JPS62162637A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To enable the expansion of controllable range of a refractive index distribution along radial direction of a large-sized porous preform in the production of an optical fiber preform by VAD process using a vertically mounted multiple tube burner, by placing a hood surrounding the multiple tube burner and supplying an inert gas and hydrogen gas to the hood. CONSTITUTION:A glass raw material supplied from the central nozzle 2a of a vertically mounted multiple tube burner 1 is hydrolyzed with oxyhydrogen flame supplied from the outer nozzles 4a, 5a. Soot is deposited on an end of a target above the burner 1 by this process to obtain an optical fiber preform. Hoods 7, 8 surrounding the oxyhydrogen flame blasted from the burner is placed at the outer circumference of the multiple tube burner 1 and an inert gas and hydrogen gas are supplied to the above soot through the hoods 7, 8. Preferably, the hood has double-walled structure (7, 8), the inner hood 7 is supplied with an inert gas (e.g. N2) and the outer hood 8 is supplied with a mixture of inert gas and hydrogen gas (the mixed gas may be supplied through one hood).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical fiber preform by the VAD method, and in particular, a method for manufacturing an optical fiber preform by using a vertically erected multi-tube burner to target glass raw materials, oxyhydrogen flame, etc. The present invention relates to a method for manufacturing an optical fiber preform in which a soot of a porous preform is formed by supplying a porous preform.

[Prior art] Optical fiber base material yJ3 by VAD method (vapor phase attachment method)
i! In the i method, glass raw material is ejected from the center of a multi-tube burner together with a carrier gas toward a target such as a quartz rod, and this is hydrolyzed by an oxyhydrogen flame supplied from the outside of the burner to inject a glass medium ( By forming a porous base material of soot) and heating and sintering it, a transparent vitrified optical fiber base material is formed.By rotating the target and pulling it upward, a circular rod-shaped porous base material is formed. There is an advantage that the base material can be formed to any length.

In this VAD method, multi-tube burners are arranged diagonally,
Glass raw materials are ejected diagonally upward, but when a multi-tube burner is placed vertically, a hood integrated with the multi-tube burner is installed around the burner to stabilize the flame and control the refractive index distribution of the optical fiber. The hood is equipped with an inert gas such as N2 gas.

When a large amount of glass raw material such as 5iC14 or Geα4 or fuel such as 112.02 is fed into a burner having such a structure, the outer diameter, growth rate, etc. of the porous base material can be increased with respect to the feeding period.

[Problems to be Solved by the Invention] However, in order to control the refractive index distribution of optical fibers, there is a limit to the inner diameter of the central part of the multi-tube burner, that is, the inner nozzle that ejects the glass raw material. You can't make it bigger. Therefore, even if you try to increase the outer diameter of the porous base material, the temperature distribution will not expand, and the range in which the refractive index distribution can be controlled is determined by the width of the flame.When the porous base material is made into transparent glass, the core rod When the outer diameter of the refractive index is 1, the refractive index distribution has a gradient and the so-called grated type portion is 0.5 to 0.7, and the remaining outer peripheral portion becomes the cladding portion.

Furthermore, when fabricated into a fiber, the boundary between the core and cladding becomes unclear, and a sloppy distribution that cannot be evaluated using the refractive index distribution constant α is likely to occur, which is a hindrance when trying to widen the transmission band. Become.

[Object of the Invention] An object of the present invention is to eliminate the drawbacks of the prior art described above, and to expand the range of control of the refractive index distribution in the radial direction of the porous base material when increasing the size of the porous base material. An object of the present invention is to provide a method for manufacturing an optical fiber preform.

[Summary of the Invention] The gist of the present invention is that a hood is provided on the outer periphery of a multi-tube burner, and inert gas and hydrogen gas are supplied to the hood. In addition, by flowing hydrogen gas, the 112 + 02 reaction occurs over a wide range, making it possible to widen the range of uniform temperature distribution and expand the range of refractive index distribution control even if the porous base material is made larger. This makes it possible to obtain a broadband optical fiber preform.

[Example] Hereinafter, a preferred example of the method for manufacturing an optical fiber preform according to the present invention will be described with reference to the accompanying drawings.

In Fig. 1, 1 is a vertically arranged multi-tube burner;
It consists of a four-layered structure of quartz glass tubes, with two raw material supply tubes extending from the center to the outside. Inert gas supply pipe 3゜Hydrogen supply pipe 4. Oxygen supply pipes 5 are arranged concentrically in order, and nozzles 2a, 3a are provided at each open end of the upper end.

4a and 5a are formed. The raw material supply pipe 2 has a diameter of 5.
6 to 7.0 shoes φ, inert gas supply 'r23 is 8.6 to 1
0.0mmφ, hydrogen supply pipe 4 is 14.0~16.0IMφ
, the oxygen supply pipe 5 is formed to have a diameter of 20.0 to 23.0 mm. 5iCQ4 is added to the raw material supply pipe 2 at a rate of 8 g/min, G
Supply eCl4 at 450 rng/ln, main 1 Syrian gas static at 1200 CC/rain, and inert gas supply pipe 3.
^r at 800CC/min, hydrogen supply pipe 4 at 112 at 7J/min, oxygen supply pipe 5 at 02 at 10
J/rain is supplied respectively.

A double hood 7 made of quartz glass tubes surrounds the flame 6 from the burner 1 on the outer periphery of the multi-tube burner 1.
．． 8 is provided.

The pipe diameter of this double hood 7.8 is that the inner hood 7 is 38.
~34#lIφ, outer hood 8 has N2. A mixed gas of inert gas such as Ar and hydrogen gas is supplied, and for example, N2 is supplied to the inner hood 7 at 10.1! /min, outer hood 8
40J of N2! , '+in and 112 to 47/In1
A mixed gas of n is supplied.

In the above, the glass raw material (Si (J4.
GaCl2) is supplied from the outside with 02, +1
A hydrolysis reaction is caused by the oxyhydrogen flame in step 2, and SiO2,G
The soot becomes eO2, which is deposited on the tip of the target and grows.

In this case, the flame 6 of the multi-tube burner 1 has a double hood 7.8
The flame 6 is stabilized by the gas flow from the outer hood 8, and the 112 gas supplied together with the N2 gas reacts with the oxygen in the flame 6, forming a porous hole at the tip of the target! ! It is possible to prevent a temperature drop in the outer circumference of the shrine, to uniformly widen the temperature distribution, and to control the refractive index distribution even if the diameter of the porous base material is increased.

Next, FIG. 2 shows the refractive index distributions of the optical fiber preform obtained by the method of the present invention and the optical fiber preform obtained by the conventional method. In this case, the conventional method uses the burner shown in FIG.
Inner hood 7 has N2jj SuwoIOJ/n+in
,' 40 J/1n of N2 gas was flowed into the outer hood 8.

In FIG. 2, in the conventional example, the core equivalent part to the lot outer diameter is 0.62, and the refractive index becomes sloppy around 0.62, but in the present invention a, the core equivalent part to the lot outer diameter is 0.62. 0.80, it can be seen that the cladding portion is reduced and the boundary between the core portion and the cladding portion is clear.

In the above-mentioned embodiment, a double hood was provided around the outer circumference of the multi-tube burner 1, and hydrogen gas was made to flow along with an inert gas through the outer two hoods. Alternatively, an inert gas and hydrogen gas may be supplied. In addition, we have shown an example in which the hydrogen gas supplied to the hood is approximately 1/10 that of inert gas.
Of course, the proportion of hydrogen gas mixed in can be increased or decreased as appropriate depending on the diameter of the porous base material to be formed.

[Effects of the Invention] As is clear from what has been described in detail below, the present invention provides the following distinct effects.

(1) A hood is installed around the outer periphery of the vertical multi-tube burner, and inert gas and hydrogen gas are supplied to the hood, so that the reaction between the hydrogen gas and the oxygen from the burner can occur over a wide range. As a result, the bottom surface temperature distribution of the porous base material becomes wider, and the refractive index distribution control range can be widened.

(υ) It is possible to increase the ratio of the core-corresponding portion to the outside diameter of the lot, and to reduce the unevenness of the refractive index distribution at the boundary, thereby achieving a wider band.

(3) Changes in the bulk density of the porous base material in the radial direction can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a hooded multi-tube burner used in the method for manufacturing an optical fiber preform of the present invention, and FIG. 2 is a diagram without showing the refractive index distribution that differs between the present invention and the conventional example. . In the figure, 1 is a multi-tube burner, 2a is a frit supply nozzle, 4a is a hydrogen supply nozzle, 5a is an oxygen supply nozzle, 6 is a flame, and 7 and 8 are hoods.

Claims (2)

[Claims] (1) Optical fiber that hydrolyzes the glass raw material supplied from the central nozzle of a vertical multi-tube burner using an oxyhydrogen flame supplied from the outer nozzle to generate soot at the target tip above the burner. In the method for manufacturing the base material,
An optical fiber characterized in that a hood is provided on the outer periphery of the multi-tube burner to surround the oxyhydrogen flame ejected from the burner, and inert gas and hydrogen gas are supplied from the hood to the soot. Method of manufacturing base material. (2) A patent claim characterized in that the hood consists of a double hood, and the inner hood is supplied with inert gas, and the outer hood is supplied with a mixed gas of inert gas and hydrogen gas. A method for manufacturing an optical fiber preform according to Item 1.