JPS6287428A - Production of porous preform for optical system - Google Patents

Abstract

PURPOSE:To produce a porous glass preform having a GI-type refractive index distribution in high reproducibility, by supplying a doping raw material gas to the 1st flow channel at the center of a burner having multi-tube structure and a glass raw material gas and hydrogen to the outer 2nd flow channel. CONSTITUTION:In a double-flame VAD process, a doping raw material such as GeCl4 is supplied to the 1st flow channel at the center of a burner 10 having a multi-tube structure. The 2nd flow channel surrounding the 1st flow channel is supplied with H2 and a glass raw material such as SiCl4, the 3rd flow channel with Ar, etc., the 4th flow channel with O2, etc., the 5th flow channel with a sealing gas such as Ar, the 6th flow channel with Ar, etc., the 7th flow channel with H2 and a glass raw material such as SiCl4, etc., the 8th flow channel with Ar, etc., and the 9th flow channel with O2, etc. Glass soot is produced by keeping the burner in combustion state and reacting the supplied components with each other. The flame of the inner region and the flame of the outer region are longitudinally connected with each other to elongate the collective flame length of the burner. Accordingly, the rate of growth and deposition of glass soot are improved and the synthesis of a porous glass preform 20 can be accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Field of Application 1 The present invention relates to a method for producing porous glass base materials for communication, optical, etc. applications by a double flame VAD method.

``Prior art 1 Optical fibers, light guides, image fibers, and rod lenses 1' used in fields such as communications and optics are MCV
A predetermined base material is created by methods such as the D method, VAD method, and OVD method, and the resulting optical fiber base material is spun,
It is manufactured by reducing the diameter of the rod lens base material.

Among the above-mentioned methods, the dual flame VAD method has already been announced as a method for high-speed synthesis of porous glass base materials for optical fibers etc. Conference proceedings-3137,
1985 National Conference of the Institute of Electrical Communication Engineers - 1138, etc.).

The outline of this dual flame VAD method is shown in FIG. 4, and will be briefly described below.

In FIG. 4, a burner 1 having a multi-tube structure consists of an inner flame generating section 2 and an outer flame generating section 4 provided on the outer periphery of the inner flame generating section 2 with a seal gas flow path 3 interposed therebetween. In the relative relationship between the two flame generating parts, the tip of the inner flame generating part 2 is located inside the tip of the outer flame generating part 4.

Both the inner flame generating section 2 and the outer flame generating section 4 consist of quadruple flow paths, and the seal gas flow path 3 interposed between the two flame generating sections 2.4 consists of a single flow path. Each flow path is arranged concentrically.

When carrying out the double flame VAD method via the burner I, the first flow path is 5iC14 and Ge
Cl4, N2 is supplied to the second flow path, At is supplied to the third flow path, and 02 is supplied to the fourth flow path, and Ar is supplied to the seal gas flow path (fifth flow path) 3. Of the sixth to ninth channels (outermost channels) constituting part 4, the sixth channel is filled with Ar, and the seventh channel is filled with 5iCI4 and N2.
, Ar is supplied to the eighth channel, and 02 is supplied to the ninth channel, and the flame hydrolysis reaction products of these gases, that is, soot-like glass particles are deposited in a desired shape to form a porous glass base material. 5 is formed.

When forming the porous glass base material 5 in this way, as shown in FIG. Since outer flames are generated and these flames are continuous in the longitudinal direction, the total flame length of the burner 1 is L = length 1 + length 2.

This combined flame is considerably longer than a single flame, and therefore the airflow of the raw material system indicated by diagonal lines in FIG. 4 stays in the flame for a long time.

As a result, the growth of the glass fine particles within the flame is promoted and the particle size becomes large, and the inertia effect at this time increases the deposition efficiency and allows the porous glass base material 5 to be synthesized at high speed.

``Problem 1 to be solved by the invention In the case of the above-mentioned double flame VAD method, it is said that it is suitable for high-speed synthesis of the porous glass base material 5, but the dope material (GeC1n) for forming the refractive index distribution is When the dopant is supplied to the first flow path (center flow path) of the inner flame generation section 2 and reacted with the flame, the dopant is diffused in the flame more than necessary due to the long residence time in the flame. , the dopant concentration distribution in the radial direction becomes broad (flattened).

Therefore, the refractive index distribution of the porous glass preform 5 becomes an SI type, and a porous glass preform for an optical fiber having a GI type refractive index distribution cannot be obtained.

In view of the above-mentioned problems, the present invention aims to provide a method by which a porous glass base material having a GI type refractive index distribution can be stably produced with good reproducibility using a dual flame VAD method.

Means for Solving Problem 1 In order to achieve the above-mentioned object, the present invention provides a method for manufacturing an optical system porous base material by a double flame type VAD method using a burner having a multi-tubular structure. A gaseous glass raw material, a gaseous dope raw material, oxygen, hydrogen, etc. are supplied to each flow path, and these gases are combusted to generate glass particles, and the glass particles are deposited to form a porous matrix. When forming the material, a dope raw material gas is supplied to a first passage at the center of the burner, and a glass raw material gas and hydrogen are supplied to a second passage outside the first passage. It is said that

r effect J In the method of the present invention, a burner with a multi-tube structure is composed of, for example, a first flow path (center flow path) to a ninth flow path (outermost circumferential flow path), and the first flow path to the fourth flow path are inside. When the flame region, the fifth flow path is a sealing gas region, and the sixth to ninth flow paths are outer flame regions, gas is supplied to each of these flow paths as described below.

That is, GeCl4 (dope raw material) is applied to the first flow path, N2 and SN3+4 (glass raw material) are applied to the second flow path, Ar is applied to the third flow path, 02 is applied to the fourth flow path, and 02 is applied to the fifth flow path. Ar on the road
(seal gas), Ar in the sixth flow path, 5iCIII (glass raw material) and N2 in the seventh flow path, and A in the eighth flow path.
r and 02 to the ninth flow path, and in this gas supply state, the burner is maintained in a combustion state to react and generate glass particles.

At this time, since the flame in the inner flame region and the flame in the outer flame region are continuous in the longitudinal direction, the overall flame length of the burner becomes longer, and therefore the long flame promotes the growth of glass particles, and the deposition rate of the particles increases. is increased, and the synthesis rate of the porous glass matrix becomes faster.

Moreover, at this time, the dope raw material, that is, Ge
Since Cl4 is encapsulated by the fast-flowing mixed gas (To and 5iCI4) that merge in the second flow path and blown out in a predetermined direction, excessive diffusion of the dopant in the flame is suppressed, resulting in CI-type refraction. When forming a porous base material having a refractive index distribution, the refractive index distribution does not become broad, and a predetermined porous base material can be manufactured with good reproducibility.

rEmbodiment A An embodiment of the burner according to the present invention will be described below with reference to the drawings.

In FIG. 1 showing an embodiment of the present invention, multiple te(
The burner lO of the original tube) structure has the first flow path (center flow path) 1
The first to ninth channels (outermost channels) 18 are provided concentrically.

In the case of such a burner, the first flow path 11 to the fourth flow path 14 are the inner flame region, the sixth flow path 16 to the ninth flow path 19 are the outer flame region, and the fifth flow path 15 is the seal gas region. There is.

When performing the dual flame VAD method using the burner 10 described above, each of the gases described above is supplied to the burner 10 to cause a flame hydrolysis reaction, and the glass particles generated thereby are rotated. The porous base material 20 is produced by continuously injecting it toward a target and depositing it to grow.

Specific examples and comparative examples in this case will be explained below with reference to the table below.

table Incidentally, the flow rate in the table is "win/win".

In the specific example shown in the table above, that is, the specific example in which the dope raw material gas is supplied to the first channel 11 and the frit gas and hydrogen are supplied to the second channel, a CI type refractive index distribution as shown in FIG. However, in the comparative example (conventional example) in which dope raw material gas and glass raw material gas were supplied to the first flow path 11 and hydrogen was supplied to the second flow path, as shown in FIG. The refractive index distribution became broad, and the refractive index distribution approximated that of the SI type.

In the illustrated example of the present invention, an example was described in which glass fine particles are generated using the burner 0 with the original tube structure. may also be used.

Effects of the Invention 1 As explained above, when the method of the present invention is used to manufacture an optical system porous base material by the double flame VAD method using a burner having a multi-tube structure, the first flow path at the center of the burner is A dope raw material gas is supplied to the second flow path outside the first flow path.
Since frit gas and hydrogen are supplied to the flow path, Gl
A high-quality porous glass base material with a mold-shaped refractive index distribution can be manufactured stably with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing one embodiment of the method of the present invention, and FIG.
Figure 3 is a refractive index distribution diagram of a porous base material obtained by a specific example of the method of the present invention and a comparative example thereof, and Figure 4 is a refractive index distribution diagram, respectively.
The figure is a schematic explanatory diagram of the dual flame VAD method. 10 battles...Multi-tube structure burner 11, fist, first flow path 12...second flow path 13, fist, third flow path 14, fourth flow path 15, meeting, fifth flow path 16 ...Sixth flow path 17...Seventh flow path 18・φ・Eighth flow path 18...Ninth flow path 20...Fist porous base material Fig. 1

Claims (1)

[Claims] In a method for manufacturing an optical system porous base material by a double flame VAD method using a burner having a multi-tube structure, gaseous glass raw materials, gaseous dope raw materials, oxygen, hydrogen, etc. are introduced into each flow path of the burner. At the same time, each of these gases is combusted to generate glass particles, and when the glass particles are deposited to form a porous base material, a dope raw material gas is supplied to the first flow path at the center of the burner. A method for producing a porous base material for an optical system, characterized in that a frit gas and hydrogen are supplied to a second flow path located outside the first flow path.