JPH06234536A - Device for producing optical fiber preform - Google Patents

Abstract

PURPOSE:To continuously and efficiently produce an optical fiber preform at the sintering temp. of a sintering furnace when a glass porous preform is vitrified by using the subject device. CONSTITUTION:This optical fiber preform producing device is provided with a sintering furnace 11 to vitrify a glass porous preform 14. Inert gas is introduced into a preform attaching and detaching room R, and the room R is opened or closed to keep a muffle 12 at a specified pressure without being affected by the attachment or detachment of the preform. Consequently, the device is continuously operated at the sintering temp. of the furnace 11, and the productivity is drastically improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing an optical fiber preform, and more particularly, it enables continuous operation at a sintering temperature of a sintering furnace in a step of making a glass porous preform transparent. The present invention relates to a manufacturing apparatus that improves productivity.

[0002]

2. Description of the Related Art Conventionally, a glass porous base material obtained by a VAD method or an OVD method is made transparent by using a manufacturing apparatus as shown in FIG. That is, in this manufacturing apparatus, the muffle (quartz tube) 2 of the sintering furnace 1 is filled with an inert gas (He gas or the like), and the temperature of the heater 3 portion of the sintering furnace 1 is raised to about 1600 ° C. In this state, the glass porous preform 4 to be made transparent is gradually lowered from above the muffle 2, and is gradually made transparent from the lower end side of the glass porous preform 4 so that the transparency becomes the upper end. When it reaches the side, it is pulled out to obtain the desired transparent optical fiber preform.

During operation of this manufacturing apparatus, an inert gas is introduced into the heater 3 portion of the sintering furnace 1 to prevent the invasion of the atmosphere into the heater 3 portion. The internal pressure of the inert gas in the heater 3 is set and maintained so as to be a positive pressure of about 5 mmH ₂ O, which is indicated by the pressure difference from the outside air. On the other hand, the internal pressure of the filling inert gas in the muffle 2 is set to be a positive pressure of about 15 mmH ₂ O, which is also shown by the pressure difference from the outside air. It keeps slightly higher than the part. The reason is that the temperature of the heater 3 becomes as high as about 1600 ° C. during sintering.
The muffle material is affected and its viscosity decreases, so that the muffle 2 is easily deformed. However, if the muffle internal pressure is slightly higher than that of the heater 3, the pressure from the outside is increased. This is because the muffle can be prevented from being deformed.

[0004]

However, when the glass porous preform 4 or the transparent optical fiber preform is put in or taken out of the muffle 2, it is necessary to open the upper part of the muffle 2. When the internal pressure of the muffle becomes equal to that of the outside air due to this release, the internal pressure of the muffle becomes a little lower than the internal pressure of the heater 3 contrary to the above, so that the muffle 2 is easily deformed and sometimes crushed. It was

Therefore, in the above conventional manufacturing method, when the base material is taken in and out, the heater temperature is once lowered to a temperature at which the shape of the muffle is not deformed, and then the upper portion of the muffle 2 is released to remove the base material. It is necessary to take it in and out, it is impossible to continuously operate the sintering furnace 1 at the temperature at the time of sintering, and there are problems such as poor workability.

The present invention has been made in view of such a conventional situation, and it is not necessary to lower the heater temperature at the time of sintering by providing the base material attaching / detaching chamber section on the upper part of the muffle of the sintering furnace. It is intended to provide an apparatus for manufacturing an optical fiber preform.

[0007]

The feature of the present invention resides in that in a manufacturing apparatus for an optical fiber preform having a sintering furnace for making a glass porous preform transparent, the above-mentioned muffle of the sintering furnace is concerned. A base material attaching / detaching chamber section that is openably / closably communicated with the inside of the muffle is provided, and by introducing an inert gas into the base material attaching / detaching chamber section and opening / closing the base material attaching / detaching chamber section, the internal pressure in the muffle is constantly maintained at a predetermined level. It is in an optical fiber preform manufacturing apparatus capable of maintaining the value.

[0008]

By providing the base material attaching / detaching chamber, the internal pressure in the muffle can be constantly maintained at a predetermined value without being influenced by the attachment / detachment of the base material. Can be continuously operated at a desired sintering temperature.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an optical fiber preform manufacturing apparatus according to the present invention. In this manufacturing apparatus, 11 is a sintering furnace, 12 is a muffle made of a quartz tube, 13 is a heater, and 15 is a quartz forming a base material attachment / detachment chamber R in the upper part of the muffle 12 so as to openably and closably communicate with the inside of the muffle. A tubular body made of a pipe or the like, 16 is a flange fixed to the upper end opening of the muffle 12 to close the lower end opening of the tubular body 15, 17 is an internal partition lid for opening and closing the upper end opening of the muffle 12, and 18 is a tube. It is an external opening / closing lid that opens and closes the upper opening of the body 15.

Further, in this manufacturing apparatus, for example, as shown in the drawing, the muffle 12 and the tubular body 15 of the base material attaching / detaching chamber R are connected to the inert gas introducing pipes 20a and 21a and the exhaust pipes 20b and 21b, respectively. At the same time, an inert gas inlet pipe 22 (an exhaust pipe may be provided) is also connected to the heater 13 of the sintering furnace 11. Then, an inert gas is introduced into the muffle 12 through the introduction pipe 20a and the exhaust pipe 20b so that the internal pressure becomes a positive pressure of about 15 mmH ₂ O due to the pressure difference with the outside air, and the heater 1
An inert gas is introduced into the three parts through the introduction pipe 22 so that the internal pressure becomes a positive pressure of about 5 mmH ₂ O due to the pressure difference from the outside air. Further, the introduction of the inert gas into the cylindrical body 15 of the base material attachment / detachment chamber R prevents the internal pressure on the muffle 12 side from becoming unstable when the internal partition lid 17 of the muffle 12 is opened. Then, the inert gas is introduced through the introduction pipe 21a and the exhaust pipe 21b so that the internal pressure becomes almost the same as the internal pressure of the muffle 12 (a positive pressure of about 15 mmH ₂ O due to the pressure difference from the outside air).

In order to make the glass porous base material 14 transparent by using such a manufacturing apparatus, the following procedure may be carried out.

(1) First, in order to make the first (first) glass porous base material 14 transparent, after putting the glass porous base material 14 in the tubular body 15, the external opening / closing lid 18 is closed, Inert gas is introduced into the cylindrical body 15, the muffle 12, and the heater 13 to make the above-mentioned desired inert gas pressure, and the heater 13 is heated to about 1600 ° C.

(2) In this state, the inner partition lid 17 at the bottom of the cylindrical body 15 is opened, the glass porous base material 14 is gradually lowered and put into the muffle 12, and the heater 13 portion is passed therethrough. Make it transparent from the lower end side. At this time, even if the internal partition lid 17 is opened, the internal pressure of the muffle 12 does not fluctuate due to the above-mentioned inert gas supply system, and the predetermined value is stably maintained.

(3) When the transparent material reaches the upper end side of the glass porous preform 14, the optical fiber preform, which is entirely transparent, is pulled up from the inside of the muffle 12 to the cylindrical body 15 portion, The partition lid 17 is closed. As a result, the inside of the muffle 12 and the base material attaching / detaching chamber R are completely separated, and the internal pressure of the inside of the muffle 12 is the same as that of the internal pressure due to the inert gas supply system (15 in terms of pressure difference from the outside air).
Since it is maintained at a positive pressure of about mmH ₂ O), the heater 13
Even if the temperature of the part is maintained at the sintering temperature (about 1600 ° C.) as it is, there is no possibility that the muffle 12 itself is deformed or crushed. On the other hand, in the cylindrical body 15 of the base material attachment / detachment chamber R, the introduction of the inert gas is stopped, the external opening / closing lid 18 is opened, and the pulled-up optical fiber base material is further taken out.

(4) Elevating means (not shown) of the manufacturing apparatus from which the optical fiber preform thus made transparent is removed.
Next, an untreated glass porous preform 14 which has not been made transparent is attached to and placed in the tubular body 15, and then the external opening / closing lid 18 is closed.

(5) When the external opening / closing lid 18 is closed in this way, an inert gas is introduced into the cylindrical body 15 by the inert gas supply system, and the pressure is adjusted to the muffle 1 as described above.
It is almost the same as the internal pressure of 2.

(6) When the internal pressure of the cylindrical body 15 becomes substantially the same as the internal pressure of the muffle 12, the inner partition lid 17 of the muffle 12 is opened and the glass porous matrix is opened, as shown in the above (2). The material 14 is gradually lowered and put into the muffle 12, and the heater 13 is passed through to make the material 14 transparent in order from the lower end side. After that, if the steps from the above (3) are repeated, the material is sintered. The continuous operation can be performed at a desired sintering temperature without lowering the heater temperature of the incinerator 11.

When the glass porous preform 14 is made transparent by the production apparatus of the present invention having the above-mentioned structure, the pressure fluctuation in the muffle 12 is a set pressure.
± ₂ mmH ₂ for pressure difference of 15 mmH ₂ O with the outside air
It was about O, and good results were obtained without any hindrance in the actual transparency treatment.

In the above embodiment, the base material attaching / detaching chamber portion R of the tubular body 15 is fixedly attached to the upper end portion of the muffle 12 via the flange 16, but the base material attaching / detaching chamber portion R itself. It is also possible to attach so that it can be detached. Further, the internal partition lid 17 is not limited to the swinging method shown in the figure, and a narrow slit (gap) is provided in the portion, and the lid is a plate type lid that is inserted into and removed from this slit, or is composed of two pieces that are opened and closed. An open / close partition cover such as a split partition cover or a shutter system (system having the same structure as a shutter of a camera) including a plurality of split pieces (diaphragm pieces) may be used. This also applies to the external opening / closing lid 18.

[0020]

As is clear from the above description, according to the optical fiber preform producing apparatus of the present invention, the optical fiber preform producing apparatus has the sintering furnace for making the glass porous preform transparent. In, in the upper part of the muffle of the sintering furnace, a base material attaching / detaching chamber part that is openably and closably connected to the inside of the muffle is provided,
The internal pressure in the muffle is constantly maintained at a predetermined value by the introduction of an inert gas into the base material attaching / detaching chamber section and the opening / closing of the base material attaching / detaching section, without being influenced by the attachment / detachment of the base material. Therefore, in the sintering process, the sintering furnace can be continuously operated at a desired sintering temperature. As a result, it is not necessary to once lower the heating temperature of the heater, and excellent productivity can be obtained. By the way, in the conventional equipment, when taking out the base material, the time required to once lower the heater temperature (about 1000 ° C) and then raise it again to the desired sintering temperature (about 1600 ° C) is about 20% of the whole process. In the present invention, this time loss is completely eliminated.

Further, in the manufacturing apparatus according to the present invention, it is not necessary to raise and lower the heater temperature as described above except at the time of initial start-up and at the end of work, so that the thermal stress on the muffle and the heater portion is relieved significantly. Therefore, the life of the entire device can be significantly extended as compared with the conventional device.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an embodiment of an optical fiber preform manufacturing apparatus according to the present invention.

FIG. 2 is a schematic explanatory view showing an example of a conventional optical fiber preform manufacturing apparatus.

[Explanation of symbols]

 11 Sintering furnace 12 Muffle 13 Heater 14 Glass porous base material 15 Cylindrical body 16 Flange 17 Internal partition lid 18 External opening / closing lid R Base material attaching / detaching chamber section

Claims (1)

[Claims] 1. A manufacturing apparatus for an optical fiber preform having a sintering furnace for making a glass porous preform transparent, in which a preform detachment chamber openably and closably connected to the inside of the muffle of the sintering furnace. By providing an inert gas into the base material attaching / detaching chamber portion and opening / closing the base material attaching / detaching chamber portion, the internal pressure in the muffle can be constantly maintained at a predetermined value. Optical fiber preform manufacturing equipment.