Optical connection structure and method for manufacturing optical connection structure

Abstract

In an optical connection structure 1, a first lens and a second lens are arranged in order from a first optical fiber assembly toward a second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly. At a first end surface, an axis passing through the center of gravity of at least one first fiber core is displaced in the vertical section direction of the at least one first fiber core with respect to the optical axis of the first lens.

Description

Optical connection structure and method for manufacturing the optical connection structure

[0001] The present disclosure relates to an optical connection structure and a method for manufacturing an optical connection structure. This application claims priority to Japanese Patent Application No. 2023-109871 filed on July 4, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] An optical connection structure for optically coupling a pair of optical fiber assemblies is known. The optical fiber assemblies include optical fibers. For example, Patent Documents 1 and 2 disclose optical connection structures in which a pair of lenses are arranged between the pair of optical fiber assemblies. The pair of optical fiber assemblies are optically coupled by the pair of lenses.

[0003] JP 2016-109887 A JP 2013-065002 A

[0004] An optical connection structure according to one aspect of the present disclosure includes a first optical fiber assembly, a second optical fiber assembly, a first lens, and a second lens. The first optical fiber assembly includes at least one first fiber core. The first optical fiber assembly has a first end face. The at least one first fiber core is exposed from the first end face. The second optical fiber assembly includes at least one second fiber core. The second optical fiber assembly has a second end face. The at least one second fiber core is exposed from the second end face and is optically coupled to the first end face. The first lens and the second lens are arranged in order from the first optical fiber assembly to the second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly. At the first end face, an axis passing through the center of gravity of the at least one first fiber core is offset from the optical axis of the first lens in a direction along a vertical cross section of the at least one first fiber core.

[0005] FIG. 1 is a cross-sectional view taken along the optical axis direction of an optical connection structure according to an embodiment. FIG. 2 is a schematic view showing the structure of an optical fiber assembly. FIG. 3 is a view showing an end face of an optical fiber. FIG. 4 is a schematic view for explaining the structure of an optical connection structure. FIG. 5 is a schematic view for explaining the structure of an optical connection structure. FIG. 6 is a cross-sectional view taken along the optical axis direction of an optical connection structure according to a modified example of this embodiment. FIG. 7 is a cross-sectional view taken along the optical axis direction of an optical connection structure according to a modified example of this embodiment. FIG. 8 is a schematic view showing the structure of an optical fiber assembly according to a modified example of this embodiment. FIGS. 9(a) to 9(c) are schematic views for explaining reflected light at a lens. FIGS. 10(a) to 10(d) are schematic views showing lenses included in an optical connection structure according to a modified example of this embodiment. FIG. 11 is a cross-sectional view of an optical fiber of an optical connection structure according to a modified example of this embodiment.

[0006] [Problem to be Solved by the Present Disclosure] When a lens is used in the optical connection structure described above, there is a risk that a portion of the light reflected at the end face of the lens may enter the end face of the optical fiber as returned light. The returned light may cause various problems. For example, the returned light may destabilize the operation of an amplifier or laser arranged upstream of the optical connection structure, degrading their performance. The occurrence of returned light also degrades signal quality in bidirectional transmission. As a result, there is a risk that the quality of optical transmission may deteriorate. [Advantages of the Present Disclosure]

[0007] According to the present disclosure, it is possible to provide an optical connection structure that improves the quality of optical transmission using a pair of optical fiber assemblies, and a method for manufacturing the optical connection structure.

[0008] First, embodiments of the present disclosure will be listed and described.

[0009] (1) An optical connection structure according to an embodiment of the present disclosure includes a first optical fiber assembly, a second optical fiber assembly, a first lens, and a second lens. The first optical fiber assembly includes at least one first fiber core. The first optical fiber assembly has a first end face. At least one first fiber core is exposed from the first end face. The second optical fiber assembly includes at least one second fiber core. The second optical fiber assembly has a second end face. At least one second fiber core is exposed from the second end face and is optically coupled to the first end face. The first lens and the second lens are arranged in order from the first optical fiber assembly to the second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly. At the first end face, an axis passing through the center of gravity of the at least one first fiber core is offset from the optical axis of the first lens in a direction along a vertical cross section of the at least one first fiber core.

[0010] In this case, the light reflected by the first lens can be prevented from entering the first fiber core, thereby improving the quality of optical transmission.

[0011] (2) In the optical connection structure of (1), the first optical fiber assembly may include a plurality of first fiber cores as the at least one first fiber core, and an axis passing through the center of gravity of the at least one first fiber core may be offset from the optical axis of the first lens in a direction perpendicular to the direction in which two of the at least one first fiber core are aligned at the first end face. In this case, the quality of optical transmission between the pair of optical fiber assemblies having the plurality of fiber cores is improved.

[0012] (3) In the optical connection structure of (2) above, the first optical fiber assembly may include a capillary and a multicore fiber. The capillary may have at least one hole extending along the longitudinal direction of the first optical fiber assembly. The multicore fiber may be provided in the hole. The multicore fiber may include a plurality of first fiber cores. In this case, since the multicore fiber is positioned by the capillary, a configuration in which an axis passing through the center of gravity of the first fiber core is shifted with respect to the optical axis of the first lens can be easily achieved, and reliability can also be improved.

[0013] (4) In the optical connection structure of (2) above, the first optical fiber assembly may include a capillary and a plurality of single-core fibers. The capillary may have a plurality of holes extending along the longitudinal direction of the first optical fiber assembly. The plurality of single-core fibers may be provided in each of the plurality of holes. Each of the plurality of single-core fibers may include a first fiber core. In this case, since the plurality of single-core fibers are positioned by the capillary, a configuration in which an axis passing through the center of gravity of the first fiber core is shifted with respect to the optical axis of the first lens can be easily realized, and reliability can also be improved.

[0014] (5) In the optical connection structure of any one of (2) to (4), the number of the plurality of first fiber cores may be three or more, the three or more first fiber cores may be arranged in a row on the first end face, and an axis passing through the centers of gravity of the three or more first fiber cores may be shifted in a direction perpendicular to the arrangement direction of the three or more first fiber cores with respect to the optical axis of the first lens. In this case, the incidence of light reflected by the first lens on the first fiber cores may be further suppressed.

[0015] (6) In the optical connection structure according to any one of (2) to (5), an axis passing through the center of gravity of at least one second fiber core at the second end face may be offset from the optical axis of the second lens in a direction perpendicular to the direction in which two of the at least one second fiber core are aligned. In this case, the incidence of light reflected by the second lens on the second fiber core can be suppressed. As a result, the quality of bidirectional optical transmission is improved.

[0016] (7) In the optical connection structure according to any one of (2) to (6), the second optical fiber assembly includes a plurality of second fiber cores as the at least one second fiber core;

[0017] (P2 / P1)×0.9 ≦ f2 / f1 ≦ (P2 / P1)×1.1

[0018] The following relationship may be satisfied: the focal length of the first lens is "f1", the focal length of the second lens is "f2", the core pitch of the plurality of first fiber cores at the first end face is "P1", and the core pitch of the plurality of second fiber cores at the second end face is "P2". In this case, leakage of incident light can be further suppressed, and optical loss in the optical fiber can be further suppressed.

[0019] (8) In the optical connection structure according to any one of (1) to (7), the first end face may be inclined with respect to a vertical cross section. In this case, optical coupling in the first fiber core of light reflected at the first end face can be suppressed.

[0020] (9) In the optical connection structure according to any one of (1) to (8), the first lens may have an opposing surface facing the first end face. The opposing surface may be inclined with respect to the optical axis of the first lens. In this case, the reflected light reflected at the opposing surface may be prevented from entering the first fiber core.

[0021] (10) In the optical connection structure according to any one of (1) to (9), the shape of the arrangement of the at least one first fiber core on the first end face as viewed from the optical axis direction of the first lens and the shape of the arrangement of the at least one plurality of second fiber cores on the second end face as viewed from the optical axis direction of the second lens may be similar to each other, thereby reducing optical loss between the fiber cores.

[0022] (11) In the optical connection structure of any one of (1) to (10), at least one first fiber core may be enlarged at the first end face. In this case, even if the beam diameter is enlarged by the first and second lenses, leakage of the incident light can be further suppressed, and optical loss in the optical fiber can be further suppressed.

[0023] (12) A method for manufacturing an optical connection structure according to an embodiment of the present disclosure includes preparing a first optical fiber assembly, a second optical fiber assembly, a first lens, and a second lens, and arranging the first lens and the second lens in sequence. The first optical fiber assembly includes at least one first fiber core. The first optical fiber assembly has a first end face from which the at least one first fiber core is exposed. The second optical fiber assembly includes at least one second fiber core. The second optical fiber assembly has a second end face from which the at least one second fiber core is exposed and optically coupled to the first end face. The first lens and the second lens are arranged in sequence from the first optical fiber assembly to the second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly. At the first end face, an axis passing through the center of gravity of the at least one first fiber core is shifted with respect to the optical axis of the first lens in a direction along a vertical cross section of the at least one first fiber core.

[0024] (13) In the manufacturing method of the optical connection structure of (12) above, the first optical fiber assembly may include a plurality of first fiber cores as the at least one first fiber core, and at the first end face, an axis passing through the center of gravity of at least one first fiber core may be shifted in a direction perpendicular to the optical axis of the first lens and the direction in which two of the at least one first fiber core are aligned at the first end face.

[0025] (14) In the method for manufacturing an optical connection structure according to (12) or (13), in the preparation of the first optical fiber assembly, at least one first fiber core is expanded by heating at the first end face. In this case, even if the beam diameter is expanded by the first and second lenses, leakage of the incident light can be further suppressed, and optical loss in the optical fiber can be further suppressed. [Details of the embodiment of the present disclosure]

[0026] Specific examples of embodiments of the present disclosure will be described below with reference to the drawings. The present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted.

[0027] First, an example of an optical connection structure according to this embodiment will be described with reference to Figures 1 to 5. Figure 1 is a cross-sectional view of an optical connection structure according to one embodiment taken along the optical axis direction.

[0028] The optical connection structure 1 includes a pair of optical fiber assemblies 10, 20, a pair of lenses 30, 40, a pair of holders 50, 60, and a sleeve 70. The optical connection structure 1 optically couples the pair of optical fiber assemblies 10, 20 to each other via the pair of lenses 30, 40. For example, the optical fiber assembly 10 corresponds to a first optical fiber assembly, and the optical fiber assembly 20 corresponds to a second optical fiber assembly. For example, the lens 30 corresponds to a first lens, and the lens 40 corresponds to a second lens.

[0029] 2 is a schematic diagram showing the structure of the optical fiber assembly 10. In the example shown in this embodiment, the optical fiber assembly 20 has a structure symmetrical to that of the optical fiber assembly 10 in the Z-axis direction. In this specification, the X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other. The optical fiber assemblies 10 and 20 each have an elongated shape. In the example shown in this embodiment, the optical fiber assemblies 10 and 20 have a cylindrical shape. The optical fiber assemblies 10 and 20 extend in the Z-axis direction.

[0030] The optical fiber assembly 10 has an end face 17 facing the lens 30. The optical fiber assembly 20 has an end face 27 facing the lens 40. In the example shown in this embodiment, the optical fiber assembly 10 includes a capillary 11 and one optical fiber 13. The optical fiber assembly 20 includes a capillary 21 and one optical fiber 23.

[0031] 2, the capillary 11 has at least one hole H1. The hole H1 passes through the capillary 11 and communicates with an opening formed in the end face 17. The hole H1 extends along the longitudinal direction of the optical fiber assembly 10. The capillary 21 has at least one hole H2. The hole H2 passes through the capillary 21 and communicates with an opening formed in the end face 27. The hole H2 extends along the longitudinal direction of the optical fiber assembly 20. In the example shown in this embodiment, the capillaries 11 and 21 each have one hole H1 and H2.

[0032] The optical fiber 13 includes at least one fiber core 15 and a cladding 16. The optical fiber 13 is disposed in the hole H1 and is exposed from an end face 17. The at least one fiber core 15 is exposed from the end face 17. The end face 17 is inclined with respect to a vertical cross section of the at least one fiber core 15. In this specification, the "vertical cross section of the fiber core" refers to a cross section perpendicular to the infinitesimal length direction of the fiber core. The "infinite length direction of the fiber core" refers to the extension direction of the fiber core viewed microscopically. The end face 17 is inclined with respect to a vertical cross section of an axis passing through the center of gravity of the at least one fiber core 15. The end face 17 is inclined with respect to a cross section perpendicular to the central axis of each fiber core 15. For example, the end face 17 is formed by polishing the optical fiber 13 and the capillary 11 together. In the example shown in this embodiment, the optical fiber 13 is a multi-core fiber including multiple fiber cores 15. In the example shown in this embodiment, the axis passing through the center of gravity of at least one fiber core 15 coincides with the central axis of each fiber core 15 .

[0033] The fiber core 15 is expanded, for example, at the end face 17 by heating. The molded field diameter (MFD) of the fiber core 15 is expanded near the end face 17 by heating, and includes a tapered portion in which the diameter increases toward the end face 17. The optical fiber 13 is, for example, a TEC (Thermally Expanded Core) fiber, and a shape in which the MFD varies partially is formed by TEC processing. For example, the tapered portion described above may be formed by TEC processing.

[0034] The optical fiber 23 includes at least one fiber core 25. The optical fiber 23 is provided in the hole H2 and exposed from an end face 27. The at least one fiber core 25 is exposed from the end face 27. The end face 27 is inclined with respect to a vertical cross section of the at least one fiber core 25. The end face 27 is inclined with respect to a vertical cross section of an axis passing through the center of gravity of the at least one fiber core 25. The end face 27 is inclined with respect to a vertical cross section of the central axis of each fiber core 25. For example, the end face 27 is formed by polishing the optical fiber 23 and the capillary 21 together. In the example shown in this embodiment, the optical fiber 23 is a multi-core fiber including multiple fiber cores 25.

[0035] At least one fiber core 25 exposed at the end face 27 and at least one fiber core 15 exposed at the end face 17 are optically coupled to each other. In the example shown in this embodiment, each of the multiple fiber cores 25 exposed at the end face 27 is optically coupled to a corresponding fiber core 25 among the multiple fiber cores 15 exposed at the end face 17.

[0036] In the example shown in this embodiment, as shown in Fig. 3, the multiple fiber cores 15 are arranged in a row in the X-axis direction on the end face 17. Fig. 3 is a diagram showing the end face of the optical fiber 13, and is a view of the end face 17 as seen from the Z-axis direction. In Fig. 3, the dashed line indicates an image of the boundary of the MFD. In the example shown in this embodiment, the optical fiber 23 has a structure similar to that of the optical fiber 13. The multiple fiber cores 25 are arranged in a row on the end face 27. In the example shown in this embodiment, five fiber cores are arranged in the X-axis direction in the optical fibers 13 and 23.

[0037] The lens 30 and the lens 40 are arranged between the optical fiber assembly 10 and the optical fiber assembly 20. The lens 30 is interposed between the end face 17 of the optical fiber assembly 10 and the lens 40. The lens 40 is interposed between the lens 30 and the end face 27 of the optical fiber assembly 20. The lenses 30 and the lens 40 are arranged in order from the end face 17 of the optical fiber assembly 10 toward the end face 27 of the optical fiber assembly 20.

[0038] The lens 30, for example, focuses the multiple light beams L emitted from each of the multiple fiber cores 15 of the optical fiber assembly 10 on the opposite side of the optical fiber assembly 10 from the lens 30. The lens 40, for example, focuses the light beams L on each fiber core 25 at the end face 27. The lenses 30 and 40 are, for example, C lenses. For example, the lens 30 is a rod lens having a spherical surface on the lens 40 side, a flat surface on the optical fiber assembly 10 side, and the same outer diameter as the optical fiber assembly 10. For example, the lens 40 is a rod lens having a spherical surface on the lens 30 side, a flat surface on the optical fiber assembly 20 side, and the same outer diameter as the optical fiber assembly 20.

[0039] An example of the characteristics of the lens 30 and the lens 40 will be described with reference to Figures 4 and 5. Figures 4 and 5 are schematic diagrams for explaining the configuration of the optical connection structure 1. Figures 4 and 5 show the relationship between the optical fiber 13, the optical fiber 23, the lens 30, and the lens 40. Figure 4 shows the configuration as viewed from the X-axis direction. Figure 5 shows the configuration as viewed from the Y-axis direction. Light L1 and light L2 are light L emitted from different fiber cores 15. Planes S1, S2, S3, S4, S5, and S6 are shown in Figures 4 and 5.

[0040] Plane S1 corresponds to a virtual plane that includes the intersection point between the central axis of the fiber core 15 and the end face 17 and extends in a direction perpendicular to the optical axis CX1 of the lens 30. Plane S2 and plane S3 each include different principal surfaces of the pair of principal surfaces of the lens 30. In this specification, the term "principal surface" refers to a surface formed by a set of points where, when a light ray parallel to the optical axis of the lens is incident, an extension line of an incident light ray at an arbitrary height intersects with an extension line of an output light ray corresponding to the incident light ray. Plane S2 corresponds to the principal surface of the pair of principal surfaces of the lens 30 that faces the optical fiber 13. Plane S3 corresponds to the principal surface of the pair of principal surfaces of the lens 30 that faces the lens 40. Plane S4 and plane S5 each include different principal surfaces of the pair of principal surfaces of the lens 40. Plane S4 corresponds to the principal surface of the pair of principal surfaces of the lens 40 that faces the lens 30. Plane S5 corresponds to the principal surface of the pair of principal surfaces of the lens 40 that faces the optical fiber 23. The plane S6 corresponds to an imaginary plane that includes the intersection of the central axis of the fiber core 25 and the emission surface and extends in a direction perpendicular to the optical axis CX2 of the lens 40.

[0041] Lens 30 has an opposing surface 31 facing end face 17 and an opposing surface 32 facing lens 40. Lens 40 has an opposing surface 41 facing end face 27 and an opposing surface 42 facing lens 30. In the example shown in FIG. 1 , opposing surface 31 is inclined with respect to the optical axis of lens 30, and opposing surface 41 is inclined with respect to the optical axis of lens 40.

[0042] At the end face 17 of the optical fiber assembly 10, an axis AX1 passing through the center of gravity of at least one fiber core 15 of the optical fiber assembly 10 is offset in a direction along a vertical cross section of the at least one fiber core 15 with respect to the optical axis CX1 of the lens 30. In other words, at the end face 17, the axis AX1 is offset in the Y-axis direction with respect to the optical axis CX1 of the lens 30. At the end face 27 of the optical fiber assembly 20, an axis AX2 passing through the center of gravity of at least one fiber core 25 of the optical fiber assembly 20 is offset in a direction along a vertical cross section of the at least one fiber core 25 with respect to the optical axis CX2 of the lens 40. At the end face 27, the axis AX2 is offset in the Y-axis direction with respect to the optical axis CX2 of the lens 40.

[0043] 2 , at the end face 17 of the optical fiber assembly 10, an axis AX1 passing through the center of gravity of at least one fiber core 15 of the optical fiber assembly 10 is offset in a direction along a vertical cross section of the at least one fiber core 15 with respect to an axis AX3 passing through the center of gravity of the optical fiber assembly 10. Similarly, at the end face 27, an axis AX2 passing through the center of gravity of the at least one fiber core 25 is offset in a direction along a vertical cross section of the at least one fiber core 35 with respect to an axis AX4 passing through the center of gravity of the optical fiber assembly 20.

[0044] The axis AX1 corresponds to an axis passing through the center of gravity of at least one hole H1 in the capillary 11 at the end face 17. The axis AX3 corresponds to an axis passing through the center of gravity of the capillary 11 at the end face 17. The axis AX2 corresponds to an axis passing through the center of gravity of at least one hole H2 in the capillary 21 at the end face 27. The axis AX4 corresponds to an axis passing through the center of gravity of the capillary 21 at the end face 27.

[0045] In the example shown in this embodiment, the multiple fiber cores 15 are arranged in a row in the X-axis direction on the end face 17, and the axis AX1 is offset with respect to the optical axis CX1 of the lens 30 in the Y-axis direction, which is orthogonal to the X-axis direction, which is the arrangement direction of the multiple fiber cores 15. On the end face 17, the axis AX1 passing through the center of gravity of at least one fiber core 15 is offset with respect to the optical axis CX1 of the lens 30 in a direction orthogonal to the direction in which two of the multiple fiber cores 15 are lined up on the end face 17. The arrangement direction of the multiple fiber cores 15 is adjusted by rotating the optical fiber 13 when the optical fiber 13 is inserted into the hole H1 of the capillary 11. Similarly, the multiple fiber cores 25 are arranged in a row in the X-axis direction on the end face 27, and the axis AX2 is offset with respect to the optical axis CX2 of the lens 40 in the Y-direction, which is orthogonal to the X-axis direction, which is the arrangement direction of the multiple fiber cores 25. At the end face 27, an axis AX2 passing through the center of gravity of at least one fiber core 25 is shifted with respect to the optical axis CX2 of the lens 40 in a direction perpendicular to the direction in which two of the plurality of fiber cores 25 are aligned at the end face 27. The arrangement direction of the plurality of fiber cores 25 is adjusted by rotating the optical fiber 23 when the optical fiber 23 is inserted into the hole H2 of the capillary 21.

[0046] For example, assume that the optical connection structure 1 includes one fiber core 15 and one fiber core 25, and is configured so that the distance between the plane S2 and the plane S1 is equal to the focal length, and the distance between the plane S3 and the plane S4 is equal to the sum of the focal lengths of the lenses 30 and 40. In this case, the fiber core 15 and the fiber core 25 can be optically coupled with a relatively low loss. For example, the fiber core 15 and the fiber core 25 can be optically coupled with a loss of less than 1 dB.

[0047] Next, it is assumed that the optical connection structure 1 includes a plurality of fiber cores 15 and a plurality of fiber cores 25, and that the optical connection structure 1 is configured so that the following formula (1) holds.

[0048] D １ / D ２ =P １ / P ２ = f１ / f ２ ...(1)

[0049] The MFD formed in the fiber core 15 is "D １ ". The MFD formed in the fiber core 25 is "D ２ ". The core pitch of the fiber cores 15 at the end face 17 is "P １ ". The core pitch of the fiber cores 25 at the end face 27 is "P ２ ". The focal length of the lens 30 is "f １ ". The focal length of the lens 40 is "f ２ ". In this specification, "core pitch" corresponds to the distance between the centers of fiber cores in the XY plane.

[0050] In this case, the shape of the arrangement of the multiple fiber cores 15 on the end face 17 of the lens 30 as viewed in the direction of the optical axis CX1 and the shape of the arrangement of the multiple fiber cores 25 on the end face 27 of the lens 40 as viewed in the direction of the optical axis are similar to each other. The light distribution formed on the end face 17 of the optical fiber 13 and the light distribution formed on the end face 27 of the optical fiber 23 are similar to each other in accordance with the ratio of the focal lengths f1 and f2 of the lenses 30 and 40. The ratio of the MFD of the fiber cores 15 on the end face 17 to the MFD of the fiber cores 25 on the end face 27 matches the ratio of the focal lengths f1 and f2 of the lenses 30 and 40. In this case, too, the fiber cores 15 and 25 can be optically coupled with relatively low loss. For example, the fiber cores 15 and 25 can be optically coupled with a loss of less than 1 dB.

[0051] In the example shown in this embodiment, the optical connection structure 1 is configured so as to satisfy the following relational expressions (2) and (3).

[0052] (P2 / P1)×0.9 ≦ f2 / f1 ≦ (P2 / P1)×1.1 ... (2)

[0053] (P2 / P1)×0.9 ≦ D2 / D1 ≦ (P2 / P1)×1.1 ... (3)

[0054] The holder 50 holds the optical fiber assembly 10 and the lens 30. The holder 50 is cylindrical. The holder 50 has an inner circumferential surface 51 and an outer circumferential surface 52. The inner circumferential surface 51 forms a through hole 55 that penetrates the holder 50 in the extension direction of the holder 50. A portion of the optical fiber assembly 10 and a portion of the lens 30 are housed in the through hole 55. The holder 50 holds the optical fiber assembly 10 and the lens 30 on the inner circumferential surface 51 that forms the through hole 55. The holder 50 fixes the capillary 11 and the lens 30 on the inner circumferential surface 51. The holder 50 fixes the lens 30 and the optical fiber assembly 10 so that an axis AX1 passing through the center of gravity of the fiber core 15 and an optical axis CX1 of the lens 30 are parallel to each other.

[0055] As a result, the end face 17 of the optical fiber assembly 10 and the opposing surface 31 of the lens 30 are positioned close to each other. The light emitted from the end face 17 of the optical fiber assembly 10 becomes parallel light via the lens 30. In other words, a collimator is formed by the optical fiber assembly 10 and the lens 30. The holder 50 is a collimator holder.

[0056] The holder 60 holds the optical fiber assembly 20 and the lens 40. The holder 60 is cylindrical. The holder 60 has an inner circumferential surface 61 and an outer circumferential surface 62. The inner circumferential surface 61 forms a through hole 65 that penetrates the holder 60 in the extension direction of the holder 60. A portion of the optical fiber assembly 20 and a portion of the lens 40 are housed in the through hole 65. The holder 60 holds the optical fiber assembly 20 and the lens 40 on the inner circumferential surface 61 that forms the through hole 65. The holder 60 fixes the capillary 21 and the lens 40 on the inner circumferential surface 61. The holder 60 fixes the lens 40 and the optical fiber assembly 20 so that an axis AX2 passing through the center of gravity of the fiber core 25 and an optical axis CX2 of the lens 40 are positioned parallel to each other.

[0057] As a result, the end face 27 of the optical fiber assembly 20 and the opposing surface 41 of the lens 40 are disposed close to each other. The light emitted from the end face 27 of the optical fiber assembly 20 becomes parallel light via the lens 40. In other words, a collimator is formed by the optical fiber assembly 20 and the lens 40. The holder 60 is a collimator holder.

[0058] The sleeve 70 holds the holder 50 and the holder 60. The sleeve 70 is cylindrical. The sleeve 70 has an inner circumferential surface 71. The inner circumferential surface 71 forms a through hole 75 that penetrates the sleeve 70 in the extension direction of the sleeve 70. A portion of the holder 50 and a portion of the holder 60 are housed in the through hole 75. The sleeve 70 holds the holder 50 and the holder 60 at the inner circumferential surface 71 that forms the through hole 75. The sleeve 70 fixes the holder 50 and the holder 60 so that the optical axis CX1 of the lens 30 and the optical axis CX2 of the lens 40 are positioned parallel to each other.

[0059] In the example shown in this embodiment, the amount of deviation in the Y-axis direction of the axis passing through the centers of gravity of the multiple fiber cores 15 at the end face 17 relative to the optical axis CX1 of the lens 30 corresponds to the amount of deviation in the Y-axis direction of the axis passing through the centers of gravity of the multiple holes H1 at the end face 17 relative to the axis passing through the center of gravity of the capillary 11. The amount of deviation in the Y-axis direction of the axis passing through the centers of gravity of the multiple fiber cores 15 at the end face 17 relative to the optical axis CX1 of the lens 30 corresponds to the amount of deviation in the Y-axis direction of the axis passing through the centers of gravity of the multiple holes H1 at the end face 17 relative to the axis passing through the center of gravity of the capillary 11. Therefore, when fixing the holders 50 and 60 to the sleeve 70, no special technique is required to adjust the amount of deviation, and the amount of deviation can be set by a known technique that simply adjusts the positional relationship between the holders 50 and 60.

[0060] Next, an example of a method for manufacturing the optical connection structure 1 will be described. First, the optical fiber assembly 10, the optical fiber assembly 20, the lens 30, and the lens 40 are prepared. In preparing the optical fiber assembly 10, at least one fiber core 15 may be expanded by heating at the end surface 17, if necessary. The fiber core 15 may be expanded by, for example, TEC treatment.

[0061] Next, the optical fiber assembly 10 and the lens 30 are placed in the through-hole 55 of the holder 50. For example, the optical fiber assembly 10 and the lens 30 are fixed to the inner circumferential surface 51 with an adhesive. The optical fiber assembly 20 and the lens 40 are placed in the through-hole 65 of the holder 60. For example, the optical fiber assembly 20 and the lens 40 are fixed to the inner circumferential surface 61 with an adhesive.

[0062] Next, the holder 50 and the holder 60 are placed in the through-hole 75 of the sleeve 70. For example, the outer peripheral surface 52 of the holder 50 and the outer peripheral surface 62 of the holder 60 are fixed to the inner peripheral surface 71 with an adhesive. When the holder 50 and the holder 60 are fixed to the sleeve 70, they are aligned so that the fiber core 15 and the fiber core 25 are optically coupled with a relatively low loss. Next, for example, the holder 50, the holder 60, and the sleeve 70 are all housed in a cylindrical housing and sealed.

[0063] As a result of the above, the lenses 30 and 40 are arranged in order between the optical fiber assembly 10 and the optical fiber assembly 20, from the optical fiber assembly 10 toward the optical fiber assembly 20. An axis AX1 passing through the center of gravity of at least one fiber core 15 at the end face 17 is arranged to be offset from the optical axis CX1 of the lens 30. An axis AX2 passing through the center of gravity of at least one fiber core 25 at the end face 27 is arranged to be offset from the optical axis CX2 of the lens 40.

[0064] Next, an optical connection structure according to a modified example of this embodiment will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view of the optical connection structure according to this modified example taken along the optical axis direction. This modified example is generally similar to or the same as the embodiment described above. This modified example differs from the embodiment described above in terms of the configuration for fixing the lens and the optical fiber assembly, the configuration of the optical fiber assembly, and the type of lens. Below, the differences between the embodiment described above and the modified example will be mainly described.

[0065] The optical connection structure 1A optically couples a multicore fiber and a fiber array. The optical connection structure 1A includes a pair of optical fiber assemblies 10, 20A, a pair of lenses 30, 40A, a pair of holders 50, 60A, 80A, and a sleeve 90A. The optical connection structure 1 optically couples the pair of optical fiber assemblies 10, 20A to each other via the pair of lenses 30, 40A. For example, the optical fiber assembly 10 corresponds to a first optical fiber assembly, and the optical fiber assembly 20A corresponds to a second optical fiber assembly. For example, the lens 30 corresponds to a first lens, and the lens 40A corresponds to a second lens.

[0066] The optical fiber assembly 20A includes a capillary 21A and a plurality of optical fibers 23A. The optical fiber assembly 20A is a fiber array including the plurality of optical fibers 23A. The optical fiber assembly 20A has an end face 27A facing the lens 40A. The plurality of optical fibers 23A are uniformly arranged on the end face 27A. The end face 27A is inclined with respect to the optical axis CX2 of the lens 40A. The end face 27A is inclined with respect to a cross section perpendicular to the central axis of the fiber core 25.

[0067] Each optical fiber 23A is a single-core fiber including one fiber core 25. The capillary 21A has a plurality of holes H2. The plurality of holes H2 may be spaced apart from one another or may be connected in the X-axis direction. The plurality of optical fibers 23A are provided in the corresponding holes H2 and exposed from the end face 27A. The plurality of fiber cores 25 are exposed from the end face 27A. At the end face 27A, an axis AX2 passing through the centers of gravity of the plurality of fiber cores 25 is offset from an axis AX4 passing through the center of gravity of the optical fiber assembly 20A.

[0068] The end face 27A and the end face 17 are optically coupled to each other. In other words, the multiple fiber cores 25 exposed at the end face 27A and the multiple fiber cores 15 exposed at the end face 17 are optically coupled to each other. The multiple fiber cores 25 of the optical fiber assembly 20A are expanded at the end face 27A by heating, for example. The MFD of the fiber cores 25 of the optical fiber assembly 20A is expanded near the end face 27A by heating, and includes a tapered portion whose diameter increases toward the end face 27A. The optical fiber 23A is, for example, a TEC fiber, and a shape with a partially different MFD is formed by TEC processing. For example, the above-mentioned tapered portion may be formed by TEC processing.

[0069] The lens 30 and the lens 40A are arranged between the optical fiber assembly 10 and the optical fiber assembly 20A. The lens 40A is interposed between the lens 30 and the end face 27A of the optical fiber assembly 20. The lenses 30 and 40A are arranged in order from the end face 17 of the optical fiber assembly 10 toward the end face 27A of the optical fiber assembly 20A. The lens 40A is, for example, a plano-convex lens. For example, the lens 40A has a convex surface on the lens 30 side and a flat surface on the optical fiber assembly 20A side.

[0070] The holder 60A holds the optical fiber assembly 20A. The holder 60A is cylindrical. The holder 60A has an inner circumferential surface 61. A portion of the optical fiber assembly 20A is housed in a through hole 65. The holder 60A holds the optical fiber assembly 20A at the inner circumferential surface 61 that forms the through hole 65. The holder 60A fixes the capillary 21A at the inner circumferential surface 61.

[0071] The holder 80A holds the lens 40A. The holder 80A is cylindrical. The holder 80A has an inner circumferential surface 81A and an outer circumferential surface 82A. The inner circumferential surface 81A forms a through-hole 85 penetrating the holder 80A in the extension direction of the holder 80A. The lens 40A is accommodated in the through-hole 85A. The holder 80A holds the lens 40A on the inner circumferential surface 81A that forms the through-hole 85A. The holder 80A fixes the lens 40A on the inner circumferential surface 81A. The through-hole 85A of the holder 80A and the through-hole 55 of the holder 50A are connected to a side surface 83A of the holder 80A and a side surface 53 of the holder 50A. The side surface 83A of the holder 80A and the side surface 53 of the holder 50A are connected to each other so that the optical axis CX1 of the lens 30 and the optical axis CX2 of the lens 40 are parallel to each other. The side surface 83A and the side surface 53 each have an annular shape.

[0072] The sleeve 90A holds the holder 60A and the holder 80A. The sleeve 90A is cylindrical. The sleeve 90A has an inner circumferential surface 91A and a side surface 93A. The inner circumferential surface 91A forms a through hole 95A that penetrates the sleeve 90A in the extension direction of the sleeve 90A. The side surface 93A is annular. A portion of the holder 80A is accommodated in the through hole 95A. The sleeve 90A holds the holder 80A at the inner circumferential surface 91A that forms the through hole 95A. The through hole 95A of the sleeve 90A and the through hole 85A of the holder 80A are connected within the through hole 95A. The through hole 95A of the sleeve 90A and the through hole 65 of the holder 60A are connected at the side surface 93A of the sleeve 90A and the side surface 63 of the holder 60A. The side surface 93A of the sleeve 90A and the side surface 63 of the holder 60A are connected to each other so that the optical axis CX2 of the lens 40A and the axis AX2 passing through the centers of gravity of the plurality of fiber cores 25 are positioned parallel to each other.

[0073] Next, an example of a method for manufacturing the optical connection structure 1A will be described. First, the optical fiber assembly 10, the optical fiber assembly 20A, the lens 30, and the lens 40A are prepared. In preparing the optical fiber assembly 20A, for example, the fiber core 25 is expanded at the end face 27A by heating. The fiber core 25 is expanded by, for example, TEC treatment.

[0074] Next, the optical fiber assembly 10 and the lens 30 are placed in the through hole 55 of the holder 50. For example, the optical fiber assembly 10 and the lens 30 are fixed to the inner circumferential surface 51 with an adhesive. The optical fiber assembly 20A is placed in the through hole 65 of the holder 60A. For example, the optical fiber assembly 20A is fixed to the inner circumferential surface 61 with an adhesive. The lens 40A is placed in the through hole 85A of the holder 80A. For example, the lens 40A is fixed to the inner circumferential surface 81A with an adhesive.

[0075] Next, the holder 80A is placed in the through-hole 95A of the sleeve 90A. Next, with the side surface 93A of the sleeve 90A in contact with the side surface 63 of the holder 60A and with the side surface 53 of the holder 50A in contact with the side surface 83A of the holder 80A, the fiber cores 15 and 25 are aligned and fixed so as to be optically coupled with relatively low loss. The sleeve 90A and the holder 80A are fixed to each other, the sleeve 90A and the holder 60A are fixed to each other, and the holder 50A and the holder 80A are fixed to each other. These are fixed by, for example, an adhesive.

[0076] Because the axis AX1 passing through the center of gravity of the multiple fiber cores 15 of the optical fiber 13 is offset from the optical axis CX1 of the lens 30, the axis passing through the center of gravity of the multiple holes H1 of the capillary 11 is offset from the axis passing through the center of gravity of the capillary 11. The arrangement of the multiple fiber cores 15 is adjusted by rotating the optical fiber 13. Due to the above-mentioned alignment and the rotation of the optical fiber 13, the axis passing through the center of gravity of the capillary 21A including the multiple fiber cores 25 is offset from the optical axis CX2 of the lens 40A in a direction perpendicular to the arrangement direction of the multiple optical fibers 23A.

[0077] In this modification, alignment is possible with the axes of the lenses 30, 40A, holders 50, 60A, 80A, and sleeve 90A parallel to one another. Therefore, gaps caused by tilting of the axes are eliminated, and the amount of resin required for fixation is reduced. As a result, reliability is improved.

[0078] Next, an optical connection structure according to a modified example of this embodiment will be described with reference to Figures 7 and 8. Figure 7 is a cross-sectional view of the optical connection structure according to this modified example taken along the optical axis direction. This modified example is generally similar to or the same as the embodiment described above. This modified example differs from the embodiment described above in terms of the configuration for fixing the lens and the optical fiber assembly, the configuration of the optical fiber assembly, and the type of lens. Below, the differences between the embodiment described above and the modified example will be mainly described.

[0079] The optical connection structure 1B optically couples a pair of fiber arrays. The optical connection structure 1B includes a pair of optical fiber assemblies 10B, 20B, a pair of lenses 30B, 40A, a pair of holders 50B, 60B, 160B, and a pair of sleeves 170B, 180B. The optical connection structure 1B optically couples the pair of optical fiber assemblies 10B, 20B to each other via the pair of lenses 30B, 40A. For example, the optical fiber assembly 10B corresponds to a first optical fiber assembly, and the optical fiber assembly 20B corresponds to a second optical fiber assembly.

[0080] The optical fiber assemblies 10B and 20B each have an elongated shape. In this modification, the optical fiber assemblies 10B and 20B each have a cylindrical shape. The optical fiber assemblies 10B and 20B extend in the Z-axis direction.

[0081] The optical fiber assembly 10B includes a capillary 11B and a plurality of optical fibers 13B. The optical fiber assembly 10B is a fiber array including the plurality of optical fibers 13B. The optical fiber assembly 10B has an end face 17B facing the lens 30B. The plurality of optical fibers 13B are arranged uniformly on the end face 17B. The end face 17B is inclined with respect to the optical axis CX1 of the lens 30B. The end face 17B is inclined with respect to a vertical cross section perpendicular to the central axes of the plurality of fiber cores 25.

[0082] Each optical fiber 13B is a single-core fiber including one fiber core 15. The capillary 11B has multiple holes H1. The multiple holes H1 may be spaced apart from one another or may be connected in the X-axis direction. The multiple optical fibers 13B are respectively provided in the corresponding holes H1 and exposed from the end face 17B.

[0083] The plurality of fiber cores 15 are exposed from the end face 17B. For example, the fiber cores 15 are expanded by heating at the end face 17B. The fiber cores 15 are expanded near the end face 17B by heating, and include a tapered portion whose diameter increases toward the end face 17B.

[0084] The optical fiber assembly 20B includes a capillary 21B and a plurality of optical fibers 23B. The optical fiber assembly 20B is a fiber array including the plurality of optical fibers 23B. The optical fiber assembly 20B has an end face 27B facing the lens 40B. The plurality of optical fibers 23B are uniformly arranged on the end face 27B. The end face 27B is inclined with respect to the optical axis CX2 of the lens 40B. The end face 27B is inclined with respect to a vertical cross section perpendicular to the central axes of the plurality of fiber cores 25.

[0085] Each of the optical fibers 23B includes one fiber core 25. The capillary 21B has a plurality of holes H2. The holes H2 may be spaced apart from one another or may be connected in the X-axis direction. The optical fibers 23B are respectively provided in the corresponding holes H2 and exposed from the end face 27B. The fiber cores 25 are exposed from the end face 27B.

[0086] The end face 27B and the end face 17B are optically coupled to each other. In other words, the plurality of fiber cores 25 exposed at the end face 27B and the plurality of fiber cores 15 exposed at the end face 17B are optically coupled to each other.

[0087] The capillary 11B has a plurality of holes H1. The holes H1 are connected to the openings formed in the end face 17B. The holes H1 extend along the longitudinal direction of the optical fiber assembly 10B. In the end face 17B, an axis AX2 passing through the centers of gravity of the holes H1 is offset from the optical axis CX1 of the lens 30B.

[0088] The capillary 21B has a plurality of holes H2. The holes H2 communicate with openings formed in the end face 27B. The holes H2 each extend along the longitudinal direction of the optical fiber assembly 20B. In the end face 27B, an axis AX4 passing through the centers of gravity of the holes H2 is offset from the optical axis CX2 of the lens 40A.

[0089] 8, in this modification, at the end face 17B, an axis AX1 passing through the center of gravity of the plurality of fiber cores 15 coincides with an axis AX3 passing through the center of gravity of the optical fiber assembly 10B. At the end face 27B, an axis AX2 passing through the center of gravity of the plurality of fiber cores 25 coincides with an axis AX4 passing through the center of gravity of the optical fiber assembly 20B.

[0090] The lenses 30B and 40A are arranged between the optical fiber assembly 10B and the optical fiber assembly 20B. The lens 30B is interposed between the lens 40A and the end face 17B of the optical fiber assembly 10B. The lenses 30B and 40A are arranged in order from the end face 17B of the optical fiber assembly 10B toward the end face 27B of the optical fiber assembly 20B. The lens 30B is, for example, a plano-convex lens. For example, the lens 30B has a convex surface facing the lens 40A and a flat surface facing the optical fiber assembly 10B.

[0091] The holder 160B holds the lens 30B and the lens 40A. The holder 160B is cylindrical. The holder 160B has an inner circumferential surface 161B and an outer circumferential surface 162B. The inner circumferential surface 161B forms a through hole 165B that penetrates the holder 160B in the extension direction of the holder 160B. The lens 30B and the lens 40A are housed in the through hole 165B. The holder 160B holds the lens 30B and the lens 40A on the inner circumferential surface 161B that forms the through hole 165B. The holder 160B fixes the lens 30B and the lens 40A on the inner circumferential surface 161B.

[0092] The sleeve 170B holds the holder 160B. The sleeve 170B is cylindrical. The sleeve 170B has an inner circumferential surface 171B and a side surface 173B. The inner circumferential surface 171B forms a through hole 175B that penetrates the sleeve 170B in the extension direction of the sleeve 170B. A portion of the holder 160B is accommodated in the through hole 175B. The sleeve 170B holds the holder 160B at the inner circumferential surface 171B that forms the through hole 175B. The sleeve 170B fixes the holder 160B at the inner circumferential surface 171B.

[0093] The through-hole 175B of the sleeve 170B and the through-hole 55 of the holder 50B communicate with a side surface 173B of the sleeve 170B and a side surface 53 of the holder 50B. The side surface 173B of the sleeve 170B and the side surface 53 of the holder 50B are connected to each other so that the optical axis CX1 of the lens 30B and the axis AX3 of the optical fiber assembly 10B are positioned parallel to each other. The side surface 173B and the side surface 53 each have an annular shape.

[0094] The sleeve 180B holds the holder 160B. The sleeve 180B is cylindrical. The sleeve 180B has an inner circumferential surface 181B and a side surface 183B. The inner circumferential surface 181B forms a through hole 185B that penetrates the sleeve 180B in the extension direction of the sleeve 180B. A portion of the sleeve 180B is accommodated in the through hole 185B. The sleeve 180B holds the holder 160B at the inner circumferential surface 181B that forms the through hole 185B. The sleeve 180B fixes the holder 160B at the inner circumferential surface 181B.

[0095] The through-hole 185B of the sleeve 180B and the through-hole 65 of the holder 60B communicate with each other at a side surface 183B of the sleeve 180B and a side surface 63 of the holder 60B. The side surface 183B of the sleeve 180B and the side surface 63 of the holder 60B are connected to each other so that the optical axis CX2 of the lens 40B and the axis AX4 of the optical fiber assembly 20B are positioned parallel to each other. The side surface 183B and the side surface 63 each have an annular shape.

[0096] Next, an example of a method for manufacturing the optical connection structure 1B will be described. First, the optical fiber assembly 10B, the optical fiber assembly 20B, the lens 30B, and the lens 40A are prepared. In preparing the optical fiber assembly 10B, for example, the fiber core 15 is expanded at the end face 17B by heating. The fiber core 15 is expanded by, for example, TEC treatment.

[0097] Next, the optical fiber assembly 10B is placed in the through hole 55 of the holder 50B. For example, the optical fiber assembly 10B and the lens 30B are fixed to the inner circumferential surface 51 with an adhesive. The optical fiber assembly 20B is placed in the through hole 65 of the holder 60B. For example, the optical fiber assembly 20B is fixed to the inner circumferential surface 61 with an adhesive. The lens 30B and the lens 40A are placed in the through hole 165B of the holder 160B. For example, the lens 30B and the lens 40A are fixed to the inner circumferential surface 161B with an adhesive.

[0098] Next, with outer peripheral surface 162B of holder 160B in contact with inner peripheral surface 171B and inner peripheral surface 181B, with side surface 173B of sleeve 170B in contact with side surface 53 of holder 50B, and with side surface 173B of sleeve 170B in contact with side surface 53 of holder 50B, the fiber cores 15 and 25 are aligned so as to be optically coupled with relatively low loss. In the aligned state, holder 160B and sleeve 170B and sleeve 180B are fixed to each other, sleeve 170B and holder 50B are fixed to each other, and sleeve 180B and holder 60B are fixed to each other.

[0099] The arrangement of the multiple fiber cores 15 is adjusted by rotating the optical fiber 13B. Alignment is performed so that the axis passing through the center of gravity of the capillary 11B containing the multiple fiber cores 15 is shifted relative to the optical axis CX2 of the lens 30B in a direction perpendicular to the arrangement direction of the multiple optical fibers 23B, and the axis passing through the center of gravity of the capillary 21B containing the multiple fiber cores 25 is shifted relative to the optical axis CX2 of the lens 40B in a direction perpendicular to the arrangement direction of the multiple optical fibers 23B. In this modified example, the above-mentioned amounts of shift are precisely adjusted. As a result, the influence of returning light on each optical fiber 13B and optical fiber 23B is easily suppressed.

[0100] Next, the effects obtained from the optical connection structure according to the embodiment will be described. When a lens is used in the optical connection structure, reflection occurs on the surface of the lens. In Fig. 9(a) to Fig. 9(c), as an example, the reflected light L ＲThe lens 230 is a plano-convex lens. FIG. 9A shows a reflected light L , which is a part of the light emitted from the fiber core 15 and reflected by the rear end face 231 of the lens 230. Ｒ 9B shows how a part of the light emitted from the fiber core 15 is reflected by the front end surface 232 of the lens 230 as reflected light L Ｒ returns to the fiber core 15.

[0101] Reflected light L at lens 230 Ｒ The reflected light L incident on the fiber core 15 from which it was emitted and on the adjacent fiber core 15, and a part of the reflected light L is coupled within the fiber core 15. Ｒ In the case of bidirectional transmission, when the light propagation direction of the fiber core 15 from which the light is emitted and the adjacent fiber core 15 are opposite to each other, the reflected light L incident on the different fiber core 15 may be destabilized. Ｒ This acts as noise to the optical signal that is originally propagating, which may result in degradation of signal quality.

[0102] 9(c), the axis AX1 passing through the center of gravity of the fiber core 15 is parallel to the optical axis CX1 of the lens 230 and is shifted from the optical axis CX1 in a direction perpendicular to the arrangement direction of the fiber cores 15. In the configuration shown in FIG. 9(c), the reflection direction at the front end surface 232 of the lens 230 is different from that in the configurations shown in FIG. 9(a) and FIG. 9(b). In the configuration shown in FIG. 9(c), the reflected light L at the front end surface 232 of the lens 230 Ｒ is warped from each fiber core 15, and is suppressed from being incident on each fiber core 15. Therefore, the effects of operational instability and degradation of signal quality caused by the reflected light being coupled to the fiber core 15 from which it originates or an adjacent fiber core 15 can be reduced.

[0103] In the optical connection structure 1, at the end face 17, an axis AX1 passing through the center of gravity of at least one fiber core 15 is shifted in a direction along a vertical cross section of at least one fiber core 15 with respect to an optical axis CX1 of the lens 30. In this case, the reflected light L reflected by the lens 30 Ｒ , can be prevented from being incident on the fiber core 15. As a result, the quality of optical transmission is improved. The optical connection structures 1A and 1B also achieve the same effects.

[0104] In the optical connection structure 1, the optical fiber assembly 10 includes a plurality of fiber cores 15 as the at least one fiber core 14. In the optical fiber assembly 10, an axis AX1 passing through the center of gravity of the at least one fiber core 15 at the end face 17 may be offset with respect to the optical axis CX1 of the lens 30 in a direction perpendicular to the direction in which two of the at least one fiber core 15 are aligned at the end face 17. In this case, the quality of optical transmission is improved between the optical fiber assembly 10 having a plurality of fiber cores 15 and the optical fiber assembly 20 having a plurality of fiber cores 25. The optical connection structures 1A and 1B also achieve the same effects.

[0105] In the optical connection structure 1, the optical fiber assembly 10 may include a capillary 11 and a multi-core fiber. The capillary 11 has at least one hole H1. The hole H1 extends along the longitudinal direction of the optical fiber assembly 10. The multi-core fiber may be provided in the hole H1. In this case, since the multi-core fiber is positioned by the capillaries 11 and 21, an axis AX1 passing through the center of gravity of the fiber core 15 can be easily realized with respect to the optical axis CX1 of the lens 30, and reliability can also be improved. The optical connection structure 1A also exhibits the same effects.

[0106] In the optical connection structure 1B, the optical fiber assembly 10B may include a capillary 11B and a plurality of single-core fibers. The capillary 11B may have a plurality of holes H1 extending along the longitudinal direction of the optical fiber assembly 10B. A plurality of single-core fibers may be provided in each of the plurality of holes H1. Each of the plurality of single-core fibers may include a fiber core 15. In this case, since the plurality of single-core fibers are positioned by the capillary 11B, an axis AX1 passing through the center of gravity of the fiber core 15 can be easily realized with respect to the optical axis CX1 of the lens 30, and reliability can also be improved. The optical fiber assembly 20A of the optical connection structure 1A also exhibits the same effects.

[0107] In the optical connection structure 1, the multiple fiber cores 15 may be arranged in a row on the end face 17 in a direction perpendicular to the direction in which an axis AX1 passing through the center of gravity of at least one fiber core 15 is shifted from the optical axis CX1 of the lens 30. In this case, the incidence of reflected light at the lens 30 on the fiber core 15 can be further suppressed. There are three or more multiple fiber cores 15, and the three or more fiber cores 15 are arranged in a row on the end face 17. The axis AX1 passing through the center of gravity of the three or more fiber cores 15 may be shifted from the optical axis CX1 of the lens 30 in a direction perpendicular to the arrangement direction of the three or more fiber cores 15. In this case, the incidence of reflected light at the lens 30 on the fiber core 15 can be further suppressed. The optical connection structures 1A and 1B also achieve the same effects.

[0108] In the optical connection structure 1, the end face 17 may be inclined with respect to a cross section perpendicular to the central axis of at least one fiber core 15. In this case, optical coupling in the fiber core 15 can be suppressed for light reflected at the end face 17. The optical connection structures 1A and 1B also achieve the same effects.

[0109] For example, in the optical connection structure 1, when the end face 17 of the optical fiber 13 is perpendicular to the axis AX1 passing through the center of gravity of the optical fiber 13, Fresnel reflection of about -15 dB occurs at the end face 17. When the end face 17 is inclined, the light reflected at the end face 17 is prevented from being recoupled into the optical fiber 13. If an anti-reflection film is vapor-deposited on the end face 17, the reflection can be reduced to an almost negligible level.

[0110] For example, when an optical fiber 13 with an MFD of 10 μm is polished 8 times for light with a wavelength of 1550 nm, the reflectance at the end face 17 for that wavelength can be reduced to -65 dB even without an anti-reflection coating (AR coating). When the same fiber is polished 4 times, the reduction in reflectance is limited to -35 dB, but if an AR coating with a reflectance of 0.25% is further deposited, the reduction can be reduced to -61 dB.

[0111] In the optical connection structure 1, the lens 30 has an opposing surface 31 that faces the end face 17. The opposing surface 31 may be inclined with respect to the optical axis CX1 of the lens 30. In this case, the reflected light reflected at the opposing surface 31 can be prevented from entering the fiber core 15. The optical connection structure 1A also achieves the same effect.

[0112] In the optical connection structure 1, the axis AX2 passing through the center of gravity of at least one fiber core 25 may be offset from the optical axis CX2 of the lens 40 on the end face 27 in a vertical cross section perpendicular to the direction in which two of the at least one fiber core 25 are aligned. In this case, the incidence of reflected light at the lens 40 on the fiber core 25 can be suppressed. As a result, the quality of bidirectional optical transmission is improved. The same effects are achieved in the optical connection structures 1A and 1B.

[0113] In the optical connection structure 1, the shape of the arrangement of at least one fiber core 15 on the end face 17 of the lens 30 as viewed from the optical axis direction and the shape of the arrangement of at least one fiber core 25 on the end face 27 of the lens 40 as viewed from the optical axis direction may be similar to each other. In this case, optical loss between the fiber cores is reduced. The same effects are achieved in the optical connection structures 1A and 1B.

[0114] In the optical connection structure 1,

[0115] (P2 / P1)×0.9 ≦ f2 / f1 ≦ (P2 / P1)×1.1

[0116] The following relationship may be satisfied: the focal length of lens 30 is "f1", the focal length of lens 40 is "f2", the core pitch of the plurality of fiber cores 15 at end face 17 is "P1", and the core pitch of the plurality of fiber cores 25 at end face 27 is "P2". In this case, leakage of incident light can be further suppressed, and optical loss in the optical fiber can be further suppressed. The optical connection structures 1A and 1B also achieve the same effects.

[0117] In the optical connection structure 1, at least one fiber core 15 may be enlarged at the end face 17. In this case, even if the beam diameter is enlarged by the lenses 30 and 40, leakage of incident light can be further suppressed, and optical loss in the optical fiber can be further suppressed. The optical connection structures 1A and 1B also achieve the same effects.

[0118] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments and can be applied to various embodiments. For example, the configurations of the optical connection structures 1, 1A, and 1B may be combined. For example, the configuration on the fiber bundle side and the configuration on the MCF side may have different configurations from those of the examples shown in the optical connection structures 1, 1A, and 1B.

[0119] For example, the multiple lenses arranged between the optical fiber assembly 10 and the optical fiber assembly 20 may include a type of lens other than the C lens used in the optical connection structures 1 and 1A and the convex lens used in the optical connection structures 1A and 1B. For example, the various lenses shown in Figures 10(a) to 10(d) may be used. Figures 10(a) to 10(d) show various lenses 30D, 30E, 30F, and 30G and the light L incident on each lens 30D, 30E, 30F, and 30G.

[0120] In FIG. 10( a), lens 30D is a biconvex lens and includes a pair of convex end faces 31D and 32D. For example, end faces 31D and 32D are aspherical. Lens 30D is formed from a single material. In FIG. 10( b), lens 30E is an achromatic lens and is formed by bonding together multiple plates. Each of the multiple plates of lens 30E has a curved surface and is made of a different material. For example, end faces 31E and 32E are aspherical. In FIG. 10( c), lens 30F is a spherical lens. Lens 30F is made of a sphere made of a single material. In FIG. 10( d), lens 30G is a GRIN lens. Lens 30G includes a pair of flat end faces 31G and 32G. Lens 30G is made of a cylindrical body with a refractive index distribution that varies in the radial direction.

[0121] The optical connection structure 1 may have a structure in which a plurality of types of lenses are combined. For example, the optical connection structure 1 may have a configuration in which two or more lenses selected from a biconvex lens, an achromatic lens, a spherical lens, a C lens, a GRIN lens, etc. In this case, for example, the lenses located at both ends correspond to the first lens and the second lens, respectively.

[0122] In the above example, five fiber cores 15 and five fiber cores 25 are arranged. However, the number and arrangement of the fiber cores are not limited to this. For example, the number of fiber cores 15 and the number of fiber cores 25 may be four or seven. The numbers of fiber cores 15 and 25 may differ from each other. FIG. 11 shows a cross-sectional view of an optical fiber 13J as a modified example. The optical fiber 13J differs from the optical fiber 13 only in the number and arrangement of the fiber cores 15. The optical fiber 13J has seven fiber cores 15. The seven fiber cores 15 have a close-packed structure in the XY plane so as to function optically.

[0123] In the above examples, the portions described as being fixed by adhesive may be fixed by welding.

[0124] DESCRIPTION OF SYMBOLS 1, 1A, 1B... Optical connection structure 10, 10B, 20, 20A, 20B... Optical fiber assembly 11, 11B, 21, 21A, 21B... Capillary 13, 13J, 23, 23A, 23B... Optical fiber 15, 25... Fiber core 16... Cladding 17, 17B, 27, 27A, 27B, 31D, 31G, 32D, 32G... End face 30, 30B, 30D, 30E, 30F, 30G, 40, 40A, 40B, 230... Lens 31, 32, 41, 42... Opposing surface 50, 50A, 50B, 60, 60A, 60B, 80A, 160B... Holder 51, 61, 71, 81A, 91A, 161B, 171B, 181B...Inner peripheral surface 52, 62, 82A, 162B...Outer peripheral surface 53, 63, 83A, 93A, 173B, 183B...Side surface 55, 65, 75, 85A, 95A, 165B, 175B, 185B... Through hole 70, 90A, 170B, 180B... Sleeve AX1, AX2, AX3, AX4... Axis CX1, CX2... Optical axis f1, f2... Focal length H1, H2... Hole L... Light S1, S2, S3, S4, S5, S6... Plane.

Claims

1. An optical connection structure comprising: a first optical fiber assembly including at least one first fiber core and having a first end face at which the at least one first fiber core is exposed; a second optical fiber assembly including at least one second fiber core and having a second end face at which the at least one second fiber core is exposed and optically coupled to the first end face; and a first lens and a second lens arranged in order from the first optical fiber assembly to the second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly, wherein at the first end face, an axis passing through the center of gravity of the at least one first fiber core is offset from the optical axis of the first lens in a direction along a vertical cross section of the at least one first fiber core.

2. The optical connection structure described in claim 1, wherein the first optical fiber assembly includes a plurality of first fiber cores as the at least one first fiber core, and at the first end face, an axis passing through the center of gravity of the at least one first fiber core is shifted with respect to the optical axis of the first lens in a direction perpendicular to the direction in which two of the plurality of first fiber cores are lined up at the first end face.

3. The optical connection structure described in claim 2, wherein the first optical fiber assembly includes a capillary having at least one hole extending along the longitudinal direction of the first optical fiber assembly, and a multi-core fiber provided in the hole, and the multi-core fiber of the first optical fiber assembly includes the plurality of first fiber cores.

4. The optical connection structure described in claim 2, wherein the first optical fiber assembly includes a capillary having a plurality of holes extending along the longitudinal direction of the first optical fiber assembly, and a plurality of single-core fibers provided in each of the plurality of holes and each of which includes the first fiber core.

5. An optical connection structure as described in any one of claims 2 to 4, wherein the number of the plurality of first fiber cores is three or more, the three or more first fiber cores are arranged in a row at the first end face, and an axis passing through the center of gravity of the three or more first fiber cores is shifted in a direction perpendicular to the arrangement direction of the three or more first fiber cores with respect to the optical axis of the first lens.

6. An optical connection structure described in any one of claims 2 to 5, wherein, at the second end face, an axis passing through the center of gravity of the at least one second fiber core is shifted with respect to the optical axis of the second lens in a direction perpendicular to the direction in which two of the at least one second fiber core are aligned.

7. An optical connection structure according to any one of claims 2 to 6, wherein the second optical fiber assembly includes a plurality of second fiber cores as the at least one second fiber core, and wherein, when the focal length of the first lens is "f1", the focal length of the second lens is "f2", the core pitch of the plurality of first fiber cores at the first end face is "P1", and the core pitch of the plurality of second fiber cores at the second end face is "P2", the relationship: (P2 / P1) x 0.9 ≦ f2 / f1 ≦ (P2 / P1) x 1.1 is satisfied.

8. An optical connection structure according to any one of claims 1 to 7, wherein the first end face is inclined with respect to the perpendicular cross section.

9. An optical connection structure described in any one of claims 1 to 8, wherein the first lens has an opposing surface facing the first end face, and the opposing surface is inclined with respect to the optical axis of the first lens.

10. An optical connection structure described in any one of claims 1 to 9, wherein the shape of the arrangement of the at least one first fiber core at the first end face viewed from the optical axis direction of the first lens and the shape of the arrangement of the at least one second fiber core at the second end face viewed from the optical axis direction of the second lens are similar to each other.

11. The optical connection structure according to any one of claims 1 to 10, wherein the at least one first fiber core is enlarged at the first end face.

12. A method for manufacturing an optical connection structure, comprising: preparing a first optical fiber assembly including at least one first fiber core and having a first end face at which the at least one first fiber core is exposed; a second optical fiber assembly including at least one second fiber core and having a second end face at which the at least one second fiber core is exposed and optically coupled to the first end face; and a first lens and a second lens; arranging the first lens and the second lens in order from the first optical fiber assembly to the second optical fiber assembly between the first optical fiber assembly and the second optical fiber assembly; and arranging, at the first end face, an axis passing through the center of gravity of the at least one first fiber core with respect to the optical axis of the first lens in a direction along a vertical cross section of the at least one first fiber core.

13. A method for manufacturing an optical connection structure as described in claim 12, wherein the first optical fiber assembly includes a plurality of first fiber cores as the at least one first fiber core, and an axis passing through the center of gravity of the at least one first fiber core at the first end face is shifted in a direction perpendicular to the direction in which two of the at least one first fiber core are aligned at the first end face with respect to the optical axis of the first lens.

14. A method for manufacturing an optical connection structure according to claim 12 or 13, wherein in preparing the first optical fiber assembly, the at least one first fiber core is expanded at the first end face by heating.