JP4169260B2 - Manufacturing method of glass preform for optical fiber by soot method with small outer diameter fluctuation and few defective parts at both ends - Google Patents

Description

[0001]
[Industrial application fields]
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 fluctuations in the outer diameter are small and there are few defective portions at both ends.
[0002]
[Prior art]
Conventionally, methods for producing glass preforms for optical fibers include the VAD method (vapor phase shaft attachment method), the MCVD method (internal attachment method), the OVD method (external attachment method), and the OVD method is particularly large. In addition to being relatively easy, a glass preform for optical fibers can be manufactured at a high speed by using a multi-burner, which is widely used. In the OVD method, a soot is deposited by reciprocating a burner for depositing glass fine particles (hereinafter referred to as soot) on a rotating starting material in the longitudinal direction of the starting material. In particular, in order to improve productivity, the starting material is used. It is preferable that a plurality of burners are arranged in a line in the longitudinal direction of the slab and the multi burners are reciprocated relatively. In the conventional multi-burner, the travel distance of each burner is about the interval of the burner, and the soot adhesion range for each burner is determined, so an uneven deposition portion occurs at the boundary between adjacent burners and soot adhesion. There are drawbacks such as fluctuations and bubbles generated inside the glass preform for optical fiber after sintering. For this reason, it was attempted to maintain the uniformity of soot adhesion by narrowing the width of multiple burner rows and making all the burners amplitude (hereinafter referred to as stroke) over the entire length of the starting material. There was a defect that the number of layers was small, the outer diameter was small, and many defective portions were generated (Patent Document 1, column 12).
[0003]
In addition, in order to increase the productivity of the optical fiber glass base material, when soot is deposited by arranging the burners over almost the entire length of the starting material, it is impossible to stroke all the burners over the entire length of the starting material. Deposition method that uses small reciprocating motions in combination with motion (Patent Document 2), or a method of depositing only in one direction of motion using two multiple burner rows instead of depositing soot on both the forward and return paths (patent) Document 3) has been proposed.
[0004]
[Patent Document 1]
JP-A-3-228845, column 12, [Patent Document 2]
JP-A-3-228845 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-137924
[Problems to be solved by the invention]
However, in the method described in Patent Document 2, not only the burner drive unit and the control system are complicated, a large-scale apparatus is required and the cost is high, but also the maintenance work is troublesome and has become a problem. Furthermore, since the airflow around the burner adversely affects the soot deposition, there has been a problem that the burner drive unit must be designed to cope with it.
[0006]
Further, the method described in Patent Document 3 has a drawback in that the number of deposited layers at both ends of the glass preform for optical fiber is small and the outer diameter is small, resulting in many defective portions.
[0007]
In view of such a current situation, the present inventors have conducted intensive research. As a result, in the reciprocating motion of the burner, the time to accelerate from deceleration when changing the motion direction to return to a constant moving speed and the constant motion in the reciprocating motion By making the relationship with the speed within a specific range, uniform soot deposition can be obtained and the burner stroke can be reduced. As a result, the outer diameter fluctuation is small and there are few defective parts at both ends. And the present invention has been completed. That is,
[0008]
An object of this invention is to provide the manufacturing method of the glass preform for optical fibers by the soot method with little fluctuation | variation in an outer diameter, and few defective parts of both ends.
[0009]
[Means for Solving the Problems]
To achieve the above object, the present invention provides a glass base material for an optical fiber in which glass fine particles are deposited by a plurality of burner arrays reciprocating in parallel with a rotating starting material, wherein the reciprocating motion is constant. The return time t from the moving speed and the deceleration, stop, and acceleration for returning to the constant moving speed after the start, stop, and acceleration of the deceleration with respect to the constant moving speed v is expressed by Equation (1).
[0010]
[Formula 1]
t (msec) ≦ v (mm / min) × 0.3 (1)
It is related with the manufacturing method of the glass preform | base_material for optical fibers characterized by being in the range represented by these.
[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 cladding portion deposited thereon, or a heat-resistant rod or tube such as ceramics. The starting material is rotated and the soot is deposited by reciprocating a plurality of burners with respect to the surface. In the reciprocating motion, the burner moves at a constant speed, and then decelerates, stops, and accelerates to return. . In the present invention, the return time t to the constant moving speed after the start, stop, and acceleration of the reciprocating motion is expressed by the equation (3).
[0012]
[Formula 3]
t (msec) ≦ v (mm / min) × 0.3 (3)
It is indispensable to be in the range represented by. By setting the amount within the above range, uniform soot deposition can be obtained, and defective portions generated at both ends can be reduced. In particular, when the burner interval is 50 to 150 mm and the burner stroke is twice or less the burner interval, the number of deposited layers is small and the number of defective portions at both ends where the outer diameter is small is further reduced.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A schematic diagram of the OVD method of the present invention is shown in FIG. 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. As shown in FIGS. 2 and 3, the plurality of burner rows 3 are juxtaposed in series with the starting material and move in parallel to the starting material. Then, the raw material gas 5 and the combustion gases 6 and 7 are introduced into each burner, a flame 4 is formed, soot is formed by flame hydrolysis, and 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 the constant movement speed after the start, stop and acceleration of the burner and the constant movement speed v are within the range of the expression (3). In particular, a reciprocating motion in which the stroke of the burner is not more than twice 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, the burners {circle around (1)} to {circle around (6)} each move with a stroke 9 twice the burner interval 8. The porous soot body obtained by this reciprocating motion is shown in FIG. 10 is a stationary part and 11 is a defective part. As is apparent from FIG. 2B, the defective portion 11 is small, and the outer diameter fluctuation is small. However, when 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 source gas include silicon tetrachloride, an organosilicon compound, and examples of the combustion gas include any one of oxygen gas, hydrogen gas, methane gas, ethylene gas, and propane gas, or a mixture thereof.
[0015]
【Example】
EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.
[0016]
Example 1
OVD with high-purity silicon tetrachloride flame hydrolyzing with oxyhydrogen flame, burner interval 8 is 100mm, burner stroke 9 is 200mm, reciprocating speed is 400mm / min, reciprocating time is 80msec. Porous soot was deposited on the quartz glass rod of the starting material 2 by the 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 portion 11 at both ends of the soot body with an outer diameter of 90% or less with respect to the average outer diameter of the entire porous soot body was 120 mm. there were. Further, the maximum outer diameter of the stationary part 10 is 101.1% and the minimum outer diameter of the stationary part is 98.97% with respect to the stationary part average outer diameter 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 sintered glass base material was visually inspected, but there was no uneven deposition and no bubbles were generated.
[0017]
Comparative Example 1
In Example 1, the porous soot body 1 was made 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 speed was 400 mm / min, and the time required for reciprocating folding was 80 msec. The outer diameter of the porous soot body was measured and the outer diameter relative to the average outer diameter of the entire porous soot body was 90% or less. The length of the defective portion 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 about 3% larger than the diameter. Further, when the glass base material after sintering was visually inspected, there was an uneven deposition inside the glass base material, and circumferential bubbles were generated in the portion where the outer diameter of the glass base material was increased.
[0018]
Comparative Example 2
A porous soot body in the same manner as in Example 1 except that the burner interval 8 is 100 mm, the burner stroke 9 is 400 mm, the reciprocating speed is 400 mm / min, and the time required for reciprocating folding is 80 msec. 1 was manufactured and the outer diameter thereof was measured, and the length of the defective portion 11 at both ends where the outer diameter was 90% or less with respect to the average outer diameter of the entire porous soot body was as large as 340 mm. The stationary part 10 of this porous soot body has a steady part maximum outer diameter of 101.3% and a steady part minimum outer diameter of 98.86% with respect to the steady part average outer diameter, and the steady part outer diameter fluctuation is the steady part. The average outer diameter was smaller than about 1%. Moreover, 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 in the same manner as in Example 1, except that the burner interval 8 is 200 mm, the burner stroke 9 is 300 mm, the reciprocating speed is 400 mm / min, and the time required for the reciprocating folding is 80 msec. When the outer diameter was measured, the defective portion at both ends where the outer diameter was 90% or less with respect to the average outer diameter of the entire porous soot body was 230 mm. The stationary part of this porous soot body has a steady part maximum outer diameter of 103.4% and a steady part minimum outer diameter of 97.10% with respect to the steady part average outer diameter. It was about 3% larger than the diameter. Moreover, when the glass base material after sintering was visually inspected, circumferential bubbles were generated inside the glass base material for optical fibers.
[0020]
【The invention's effect】
The present invention is a method for producing a glass preform for an optical fiber by an OVD method, which can produce a glass preform for an optical fiber at a low cost with few defective parts at the end, and is excellent in uniformity of a stationary part, This is a manufacturing 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 diagram of a stationary part and a defective part when the stroke of the burner 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 stroke of the burner is three times the burner interval.
[Explanation of symbols]
1: Porous soot body 2: Starting material 3: Multiple burner rows 4: Flame 5: Raw material gas supply pipe 6, 7: Combustion gas supply pipe 8: Burner interval 9: Burner has maximum stroke position 10: Steady body steady state Part 11: Bad part of soot body (1) to (6): Burner number

Claims (2)

In a method for manufacturing a glass preform for optical fiber in which glass particles are deposited by a plurality of burner arrays reciprocating in parallel with a rotating starting material, the reciprocating motion is decelerated, stopped, and accelerated so that the reciprocating motion returns with a constant moving speed. The return time t until the constant moving speed after starting, stopping and accelerating the deceleration is equal to the constant moving speed v.
[Formula 1]
t (msec) ≦ v (mm / min) × 0.3 (1)
The manufacturing method of the glass preform | base_material for optical fibers characterized by being in the range represented by these. The method for producing a glass preform for an optical fiber according to claim 1, wherein the interval between the burners in the plurality of burner rows is 50 to 150 mm, and the amplitude of the reciprocating motion of the plurality of burners is not more than twice the burner interval.

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