JPS58125619A - Production of parent material for light transmission glass - Google Patents

Abstract

PURPOSE:In the production of a parent material for optical fiber through the VAD process, the sintering is carried out in a specific gas atmosphere to form the parent material with less deviation in refractive index distribution. CONSTITUTION:In the reaction vessel 30, starting gas materials are burnt with the burner 31 and the resultant glass fine particles are deposited on the starting material 32 which is being pulled up under rotation to form the fine particle aggregate 36 (its bulk density is about 0.1-0.5g/cm<3> and the refractive index is lower in the outer part than in the core part). Then, the aggregate is sintered with the heater 33 in the course of pulling-up to give the objective parent material for glass fiber wherein the sintering is carried out in such a gas atmosphere as containing halogen or a halogen compound and effecting dehydration and dopant vaporization, e.g., a helium gas containing about 0.1-10mol% of molecular chlorine.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a glass preform for optical transmission having an optimal parabolic distribution.

One of the methods for producing a glass matrix for optical transmission is the 0 method.

This method enables arbitrary refractive index distribution in the radial direction with low loss.
- This is a manufacturing method suitable for obtaining materials for making inexpensive optical transmission fibers that have a uniform composition in the circumferential and longitudinal directions, and produces high-purity products with good raw material yields. In addition, it has been pointed out that in addition to the production time being less than half that of other methods, dehydration is easy to stir and the number of steps is small when sintering fine particle aggregates. It has many advantages. Here, to explain the outline of the conventional method 0, as shown in Figure 1, a raw material gas for fine particles, a combustion gas, and a dough gas are supplied to a burner 2 installed at the bottom of a container 1. , starting material 3 from burner 2
The soot of the glass particles is deposited on the lower surface of the starting material 'Jt3 by blowing a flame toward the starting material 3. While the starting material 3 is rotated and pulled up, the glass particle medium is grown to form the aggregate 4. When soot adheres to the lower surface of the glass fine particle body, a large amount of soot is deposited in the center and a small amount is deposited in the periphery. A glass base material having the refractive index distribution shown in the figure is obtained. Here n. is the refractive index level of silica glass, △n is the refractive index level increased by GeO2, and α is the index of the refractive index distribution curve denoted by △n-△n(1-(L)a). Oru.

By the way, the above-mentioned VAD method also has points to be improved, such as a method having several advantages mentioned above. For example, when comparing in detail the refractive index distribution of glass base materials manufactured by the conventional VAD method, α=2.
There is a variation of about ±0.3 around 0, and
In the previous ■0 method, which simply sintered the media aggregate, α=
It is difficult to control the refractive index distribution within a range of 2.0±0.1. Another problem is that the dehydration effect during sintering is not sufficient. The quality of the above-mentioned dehydration effect greatly affects the transmission wavelength band of Hikari 7-IPA. In recent years, there has been an increasing demand for the use of wavelengths around 1 and 30 μm, which have the lowest absorption loss, as wavelengths for optical communications.3 However, this wavelength band is a region where absorption losses are large due to residual OH groups in optical fibers. Yes, in order to use this wavelength band, the O in the optical fiber is
1 dB/Km at H base liquid absorption loss value of 1.38 μm
It is desirable to do the following. For this purpose, it is necessary not only to reduce the amount of residual OH in the core part, but also to reduce the amount of residual OH in the cladding layer.
- The ML must be slightly less than that, and the clad layer near the core must have a thickness of 2 to 3 μm, preferably 7 μm or more, and must be an anhydrous clad layer with almost no residual OH. be. Conventionally, in order to manufacture an optical fiber having such an anhydrous cladding layer, first, a fine particle aggregate with a refractive index distribution is made anhydrous to form a transparent glass, and then the transparent glass is coated on a pipe pre-coated with anhydrous quartz or an anhydrous layer. By inserting a glass body, a glass base material of an anhydrous rad layer is obtained. However, in the conventional method, it is necessary to use an oxyhydrogen flame to further stretch the transparent glass body to a predetermined diameter.) There is a risk that moisture may enter and diffuse during this process, and the manufacturing process is complicated and dehydration is difficult. There are limits to its effectiveness.

The present invention solves the above-mentioned problems of the conventional method, and has a structure in which a glass imitation particle aggregate is placed in a gas atmosphere containing a halogen or a halide and having a dehydrating action and a dopant volatilization action. By sintering, the glass fine particle aggregate is simultaneously dehydrated and evaporated to modify the refractive index distribution.

The present invention will be explained in detail below using the Ida method as an example.

FIG. 3 shows an example of an apparatus configuration for implementing the present invention. In this example of the apparatus, a burner 31 is provided at the lower part of the reaction container 30, while a starting material 32 is rotatably suspended inside the container, and a heater 33 is further provided around the outer periphery of the reaction container 30. Further, a gas supply path 34 is provided in the upper part of the reaction container 30 to supply a predetermined gas into the container, and an exhaust path 35 is provided in the lower part of the reaction container 30 to discharge the gas in the container. There is.

Using the above device f, the raw material gas is combusted from the burner 31, and the soot of the generated glass particles is deposited on the lower surface of the starting material 32, thereby forming the glass particle aggregate 36. In this case, a gas containing halodan or a halodan compound and having a dehydrating action and a dopant volatilization action is supplied into the reaction container through the gas supply path 34tl to create the above-mentioned gas atmosphere inside the reaction container 30. At the same time as forming a glass particle aggregate 36, the glass particles 36 are pulled upward and sintered by the heater 33.

To explain the case where chlorine gas C1z is used as an example of the above gas atmosphere, when sintering a glass particle aggregate having the Goms concentration distribution shown in FIG. When sintering is carried out while being supplied into a reaction vessel at a ratio of , a glass base material having a refractive index distribution shown in FIG. 5(a) is obtained. It can be seen that the refractive index distribution of the glass base material is α=2.0±0.05, and the distribution can be controlled with high accuracy. On the other hand, when a glass particle aggregate having the same GeO @Refractive index distribution is α-2,0
±0.15) The sillage is thicker than that of the present invention. The above gas atmosphere includes Ct and He gas! In addition to S, Ar, N, Io, etc. are suitable. Next, to explain the optimum range of the proportion of halodane in the gas atmosphere, when sintering the f or more fine particle aggregate G)@θ having the Gem2 concentration distribution shown in FIG.
When Ct2 gas was supplied at the ratio shown in the table, Figure 6 ■@
A glass base material with a refractive index distribution shown in O is obtained, and these O
The amount of H groups remaining is shown in Table 1. Furthermore, the transmission characteristics for each glass base material are shown in Table 1 for each transmission band f. As is clear from this example, 0
If the amount of C4 is less than 0.1 vot%, the amount of dehydration is insufficient; on the other hand, if it is more than 10 qoL, the amount of C
Bubbles of the four gases occur frequently and do not adversely affect the transmission characteristics of the optical fiber. Therefore, it is preferable that the Ctl amount is 0.1 to 10 yots.

Table 1) 0.05 15 600 fat @ 1 1. 800θ 1
3 1 400 Since the refractive index distribution in order of bubble density is also related to the bulk density of the glass fine particle aggregate, this relationship will be explained.

Glass fine particle aggregate A having a bulk density distribution p and a refractive index distribution Δn as shown in FIG. 7(I)(b)(c)
.

B and C were inserted into a heating furnace with a heating temperature of 1550°C at a rate of 2 strokes/min in a gas W atmosphere supplied with Ha 51 and CL at a rate of 0.0517 to form transparent vitrification. . The results are shown in Table 2 and FIG.

Table 2 Bulk density (r/cJ) Residual OH absorption loss Transmission band (■1z) A 1.38μm 3
dB/Km 150B 0.1~0.5
2 fiyn-1dB/Km 800CO
,3~0.8 1.38μm -20dB/Km
250 Also, (a) (b) in Figures 7 and 8
(c) is trial A above.

Cases B and C are shown. As is clear from this result, Sample B has the least amount of residual OHi. Sample B has a bulk density of 0.1
~(Available at 1.5 r/m, and the inner part is equal to or thicker than the outer part. From the above results, the refractive index distribution of the transparent glass body obtained in this case is generally the same as that of trial B. The same tendency occurs, and a cladding composite layer with a smooth distribution and no rise (refractive index △n') at the periphery tends to be formed, and such a refractive index distribution can be obtained with good reproducibility. It can be seen that a refractive index distribution like that of sample B is essential to obtain a low-loss and high-bandwidth fiber. - A refractive index distribution like that of actual samples A and C is disadvantageous for the band characteristics. In this respect, the present invention has a significant practical advantage.

Next, the relationship between the amount of dopant at the outermost periphery and the refractive index distribution will be explained. FIG. 9 Gi) (e) A glass particle aggregate having the refractive index distribution shown in (f), E.

It was inserted into a heating furnace at a heating temperature of 1550° C. at a speed of 2 m/min in a gas atmosphere in which F was supplied at a rate of 7 minutes of He 5 L and 40.0517 minutes of C to produce transparent vitrification.

The results are shown in FIG. 10 and Table 3. Figure 9, 1st
In Figure 0, (d) (e) (f) are the samples, E, F
The case is shown below.

Table 3 D IF transmission band (MI(z) 800 2
00 200Residual OH of samples D, E, F
When the base is 1.38/jm, it is 1 dB/Km. , J.
:As is clear from the distribution results, the frequency characteristics of the sample are in a high band, while the sample E, l! ” is unfortunate. This is due to the widening of the refractive index difference between Δn′ and the peripheral portion (base reduction @t).

When the dopant concentration at the periphery of the fine particle aggregate is 50% or more of the dopant concentration at the center (sample E), △n'
becomes noticeable. On the other hand, when it is less than 2% (sample F), it can be seen that the skirt pull t becomes noticeable and deteriorates the frequency characteristics of the optical fiber.

Next, let's look at the relationship between the heating method and the refractive index distribution. A fine particle aggregate having a refractive index distribution as shown in FIG. 9(d) was heated by two different heating methods at He5t/min ct, 0
．． 155 in an atmosphere with a gas flow rate of 0.05 t7 minutes.
A case where the film becomes transparent at a heating temperature of 0°C will be explained.

First, sample G was placed in a heating furnace with a uniform temperature distribution and heated to 800°C.
The temperature was increased from 300°C to 1550°C at a rate of 300°C/min.

The refractive index distribution of the obtained transparent glass body was the same as that shown in FIG. 10(e), and there was some variation in the distribution in the longitudinal direction.
Moreover, the cladding thickness also varied by about 2 to 5 μm, making it unsuitable as an optical fiber base material. On the other hand, the sample tube is made transparent by inserting a glass particle aggregate into the heating furnace at a speed of 2 cm/min while rotating it from a low-temperature part to a high-temperature part. d) It has good refractive index distribution and transmission characteristics as shown in Table 3. In addition, the cladding thickness and transmission characteristics in the longitudinal direction of the specimen are also stable. From the above, it can be seen that in order to sinter a glass particle aggregate, it is better to sinter it by gradually inserting it into the sintering temperature range from one end, rather than placing the aggregate in a furnace in advance. The reason why the refractive index distribution and cladding thickness of Sample G vary is considered to be as follows. That is, GeQ + 2
Due to the reaction of C4→GeC4+Ox! This is probably because 0 C4 is consumed and the Ct concentration decreases at the end of the particulate aggregate on the side υ away from the gas supply port. In fact, experiments have shown that the cladding thickness m and the refractive index n change as the C4 concentration changes, as shown in FIG. 11, supporting the above speculation. In addition, in the method of inserting a glass particle aggregate into a heating furnace, if the insertion speed is 1 t, a semitransparent base material can be obtained, but if it is made transparent again in a pure He atmosphere, there will be no change in band loss. is obtained. Therefore, depending on the synthesis conditions of the fine particle aggregate, there is the advantage of obtaining a transparent glass base material at a very high speed9.Next, the relationship between the core diameter of the heating furnace and the refractive index distribution will be explained.

Fine particle aggregate H with a refractive index distribution as shown in Figure 8(d)
. The tips of the fine particle aggregates were inserted into a heating furnace at a heating temperature of 1550°C in an atmosphere with a gas flow rate of 1,500°C at a speed of 2 m+/min to form transparent vitrification. This result is shown in Figure 12 and Figure 4.
Shown in the table.

Table 4 H2,0300 I 2.0 800J
3.0 100 In Fig. 12, (h), (1), and (j) are samples H, I, and J, respectively.
The results are shown below. As is clear from the above results, sample H has a Δn in the refractive index distribution, and sample J has a trailing edge, both of which are unfavorable in terms of transmission characteristics. On the other hand, the sample material has a suitable refractive index distribution and good transmission characteristics. From this, it can be seen that the diameter ratio φ is preferably within the range of 0.95 to 0.5. The diameter ratio φ is 0.5
In the above case, the base material tends to curve during sintering, which is also undesirable.

As explained above, the present invention dehydrates fine particle aggregates with a predetermined refractive index distribution in a gas atmosphere that also contains 7. At the same time, the added dopant is volatilized to modify the refractive index distribution, and an anhydrous Fujirad layer is formed to obtain a rod-shaped glass object with a precise refractive index distribution. It has the practical advantage of being able to stably produce a glass base material with

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the equipment configuration for the VAD method, Figure 2 is a refractive index distribution diagram of a conventional glass base material, Figure 3 is a schematic diagram of the equipment configuration used to implement the present invention, and Figure M4 is a GeO2 concentration distribution diagram. Fifth
Fig. 6 and Fig. 6 are refractive index distribution maps, Fig. 7, t) r)
, (c) is a distribution diagram showing the relationship between the refractive index distribution and bulk density distribution of a glass particle aggregate, Figure 8 (a) Q))
(c) is a refractive index distribution diagram of the glass matrix phase, and Figure 9 (d) (
e) (f) is a refractive index distribution diagram of a glass particle aggregate, and Figure 10 (d) (e) (f) is a refractive index distribution diagram of a glass base material. In each figure, ←) (b) ( C) (d
) (e) (f) shows samples A, B, C, D, E, and F. Figure 11 is a graph showing the relationship between C/9 degrees, refractive index, and cladding thickness, Figure 12 (h) (1) (j) is a refractive index distribution diagram of the glass base material (h) Q) (j) is sample H, I. Showing those of J. In the drawing, 1.30 is a reaction vessel, 2.31 is a burner, 3.32 is a starting material, 4.36 is a glass particle aggregate, 34 is a gas supply path, and 35 is an exhaust path. Patent applicant: Nippon Telegraph and Telephone Public Corporation Sumitomo Electric Industries, Ltd.

Claims (1)

[Scope of Claims] (1) In a method for manufacturing a glass base material in which a transparent glass body is produced by sintering a glass particle aggregate, a single glass particle aggregate whose outer peripheral part has a smaller refractive index than the inner part is made into a halo. It is characterized by modifying the refractive index distribution by sintering in a gas atmosphere containing a halide or a halide and having a dehydration action and a Do-Yant volatilization effect, thereby simultaneously dehydrating and volatilizing Do-Yand from the glass fine particle aggregate. Method for manufacturing a glass base material for optical transmission 1° (2. In claim 1, the bulk density of the glass fine particle aggregate is 0.1 to 0.1.
0.5 f/cd, and the bulk density of the inside is equal to or larger than the bulk density of the outer peripheral portion. (3) % Permissible scope In claim 1, the glass beam for light transmission is characterized in that the dopant cover at the outermost periphery of the glass fine particle aggregate has a dopant content of 2 to 50wttI6 relative to the dopant amount at the center. Production method. (4) % Scope of claim 1, wherein the glass base material for optical transmission is characterized in that the glass particle aggregate is rotated and progressed from a low-temperature section to a high-temperature section of a heating furnace for sintering. manufacturing method. (5) A method for manufacturing a glass base material for optical transmission according to claim 4, characterized in that the glass particle aggregate is advanced in a heating furnace at a speed of 1 m/min to 10 m/min. (6) A method for manufacturing a glass base material for optical transmission according to claim 4, characterized in that the particle aggregate diameter/heating furnace tube diameter is in the range of 0.95 to (1,50). (Power) In claim 1, the gas atmosphere is C4
It is a gas that is a mixture of
A method for manufacturing a glass base material for optical transmission, characterized in that the glass base material is in a range of ot%.