JPS61281038A - Apparatus for producing optical fiber preform - Google Patents

Abstract

PURPOSE:An apparatus for producing optical fiber preform, consisting of a reacting and sintering chamber having a specific structure and an apparatus to rotate the starting rod by a rotary magnetic field or with a motor, free of generation of toxic gas, and capable of producing a high-purity preform preventing the intrusion of impurities. CONSTITUTION:The reacting and sintering chamber 6 having closed structure is made to be movable vertically by the vertical motion of a supporting table arm 17 by placing a stretchable member at a part of the partition wall 13. The starting rod 2 fixed with the starting rod chuck 15 is rotated by the cooperative action of the external rotary magnetic disk 12 and the inner magnetic disk 14 and lowered with the supporting table arm 17. Glass soot generated by an oxyhydrogen flame burner 7 is deposited to the lower end of the starting rod 2 to obtain a porous preform 3. The objective optical fiber preform 5 can be produced by dehydrating and sintering the porous preform in the heating furnace 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical fiber preform manufacturing apparatus using the VAD method, and particularly relates to a rotational drive apparatus for an optical fiber preform.

[Conventional technology]

As is well known, the VAD method is known as one of the methods for manufacturing optical fibers, and in this method, a raw material gas is subjected to a hydrolysis reaction in an oxyhydrogen flame to generate glass particles, which are then rotated. It is attached and deposited on a starting rod to form a porous base material, and then dehydrated and sintered in a heating furnace to obtain an optical fiber base material.The obtained base material is then stretched and jacketed as necessary. It is then heated and spun in a drawing furnace to become an optical fiber.

FIG. 5 is a schematic diagram of an optical fiber preform manufacturing apparatus using such a VAD method, in which 1 fixes a starting rod 2 at a chuck la, rotates the starting rod 2, and simultaneously moves it in the axial direction. The driving part 2 is a starting rod that serves as a target for depositing glass particles produced by a flame hydrolysis reaction.

This starting rod 2 has a molecular weight of 700 to aOO when producing a porous base material.
Also, quartz rods are usually used because they are exposed to high temperatures of 1,400 to 1,500 degrees during sintering.

3 is an optical fiber porous base material obtained by an oxyhydrogen flame hydrolysis reaction, 4 is a heating furnace for sintering the porous base material 3 deposited on the starting rod 2, and 5 is a light beam obtained by sintering. A fiber base material, 6 a reaction vessel, a 7-oxyhydrogen burner, and 8 an exhaust gas treatment device for drawing out the exhaust gas in the reaction vessel 6.

9 also connects the starting rod 2 to the reaction vessel 6. Heating furnace 4 (hereinafter referred to as
This space is a through hole for penetrating into the reaction sintering chamber.

As described above, in the conventional optical fiber preform manufacturing apparatus using the VAD method, the starting rod 2, which is rotated and supported in the axial direction, is introduced into the heating furnace and the reaction vessel.
Glass particles are deposited on the starting rod 2, and an optical fiber preform is grown by sintering while gradually pulling up and rotating the rod. Therefore, in order to manufacture a high-purity optical fiber preform 5, the reaction sintering chamber is required to be sealed with high precision from the outside.

By the way, the raw materials for glass are halogen compounds such as 5iC14 and Ge CI4, and in addition to glass particles, toxic gases such as chlorine gas and hydrogen chloride are generated as products of the hydrolysis reaction, and these are excess gases that do not adhere to the target. It is necessary to control the flow of gas in the reaction sintering chamber so that it is guided to the exhaust gas treatment device 8 without being released into the atmosphere together with the glass particles. Therefore, usually
The reaction and sintering chamber is set to negative pressure (1 to several mmH20), but as mentioned above, if there is a through hole 9 through which the starting rod 2 passes, the atmosphere may leak into the heating furnace 4 or the reaction vessel 6. It invades.

On the other hand, although a high-purity carbon heater 4a is normally used in the heating furnace 4, there is a problem in that this heater 4a is considerably consumed when heated in the atmosphere. Therefore, an inert gas such as He, Ar, N2, etc. is supplied to the heating furnace in order to suppress the consumption of the heater 4a described above.

However, since the reaction sintering chamber is kept under negative pressure,
If left as is, outside air will flow in through the through hole 9 and the heating furnace 4 will
cannot be in an inert gas atmosphere.

Therefore, as a method for sealing the through hole 9, various methods as shown below have been considered.

[Problem that the invention seeks to solve]

FIG. 6(a) shows what is generally called a gas seal, and there is a small hole 10a in the side wall of the through hole 9.

10b, and seal gas Gs and inert gas Gi are injected as shown by arrows. The purpose is to seal the through hole 9 to the starting rod 2 without contacting it.

However, this method is extremely uneconomical because a large amount of expensive inert gas Gi such as He, Ar, and N2 is used in order to completely isolate the reaction sintering chamber from the outside air.

In the case of FIG. 6(b), the sealing gas Gs is injected through the hole 10a and exhausted through the hole 10b, thereby simultaneously preventing the intrusion of outside air and injecting the inert gas. There is a drawback similar to that shown in FIG. 6(a).

FIG. 6(C) is an example in which a mechanical seal MS is applied to the through hole 9. Since quartz glass is normally used as the starting rod 2, the external shape of the starting rod 2 in the longitudinal direction is
Also, high precision bending cannot be obtained. Therefore, even when creating a mechanical seal, it is necessary to make the clearance with the starting rod 2 larger than under the conditions for using a general mechanical seal, and it is extremely difficult to achieve a perfect seal under the conditions for using a mechanical seal. Therefore, we ended up using a gas seal, as shown in Figure 6(a).

A problem similar to that in case (b) occurs.

This invention was made in order to solve these problems, and it is a light that allows the starting rod to rotate and move in the axial direction in the same manner as before while the reaction sintering chamber is completely sealed. The present invention provides a fiber preform manufacturing device.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention.
1 is a rotary drive unit, 12 is an external magnetic plate attached to the rotary drive unit 11, 13 is a partition made of a non-magnetic material, 14 is an internal magnetic plate, 15 is a starting rod chuck attached to the internal magnetic plate 14, 16 is a stretchable body that is stretchable in the axial direction of the starting rod and has airtightness, and shields the space between the non-magnetic partition wall 13 and the upper part of the heating furnace from the outside.

As mentioned above, 2 is the starting rod, 3 is the porous base material, and 4 is the starting rod.
5 is a heating furnace, 5 is an optical fiber preform, 6 is a reaction vessel, 7 is an oxyhydrogen burner, and 8 is an exhaust gas treatment device.

The rotation drive unit 11 and the partition wall 13 are configured to move integrally in the axial direction by a support arm 17.

The inner and outer magnetic plates 12.14 are made up of two multipolar permanent magnets 8.18 facing each other with a non-magnetic partition wall 13 in between, as shown in FIG. By selecting the diameter of the magnetic plate, a magnetic coupling is constructed that can transmit sufficient rotational force from the input side to the output side without contact.

FIG. 3 shows a concrete example of attaching such a magnetic coupling part to a starting rod, 21
is the axis of the rotation drive unit, 22.24 is the external and internal magnetic plate, 2
3 is a non-magnetic sealing cover (partition wall), and 25 is a rotating shaft that connects the internal magnetic plate 24 to the chuck 26 that fixes the starting rod.

27 is a base fixed to the support arm 17, and the sealing cover 2 is attached to the base 27 via an O-ring 28.
3 is fixed with screws. Further, the rotating shaft 25 is supported by bearings 29 and 30. A bellows-shaped expandable body 32 is hermetically fixed to the outer periphery of the base 27 by screws 31, and the starting rod 2 can be replaced by removing the screws 31. There is. Note that the inert gas may be injected by opening a small hole in the side wall of the sealing cover 23 or the base 27.

Since the optical fiber preform manufacturing apparatus of the present invention has the above-described structure, the reaction sintering chamber and the outside air are sealed by the sealing cover 23. It is completely blocked by the elastic body 32,
At the same time, the driving force for the starting rod 2 can be achieved by magnetic force and compression. Therefore, it becomes easy to control the flow of gas in the reaction sintering chamber, and it is possible to manufacture an optical fiber preform with high purity.

FIG. 4 shows another embodiment of the invention, in which the same parts as in FIG. 3 are indicated by the same symbols. The starting rod 2 is rotated by supplying electric power from a needle 34 drawn into a motor 33 in a sealed cover 23 in a sealed structure. In addition, as the material of the elastic body 32, for example, fluororubber and tetrafluoroethylene (Teflon) are preferable.

〔Effect of the invention〕

As explained above, the optical fiber preform manufacturing apparatus of the present invention has a structure in which the reaction sintering chamber is sealed from the outside air by employing an expandable body and an electric drive system, and a rotational force is applied to the starting rod. Since it is configured to perform transmission, it eliminates the need for large amounts of gas as in the past, and
This has the great effect of not releasing toxic gases into the atmosphere.

Furthermore, since the reaction sintering chamber is completely shielded from the outside air, it is easier to control the gas flow within the device, and impurities are completely eliminated, allowing the production of highly pure optical fiber preforms. It has the excellent effect of being able to

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of a magnetic coupling, Fig. 3 is a side view showing a specific embodiment of the rotation drive section, and Fig. 4 is a rotation FIG. 5 is a side view showing another embodiment of the drive unit, FIG. 5 is a schematic diagram showing a conventional optical fiber preform manufacturing apparatus, and FIG. 6 is an explanatory diagram of a conventional sealing method. In the figure, 2 is a starting rod, 4 is a heating furnace, 6 is a reaction vessel, 7 is an oxyhydrogen burner, 8 is an exhaust gas treatment device, 11 is a rotation drive unit,
12 is an external magnetic plate, 13 is a partition wall, 14 is an internal magnetic plate, 1
6 indicates a stretchable body. Figure 2 Figure 6

Claims (3)

[Claims] (1) In an optical fiber preform manufacturing device using the VAD method, a part of the partition wall of the reaction sintering chamber for the optical fiber preform, which is tightly sealed from the outside air, is constructed of an expandable body and is movable in the vertical direction. An optical fiber characterized in that the starting rod in the reaction sintering chamber is rotated by a rotating magnetic force from outside the partition wall in the reaction sintering chamber or by a motor disposed within the partition wall. Base material manufacturing equipment. (2) The optical fiber preform manufacturing apparatus according to claim (1), wherein the rotating magnetic force is transmitted by rotating magnetic plates provided inside and outside the partition wall of the reaction sintering chamber. (3) The optical fiber preform manufacturing apparatus according to claim (1), wherein the expandable body has a bellows structure.