JP7829384B2 - Clad rod, method for manufacturing a preform for optical fibers using the same, and method for manufacturing optical fibers - Google Patents

Description

This invention relates to a clad rod, a method for manufacturing a preform for optical fibers using the same, and a method for manufacturing optical fibers.

As a method for manufacturing optical fiber preforms for optical fiber production, for example, the drilling method is known, and this method is disclosed in Patent Document 1 below. In the drilling method, through holes are made in the cladding rod, which will become the cladding, using a drill or the like, and the core rod, which will become the core, the marker rod, and the glass body, which will become the stress-applying part, are inserted into the through holes through one opening, thereby manufacturing the optical fiber preform.

Japanese Patent Publication No. 2019-031427

In this type of hole-drilling method, before inserting a glass rod such as a core rod into the through-hole, the end of the clad rod may be heated from the outer circumference with a flame from a burner or similar device, and a glass tube or similar material may be welded to the end face of the clad rod. In this heating process, the position of the flame along the longitudinal direction of the clad rod is adjusted so that a portion of the flame strikes the end face of the clad rod. As a result, the edge defining the opening in the clad rod may melt, reducing the diameter of the opening. In this case, there is a concern that it may become difficult to insert the glass rod, such as a core rod, into the through-hole through the opening.

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.

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

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 pre-defined glass body that forms a predetermined part of the optical fiber different from the cladding; and an insertion step of inserting the glass rod into the hole through the opening. The inner circumferential surface of the hole is characterized in that, at the one end, the diameter of the hole expands from a position away from the opening toward the opening, and the tapered portion extends to the one end face of the clad rod.

In the above-described method for manufacturing clad rods and optical fiber base materials, the edge defining one end of the clad rod 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 opposite the opening 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 applying a flame to one end, this diameter is unlikely to become smaller than the diameter of the hole at the edge opposite the opening side of the tapered section. Consequently, this method for manufacturing clad rods and optical fiber base materials can suppress the difficulty in inserting a glass rod into the hole from one end of the opening, even when the clad rod is heated as described above, compared to a 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 opposite the opening side of the tapered section.

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. This clad rod allows for the formation of an annular, flat region extending along the entire circumference of the outer peripheral edge on one end face. Therefore, compared to the case where the opening edge of the tapered portion is connected to the outer peripheral edge of one end face 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 one end face of the clad rod in a coaxial manner.

The clad rod described above may have multiple of the aforementioned holes.

In this case, the opening-side edges of the tapered portions of at least two adjacent holes may be separated from each other. This configuration allows for greater strength between the two tapered portions compared to the case where the opening-side edges of the two tapered portions are connected.

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 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 in question when the clad rod is heated so that the end face of one side is exposed to flame. Therefore, with this clad rod, it is possible to make the portion in question less likely to melt compared to the above case.

Furthermore, the optical fiber manufacturing method of the present invention is characterized by comprising a drawing step of drawing the optical fiber preform manufactured by the above-described optical fiber preform manufacturing method.

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.

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 1 is a cross-sectional view along the longitudinal direction of the optical fiber base material used to manufacture the optical fiber shown. Figure 2 shows a cross-sectional view perpendicular to the longitudinal direction of the optical fiber base material. This figure shows the cladding rod of this embodiment used to manufacture the optical fiber base material shown in Figure 2. Figure 4 is a cross-sectional view of the clad rod along the line V-V. This flowchart shows the steps for manufacturing an optical fiber, including the manufacturing method for optical fiber preforms produced using the clad rods shown in Figure 4. This diagram shows the process of welding dummy glass tubes. This diagram shows the etching process. This figure shows the state after the insertion process. This is a diagram showing the blockage process. This figure shows a modified clad rod similar to that in Figure 4.

The following examples illustrate, with accompanying drawings, embodiments for carrying out the clad rod according to the present invention, a method for manufacturing a preform for optical fibers using the same, and a method for manufacturing optical fibers. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments without departing from its spirit. Furthermore, in this specification, the dimensions of each component may be exaggerated for the sake of clarity.

Figure 1 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. As shown in Figure 1, the optical fiber 1 of this embodiment is a multi-core fiber and mainly comprises a plurality of cores 10, markers 15, a cladding 20 surrounding the outer surfaces of each core 10 and marker 15, and a coating layer 30 covering the outer surface of the cladding 20. In this embodiment, there are four cores 10, and each core 10 is arranged at approximately equal intervals on the circumference of the optical fiber 1 centered on the central axis. Furthermore, although the outer shapes of the cores 10, markers 15, and cladding 20 in this cross-section are circular, their outer shapes may be non-circular, such as elliptical. Also, the number of cores 10 is not limited; for example, the optical fiber 1 may be a single-core fiber having one core 10.

The refractive index of the core 10 is higher than that of the cladding 20. In this embodiment, the core 10 is made of silica glass to which a dopant that increases the refractive index, such as germanium, is added, and the cladding 20 is made of silica glass without any additives. Alternatively, the core 10 may be made of silica glass without any additives, and the cladding 20 may be made of silica glass to which a dopant that decreases the refractive index, such as fluorine (F), is added; the dopant that changes the refractive index is not limited.

The marker 15 is made of silica glass with a refractive index different from that of the cladding 20. The refractive index of the marker 15 may be higher or lower than that of the cladding 20. The diameter of the marker 15 is smaller than the diameter of the core 10. Furthermore, the position and number of the markers 15 are not restricted; for example, the optical fiber 1 may not even have markers 15.

The coating layer 30 is made of a resin, such as a thermosetting resin or an ultraviolet-curing resin.

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 portion described later. As shown in Figures 2 and 3, the optical fiber base material 1P mainly comprises a plurality of core rods 110R, marker rods 115R, and cladding rods 120R. The number of core rods 110R is four, the same as the number of cores 10 in the optical fiber 1.

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, a predetermined portion distinct from the cladding 20 in the optical fiber 1. In this embodiment, the core rod 110R 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.

The marker rod 115R is a glass rod consisting of a rod-shaped marker glass body 15P that serves as a marker 15, a predetermined portion distinct from the cladding 20 in the optical fiber 1.

The clad rod 120R includes a clad glass body 20P that forms at least a portion 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. Four of the holes 125a to 125d correspond one-to-one with the core rods 110R, and hole 125e corresponds to the marker rod 115R. Therefore, the number of holes 125a to 125e in the clad rod 120R changes depending on the number of core rods 110R and marker rods 115R.

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 holes 125a to 125d and hole 125e, relative to the central axis of the cladding rod 120R, are approximately similar to the positions of the core 10 and marker 15, relative to the central axis of the optical fiber 1.

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 "end 1," and the other end as "end 2."

The first sealing portion 121 is formed in a tapered shape, with its outer diameter decreasing from one side to the other. It surrounds one end of each core rod 110R and marker rod 115R, welding it to that end and sealing one end of each hole 125a to 125d. The portion of the core rod 110R surrounded by the first sealing portion 121 is also 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.

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 spaces within these holes 125a to 125e, specifically 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, is lower than atmospheric pressure, for example, around ^10⁻⁵ Pa to ^10⁻⁸ Pa.

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 this portion is smaller than the diameter of the core rod 110R at the portion surrounded by the main body 123.

Next, we will describe the cladding rod used to manufacture such a preform material 1P for optical fibers.

Figure 4 shows a 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 generally 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, the pairs of holes 25a and 25b, 25b and 25c, 25c and 25d, 25d and 25a, and 25e and 25d are adjacent to each other. Note that holes 25a to 25d have the same configuration, and hole 25e has generally the same configuration as the other holes 25a to 25d, except for its smaller diameter. Therefore, the following description will focus on hole 25a, and descriptions of the other holes 25b to 25e will be omitted as appropriate.

Figure 5 is a cross-sectional view of the clad rod 20R along the line V-V 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 on the opening side of the tapered portion 27, and the diameter D1 of hole 25a at this edge 28 is larger than the diameter D2 of hole 25a at the edge 29 on the opposite side of the tapered portion 27 from the opening side. The diameter of hole 25a on the opposite side of 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 by at least two holes with respect to the tapered portion 27 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.

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. Consequently, with the clad rod 20R of this embodiment, compared to the case where the edge 28 is connected to the outer peripheral edge 20Rfe, it is easier to firmly weld one end face of a glass tube with the same outer diameter as the clad rod 20R to the end face 20Rf of the clad rod 20R in a coaxial manner. Note that in Figure 4, the boundary of region FA is shown by a dashed line. Also, the edge 28 may be connected to the outer peripheral edge 20Rfe.

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.

Next, the manufacturing method of the optical fiber preform 1P and the manufacturing method of the optical fiber 1 will be described.

Figure 6 is a flowchart showing the steps of the manufacturing method for the optical fiber 1, including the manufacturing method for the optical fiber preform 1P according to this embodiment. As shown in Figure 6, the manufacturing method for the optical fiber preform 1P 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 manufacturing method for the optical fiber 1 also includes a drawing step P7 for drawing the manufactured optical fiber preform 1P.

<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. For this reason, 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.

<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.

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. In the state where the first glass tube 41 and the second glass tube are welded together, the entire opening on one side of each of the holes 25a to 25e in 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 of the holes 25a to 25e opens into the internal space of the second glass tube.

<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.

<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 to form a rod assembly RA consisting of the core rod, marker rod, and clad rod 20R. The cross-sectional view perpendicular to the longitudinal direction of this rod assembly RA 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 not shown in the diagram, 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.

<Closing 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 opening 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 of the holes 25a to 25e of the clad rod 20R is blocked by the dummy rod 43 and the first glass tube 41.

<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 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.

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

<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 detail, as it is not shown in the diagram. 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, with the core glass body 10P becoming the core 10, the marker glass body 15P becoming the marker 15, and the cladding glass body 20P becoming the cladding 20, resulting in a bare optical fiber composed of the core 10, the marker 15, and the cladding 20. A coating layer 30 is then applied to the outer surface of this bare optical fiber to obtain the optical fiber 1 shown in Figure 1.

As described above, the clad rod 20R of this embodiment includes a clad glass body 20P that forms 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 extending along the longitudinal direction and having 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 at one end, where the diameter of the holes 25a to 25e expands from a position spaced away from the opening toward the opening, extending to the end face 20Rf of the clad rod 20R.

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, which are glass rods, are prepared. In the insertion step P4, the core rod 10R and marker rod are inserted into the holes 25a to 25d through the opening on one side of the clad rod 20R.

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 one side of the opening.

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 more difficult 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 28 compared to the above case. In this regard, it is sufficient that, in at least two adjacent tapered portions 27, 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, and that it 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 that of the end face 20Rf.

The present invention has been described above using the above embodiments as examples, but the present invention is not limited thereto.

For example, in the above embodiment, a clad rod 20R was described as having edges 28 of tapered portions 27 in adjacent holes connected to each other. However, as shown in Figure 11, the edges 28 of tapered portions 27 in adjacent holes may be separated from each other. Figure 11 shows a modified clad rod 20R similar to Figure 4. With this configuration, the strength between the tapered portions 27 in the clad rod 20R can be increased compared to the case where the edges 28 of the tapered portions 27 are connected. Furthermore, the edges 28 of the tapered portions 27 in at least 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.

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. Also, the clad rod 20R may be provided with voids extending along the longitudinal direction into which the glass rod is not inserted.

Furthermore, in the above embodiment, a clad rod 20R was described as an example, 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 insertion of a glass rod containing a predetermined glass body that is a predetermined part different from the clad 20 in the optical fiber 1, from one side of the opening. For example, the predetermined glass body contained in the insertable glass rod may be a glass body that serves as a stress-applying part. Also, the insertable glass rod may be a glass rod in which a core glass body 10P, which forms the core 10, is covered with a glass body that forms a low refractive index layer surrounding the core 10.

Furthermore, the above embodiment described an example of a clad rod 20R provided with a plurality of holes 25a to 25e having openings at both ends. However, the number of holes provided in the clad rod 20R is not limited. Also, the holes only need to 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 separated from the other opening toward the opening, and extends to the other end face of the clad rod 20R.

Furthermore, in the above embodiment, an oxyhydrogen burner 50 was used to heat the glass component. However, the heating device for heating the glass component is not limited and may be, for example, an electric furnace. From the viewpoint of reducing processing waste, it is preferable to perform the cutting of 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 that 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 using an electric furnace, thereby reducing processing waste. Also, 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 create an arbitrary distribution of heat spots, making it possible to achieve optimal heating for the size and material of the base material.

Furthermore, in the above embodiment, the cutting process P6, in which both ends of the rod assembly RA are cut by melting, was described as an example. However, in the cutting process P6, the other end of the rod assembly RA may not be cut by melting, and only the first sealing portion 121 may be formed, without welding the support rod 40 to the tip of the first sealing portion 121. In this case, the configuration of the optical fiber base material 1P is one without 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, while the wire is drawn from the end on the side of the first sealing portion 121.

According to the present invention, a clad rod capable of suppressing 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.

1... Optical fiber 1P... Optical fiber base material 10... Core 10P... Core glass body 10R... Core rod (glass rod)
15...Marker 15P...Marker glass body 20...Cladding 20P...Cladding glass body 20R...Cladding rod 25a, 25b, 25c, 25d, 25e...Hole 26...Inner circumferential surface 27...Tapered portion 28...Edge on the opening side P1...Preparation process P2...Dummy glass tube welding process P3...Etching process P4...Insertion process P5...Cladding process P6...Cutting process P7...Line drawing process

Claims (6)

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 clad rod is characterized in that the inner circumferential surface of the plurality of holes has a tapered portion that extends to the end face of the clad rod, with the diameter of the holes increasing from a position away from the opening toward the opening at one end, and extending to the end face of the clad rod. The clad rod according to claim 1, characterized in that 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 claim 1 , characterized in that the opening-side edges of the tapered portions of at least two adjacent holes are spaced apart from each other. The clad rod according to claim 1, characterized in that 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 one clad rod. 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,
A method for manufacturing a preform for optical fibers, characterized in that the inner circumferential surface of the hole has a tapered portion that, at one end, expands in diameter toward the opening from a position away from the opening toward the opening and extends to the end face of the cladding rod on one side. A method for manufacturing optical fibers, characterized by comprising a drawing step of drawing a wire on an optical fiber preform manufactured by the method for manufacturing optical fiber preforms described in claim 5 .