JPS63159231A - Production apparatus for optical fiber preform - Google Patents

Abstract

PURPOSE:To obtain optical fibers having excellent characteristics, by controlling a flow control valve according to internal pressure of a sintering chamber for sintering a preform, etc., to keep the internal pressure at a constant value so as to prevent entry of impurities from the outside into the sintering chamber. CONSTITUTION:This production apparatus for optical fiber preforms is formed from a vent cylindrical unit 5, the first and second lid units 8 and 9, an inert gas supply passage 8, a flow control valve 19 provided therein, a pressure detector 15, a controller 16 for controlling the above-mentioned valve 19 by an output from the pressure detector 15 and a vent passage 23. The above-mentioned vent cylindrical unit 5 is connected to the upper side of a furnace core tube 1 forming a sintering chamber 12 to form a vent chamber 13. The afore- mentioned lid units and 9 have through-holes 10 and 11 for passing a seed rod 3 therethrough and divide the sintering chamber 12 from the vent chamber 13 and the vent chamber 13 from the outside. When the pressure of the afore- mentioned sintering chamber 12 is increased, the volume of an inert gas is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical fiber preform manufacturing apparatus for obtaining an optical fiber preform by dehydrating and vitrifying an optical fiber preform soot.

(Prior art and its problems) As a method for manufacturing an optical fiber base material, an optical fiber base material suit consisting of porous glass fine particles in which GeO□ as a dopant for adjusting the refractive index is distributed in 5i02,
There is a method of dehydration and vitrification by sintering in a sintering furnace.

By such a method, optical fiber f! 1' material, conventionally, as shown in FIG.
A seed rod 51 made of quartz glass with 0 formed at the tip is inserted into the core tube 52 of the sintering furnace from the tip side, and He gas and 012 gas as a dehydrating agent are supplied from the lower end of the core tube 52. The rod 51 is rotated and gradually lowered, and the heater 5
3. By heating the optical fiber base material soot 50
The optical fiber preform 54 was obtained by dehydration and vitrification. The He and C12 gases in the reactor core tube 52 are then transferred to the exhaust cylinder 5.
5 was suctioned by an exhaust treatment device through an exhaust flow path 56 connected to the exhaust flow path 56. Note that the inside of the furnace core tube 52 and the exhaust cylinder body 55
The inside of the exhaust cylinder body 55 is separated from the atmosphere by a lid body 57, and the inside of the exhaust cylinder body 55 and the atmosphere are divided by a lid body 58. The lid bodies 57 and 58 have a through hole through which the seed rod 51 passes. It is perforated.

Further, a manual pulp 59 is installed in the exhaust flow path 56.

However, the internal pressure of the reactor core tube 52 is affected by fluctuations in the suction pressure on the exhaust side,
It fluctuates due to changes in the gap between the seed rod 51 and the lid body 57 due to distortion or non-uniform diameter of the seed rod 51, and fluctuations in the actual volume of exhaust gas due to temperature changes inside the core tube 52.

If the internal pressure of the core 1 ft 52 changes in this way, the dehydration effect will change during the dehydration and vitrification process of the optical fiber preform soot 50, and the loss characteristics in the longitudinal direction of the optical fiber obtained from the optical fiber preform 54 will deteriorate. .

Also, during the dehydration and vitrification process, a part of GeO2 as a dopant for adjusting the refractive index is scattered due to the chlorination reaction to achieve the desired refractive index, but due to internal pressure fluctuations in the core tube 52, the rate of this reaction, that is, the amount of scattering is As a result, the refractive index difference and the refractive index distribution shape of the optical fiber preform 54 change in the longitudinal direction, and the transmission characteristics of the optical fiber obtained from the optical fiber preform 54 deteriorate. If the furnace is operated in a state where the difference between the internal pressure of the furnace core tube 52 and the similar seal gas pressure is ±201111820 or more, the furnace core tube 52 will be deformed during the long dehydration and vitrification process, leading to destruction. For example, if the exhaust negative pressure fluctuates rapidly, a pulsation phenomenon occurs in the gas flow, and the gas flow alternates between suction and exhaust (breathing) at the through hole of the lid 57, causing the exhaust to flow back into the core tube 52, causing air and gas to flow from the outside. There is a risk of impurities such as metal ions entering.

However, in the conventional optical fiber base material manufacturing equipment, the internal pressure of the reactor core tube 52 was adjusted and stabilized by adjusting the opening degree of the manual valve 59 and changing the total amount of exhaust gas. Unable to respond to changes, etc.
There was a problem in that the internal pressure of the furnace core tube 52 could not be kept constant.

(Means for Solving the Problems) In order to solve the above problems, the optical fiber preform manufacturing apparatus of the present invention has an exhaust chamber connected to the upper side of a core tube forming a sintering chamber of a sintering furnace. an exhaust cylinder body to be formed; a first lid body having a through hole through which the seed rod passes and partitioning the sintering chamber and the exhaust chamber; and a first lid body having a through hole through which the seed rod passes through and the exhaust chamber; a second lid body that partitions the chamber and the outside; an inert gas supply channel that supplies inert gas to the exhaust chamber; a flow rate control valve disposed in the inert gas supply channel; A pressure detector detects the pressure in the sintering chamber, and a signal from the pressure detector controls the flow R control valve according to the pressure in the sintering chamber.
tll and an exhaust flow path that communicates the exhaust chamber with an exhaust treatment device to reduce loss of inert gas supplied to the exhaust chamber when the pressure in the sintering chamber increases; The structure is such that when the pressure in the sintering chamber decreases, the amount of inert gas supplied to the exhaust chamber is increased.

(Function) The gas supplied to the sintering chamber reaches the exhaust chamber through the gap between the first lid and the seed rod, and is sucked and exhausted through the exhaust flow path by the exhaust treatment device. Then, the pressure in the sintering chamber is detected by a pressure detector, and the control device controls the flow in and i1 control valves according to the signal from the pressure detector, so that when the pressure in the sintering chamber increases, supply is supplied to the exhaust chamber. When the pressure in the sintering chamber decreases, the amount of inert gas supplied to the exhaust chamber is increased to keep the internal pressure of the furnace tube constant.

(Example) Hereinafter, an example of the present invention will be described based on FIGS.

FIG. 1 is a schematic configuration diagram of optical fiber Bl material production V41 in one embodiment of the present invention, 1 is a core tube of a sintering furnace,
The reactor core 11 is supplied with the To 1e gas and the C12 gas as a dehydrating agent from the lower end, and the tip of the seed rod 3 having the optical fiber preform soot 2 formed at its tip is inserted from the upper side. Further, in the furnace core tube 1, a heater 4 such as a carbon heater is installed outside at a proper position in the middle portion, and an exhaust cylinder body 5 made of, for example, quartz glass is connected to the upper side.

This exhaust cylinder body 5 has a tubular gas discharge part 6 and an inert gas introduction part 7 on the side surface, a first lid body 8 is provided on the flange part of the lower end 7, and a second lid part is provided on the upper end flange part. A body 9 is placed respectively. These first lid body 8 and second lid body 9
is in the shape of a disc divided into two in the circumferential direction, and has a through hole 10 or 11 in the center through which the seed rod 3 passes. Said first
The lid 8 separates a sintering chamber 12 formed by the furnace core tube 1 and an exhaust chamber 13 formed by the exhaust cylinder 5, and the second lid 9 separates the exhaust chamber 13 from the exhaust chamber 13. It is separated from the atmosphere. The sintering chamber 12 communicates with a conduit 14 whose one end is closed, and a pressure detector 15 with an indicator is installed in this conduit 14. This pressure detector 15
is connected to the control device 16, and a setting device 17 is connected to the connection point between the pressure detector 15 and the control device @16. The inert gas supply section 7 is connected to an inert gas supply device (not shown) via an inert gas supply channel 18, and the inert gas supply channel 18 is controlled by the control device 16.
IB flow rate: J4W1 valve 19 is installed. The tip of the gas exhaust section 6 is connected to the exhaust box 20,
This exhaust box 20 has an inert gas inlet 21 and an exhaust gas outlet 22.

The inert gas inlet 21 is connected to the inert gas supply device via a pipe (not shown), and the exhaust gas outlet 22 is connected to the exhaust treatment Q unit 24 via an exhaust flow path 23. ing. Note that 25 is an optical fiber base material made by dehydrating and vitrifying the optical fiber base material soot 2.

Next, the effect will be explained. First, the first lid 8 and the second lid 9 are removed, and the seed rod 3 having the optical fiber base material soot 2 formed at its tip is mounted on a chuck device (not shown) with the tip facing downward. Then, the seed rod 3 is lowered so that the optical fiber base material soot 2 portion is located at the upper end of the sintering chamber 12, the first lid 8 is placed on the lower end flange of the exhaust cylinder 5, and the second Place the lid 9 on the flange portion of the upper end 7 of the exhaust cylinder 5. In this state, He gas and 012 gas as a dehydrating agent are supplied to the sintering chamber 12, the sintering chamber 12 is heated by the heater 4, and the seed rod 3 is gradually lowered while rotating around its axis. The optical fiber preform soot 2 is gradually dehydrated and vitrified from the tip side to reduce its volume and become an optical fiber preform 25. At this time, the gas supplied to the sintering chamber 12 is
The gas flows into the exhaust chamber 13 through the gap between the gas and the first lid 8 and is exhausted through the gas exhaust section 6. Then, the internal pressure of the sintering chamber 12 is detected by the pressure detector 15, and a signal from the pressure detector 15 is supplied to the control device E16, whereby the control device 16 controls the flow control valve 19. That is, when the internal pressure of the sintering chamber 12 is higher than the set value set by the setting device 17,
The control device 16 throttles the flow rate control valve 19 to reduce the amount of inert gas such as He, Ar, or a mixture of these flowing into the exhaust chamber 13, and conversely, the internal pressure of the sintering chamber 12 is controlled by the setting device 17. If it is smaller than the set value, the control device 16 further opens the flow control valve 19 to increase the amount of inert gas flowing into the exhaust chamber 13. As a result, the internal pressure of the exhaust chamber 13 is controlled, and the flow of exhaust gas flowing from the sintering chamber 12 into the exhaust chamber 13 through the gap between the seed rod 3 and the first lid 8 changes, and the sintering The internal pressure of chamber 12 is kept constant. On the other hand, the mixed exhaust gas of exhaust gas and inert gas that has flowed into the inside of the exhaust box 20 from the gas discharge section 6 is mixed with H, G, Ar, etc., or a mixture thereof supplied from the inert gas inflow section 21. The exhaust gas is sucked and exhausted from the exhaust gas outlet 22 together with an inert gas consisting of gas.

In this way, since the internal pressure of the sintering chamber 12 is detected and the flow rate of the inert gas supplied to the exhaust chamber 13 is controlled accordingly, the internal pressure of the sintering chamber 12 can always be kept constant. Moreover, since inert gas is supplied to the exhaust chamber 13,
The exhaust gas in the exhaust chamber 13 is transferred to the gas exhaust section 6 by inert gas.
Since the exhaust chamber 13 is filled with inert gas, even if the internal pressure of the sintering chamber 12 fluctuates and the gas flows back into the sintering chamber 12 from the exhaust chamber 13. It is extremely likely that impurities such as air or metal ions will enter the sintering chamber 12. Moreover, in this embodiment, the exhaust box 20 is provided, and inert gas is supplied from the inert gas inlet 21 to the inside thereof, so that the inside of the exhaust chamber 13 and the exhaust box 20 are filled with inert gas. Therefore, it is possible to more reliably prevent impurities from entering the sintering chamber 12. This exhaust box 20 is particularly effective in preventing impurities such as metal ions in the pipe constituting the exhaust flow path 23 from entering the sintering chamber 12. ″ Using the apparatus of the above embodiment, He and C1 are added to the sintering chamber 12.
2 gas is supplied at 10 liters per minute, He gas is supplied at 10 liters per minute to the exhaust gas 113, and the inert gas inlet 21 is closed. When the amount of He gas supplied to the exhaust chamber 13 was controlled to change at a rate of ±5 liters per minute, the internal pressure of the sintering chamber 12 was -1.2a*H20±0.2.
Completely stable in the sw H20 range.

Furthermore, 10 liters of He and C1° gas are supplied per minute to the sintering chamber 12, 20 liters of Le gas is supplied to the exhaust chamber 13, and the inert gas inlet 21 is closed.
When controlling the supply amount of He gas to be supplied to the exhaust chamber 13 at a rate of ±5 liters per minute in response to a change in the internal pressure of sintering chamber 1 by ±0.2txtx H20,
The internal pressure of 2 is +0.4as+Ho±0.2ms H20
completely stable in the range of .

In addition, 10 liters of He and C1□ gas are supplied per minute to the sintering chamber 12, 20 liters of He gas is supplied per minute to the exhaust chamber 13, and inert gas is supplied from the inert gas inlet 21 into the exhaust box 20. Supplying 10 liters per minute, the supply amount of 1-18 gas supplied to the exhaust chamber 13 is changed at a rate of ±5 liters per minute in response to a ±0.2a*H20 change in the internal pressure of the sintering chamber 12. When controlled as follows, the internal pressure of the sintering chamber 12 was completely stabilized within the range of +1.5smHo±0.2a*H20.

(Another Example) In the above example, the reference value of the internal pressure of the sintering chamber 12 can be set using the setting device 17.
If the reference value of the internal pressure 2 is always constant and does not need to be changed, the setting device 17 may not be provided.

Further, in the above embodiment, the exhaust box 20 is provided to reliably prevent impurities from entering the sintering chamber 12, but the exhaust 1i20 is not necessarily required.

(Effects of the Invention) As explained above, according to the present invention, the internal pressure of the sintering chamber is detected by the pressure detector, and the inert gas is supplied to the exhaust chamber by controlling the flow control valve by the control device accordingly. Since the gas flow rate is controlled, the internal pressure in the sintering chamber can be kept constant at all times. Moreover, since the inert gas is supplied to the exhaust chamber through the inert gas supply channel, the exhaust gas in the exhaust chamber is pushed toward the exhaust channel by the inert gas, and the exhaust chamber is filled with inert gas. Therefore, even if the internal pressure of the sintering chamber fluctuates and gas flows back into the sintering chamber from the exhaust chamber, impurities such as air or metal ions will hardly enter the sintering chamber. From the above, it is possible to obtain an optical fiber with extremely excellent characteristics without fluctuations in the dehydration effect during the dehydration vitrification process or fluctuations in the amount of scattering dopants for adjusting the refractive index caused by fluctuations in the internal pressure of the sintering chamber. It is possible to stably produce optical fiber base materials that can achieve

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical fiber preform manufacturing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional optical fiber preform manufacturing apparatus. 1... Furnace core tube, 3... Seed rod, 5... Exhaust tube body, 8
...first lid body, 9...second lid body, 10.11.
...Through hole, 12...Sintering chamber, 13...Exhaust chamber, 15
...Pressure detector, 16...Control device, 18...Inert gas supply channel, 19...Flow rate control valve, 23...
Exhaust flow path, 24...Exhaust treatment device Patent applicant: Mitsubishi Cable Industries, Ltd. lIJ; 1 Agent: Patent attorney Tadaka Oshiki Shi, Te,, 11o...ノ2゛Figure 1 Cow e 7...・Core Vt C/, 13
...Prayer! 3... Seed stick 7
5... Pressure detector 5 -nF air+tr+s
76・-8F1111ii18...7th
Lid body 78...Inert Guess 4A bow 1st route 9...Second body
79...Flow rate 11 section valve 10.11...Through hole
23...Exhaust i-way 72...Yaki! 4”l
24...↑Air processing device lz

Claims (1)

[Claims] an exhaust cylinder connected to the upper side of a furnace core tube forming a sintering chamber of a sintering furnace to form an exhaust chamber; and a through hole through which a seed rod passes, and partitioning the sintering chamber and the exhaust chamber. a first lid body, a second lid body having a through hole through which the seed rod passes and partitioning the exhaust chamber from the outside; and an inert gas supply flow that supplies inert gas to the exhaust chamber. a flow rate control valve disposed in the inert gas supply channel, a pressure detector for detecting the pressure in the sintering chamber, and a signal from the pressure detector according to the pressure in the sintering chamber. A control device that controls the flow rate adjustment valve and an exhaust flow path that communicates the exhaust chamber and the exhaust treatment device are provided, and when the pressure in the sintering chamber increases, the amount of inert gas to be supplied to the exhaust chamber. An optical fiber preform manufacturing apparatus characterized in that the amount of inert gas supplied to the exhaust chamber is increased when the pressure in the sintering chamber is decreased.