Optical fiber bundle structure, method for manufacturing an optical fiber bundle structure

Abstract

The present invention provides an optical fiber bundle structure that can reliably bundle the small-diameter portions in the most dense arrangement, even when the number of bundled optical fibers increases. [Solution] The optical fiber core 19 is composed of a glass fiber section 7 and a resin-coated section 9, in order from the tip. The tip of the glass fiber section 7 is a narrow-diameter section 13, which has a smaller diameter than the glass fiber diameter in the resin-coated section 9. The ends of the narrow-diameter section 13 are arranged in a nearly close-packed structure and fixed to the reduced-diameter section 21 of the holding member 15 with adhesive. The constant-diameter section 11 is arranged in a nearly close-packed structure inside the holding member 15. The tip of the resin-coated section 9 is inserted into the enlarged-diameter section 23. In other words, the holding member 15 houses the glass fiber section 7 and a part of the resin-coated section 9.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber bundle structure, etc., that can be connected to a multicore fiber, etc., in which cores are arranged at predetermined intervals. [Background technology]

[0002] The recent surge in optical communication traffic has created a demand for increased transmission capacity. Therefore, as a means of further expanding communication capacity, multi-core fibers, in which multiple cores are formed within a single optical fiber, have been proposed as an alternative to single-core optical fibers.

[0003] When a multicore fiber is used as a transmission path, each core of the multicore fiber needs to be connected to the corresponding core of another multicore fiber, or to a separate single-core fiber or light-emitting / receiving device, to send and receive transmission signals. As a method for connecting a multicore fiber and a single-core fiber, a method has been proposed in which a bundle fiber, in which single-core optical fibers are arranged at positions corresponding to the cores of the multicore fiber, is connected to send and receive transmission signals (Patent Document 1).

[0004] Patent Document 1 describes a method for forming a bundle structure by assembling small-diameter glass fibers in a close-packed arrangement using the surface tension of an adhesive. Patent Document 1 discloses a 7-core bundle structure in which six optical fiber cores are arranged in a single layer around a central optical fiber core. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-181791 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, as described in Patent Document 1, if, for example, the resin coating of a normal-diameter resin-coated optical fiber is removed, the exposed glass fiber is thinned by etching or the like, and the thinned portion is bundled, then it is necessary to move the thinned portion toward the center by an amount corresponding to the difference in diameter between the normal-diameter portion and the thinned portion. This amount of movement increases as the difference in diameter between the thinned portion and the normal-diameter portion increases, and as the number of bundled fibers increases (i.e., when multiple layers of optical fibers are bundled around the outer circumference of a central optical fiber).

[0007] As the amount of movement of the optical fiber increases, the amount of bending of the optical fiber also increases, resulting in a greater restoring force in the radially outward direction of the optical fiber. This makes it difficult for the surface tension of the adhesive to assemble the narrow-diameter portions of the optical fiber into a close-packed arrangement.

[0008] In contrast, if thin optical fibers with no diameter change are bundled together and connected to standard-diameter optical fibers, the difference in fiber diameter between the connected fibers is large, which may increase connection loss during fusion splicing, for example. Furthermore, thin optical fibers are difficult to handle.

[0009] On the other hand, conventional optical fibers use resin-coated optical fibers, in which the outer circumference of a glass fiber is coated with resin. Because the outer diameter of the resin-coated portion is larger, glass fibers from which the resin has been removed are bundled together to reduce the difference in diameter between the resin-coated portion and the smaller portion. However, if the edges of the holding members that support the bundle structure come into contact with the glass fibers, the glass fibers may be damaged, leading to malfunctions that degrade reliability or even breakage.

[0010] This invention has been made in view of the above problems, and aims to provide an optical fiber bundle structure, etc., that can reliably bundle the small-diameter portions in the closest possible arrangement, even when the number of bundled optical fibers increases. [Means for solving the problem]

[0011] To achieve the aforementioned objective, the first invention is an optical fiber bundle structure comprising a plurality of optical fiber cores and a holding member for holding the plurality of optical fiber cores, wherein the optical fiber cores, in order from the tip, comprise a glass fiber portion and a resin-coated portion in which the glass fiber is coated with resin, the tip of the glass fiber portion is a narrow-diameter portion with a diameter smaller than the glass fiber diameter in the resin-coated portion, the glass fiber portion, in order from the tip, comprises the narrow-diameter portion and a constant-diameter portion having a diameter substantially the same as the glass fiber diameter in the resin-coated portion, the holding member houses a portion of the glass fiber portion and the resin-coated portion, the ends of the narrow-diameter portion are arranged in a substantially close-packed structure and fixed with adhesive, and the constant-diameter portion is arranged in a substantially close-packed structure and fixed with adhesive.

[0012] The optical fiber cores may consist of 19 or more fibers, with one fiber at the center, six fiber at the center arranged in the densest possible arrangement as a first layer, and twelve fiber at the densest possible arrangement as a second layer around the first layer.

[0013] Preferably, the diameter of the optical fiber core in the resin-coated portion is 255 μm or less, the diameter of the glass fiber in the resin-coated portion is 50 μm or more and 125 μm or less, the diameter of the glass fiber in the narrow-diameter portion is 25 μm or more and 45 μm or less, and the length of the narrow-diameter portion is 5 mm or more and 30 mm or less.

[0014] Furthermore, it is desirable that the glass fiber diameter in the resin-coated portion is 75 μm or more and 85 μm or less, and the diameter of the optical fiber core in the resin-coated portion is 160 μm to 170 μm.

[0015] The thickness of the resin layer in the aforementioned resin-coated portion is preferably 5 μm or more.

[0016] At least the small diameter portion may be surface-modified with plasma or ultraviolet light.

[0017] The holding member has a reduced-diameter portion disposed on the tip side and an enlarged-diameter portion disposed on the rear end side and having an inner diameter larger than that of the reduced-diameter portion. The enlarged-diameter portion has a diameter into which the resin-coated portions arranged in the closest packing can be inserted. The reduced-diameter portion is provided with the thin-diameter portion, and the sizing portion is disposed in the enlarged-diameter portion, and the tip of the resin-coated portion is inserted. The thin-diameter portion may be fixed to the reduced-diameter portion, and the tip of the resin-coated portion may be fixed to the enlarged-diameter portion.

[0018] In order to achieve the above object, a second invention is a method for manufacturing an optical fiber bundle structure according to the first invention. When arranging the ends of the thin-diameter portions in a substantially closest-packed structure and fixing them with an adhesive, the surface tension s = (P × r L / M) 4 of the adhesive, and the restoring force ω = 8EIσ / L from the bending of the glass fiber portion 4 (where P: paracol, r L : the liquid density of the adhesive (g / cm 3 ), M: the molecular weight of the adhesive (g / mol), E: the Young's modulus of the glass fiber portion (GPa), I: the second moment of area in the thin-diameter portion (mm 4 ), σ: the amount of bending of the thin-diameter portion (mm), L: the length of the glass fiber portion (mm)), when s > ω, the holding member houses a part of the glass fiber portions arranged in the closest packing and the resin-coated portion, and fixes the thin-diameter portion and the tip of the resin-coated portion to the holding member. This is a method for manufacturing an optical fiber bundle structure.

Effect of the Invention

[0019] According to the present invention, even when the number of optical fibers to be assembled increases, it is possible to provide an optical fiber bundle structure or the like that can surely assemble the thin-diameter portions in the closest packing.

Brief Description of the Drawings

[0020] [Figure 1] A cross-sectional view showing the optical fiber connection structure 1. [Figure 2] (a) is a cross-sectional view taken along line A-A of FIG. 1, and (b) is a cross-sectional view taken along line B-B of FIG. 1. [Figure 3] (a) is a cross-sectional view taken along line C-C of FIG. 1, and (b) is a cross-sectional view taken along line D-D of FIG. 1. [Figure 4] A view showing an end portion of the optical fiber core wire 19. [Figure 5] A view showing a process of gathering the optical fiber core wires 19 to form a bundle structure. [Figure 6] (a) is a view showing the optical fiber connection structure 1a, and (b) is a view showing the optical fiber connection structure 1b.

Embodiments for Carrying out the Invention

[0021] Hereinafter, the bundle structure of the optical fiber will be described. FIG. 1 is a view showing an optical fiber connection structure 1 in which a bundle structure 5 and a multi-core fiber are connected. Further, FIG. 2(a) is a cross-sectional view taken along line A-A of FIG. 1, FIG. 2(b) is a cross-sectional view taken along line B-B of FIG. 1, FIG. 3(a) is a cross-sectional view taken along line C-C of FIG. 1, and FIG. 3(b) is a cross-sectional view taken along line D-D of FIG. 1.

[0022] The multi-core fiber 3 is inserted into and fixed to the capillary 17. The multi-core fiber 3 has a plurality of cores arranged at a predetermined interval, and a cladding is provided so as to surround the cores. In the example shown in FIG. 2(a), the multi-core fiber 3 has 19 cores arranged at equal intervals.

[0023] The bundle structure 5 connected to the multi-core fiber 3 includes a plurality of optical fiber core wires 19 having the same diameter and a holding member 15 for holding the plurality of optical fiber core wires 19. The holding member 15 can be used as a ferrule.

[0024] The optical fiber core 19 is a single-core optical fiber consisting of a core and a cladding surrounding the core. The optical fiber core 19 is composed of a glass fiber section 7 and a resin-coated section 9, where the glass fiber is coated with resin, starting from the tip. The glass fiber section 7 is composed of a narrow-diameter section 13 and a constant-diameter section 11, which has a larger outer diameter than the narrow-diameter section 13 and is approximately the same diameter as the glass fiber in the resin-coated section 9. In other words, the resin-coated section 9 is formed by coating the glass fiber in the constant-diameter section 11 with resin, and the tip of the glass fiber section 7 becomes a narrow-diameter section 13, which has a smaller diameter than the glass fiber in the resin-coated section 9.

[0025] The narrow-diameter portion 13 is formed by removing the resin from the resin-coated portion 9 to expose the internal glass fibers, and then performing chemical etching on a predetermined length of the tip end of the exposed glass fibers. In other words, the constant-diameter portion 11 is a larger diameter portion relative to the narrow-diameter portion 13. The narrow-diameter portion 13 may also be designed so that its diameter gradually decreases from the boundary with the constant-diameter portion 11 towards the tip.

[0026] Furthermore, the outer diameter of the small-diameter section 13 is approximately equal to the core pitch of the multicore fiber 3, and is preferably, for example, 25 μm to 45 μm, in order to connect with a high-density multicore fiber. Also, the length of the small-diameter section 13 is preferably 5 mm to 30 mm. If the length of the small-diameter section 13 is less than 5 mm, bundling of the small-diameter section 13 becomes difficult, and if the length of the small-diameter section 13 exceeds 30 mm, the length of the bundle structure 5 increases, and the transmission loss leaking from the cladding becomes negligible.

[0027] Furthermore, the outer diameter of the constant diameter section 11 (the outer diameter of the maximum outer diameter section excluding the diameter change section in the constant diameter section 11, and the glass fiber diameter in the resin-coated section 9) is preferably, for example, 50 μm or more and 125 μm or less, and more preferably 75 μm or more and 85 μm or less. Also, the length of the constant diameter section 11 (the length from the end of the resin-coated section 9 to the end of the thin diameter section 13, which is the sum of the length of the section with the same diameter as the glass fiber diameter in the resin-coated section 9 and the length of the diameter change section where the diameter changes towards the thin diameter section 13) is preferably, for example, 1 mm or more and 5 mm or less. In other words, the total length of the glass fiber section 7 is preferably 35 mm or less. Note that the straight section with the same diameter as the glass fiber diameter in the resin-coated section 9 may be eliminated in the constant diameter section 11, and the diameter change section may be made from the end of the resin-coated section 9.

[0028] The diameter of the optical fiber core 19 in the resin-coated portion 9 (the outer diameter of the resin coating around the glass fiber) is preferably 255 μm or less, and more preferably 160 μm to 170 μm. Furthermore, the thickness of the resin layer in the resin-coated portion 9 is preferably 5 μm or more. However, if the thickness of the resin layer in the resin-coated portion 9 becomes too thick, the outer diameter difference described later will increase; therefore, the thickness of the resin layer is preferably 65 μm or less, and more preferably 40 μm or less.

[0029] The optical fiber core 19 is inserted through a hole in the retaining member 15 and fixed to the retaining member 15 with adhesive. The retaining member 15 has a rear end portion 23 with a relatively large inner diameter and a front end portion 21 with a relatively small inner diameter.

[0030] As shown in Figure 2(b), the small diameter portion 13 of the optical fiber core 19 is inserted through the diameter-reducing portion 21 formed at the tip of the holding member 15. The ends of the small diameter portion 13 are arranged in a nearly close-packed structure and fixed to the diameter-reducing portion 21 of the holding member 15 with adhesive. The inner diameter of the diameter-reducing portion 21 is made to be approximately the same diameter as the circumscribed circle of the closest arrangement (for example, the diameter of the circumscribed circle + 1 μm or less) so as to allow insertion of the closely arranged small diameter portion 13 and to hold the closely arranged small diameter portion 13. In this way, the small diameter portion 13 can be arranged in a close-packed arrangement with high precision in the diameter-reducing portion 21.

[0031] As shown in Figure 3(a), the diameter-regulating portion 11 is positioned on the enlarged diameter portion 23 of the holding member 15. The diameter-regulating portions 11 are arranged in a nearly close-packed structure inside the holding member 15. Note that the diameter-regulating portions 11 do not necessarily have to be in close contact with each other.

[0032] Furthermore, the tip of the resin-coated portion 9 is inserted into the enlarged diameter portion 23. In other words, the holding member 15 houses the glass fiber portion 7 and a part of the resin-coated portion 9. As shown in Figure 3(b), the resin-coated portions 9 are arranged in a nearly close arrangement. The inner diameter of the enlarged diameter portion 23 is configured to be approximately the same diameter as the circumscribed circle of the closely arranged resin-coated portion 9, to the extent that the closely arranged resin-coated portion 9 can be inserted into and the closely arranged resin-coated portion 9 can be held in place.

[0033] Next, the manufacturing method of the bundle structure 5 will be described. First, as shown in Figure 4, the coating is removed from a predetermined number of optical fiber cores 19. The tip portions of the exposed glass fiber sections 7 are then thinned by etching or the like to form thinned sections 13 on the end side of the constant diameter section 11. Next, the formed thinned sections 13 are assembled and inserted into the temporary holding member 27. The temporary holding member 27 has holes into which the glass fiber sections 7 can be inserted. The diameter of the holes decreases from the insertion end to the other end.

[0034] Figure 5 shows that the glass fiber portion 7 is inserted into the temporary holding member 27, and the tip of the glass fiber portion 7 protruding from the end of the temporary holding member 27 is immersed in the adhesive 25 that has been pre-prepared in a container. At this time, the optical fiber core wire 19 is inserted into the temporary holding member 27 such that the tips of the thin diameter portions 13 protrude by approximately the same length (for example, about 10 mm) from the end of the temporary holding member 27. The temporary holding member 27 is temporarily fixed to the optical fiber core wire 19, for example.

[0035] The adhesive 25 is, for example, a solution-based adhesive, in which high-molecular-weight solid components such as synthetic resins are dissolved in a solvent such as water, alcohol, or an organic solvent. In such solution-based adhesives, bonding occurs when the solute remaining after the solvent vaporizes hardens. It is desirable that the adhesive 25 be diluted even further than the solute concentration normally used. This reduces the viscosity of the adhesive and suppresses the amount of residual solute. As a result, the adhesive layer in the gaps between optical fiber cores can be made thinner, and the spacing between the small diameter sections 13 can be made more precise and consistent.

[0036] Here, within the temporary holding member 27, the small diameter portions 13 are inserted in a nearly close-to-close state. However, before the tips of the small diameter portions 13 are immersed in the adhesive 25, gaps are formed between them in some places, while they are in close contact with each other in other places, making it difficult to achieve a perfectly close arrangement (constant core spacing).

[0037] Thus, when the parts are simply inserted into the temporary holding member 27, gaps may form between the small diameter parts 13. However, because the viscosity of the adhesive 25 is low, the adhesive 25 is drawn into the gaps between the small diameter parts 13 by surface tension (capillary action). At this time, the small diameter parts 13 are brought into close contact with each other by their respective surface tensions.

[0038] That is, even if there are somewhat non-uniform gaps formed between the gathered small-diameter portions 13, the adhesive 25 is sucked into the gaps, and the small-diameter portions 13 are brought into close contact with each other. At this time, the surface tension of the adhesive existing by being sucked between the respective fibers is stabilized, that is, the small-diameter portions 13 are surely arranged in the closest packing, and by curing the adhesive 25 in this state, they can be adhered to each other.

[0039] Here, in the present invention, the number of optical fiber cores 19 constituting the bundle structure 5 is not particularly limited, but it is preferably 19 or more. That is, one optical fiber core 19 is arranged at the center, and six optical fiber cores 19 are arranged in the closest packing as the first layer around it, and further, twelve optical fiber cores 19 are arranged in the closest packing as the second layer around it. Further, optical fiber cores 19 may be arranged in the closest packing in the third layer and above.

[0040] Here, even if the resin coating portions 9 are arranged in the closest packing, the small-diameter portions 13 of the first layer need to move closer to the central small-diameter portion 13 by a radial distance corresponding to the outer diameter difference between the resin coating portion 9 and the small-diameter portion 13. Further, the small-diameter portions 13 of the second layer require a movement amount twice that of the small-diameter portions 13 of the first layer. That is, the optical fiber cores 19 of the second layer require a larger amount of deformation than the optical fiber cores 19 of the first layer.

[0041] Here, the surface tension s of the adhesive 25 is represented by (P×r L / M) 4 [[ID=1in]]and the restoring force ω from the deflection of the glass fiber portion 7 is represented by 8EIσ / L [[ID=ins]] 4 4 . However, P: para-cresol, r L : liquid density of the adhesive 25 (g / cm 3 ), M: molecular weight of the adhesive 25 (g / mol), E: Young's modulus of the glass fiber portion 7 (GPa), I: second moment of area in the small-diameter portion 13 (mm 4 ), σ: deflection amount of the small-diameter portion 13 (mm), L: length of the glass fiber portion 7 (mm). In this case, it is necessary that s>ω. [[ID=ins]]

[0042] Furthermore, as mentioned above, the amount of deflection of the optical fiber core 19 is greater in the second layer than in the first layer. For example, in a 19-core (two-layer close-packed arrangement), the second layer of optical fiber core requires a deflection of (outer diameter of resin-coated portion 9 - outer diameter of thin portion 13) × 2. Therefore, to satisfy the above inequality, it is desirable to increase L or decrease the outer diameter of the thin portion 13 to reduce ω, thereby increasing the amount of deflection.

[0043] On the other hand, reducing the outer diameter of the narrow-diameter portion 13 increases the difference in outer diameters mentioned above, so it is necessary to set an appropriate outer diameter of the narrow-diameter portion 13 so as to satisfy the above inequality. In other words, it is necessary to set the outer diameter of the resin-coated portion 9, etc., so as to satisfy the above inequality with respect to a predetermined outer diameter of the narrow-diameter portion 13.

[0044] Furthermore, at least a portion of the narrow diameter portion 13 may be surface-modified with plasma or ultraviolet light. Doing so improves wettability with the adhesive 25, allowing the adhesive 25 to be absorbed more smoothly, and enabling the narrow diameter portions 13 to be bonded to each other more reliably by satisfying the above inequality. The surface modification may be performed on the entire narrow diameter portion 13, only on the tip of the narrow diameter portion 13, or on a predetermined area excluding the tip of the narrow diameter portion 13.

[0045] Furthermore, when assembling and bonding the small diameter sections 13, the standard diameter sections 11 may also be assembled and bonded together. When the standard diameter sections 11 are arranged in a nearly close-packed configuration, for example, even with 19 cores (two layers in a close-packed configuration), the required amount of deflection described above becomes (outer diameter of the resin-coated section 9 - outer diameter of the standard diameter section 11) × 2, which is smaller than when the small diameter sections 13 are assembled from the resin-coated section 9 (in this case, L = length of the standard diameter section 11 excluding the tapered section). Also in this case, the required amount of deflection for the small diameter sections 13 becomes (outer diameter of the standard diameter section 11 - outer diameter of the small diameter section 13) × 2, which is smaller than when the small diameter sections 13 are assembled from the resin-coated section 9. By doing so, by forming a close-packed configuration of standard diameter sections 11 in the middle, the restoring force due to the deflection of the optical fiber is dispersed, and the small diameter sections 13 can be more reliably arranged and fixed in a close-packed configuration.

[0046] Next, the temporary holding member 27 is removed, and with the small diameter portions 13 bonded together in the tightest possible position, the optical fiber core 19 is inserted into the holding member 15, thereby bonding the holding member 15 to the small diameter portions 13. Also, as mentioned above, since a portion of the resin coating portion 9 is inserted into the holding member 15, the resin coating portion 9 and the holding member 15 are bonded together with adhesive. Alternatively, the small diameter portions 13 may be assembled and bonded directly using the holding member 15 without using the temporary holding member 27.

[0047] Finally, the bundle structure 5 is formed by polishing the optical fiber core 19 protruding from the holding member 15 and a portion of the holding member 15. Note that instead of obtaining a uniform surface on the end face of the bundle structure by polishing, a uniform surface may be obtained by cutting, for example, with a dicing saw.

[0048] A multicore fiber 3 is optically connected to the tip (end face of the narrow-diameter section 13) of the resulting bundle structure 5 by fusion splicing. At this time, the capillary 17 and the holding member 15 are also connected. In addition, a normal single-mode optical fiber is connected to the other end (the end on the resin-coated section 9 side) of the bundle structure 5.

[0049] In the optical fiber connection structure obtained in this manner, it is desirable that the sum of the insertion loss of the bundle structure 5, the connection loss between the multicore fiber 3 and the bundle structure 5, and the connection loss between the bundle structure and the single-mode optical fiber be 3.0 dB or less, and more preferably 0.5 dB or less.

[0050] As mentioned above, when connecting the bundle structure 5 and the multicore fiber 3 by fusion splicing, a heat-resistant adhesive may be used as the adhesive. Alternatively, glass powder may be mixed with a solvent, the fiber cores may be brought into close contact by capillary action using the method described above, and then the solvent may be evaporated, leaving only the glass powder. Water glass (liquid glass / sol-gel glass) may also be used as the adhesive.

[0051] As described above, according to this embodiment, even in bundle structures with 19 or more cores (two or more layers excluding the center) arranged in the closest possible density, the small diameter portion 13 can be reliably arranged in the closest possible density and bonded and fixed. Furthermore, since a part of the resin coating portion 9 is inserted at the rear end of the holding member 15, the rear edge of the holding member 15 and the glass fiber do not come into direct contact, thereby suppressing damage to the glass fiber.

[0052] Note that the form of the retaining member is not limited to the example shown in Figure 1. For example, as shown in Figure 6(a), an optical fiber connection structure 1a using a retaining member 15a may also be used. The retaining member 15a has a structure substantially the same as that of the retaining member 15, but a tapered shape is formed between the enlarged diameter portion 23 and the reduced diameter portion 21. By creating a tapered shape in which the diameter gradually decreases from the enlarged diameter portion 23 to the reduced diameter portion 21, the insertability of the bundle structure 5 is improved.

[0053] Alternatively, as shown in Figure 6(b), an optical fiber connection structure 1b using a holding member 15b may be used. The holding member 15b has substantially the same structure as the holding member 15, but the enlarged diameter portion 23 has two diameter stages, consisting of a first enlarged diameter portion into which the resin coated portion 9 is inserted, and a second enlarged diameter portion connected to the first enlarged diameter portion via a tapered portion, and having a smaller diameter than the first enlarged diameter portion. The resin coated portion 9 is held in the first enlarged diameter portion, and the constant diameter portion 11 is held in the second enlarged diameter portion. For example, the second enlarged diameter portion makes it easy to arrange and fix the constant diameter portion 11 in substantially the closest arrangement, and the small diameter portion 13 can be fixed in a closer arrangement more reliably. Furthermore, a tapered shape may be formed on the rear end side of the enlarged diameter portion 23 to improve insertability. [Examples]

[0054] A bundle structure was created and its losses were evaluated. A multicore fiber with 19 cores and a core pitch of 40 μm was used. For the optical fiber cores used in the bundle structure, a predetermined length of resin coating was removed, and a predetermined length of the tip was etched with hydrofluoric acid to form a narrow section with an outer diameter of 40 μm. The core pitch (outer diameter) of the resulting optical fiber cores was set to 40 μm for the narrow section when closely packed, 80 μm for the standard-diameter section, and 165 μm for the resin-coated section. In addition, narrow sections of 10 mm and 20 mm in length were prepared.

[0055] The retaining member has the same internal configuration as shown in Figure 6(a). The reduced diameter section has an inner diameter of approximately 200 μm (an inner diameter that can accommodate five 40 μm thin sections) and a length of 8 mm, while the expanded diameter section has an inner diameter of approximately 825 μm (an inner diameter that can accommodate five 165 μm resin-coated sections). The minimum wall thickness of the retaining member is 0.1 mm.

[0056] The bundle structure described above was fabricated without any degradation in characteristics or damage to the components. The insertion loss of the optical fiber bundle was measured as follows: Light was incident on the single-mode optical fiber of each fiber in the bundle structure, and the light was received by the single-mode optical fiber at the other end via the bundle structure and measured with a power meter (P1). Furthermore, the bundle structure portion was cut off and measured similarly (P0), and the difference (P0-P1) was taken as the difference in received power with and without the optical fiber bundle, and this difference was taken as the insertion loss of the optical fiber bundle. This measurement was performed on all 19 fibers.

[0057] Furthermore, the optical fiber bundle structure, whose insertion loss was known from the above measurements, was bonded and fixed to the multicore fiber with the core positions aligned. Light was then incident from the single-mode optical fiber side of one end of the optical fiber bundle, and the output on the multicore fiber side was measured with a power meter (P2). In this case, the increase from the insertion loss of the optical fiber bundle (P1-P2) was defined as the connection loss between the multicore fiber and the optical fiber bundle structure.

[0058] Furthermore, fusion splicing was performed between the fiber on the resin-coated side of an optical fiber bundle with known insertion loss based on the above measurements and a standard 125 μm outer diameter single-mode optical fiber. Similarly, light was incident from the single-mode fiber side, and the output on the multi-core fiber side was measured with a power meter (P3). In this case, the increase in loss (P2-P3) was taken as the fusion splicing loss between the optical fiber bundle and the single-mode optical fiber.

[0059] Measurements taken using the above method showed that the insertion loss of the optical fiber bundle was a maximum of 1.5 dB, the connection loss between the multicore fiber and the optical fiber bundle structure was a maximum of 1.2 dB, and the fusion splicing loss between the optical fiber bundle and the single-mode optical fiber was 0.3 dB. The results were similar for both the 10 mm and 20 mm diameter sections. It is also possible to achieve a total loss of 0.5 dB by improving the outer diameter accuracy to match the core pitch of the multicore fiber with the outer diameter of the small-diameter fiber.

[0060] Although embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the embodiments described above. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also fall within the technical scope of the present invention. [Explanation of Symbols]

[0061] 1, 1a, 1b... Optical fiber connection structure 3… Multicore fiber 5… Bundle structure 7………Glass fiber section 9………Resin coated part 11... Diameter-regulating section 13...Narrow section 15, 15a, 15b... Retaining members 17... Capillary 19… Optical fiber core 21……Reduced diameter part 23……Expanded diameter part 25… Adhesive 27... Temporary holding member

Claims

1. Multiple optical fiber cores, A holding member that holds multiple optical fiber cores, It is equipped with, The aforementioned optical fiber core comprises, in order from the tip, a glass fiber portion and a resin-coated portion in which the glass fiber is coated with resin. The tip of the glass fiber portion is a narrow-diameter portion with a diameter smaller than the glass fiber diameter in the resin-coated portion, and the glass fiber portion comprises, in order from the tip, the narrow-diameter portion and a constant-diameter portion having approximately the same diameter as the glass fiber diameter in the resin-coated portion. The holding member houses the glass fiber portion and a portion of the resin coating portion, and the ends of the small diameter portion are arranged in a substantially close-packed structure and fixed with adhesive. An optical fiber bundle structure characterized in that the constant diameter portions are arranged in a substantially close-packed structure and fixed with an adhesive.

2. The optical fiber bundle structure according to claim 1, characterized in that the optical fiber cores consist of 19 or more fibers, with one optical fiber core positioned in the center, six optical fiber cores arranged in the densest possible way around it as a first layer, and twelve optical fiber cores arranged in the densest possible way around the first layer as a second layer.

3. The diameter of the optical fiber core in the resin-coated portion is 255 μm or less. The glass fiber diameter in the resin-coated portion is 50 μm or more and 125 μm or less. The glass fiber diameter in the aforementioned narrow portion is 25 μm or more and 45 μm or less. The optical fiber bundle structure according to claim 1, characterized in that the length of the small diameter portion is 5 mm or more and 30 mm or less.

4. The glass fiber diameter in the resin-coated portion is 75 μm or more and 85 μm or less. The optical fiber bundle structure according to claim 3, characterized in that the diameter of the optical fiber core in the resin-coated portion is 160 μm to 170 μm.

5. The optical fiber bundle structure according to claim 1, characterized in that the thickness of the resin layer in the resin-coated portion is 5 μm or more.

6. The optical fiber bundle structure according to claim 1, characterized in that at least a portion of the small diameter portion is surface modified with plasma or ultraviolet light.

7. The holding member has a reduced diameter portion located at the front end and a widened diameter portion located at the rear end, which has a larger inner diameter than the reduced diameter portion. The enlarged diameter portion has a diameter into which the closely arranged resin-coated portions can be inserted. The reduced diameter portion is arranged in the reduced diameter portion, the constant diameter portion is arranged in the enlarged diameter portion, and the tip of the resin-coated portion is inserted into it. The optical fiber bundle structure according to claim 1, characterized in that the small diameter portion is fixed to the reduced diameter portion, and the tip of the resin-coated portion is fixed to the enlarged diameter portion.

8. A method for manufacturing an optical fiber bundle structure according to claim 1, When arranging the ends of the aforementioned small diameter portions in a nearly close-packed structure and fixing them with adhesive, The surface tension s = (P × r) due to the adhesive Ｌ / M) ４ The restoring force from the bending of the glass fiber portion is ω = 8EIσ / L ４ (However, P: parachol, r Ｌ : Liquid density of the adhesive (g / cm³) ３ ), M: Molecular weight of the adhesive (g / mol), E: Young's modulus of the glass fiber portion (GPa), I: Second moment of area of ​​the narrow diameter portion (mm ４ ), when σ: amount of deflection of the thin diameter part (mm), L: length of the glass fiber part (mm), s > ω, A method for manufacturing an optical fiber bundle structure, characterized in that the close-packed glass fiber portion and a portion of the resin coating portion are housed in the holding member, and the tip of the small-diameter portion and the resin coating portion are fixed to the holding member.

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