JP2007210837A - Apparatus for producing porous glass preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus that enables production of a porous glass preform by a VAD method, efficiently discharges fine glass particles which are not deposited on the porous preform, can stably deposit the fine glass particles without causing turbulent air flow in a chamber and have less generation of bubbles or foreign materials. <P>SOLUTION: In the production apparatus, a reaction vessel has an upper deposition chamber having the air supply and discharge openings, a lower deposition chamber having an air supply opening, and an upper chamber in which the porous preform formed by deposition is pulled and stored. The floor face of the upper deposition chamber is set in height between the lower end of a straight body and the tip part of deposition of the depositing preform, and a connection opening for connecting the upper and lower deposition chambers is set on the floor of the upper chamber. Assuming that the diameter of the connection opening is A, and the diameter of the porous preform passing through the connection opening is B, the ratio of B/A satisfies the inequality, 0.05≤B/A≤0.6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glass base material for a large optical fiber (hereinafter simply referred to as an optical fiber base material) used for manufacturing an optical fiber, in particular, glass fine particles generated by a flame hydrolysis reaction of a glass raw material in a burner flame. It is related with the manufacturing apparatus of the porous glass base material which deposits and manufactures.

  The VAD method is well known as a method for manufacturing an optical fiber preform. This method attaches a starting member to a rotating and rising shaft supported by the upper structure of the apparatus and hangs down in a reaction chamber, and generates glass particles generated by a core deposition burner and a cladding deposition burner installed in the reaction chamber. By depositing on the tip of the starting member, a porous glass base material (hereinafter simply referred to as a porous base material) composed of a core layer and a clad layer is manufactured.

  Not all of the generated glass particles are deposited, and undeposited glass particles that have not been deposited are generated throughout the production. Most of the unadhered glass particles are discharged out of the reaction chamber through an exhaust port separately provided in the reaction chamber together with other gases such as exhaust gas.

  However, part of the glass particles adheres to the ceiling and side walls in the reaction chamber after being generated by the burner flame and discharged. The fine glass particles adhering / depositing on the ceiling or side wall may peel off and drop and adhere to the porous base material being manufactured, which may cause bubbles and foreign matter in the optical fiber base material after forming into a transparent glass. .

  In recent years, cost reduction has been demanded, and there is an urgent need to increase the size of optical fiber preforms. In order to increase the optical fiber preform to be manufactured, it is necessary to increase the raw material input amount. However, as the raw material supply amount increases, even if the deposition efficiency does not change, the amount of excess glass fine particles not deposited increases. As a result, the frequency with which the glass particles adhering to the inner wall of the reaction chamber are peeled off and dropped also increases.

In order to solve such a problem, according to Patent Document 1, a slit-like air supply port is provided along the vicinity of the ceiling of the reaction chamber side wall surface on which the burner is installed, and the side facing this air supply port A method of reducing the adhesion of glass particles, that is, soot adhering to the ceiling by providing an exhaust port on the wall surface is shown.
JP2002-193633

  However, the method according to Patent Document 1 cannot avoid the soot adhesion to the ceiling, which is the back side of the porous base material, as viewed from the air supply port side, and it is difficult to eliminate the peeling of the accumulated soot. Therefore, if you try to avoid soot adhesion by increasing the exhaust efficiency and increasing the supply and exhaust volume, the airflow in the chamber will be disturbed, the flame of the core deposition burner will be disturbed, and stable deposition will not be possible. As a result, a new problem arises that striae occur in the obtained optical fiber preform and the optical characteristics fluctuate in the longitudinal direction.

  An object of the present invention is to provide a glass base material in a device for producing a porous base material by the VAD method, which has a high discharge efficiency of glass fine particles not attached to the porous base material and does not cause turbulence in the air flow in the chamber. It is an object of the present invention to provide an apparatus for producing a porous base material that can be stably deposited and has less generation of bubbles and foreign matters.

  The apparatus for producing a porous base material of the present invention supplies a raw material for glass, a combustible gas, and an auxiliary combustible gas to a burner, and deposits fine glass particles generated by a flame hydrolysis reaction of the glass raw material to form a porous base material. In an apparatus to be manufactured, an upper deposition chamber having an air supply port and an exhaust port, a lower deposition chamber having an air supply port, and a porous base material formed by deposition are pulled up and stored above the upper deposition chamber. In a reaction vessel having an upper chamber, the floor surface of the upper deposition chamber is installed at a height between the lower end of the straight body of the porous glass base material being deposited and the deposition tip portion, Is provided with a connection port for connecting the upper deposition chamber and the lower deposition chamber, where the opening diameter of the connection port is A and the diameter of the porous base material passing through the connection port is B, B / A is expressed by the formula 0.05 ≦ B It is characterized by satisfying /A≦0.6.

In the apparatus of the present invention, the distance from the center of the connection port to the inner wall of the upper deposition chamber is preferably A or more, and the distance from the center of the connection port to the inner wall of the lower deposition chamber is preferably 0.7 A or more. The connection port between the upper deposition chamber and the lower deposition chamber has a structure in which the inner surface thereof is chamfered or curved to be removable from the upper deposition chamber floor. Further, when the angle when the exhaust port and the air supply port of the upper deposition chamber look up from the upper end of the exhaust port to the upper end of the air supply port provided on the opposite wall is assumed to be θ, the equation 5 ° ≦ θ Each is provided at a position satisfying ≦ 50 °.
The gas supplied from the air supply port uses indoor air that has passed through a filter. The pressure in the reaction vessel is controlled by an automatic pressure control device installed downstream of the exhaust port.

  According to the porous base material manufacturing apparatus of the present invention, even when a large porous base material is manufactured, since the flame of the deposition burner is stable, stable optical characteristics can be obtained in the longitudinal direction. In addition, since the discharge efficiency of the glass fine particles is high, an optical fiber preform with less generation of bubbles and foreign matters can be obtained.

As a result of intensive studies, in order to increase the discharge efficiency of unadhered glass particles and stabilize the flame of the deposition burner even when the air flow in the chamber becomes faster, the height of the opening at the connection port of the upper and lower deposition chambers can be increased. It was found that the condition of the aperture diameter is important.
The present invention clarifies these conditions.

Hereinafter, the present invention will be described in detail with reference to FIGS.
FIG. 1 is a longitudinal sectional view schematically showing a production apparatus of the present invention. A production apparatus for a porous base material 1 includes an upper deposition chamber 2 having an exhaust port 5 and an air supply port 6, and an air supply port 7. A reaction vessel 16 having a lower deposition chamber 3 and an upper chamber 4 in the upper portion of the upper deposition chamber 2 for pulling up and storing the porous base material 1 formed by deposition is provided. The floor surface 11 of the upper deposition chamber 2 is installed at a height position between the lower end 13 of the straight body portion and the deposition tip portion 14 of the porous base material 1 being deposited, A connection port 12 for connecting the upper deposition chamber 2 and the lower deposition chamber 3 is provided.
The core of the porous base material 1 is deposited by the core deposition burner 8 in the lower deposition chamber 3, and a part of the cladding is deposited by the cladding deposition burner 9. Further, in the upper deposition chamber 2, the cladding is deposited by the cladding deposition burner 10 until the cladding reaches a predetermined diameter.

FIG. 2 is an enlarged schematic longitudinal sectional view showing the relationship between the opening diameter of the connection port 12 and the diameter of the porous base material 1, where the opening diameter of the connection port 12 is A and the porous base material passing through the connection port 12. When the diameter of 1 is B, the connection port 12 is provided so that B / A satisfies the formula 0.05 ≦ B / A ≦ 0.6. Since the porous base material 1 is pulled up in accordance with its growth due to deposition, the diameter B of the porous base material 1 passing through the connection port 12 is kept substantially constant during manufacture.
As a result, a uniform air flow is formed along the shape of the porous base material 1 from the front end portion of the porous base material 1 to the straight body portion. As a result, even when the supply / exhaust amount of the upper deposition chamber 2 is increased in order to increase the exhaust efficiency of the excessive glass fine particles that have not adhered, the frequency at which the air flow in the upper deposition chamber 2 enters the lower deposition chamber 3 is effective. Therefore, the flame of the core deposition burner 8 can be stabilized. Furthermore, it is possible to suppress the adhesion of excess glass particles near the connection port 12 between the upper deposition chamber 2 and the lower deposition chamber 3. If B / A is less than 0.05, the frequency of the turbulent airflow in the upper deposition chamber 2 entering the lower deposition chamber 3 increases. On the other hand, when B / A exceeds 0.6, the gap between the porous base material 1 and the connection port 12 is narrow, so that unadhered glass particles generated in the lower deposition chamber 3 are likely to adhere to the connection port 12.

The distance from the center of the connection port 12 to the inner wall of the upper deposition chamber 2 is preferably A or more, and the distance from the center of the connection port 12 to the inner wall of the lower deposition chamber 3 is preferably 0.7 A or more, Even when the air flow in the upper deposition chamber 2 flows into the lower deposition chamber 3, it serves as a buffer due to the large volume of the lower deposition chamber 3, and the influence of the core deposition burner 8 on the flame is reduced. Is possible.
In addition, when the distance from the center of the connection port 12 to the inner wall of the upper deposition chamber 2 is set to A or more, the supply amount of raw materials increases with the increase in the size of the optical fiber preform, and surplus glass particles increase. However, the adhesion of excess glass particles to the upper deposition chamber wall can be effectively suppressed.

Since the glass particles that have not adhered to the porous base material are included in the airflow, the glass particles adhere to and accumulate on the connection port 12 by the airflow passing through the connection port 12, as shown in FIG. Furthermore, by providing the chamfer 17 or the curved surface 18 on the inner surface of the connection port 12, it is possible to suppress the excessive glass fine particles from adhering to the inner surface of the connection port 12 and growing.
FIG. 3 shows an example in which chamfering 17 is performed on the opening of the connection port 12 provided on the floor of the upper deposition chamber 2, and FIG. 4 shows an example in which a curved surface 18 is provided on the opening of the connection port 12. ing.

  Further, as shown in FIG. 5 as an example, by providing a detachable connection port 15 so that a portion constituting the connection port 12 can be removed and replaced, cleaning and washing can be easily performed. In addition, by simply exchanging these parts, the opening diameter of the connection port 12 and the height of the connection port 12 can be easily changed according to the size of the porous base material to be manufactured without replacing the reaction vessel 16. It becomes possible.

  Furthermore, as shown in FIG. 6, in the upper deposition chamber 2, the angle θ when looking up from the upper end of the exhaust port 5 to the upper end of the air supply port 6 provided on the wall on the burner side facing this is 5 °. By providing the exhaust port 5 and the air supply port 6 so as to satisfy ≦ θ ≦ 50 °, excessive glass fine particles not attached to the porous base material 1 do not reach the ceiling 19 on the exhaust port side, It becomes possible to discharge from the exhaust port 5, and it is possible to reduce excess glass fine particles adhering to the ceiling on the back side of the porous base material 1 when viewed from the burner side.

In addition, since the pressure in the reaction vessel affects the state of the airflow in the combustion frame and the chamber, it is necessary to manage the inside of the vessel so as to maintain a predetermined pressure. For this, an automatic pressure control device ( It is preferable to install and control the exhaust port 5 downstream of the exhaust port 5.
In addition, the room air which passed the filter is used for the gas supplied from the air inlets 6 and 7. FIG.
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to these, Various aspects are possible.

Example 1
Using the reaction vessel shown in FIG. 1, a porous preform for optical fiber was manufactured under the following conditions.
2 [m ³ / min] of air is supplied from the air inlet 6 of the upper deposition chamber 2, and 100 [l / min] of air is supplied from the air inlet 7 of the lower deposition chamber 3, and the core deposition burner 8 was supplied with SiCl ₄ 450 [ml / min] and GeCl ₄ 25 [ml / min] as source gases. SiCl ₄ 1.0 [l / min] and 3.0 [l / min] were supplied to the cladding deposition burners 9 and 10 as source gases, respectively. Further, each deposition burner was supplied with H _{2 as} a combustion gas and O ₂ as an auxiliary combustion gas.

  The floor surface 11 of the upper deposition chamber 2 was placed so as to be at a height between the lower end 13 of the straight body portion and the deposition tip portion 14 of the porous base material 1. When the opening of the connection port 12 has an opening diameter of A [mm] and the diameter of the porous base material 1 passing through the connection port 12 is B [mm], B / A is 0.05 ≦ B / A ≦ It was set to be in the range of 0.6.

After depositing glass particles for 24 hours, the amount of deposited glass particles on the ceiling, wall, and connection port in the upper chamber 4 and the upper and lower deposition chambers was examined. There was no such thing.
When the obtained porous base material 1 was dehydrated and made into a transparent glass, the presence of bubbles and foreign matters was not recognized. When the refractive index distribution of the optical fiber preform thus obtained was measured, it was stable in the longitudinal direction and had excellent optical characteristics.

(Comparative Example 1)
Glass particulates were deposited under the same gas conditions as in Example 1. At this time, if the floor surface 11 of the upper deposition chamber 2 is installed above the lower end of the straight body of the porous base material 1 or if the opening diameter of the connection port 12 is B / A> 0.6, the core Although the flame of the deposition burner was stable, a large amount of excess soot adhered to the vicinity of the connection port and peeled off. Moreover, when it was transparent vitrified, many bubbles were generated.

(Comparative Example 2)
Glass particulates were deposited under the same gas conditions as in Example 1. At this time, when the floor surface 11 of the upper deposition chamber 2 is installed below the deposition tip of the porous base material 1 or when the opening diameter of the connection port 12 is B / A <0.05, the connection port The amount of surplus soot attached in the vicinity was kept small, there was no peeling / falling, and there was no generation of bubbles after vitrification.
However, it was not possible to prevent the air flow in the upper deposition chamber 2 from entering the lower deposition chamber 3, and the flame of the core deposition burner 8 was greatly disturbed. Therefore, when the refractive index distribution was measured, the distribution characteristics changed in the longitudinal direction, and strong striae were generated.

(Example 2)
The floor surface 11 of the upper deposition chamber 2 is installed so that it is at the height of the intermediate point between the lower end of the straight body portion of the porous base material and the deposition tip portion. Under the same gas conditions as in Example 1, B / A = 0.3 As a deposit for 24hrs.
Here, the exhaust port 5 has an angle θ of 5 ° ≦ θ ≦ 50 ° when looking up from the upper end of the exhaust port 5 of the upper deposition chamber 2 to the upper end of the air supply port 6 provided on the burner side wall. When the air supply port 6 is provided, surplus glass particles can be discharged from the exhaust port 5 without floating up to the ceiling 19, and the glass particles to the ceiling 19 on the back side of the porous base material as viewed from the burner side. The thickness of the adhesive was greatly reduced from the conventional 10 mm to 2 mm. Further, since the glass particles do not stay in the lower part of the upper deposition chamber, adhesion to the lower part of the upper deposition chamber side wall was not recognized.

(Comparative Example 3)
Glass particulates were deposited under the same gas conditions as in Example 2. At this time, when the exhaust port 5 and the air supply port 6 are provided so that the angle θ at which the burner side air supply port upper end is looked up from the exhaust port upper end of the upper deposition chamber 2 is 5 °> θ, excessive glass fine particles are formed. Since it floats to the ceiling 19 of the upper deposition chamber 2 before being discharged from the exhaust port 5, a large amount of glass particles adhere to the ceiling 19, especially the ceiling 19 on the back side of the porous base material when viewed from the burner side. Reached 8mm.

(Comparative Example 4)
Glass particulates were deposited under the same gas conditions as in Example 2. At this time, when θ> 50 °, the surplus glass fine particles adhering to the ceiling 19 disappeared, but the surplus glass fine particles stayed in the lower part of the upper deposition chamber 2 and surplus below the side wall of the upper deposition chamber 2. Glass fine particles adhered, and the thickness reached 4 mm.

  Contributes to quality improvement and cost reduction of optical fiber preform.

It is a longitudinal cross-sectional view which shows the outline of the manufacturing apparatus of this invention. It is an expansion schematic longitudinal cross-sectional view which shows the relationship between the opening diameter of a connection port, and the diameter of a porous preform | base_material. It is a schematic longitudinal cross-sectional view which shows the example which chamfered to the opening part of the connection port. It is a schematic longitudinal cross-sectional view which shows the example which gave the curved surface process to the opening part of the connection port. It is a schematic longitudinal cross-sectional view which shows an example of the manufacturing apparatus which has a detachable connection port. It is a schematic longitudinal cross-sectional view which shows the relationship between an exhaust port and an air supply port.

Explanation of symbols

1: porous matrix,
2: Upper deposition chamber,
3: Lower deposition chamber,
4: Upper room,
5: Exhaust port
6, 7: Air inlet,
8: Burner for core deposition,
9, 10: Clad deposition burner,
11: floor surface,
12: Connection port
13: Straight barrel lower end,
14: Deposition tip
15: Detachable connection port,
16: reaction vessel,
17: Chamfering,
18: curved surface,
19: Ceiling.

Claims (8)

  In an apparatus for supplying a glass raw material, a flammable gas and a combustible gas to a burner, and depositing glass fine particles produced by a flame hydrolysis reaction of the glass raw material to produce a porous glass base material, an air supply port and an exhaust port A reaction vessel having an upper deposition chamber having a lower deposition chamber having an air supply port, and an upper chamber at the upper portion of the upper deposition chamber for pulling up and storing a porous glass base material formed by deposition. The floor of the deposition chamber is installed at a height between the bottom of the straight body of the porous glass base material being deposited and the top of the deposition chamber, and the upper and lower deposition chambers are connected to the floor of the upper deposition chamber. A connection port is provided, and when the opening diameter of the connection port is A and the diameter of the porous glass base material passing through the connection port is B, B / A satisfies the formula 0.05 ≦ B / A ≦ 0.6 An apparatus for producing a porous glass base material.   The apparatus for producing a porous glass base material according to claim 1, wherein the distance from the center of the connection port to the inner wall of the upper deposition chamber is A or more.   The apparatus for producing a porous glass base material according to claim 1 or 2, wherein a distance from the center of the connection port to the inner wall of the lower deposition chamber is 0.7 A or more.   The manufacturing apparatus of the porous glass base material in any one of the Claims 1 thru | or 3 by which the inner surface of the said connection port was processed into the chamfering or the curved surface.   The manufacturing apparatus of the porous glass base material in any one of Claims 1 thru | or 4 with which the said connection port has a structure removable from an upper deposition chamber floor part.   When the angle when the exhaust port and the air supply port of the upper deposition chamber look up from the upper end of the exhaust port to the upper end of the air supply port is θ, θ is expressed by the equation 5 ° ≦ θ ≦ The apparatus for producing a porous glass base material according to claim 1, which is provided at a position satisfying 50 °.   The apparatus for producing a porous glass base material according to claim 1, wherein the gas supplied from the air supply port is room air that has passed through a filter. The apparatus for producing a porous glass base material according to claim 1, wherein the pressure in the reaction vessel is controlled by an automatic pressure control device installed downstream of the exhaust port.

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