JPH0585780A - Production of quartz glass-based optical fiber - Google Patents

Abstract

PURPOSE:To efficiently provide a quartz glass-based optical fiber having excellent water and hydrogen resistance, strength, etc., by mixing hydrocarbon and/or halogenated hydrocarbon with halogen, thermally decomposing this mixture and coating an optical fiber with carbon produced. CONSTITUTION:Hydrocarbon such as methane or a mixture of hydrocarbon with halogenated hydrocarbon such as trichloethane is mixed with halogen such as Cl so that the ratio between the total number of halogen atoms and that of hydrogen atoms is preferably regulated to 10:(5-15). The resulting mixture is thermally decomposed at the high temp. of an optical fiber immediately after drawing from a heated base material and a carbon coating layer is directly formed on the surface of the optical fiber to obtain a quartz glass-based optical fiber. The rate of deposition of carbon on an optical fiber can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a silica glass optical fiber which is water and hydrogen resistant treated by carbon coating.

[0002]

2. Description of the Related Art A silica glass optical fiber has a problem that conduction loss gradually increases when it is in contact with hydrogen gas or water for a long time. The reason for this is that absorption loss due to molecular motion of hydrogen molecules diffused in the optical fiber or B ₂ O ₃ , P contained as a dopant in the optical fiber.
It has been considered that OH groups produced by the reaction of ₂ O ₅ , GeO ₂ , Na ₂ O and the like with hydrogen increase absorption loss.

For this reason, conventionally, it has been proposed to pyrolyze hydrocarbons or chlorine-containing hydrocarbons to form a carbon film on the surface of the optical fiber and to carry out a water resistance and a hydrogen resistance treatment. By the way, in the case of industrially forming a carbon film on the surface of an optical fiber, the rate of formation of the carbon film cannot be said to be sufficiently fast, and a more efficient industrial treatment method is desired. Further, the carbon coating formed by the conventional method does not have a sufficient shielding effect against both water and hydrogen gas. Moreover, if the thickness of the carbon coating is increased to enhance the shielding effect, there is a problem that the tensile strength of the obtained optical fiber decreases.
Furthermore, the carbon deposition rate in the conventional method is not sufficient, which causes a problem in industrial production.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides an industrially efficient method for producing a carbon-coated silica glass optical fiber having improved water resistance, hydrogen resistance and tensile strength. Is an issue.

[0005]

In order to solve the above-mentioned problems, a method for producing a silica glass optical fiber according to the present invention comprises a hydrocarbon or a mixture of a halogenated hydrocarbon and a hydrocarbon (component A) and a halogen ( It is characterized in that the mixture with the (B component) is thermally decomposed to coat the optical fiber with carbon.

[0006]

According to the present invention, the halogen radical generated by adding the component B to the component A accelerates the hydrogen abstraction reaction of the raw material gas, so that a dense carbon coating layer is formed on the surface of the optical fiber. As a result, the formation of OH groups and silanol groups on the surface of the optical fiber is prevented, and the carbon-coated light having excellent water resistance, hydrogen resistance, and mechanical strength, particularly tensile strength, is improved. Fiber,
You can get it quickly.

The present invention will be described in detail below. As the hydrocarbon which is the component A in the present invention, for example, methane, ethane, propane, butane, pentane, hexane, cyclopropane, cyclohexane, ethylene, propylene, butylene, pentene, acetylene, or those forming isomers are those. Appropriate isomers, benzene,
It is appropriately selected from aliphatic and aromatic hydrocarbons such as toluene and xylene.

The halogenated hydrocarbon which is the component A in the present invention is a halogen atom such as chlorine or bromine.
Aliphatic and aromatic hydrocarbons having the above are used. Chlorine is particularly preferable as the halogen atom. Examples of such halogenated hydrocarbons include chloromethane, dichloromethane, trichloroethane, carbon tetrachloride,
Chlorethane, dichloroethane, trichloroethane, tetrachloroethane, propane having a chlorine number of 1 to 5, chlorobutane having a chlorine number of 1 to 6, chloropentane having a chlorine number of 1 to 7, chlorohexane having a chlorine number of 1 to 7, chlorohexane having a chlorine number of 1 to 1
7 chlorocyclohexane, 1 to 4 chloroethylene, 1 to 5 chloropropylene, 1 to 5 chlorobutene, 1 to 5 chloropentene, or those forming isomers Various isomers, chlorobenzene having 1 to 3 carbon atoms, chlorotoluene,
And compounds in which chloro is replaced by bromine.

In the present invention, as the component A, only a hydrocarbon or a mixture of a halogenated hydrocarbon (single or a mixture) and a hydrocarbon is used. In the case of the combination, the ratio of both is a halogenated carbon. Hydrogen 1
Hydrocarbons 1 to 500 parts by volume, preferably 10 to 300 parts by volume, more preferably 50 to 20 parts by volume with respect to 00 parts by volume.
It is 0 volume part.

In the present invention, examples of the halogen as the component B include chlorine, bromine, fluorine and the like, and chlorine is particularly preferable.

In the present invention, the blending ratio of the component A and the component B is such that the ratio of the total number of halogen atoms to the total number of hydrogen atoms in both components is 5 to 15 hydrogen atoms per 10 halogen atoms, preferably. Is a ratio corresponding to 8 to 12, especially 9 to 11, and most preferably a mixing ratio corresponding to the same number of both atoms. Examples of preferable A component and B component and the mixing ratio thereof are as follows.

[0012]

[Table 1]

In the present invention, the operation of coating the optical fiber with carbon may be carried out by a method known per se, but it is preferably carried out as follows. That is, due to the high temperature of the optical fiber immediately after being heated and drawn from the optical fiber preform,
This is a method of directly decomposing a carbon coating layer on the surface of the optical fiber by thermally decomposing a mixture of the above-mentioned A component and B component (hereinafter, these may be collectively referred to as a carbon coating forming gas).

The silica glass optical fiber preform is usually 20
Heat drawing is performed in a high temperature furnace of 00 ° C or higher. Utilizing the residual heat temperature for drawing at that time, the carbon coating forming gas is thermally decomposed to form a carbon coating layer on the surface of the optical fiber. The residual heat temperature in this case is a temperature range in which the carbon coating forming gas to be supplied can be thermally decomposed, and is generally expressed as the temperature of the optical fiber when the gas comes into contact with the optical fiber and starts thermal decomposition. Is 800 to 1900 ° C., preferably 1000
~ 1800 ° C is suitable. In particular, from the viewpoint of improving hydrogen resistance, the temperature is slightly lower than 1800 ° C., particularly 1000 to 1
700 ° C is preferred. The reason why the thermal decomposition in the low temperature region is preferable is that, unlike the rapid reaction at the high temperature, the thermal decomposition proceeds relatively slowly at the low temperature and the grain size of the produced carbon becomes finer to the hydrogen gas. It is considered that the shielding effect is improved.

For forming the carbon coating, a method for directly spraying the carbon coating forming gas onto the optical fiber when the residual heat temperature of the optical fiber after drawing is within the above-mentioned temperature range, or a carbon coating forming gas is continuously supplied. An appropriate means can be adopted as long as the object of the present invention can be achieved, such as a method in which a reaction tube is installed and an optical fiber is passed through the reaction tube. In order to maintain the reaction temperature, it is desirable to carry out the reaction under heat-retaining conditions using a heat-resistant reaction tube such as quartz glass or ceramic.

The supply amount of the carbon coating forming gas is usually 30.
0-5000cc / min, preferably 500-3000cc
/ Min. The carbon coating forming gas may be diluted with an inert gas such as helium or argon. In that case, the concentration in the diluent gas is 30 to 90% by volume, preferably 50 to 80% by volume. .. The carbon coating layer formed on the surface of the optical fiber has a thickness of 300 to 100.
It is 0Å, preferably 400 to 600Å. The time required for the thermal decomposition of the carbon coating forming gas is appropriately selected depending on the type of the gas, the gas concentration, etc., but is 0.05 to 5 seconds, preferably 0.05 to 1 second, and particularly 0.1 to 0. 0.5 second is appropriate. The carbon coating is not limited to one layer, and two or more coating films may be formed by repeatedly coating.

The carbon fiber thus coated is usually resin-coated. A curable resin is preferable as the resin, and the resin protective layer is formed by being cured by heat, ultraviolet rays, or another curing device through a curable resin liquid coating device.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Comparative Example 1, Examples 1-2 An optical fiber preform having a B- and F-doped silica glass cladding layer on a Ge-doped silica glass core was heated in a drawing furnace at a temperature of 2200 ° C. and a linear velocity of 350 m / min. Outer diameter is 125μ
It was drawn to m optical fiber. Next, the obtained optical fiber was immediately passed continuously through a reaction tube (length 1 m) made of quartz glass installed under the drawing furnace to coat the surface of the optical fiber with carbon. A gas supply means is installed at the inlet of the reaction tube, and propane as a gas for forming a carbon coating is supplied at a flow rate of 200 cc / min, and chlorine gas is supplied at 0 cc / min (Comparative Example 1) and 200 cc / min, respectively. Min (Example 1) and 400 cc / min (Example 2) at continuous flow rates into the reaction tube. Reaction temperature is 1400
℃. Finally, the carbon-coated optical fiber was treated with an ultraviolet curable resin by a conventional method to form a protective layer.

With respect to the carbon-coated silica glass optical fiber thus obtained, the carbon layer thickness and the tensile strength were measured by measuring the electric resistance. The result is as shown in FIG. Among the characteristics of optical fiber, the tensile strength is length 1
The electrical resistance is the average electrical resistance of the carbon coating per unit length under a tensile condition of a strain rate of 5% / min for 20 samples of 0 m, and the water resistance is 200 in pure water at 80 ° C. The tensile strength of the optical fiber after immersion for a period of time, hydrogen resistance is
An optical fiber sample of 1000 m was left in a hydrogen atmosphere of 3 atm (gauge pressure) for 300 hours, and the loss increase amount at a wavelength of 1.24 μm before and after that was measured.

[0021]

According to the present invention, since a mixture of hydrocarbon or halogenated hydrocarbon and hydrocarbon (component A) and halogen (component B) is used as the carbon coating forming gas, the gas for forming an optical fiber is The carbon deposition rate is increased, and thus the optical fiber is economical to manufacture, and the optical fiber obtained has high performance in terms of water resistance, hydrogen resistance, and mechanical strength, especially tensile strength. , It can be applied to optical communication in various fields with peace of mind.

[Brief description of drawings]

FIG. 1 is a graph showing the electrical resistance and tensile strength of a silica glass optical fiber manufactured by the manufacturing method of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaaki Morisawa, 4-3 Ikejiri, Itami City, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd., Itami Works (72) Inventor Protected, 8 Nishinocho, Higashimukaijima, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Wire Industry Co., Ltd. (72) Inventor Hiroyuki Tanaka, 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Works

Claims (3)

[Claims] 1. A silica glass system characterized by thermally decomposing a mixture of a hydrocarbon or a mixture of a halogenated hydrocarbon and a hydrocarbon (component A) and a halogen (component B) to coat an optical fiber with carbon. Optical fiber manufacturing method. 2. The proportion of the component A and the component B is such that the ratio between the total number of halogen atoms and the total number of hydrogen atoms in both components is 5 to 15 hydrogen atoms per 10 halogen atoms. The method according to claim 1, wherein 3. A chlorine is used as the halogen.
Or the manufacturing method of 2.