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

Abstract

An optical fiber fan-out (60) comprises a plurality of coated optical fibers (60a), and a capillary (620). The coated optical fiber (60a) comprises a glass fiber part having a core (601) and a cladding (602), and a resin coating part (603). The glass fiber part is inserted into the capillary (620), and when the diameter of the core of the glass fiber part at a rear end of the capillary (620) is denoted by d1, and the diameter of the core of the glass fiber part at a front end of the capillary (620) is denoted by d2, d2 / d1 is 0.57 or more but less than 1.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber bundle structure, an optical fiber connection structure, and a method for manufacturing an optical fiber bundle structure. [Background technology]

[0002] An optical fiber bundle structure for connecting a single-mode or few-mode optical fiber to a multimode optical fiber is disclosed in Patent Document 1. The optical fiber bundle structure disclosed in Patent Document 1 is formed by inserting a hexagonally arranged fiber bundle into a cladding tube so that the single-mode or few-mode cores are parallel, and drawing the fiber bundle and the cladding tube so that they taper. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5738275 Summary of the Invention [Problem to be solved by the invention]

[0004] The optical fiber bundle structure disclosed in Patent Document 1 has a taper ratio, which is the first outer diameter at the input end divided by the second outer diameter at the output end, of 3 to 10. When the optical fiber is drawn to have such a taper ratio, the distance between the cores becomes narrow, causing crosstalk. Therefore, this is not preferable as an optical fiber bundle structure for connecting single-mode or few-mode optical fibers to each core portion of a multicore fiber, which is an optical fiber having multiple cores.

[0005] The present invention has been made in view of the above, and has as its object to provide an optical fiber bundle structure, an optical fiber connection structure, and a method for manufacturing an optical fiber bundle structure, in which crosstalk is suppressed. [Means for solving the problem]

[0006] One aspect of the present invention is an optical fiber bundle structure comprising a plurality of optical fiber cores and a capillary, wherein the optical fiber cores comprise a glass fiber portion having a core and a cladding, and a resin coating portion, and the capillary has the glass fiber portion inserted therein, and where the diameter of the core of the glass fiber portion at the rear end of the capillary is d1 and the diameter of the core of the glass fiber portion at the front end of the capillary is d2, d2 / d1 is 0.57 or more and less than 1.

[0007] In one aspect of the present invention, the optical fiber core may have a single-peak refractive index profile in which the relative refractive index difference of the core with respect to the cladding is set so as to propagate light in a predetermined wavelength band in a single mode.

[0008] In one aspect of the present invention, the optical fiber may propagate light having a wavelength of 950 nm or more in a single mode.

[0009] In one aspect of the present invention, the optical fiber may propagate light having a wavelength of 1260 nm or more in a single mode.

[0010] In one aspect of the present invention, a sol-gel glass, an inorganic adhesive or water glass may be filled between the inner wall of the capillary and the cladding of the optical fiber.

[0011] In one aspect of the present invention, the capillary may be hollow and have a large diameter portion, a tapered portion, and a small diameter portion.

[0012] In one aspect of the present invention, in the thin-diameter portion, at least a portion of the claddings of the plurality of optical fiber cores, or a portion of the claddings of the optical fiber cores and the inner wall of the capillary, may be fused.

[0013] In one aspect of the present invention, the diameter of the cladding located in the narrow diameter portion may be smaller than the diameter of the cladding located in the large diameter portion.

[0014] In one aspect of the present invention, the cladding may have a tapered portion whose diameter decreases toward the tip side, and the tapered portion may be located inside the tapered portion.

[0015] In one aspect of the present invention, when the thickness of the thin-diameter portion of the capillary is t and the distance between the cores of the plurality of optical fibers located in the thin-diameter portion is Λ, t≦3.1Λ. So that's fine.

[0016] In one embodiment of the present invention, the number of the cores may be 4, and t≦2.0Λ.

[0017] In one embodiment of the present invention, the number of the cores may be 7, and t≦2.5Λ.

[0018] In one embodiment of the present invention, the number of the cores may be 19, and t≦3.1Λ.

[0019] One aspect of the present invention is an optical fiber connection structure comprising any one of the optical fiber bundle structures described above, a multi-core fiber having a plurality of core portions connected to the cores of the plurality of optical fiber coated wires, and a cladding portion formed on the outer periphery of the core portions.

[0020] One aspect of the present invention is a method for manufacturing an optical fiber bundle structure, comprising: an insertion step of inserting a glass fiber portion of an optical fiber core wire having a glass fiber portion with a core and a clad and a resin coating portion into a capillary; a melting and drawing step of melting and drawing the capillary and the glass fiber portion inserted into the capillary so that d2 / d1 is 0.57 or more and less than 1, where d1 is the diameter of the core of the glass fiber portion at the rear end of the capillary and d2 is the diameter of the core of the glass fiber portion at the front end of the capillary; and a cutting step of cutting the portion drawn by the melting and drawing step so that a cross section intersecting the axial direction of the capillary is exposed. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an optical fiber bundle structure, an optical fiber connection structure, and a method for manufacturing an optical fiber bundle structure, in which crosstalk is suppressed. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an optical amplifier according to an embodiment. [Figure 2] FIG. 2 is an axial cross-sectional view of a single-mode optical fiber. [Figure 3] FIG. 3 is an axial cross-sectional view of an optical fiber fan-out. [Figure 4] FIG. 4 is a cross-sectional view in the radial direction of the small diameter portion of the optical fiber fan-out. [Figure 5A] FIG. 5A is a diagram showing the simulation results of a single-mode optical fiber. [Figure 5B] FIG. 5B is a diagram showing the simulation results of a single-mode optical fiber. [Figure 5C] FIG. 5C shows the simulation results for a single-mode optical fiber. [Figure 6A] FIG. 6A is a diagram showing the simulation results of a single-mode optical fiber. [Figure 6B] FIG. 6B is a diagram showing the simulation results of a single-mode optical fiber. [Figure 6C] FIG. 6C shows the simulation results for a single-mode optical fiber. [Figure 6D] FIG. 6D shows the simulation results for a single-mode optical fiber. [Figure 7] FIG. 7 is a diagram showing the refractive index profile of a single-mode optical fiber. [Figure 8A] FIG. 8A is a diagram showing the simulation results of a single-mode optical fiber. [Figure 8B] FIG. 8B is a diagram showing the simulation results of a single-mode optical fiber. [Figure 8C] FIG. 8C is a diagram showing the simulation results of a single-mode optical fiber. [Figure 8D] FIG. 8D shows the simulation results for a single-mode optical fiber. [Figure 9A] FIG. 9A is a diagram showing the simulation results of a single-mode optical fiber. [Figure 9B] FIG. 9B is a diagram showing the simulation results of a single-mode optical fiber. [Figure 9C] FIG. 9C is a diagram showing the simulation results of a single-mode optical fiber. [Figure 10] FIG. 10 is a flowchart of a method for manufacturing an optical fiber fan-out. [Figure 11] FIG. 11 is a cross-sectional view of an optical fiber fan-out during the manufacturing process. [Figure 12] FIG. 12 is a cross-sectional view of an optical fiber fan-out during the manufacturing process. [Figure 13] FIG. 13 is a cross-sectional view of an optical fiber fan-out during the manufacturing process. [Figure 14] FIG. 14 is a cross-sectional view of an optical fiber fan-out during the manufacturing process. [Figure 15]FIG. 15 is a cross-sectional view of an optical fiber fan-out during the manufacturing process. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the drawings, identical or corresponding elements are appropriately designated by the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationships between elements may differ from those in reality. The dimensional relationships and ratios may differ between drawings. In this specification, the term cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength defined in ITU-T G.650.1 of the International Telecommunications Union (ITU). Other terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0024] [Embodiment] 1 is a schematic diagram showing the configuration of a multi-core optical fiber amplifier according to an embodiment of the present invention. Hereinafter, the multi-core optical fiber amplifier may be simply referred to as an optical amplifier. The optical amplifier 100 includes seven optical isolators 10, an optical fiber fan-in (FAN IN) 20, a semiconductor The system includes a laser 30, an optical coupler 40, a multi-core optical amplifying fiber 1, a pump stripper 50, an optical fiber fan-out (FAN OUT) 60, and seven optical isolators 70. In the figure, the "x" symbol indicates the fusion splice points of the optical fibers.

[0025] The optical fiber fan-in 20 includes seven bundled single-mode optical fibers 20a and one multi-core fiber 20b having seven core portions, and is configured so that each core portion of the seven single-mode optical fibers 20a is optically coupled to each core portion of the multi-core fiber 20b.

[0026] The seven single-mode optical fibers 20a are standard single-mode optical fibers defined in, for example, ITU-T G.652, and each is provided with an optical isolator 10. The optical isolator 10 allows light to pass in the direction indicated by the arrow and blocks light from passing in the opposite direction.

[0027] The multi-core fiber 20b of the optical fiber fan-in 20 has seven cores arranged in a triangular lattice pattern and claddings located on the outer periphery of each core and having a refractive index lower than the maximum refractive index of each core. When signal light is input to each single-mode optical fiber 20a of the optical fiber fan-in 20, each optical isolator 10 passes each signal light, and each core of the multi-core fiber 20b propagates each signal light.

[0028] The end faces where the bundled seven single-mode optical fibers 20a and the multi-core fiber 20b are optically coupled are processed at an angle to the optical axis to suppress reflection, but may be perpendicular to the optical axis. The multi-core fiber 20b of the optical fiber fan-in 20 is connected to an optical coupler 40.

[0029] The semiconductor laser 30, which serves as the pumping light source, is a transverse multimode semiconductor laser and outputs pumping light. The wavelength of the pumping light is 976 nm, which is approximately the same as the wavelength of the absorption peak of Er in the 900 nm wavelength band. This allows the pumping light to optically pump erbium ions. The semiconductor laser 30 outputs the pumping light from a multimode optical fiber 30a. This multimode optical fiber 30a is a step-index type with a core diameter / cladding diameter of, for example, 105 μm / 125 μm, and an NA of, for example, 0.16 or 0.22.

[0030] The optical coupler 40 includes a main optical fiber 40b and an optical fiber 40a for supplying pumping light. The main optical fiber 40b is a double-clad optical fiber including seven cores arranged in a triangular lattice pattern (i.e., hexagonal close-packed pattern) similar to the cores of the multi-core fiber 20b of the optical fiber fan-in 20, inner claddings positioned on the outer periphery of each core and having a refractive index lower than the maximum refractive index of each core, and an outer cladding positioned on the outer periphery of the inner cladding and having a refractive index lower than that of the inner cladding. The cores and the inner cladding are made of silica-based glass, and the outer cladding is made of resin.

[0031] The pumping light supplying optical fiber 40a is a multimode optical fiber of the same type, with the other end connected to the multimode optical fiber 30a of the semiconductor laser 30, and is a step-index type with a core diameter / cladding diameter of, for example, 105 μm / 125 μm, and an NA of, for example, 0.16 or 0.22. Pumping light is input into the pumping light supplying optical fiber 40a from the semiconductor laser 30, and the optical fiber 40a supplies this pumping light to the main optical fiber 40b. The inner cladding propagates the pumping light.

[0032] One end of the main optical fiber 40b of the optical coupler 40 is connected to the multi-core fiber 20b of the optical fiber fan-in 20. The main optical fiber 40b is a double-clad optical fiber including seven cores arranged in a triangular lattice pattern similar to the cores of the multi-core fiber 20b, an inner clad surrounding each core and having a lower refractive index than the cores, and an outer clad surrounding the inner clad and having a lower refractive index than the inner clad. The cores and the inner clad are made of silica-based glass, and the outer clad is made of resin.

[0033] Each core part of the multi-core fiber 20b is connected to each core part of the main optical fiber 40b. Therefore, when each signal light propagating through each core part of the multi-core fiber 20b enters the main optical fiber 40b, it is optically coupled to each core part. Each core part propagates each signal light. The pumping light and the signal light are output from the main optical fiber 40b to the multi-core optical amplifying fiber 1.

[0034] The multi-core optical amplifying fiber 1 is a seven-core type that includes seven optical amplifying cores arranged in a triangular lattice pattern similar to the main optical fiber 40b, an inner cladding formed around the outer periphery of the optical amplifying cores and having a lower refractive index than the optical amplifying cores, and an outer cladding formed around the outer periphery of the inner cladding and having a lower refractive index than the inner cladding. The multi-core optical amplifying fiber 1 is a known cladding-pumped optical amplifying fiber that contains erbium ions as an optical amplification medium in the optical amplifying cores.

[0035] One end of the multi-core optical amplifying fiber 1 is connected to the main optical fiber 40b of the optical coupler 40. Each optical amplifying core of the multi-core optical amplifying fiber 1 is connected to each core of the main optical fiber 40b. Furthermore, the inner cladding of the multi-core optical amplifying fiber 1 is connected to the inner cladding of the main optical fiber 40b. Therefore, when each signal light and pumping light propagating through the main optical fiber 40b are input to the multi-core optical amplifying fiber 1, they propagate in the same direction through each optical amplifying core and the inner cladding. The pumping light optically pumps erbium in each optical amplifying core while propagating through the inner cladding. Each signal light propagating through each optical amplifying core is optically amplified by the action of stimulated emission of erbium. The multi-core optical amplifying fiber 1 outputs each optically amplified signal light and pumping light that did not contribute to optical amplification.

[0036] The pump stripper 50 is a known device that removes pump light that did not contribute to optical amplification. The pump stripper 50 has a configuration in which, for example, a part of the outer cladding of a double-clad multicore fiber having seven cores is removed, and the pump light is extracted from the surface of the inner cladding of the removed part, irradiated onto a heat sink or the like, and absorbed, converting the energy of the pump light into thermal energy and dissipating it. The pump stripper 50 propagates each signal light through the multicore fiber, and reduces the power of the pump light to a level that will not cause any problems even if it is output from the optical amplifier 100.

[0037] The optical fiber fan-out 60, like the optical fiber fan-in 20, includes seven bundled single-mode optical fibers 60a and one multi-core fiber 60b having seven cores, and is configured so that each core of the seven single-mode optical fibers 60a is optically coupled to each core of the multi-core fiber 60b at a coupling portion described later. The optical fiber fan-out 60 is an example of an optical fiber connection structure.

[0038] The single-mode optical fiber 60a propagates light with wavelengths of 950 nm or more in a single mode, but may also propagate light with wavelengths of 1260 nm or more in a single mode. Such single-mode optical fiber 60a is an example of an optical fiber having a single-peak refractive index profile in which the relative refractive index difference of the core with respect to the cladding is set to, for example, 0.35% so that light in a predetermined wavelength band propagates in a single mode. Such single-mode optical fiber 60a is, for example, a standard single-mode optical fiber defined in ITU-T G.652. Each single-mode optical fiber 60a is provided with an optical isolator 70.

[0039] The multi-core fiber 60b is connected to the pump stripper 50. The end faces where the bundled seven single-mode optical fibers 60a and the multi-core fiber 60b are optically coupled are processed at an angle to the optical axis to suppress reflection, but may be perpendicular to the optical axis.

[0040] When signal light is input from each core of the multi-core fiber of the pump stripper 50 to each core of the multi-core fiber 60b of the optical fiber fan-out 60, each signal light propagates through each core of each single-mode optical fiber 60a and is output 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. Note that instead of the seven optical isolators 10, 70, an optical isolator configured to integrate a plurality of (seven in this embodiment) single-mode optical fibers may be used.

[0041] 2 is a schematic cross-sectional view of a single-mode optical fiber 60a before being bundled into the optical fiber fan-out 60, showing a cross section of the single-mode optical fiber 60a in the axial direction. The single-mode optical fiber 60a has a core 601, a cladding 602 formed on the outer periphery of the core 601, and a coating 603 formed on the outer periphery of the cladding 602. The coating 603 is made of a resin that can be used to coat optical fibers. The single-mode optical fiber 60a is an example of an optical fiber core. The core 601 and the cladding 602 are examples of glass fiber portions, and the coating 603 is an example of a resin coating.

[0042] The single mode optical fiber 60a is roughly divided into a small diameter portion 611, a tapered portion 612, and a large diameter portion 613 in the axial direction. The tapered portion 612 is a portion formed by etching the cladding portion 602 and tapering it so that the outer diameter of the cladding portion 602 decreases from the large diameter portion 613 toward the small diameter portion 611. The tapered portion 612 is an example of a tapered portion. The large diameter portion 613 is a portion of the cladding portion 602 that is not etched and has a predetermined outer diameter. The outer diameter of the cladding portion 602 in the large diameter portion 613 is, for example, 80 to 125 μm. The small diameter portion 611 is a portion formed by etching the cladding portion 602 and having a smaller outer diameter than the cladding portion 602 in the large diameter portion 613. The outer diameter of the cladding portion 602 in the small diameter portion 611 is, for example, less than 45 μm. Furthermore, the single mode optical fiber 60a has a mode field diameter of, for example, 7 μm for light with a wavelength of 1550 nm.

[0043] 3 is a schematic cross-sectional view of the optical fiber fan-out 60, showing an axial cross section of the optical fiber fan-out 60. The optical fiber fan-out 60 is composed of seven single-mode optical fibers 60a, a multi-core fiber 60b, and a capillary 620 into which the seven single-mode optical fibers 60a are inserted.

[0044] The multi-core fiber 60b has seven cores 651 and clads 652 that are located on the outer peripheries of the cores 651 and have a refractive index lower than the maximum refractive index of the cores 651. In the multi-core fiber 60b, for example, the outer diameter of the clad 652 is 135 μm, the core pitch 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.

[0045] The capillary 620 is made of, for example, quartz, and is roughly divided into a small diameter portion 621, a medium diameter portion 622, a tapered portion 623, and a large diameter portion 624 in the axial direction.

[0046] The large diameter portion 624 is a portion formed with the largest inner and outer diameters, and has an inner diameter that allows the large diameter portions 613 of the seven single mode optical fibers 60a to be inserted therein. The tapered portion 623 is a portion formed in a tapered shape such that the inner and outer diameters decrease from the large diameter portion 624 toward the medium diameter portion 622. The tapered portion 612 of the inserted single mode optical fiber 60a is located inside the tapered portion 623. The medium diameter portion 622 is a portion formed between the small diameter portion 621 and the tapered portion 623, with the inner and outer diameters smaller than those of the large diameter portion 624.

[0047] The small diameter portion 621 is a portion formed so that its inner and outer diameters are smaller than those of the medium diameter portion 622. Fig. 4 shows a radial cross section of the small diameter portion 621. The small diameter portion 621 is formed by melting and drawing the small diameter portions 611 of the single mode optical fibers 60a while they are arranged in a triangular lattice pattern. By this melting and drawing, the small diameter portions 611 of the single mode optical fibers 60a are arranged and positioned in a triangular lattice pattern in the small diameter portion 621, and at least the capillary 620 and the small diameter portions 611 of the cladding portion 602, or the small diameter portions 611 of the cladding portions 602 of the seven single mode optical fibers 60a are fused together.

[0048] In the optical fiber fan-out 60, the core portions 601 of the seven single-mode optical fibers 60a are fused to the core portions 651 of the multi-core fiber 60b so as to be optically coupled. Also, in the optical fiber fan-out 60, the small-diameter portion 621 of the capillary 620 and the cladding portions 602 of the seven single-mode optical fibers 60a are fused to the cladding portion 652 of the multi-core fiber 60b. The portion indicated by the dashed line in Fig. 3 where the capillary 620 and the seven single-mode optical fibers 60a and the multi-core fiber 60b are fusion-spliced ​​is an example of a coupling portion where the seven core portions 601 and the core portions 651 are optically coupled.

[0049] The outer diameter of the thin-diameter portion 621 is preferably equal to or less than twice the outer diameter of the cladding portion 652 of the multi-core fiber 60b, and is preferably the same as the outer diameter of the multi-core fiber 60b from the viewpoint of ensuring stability of fusion with the multi-core fiber 60b and strength of the fusion point. Note that if there is a large difference between the outer diameter of the thin-diameter portion 621 and the outer diameter of the multi-core fiber 60b, fusion between the thin-diameter portion 621 and the multi-core fiber 60b becomes unstable. For this reason, in the thin-diameter portion 621, when the distance between the centers of the core portions 601 of the single-mode optical fibers 60a arranged in a triangular lattice pattern is Λ, it is preferable that the wall thickness t of the thin-diameter portion 621 of the capillary 620 is 10 μm or more and t≦2.5Λ. When the number of single-mode optical fibers 60a inserted in the capillary 620 is four, t is preferably 10 μm or more and t≦2.0Λ, and when the number is 19, t is preferably 10 μm or more and t≦3.1Λ. The reason why t is set to 10 μm or more is that if t is too small, the capillary 620 will deform during manufacturing, making it difficult to maintain a circular cross section.

[0050] Also, in the optical fiber fan-out 60, when the diameter of the core portion 601 of the single-mode optical fiber 60a located at the large-diameter portion 624 which is the rear end portion of the capillary 620 is d1, and the diameter of the core portion 601 of the single-mode optical fiber 60a located at the small-diameter portion 621 which is the front end portion of the capillary 620 is d2, when the value of d2 / d1 becomes small, the guided mode becomes leaky and crosstalk occurs between the cores. Therefore, the value of d2 / d1 is preferably set to a value at which the guided mode does not become leaky.

[0051] FIG. 5A is a graph showing the result of simulating the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the core portion 601 when the single-mode optical fiber 60a is a single-mode fiber having a cable cut-off wavelength of 1267 nm and a refractive index profile with a relative refractive index difference Δ of 0.35% and a single-peak type. For convenience of explanation, the single-mode optical fiber 60a having this configuration is referred to as fiber A. FIG. 5B is a graph showing the relationship between the mode field diameter (MFD) of fiber A and d2 / d1, and FIG. 5C is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber A and d2 / d1.

[0052] In the present embodiment, a region where the normalized mode field diameter exceeds 1 is defined as a region where the guided mode becomes leaky. Therefore, according to the graph of FIG. 5C, when d2 / d1 becomes 0.69 or less, the normalized mode field diameter exceeds 1. For fiber A, it is preferable that 0.69 < d2 / d1 < 1. The core diameter when d2 / d1 = 1 is 9 μm, the mode field diameter is 10.3 μm, and the core diameter when d2 / d1 = 0.69 is 6.2 μm.

[0053] FIG. 6A is a graph showing the result of simulating the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the core portion 601 in the case where the single-mode optical fiber 60a is a dispersion-shifted fiber (DSF) having a stepped refractive index profile as an example of a single-peak type with a relative refractive index difference Δ of 0.83% and is drawn so that the cable cut-off wavelength is 1507 nm. For the sake of convenience of explanation, the single-mode optical fiber 60a having this configuration is referred to as fiber B. FIG. 6B is a graph showing the relationship between the mode field diameter (MFD) of fiber B and d2 / d1, and FIGS. 6C and 6D are graphs showing the relationship between the normalized mode field diameter (MFD) of fiber B and d2 / d1. According to the graphs of FIGS. 6C and 6D, when d2 / d1 is 0.68 or less, the normalized mode field diameter exceeds 1. Therefore, for fiber B, it is preferable that 0.68 < d2 / d1 < 1. The core diameter at d2 / d1 = 1 was 6 μm, the mode field diameter was 7 μm, and the core diameter at d2 / d = 0.68 was 4.0 μm.

[0054] <S FIG. 8A is a graph showing the result of simulating the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the core portion 601 in the case where the single-mode optical fiber 60a is a single-mode fiber having a single-peak type refractive index profile with a relative refractive index difference Δ of 1% and is drawn so that the cable cut-off wavelength is 1497 nm. For the sake of convenience of explanation, the single-mode optical fiber 60a having this configuration is referred to as fiber C. FIG. 8B is a graph showing the relationship between the mode field diameter (MFD) of fiber C and d2 / d1, and FIGS. 8C and 8D are graphs showing the relationship between the normalized mode field diameter (MFD) of fiber C and d2 / d1. According to the graphs of FIGS. 8C and 8D, when d2 / d1 is less than 0.57, the normalized mode field diameter exceeds 1. Therefore, for fiber C, it is preferable that 0.57 ≦ d2 / d1 < 1. The core diameter at d2 / d1 = 1 was 6 μm, the mode field diameter was 7 μm, and the core diameter at d2 / d1 = 0.57 was 4.4 μm.

[0055] FIG. 9A is a graph showing the result of simulating the relationship between the mode field diameter (MFD) at a wavelength of 1550 nm and the diameter of the core portion 601 for a single-mode optical fiber in which the single-mode optical fiber 60a is drawn with a relative refractive index difference Δ1% such that the cable cut-off wavelength is 1268 nm and the refractive index profile is unimodal. For convenience of explanation, the single-mode optical fiber 60a having this configuration is referred to as fiber D. FIG. 9B is a graph showing the relationship between the mode field diameter (MFD) of fiber D and d2 / d1, and FIG. 9C is a graph showing the relationship between the normalized mode field diameter (MFD) of fiber D and d2 / d1. According to the graph of FIG. 9C, when d2 / d1 is 0.75 or less, the normalized mode field diameter exceeds 1. Therefore, for fiber D, it is preferable that 0.75 < d2 / d1 < 1. The core diameter when d2 / d1 = 1 is 5.1 μm, the mode field diameter is 6.1 μm, and the core diameter when d2 / d1 = 0.75 is 4.4 μm.

[0056] 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, it is preferable from the simulation results that 0.57 ≦ d2 / d1 < 1.

[0057] Next, a method for manufacturing the optical fiber fan-out 60 will be described. FIG. 10 is a flowchart of a method for manufacturing the optical fiber fan-out 60, and FIGS. 11 to 15 are cross-sectional views in the axial direction in the manufacturing process of the capillary used for manufacturing the optical fiber fan-out 60 and the optical fiber fan-out 60.

[0058] FIG. 11 is a view showing the state of the capillary 620 before melt drawing. The capillary 620a before melt drawing is formed in a cylindrical shape. The inner diameter of the capillary 620a is larger than three times the outer diameter of the thick-diameter portion 613 including the coating portion 603 of the single-mode optical fiber 60a, for example, 400 to 450 μm. The outer diameter of the capillary 620a is preferably about 1.2 times the inner diameter, for example, 480 to 540 μm.

[0059] When manufacturing the optical fiber fan-out 60, first, a capillary 620a is melt-drawn (primary drawing) (step S101) to form a capillary 620b having an inner and outer diameters smaller than those at both ends, as shown in FIG. 12. When the outer diameter of the small-diameter portion 611 of the single-mode optical fiber 60a is d μm, the small-diameter portion 6201 of the capillary 620b formed by the primary drawing, in which the outer and inner diameters are narrower, preferably has an inner diameter of 3d+1 to 8 μm. Furthermore, the axial length L1 of the tapered portion on the side into which the single-mode optical fiber 60a is inserted is preferably 5 to 10 μm, and the axial length L2 of the small-diameter portion 6201 formed by the primary drawing is preferably, for example, around 5 mm. The axial length of the tapered portion on the side opposite to the side into which the single-mode optical fiber 60a is inserted is set to an appropriate length in consideration of compatibility with equipment used in subsequent processes.

[0060] Next, the small diameter portions 611 of the seven single mode optical fibers 60a are arranged in a triangular lattice pattern and inserted into the small diameter portion 6201 of the capillary 620b as shown in Fig. 13 (step S102). Step S102 is an example of an insertion step.

[0061] Next, the small diameter portion 6201 of the capillary 620b and the small diameter portions 611 of the seven single mode optical fibers 60a are melt-drawn (secondary drawing) (step S103). Step S103 is an example of the melt-drawing process. FIG. 14 is a diagram showing a capillary 620c formed by the second drawing of the capillary 620b and the small diameter portion 611 of the secondarily drawn single mode optical fiber 60a. This secondary drawing forms the small diameter portion 621 and the medium diameter portion 622, and fusion-splices the capillary 620c and the small diameter portion 611 of the cladding portion 602, and the small diameter portions 611 of the cladding portions 602 of the seven single mode optical fibers 60a together. In this way, the capillary 620c and the cladding portion 602 are fused together, and the narrow diameter portions 611 of the cladding portion 602 are fused together, thereby preventing the position of the core portion 601 from changing in the fusion splicing step described below. Furthermore, the inner diameter of the narrow diameter portion 621 formed by the secondary drawing is less than three times the outer diameter of the narrow diameter portion 611 of the single mode optical fiber 60a before the secondary drawing. The axial length L5 of the narrow diameter portion 621 formed after the secondary drawing is preferably around 5 mm, for example.

[0062] When heat is applied during the secondary drawing, the change in the triangular lattice arrangement of the core portion 601 of the single-mode optical fiber 60a is suppressed by the balance between the surface tension from the capillary 620c and the surface tension between the thin-diameter portions 611 of the cladding portion 602 of the single-mode optical fiber 60a.

[0063] Next, in order to connect the multi-core fiber 60b, the small diameter portion 621 of the capillary 620c and the single-mode optical fiber 60a located inside the small diameter portion 621 are cut in the radial direction, for example, at the axial center portion of the small diameter portion 621, as shown in Fig. 15 so as to obtain a flat end face (step S104). Step S104 is an example of a cutting step. The configuration before the multi-core fiber 60b is connected, as shown in Fig. 15, is an example of an optical fiber bundle structure.

[0064] Next, the end face of the cut small diameter portion 621 of the capillary 620 and the single mode optical fiber 60a are fusion spliced ​​to the end face of the multi-core fiber 60b to form the optical fiber fan-out 60 shown in FIG. 3 (step 105).

[0065] In the optical amplifier 100, a fan-out with high light resistance, i.e., a fan-out without the use of adhesive in the optical path, is required. However, according to the optical fiber fan-out 60 of this embodiment, the multi-core fiber 60b and the single-mode optical fiber 60a are connected without using adhesive, so that high light resistance can be obtained.

[0066] According to the optical fiber fan-out 60 of this embodiment, the connection between the single-mode optical fiber 60a and the multi-core fiber 60b is a connection between single-mode cores, so that loss in the connection can be reduced.

[0067] Furthermore, according to the present embodiment, at the position where the multicore fiber 60b and the core portion 601 of the single-mode optical fiber 60a are optically coupled, changes in the triangular lattice arrangement of the core portions 601 are suppressed, and the single-mode optical fiber 60a is prevented from reducing in outer diameter on the side connected to the multicore fiber 60b, so that the guided mode can be prevented from becoming leaky, and ultimately crosstalk is suppressed.

[0068] Moreover, according to this embodiment, the single-mode optical fiber 60a is an optical fiber in which the cladding portion 602 is etched, and the core portion 601 has a constant outer diameter except for the portion located at the small-diameter portion 621. Therefore, it is easy to match the pitch with the core portion 601 of the multi-core fiber 60b, and it is possible to prevent the waveguide mode from becoming leaky.

[0069] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0070] In the above-described embodiment, the optical fiber fan-in 20 may have the same configuration and may be manufactured by the same manufacturing method as the optical fiber fan-out 60. Therefore, the optical fiber fan-in 20 can be an example of an optical fiber connection structure.

[0071] In the above-described embodiment, the number of single mode optical fibers 60a included in the optical fiber fan-out 60 is seven, but this is not limited to seven and may be, for example, four or seventeen.

[0072] In the above-described embodiment, the space between the capillary 620 and the cladding portion 602 may be filled with sol-gel glass, an inorganic adhesive, or water glass.

[0073] In the above-described embodiment, the small diameter portion 611 and the tapered portion 612 of the single mode optical fiber 60a are formed by etching, but they may also be formed by physical polishing or flame polishing.

[0074] In the above-described embodiment, the portion of the single mode optical fiber 60a before being inserted into the capillary 620b where the coating 603 has been removed and the cladding 602 is exposed has a configuration including the small diameter portion 611 and the tapered portion 612, but the portion where the cladding 602 is exposed may not have the small diameter portion 611 or the tapered portion 612, and the diameter of the cladding 602 may be the same as the large diameter portion 613. Furthermore, the portion of the single mode optical fiber 60a before being inserted into the capillary 620b where the cladding 602 is exposed may not have the small diameter portion 611 and may have the tapered portion 612 up to the tip.

[0075] In the above-described embodiment, the optical fiber fan-out 60 is used in the optical amplifier 100, but the use of the optical fiber fan-out 60 is not limited to the optical amplifier 100, and it may also be applied to applications that operate at high optical power, such as CATV and sensing equipment. [Explanation of symbols]

[0076] 1. Multi-core optical amplifier fiber 10 Optical isolator 20 Fiber Optic Fan-in 20a single mode optical fiber 20b multicore fiber 30 Semiconductor laser 30a multimode optical fiber 40 Optical coupler 40a Optical fiber for supplying pumping light 40b Main optical fiber 50 Pump Stripper 60 optical fiber fanout 60a single mode optical fiber 60b multicore fiber 70 Optical isolator 100 Optical Amplifier 601 Core 602 Cladding part 603 Covering part 611 Thin diameter part 612 Tapered section 613 Large diameter part 620, 620a, 620b, 620c capillaries 621 Thin section 622 Medium diameter section 623 Tapered section 624 Large diameter part 651 Core 652 Cladding section 6201 Thin diameter part

Claims

1. A plurality of optical fiber cores; Capillary and Equipped with The optical fiber core comprises a glass fiber portion having a core and a cladding, and a resin coating portion, the capillary has the glass fiber portion inserted therein; When the diameter of the core of the glass fiber portion at the rear end of the capillary is d1 and the diameter of the core of the glass fiber portion at the front end of the capillary is d2, d2 / d1 is greater than 0.68 and less than 1. Optical fiber bundle structure.

2. The optical fiber has a single-peak refractive index profile in which the relative refractive index difference of the core with respect to the cladding is set so as to propagate light in a predetermined wavelength band in a single mode.

10. The optical fiber bundle structure of claim 1.

3. The optical fiber core propagates light with a wavelength of 950 nm or more in a single mode.

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

4. The optical fiber core propagates light having a wavelength of 1260 nm or more in a single mode.

4. The optical fiber bundle structure according to claim 1.

5. The space between the inner wall of the capillary and the cladding of the optical fiber is filled with sol-gel glass, inorganic adhesive or water glass.

5. The optical fiber bundle structure according to claim 1.

6. The capillary is hollow and has a large diameter portion, a tapered portion, and a small diameter portion.

6. The optical fiber bundle structure according to claim 1.

7. In the small diameter portion, at least a part of the clads of the optical fibers or a part of the clads of the optical fibers and the inner wall of the capillary are fused.

7. The optical fiber bundle structure of claim 6.

8. The diameter of the cladding located in the narrow diameter portion is smaller than the diameter of the cladding located in the wide diameter portion.

8. The optical fiber bundle structure according to claim 6 or 7.

9. The clad has a tapered portion whose diameter decreases toward the tip side, The tapered portion is located inside the tapered portion.

9. The optical fiber bundle structure according to claim 6.

10. When the wall thickness of the thin-diameter portion of the capillary is t and the distance between the cores of the plurality of optical fibers located in the thin-diameter portion is Λ, t≦3.1Λ.

10. The optical fiber bundle structure according to claim 6.

11. The number of the cores is 4, and t≦2.0Λ 11. The optical fiber bundle structure of claim 10.

12. The number of cores is 7, and t≦2.5Λ 11. The optical fiber bundle structure of claim 10.

13. The number of cores is 19, and t≦3.1Λ 11. The optical fiber bundle structure of claim 10.

14. an optical fiber bundle structure according to any one of claims 1 to 13; a multi-core fiber having a plurality of core portions connected to cores of the plurality of coated optical fibers and a clad portion formed on the outer periphery of the core portions; An optical fiber connection structure comprising:

15. an insertion step of inserting a glass fiber portion of an optical fiber core wire having a core and a cladding and a resin coating portion into a capillary; a melt-drawing step of melting and drawing the capillary and the glass fiber portion inserted into the capillary so that d2 / d1 is greater than 0.68 and less than 1, where d1 is the diameter of the core of the glass fiber portion at the rear end of the capillary and d2 is the diameter of the core of the glass fiber portion at the front end of the capillary; a cutting step of cutting the portion drawn in the melt-drawing step so as to expose a cross section intersecting the axial direction of the capillary; A method for manufacturing an optical fiber bundle structure comprising:

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