JPH02124737A - Production of optical finer preform - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing an optical fiber preform, and in particular to a method for producing a step index type optical fiber preform that can optimally control the refractive index distribution coefficient. It relates to a method of manufacturing.

(Prior art) Optical fiber preforms are usually manufactured by introducing a gaseous glass raw material such as silicon tetrachloride into an oxyhydrogen flame, and then rotating the glass particles produced by flame hydrolysis in this flame. It is made by depositing materials in the axial direction to create a porous glass matrix and vitrifying it at high temperatures.
In the production of step-index type optical fiber preforms used for high NA optical fibers, in order to obtain the desired refractive index distribution coefficient, the temperature distribution on the base material bottom surface is adjusted by adjusting the composition of the raw gas (6) and the positional relationship between the flame center axis and the bottom surface. The refractive index distribution is finely adjusted by controlling the atmospheric gas during sintering.

(Issues to be solved) However, when producing a high NA optical fiber base material, this reaction needs to be carried out at a lower temperature than usual because a large amount of GeO2 is doped, and this method does not allow for control of temperature distribution. However, it is difficult to produce a high NA step index optical fiber with a stable refractive index distribution coefficient. is difficult,
Further, in this case, it is necessary to set the refractive index distribution coefficient α to 3 or more, but it is currently difficult to stably manufacture such a product industrially.

(Means for Solving the Problems) The present invention relates to a method for producing an optical fiber preform that solves the above-mentioned disadvantages. In the method of depositing glass particles in the axial direction of a starting base material to create a porous glass base material, and vitrifying this at high temperature to form an optical fiber base material, the gaseous glass raw material is transported with a carrier gas containing oxygen gas. It is characterized by:

That is, as a result of various studies conducted by the present inventors regarding methods for efficiently and stably manufacturing a high NA step index optical fiber having a refractive index distribution coefficient α of 3 or more,
The refractive index of an optical fiber obtained when oxygen gas is included in a carrier gas, such as argon gas, helium gas, or nitrogen gas, used to introduce a gaseous glass raw material such as silicon tetrachloride into an oxyhydrogen flame. We found that the distribution coefficient α can be easily set to 3 or more, and
The ratio of this oxygen gas in the carrier gas is 0.1 to 0.
．． 5, and in order to make this refractive index distribution coefficient α 3 or more, the position of the oxyhydrogen flame burner should be set by depositing glass particles generated by hydrolysis in the oxyhydrogen flame burner. The present invention was completed after confirming that it would be more effective if the obtained porous glass base material was eccentrically placed.

This will be explained in more detail below.

The method of the present invention is carried out using a gas phase coagulation method. therefore,
This involves introducing a silicon compound such as silicon tetrachloride into an oxyhydrogen flame, flame-hydrolyzing it into gas particles, which are then transferred to a rotating refractory starting substrate 2, such as quartz. , to create a porous glass matrix by depositing it on a rod-shaped body such as silicon carbide, and then heating it to a high temperature to vitrify it. is introduced into the oxyhydrogen flame burner, usually accompanied by an inert gas such as argon gas, helium gas, or nitrogen gas as a carrier gas.

In the method of the present invention, oxygen is contained in the carrier gas, but the amount of oxygen is O2 relative to the carrier gas.
If it is less than 61, the amount is too small and there is no effect of the addition.
, If it is more than 5, the refractive index distribution in the center of the target optical fiber will be disturbed and it will become worse, so this value is less than 0.
．． It needs to be in the range of 1 to 0.5. Oxygen gas may be introduced into the carrier gas by introducing a calculated amount of oxygen into the carrier gas before or after mixing the carrier gas and the gaseous raw material, but the amount added is determined according to the refractive index distribution of the optical fiber. It can be determined according to the coefficient,
This is an example! If the initial position is 0.2, the refractive index distribution coefficient α of the optical fiber can be set to about 3, and the oxygen content can be set to 0.
．． If it is set to 4, the refractive index distribution coefficient α can be set to about 5.

Adding 0.1 to 0.5 of oxygen gas to the carrier gas for conveying the gaseous frit according to the method of the present invention achieves the objective of smoothing the temperature distribution in the radial direction of the flame. The effect of increasing the refractive index distribution coefficient α of the optical fiber base material to 3 or more is given, but this improvement in the refractive index distribution coefficient is due to the glass obtained by hydrolyzing the gaseous glass raw material in an oxyhydrogen flame. This can be facilitated by eccentrically placing an oxyhydrogen flame burner on a porous glass matrix obtained by depositing fine particles on a starting substrate.

The eccentricity value (X) of this oxyhydrogen flame burner is particularly thick (there is no need to do so; this is +4 mm when the center line of the porous glass base material is 0, the deviation to the right is +, and the deviation to the left is -). If the refractive index distribution coefficient α is above 3, it will not be more than 3, and if it is more than -6 mm, the refractive index distribution of the step index type will be adversely affected, so it may be set in the range of -6 m to +4 m.

Next, the method of the present invention will be explained based on the attached drawings. FIG. 1 shows a longitudinal cross-sectional view of an optical fiber preform manufacturing apparatus according to an example method of the present invention, in which a silicon tetrachloride container 1. Germanium tetrachloride container 2 as a doping agent
A mixed gas of silicon tetrachloride and germanium tetrachloride is mixed with oxygen gas as a carrier gas, and is introduced into the oxyhydrogen flame burner 4 together with the oxygen gas and hydrogen gas, which is introduced into the oxyhydrogen flame burner 4 through the path 3 along with the argon gas. Ru. The silicon tetrachloride and germanium tetrachloride are hydrolyzed in the flame of the oxyhydrogen flame burner to become fine glass powder, which is deposited on the rotating starting base material 5 to form the porous glass base material 6. However, in this case, since 0.1 to 0.5 of r is mixed in the argon gas as the carrier gas, the porous glass base material 6 is vitrified at high temperature. This provides the effect of increasing the refractive index distribution coefficient of the optical fiber base material.

In addition, in this case, the oxyhydrogen flame burner 4 is attached to the porous glass base material 6 formed here by
Since it is installed with n-eccentricity, there is an advantage that the refractive index distribution coefficient α of the target optical fiber base material is between 3 and 4.

(Example) Next, examples using the method of the present invention will be given.

Example Using the apparatus shown in FIG. 1, 5iC1,0,32Q/min and GeC1°0.06912 were used as gaseous glass raw materials.
Argon gas mixed with 0.3.0.5 Q/min of oxygen gas is sent to the oxyhydrogen flame burner as a gear gas, and to this oxyhydrogen flame burner, 6.021 min of hydrogen gas and 10Q of oxygen gas as combustion gas are sent to the oxyhydrogen flame burner. /min, and this oxyhydrogen flame burner is placed Xmm eccentrically from the center line.
Light the burner and 5iCL4. GeCl4 is hydrolyzed to produce glass particles, which are deposited on a quartz glass carrier to create a porous glass base material with an outer diameter of approximately 80 m+ and a length of approximately 700 mm, which is then heated to 1,400°C to form transparent glass. The refractive index Δn is approximately 2.0 to 2.1 and the outer diameter is approximately 4.
The optical fiber base material had a length of 0 mn+ and a length of about 350 am.

Next, we measured the refraction distribution coefficient α of the optical fiber base material in this way and investigated the relationship between the oxygen ratio y in the carrier gas and the eccentricity value X + m of the oxyhydrogen flame burner, as shown in Figure 2. The following results were obtained.

In addition, FIGS. 3 to 6 show refractive index distribution maps of the optical fiber base material obtained by this method, and the one in FIG. 3 has Δn=2.1% and refractive index distribution coefficient α= 4, Fig. 4 shows Δn=2.0% and refractive index distribution α=6, while Fig. 5 shows Δn=2.1%, but refractive index distribution coefficient α
Figure 6 shows the comparative example in which the oxygen content is 0.6 with respect to the carrier gas, and the refractive index distribution coefficient α is 8 when Δn = 1.9%, and the refractive index distribution is This is a comparative example of a disordered item.

(Effects of the Invention) As described above, the method of the present invention includes oxygen in the carrier gas for transporting the gaseous glass raw material, and
If necessary, the oxyhydrogen flame burner is placed eccentrically from the center line of the porous glass base material, but this allows the target high NA step type optical fiber to be easily made into one with a high refractive index distribution coefficient. It also has the advantage of being stably obtainable.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of an optical fiber preform manufacturing apparatus according to the method of the present invention, and Fig. 2 shows the amount of oxygen (y) in the carrier gas during the production of the optical fiber m material obtained in the example.
Figures 3 to 6 show the relationship between the eccentricity value (x-a) and the refractive index distribution coefficient (α) of the oxyhydrogen flame burner. It shows a refractive index distribution map. ---1-S1 and I linear χ (mm)

Claims (1)

[Claims] 1. Flame hydrolyze the gaseous glass raw material in an oxyhydrogen flame burner, deposit the generated glass particles in the axial direction of the starting base material to create a porous glass base material, and heat this at high temperature. 1. A method for producing an optical fiber preform by vitrifying the material, the method comprising: transporting a gaseous glass raw material with a carrier gas containing oxygen gas. 2. The ratio of oxygen gas in the carrier gas is 0.1
2. The method for manufacturing an optical fiber preform according to claim 1, wherein the preform is 0.5. 3. The method for producing an optical fiber according to claim 1, wherein a carrier gas containing oxygen gas is used and the oxyhydrogen flame burner is eccentric with respect to the starting substrate.