JPS6048456B2 - Method for manufacturing base material for optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber preform by a vapor deposition method (VAD method).

A conventional manufacturing method of this type will be described below with reference to the illustrative diagram of FIG. In FIG. 1, raw materials supplied from a line 11 form a flow 2 of core glass particles synthesized by a core particle synthesis torch 1.

The raw material supplied from the line 12 forms a flow 4 of glass fine particles for cladding which are synthesized by the fine particle synthesis torch 3 for cladding. The exhaust gas is discharged from the line 14 via the displacement regulator 16. Flow of glass particles for core 2
With the flow 4 of glass particles for cladding, a porous glass body for a core is adhered to the center and a porous glass layer for cladding is attached to the outer periphery of the sintered rod-shaped glass sintered body 7. The protective container 15 is rotated and pulled up by a rotary pulling device 10 provided above the protective container 15 via the support rod 9, thereby causing growth. The rod-shaped sintered body thus produced is heated at 1500 to 1600°C to become a transparent vitrified optical fiber base material.

According to such a conventional method, a flow 2 of core glass particles and a flow 4 of cladding glass particles synthesized by the core particle synthesis torch 1 and the cladding particle synthesis torch 3 are diffused into each other. It is very difficult to prevent mixing, and as a result, the base material of the refractive index distribution spreads at the boundary between the core and the cladding in the transparent vitrified optical fiber base material made from the bar-shaped glass sintered body. An example of this is shown in the graph of refractive index distribution versus diameter in FIG.

In FIG. 2, X1-X2, X3-X are the outer circumferential portions which are cladding, . . . -X3 are the central portion which is the core. Because of this, when fabricating a single-mode optical fiber that is strongly affected by the spread of optical power to the cladding layer, it will be more affected by the spread of optical power due to this base spread. There were problems such as insufficient cladding layer thickness and difficulty in reducing loss.
In addition, there have been other problems such as foreign glass fine particles and other impurities adhering to the surface of the porous base material for the core, causing air bubbles to remain during transparent vitrification.

An object of the present invention is to provide a method for manufacturing an optical fiber preform that solves the problems of the conventional technology as described above. The method for manufacturing an optical fiber preform of the present invention is characterized by depositing glass particles for a cladding on the side surface of a porous glass body for a core formed by depositing glass particles for a core. When forming the quality glass layer, a gas is blown from a gas blowing nozzle between the porous glass body deposited part for the core and the porous glass body deposited part for the cladding to mix the glass fine particles for the core and the glass fine particles for the cladding. It is about restraining.

According to the method of the present invention, it is possible to prevent the refractive index distribution from widening at the boundary between the core and the cladding. The invention will now be described in one embodiment with reference to the schematic diagram of the apparatus shown in FIG. The apparatus shown in FIG. 3 differs from the apparatus shown in FIG. , flow 2 of glass particles for the core and glass particles for the cladding.
This is to prevent the particle streams 4 from mixing.

That is, this gas flow suppresses mixing of the core glass particles with the cladding glass particles at the boundary between the core porous glass body deposition section and the cladding porous glass body deposition section. The other points are completely the same as those shown in FIG. 1, and therefore, all the same parts are indicated by the same reference numerals. Gas nozzle 5 uses gas from gas line 13 to generate gas stream 6 .

In this case, an inert gas such as Ar may be used as the blowing gas. However, care should be taken to prevent the surface temperature of the porous glass body deposit from dropping too much due to the core glass particles. It is preferable to mix a mixture of combustible gases such as , H. and combustible gases such as 0.
As shown in the cross-sectional view of the figure, there is a mixing prevention gas in the center.
For example, an Ar gas outlet 17 may be provided, a concentric annular cylindrical hydrogen gas outlet 18 may be provided on the outside of the Ar gas outlet 17, and a concentric annular cylindrical oxygen gas outlet 19 may be further provided outside of the hydrogen gas outlet 18. Next, a specific example of reaction conditions in Examples of the present invention is as follows.

The fine particle synthesis torch 1 for the core is supplied with SiC from the line 11.
92:7:1 (MO
A mixed gas of
Hydrolysis was carried out using an oxyhydrogen flame composed of 2 gases at 31/min, O2 gas at 51/min, and He gas at 11/min to deposit a porous glass body for the core.

In addition, the fine particle synthesis torch 3 for cladding includes a line 12.
99:1 (MOl%) of SiCL4, POCI-3
A mixed gas of 300 cc/Min was sent together with 300 cc/Min of He gas for carrier at a flow rate of 300 cc/Min. Gas 51/Min, He gas 11
A porous glass layer for cladding was deposited by hydrolysis with an oxyhydrogen flame consisting of /Min. Furthermore, the gas nozzle 5, which constitutes the feature of the present invention, is supplied with Ar gas 11/Mln to the outlet 17, Lu gas 0.51/Min to the outlet 18, and 02 gas to the outlet 19 from the line 13. 11/Min was supplied to generate a flame flow 6, thereby suppressing the mixing of the glass fine particles for the core and the glass fine particles for the cladding. The rod-shaped glass sintered body thus obtained was heated at a temperature of 1500° C. to 16000° C. to obtain a base material for a transparent vitrified optical fiber.

The step-type refractive index distribution of this optical fiber base material is shown in the graph of FIG.

In Fig. 5, X2 to X3 are the core parts, and X1
~X2, X3~X. is the cladding part. As is clear from FIG. 5, there was hardly any sagging at the boundary between the core and the cladding. Furthermore, when this manufacturing method was applied to the manufacturing of a single mode optical fiber, it was found that the spread of optical power to the cladding portion could be suppressed. FIG. 6 shows the loss characteristics of a single mode optical fiber obtained from a base material manufactured by an example of a conventional method and an optical fiber according to an embodiment of the present invention. The dashed curve a is for the conventional method, and the solid curve b is for the present invention. The synthetic rat/core diameter ratio of all fibers is about 4, but 1.39
Looking at the OH group absorption loss in μm, it is about 2 ppm in the conventional method and about 0.5 ppm in the method according to the present invention. The spread of optical power is 0H in the cladding part.
This extends to the jacket tube with a high group content in all fibers, but in the case of the fiber of the present invention, there is almost no skirting in the refractive index distribution, so the 0H group absorption loss is lower. be. As explained above, according to the method of the present invention, the skirting of the core/cladding boundary portion of the refractive index distribution can be suppressed.

If this is applied to a method for manufacturing a single mode optical fiber, the spread of optical power will be suppressed compared to conventional methods, making it easier to achieve lower loss. Furthermore, the gas from the gas nozzle protects the surface of the base material, preventing impurities from adhering to the porous glass body for the core, making it possible to easily obtain a homogeneous base material for optical fiber. Furthermore, the method of the present invention can be applied to the production of base J material for multimode optical fibers, and can also be applied to the production of so-called fully synthetic optical fibers that do not use jacket tubes. It is effective in preventing diffusion mixing.

[Brief explanation of the drawing]

Fig. 1 is an illustrative diagram of an apparatus for explaining a conventional method for manufacturing an optical fiber preform, and Fig. 2 is a graph showing an example of the refractive index distribution of an optical fiber preform manufactured by the conventional method. . FIG. 3 is an illustrative diagram of an apparatus for explaining one embodiment of the method of the present invention, FIG. 4 is a cross-sectional view of the gas nozzle for preventing mixing of glass particles in FIG. 3, and FIG. 5 is an embodiment of the present invention. FIG. 6 is a graph showing a comparison of loss characteristics of a conventional example and a single mode optical fiber manufactured according to an embodiment of the present invention. be. 1...Fine particle synthesis torch for core, 2...Flow of glass particles for core, 3...Fine particle synthesis torch for cladding, 4...Flow of glass particles for cladding, 5
... Gas nozzle, 6 ... Gas flow from the gas nozzle, 7 ... Rod-shaped glass sintered body, 8 ... Starting material substrate, 9 ... Support rod, 10 ... Rotary pulling device,
11, 12... Raw material line, 13... Gas line,
14... Exhaust line, 15... Protective container, 16...
・Exhaust volume regulator, 17...Mixing prevention gas outlet, 18
...Hydrogen gas outlet, 19...Oxygen gas outlet.

Claims (1)

[Claims] 1 Glass fine particles for the core are synthesized using a fine particle synthesis torch for core, and deposited on one end of the support rod to grow a porous glass body for the core in the axial direction.At the same time, glass fine particles for the cladding are synthesized using a fine particle synthesis torch for cladding. In a method for manufacturing an optical fiber base material which is a rod-shaped glass sintered body by depositing it around a core porous glass body to form a cladding porous glass layer, a core porous glass body deposition part A method for producing an optical fiber base material, comprising: blowing gas from a gas blowing nozzle between the core glass particles and the clad glass particles to suppress mixing of the core glass particles and the cladding glass particles.