JPS61117127A - Treatment of parent material comprising porous glass for optical fiber - Google Patents

Abstract

PURPOSE:To obtain an almost completely vitrified glass from an SiO2-GeO2 porous parent material for optical fiber having at least one condition such as presence of fine glass particles of a specified particle size or presence of crystalline GeO2, etc., by treating the parent material in an oxygen free atmosphere. CONSTITUTION:A crystalline GeO2 type porous parent material for optical glass is prepd., which is regulated by at least one condition such as that where the diameter of the fine glass particles is >=0.2mum, or, crystalline GeO2 is present, or sintering of the fine glass particles is begun already. When the parent material is dehydrated or virified in an oxygenfree atmosphere, the material is vitrified almost completely. When such parent material is drawn, high quality optical fiber causing small transmission loss and absorption loss due to OH group and contg. no foams is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 1 The present invention relates to a processing method for dewatering and transparent vitrifying a porous glass preform for optical fibers.

``Prior Art 1'' When producing a porous glass base material for optical fiber by the general AD method, a flame burner having a known multi-tube structure is used.

In the VAD method using a normal flame burner, the synthesis rate of glass particles constituting the porous glass matrix is 0.3 g/
The diameter of the glass fine particles is about 0.2 p-m or less, and the porous glass matrix is, for example, SiO2-GeO
Even in the case of the 2-system, the amount of crystalline GaO2 is not so large.

Therefore, in the case of the porous glass base material obtained as described above, the base material is placed in an oxic dehydration gas atmosphere (SOCl2,
C12, temperature 1400 DEG C.) at a speed of about 200 to 300 mm/hour, a sufficiently transparent glass is obtained.

However, when producing a porous glass base material by implementing the VAD method using a double flame burner in order to increase the synthesis rate of glass particles, the diameter of the glass particles is approximately 0.3 to 0.4.
In addition, due to the high flame temperature, sintering of the particles during glass particle synthesis was observed.
Crystalline GeO2 is also present in large quantities.

Even if such a porous glass base material is processed under the above-mentioned existing conditions, a satisfactory transparent glass base material cannot be obtained.

One of the reasons is that aerobic C12 and 5OC121
When a porous glass base material is exposed to an atmosphere such as 0□ and dehydrated and made into transparent glass, a reversible reaction shown by the following formula occurs.

GaC14+02. :GeO2+2CI2 Through this reversible reaction, the volatilized G eCI a is oxidized to G e O
2 or because the diameter of the glass particles is large (specific surface area is small), G e O2 that should be volatilized remains.

In addition, during the synthesis of high-temperature glass particles, sintering of the particles begins and the density of the porous glass base material becomes high, resulting in less volatilization of G eCI a during subsequent dehydration and transparent vitrification. This may cause a situation where a Ge-rich portion is generated in the base material or crystalline GeO2 remains.

Therefore, in the case of a porous glass base material produced by the VAD method using a double flame burner, existing treatment methods can only yield a glass base material that is milky white and not sufficiently transparent. Even if it is processed into a fiber, the transmission loss of the optical fiber and absorption loss due to OH groups will be large, and glass drawing processing 1. Foaming also occurs when necessary processing is performed, such as jacketing glass pipes.

1. Problems to be Solved by the Invention" In view of the above-mentioned problems, the present invention solves the problems by solving known means such as the large particle size, the presence of crystalline Geo 2, and the beginning of sintering of glass particles. The present invention aims to provide a processing method that can satisfactorily dehydrate and transparentize a porous glass preform for optical fibers, which is difficult to process.

The method of the present invention is applicable to glass fine particles having a diameter of 0.24 m or more,
The presence of crystalline G e 02, the beginning of sintering of glass particles, and the S r 02-G e O2-based porous glass base material having one or more of these conditions are heated in an oxygen-free atmosphere. It is characterized by dehydration and transparent vitrification.

Effect 1 In the method of the present invention, when the S+02-GeO2-based porous glass base material is dehydrated and made transparent vitrified in an oxygen-free atmosphere, an irreversible reaction shown by the following formula occurs.

GeO2+2SOC12-'GeCl4''2S02 In such a unidirectional reaction, the volatilization of crystalline GeO2 progresses, the specified reaction is also promoted, and the transparency of the base material after transparent vitrification is also improved. Even if the porous glass base material is larger than the pore size, contains crystalline GeO2, or has already started sintering of glass particles, it can be processed without problems.

At this time, it is preferable that the moving speed of the porous glass base material in an oxygen-free atmosphere be low and the transparent vitrification temperature be high.
This makes the above reaction more sufficient when the glass fine particles have a large diameter.

Embodiments Embodiments of the method of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a known heating furnace equipped with an electric heater 2 and a furnace tube 3, and a gas inlet 4 and a gas outlet 5 are provided at the lower and upper portions of the furnace tube 3, respectively.

Reference numeral 8 denotes a Si0102-Ge-based porous glass base material produced through the VAD method using the double flame burner, and this porous glass base material 6 is attached to the lower end of the quartz-based support rod 7. .

When processing the porous glass preform 6 in FIG. is maintained in a predetermined oxygen-free atmosphere.

The porous glass base material 6 inserted into the furnace core tube 3 in the oxygen-free atmosphere is moved downward to the heating part of the electric furnace 1 (the part where the heater 2 is located) in a rotating state, and is sequentially dehydrated from its lower end. Transparent vitrification.

When the porous glass preform B is composed of, for example, Sin2-Gem2 (core part) and 5i02 (clad part), the preform after being made transparent as described above is spun by heating and drawing to form an optical fiber. Become.

When the porous glass preform B consists of, for example, only Sin2-Gem2 (core part), a pure quartz glass pipe is jacketed around the outer periphery of the preform after the transparent vitrification, and these are spun to become an optical fiber. .

The porous glass base material 8 may also contain other dopants than GeO□.

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

Specific Example: When dehydrating the porous glass base material 8 described above to make it transparent and vitrifying, the furnace core tube 3 of the electric furnace 1 is supplied with 1 min/min of SOC+ bubbled with He and 30 min/min of He. Then, the inside of the furnace core tube 3 was made into an oxygen-free atmosphere, the transparent vitrification temperature by the heater 2 was set to about 1400° C., and the moving speed (lowering speed) of the porous glass base material 8 inside the furnace core tube 3 was 120 l/min. The porous glass base material B was treated as follows.

Next, the base material after transparent vitrification was spun by heating and drawing to obtain an optical fiber having an outer diameter (diameter) of 125 l and a core diameter of 50 l+s.

In this specific example, the optical fiber has a wavelength of 9.5 mm as shown in FIG.
Transmission loss at 854tm is 2.82dB 8 layers, transmission loss at wavelength 1.30pm is 0.48dB/km
, transmission loss at wavelength 1.551Lm is 0.24dB
Eight ■.

Absorption loss due to OH group at 1.38 ru 0.30dB
/ showed very good results.

Comparative Example When processing the same porous glass base material as in the specific example, 0.31 min CI2 and 30 min Hs were supplied into the furnace tube 3 to create an oxic atmosphere inside the furnace tube 3 , the transparent vitrification temperature by the heater 2 is about 131110°C, and the moving speed (falling speed) of the porous glass base material in the furnace tube 3.
The porous glass preform was dehydrated and made into transparent vitrification at a speed of 240 mm/min, and the preform after transparent vitrification was heated and stretched to form an optical fiber with an outer diameter (diameter) of 125 IL and a core diameter of 50 Hm. Obtained.

The optical fiber in this comparative example had a wavelength of 0.05 as shown in FIG.
The transmission loss in the 85 Hiro layer is 3.21 dB/km, and the transmission loss at a wavelength of 1.30 pm is 1.37 dB/)o
w, transmission loss at wavelength 1.55pm is 1.08d
B/km, and the absorption loss due to OH groups at 1.39 pm was 2.30 dB/km, which was considerably lower than the result of the specific example.

The most effective condition for the method of the present invention is to make the atmosphere during dehydration and transparent vitrification an oxygen-free atmosphere. The moving speed (descending speed) of the material 6,
The next most effective condition is the transparent vitrification temperature of the porous glass base material 8 in an oxygen-free atmosphere.

At this time, the base material movement speed is preferably 20Q+s+a/hour or less, and the transparent vitrification temperature is preferably 1400° C. or higher.

rEffect of invention J As explained above, when using the method of the present invention.

By dehydrating a predetermined porous glass base material in an oxygen-free atmosphere and turning it into transparent vitrification, a completely transparent glass base material for optical fibers can be obtained, and the transparent glass base material can be spun into yarn. By doing so, it is possible to obtain a high-performance optical fiber that has small transmission loss, absorption loss due to OH groups, etc., and is free from bubbles.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing one embodiment of the method of the present invention, and FIG.
The figure is an explanatory diagram showing the transmission characteristics of an optical fiber. 1... Electric, actual furnace 2 mm1 heater 3-e red furnace tube (oxygen-free atmosphere) 6 @+Iψ porous glass base material

Claims (3)

[Claims] (1) Glass particles have a diameter of 0.2 μm or more, crystalline G
The presence of eO_2, the beginning of sintering of glass particles, and SiO_2 having one or more of these conditions.
A method for processing a porous glass preform for optical fibers, which comprises dehydrating and transparent vitrifying a 2-GeO_2-based porous glass preform in an oxygen-free atmosphere. (2) The method for processing a porous glass preform for an optical fiber according to claim 1, wherein the moving speed of the porous glass preform into an oxygen-free atmosphere is 200 mm/hour or less. (3) The method for processing a porous glass preform for optical fiber according to claim 1, wherein the transparent vitrification temperature is 1400° C. or higher.