JP5513357B2 - Optical fiber preform manufacturing method and optical fiber manufacturing method using the same - Google Patents

Description

  The present invention relates to a method for manufacturing an optical fiber preform, and an optical fiber manufacturing method using the same, and in particular, a longer optical fiber preform is manufactured without changing the structure of a cross section perpendicular to the longitudinal direction. The present invention relates to a method for manufacturing a preform for optical fiber, and a method for manufacturing an optical fiber using the same.

  As a kind of optical fiber, a holey fiber is known in which a plurality of holes are formed in a clad along the longitudinal direction of the optical fiber. In the optical fiber preform for manufacturing the holey fiber, holes serving as hole of the holey fiber are formed along the longitudinal direction of the optical fiber preform. The length of the optical fiber preform is usually 200 mm to 400 mm.

  Patent Document 1 listed below describes a method for manufacturing such an optical fiber preform. In this optical fiber manufacturing method, a hole is formed in a glass body serving as a clad in an intermediate preform of an optical fiber preform. In forming this hole, a pipe-shaped drill tool is used. Then, the drill tool is inserted while being rotated into the glass body serving as the cladding, and drilling is performed. At this time, a liquid such as water flows into the through hole of the drill tool, and the glass waste generated by the drilling is discharged. Specifically, the flowed-in liquid flows out from the through hole at the tip of the drill tool, flows back between the drill tool and the glass body, and the drill tool for the glass body hole is inserted together with the glass waste. It is discharged from the side. In addition, the liquid flowing back between the drill tool and the glass body in this way reduces friction between the drill tool and the glass body, and the inner wall surface of the glass body is unnecessarily heated and oxidized. Can be prevented. In this drilling, holes are formed from both ends of the intermediate base material using a drill tool having a length that is half the length of the intermediate base material.

JP 2002-145634 A

  However, in the method for manufacturing an optical fiber preform described in Patent Document 1, since holes are formed from both ends of the intermediate preform, the positions of the respective holes may be displaced. For this reason, it is preferable to form the hole formed in the intermediate base material from one end side of the intermediate base material. By the way, in recent years, there has been a demand for manufacturing an optical fiber using an optical fiber preform longer than a conventional optical fiber preform such as a length of 800 mm to 1000 mm. When the optical fiber base material is long as described above, it is necessary to use a long drill tool if a hole is formed in the glass rod serving as the optical fiber base material from one end side of the intermediate base material. However, since the drill tool needs to allow the liquid to flow out from the tip as described above, it is pipe-shaped and weak in strength. Therefore, when a long drill tool is used, there is a problem that the drill tool is easily bent between the chucking portion of the drilling device chucking the drill tool and the intermediate base material to be drilled. If the drill tool is curved in this manner, the hole formed in the intermediate base material may be bent. For this reason, the structure in the cross section perpendicular to the longitudinal direction of the optical fiber preform changes, and there is a possibility that an optical fiber as designed cannot be manufactured.

  Accordingly, the present invention provides a method for manufacturing an optical fiber preform that can prevent a change in the structure of a cross section perpendicular to the longitudinal direction and that can produce a longer optical fiber preform, and an optical fiber using the same. It aims at providing the manufacturing method of.

  That is, the method for manufacturing an optical fiber preform of the present invention includes a preparation step of preparing an intermediate preform having a glass body to be a cladding, a chucking step of chucking a pipe-shaped drill tool on a drill chuck, A drilling step of forming a hole in the glass body from one end side of the intermediate base material by pushing along the longitudinal direction of the intermediate base material while rotating the drill tool by a drill chuck, and the chucking step And the drilling step are alternately repeated a plurality of times, and in the chucking step, the distance from the tip of the drill tool to the tip of the drill chuck is increased each time the chucking step is repeated, and The drill chuck from the upper surface of the intermediate base material when the tip of the drill tool is in contact with the glass body Distance to the tip, is characterized in that the smaller than the length of the intermediate preform.

  According to such a method for manufacturing an optical fiber preform, chucking is performed so that the length from the drill chuck to the tip of the drill tool gradually increases each time chucking is performed, and along the longitudinal direction of the intermediate preform. By alternately repeating the drilling for forming the holes in the glass body serving as the cladding, the holes formed in the glass body serving as the cladding of the intermediate base material can be deepened. When the drill tool is chucked, the distance from the upper surface of the intermediate base material to the tip of the drill chuck is smaller than the length of the intermediate base material when the tip of the drill tool is in contact with the glass body. The drill tool is chucked. Therefore, compared with the case where one end of a drill tool having a length longer than the length of the intermediate base material is chucked by the drill chuck, the drill tool bends as compared with the case where a hole is formed in the glass body that becomes the clad at once. Can be suppressed. For this reason, even when an intermediate | middle base material is long, it can suppress that a drill tool bends and advances a glass body. Therefore, the position of the structure based on the hole in the cross section perpendicular to the longitudinal direction of the optical fiber preform can be made the same at any location along the longitudinal direction of the optical fiber preform. Thus, the change in the structure of the cross section perpendicular to the longitudinal direction is prevented, and a longer optical fiber preform can be manufactured.

  In the method for manufacturing an optical fiber preform, it is preferable that chucking is performed so that the distance from the upper surface of the glass body to the tip of the drill chuck is increased every time the chucking step is performed.

  In the second and subsequent piercing steps, holes are formed in the glass body by the previous piercing step. Therefore, in the second and subsequent drilling steps, the holes formed by the previous drilling step serve as a guide for the drill tool. And since this guide becomes long whenever it repeats a drilling process, a drill tool becomes difficult to bend. Therefore, every time the drilling process and the chucking process are repeated and the chucking process is performed, the drill tool is prevented from bending even if the distance from the upper surface of the glass body to the tip of the drill chuck is increased. Can do. Then, by performing chucking as in the optical fiber preform manufacturing method, the number of times the drilling process and the chucking process are repeated can be reduced. Therefore, the man-hours for manufacturing the optical fiber preform can be reduced.

  Further, it is also preferable that the chucking is performed so that the distance from the upper surface of the glass body to the tip of the drill chuck is constant in each chucking step in the method for manufacturing the optical fiber preform.

  According to such a method for manufacturing an optical fiber preform, it is sufficient to always shift the chucking position by the same length when chucking. Therefore, the chucking control is simplified.

  Further, in the optical fiber preform manufacturing method, the distance from the upper surface of the glass body to the tip of the drill chuck is increased every time the chucking process is performed until the hole has a predetermined length. After the holes have become a predetermined length, the chucking is performed so that the distance from the upper surface of the glass body to the tip of the drill chuck is constant in each chucking step. It is preferable to do.

  As described above, in the second and subsequent drilling processes, the holes formed by the previous drilling process serve as a guide for the drill tool. And since this guide becomes long whenever it repeats a drilling process, a drill tool becomes difficult to bend. However, the difficulty of bending such a drill tool does not change significantly as the hole becomes longer to a predetermined length. Therefore, as in the optical fiber preform manufacturing method, the distance from the upper surface of the glass body to the tip of the drill chuck is increased every time the chucking process is performed until the hole has a predetermined length. By reducing the number of times to repeat the drilling process and the chucking process, and after the hole becomes longer than a predetermined length, by shifting the chucking position by the same length for each chucking process, Control of chucking can be simplified.

  Moreover, in the manufacturing method of the optical fiber preform, it is preferable that the hole formed in the glass body finally penetrates the intermediate preform.

  According to such a method for manufacturing an optical fiber preform, it is possible to easily remove rod-like glass debris remaining in a through hole of a pipe-like drill tool.

  In the method for manufacturing an optical fiber preform, it is preferable that a plurality of the holes are formed around a position to be a core.

  By forming a plurality of holes in this way, a holey fiber preform such as a hole assist fiber or a photonic band gap fiber having holes around the core can be manufactured.

  Further, in the method for manufacturing an optical fiber preform, an insertion step of inserting a glass rod having a refractive index different from the refractive index of the glass body into the hole, and a collapse for integrating the glass body and the glass rod. It is preferable to further include a process.

  In this way, a glass rod having a different refractive index is inserted into each of a plurality of holes, and integrated by collapse, so that a plurality of portions having different refractive indexes from the cladding are formed around the core, etc. An optical fiber preform used for manufacturing the optical fiber can be manufactured.

  Further, in the method for manufacturing an optical fiber preform, the hole is formed at a position to be a core, and an insertion step of inserting a glass rod having a refractive index higher than the refractive index of the glass body into the hole, It is preferable to further comprise a collapsing step for integrating the glass body and the glass rod.

  According to such an optical fiber preform manufacturing method, it is possible to manufacture an optical fiber preform that is prevented from changing the position of the core in a cross section perpendicular to the longitudinal direction.

  Moreover, the manufacturing method of the optical fiber of this invention is equipped with the drawing process which draws the optical fiber preform | base_material manufactured with said optical fiber preform | base_material.

  As described above, according to the above method for manufacturing an optical fiber preform, an optical fiber preform in which the change in the structure of the cross section perpendicular to the longitudinal direction can be prevented can be manufactured. By drawing the optical fiber preform manufactured by the method, an optical fiber with less loss can be manufactured. Furthermore, according to the optical fiber preform manufacturing method described above, a longer optical fiber preform can be appropriately manufactured. Therefore, the optical fiber preform manufactured by such a manufacturing method is drawn. Accordingly, a longer optical fiber can be continuously manufactured.

  As described above, according to the present invention, a change in the structure of the cross section perpendicular to the longitudinal direction can be prevented, and a longer optical fiber preform can be produced. A method of manufacturing an optical fiber using the optical fiber is provided.

It is a figure which shows the mode of the structure in the cross section perpendicular | vertical to the longitudinal direction of the optical fiber which concerns on 1st Embodiment of this invention. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the preform | base_material for optical fibers for manufacturing the optical fiber of FIG. It is a flowchart which shows the process of the manufacturing method of the optical fiber of FIG. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the intermediate | middle base material prepared by the preparatory process shown in FIG. It is a figure which shows the drill tool used for a drilling process. It is a figure which shows a mode when a drill tool is chucked to a drill chuck | zipper in the first chucking process. It is a figure which shows the mode of a punching process. It is a figure which shows a mode when a drill tool is chucked to a drill chuck | zipper in the 2nd chucking process. It is sectional drawing along the longitudinal direction of the intermediate | middle base material which shows the mode of a sealing process. It is a figure which shows the grinding | polishing tool used for a grinding | polishing process. It is sectional drawing along the longitudinal direction of the intermediate | middle base material which shows the mode of a grinding | polishing process. It is a figure which shows the mode of a drawing process. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the optical fiber which concerns on 2nd Embodiment of this invention. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the preform | base_material for optical fibers for manufacturing the optical fiber of FIG. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the intermediate | middle base material of the optical fiber base material shown in FIG. It is a figure which shows the mode of the structure in a cross section perpendicular | vertical to the longitudinal direction of the optical fiber which concerns on 3rd Embodiment of this invention. It is a figure which shows the mode of the structure in the cross section perpendicular | vertical to the longitudinal direction of the preform | base_material for optical fibers for manufacturing the optical fiber of FIG. It is a figure which shows the mode of the structure in the cross section perpendicular | vertical to the longitudinal direction of the intermediate | middle base material of the optical fiber base material shown in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a method for producing an optical fiber preform according to the present invention and a method for producing an optical fiber using the same will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a structure in a cross section perpendicular to the longitudinal direction of an optical fiber according to a first embodiment of the present invention.

  As shown in FIG. 1, an optical fiber 10 according to the present embodiment includes a core 11, a cladding 12 that covers the core 11, a first coating layer 16 that covers the cladding 12, and a second coating that covers the first coating layer 16. It is comprised from the coating layer 17. An optical fiber in which such a cladding is coated with a coating layer is also called an optical fiber. The clad 12 has a lower refractive index than the core 11, and the clad 12 has a plurality of holes 13 surrounding the core 11 around the core 11. Thus, the optical fiber 10 of this embodiment is a holey fiber having a plurality of holes in the cladding.

  Further, the diameter, outer diameter, and distance shown below are exemplifications and are not particularly limited. For example, the diameter of the core 11 is 7 to 10 μm, the outer diameter of the cladding 12 is 125 μm, and the second coating layer 17 The outer diameter is 250 μm, the diameter of the hole 13 is 3 to 8 μm, and the distance from the center of the core 11 to the center of the hole 13 is 8 to 20 μm.

Further, the materials shown below are exemplifications, and are not particularly limited. For example, examples of the material constituting the core 11 include quartz (SiO ₂ ) to which a dopant for increasing the refractive index such as germanium (Ge) is added. Examples of the material constituting the clad 12 include pure quartz to which no dopant is added and quartz to which fluorine (F) for lowering the refractive index is added, and the first coating layer 16 Examples of the material constituting the second coating layer 17 include different types of ultraviolet curable resins.

  Such an optical fiber 10 is particularly called a hole assist fiber among holey fibers, and a gas such as air is sealed in the hole 13, and when the light propagates to the core 11, the hole 13 is highly effective. The refractive index can be obtained, the light confinement effect is enhanced, the light can be prevented from leaking from the core 11, the loss of light propagating through the core 11 can be suppressed, and the holes are formed. Bending loss and the like can be suppressed as compared with an optical fiber in the case of no optical fiber.

  FIG. 2 is a diagram showing a structure in a cross section perpendicular to the longitudinal direction of an optical fiber preform for manufacturing the optical fiber 10 of FIG.

  As shown in FIG. 2, the optical fiber preform 10P has a substantially columnar shape, and a rod-shaped core glass body 11P that becomes the core 11 and a rod-shaped clad glass that covers the core glass body 11P. It is comprised from the body 12P. The cladding glass body 12P has a plurality of through holes 13P surrounding the core glass body 11P around the core glass body 11P. Such an optical fiber preform 10P is drawn and coated as will be described later, whereby the optical fiber 10 shown in FIG. 1 is obtained.

  Next, the optical fiber preform 10P in FIG. 2 and the method for manufacturing the optical fiber 10 in FIG. 1 will be described.

  FIG. 3 is a flowchart showing the steps of the optical fiber preform 10P and the optical fiber 10 manufacturing method. As shown in FIG. 3, the optical fiber preform 10P is manufactured by preparing a preparatory process P1 for preparing an intermediate preform including a core glass body 11P and a clad glass body 12P in which a through hole 13P is not formed, and a drill. A chucking process P2 for chucking a drill tool to the chuck, a drilling process P3 for forming a hole in the clad glass body 12P of the intermediate base material, and a chucking process P2 and a drilling process P3 are alternately repeated a plurality of times. After the penetration, a sealing step P4 for sealing one end side of the through hole and a polishing step P5 for polishing the inner wall surface of the clad glass body 12P in which the through hole is formed are provided. And the manufacturing method of the optical fiber 10 is further provided with the drawing process P6 which draws the preform | base_material for optical fibers manufactured in this way.

<Preparation process P1>
FIG. 4 is a diagram showing a structure in a cross section perpendicular to the longitudinal direction of the intermediate base material prepared in the preparation step P1. As shown in FIG. 4, the intermediate base material 19P is composed of a core glass body 11P shown in FIG. 2 and a clad glass body 12P that does not have the through holes 13P shown in FIG. 2 and covers the core glass body 11P. The

  In preparation of the intermediate | middle base material 19P, the method of forming the core glass body 11P and the clad glass body 12P continuously is mentioned, for example. Such a method is not particularly limited, and examples thereof include a method using a soot process such as an MCVD method, a VAD method, and an OVD method. In this way, an intermediate base material 19P shown in FIG. 4 is obtained.

<Chucking process P2>
Next, the first chucking process P2 is performed. Specifically, a drill tool for making a hole in the clad glass body 12P of the intermediate base material 19P is prepared, and this is chucked on a drill chuck of a drilling device (not shown).

  FIG. 5 is a diagram showing this drill tool. As shown in FIG. 5, the drill tool 50 includes a pipe 52 and a cutting portion 51 provided at the tip of the pipe 52 as main components.

  The pipe 52 has a cylindrical shape and has an outer diameter slightly smaller than the diameter of the hole formed in the intermediate base material 19P. The outer diameter of the pipe 52 is preferably smaller by 0.1 to 0.3 mm than the diameter of the hole formed in the intermediate base material 19P. The cutting part 51 has a cylindrical shape and has an outer diameter similar to the diameter of the hole formed in the intermediate base material 19P. Therefore, the cutting part 51 has an outer diameter larger than the outer diameter of the pipe 52. For example, the outer diameter of the cutting part 51 is larger than the outer diameter of the pipe 52 by 0.1 to 0.3 mm. If the difference between the outer diameter of the pipe 52 and the outer diameter of the cutting portion 51 is 0.3 mm or less, it is preferable because the strength of the pipe 52 can be prevented from being weakened. For example, it is preferable that the pipe 52 can be appropriately prevented from being clogged in the holes formed in the intermediate base material 19P when drilling. Further, the through holes of the pipe 52 and the cutting part 51 are connected to each other, and thus the through hole 53 is formed in the drill tool 50.

  FIG. 6 is a diagram showing a state when the drill tool 50 is chucked on the drill chuck 40 in the first chucking step P2. As shown in FIG. 6, the drill chuck 40 has a through hole through which the drill tool 50 passes, and includes a flange 42 and a shank 41 fixed to the flange 42. The shank 41 is configured so that the size of the through hole on the tip side of the shank 41 can be changed by a tightening mechanism (not shown). Then, on the tip side of the shank 41, the drill tool 50 penetrating the through hole is chucked.

  In the chucking process P2, the distance from the upper surface of the intermediate base material 19P to the front end of the drill chuck 40 (the distance to the front end of the shank 41) when the front end of the drill tool 50 and the clad glass body 12P are in contact with each other. The drill tool 50 is chucked to the drill chuck 40 so as to be smaller than the length of the material 19P. The distance from the upper surface of the intermediate base material 19P to the tip of the drill chuck 40 when the tip of the drill tool 50 and the clad glass body 12P are in contact is defined as the free gripping length. As shown in FIG. 6, in the first chucking step P <b> 2, since no hole is formed in the intermediate base material 19 </ b> P, the free gripping length L <b> 1 is from the tip of the drill tool 50 to the tip of the drill chuck 40. Equal to the distance. Note that the free gripping length L1 in the first chucking step P2 is preferably as short as possible. For example, the free gripping length L1 may be set as the length of the cutting portion 51 of the drill tool 50 so that the pipe 52 is not exposed.

  During the chucking of the drill tool 50 to the drill chuck 40, the tip of the drill tool 50 does not need to be in contact with the clad glass body 12P.

<Punching process P3>
Next, the first drilling process P3 is performed. Specifically, a hole is formed by the drill tool 50 along the longitudinal direction of the clad glass body 12P of the prepared intermediate base material 19P.

  FIG. 7 is a diagram illustrating a state of the punching process P3. As shown in FIG. 7, in this step, the length of the intermediate base material 19P is rotated while the drill tool 50 is rotated by advancing toward the clad glass body 12P while rotating the drill chuck 40 by means not shown. It pushes along a direction and a hole is formed in the clad glass body 12P from the one end side of the intermediate | middle base material 19P. At this time, the liquid is introduced from the pipe 52 side of the through hole 53 of the drill tool 50. An example of this liquid is a water-soluble cutting fluid.

  The liquid thus introduced flows through the through hole 53 and flows out from the tip of the cutting part 51. In a state in which the cutting part 51 has advanced to the middle of the clad glass body 12P, since the holes of the clad glass body 12P do not penetrate, the liquid flowing out from the tip of the cutting part 51 loses its place and the cutting part 51 and the clad The glass body 12P flows backward from the inner wall surface, and is discharged from the side where the drill tool 50 is inserted by the drill tool 50. Accordingly, the temperature of the clad glass body 12P is prevented from excessively rising due to friction between the cutting portion 51 and the clad glass body 12P until the hole formed in the intermediate base material 19P penetrates, Further, glass waste generated by the perforation is discharged from the side where the drill tool 50 is inserted together with the liquid.

  In the first drilling step P3, it is preferable to drill until just before the tip of the drill chuck 40 contacts the end surface of the intermediate base material 19P. Even when drilling in this way, as described above, the free grip length L1 from the upper surface of the intermediate base material 19P to the tip of the drill chuck 40 is shorter than the length of the intermediate base material 19P. And the depth of the hole is substantially equal to the free gripping length L1.

<Chucking process P2>
Next, a second chucking process is performed. FIG. 8 is a diagram showing a state when the drill tool 50 is chucked on the drill chuck 40 in the second chucking step P2. At this time, when performing the second drilling step P3, it is necessary to make the hole deeper than in the first drilling step P3, and therefore the distance from the tip of the drill tool 50 to the tip of the drill chuck 40 is the first chucking. The distance is longer than the distance from the tip of the drill tool 50 to the tip of the drill chuck 40 in the process P2.

  Also in the second chucking process P2, as in the first chucking process P2, the drill tool 50 is chucked on the drill chuck 40 so that the free gripping length is smaller than the length of the intermediate base material 19P. King. However, in this process, since the hole is already formed in the cladding glass body 12P in the first drilling process P3, the free gripping length is such that the tip of the drill tool 50 and the cladding glass body 12P are in contact with each other in this hole. In this state, the distance is from the upper surface of the intermediate base material 19P to the tip of the drill chuck 40. Then, in the second chucking step P2, as shown in FIG. 8, the free gripping length L2 is set to be larger than the free gripping length L1 in the first chucking step P2.

  In this step, the chucking may be performed with the drill tool 50 taken out of the hole or with the drill tool 50 in the hole.

<Punching process P3>
Next, the second punching step P3 is performed in the same manner as the first punching step P3. In the second drilling step P3, it is preferable to drill until the tip of the drill chuck 40 comes into contact with the end surface of the intermediate base material 19P. By drilling in this way, the depth of the hole formed in the intermediate base material 19P is made substantially equal to the sum of the free gripping length L1 and the free gripping length L2.

  Next, the third chucking process P2 is performed in the same manner as the second chucking process P2. At this time, the distance from the tip of the drill tool 50 to the tip of the drill chuck 40 is set to be longer than the distance from the tip of the drill tool 50 to the tip of the drill chuck 40 in the second chucking step P2. In the chucking step P2, the free gripping length is set to be larger than the free gripping length L2 in the second chucking step P2. Then, the third drilling process P3 is performed in the same manner as the second drilling process P3. In this way, the chucking process P2 and the drilling process P3 are alternately repeated a plurality of times. In the chucking process P2, the distance from the tip of the drill tool 50 to the tip of the drill chuck 40 is determined by the chucking process P2. Each time it is repeated, the length becomes longer and the free gripping length becomes smaller than the length of the intermediate base material 19P. In this embodiment, every time the chucking step P2 is performed, chucking is performed so that the free gripping length is increased.

  And in this embodiment, as shown in FIG. 3, the chucking process P2 and the punching process P3 are repeatedly performed until a hole penetrates the clad glass body 12P. In this way, the through hole 13P is formed in the clad glass body 12P. In addition, after penetrating, rod-shaped glass waste is generated in the through hole 53 of the drill tool 50, but this glass waste is removed because it is unnecessary. In this way, the same number of through holes as the through holes 13P of the optical fiber preform 10P are formed in the intermediate preform 19P shown in FIG.

<Sealing process P4>
Next, one end side of the formed through hole is sealed. FIG. 9 is a cross-sectional view along the longitudinal direction of the intermediate base material showing the state of the sealing step P4. As shown in FIG. 9, when sealing, the sealing material 55 is pressure-bonded to one end surface of the intermediate base material 19P in which the through holes 13P are formed so as to close one end side of the through holes 13P.

  This sealing material 55 is comprised from the material which has the expansibility by a liquid. Examples of such a material include a mixture obtained by foam molding of synthetic rubber and a highly water-absorbent resin, examples of the synthetic rubber include chloroprene rubber, and examples of the highly water-absorbing resin include water expansion. Can be mentioned. By being comprised with such a material, the sealing material 55 expand | swells with water. In order to improve the sealing property between the sealing material 55 and the through hole, the volume expansion coefficient of the sealing material 55 is preferably 110% / day or more. Moreover, since the hydraulic pressure of the cutting fluid is applied to the sealing material 55 as described later, the tensile strength of the sealing material 55 is preferably 0.1 MPa or more. Moreover, when inserting a part of sealing material 55 into a through-hole like the after-mentioned, it is preferable that elongation of a sealing material is 100% or more.

  In the sealing step P4, it is preferable that a part of the sealing material 55 is inserted into a part of the through hole 13P. In order to insert a part of the sealing material 55 into a part of the through hole 13P in this way, a part of the sealing material 55 is formed in a convex shape in advance in accordance with the position of the through hole 13P. You should do it. Alternatively, the sealing material 55 may be strongly pressed against the clad glass body 12P to deform the sealing material 55 so that a part of the sealing material 55 is inserted into a part of the through hole 13P.

<Polishing process P5>
Next, the inner wall surface of the clad glass body 12P that forms the through hole 13P is polished and smoothed. FIG. 10 is a diagram showing a polishing tool used in the polishing step P5. Specifically, FIG. 10A is a cross-sectional view along the longitudinal direction of the polishing tool, and FIG. 10B is a view of the polishing tool as viewed from the front end side. As shown in FIG. 10A, the polishing tool 60 includes a pipe 62 and a polishing unit 61 provided at the tip of the pipe 62 as main components.

  The pipe 62 has a cylindrical shape similar to the pipe 52 of the drill tool 50, and has an outer diameter slightly smaller than the diameter of the through hole 13P after the polishing step P5. Further, the polishing unit 61 has a through hole connected to the through hole of the pipe 62. For this reason, the polishing tool 60 is formed with a through hole 66 leading from the pipe 62 to the polishing portion 61.

  A plurality of convex portions 65 and concave portions 64 are formed along the longitudinal direction of the polishing tool 60 on the pipe 62 side on the outer peripheral surface of the polishing portion 61. The outer diameter of the polishing portion 61 with the convex portion 65 as a reference is slightly larger than the diameter of the through hole 13P formed by the drilling step P3. Therefore, when the polishing tool 60 rotates about the axis, the outer diameter of the polishing portion 61 on the pipe 62 side is slightly larger than the diameter of the through hole 13P.

  Furthermore, a taper portion 63 whose outer diameter gradually decreases toward the tip is formed on the outer peripheral surface on the tip side in the polishing portion 61. In the polishing portion 61, the outer diameter of the tapered portion 63 on the tip side is made smaller than the diameter of the through hole 13P formed by the drilling step P3, and the outer diameter of the tapered portion 63 on the opposite side to the tip side. However, it is slightly larger than the diameter of the through hole 13P formed by the drilling step P3.

  FIG. 11 is a cross-sectional view along the longitudinal direction of the intermediate base material showing the state of the polishing step P5. However, in FIG. 11, the polishing tool 60 is not illustrated in a cross-sectional view for easy understanding. As shown in FIG. 11, in the polishing step P5, the through hole 13P formed in the clad glass body 12P is inserted into the through hole 13P from the unsealed side while rotating the polishing tool 60 about the axis. To do. At this time, since the outer diameter at the tip of the polishing part 61 is smaller than the diameter of the through hole 13P as described above, the tip of the polishing part 61 can be appropriately inserted into the through hole 13P. As described above, when the polishing tool 60 rotates along the axis, the outer diameter of the polishing part 61 on the pipe 62 side is slightly larger than the outer diameter of the cutting part 51. The inner wall of the clad glass body 12P is polished by inserting it into the through hole 13P while rotating. Moreover, since it can grind | polish, inserting the front-end | tip of the grinding | polishing part 61 into the through-hole 13P appropriately, when pushing forward the polishing tool 60, the center axis | shaft of the polishing tool 60 has shifted | deviated from the central axis of the through-hole 13P. Thus, it is possible to prevent the inner wall surface of the clad glass body 12P from being polished, and the inner wall surface can be evenly polished.

  Further, when the polishing tool 60 is rotated and inserted into the through hole 13 </ b> P, the liquid is introduced into the through hole 66 of the polishing tool 60. This liquid is absorbed by the sealing material 55 and expands. For example, when the sealing material 55 is expandable by water, water is introduced into the through hole 66 of the polishing tool 60. And the liquid introduce | transduced into the through-hole 66 flows out from the front-end | tip of the grinding | polishing tool 60, and also advances the through-hole 13P of the clad glass body 12P. Then, the liquid traveling through the through hole 13P comes into contact with the sealing material 55, a part of the liquid is absorbed by the sealing material 55, and the sealing material 55 expands so as to bite into the through hole 13P. At this time, as described above, when a part of the sealing material 55 is inserted into the through-hole 13P in the sealing step P4, the sealing material 55 inserted into the through-hole 13P is removed. A part expands in the radial direction of the through hole 13P, and the sealing material 55 can seal the through hole 13P more strongly.

  Thus, since the one end side of the through-hole 13P is sealed with the sealing material 55, the liquid which flows out from the front-end | tip of the grinding | polishing part 61 loses a place, and is between the grinding | polishing part 61 and the inner wall face of the clad glass body 12P. Are discharged from the side of the through hole 13P where the polishing tool 60 is inserted. At this time, since a plurality of concave portions 64 along the longitudinal direction are formed on the outer peripheral surface of the polishing portion 61, the liquid flows through the concave portions 64, so that the liquid flows between the polishing portion 61 and the inner wall surface of the cladding glass body 12 </ b> P. It is easy to reverse flow between. In this way, the temperature of the clad glass body 12P is prevented from excessively rising due to the friction between the polishing portion 61 and the clad glass body 12P, and the glass dust generated by the polishing is discharged together with the liquid from the side where the polishing tool 60 is inserted. Is done. In this manner, the inner wall surface of the clad glass body 12P forming the through hole 13P is polished and smoothed by the polishing tool 60. In this way, by polishing all the through holes 13P, the optical fiber preform 10P shown in FIG. 2 is obtained.

<Drawing process P6>
FIG. 12 is a diagram showing a state of the drawing process P6.

  First, as a preparation stage for performing the drawing process P6, a plurality of glass tubes are connected to the optical fiber preform 10P manufactured by the preparation processes P1 to P5. The plurality of glass tubes are connected to the optical fiber preform 10P such that the through holes of the respective glass tubes and the respective through holes 13P of the optical fiber preform 10P communicate with each other. Next, the inside of the through hole 13P is etched. In this etching process, small irregularities in the through hole 13P are removed, and impurities such as hydroxyl groups are removed from the inner wall of the through hole 13P. The etching solution used for the etching process is introduced into each through hole 13P of the optical fiber preform 10P through the through hole of the glass tube connected to the optical fiber preform 10P.

  Next, the optical fiber preform 10P that has been subjected to the etching process is placed in the spinning furnace 110. In FIG. 10, the glass tube is omitted. And the heating part 111 of the spinning furnace 110 is made to generate heat, and the optical fiber preform 10P is heated. At this time, the lower end of the optical fiber preform 10P is heated to, for example, 2000 ° C. and is in a molten state. Then, the glass melts from the optical fiber preform 10P, and the glass is drawn. The drawn molten glass immediately solidifies as it exits the spinning furnace 110, and the core glass body 11 </ b> P becomes the core 11, the clad glass body 12 </ b> P becomes the clad 12, and the core 11 and the clad 12 are configured. Optical fiber. Thereafter, the optical fiber passes through the cooling device 120 and is cooled to an appropriate temperature. When entering the cooling device 120, the temperature of the optical fiber is, for example, about 1800 ° C., but when exiting the cooling device 120, the temperature of the optical fiber is, for example, 40 ° C. to 50 ° C. In the drawing step P6, a gas such as an inert gas for pressure control is supplied from the plurality of glass tubes previously connected to the optical fiber preform 10P to the respective through holes 13P of the optical fiber preform 10P. Is introduced. In this way, it is possible to prevent variations in the diameter of the hole 13 of the optical fiber after drawing by drawing while adjusting the pressure in each through hole 13P of the optical fiber preform 10P.

  Next, the optical fiber passes through the coating device 131 containing the ultraviolet curable resin to be the first coating layer 16 and is coated with the ultraviolet curable resin. Further, when passing through the ultraviolet irradiation device 132 and being irradiated with ultraviolet rays, the ultraviolet curable resin is cured and the first coating layer 16 is formed. Next, the optical fiber passes through the coating device 133 containing the ultraviolet curable resin to be the second coating layer 17 and is coated with the ultraviolet curable resin. Further, when passing through the ultraviolet irradiation device 134 and being irradiated with ultraviolet rays, the ultraviolet curable resin is cured and the second coating layer 17 is formed, and the optical fiber 10 shown in FIG. 1 is obtained.

  Then, the direction of the optical fiber 10 is changed by the turn pulley 141, and the optical fiber 10 is taken up by the reel 142.

  Thus, the optical fiber 10 which is a holey fiber shown in FIG. 1 is manufactured.

  As described above, according to the manufacturing method of the optical fiber preform 10P according to the present embodiment, the length from the tip of the drill tool 50 to the tip of the drill chuck 40 is gradually increased every time chucking is performed. The holes formed in the clad glass body 12P of the intermediate base material 19P are alternately repeated by repeating the chucking that becomes longer and the perforations that form holes in the clad glass body 12P along the longitudinal direction of the intermediate base material. Can be deep. Then, when the drill tool 50 is chucked, the drill tool 50 is chucked so that the free gripping length is smaller than the length of the intermediate base material 19P. Accordingly, the drill tool 50 is bent as compared with the case where one end of the drill tool having a length equal to or longer than the length of the intermediate base material 19P is capped on the drill chuck and a hole is formed in the glass body serving as a clad at once. This can be suppressed. For this reason, even when the intermediate | middle base material 19P is long, it can suppress that the drill tool 50 bends and advances the clad glass body 12P. Therefore, the position of the through hole 13P in the cross section perpendicular to the longitudinal direction of the optical fiber preform 10P can be made the same at any location along the longitudinal direction of the optical fiber preform 10P. Thus, a change in the structure of the cross section perpendicular to the longitudinal direction is prevented, and a longer optical fiber preform 10P can be manufactured.

  Further, in the second and subsequent piercing steps P3, holes are formed in the clad glass body 12P by the previous piercing step P3. Accordingly, in the second and subsequent drilling steps P3, the holes formed in the previous drilling step P3 serve as a guide for the drill tool 50. And since this guide becomes long whenever it repeats the drilling process P3, the drill tool 50 becomes difficult to bend. Therefore, as described above, every time the chucking step P2 is performed, the drill tool 50 can be prevented from bending even if the free gripping length is increased. And by performing chucking in this way, the frequency | count of repeating the chucking process P2 and the punching process P3 can be reduced. Therefore, the man-hours for manufacturing the optical fiber preform 10P can be reduced.

  Further, in the sealing step P4, one end side of the through hole 13P formed in the clad glass body 22P of the intermediate base material 19P is sealed with a sealing material 55 having a liquid expandability. The stop material 55 absorbs a part of the liquid flowing out from the tip of the polishing tool 60 and expands. At this time, since the liquid is absorbed by the sealing material 55 from the through hole 13P of the clad glass body 12P, the sealing material 55 expands so as to bite into the through hole 13P from one end of the through hole 13P. Thus, even when the end portion of the clad glass body 12P is chipped by the sealing material 55 expanded by the liquid, the sealing is performed strongly. Accordingly, it is possible to effectively prevent a gap from being generated between the sealing material 55 and the clad glass body 12P, and the liquid is appropriately backflowed between the polishing portion 61 of the polishing tool 60 and the inner wall surface of the clad glass body 12P. Can be made. For this reason, glass waste can be discharged out of the through hole 13P together with the liquid, and the inner wall surface of the clad glass body 12P can be prevented from being unnecessarily heated and oxidized by the liquid. In this way, the inner wall surface of the clad glass body 12P can be appropriately polished and smoothed.

  Further, according to the optical fiber manufacturing method of this embodiment using the optical fiber base material 10P manufactured by such an optical fiber base material manufacturing method, the change in the structure of the cross section perpendicular to the longitudinal direction is prevented. Therefore, the optical fiber 10 with less loss can be manufactured. Furthermore, according to the manufacturing method of the optical fiber preform 10P, a longer optical fiber preform can be appropriately manufactured. Therefore, the optical fiber preform 10P manufactured by such a manufacturing method is used. By drawing, a longer optical fiber 10 can be continuously manufactured.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIGS. In addition, about the component which is the same as that of 1st Embodiment, or an equivalent component, the overlapping description is abbreviate | omitted except the case where it attaches | subjects the same referential mark and demonstrates in particular. FIG. 13 is a diagram showing a structure in a cross section perpendicular to the longitudinal direction of an optical fiber according to the second embodiment of the present invention.

  As shown in FIG. 13, the optical fiber 20 of the present embodiment includes a core 21, a cladding 22 that covers the core 21, a first coating layer 26 that covers the cladding 22, and a second coating that covers the first coating layer 26. And a coating layer 27. The clad 22 is provided with a plurality of high refractive index portions 24 surrounding the core 21, and a band gap region 28 is formed by the plurality of high refractive index portions 24. Specifically, some high refractive index portions 24 are arranged in a hexagonal shape so as to surround the core 21. The other high refractive index portions 24 are arranged in a triangular lattice pattern with reference to the high refractive index portions 24 arranged in a hexagonal shape. The region where the high refractive index portions 24 are arranged is a band gap region 28. Thus, the optical fiber 20 of this embodiment is a photonic bandgap fiber. In the present embodiment, the periodic structure of the high refractive index portion 24 in the band gap region 28 is four layers as shown in FIG. 13, but the periodic structure may be other than four layers.

  The diameter and material of the core 21 are not particularly limited, but are the same as the core 11 of the optical fiber 10 of the first embodiment, for example.

The outer diameter of the cladding 22 and the refractive index and material other than the high refractive index portion 24 of the cladding 22 are not particularly limited. For example, the outer diameter, the refractive index, and the material of the cladding 12 of the optical fiber 10 according to the first embodiment. The same is said. Further, the refractive index of each high refractive index portion 24 is higher than that of the portion other than the high refractive index portion 24 of the cladding 22. Examples of such a material of the high refractive index portion 24 include quartz (SiO ₂ ) to which a dopant that increases the refractive index of the core 11 such as germanium (Ge) is added.

  The outer diameter, refractive index, and material of the first coating layer 26 and the second coating layer 27 are not particularly limited. For example, the first coating layer 16 and the second coating layer of the optical fiber 10 of the first embodiment are used. The refractive index and material of the layer 17 are the same.

  In such an optical fiber 20, when light propagates to the core 21, for example, the light confinement effect is enhanced by the band gap region 28, and light can be prevented from leaking from the core 21. Loss can be suppressed.

  FIG. 14 is a view showing a structure in a cross section perpendicular to the longitudinal direction of the optical fiber preform for manufacturing the optical fiber 20 of FIG.

  As shown in FIG. 14, the optical fiber preform 20P has a substantially columnar shape, and a rod-shaped core glass body 21P that becomes the core 21 and a rod-shaped clad glass that covers the core glass body 21P. The body 22P and the clad glass body 22P are provided so as to surround the core glass body 21P, and are composed of a rod-shaped high refractive index glass body 24P that becomes the high refractive index portion 24. Such an optical fiber preform 20P is drawn and coated as will be described later to form the optical fiber 20 shown in FIG.

  Next, a method for manufacturing the optical fiber preform 20P of FIG. 14 and the optical fiber 20 of FIG. 13 will be described.

  First, as in the first embodiment, the preparation step P1 is performed to prepare an intermediate base material in which no through-hole is formed in the clad glass body. Next, similarly to the first embodiment, the chucking process P2 and the punching process P3 are alternately repeated. However, in the punching step P3, a through hole is formed at a location corresponding to the high refractive index glass body 24P shown in FIG. Then, the sealing process P4 and the polishing process P5 are performed in the same manner as in the first embodiment. Thus, an intermediate base material 29P having through holes 23P formed as shown in FIG. 15 is obtained.

<Insertion process>
Next, in this embodiment, a glass rod having a refractive index higher than that of the clad glass body is inserted into each polished through hole 23P. At this time, the diameter of the glass rod is made smaller than the diameter of the through hole 23P so that the glass rod does not rub against the inner wall surface of the clad glass body 22P during insertion. Thus, the intermediate base material 29P is in a state in which the glass rod with a high refractive index is inserted into each through hole 23P.

<Collapse process>
Next, the intermediate base material 29P in which the glass rod is inserted into each through hole 23P is put into a vacuum furnace and collapsed. That is, an unnecessary space of the through hole 23P between the glass rod and the inner wall surface of the clad glass body 22P is crushed to integrate the glass rod and the clad glass body 22P. Thus, the glass rod is made into the high refractive index glass body 24P shown in FIG. 14, and the optical fiber preform 20P shown in FIG. 14 is obtained.

  Next, as in the first embodiment, by performing the drawing step P6, the core glass body 21P becomes the core 21, the clad glass body 22P becomes the clad 22, and the high refractive index glass body 24P becomes the high refractive index portion. 24. Then, the cladding 22 is covered with the first coating layer 26 and the second coating layer 27 in the same manner as the cladding 12 is coated with the first coating layer 16 and the second coating layer 17 in the first embodiment. 13 is obtained.

  According to the optical fiber preform manufacturing method of the present embodiment, the position of the structure based on the through hole 23P in the cross section perpendicular to the longitudinal direction of the optical fiber preform 20P is set in the longitudinal direction of the optical fiber preform 20P. It can be the same everywhere along. That is, the position of the high refractive index glass body 24P can be made the same at any location along the longitudinal direction of the optical fiber preform 20P. Accordingly, in the cross section perpendicular to the longitudinal direction, it is possible to manufacture the optical fiber 20 in which the position of the high refractive index portion 24 is constant at any position along the longitudinal direction.

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIGS. In addition, about the component which is the same as that of 1st Embodiment, or an equivalent component, the overlapping description is abbreviate | omitted except the case where it attaches | subjects the same referential mark and demonstrates in particular. FIG. 16 is a diagram showing a structure in a cross section perpendicular to the longitudinal direction of an optical fiber according to the third embodiment of the present invention.

  As shown in FIG. 16, the optical fiber 30 of this embodiment includes a core 31, a clad 32 that covers the core 31, a first coating layer 36 that coats the clad 32, and a second coating that coats the first coating layer 36. And a coating layer 37.

  The diameter and material of the core 31 are not particularly limited. For example, the core 31 is the same as the core 11 of the optical fiber 10 according to the first embodiment. The outer diameter, the refractive index, and the material of the clad 32 are not particularly limited. For example, the clad 32 is the same as the clad 12 of the optical fiber 10 of the first embodiment. The refractive index and material of the first coating layer 26 and the second coating layer 27 are not particularly limited. For example, the first coating layer 16 and the second coating layer 17 of the optical fiber 10 according to the first embodiment The same is said.

  FIG. 17 is a view showing a structure in a cross section perpendicular to the longitudinal direction of the optical fiber preform for manufacturing the optical fiber 30 of FIG.

  As shown in FIG. 17, the optical fiber preform 30P has a substantially cylindrical shape, and a rod-shaped core glass body 31P that becomes the core 31 and a rod-shaped clad glass that covers the core glass body 31P. It is comprised from the body 32P. Such an optical fiber preform 30P is drawn and coated as will be described later, whereby the optical fiber 20 shown in FIG. 16 is obtained.

  Next, a method for manufacturing the optical fiber preform 20P of FIG. 17 and the optical fiber 20 of FIG. 16 will be described.

  First, the preparation process P1 is performed as in the first embodiment. However, in the preparatory process P1 of this embodiment, it does not have the core glass body 31P, but the cylindrical glass rod which consists only of the clad glass body 32P is produced, and this is made into an intermediate | middle base material.

  Next, similarly to the first embodiment, the chucking process P2 and the punching process P3 are alternately repeated. However, in the perforation process P3, one through hole is formed along the longitudinal direction at the radial center of the intermediate base material obtained in the preparation process P1. Then, the sealing step P4 and the polishing step P5 are performed on the inner wall surface of the clad glass body 32P forming this one through hole in the same manner as in the first embodiment. Thus, an intermediate base material 39P having through holes 33P formed as shown in FIG. 18 is obtained.

<Insertion process>
Next, a glass rod that is higher than the refractive index of the clad glass body 32P and becomes the core glass body 31P is inserted into the polished through-hole 33P. At this time, the diameter of the glass rod is made smaller than the diameter of the through hole 33P so that the glass rod does not rub against the inner wall surface of the clad glass body 32P during insertion. Thus, the intermediate base material 39P is in a state in which the glass rod to be the core glass body 31P is inserted into the through hole 33P.

<Collapse process>
Next, the intermediate base material 39P in which the glass rod is inserted into the through hole 33P is put into a vacuum furnace and collapsed. Thus, an unnecessary space of the through-hole 33P between the glass rod and the inner wall surface of the clad glass body 32P is crushed, and the glass rod and the clad glass body 32P are integrated, and the glass rod becomes the core glass body 31P. . In this way, the optical fiber preform 30P shown in FIG. 17 is obtained.

  Next, the drawing process P6 is performed in the same manner as in the first embodiment. In this way, the optical fiber 30 shown in FIG. 16 is obtained.

  According to the method for manufacturing an optical fiber preform according to the present embodiment, the position of the core glass body 31P is along the longitudinal direction of the optical fiber preform 30P in the cross section perpendicular to the longitudinal direction of the optical fiber preform 30P. It can be the same everywhere. Accordingly, in the cross section perpendicular to the longitudinal direction, it is possible to manufacture the optical fiber 30 in which the position of the core 31 is constant at any position along the longitudinal direction.

  Although the present invention has been described above by taking the first to third embodiments as examples, the present invention is not limited to these.

  Specifically, the optical fiber preform manufacturing method of the present invention is not limited to the above-described embodiment, and any optical fiber preform having a structure for forming holes may be used. It can also be applied to a manufacturing method of a base material.

  For example, the optical fiber 20 as the photonic bandgap fiber of the second embodiment includes the core 21, but the core 21 is not an essential configuration. For example, the optical fiber 20 does not include the core 21 and the bandgap region 28. Thus, the core region may be formed. Alternatively, the band gap region 28 may be disposed so as to sandwich the core 21 by forming a set of two band gap regions in which a plurality of high refractive index portions 24 are gathered without surrounding the core 21.

  In the photonic band gap fiber of the second embodiment, the high refractive index portion 24 can be a low refractive index portion having a lower refractive index than the portion other than the high refractive index portion 24 of the cladding 22.

  Moreover, in the preparation process P1 of 1st, 2nd embodiment, although the intermediate | middle base materials 19P and 29P which have the core glass bodies 11P and 21P were prepared, the intermediate | middle base material which does not have the core glass bodies 11P and 21P was prepared. In the same manner as in the third embodiment, the core glass bodies 11P and 21P and the clad glass bodies 12P and 22P may be integrated.

  Further, in the optical fiber 10 that is the holey fiber of the first embodiment, the size, number, and arrangement of the holes may be changed as long as the optical fiber has a plurality of holes around the core. For example, the hole size and arrangement may be the same as the high refractive index portion 24 of the optical fiber of the second embodiment, and a holey fiber as a photonic bandgap fiber may be used.

  Further, in the embodiment in which glass is inserted into the through-hole formed as in the second embodiment, the number of high refractive index portions 24 and the refractive index may be changed. For example, the present invention can be applied to a polarization maintaining optical fiber (PANDA type fiber) in which two stress applying portions are provided so as to sandwich the core. In this case, the refractive index of the stress applying portion is not particularly limited, but is, for example, −0.1% to 0.1% with respect to the cladding.

  In the first to third embodiments, every time the chucking step P2 is performed, the chucking is performed so that the free gripping length becomes longer. However, the present invention is not limited to such chucking. For example, in each chucking step P2, it is also preferable to perform chucking so that the free gripping length is constant. By performing the chucking process in this way, it is sufficient to always shift the chucking position by the same length when chucking, and the control of chucking is simplified. Further, for example, until the hole formed by the punching process P3 has a predetermined length, the chucking is performed so that the free gripping length is increased every time the chucking process P2 is performed, and the hole has a predetermined length. After that, it is preferable to perform chucking so that the free gripping length becomes constant. As described above, in the second and subsequent drilling steps P3, the holes formed in the previous drilling step P3 serve as a guide for the drill tool. And since this guide becomes long whenever it repeats the drilling process P3, the drill tool 50 becomes difficult to bend. The difficulty of bending such a drill tool 50 does not change greatly when the hole becomes long to a predetermined length. Therefore, until the hole reaches a predetermined length, each time the chucking process P2 is performed, the free gripping length is increased, so that the number of times of repeating the drilling process P3 and the chucking process P2 is reduced, and the hole is predetermined. After the length becomes longer, the chucking control can be simplified by shifting the chucking position by the same length for each chucking step P2.

  Further, the through holes 13P (23P, 33P) are formed by repeating the chucking process P2 and the drilling process P3. However, in the present invention, it is not always necessary to form the through holes, and one end side of the intermediate base material. May be formed, and the formation of the hole may be stopped in the vicinity of the other end. By doing so, the sealing step P4 can be omitted. In addition, when doing in this way, although the rod-shaped glass waste produced in the through-hole 53 of the drill tool 50 is connected to the clad glass body in the vicinity of the edge part of the other side, this glass waste is removed.

  Further, in the polishing portion 61 of the polishing tool 60 used in the polishing step P5, the tapered portion 63 may not be formed, and the concave portion 64 may not be formed.

  Moreover, in the said embodiment, although each optical fiber has a 1st coating layer and a 2nd coating layer, a 1st coating layer is not an essential structure but a 1st coating layer and a 2nd coating layer. At least one of the layer and the second coating layer may be absent.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1
A cylindrical intermediate base material having an outer diameter of 150 mm and a length of 900 mm was prepared. This intermediate base material is provided with a core glass body at the center in the radial direction, and the core glass body is covered with a clad glass body. This clad glass body was made of quartz to which no dopant was added.

  Next, a drill tool was prepared. In this drill tool, a cylindrical grindstone is provided as a cutting portion at the tip of a pipe, the length is 1000 mm, the outer diameter of the cutting portion is 1.5 mm, and the particle size of the cutting portion is # 280. Diamond abrasive grains are attached.

  The drill tool was then chucked on the drill chuck of the drilling device. At this time, the distance from the upper surface of the intermediate base material to the tip of the drill chuck was set to 50 mm while the tip of the drill tool was in contact with the clad glass body. That is, the free grip length was set to 50 mm. Next, while rotating the drill tool, cutting water was passed through the pipe of the drill tool, and a hole was formed in the intermediate base material until just before the tip of the drill chuck contacted the intermediate base material. Thus, a hole of about 50 mm was formed.

  Next, the drill tool was chucked on the drill chuck such that the distance from the tip of the drill tool to the tip of the drill chuck was further increased by 50 mm. Therefore, the distance from the upper surface of the intermediate base material to the tip of the drill chuck is set to 50 mm again with the tip of the drill tool in contact with the clad glass body at the bottom of the hole. That is, the free grip length was set to 50 mm again. Next, the hole formed in the intermediate base material was deepened until just before the tip of the drill chuck contacted the intermediate base material.

  In this way, the hole formed in the intermediate base material is deeply deepened until the distance from the tip of the drill tool to the tip of the drill chuck is increased by 50 mm, and just before the tip of the drill chuck contacts the intermediate base material. This operation was repeated to penetrate the intermediate base material to form a through hole.

  Through holes were formed by the same procedure, and six through holes were formed at positions 25 mm away from the center of the intermediate base material in the radial direction so as to surround the core glass body.

  Next, for each hole, the positional deviation of the holes on both end faces of the intermediate base material was measured, and the average of the positional deviations of the six through holes was obtained. This value is shown in Table 1.

Next, a plurality of intermediate base materials were prepared. Then, for each intermediate base material, the free gripping length becomes the length shown in Table 1, and the drill tool is chucked on the drill chuck of the drilling device. A hole was formed in the intermediate base material until just before contact with the intermediate base material. Next, for each intermediate base material, an operation for increasing the distance from the tip of the drill tool to the tip of the drill chuck by the length shown in Table 1 (operation for setting the free gripping length as shown in Table 1), and drilling Repeat the process of deepening the hole formed in each intermediate base material until the tip of the chuck comes into contact with the intermediate base material, and pass through each intermediate base material. A hole was formed. And the positional deviation of each through-hole in each intermediate | middle base material was measured, and the average value of the positional deviation of a through-hole was calculated | required for every intermediate | middle base material. This value is shown in Table 1.

  As shown in Table 1, it was found that the shorter the free grip length, the smaller the amount of displacement of the through holes at both ends of the intermediate base material.

(Example 2)
Similar to Example 1, except that an intermediate base material similar to that in Example 1 was prepared and the outer diameter of the drill tool was set to 3.0 mm, six through-holes were made for a plurality of intermediate base materials. A hole was formed. At this time, for each intermediate base material, the free gripping length was made the same as in Example 1. Then, in the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained for each intermediate base material. This value is shown in Table 2.

(Example 3)
Similar to Example 1, except that an intermediate base material similar to that in Example 1 was prepared and the outer diameter of the drill tool was set to 4.0 mm, a plurality of intermediate base materials were penetrated by six. A hole was formed. At this time, for each intermediate base material, the free gripping length was made the same as in Example 1. Then, in the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained for each intermediate base material. This value is shown in Table 3.

(Example 4)
Similar to Example 1, except that an intermediate base material similar to that in Example 1 was prepared and the outer diameter of the drill tool was set to 15.0 mm, a plurality of intermediate base materials were penetrated by six. A hole was formed. At this time, for each intermediate base material, the free gripping length was made the same as in Example 1. Then, in the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained for each intermediate base material. This value is shown in Table 4.

(Comparative Example 1)
The same intermediate base material and drill tool as in Example 1 were prepared, and the end of the drill tool was chucked on the drill chuck. Then, six through holes were formed in the same manner as in Example 1 except that the through holes were formed all at once from one end side to the other end side of the intermediate base material. In the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained. This value is shown in Table 5.

(Comparative Example 2)
The same intermediate base material and drill tool as in Example 2 were prepared, and the end of the drill tool was chucked on the drill chuck. Then, six through holes were formed in the same manner as in Example 2 except that the through holes were formed all at once from one end side to the other end side of the intermediate base material. In the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained. This value is shown in Table 5.

(Comparative Example 3)
The same intermediate base material and drill tool as in Example 3 were prepared, and the end of the drill tool was chucked on the drill chuck. Then, six through holes were formed in the same manner as in Example 3 except that the through holes were formed all at once from one end side to the other end side of the intermediate base material. In the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained. This value is shown in Table 5.

(Comparative Example 4)
The same intermediate base material and drill tool as in Example 4 were prepared, and the end of the drill tool was chucked on the drill chuck. Then, six through holes were formed in the same manner as in Example 4 except that the through holes were formed all at once from one end side to the other end side of the intermediate base material. In the same manner as in Example 1, the average value of the positional deviation of the through holes was obtained. This value is shown in Table 5.

  As shown in Table 5, the amount of displacement in Comparative Example 1 was larger than the amount of displacement in Example 1. Similarly, the amount of positional deviation in Comparative Example 2 is larger than the amount of positional deviation in Example 2, and the amount of positional deviation in Comparative Example 3 is larger than the amount of positional deviation in Example 3. The amount of misalignment in Example 4 was larger than the amount of misalignment in Example 4.

  Therefore, according to Examples 1-4 using this invention, it turned out that the change of the structure of a cross section perpendicular | vertical to a longitudinal direction can be prevented. Therefore, according to the present invention, it is considered that a longer optical fiber preform can be manufactured.

  According to the present invention, according to the present invention, a change in the structure of the cross section perpendicular to the longitudinal direction is prevented, and a method for manufacturing an optical fiber preform that can produce a longer optical fiber preform, and An optical fiber manufacturing method using the same is provided.

10 ... Optical fiber (Holy fiber)
11, 21, 31 ... core 12, 22, 32 ... cladding 13 ... hole 16, 26, 36 ... first coating layer 17, 27, 37 ... second coating layer 10P, 20P, 30P ... Optical fiber base material 11P, 21P, 31P ... Core glass body 12P, 22P, 32P ... Clad glass body 13P, 23P, 33P ... Through hole 19P ... Intermediate base material 20 ... Optical fiber (photonic band gap fiber)
24 ... High refractive index portion 28 ... Band gap region 24P ... High refractive index glass body 29P ... Intermediate base material 30 ... Optical fiber 39P ... Intermediate base material 40 ... Drill chuck DESCRIPTION OF SYMBOLS 41 ... Shank 42 ... Flange 50 ... Drill tool 51 ... Cutting part 52 ... Pipe 53 ... Through-hole 55 ... Sealing material 60 ... Polishing tool 61 ... Polishing part 62 ... pipe 63 ... taper part 64 ... concave part 65 ... convex part 66 ... through hole 110 ... spinning furnace 111 ... heating part 120 ... cooling device 131 ..Coating device 132 ... UV irradiation device 133 ... Coating device 134 ... UV irradiation device 141 ... Turn pulley 142 ... Reel L1, L2 ... Free gripping length P1 ... Preparation Process P2 ... Chucking process P3 ... Drilling process P4 ... Sealing process P5 ... Polishing process P6 ... Drawing process

Claims (9)

A preparation step of preparing an intermediate base material having a glass body to be clad;
A chucking process for chucking a pipe-shaped drill tool to the drill chuck;
A drilling step of forming a hole in the glass body from one end side of the intermediate base material by pushing along the longitudinal direction of the intermediate base material while rotating the drill tool by the drill chuck;
With
The chucking step and the drilling step are alternately repeated a plurality of times,
In the chucking step, the distance from the tip of the drill tool to the tip of the drill chuck is increased every time the chucking step is repeated, and the tip of the drill tool and the glass body are in contact with each other A method for producing an optical fiber preform, wherein the distance from the upper surface of the intermediate preform to the tip of the drill chuck is smaller than the length of the intermediate preform.   2. The optical fiber preform manufacturing method according to claim 1, wherein each time the chucking step is performed, chucking is performed such that a distance from an upper surface of the glass body to a tip of the drill chuck is increased. .   2. The method of manufacturing an optical fiber preform according to claim 1, wherein in each chucking step, chucking is performed so that a distance from an upper surface of the glass body to a tip of the drill chuck is constant. . Until the hole reaches a predetermined length, every time the chucking process is performed, the chucking is performed so that the distance from the upper surface of the glass body to the tip of the drill chuck is increased,
The chucking is performed so that the distance from the upper surface of the glass body to the tip of the drill chuck is constant in each chucking step after the hole has reached a predetermined length. Item 2. A method for manufacturing an optical fiber preform according to Item 1.   The hole formed in the said glass body finally penetrates the said intermediate | middle base material, The manufacturing method of the base material for optical fibers of any one of Claims 1-4 characterized by the above-mentioned.   The said hole is formed in multiple numbers around the position used as a core, The manufacturing method of the preform for optical fibers of any one of Claims 1-5 characterized by the above-mentioned. An insertion step of inserting a glass rod having a refractive index different from that of the glass body into the hole;
A collapsing step of integrating the glass body and the glass rod;
The optical fiber preform manufacturing method according to claim 6, further comprising: The hole is formed at a position to be a core,
An insertion step of inserting a glass rod having a refractive index higher than that of the glass body into the hole;
A collapsing step of integrating the glass body and the glass rod;
The method for manufacturing an optical fiber preform according to any one of claims 1 to 5, further comprising:   An optical fiber manufacturing method comprising a drawing step of drawing an optical fiber preform manufactured from the optical fiber preform according to claim 1.

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