JPS6289B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a material for a glass fiber for light transmission.

A glass material for optical transmission usually has a central part through which light passes, called the core, which has a high refractive index, and an outer peripheral part, called the cladding, which has a low refractive index. GeO ₂ is added to silica glass as a method to change the refractive index.
There is a method of adding dopants such as. Conventionally used dopants are added at the same time as glass is produced, so they are required to be extremely pure and are extremely expensive chemicals. However, in the method according to the present invention, fluorine as a dopant agent is added after the glass fine particles are produced. Fluorine produced by the decomposition of fluorine compound gas is
Because it is highly reactive, it can be sufficiently added to glass even when other impurities are not added to the glass. Therefore, it was found that even if a material with relatively low purity and low price was used, the light would not be attenuated. In addition, fluorine is a dopant that lowers the refractive index of glass, so in a step-index type fiber in which the refractive index changes stepwise, fluorine is not added to the core portion through which light passes.

Therefore, light scattering loss caused by additives can be minimized. Here, it is necessary that fluorine is added uniformly to the glass for the cladding.

It took a relatively low temperature (800
It was found that when the glass fine particles were introduced into a fluorine atmosphere and heat-treated at a temperature of 100°F (°C), the fluorine easily penetrated into the glass fine particles and had a good dehydration effect.

However, when this glass particulate body is subsequently melted and sintered at a high temperature to vitrify it, a problem arises in that the periphery of the resulting glass body contains less fluorine than the inside, making it difficult to obtain a uniform glass. Ta. As a result of considering this point, we found that when the treatment temperature is increased to vitrify, the closer to 1400℃, which is the point at which SiO ₂ melts and vitrifies, the more fluorine that has been added evaporates significantly, and the more fluorine is formed mainly on the surface of the glass body. I understood that. The present invention has been made to solve this problem, and as described in the claims, a laminate of glass particles formed by flame hydrolysis is heated to 1400°C or higher in an atmosphere of fluorine compound gas and inert gas. The present invention provides a method for producing a glass material for optical transmission, which comprises heating to form a glass body uniformly containing fluorine. In addition, fluorine is OH in glass.
It was found that hydrogen can be eliminated from the group. This is considered to be one of the ways in which fluorine reacts with glass, and is expressed by the following formula.

SiOH+F ₂ →Si-O-F+HF Therefore, as a result of the fluorine addition effect of the present invention, the OH group concentration in glass, which is a drawback of flame hydrolysis reaction, is reduced from several tens of ppm to several ppm, and the wavelength caused by OH groups is reduced. Light absorption loss in the vicinity of 0.95μm has been significantly improved, making it possible to improve the optical absorption loss in the vicinity of 0.85μm, which is normally used in optical communications.
Alternatively, it also has the advantage of further reducing light absorption loss at 1.05 μm.

The details of the present invention will be described below.

In order to generate quartz glass fine particles by a flame hydrolysis reaction, as shown in Fig. 1, a quartz concentric multi-tube burner 1 is used, oxygen 2, hydrogen 3 and SiCl ₄ are used as the raw material gas. Ar gas may be used as a carrier gas and sent to the center 5 of the oxyhydrogen flame to cause a reaction. At 4 in the figure, Ar gas is flowed as a shield so that the raw material gas reacts in a space several mm away from the tip of the burner. When obtaining a rod of glass fine particles, glass fine particles are laminated in the axial direction from the tip of the rotating starting member 6. Further, when obtaining a pipe-shaped glass particle body, glass particles are laminated on the outer circumference of a rotating quartz rod or carbon rod 7 while traversing the burner 1 as shown in FIG.

The transparentization temperature of the fluorine-doped glass particles varies depending on the amount of fluorine added, the type of atmospheric gas, and the processing time. In the case of glass used as optical fiber,
The maximum amount of fluorine added is 10% by weight. When the concentration is higher than this, the viscosity of the glass becomes low and the compatibility with quartz glass deteriorates, causing problems in the structure of the fiber having the structure obtained by the present invention. The transparentization temperature of the glass fine particles in this component is preferably 1400°C or higher. When the amount of fluorine added is small, it is necessary to set this temperature higher.

As for the atmospheric gas during the treatment, it is desirable to use an inert gas in order to introduce fluorine. The presence of gases other than inert gases is due to the effective fluorine gas (oxygen in Si-O bonds in glass or Si
This is not preferable because it reduces the amount of highly active fluorine species that replace hydrogen in -OH with fluorine.

In this process, He is the most preferable inert gas in terms of causing the fluorine addition reaction and melting and making the glass particles transparent. When the molecular radius is larger, such as Ar or N ₂ , it takes a long time to clear the glass, and bubbles tend to remain in the glass.

As described above, the required glass material can be obtained in one step by mixing the fluorine compound gas into the inert gas of the sintering furnace.

The fluorine compound gas that can be used must be one that does not affect the transmission loss of light even if the decomposition products of the compound gas are incorporated into the glass.

As an auxiliary means for generating fluorine gas, the third
In the figure, an ultraviolet lamp 12 is installed in a heating furnace 11 for heat treatment, and when fluorine compound gas is decomposed by photolysis using ultraviolet rays and fluorine gas is generated, the reaction time is 40% faster than when only heating is used. It turns out that it can be shortened to. The processing time may have been shortened because the high-energy ultraviolet rays can dissociate the fluorine bonds.
Of course, the fluorine compound gases shown here include fluorinated carbon gas, fluorinated carbon chloride gas, sulfur fluoride, silicon fluoride, elemental fluorine, hydrogen fluoride, fluorinated halogen gas, etc. Carbon dioxide gas, fluorochloride carbon gas, silicon fluoride, fluorine gas, etc. are easy to gasify;
This is preferable for use in the present invention because the decomposed products hardly affect the transmission loss of light in the glass. Furthermore, it is well understood that treatment conditions vary depending on each compound.

Example Using a concentric quadruple tube burner, Ar
SiCl ₄ , Ar, H ₂ , and O ₂ using gas as a carrier were flowed at flow rates of 0.3, 2, 5, and 10/min, respectively, and glass particles were deposited on a rotating starting carbon rod (outer diameter 10 mm). Glass fine particle bodies with an outer diameter of 30 mm were formed. The starting carbon rod was removed, the glass particles were set in the furnace body, and SF ₆ was fed at 500 c.c./min and He was heated at 10 c.c./min.
The temperature was raised from 800° C. to 1450° C. at a rate of 5° C./min while flowing from the lower part of the furnace body to the entire area of the furnace body at a flow rate of 5° C./min, and maintained at this temperature for 3 hours. A glass tube with almost uniform fluorine concentration was obtained. Next, the inner surface of this glass tube was polished to obtain a glass tube with an inner diameter of 10 mmφ and a wall thickness of 2 mmφ.

This was combined with a separately prepared pure quartz glass rod having an outer diameter of 9 mm to form a drawn fiber. The resulting fiber had a refractive index difference of 0.5%, and had excellent properties with no impurity loss in the cladding layer.

Comparative Example A glass particle body was formed in the same manner as in the example, and this was set in a furnace body, and SF ₆ was fed at 500 c.c./min and He was heated at 10 c.c./min.
The temperature was raised from 800° C. to 1200° C. at a temperature increase rate of 5° C./min with a split flow of 100° C./minute, and after holding at this temperature for 3 hours, the SF ₆ was stopped and sintered into a transparent glass tube.

The obtained glass tube contained less fluorine in the periphery than in the central part of the wall thickness of the tube, and a uniform condition could not be obtained. This is thought to be because the fluorine doped once volatilized during sintering.

As described above, the present invention has the advantage that by using fluorine as a dopant, light scattering loss due to the dopant can be minimized, and the OH group concentration in glass, which was a drawback of flame hydrolysis, can be significantly reduced. have.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the manufacturing method of a rod-shaped glass fine particle laminate. 1...Multi-tube burner (the figure shows a quadruple tube), 2...
Oxygen supply port, 3...Hydrogen supply port, 4...Ar gas supply port, 5...Raw material gas supply port, 6...Seed rod Fig. 2 is a diagram showing the manufacturing method of a cylindrical glass particle laminate.7... ...Central core rod (starting member) Fig. 3 is a diagram of a high-temperature furnace for sintering and transparent vitrification, and shows 10...sintering furnace, 11...heating body, 12...ultraviolet lamp.

Claims (1)

[Scope of Claims] 1. A method for producing a glass material for optical transmission that uniformly contains fluorine by forming a laminate of glass particles by flame hydrolysis, and then treating the laminate of glass particles with a fluorine compound gas. A method for producing a glass material for optical transmission, characterized by introducing an inert gas and processing in an atmosphere heated to 1400°C or higher. 2. The method according to claim 1, wherein any one of carbon fluoride gas, carbon fluoride chloride gas, sulfur fluoride, silicon fluoride, fluorine, and halogen fluoride is used as the fluorine compound. Manufacturing method of glass for optical transmission.