Optical fiber bundle structure, optical fiber connection structure, and method for manufacturing optical fiber bundle structure

Abstract

An optical fiber fanout (60) has a plurality of optical fiber cores (60a) and capillary tubes (620), the optical fiber core (60a) has a glass fiber portion having a core (601) and a cladding (602), and a resin covering portion (603), the capillary tube (620) is inserted by the glass fiber portion, in a case where a diameter of the core of the glass fiber portion at a rear end portion of the capillary tube (620) is set as d1, and a diameter of the core of the glass fiber portion at a front end portion of the capillary tube (620) is set as d2, d2 / d1 is 0.57 or more and less than 1.

Description

Technical Field

[0001] This invention relates to optical fiber bundle structures, optical fiber connection structures, and methods for manufacturing optical fiber bundle structures. Background Technology

[0002] As a fiber bundle connection structure for connecting single-mode or minority-mode optical fibers with multimode optical fibers, there is an optical fiber bundle structure disclosed in Patent Document 1. A fiber bundle with single-mode or minority-mode fiber cores arranged in a hexagonal configuration is inserted into a cladding tube, and then drawn to make both the fiber bundle and the cladding tube tapered, thereby forming the optical fiber bundle structure disclosed in Patent Document 1.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: JP Patent No. 5738275 Summary of the Invention

[0006] -The problem the invention aims to solve-

[0007] In the fiber bundle structure disclosed in Patent Document 1, the taper obtained by dividing the first outer diameter of the input end by the second outer diameter of the output end is set to 3 or more and 10 or less. When drawing the fiber to achieve such a taper, the distance between the fiber cores becomes narrower, resulting in crosstalk. Therefore, this fiber bundle structure is not preferred as it connects the core portions of single-mode or few-mode optical fibers with the core portions of multi-core optical fibers.

[0008] The present invention was made in view of the above circumstances, and its object is to provide an optical fiber bundle structure, an optical fiber connection structure, and a method for manufacturing an optical fiber bundle structure that suppresses crosstalk.

[0009] -Methods for solving problems-

[0010] One aspect of the present invention is an optical fiber bundle structure comprising: a plurality of optical fiber cores; and a capillary, wherein each optical fiber core comprises: a glass optical fiber portion having a core and a cladding; and a resin covering portion, and the capillary is inserted into the glass optical fiber portion, wherein when the diameter of the core of the glass optical fiber portion at the rear end of the capillary is set to d1 and the diameter of the core of the glass optical fiber portion at the front end of the capillary is set to d2, d2 / d1 is 0.57 or more and less than 1.

[0011] In one embodiment of the invention, the optical fiber core may have a single-peak refractive index distribution that sets a relative refractive index difference between the core and the cladding to enable single-mode propagation of light in a given wavelength band.

[0012] In one embodiment of the invention, the optical fiber core may propagate light with wavelengths above 950 nm in single mode.

[0013] In one embodiment of the invention, the optical fiber core may propagate light with wavelengths above 1260 nm in single mode.

[0014] In one embodiment of the invention, the space between the inner wall of the capillary and the cladding of the optical fiber core may be filled with sol-gel glass, inorganic adhesive, or water glass.

[0015] In one embodiment of the invention, the capillary may be hollow and have a large diameter portion, a tapered portion, and a small diameter portion.

[0016] In one embodiment of the invention, at least a portion of the cladding of the plurality of optical fiber cores or a portion of the cladding of the optical fiber cores and the inner wall of the capillary may be fused together in the narrow diameter portion.

[0017] In one embodiment of the invention, the diameter of the cladding located in the narrower diameter portion may be smaller than the diameter of the cladding located in the wider diameter portion.

[0018] In one embodiment of the invention, the cladding may have a pointed portion that tapers in diameter toward the front end, the pointed portion being located inside the tapered portion.

[0019] In one embodiment of the invention, t ≤ 3.1Λ may be used when the wall thickness of the narrow diameter portion of the capillary is set to t and the distance between the fiber cores of the plurality of optical fiber cores located in the narrow diameter portion is set to Λ.

[0020] In one embodiment of the invention, the number of fiber cores may be 4, and t≤2.0Λ.

[0021] In one embodiment of the invention, the number of fiber cores may be 7, and t≤2.5Λ.

[0022] In one embodiment of the invention, the number of fiber cores may be 19, and t≤3.1Λ.

[0023] One aspect of the present invention is an optical fiber connection structure comprising: an optical fiber bundle structure as described in any of the preceding claims; and a multi-core optical fiber having a plurality of core portions connected to the cores of the plurality of optical fiber cores and a cladding portion formed on the outer periphery of the core portions.

[0024] One aspect of the present invention is a method for manufacturing an optical fiber bundle structure comprising the following steps: an insertion step in which a glass optical fiber portion having a glass optical fiber portion and a resin-coated optical fiber core is inserted into a capillary tube, wherein the glass optical fiber portion has a fiber core and a cladding; a melt-stretching step in which the diameter of the fiber core of the glass optical fiber portion at the rear end of the capillary tube is set to d1 and the diameter of the fiber core of the glass optical fiber portion at the front end of the capillary tube is set to d2, and the capillary tube and the glass optical fiber portion inserted into the capillary tube are melted and stretched such that d2 / d1 is 0.57 or more and less than 1; and a cutting step in which the portion extended by the melt-stretching step is cut off such that a cross-section intersecting the axial direction of the capillary tube is exposed.

[0025] -Invention Effects-

[0026] According to the present invention, it is possible to provide an optical fiber bundle structure that suppresses crosstalk, an optical fiber connection structure, and a method for manufacturing the optical fiber bundle structure. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the structure of the optical amplifier involved in the embodiment.

[0028] Figure 2 This is an axial cross-sectional view of a single-mode optical fiber.

[0029] Figure 3 It is a cross-sectional view of the axial direction of the fiber fan-out.

[0030] Figure 4 It is a radial cross-sectional view of the narrow section fanned out by the optical fiber.

[0031] Figure 5A This is a graph representing the simulation results of single-mode optical fiber.

[0032] Figure 5B This is a graph representing the simulation results of single-mode optical fiber.

[0033] Figure 5C This is a graph representing the simulation results of single-mode optical fiber.

[0034] Figure 6A This is a graph representing the simulation results of single-mode optical fiber.

[0035] Figure 6B This is a graph representing the simulation results of single-mode optical fiber.

[0036] Figure 6C This is a graph representing the simulation results of single-mode optical fiber.

[0037] Figure 6D This is a graph representing the simulation results of single-mode optical fiber.

[0038] Figure 7 This is a graph showing the refractive index distribution of a single-mode optical fiber.

[0039] Figure 8A This is a graph representing the simulation results of single-mode optical fiber.

[0040] Figure 8B This is a graph representing the simulation results of single-mode optical fiber.

[0041] Figure 8C This is a graph representing the simulation results of single-mode optical fiber.

[0042] Figure 8D This is a graph representing the simulation results of single-mode optical fiber.

[0043] Figure 9A This is a graph representing the simulation results of single-mode optical fiber.

[0044] Figure 9B This is a graph representing the simulation results of single-mode optical fiber.

[0045] Figure 9C This is a graph representing the simulation results of single-mode optical fiber.

[0046] Figure 10 This is a flowchart of the manufacturing method for fiber fan-out.

[0047] Figure 11 This is a cross-sectional view of the fiber fan-out manufacturing process.

[0048] Figure 12 This is a cross-sectional view of the fiber fan-out manufacturing process.

[0049] Figure 13 This is a cross-sectional view of the fiber fan-out manufacturing process.

[0050] Figure 14 This is a cross-sectional view of the fiber fan-out manufacturing process.

[0051] Figure 15 This is a cross-sectional view of the fiber fan-out manufacturing process. Detailed Implementation

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in the accompanying drawings, the same or corresponding elements are appropriately labeled with the same reference numerals. It should be noted that the drawings are schematic, and the dimensional relationships of the elements may sometimes differ from reality. The drawings may also include portions with different dimensional relationships or ratios. In this specification, the cutoff wavelength or effective cutoff wavelength refers to the optical fiber cutoff wavelength defined in ITU-T G.650.1 of the International Telecommunication Union (ITU). Additionally, terms not specifically defined in this specification follow the definitions and measurement methods in G.650.1 and G.650.2.

[0053] [Implementation Method]

[0054] Figure 1 This is a schematic diagram illustrating the structure of a multi-core fiber amplifier according to an embodiment of the present invention. Hereinafter, the multi-core fiber amplifier will sometimes be referred to simply as an optical amplifier. The optical amplifier 100 includes seven optical isolators 10, a fan-in fiber 20, a semiconductor laser 30, an optical coupler 40, a multi-core optical amplifying fiber 1, a pump stripper 50, a fan-out fiber 60, and seven optical isolators 70. Furthermore, the symbol "×" in the figure indicates a fusion splice of the optical fiber.

[0055] The fiber fan-in 20 comprises seven bundled single-mode fibers 20a and one multi-core fiber 20b having seven fiber cores, wherein each fiber core of the seven single-mode fibers 20a is optically coupled to each fiber core of the multi-core fiber 20b.

[0056] The seven single-mode optical fibers 20a are, for example, standard single-mode optical fibers as defined by ITU-T G.652, each equipped with an optical isolator 10. The optical isolator 10 allows light to pass through in the direction indicated by the arrow, blocking the passage of light in the opposite direction.

[0057] The multi-core fiber 20b of the fiber fan-in 20 includes: seven cores configured in a triangular lattice shape; and a cladding portion located on the outer periphery of each core with a refractive index lower than the maximum refractive index of each core. If signal light is input to each single-mode fiber 20a of the fiber fan-in 20, each optical isolator 10 allows each signal light to pass through, and each core of the multi-core fiber 20b propagates the signal light.

[0058] In addition, the end faces of the bundled seven single-mode fibers 20a and multi-core fibers 20b for optical coupling are processed at an angle relative to the optical axis to suppress reflection, but they can also be perpendicular to the optical axis. The multi-core fiber 20b fan-in of the fiber optic cable 20 is connected to the optical coupler 40.

[0059] The semiconductor laser 30, serving as the excitation source, is a multi-mode semiconductor laser that outputs excitation light. The wavelength of the excitation light is approximately 976 nm, which is roughly the same as the wavelength of the absorption peak of Er in the 900 nm band. Therefore, the excitation light can photoexcite erbium ions. The semiconductor laser 30 outputs excitation light from a multimode fiber 30a. This multimode fiber 30a is a step-index type with a core diameter / cladding diameter of, for example, 105 μm / 125 μm, and a refractive index (NA) of, for example, 0.16 or 0.22.

[0060] The optical coupler 40 includes a main optical fiber 40b and an excitation light supply optical fiber 40a. The main optical fiber 40b is a double-clad optical fiber, comprising: seven cores arranged in a triangular lattice (i.e., hexagonal close-packed) configuration, similar to the cores of the multi-core optical fiber 20b of the fiber fan-in 20; an inner cladding portion located on the outer periphery of each core, having a refractive index lower than the maximum refractive index of each core; and an outer cladding portion located on the outer periphery of the inner cladding portion, having a refractive index lower than the inner cladding portion. The cores and inner cladding portions contain quartz glass, and the outer cladding portion contains resin.

[0061] The excitation light supply fiber 40a is another multimode fiber of the same type, connected at one end to the multimode fiber 30a of the semiconductor laser 30. It is a step-index fiber with a core diameter / cladding diameter of, for example, 105 μm / 125 μm, and an NA of, for example, 0.16 or 0.22. The excitation light supply fiber 40a receives excitation light from the semiconductor laser 30 and supplies it to the main fiber 40b. The excitation light propagates in the inner cladding portion.

[0062] The main optical fiber 40b of the optical coupler 40 connects one end to the multi-core optical fiber 20b of the optical fiber fan-in 20. The main optical fiber 40b is a double-clad optical fiber, comprising: seven cores arranged in a triangular lattice pattern, similar to the cores of the multi-core optical fiber 20b; an inner cladding surrounding each core and having a lower refractive index than the cores; and an outer cladding surrounding the inner cladding and having a lower refractive index than the inner cladding. The cores and inner cladding contain quartz glass, and the outer cladding contains resin.

[0063] Each core of the multi-core fiber 20b is connected to each core of the main fiber 40b. Therefore, if the signal light propagating in each core of the multi-core fiber 20b is input into the main fiber 40b, it will be optically coupled to each core. Each core propagates its own signal light. The excitation light and signal light are output from the main fiber 40b to the multi-core optical amplification fiber 1.

[0064] The multi-core optical amplifying fiber 1 is a 7-core type, comprising: seven optical amplifying cores arranged in a triangular lattice pattern similar to the main fiber 40b; an inner cladding portion formed on the outer periphery of the optical amplifying cores and having a lower refractive index than the optical amplifying cores; and an outer cladding portion formed on the outer periphery of the inner cladding portion and having a lower refractive index than the inner cladding portion. The multi-core optical amplifying fiber 1 is a known cladding-excitation type optical amplifying fiber in which erbium ions, serving as the optical amplification medium, are included in the optical amplifying cores.

[0065] A multi-core optical amplifying fiber 1 is connected at one end to the main fiber 40b of an optical coupler 40. Each optical amplifying core of the multi-core optical amplifying fiber 1 is connected to each core of the main fiber 40b. Furthermore, the inner cladding of the multi-core optical amplifying fiber 1 is connected to the inner cladding of the main fiber 40b. Therefore, when the signal light and excitation light propagating in the main fiber 40b are input into the multi-core optical amplifying fiber 1, they propagate in the same direction in each optical amplifying core and the inner cladding, respectively. While the excitation light propagates in the inner cladding, it optically excites the erbium in each optical amplifying core. The signal light propagating in each optical amplifying core is optically amplified under the stimulated emission of the erbium. The multi-core optical amplifying fiber 1 outputs the optically amplified signal light and the excitation light that does not contribute to optical amplification.

[0066] The pump stripper 50 is a known device for removing excitation light that does not contribute to optical amplification. The pump stripper 50 has the following structure: for example, a portion of the outer cladding of a double-clad multi-core fiber with seven cores is removed; excitation light is extracted from the surface of the inner cladding portion of the removed portion and irradiated onto a heat sink or similar surface, where it is absorbed, converting the energy of the excitation light into heat energy and dissipating it. The pump stripper 50 enables the multi-core fiber to propagate individual signal lights and reduces the excitation light power to a level that is acceptable even when output from the optical amplifier 100.

[0067] Similar to the fiber fan-in, the fiber fan-out 60 includes seven bundled single-mode fibers 60a and one multi-core fiber 60b with seven cores, configured such that each core of the seven single-mode fibers 60a is optically coupled to each core of the multi-core fiber 60b in the coupling section described later. The fiber fan-out 60 is an example of a fiber optic connection structure.

[0068] In single-mode fiber 60a, light with wavelengths above 950 nm propagates in single-mode, but light with wavelengths above 1260 nm can also propagate in single-mode. Such single-mode fiber 60a is an example of an optical fiber core with a single-peak refractive index distribution, where the relative refractive index difference between the core and cladding is set, for example, to 0.35%, to allow single-mode propagation of light in a given wavelength band. Such single-mode fiber 60a is, for example, a standard single-mode fiber defined by ITU-T G.652. Each single-mode fiber 60a is equipped with an optical isolator 70.

[0069] The multi-core fiber 60b is connected to the pump stripper 50. Additionally, the end faces of the bundled seven single-mode fibers 60a and the multi-core fiber 60b that are optically coupled are processed at an angle relative to the optical axis to suppress reflection, but they can also be perpendicular to the optical axis.

[0070] If signal light is input from the cores of the multi-core fiber of the pump stripper 50 to the cores of the multi-core fiber 60b fan-out 60, then each signal light propagates in the core of each single-mode fiber 60a and is output after passing through the optical isolator 70. The optical isolator 70 allows light to pass in the direction indicated by the arrow and blocks light from passing in the opposite direction. Alternatively, instead of the seven optical isolators 10 and 70, an optical isolator integrating multiple (seven in this embodiment) single-mode fibers can be used.

[0071] Figure 2 This is a schematic cross-sectional view of a single-mode optical fiber 60a bundled before the optical fiber fan-out lens 60, showing an axial cross-section of the single-mode optical fiber 60a. The single-mode optical fiber 60a has a core portion 601, a cladding portion 602 formed on the outer periphery of the core portion 601, and a cover portion 603 formed on the outer periphery of the cladding portion 602. The cover portion 603 contains resin suitable for covering the optical fiber. The single-mode optical fiber 60a is an example of an optical fiber core. Furthermore, the core portion 601 and the cladding portion 602 are examples of glass optical fiber portions, and the cover portion 603 is an example of a resin cover portion.

[0072] Furthermore, the single-mode fiber 60a is generally divided into a narrow diameter portion 611, a tapered portion 612, and a wide diameter portion 613 along its axial direction. The tapered portion 612 is formed by etching the cladding portion 602 into a tapered shape, such that the outer diameter of the cladding portion 602 decreases from the wide diameter portion 613 towards the narrow diameter portion 611. The tapered portion 612 is an example of a pointed portion. The wide diameter portion 613 is the portion of the cladding portion 602 that has not been etched and has a given outer diameter. The outer diameter of the cladding portion 602 located in the wide diameter portion 613 is, for example, 80–125 μm. The narrow diameter portion 611 is the portion of the cladding portion 602 that has been etched and has an outer diameter smaller than that of the cladding portion 602 located in the wide diameter portion 613. The outer diameter of the cladding portion 602 in the narrow diameter portion 611 is, for example, less than 45 μm. Furthermore, the mode field diameter of the single-mode fiber 60a at a wavelength of 1550 nm is, for example, 7 μm.

[0073] Figure 3 This is a schematic cross-sectional view of the fiber fan-out 60, showing the axial section of the fiber fan-out 60. The fiber fan-out 60 consists of seven single-mode fibers 60a, a multi-core fiber 60b, and a capillary tube 620 into which the seven single-mode fibers 60a are inserted.

[0074] The multi-core fiber 60b has: seven core portions 651; and a cladding portion 652 located on the outer periphery of each core portion 651, with a refractive index lower than the maximum refractive index of each core portion 651. For the multi-core fiber 60b, for example, the outer diameter of the cladding portion 652 is 135 μm, the core spacing is 38.5 μm, and the mode field diameter of light at a wavelength of 1550 nm is 7 μm. One end of the multi-core fiber 60b is connected to an optical fiber that propagates light output from the pump stripper 50.

[0075] The capillary 620, for example, contains quartz and is generally divided into a narrow diameter section 621, a medium diameter section 622, a tapered section 623, and a large diameter section 624 in the axial direction.

[0076] The coarse-diameter portion 624 is the part with the largest inner and outer diameters, forming the inner diameter into which the coarse-diameter portion 613 of the seven single-mode optical fibers 60a can be inserted. The tapered portion 623 is formed in a tapered shape so that the inner and outer diameters decrease from the coarse-diameter portion 624 to the intermediate-diameter portion 622. The tapered portion 612 of the inserted single-mode optical fiber 60a is located inside the tapered portion 623. The intermediate-diameter portion 622 is formed between the fine-diameter portion 621 and the tapered portion 623, and its inner and outer diameters are smaller than those of the coarse-diameter portion 624.

[0077] The narrow diameter portion 621 is the portion whose inner and outer diameters are smaller than those of the intermediate diameter portion 622. Figure 4 This is a radial cross-sectional view showing the narrow diameter portion 621. The narrow diameter portion 621 is formed by fusion stretching with the narrow diameter portions 611 of the single-mode fiber 60a configured in a triangular lattice shape. Through this fusion stretching, in the narrow diameter portion 621, the narrow diameter portions 611 of the single-mode fiber 60a are configured in a triangular lattice shape, and at least the capillary 620 and the narrow diameter portions 611 of the cladding portion 602 are fused together, or the narrow diameter portions 611 of the cladding portions 602 of the seven single-mode fibers 60a are fused together with each other.

[0078] In the fiber fan-out 60, the core portions 601 of the seven single-mode fibers 60a are fused with the core portions 651 of the multi-core fiber 60b to achieve optical coupling. Furthermore, in the fiber fan-out 60, the narrow diameter portion 621 of the capillary 620 and the cladding portions 602 of the seven single-mode fibers 60a are fused with the cladding portions 652 of the multi-core fiber 60b. The fusion of the capillary 620 and the seven single-mode fibers 60a and the multi-core fiber 60b... Figure 3 The part shown by the dashed line is an example of the coupling part of the optical coupling of the seven fiber cores 601 and 651.

[0079] The outer diameter of the narrow-diameter portion 621 is preferably less than twice the outer diameter of the cladding portion 652 of the multi-core fiber 60b. From the viewpoint of ensuring the stability of the fusion splice with the multi-core fiber 60b and the strength of the splice point, it is preferable that the outer diameter of the narrow-diameter portion 621 is the same as that of the multi-core fiber 60b. Furthermore, if the difference between the outer diameter of the narrow-diameter portion 621 and the outer diameter of the multi-core fiber 60b is large, the fusion splice between the narrow-diameter portion 621 and the multi-core fiber 60b becomes unstable. Therefore, in the narrow-diameter portion 621, when the distance between the centers of the core portions 601 of the single-mode fiber 60a arranged in a triangular lattice is set to Λ, the wall thickness t of the narrow-diameter portion 621 of the capillary 620 is 10 μm or more, preferably t ≤ 2.5Λ. Furthermore, when there are 4 single-mode optical fibers 60a inserted into the capillary 620, t is 10 μm or more, preferably t ≤ 2.0Λ; when there are 19 fibers, t is 10 μm or more, preferably t ≤ 3.1Λ. t is set to 10 μm or more because if t is too small, the capillary 620 will deform during manufacturing, making it difficult to maintain a circular cross-section.

[0080] Furthermore, when the diameter of the core portion 601 of the single-mode fiber 60a located at the rear end of the capillary 620, i.e., the coarse diameter portion 624, is set to d1, and the diameter of the core portion 601 of the single-mode fiber 60a located at the front end of the capillary 620, i.e., the fine diameter portion 621, is set to d2, if the value of d2 / d1 becomes small, the waveguide mode of the fiber fan-out 60 will leak, generating crosstalk between the fiber cores. Therefore, the value of d2 / d1 is preferably a value that will not cause the waveguide mode to leak.

[0081] Figure 5A This is a graph showing the simulation results of the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the fiber core 601, when the single-mode fiber 60a is configured as a single-mode fiber with a cutoff wavelength of 1267 nm, a relative refractive index difference Δ0.35%, and a single-peak refractive index distribution. For ease of explanation, the single-mode fiber 60a with this structure is referred to as fiber A. Figure 5B This is a graph showing the relationship between the mode field diameter (MFD) of fiber A and d2 / d1. Figure 5C This is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber A and d2 / d1.

[0082] In this embodiment, the region where the normalized mode field diameter exceeds 1 is defined as the region where the waveguide mode becomes leaky. Therefore, according to Figure 5C According to the graph, if d2 / d1 is below 0.69, the normalized mode field diameter exceeds 1. Therefore, for fiber A, it is preferable to have 0.69 < d2 / d1 < 1. The core diameter is 9 μm and the mode field diameter is 10.3 μm when d2 / d1 = 1, and the core diameter is 6.2 μm when d2 / d1 = 0.69.

[0083] Figure 6A This indicates that in single-mode fiber 60a, the cutoff wavelength when drawn into an optical cable is 1507nm, the relative refractive index difference Δ is 0.83%, and as... Figure 7 The figure shown is a graph illustrating the simulation results of the relationship between the mode field diameter (MFD) at wavelength 1550 nm and the diameter of the core 601 in the case of a dispersion-shifted fiber (DSF) with a stepped refractive index distribution, which is an example of a single-peak type. For ease of explanation, the single-mode fiber 60a with this structure will be referred to as fiber B. Figure 6B This is a graph showing the relationship between the mode field diameter (MFD) of fiber B and d2 / d1. Figure 6C as well as Figure 6D This is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber B and d2 / d1. According to... Figure 6C as well as Figure 6D According to the chart, when d2 / d1 is below 0.68, the normalized mode field diameter exceeds 1. Therefore, for fiber B, it is preferable to have 0.68 < d2 / d1 < 1. The core diameter is 6 μm and the mode field diameter is 7 μm when d2 / d1 = 1, and the core diameter is 4.0 μm when d2 / d1 = 0.68.

[0084] Figure 8A This is a graph showing the simulation results of the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the fiber core 601, when the single-mode fiber 60a is a single-mode fiber drawn into an optical cable with a cutoff wavelength of 1497 nm, a relative refractive index difference of Δ1%, and a single-peak refractive index distribution. For ease of explanation, the single-mode fiber 60a with this structure is referred to as fiber C. Figure 8B This is a graph showing the relationship between the mode field diameter (MFD) of fiber C and d2 / d1. Figure 8C as well as Figure 8D This is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber C and d2 / d1. According to... Figure 8C as well as Figure 8D According to the graph, if d2 / d1 is less than 0.57, the normalized mode field diameter exceeds 1. Therefore, for fiber C, it is preferable to have 0.57 ≤ d2 / d1 < 1. The core diameter is 6 μm and the mode field diameter is 7 μm when d2 / d1 = 1, and the core diameter is 4.4 μm when d2 / d1 = 0.57.

[0085] Figure 9AThis is a graph showing the simulation results of the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the fiber core 601, when the single-mode fiber 60a is a single-mode fiber drawn into an optical cable with a cutoff wavelength of 1268 nm, a relative refractive index difference of Δ1%, and a single-peak refractive index distribution. For ease of explanation, the single-mode fiber 60a with this structure is referred to as fiber D. Figure 9B This is a graph showing the relationship between the mode field diameter (MFD) of fiber D and d2 / d1. Figure 9C This is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber D and d2 / d1. According to... Figure 9C According to the graph, if d2 / d1 is below 0.75, the normalized mode field diameter exceeds 1. Therefore, for fiber D, it is preferable to have 0.75 < d2 / d1 < 1. The core diameter is 5.1 μm and the mode field diameter is 6.1 μm when d2 / d1 = 1, and the core diameter is 4.4 μm when d2 / d1 = 0.75.

[0086] In summary, regarding the relationship between d1 and d2 of the core portion 601 of the single-mode optical fiber 60a located in the narrow diameter portion 621, the simulation results indicate that the preferred relationship is 0.57 ≤ d2 / d1 < 1.

[0087] Next, the manufacturing method of the fiber fan-out 60 will be explained. Figure 10 This is a flowchart of the manufacturing method for a 60° fan-out optical fiber. Figures 11-15 This is an axial cross-sectional view of the capillary tube used in the manufacture of the fiber fan-out 60 and the manufacturing process of the fiber fan-out 60.

[0088] Figure 11 This diagram shows the state of the capillary 620 before fusion stretching. Before fusion stretching, the capillary 620a is formed in a cylindrical shape. The inner diameter of the capillary 620a is three times larger than the outer diameter of the coarse-diameter portion 613 including the cover portion 603 of the single-mode optical fiber 60a, for example, 400–450 μm. The outer diameter of the capillary 620a is preferably about 1.2 times the inner diameter, for example, 480–540 μm.

[0089] In manufacturing the optical fiber fanout 60, the capillary 620a is first melt-stretched (single stretching) (step S101), as follows: Figure 12As shown, a capillary tube 620b is formed with an inner diameter and an outer diameter that are thinner than both ends. When the outer diameter of the thinner diameter portion 611 of the single-mode fiber 60a is set to d μm, the inner diameter of the thinner diameter portion 6201, which has a thinner outer and inner diameter, in the capillary tube 620b formed by a single extension is preferably 3d+1 to 8 μm. Furthermore, the axial length L1 of the tapered portion on the side where the single-mode fiber 60a is inserted is preferably 5 to 10 μm, and the axial length L2 of the thinner diameter portion 6201 formed by a single extension is preferably, for example, about 5 mm. Considering compatibility with the apparatus used in subsequent processes, the axial length of the tapered portion on the opposite side from the side where the single-mode fiber 60a is inserted is set to an appropriate length.

[0090] Next, the narrower sections 611 of the seven single-mode optical fibers 60a are arranged in a triangular lattice pattern, as follows: Figure 13 The narrow diameter portion 6201 of the capillary tube 620b is shown to be inserted (step S102). Step S102 is an example of the insertion process.

[0091] Next, the narrow diameter portion 6201 of the capillary 620b and the narrow diameter portion 611 of the seven single-mode optical fibers 60a are subjected to melt stretching (secondary stretching) (step S103). Step S103 is an example of the melt stretching process. Figure 14 This diagram illustrates a capillary 620c formed by a secondary extension of capillary 620b and a narrow-diameter portion 611 of a secondary-extended single-mode fiber 60a. Through this secondary extension, a narrow-diameter portion 621 and a medium-diameter portion 622 are formed. The capillary 620c is fused with the narrow-diameter portion 611 of the cladding portion 602, and the narrow-diameter portions 611 of the cladding portions 602 of the seven single-mode fibers 60a are fused together. Thus, by fusing the capillary 620c with the cladding portion 602 and fusing the narrow-diameter portions 611 of the cladding portion 602 with each other, positional changes in the core portion 601 can be suppressed during the fusion splicing process described later. Furthermore, the inner diameter of the narrow-diameter portion 621 formed by the secondary extension is a value smaller than three times the outer diameter of the narrow-diameter portion 611 of the single-mode fiber 60a before the secondary extension. The axial length L5 of the narrow-diameter portion 621 formed after the secondary extension is preferably, for example, about 5 mm.

[0092] When heat is applied during the secondary extension, the change in the triangular lattice configuration of the core portion 601 of the single-mode fiber 60a is suppressed by balancing the surface tension from the capillary 620c and the surface tension of the cladding portion 602 and the narrow diameter portion 611 of the single-mode fiber 60a.

[0093] Next, in order to connect the multi-core fiber 60b, the single-mode fiber 60a located in the narrow section 621 of the capillary 620c and inside the narrow section 621 is, for example, located in the central portion of the narrow section 621 along the axial direction. Figure 15Cut radially as shown to obtain a flat end face (step S104). Step S104 is an example of a cutting process. Figure 15 The structure shown before connecting the multi-core fiber 60b is an example of fiber bundle construction.

[0094] Next, the narrow section 621 of the cut capillary 620 and the end face of the single-mode fiber 60a are fused together with the end face of the multi-core fiber 60b to form a... Figure 3 The fiber fan-out is shown as 60 (step 105).

[0095] In the optical amplifier 100, a fan-out with high light resistance is required, that is, a fan-out without adhesive in the optical path. However, according to the fiber fan-out 60 of this embodiment, since the multi-core fiber 60b and the single-mode fiber 60a are connected without the use of adhesive, high light resistance can be obtained.

[0096] According to the fiber fanout 60 involved in this embodiment, the connection between the single-mode fiber 60a and the multi-core fiber 60b is a connection between the single-mode fiber cores, thus suppressing the loss in the connection.

[0097] Furthermore, according to this embodiment, at the position where the core portion 601 of the multi-core fiber 60b and the single-mode fiber 60a are optically coupled, the change in the triangular lattice configuration of the core portion 601 is suppressed, and the single-mode fiber 60a suppresses the reduction of its outer diameter on the side connected to the multi-core fiber 60b. Therefore, waveguide mode leakage can be suppressed, thereby suppressing crosstalk.

[0098] Furthermore, according to this embodiment, the single-mode fiber 60a is an optical fiber in which the cladding portion 602 has been etched. As for the core portion 601, except for the portion located in the narrow diameter portion 621, the outer diameter is constant. Therefore, it is easy to match the spacing with the core portion 601 of the multi-core fiber 60b, and the waveguide mode leakage can be suppressed.

[0099] [Variation Example]

[0100] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described above and can be implemented in various other ways. For example, the present invention can also be implemented by modifying the embodiments described above as follows. In addition, the embodiments described above and the following modifications can also be combined separately. Structures constructed by appropriately combining the structural elements of the various embodiments and modifications described above are also included in the present invention. Furthermore, those skilled in the art can easily derive further effects and modifications. Therefore, the present invention is not limited to the embodiments and modifications described above, and various changes can be made.

[0101] In the above embodiments, the fiber fan-in 20 can also be configured with the same structure as the fiber fan-out 60 and manufactured using the same manufacturing method. Therefore, the fiber fan-in 20 can serve as an example of a fiber optic connection structure.

[0102] In the above embodiment, the number of single-mode optical fibers 60a in the optical fiber fanout 60 is 7, but it is not limited to 7. For example, it can also be 4 or 17.

[0103] In the above embodiments, the space between the capillary 620 and the cladding portion 602 may also be filled with sol-gel glass, inorganic adhesive, or water glass.

[0104] In the above embodiments, the narrow diameter portion 611 and the tapered portion 612 of the single-mode optical fiber 60a are formed by etching, but they can also be formed by physical grinding or flame grinding.

[0105] In the above embodiment, the portion of the single-mode fiber 60a where the covering portion 603 is removed and the cladding portion 602 is exposed before the capillary tube 620b is inserted has a structure with a narrow diameter portion 611 and a tapered portion 612. However, the exposed portion of the cladding portion 602 may not have a narrow diameter portion 611 and a tapered portion 612, and the diameter of the cladding portion 602 may be the same as the diameter of the wide diameter portion 613. Furthermore, the exposed portion of the cladding portion 602 in the single-mode fiber 60a before the capillary tube 620b is also a structure that does not have a narrow diameter portion 611 and has a tapered portion 612 at the front end.

[0106] In the above embodiments, the fiber fan-out 60 is used in the optical amplifier 100, but the use of the fiber fan-out 60 is not limited to the optical amplifier 100, and can also be applied to applications that use high optical power, such as CATV and sensing equipment.

[0107] -Explanation of Figure Markers-

[0108] 1 Multi-core optical fiber

[0109] 10 optical isolators

[0110] 20 fiber fan-in

[0111] 20A single-mode fiber

[0112] 20b multi-core optical fiber

[0113] 30 Semiconductor Laser

[0114] 30A multimode fiber

[0115] 40 Optical Coupler

[0116] 40A excitation light supply fiber

[0117] 40b main fiber

[0118] 50 pump stripper

[0119] 60 fiber fan-out

[0120] 60A single-mode fiber

[0121] 60b multi-core optical fiber

[0122] 70 optical isolator

[0123] 100 Optical Amplifier

[0124] 601 fiber core

[0125] 602 cladding section

[0126] 603 Coverage Department

[0127] 611 Fine Diameter Section

[0128] 612 Conical Part

[0129] 613 rough diameter section

[0130] 620, 620a, 620b, 620c capillary tubes

[0131] 621 Narrow Diameter Section

[0132] 622 Middle Diameter

[0133] 623 Conical Part

[0134] 624 rough diameter section

[0135] 651 fiber core

[0136] 652 cladding section

[0137] 6201 Fine Diameter Section

Claims

1. A fiber bundle structure, characterized in that, have: Multiple fiber cores; and capillary The optical fiber core includes: a glass optical fiber portion having a core and a cladding; and a resin covering portion. The capillary is inserted into the glass optical fiber section. When the diameter of the fiber core of the glass fiber section at the rear end of the capillary is set to d1 and the diameter of the fiber core of the glass fiber section at the front end of the capillary is set to d2, d2 / d1 is greater than 0.68 and less than 1.

2. The fiber bundle structure according to claim 1, wherein, The fiber core has a single-peak refractive index distribution that sets a relative refractive index difference between the core and the cladding to enable single-mode propagation of light in a given wavelength band.

3. The fiber bundle structure according to claim 1 or claim 2, wherein, The optical fiber core transmits light with wavelengths above 950nm in single-mode.

4. The fiber bundle structure according to claim 1 or claim 2, wherein, The optical fiber core transmits light with wavelengths above 1260nm in single mode.

5. The fiber bundle structure according to claim 1 or claim 2, wherein, The space between the inner wall of the capillary and the cladding of the optical fiber core is filled with sol-gel glass, inorganic adhesive, or water glass.

6. The fiber bundle structure according to claim 1 or claim 2, wherein, The capillary is hollow and has a large diameter section, a tapered section, and a small diameter section.

7. The fiber bundle structure according to claim 6, wherein, In the narrow section, at least a portion of the cladding of the plurality of optical fiber cores is fused between each other or between the cladding of the optical fiber cores and the inner wall of the capillary.

8. The fiber bundle structure according to claim 6, wherein, The diameter of the cladding located in the narrower diameter portion is smaller than the diameter of the cladding located in the wider diameter portion.

9. The fiber bundle structure according to claim 6, wherein, The cladding has a pointed tip that tapers in diameter toward the front end. The pointed portion is located inside the tapered portion.

10. The fiber bundle structure according to claim 6, wherein, When the wall thickness of the narrow section of the capillary is set as t and the distance between the fiber cores of the plurality of optical fibers located in the narrow section is set as Λ, t≤3.1Λ.

11. The fiber bundle structure according to claim 10, wherein, The number of fiber cores is 4, and t≤2.0Λ.

12. The fiber bundle structure according to claim 10, wherein, The number of fiber cores is 7, and t≤2.5Λ.

13. The fiber bundle structure according to claim 10, wherein, The number of fiber cores is 19, and t≤3.1Λ.

14. An optical fiber connection structure, characterized in that, have: The fiber bundle structure according to any one of claims 1 to 13; and A multi-core optical fiber having multiple core portions connected to the cores of the multiple optical fiber cores and a cladding portion formed on the outer periphery of the core portions.

15. A method for manufacturing an optical fiber bundle structure, characterized in that, have: In the insertion process, the glass fiber portion of the optical fiber core, which has a glass fiber portion and a resin covering portion, is inserted into the capillary tube, wherein the glass fiber portion has a fiber core and a cladding. In the melt-stretching process, with the diameter of the core of the glass fiber portion at the rear end of the capillary set to d1 and the diameter of the core of the glass fiber portion at the front end of the capillary set to d2, the capillary and the glass fiber portion inserted into the capillary are melted and stretched so that d2 / d1 is greater than 0.68 and less than 1; and The cutting process cuts off the portion that has been extended by the melt-stretching process, so that a cross-section intersecting the axial direction of the capillary is exposed.

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