JPS60200835A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To reduce a transitional part and a transitional time in the early stage when a porous glass base material for an optical fiber is manufactured by a VAD method, by heating a starting member with a heat source other than a burner for synthesizing fine glass particles before depositing fine glass particles on the starting member. CONSTITUTION:When a porous glass base material for an optical fiber is produced by a VAD method, the surface of a starting member 2 is heated to about 1,200 deg.C with an oxyhydrogen burner 6 which is not used as a burner 1 for synthesizing fine glass particles. Starting materials for glass are then fed to the burner 1 to start the deposition of fine glass particles 4, and at the same time, the oxyhydrogen burner 6 is moved backward. The starting member 2 is required to have >=20mm. outside diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a glass preform for optical fibers, and particularly to a method for forming a porous glass preform for optical fibers by a VAD method.

(Technical Background) The VAD method is known as a method for manufacturing optical fiber base materials that is highly mass-producible. Figure 1 shows the basic configuration of the VAD method. In the burner 1 for glass particle synthesis, 5iC14,
A glass raw material such as GeCl4 and a combustion gas such as H2,0□ are supplied.

The glass raw material becomes fine glass particles through a flame hydrolysis reaction in the flame, and is deposited near the tip of the rotating starting material 2. By pulling the starting material upward using the rotary pulling device 3 according to the amount of deposited glass particles, the deposited body of glass particles grows in the direction of the rotation axis, forming a porous glass base material for optical fiber. It becomes 4. In addition, 5 is a reaction container.

Conventionally, the shape of the starting material 2 is often a disk-like shape as schematically shown in FIG. 2(a) or a rod-like shape as shown in FIG. 2(b).

The former has the advantage that the surface area on which the glass particles are deposited is wide at the start of glass particle deposition, and the adhesion efficiency of the glass particles is good, but it is difficult to process and mold, and is not suitable for practical use. On the other hand, the latter has the disadvantage that the initial glass particle adhesion efficiency is low because the area of the glass particle deposition surface is small, but processing and forming is extremely simple and it is widely used in practical use.

However, to improve optical fiber productivity,
As the size of the porous glass body increases and the growth rate of the porous glass body increases, the following requirements arise when using a rod-shaped starting material as shown in FIG. 2(b). come.

That is, there is a transitional period from when the glass particles begin to accumulate on the starting material 2 until the glass particle deposit reaches a predetermined diameter and becomes a uniform portion that can be used as the porous glass base material 4 (the diagonal line in FIG. 6). ), and the transition time required to form this transition portion increases as the diameter of the porous matrix increases. On the other hand, if the growth rate of the porous glass body is fast (as the growth rate of the porous glass body becomes faster), the proportion of the transient time in the total time required to form the porous glass body increases relatively. From the viewpoint of improving productivity, it is necessary to reduce the number of targets.

By the way, in order to meet the above requirements, (1) improve the efficiency of glass particle adhesion to the starting material and shorten the transition time, (2) change the shape of the starting material to a porous glass uniform portion, that is, a third Possible countermeasures include making the transitional part smaller and shortening the transition time to approximate the tip shape of 4 in the figure. To this end, as shown in Figure 4, by increasing the dimensions (body fR) of the starting material, the area of the initial glass particle deposition surface is increased and the adhesion efficiency of glass particles is improved, and the transitional portion is It is desirable to reduce the volume at the same time.

However, when the size of the starting material is increased, the temperature of the surface of the starting material, which has been heated by the flame of the burner for glass particle synthesis, decreases.

When attaching glass particles to the starting material, the surface of the starting material should be sufficiently heated and the surface temperature of the starting material should be kept high enough to reduce the viscosity of the attached glass particles and allow the starting material and glass particles to be sufficiently bonded. However, as the size of the starting material increases, the surface temperature of the starting material decreases, and the adhesion force between the starting material and the glass particles decreases. This may cause problems such as the glass base material falling.

In order to prevent this drawback, it is possible to heat the starting material sufficiently by the flame of a glass particle synthesis burner before depositing the glass particles on the starting material. If the power is too strong, the tip of the burner may be worn out.Furthermore, the glass particle synthesis burner is originally designed to efficiently react glass raw materials and ideally deposit glass particles. It is difficult to set it effectively for the purpose of heating.

(Object of the Invention) In view of the points detailed above, the object of the present invention is to reduce the transient part and transient time in the initial stage of depositing glass particles on a starting material, and to reduce the adhesion between the starting material and the glass particles. It is an object of the present invention to provide a method for manufacturing an optical fiber base material, which increases productivity and improves productivity as a result.

(Structure of the Invention) That is, the present invention provides a porous glass base material for optical fiber with V
A base material for an optical fiber, which is produced by the AD method and is characterized in that the starting material is preheated by a heat source other than a burner for synthesizing glass fine particles before starting to deposit glass fine particles on the starting material. manufacturing method), etc.

The preheating temperature of the starting material cannot be absolutely limited because it varies depending on the type of glass, but it is necessary to set the temperature at which the glass fine particles can be sufficiently fused to the starting material.

The present invention aims to reduce the transient part and transient time in the initial stage of depositing glass particles on a starting material in order to increase the productivity of optical fibers, and to strengthen the adhesion between the starting material and the glass particles. Glass particles are deposited on the starting material (
The present invention is characterized in that the starting material is previously heated by a heat source other than a burner for synthesizing glass fine particles.The present invention will be explained below based on Examples.

(Example 1) As shown in Figure 5 0), a glass particle synthesis burner 1
In addition, an acid/hydrogen burner 6 for heating the starting material 2 was installed, and after heating the surface temperature of the starting material 20 to about 1200° C., the glass raw material was supplied to the burner for synthesizing glass fine particles, and deposition of the glass fine particles 4 was started. The heating burner 6 is shown in Fig. M5 (b
), the glass particles 4 were moved backward at the same time as the adhesion started, and the fire was extinguished so as not to interfere with the formation of the porous glass base material.

As a result, using a starting material with an outer diameter of 40 mm, the outer diameter was 120 mm.
A porous glass base material having a diameter of 600 mm and a length of 600 mm was obtained. The time required to synthesize the porous glass base material was 8 hours, of which the transient time was 25 minutes. On the other hand, when the heating burner was not used under the same conditions, the porous glass base material fell from the starting material when the porous base material was synthesized to a length of 550 m. In addition, when using a starting material with an outer diameter of 15 + mnφ, in order to obtain a porous base material of the same size,
It took 30 minutes, of which the transient time was 55 minutes.

(Example 2) In (Example 1), a burner using methane gas as a combustion source was used instead of the heating acid/hydrogen burner, and after heating the starting material surface temperature to about 1200°C, the same as (Example 1) was used. As a result of synthesizing a porous glass base material under these conditions, it was possible to obtain a porous glass base material with an outer diameter of 120 mm and a length of 600 mm.

The use of methane gas as a combustion source is inexpensive and therefore advantageous in terms of cost.

As can be seen from the above examples, it is effective to use a starting material with a large diameter in order to shorten the initial transition time for the purpose of shortening the synthesis time of the porous glass base material. When using , it is effective to sufficiently heat the starting material with a heating heat source.

[Brief explanation of the drawing]

FIG. 1 + A schematic explanatory diagram of a porous glass base material synthesis method using the VAD method. FIG. 2: A diagram illustrating the shape of the starting material. 3 and 4: Explanatory diagrams of the shape of the porous glass base material near the tip of the starting material. FIG. 3 shows the case of a rod-shaped starting material, and FIG. 4 shows the case of a large diameter starting material. FIGS. 5(a) and 5(b): Diagrams explaining the method of Example 1 of the present invention. Agents 1) Akira Agent Ryo Hagiwara - Commissioner of the Japan Patent Office Shiga Character Number 1982 '115 Patent Application No. 56188 3 Relationship with the person making the amendment Case Patent Applicant Address Mr. 5-15 Kitahama, Higashi-ku, Osaka Name (31, #+;) (21” Sumitomo Electric Industries, Ltd. 4,
Agent F” Address: 16-2 Toranomon Chiyoda Building, Minato-ku, Tokyo Telephone: (504) 1894 City Name: Patent Attorney (7179) Ill Akira (and 1 other person) 5. Amendment Order Date Subject of spontaneous amendment Z amendment (1) “Claims” column of the specification. (2) Contents of amendment to column a of “Detailed Description of the Invention” of the specification (1) The “Scope of Claims” on page 1 of the specification will be corrected as attached. 12) On page 6, line 3 of the same page, after the statement “On occasion,” K “
The outer diameter of the starting material is 20wφ or more, and the statement "and" is inserted, and the statement "after increasing the diameter of the starting material" after the statement "for the purpose of strengthening" in lines 15 and 16 is inserted. insert. Furthermore, insert the following description between the 19th line and the 20th line. "According to experiments conducted by the present inventors, it has been found that the outer diameter of the starting material that satisfies the above objective is preferably 20III!φ or more." (3) Page 7, lines 10 and 11. Insert the following statement in between. ``In addition, if there is no particular hindrance to the formation of the porous base material, there is no need to extinguish the moved heating burner when starting to feed the raw materials.''
In order to shorten the claim, the claim is characterized by the statement ``with an outer diameter of 20 shoulder φ or more'' after the statement. , the outer diameter of the starting material is 20 mφ or more, and the starting material is preheated (by a heat source other than the burner for synthesizing glass particles) before starting to deposit the glass particles on the starting material. Method for manufacturing optical fiber base material 0

Claims (1)

[Claims] When producing a porous glass base material for optical fiber by the VAD method, before starting to deposit glass particles on the starting material, using a heat source other than the burner for synthesizing glass particles,
A method for producing an optical fiber base material, which comprises heating a starting material in advance.