JP3400006B2 - Manufacturing method of optical fiber preform - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform which enables efficient deposition of glass soot by an external attachment method.

[0002]

2. Description of the Related Art As a method for producing an optical fiber preform, SiO ₂ glass fine particles (glass soot) produced by flame hydrolysis of a SiCl ₄ starting material in an oxyhydrogen flame are deposited on the outer periphery of a starting core material. An external method has been proposed. In this external attachment method, it is extremely difficult as a practical matter to deposit all the glass soot ejected from the burner flame on the starting core material. It is surrounded by a cover called a chamber, and flames ejected from one side and glass soot that has not accumulated are forcedly discharged from the other exhaust port for processing.

[0003]

In such forced exhaust, if the exhaust is strengthened, the amount of glass soot that is not deposited and sucked into the exhaust pipe increases, so that the soot deposition efficiency deteriorates. Therefore, from the viewpoint of increasing the deposition efficiency and improving the production rate of the optical fiber preform, it is better to set the exhaust gas to be weaker. However, if the exhaust gas is too weak, the glass soot blown from the burner onto the starting core material bounces off and scatters, and a part of it leaks out of the chamber. The treatment of this leaked glass soot is
Considering the great corrosiveness of the soot and its treatment facility, it is quite difficult. From this point of view, strong exhaust is required to some extent.

Therefore, under the present circumstances, the glass soot is fixed to a constant exhaust strength (for example, the exhaust strength within a range where the glass soot does not leak from the chamber in the latter half of the deposition) from the initial stage to the end of the deposition. It is accumulating.

However, as a result of diligent studies by the present inventors, the deposition soot deposited on the starting core material grows with the progress of deposition, and the diameter of the deposition soot increases, so that the exhaust environment in the chamber is increased. Therefore, it was found that efficient deposition of glass soot cannot be obtained by the method in which the deposition exhaust strength is constant as described above. In other words, when the deposition soot diameter of the starting core material is thin with respect to the burner flame, there is almost no glass soot leaking from the chamber even if the exhaust gas is fairly weak.
At this time, if the exhaust gas is made stronger, most of the glass soot will be sucked into the exhaust pipe side without being accumulated, while if the deposition soot diameter of the starting core material is large against the burner flame, the exhaust gas will be considerably strong. Otherwise, it has been found that more glass soot bounces on the starting core material and is more likely to leak from the chamber.

From the above facts, it is desirable for the present inventors to set the exhaust gas weakly in the initial stage of deposition in the external attachment method and to strengthen the exhaust gas as the deposition soot grows. Furthermore, they have found that the growth of this deposition soot can be grasped by monitoring the contact area between the deposition soot and the flame with a radiation thermometer.

The present invention has been made from such a point of view, and when the glass soot is deposited by the external attachment method, the strength of the exhaust gas is appropriately controlled to improve the deposition efficiency of the optical fiber preform. It is intended to provide a manufacturing method of.

[0008]

According to the present invention, in the deposition by the external method, the chamber exhaust volume is increased as the contact area between the deposition soot and the burner flame is increased. It is in a method for manufacturing a fiber preform.

[0009]

As described above, according to the present invention, the chamber exhaust amount is controlled in conjunction with the increase in the contact area between the deposition soot and the burner flame, so that the glass soot is not excessively exhausted and rebounds. The glass soot does not escape to the outside of the chamber, and the glass soot is deposited quickly and efficiently.

[0010]

FIG. 1 shows an example of an apparatus system for carrying out the method for producing an optical fiber preform according to the present invention. In this apparatus system, a chamber 2 is installed in the axial direction outside the rotating starting core material 1 so as to surround the starting core material 1, and one of the chambers 2 (on the right side in the drawing) has an opening 2a. Is opposed to the oxyhydrogen burner 3 that traverses (reciprocates) in the axial direction of the starting core material 1, and the exhaust pipe 4 is provided in the opening 2b on the other side (left side in the figure) of the chamber 2. It is connected. Further, a radiation thermometer T is installed, for example, on the opening 2a side of the chamber 2.

In this apparatus system, in order to deposit the glass soot 6 contained in the flame 5 from the oxyhydrogen burner 3 on the starting core material 1, first, suction from the exhaust pipe 4 side of the chamber 2 is performed. A forced exhaust system of appropriate strength is created in the chamber 2, and in this state, the starting core material 1 is rotated, while the glass soot 6 is jetted to the outer periphery of the starting core material 1 while the oxyhydrogen burner 3 is traversed. You can do it. As a result, the glass soot 6 is gradually deposited on the outer periphery of the starting core material 1 and grows as the deposition soot 6a. At this time, the glass soot 6 which is not deposited and is exhausted from the exhaust pipe 4 increases or the glass soot 6 which scatters and leaks from the opening 2a on the oxyhydrogen burner 3 side of the chamber 2 is generated due to the strength of the exhaust. There are many.

Therefore, in the present invention, in the initial stage of deposition, the exhaust gas of the chamber 2 is set to be weak and the glass soot 6 is deposited, and when the deposition soot 6a of the starting core material 1 grows, it grows. Accordingly, the exhaust is gradually strengthened. The control of the exhaust gas accompanying the growth of the deposition soot 6a catches the growth of the glass soot 6 as an increase in the effective contact area between the deposition soot 6a and the burner flame 5, and this contact area is the radiation thermometer T. The measurement information is fed back to the suction means of the exhaust system. Here, the contact area is determined by calculating the temperature distribution from the infrared rays emitted from the glass soot 6 heated by the burner flame 5 using the radiation thermometer T and exceeding the reference temperature (for example, set to 600 ° C.). The area. The relationship between the contact area thus obtained and the exhaust amount of the chamber 2 is illustrated in FIG.

Thus, in the initial stage of deposition,
When the exhaust of the chamber 2 is set weakly, the glass soot 6 does not excessively exhaust, and even when only the starting core material 1 at the time of departure or the deposition soot 6a portion is still ungrown and thin, Are quickly and efficiently deposited on the starting core material 1 and the deposition soot 6a. When the deposition soot 6a grows in this way and its diameter becomes thicker, the contact area between the deposition soot 6a and the flame 5 increases and scattering occurs due to the bounce of the deposition soot 6a, resulting in insufficient exhaust gas. Therefore, the rapid attachment of the glass soot 6 tends to be hindered, and the glass soot 6 tends to leak out of the chamber 2. However, in the present invention, the exhaust gas is exhausted due to the increase in the contact area. Since the glass soot 6 is strengthened, the glass soot 6 can be quickly attached thereto, and the glass soot 6 can be effectively prevented from leaking.

Incidentally, when the deposition rate per unit time during deposition according to the present invention is compared with that when the conventional exhaust amount is always constant, it is as shown in FIG. The rate curve L ₁ is always above the deposition rate curve L ₂ of the conventional method, and it can be seen that an excellent deposition rate can be obtained.

[0015]

As is apparent from the above description, according to the present invention, in the deposition by the external method, the chamber exhaust amount is increased with an increase in the contact area between the deposition soot and the burner flame. The amount of exhaust is always appropriate, and the deposition efficiency is reduced due to excessive exhaust during the initial stage of deposition, and the glass soot does not leak into the room (outside the chamber) due to insufficient exhaust after growth of deposition soot. An excellent method for producing an optical fiber preform is obtained, in which a conventional glass soot is deposited.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an example of an apparatus system for carrying out a method for producing an optical fiber preform according to the present invention.

FIG. 2 is a graph showing a relationship between a contact area between a deposition soot and a burner flame and a chamber exhaust amount.

FIG. 3 is a graph showing the relationship between the deposition rate per unit time and the elapsed deposition time according to the method of the present invention and the conventional method.

[Explanation of symbols]

1 Starting core material 2 chamber 2a, 2b openings 3 oxyhydrogen burner 4 exhaust pipe 5 flames 6 glass soot 6a deposition suit

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Claims (2)

(57) [Claims] 1. A method for manufacturing an optical fiber preform, wherein the chamber exhaust amount is increased with an increase in the contact area between the deposition soot and the burner flame in the deposition by an external method. 2. The method for producing an optical fiber preform according to claim 1, wherein the contact area between the deposition soot and the burner flame is measured by a radiation thermometer.