JPH02172839A - Production of base material for optical fiber - Google Patents

Abstract

PURPOSE:To improve production efficiency by depositing fine glass particle layers for a clad around a rod for a core and depositing the layers while increas ing the spacings between adjacent burners with an increase in the deposition thickness. CONSTITUTION:The previously formed transparent glass rod 1 of GeO2-doped SiO2 is rotated at about 30rpm and is traversed at about 40mm/min speed in an axial direction. The multinozzle burners 3, 3 which supply SiOCl4 as a glass raw material to a central part 10, gaseous Ar to the 2nd layer 12, H2 to the 3rd layer 14, and O2 to nozzles 16 are disposed to the lower part at the right end of the rod 1 to supply burner flames. The spacing D between the burner 3, 3 is first kept at about 65mm. This spacing is increased successively by about 5mm each at every one traversing in one way of the rod 1 so that the burners are spaced at about 130mm at the time of the final 14th traversing. The base material for optical fibers having about 50mm thickness of the fine glass particle deposited layers 2 (e.g.: porous SiO2 glass layer) for the clad is produced while the interference of the burner flames with each other is prohibited.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for manufacturing an optical fiber preform, which includes a step of depositing a glass fine particle layer to serve as a cladding around a core rod using a plurality of burners. The aim is to improve productivity by preventing a decrease in the deposition rate.

(Prior art) In this type of conventional method, as shown in FIG. 3, a plurality of burners, for example two burners 3.3, are used on a core rod l, and the burners are traversed in the axial direction of the rod. The glass fine particle layer 2 for cladding is deposited while
Even though the deposition thickness gradually increased, the distance d between the burners 3.3 remained constant during production. Note 4
．． 4 is burner flame.

(Problem to be Solved by the Invention) However, at the beginning of the deposition of the glass fine particle layer, the flames of adjacent burners are far apart and do not interfere with each other, so there is no problem, but as shown in FIG. As the flame progresses, the thickness increases and the outer diameter gradually increases (as the distance between the burner 3.3 and the rod 1 approaches, the burner flames 4.4 partially overlap on the deposition surface, and the deposition surface There is a correlation between the temperature of the deposition surface and the deposition rate of glass particles, and as the temperature increases, the deposition rate decreases.This leads to a decrease in the manufacturing efficiency of the base material, so it is necessary to improve it. was desired.

(Means for Solving the Problems) From the above points of view, the present invention is directed to forming a porous glass by depositing a layer of glass fine particles that will become a cladding around a core glass rod using a plurality of burners. In a method for manufacturing an optical fiber preform including a step of making a preform, as the deposited thickness of the glass fine particle layer for cladding increases, the distance between adjacent burners is increased to prevent interference between burner flames while depositing. In particular, when manufacturing a base material for single mode fiber using this method, the number of burners is 3 because it is necessary to have a sufficient cladding thickness.
It is effective because there are as many as ~5 trees.

(Function) Since there is no mutual interference between adjacent burners, the surface temperature of the surface on which the glass fine particles are deposited can always be maintained constant, and a decrease in the deposition rate of the glass fine particles can be prevented.

(Example) FIG. 1 shows how a glass fine particle layer for cladding is formed on a core rod by the method of the present invention, and the same reference numerals indicate the same parts as in FIG. 3. Further, FIG. 2 shows the specific structure of the multi-nozzle burner 3 used. In Figure 2, the central part 0 has 5tOCj as a glass raw material! 4. A as a seal gas in the second layer 12
r, H2 is supplied to the third layer 14, and 02 is supplied to 12 nozzles 16 formed concentrically inside this third layer. In the above, 1 is pre-formed GeO□-doped Sin transparent glass fine particles, the outer diameter of which is 17III.
III. The total length is 1800 mm, of which the effective length that can eventually become the base material is approximately 750 mm. While rotating this rod 1 at 3Orρm, it is rotated 40M/in the axial direction.
traversed at a speed of 1 minute. At this time, each of the multi-nozzle burners 3.3 with the structure shown in FIG.
Ce s 3.0~5.011/min, ^r1.8j2/
Minutes, Hz30-451! /min, 0°15-2317 min.

Initially, the spacing between the burners 3.3 is kept at 65+nm, and the spacing is sequentially increased to 70nnu, 75mm, 80mm, and 5IIIIl for each one-way traverse of the rod L.
13 by the time of the final 144th layer traverse.
0mm apart. Here, the reason why the burner spacing is gradually lowered for each traverse is due to the accumulation of Sin deposited on the rod l.As the outer diameter increases, the lateral spread of the flame increases and the adhesion area increases due to the deposition of a glass fine particle layer. This is to do so.

The time it took for the thickness of the thus obtained Sin and porous glass layer to reach the predetermined thickness of 50 mm was 417 minutes, which was significantly improved compared to the conventional method, which took about 490 minutes.

In the embodiment of the present invention, the core rod is used as the traverse, but the burner may also be the traverse.

(Effects of the Invention) As described above, this invention keeps the deposition rate of glass fine particles for cladding on the core rod always at a predetermined amount by preventing mutual interference of the burner flame. production efficiency can be increased.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram showing a method for manufacturing an optical fiber preform according to the present invention, Fig. 2 is an explanatory diagram of a burner used in Fig. 1, and Figs. 3 and 4 are diagrams showing a conventional optical fiber preform. FIG. 2 is a schematic explanatory diagram showing a manufacturing method. In the figure, 2: glass fine particle deposition layer for gland; 3.
3: Burner, D: Burner interval.

Claims (1)

[Claims] A method for producing an optical fiber preform comprising the step of depositing a glass fine particle layer to become a cladding around a core glass rod by an external method using a plurality of burners to form a porous glass preform. A method for manufacturing an optical fiber preform, characterized in that as the deposited thickness of the glass fine particle layer increases, the distance between adjacent burners is increased to prevent interference between the burner flames while depositing the layer.