JPS60239336A - Heat-treatment of quartz-based parent material for porous glass - Google Patents

Abstract

PURPOSE:To prepare a parent material for a light transmitting body having low transmitting loss and suitable for wide range of the wavelength of light by heat- treating a quartz-based parent material of porous glass in a gaseous mixture consisting of SOCl2 and He at a temp. below a vitrification temp. of the glass, and heat-treating further in an atmosphere contg. O2. CONSTITUTION:A quartz-based parent material for the porous glass 1 prepd. by the VAD process, etc. is placed in a heating furnace 11 provided with a carbon heater 17 and an intermediate cylinder 16 included therein, which is interposed between a bottom cylinder 13 provided with a gas inlet 12 and a top cylinder 15 provided with a gas outlet 14, and the parent material is heat-treated by rotating and moving downward. The heat-treatment is performed in the first stage in SOCl2, then in a gaseous mixture consisting of about 0.25-2.5vol% SOCl2 and He, at a temp. below the vitrification temp. of the glass, i.e. 700-1,400 deg.C. Then, the heat-treatment is carried on further at >=700 deg.C preferably by changing the atmosphere in the furnace to the atmosphere contg. O2 to remove chlorine in the parent material. Finally, the heat-treatment is executed at >=1,300 deg.C to cause vitrification.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for heat treating a silica-based porous glass base material made for use in required optical transmission bodies such as optical fibers, image guides, and light guides.

(Prior art) A quartz-based porous glass base material produced by the known VAD method, OVD method, etc. is heat-treated in a mixed gas atmosphere of SOC + 2 and He to make it transparent vitrified. An optical fiber is obtained by jacketing a glass pipe made of natural quartz or synthetic quartz around the outer periphery of the base material and spinning it.

Figure 5 shows the optical fiber obtained as described above.
The refractive index distribution is measured and shown.
l is the refractive index of the core, n2 is the refractive index of the cladding, and n3 is the refractive index of the jacket layer.

Here, it is natural that nl)n2, but by using a commercially available quartz glass pipe in the above, n
The relationship between 2 and 13 is n2)n3, and specifically, n2 exceeds n3 by 0.04% in terms of relative refractive index, which causes a phenomenon in which light also propagates through the cladding.

In particular, when forming a jacket layer using a ready-made quartz glass pipe, there tends to be a problem that low loss cannot be achieved when manufacturing a single mode optical fiber. Things are hard to obtain.

In order to investigate the cause of the increase in the relative refractive index difference of the cladding, the elements contained in the optical fiber (glass) were line analyzed using an XklA microanalyzer, and the results shown in FIG. 6 were obtained.

As is clear from FIG. 6, the cladding is doped with an abnormally high concentration of chlorine.

This phenomenon is in good agreement with the high relative refractive index.
This revealed that the relative refractive index difference of the cladding increases with chlorine doping.

(Problems to be Solved by the Invention) Based on the above study results, the present invention has been developed to prevent deterioration of transmission characteristics, band characteristics, etc., even when a ready-made glass pipe made of natural quartz or synthetic quartz is jacketed. It is an object of the present invention to provide a method for heat treatment of a silica-based porous glass base material, which can obtain a base material for an optical transmission body in which no propagation of light occurs.

(Means for solving the problem) The present invention uses a quartz-based porous glass base material of 5OC12 and H8.
This problem is solved by heat treating the base material in an atmosphere containing oxygen at a temperature below the transparent vitrification temperature in a mixed gas atmosphere with It is used as a means.

(Function) Si02+5OC12→ 5iOC12+502- ・
Table ・ (1) Ge02+2SOCI2- Ge
C:I4+2S02'---(2)SiOC:12+
1/202→5102...φΦ...(3) GeC:
I4+02+ ' G[ICI2+2CI2* * *
* 11 @ (4) GeO2+2CI2: GeG
14+02* * * e a * (5) When the preceding heat treatment step in the method of the present invention is carried out in a predetermined atmosphere, the reaction of the above formula (1) occurs due to the effect of 5OC12, and chlorine is doped into the quartz glass. Furthermore, as an effect of the thionyl chloride, for example, as shown in the above equation (2), the dopant on the outer periphery of the Sin2-Gem2 base material evaporates, and a cladding glass layer (pure Si 02 ) is formed.

In the subsequent heat treatment in the method of the present invention, the base material that has undergone the previous heat treatment is further heat treated in an atmosphere where oxygen exists, and at this time, chlorine in the base material is removed using equation (3) described above. Therefore, optical fibers and the like having various excellent properties can be manufactured from the base material that has undergone the subsequent heat treatment.

As a matter related to the subsequent heat treatment, it is best not to coexist gases that volatilize dopants such as 5OC12 and C12 in the atmosphere in this step. For example, when the dopant is G e 02 and the atmospheric gas is C12, , due to the diffusion of the dopant by the reversible reaction of equation (5) above,
Due to irregularities in the refractive index called sag, the boundary between the core glass layer and the cladding glass layer becomes unclear, resulting in C.
As a base material for an I-type optical fiber, sufficient band characteristics cannot be expected, and as a base material for a single optical fiber, sufficient transmission characteristics cannot be expected.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(A) shows a quartz-based porous glass base material 1 that is heat-treated by the method of the present invention, FIG. ) indicates a jacket pipe 3 made of anhydrous or water-containing synthetic quartz that covers the outer periphery of the glass base material 2, and as the jacket pipe 3, one sold under a trade name such as SBRAZIL is used as an example. be done.

The porous glass base material 1 is produced by a flame hydrolysis method such as a VAD method or an OVD method, an oxidative decomposition method, a sol-gel method, etc.
2 as the main component, Ge, P, B, A1. Sb,
It contains an oxide such as Ti as a dopant.

When producing the porous glass base material 1 by the t-VAD method, the method illustrated in FIG. 2 is carried out.

In FIG. 2, 4 is a reaction vessel made of quartz glass;
Numerals 5, 8, and 7 are multi-tube structure burners whose tips are inserted into the reaction vessel 4, and 8 is an exhaust pipe of the reaction vessel.

When carrying out the VAD method in the reaction vessel 4, the burner 5 is filled with combustion gas (N2), combustion supporting gas (02), and buffer gas (Ar).
), main raw material (SICI4), dope raw material (GeCla
) is supplied in a predetermined amount, and combustion gas (N2), combustion supporting gas (02), and buffer gas (A
r) A predetermined amount of the main raw materials (S+C: 14) is supplied, and the soot-like glass particles produced by the flame hydrolysis reaction are deposited in a predetermined shape to form the porous glass base material 1.

Initially, the atmosphere in which the porous glass base material 1 is heat-treated is a mixed gas atmosphere of 5OC12 and He, but the atmosphere does not contain oxygen.

The temperature at which the porous glass base material 1 is heat treated in the above atmosphere is the temperature at which the porous glass base material 1 is heat treated in the above atmosphere. The temperature is lower than the temperature at which the porous glass base material 1 becomes transparent vitrified, and the specific temperature is 700° C. or more and 1400° C. or less, but this is appropriately set depending on the composition of the porous glass base material 1.

The SOC12 concentration in the heat treatment atmosphere is about 0.25 to 2.5 MaoH, and the preferable range is 1 MaoH or less.

5 when heat treatment is carried out at a low temperature within the above temperature range.
OC12 may be higher than the above concentration range.

This atmosphere may contain chlorine compound gases such as C12 and CCl2, and inert gases such as N2 and Ar, together with He.

The base material movement speed when inserting the porous glass base material 1 into the above atmosphere is set within the range of 10-1000+i+a/hour.

FIG. 3 shows an example of a heating furnace 11 for heat-treating a porous glass base material l, and this heating furnace 11 has a gas inlet 12
a lower cylinder I3 having a gas outlet; and an upper cylinder 1 having a gas outlet ]4.
5, an intermediate cylinder 16 interposed between the lower cylinder 13 and the upper cylinder 15, and a carbon acid heater 17 provided on the outer periphery of the intermediate cylinder 1B.

When heat treating the porous glass base material 1 using this heating furnace 11, SOC:I2. While supplying He, the interior of the intermediate cylinder 1θ heated via the electric heater 17 is maintained below the transparent vitrification temperature, and then, while the porous glass base material 1 is in a rotating state, the heating furnace 11 is heated from above to below. That is, the base material 1 is moved into the intermediate cylinder IB, and thereby the base material 1 is heat-treated in the above atmosphere to bring it into a sintered state before becoming transparent and vitrified.

Next, the base material 1 after the preliminary heat treatment is heat treated in an atmosphere containing oxygen to remove chlorine from the base material 1, but the heat treatment at this time can also be carried out in the heating furnace 11, and as described above,
A predetermined atmospheric gas may be supplied into the heating furnace 11.

The subsequent heat treatment temperature is preferably 700°C or higher, and when converting the base material l into transparent glass in this step, the temperature should be set at 130°C or higher.
The temperature shall be 0°C or higher.

Furthermore, in the subsequent heat treatment, the main atmospheric gas is 0.
The higher the concentration of 2, the better, and this can be diluted with an inert gas such as He, Ar, or N2.

When converting the base material 1 into transparent glass in this step, 70 MaO1% or more of He is contained as a diluent gas in the atmospheric gas 02 to prevent air bubbles from being included in the transparent glass base material.

In this step, when the base material 1 is in a sintered state before being made into transparent vitrification, it is made into transparent vitrification by subsequent heat treatment.

The preceding heat treatment step, the subsequent heat treatment step, the transparent vitrification step, etc. may be carried out continuously using the heating furnace 11, or may be carried out separately. The inside of the heating furnace 1 is purged every time a process changes.

Thus, the porous glass base material l shown in FIG. 1(A) has a core glass layer 2a and a cladding glass layer 2b.
It becomes the transparent glass base material 2 of b).

The outer periphery of the transparent glass base material 2 obtained by the above heat treatment is covered with a jacket glass pipe 3 made of natural quartz or synthetic quartz as shown in FIG. , resulting in an optical fiber with a jacket layer.

Of course, an optical fiber can also be obtained by spinning the transparent glass preform 2 without jacketing the glass pipe 3.

In the case of the base material obtained by the method of the present invention, it can be fully expected to improve the band characteristics and transmission characteristics, and prevent the propagation of cladding mode when jacketing a glass pipe.In addition, the base material contains almost no chlorine. Therefore, environmental resistance and corrosion resistance can be expected, and therefore there is no particular need to cover the base material with a protective jacket such as natural quartz or synthetic quartz with low chlorine content.

Next, an experimental example using pure S + 02 as the material to be doped will be explained regarding chlorine doping and its removal.

Experimental Example I A porous glass base material made of S102 was created by depositing glass particles generated by a flame hydrolysis reaction of S + CI 4 gas in the axial direction.
lχ, osOc:l,, t, trHeka, 7□o9
It was made into transparent glass at 3°C and 1480°C.

The resulting pure 5102 glass has a refractive index 0.04% higher than that of natural silica glass, and has a chlorine content of 11000%.
pp was included.

Experimental Example 2 The same porous glass base material as Experimental Example 1 was used at 0.88vo1%.
1100° in a He gas atmosphere containing 5OC12.
After sintering with C, chloride in the atmosphere is removed with He gas.
After purging, the atmosphere was changed to a He gas atmosphere containing 02 at 8.3 vol$, and the temperature was set at 1460° C. to turn the sintered glass base material into transparent vitrification.

The resulting pure S+02 glass has approximately the same refractive index as natural silica glass and has a chlorine content of 50 ppp.
It was m.

Experimental Example 3 The same porous glass base material as Experimental Example 1 was mixed with 0.88 Maol
The sample was placed in a He gas atmosphere containing 012 of 1,460° C. and turned into transparent glass at 1,460° C.

The pure SiO2 glass thus obtained had approximately the same refractive index as natural silica glass.

When heat-treated in an atmosphere of 012 and He as described above, it seems desirable in terms of refractive index, but in terms of forming a cladding glass layer by volatilizing the dopant in the base material, that is, in terms of the ability to form a synthetic cladding. CI2”He
and SCL:12”He are completely different, and C12”He
has extremely poor cladding ability, as is clear from the following experimental examples.

Experimental Example 4 SIO'2-G [! A porous glass base material made of 02 series was made, and this was mixed with 0.88vo1% (7) SOCl2
The sample was placed in a He gas atmosphere containing 1,460° C. and turned into transparent glass.

In the case of the base material obtained in this manner, the cladding glass layer reached as much as 40% of the area from the outer peripheral surface of the base material.

Experimental Example 5 The same porous glass base material as Experimental Example 4 was used at 0.88 vol$.
The sample was placed in a He gas atmosphere containing C12 and turned into transparent vitrification at 1460°C.

In the case of the base material obtained in this way, the glass layer for cladding was only 4z from the outer circumferential surface of the base material, and the above-mentioned refractive index defect called sagging also occurred.

These experiments also demonstrate the effectiveness of the method of the present invention regarding refractive index.

Next, specific examples of the present invention and comparative examples thereof will be explained.

Specific example 1 When implementing the VAD method illustrated in Fig. 2, each burner 5
．． Various gases shown in Table 1 were supplied to 6.7, and the glass particles produced by these flame hydrolysis reactions were deposited in a predetermined shape to produce a porous glass base material 1 having an outer diameter of 90 mm.

This porous glass base material 1 has a core porous glass layer of S
+ 02-G e 02, and the porous glass layer for cladding is made of S + 02.

Table 1 When the above-mentioned porous glass preform 1 is heat-treated in the heating furnace 11 shown in FIG. 3, this is carried out under the conditions 1 shown in Table 2. The sintered base material was removed from the furnace, and then the sintered base material was made into transparent glass under Condition 2 in Table 2 to obtain a transparent glass base material 2.

The transparent glass base material 2 obtained in Example 1 had a good refractive index distribution as shown in FIG. 4, and the cladding glass layer 2b had the same refractive index as natural quartz.

Comparative Example The same porous glass base material as in Specific Example 1 was heated as described above in Furnace 1.
When the heat treatment is carried out under 1, this is carried out under the same conditions 1 in Table 2 as above, and then the inside of the heating furnace 1 is purged with He while being removed from the furnace. The bonding matrix was made into transparent glass to obtain a transparent glass matrix.

When the refractive index distribution of the transparent glass base material obtained in this comparative example was measured, the refractive index was as shown in FIG. 5, which was a poor result as expected.

This can be said to be due to the presence of 02 in condition 2 and the fact that C12 is not doped.

Table 2 Specific example 2 When implementing the VAD method using one multi-tube burner,
Various gases shown in Table 3 were supplied to the burner, and glass fine particles produced by these flame hydrolysis reactions were deposited in a predetermined shape to produce a porous glass base material 1 having an outer diameter of 58 mm.

When the above-mentioned porous glass base material 1 is heat-treated in the heating furnace 11 shown in FIG. 3, this is carried out under the conditions 1 shown in Table 4, and then the inside of the heating furnace 1 is purged with He and removed from the -tan furnace. Thereafter, the sintered base material was made into transparent glass under Condition 2 in Table 4 to obtain a transparent glass base material 2.

When the refractive index distribution of the transparent glass base material 2 obtained in Example 1 was measured, the refractive index of the cladding glass layer 2b was the same as that of natural quartz.

Table 3 Table 4 (Effects of the invention) As explained above, when using the method of the present invention, a quartz-based porous glass base material is heat-treated at a temperature below the transparent vitrification temperature in a mixed gas atmosphere of 5OC12 and He. and a step of heat-treating the base material after the heat treatment step in an atmosphere containing oxygen, so that the outer periphery of the base material after being treated by the method is coated with natural quartz, synthetic quartz, etc.
Even when a ready-made glass pipe is jacketed, the refractive index of the cladding glass layer does not exceed the refractive index of the jacket layer, and therefore the propagation of the cladding mode does not occur, and the material is a low-loss, broadband optical transmission material. Now that the material can be obtained, it is expected that the optical transmission material will have environmental resistance and corrosion resistance.

[Brief explanation of the drawings] Figure 1 (a), (b), and (c) are explanatory diagrams showing the porous glass base material, transparent glass base material, and glass pipe for jacket in the method of the present invention, respectively. The figure is an explanatory diagram schematically showing the VAD method of the present invention, Figure 3 is an explanatory diagram schematically showing an example of heat treatment by the method of the present invention, and Figure 4 is the refractive index of a transparent glass base material in a specific example of the method of the present invention. Figure 5 is a diagram showing the refractive index distribution of an optical fiber in a conventional example, and Figure 6 is a diagram showing the distribution of the refractive index of an optical fiber in a conventional example.
The figure is a compositional analysis diagram of the optical fiber. l...Porous glass base material 2 Φ...Transparent glass base material 2a...Glass layer for core 2b...Glass layer for cladding 3 Glass pipe 11...Heating furnace agent Patent attorney Sai Yoshio Fuji Figure 1 Figure 3 Figure 2 Figure 4 Kfσm Figure 5 Continuation of page 1 ■Int, C1,' Identification code Internal reference number 0 Inventor Katsumi Orishige To Ichihara City Inside Hatakaigandori Factory

Claims (1)

[Claims] A step of heat-treating a quartz-based porous glass base material in a mixed gas atmosphere of SOC + 2 and He at a temperature below the transparent vitrification temperature, and heat-treating the base material after the heat treatment step in an atmosphere containing oxygen. A heat treatment method for a quartz-based porous glass base material, the method comprising a heat treatment step.