JPS597649B2 - Manufacturing method of optical fiber material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a material for a low-loss optical fiber used in communications.

Communication using optical fibers is viewed as extremely promising due to the reduction in transmission loss of optical fibers and the improvement in the performance of optical semiconductors.

Methods for manufacturing optical fibers used in such optical fiber communications include the pot method, in which glass material is melted in a pot and spun, and the rod method, in which the glass material is formed into a rod shape and then the rod-shaped glass material is spun. . Chemical vapor deposition method (Chemical vapor deposition method), which allows high-purity glass materials to be obtained relatively easily.
VaporDeposition) (abbreviated as CVD method)
belongs to the latter manufacturing method. The most common CVD method 10 is a method called internal CVD method, in which silicon tetrachloride, germanium tetrachloride, etc. are reacted inside a quartz tube by heating from the outside, and silicon dioxide,
This is a method in which a reaction product such as germanium dioxide is deposited on the inner wall of a quartz tube, and then heated to obtain a rod-shaped glass material with no voids. In the above method, the thickness of the glass layer deposited varies as shown in FIG. This is because the gas flow with a constant flow is oriented in one direction, so the tin-shaped glass blown by the gas flow is carried downstream and
This is because it is deposited with zero flow. The optical fiber obtained by spinning this axially non-uniform rod-shaped glass raw material is
Again, it is non-uniform in the axial direction. Furthermore, the non-uniformity of the core diameter of the optical fibers causes an increase in connection loss between the optical fibers, an increase in scattering loss, etc.25. Conventionally, due to the above-mentioned non-uniformity in the axial direction, in the case shown in FIG. 1, about 20 portions on the raw material inlet side were discarded and the remaining approximately uniform portion was used. In the above method, the effective part of the entire area subjected to CVD is small and the bar-shaped glass 30
The utilization efficiency of space materials is very poor. Axially uniform CVD
As an attempt to obtain a film, there is a method in which the direction of the gas flow in a quartz tube is alternately changed only when the film thickness to be deposited in one CVD is several μm, but even with this method, in principle,
Axial nonuniformities within 2%35 cannot be removed.

In addition, in CVD where the film thickness deposited in one CVD is about 10 μm, a large amount of tin is generated in the reacted glass, and in the method of alternating the flow direction as described above, tin is It returns to the raw material gas supply system and obstructs the flow state of the piping system. Therefore, an object of the present invention is to prevent the glass tin produced by reaction from returning to the raw material gas supply system in the method for manufacturing optical fiber material by the internal CVD method in which a high-purity glass substance is vapor-deposited on the inner wall of a quartz tube. without interfering with the flow of the piping system.
It is an object of the present invention to provide a method for manufacturing an optical fiber material that can deposit a CVD film that is more uniform in the axial direction on the inner wall of a quartz tube than in conventional methods.

According to the present invention, in a method for manufacturing an optical fiber material that includes a step of depositing a glassy thin film multiple times on the inner wall of a hollow glass tube, a gaseous glass raw material is heated while depositing one layer of the glassy thin film. According to the present invention, there is provided a method for depositing a glassy thin film while gradually increasing the sweeping speed of a heating element for heating a gaseous glass raw material. The method for manufacturing the above-mentioned optical fiber material exponentially increases the sweeping speed of the heating body, and according to the present invention, the sweeping speed of the heating body for heating the gaseous glass raw material is increased stepwise. The method for manufacturing the optical fiber material described above is obtained, and furthermore, according to the present invention, the method for manufacturing the optical fiber material described above in which the flow rate of the gaseous glass raw material is linearly increased is obtained. Next, the present invention will be explained in detail with reference to the drawings. FIG. 2 is a diagram illustrating a first embodiment of the present invention. Second
The upper part of the figure shows the sweep speed of the flame for heating the frit gas flowing inside the hollow quartz tube, and the lower part shows the axial change in the film thickness of one CVD film deposited on the hollow quartz tube as the flame moves. It shows. As shown in Figure 2, the flame sweep speed is O(1V) at the CVD position 0crfL.
7! /-, and the flame sweep speed was increased exponentially as the CVD position moved to the right. The relationship between the flame sweep speed (v) and the CVD position (x) at this time was controlled according to equation (1). As shown in the figure below, 0CTL at CVD position
Except for the section of 5CTrL, it remained constant in the section of 45Cr1L.

When the flame is deposited at a constant speed without increasing the flame speed as in the conventional method, as shown in the lower part of Figure 1,
The CVD film thickness is increasing exponentially, and it is not possible to obtain a constant CVD film thickness over the entire CVD area, and even if a 10% change is allowed, the thickness will be 25 ) can only be used. On the other hand, according to the present example, a region having a uniform CVD film thickness can be obtained over 90% of the CVD region. In the above method, since the glass raw material flows in one direction, the flow state of the piping system is not inhibited due to the glass tin produced by the reaction returning to the raw material gas supply system. Here, a flame is used as a heat source for heating, but the heat source of the present invention is not limited to flame as long as it provides a high temperature state of 1000°C or more. Figure 3 shows a second embodiment of the present invention. FIG.

The upper diagram in Figure 3 shows the sweep speed of the flame for heating the frit gas flowing inside the hollow quartz tube, and the lower diagram shows the axis of the film thickness of one CVD film deposited on the hollow quartz tube as the flame moves. It shows a change in direction. As shown in the upper part of Figure 3, the sweep speed of the fire is determined by whether the CVD position is O? ~5? 10 in the section?
/Mm, 5? I increased the number of dogs step by step at 5? ~50
? It was set as 20CrIL/Mm in the interval. The thickness of the CVD film deposited under these conditions is as shown in the lower part of Figure 3.
5CT from 0CTn at position D! 45 excluding section L
? It became constant in the interval. It is clear that in this case stepwise changes in the flame sweep speed may be carried out many times. FIG. 4 is a diagram illustrating a third embodiment of the present invention.

The upper diagram in Figure 4 shows the sweep speed of the flame for heating the frit gas flowing inside the hollow quartz tube, and the lower diagram shows the axis of the film thickness of one CVD film deposited on the hollow quartz tube as the flame moves. It shows a change in direction. As shown in the upper diagram of Figure 4, the flame sweep speed was set at 15 (177
1/Mx, and the flame sweep speed was linearly increased as the CVD position moved to the right. The relationship between the flame sweep speed (v) and the CVD position (x) at this time was controlled according to equation (2). The thickness of the CVD film deposited under these conditions is the third
As shown in the figure below, 15Cr from 0cm of CVD position
! It became constant in the 35 cm section except for the 1 section.

The present invention has been explained above using the first, second, and third embodiments, but as is clear from the purpose of the present invention, the flame sweep speed is limited to the values shown in Figures 2, 3, and 4. It is natural that it will not be done. Finally, the features of the present invention are listed as follows:
Internal attachment C that deposits high-purity glass material on the inner wall of the quartz tube
In the method for manufacturing optical fiber materials using the VD method, a uniform CVD film can be spread in the axial direction without disturbing the flow state of the piping system due to the tin of the reacted glass returning to the raw material gas supply system. It is possible to deposit on the inner wall of a quartz tube over a wide range.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the sweep speed of the flame for heating the glass raw material in the conventional manufacturing method and the change in CVD film thickness in the axial direction of the quartz tube, and Fig. 2, Fig. 3, and Fig. 4, respectively. FIG. 3 is a diagram showing the sweep speed of a flame for heating a glass raw material and the change in CVD film thickness in the axial direction of a quartz tube, explaining the first, second, and third embodiments of the present invention.

Claims (1)

[Scope of Claims] 1. A method for manufacturing an optical fiber material including the step of depositing a glassy thin film multiple times on the inner wall of a hollow glass tube, comprising: 1
1. A method for producing an optical fiber material, characterized in that the glassy thin film is deposited while gradually increasing the sweep speed of a heating element for heating a gaseous glass raw material during the deposition of the glassy thin film of the layer. 2. The method for manufacturing an optical fiber material according to claim 1, wherein the sweep speed of the heating element for heating the gaseous glass raw material is increased exponentially. 3. The method for manufacturing an optical fiber material according to claim 1, wherein the sweep speed of the heating element for heating the gaseous glass raw material is increased stepwise. 4. The method for manufacturing an optical fiber material according to claim 1, wherein the sweep speed of the heating element for heating the gaseous glass raw material is linearly increased.