JPS5924743B2 - Manufacturing method of optical fiber base material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical fiber preform by a VAD method.

Conventionally, optical fibers used for optical communications have been manufactured by various methods, but the VAD method has recently been attracting attention.

In the VAD method (vapor phase attachment method), soot-like glass particles are attached and deposited on the lower end of a rod-shaped base material that moves upward while rotating.
In this method, soot-like glass particles are grown in the axial direction while pulling up a rod-shaped base material to form a rod-shaped porous glass lariform, and then a predetermined process is performed to form an optical fiber preform. Then, this optical fiber preform is spun to form an optical fiber. By the way, as a manufacturing method for an optical fiber preform, a porous glass lariform is formed by the VAD method, heated to make it transparent, and stretched to form a stretched rod, and then a quartz jacket is attached to the stretched rod. There is a method of manufacturing an optical fiber preform having a predetermined core/outer diameter ratio by providing a predetermined core/outer diameter ratio.

However, the optical fiber obtained by spinning the optical fiber preform manufactured by this method has an optical transmission loss of 2 dB/
The reality is that there is a large variation between 1n and 5dB/kln. When the inventors investigated the cause of this, they found that G exists in a free state on the surface of the stretching rod.
This is because e02 and GeO have high vapor pressure, so they turn into vapor during spinning at high temperatures, grow into bubbles at the interface between the drawing rod and the quartz jacket, and as a result, gaps are created at the interface between them. It has been found that if the inner wall of the quartz jacket is damaged, the damage is amplified by the above-mentioned GeO2 and GeO bubbles, resulting in an optical fiber with a large optical transmission loss.

As a result of further intensive research to eliminate these drawbacks, the present inventors heat-treated porous glass lariform in an H2 atmosphere to evaporate and remove e02 and GeO near the surface of porous glass lariform. However, if a layer containing a large amount of SiO2 is formed near the outside of the porous glass lariform, and then normal post-treatment is performed to form an optical fiber base material and then an optical fiber is formed, an optical fiber with low optical transmission loss can be obtained. was found to be formed. The present invention was completed based on this knowledge, and its characteristics are that after forming a porous glass preform by the VAD method, it is made into transparent glass, stretched, and then a quartz jacket is provided to form an optical fiber base material. During manufacturing, the porous glass preform is heat treated in an H2 atmosphere. The present invention will be explained in detail below.

First, by the VAD method, soot-like glass particles are deposited on the lower end of a rod-shaped base material that moves upward while rotating, and the soot-like glass particles are grown in the axial direction while pulling up the rod-shaped base material to form a rod-shaped porous material. Form a glass preform.

Next, the porous glass preform formed as described above is heat treated at a high temperature of about 800 to 1000° C. in an H2 atmosphere.

Then, GeO2 and GeO existing in a free state near the surface of the porous glass preform are evaporated and removed in a form that is more easily volatilized, and a layer containing a large amount of SiO2 is formed near the outside of the porous glass preform. Next, the porous glass preform heat-treated in an H2 atmosphere as described above is heated to make it transparent, stretched to form a stretched rod, and a quartz jacket is provided on the stretched rod, which is then heated and fused. Form an optical fiber base material. Thereafter, the optical fiber preform is spun to form an optical fiber. By this method, both step type and square distribution type optical fibers can be formed. By the way, as mentioned above, in the present invention,
The porous glass preform is heat-treated in an H2 atmosphere to remove GeO2 and GeO near the surface of the porous glass preform.
is removed by evaporation, and a layer containing a large amount of SiO2 is formed near the outside.

Therefore, even if a spinning process is performed after applying a quartz jacket, the outer part of the drawing rod and the quartz jacket are made of the same material, so not only no bubbles due to GeO2 or GeO are generated, but also no local expansion occurs. No gaps occur at their interfaces. Further, even if the quartz jacket is damaged, the damage will not be magnified, and an optical fiber with low optical transmission loss can be obtained. As explained above, in the present invention, a porous glass preform formed by the VAD method is heat-treated in an H2 atmosphere. Therefore, the porous glass preform after heat treatment is made into transparent glass, stretched, and then provided with a quartz jacket to produce an optical fiber preform, and the optical fiber preform is spun at a high temperature to produce an optical fiber. During this process, unlike the conventional method, no bubbles are generated due to GeO2 or GeO, and no gaps are formed near the boundary between the drawing rod and the quartz jacket, and an optical fiber with low optical transmission loss is reliably formed. In addition, even if the quartz jacket is damaged, the damage will not be magnified, so standard quartz jackets can be used as is without any treatment, and therefore light production can be achieved at low manufacturing costs. Practical effects such as the ability to manufacture fibers are also achieved. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples.

[Example 1] First, a diameter of 60 mmφ was attached to the lower end of a rod-shaped base material using the VAD method.
, a porous glass preform with a length of 300 mu was formed.

Next, as shown in FIG. 1, the porous glass preform 1a formed at the lower end of this rod-shaped base material 1 is heated in a heating furnace 2, a quartz tube 3, an H2 inlet pipe 4, and an H2 exhaust pipe 5. It was placed in apparatus 6 and heat treated under the following conditions. H2 flow rate: 21/min Heat treatment temperature: 1200 minutes C Heat treatment time: 1 hour The porous glass preform heat-treated in the above H2 atmosphere is heated to become transparent vitrified, stretched to form a stretched rod, and a quartz jacket is attached to this stretched rod. The fibers were then heat fused and spun to form an optical fiber.

When the wavelength characteristics of optical transmission loss of an optical fiber with a length of 1500 m were measured, the results shown by curve A in FIG. 2 were obtained. For comparison, we also measured the wavelength characteristics of optical transmission loss for an optical fiber that was not heat-treated in an H2 atmosphere.
Curve B in FIG. 2 was obtained. By comparing curves A and B in FIG. 2, it can be seen that the untreated curve B has a high optical transmission loss due to structural imperfections, whereas the curve A of the optical fiber treated by the method of the present invention has a high optical transmission loss due to structural imperfections. It can be seen that in the case of curve B, the optical transmission loss is small, and is reduced by about 1 dB/1Cff1 compared to the case of curve B.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a heating device used to carry out the method of the present invention, and FIG. 2 is a graph showing wavelength characteristics of optical transmission loss of optical fibers obtained by the method of the present invention and the conventional method. 1a...Porous glass preform, 2...
...Heating furnace, 3...Quartz tube, 6...
heating device.

Claims (1)

[Claims] 1 After forming a porous glass preform by the VAD method, this porous glass preform is heat-treated in an H_2 atmosphere, and then it is made into transparent glass and stretched. After that, a quartz jacket is provided and an optical fiber base material is formed. 1. A method for manufacturing an optical fiber base material, the method comprising: manufacturing an optical fiber base material.