JP2004238228A - Method for producing optical fiber glass preform with reduced outside diameter fluctuation and few defective ends by soot method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber glass preform with reduced outside diameter fluctuation and few defective parts by a soot method. <P>SOLUTION: The method for producing an optical fiber glass preform is characterized in that, in a method for producing an optical glass fiber preform comprising depositing glass soot on a rotating starting material by means of a row of a plurality of burners which reciprocates in parallel with the starting material, the reciprocating movement comprises a constant movement speed and deceleration/stop/acceleration for turning back movement, and the time t necessary to restore the constant movement speed after the start of the deceleration, stop, and acceleration and the constant movement speed v satisfy the relationship (1): t (msec)≤v (mm/min)×0.3. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a glass base material for optical fibers, and more particularly, to a method for manufacturing a glass base material by a soot method in which variation in outer diameter is small and defective portions at both ends are small.
[0002]
[Prior art]
Conventionally, methods for producing a glass base material for optical fibers include a VAD method (gas phase shaft attaching method), an MCVD method (internal attaching method), an OVD method (external attaching method), and the like. In addition to being relatively easy, a multi-burner method can be used to produce a glass base material for optical fibers at high speed, so that it is widely used. In the OVD method, a burner for depositing glass particles (hereinafter referred to as soot) on a rotating starting material is reciprocated in the longitudinal direction of the starting material to deposit soot. In particular, in order to improve productivity, the starting material is deposited. It is preferable to arrange a plurality of burners in a line in the longitudinal direction, and to make a relative reciprocating movement of the burners. In the conventional multi-burner method, the moving distance of each burner is about the distance between the burners, and the adhesion range of the soot for each burner is determined. Of the optical fiber glass base material after sintering. For this reason, it was attempted to maintain uniform soot deposition by reducing the width of the plurality of burner rows and making the entire burner amplitude (hereinafter referred to as stroke) over the entire length of the starting material. There was a disadvantage that the number of layers was small, the outer diameter was small, and many defective portions were generated (Patent Document 1, column 12).
[0003]
Further, when soot is deposited by arranging burners over almost the entire length of the starting material in order to increase the productivity of the glass base material for optical fibers, it is impossible to stroke all the burners over the entire length of the starting material, so that a large reciprocation is required. A deposition method that uses a small reciprocating motion in combination with a motion (Patent Document 2), and a method in which soot is not deposited on both the forward and return paths, but is deposited only during one-way motion using two or more burner rows (Patent Document 2). Reference 3) has been proposed.
[0004]
[Patent Document 1]
JP-A-3-228845, column 12, [Patent Document 2]
JP-A-3-228845 [Patent Document 3]
JP-A-2002-137924 [0005]
[Problems to be solved by the invention]
However, the method described in Patent Literature 2 has a problem that not only the driving section and the control system of the burner are complicated, a large-scale device is required and the cost is increased, but also maintenance and management are troublesome. Further, there is another problem that the burner drive unit must be designed to cope with the soot accumulation due to the airflow around the burner.
[0006]
Further, the method described in Patent Document 3 has a disadvantage that the number of deposited layers at both ends of the glass base material for an optical fiber is small, the outer diameter is reduced, and many defective portions are generated.
[0007]
In view of this situation, the present inventors have conducted intensive studies and found that in the reciprocating motion of the burner, the time required to accelerate from deceleration when changing the direction of motion to returning to a constant moving speed and a constant movement in the reciprocating motion. By setting the relationship with the speed to a specific range, uniform soot deposition can be obtained and the stroke of the burner can be reduced, and as a result, the outer diameter variation is small and the defective portion at both ends is small, and the glass base material for optical fiber is small. Have been obtained, and the present invention has been completed. That is,
[0008]
An object of the present invention is to provide a method of manufacturing a glass preform for an optical fiber by a soot method with a small variation in outer diameter and a small number of defective portions at both ends.
[0009]
[Means for Solving the Problems]
The present invention for achieving the above object provides a method of manufacturing a glass preform for an optical fiber in which glass fine particles are deposited by a plurality of burner rows reciprocating in parallel to a rotating starting material, wherein the reciprocating movement is constant. The deceleration / stop / acceleration for turning back the moving speed and the return time t until the deceleration starts, stops, and accelerates to a certain moving speed after the acceleration are given by the following equation (1).
[0010]
(Equation 1)
t (msec) ≦ v (mm / min) × 0.3 (1)
The present invention relates to a method for producing a glass preform for an optical fiber, characterized by being in the range represented by
[0011]
Examples of the starting material used in the above manufacturing method include a core rod prepared by the MCVD method or the VAD method, a quartz glass rod having a clad portion deposited thereon, or a heat-resistant rod or tube such as a ceramic. The starting material is rotated, and soot is deposited by reciprocating a plurality of burners against the surface.In the reciprocating motion, the burner moves at a constant speed, and then decelerates, stops, and accelerates in order to turn back. . In the present invention, the return time t to the constant moving speed after the start, stop, and acceleration of the deceleration of the reciprocating motion is expressed by the following formula (3) for a constant moving speed v
[0012]
[Equation 3]
t (msec) ≦ v (mm / min) × 0.3 (3)
Must be within the range represented by. By setting the content in the above range, uniform soot deposition can be obtained, and defective portions generated at both ends can be reduced. Particularly, when the burner interval is 50 to 150 mm and the stroke of the burner is twice or less the burner interval, the number of defective portions at both ends where the number of deposited layers is small and the outer diameter is small is further reduced, which is preferable.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic diagram of the OVD method of the present invention. 1 is a porous soot body, 2 is a starting material, 3 is a plurality of burner rows, 4 is a flame, 5 is a raw material gas supply pipe, 6 and 7 are combustion gas supply pipes, and 8 is a burner interval. The plurality of burner rows 3 are juxtaposed in series with the starting material and move parallel to the starting material as shown in FIGS. Then, the raw material gas 5 and the combustion gases 6, 7 are introduced into each burner, a flame 4 is formed, soot is formed by flame hydrolysis, and the soot is deposited on the starting material to produce the soot body 1. In the reciprocating motion of the burner, it is important that the return time t to a constant moving speed after the start, stop, and acceleration of deceleration and the constant moving speed v are within the range of Expression (3). In particular, a reciprocating motion in which the burner stroke is twice or less the burner interval and the burner interval is in the range of 50 to 150 mm is preferable. FIGS. 2A and 2B schematically show an example in which the burner stroke is twice the burner interval. In FIG. 2A, each of the burners (1) to (6) moves with a stroke 9 twice the burner interval 8. FIG. 2B shows the porous soot body obtained by this reciprocating motion. Reference numeral 10 denotes a stationary part, and 11 denotes a defective part. As is clear from FIG. 2B, the defective portion 11 is small, and the variation in the outer diameter is small. However, if the burner stroke 9 is three times the burner interval 8, the defective portion 11 becomes large as shown in FIGS. 3 (a) and 3 (b).
[0014]
Examples of the raw material gas include silicon tetrachloride and an organic silicon compound. Examples of the combustion gas include oxygen gas, hydrogen gas, methane gas, ethylene gas, and propane gas, or a mixture thereof.
[0015]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.
[0016]
Example 1
OVD with a burner interval 8 of 100 mm, a burner stroke 9 of 200 mm, a reciprocating speed of 400 mm / min, and a time required for reversing the reciprocating motion of 80 msec, for flame-hydrolyzing high-purity silicon tetrachloride with an oxyhydrogen flame. Porous soot was deposited on a quartz glass rod as a starting material 2 by a method to obtain a porous soot body 1. When the outer diameter was measured with a laser outer diameter measuring device at a pitch of 10 mm, the length of the defective portions 11 at both ends of the soot body whose outer diameter was 90% or less of the average outer diameter of the entire porous soot body was 120 mm, respectively. there were. In addition, the maximum outer diameter of the stationary portion 10 is 101.1% and the minimum outer diameter of the stationary portion is 98.97% of the average outer diameter of the stationary portion of the porous soot body. It was within about 1% of the diameter. Further, the irregularities generated on the surface were sufficiently small, and the inside of the glass base material after sintering was visually inspected. As a result, there was no uneven deposition and no generation of bubbles.
[0017]
Comparative Example 1
In the same manner as in Example 1, except that the burner interval 8 was 100 mm, the burner stroke 9 was 200 mm, the reciprocating motion speed was 400 mm / min, and the time required for the reciprocating motion to return was 80 msec. When the outer diameter of the porous soot body was measured and the outer diameter thereof was 90% or less with respect to the average outer diameter of the entire porous soot body, the length of the defective portions 11 at both ends of the porous soot body was as small as 130 mm. The stationary part 10 of the porous soot body has a stationary part maximum outer diameter of 102.9% and a stationary part minimum outer diameter of 97.34% with respect to the stationary part average outer diameter. It was as large as about 3% of the diameter. Further, when the glass base material after sintering was visually inspected, it was found that there was uneven deposition inside the glass base material, and peripheral bubbles were generated at the portion where the outer diameter of the glass base material became large.
[0018]
Comparative Example 2
A porous soot body was produced in the same manner as in Example 1 except that the burner interval 8 was 100 mm, the burner stroke 9 was 400 mm, the reciprocating speed was 400 mm / min, and the time required for the reciprocating motion was 80 msec. 1 was manufactured and its outer diameter was measured. As a result, the length of the defective portion 11 at both ends where the outer diameter was 90% or less of the average outer diameter of the entire porous soot body was as large as 340 mm. The stationary part 10 of the porous soot body has a stationary part maximum outer diameter of 101.3% and a stationary part minimum outer diameter of 98.86% with respect to the stationary part average outer diameter. It was smaller than about 1% of the average outer diameter. When the glass base material after sintering was visually inspected, no bubbles were found inside the glass base material for optical fibers.
[0019]
Comparative Example 3
A porous soot body was produced in the same manner as in Example 1 except that the burner interval 8 was 200 mm, the burner stroke 9 was 300 mm, the reciprocating speed was 400 mm / min, and the time required for the reciprocating motion was 80 msec. Was manufactured and its outer diameter was measured. As a result, the defective portion at both ends where the outer diameter was 90% or less of the average outer diameter of the entire porous soot body was 230 mm. The steady portion of the porous soot body has a maximum constant portion outer diameter of 103.4% and a constant portion minimum outer diameter of 97.10% with respect to the constant portion average outer diameter. It was as large as about 3% of the diameter. Further, when the glass base material after sintering was visually inspected, circumferential bubbles were generated inside the glass base material for optical fiber.
[0020]
【The invention's effect】
The present invention is a method for producing a glass preform for optical fiber by the OVD method, in which a glass preform for optical fiber can be produced at a low cost with few defective portions at the ends, and further, the uniformity of the steady portion is excellent, This is a production method with high industrial value.
[Brief description of the drawings]
FIG. 1 shows a schematic diagram of the OVD method of the present invention.
FIG. 2 is a schematic view of a steady portion and a defective portion when the burner stroke is twice the burner interval in the manufacturing method of the present invention.
FIG. 3 is a schematic diagram of a steady portion and a defective portion when the burner stroke is three times the burner interval.
[Explanation of symbols]
1: Porous soot body 2: Starting material 3: Plural burner rows 4: Flame 5: Source gas supply pipes 6, 7: Combustion gas supply pipe 8: Burner interval 9: Burner is at maximum stroke position 10: Steady state of the soot body Part 11: defective part of soot body [1] to [6]: burner number

Claims (2)

In a method for manufacturing a glass preform for an optical fiber, in which glass fine particles are deposited by a plurality of burner rows reciprocating in parallel with a rotating starting material, deceleration, stop, and acceleration for the reciprocation to return at a constant moving speed. The return time t required to reach a constant moving speed after the start, stop, and acceleration of the deceleration is equal to the constant moving speed v by the formula (1).
(Equation 1)

A method for producing a glass preform for an optical fiber, characterized by being in the range represented by: 2. The method according to claim 1, wherein the interval between the burners in the plurality of burners is 50 to 150 mm, and the amplitude of the reciprocating motion of the plurality of burners is not more than twice the interval between the burners.

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