JPS60137840A - Production unit for parent material of optical fiber - Google Patents

Abstract

PURPOSE:To maintain inner pressure of a reaction pipe at constant positive pressure, and to prevent transformation of the pipe, by setting a control chamber having a device to measure pressure, a high-pressure gas inlet, and an exhaust vent at one end of a reaction pipe, connecting a control system to regulate a control valve set at the exhaust vent depending upon the measured value of the device to measure pressure to the control valve. CONSTITUTION:When glass is piled on the reaction pipe 1, measured pressure by the device 7 to measure pressure is compared with measured pressure by the outside instrument 15 by the calculating part 14. When there is difference between them, the control signal is sent to the drive part 13 of the electrically- operated valve 11, the motor 12 of the electrically-operated valve 11 is rotated and controlled to maintain the inner pressure of the reaction pipe 1 at set pressure. In this way, inner pressure of the reaction pipe 1 can be maintained at constant positive pressure, so that transformation of the reaction pipe can be prevented.

Description

[Detailed description of the invention] The present invention relates to an optical fiber preform manufacturing apparatus.

A so-called internal CVD method is known as a typical manufacturing method for optical fiber/base materials.

Although the above method can produce a low-loss optical fiber, it also has the following drawbacks.

That is, the inner tube that forms a glass layer on the inner circumferential surface of a reaction tube made of quartz tube or the like is heated to a high temperature of, for example, 1,400 to 1,600°C, so it softens and gradually contracts due to its own surface tension. Eventually, it becomes difficult to form a homogeneous glass layer on the inner surface, which limits the thickness of the glass layer that can be formed, and the length of the optical fiber that can be obtained from one preform is approximately IKm. Therefore, we cannot hope for a longer optical fiber.

This tendency is especially true for pure silica glass (SiO2), which requires high temperatures.
Also, since the quartz tube is heated to a high temperature during the formation of the crow, deformations such as ovalization are likely to occur in the cross section of the quartz tube, resulting in the preform obtained, and ultimately the cut Hrii dimension at the optical fiber stage. Accuracy decreases.

(In order to deal with the problem mentioned above, a proposal has already been made to control the diameter of the quartz tube at a constant level by keeping the internal pressure of the quartz tube higher than its external pressure during glass formation. In order to generate an internal pressure that is balanced with the contraction force of the tube, an internal pressure adjustment part is provided at one end of the tube, and the internal pressure of the quartz tube is adjusted according to the measured value of the outside diameter of the quartz tube. .

However, in this case, the internal pressure of the reaction tube fluctuates due to changes in the pressure and flow rate of the quartz gas inside the tube, so the internal pressure regulator must be operated constantly, and the pressure must be adjusted while monitoring the deformation of the quartz tube. Therefore, it was difficult to precisely control the bond diameter.

The present invention has been made to solve the above problems, and the configuration thereof will be explained below with reference to the illustrated embodiment.The reaction tube 1 is rotatably held by a rotating part 2. One end of the reaction tube 1 is connected to a glass raw material supply section (not shown) via a pipe 3, and from this supply section, a glass raw material in a gas phase, such as oxygen, and silicon tetrachloride (main raw material) are supplied into the reaction tube 1. , germanium tetrachloride (dope raw material)
etc. are being introduced.

A heating section 4 consisting of a burner for heating the reaction tube is movable along the longitudinal direction of the reaction tube 1, and oxygen and hydrogen are supplied to this heating section 4.

A control chamber 6 is connected to the other end of the reaction tube 1 via a rotary tube 6.
In addition, this control chamber 6 is provided with a pressure measuring device 7, a high pressure gas inlet 8, and an IJ1 air inlet 9, and a high pressure gas inlet 8 is connected to a high pressure gas inlet 10. A supply source (not shown) is connected through the port 8, and high pressure gas is introduced from the supply source into the port 8.

On the other hand, an electric valve 11 is connected to the exhaust port 9, and the orifice of this electric valve 11 is controlled to open and close by a motor 12, so that the internal pressure of the control chamber 6 can be kept higher than the external pressure. The motor 12 makes the orifice smaller so that the gas phase is supplied to the reaction tube 1 only, and the orifice diameter must be made extremely small, which is difficult to control. The diameter of the orifice can be increased by introducing high-pressure gas from the high-pressure gas inlet 8, since the orifice will be immediately blocked by a large amount of fine glass powder such as 5i0zG 402 present in the orifice.

A calculation section 14 is connected to the motor 12 of the electric valve 11 via a drive section 13, and on the input side of this calculation section 140 there is an external setting device 16 and the output i1! II'
)i: Device 7 is connected.

The control room 6 also serves as a collector for glass fine powder.

As is known in the present invention, the reaction tube 1 is set in the rotating part 2, and while the reaction tube 1 is being rotated, the glass raw material in the vapor phase is passed inside through the piping 3, and heated from the outside in the heating part 4. 2f, 2(L, C -V where the glass fine powder produced by the reaction of the Karasuhara No. 31 and oxygen is internally attached to the reaction f1
Applies to Law D.

Now, to describe the operation of the above device, reaction iB:
Glass deposition in 11. The pressure measured by the J's pressure measuring device 7 and the set pressure of the external setting device 16 are compared in the calculation section 14, and if there is a difference between them, the control (Ij is sent to the drive section 13 of the electric valve 11). The rotation of the motor 12 for opening the valve 11 is controlled so that the internal pressure of the reaction tube 1 is maintained at the set pressure.

That is, when the set pressure is higher than the measured pressure, the drive unit 13
The motor 12 is operated to close the electric valve 11 by the output of lIl! When the constant pressure is higher than the set pressure, the motor 12 is operated to open the opening valve 11, and the reaction
The internal pressure of i'1 is controlled to be constant.

〔Example〕

The reaction tube 1 has an outer diameter of 24 mm and an inner diameter of 21 mm.
Glass was deposited using one capsule at a surface temperature of 1800°C.
An optical fiber motherboard 4A having 90 layers was manufactured.

When the internal pressure was the same as the external pressure, it contracted to an outer diameter of 20cm, but when the internal pressure was a positive pressure of 20mm H2O, the outer diameter was kept within ±0.2cm. Ta.

As explained above, the present invention includes a rotating part that rotatably holds a reaction tube, a raw material supply part that supplies a vapor phase glass raw material from one end of the reaction tube to the inside of the reaction tube, and a raw material supply part that heats the reaction tube. In the optical fiber base material manufacturing apparatus, the other end of the reaction tube is provided with a pressure measuring device, a pressurized gas inlet and an exhaust port, and a control chamber is provided at the other end of the reaction tube. Since the control valve is connected to a control system that controls the opposite valve based on the measured value of the pressure measuring device, the internal pressure of the reaction tube can be maintained at a constant positive pressure and deformation of the intermediate tube can be prevented. be able to.

[Brief explanation of drawings]

Figure 11 is an explanatory diagram showing an embodiment of the optical fiber matrix manufacturing apparatus according to the present invention. 1... Reaction 'ilj' 2... Rotating part 4... φ Heating section 6...Control room 7...-Pressure measuring device 8...High pressure gas inlet 9...(J1 air port 11...-1"4 section Patent attorney Makoto Ito, patent attorney for electric valve patent

Claims (1)

[Claims] An optical fiber matrix comprising: a rotating part that rotatably holds a reaction tube; a raw material supply part that supplies a vapor phase glass raw material from one end of the reaction tube to the inside of the reaction tube; and a heating part that heats the reaction tube. In the manufacturing equipment of G', a control chamber having a pressure measuring device, a high-pressure gas inlet, and an exhaust port is provided at the other end of the reaction tube, and a control valve is provided at the exhaust port. An optical fiber matrix manufacturing device characterized by being connected to a control system that controls a volume valve based on the measured values of a measuring device.