JPS61197438A - Method of converting porous parent material for optical fiber into clarified glass - Google Patents

Abstract

PURPOSE:A porous parent material is heat-treated in a specific atmosphere containing a gas which reduces and dissipates dopants and clarified in a specific atmosphere to give the clarified parent material which has appropriate distribution in refractive indexes in the core and clad parts and causes no dimensional fluctuation. CONSTITUTION:The porous parent material is heat-treated in an atmosphere containing a gas which reduces and dissipates dopants such as GeO2 in the porous material of doped quartz optical fibers such as an atmosphere containing SOCl2 but no oxygen at such a temperature as the material is not completely shrunk. Then, the material is clarified by treating it in an oxygen-containing and reducing agent-free atmosphere such as an atmosphere containing 5-50% of oxygen and the rest of inactive gases. Thus, distribution of refractive index becomes appropriate in the core and clad parts and the dimensional accuracy becomes high in individual parts.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 1 The present invention relates to a method for transparently vitrifying a porous base material for optical fibers made of doped quartz.

rPrior Art J The known VAD method is one of the methods adopted as a method for producing a silica-based optical fiber preform, and at present, the following two methods are mainstream.

One of them is to use a reaction burner 1a for the core and a reaction burner lb for the cladding as shown in FIG. 6(A).
02-G e Porous layer 2 for core consisting of 02, G
In this method, porous layers 3 for cladding made of em2 are synthesized, and the porous base material 4 obtained thereby is made into transparent glass.

The other method is to prepare a porous base material 4 made of S+02-GeO2 using one reaction burner lc, as shown in FIG. This is a method in which a dopant is volatilized from the outer periphery to form a cladding layer around the outer periphery of a core layer, and the treated base material is then turned into transparent glass.

When producing a base material for an optical fiber by these VAD methods, it is considered ideal to obtain a refractive index distribution as shown in FIG.

Problems to be Solved by the Invention J By the way, when producing a porous base material by the method shown in FIG. Difficult.

Refractive index irregularities may occur at the interface between the core porous layer 2 and the cladding porous layer 3, and in addition, the core glass fine particles may scatter during base material synthesis, and the core dopant may volatilize during transparent vitrification. As a result, the high refractive index dopant diffuses to the cladding side.
), refractive index abnormalities such as ``sagging'' and ``corner'' may occur.

On the other hand, when using the method shown in FIG. 6(B), the method shown in FIG. 8(B-
1) The refractive index abnormality shown in (B-2) occurs.

The cause of the occurrence of "r tail sagging" in Figure 8 (B-1) is that when dopant (Ge02) is volatilized from the outer periphery of the porous base material 4, C12 is used as a reducing agent in the base material processing atmosphere. It depends.

In other words, in the above-mentioned base material treatment, since the reversible reaction shown in the following reaction formula (1) is utilized, -tan G e CI 4 that jumps out of the base material becomes G e 02 again and is transferred to the base material. It adheres to the outer periphery (cladding part), and this phenomenon occurs constantly, resulting in ``sagging''.

GeO2+2CI2: GeCl, +02@@ ＊ ＊
(1) The cause of the abnormally high refractive index shown in FIG. 8 (B-2) is that SOCl2 is used as a reducing agent in the base material processing atmosphere.
This is due to the use of 2.

The reaction in this case is an irreversible reaction shown in the following formula (2), and what becomes -phenium G e C1a does not return to G e 02 in an oxygen-free atmosphere. Therefore, the -phosphorus volatilized G e 02 is However, the 5OC12 used here has extremely strong reducing power, and after GeO2 volatilizes, it also reduces 5I02, so CI is attached to the outer periphery of the base material in the form of 5i-0-C:I. As a result, the content of CI increases and the refractive index of the cladding portion increases.

GeO2+2SOC12-+GeCl4+2S02--
-- (2) As mentioned above, when conventional method 2 is used, the ideal refractive index distribution shown in Figure 7 cannot be obtained, so when the above base material is processed into an optical fiber, its transmission characteristics are As a result, the dimensions of the core and cladding cannot be completed as specified.

In view of the above-mentioned problems, the present invention aims to provide a transparent vitrification method for a porous preform for an optical fiber, which does not cause irregularities in the refractive index distribution and does not cause variations in the dimensions of the core and cladding. .

"Means for Solving Problems" The present invention heat-treats a doped quartz-based porous base material for optical fibers made of deposits of glass particles in a high-temperature atmosphere to turn the porous base material into transparent vitrification. In the method of
The porous base material is treated in a heat treatment atmosphere that contains a gas that reduces and volatilizes the dopant in the porous base material and has a temperature that does not completely shrink the porous base material. The method is characterized in that the treated base material is transparently vitrified in a transparent vitrification atmosphere containing.

Effect 1 In the case of the method of the present invention, a doped quartz-based porous base material containing a dopant such as Ge 02 is prepared, for example, by the method shown in FIG. 6(B), and the porous base material is heated to a high temperature. When transparent vitrification is performed by heat treatment in an atmosphere, the base material treatment process is divided into the following two steps.

In the first treatment step, a heat treatment atmosphere (1000 to 1300°C) containing a gas that reduces and volatilizes the dopant in the porous base material and does not completely shrink the porous base material (1000 to 1300 ° C.) is used.
The porous base material is treated in an electric furnace (electric furnace), and the atmosphere at this time is formed of an inert gas such as He, Ar, or N2 and a reducing agent SOCl2 or (COCl)2, and oxygen is not added.

When a porous base material is treated in such a heat treatment atmosphere, a reaction as shown in equation (3) or (4) below occurs, and the dopant (G
As e02) is volatilized, CI is attached to the part where G e O2 has escaped in the form of 5i-0-CI with respect to S io 2.

Therefore, this treated base material has C in the part that will become the cladding.
Contains a lot of I.

GeO+2SOCI −GeC1↑ +2SO−−−
”(3) GeO+2 (GeC12) → GeCl4↑
+2002+2GO--(4) In the next treatment step, the treated base material is placed in a transparent vitrification atmosphere containing oxygen (14
The above-mentioned treated base material is made into transparent glass at a temperature of 00 to 1,600° C., and the atmosphere at this time is formed of an inert gas and an appropriate amount of oxygen, and does not contain any reducing agent gas.

Through this treatment step, the base material is made into transparent glass, but since the atmosphere does not contain a reducing agent, Sio
Since a reaction such as reducing 2 does not occur and the atmosphere is an oxygen atmosphere, volatilization of G e 02 is suppressed and CI is released.

Note that CI is removed even when oxygen is not included in the atmosphere in the second treatment step, that is, in the atmosphere for transparent vitrification, but in this case, Ge volatilization occurs, so "sagging" etc. occur.

Thus, the base material transparently vitrified by the method of the present invention is
The refractive index distribution has no irregularities and exhibits an almost ideal refractive index distribution.

``Example 1'' A specific example of the method of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is an electric furnace for forming a predetermined heat treatment atmosphere, and this electric furnace 10 includes a furnace core tube 11 and an electric heater 12 on the outer periphery of the furnace core tube.

The core tube 11 has a gas port 13 formed in its lower part and a gas outlet 14 formed in its upper part.

In the method of the present invention, the porous base material 4 is
Perform each process.

This porous base material 4 is made of a Sin2-Gem2 system produced by the method shown in FIG. 6(B), for example, but may contain other dopants other than Ge 02 if necessary.

When the porous base material 4 is put into the electric furnace IO and subjected to the first heat treatment, the gas inlet 1 is inserted into the furnace core tube 11.
The inert gas and the reducing agent are supplied from
The temperature is maintained at around 0°C.

When the porous base material 4 is inserted into the furnace core tube 11 and the first heat treatment is performed, a reaction like the above-mentioned equation (3) or equation (4) occurs in the furnace core tube 11.

In this process, as mentioned above, the dopant (Ge02) is volatilized from the outer periphery of the base material, which is easily exposed to the reducing agent, and the part where the Ge02 is removed is S +
At is attached to 02 in a form such as 5i-0-CI, and due to the base material treatment, the porous base material 4 exhibits an element distribution as shown in FIG.

The second heat treatment is carried out in the electric furnace 10 after the -tan purge or in the separately prepared electric furnace 10.

At this time, 5 to 30% of the inert gas and
of oxygen is supplied, and the inside of the core v11 is 14
The temperature is maintained at about 00 to 1800°C, and then the porous base material 4 subjected to the above treatment is inserted into the furnace core tube 11.

The porous base material 4 inserted into the reactor core tube ll in this way is
e Transparent vitrification is achieved while suppressing the volatilization of O2 and promoting the separation of CI.

In this way, a desired transparent vitrified base material is obtained, and the base material after transparent vitrification exhibits an element distribution as shown in FIG.

Next, experimental examples related to the method of the present invention will be explained.

In the experimental example described below, a multi-tube structure was used as shown in Figure 6 (B
) (7) Supply gaseous raw materials such as 5rCI4 and GeCIa to the reaction burner 1c, cause these gaseous raw materials to react with flame hydrolysis, and deposit the glass fine particles thus generated in the axial direction to create a porous base material. did.

The distribution of Ge02 in this porous matrix is Δ-1,0X
It corresponds to the Cl type.

When processing the above porous base material, the porous base material was placed in an electric furnace that was supplied with 30 fL/win of He and 0.3 JJ/win of 5OC12, and whose internal temperature was set at 1250°C. The first treatment was performed by inserting at a descending speed of 3+sm/sin.

Next, the base material after the above treatment was placed in an electric furnace with each atmosphere shown in the table below, and a second treatment, that is, transparent vitrification was performed.

In the above experimental example, N001 to N003 were able to make the base material transparent vitrified, but in the case of N004, 02
Due to excessive amount, defoaming of the base material was incomplete.

For reference, we also produced a sample in which the base material was made into transparent glass under the conditions shown in the table below, and synthetic rad was generated. This is designated as Experimental Example No. 005.

In the case of this experimental example (NO, 5), since the treatment was performed in an oxygen-free atmosphere, synthetic rad was generated due to the volatilization of Ge, as shown in the element distribution in Figure 2, but CI was present in the cladding. A large amount will adhere.

Among the above experimental examples, N08 cannot be measured due to foaming.
Except for No. 4, the refractive index distributions of the transparent vitrified base materials of N091 to N003 and N005 were measured using a preform analyzer.

As is clear from FIG. 5 showing the measurement results, the transparent vitrified base materials of N002 and N013, which were made into transparent vitrification in an oxygen-containing atmosphere after forming a large amount of rad parts by a predetermined treatment, were used in the present invention. In the base material treated by this method, the cladding part has a flat refractive index that is the same as that of silica glass, and the core has an almost ideal refractive index distribution with no tail. In the experimental example of N001 (outside the present invention) in which the transparent vitrification was carried out in an oxygen-free atmosphere, ``sagging j'' had occurred, and further N0
Also in the experimental example No. 05 (outside the present invention), an abnormally high refractive index of the cladding portion due to CI occurs.

When the base materials of N092 and N003 were spun into optical fibers with a core diameter of 50g and an outer diameter (cladding diameter) of 125ILm and the dimensions of each part of these optical fibers were measured, the boundaries between the core and cladding were extremely clear. Both optical fibers had good transmission characteristics.

The technique of the method of the present invention described above is effective as a means for transparent vitrification of a base material when obtaining a single mode optical fiber, and is also effective in improving accuracy such as low loss, dispersion control, and power 7 to-off wavelength.

"Effects of the Invention" As explained above, when the method of the present invention is used to make a porous base material transparent, it contains a gas that reduces and volatilizes the dopant in the porous base material, and the porous base material is completely destroyed. The porous base material is treated in a heat treatment atmosphere at a temperature that does not cause shrinkage, and then the treated base material is transparently vitrified in a transparent vitrification atmosphere that does not contain a reducing agent but contains oxygen. A transparent vitrified base material having an appropriate refractive index distribution in the cladding portion and good dimensional accuracy in each of these portions can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing an embodiment of the method of the present invention, and FIG.
The figure is an elemental distribution diagram of the base material subjected to the first heat treatment in the method of the present invention, and Figure 3 is the element distribution of the base material subjected to the second heat treatment (transparent vitrification treatment) in the method of the present invention. Figure 4 is an elemental distribution diagram of the base material in a reference example to be compared with the method of the present invention, Figure 5 is a refractive index distribution diagram of the transparent vitrified base material in various experimental examples of the method of the present invention, and Figure 6 ( A)
(B) is an explanatory diagram schematically showing an example of manufacturing a porous base material, No. 7
The figure is a refractive index distribution diagram of an ideal transparent vitrified base material, and FIGS. 8(A), (B-1, and CB-2) are refractive index distribution diagrams of a base material that has been transparently vitrified by a conventional method. 4@... Porous base material lO... Fist electric furnace 11... Electric furnace core tube (heat treatment atmosphere) 12... Φ
Electric Furnace Heater Agent Patent Attorney Yoshio Saito Figure 1 Figure 2 Figure 4

Claims (3)

[Claims] (1) In a method in which a doped quartz-based porous base material for an optical fiber consisting of deposits of glass particles is heat-treated in a high-temperature atmosphere to make the porous base material transparent vitrification, The porous base material is treated in a heat treatment atmosphere containing a gas that reduces and volatilizes the dopant and at a temperature that does not completely shrink the porous base material, and then in a transparent vitrification atmosphere that does not contain a reducing agent but contains oxygen. A method for transparently vitrifying a porous preform for an optical fiber, the method comprising: converting the treated preform into transparent vitrification. (2) The preceding heat treatment atmosphere uses SOCl_2 or (COCl)_ as a gas to reduce and volatilize the dopant.
2. A method for transparent vitrification of a porous preform for an optical fiber according to claim 1, which contains no oxygen. (3) The subsequent transparent vitrification atmosphere is about 5% or more
2. The method for transparent vitrification of a porous preform for an optical fiber according to claim 1, wherein the preform contains less than 0% oxygen and the remainder is an inert gas.