JPH02307838A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To equalize the bulk densities of fine grain layers and to produce the preform having a stabilized specific refractive index between the core and clad by monitoring the surface temp. of the fine glass grain deposit and controlling the amt. of a gas to be supplied into the burner. CONSTITUTION:A rod 1 is rotated, plural burners 3 and 4 are traversed in the axial direction of the rod 1, and a gas is supplied at a specified flow rate to deposit fine quartz glass grains. The temp. of the surface layer 21 of the grains formed by the preceding burner 3 is measured by a radiation thermometer 31, etc., and the temp. of the surface layer 22 of the fine glass grains formed by the succeeding burner 4 is measured. The amt. of the gas to be supplied to the preceding burner 3 is adjusted in each traverse so that both temps. are equalized, and the bulk density of the entire grain layer is uniformized. The fine glass grain layer is placed in a heating furnace and dehydrated, then the furnace is filled with a high-temp. gaseous fluorine atmosphere to vitrify the layer, and a fluorine-doped Si layer is obtained. As a result, an optical fiber preform in which the refractive index in the clad is not fluctuated is obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention involves depositing glass particles around a core rod using a plurality of burners, and doping it with fluorine to form a cladding when making it transparent. This relates to a method of manufacturing an optical fiber preform, in which the refractive index of the cladding is kept constant by uniformly doping fluorine, and the transmission characteristics of the resulting fiber are improved.

(Prior Art) In this type of conventional method, as shown in FIG. , 4 in the axial direction of the rod 1 to form the Sing glass fine particle layer 2. In the figure, 21 is a glass fine particle layer formed by the preceding burner 3, and 22 is a glass fine particle layer formed by the following burner 4. Next, this glass fine particle layer 2 is subjected to dehydration treatment as necessary, and then heated to a high temperature in a fluorine gas atmosphere to make it transparent vitrified to form a fluorine-doped SiO□ glass whose refractive index is lowered by fluorine. Use as optical fiber base material.

(Problem to be Solved by the Invention) However, since the heat of the preceding burner flame is absorbed by the core rod 1 and the glass fine particle layer 21 deposited earlier, the deposition surface of the preceding burner flame is smaller than that of the following burner flame. A phenomenon occurs in which the temperature of Therefore, the bulk density of the glass fine particle layer 21 obtained by the preceding burner is different from the bulk density of the glass fine particle layer 22 obtained by the succeeding burner, and as a result, the amount of fluorine to be doped during transparent vitrification is affected. As shown in FIG. 4, slight fluctuations in the refractive index occur within the cladding, and the relative refractive index difference between the core and the cladding becomes unstable. In addition, the burner temperature and the temperature of the glass particle deposition surface,
Regarding the relationship between the bulk density of the obtained glass particles, the lower the temperature, the softer the layer becomes with a lower bulk density, and the easier it is to dope with fluorine.

(Means for Solving the Problems) In view of the above, this invention deposits a glass fine particle layer around a core glass iron by an external method using a plurality of burners, and this glass fine particle layer is coated with fluorine. When creating a fluorine-doped clad preform by transparent vitrification in a gas atmosphere, the amount of gas supplied to the burners is adjusted so that the temperature of the surface on which glass particles are deposited by each burner is constant, so that the bulk density is equal. It was made so that it would become so.

Note that the temperature of the surface on which the glass particles are deposited and grown is measured using, for example, a radiation thermometer.

(Function) The surface temperature of the surface on which the glass particles generated by each burner are deposited is constantly monitored, and the amount of gas supplied to each burner is adjusted so that the temperatures are equal. The bulk density of the fine particle layer becomes equal. the result,
Since the fluorine doping profile is constant, there is no variation in the refractive index within the cladding, and a constant value can be obtained in the radial direction.

(Example) This invention will be explained based on FIG. 1. In the figure, the same parts as in FIG. 3 are given the same reference numerals.

GeO□ doped Si is pre-coated for the core by VAD method.
A 0g transparent glass rod 1 was prepared. The rod 1 has an outer diameter of 14 m and a total length of 1800 mm, of which the effective length is approximately 750 mm. This rod 1 was rotated at 2 rpm. On the other hand, a double nozzle type burner shown in FIG. 2 was used as the burner 3.4. In the figure, reference numeral 10 denotes two nozzles arranged in parallel in the center, each of which has a concentric double pipe structure, with 5iC24 supplied to the inner pipe 12 and Ar as a sealing gas supplied to the outer pipe 14. Ru. 1
Reference numeral 6 denotes a group of annular pipes located so as to surround this double nozzle 10, each of which is supplied with oxygen gas. 18 is an outer tube into which hydrogen gas is supplied. These two burners 3.4 were traversed in the axial direction of the rod 1 at a speed of 40 mm/min, and gas was supplied to both of them at the flow rates shown in Table 1.

Table 1 Internal Vibrator 12 5iCfa 2.5 SLM
Ar 1.5 SLM external pipe 14 Ar 3.5 SLM annular pipe group 16 o, 11.5 SLM external pipe 18 Hz 23. However, the temperature of the radiation thermometer 31 of the glass particle surface layer 21 by the leading burner 3 showed 1100°C, and the temperature of the radiation thermometer 4A of the glass particulate surface layer 22 by the trailing burner 4 showed 1200°C. The amount of gas supplied into the burner 3 was changed as shown in Table 2 below.

Table 2 Internal Vibrator 12 5iC1< 2.5 SLM
Ar 1.5SLM external pipe 14 Ar 3.5SLM circulation vibe group 16 0! 11.5 SLM outer tube 1
8 H223, OSLM As a result, the temperatures of the glass particle surface layers 21 and 22 obtained by the leading burner 3 and the trailing burner 4 became equal.

Thereafter, the amount of gas supplied to the preceding burner 3 was adjusted every time the traversal was carried out, and the bulk density of all the glass fine particle layers was made equal. Subsequently, this glass fine particle layer was placed in a heating furnace and heated to C.
2! After dehydration treatment, the temperature was raised to a higher temperature and the inside of the furnace was made into a fluorine gas atmosphere to achieve transparent vitrification to obtain a fluorine-doped 5T (h layer) and a core clad preform.

When the refractive index of the second preform was measured, the cladding portion was uniform in the radial direction.

(Effect of the invention) As described above, this invention uses a plurality of burners to
When obtaining a layer of glass particles consisting of By doing so, the refractive index of the resulting fluorine-doped 5iOz cladding can be maintained constant, and a base material with a stable relative refractive index difference between the core claddings can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a method for manufacturing a SiO□ glass particle layer according to the present invention, FIG. 2 is a burner for manufacturing glass particles, and FIG. 3 is a schematic diagram showing a conventional method for manufacturing an optical fiber preform. The explanatory diagram, FIG. 4, is a schematic diagram showing the refractive index distribution of the base material obtained by the conventional method. In the figure, 2: Sin, glass fine particle layer, 21
: 5iOz glass fine particle layer by preceding burner 3, 22:
Sing glass fine particle layer by trailing burner 4, 31°4
1: Radiation thermometer.

Claims (1)

[Claims] Silica glass fine particles are deposited around a rod for a quartz glass core by an external method using multiple burners, and the resulting quartz glass fine particle layer is made into transparent glass in a fluorine-containing gas atmosphere to form a fluorine-doped silica glass cladding. In the method for manufacturing an optical fiber preform, the amount of gas supplied to each of the burners is adjusted so that the bulk density of the silica glass fine particle layer obtained by each burner is equalized and deposited. Method for manufacturing fiber base material.