JPH0733467A - Production of porous glass preform for optical fiber - Google Patents

Abstract

PURPOSE:To provide a preform having a uniform refractive index distribution of a side core part and having good reproducibility of dispersion characteristics at the time of reproducing the porous glass preform for the double core type optical fiber by a VAD method and by controlling a burner for a side core in specific range. CONSTITUTION:A burner for a center core for forming a center core part and the burner 2 for a side core for forming a side core part are disposed and the numerical value of equation I consisting of a distance X(m) between a combustible gas blow-off port 3 of the burner 2 for the side core and the deposition surface of the side core part of a soot preform 1, the linear velocity of flow V(m/sec) of the combustible gas and the inside diameter D(m) of the combustible gas blow-off port 3 are so set as to attain the range of formula II. Gaseous raw materials and the combustible gas are passed to the burners for the center core and the side core and the combustible gas is ignited to form flames. The gaseous raw materials are then flame hydrolyzed in the flames to form start flow. The soot flow is thus deposited on the rotating soot preform 1 by integrating the center core part and the side core part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous glass preform for an optical fiber, and more particularly to a soot preform for a double core type dispersion shift fiber having a center core portion, a side core portion and a clad portion by the VAD method. The present invention relates to a method for producing a porous glass preform for optical fibers, in which soot is deposited on the substrate.

[0002]

2. Description of the Related Art A method for manufacturing a porous glass preform for optical fibers is as follows. A raw material gas such as silicon tetrachloride is fed into a hydrogen flame resistant burner, and silica fine particles generated by flame hydrolysis in the flame. A flow (hereinafter abbreviated as soot) (hereinafter referred to as soot flow) is erected upright and deposited on a rotating heat-resistant carrier (soot base material), and this soot base material is sequentially pulled upward and perforated there. A method for growing a high quality glass base material is known as a VAD method.

However, also in this VAD method, the oxyhydrogen flame burner is divided into a center core burner, a side core burner, and a clad burner, and the soot flow from the center core burner forms the center core portion to form a side core. It is also possible to deposit the soot flow from the burner for use on the center core to form the side core, and then to deposit the soot flow from the burner for cladding on the side core to form the porous glass preform for optical fibers. It is known that, in this case, the center core burner is supplied with the glass raw material gas (SiCl ₄ ) and the combustible gas (H ₂ ) and the combustion supporting gas (O ₂ ), but the side core burner and the cladding are The dope raw material gas (CeCl ₄ ) is also supplied to the burner for use.

[0004]

The double core type dispersion shaft soot base material produced in this manner has a refractive index distribution in the core portion, because the side core portion and the cladding portion contain dopants. Let n _{1 be} the refractive index of the side core, n _{2 be} the refractive index of the clad, and n _{3 be} the refractive index of the clad, then n ₁ > n ₂ > n ₃ , and ideally these are as shown in FIG. There are two types of dopant (Ge) added to adjust the refractive index, GeO ₂ particles and Si-Ge-O solid solution. Of these, GeO ₂
Since the fine particles volatilize in the dehydration process, they hardly contribute to the refractive index adjustment, and Si-Ge-O contributes substantially to the refractive index adjustment.
Although it becomes a solid solution, since this Si-Ge-O solid solution is formed by melting SiO ₂ particles and GeO ₂ particles in the high temperature region of the flame, the Si-Ge blown out from the multi-tube burner Figure 5 shows the distribution of -O solid solution in the radial direction of the burner.
Corresponding to the inner diameter of the combustible gas outlet of (b), FIG.
The distribution is as shown in (a).

Therefore, the refractive index distribution of the soot base material obtained in this case is such that the refractive index distribution in the side core portion is disturbed as shown in FIG. 6A, and this soot base material is obtained by heating and making it transparent. The optical fiber obtained by spinning the synthetic quartz glass base material for optical fiber has the disadvantage that it becomes very difficult to control the dispersion characteristics with high accuracy.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a porous glass preform for an optical fiber, which solves the above disadvantages, which is a burner for a center core forming a center core portion and a side core portion. Equipped with a side core burner to form a soot stream formed by flame hydrolysis in the flame of the source gas by flowing the source gas and a flammable gas into these burners and igniting the flammable gas to form a flame. In the method for producing a porous glass preform by depositing the center core part and the side core part on the rotating double core type optical fiber soot preform, the flammable gas blowing of the side core burner is performed. It consists of the distance X (m) between the outlet and the deposition surface of the side core of the soot base material, the linear velocity of the combustible gas (V / sec), and the inner diameter D (m) of the combustible gas outlet. In which numerical equation D ² / (X / V), characterized in that the set to be in the range of 0.001 <D ² /(X/V)≦0.1.

That is, the present inventors have developed a method for producing a porous glass preform for producing an optical fiber preform having a uniform refractive index distribution in the side core portion and excellent reproducibility and controllability of dispersion characteristics. As a result of various studies to make it possible, the distance X (m) between the flammable gas outlet of the side core burner and the side core deposition surface of the soot base metal, and the linear flow velocity V of the flammable gas
(M / sec) ratio X / V generated Si-Ge in the burner
-O solid solution is a value representative of the time until it deposits on the side core part, and the inner diameter D (mm) of this combustible gas outlet represents the radial distribution position of the Si-Ge-O solid solution near the burner. Paying attention to the fact that the value becomes D ² / (X / V) within a certain range from these values, the refractive index distribution of the side core part of the porous glass base material obtained becomes uniform. It was found that the value of D ² / (X / V) was 0.001 <D ² /(X/V)≦0.1.
The present invention was completed after confirming that the above range was satisfied. This will be described in more detail below.

[0008]

The present invention relates to a method for producing a porous glass preform for optical fibers, which is produced by flame hydrolysis of a raw material gas using a center core burner and a side core burner as described above. In a method for producing a porous glass preform for optical fibers by depositing a soot flow composed of silica fine particles on a rotating soot preform for double-core optical fiber, a combustible gas outlet and a soot of a side core burner are used. The numerical value of the formula D ² / (X / V) consisting of the distance X from the soot deposition surface of the side core of the base metal, the linear velocity V of the combustible gas, and the inner diameter D of the combustible gas outlet is 0.001.
The feature is that <D ² /(X/V)≦0.1 is satisfied, which makes the target refractive index distribution of the side core portion of the porous glass preform uniform. The advantage is that it can be done.

That is, in the conventional method, as shown in FIG. 4, soot streams from the center core burner 13 and the side core burners 14 are deposited on the soot base material 12 installed in the reactor 11, and then the clad burner is deposited. The soot flow from 15 is deposited and the clad layer is formed there to manufacture the porous glass preform. The combustible gas outlet 16 of this side core burner is shown in Fig. 5 (b). The S generated in this burner is
The distribution of the i-Ge-O solid solution in the burner radial direction is as shown in FIG. 5 (a). Therefore, as shown in FIG. 6 (a), the porous glass base material obtained here has the side core portion 17 The refractive index distribution becomes disordered, and the optical fiber obtained by spinning the synthetic quartz glass preform for optical fiber obtained by heating and transparentizing this porous glass preform cannot accurately control the dispersion characteristics. There is a drawback that

However, in this case, according to the present invention, as shown in FIG. 1, the combustible gas outlet 3 of the side core burner 2 for the soot base material 1 and the soot deposition surface 4 for the side core portion of the soot base material 1 are formed. Distance is X (m)
And the linear velocity V (m / sec) of this flammable gas and the inner diameter D (m) of this flammable gas outlet are specified, and this D ² / (X /
V) within the range of 0.001 ≦ D ² /(X/V)≦0.1 Si-Ge-O generated in the side core burner
Since it takes a sufficient time for the solid solution to be deposited on the side core portion deposition surface, the solid solution can be uniformly diffused and deposited in the radial direction of the side core burner, and thus the center core portion 5 thus produced. The refractive index distribution of the porous glass base material including the side core portion 6 and the clad portion 7 is substantially uniform.
The advantage is given that it can be as shown in (a).

In this case, if the value of D ² / (X / V) is less than 0.001 (m ² / sec), the flame temperature near the soot deposition surface decreases and the bulk density of the soot base material decreases,
During manufacture of the soot base material, cracks and deformations occur, and if it is larger than 0.1, the refractive index distribution of this side core part becomes disordered as shown in Fig. 6 (a). , Which is required to be in the range of 0.001 ≦ D ² /(X/V)≦0.1.

[0012]

EXAMPLES Next, examples of the present invention will be given. Example The apparatus shown in FIG. 4 was used, but in this case, as shown in FIG. 1, the distance X between the flammable gas outlet of the side core burner and the soot deposition surface on the side core portion of the soot base material was measured.
(M) is X = 2 × 10 ⁻² m, the linear velocity V of this flammable gas is V = 4 m / sec, and the inner diameter D of this flammable gas outlet is D = 1.5 × 10 ⁻² m. D ² /(X/V)=7.5×10
^The soot base material was formed as ^-3 .

Then, the soot base material (porous glass base material) having a diameter of 100 mm and a length of 1,000 mm is heated to 1,500 ° C. to be transparent vitrified to prepare a synthetic quartz glass base material for an optical fiber, and its refractive index distribution As a result, the refractive index distribution of the side core portion was almost uniform, and the result as shown in FIG. 2A was obtained. The optical fiber obtained by drawing and spinning the base material was dispersed in the longitudinal direction. When the characteristics were measured, the results as shown in FIG. 2 (b) were obtained, which showed little variation in the zero dispersion wavelength and had stable characteristics in the longitudinal direction.

COMPARATIVE EXAMPLE 1 In the apparatus shown in FIG. 1, X, V and D are X = 2 × 10 ^-2.
m, V = 4 m / sec, D = 3 × 10 ⁻² m, D ² / (X / V)
= 0.18, a soot base material with a diameter of 100 mm and a length of 1,000 mm was made, and after vitrifying it, the refractive index distribution of this material was measured. As shown in Fig. 6 (a), this was the side core. The refractive index distribution of the part was disturbed, and the dispersion characteristic of the optical fiber obtained by spinning this was measured, and it showed the result as shown in FIG. 6 (b). This zero-dispersion wavelength also had unstable characteristics with large variations in the longitudinal direction.

COMPARATIVE EXAMPLE 2 In the apparatus shown in FIG. 1, X, V and D are X = 15 × 10 ^-2.
When the soot base material was made with m, V = 1 m / sec and D = 1 × 10 ⁻² m, in this case, D ² / (X / V) was 6.7 × 10
^Since it became ^-4 , when this soot base material grew about 200 mm, the soot base material deformed and cracked.

[0016]

The present invention relates to a method for manufacturing a porous glass preform for optical fibers, which comprises a center core burner forming a center core portion and a side core burner forming a side core portion as described above. Equipped with
A source gas and a flammable gas are caused to flow through these burners, and the soot stream formed by flame hydrolysis of the flame of the source gas is formed by igniting the flammable gas and the center core portion and the side core portions. In a method for producing a porous glass preform by depositing on a soot preform for a dual core type optical fiber that rotates integrally, a flammable gas outlet of the side core burner and a side core part of the soot preform Distance X (m) from the deposition surface, linear velocity V (m /
Second) and the inner diameter D (m) of the combustible gas outlet, the numerical value of the equation D ² / (X / V) is 0.001 ≦ D ² / (X / V) ≦ 0.
It is characterized in that it is set within the range of 1 (m ² / sec). According to this, an optical fiber made from this porous glass preform has a uniform refractive index distribution in the side core part. The advantage is that reproducibility of dispersion characteristics and controllability can be excellent.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a porous glass preform manufacturing apparatus according to the present invention.

FIG. 2 (a) shows a refractive index distribution of a synthetic quartz glass base material for an optical fiber obtained in an example, (b).
Shows a graph of the value of the zero dispersion wavelength in the longitudinal direction of the optical fiber made from this.

FIG. 3 shows an ideal refractive index distribution of a porous glass preform obtained according to the present invention.

FIG. 4 is a vertical sectional view of a porous glass preform manufacturing apparatus according to a conventional method.

FIG. 5 (a) is a distribution diagram of a Si—Ge—O solid solution of a porous glass base material obtained by a conventional method in a burner radial direction, and FIG. 5 (b) shows the combustible gas outlet. 3 is a perspective view of FIG.

FIG. 6 (a) shows a refractive index distribution of a porous glass preform obtained by a conventional method, and FIG. 6 (b) shows a zero-dispersion wavelength value in the longitudinal direction of an optical fiber made from this. This is a graph.

[Explanation of symbols]

 1, 12 ... soot base material, 2, 14 ... side core burner, 3, 16 ... flammable gas outlet for side core burner, 4 ... soot accumulation surface of side core part, 5 ... center core part, 6, 17 ... side core Part, 7 ... Clad part, 11 ... Reaction vessel, 13 ... Center core burner, 15 ... Clad burner,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory

Claims (1)

[Claims] 1. A center core burner forming a center core portion and a side core burner forming a side core portion are provided, and a raw material gas and a combustible gas are caused to flow through these burners, and the combustible gas is ignited to generate a flame. The soot flow formed by flame hydrolysis in the flame of the raw material gas is deposited on the rotating soot base material for the double core type optical fiber by integrating the center core part and the side core parts, and is then porous. In the method for producing a high quality glass base material, the distance X (m) between the flammable gas outlet of the side core burner and the side core portion deposition surface of the soot base material, and the linear flow velocity V (m / sec) of the combustible gas. And inner diameter D of flammable gas outlet
(M) and the value of the formula D ² / (X / V) which is set to be in the range of 0.001 <D ² /(X/V)≦0.1 (m ² / sec) A method for manufacturing a porous glass preform for fibers.