Optical fiber connection structure

Abstract

An optical fiber connection structure according to an embodiment of the present invention is provided with: a tubular member; a first collimator attached to a first end of the tubular member in an axis direction; and a second collimator attached to a second end of the tubular member. The first collimator has a first optical fiber, a first ferrule that holds the first optical fiber, a first lens, and a first sleeve that holds the first lens and the first ferrule therein. The second collimator has a second optical fiber, a second ferrule that holds the second optical fiber, a second lens, and a second sleeve that holds the second lends and the second ferrule therein. The first sleeve is fixed to the first end by means of an adhesive in a state where the first lens is opposing the tubular member. The second sleeve is fixed to the second end by means of an adhesive in a state where the second lens is opposing the tubular member. The outer diameter of the second ferrule is larger than that of the second lens.

Description

[Technical field]

[0001] The present disclosure relates to optical fiber connection structures. This application claims priority to Japanese Application No. 2020-111739 filed on June 29, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 describes an optical functional component equipped with a collimator. The collimator includes a lens and a ferrule that holds an optical fiber. The optical functional component includes a cylindrical tube that holds a pair of collimators therein so that the pair of lenses face each other. A WDM filter or an isolator is disposed between the pair of lenses inside the cylindrical tube.

[0003] Patent Document 2 discloses a lens-type device equipped with an optical functional component such as an isolator. The lens-type device has a tubular member. Inside the tubular member, a pair of lenses and a Faraday element disposed between the pair of lenses are disposed.

[0004] Patent Document 3 describes an optical isolator device. The optical isolator device includes a metal tubular member, an optical isolator disposed inside the tubular member, and a pair of collimators fixed to the tubular member. The collimator has a ferrule that holds an optical fiber and a lens that optically couples with the isolator. Each collimator is fixed to the tubular member by spot welding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Pat. No. 5,652,814 [Patent Document 2] International Publication No. 2009 / 075168 [Patent Document 3] Japanese Patent Application Publication No. 9-61683 Summary of the Invention

[0006] The optical fiber connection structure according to the present disclosure includes a tubular member, a first collimator attached to a first end in an axial direction, which is a direction in which the axis of the tubular member extends, and a second collimator attached to a second end of the tubular member opposite the first end. The first collimator has a first optical fiber, a first ferrule that holds the first optical fiber, a first lens that faces the first ferrule via a gap, and a first sleeve that holds the first lens and the first ferrule internally. The second collimator has a second optical fiber, a second ferrule that holds the second optical fiber, a second lens that faces the second ferrule via a gap, and a second sleeve that holds the second lens and the second ferrule internally. The outer surface of the first ferrule and the inner surface of the first sleeve, the outer surface of the first lens and the inner surface of the first sleeve, the outer surface of the second lens and the inner surface of the tubular member, and the outer surface of the second ferrule and the inner surface of the second sleeve are each fixed with an adhesive, the first sleeve is fixed to the first end with the first lens facing the tubular member, and the second sleeve is fixed to the second end with the second lens inserted into the tubular member. The outer diameter of the second ferrule is larger than the outer diameter of the second lens. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing an optical fiber connection structure according to one embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the optical fiber connection structure of FIG. [Diagram 3] FIG. 3 is a cross-sectional view showing a ferrule and a lens of an optical fiber connection structure according to a comparative example. [Figure 4] FIG. 4 is a cross-sectional view showing a ferrule and a lens of an optical fiber connection structure according to one embodiment. [Diagram 5] FIG. 5 is a diagram showing a step of a method for assembling an optical fiber connection structure according to an embodiment. [Figure 6]FIG. 6 is a diagram showing a process of an assembly method for an optical fiber connection structure according to an embodiment. [Figure 7] FIG. 7 is a diagram showing a step of a method for assembling an optical fiber connection structure according to an embodiment. [Figure 8] FIG. 8 is a diagram showing a step of a method for assembling an optical fiber connection structure according to an embodiment. [Figure 9] FIG. 9 is a diagram showing a step of a method for assembling an optical fiber connection structure according to an embodiment. [Figure 10] FIG. 10 is a diagram showing an optical fiber connection structure according to an embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing an optical fiber connection structure according to a modified example. [Figure 12] FIG. 12 is a cross-sectional view showing an optical fiber connection structure according to another modified example. [Figure 13] FIG. 13 is a perspective view showing an optical fiber connection structure according to another modified example. [Figure 14] FIG. 14 is a cross-sectional view showing an optical fiber connection structure according to another modified example. [Figure 15] FIG. 15 is a diagram showing an example of a single-core fiber. [Figure 16] FIG. 16 is a cross-sectional view showing a ferrule and a lens of an optical fiber connection structure according to another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In the optical fiber connection structure, when the ferrule is fixed to the tubular member by adhesive while the ferrule is inserted in the tubular member, the ferrule may tilt due to environmental changes such as temperature and humidity depending on the thickness of the adhesive. In this case, the reliability of the optical connection may decrease. In addition, when the collimator is fixed to the metal tubular member by welding, advanced welding technology and various tools are required, so that the collimator may not be easily fixed.

[0009] An object of the present disclosure is to provide an optical fiber connection structure that allows for easy fixing of a collimator and improves the reliability of optical connection.

[0010] According to the present disclosure, the collimator can be easily fixed and the reliability of the optical connection can be improved.

[0011] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. An optical fiber connection structure according to one embodiment includes a tubular member, a first collimator attached to a first end in an axial direction, which is a direction in which the axis of the tubular member extends, and a second collimator attached to a second end of the tubular member opposite the first end. The first collimator has a first optical fiber, a first ferrule that holds the first optical fiber, a first lens that faces the first ferrule via a gap, and a first sleeve that holds the first lens and the first ferrule internally. The second collimator has a second optical fiber, a second ferrule that holds the second optical fiber, a second lens that faces the second ferrule via a gap, and a second sleeve that holds the second lens and the second ferrule internally. The outer surface of the first ferrule and the inner surface of the first sleeve, the outer surface of the first lens and the inner surface of the first sleeve, the outer surface of the second lens and the inner surface of the tubular member, and the outer surface of the second ferrule and the inner surface of the second sleeve are each fixed with an adhesive, the first sleeve is fixed to the first end with the first lens facing the tubular member, and the second sleeve is fixed to the second end with the second lens inserted into the tubular member. The outer diameter of the second ferrule is larger than the outer diameter of the second lens.

[0012] In this optical fiber connection structure, a first collimator is attached to a first end of a tubular member, and a second collimator is attached to a second end of the tubular member opposite to the first end. The first collimator has a first sleeve, and a first ferrule for holding a first optical fiber and a first lens are held inside the first sleeve. The second collimator has a second sleeve, and a second ferrule for holding a second optical fiber and a second lens are held inside the second sleeve. The first sleeve is fixed to the first end with the first lens facing the tubular member, and the second sleeve is fixed to the second end with the second lens inserted into the tubular member. Therefore, since the first collimator and the second collimator are fixed to the first end and the second end of the tubular member, respectively, in the axial direction, the first collimator and the second collimator can be easily fixed to the tubular member. In addition, since the first collimator and the second collimator are fixed to the first end and the second end, respectively, the inclination of the ferrule can be suppressed to increase the reliability of the optical connection. The outer diameter of the second ferrule of the second collimator is larger than the outer diameter of the second lens, so that the second ferrule can be aligned in a direction perpendicular to the optical axis of the second lens while the second lens is fixed to the tubular member, facilitating alignment and assembly of the components.

[0013] The end of the first sleeve and the first end of the tubular member, and the end of the second sleeve and the second end of the tubular member may be fixed with an adhesive, which can suppress tilt between the first sleeve and the tubular member, and between the second sleeve and the tubular member, and can increase the reliability of the optical connection.

[0014] The first lens may have a first lens end face facing the first ferrule. The first ferrule may have a first ferrule end face facing the first lens. The inclination angle of the first lens end face with respect to a plane perpendicular to the axial direction may be different from the inclination angle of the first ferrule end face with respect to the plane perpendicular to the axial direction, and light may be emitted from the first lens along the axial direction toward the tubular member. In this case, since light is emitted along the axial direction of the tubular member, beam distortion can be reduced and the reliability of optical coupling can be further improved.

[0015] The second lens may have a second lens end face facing the second ferrule. The second ferrule may have a second ferrule end face facing the second lens. The inclination angle of the second lens end face with respect to a plane perpendicular to the axial direction may be different from the inclination angle of the second ferrule end face with respect to a plane perpendicular to the axial direction, and light may be emitted from the second lens along the axial direction toward the tubular member. In this case, as described above, it is possible to reduce beam distortion and further increase the reliability of optical coupling.

[0016] The end face of the first lens facing the tubular member may be recessed further into the first sleeve than the end face of the first sleeve facing the tubular member. In this case, since the first lens does not protrude from the first sleeve, it is possible to prevent the first lens from interfering with the tubular member when aligning the first collimator in a direction perpendicular to the optical axis of the first lens. Therefore, the first collimator can be easily aligned and fixed.

[0017] At least one of an end face of the first lens facing the tubular member and an end face of the second lens entering the tubular member may be spherical. At least one of the first lens and the second lens may be a GRIN lens.

[0018] The optical fiber connection structure may include a Faraday element disposed inside the tubular member, in which case the optical fiber connection structure can function as an optical isolator.

[0019] The first optical fiber may be a multi-core fiber. The second optical fiber may be a plurality of single-core fibers. Each of the plurality of single-core fibers may have a beam expansion portion capable of expanding a mode field diameter of light propagating through the core of the single-core fiber. In this case, the optical fiber connection structure may be a fan-in / fan-out device for a multi-core fiber.

[0020] Either the first optical fiber or the second optical fiber may be a two-core optical fiber. The optical fiber connection structure may include a WDM filter disposed inside the tubular member. In this case, the optical fiber connection structure can be a WDM multiplexing / demultiplexing device.

[0021] The maximum thickness of the adhesive may be 50 μm or less. In this case, since the maximum thickness of the adhesive can be made thin, 50 μm or less, it is possible to more easily fix the collimator and further increase the reliability of the optical connection.

[0022] [Details of the embodiment of the present disclosure] Specific examples of the optical fiber connection structure of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to the examples described below, but is intended to include all modifications within the scope of the claims and equivalents thereto. In the description of the drawings, the same or corresponding elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the drawings may be partially simplified or exaggerated to facilitate understanding, and the dimensional ratios and angles are not limited to those in the drawings.

[0023] FIG. 1 is a perspective view showing an optical fiber connection structure 1 according to an embodiment. FIG. 2 is a cross-sectional view showing the optical fiber connection structure 1. As shown in FIG. 1 and FIG. 2, the optical fiber connection structure 1 includes a first collimator 2, a second collimator 3, and a tubular member 4. The first collimator 2 has a first optical fiber 10, a first ferrule 13, a first lens 14, and a first sleeve 5. The second collimator 3 has a second optical fiber 20, a second ferrule 23, a second lens 24, and a second sleeve 6. The tubular member 4 connects the first collimator 2 and the second collimator 3 to each other. The tubular member 4 is made of, for example, glass.

[0024] The first collimator 2 is attached to the first end 4b in the axial direction D, which is the direction in which the axis of the tubular member 4 extends. The first sleeve 5 of the first collimator 2 is fixed to the first end 4b, and various fixing methods such as adhesion can be used. When an adhesive is used, it is, for example, a UV (ultraviolet) curing adhesive. The first sleeve 5 and the first ferrule 13 are made of, for example, glass. When the tubular member 4 and the first sleeve 5 are made of glass and the first sleeve 5 is fixed to the tubular member 4 with a UV curing adhesive, the difference in the linear expansion coefficient between the tubular member 4 and the first sleeve 5 can be reduced, thereby improving the reliability of the connection.

[0025] The first ferrule 13 holds the first optical fiber 10, and the tip surface of the first optical fiber 10 faces the first lens 14. The first sleeve 5 is fixed to the first end 4b with the first lens 14 facing the tubular member 4. The first lens 14 faces the first ferrule 13 and the first optical fiber 10 via a gap S1. The first sleeve 5 has a cylindrical shape. The first ferrule 13 and the first lens 14 are held inside the first sleeve 5. The outer surface of the first ferrule 13 and the inner surface of the first sleeve 5, and the outer surface of the first lens 14 and the inner surface of the first sleeve 5 are fixed together with an adhesive.

[0026] The second collimator 3 is attached to the second end 4c of the tubular member 4, which is opposite to the first end 4b. The second sleeve 6 of the second collimator 3 is fixed to the second end 4c, for example, via an adhesive, but various other fixing methods can be used. The second ferrule 23 holds the second optical fiber 20, and the tip face of the second optical fiber 20 faces the second lens 24. The second sleeve 6 is fixed to the second end 4c with the second lens 24 inserted into the tubular member 4. The second lens 24 faces the second ferrule 23 and the second optical fiber 20 via a gap S2. The second sleeve 6 has a cylindrical shape. The second ferrule 23 and the second lens 24 are held inside the second sleeve 6. The outer surface of the second ferrule 23 and the inner surface of the second sleeve 6 are fixed to each other via an adhesive.

[0027] The first lens 14 is, for example, a spherical rod lens. The outer diameter of the first lens 14 is approximately the same as the outer diameter of the first ferrule 13. The inner diameter of the first sleeve 5 is slightly larger than the outer diameter of the first lens 14 and the outer diameter of the first ferrule 13. A gap of, for example, 0 μm or more and 20 μm or less is formed between the outer peripheral surface of the first lens 14 and the outer peripheral surface of the first ferrule 13 and the inner peripheral surface of the first sleeve 5. The end face 14c of the first lens 14 facing the tubular member 4 is recessed further into the first sleeve 5 than the end face 5b of the first sleeve 5 facing the tubular member 4. This makes it possible to avoid the first lens 14 from interfering with the tubular member 4 when the first collimator 2 is aligned in a direction perpendicular to the axial direction D.

[0028] For example, the second lens 24 of the second collimator 3 is a spherical rod lens. A part of the second lens 24 is inserted inside the tubular member 4. The outer diameter of the second lens 24 is slightly smaller than the inner diameter of the tubular member 4, smaller than the outer diameter of the second ferrule 23, and smaller than the inner diameter of the second sleeve 6. The outer diameter of the second ferrule 23 is larger than the inner diameter of the tubular member 4 and slightly smaller than the inner diameter of the second sleeve 6.

[0029] The length in the axial direction D of a gap S1 formed between the first optical fiber 10 (first ferrule 13) and the first lens 14 is adjusted so that light emitted from the first lens 14 toward the second lens 24 becomes collimated light. Fig. 4 is a diagram showing the first optical fiber 10, the first ferrule 13, and the first lens 14 according to the embodiment, and Fig. 3 is a diagram showing the first optical fiber 110, the first ferrule 113, and the first lens 114 according to a comparative example.

[0030] Incidentally, the refractive index of the first lens 114 may be different from that of the first optical fiber 110, and may be higher than that of the first optical fiber 110. In this case, as shown in Fig. 3, when an end face 113b (the tip face of the first optical fiber 110) of the first ferrule 113 facing the first lens 114 and a face 114b of the first lens 114 facing the first ferrule 113 are parallel to each other, the light L emitted from the first optical fiber 110 may be inclined at the first lens 114 from the optical axis direction (axial direction D) of the first optical fiber 110.

[0031] 2 and 4, when the first ferrule end face 13b (the tip face of the first optical fiber 10) of the first ferrule 13 facing the first lens 14 and the first lens end face 14b of the first lens 14 facing the first ferrule 13 are non-parallel to each other, the light L emitted from the first optical fiber 10 is emitted parallel to the optical axis direction of the first optical fiber 10 at the first lens 14. As a result, the light L is emitted parallel to the axial direction D from the first lens 14 toward the second lens 24, so that the optical coupling loss can be suppressed. When the refractive index of the first lens 14 is higher than that of the first optical fiber 10, the inclination angle of the first ferrule end face 13b with respect to the plane perpendicular to the axial direction D is larger than the inclination angle of the first lens end face 14b with respect to the plane perpendicular to the axial direction D. The second ferrule end face 23b of the second ferrule 23 facing the second lens 24 and the second lens end face 24b of the second lens 24 facing the second ferrule 23 may be non-parallel to each other. In this case, the same effects as those of the first lens 14 and the first ferrule 13 described above can be obtained.

[0032] Next, an example of a method for assembling the optical fiber connection structure 1 will be described. First, as shown in Fig. 5, the first sleeve 5 of the first collimator 2, the first ferrule 13 for holding the first optical fiber 10, and the first lens 14 are prepared. The first lens 14 is inserted into the first sleeve 5, and the first lens 14 inserted into the first sleeve 5 is fixed to the first sleeve 5 by an adhesive. At this time, the first lens 14 is inserted inside the first sleeve 5 so that the end face 14c of the first lens 14 does not protrude from the end face 5b of the first sleeve 5.

[0033] Then, the first ferrule 13 is inserted into the first sleeve 5. The first ferrule 13 is inserted into the first sleeve 5 from the side opposite to the end face 14c of the first lens 14. At this time, the rotational position of the first ferrule 13 around the first optical fiber 10 is adjusted so that the inclination direction of the first ferrule end face 13b of the first ferrule 13 matches the inclination direction of the first lens end face 14b of the first lens 14. After the first ferrule 13 is inserted into the first sleeve 5, the length of the gap S1 between the first lens 14 and the first ferrule 13 in the axial direction D is adjusted.

[0034] 6, for example, a mirror M is disposed on the side of the first sleeve 5 opposite the first optical fiber 10. The above-mentioned adjustment of the gap S1 is performed while the mirror M reflects the light L that passes through the first optical fiber 10 and is emitted from the first lens 14, and the power of the light L that is reflected by the mirror M and returns to the first optical fiber 10 is detected. When the direction extending from the first optical fiber 10 along the axial direction D is defined as the Z direction, the direction perpendicular to the Z direction is defined as the X direction, and the direction perpendicular to both the Z direction and the X direction is defined as the Y direction, for example, the mirror M is tiltable in the θx direction around the X direction and the θy direction around the Y direction.

[0035] The light L collimated from the first optical fiber 10 and passing through the first lens 14 is reflected by the mirror M, and the gap S1 is adjusted so that the power of the light L returning from the mirror M to the first optical fiber 10 is maximized. Instead of using the mirror M to adjust the gap S1, a beam profiler may be disposed at a position facing the end face 14c of the first lens 14, and the gap S1 may be adjusted while observing the light L with the beam profiler. In this case, the gap S1 is adjusted so that the beam diameter of the light L emitted from the end face 14c of the first lens 14 becomes a desired beam diameter. After the gap S1 is adjusted as described above, the first ferrule 13 is fixed to the first sleeve 5 with an adhesive, and the first collimator 2 is completed.

[0036] As shown in Figs. 7 and 8, the first collimator 2 is fixed to the tubular member 4. At this time, the position of the tubular member 4 in the direction (XY direction) perpendicular to the axial direction D and the position of the first sleeve 5 are adjusted. That is, the position of the first sleeve 5 in the XY direction relative to the tubular member 4 is adjusted so that the position of the axis of the tubular member 4 matches the position of the axis of the first sleeve 5. The position adjustment of the first sleeve 5 in the XY direction relative to the tubular member 4 may be performed by a pinhole jig P inserted into the tubular member 4. The pinhole jig P has a cylindrical insertion part P1 inserted into the tubular member 4 and a flange part P2 expanding in diameter from the insertion part P1. The pinhole jig P has a through hole P3 penetrating the insertion part P1 and the flange part P2 in the axial direction D.

[0037] For example, the insertion portion P1 of the pinhole jig P is inserted into the tubular member 4 from the opposite side of the first sleeve 5, and the position of the first sleeve 5 is adjusted so that the light L emitted from the first lens 14 through the first optical fiber 10 passes through the through hole P3 of the pinhole jig P. After the position of the first sleeve 5 relative to the tubular member 4 is adjusted so that the light L passes through the through hole P3, the end face 5b of the first sleeve 5 is fixed to the first end 4b of the tubular member 4. Thereafter, the pinhole jig P is removed from the tubular member 4. Through the above steps, the fixing of the first collimator 2 to the tubular member 4 is completed. The first sleeve 5 and the tubular member 4 can be fixed by various fixing methods such as adhesive bonding.

[0038] Next, as shown in Fig. 9, the second lens 24 is inserted into the tubular member 4 from the opposite side of the first collimator 2. At this time, the rotational position of the second lens 24 around the optical axis direction of the first optical fiber 10 is adjusted and fixed via an adhesive. Then, as shown in Fig. 10, the second sleeve 6 with the second ferrule 23 inserted therein is attached to the second end 4c of the tubular member 4.

[0039] At this time, after the second optical fiber 20 is aligned with the second lens 24 in the X direction, Y direction, Z direction, and the θz direction around the Z direction, the second ferrule 23 is fixed to the second sleeve 6 with an adhesive. Then, the second sleeve 6 is aligned with the tubular member 4 in the X direction and Y direction, and thereafter the end face 6b of the second sleeve 6 is fixed to the second end 4c of the tubular member 4. The second sleeve 6 and the tubular member 4 can be fixed by various fixing methods such as adhesive.

[0040] Through the above steps, the second collimator 3 is fixed to the tubular member 4. The adhesive is applied between the first sleeve 5 and the first ferrule 13, between the first sleeve 5 and the first lens 14, between the tubular member 4 and the second lens 24, and between the second sleeve 6 and the second ferrule 23. When the adhesive is applied to these locations, the thickness of the adhesive can be made thin.

[0041] The maximum thickness of the adhesive of the optical fiber connection structure 1 is, for example, 50 μm or less. The "maximum thickness of the adhesive" refers to the maximum thickness of the adhesive applied between a plurality of components for the purpose of fixing the components, which is filled into the gaps between the components. As an example, the lower limit of the maximum thickness of the adhesive is 5 μm. The maximum thickness of the adhesive may be 10 μm or more, or 20 μm or more. And, the maximum thickness of the adhesive may be 40 μm or less, or 30 μm or less. As described above, the adhesive is, for example, a UV-curable adhesive. However, the adhesive may be other than a UV-curable adhesive, and may be, for example, a visible light-curable adhesive, a heat-curable adhesive, or a room temperature-curable adhesive.

[0042] Next, the effects of the optical fiber connection structure 1 according to the embodiment will be described. In the optical fiber connection structure 1, a first collimator 2 is attached to a first end 4b of a tubular member 4, and a second collimator 3 is attached to a second end 4c opposite to the first end 4b of the tubular member 4. The first collimator 2 has a first sleeve 5, and a first ferrule 13 for holding a first optical fiber 10 and a first lens 14 are held inside the first sleeve 5. The second collimator 3 has a second sleeve 6, and a second ferrule 23 for holding a second optical fiber 20 and a second lens 24 are held inside the second sleeve 6. The first sleeve 5 is fixed to the first end 4b with the first lens 14 facing the tubular member 4, and the second sleeve 6 is fixed to the second end 4c with the second lens 24 inserted into the tubular member 4. Therefore, since the first collimator 2 and the second collimator 3 are fixed to the first end 4b and the second end 4c, respectively, in the axial direction D of the tubular member 4, the first collimator 2 and the second collimator 3 can be easily fixed to the tubular member 4. The first sleeve 5 and the tubular member 4, and the second sleeve 6 and the second lens 24 can be fixed to each other by various fixing methods such as adhesive.

[0043] Furthermore, since the first collimator 2 and the second collimator 3 are fixed to the first end 4b and the second end 4c, respectively, tilting of the first ferrule 13 and the second ferrule 23 can be suppressed to improve the reliability of the optical connection. The outer diameter of the second ferrule 23 of the second collimator 3 is larger than the outer diameter of the second lens 24. Therefore, with the second lens 24 fixed to the tubular member 4, the second ferrule 23 can be aligned in a direction perpendicular to the optical axis of the second lens 24 (direction perpendicular to the axial direction D), and therefore alignment and assembly of parts can be easily performed.

[0044] 2 and 4, the first lens 14 has a first lens end face 14b facing the first ferrule 13, and the first ferrule 13 has a first ferrule end face 13b facing the first lens 14. The inclination angle of the first lens end face 14b with respect to a plane perpendicular to the axial direction D may be different from the inclination angle of the first ferrule end face 13b with respect to a plane perpendicular to the axial direction D, and light L is emitted from the first lens 14 toward the second lens 24 along the axial direction D. Thus, since the light L is emitted along the axial direction D of the tubular member 4, it is possible to suppress beam distortion and further improve the reliability of optical coupling.

[0045] In this embodiment, the second lens 24 has a second lens end face 24b facing the second ferrule 23, and the second ferrule 23 has a second ferrule end face 23b facing the second lens 24. The inclination angle of the second lens end face 24b with respect to a plane perpendicular to the axial direction D may be different from the inclination angle of the second ferrule end face 23b with respect to a plane perpendicular to the axial direction D, and light may be emitted from the second lens 24 in the axial direction D toward the first lens 14. In this case, as in the case described above, the beam distortion can be reduced and the reliability of the optical coupling can be further improved.

[0046] In this embodiment, the end face 14c of the first lens 14 facing the tubular member 4 is recessed further into the first sleeve 5 than the end face 5b of the first sleeve 5 facing the tubular member 4. Therefore, since the first lens 14 does not protrude from the first sleeve 5, it is possible to prevent the first lens 14 from interfering with the tubular member 4 when aligning the first collimator 2 in a direction perpendicular to the optical axis of the first lens 14 (for example, the X direction and the Y direction). Therefore, the alignment and fixing of the first collimator 2 can be easily performed. In addition, at least one of the end face 14c of the first lens 14 facing the tubular member 4 and the end face 24c of the second lens 24 facing the tubular member 4 may be spherical.

[0047] In this embodiment, the maximum thickness of the adhesive is 50 μm. Therefore, since the maximum thickness of the adhesive can be reduced to 50 μm or less, the first collimator 2 and the second collimator 3 can be fixed more easily and the reliability of the optical coupling can be further improved.

[0048] Next, various modified examples of the optical fiber connection structure will be described. Fig. 11 is a cross-sectional view showing an optical fiber connection structure 31 according to a modified example. A portion of the configuration of the optical fiber connection structure 31 is the same as a portion of the configuration of the optical fiber connection structure 1 described above. Therefore, in the following, the same reference numerals are used to denote the same explanation as for the optical fiber connection structure 1, and the explanation will be omitted as appropriate. In the optical fiber connection structure 31, an optical functional part 32 is disposed inside the tubular member 4. As an example, the optical functional part 32 is a Faraday element. In this case, the optical fiber connection structure 31 can function as an optical isolator.

[0049] 12 is a cross-sectional view showing an optical fiber connection structure 41 according to another modified example different from that shown in FIG. 11. In the optical fiber connection structure 1 shown in FIG. 2 described above, the outer diameter of the first ferrule 13 is different from and smaller than the outer diameter of the second ferrule 23. In contrast, the optical fiber connection structure 41 shown in FIG. 12 includes a first ferrule 43, a first lens 44, and a first sleeve 45 having substantially the same outer diameter as the outer diameter of the second ferrule 23, instead of the first ferrule 13, the first lens 14, and the first sleeve 5 described above. The inner diameter of the first sleeve 45 is larger than the inner diameter of the tubular member 4. The outer diameter of the first lens 44 is larger than the inner diameter of the tubular member 4 and the outer diameter of the second lens 24.

[0050] The second ferrule 23 holds a two-core second optical fiber 20A instead of the above-mentioned second optical fiber 20. For simplification, FIG. 12 does not show the two-core state. An optical functional component 42 is disposed inside the tubular member 4. The optical functional component 42 is, for example, a WDM filter. In this case, the optical fiber connection structure 41 can be a WDM multiplexing / demultiplexing device. In the above example, the second fiber is a two-core second optical fiber 20A. However, it is sufficient that either the first optical fiber or the second optical fiber is a two-core optical fiber, and for example, the first optical fiber 10 may be a two-core optical fiber.

[0051] Fig. 13 is a perspective view showing an optical fiber connection structure 51 according to another modified example. Fig. 14 is a cross-sectional view showing the optical fiber connection structure 51. As shown in Fig. 13 and Fig. 14, the optical fiber connection structure 51 includes a first collimator 62, a second collimator 63, and a tubular member 4. In the first collimator 62, the first ferrule 13 holds the multi-core fiber 60, and in the second collimator 63, the second ferrule 23 holds a plurality of single-core fibers 65.

[0052] As shown in Fig. 15, for example, the single-core fiber 65 is a TEC (Thermally Expanded Core) fiber. The single-core fiber 65 has, for example, a beam expansion section 68 capable of expanding a mode field diameter of light propagating through a core 67. The beam expansion section 68 is, for example, a core expansion section in which the core diameter of the core 67 is expanded at an end face 66 facing the second lens 24. For example, the beam expansion section 68 includes a tapered section 68b in which the core 67 is expanded in a tapered shape. In this case, since the core 67 is expanded at the end face 66, the mode field diameter of the light propagating through the single-core fiber 65 expands in the beam expansion section 68 in a direction perpendicular to the axial direction D.

[0053] As described above, in the optical fiber connection structure 51 according to the modified example, the first optical fiber is a multi-core fiber 60, and the second optical fiber is a plurality of single-core fibers 65. Each of the plurality of single-core fibers 65 has a beam expanding portion 68 capable of expanding a mode field diameter of light propagating through a core 67 of the single-core fiber 65. Therefore, the optical fiber connection structure 51 can be used as a fan-in / fan-out device for the multi-core fiber 60.

[0054] Fig. 16 is a cross-sectional view showing an optical fiber connection structure 71 according to a further modified example. As shown in Fig. 16, the optical fiber connection structure 71 constitutes, for example, a fan-in fan-out device (Fan-In / Fan-Out: FIFO) of a lens-coupled multicore fiber. The optical fiber connection structure 71 includes a multicore fiber 80, a plurality of single-core fibers 90, a first lens 70A interposed between the multicore fiber 80 and the plurality of single-core fibers 90, and a second lens 70B interposed between the plurality of single-core fibers 90 and the first lens 70A.

[0055] The multi-core fiber 80 has a plurality of cores 81 and a clad 82, and each single-core fiber 90 has a core 91 and a clad 92. In FIG. 16, the cores 81 and 91 are illustrated linearly for simplification. The plurality of single-core fibers 90 are bundled in a second ferrule 93. The multi-core fiber 80 is held in a first ferrule 83. The multi-core fiber 80 has a first end face 84 facing the first lens 70A. For example, the first end face 84 is flat and inclined with respect to a plane perpendicular to the axial direction D. Each single-core fiber 90 has a second end face 94 facing the second lens 70B. The second end face 94 is flat like the first end face 84, and inclined with respect to a plane perpendicular to the axial direction D.

[0056] The first lens 70A is disposed at a position facing the multi-core fiber 80 along the axial direction D. The first lens 70A collects the multiple light beams L emitted from each of the multiple cores 81 of the multi-core fiber 80 on the side opposite to the multi-core fiber 80. The second lens 70B is disposed at a position facing the single-core fiber 90 along the axial direction D.

[0057] Each of the first lens 70A and the second lens 70B is a GRIN lens. For example, the second lens 70B may be a GRIN lens that functions as a beam expanding section. An anti-reflection (AR) coating may be applied between the first lens 70A and the first end face 84, or a small gap may be provided. In addition, an adhesive (for example, a gel-like adhesive) may be interposed between the first lens 70A and the first end face 84. The same applies to the gap between the second lens 70B and the second end face 94. In the above, in FIG. 16, an example in which the first lens 70A and the second lens 70B are GRIN lenses has been described. However, it is sufficient that at least one of the first lens 70A and the second lens 70B is a GRIN lens. In this way, it is also possible to use a GRIN lens as the first lens and the second lens.

[0058] The above describes the embodiments and modifications of the optical fiber connection structure according to the present disclosure. However, the present invention is not limited to the above-described embodiments or modifications. In other words, it is easily recognized by those skilled in the art that the present invention can be modified and changed in various ways within the scope of the gist of the claims. For example, the shape, size, material, number, and arrangement of each part of the optical fiber connection structure can be appropriately changed within the scope of the gist of the above. [Explanation of symbols]

[0059] 1, 31, 41, 51, 71...Optical fiber connection structure 2,62…First collimator 3,63…Second collimator 4...Tubular member 4b…1st end 4c…Second end 5,45…First sleeve 5b...end face 6…Second sleeve 6b...end face 10…First optical fiber 13,43,83…First ferrule 13b…First ferrule end face 14,44,70A…1st lens 14b...First lens end surface 14c...end face 20,20A…Second optical fiber 23,93…Second ferrule 23b…Second ferrule end face 24,70B…2nd lens 24b...Second lens end surface 24c...end face 32, 42...Optical functional components 60,80...Multi-core fiber (first optical fiber) 65,90...Single-core fiber (second optical fiber) 66…End face 67…Core 68…Beam expansion section 68b...Tapered section 81…Core 82…Clad 84...First end surface 91…Core 92…Clad 94…Second end face D…Axis direction L…Light M…Mirror P…Pinhole jig P1: Insertion part P2: Flange part P3...Through hole S1, S2...Gap S2…Gap

Claims

1. A tubular member; A first collimator attached to a first end in an axial direction, which is a direction in which the axis of the tubular member extends; a second collimator attached to a second end of the tubular member opposite the first end, the first collimator includes a first optical fiber, a first ferrule that holds the first optical fiber, a first lens that faces the first ferrule via a gap, and a first sleeve that holds the first lens and the first ferrule therein; the second collimator includes a second optical fiber, a second ferrule that holds the second optical fiber, a second lens that faces the second ferrule via a gap, and a second sleeve that holds the second lens and the second ferrule therein, the first lens is a spherical rod lens or a GRIN lens, the second lens is a spherical rod lens or a GRIN lens, an outer surface of the first ferrule and an inner surface of the first sleeve, an outer surface of the first lens and an inner surface of the first sleeve, an outer surface of the second lens and an inner surface of the tubular member, and an outer surface of the second ferrule and an inner surface of the second sleeve are fixed to each other via an adhesive, the first sleeve is fixed to the first end with the first lens facing the tubular member, and the second sleeve is fixed to the second end with the second lens inserted into the tubular member; an end portion of the first sleeve and a first end portion of the tubular member, and an end portion of the second sleeve and a second end portion of the tubular member are fixed to each other via an adhesive; the second lens has a second lens end surface facing the second ferrule, the second lens end surface protruding from the tubular member; an end surface of the first lens facing the tubular member is recessed further into the first sleeve than an end surface of the first sleeve facing the tubular member, an outer diameter of the second ferrule is larger than an outer diameter of the second lens; the first optical fiber is a multi-core fiber; the second optical fiber is a plurality of single-core fibers; Each of the plurality of single-core fibers has a beam expansion portion capable of expanding a mode field diameter of light propagating within a core of the single-core fiber, a plurality of beams propagating between the first lens and the second lens within the tubular member; Optical fiber connection structure.

2. the first lens has a first lens end surface facing the first ferrule, the first ferrule has a first ferrule end surface facing the first lens, an inclination angle of the first lens end face with respect to a plane perpendicular to the axial direction is different from an inclination angle of the first ferrule end face with respect to the plane perpendicular to the axial direction, Light is emitted from the first lens toward the second lens along the axial direction.

2. The optical fiber connection structure according to claim 1.

3. The second ferrule has a second ferrule end face facing the second lens, an inclination angle of the second lens end face with respect to a plane perpendicular to the axial direction is different from an inclination angle of the second ferrule end face with respect to a plane perpendicular to the axial direction, Light is emitted from the second lens toward the first lens along the axial direction.

3. The optical fiber connection structure according to claim 1 or 2.

4. a Faraday element disposed inside the tubular member; The optical fiber connection structure according to any one of claims 1 to 3.

5. Either the first optical fiber or the second optical fiber is a dual-core optical fiber, a WDM filter disposed inside the tubular member; The optical fiber connection structure according to any one of claims 1 to 3.

6. The maximum thickness of the adhesive is 50 μm or less. The optical fiber connection structure according to any one of claims 1 to 5.

Images