JPH0226849A - Production of optical fiber bace material - Google Patents

Abstract

PURPOSE:To stably produce the optical fiber of a graded index type having an excellent transmission characteristic by growing a porous glass material by using gaseous glass raw materials which consist of silicon tetrachloride and dopant and are corrected in change rate. CONSTITUTION:The gaseous glass raw materials which consist of the silicon tetrachloride and the dopant and are regulated in quantity are introduced to an oxyhydrogen flame burner and is subjected to a flame hydrolysis. The formed fine glass particles are deposited on a rotating base material. This base material is then pulled up, by which a porous glass body is grown thereon in the axial direction thereof. The quantity of the gaseous raw materials regulated in the method of producing the optical fiber base material by nitrifying the above- mentioned porous glass material to transparent glass is specified to the value corrected of the change rate by the atm. pressure. The correction of the quantity of the gaseous raw materials to be supplied may be executed by determining the change in the evaporation rate of the silicon tetrachloride and germanium tetrachloride as the dopant with the fluctuation in, for example, the atm. pressure, from the figure, then by determining the correction rate of the carrier gas to correct this change rate from the figure.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an optical fiber base material, and particularly to a method for continuously and stably manufacturing a graded index type optical fiber with excellent transmission characteristics. It is.

(Prior art) An optical fiber base material is produced by bubbling carrier gas into a glass material such as silicon tetrachloride to gasify it, and introducing this gas into a burner to cause a flame hydrolysis reaction with an oxyhydrogen flame. It is already well known that optical fibers can be obtained by depositing glass particles on a rotating starting base material to grow a porous glass base material in the axial direction, and then heating and melting this material to make it transparent glass. It is a known place.

However, in recent years, it has become possible to increase the transmission band characteristics of graded-index optical fibers to values that reach theoretical values by optimizing the refractive index distribution shape inside the core. In long fibers, the transmission band in the longitudinal direction often becomes uneven due to fluctuations during the manufacturing of the optical fiber base material, and it is not possible to stably manufacture an optical fiber base material with an excellent transmission band over a long period of time. There is a disadvantage that special products are produced frequently.

Therefore, in order to make the refractive index distribution of the optical fiber base material uniform in its longitudinal direction, various methods have been proposed for controlling the supply amount of raw material gas (Japanese Patent Laid-Open Nos. 149335-1982 and 1983-1999). No. 45936, JP 59-13733
No. 1 and Japanese Patent Application Laid-Open No. 60-81035). However, it is difficult to accurately control the amount of raw material gas supplied, and if there is a slight change in the amount of silicon tetrachloride or dopant, the dopant ratio will change, making it impossible to obtain a uniform optical fiber. 6 (Structure of the Invention) The present invention relates to a method for producing an optical fiber preform that solves the above disadvantages, and is a method for producing an optical fiber preform by using a predetermined amount of a gaseous glass raw material consisting of silicon tetrachloride and a dopant. is introduced into an oxyhydrogen flame burner for flame hydrolysis, the resulting glass fine particles are deposited on a rotating base material, and this base material is pulled up to grow a porous glass body in its axial direction. A method for manufacturing an optical fiber preform by converting a porous glass preform into transparent vitrification, characterized in that the controlled amount of gaseous glass raw material is set to a value corrected for the amount of change due to atmospheric pressure.

To explain this, the inventors of the present invention have conducted various studies on methods for continuously and stably manufacturing grade index type optical fibers with excellent transmission characteristics. In order to obtain a porous glass base material with a uniform structure and shape, it is necessary to obtain a porous glass base material with a uniform structure and shape. We have discovered a method to precisely control the amount of gaseous frit supplied to Furthermore, the present invention was completed by confirming that this can be easily achieved by setting the amount of the gaseous glass raw material to a value that corrects the amount of change due to atmospheric pressure.

This will be explained in more detail below.

The method of the invention can basically be carried out using the known gas phase shafting method (
Therefore, this can be done by feeding the frit carrier gas 3 to the silicon tetrachloride unsupplied bubbler 1 and dopant supply bubbler 2 through mass flow controllers 4 and 5 as shown in FIG. A predetermined amount of silicon tetrachloride and the calculated amount of dopant to be added to it are gasified and mixed,
This is sent to an oxyhydrogen flame burner 7 along with calculated amounts of oxygen gas and hydrogen gas sent from a combustion gas supply pipe 6, and this flame is sent to a reaction vessel 9 having an exhaust port 8 made of quartz, carbon, silicon carbide, etc. Porous glass may be deposited on a heat-resistant starting base material 10 such as the above, and the porous glass may be pulled up vertically using a rotary pulling device 11 to form a porous base material 12.

The method of the present invention is to make the refractive index distribution of the porous preform 12 grown in this manner uniform, thereby making the transmission band characteristics of the optical fiber produced from it uniform. That is, in the method of the present invention, as shown in FIG. Since the fluctuation value of the atmospheric pressure is fed back to the mass flow controller control bag [16], the supply amount of the raw material gas can be corrected based on this. To correct this raw material gas supply amount, for example, the changes in the evaporation amount of silicon tetrachloride and germanium tetrachloride as a dopant due to fluctuations in atmospheric pressure are determined from Fig. 2, and then the amount of carrier gas is adjusted to correct the amount of change. The corrected flow rate may be determined using FIG. However, the relationship between the change in the amount of evaporation of the raw material gas due to the atmospheric pressure fluctuation shown in FIG. 2 and the carrier gas correction amount to keep the raw material gas supply amount constant in response to the atmospheric pressure fluctuation shown in FIG. If stored, the mass flow controller control device 16 can control the mass flow controllers 4 and 5 in response to changes in atmospheric pressure, control the carrier gas, and accurately correct the amount of evaporation of the raw material gas. .

In this case, it is necessary to control the ratio of silicon tetrachloride as the raw material gas and the dopant to be constant, but instead of correcting the amount of carrier gas as described above, it is necessary to control the temperature of the raw material bubbler. The change in the amount of evaporation of the raw material gas due to atmospheric pressure may be corrected by The advantage is that the material can be easily obtained.

In addition, by the method of the present invention, for example, an outer diameter of 80III
m, length 800 ■ When producing an ugly graded index type optical fiber base material, the pulling speed of the porous base material is set to 51°5 to 51.7 mm/min by the method described above.
and the amount of silicon tetrachloride carrier gas is 0.2
7 to 0.31 fl/min, dopant carrier gas amount to 0
．． It should be controlled within the range of 20 to 0.22 Ω/min, but according to this, the outer diameter is 79 to 81 am and the length is 800 ohms! It is possible to stably obtain a graded index type optical fiber base material with a transmission band of about 1,200±150 MH2-1 in the length direction, for example, by continuous operation for two months, The advantage is that you can stably obtain as many as 50 of these, instead of having a single one.

Next, examples of the method of the present invention will be shown.

Example Using the apparatus shown in Fig. 1, the internal volume was 1°312
A starting substrate made of quartz glass with a diameter of 16III and a length of 200 mm was suspended in a rotating lifting device in a reaction vessel, and 5iC1 and gas of 0.3
8Q1 min, G e C1 as dopant, gas 0.
036 A/min, a mixed gas consisting of 10°001 min of oxygen gas and 6.8 Q1 min of hydrogen gas was introduced, and the oxyhydrogen flame was applied to the starting substrate to deposit porous glass on the N plate.
The starting substrate was pulled up at a constant speed of 51.5 mm/hour to produce a porous glass preform.

At this time, the bottom of the porous base material 12 is monitored with a television camera in the television display 13 so as to be in contact with the base line 17, and the pulling speed is controlled.
S i C14 carrier gas amount 0.27 to 0.316
1 minute, GeC1, carrier gas amount 0.20-0.22
When the mass flow controller 4,511 was used to control the amount within each specified amount for Q1 minutes and the system was operated continuously for two months, 50 graded index type optical fiber base materials with an outer diameter of 80 mm and a length of 800 mm were obtained. However, the transmission band (1,3Im) of these is 1
It was stable at 050~1, 790MHz, 4m, and there were no low transmission bands, and these showed the results shown in Table 1.

However, for comparison, an optical fiber base material was prepared in the same manner as above except that the device other than the barometer 18' in Fig. 1 was used. The results obtained showed that the transmission band was low and had large variations.

Table 1

[Brief explanation of the drawing]

Fig. 1 shows a longitudinal cross-sectional view of the manufacturing equipment used in the method of manufacturing an optical fiber preform according to the method of the present invention, Fig. 2 shows changes in evaporation amount due to atmospheric pressure fluctuations, and Fig. 3 shows changes in the amount of evaporation due to atmospheric pressure fluctuations. 3 is a graph showing a correction amount of carrier gas for making the raw material gas constant with respect to FIG. 1.2... Bubbler for raw material gas supply, 3... Carrier gas supply port, 4.5... Mass flow controller 6... Combustion gas, 7... Burner, 8... Exhaust port, 9 ... Reaction container, 10... Starting base material, 11... Rotary pulling device, 12... Porous base material. 13... Television display, 14... Television camera, 15... Lifting control device,

Claims (1)

[Scope of Claims] 1. A base material in which a specified amount of gaseous glass raw material consisting of silicon tetrachloride and a dopant is introduced into an oxyhydrogen flame burner and subjected to flame hydrolysis, and the resulting glass particles are rotated. In this method, a porous glass body is grown in the axial direction by pulling up the base material, and the porous glass base material is made into transparent glass to produce an optical fiber base material. A method for producing an optical fiber base material, characterized in that the amount of glass raw material is set to a value that corrects the amount of change due to atmospheric pressure. 2. The method for manufacturing an optical fiber preform according to claim 1, wherein the amount of change in the barometer is fed back to a system comprising a mass flow controller and a mass flow controller control device to control the amount of gaseous glass raw material to be constant.