JPH0437623A - Manufacturing method of optical fiber base material - Google Patents

Abstract

PURPOSE:To obtain a high-strength optical fiber by subjecting a glass rod to heat treatment and depositing fine particles of quartz glass containing no fluorine on the glass rod, in the process of forming a porous glass layer on a glass rod by external chemical vapor deposition method. CONSTITUTION:Before glass fine particles are deposited on a quartz glass rod 11 containing fluorine, this glass rod 11 is subjected to heat treatment. By this treatment, fluorine contained near the surface of the glass rod 11 is ejected and the fluorine density near the surface is decreased. Then fine particles of quartz glass containing no fluorine prepared by flame hydrolysis of a vapor- phase glass source material are deposited on outer circumference of the glass rod 11 to form the porous glass layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an optical fiber preform by forming a porous glass layer on the outer periphery of a glass rod through an external CVD method.

``Conventional Technology J'' One of the glass synthesis methods based on flame hydrolysis reaction,
There is an external CVD method in which fine glass particles are generated using an eight-tube structure and the glass particles are deposited on the deposition surface of a glass rod.

When making optical fiber material through external CVD method,
Fuel gas (H2) and auxiliary combustion gas (0
2), Gas phase (7):ff7. original) 1 (e.g. SiC: 1
4) By supplying nitrogen gas, these gases undergo a flame hydrolysis reaction, and the soot-like glass particles generated by this reaction are deposited and grown on the deposition surface (outer surface) of the quartz-based glass rod to form porous glass. form a layer.

Thereafter, the porous glass layer is heat treated in a predetermined atmosphere 1' to dehydrate it and make it transparent vitrified.

- As an example, it has been carried out to form a cladding glass layer of fluorine-doped quartz (Si02-F) around a core glass of pure quartz (Si07).

However, in this example, when spinning the optical fiber preform, the soil force tends to concentrate on the core glass.

In order to solve this problem, a glass rod with a softening temperature higher than that of S102-F glass was added to the outer periphery of a glass rod consisting of core glass (Si02) and cladding glass (Si02-F) using an external CVD method. A glass layer (Si02) is formed.

When such a method is used, stress concentration on the core glass is reduced.
It is tempered by an outer high softening point (high melting point) glass layer.

“Problem to be solved by the invention 1 In the above-mentioned prior art, cladding glass (Si0
2-F), when a high softening point glass layer (Si02) is formed on the outer periphery of the optical fiber, microbubbles are generated at the interface between the 5iOz-F glass and the 5i02 glass, which reduces the breaking strength of the optical fiber.

In view of such technical problems, the present invention provides a method that does not generate microbubbles at a predetermined glass interface, that is, it is possible to obtain an optical fiber preform with excellent mechanical properties. That is.

In order to achieve the intended purpose of the present invention, quartz-based glass fine particles produced by a flame hydrolysis reaction of a vapor-phase glass raw material are added to the outer periphery of a fluorine-containing quartz-based glass rod. Let it accumulate,
In the method for manufacturing an optical fiber preform in which a porous glass layer is formed on the outer periphery of the glass rod, before depositing glass particles,
The method is characterized in that the glass rod is heat-treated, and then fluorine-free quartz-based glass fine particles are deposited on the outer periphery of the glass rod.

r Effect 1 In the method of the present invention, the glass rod is heat treated before the glass fine particles are deposited.

When the glass rod is heat-treated in this manner, a part of the fluorine contained near the outer surface of the cladding glass is scattered toward the core glass side, and the fluorine concentration near the outer surface of the cladding glass is reduced.

Furthermore, the outer peripheral surface of the glass rod that has undergone such heat treatment, that is, the surface of the cladding glass, has a reduced fluorine concentration and is smoothed, and does not have any factors that would cause bubbles to form.

Therefore, after the above heat treatment, if a porous glass layer is formed by depositing fluorine-free quartz-based glass particles on the outer periphery of the glass rod and this is made into transparent glass by a predetermined means, the transparent glass and craft glass A high-strength optical fiber preform that does not generate bubbles at the interface with the optical fiber and is difficult to break during the optical fiber stage can be obtained.

Example of implementation Examples of the method of the present invention will be described with reference to the drawings.

In FIG. 1, glass R511 is composed of a core glass 12 at the axis and a cladding glass 13 on its outer periphery. A glass layer I4 is formed.

The core glass 12 is made of synthetic quartz containing Ili fluorine, the cod 7F glass 13 is made of synthetic quartz containing more fluorine, and the porous glass layer 14 is made of
It consists of deposits of glass fine particles (Si02).

In FIG. 1, a glass rod 11 is supported at both ends via rotary chucks of a glass lathe (not shown), and
The glass rod 11 is reciprocated along the length of the glass rod 11 via a traverse mechanism (not shown) with respect to a burner 21 having a multi-tube structure disposed close to the glass rod 11 .

As is well known, the burner 21 having a multi-tubular structure has a plurality of channels arranged concentrically, and each channel of the eight-tube 21 is filled with fuel gas, auxiliary gas, glass raw material in a vapor phase, A piping system is connected to supply gas phase tope raw material, buffer gas, etc.

Next, an example of placing a body according to the method of the present invention and a comparative example thereof will be explained.

[Specific example] Glass for core] As shown in 2, the glass was sufficiently dehydrated. Moreover,
Rod-shaped doped quartz containing trace amounts of 2 and 2 elements was used.

The relative refractive index difference of the core glass 12 with respect to pure quartz is -
It is 0.02%.

After the core glass 12 was heated and stretched to an outer diameter of 105 mφ, a porous glass layer was deposited on the outer periphery of the core glass 12 by an external C/D method.

As this external CVD method, the same means as illustrated in FIG. 1 is adopted.

That is, 0, 5iC14 was added to the flame of the oxyhydrogen flame burner.
The glass particles produced by the flame hydrolysis reaction were deposited to a thickness of 70+*m (the temperature of the deposition surface was 500°C).

Next, the porous glass layer formed on the outer periphery of the core glass 12 is made into transparent vitrification using a transparent vitrification furnace, and the outer diameter ratio of the core glass 12 and the glass formed on the outer periphery is Glass drawing, glass fine particle deposition, and transparent glass were repeated to form a fluorine-containing glass 13 for cladding so that the ratio was 1:1O.

In the above, the conditions when converting the porous glass layer for cladding into transparent vitrification, that is, the temperature inside the furnace, the atmosphere inside the furnace, and the insertion speed (lowering speed) of the glass rod into the furnace are shown in Table 1 below.
As shown.

Table 1 As mentioned above, when the outer diameter ratio of the core glass 12 and the cladding glass 13 is 1:10, the glass is heated through an oxyhydrogen flame burner in order to diffuse the fluorine in the cladding glass 13. The surface of the rod 11 (the outer peripheral surface of the cladding glass 13) was heated to 1000° C. or higher.

Thereafter, glass fine particles are deposited again on the outer peripheral surface of the glass rod 11 so that the outer diameter ratio of the core glass 12 and the crat glass 13 is 1:12.5 to form the porous glass layer 14. This porous glass layer 14 was transparently vitrified using a transparent vitrification furnace under the conditions of Coating 2 below in the same manner as described above.

Table 2 The optical fiber base material of this specific example was drawn at +80/win in a drawing furnace (electric furnace), and an ultraviolet curable resin was applied to the outer periphery of the optical fiber immediately after the drawing to form a coating layer. Thus, the outer diameter of the optical fiber is 125 μm and the outer diameter of the coating is 400 μm.
An optical fiber core of φ was obtained.

The refractive index distribution of the optical fiber in the specific example is as shown in FIG. After forming the crat glass 13 on the outer periphery of the glass 12, a porous glass layer is formed on the outer periphery of the craft glass 13 so that the outer diameter ratio of the core glass 12 and the cladding glass 13 is l:12.5. 1
4, the porous glass layer 14 was formed without heat-treating the outer circumferential surface of the glass rod 11, that is, without diffusing fluorine on the surface of the glass for clamping.

The other π terms in the comparative example are specific examples and rotations.

The optical fiber <fJ material of this comparative example was also drawn and coated in the same manner as in the specific example to obtain a cored optical fiber having an optical fiber/゛・outer diameter of 125 g+*φ coated outer diameter of 400 μm×φ.

A sufficient refraction cloth of the optical fiber in the comparative example is as shown in FIG.

FIG. 4 shows the results of a long tensile test performed on each of the optical fiber cores of the specific example and the comparative example.

As is clear from FIG. 4, the optical fiber core of the specific example (marked with white squares) has excellent breaking strength, whereas the optical fiber core of the comparative example (marked with black squares) has excellent breaking strength. is inferior.

This is because, in a specific example in which a heat treatment method was used to scatter fluorine, bubbles were observed to occur at the interface between the cladding glass (SiO2-F) and the transparent glass (Si02) surrounding it, which caused strength deterioration. This is because bubbles were generated at the interface mentioned above in the comparative example in which the heat treatment method was not applied.

As mentioned above, the heat treatment temperature for fluorine scattering in the method of the present invention is preferably 1000°C or higher, but the heat source for carrying out the heat treatment may be a flame other than an oxyhydrogen flame, an electric heater, etc. It can be adopted as well.

However, if the outer diameter ratio of the core glass and the cladding glass is I:5 or less, in order to ensure good transmission characteristics of the optical fiber, it is necessary to avoid heat sources that may contain OH groups and other impurities. , it is best to avoid using this.

``Effects of the Inventionj'' As explained above, when using the method of the present invention, when creating an optical fiber preform, the glass rod is heat-treated before the glass fine particles are deposited, and some of the fluorine near the surface of the rod is scattered. Even if fluorine-free quartz-based glass fine particles are deposited on the outer periphery of a glass rod after heat treatment, the generation of bubbles at the interface is extremely small, and therefore it is possible to obtain an optical fiber with higher strength than such a base material. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing an embodiment of the method of the present invention, and FIG.
The figure is a refractive index distribution diagram of an optical fiber produced in a specific example of the method of the present invention, Figure 3 is a refractive index distribution diagram of an optical fiber produced in a comparative example of the method of the present invention, and Figure 4 is a specific example of the method of the present invention. FIG. 2 is a diagram showing the results of measuring the intensity of an optical fiber manufactured in a comparative example. 11...Glass rod 12...Glass for core 13...Glass for cladding 14...Porous glass layer Agent Patent attorney Yoshiyoshi Saito Yuyabu-ku I'm sorry for my loss

Claims (1)

[Claims] An optical fiber base material that forms a porous glass layer around the outer periphery of a fluorine-containing quartz glass rod by depositing quartz glass fine particles generated by flame hydrolysis reaction of a vapor-phase glass raw material on the outer periphery of the glass rod. In the manufacturing method, the glass rod is heat-treated before the glass fine particles are deposited, and then,
A method for manufacturing an optical fiber preform, comprising depositing fluorine-free quartz-based glass fine particles on the outer periphery of the glass rod.