JP3169503B2 - Method for producing porous glass preform for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a porous glass preform for an optical fiber, and more particularly to a core-cladding structure for preventing formation of core eccentricity and cracking of a preform at an early stage of production where the core diameter is small. The present invention relates to a method for producing a porous glass preform for optical fibers having the following.

[0002]

2. Description of the Related Art As a method of manufacturing a porous glass preform for an optical fiber having a core-clad structure, a core burner and a plurality of clad burners are provided at a lower portion of a reaction vessel.
A glass raw material gas, oxygen gas and hydrogen gas, a refractive index increasing dopant gas and an inert gas are supplied to the core burner, and a glass raw material gas, oxygen gas and hydrogen gas, and an inert gas are supplied to each clad burner. Supply,
In the flame of these burners, glass microparticles are generated by flame hydrolysis of glass raw material gas, and these glass microparticles are deposited around a rotating target such as quartz glass to form a core part and a cladding layer. Although the VAD method is known, the porous glass base material thus produced is made into a transparent glass by heat sintering at a high temperature to obtain a quartz glass base material for an optical fiber.

[0003]

However, this method of manufacturing a porous glass preform for an optical fiber requires a very small core diameter as in the case of a single mode, so that the porous glass preform at the initial stage of the production becomes very difficult. Because of the unstable state,
In this manufacturing process, there is a risk that a manufacturing problem such as breakage of the base material or deformation of the shape of the base material may occur. For this reason, in this early stage of production, the flow rate of H ₂ gas is increased to increase the bulk density of the base material, or the production conditions such as the burner position are changed to make the production of the base material different from the steady stage. It has also been proposed to stabilize and return to desired manufacturing conditions when the base material grows due to the deposition of glass particles and reaches a steady state (Japanese Patent Application Laid-Open No.
No. 149335).

[0004] However, such an unstable state of the initial conditions is not particularly problematic as long as the core diameter is sufficiently large, but when the core diameter is small, the core becomes very eccentric. Once eccentric, eccentricity often continues until the end of manufacturing, and even if this is corrected during manufacturing, this part will be defective, so this will reduce productivity, and this will also reduce the core part. There was also a problem that cracks easily occurred.

[0005]

The present invention relates to a method of manufacturing a porous glass preform for an optical fiber which solves such disadvantages and problems. The method comprises the steps of providing a glass source gas to a core burner and a cladding burner. And oxygen gas and hydrogen gas are supplied, and glass fine particles generated by the flame hydrolysis of the glass raw material gas in the oxyhydrogen flame are deposited on a target member to form a porous glass base material having a core portion and a cladding layer. In the method for producing a porous glass preform for an optical fiber to be produced, a core diameter at the start of production of the porous glass preform at the beginning of production is formed to be larger than a desired diameter, and the core diameter includes a clad including the core. As the outer diameter of the porous glass base material increases and gradually narrows as the layer grows, the outer diameter of the porous glass base material becomes constant and the porous glass base material straight body is formed. When in, it is characterized in that as the core diameter to a desired value.

That is, the inventors of the present invention have developed a method of manufacturing a porous glass preform for an optical fiber which can prevent formation of core eccentricity and cracking of the preform in the early stage of production, in which the core diameter is small. As a result of various investigations, the core diameter in the initial stage of the production was unstable, the production was started to be larger than the desired diameter, and the production was started to produce a porous glass preform. After that, if the porous glass preform is manufactured with the core diameter as a desired diameter, there is no eccentricity, and it is possible to manufacture a porous glass preform having a small-diameter core without cracking of the base material, According to this, the core diameter in the initial stage of production becomes large, and it has been confirmed that the porous glass base material having the maximum outer diameter can have the outer diameter at the steady state in a short time, and the present invention has been completed.

[0007]

In the production of a porous glass preform for an optical fiber by the VAD method, there is unevenness in the rotation of the target, and when the core diameter is small, the eccentricity increases in the initial stage when the outer diameter of the porous preform is small. Would. Therefore, when manufacturing a porous glass preform having a small core diameter, when the outer diameter of the porous glass preform at the start of the production is small, if the core diameter is made larger than the desired outer diameter and the production is started, the initial stage can be started. The eccentricity due to the rotation unevenness can be reduced, and then the core diameter is gradually reduced as the maximum outer diameter of the base material increases due to the growth of the cladding layer, and the maximum outer diameter of the base material becomes constant Therefore, the manufacturing conditions are gradually made to be the steady conditions so that the desired core diameter is obtained when the manufacturing conditions are in the steady state.Accordingly, the eccentricity of the base material can be suppressed small, Furthermore, the advantage of preventing deformation of the pile due to bending of the seed rod and eliminating the disadvantage of cracking the base material is provided. The initial portion of the porous glass base material other than the straight body portion is practically cut and not used, so there is no problem.

The production of a porous glass preform for an optical fiber having a core-cladding structure according to the present invention is performed by a porous glass preform manufacturing apparatus having a core burner and a cladding burner. It is necessary that the core diameter is at least larger than the outer diameter of the core burner, which is preferably larger than the steady core diameter and not more than 3 times, preferably about 2 times. When the core diameter is 15 mm, this is preferably about 30 mm.

The apparatus for producing a porous glass base material used in the present invention may be based on a known apparatus based on the VAD method, and therefore may be the apparatus shown in FIG.
FIG. 1 is a longitudinal sectional view of a manufacturing apparatus for a porous glass base material having a core-cladding structure used in the present invention. 3. A plurality of clad burners 4, 5 are provided, and a target member 6 made of synthetic quartz glass or the like held by a rotating holding tool is suspended in the reaction vessel. Burner 3 includes silicon tetrachloride (SiCl ₄ ) as a glass material gas and oxygen gas (O ₂ ).
₂ ), hydrogen gas (H ₂ ), germanium tetrachloride (GeCl ₄ ) as a dopant, and argon gas (Ar) as an inert gas are supplied.
iCl ₄ , O ₂ , H ₂ and Ar are supplied.

In the production of the porous glass base material, the core burner 3 is ignited, and silica fine particles generated in the burner flame are adhered to the rotating target member 6 and deposited to form a core portion. , Burner for cladding 4,
The silica fine particles generated in the flame of No. 5 are adhered and deposited on the core portion to produce the porous glass base material 8. When the desired core diameter is 15 mm, the initial core diameter is set to the initial value. At the stage, this is about three times, preferably about twice, 30 mm.

However, if the initial core diameter is three times or more, it takes a long time to obtain a desired core diameter, and disadvantages such as a large loss occur. Therefore, if the initial core diameter is three times or less, preferably about two times. Good.

Therefore, in the present invention, as shown in FIG. 2, the deposition of the glass fine particles is carried out in the initial stage by setting the outer diameter of the core to about three times the desired value, preferably twice the target core diameter. The core diameter is increased by increasing the amount of SiCl ₄ , GeCl ₄ , O ₂ , H ₂ , Ar, etc. supplied to the core burner so that the core diameter becomes about The glass fine particles from the burner are adhered, deposited and grown, and as the outer diameter of the porous base material increases, the amount of gas supplied to the core burner is reduced, and the core diameter is gradually reduced until steady state. May be reduced so that the core diameter becomes a desired diameter when the maximum outer diameter of the porous glass base material becomes constant.

In this case, the amount of gas to be supplied to the core burner is set to be larger at the start of the production than in the steady state as described above. This is for the purpose of increasing the core diameter. Since Ge is not used, for example, as shown in Table 1, it is not necessary to particularly increase GeCl ₄ as a dopant, but for SiCl ₄ , the steady 20 L / min is reduced to 100 L / min, and the H ₂ gas is Regular
0.5 liters / minute can be increased to 1.4 liters / minute, O ₂ gas can be increased from 4 liters / minute at steady state to 8 liters / minute, and Ar gas can be increased from 0.8 liters / minute at steady state to 2 liters / minute. Good.

[0014]

[Table 1]

[0015]

Next, examples of the present invention and comparative examples will be described. Example A core burner and two clad burners were arranged at the lower part of a reaction vessel, and the diameter of the apparatus was 10 mm and the length was 1 mm.
A target member made of 00 mm synthetic quartz glass was suspended,
Using the porous glass preform manufacturing apparatus shown in FIG. 1, silicon tetrachloride (SiCl ₄ ) was supplied to this core burner at the start of production as shown in Table 1 at a rate of 100 liters / minute and germanium tetrachloride (GeCl _4). ) At 5 liters / minute, oxygen gas (O ₂ ) at 8 liters / minute, and hydrogen gas (H ₂ ) at 1.4 liters / minute.
Minute, argon gas (Ar) is supplied at 2 liters / minute,
The amount of these gases is gradually reduced, and is supplied at a constant flow rate shown in Table 1 in a steady state, and glass fine particles generated by flame hydrolysis of SiCl ₄ and GeCl ₄ are attached to and deposited on the target member. As shown in the figure, the initial core diameter was 30.7 mm, and gradually decreased as the outer diameter of the porous base material increased, and when this became 200 mm in a steady state, the core portion was formed so as to be 15.5 mm, Each clad burner is fed with SiCl ₄ , O ₂ , H ₂ gas and Ar gas, respectively.
Silica fine particles generated by flame hydrolysis of SiCl ₄ are adhered and deposited on the core, and have an outer diameter of 200 mm and a length of 1,000 mm.
When the porous glass preform was manufactured, it did not crack, and was sintered at 1,500 ° C to produce a transparent optical fiber glass preform with an outer diameter of 98 mm, a length of 500 mm, and a core diameter of 7 mm. As a result, a single-mode optical fiber glass preform without eccentricity was obtained, and ten porous glass preforms were manufactured by this method, which were sintered at 1,500 ° C to obtain a transparent glass preform. This is drawn at 2,100 ° C and the outer diameter is 125
When the core eccentricity was measured with an optical fiber of μm, the maximum value was 0.3 μm and the average was 0.1 μm.

[0016] comparative examples using the same apparatus as the above-mentioned embodiments, SiCl ₄ 20 l / min the feed rate of the raw material gas to the core burner for comparison, a GeCl ₄ 5 l / min, O ₂ gas 4 Liter / min, H ₂ gas 0.5 liter / min, Ar gas 0.8 liter / min, except that a porous glass preform having an outer diameter of 200 mm and a length of 1,000 mm was produced under the same conditions as in the example. This is because 5 out of 10 cracks are broken, and 5 unbroken pieces are sintered at 1,500 ° C to make a transparent glass base material.
These were drawn at 2,100 ° C. to produce an optical fiber having an outer diameter of 125 μm, and the eccentricity of this core was determined. The maximum eccentricity was 1.0 μm, and the average was 0.8 μm.

[0017]

The present invention relates to a method for producing a porous glass preform for an optical fiber, which comprises supplying a glass source gas, an oxygen gas and a hydrogen gas to a core burner and a clad burner as described above. A porous glass matrix for an optical fiber for producing a porous glass matrix having a core portion and a clad layer by depositing glass fine particles generated by flame hydrolysis of a glass raw material gas in this oxyhydrogen flame on a target member. In the method of manufacturing a material, a core diameter at the start of the production of the porous glass base material at the beginning of production is formed larger than a desired diameter, and the porous glass base material is formed by depositing and growing a cladding layer including the core. When the outer diameter of the material increases and gradually narrows, when the outer diameter of the porous glass preform becomes constant and the porous glass preform straight body is formed,
It is characterized in that the core diameter is set to a desired value. According to this, when manufacturing a porous glass base material having a small core diameter, formation of eccentricity of the core and cracking of the core are prevented. Therefore, the advantage that the productivity of good products can be increased is provided.

[Brief description of the drawings]

FIG. 1 illustrates a vertical cross-sectional view of an apparatus for manufacturing a porous glass preform for an optical fiber according to the present invention.

FIG. 2 illustrates a relationship diagram between a core diameter and the passage of time during the production of a porous glass base material according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction container 2 ... Exhaust port 3 ... Core burner 4, 5 ... Clad burner 6 ... Target member 7 ... Initial part of porous glass base material 8 ... Straight body part of porous glass base material

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Koyamada 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd.Precision Functional Materials Laboratory (72) Inventor Hideo Hirasawa Isobe, Annaka-shi, Gunma 2-13-1 Shin-Etsu Chemical Co., Ltd. Precision Functional Materials Laboratory (56) References JP-A-62-187133 (JP, A) JP-A-58-213644 (JP, A) JP-A-63-60123 (JP, A) JP-A-60-48942 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 37/018 C03B 8/04

Claims (1)

(57) [Claims] 1. A glass raw material gas, an oxygen gas and a hydrogen gas are supplied to a core burner and a clad burner, and glass fine particles generated by flame hydrolysis of the glass raw material gas in the oxyhydrogen flame are deposited on a target member. In the method for producing a porous glass preform for an optical fiber for producing a porous glass preform having a core portion and a cladding layer, the core diameter at the start of production in the initial stage of production of the porous glass preform is set to a desired diameter. The outer diameter of the porous glass base material is gradually increased as the outer diameter of the porous glass base material is increased by the deposition growth of the cladding layer including the core, so that the outer diameter of the porous glass base material is constant. A method for producing a porous glass preform for an optical fiber, wherein the core diameter is set to a desired value when the porous glass preform straight body is formed.