outer diameter that is different
from that of the first multi-core fiber and a plurality of cores
that are optically connected with the cores of the first multi-core
fiber; at least one of the first multi-core fiber and the second
multi-core fiber has an outer diameter varying section; and the
outer diameters of the end part of the first multi-core fiber on
the connection-side and the end part of the second multi-core fiber
on the connection part are almost equivalent.
9. The connection structure for multi-core fibers according to
claim 8, wherein: the outer diameter varying section is formed by
drawing a multi-core fiber and includes a section in which the core
pitch at the cross-section thereof varies along with the outer
diameter.
10. The connection structure for multi-core fibers according to
claim 8, wherein: the outer diameter varying section is formed by
etching a multi-core fiber and includes a section in which the core
pitch at the cross-section thereof does not vary and only the outer
diameter varies.
11. A method for exciting a rare-earth doped multi-core fiber,
comprising a step of: connecting an optical-fiber-bundle structure
comprising a plurality of signal light optical fibers that transmit
signal lights, which are arranged at a predetermined pitch, and a
pump light optical fiber that transmits pump light; a multi-core
fiber comprising cores, which are optically connected to the signal
light optical fibers that transmit signal lights at a first end
thereof on the connection-side that is connected with the
optical-fiber-bundle structure, and a cladding having a refractive
index lower than that of the cores and covering the cores; and an
rare-earth doped multi-core fiber comprising cores and claddings
that are doped with a rare-earth material, the cores and the
claddings being optically connected to the cores and the claddings
of the multi-core fiber respectively at a second end that is on the
opposite side of the connection part of the multicore fiber and the
optical-fiber-bundle structure, wherein the multi-core fiber is a
tapered fiber having a tapered section in which the outer diameter
thereof varies and the outer diameter and the core pitch at the
first end of the multi-core fiber are wider than the outer diameter
and the core pitch at the second end; the pump light optical fiber
that transmits pump light is a multi-mode fiber and the core of the
pump light optical fiber that transmits pump light is connected to
the cladding of the first end of the multi-core fiber; pump light
is introduced into the pump light optical fiber that transmits pump
light; and the pump light is transmitted through the cladding of
the multi-core fiber, introduced into the cladding of the
rare-earth doped multi-core fiber, and excites a rare-earth
material included in the cores of the rare-earth doped multi-core
fiber.
12. A multi-core-optical-fiber amplifier, comprising: an
optical-fiber-bundle structure comprising a plurality of signal
light optical fibers that transmit signal lights, which are
arranged at a predetermined pitch, and a pump light optical fiber
that transmits pump light; a multi-core fiber comprising cores,
which are optically connected to the signal light optical fibers
that transmit signal lights at a first end thereof on the
connection-side that is connected with the optical-fiber-bundle
structure, and a cladding having a refractive index lower than that
of the cores and covering the cores; an rare-earth doped multi-core
fiber comprising cores and claddings that are doped with a
rare-earth material, the cores and the claddings being optically
connected to the cores and the claddings of the multi-core fiber
respectively at a second end that is on the opposite side of the
connection part of the multicore fiber and the optical-fiber-bundle
structure; and a light source that introduces pump light into the
core of the pump light optical fiber that transmits pump light,
wherein the multi-core fiber is a tapered fiber having a tapered
section in which the outer diameter thereof varies and the outer
diameter and the core pitch at the first end of the multi-core
fiber are wider than the outer diameter and the core pitch at the
second end; and the pump light optical fiber that transmits pump
light is a multi-mode fiber and the core of the pump light optical
fiber that transmits pump light is connected to the cladding of the
first end of the multi-core fiber.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to a connection structure for a
multi-core fiber having a plurality of cores and an
optical-fiber-bundle structure, and a connection structure for
multi-core fibers.
BACKGROUND OF THE INVENTION
[0002] The transmission capacity of single-core optical fibers used
in the present situations is approaching its limit due to the
recent rapid traffic increase in optical communications. As a means
for further expanding the communication capability, a multi-core
fiber, which is a fiber having a plurality of cores formed therein,
has been proposed. Using a multi-core fiber reduces the cost for
laying optical fibers and allows the communication capability to
expand.
[0003] When a multi-core fiber is used as a transmission line,
fan-out, which separates each core of the multi-core fiber into
single-core fibers, is required. To connect such a multi-core fiber
and single-core fibers, there is a method in which optical fibers
are in a close-packed arrangement, forming a bundle structure that
is to be connected with the multi-core fiber (Patent Document
1).
[0004] Also, there is another method in which a plurality of
single-core fibers is bundled to be drawn, integrated, and then
connected to a multi-core fiber (Patent Document 2).
[0005] Also, there is another method in which the diameter of one
end of a multi-core fiber is enlarged and the light is introduced
into the core of the multi-core fiber (Patent Document 3).
RELATED ART
Patent Documents
[0006] [Patent Document 1] WO2012121320A1 [0007] [Patent Document
2] Japanese Patent No. 3415449 [0008] [Patent Document 3] Japanese
Unexamined Patent Application Publication No. 2001-145562
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009] Since manufacturing of an optical-fiber-bundle structure is
easy, such a method proposed in Patent Document 1, in which
single-core fibers having a cladding diameter equivalent to a core
pitch of a multi-core fiber are bundled, has high practicability.
Particularly, a multi-core fiber used for long distance
transmission requires a large core pitch to prevent deterioration
by crosstalk. In this case, it is possible to use single-core
fibers having diameters that correspond to the core pitch of the
multi-core fiber.
[0010] On the other hand, for short-distance transmission such as
in office, it is possible to decrease the core pitch of a
multi-core fiber. Therefore, in view of capacity and handling
properties (allowable bending radius), it is preferable to reduce
the diameter as much as possible. Also, a rare-earth doped
multi-core fiber used as an optical amplifier (erbium doped
multi-core fiber for example) is used in short distances.
Particularly, it is preferable for a cladding-pumped
rare-earth-doped multi-core fiber to reduce the cladding diameter
and the core pitch in view of pump efficiency. This is because, if
the cladding diameter of a rare-earth-doped multi-core fiber is
large, the optical density decreases to the pump light of the
cladding region so to lower the pump efficiency.
[0011] Thus, if the core pitch of a multi-core fiber is decreased
(50 .mu.m or less for example), it is necessary to reduce the
diameters of the corresponding single-core fibers. However, such
small-diameter optical fibers have low rigidity and poor handling
properties. Also, since the cladding thickness is thin, sealing of
light into the core becomes leaky and the transmission loss is
large. Furthermore, the thin cladding thickness is likely to cause
micro-bend loss against external force to occur. Therefore, there
is a limit in reducing the diameter of single-core fibers that form
an optical-fiber-bundle structure.
[0012] However, as in Patent Document 2, with a method in which a
plurality of optical fibers is bundled and then heated and melted
to reduce the diameters, the external form of the bundle structure
is deformed so that deformation of the cores or un-uniformity of
core positions may occur. Therefore, connection loss with a
multi-core fiber may become large.
[0013] In the method described in Patent Document 3, sections in
which the core pitch is wide are made by changing drawing
conditions and the like. However, this method has a problem that it
is not possible to cut and connect at any desired places after
drawing.
[0014] The present invention was achieved in view of such problems.
Its object is to provide a connection method for a multi-core fiber
and an optical-fiber-bundle structure with less transmission loss
and the like.
Means for Solving Problems
[0015] To achieve the above object, a first invention is a
connection structure for a multi-core fiber and an
optical-fiber-bundle structure wherein the optical-fiber-bundle
structure comprises a plurality of signal light optical fibers that
transmit signal lights that are arranged at predetermined
intervals, the multi-core fiber comprises cores, which are
optically connected to the signal light optical fibers that
transmit signal lights at a first end on the connection side that
is connected to the optical-fiber-bundle structure, and a cladding
covering the cores and having a refractive index lower than that of
the cores. The multi-core fiber is a tapered fiber having a tapered
section in which an outer diameter thereof varies. The outer
diameter and the core pitch of the multi-core fiber at the first
end are wider than the outer diameter and the core pitch of the
multi-core fiber at a second end, which is on the opposite side of
the connection part of the optical-fiber-bundle structure.
[0016] The multi-core fiber may be further connected to a second
multi-core fiber and the core of the second multi-core fiber may be
optically connected with the core of the multi-core fiber.
[0017] The second end of the multi-core fiber approximately matches
with the outer diameter of an opposing end of the second multi-core
fiber and the outer diameter of at least one of the second end of
the multi-core fiber and the opposing end of the second multi-core
fiber may be reduced by etching without any changes in the core
pitch
[0018] The optical-fiber-bundle structure may further comprise a
pump light optical fiber that transmits pump light, and the second
multi-core fiber may be a rare-earth-doped multi-core fiber. In
this case, the pump light optical fiber that transmits pump light
is a multi-mode fiber and the core of the pump light optical fiber
that transmits pump light may be connected to the cladding of the
first end of the multi-core fiber.
[0019] The pump light optical fiber that transmits pump light may
be arranged at the center of the optical-fiber-bundle structure and
the signal light optical fibers that transmit signal lights may be
arranged on the outer circumference of the pump light optical fiber
that transmits pump light.
[0020] The diameter of the pump light optical fiber that transmits
pump light may be larger than the diameter of the signal light
optical fiber that transmits signal light.
[0021] According to the first invention, since the multi-core fiber
is a tapered fiber in which the outer diameter and the core pitch
vary, the core pitch on the side of connection part that is
connected with the optical-fiber-bundle structure can be increased.
Therefore, it is possible to increase the outer diameter of the
signal light optical fiber that transmits signal light which is
connected with the multi-core fiber. Therefore, the handling
properties of the signal light optical fibers that transmit signal
lights are excellent and the optical transmission loss can be
suppressed.
[0022] Also, by further connecting with a second multi-core fiber,
a desired optical connection between a multi-core fiber and an
optical-fiber-bundle structure can be established with a multi-core
fiber for pitch conversion.
[0023] Also, matching the outer diameters at the connection part
between the multi-core fiber for pitch conversion and the second
multi-core fiber can suppress position shifting of the cores at the
time of fusion splicing. On this occasion, it is possible to match
both outer diameters easily by reducing the diameter of at least
one end of the multi-core fiber for pitch conversion and the other
multi-core fiber by etching.
[0024] Also, if the optical-fiber-bundle structure includes the
pump light optical fiber that transmits pump light and the second
multi-core fiber is a rare-earth doped multi-core fiber, the
optical-fiber-bundle structure and the rare-earth doped multi-core
fiber can be connected by the multi-core fiber for pitch
conversion. On this occasion, it is not necessary to excessively
decrease each fiber-diameter of the optical-fiber-bundle structure,
and it is also unnecessary to excessively increase the diameter of
the rare-earth doped multi-core fiber.
[0025] Also, arranging the pump light optical fiber that transmits
pump light at the center of the optical-fiber-bundle structure
makes it possible for the pump light to be introduced into the
center of the rare-earth doped multi-core fiber. On this occasion,
since it is possible to use a larger pump light optical fiber that
transmits pump light by making the outer diameter of the pump light
optical fiber that transmits pump light larger than the outer
diameter of the signal light optical fiber that transmits signal
light, large output of pump light can be introduced into the
rare-earth doped multi-core fiber.
[0026] A second invention is a connection structure for multi-core
fibers, wherein a first multi-core fiber having a plurality of
cores is connected with a second multi-core fiber having an outer
diameter that is different from that of the first multi-core fiber
and a plurality of cores that are optically connected with the
cores of the first multi-core fiber. At least one of the first
multi-core fiber and the second multi-core fiber has an outer
diameter varying section, and the outer diameters of the end part
of the first multi-core fiber on the connection-side and the end
part of the second multi-core fiber on the connection part are
almost equivalent.
[0027] The outer diameter varying section is formed by drawing a
multi-core fiber and may include a section in which the core pitch
at the cross-section varies along with the outer diameter.
[0028] The outer diameter varying section is formed by etching a
multi-core fiber and may include a section in which the core pitch
at the cross-section does not vary and only the outer diameter
varies.
[0029] According to the second invention, it is possible to
efficiently connect multi-core fibers having different outer
diameters.
[0030] On this occasion, forming the outer diameter varying section
by drawing at least one of the multi-core fibers can vary the core
pitch. Also, if the outer diameter varying section is formed by
etching, only the outer diameter can be varied without varying the
core pitch.
[0031] A third invention is a method for exciting a multi-core
fiber, comprising a step of connecting an optical-fiber-bundle
structure, a multi-core fiber, and a rare-earth doped multi-core
fiber. The optical-fiber-bundle structure comprises a plurality of
signal light optical fibers that transmit signal lights, which are
arranged at a predetermined pitch, and a pump light optical fiber
that transmits pump light. The multi-core fiber comprises cores,
which are optically connected to the signal light optical fibers
that transmit signal lights at a first end thereof on the
connection-side that is connected with the optical-fiber-bundle
structure, and a cladding having a refractive index lower than that
of the cores and covering the cores. The rare-earth doped
multi-core fiber comprises cores, which are optically connected to
the cores of the multi-core fiber at a second end that is on the
opposite side of the connection part of the multicore fiber and the
optical-fiber-bundle structure, and a cladding having a refractive
index lower than that of the cores and covering the cores. The
multi-core fiber is a tapered fiber having a tapered section in
which the outer diameter thereof varies and the outer diameter and
the core pitch at the first end of the multi-core fiber are wider
than the outer diameter and the core pitch at the second end. The
pump light optical fiber that transmits pump light is a multi-mode
fiber and the core of the pump light optical fiber that transmits
pump light is connected to the cladding of the first end of the
multi-core fiber.
[0032] A fourth invention is a multi-core amplifier, comprising an
optical-fiber-bundle structure, a multi-core fiber, and a
rare-earth doped multi-core fiber. The optical-fiber-bundle
structure comprises a plurality of signal light optical fibers that
transmit signal lights, which are arranged at a predetermined
pitch, and a pump light optical fiber that transmits pump light.
The multi-core fiber comprises cores, which are optically connected
to the signal light optical fibers that transmit signal lights at a
first end thereof on the connection-side that is connected with the
optical-fiber-bundle structure, and a cladding having a refractive
index lower than that of the cores and covering the cores. The
rare-earth doped multi-core fiber comprises cores, which are
optically connected to the cores of the multi-core fiber at a
second end that is on the opposite side of the connection part of
the multicore fiber and the optical-fiber-bundle structure, and a
cladding having a refractive index lower than that of the cores and
covering the cores. The multi-core fiber is a tapered fiber having
a tapered section in which the outer diameter thereof varies and
the outer diameter and the core pitch at the first end of the
multi-core fiber are wider than the outer diameter and the core
pitch at the second end. The pump light optical fiber that
transmits pump light is a multi-mode fiber and the core of the pump
light optical fiber that transmits pump light is connected to the
cladding of the first end of the multi-core fiber.
[0033] According to the third and the fourth inventions, it is
possible to efficiently amplify signal light in multi-core
fibers.
Effects of the Invention
[0034] The present invention can provide a connection method for a
multi-core fiber and an optical-fiber-bundle structure with less
transmission loss and the like.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 shows a connection structure for an optical fiber
1.
[0036] FIG. 2(a) shows a cross-sectional view of A-A line of the
connection structure for an optical fiber 1 in FIG. 1.
[0037] FIG. 2(b) shows a cross-sectional view of B-B line of the
connection structure for an optical fiber 1 in FIG. 1.
[0038] FIG. 3(a) shows a cross-sectional view of C-C line of the
connection structure for an optical fiber 1 in FIG. 1.
[0039] FIG. 3(b) shows a cross-sectional view of D-D line of the
connection structure for an optical fiber 1 in FIG. 1.
[0040] FIG. 4(a) shows a cross-sectional view of E-E line of the
connection structure for an optical fiber 1 in FIG. 1.
[0041] FIG. 4(b) shows a cross-sectional view of F-F line of the
connection structure for an optical fiber 1 in FIG. 1.
[0042] FIG. 5(a) to FIG. 5(c) show a forming process of a tapered
section.
[0043] FIG. 6(a) to FIG. 6(c) show a connection process of the
tapered section and a capillary 21c.
[0044] FIG. 7 shows a connection structure for an optical fiber
1a.
[0045] FIG. 8(a) shows a cross-sectional view of G-G line of the
connection structure for an optical fiber 1a in FIG. 7.
[0046] FIG. 8(b) shows a cross-sectional view of H-H line of the
connection structure for an optical fiber 1a in FIG. 7.
[0047] FIG. 9 shows a connection structure for an optical fiber
1b.
[0048] FIG. 10 shows a connection structure for an optical fiber
1c.
[0049] FIG. 11(a) shows a cross-sectional view of I-I line of the
connection structure for an optical fiber 1c in FIG. 10.
[0050] FIG. 11(b) shows a cross-sectional view of J-J line of the
connection structure for an optical fiber 1c in FIG. 10.
[0051] FIG. 12(a) shows a cross-sectional view of M-M line of the
connection structure for an optical fiber 1c in FIG. 10.
[0052] FIG. 12(b) shows a cross-sectional view of N-N line of the
connection structure for an optical fiber 1c in FIG. 10.
[0053] FIG. 13 shows a connection structure for an optical fiber
1d.
[0054] FIG. 14(a) shows a cross-sectional view of O-O line of the
connection structure for an optical fiber 1d in FIG. 13.
[0055] FIG. 14(b) shows a cross-sectional view of P-P line of the
connection structure for an optical fiber 1d in FIG. 13.
[0056] FIG. 15(a) shows a cross-sectional view of Q-Q line of the
connection structure for an optical fiber 1d in FIG. 13.
[0057] FIG. 15(b) shows a cross-sectional view of R-R line of the
connection structure for an optical fiber 1d in FIG. 13.
[0058] FIG. 16(a) shows a cross-sectional view of S-S line of the
connection structure for an optical fiber 1d in FIG. 13.
[0059] FIG. 16(b) shows a cross-sectional view of T-T line of the
connection structure for an optical fiber 1d in FIG. 13.
[0060] FIG. 17(a) shows a cross-sectional view of a bundle
structure 5c.
[0061] FIG. 17(b) shows a cross-sectional view of a bundle
structure 5d.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0062] Hereinafter, a connection structure for an optical fiber 1
will be described with reference to the accompanying drawings. FIG.
1 shows the connection structure for an optical fiber 1, FIG. 2(a)
is a cross-sectional view of A-A line in FIG. 1, FIG. 2(b) is a
cross-sectional view of B-B line in FIG. 1, FIG. 3(a) is a
cross-sectional view of C-C line in FIG. 1, FIG. 3(b) is a
cross-sectional view of D-D line in FIG. 1, FIG. 4(a) is a
cross-sectional view of E-E line in FIG. 1, and FIG. 4(b) is a
cross-sectional view of F-F line in FIG. 1.
[0063] The connection structure for an optical fiber 1 is a
connection structure of a bundle structure 5 and multi-core fibers
3a, 3b. The multi-core fibers 3a, 3b and an optical fiber 7a are
made of, for example, quartz glass.
[0064] The bundle structure 5 comprises optical fibers 7a that are
bundled. The optical fibers 7a are signal light optical fibers that
transmit signal lights. The optical fibers 7a are preferably
single-mode optical fibers that are appropriate for long distance
transmission and, in this case, the signal light is, for example,
single mode at 1550 nm band.
[0065] As shown in FIG. 2(a), the bundle structure 5 has a
plurality of optical fibers 7a assembled together in a close-packed
arrangement. That is, one optical fiber 7a is arranged at the
center with six optical fibers 7a arranged on the circumference
thereof. Therefore, all cores 15a of each of the optical fibers 7a
are arranged at equal intervals. Hereinafter, unless specified,
each of the optical fibers 7a has a fixed outer diameter from one
end of the bundle structure 5 to the outside of the other end of
the bundle structure 5. The outer diameters of optical fibers 7a
may be bundled after being adjusted by chemical etching using
hydrofluoric acid and the like, drawing by heating and melting, or
the like.
[0066] Although the example in the drawing shows an example having
the seven optical fibers 7a, the present invention is not limited
thereto. It is only necessary that the number of optical fibers 7a
is six or more and the close-packed arrangement is possible. For
example, the outer diameter of the optical fiber 7a in the center
may be larger than the outer diameter of the optical fiber 7a on
the outer circumference side. In this case, it is necessary that
the optical fiber in the center is in contact with all the optical
fibers on the outer circumference and the adjacent optical fibers
on the outer circumference are arranged to be in contact with each
other without any gaps. Using the dense bundle structure as above
facilitates the optical connection with a plurality of cores of the
multi-core fiber 3a.
[0067] The optical fibers 7a are arranged inside a capillary 21b.
The optical fibers 7a and the capillary 21b are bonded with resin
19. The capillary 21b is made of a material having a refractive
index lower than the refractive index of the material forming the
resin 19. The resin 19 is made of a material having a refractive
index lower than the refractive index of the material forming a
cladding 17a of the optical fiber 7a.
[0068] The bundle structure 5 is connected to one end of the
multi-core fiber 3a. The end face of the multi-core fiber 3a and
the end face of the bundle structure 5 are both grounded and
arranged to be facing each other. On this occasion, each of the
cores 15a and the cores 22a face each other at the positions in
which each of the cores 15a and the cores 22a are optically
connected. The multi-core fiber 3a and the bundle structure 5 are
connected by bonding or fusion splicing. Also, the capillary 21a,
21b are bonded. The multi-core fiber 3a is, for example, a
single-mode fiber, and has a tapered section 27 which is an
outer-diameter varying section formed on a part thereof.
[0069] As shown in FIG. 2(b), the end part of the multi-core fiber
3a on the connection-side connected to the bundle structure 5 (the
one end) is inserted into the capillary 21a and fixed with the
resin 19. The capillary 21a is made of a material having a
refractive index lower than the refractive index of the material
forming the resin 19. The resin 19 is made of a material having a
refractive index lower than the refractive index of the material of
a cladding 23a of the multi-core fiber 3a.
[0070] Also, the outer diameter of the cladding 23a is
approximately equivalent to or slightly larger than a circle
circumscribing the optical fibers 7a that configure the bundle
structure 5. The cores 22a of the multi-core fiber 3a are arranged
in the positions and at the pitch that correspond to the cores 15a
of the bundle structure 5 (the optical fibers 7a), and the cores
15a and the cores 22a are optically connected. That is, the seven
cores 22a in total are arranged at the center of the multi-core
fiber 3a and at each vertex of a hexagon surrounding it. In this
case, all the distances between the core 22a at the center and each
of the six surrounding cores 22a are the same. Also, for the six
cores 22a, the distances between each of the adjacent cores 22a are
the same.
[0071] For example, the core pitch of the cores 22a of the
multi-core fiber 3a is 50 .mu.m, and, in this case, the cladding
diameter of the optical fiber 7a forming the bundle structure 5 is
50 .mu.m.
[0072] As shown in FIG. 3(a), a resin-coating layer 25 is provided
on the outer circumference of the part of the multi-core fiber 3a
that is exposed outside the capillary 21a. The resin forming the
resin-coating layer 25 is made of a material having a refractive
index lower than the refractive index of the material forming the
cladding 23a of the multi-core fiber 3a.
[0073] In FIG. 3(a), the pitch of the cores 22a is P1 and the outer
diameter of the cladding 23a is D1. P1 is almost equal to the outer
diameter of the optical fiber 7a.
[0074] As shown in FIG. 3(b), the outer diameter and the core pitch
of the multi-core fiber 3a decrease in the tapered section 27. That
is, the multi-core fiber 3a is reduced in the diameter at the
vicinity of the end which is opposite to the connection-side of the
bundle structure 5 of the multi-core fiber 3a (the other end).
Therefore, in the tapered section, a core pitch P2 is smaller than
P1, and a cladding diameter D2 is smaller than D1. Since the
thickness of the resin-coating layer 25 increases in the tapered
section 27, the overall outer diameter including the resin-coating
layer 25 remains substantially constant.
[0075] As shown in FIG. 4(a), the other end of the multi-core fiber
3a is inserted into the capillary 21c and fixed with the resin 19.
The capillary 21c is made of a material having a refractive index
lower than the refractive index of the material forming the resin
19. The resin 19 is made of a material having a refractive index
lower than the refractive index of the material forming a cladding
23a of the multi-core fiber 3a. A core pitch P3 at the other end of
the multi-core fiber 3a is further smaller than P2, and an outer
diameter D3 is further smaller than D2.
[0076] Although the illustrated example shows the tapered section
27 being inserted into the capillary 21c at the middle of the
tapered section, the entire tapered section 27 may be inserted into
the capillary 21c, or only the tip side of the tapered section 27
(reduced diameter side) may be inserted into the capillary 21c.
Also, although the illustrated example shows that the inner
diameter of the capillary 21c is set between the maximum outer
diameter part (D1) and the minimum outer diameter part (D3) of the
multi-core fiber 3a (the outer diameters at the both ends of the
tapered section 27 respectively), the inner diameter of the
capillary 21c may be larger than D1.
[0077] The multi-core fiber 3a is, for example, fusion spliced with
another multi-core fiber 3a. The multi-core fiber 3b is, for
example, a single-mode fiber. As shown in FIG. 4(b), the end part
of the multi-core fiber 3b on the connection-side with the
multi-core fiber 3a is inserted into a capillary 21d and fixed with
the resin 19. The capillary 21d is made of a material having a
refractive index lower than the refractive index of the material
forming the resin 19. The resin 19 is made of a material having a
refractive index lower than the refractive index of the material
forming a cladding 23b of the multi-core fiber 3b.
[0078] The core pitch P3 of the other end of the multi-core fiber
3a is equivalent to a core pitch P4 of the multi-core fiber 3b. For
example, the core pitch P4 is 50 .mu.m or less. If P4 is 45 .mu.m,
for example, the core pitch at the one end of the multi-core fiber
3a is 50 .mu.m and the core pitch at the other end can be 45
.mu.m.
[0079] An outer diameter of the cladding 23b (D4) is approximately
equivalent to the outer diameter of the cladding 23a (D3) or
slightly larger than the outer diameter of the cladding 23a (D3).
That is, D3.ltoreq.D4. Also, the cores 22b of the multi-core fiber
3b are arranged in the positions corresponding to the cores 22a of
the multi-core fiber 3a. Therefore, the cores 22a and the cores 22b
are optically connected.
[0080] Thus, the core pitch can be changed by using the multi-core
fiber 3a, which is a tapered fiber. That is, the multi-core fiber
3a can be used as a pitch-changing multi-core fiber. Therefore, it
is possible to make the core pitch and the outer diameter of the
bundle structure 5 larger than the core pitch and the outer
diameter of the multi-core fiber 3b.
[0081] Next, a manufacturing method for a tapered fiber will be
described. As shown in FIG. 5(a), the multi-core fiber 3a having
the resin-coating layer 25 on the outer circumference thereof is
used. First, as shown in FIG. 5(b), a predetermined range of the
resin-coating layer 25 from the end part of the multi-core fiber 3a
is peeled off. Next, as shown in FIG. 5(c), the part in which the
resin-coating layer 25 is peeled off is heated and melted to be
drawn. The tapered section 27 is then formed in this way.
[0082] Next, as shown in FIG. 6(a), the outer circumference of the
multi-core fiber 3a, including the tapered section 27, is coated by
resin to form the resin-coating layer 25 once again. As above, a
tapered fiber is formed. Furthermore, as shown in FIG. 6(b), a part
of the resin-coating layer 25 from the end part of the multi-core
fiber 3a to the middle of the tapered section 27 is peeled off. In
this state, as shown in FIG. 6(c), the end part of the multi-core
fiber 3a in which the resin-coating layer 25 is peeled off is
inserted into the capillary 21c and fixed with the resin 19.
Furthermore, grinding the end face of the capillary 21c allows a
connection with the multi-core fiber 3b.
[0083] As described above, according to the present embodiment, it
is possible to easily connect the bundle structure having a
relatively wide core pitch with the multi-core fiber 3b having a
relatively narrow core pitch.
[0084] The multi-core fiber 3a has different mode-field diameters
at the one end and the other end. Also, in this case, it is
preferable to approximately match the mode-field diameter of the
one end of the multi-core fiber 3a and the mode-field diameter of
the optical fiber 7a. Also, it is preferable to approximately match
the mode-field diameter of the other end of the multi-core fiber 3a
and the mode-field diameter of the end part of the multi-core fiber
3b. This can solve the increase in the transmission loss caused by
the mismatching of mode-field diameters at each connection
part.
[0085] Although the multi-core fiber 3b and the bundle structure 5
are connected through the medium of multi-core fiber 3a in this
embodiment, the multi-core fiber 3a and the multi-core fiber 3b may
be integrated. That is, the object of the present invention can be
achieved by connecting the bundle structure 5 with a multi-core
fiber with varying core pitch.
Second Embodiment
[0086] Next, a second embodiment will be described. FIG. 7 shows a
connecting structure for an optical fiber 1a, and FIG. 8(a) is a
cross-sectional view of G-G line in FIG. 7 and FIG. 8(b) is a
cross-sectional view of H-H line in FIG. 7. For the embodiments
below, the same notations will be used for the components
performing the same functions as in the connection structure for an
optical fiber 1, and redundant explanations will be omitted.
[0087] The connection structure for an optical fiber 1a has a
configuration that is almost the same as that of the connection
structure for an optical fiber 1 except that a diameter-reduction
section 29, which is an outer diameter varying section, is formed
at the tip part of a multi-core fiber 3a. The diameter-reduction
section 29 can be formed by chemical etching using fluoric acid and
the like.
[0088] The core pitch and the cladding diameter of the multi-core
fiber 3a are changed by the tapered section 27. As shown in FIG.
8(a), the core pitch is P5 and the cladding diameter is D5 after
diameter reduction. Also, as shown in FIG. 8(b), the core pitch at
the diameter-reduction section 29 is P6 and the cladding diameter
is D6. In this case, the core pitch P5 and P6 are equivalent, but
the cladding diameter D6 is smaller than the cladding diameter D5.
That is, only the outer diameter becomes smaller at the
diameter-reduction section 29 while the core pitch remains the
same.
[0089] Here, it is preferable that the cladding diameter at the end
part of the multi-core fiber 3a is smaller than the cladding
diameter of the multi-core fiber 3b. For example, if D5>D6, only
the outer diameter of the end part of the multi-core fiber 3a is
reduced so that D5<D6. It is not likely for the position
shifting between cores at the time of fusion splicing to occur if
the cladding diameter of the end part of the multi-core fiber 3a
matches the cladding diameter of the multi-core fiber 3b. That is,
the diameter-reduction section 29 can match the cladding diameter
of the end part of the multi-core fiber 3a with the cladding
diameter of the multi-core fiber 3b.
[0090] The diameter-reduction section 29 may be formed at the end
part of the multi-core fiber 3b as in a connection structure for an
optical fiber 1b shown in FIG. 9. Also, although drawing is
omitted, the diameter-reduction section 29 may be formed at the
both end parts of the multi-core fiber 3a, 3b. Thus, using the
diameter-reduction section 29 allows multi-core fibers with
different outer diameters to easily connect with each other. For
example, the tapered section 27 is formed by drawing process to
match the core pitch, and with the matched core pitch, the
diameter-reduction section 29 may be formed by etching at the end
part of the multi-core fiber on the side with a larger cladding
diameter.
[0091] Thus, according to the second embodiment, it is possible to
easily connect multi-core fibers having different outer diameters
with each other. On this occasion, by matching the outer diameters,
it is unlikely for deformation or misalignment of axis of the cores
to occur at the time of fusion splicing. Although the bundle
structure 5 is connected with the multi-core fibers 3a, 3b in the
illustrated example, the use of the diameter-reduction section 29
and the tapered section 27 makes it effective for connecting
multi-core fibers without the bundle structure 5.
Third Embodiment
[0092] Next, a third embodiment will be described. FIG. 10 shows a
connecting structure for an optical fiber 1c, and FIG. 11(a) is a
cross-sectional view of I-I line in FIG. 10, FIG. 11(b) is a
cross-sectional view of J-J line in FIG. 10, FIG. 12(a) is a
cross-sectional view of M-M line in FIG. 10, and FIG. 12(b) is a
cross-sectional view of N-N line in FIG. 10.
[0093] The connection structure for an optical fiber 1c has a
configuration that is almost the same as that of the connection
structure for an optical fiber 1 except that the bundle structure
5a is used therein. In addition to the optical fibers 7a, the
bundle structure 5a further includes an optical fiber 7b bundled.
The optical fiber 7b is a pump light optical fiber that transmits
pump light introduction. Hereinafter, unless specified, each
optical fiber 7b has a fixed diameter from an end face of the
bundle structure 5 to the outside of the bundle structure 5 on the
side of the other end.
[0094] A light source 8 for pump light is connected to the optical
fiber 7b. The light source 8 is, for example, a multi-mode pump
light emitter with a wavelength of 980 nm. Although the optical
fiber 7b may be a single-mode or multi-mode optical fiber, a
multi-mode optical fiber is preferable because the core diameter
can be increased for high power. In this case, the pump light is,
for example, multi-mode light in the wavelength band of 980 nm.
[0095] In the bundle structure 5a, the optical fibers 7a are in a
close-packed arrangement, and the optical fiber 7b is further
arranged on the outer circumference thereof. The outer diameter of
the optical fiber 7b is larger than the outer diameter of the
optical fiber 7a. The optical fiber 7b comprises a core 15b and a
cladding 17b. The diameter of the core 15b of the optical fiber 7b
is larger than the diameter of the core 15a of the optical fiber
7a. In this way, light with more power can be introduced.
[0096] The bundle structure 5a is spliced with one end part of the
multi-core fiber 3a. The outer diameter of the cladding 23a of the
multi-core fiber 3a is approximately equivalent to or slightly
larger than a circle circumscribing the optical fibers 7a, 7b that
configure the bundle structure 5a. The core 15b of the optical
fiber 7b corresponds to the position of the cladding 23a of the
multi-core fiber 3a. That is, as shown in FIG. 11(b), a pump light
introduction section 31 is positioned in the cladding 23a.
[0097] If the core pitch of the multi-core fiber 3a is 50 .mu.m and
the cladding thickness (the distance from the outermost core to the
cladding surface) is 75 .mu.m, the outer diameter of the optical
fiber 7b can be increased up to 62 .mu.m. Furthermore, if the core
15b of the optical fiber 7b is made to be included in the cladding
23a of the multi-core fiber 3a, then the outer diameter of the
optical fiber 7b can be increased up to 73 .mu.m.
[0098] A tapered fiber may also be used as the optical fiber 7b.
For example, a step index multi-mode optical fiber with a core
diameter of 105 .mu.m and cladding diameter of 125 .mu.m can be
used as the optical fiber 7b before taper processing and the outer
diameter at the connection part with the multi-core fiber 3a may be
drawn processed by heating and melting or the like to correspond to
the multi-core fiber 3a.
[0099] The pump light is confined in the cladding 23a by the resin
19. Since the resin-coating layer 25 is provided on the part of the
multi-core fiber 3a that is exposed out of the capillary 21a, the
pump light is confined in the cladding 23a.
[0100] FIG. 12(a) is an end part of the multi-core fiber 3a and
FIG. 12(b) is an end part of the multi-core fiber 3b. In the
present embodiment, the multi-core fiber 3b is a rare-earth doped
multi-core fiber. The rare-earth doped multi-core fiber is, for
example, an erbium-doped multi-core fiber (EDF).
[0101] The claddings 23a, 23b of the multi-core fibers 3a, 3b are
optically connected. Therefore, the pump light introduced into the
cladding 23a of the multi-core fiber 3a is transmitted through the
cladding 23a of the multi-core fiber 3a and then introduced into
the cladding 23b of the multi-core fiber 3b. Introducing the pump
light into the multi-core fiber 3b can excite an rare-earth element
included in the core 22b, which is doped by a rare-earth material
such as erbium, of the multi-core fiber 3b and amplify the signal
light inside the core 22b. That is, the pump light can bring the
energy level of the erbium ions in the core 22b to an excited
state. By introducing the signal light into the core 22b in this
state, stimulated emission of the excited erbium ions occurs and
the intensity of the signal light is amplified.
[0102] The diameter-reduction section 29 may also be formed in the
present embodiment on an end part of either the multi-core fiber 3a
or 3b.
[0103] As described above, according to the third embodiment, the
multi-core fiber 3b can perform optical amplification. On this
occasion, since it is possible to decrease the cladding diameter of
the multi-core fiber 3b, pump efficiency is excellent. Thus, an
efficient multi-core-optical-fiber amplifier can be formed
according to the present embodiment.
[0104] Also, the core pitch of the bundle structure 5a that is
connected with the multi-core fiber 3b can be wider than the core
pitch of the multi-core fiber 3b. Therefore, the outer diameter of
the optical fiber 7a can be larger than the core pitch of the
multi-core fiber 3b. Therefore, a connection structure for an
optical fiber that is excellent in handling properties and has
small optical transmission loss can be obtained.
Fourth Embodiment
[0105] Next, a fourth embodiment will be described. FIG. 13 shows a
connecting structure for an optical fiber 1d, and FIG. 14(a) is a
cross-sectional view of O-O line in FIG. 13, FIG. 14(b) is a
cross-sectional view of P-P line in FIG. 13, FIG. 15(a) is a
cross-sectional view of Q-Q line in FIG. 13, FIG. 15(b) is a
cross-sectional view of R-R line in FIG. 13, FIG. 16(a) is a
cross-sectional view of S-S line in FIG. 13, and FIG. 16(b) is a
cross-sectional view of T-T line in FIG. 13.
[0106] The connection structure for an optical fiber 1d has a
configuration that is almost the same as that of the connection
structure for an optical fiber 1c except that a bundle structure 5b
is used therein. As shown in FIG. 14(a), the bundle structure 5b
has an optical fiber 7b arranged at the center. The optical fiber
7b is connected with the light source 8, which is omitted in the
drawing. Also, the cladding diameter of the optical fiber 7b is
larger than the cladding diameter of the optical fiber 7a. The
optical fibers 7a are arranged close-packed on the outer
circumference of the optical fiber 7b.
[0107] In the example shown in the drawing, ten optical fibers 7a
are arranged close-packed on the outer circumference of the optical
fiber 7b. In the present invention, as shown in FIG. 14(a), the
close-packed arrangement is an arrangement in which the optical
fibers 7a are positioned at predetermined intervals so to be in
contact with each other.
[0108] The bundle structure 5b is fusion spliced with the one end
of the multi-core fiber 3a. As shown in FIG. 14(b), the outer
diameter of the cladding 23a of the multi-core fiber 3a is
approximately equivalent to or slightly larger than the circle
circumscribing the optical fibers 7a that configure the bundle
structure 5b. The core 15b of the optical fiber 7b corresponds to
the approximately center position of the cladding 23a of the
multi-core fiber 3a. That is, the pump light introduction section
31 is positioned at the approximately center of the cladding 23a.
The pump light introduced into the cladding 23a is confined inside
the cladding 23a by the resin 19.
[0109] As shown in FIG. 15(a) and FIG. 15(b), the resin-coating
layer 25 is provided on the outer circumference of the multi-core
fiber 3a that is exposed out of the capillary 21a. Thus, since the
part of the multi-core fiber 3a that is exposed out of the
capillary 21a is provided with the resin-coating layer 25 on the
outer circumference, the pump light is transmitted being confined
in the cladding 23a.
[0110] FIG. 16(a) shows an end part of the multi-core fiber 3a and
FIG. 16(b) shows an end part of the multi-core fiber 3b. Also, in
the present embodiment, the multi-core fiber 3b is a rare-earth
doped multi-core fiber.
[0111] The claddings 23a, 23b of the multi-core fibers 3a, 3b are
optically connected. Therefore, the pump light is introduced into
the cladding 23a of the multi-core fiber 3a. Therefore, by
introducing the signal light into the core 22b, stimulated emission
of the excited erbium ions occurs and the intensity of the signal
light is amplified.
[0112] The diameter-reduction section 29 may also be formed in the
present embodiment on an end part of either of the multi-core fiber
3a and 3b.
[0113] According to the fourth embodiment, the same effects as the
third embodiment can be obtained. Also, since the pump light is
introduced to the approximately center of the cladding 23a, it is
possible to introduce the pump light almost uniformly to each of
the cores 22b.
[0114] A bundle structure 5c as shown in FIG. 17(a) may also be
used as another bundle structure having the optical fiber 7b
arranged at the center thereof. The bundle structure 5c includes
the optical fibers 7a, 7b having approximately the same diameters.
Therefore, six signal light introduction fibers are arranged on the
outer circumference of the pump light introduction fiber at the
center.
[0115] Also, a bundle structure 5d as shown in FIG. 17(b) may be
used. The bundle structure 5d includes eight optical fibers 7a
arranged close-packed on the outer circumference of the optical
fiber 7b. Thus, in the present invention, it is required that the
outer diameter of the optical fiber 7b is equal to or larger than
the diameter of the optical fiber 7a and the optical fibers 7a are
arranged close-packed without any gaps.
[0116] Although the embodiments of the present invention have been
described referring to the attached drawings, the technical scope
of the present invention is not limited to the embodiments
described above. It is obvious that persons skilled in the art can
think out various examples of changes or modifications within the
scope of the technical idea disclosed in the claims, and it will be
understood that they naturally belong to the technical scope of the
present invention.
DESCRIPTION OF NOTATIONS
[0117] 1, 1a, 1b, 1c, 1d . . . connection structure for optical
fiber [0118] 3a, 3b . . . multi-core fiber [0119] 5, 5a, 5b, 5c, 5d
. . . optical-fiber-bundle structure [0120] 7a, 7b . . . optical
fiber [0121] 8 . . . light source [0122] 15a, 15b . . . core [0123]
17a, 17b . . . cladding [0124] 19 . . . resin [0125] 21a, 21b, 21c,
21d . . . capillary [0126] 22a, 22b . . . core [0127] 23a, 23b . .
. cladding [0128] 25 . . . resin-coating layer [0129] 27 . . .
tapered section [0130] 29 . . . diameter-reduction section [0131]
31 . . . pump light introduction section
* * * * *