JPS61215229A - Production of parent material for optical fiber - Google Patents

Abstract

PURPOSE:To produce a parent material for optical fiber having neither occurrence of foams nor deformation, by heating a glass tube in which a glass rod is set from the outside by a heat source moving relatively to the glass tube to contract the glass tube, and cooling the vicinity of the heat source. CONSTITUTION:The glass rod 2 is set in the glass tube, heated from the outside of the glass tube 1 by the burner 3 moving relatively in the arrow direction while being synchronously rotated, the glass tube 1 is contracted, the glass tube 1 is successively fused to the glass rod 2 in the axial direction, and integrated. The unfused part of the glass tube 1 in the vicinity of the burner 3 on the side of the arrow progress direction of the burner 3 is sprayed with a N2 gas from the nozzle 4, and cooled. Consequently, the contraction of the glass tube 1 is prevented, the inner face of the glass tube 1 and the glass rod 2 are sufficiently heated and fused. Consequently, a parent material for optical fiber can be obtained stably while leaving foams on the interface, preventing deformation.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a method for manufacturing an optical fiber base material, and particularly relates to a method for manufacturing an optical fiber base material, which includes a step of arranging a glass rod in a glass tube and heating and integrating the two. The invention relates to a method for manufacturing materials.

<Prior art>'As a method for manufacturing optical fiber preforms, especially quartz-based optical fiber preforms, for example, the rod-in-tube method, VAD
method and MOVD method are known. In the rod-in-tube method, a high-purity glass rod whose main component is quartz is placed inside a quartz-based glass tube, which is a crat with a lower refractive index than the core, and the two are heated and integrated to produce a rod-shaped light beam. Use as base material for fiber. In the VAD method, a glass raw material such as 5icz, etc. is fed into a burner for synthesizing glass fine particles together with O3, H2, etc., and glass fine particles formed in the flame are deposited on the end of the rod-shaped starting material by a flame hydrolysis reaction. By rotating and moving the starting material in the axial direction, a deposit of glass particles is formed in the axial direction,
Thereafter, the deposited body of glass particles is subjected to a heating dehydration treatment as necessary, and then heated to become transparent vitrification,
A rod-shaped high-purity base material is used.

This base material is stretched to a predetermined diameter, placed inside a quartz glass tube, and heated and integrated to obtain a drawable rod-shaped optical fiber base material.

In the MCVD method, glass raw materials such as 5iCt and 01 are supplied into a starting quartz glass tube and heated from the outside to form a glass layer mainly composed of high-purity quartz on the inner surface of the starting quartz glass tube. After forming the starting quartz glass tube, the starting quartz glass tube is heated from the outside and solidified to obtain a rod-shaped optical fiber preform.

In some cases, the rod-shaped optical fiber base material is placed inside another quartz tube and the two are heated and integrated.

As mentioned above, when manufacturing an optical fiber preform, a rod-shaped glass preform is often placed inside a glass tube and the two are heated and integrated.

A method for integrating such a rod-shaped glass base material (hereinafter referred to as a glass rod) and a glass tube is normally carried out by the method schematically shown in FIG. 2. In Figure 2, ■ is a glass tube,
2 is a glass rod placed inside the glass tube l, and 3 is a heating burner. Fix the glass tube 1 to a glass lathe etc.
While rotating the glass tube 1 and the glass rod 2 synchronously, a heating burner 3 (hereinafter referred to as burner) is moved parallel to the axial direction of the glass tube 1 relative to the glass tube 1. When heated, the glass tube 1 contracts in the radial direction and is sequentially fused to the glass rod 2 in the axial direction, so that the glass tube 1 and the glass rod 2 are integrated.

At this time, the space between the glass tube 1 and the glass rod 2 may be depressurized to promote integration.

<Problems to be Solved by the Invention> In the above-mentioned integration method, the inner surface of the unfused portion of the glass tube l and the surface of the glass rod 2 must be sufficiently heated by the burner 3. is desirable. This is because by heating the glass surface to a high temperature, the viscosity of the glass surface decreases, and the surface tension eliminates the remaining unevenness and minute scratches on the glass surface, so that the inner surface of the glass tube 1 and the glass rod 2
In addition to smoothing the surface of the glass, it also has the effect of volatilizing foreign matter adhering to the glass surface. As a result, the unfused portions of the inner surface of the glass tube 1 and the surface of the glass rod 2 are sufficiently heated, so that unevenness, minute scratches, foreign objects, etc. that cause bubbles after integration are eliminated, and the glass tube Air bubbles at the interface between the glass rod 1 and the glass rod 2 can be eliminated.

In addition, in the high temperature state, the viscosity of the inner surface of the glass tube l and the surface of the glass rod 2 is sufficiently reduced, so that the stress at the interface induced during fusion can be reduced, and the occurrence of 1-lack after integration,
Deterioration of transmission characteristics due to residual stress within the optical fiber can be prevented.

However, in reality, if the glass tube 1 is strongly heated from the outside in an attempt to sufficiently heat the inner surface of the glass tube 1 and the surface of the glass rod 2, the glass tube 1 may be deformed, or as shown in FIG. As shown, only the temperature of the glass tube 1 near the burner 3 on the burner 3 advancing direction side increases, the glass tube 1 begins to shrink, and while the surface temperature of the glass rod 2 does not rise sufficiently, one fusion occurs. In many cases, stable integration is not possible due to inconveniences such as the formation of a metal.

Particularly when the glass tube 1 is thin, the glass tube 1 tends to shrink or deform due to external heating.

<Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention, when integrating the glass tube 1 and the glass rod 2, solves the problem by: Provide cooling of the outer surface of the unfused portion.

Function> As shown in Fig. 3, in order to make the temperature of the surface of the glass rod 2 and the inner surface of the glass tube 1 sufficiently high when the glass tube 1 and the glass rod 2 are integrated, it is necessary to simply use a burner. It is not possible to increase the heating effect from the outside of the glass tube 1 by simply increasing the heating power of the burner 3 or slowing down the moving speed of the burner 3.

This is because if the glass tube 1 is only strongly heated from the outside, in the vicinity of the burner 3 on the side in the direction in which the burner 3 advances,
This is because the temperature is such that only the glass tube 1 can contract, and the surface of the glass rod 2 and the inner surface of the glass tube 1 become sufficiently hot and there are areas that are not fully cut, and the integration progresses from these areas. It is.

Therefore, as a result of intensive research, we found that the surface of glass rod 2 and the glass tube 1
A state in which the temperature of the inner surface of the glass tube 1 is sufficiently high and the glass tube 1 does not shrink is achieved by forcibly cooling the surface of the glass tube 1 near the burner 3 on the burner 3 advancing direction side from the outside. However, it has been found that the temperature of the unfused portions of the inner surface of the glass tube 1 and the surface of the glass rod 2 can be increased. That is, by forcibly cooling the surface of the glass tube 1 in the vicinity of the burner 3 on the side in the advancing direction of the burner 3, shrinkage of the glass tube 1 in the cooled portion can be prevented, while the glass tube Since the thermal conductivity of the glass tube 1 is low on the inner surface and the glass rod 2, the temperature does not drop much even by external cooling, and a sufficiently heated state can be maintained.

1 <Example> Gems produced by the VAD method have an average diameter of about 3
A quartz glass base material containing 5% by weight was stretched to an outer diameter of 12 mm, placed in a glass tube formed to have an outer diameter of 18.3 tmφ and an inner diameter of 14 mm, and heated with a heating temperature of 0.5 mm. -H, While heating the glass tube from the outside with a burner, the burner was moved at a speed of 20-7 minutes to integrate the glass tube and the glass base material. At this time, as schematically shown in FIG. 1, a cooling nozzle 4 (hereinafter referred to as the nozzle) with an inner diameter of 8 Iφ is provided near the burner 3, and the gas is supplied to the nozzle 4 at a flow rate of 10 t/min.
on the outer surface of the glass tube 1 at a distance of about 15 m+ from the part where the flame of the burner 3 is concentrated and the glass tube 1 is heated most intensely.

N gas was blown to constantly cool the outer surface of the glass tube. As a result, the fusion between the glass tube 1 and the glass rod 2 progresses at a location that almost coincides with the location where the flame of the burner 3 is concentrated, and after the integration, there are bubbles at the interface between the glass tube 1 and the glass rod 2. There was no occurrence of

At this time, burner 3 has 0. The amount of H8 was supplied at 35 t/min, and the amount of H8 was supplied at 100 L/min.

Comparative Example 1 Under the same conditions as the example, a glass tube l was used without providing the nozzle 4.
When the glass rod 2 and the glass rod 2 were integrated, fusion occurred at a location approximately 5 m away from the location where the flame of the burner 3 was concentrated in the direction in which the burner 3 was traveling.

At this time, at the interface between the glass tube 1 and the glass rod 2, after integration,
Many air bubbles remained.

Comparative Example 2 In the example, the amount of Hl supplied to the burner 3 was set to 12
When the amount of 01/fj, O, was increased to 40 t/min and the integration was performed without installing the nozzle 4, the fusion was limited to a traveling direction of 10 m from the place where the flame of the burner 3 was concentrated.
It happened in a remote location.

At this time, a large number of bubbles exist at the interface between the glass tube 1 and the glass rod 2, and the glass tube 1 shrinks unevenly during shrinkage, causing eccentricity in the base material and bending in the longitudinal direction after integration. also occurred.

<Effects of the Invention> As described above, the present invention is effective for stably integrating a glass tube and a glass rod without the problem of bubble formation or deformation. In particular, the present invention is suitable for cases where the glass tube used is thin and easily shrinks or deforms due to external heating, or when the inner surface of the glass tube or the surface of the glass rod is contaminated or uneven. It is valid.

In the present invention, only a method of cooling the glass tube by blowing N2 gas onto the glass tube is shown, but the type of gas to be sprayed may be an easily handled inert gas or air. As for the cooling method, in addition to the method of blowing gas, a method of water cooling is also effective.

Although the present invention uses a burner as a heat source, it is also effective for electric heat sources such as electric resistance furnaces and induction heating furnaces.

Moreover, the present invention is also effective for cleaning and smoothing the inner surface of a glass tube and mitigating deformation during solidification when solidifying a glass tube using the MOVD method or the like.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an embodiment of the present invention. Figures 2 and 3 are diagrams schematically showing a method of fusing and integrating a glass tube and a glass rod, and Figure 3 is simply a diagram showing a situation that often occurs when a glass tube is strongly heated. be. Figure 1 Figure 3

Claims (2)

[Claims] (1) In the process of manufacturing optical fiber preforms, a glass rod is placed inside a glass tube, a heating source is installed outside the glass tube, and the heating source is moved relatively parallel to the axis of the glass tube. The glass tube is heated and shrunk, and the glass tube is sequentially fused to the glass rod in the axial direction, and when the glass tube and the glass rod are integrated, the glass near the heating source on the heating source advancing direction side is A method for producing an optical fiber base material, the method comprising cooling the outer surface of an unfused portion of a tube. (2) The optical fiber motherboard according to claim (1), wherein the unfused portion of the glass tube is cooled by blowing gas onto the outer surface of the unfused portion. Method of manufacturing wood.