Clad rod, method for manufacturing a preform for optical fibers using the same, and method for manufacturing optical fibers

Abstract

To provide: a clad rod capable of preventing a glass rod from having difficult insertion; a method for manufacturing an optical fiber preform using the same; and a method for manufacturing optical fiber.SOLUTION: A clad rod 20R including a clad glass body 20P formed as at least a part of a clad 20 in an optical fiber 1 extends in the longitudinal direction and has an opening at an end on at least one side. There are provided holes 25a-25e capable of accepting insertion of a core rod 10R including a core glass body 10P formed as a core 10 in the optical fiber 1 and a marker rod consisting of a marker glass body 15P formed as a marker 15 from the opening; and the inner peripheral surfaces 26 of the holes 25a-25e include a taper part 27 having the diameters of the holes 25a-25e expanding toward the opening from a position separated from the opening at the end on the one side and extending to an end surface 20Rf on the one side of the clad rod 20R.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a clad rod, a method for manufacturing a preform for an optical fiber using the same, and a method for manufacturing an optical fiber.

Background Art

[0002] As a method for manufacturing a preform for an optical fiber for manufacturing an optical fiber, for example, a hole opening method is known, and the following Patent Document 1 discloses the method. In the hole opening method, a through hole is provided in a clad rod serving as a clad using a drill or the like, and a core rod serving as a core, a marker rod serving as a marker, a glass body serving as a stress applying portion, or the like is inserted into the through hole from one opening of the through hole, whereby a preform for an optical fiber is manufactured.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a hole opening method, before inserting a glass rod such as a core rod into the through hole, the end portion of the clad rod may be heated from the outer peripheral side by a flame of a burner or the like, and a glass tube or the like may be welded to the end face of the clad rod. In such heating, the position of the flame in the longitudinal direction of the clad rod is adjusted so that a part of the flame hits the end face of the clad rod. Therefore, the edge portion defining the opening in the clad rod may be melted, and the diameter at the opening may become smaller. In this case, there is a concern that it may be difficult to insert a glass rod such as a core rod into the through hole from the opening.

[0005] Therefore, the present invention aims to provide a clad rod that can suppress the difficulty in inserting a glass rod, a method for manufacturing a preform for optical fibers using the same, and a method for manufacturing optical fibers. [Means for solving the problem]

[0006] To achieve the above objective, the present invention provides a clad rod comprising a clad glass body which constitutes at least a part of the cladding in an optical fiber, wherein the rod extends along the longitudinal direction and has an opening at at least one end, and a hole is provided through the opening into which a glass rod comprising a predetermined glass body which constitutes a predetermined part different from the cladding in the optical fiber can be inserted, and the inner circumferential surface of the hole has a tapered portion which, at the one end, expands in diameter toward the opening from a position away from the opening and extends to the one end face of the clad rod.

[0007] Furthermore, the present invention provides a method for manufacturing a preform for optical fibers, comprising: a preparation step of preparing a clad rod containing a clad glass body that forms at least a part of the cladding in an optical fiber, and a preform for a glass rod containing a preform for a preform for a part of the optical fiber that is different from the cladding; and an insertion step of inserting the glass rod into the hole through the opening, wherein the inner circumferential surface of the hole has a tapered portion that expands in diameter from a position away from the opening toward the opening at the one end, and extends to the one end face of the clad rod.

[0008] In the above-described method for manufacturing clad rods and optical fiber base materials, the edge defining one side of the clad rod opening is the edge on the opening side of the tapered section, and the diameter of the hole at this edge is larger than the diameter of the hole at the edge on the opposite side of the tapered section. Therefore, even if the edge on the opening side of the tapered section melts and the diameter of the opening decreases due to heating of the clad rod, such as by exposing one end to a flame, this diameter is unlikely to become smaller than the diameter of the hole at the edge on the opposite side of the tapered section. Consequently, this method for manufacturing clad rods and optical fiber base materials can suppress the difficulty of inserting a glass rod into the hole from one side of the opening, even when the clad rod is heated as described above, compared to the case where the inner circumferential surface of the hole does not have the tapered section and the diameter of the hole is the same as the diameter of the hole at the edge on the opposite side of the tapered section.

[0009] In the above-described method for manufacturing clad rods and optical fiber base materials, the opening edge of the tapered portion may be separated from the outer peripheral edge of the end face on one side of the clad rod. With this clad rod, an annular, flat region can be formed on the end face on one side that extends along the entire circumference of the outer peripheral edge. Therefore, compared to the case where the opening edge of the tapered portion is connected to the outer peripheral edge of the end face on one side of the clad rod, it is easier to firmly weld a glass tube with the same outer diameter as the outer diameter of the clad rod to the end face on one side of the clad rod in a coaxial manner.

[0010] The clad rod described above may have multiple holes.

[0011] In this case, the opening-side edges of the tapered portions of at least two adjacent holes may be spaced apart from each other. With this configuration, the strength between the two tapered portions can be increased compared to the case where the opening-side edges of the two tapered portions are connected.

[0012] Alternatively, in the tapered portions of at least two adjacent holes, a portion of the opening-side edge of one tapered portion may also serve as a portion of the opening-side edge of the other tapered portion, and may be located on the other side of the end face of the clad rod. With this configuration, compared to the case where the position in the longitudinal direction of the clad rod of the portion of the opening-side edge of one tapered portion that also serves as a portion of the opening-side edge of the other tapered portion is the same as the end face of one side of the clad rod, it is possible to make it more difficult for the flame to hit the portion when the clad rod is heated so that the flame hits the end face of one side. For this reason, with this clad rod, it is possible to make it more difficult for the portion to melt compared to the case described above.

[0013] Furthermore, the optical fiber manufacturing method of the present invention is characterized by comprising a drawing step of drawing a wire onto the optical fiber preform manufactured by the above-described optical fiber preform manufacturing method. [Effects of the Invention]

[0014] As described above, the present invention provides a clad rod that can suppress the difficulty in inserting a glass rod, a method for manufacturing a preform for optical fibers using the same, and a method for manufacturing optical fibers. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber manufactured from a pre-material for optical fibers manufactured using a clad rod according to an embodiment of the present invention. [Figure 2] Figure 1 is a cross-sectional view along the longitudinal direction of the optical fiber base material used to manufacture the optical fiber shown. [Figure 3] Figure 2 shows a cross-sectional view of the optical fiber base material perpendicular to the longitudinal direction. [Figure 4] This figure shows the cladding rod of this embodiment used to manufacture the optical fiber base material shown in Figure 2. [Figure 5] Figure 4 is a cross-sectional view of the clad rod along the VV line. [Figure 6] It is a flowchart showing the steps of a method for manufacturing an optical fiber, including a method for manufacturing a preform for an optical fiber manufactured using the clad rod shown in FIG. 4. [Figure 7] It is a diagram showing the state of the dummy glass tube welding process. [Figure 8] It is a diagram showing the state of the etching process. [Figure 9] It is a diagram showing the state after the insertion process. [Figure 10] It is a diagram showing the state of the closing process. [Figure 11] It is a diagram showing the clad rod in a modified example in the same manner as FIG. 4.

Best Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments for implementing the clad rod according to the present invention, a method for manufacturing a preform for an optical fiber using the same, and a method for manufacturing an optical fiber will be illustrated together with the accompanying drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. The present invention can be changed and improved from the following embodiments without departing from the gist thereof. Also, in this specification, for ease of understanding, the dimensions of each member may be shown exaggerated.

[0017] FIG. 1 is a cross-sectional view perpendicular to the longitudinal direction of an optical fiber manufactured from a preform for an optical fiber manufactured using a clad rod according to an embodiment of the present invention. As shown in FIG. 1, the optical fiber 1 of the present embodiment is a multi-core fiber, and mainly includes a plurality of cores 10, a marker 15, a clad 20 surrounding the outer peripheral surfaces of the respective cores 10 and the marker 15, and a coating layer 30 covering the outer peripheral surface of the clad 20. In the present embodiment, the number of cores 10 is four, and the respective cores 10 are arranged at substantially equal intervals on a circumference centered on the central axis of the optical fiber 1. Further, although the outer shapes of the core 10, the marker 15, and the clad 20 in the cross section are circular, these outer shapes may be non-circular such as an ellipse. Further, the number of cores 10 is not limited. For example, the optical fiber 1 may be a single-core fiber having one core 10.

[0018] The refractive index of the core 10 is higher than that of the clad 20. In the present embodiment, the core 10 is made of silica glass to which a dopant having a high refractive index such as germanium is added, and the clad 20 is made of silica glass without any additives. Note that the core 10 may be made of silica glass without any additives, and the clad 20 may be made of silica glass to which a dopant having a low refractive index such as fluorine (F) is added, and the dopant for changing the refractive index is not limited.

[0019] The marker 15 is made of silica glass having a refractive index different from that of the clad 20, and the refractive index of the marker 15 may be higher or lower than that of the clad 20. Note that the diameter of the marker 15 is smaller than the diameter of the core 10. Further, the position, number, etc. of the marker 15 are not limited. For example, the optical fiber 1 may not include the marker 15.

[0020] The coating layer 30 is made of a resin such as a thermosetting resin or an ultraviolet curable resin.

[0021] Figure 2 is a cross-sectional view along the longitudinal direction of the optical fiber base material used to manufacture the optical fiber 1 shown in Figure 1. Figure 3 is a cross-sectional view perpendicular to the longitudinal direction of the optical fiber base material 1P shown in Figure 2, and is a cross-sectional view of the main body, which will be described later. As shown in Figures 2 and 3, the optical fiber base material 1P mainly comprises a plurality of core rods 110R, a marker rod 115R, and a cladding rod 120R. The number of core rods 110R is four, the same as the number of cores 10 in the optical fiber 1.

[0022] Each core rod 110R has a similar configuration to the others and includes a rod-shaped core glass body 10P that forms the core 10 as a predetermined part distinct from the cladding 20 in the optical fiber 1. The core rod 110R in this embodiment is a glass rod in which the outer surface of the core glass body 10P is covered with a coating layer 110RL made of the same glass material as the cladding glass body described later.

[0023] The marker rod 115R is a glass rod consisting of a rod-shaped marker glass body 15P that becomes a marker 15 as a predetermined part distinct from the cladding 20 in the optical fiber 1.

[0024] The clad rod 120R includes a clad glass body 20P which is at least part of the clad 20 of the optical fiber 1. In this embodiment, the clad rod 120R consists of a rod-shaped clad glass body 20P. The clad rod 120R is provided with five holes 125a to 125e extending along its longitudinal direction, with four holes 125a to 125d corresponding one-to-one to the core rod 110R, and hole 125e corresponding to the marker rod 115R. Therefore, the number of holes 125a to 125e provided in the clad rod 120R changes depending on the number of core rods 110R and marker rods 115R.

[0025] A core rod 110R is held in each of the holes 125a to 125d, and a marker rod 115R is held in hole 125e. The positions of each of the holes 125a to 125d and hole 125e, relative to the central axis of the cladding rod 120R, are roughly similar to the positions of the core 10 and the marker 15, relative to the central axis of the optical fiber 1.

[0026] The clad rod 120R has a first sealing portion 121 at one end and a second sealing portion 122 at the other end, with the portion between the first sealing portion 121 and the second sealing portion 122 being the main body portion 123. In the following, one end may be referred to as the first end and the other end as the other end.

[0027] The first sealing portion 121 is formed in a tapered shape with its outer diameter decreasing from one side to the other, surrounding one end of each core rod 110R and marker rod 115R, and welded to that end to seal one end of each hole 125a to 125d. The portion of the core rod 110R surrounded by the first sealing portion 121 is formed in a tapered shape with its outer diameter decreasing from one side to the other. One end of a support rod 40 made of silica glass is welded to the tip of this first sealing portion 121, and the central axis of the support rod 40 and the central axis of the clad rod 120R are roughly aligned.

[0028] The second sealing portion 122 is formed in a tapered shape with its outer diameter decreasing from one side to the other, surrounding the other end of each core rod 110R and marker rod 115R and welding it to the other end, sealing the other end of each hole 125a to 125e. The portion of the core rod 110R surrounded by the second sealing portion 122 is formed in a tapered shape with its outer diameter decreasing from one side to the other. In this way, both ends of each hole 125a to 125e are sealed by the first sealing portion 121 and the second sealing portion 122, and the inside of each hole 125a to 125d is a closed space. The pressure in the space between the clad rod 120R and the core rod 110R and the space between the clad rod 120R and the marker rod 115R, which are the spaces inside these holes 125a to 125e, is lower than atmospheric pressure, for example, 10-5 Pa to 10 -8 It's around Pa.

[0029] The cross-sectional shape of the main body 123 is circular, and its outer diameter is approximately constant in the longitudinal direction. The diameters of the holes 125a to 125e in the main body 123 are approximately constant in the longitudinal direction, the diameters of the holes 125a to 125d corresponding to the core rod 110R are approximately the same, and the diameter of the hole 125e corresponding to the marker rod 115R is smaller than the diameters of the other holes 125a to 125d. Furthermore, the diameter of the portion of each core rod 110R surrounded by the main body 123 is approximately constant in the longitudinal direction, and the diameters of these core rods 110R at these portions are approximately the same. Similarly, the diameter of the portion of the marker rod 115R surrounded by the main body 123 is approximately constant in the longitudinal direction, and the diameter of the marker rod 115R at these portions is smaller than the diameter of the portion of the core rod 110R surrounded by the main body 123.

[0030] Next, we will describe the cladding rod used to manufacture such optical fiber base material 1P.

[0031] Figure 4 shows the clad rod of this embodiment used to manufacture the optical fiber base material 1P shown in Figure 2, and is a view of the clad rod from one side along its longitudinal direction. As shown in Figure 4, the clad rod 20R of this embodiment is a rod-shaped member with a circular cross-section, and, like the clad rod 120R of the optical fiber base material 1P, is made of a clad glass body 20P. The outer diameter of the clad rod 20R is approximately constant in the longitudinal direction and is the same as the outer diameter of the main body portion 123 of the clad rod 120R. The clad rod 20R is longer than the clad rod 120R, and both end faces of the clad rod 20R are flat surfaces perpendicular to the central axis of the clad rod 20R. The clad rod 20R is provided with five holes 25a to 25e that extend along its longitudinal direction. The positions of these holes 25a to 25e relative to the central axis of the clad rod 20R are the same as the positions of the holes 125a to 125e relative to the central axis of the main body 123. Furthermore, these holes 25a to 25e are through holes with openings at both ends in the longitudinal direction of the clad rod 20R, and these openings are located on both end faces of the clad rod 20R. In these holes 25a to 25e, each pair of hole 25a and hole 25b, hole 25b and hole 25c, hole 25c and hole 25d, hole 25d and hole 25a, and hole 25e and hole 25d are adjacent to each other. Note that holes 25a to 25d have the same configuration, and hole 25e has a configuration that is generally the same as the other holes 25a to 25d except for its smaller diameter. For this reason, the following will describe hole 25a, and the descriptions of the other holes 25b to 25e will be omitted as appropriate.

[0032] Figure 5 is a cross-sectional view of the clad rod 20R along the VV line in Figure 4, and is a cross-sectional view along the central axis of holes 25a and 25b. As shown in Figures 4 and 5, the inner circumferential surface 26 of the clad rod 20R defining hole 25a has a tapered portion 27 at one end where the diameter of hole 25a expands from a position away from the opening toward the opening, and extends to the end face 20Rf on one side of the clad rod 20R. Therefore, the opening on one side of hole 25a is defined by the edge 28 of the tapered portion 27 on the opening side, and the diameter D1 of hole 25a at this edge 28 is greater than the diameter D2 of hole 25a at the edge 29 of the tapered portion 27 opposite to the opening side. The diameter of hole 25a on the side opposite to the opening side with respect to the edge 29 is approximately the same as the diameter D2 and is approximately constant in the longitudinal direction. The diameter D2 in holes 25a to 25d is the same as the diameter of holes 125a to 125d in the main body portion 123 of the clad rod 120R of the optical fiber base material 1P, and the diameter D2 in hole 25e is the same as the diameter of hole 125e in the main body portion 123. For this reason, a straight core rod 110R with no reduction in diameter at both ends can be inserted into holes 25a to 25d, and a straight marker rod 115R with no reduction in diameter at both ends can be inserted into hole 25e. The angle θ between the tapered portion 27 and the end face 20Rf on the opening side is, for example, 190 degrees or more and 240 degrees or less. The ratio D1 / D2 of the diameter D1 of holes 25a to 25e at the edge portion 28 to the diameter D2 of holes 25a to 25e at the edge portion 29 is, for example, 1.1 or more and 2.0 or less. Furthermore, the angle θ and ratio D1 / D2 formed with respect to the tapered portion 27 in at least two holes may be different or the same. Also, in this embodiment, the end face 20Rf is perpendicular to the central axis of the clad rod 20R, but it may not be perpendicular.

[0033] The edges 28 of the tapered portions 27 in these holes 25a to 25e are separated from the outer peripheral edge 20Rfe of the end face 20Rf of the clad rod 20R. Therefore, the end face 20Rf has an annular, flat region FA that extends along the entire circumference of the outer peripheral edge 20Rfe. Accordingly, with the clad rod 20R of this embodiment, it is easier to firmly weld one end face of a glass tube with the same outer diameter as the outer diameter of the clad rod 20R to the end face 20Rf of the clad rod 20R in a coaxial manner, compared to the case where the edges 28 are connected to the outer peripheral edge 20Rfe. In Figure 4, the boundary of region FA is shown by a dashed line. The edges 28 may also be connected to the outer peripheral edge 20Rfe.

[0034] Furthermore, in the tapered portions 27 of adjacent holes 25a and 25b, a portion 28P of the edge 28 of the tapered portion 27 of hole 25a also serves as a portion of the edge 28 of the tapered portion 27 of hole 25b. Similarly, a portion 28P of the edge 28 in hole 25b also serves as a portion of the edge 28 in hole 25c, a portion 28P of the edge 28 in hole 25c also serves as a portion of the edge 28 in hole 25d, a portion 28P of the edge 28 in hole 25d also serves as a portion of the edge 28 in hole 25a, and a portion 28P of the edge 28 in hole 25e also serves as a portion of the edge 28 in hole 25d. These portions 28P of the edges 28 are located on the other side of the end face 20Rf of the clad rod 20R.

[0035] Next, the manufacturing method of the optical fiber base material 1P and the manufacturing method of the optical fiber 1 will be described.

[0036] Figure 6 is a flowchart showing the steps of a method for manufacturing an optical fiber 1, including a method for manufacturing a preform 1P for optical fibers according to this embodiment. As shown in Figure 6, the method for manufacturing a preform 1P for optical fibers according to this embodiment includes a preparation step P1, a dummy glass tube welding step P2, an etching step P3, an insertion step P4, a closure step P5, and a cutting step P6. The method for manufacturing an optical fiber 1 also includes a drawing step P7 for drawing the manufactured preform 1P for optical fibers.

[0037] <Preparation process P1> This step involves preparing multiple glass components. In this embodiment, the multiple glass components to be prepared are multiple core rods, marker rods, and the clad rod 20R shown in Figure 4. The core rods have the same configuration as the core rod 110R of the optical fiber base material 1P, except that the diameter at both ends extends linearly without reduction and the length is increased. Similarly, the marker rods have the same configuration as the marker rod 115R of the optical fiber base material 1P, except that the diameter at both ends extends linearly without reduction and the length is increased. Therefore, a detailed illustration of the core rods and marker rods is omitted. In this embodiment, the lengths of the core rods, marker rods, and clad rod 20R are the same, and there are four core rods. These glass components may be washed beforehand using pure water, ethanol, hydrofluoric acid, etc.

[0038] <Dummy glass tube welding process P2> This step involves welding dummy glass tubes to each of the end faces of the clad rod 20R prepared in preparation step P1. The dummy glass tubes in this embodiment are cylindrical tubes made of silica glass with an outer diameter approximately the same as the outer diameter of the clad rod 20R. In the following description, the dummy glass tube welded to one end face 20Rf on the inner circumferential surface 26 of the clad rod 20R, where the tapered portion 27 is located, will be referred to as the first glass tube, and the dummy glass tube welded to the other end face will be referred to as the second glass tube.

[0039] Figure 7 shows the process. In this embodiment, the clad rod 20R is rotated around its central axis using a lathe (not shown) so that its central axis is approximately horizontal, while one end of the clad rod 20R is heated by an oxyhydrogen burner 50. Next, the first glass tube 41, which is positioned so that one end face faces the end face 20Rf of the clad rod 20R at a predetermined distance, is rotated around its central axis using a lathe (not shown). The rotation of the clad rod 20R and the first glass tube 41 are synchronized, and in this state, one end of the clad rod 20R and the end of the first glass tube 41 on the clad rod 20R side are heated by the flame of the oxyhydrogen burner 50. At this time, the position of the oxyhydrogen burner 50 in the longitudinal direction of the clad rod 20R is adjusted so that a part of the flame hits the end face 20Rf of the clad rod. Next, one end face of the first glass tube 41 is abutted against the end face 20Rf of the clad rod 20R, and the first glass tube 41 is welded to the end face 20Rf of the clad rod 20R so that the clad rod 20R and the first glass tube 41 are approximately coaxial. Similarly, the second glass tube is welded to the other end face of the clad rod 20R. With the first glass tube 41 and the second glass tube welded together, the entire opening on one side of each hole 25a to 25e of the clad rod 20R opens into the internal space of the first glass tube 41, and the entire opening on the other side of each hole 25a to 25e opens into the internal space of the second glass tube.

[0040] <Etching process P3> This process involves etching the inner circumferential surface 26 that defines each of the holes 25a to 25e in the clad rod 20R. Figure 8 shows the process. In this embodiment, the clad rod 20R, to which glass tubes 41 and 42 are welded by a lathe (not shown), is rotated around its central axis while its central axis is approximately horizontal, and an etching gas such as sulfur hexafluoride (SF6) gas is flowed from the second glass tube 42 into the holes 25a to 25e of the clad rod 20R. At this time, an oxyhydrogen burner 50 is traversed along the longitudinal direction of the clad rod 20R to heat it. In this way, the inner circumferential surface 26 is etched. The etching method is not particularly limited, and etching may be performed using an etching solution such as hydrofluoric acid (HF), for example.

[0041] <Insertion process P4> This step involves inserting the core rod and marker rod prepared in preparation step P1 into the holes 25a to 25e of the clad rod 20R from one opening on the side where the tapered portion 27 is located. Figure 9 shows the state after this step. In this embodiment, first, a part of the first glass tube 41 is cut using an oxyhydrogen burner 50 to shorten the first glass tube 41. Next, the prepared core rod and marker rod are inserted into the corresponding holes 25a to 25e of each rod from one opening on the side to form a rod assembly RA consisting of the core rod, marker rod, and clad rod 20R. The cross-sectional view of this rod assembly RA perpendicular to the longitudinal direction is the same as in Figure 3. In this embodiment, the core rod 10R is inserted such that one end of the core rod 10R is surrounded by one end of the clad rod 20R, and the other end is surrounded by the other end of the clad rod 20R. Although a diagrammatic explanation is omitted, the marker rod 115R is inserted in the same way as the core rod 10R, such that one end of the marker rod is surrounded by one end of the clad rod 20R and the other end is surrounded by the other end of the clad rod 20R.

[0042] <Closure process P5> This step involves attaching a closure member to one end face 20Rf of the clad rod 20R so as to block at least a portion of one side of the openings of holes 25a to 25e. Figure 10 shows the process of this step. In this embodiment, the closure member is a cylindrical dummy rod 43 made of silica glass, and the diameter of the dummy rod 43 is smaller than the inner diameter of the first glass tube 41. The dummy rod 43 is inserted into the internal space of the first glass tube 41 so that one end face of the dummy rod 43 is in contact with the end face 20Rf of the clad rod 20R. The central axis of the clad rod 20R and the central axis of the dummy rod 43 are roughly coincide, and in this embodiment, in this state, the entire opening on one side of each of the holes 25a to 25e is covered by the dummy rod 43. Next, the rod assembly RA and the dummy rod 43 are rotated synchronously around the central axis using a lathe (not shown) with the central axis being approximately horizontal, while one end of the rod assembly RA, the end of the dummy rod 43 on the rod assembly RA side, and the first glass tube 41 are heated with an oxyhydrogen burner 50. The first glass tube 41 is then welded to the dummy rod 43, and the dummy rod 43 is also welded to the end face 20Rf of the clad rod 20R of the rod assembly RA. In this way, the dummy rod 43 is attached to the end face 20Rf of the clad rod 20R, and as a result, in this embodiment, the entire opening on one side of each hole 25a to 25e of the clad rod 20R is blocked by the dummy rod 43 and the first glass tube 41.

[0043] <Cutting process P6> This process involves melting both ends of the rod assembly RA to form a first sealing portion 121 at one end of the clad rod 20R and a second sealing portion 122 at the other end of the clad rod 20R. This process will be described in detail without showing the figures. In this embodiment, while evacuating the holes 25a to 25e of the clad rod 20R of the rod assembly RA with a vacuum pump (not shown) connected to the second glass tube 42, the rod assembly RA is rotated around the central axis of the clad rod 20R using a lathe (not shown) so that the central axis of the clad rod 20R is approximately horizontal. In this state, one end of the rod assembly RA is heated and melted with an oxyhydrogen burner 50. This melting forms the first sealing portion 121, and one end of the support rod 40 is welded to the tip of the first sealing portion 121. Furthermore, similar to the cutting of one end, the rod assembly RA is rotated by a lathe (not shown) while the holes 25a to 25e are evacuated, and in this state, the other end of the rod assembly RA is heated and cut by an oxyhydrogen burner 50. This cutting forms the second sealing portion 122.

[0044] With the formation of the first sealing portion 121 and the second sealing portion 122 in this manner, the clad rod 20R of the rod assembly RA becomes the clad rod 120R of the optical fiber base material 1P, the holes 25a to 25e of the clad rod 20R of the rod assembly RA become the holes 125a to 125e of the clad rod 120R of the optical fiber base material 1P, the core rod 10R of the rod assembly RA becomes the core rod 110R of the optical fiber base material 1P, and the marker rod of the rod assembly RA becomes the marker rod 115R of the optical fiber base material 1P, thereby obtaining the optical fiber base material 1P shown in Figure 2.

[0045] <Drawing process P7> This process involves drawing a wire from a fiber optic base material 1P to obtain an optical fiber 1. This process will be explained without further explanation. In this process, the fiber optic base material 1P is heated in a spinning furnace, and glass is drawn from the end of the fiber optic base material 1P on the side of the second sealing portion 122. This drawn glass solidifies immediately, and the core glass body 10P becomes the core 10, the marker glass body 15P becomes the marker 15, and the cladding glass body 20P becomes the cladding 20, resulting in a bare optical fiber wire composed of the core 10, the marker 15, and the cladding 20. A coating layer 30 is applied to the outer surface of this bare optical fiber wire to obtain the optical fiber 1 shown in Figure 1.

[0046] As described above, the clad rod 20R of this embodiment includes a clad glass body 20P which is at least a part of the clad 20 in the optical fiber 1. The clad rod 20R of this embodiment is provided with a plurality of holes 25a to 25e that extend along the longitudinal direction and have openings at both ends. A core rod 10R as a glass rod can be inserted into holes 25a to 25d from one opening, and a marker rod as a glass rod can be inserted into hole 25e from one opening. The inner circumferential surface 26 of holes 25a to 25e has a tapered portion 27 that expands in diameter from a position spaced apart from the opening on one end toward the opening, and extends to the end face 20Rf on one side of the clad rod 20R.

[0047] Furthermore, the manufacturing method of the optical fiber base material 1P of this embodiment comprises a preparation step P1 and an insertion step P4. In the preparation step P1, the clad rod 20R and the core rod 10R and marker rod as glass rods are prepared, and in the insertion step P4, the core rod 10R and marker rod are inserted into the holes 25a to 25d from the opening on one side of the clad rod 20R.

[0048] In the manufacturing method of the clad rod 20R and optical fiber base material 1P of this embodiment, the edge portion defining the opening on one side of the clad rod 20R is the edge portion 28 on the opening side of the tapered portion 27. The diameter D1 of the holes 25a to 25e at this edge portion 28 is larger than the diameter D2 of the same holes 25a to 25e at the edge portion 29 on the opposite side of the opening side of the tapered portion 27. Therefore, even if the edge portion 28 of the tapered portion 27 at each of the holes 25a to 25e melts due to heating of the clad rod 20R such that a flame hits the end face 20Rf, which is one end, as in the dummy glass tube welding process P2 described above, and the diameter D1 at the opening becomes smaller, the diameter D1 is unlikely to become smaller than the diameter D2. Furthermore, since the tapered portion 27 opposite to one of the openings is located on the other side of the end face 20Rf of the clad rod 20R, the flame is less likely to hit the tapered portion 27 opposite to one of the openings, and therefore it is less likely to melt than the edge 28 of the tapered portion 27. For this reason, compared to the case where the inner circumferential surface 26 of the holes 25a to 25e does not have a tapered portion 27 and the diameter of the holes 25a to 25e is the same as the diameter D2 of the holes 25a to 25e at the edge 29 of the tapered portion 27, even if the clad rod 20R is heated so that the flame hits the end face 20Rf, the diameter of the holes 25a to 25e near one of the openings is less likely to become smaller than the diameter of the core rod 10R or marker rod that can be inserted into the holes 25a to 25e. Therefore, according to the manufacturing method of the clad rod 20R and optical fiber base material 1P of this embodiment, compared to the above case, even if the clad rod 20R is heated as described above, as in the dummy glass tube welding step P2, it is possible to suppress the difficulty in inserting the core rod 10R and marker rod into the holes 25a to 25e from the opening on one side.

[0049] In the manufacturing method of the clad rod 20R and optical fiber base material 1P of this embodiment, in the tapered portions 27 of adjacent holes, a portion 28P of the edge 28 of one tapered portion 27 also serves as a portion of the edge 28 of the other tapered portion 27. Furthermore, this portion 28P of the edge 28 is located on the other side of the end face 20Rf of the clad rod 20R. Therefore, compared to the case where the position of the portion 28P of the edge 28 of one tapered portion 27 that also serves as a portion of the edge 28 of the other tapered portion 27 in the longitudinal direction of the clad rod 20R is the same as the end face 20Rf of the clad rod 20R, it is possible to make it less likely for the flame to hit the portion 28P of the edge 28 when the clad rod 20R is heated so that the flame hits the end face 20Rf. Therefore, according to the manufacturing method of the clad rod 20R and optical fiber base material 1P of this embodiment, it is possible to make it more difficult to melt a portion 28P of the edge portion 28 compared to the above case. In this regard, it is sufficient that in at least two adjacent holes in the tapered portion 27, a portion 28P of the edge portion 28 of one tapered portion 27 also serves as a portion of the edge portion 28 of the other tapered portion 27, and is located on the other side of the end face 20Rf. Furthermore, the position of the above portion 28P in the longitudinal direction of the clad rod 20R may be the same as the end face 20Rf.

[0050] Although the present invention has been described above with reference to the above embodiments, the present invention is not limited thereto.

[0051] For example, in the above embodiment, a clad rod 20R in which the edges 28 of the tapered portions 27 in adjacent holes are connected was described as an example. However, as shown in Figure 11, the edges 28 of the tapered portions 27 in adjacent holes may be separated from each other. Figure 11 is a diagram showing a modified clad rod 20R in the same manner as Figure 4. With this configuration, the strength between the tapered portions 27 in the clad rod 20R can be increased compared to the case in which the edges 28 of the tapered portions 27 are connected. At least the edges 28 of the tapered portions 27 in two adjacent holes may be separated from each other. With this configuration, the strength between two tapered portions 27 whose edges 28 are separated from each other can be increased.

[0052] Furthermore, in the above embodiment, a clad rod 20R made of a clad glass body 20P was described as an example. However, the clad rod 20R only needs to include the clad glass body 20P, and may further include a predetermined glass body that is different from the clad 20 in the optical fiber 1. Examples of such predetermined parts include the core 10, the marker 15, and the stress-applying part that applies stress to the core 10. In addition, the clad rod 20R may be provided with a void that extends along the longitudinal direction into which the glass rod is not inserted.

[0053] Furthermore, in the above embodiment, a clad rod 20R was described as having holes 25a to 25d into which a core rod 10R can be inserted, and a hole 25e into which a marker rod can be inserted. However, the holes provided in the clad rod 20R only need to allow a glass rod containing a predetermined glass body that is a predetermined part different from the clad 20 in the optical fiber 1 to be inserted from one side of the opening. For example, the predetermined glass body contained in the insertable glass rod may be a glass body that becomes a stress-applying part as the predetermined part. Also, the insertable glass rod may be a glass rod in which a core glass body 10P that becomes the core 10 is covered with a glass body that becomes a low refractive index layer surrounding the core 10.

[0054] Furthermore, in the above embodiment, a clad rod 20R having a plurality of holes 25a to 25e with openings at both ends was described as an example. However, the number of holes provided in the clad rod 20R is not limited. Also, it is sufficient that the holes have an opening at at least one end, and the other end of the hole may be closed. In addition, if the holes have openings at both ends, the inner circumferential surface 26 of the hole may further have another tapered portion at the other end, where the diameter of the hole expands from a position spaced away from the other opening toward the opening, and extends to the other end face of the clad rod 20R.

[0055] Furthermore, in the above embodiment, an oxyhydrogen burner 50 was used to heat the glass member. However, the heating device for heating the glass member is not limited and may be, for example, an electric furnace. From the viewpoint of reducing processing waste, it is preferable to cut the rod assembly RA in the cutting process P6 using an oxyhydrogen burner 50. Generally, the heat spot of an oxyhydrogen burner is narrower than the heat spot of an electric furnace. Therefore, by using an oxyhydrogen burner, the length of the first sealing portion 121 and the second sealing portion 122 formed by the cutting process can be shortened compared to when an electric furnace is used, thereby reducing processing waste. In addition, the heat source may be light with a high absorption rate for glass, such as a CO2 laser. When a laser is used as the heat source, it is possible to make the heat spot distribution arbitrary, and it is possible to achieve optimal heating depending on the size and material of the base material.

[0056] Furthermore, in the above embodiment, the cutting process P6, in which both ends of the rod assembly RA are cut off, was described as an example. However, in the cutting process P6, the other end of the rod assembly RA is not cut off, and only the first sealing portion 121 is formed, and the support rod 40 is not welded to the tip of the first sealing portion 121. In this case, the configuration of the optical fiber base material 1P is one that does not have a second sealing portion 122. For example, in the wire drawing process P7, the holes 25a to 25e are evacuated using a vacuum pump (not shown) connected to the second glass tube 42, and the wire is drawn from the end on the side of the first sealing portion 121.

[0057] According to the present invention, a clad rod that can suppress the difficulty in inserting a glass rod, a method for manufacturing a preform for optical fibers using the same, and a method for manufacturing optical fibers are provided, which can be used in various fields related to optical fibers. [Explanation of Symbols]

[0058] 1. Optical fiber 1P... Fiber optic base material 10 cores 10P...Core glass body 10R... Core rod (glass rod) 15.. Marker 15P... Marker glass body 20.. Clad 20P... Clad glass body 20R...Clad Rod 25a,25b,25c,25d,25e...hole 26...Inner surface 27. Tapered section 28. Edge on the opening side P1...preparation process P2...Dummy glass tube welding process P3... Etching process P4...Insertion process P5...Closure process P6... Cutting process P7...Drawing process

Claims

1. A clad rod comprising a clad glass body that forms at least part of the cladding in an optical fiber, Multiple holes are provided through which a glass rod, which extends along the longitudinal direction and has an opening at at least one end, and which includes a predetermined glass body that is a predetermined part different from the cladding in the optical fiber, can be inserted through the opening. The inner circumferential surface of the plurality of holes has a tapered portion that, at one end, expands in diameter from a position away from the opening toward the opening and extends to the end face of the clad rod on one side. A clad rod characterized by its features.

2. The edge of the tapered portion on the opening side is separated from the outer peripheral edge of the end face on one side. The clad rod according to feature 1.

3. At least two adjacent holes have edges on the opening side of the tapered portion that are spaced apart from each other. The clad rod according to feature 1.

4. In the tapered portions of at least two adjacent holes, a portion of the opening-side edge of one tapered portion also serves as a portion of the opening-side edge of the other tapered portion, and is located on the other side of the end face of the clad rod. The clad rod according to feature 1.

5. A preparation step of preparing a clad rod including a clad glass body that extends along the longitudinal direction and has a hole with an opening at at least one end, and which is at least a part of the cladding in an optical fiber, and a glass rod including a predetermined glass body that is a predetermined part different from the cladding in the optical fiber, An insertion step of inserting the glass rod into the hole through the opening, Equipped with, The inner circumferential surface of the hole has a tapered portion that, at one end, expands in diameter from a position away from the opening toward the opening and extends to the end face of the clad rod on one side. A method for manufacturing a preform for optical fibers, characterized by the following features.

6. The method comprises a drawing step for drawing lines on an optical fiber preform manufactured by the method for manufacturing an optical fiber preform described in claim 5. A method for manufacturing optical fibers, characterized by the following:

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