JP2011230985A - Manufacturing method for glass preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for high-yield manufacture of glass preform.SOLUTION: In the manufacturing method for glass preform, glass preform is produced through a fixation step, a deposition step, a drawing step, a clarification step, and a solidification step, in that order. In the deposition step, the mean density of fine glass particles deposited around a starter rod 11 is controlled to 0.1 to 0.3 g/cc, and also the mean density of fine glass particles deposited around a seed bar pipe 12 is made equal to or greater than 0.4 g/cc from the beginning of glass particle deposition until the 10th layer. Further, in the deposition step S2, variation in the longitudinal direction of the mean density of the fine glass particles deposited within a range of ±50 mm in the longitudinal direction from the boundary position of the starter rod 11 and the seed bar pipe 12, is preferably 0.01 g/cc/mm or less from the beginning of glass particle deposition until the 10th layer.

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 starting rod and the glass along the axial direction of the starting rod during the deposition process in which glass particulates are deposited on the outer periphery of the starting rod to produce a glass particulate deposit. A fine particle synthesizing burner is relatively reciprocated to deposit glass fine particles on the outer periphery of the starting rod from the tip of the starting rod to a part of the seed rod pipe to produce a glass fine particle deposit. When producing a glass fine particle deposit by such a deposition process, the glass fine particle deposit may be broken and the yield of manufacturing the glass base material 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 step of depositing glass particulates on the outer periphery of the rod to produce a glass particulate deposit; (3) a withdrawal step of pulling the starting rod from the seed rod pipe and the glass particulate deposit after the deposition step; and (4) a withdrawal step. And a transparent step of heating the glass particulate deposit to produce a transparent glass tube, and (5) reducing the pressure inside the transparent glass tube and heating the transparent glass tube after the transparent step A solidification process for producing the material, Obtain.

  In the glass base material manufacturing method according to the present invention, in the deposition step, the average density of the glass particles deposited around the starting bar is 0.1 g / cc or more from the start of the deposition of the glass particles to the 10th layer. The average density of the fine glass particles deposited around the seed rod pipe is 0.4 g / cc or more.

  Further, in the glass base material manufacturing method according to the present invention, in the deposition step, from the start of deposition of the glass fine particles to the 10th layer, within the range of ± 50 mm in the longitudinal direction with respect to the boundary position between the starting rod and the seed rod pipe. It is preferable that the amount of longitudinal change in the average density of the fine glass particles to be deposited is 0.01 g / cc / mm or less.

  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. It is the table | surface which put together the density and favorable manufacturing rate of the glass fine particle in each of an Example and a 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 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 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 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 the deposition step S2, from the start of deposition of the glass particulates to the 10th layer, the average density of the glass particulates deposited around the starting rod 11 is 0.1 g / cc or more and 0.3 g / cc or less, and the seed rod pipe The average density of the glass particles deposited around 12 is set to 0.4 g / cc or more. In addition, in the deposition step S2, from the start of deposition of the glass particulates to the 10th layer, the average density of the glass particulates deposited within a range of ± 50 mm in the longitudinal direction with respect to the boundary position between the starting rod 11 and the seed rod pipe 12. It is preferable that the amount of change in the longitudinal direction is 0.01 g / cc / mm or less. Although depending on the traverse speed, the thickness is about 0.03 to 0.6 mm per layer, so 10 layers correspond to a thickness of about 0.3 to 6 mm. Usually, a total of about 100 to 2000 layers of glass particles are deposited.

  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.

  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, from the start of deposition of the glass fine particles to the 10th layer, the average density of the glass fine particles deposited around the starting rod 11 is 0.1 g / cc or more and 0.3 g / cc or less. The average density of the fine glass particles deposited around the seed rod pipe 12 is 0.4 g / cc or more. Thereby, the crack of the glass particulate deposit is prevented, and the inner surface in the central hole of the transparent glass tube is smoothed.

  By controlling the average density of the glass fine particles deposited around the starting rod 11 from the beginning of the deposition of the glass fine particles to the 10th layer to a low density of 0.1 to 0.3 g / cc, the starting rod in the drawing step S3 The inner surface of the center hole of the glass fine particle deposit after 11 is pulled out is smoothed. As a result, the inner surface of the center hole of the transparent glass tube material after the transparentizing step S4 is also smoothed. In addition, when it becomes less than 0.1 g / cc, the strength of the glass fine particle deposit cannot be maintained sufficiently. Further, by controlling the average density of the glass particles deposited around the seed rod pipe 12 made of quartz glass from the start of the deposition of the glass particles to the 10th layer to 0.4 g / cc or more, the total weight of the glass particles The adhesion force and strength between the seed rod pipe 12 supporting the surroundings and the surrounding glass particulate deposits are increased, and the glass particulates deposited on the lower portion can be supported, and cracking is prevented.

  On the other hand, if the density of the glass particulates changes rapidly in the vicinity of the boundary between the starting rod 11 and the seed rod pipe 12, when the temperature near the boundary decreases (that is, away from the flame), the glass particulates Since there is a difference in the amount of expansion, peeling (breaking) of the glass particles tends to occur near this boundary. Therefore, from the start of the deposition of the glass fine particles to the 10th layer, by managing the glass fine particles near the boundary between the starting rod 11 and the seed rod pipe 12 to a gentle density distribution (0.01 g / cc / mm or less), Peeling (cracking) during glass fine particle deposition as described above can be prevented.

  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. The density of the glass particles to be deposited can be adjusted by increasing the hydrogen gas flow rate, decreasing the raw material gas flow rate, decreasing the relative movement speed of the glass particle synthesis burner 21 and the starting rod 10, or the like. When the density is lowered, the reverse adjustment described above may be performed.

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 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 density of fine glass particles and the good production rate in each of the examples and comparative examples. Here, X (g / cc) is the average density of the glass particles deposited around the starting rod 11 from the beginning of the deposition of the glass particles to the 10th layer, and the seed rod pipe from the beginning of the deposition of the glass particles to the 10th layer. The average density of the glass particles deposited around 12 is Y (g / cc), and the longitudinal direction relative to the boundary position between the starting rod 11 and the seed rod pipe 12 from the beginning of the deposition of the glass particles to the 10th layer. The longitudinal change amount of the average density of the glass fine particles deposited within a range of ± 50 mm is set to Z (g / cc / mm), and each value is set so that no crack occurs in the glass fine particle deposit or the transparent glass tube. A good production rate A (%) which is a probability is compared and evaluated.

  As shown in this chart, the average density X of the glass particles deposited around the starting rod 11 from the start of the deposition of the glass particles to the 10th layer is 0.1 g / cc or more and 0.3 g / cc or less, If the average density Y of the glass particles deposited around the seed rod pipe 12 from the start of the deposition of the glass particles to the 10th layer is 0.4 g / cc or more, the good production rate Z is 87% or more and high. A glass base material can be manufactured with a yield. Further, the longitudinal change amount Z of the average density of the glass fine particles deposited within the range of ± 50 mm in the longitudinal direction with respect to the boundary position between the starting rod 11 and the seed rod pipe 12 from the beginning of the deposition of the glass fine particles to the tenth layer is If it is 0.01 g / cc / mm or less, the good production rate Z is 97% or more, and a glass base material can be produced with an extremely high yield. The “clear glass tube crack” in the chart indicates that the density X of the glass particles deposited around the starting bar 11 is too high, and the inner surface of the hole of the glass particle deposit is scratched when the starting bar is pulled out. Although it did not break during the deposition of the glass fine particles, it means that it broke after clearing.

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 (2)

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 particulates on the outer periphery of the starting rod to produce a glass particulate 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 deposition step, from the start of deposition of the glass fine particles to the tenth layer, the average density of the glass fine particles deposited around the starting rod is 0.1 g / cc or more and 0.3 g / cc or less, and the seed rod The average density of glass particles deposited around the pipe is 0.4 g / cc or more,
The glass base material manufacturing method characterized by the above-mentioned. In the deposition step, from the beginning of the deposition of the glass fine particles to the tenth layer, the average length of the glass fine particles deposited within a range of ± 50 mm in the longitudinal direction with respect to the boundary position between the starting rod and the seed rod pipe. The glass base material manufacturing method according to claim 1, wherein the amount of change is 0.01 g / cc / mm or less.

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