JP2011230986A - Manufacturing method for glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can manufacture a glass preform at high yield and high productivity.SOLUTION: In the manufacturing method for glass preform, glass preform is produced through a fixation step, a carbon film formation step, a deposition step, a drawing step, a clarification step, and a solidification step, in that order. In the carbon film formation step, a starter rod and a burner for carbon film formation are relatively reciprocated along the axial direction of a starting rod to form a carbon film at the outer circumference of the starting rod. At this time, the flow rate of a gas around the starter rod is controlled to ≤0.5 m/s.

Description

  The present invention relates to a method for producing a glass preform for an optical fiber.

  An optical fiber is manufactured by heating and softening one end of a glass base material having a substantially cylindrical shape and drawing. Moreover, the glass base material for optical fibers is manufactured by manufacturing methods, such as OVD method and MCVD method. Patent Document 1 discloses a glass base material manufacturing method by the OVD method.

  The glass base material manufacturing method disclosed in Patent Document 1 is intended to manufacture a glass base material for an optical fiber having a low moisture content, and the starting bar is inserted into a seed bar pipe. A glass fine particle deposit is produced by depositing glass fine particles on the outer periphery of the rod, and a starting rod is pulled out from the glass fine particle deposit to obtain a glass fine particle deposit having a central hole extending in the axial direction. Then, the glass fine particle deposit is heated to dry and solidify, and the central hole is closed to produce a transparent glass base material.

Japanese translation of PCT publication No. 2002-543026

  In the glass base material manufacturing method as disclosed in Patent Document 1, a carbon film is formed on the outer periphery of the starting rod prior to the deposition step in which the glass fine particles are deposited on the outer periphery of the starting rod. There is a case. This prevents the inner wall surface of the central hole of the glass particulate deposit from being scratched when the starting rod is pulled out of the glass particulate deposit after the deposition step, thereby producing a glass base material with a high yield. Can be done. However, if it takes more time than necessary to form this carbon film, the glass base material manufacturing time also becomes longer, and the productivity deteriorates.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of producing a glass base material with high yield and high productivity.

  The glass base material manufacturing method according to the present invention includes: (1) a fixing step of making a starting rod by inserting and fixing the starting rod into the seed rod pipe such that the tip of the starting rod protrudes from one end of the seed rod pipe; (2) after the fixing step, the carbon film forming step of relatively reciprocating the starting rod and the carbon film forming burner along the axial direction of the starting bar to form a carbon film on the outer periphery of the starting bar; (3) After the carbon film forming step, the starting rod and the glass particle synthesizing burner are reciprocated relatively along the axial direction of the starting rod, and from the tip of the starting rod to a part of the seed rod pipe. A deposition step of depositing glass particles on the outer periphery of the starting rod to produce a glass particle deposit; (4) a drawing step of drawing the starting rod from the seed rod pipe and the glass particle deposit after the deposition step; and (5) drawing. After the process A transparentization step of heating the body to produce a transparent glass tube, and (6) depressurizing the inside of the transparent glass tube after the transparentization step and heating the transparent glass tube to produce a solid glass base material And a realization step. The glass base material manufacturing method according to the present invention is characterized in that the gas flow velocity around the starting rod is controlled to 0.5 m / s or less in the carbon film forming step.

  The glass base material manufacturing method according to the present invention can manufacture a glass base material with a high yield.

It is a flowchart of the glass base material manufacturing method which concerns on this embodiment. It is a figure explaining fixing process S1 and carbon membrane formation process S2 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining deposition process S3 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining drawing-out process S4 of the glass base material manufacturing method which concerns on this embodiment. It is a figure explaining transparentization process S5 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining solidification process S6 of the glass base material manufacturing method concerning this embodiment. It is the table | surface which put together the gas flow rate and carbon film formation time around the starting rod in the carbon film formation process in an Example and each comparative example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a flowchart of the glass base material manufacturing method according to the present embodiment. As shown in this figure, the glass base material manufacturing method according to this embodiment includes a fixing step S1, a carbon film forming step S2, a deposition step S3, a drawing step S4, a transparentizing step S5, and a solidifying step S6 in order. After that, a glass base material is manufactured. In addition, the glass base material manufactured by this glass base material manufacturing method is an optical fiber base material for manufacturing an optical fiber by drawing, for example, or becomes a core part among the optical fiber base materials. It should be a core base material.

  FIG. 2 is a view for explaining a fixing step S1 and a carbon film forming step S2 of the glass base material manufacturing method according to the present embodiment. FIG. 3 is a view for explaining the deposition step S3 of the glass base material manufacturing method according to the present embodiment. FIG. 4 is a view for explaining a drawing step S4 of the glass base material manufacturing method according to the present embodiment. FIG. 5 is a view for explaining the transparency step S5 of the glass base material manufacturing method according to the present embodiment. Moreover, FIG. 6 is a figure explaining solidification process S6 of the glass base material manufacturing method which concerns on this embodiment.

  In the fixing step S1 (FIGS. 2A and 2B), the starting rod 11 is inserted into the seed rod pipe 12 and fixed so that the tip 11a of the starting rod 11 protrudes from one end 12a of the seed rod pipe 12. Thus, the starting rod 10 is produced. The starting rod 11 is made of a material such as alumina, glass, refractory ceramics, or carbon. The seed rod pipe 12 is made of quartz glass.

  In the carbon film forming step S2 (FIG. 2C) after the fixing step S1, the outer periphery of the portion of the starting rod 11 protruding from the one end 12a of the seed rod pipe 12 in the starting rod 10 is a city gas burner or an acetylene burner. The carbon film 11b is formed by the flame from the carbon film forming burner 20 using the above. Even during the formation of the carbon film, the starting rod 10 rotates about the central axis of the starting bar 11, and the carbon film forming burner 20 reciprocates relative to the starting rod 10 along the axial direction of the starting bar 11. repeat. Further, the gas flow velocity around the starting rod 10 is controlled to 0.5 m / s or less.

  In the deposition step S3 (FIG. 3) after the carbon film forming step S2, the starting rod 10 in which the starting rod 11 is inserted and fixed in the seed rod pipe 12 is rotated about the central axis of the starting rod 11. Further, the glass fine particle synthesis burner 21 that is arranged on the side of the starting rod 10 and forms an oxyhydrogen flame repeats reciprocating movement relative to the starting rod 10 along the axial direction of the starting rod 11. Then, by the OVD method, glass fine particles are deposited on the outer periphery of the starting rod 10 from the tip portion 11a of the starting rod 11 to a part of the seed rod pipe 12, whereby the glass fine particle deposit 13 is produced.

  In the deposition step S3, the feed material flow rate in the glass fine particle synthesis burner 21 is adjusted for each traverse. Thereby, the glass fine particles deposited on the outer periphery of the starting rod 11 have a predetermined composition distribution in the radial direction (that is, a refractive index distribution in the radial direction in the subsequent glass preform or optical fiber).

  In the drawing step S4 (FIG. 4) after the deposition step S3, the starting rod 11 is drawn from the seed rod pipe 12 and the glass particulate deposit 13. At this time, the seed rod pipe 12 and the glass fine particle deposit 13 remain fixed to each other. In addition, in order to form a carbon film on the outer periphery of the portion of the starting rod 11 protruding from the one end 12a of the seed rod pipe 12 in the carbon coating forming step S2, glass particulates are deposited when the starting rod 11 is pulled out in the drawing step S4. The inner wall surface of the center hole of the body 13 is prevented from being scratched.

In the clearing step S5 (FIG. 5) after the drawing step S4, the glass fine particle deposit 13 is placed inside the heating furnace 22 into which He gas and Cl ₂ gas are introduced, together with the integrated seed rod pipe 12. It is put in and heated by the heater 23. Thereby, the transparent glass tube material 14 is produced.

In the solidification step S6 (FIG. 6) after the transparentization step S5, the transparent glass tube 14 is placed in a heating furnace and rotated, and SF ₆ is introduced into the center hole and heated by the heater 24. The inner wall surface of the center hole is vapor-phase etched (FIG. 1A). Next, the transparent glass tube material 14 is decompressed and heated by the heater 24 to be solidified (FIG. 5B), whereby a solid glass base material is produced.

  The transparent glass preform manufactured in this way is further formed into a clad layer on the outside and subjected to a transparent treatment, and then preformed, and then the tip is heated and softened to draw an optical fiber. Is manufactured.

  In the present embodiment, the gas flow velocity around the starting rod 10 is controlled to 0.5 m / s or less in the carbon film forming step S2. Thereby, the formation of the carbon film is accelerated, the time required for forming the carbon film is shortened, and the productivity of the glass base material is improved. On the other hand, when the gas flow rate around the starting rod 10 exceeds 0.5 m / s in the carbon film forming step S2, the flame coming out from the carbon film forming burner 20 is disturbed, and the carbon film forming speed is reduced.

The chemical reaction during the formation of the carbon film is a combustion reaction of methane gas, which is the main component of city gas. If oxygen is insufficient in this reaction, incomplete combustion occurs and carbon is released from CH ₄ and released. Carbon is produced. A carbon film is formed by the free carbon adhering around the starting rod 11.

  Next, examples of the glass base material manufacturing method according to the present embodiment will be described. In the present embodiment, a glass base material for manufacturing a graded index optical fiber by drawing is manufactured.

  In the deposition step S3, glass particles are deposited using an OVD apparatus. The starting rod 11 is made of alumina having an outer diameter of 9 to 10 mm and a length of 1200 mm. The seed rod pipe 12 is made of quartz glass having a length of 600 mm, an outer diameter of 20 to 40 mm, and an inner diameter of 9.8 to 21 mm.

  In the carbon film forming step S2, the starting rod 10 is rotated around the axis at a rotation speed of 15 rpm, and a flame is formed by the carbon film forming burner 20 supplied with city gas (flow rate of 1.5 L / min). The starting rod 10 is reciprocated with respect to the burner 20 at a speed of 1000 mm / min, and a carbon film is formed on the outer periphery of the starting rod 11 protruding from the seed rod pipe 12.

The glass raw material gases introduced into the glass fine particle synthesis burner 21 that forms an oxyhydrogen flame in the deposition step S3 are SiCl ₄ (input amount 1 to 3 SLM / piece) and GeCl ₄ (input amount 0.0 to 0.3 SLM). It is. The relative moving speed of the starting rod 10 with respect to the glass fine particle synthesizing burner 21 is 3 to 1500 mm / min, and the rotating speed of the starting rod 10 is 60 rpm.

After such a deposition step S3, a solidification step S6 is performed through a drawing step S4 and a transparency step S5. In the solidification step S6, the transparent glass tube 14 is set in a heating furnace, rotated at 30 rpm, and moved to the longitudinal direction of the transparent glass tube 14 at a speed of 5 to 20 mm / min. Heated. The heating means in the solidification step S5 may use an oxyhydrogen burner lathe instead of a heating furnace that uses a carbon heater, an electromagnetic induction coil heating element, or the like as a heat source. At this time, 50 to 100 sccm of SF ₆ gas is flowed into the center hole of the transparent glass tube material 14, and the inner wall surface of the center hole of the transparent glass tube material 14 is vapor-phase etched.

  Next, the transparent glass tube material 14 is decompressed to 0.1 to 10 kPa in the center hole, and is solidified at the same temperature as during the etching to produce a glass base material.

  The glass base material manufactured in this way is stretched to a desired diameter, and jacket glass is synthesized on the outer periphery thereof by the OVD method to manufacture a glass base material for an optical fiber. This glass preform for optical fiber is drawn to produce a graded index type multimode fiber.

  FIG. 7 is a table summarizing the gas flow rate around the starting rod and the carbon film forming time in the carbon film forming step in each of the example and the comparative example. Here, the gas flow velocity X (mm / s) around the starting rod in the carbon film forming step is set to each value, and the carbon film forming time A (H) on the starting rod 11 protruding from the seed rod pipe 12 is compared. Be evaluated. The carbon film formation time A is a time until the carbon deposition weight reaches a predetermined weight. As shown in this chart, when the gas flow velocity X around the starting rod is 0.5 m / s or less, the carbon film formation time A is 1 hour or less, and the productivity of the glass base material is improved. If it exceeds .5 m / s, the carbon film formation time A increases rapidly, and the productivity of the glass base material is extremely deteriorated. In addition, in the comparative example 3 in a figure, since the city gas flame misfired, the carbon film was not formed.

  DESCRIPTION OF SYMBOLS 10 ... Departure rod, 11 ... Departure rod, 12 ... Seed rod pipe, 13 ... Glass particulate deposit, 14 ... Transparent glass tube, 20 ... Carbon film formation burner, 21 ... Glass particulate synthesis burner, 22 ... Heating furnace, 23, 24 ... heaters.

Claims (1)

A fixing step of making the starting rod by inserting and fixing the starting rod into the seed rod pipe such that the tip of the starting rod protrudes from one end of the seed rod pipe;
After the fixing step, the starting rod and the carbon film forming burner are relatively reciprocated along the axial direction of the starting bar, and a carbon film forming step of forming a carbon film on the outer periphery of the starting bar;
After the carbon film forming step, the starting rod and the glass fine particle synthesizing burner are relatively reciprocated along the axial direction of the starting rod, and from the tip of the starting rod to a part of the seed rod pipe A deposition step of depositing glass particles on the outer periphery of the starting rod to produce a glass particle deposit;
A drawing step of drawing the starting rod from the seed rod pipe and the glass particulate deposit after the deposition step;
A transparentization step of heating the glass particulate deposit after the drawing step to produce a transparent glass tube,
A solidification step of reducing the inside of the transparent glass tube material after the transparentizing step and heating the transparent glass tube material to produce a solid glass base material,
With
In the carbon film forming step, the gas flow velocity around the starting rod is controlled to 0.5 m / s or less.
The glass base material manufacturing method characterized by the above-mentioned.

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