JP2011230988A - Manufacturing method for glass preform - Google Patents

Abstract

The present invention provides a method capable of producing a glass base material with a high yield.
A glass base material manufacturing method according to the present invention manufactures a glass base material through a fixing process, a deposition process, a drawing process, a transparentizing process, and a solidifying process in order. In the deposition step, a glass fine particle deposit is formed so that the concentration of additives other than quartz glass is 8 wt% or less in the region from the inner wall surface of the hollow hole of the transparent glass tube 14 after the transparentization step to 1.7 mm in the radial direction. 13 is produced. In the solidification step, the temperature of the transparent glass tube 14 is maintained at 500 ° C. or higher during the period from the end of the vapor phase etching to the production of the solid glass base material.
[Selection] Figure 6

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 disclosed in Patent Document 1, the glass base material may be broken in a state of becoming a transparent glass tube material, and the yield of glass base material manufacturing may deteriorate.

  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 a high yield.

  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 starting rod and the glass fine particle synthesizing burner are relatively reciprocated along the axial direction of the starting rod to start from the tip of the starting rod to a part of the seed rod pipe. A deposition process in which glass particulates mainly composed of quartz glass are deposited on the outer periphery of the rod to produce a glass particulate deposit, and (3) a drawing process in which the starting rod is pulled out from the seed rod pipe and the glass particulate deposit after the deposition process. And (4) a transparentization step in which the glass particulate deposit is heated after the drawing step to produce a transparent glass tube, and (5) after the clearing step, the inner wall surface of the central hole of the transparent glass tube is vapor-phase etched. Reduce the inside of the transparent glass tube And a collapsing step of preparing a solid glass preform by heating the transparent glass tubing while.

  And the glass base material manufacturing method which concerns on this invention WHEREIN: The density | concentration of additives other than quartz glass in the area | region to 1.7 mm in radial direction from the inner wall face of the hollow hole of the transparent glass tube material after a transparentization process in a deposition process. The glass fine particle deposit is prepared so that the amount becomes 8 wt% or less, and in the solidification step, the temperature of the transparent glass tube is set to 500 in the period from the end of the vapor phase etching to the production of the solid glass base material. It is characterized by being kept at a temperature of ℃ or higher.

  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 of the glass base material manufacturing method which concerns on this embodiment. It is a figure explaining deposition process S2 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining drawing-out process S3 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining transparentization process S4 of the glass base material manufacturing method concerning this embodiment. It is a figure explaining solidification process S5 of the glass base material manufacturing method which concerns on this embodiment. The maximum concentration of the additive in the region from the inner wall surface of the transparent glass tube material to 1.7 mm in each of the examples and comparative examples, the minimum temperature of the transparent glass tube material from vapor phase etching to solidification, and glass It is the table | surface which put together the favorable manufacturing rate of the base material.

  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 the present embodiment passes through a fixing step S1, a deposition step S2, a drawing step S3, a clarification step S4 and a solidification step S5 in order, To manufacture. 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 the fixing step S1 of the glass base material manufacturing method according to the present embodiment. FIG. 3 is a view for explaining the deposition step S2 of the glass base material manufacturing method according to the present embodiment. FIG. 4 is a view for explaining the drawing step S3 of the glass base material manufacturing method according to the present embodiment. FIG. 5 is a diagram for explaining the transparency step S4 of the glass base material manufacturing method according to the present embodiment. Moreover, FIG. 6 is a figure explaining solidification process S5 of the glass base material manufacturing method which concerns on this embodiment.

  In the fixing step S1 (FIG. 2), the starting rod 11 is inserted into the seed rod pipe 12 and fixed so that the tip end portion 11a of the starting rod 11 protrudes from the one end 12a of the seed rod pipe 12, whereby the starting rod 10 Is produced (see FIGS. 1A and 1B). 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 starting rod 10, a carbon film 11 b is preferably formed on the outer periphery of the portion of the starting rod 11 protruding from the one end 12 a of the seed rod pipe 12 by a flame from the burner 20 using a city gas burner or an acetylene burner. ((C) in the figure). Even during the formation of the carbon film, the starting rod 10 rotates about the central axis of the starting rod 11, and the burner 20 repeatedly reciprocates relative to the starting rod 10 along the axial direction of the starting rod 11.

  In the deposition step S2 (FIG. 3) after the fixing step S1, 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 mainly composed of quartz glass 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 a glass particulate deposit is obtained. 13 is produced.

  In the deposition step S2, 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 this deposition step S2, the concentration of additives other than quartz glass is 8 wt% or less in the region from the inner wall surface of the hollow hole of the transparent glass tube 14 after the subsequent transparentization step S4 to 1.7 mm in the radial direction. As described above, the glass fine particle deposit 13 is produced. Specifically, the raw material flow rate introduced as a main additive is adjusted. The concentration of the additive added to the transparent glass tube material 14 is about 20 wt% at maximum.

  In the extraction step S3 (FIG. 4) after the deposition step S2, the starting rod 11 is extracted 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 after the fixing step S1, when the starting rod 11 is pulled out in this drawing step S3, a glass particulate deposit It is possible to prevent the inner wall surface of the 13 central hole from being scratched.

In the clearing step S4 (FIG. 5) after the drawing step S3, 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 S5 (FIG. 6) after the transparentization step S4, 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. In the solidification step S5, the temperature of the transparent glass tube material 14 is maintained at 500 ° C. or higher during the period from the completion of the vapor phase etching to the production of the solid glass base material.

  FIG. 3C shows an example of the additive concentration distribution in the radial direction in the transparent glass tube material 14 before vapor phase etching. FIG. 4D shows an example of the additive concentration distribution in the radial direction in the transparent glass tube material 14 after vapor phase etching. Moreover, the figure (e) shows the example of the additive concentration distribution of the radial direction in the glass base material after solidification.

  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, in the deposition step S2, the concentration of additives other than quartz glass is 8 wt% in the region from the inner wall surface of the hollow hole of the transparent glass tube material 14 after the subsequent transparentization step S4 to 1.7 mm in the radial direction. The glass fine particle deposit 13 is produced so as to be as follows. Further, in the solidification step S5, the inner wall surface of the central hole of the transparent glass tube material 14 is vapor-phase etched, and the transparent glass is produced in a period from the completion of the vapor-phase etching to the production of the solid glass base material. The temperature of the tube material 14 is maintained at 500 ° C. or higher. By doing in this way, when manufacturing the transparent glass preform | base_material by obstruct | occluding the center hole of a transparent glass tube material, it is prevented that a transparent glass tube material cracks, and a glass preform | base_material can be manufactured with a high yield.

  If the concentration of the additive other than the quartz glass component (mainly Ge) exceeds 8 wt% in the region from the inner wall surface of the central hole of the transparent glass tube to 1.7 mm in the radial direction, the transparent glass tube The transparent glass tube material is easily broken after production. Moreover, if the inner wall surface of the central hole of the transparent glass tube material is etched and the region where the additive is added in a high concentration is exposed, and the temperature of the transparent glass tube material is lowered below 500 degrees, the transparent glass tube material is easily broken. Become. As a mechanism for generating cracks, in the region where the additive is added at a high concentration, the surface state is rough, and thus scratches are likely to occur. Furthermore, from the difference in additive concentration between the core layer and the clad layer (difference in thermal expansion coefficient), It is considered that cracks progress from the scratch when the temperature is lowered due to the difference in thermal expansion.

  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 S2, an OVD apparatus is used to deposit glass particles. 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.

The glass raw material gases introduced into the glass fine particle synthesis burner 21 forming an oxyhydrogen flame in the deposition step S2 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 S2, a solidification step S5 is performed through a drawing step S3 and a transparency step S4. In the solidification step S5, 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 caused to flow into the center hole of the transparent glass tube 14, and an area of 1.5 to 2.5 mm in the radial direction from the inner wall surface of the center hole of the transparent glass tube 14 is aired. 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 shows the maximum concentration of additives in the region from the inner wall surface of the transparent glass tube material to 1.7 mm in each of the example and the comparative example, the minimum temperature of the transparent glass tube material from vapor phase etching to solidification. It is the table | surface which put together the favorable manufacturing rate of the glass base material. Here, the maximum concentration X (wt%) of the additive in the region from the inner wall surface of the transparent glass tube material to 1.7 mm, and the minimum temperature Z of the transparent glass tube material from vapor phase etching to solidification ( C)) each value is taken as a value, and the good production rate A (%) of the glass base material is comparatively evaluated. As shown in this chart, the maximum concentration X of the additive in the region from the inner wall surface of the transparent glass tube material to 1.7 mm is 8 wt% or less, and the transparent glass tube material from vapor phase etching to solidification If the minimum temperature Z of the glass base material is 500 ° C. or higher, the good manufacturing rate A of the glass base material is 95% or higher, and the productivity of the glass base material is improved.

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

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 glass fine particle synthesizing burner are reciprocated relatively along the axial direction of the starting rod, and extend from the tip of the starting rod to a part of the seed rod pipe. A deposition step of depositing glass particles mainly composed of quartz glass 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,
After the transparentizing step, the inner wall surface of the central hole of the transparent glass tube is vapor-phase etched, and then the inside of the transparent glass tube is decompressed and the transparent glass tube is heated to produce a solid glass base material A solidification process,
With
In the deposition step, the glass fine particles are adjusted so that the concentration of additives other than quartz glass is 8 wt% or less in the region from the inner wall surface of the hollow hole of the transparent glass tube material after the transparentizing step to 1.7 mm in the radial direction. Make a deposit,
In the solidification step, the temperature of the transparent glass tube material is maintained at 500 ° C. or higher in a period from the end of vapor phase etching to the production of a solid glass base material.
The glass base material manufacturing method characterized by the above-mentioned.

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