JPH02296746A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To stabilize a burner flame and to obtain the preform with good reproducibility by introducing the external air into a reaction chamber from a specified suction hole, uniformizing the external air current and depositing soot on a core rod. CONSTITUTION:The upper lid 8 of the reaction chamber of the optical fiber preform producing device consisting of the lower chamber 6 and the upper chamber 7 is pierced with 100-150 suction holes 9 so that the area of the holes 9 is controlled to 5-10% of the area of the upper lid 8. A target rod 1 with a target 3 connected to the core rod 2 fixed at the lower end is then inserted into the chamber from an insertion hole 10 of the lid 8. The raw gas and a combustion gas are supplied to a clad burner 4 and burned, and air is uniformly sucked from the suction holes 9 and allowed to flow downward from the chamber 7. The clad soot formed by flame hydrolysis is deposited on the rod 2, the rod 2 is pulled up while being rotated, the surplus soot is discharged from an exhaust pipe 5, and an optical fiber preform is produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical fiber preform, in particular, supplying a raw material gas and a fuel gas from a clad burner to a core rod stretched to a predetermined diameter, and performing a hydrolysis reaction. The external method of depositing the generated soot to form a soot matrix is related to a method of manufacturing a matrix by a synthetic method.

[Prior Art] Excess soot generated when manufacturing an optical fiber base material by a so-called external synthesis method becomes bubbles when it adheres to the surface of a core rod. On the other hand, if excess soot adheres to the inner surface of the reaction chamber of the optical fiber preform manufacturing apparatus, the flow of the flame will change, causing the above-mentioned bubble generation. Therefore, it is necessary to stabilize the flow of the flame so that excess soot is not deposited on the inner surface of the reaction chamber as much as possible.

Therefore, there is a method of increasing the chamber internal pressure to about five times that of the conventional core rod V type, and also providing an intake hole on the side of the upper chamber, and using the flow of outside air introduced from there to prevent excess soot from adhering to the inner surface of the chamber. . Examples of structures that allow air to be taken in include, for example, a structure in which the upper chamber is split in half and outside air is introduced through the gap between the halves, or a flange for air intake is attached to the side surface of the upper chamber.

[Problems to be Solved by the Invention] However, it has been found that the method of sucking air from the side of the upper chamber creates a flow of air in a fixed direction within the chamber, which causes the burner flame to become unstable. Furthermore,
Depending on how the gap is created, the direction of air flow may be clockwise or in the direction of the half-hour hand, so even if manufactured under the same working conditions, reproducibility is poor and this can cause variations in the outer diameter of the optical fiber base material. was.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, stabilize the burner flame, and make it possible to manufacture a fully synthetic base material with good reproducibility.

[Means for Solving the Problems] A method for manufacturing an optical fiber preform according to the present invention includes supplying raw material gas and fuel gas from a clad burner to a core rod stretched to a predetermined diameter to deposit soot to form a soot preform. In doing so, an appropriate number of intake holes are formed at equal intervals throughout the upper lid of the reaction chamber, and the flow of outside air introduced into the reaction chamber through the intake holes during deposition is made uniform.

The material used for the top cover is preferably vinyl chloride or glass, considering that it will not rust and is easy to process.

C effect] An appropriate number of intake holes are drilled at equal intervals throughout the upper lid of the reaction chamber, and are uniformly distributed, so that the flow of outside air introduced into the reaction chamber during deposition through these intake holes. will be uniform with no deviation or swirl. As a result, fluctuations in the burner flame become smaller and the burner flame becomes more stable.
Excess soot is not deposited on the inner surface of the reaction chamber, improving the reproducibility of manufacturing conditions when used for a long time.

[Example] Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a schematic diagram showing an example of an optical fiber preform manufacturing apparatus that implements the manufacturing method of the present invention, and the reaction chamber is composed of a lower chamber 6 and an upper chamber 7.

A target rod 1 is inserted into the upper chamber 7 through an insertion hole 10 provided in the center of the upper lid 8, and a core rod 2 is connected to the lower end of the target rod 1. Target 3 is attached.

When manufacturing optical fiber preform, this target rod 1
．． Therefore, while rotating the core rod 2, it is gradually pulled up, and the clad burner 4 is moved inside the lower chamber 6.
The raw material gas and fuel gas are supplied and combusted, and 1 # of clad soot generated by the flame hydrolysis is deposited on the outer periphery of the core rod 2 to grow the soot base material. It is important to avoid adding excess suit. The reason for this is that if excess soot powder adheres to the core rod 2 during clad soot deposition, it will cause bubbles.

Therefore, the lower chamber 6 is provided with an exhaust pipe 5 on the side opposite to the clad burner 4, and excess soot generated during the deposition process of clad soot on the core rod 2 is exhausted from the exhaust pipe 5 on the opposite side. , to prevent soot powder from adhering to the lower chamber 6. Also 1, E part chamber 7
In order to prevent excess soot from accumulating on the upper cover 8, as shown in Fig. 2, a suitable number of intake holes 9 are provided at equal intervals throughout the upper cover area, through which air can be drawn out. The air is uniformly drawn in and flows through the upper chamber 7 from top to bottom.

Even in the conventional method, the insertion hole 1 for the target rod 1 is provided in the upper lid 8.
0 was bored, and outside air was introduced through the gap between the target rod 1 and the intake hole 9. However, when air is taken in from a single central location, air flows in a fixed direction within the upper chamber, causing the burner flame to oscillate and become unstable.

However, as mentioned above, by opening the intake holes 9 all over the upper fi 8 and taking in air from the entire top lid, the air flow after intake becomes smoother. , the fluctuation of the burner flame becomes stable.

The area of the intake hole 9 is 5 to 10% of the area of the upper cover 8.
The appropriate number is 100 to 150.

[Effects of the Invention] Since the present invention is configured as described above, the following effects are achieved.

(1) The stability of the burner flame is improved because the air flow in the reaction chamber does not become a vortex.

(2) Since the stability of the burner flame is improved, a stable soot diameter t gain in the longitudinal direction can be obtained.

(3) Reproducibility under the same manufacturing conditions is improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical fiber preform manufacturing apparatus to which the method of the present invention is applied, and FIG. 2 is a diagram showing an example of the distribution of intake holes in the upper cover thereof. In the figure, 1 is a target rod, 2 is a core rod, 3 is a target, 4 is a clad burner, 5 is an exhaust pipe, 6 is a lower chamber, 7 is a partial chamber, 8 is an upper cover, 9 is an intake hole, 10
indicates an insertion hole.

Claims (1)

[Claims] 1. When supplying raw material gas and fuel gas from a clad burner to a core rod stretched to a predetermined diameter to deposit soot and form a soot base material, an appropriate number of intake holes are placed at equal intervals throughout the upper lid of the reaction chamber. 1. A method for producing an optical fiber preform, characterized in that the flow of outside air introduced into a reaction chamber through the intake hole during deposition is made uniform.