JPS6227342A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To efficiently produce fluorine-contg. quartz glass having high purity and high concn. by sintering porous glass obtd. by a CVD method or outside vapor-phase deposition method under pressurization in a mixed atmosphere composed of He and gaseous fluorine thereby forming transparent glass. CONSTITUTION:A sintering furnace 11 consists of a furnace core tube 12, a heater 13 and an alumina or carbon plate 14 and a porous glass base material 15 is disposed in the tube 12. The deformation of the tube 12 is prevented by the plate 14. The base material 15 is formed by an ordinary CVD method, etc. at the top end of a target 16 which is airtightly held by an O-ring 17. The gaseous fluoring such as SF6, CF4 or CCl2F2 is filled together with He in the tube 12 and a gaseous mixture of the He and gaseous fluorine is controlled by a regulator 18 to about 0-20,000mmH2O pressure. The tube is heated by a heater 13 to the sintering initiation temp. and the material 15 is sintered when said material passes the high-temp. part thereof, by which the material is formed into the transparent glass; at the same time, the fluorine is doped therein. The fluorine-contg. transparent glass base material 19 is thus formed from the top end part of the material 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing an optical fiber, and more particularly to a method for manufacturing fluorine-containing quartz glass, which is an Ifj material for an optical fiber.

BACKGROUND OF THE INVENTION Silica glass containing Hungtung has conventionally been produced by a plasma method, a CVD method, or a sintering method. In the plasma method, as shown in FIG. 4, a plasma flame formed in an RF coil 41 contains 5iC14, SiF*, etc., which are the main components of glass, as well as CFa and SFa.

Injecting fluorine gas such as CCl2F2 together,
A fluorine-containing quartz glass base material 42 is directly produced.

In this method, the amount of fluorine doped can be up to a relative refractive index of Δ=-1.2%.

Next, in the CVD method, as shown in FIG. 5, 02.5iC1* and 5iFn are placed in the starting quartz tube 51.

A gas such as S F * or CCl 2 F z is fed into the quartz tube 51 and heated with a burner 52 from the outside to form a glass layer 53 on the inner wall of the quartz tube 51 to a temperature of 14 vJIt.

- In the case of the sintering method, first, as shown in Figure 6, the normal VAD
Hōniyo River + 6 L L: H2, 02, S i
A gas such as C14 is sent to form glass fine powder in a flame, and this is deposited to form a porous glass base material 62. Alternatively, it may be made by an external CVD method, and this porous glass base material 62 is placed in a sintering furnace 63 as shown in FIG.
Helium and CF4. A transparent glass base material 64 is produced by sintering in a fluorine gas atmosphere such as SF, CCl2F2, etc. Fluorine is doped during this sintering process. Since this sintering method does not synthesize the porous glass base material 62 in a fluorine gas atmosphere, the synthesis rate can be as high as 3 to 5 g/min.

Problems to be Solved by the Invention However, all of the above conventional manufacturing methods have drawbacks. First, the plasma method has a problem in that the synthesis rate is quite low at 0.1 g/min or less. This is because the plasma method is a method for directly depositing glass, and the etching effect of fluorine gas also becomes effective during this deposition process.

Furthermore, in the CVD method, since heat is applied through a quartz tube, the reaction temperature is lower than that of a plasma flame, and the maximum relative refractive index difference that can be obtained is about Δ=-0.4%. In addition, since the glass is deposited inside the quartz tube, the amount of glass obtained is small.
The shape is also difficult to process. Furthermore, the deposition rate is as low as 0.05 g/min.

In the case of the sintering method, the fluorine gas concentration in the sintering furnace is set to 100%.
However, the relative refractive index difference of the obtained fluorine-containing quartz glass is 0.7% at most, and there is a problem that the fluorine content is limited.

This invention solves the problems with the above conventional manufacturing method,
It is an object of the present invention to provide a method for efficiently manufacturing fluorine-containing quartz glass with high purity and high concentration.

Means for Solving the Problems The optical fiber manufacturing method of the present invention basically belongs to the sintering method, in which porous glass obtained by the VAD method or the external deposition method is placed in a mixed atmosphere of helium and fluorine gas. It is characterized by being sintered under pressure and turned into transparent glass.

Function: When porous glass is sintered in a mixed atmosphere of helium and fluorine gas to form transparent glass, it is doped with 2 elements, but in the present invention, the fluorine concentration in this quartz glass can be reduced within the sintering furnace. This was done by focusing on the fact that it depends on the pressure of That is, when sintered and made into transparent glass under high pressure, quartz glass containing a high concentration of fluorine can be obtained.

Embodiment In FIG. 1, a sintering furnace 11 has a furnace core tube 12 and a heater 13.
and an alumina or carbon plate 14, and a porous glass IiI material 15 is disposed within this furnace core tube 12. Alumina or carbon plate 14 is used to prevent deformation of furnace tube 12. This porous glass base material 15 is
It is formed at the tip of the target 16 by a normal VAD method, and the target layer 16 is held airtight by an O-ring 17. Inside the reactor core tube 12, along with helium, CF 4 , SF@, CCl 2 F
Although the fluorine gas is filled with fluorine gas such as g, the pressure of the mixed gas of helium and fluorine gas in the core tube 12 is controlled by the regulator 18 to be at a pressure of O to 2000 mmH,O.

The temperature is raised by the heater 13 to a temperature at which sintering begins. When the porous glass base material 15 passes through the high-temperature portion, it is sintered and becomes transparent vitrified, and at the same time it is doped with fluorine. In this way, the porous glass base material 15
From the tip of the fluorine-containing transparent glass base material 19
is being formed.

When the dependence of the fluorine-doped quartz glass produced in this manner on the fluorine gas concentration in the furnace and the dependence on the atmospheric pressure in the furnace was investigated, the results shown in FIG. 2 were obtained. As is clear from this Figure 2, the pressure inside the furnace is 500mm1
(, 0, a fluorine-doped quartz glass with a maximum relative refractive index difference of -1.2% was obtained, and at 1000 m 100O, a fluorine-doped quartz glass with a maximum relative refractive index difference of -1.5% was obtained.

Furthermore, when the dependence of the amount of fluorine doped on the atmospheric pressure in the furnace was investigated when the fluorine gas concentration in the furnace was kept constant, data as shown in FIG. 3 was obtained.

Note that the pressure inside the furnace tube was kept constant at 1111 using a pressure gauge, and the refractive index of the fluorine-doped quartz glass was measured using a preform analyzer and an interference microscope.

Effects of the Invention Since the present invention basically relies on a sintering method, the synthesis rate is essentially higher than other plasma methods, CVD methods, etc., and it is highly suitable for mass production. Furthermore, since the pressure inside the sintering furnace is increased, fluorine-doped quartz glass with a high concentration that could not be obtained by conventional sintering methods can be produced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining one embodiment of the present invention,
FIGS. 2 and 3 are graphs showing the obtained data, and FIGS. 4, 5, 6, and 7 are schematic diagrams of conventional examples. 11.63...Sintering furnace 12...Furnace core tube 13...
・Heater 14...Alumina or carbon plate 15.62...Porous glass base material 16...Data tip 17...0 ring 1
8...Regulator 19.64...Transparent glass base material 41...RF coil 4z...Glass base material 51
... Starting quartz tube 52.61 ... Burner 53.
・Glass layer

Claims (1)

[Claims] (1) A method for manufacturing an optical fiber, which comprises sintering porous glass under pressure in a mixed atmosphere of helium and fluorine gas to form transparent glass.