JPS6016827A - Manufacture of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber which can be exposed to a high-temperature environment for a long period without increasing the transmission loss caused by the hydroxyl group, by melt-spinning an optical fiber preform having a specific hydroxyl group-content in a specific atmosphere, and coating the fiber with a metal. CONSTITUTION:An anhydrous glass preform 9 is attached in the preform-feeing zone 4, and the lower end of the preform is positioned to the level of the heater 1b. Molten metal 10 such as aluminum, indium, etc. is supplied from the molten metal reservior 8 to the crucible 7. High-purity dried argon gas or helium gas which may contain a small amount of dry halogen gas, is introduced through the gas inlet 5 into the apparatus. The end part of the glass preform 9 is melted by the heater 1b, and the spun optical fiber 11 is introduced continuously into the crucible 7 containing the molten metal to obtain the objective metal-coated optical fiber 12. Since the inner space of the apparatus is shielded completely from the outer atmosphere, and is supplied with dry gas or dry halogen-containing gas, the atmosphere in the apparatus is maintained to the perfect anhydrous state or the dehydrated state by the halogen gas.

Description

Detailed Description of the Invention When used above, silicone rubber is used as the coating material.By the way, when such a metal-coated optical fiber is used at high temperatures, the loss of the optical fiber increases due to the diffusion of hydroxyl groups in the glass. There is a phenomenon.

This is because the hydroxyl groups mixed in the cladding or jacket diffuse and invade the core.

In order to prevent this phenomenon, at the manufacturing stage of fiber optics, anhydrous quartz glass tubes are used for the cladding or exposed parts, or a fully synthetic base material that has been dehydrated using the VAp method is used. However, even if such an anhydrous optical fiber preform is prepared, it may be contaminated with hydroxyl groups at the stage of obtaining an optical fiber from this anhydrous optical fiber preform.For example,
If an oxyhydrogen flame is used when drawing an optical fiber cut material, a layer containing 100 ppm or more of hydroxyl groups is formed over several micrometers on the surface of the drawn glass preform. 'i/ko,
□! , ''Spread and permeate into the city. This causes a decrease in the front fiber strength of the optical fiber.

This EA was made in view of the above circumstances, and it is not contaminated with hydroxyl groups during the process from the anhydrous optical fiber base material to obtaining the optical fiber, and even if the equipment is exposed to high temperatures for a long time, the transmission loss due to hydroxyl groups will increase. The object of the present invention is to provide a method for manufacturing an optical fiber that can produce an optical fiber free of .

The present invention will be explained in detail below.

The method for producing an optical fiber of the present invention is characterized by performing melt spinning and metal coating on an anhydrous optical fiber base material in an atmosphere containing anhydrous or halogen.

First, an anhydrous profile fiber preform, that is, an optical fiber preform having a hydroxyl group content of 0.1 ppnn or less in all parts, is prepared. Various known methods can be used to obtain this anhydrous optical fiber preform. For example, a fully synthetic optical fiber preform obtained by the VAD method is dehydrated using a halogen gas such as chlorine gas or fluorine gas, and the preform is made into a transparent glass. An example is an optical fiber base material made of a jacketed glass tube. The above hydroxyl group content is 0. lp
After increasing the pm to 114 pm, this anhydrous optical fiber preform is installed in the manufacturing equipment shown in the drawings for melt spinning and metal coating. ζ Here, the anhydrous optical fiber cube is always stored or handled in an anhydrous atmosphere. This can be done using dry alcohol or dry nitrogen (dew point -50°C).
Measures such as storing the optical fiber in a container filled with a drying gas such as those listed below, or handling the optical fiber while blowing the drying gas onto the optical fiber base material are taken.

In the drawings, reference numeral 1 denotes a spinning furnace section, and this spinning furnace section 1 is composed of a furnace body 1a and a heating element 1b. The furnace body 1au is a cylindrical body made of a refractory material such as zirconia, alumina, graphite, or silicon nitride. Further, the heating element 1b is provided outside the furnace body 1a so as to surround the furnace body 1a.

1. A drawer section 2 made of a cylindrical quartz tube or the like is connected to the lower part of the furnace body 1a.
The connecting portion between the furnace body 1a and the drawer portion 2 is hermetically sealed by an O-ring 3. In addition, the removal part 4 of the furnace body 1a
Exhaust pipes 6 are provided above the respective exhaust pipes.

1. A crucible 7 made of graphite or the like for metal coating is provided at the bottom of the drawer 2.
The connecting part between and drawer part 2 is the same.

It is hermetically sealed with ring 3. Also, Ruggi 7 is
It is connected to a bath molten metal storage tank 8, so that molten metal can be supplied thereto.

In such a manufacturing apparatus, the anhydrous glass base material 9 is placed in the base material delivery section 4, and its tip end is connected to the heating element 1b.
A molten metal 10 such as aluminum or indium is supplied to the crucible 7 from a molten metal storage tank 8. From the cut air supply pipe 5, a small amount of high-purity and dry alco gas, helium gas, or dry chlorine gas or dry fluorine gas is added to this, but the internal space is completely freed from outside air. Since it is shut off and a dry gas or a dry halogen-containing gas is injected into the internal space, the atmosphere inside the device becomes completely anhydrous or dehydrated by the halogen gas.

Therefore, if bath melt spinning is performed from the anhydrous glass base material 9 in this internal space and metal coating is performed, the metal will be coated not only inside the optical fiber 11 but also on the surface with no hydroxyl groups present at all. .

Therefore, since the metal-coated optical fiber 12 obtained by such a method has extremely small hydroxyl groups, there is no increase in transmission loss due to diffusion of hydroxyl groups and no decrease in strength even when used continuously at high temperatures.

Hereinafter, the present invention will be specifically explained with reference to Examples.

It was attached to the device shown in Figure 9. The diameter of the furnace body 1a was 30 mm. Helium gas 1.31△chlorine gas 2 from air supply pipe 5
A mixed gas was fed at a rate of cc/min, the crucible 7 was filled with molten aluminum, and bath melt spinning and metal coating were performed. The obtained metal coated optical fiber 12 has a coat diameter of 160
The diameter of the core was 50 μm and 125 μm. This optical fiber 12 was left at a temperature of 350° C., and the increase in hydroxyl groups was determined by continuously measuring the absorption peak characteristic of hydroxyl groups at 0.945 μm. As a result, 6
No increase in the hydroxyl group characteristic absorption peak was observed in continuous measurement for 0 hours.

In the above explanation, the molten metal dipping method is used as the metal coating method, but this is not the only method.If the surrounding atmosphere can be maintained in an anhydrous or location-containing atmosphere,
CVD method, snow? There would be no such thing as the Tsutaring method. Therefore, even if this optical fiber is left at high temperatures, the hydroxyl groups will not diffuse into the core, and the increase in transmission loss caused by these hydroxyl groups can be prevented, making it possible to withstand continuous use under high temperatures. becomes. Furthermore, since it is a metal-coated optical fiber, it has good water resistance and high reliability.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view showing an example of a manufacturing apparatus used in the manufacturing method of the present invention. In the figure, l: spinning furnace, 5: air supply pipe, 6: exhaust pipe, lO
: Molten metal, 11: Optical fiber.

Claims (1)

[Claims] Hydroxyl group content in all parts is 0.1 pprrJJ
A method for producing an optical fiber, which comprises melt-spinning a lower optical fiber base material in an anhydrous or halokene-containing atmosphere, and then coating the obtained fiber with a metal in the same atmosphere as the above-mentioned atmosphere.