JPH0497925A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical fiber excellent in mechanical strength, hydrogen resistance, and stress fatigue resistance by using a specified gaseous starting material in the process of forming a carbon film on the surface of an optical fiber wire by thermal decomposition of the gaseous starting material using excess heat produced during spinning the optical fiber. CONSTITUTION:A carbon film is formed on the surface of an optical fiber wire by thermal decomposition of the gaseous starting material using excess heat produced during spinning the optical fiber. The gaseous starting material used consists of a hydrocarbon compd. (e.g. benzene) with addition of chlorine gas.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a method for manufacturing an optical fiber having a carbon film formed on its surface, and by limiting the raw material gas.
This makes it possible to obtain an optical fiber with excellent hydrogen resistance and stress fatigue resistance.

"Prior Art" When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to the molecular vibration of hydrogen molecules diffused within the fiber increases, and furthermore, when a silica-based optical fiber comes into contact with hydrogen, the absorption loss caused by the molecular vibration of hydrogen molecules diffused into the fiber increases.
eO! , B, ○, etc., react with hydrogen, resulting in an increase in transmission loss due to absorption of OH groups.

Furthermore, when stress is applied to a silica-based optical fiber for a long period of time, there is a stress fatigue phenomenon in which the fiber breaks even if the stress is sufficiently smaller than the breaking strength of the optical fiber.

This stress fatigue phenomenon is also accelerated by high temperature and humidity.

For this reason, the environments in which silica-based optical fibers can be used are limited, and in commonly used optical fiber cables, optical fibers are maintained by dry gas maintenance, moisture-proof jelly filling, etc. in order to prevent optical fiber breakage. Protecting.

In order to solve these problems, chemical vapor deposition method (
Hereinafter, this method will be abbreviated as CVD method. ) has been announced to form a carbon film on the surface of an optical fiber, thereby improving the hydrogen resistance and stress fatigue resistance of the optical fiber.

``Problems to be Solved by the Invention'' However, although the above method improves the hydrogen resistance properties of the optical fiber, there is a problem in that the tensile strength of the optical fiber decreases when the carbon coating is formed. For example, the tensile strength at break of an ordinary ultraviolet curable resin-coated fiber is approximately 6 to 6.5 kg, whereas the tensile strength of an optical fiber with a carbon coating formed by the CVD method is approximately 4 to 5 kg.
As low as kg. Therefore, although the optical fiber on which a carbon film is formed has excellent properties, its use is limited due to its low mechanical strength, and improvements have been desired.

The present invention was made to solve the above problems, and an object of the present invention is to provide an optical fiber that has excellent mechanical strength as well as hydrogen resistance and stress fatigue resistance.

``Means for Solving the Problems'' The method for manufacturing an optical fiber according to claim 1 of the present invention provides a method for producing an optical fiber, in which a carbon film is formed on the surface of a bare optical fiber by thermally decomposing a raw material gas using residual heat from spinning the optical fiber. A method for producing an optical fiber according to claim 2 of the present invention uses a raw material gas obtained by adding chlorine gas to a hydrocarbon compound as a solution, and a method for producing an optical fiber according to claim 1 In each fiber manufacturing method, the solution was to use a raw material gas in which 0.3 to 0.6 mol of chlorine was added to 1 mol of hydrogen in a hydrocarbon compound.

"Operation" By limiting the amount of chlorine gas added to the hydrocarbon compound, a carbon film is formed without reducing the mechanical strength of the optical fiber, creating an optical fiber with excellent hydrogen resistance and stress fatigue resistance. can be obtained.

The present invention will be described in detail below.

FIG. 1 shows an example of an optical fiber manufacturing apparatus suitably used in the optical fiber manufacturing method of the present invention.

In FIG. 1, reference numeral 1 indicates a bare optical fiber. This optical fiber bare wire 1 is produced by spinning an optical fiber base material 2 into an optical fiber spinning furnace 3.
It is heated and spun inside. The bare optical fiber 1 is spun and then supplied into a CVD reactor 4 provided at the lower stage of the optical fiber spinning furnace 3 .

The CVD reactor 4 is for forming a carbon film on the surface of the bare optical fiber 1 spun in the upper optical fiber spinning furnace 3 by a CVD method using residual heat from spinning. This CVD reactor 4 consists of a roughly cylindrical reaction tube 5 in which the CVD reaction proceeds, with a raw material gas supply pipe 6 for supplying raw material gas in the upper part and unreacted gas in the lower part. Exhaust pipes 7 for exhausting the air and the like are respectively attached. Further, gas seal mechanisms 8.8 for sealing the inside of the reaction tube 4 are provided at the upper and lower portions of the reaction tube 5.
is connected.

In order to manufacture an optical fiber according to the manufacturing method of the present invention using the above-mentioned manufacturing apparatus, the following steps are performed.

First, an optical fiber base material 2 is heated and spun in an optical fiber spinning furnace 3 to form a bare optical fiber 1. Next, this bare optical fiber I is inserted into the lower CVD reactor 4 and fed so as to run on the central axis at a predetermined linear speed.

Next, a sealing gas consisting of an inert gas such as helium gas or nitrogen is supplied into the reaction tube 5 from the gas sealing mechanism 8.8 to seal the inside of the reaction tube 5.

At the same time, the raw material gas is supplied from the raw material gas supply pipe 6 to the reaction tube 5.
The raw material gas is brought into contact with the bare optical fiber 1 to form a carbon film on the surface of the bare optical fiber 1. The bare optical fiber l inserted into the reaction tube S is heated by residual heat from spinning, so when it comes into contact with the raw material gas, it thermally decomposes hydrocarbon compounds in the raw material gas and strips the optical fiber. A carbon film can be deposited on the surface of the wire 1.

The raw material gas is made by adding chlorine gas to a hydrocarbon compound, and is usually diluted with an inert gas such as helium or a carrier gas such as nitrogen.

Hydrocarbon compounds are not particularly limited as long as they form a carbon film when thermally decomposed, and examples include aliphatic hydrocarbons such as methane, ethane, propane, ethylene, acetylene, pentane, and hexane, as well as benzene. , naphthalene, and other aromatic hydrocarbons can be used.

The concentration of the hydrocarbon compound in the raw material gas is preferably 0.5 to 2 mol% in terms of carbon atom concentration. This is because if it is less than 0.5 mol %, the precipitation rate of the carbon film is low, and if it exceeds 2 mol %, soot tends to be generated.

Further, the amount of chlorine gas added to the hydrocarbon compound is not particularly limited, but it is preferable that the ratio is 0.3 to 0.6 moles of chlorine atoms per mole of hydrogen in the hydrocarbon compound. preferable. This is because if the amount is less than 0.3 mol, the mechanical strength of the optical fiber obtained will decrease, and if it exceeds 0.6 mol, the hydrogen resistance will decrease.

The feed rate of the raw material gas is appropriately selected depending on the type of hydrocarbon compound, the amount of chlorine gas added, the spinning speed of the bare optical fiber l, etc., but is usually o2 to o1. An OQ of about 1 minute is suitable.

The spinning speed of the bare optical fiber 1 is appropriately selected depending on the concentration of hydrocarbon compounds and chlorine gas in the raw material gas, etc., but the surface of the bare optical fiber 1 has sufficient residual heat to thermally decompose the hydrocarbon compound. It must be inserted into the reaction tube 5 in a heated state. i.e. 500-1400℃
Usually, it is preferable to insert the reaction tube 5 into the reaction tube 5 at 1 oon+/min or more. Furthermore, for the reasons stated below,
In principle, there is no upper limit to linear velocity. This is because as the spinning speed increases, the temperature of the bare optical fiber 1 in the reaction tube 5 increases, so in such a case, the bare optical fiber 1 can be appropriately cooled before use.

In this way, a carbon coating having excellent hydrogen resistance and stress fatigue resistance can be formed on the surface of the bare optical fiber I without reducing its mechanical strength.

``Example'' A quartz tube reaction tube was connected to the lower stage of an optical fiber spinning furnace for tying bare optical fibers from an optical fiber base material to form a CVD reaction furnace, and an optical fiber similar to that shown in FIG. Manufacturing equipment.

A single-mode fiber preform having an outer diameter of 30 mm and having a core doped with Ge 2 O as a dopant was installed in the fiber manufacturing apparatus. This optical fiber base material is
It was heated to 800-2000 °C and spun at a spinning speed of 200 m,/min into a single mode optical fiber with an outer diameter of 125 μm.

Benzene was used as a hydrocarbon compound, and chlorine gas concentration was added to this while changing the concentration as appropriate to form a carbon film on the surface of a bare optical fiber. The tensile breaking strength, IT hydrogen properties, and stress fatigue resistance of the optical fiber thus obtained were examined.

FIG. 2 shows the test results for tensile rupture strength, FIG. 3 shows the evaluation results for hydrogen resistance, and FIG. 4 shows the evaluation results for stress fatigue resistance. In the figure, the solid line indicates that the benzene concentration in the raw material gas is 5vt%, and the broken line indicates that the benzene concentration is 1%.
0v t%, - dotted line indicates benzene concentration 30w
t% are shown respectively. Moreover, the horizontal axis of each figure shows the molar ratio of chlorine gas added to 1 mole of benzene.

From Figure 2, it is clear that more than 1 mole of chlorine gas is added to 1 mole of benzene, that is, 1 mole of hydrogen atom in the hydrocarbon compound.
By adding 03 moles or more of chlorine to the mole,
It has been found that it is possible to prevent a decrease in the mechanical strength of an optical fiber during the formation of a carbon film. It has also been found that as the amount of hydrocarbon compounds in the raw material gas increases, the effect of suppressing strength reduction due to the addition of chlorine gas diminishes.

Furthermore, from FIG. 3, it was found that when the concentration of chlorine gas added exceeds a certain value, the hydrogen resistance of the resulting optical fiber decreases rapidly. In Fig. 3, the vertical axis represents the increase in transmission loss of the optical fiber at a wavelength of 1.24 μm before and after leaving the obtained optical fiber in a hydrogen atmosphere with a hydrogen partial pressure of 1a t 11°80°C for 24 hours. It shows. For example, when the benzene concentration is 5 wt%, when 0 to 17 moles of chlorine gas is added to 1 mole of benzene, the increase in transmission loss is OdB, whereas the increase in transmission loss is 1 dB.
．． It has been found that when 7 mol or more is added, the transmission loss increases or increases rapidly. In other words, it has been found that when more than 0.6 moles of chlorine is added to 1 mole of hydrogen in a hydrocarbon compound, the hydrogen resistance of the resulting optical fiber deteriorates. Further, the region where an increase in transmission loss occurs due to excessive addition of chlorine gas shifts to a region where the amount of chlorine added is small as the concentration of hydrocarbon compounds in the raw material gas increases.

Furthermore, the influence of chlorine concentration on the stress corrosion coefficient n value of optical fibers was investigated and is shown in FIG.

It has been reported that the n value of an optical fiber coated with an ultraviolet curable resin is usually 20 to 28 in an environment of normal temperature and normal humidity.

In general, many literatures have shown that the larger the n value, the stronger the fiber is resistant to stress fatigue and is not affected by the environment in which the fiber is placed, and is an indicator of the stress fatigue resistance of optical fiber. .

The n value decreases with the addition of chlorine gas, but for example, when the benzene concentration is 5vt%, the n value decreases to 3 when the amount of chlorine gas added to 1 mole of benzene ranges from 1 to 1.7 moles.
00 to 100, and it can be confirmed that the characteristics of the carbon-coated optical fiber are sufficiently exhibited. This also confirmed that the concentration of chlorine gas added to the hydrocarbon compound was required to be 0.6 mol or less of chlorine per 1 mol of hydrogen in the hydrocarbon compound.

The results shown in FIGS. 2 to 4 above were exactly the same when not only benzene but also aliphatic hydrocarbon compounds such as acetylene were used.

Therefore, from FIGS. 2 to 4 above, when the carbon atom concentration in the raw material gas is in the range of 0.5 to 2 molar concentration, that is, in the case of benzene, it is 3 to 12 V.

1%, and in the case of acetylene, 9 to 36vol%, by adding chlorine atoms at a ratio of 0.3 mol to 0.6 mol to 1 mol of hydrogen atoms in the hydrocarbon compound. It was confirmed that a carbon-coated optical fiber with excellent hydrogen resistance and stress fatigue resistance could be obtained without causing a decrease in strength.

"Effects of the Invention" As explained above, the optical fiber manufacturing method of the present invention uses a raw material gas made by adding chlorine gas to a hydrocarbon compound, so it reduces the mechanical strength of the optical fiber. It is possible to obtain an optical fiber formed with a carbon coating having excellent hydrogen resistance and stress fatigue resistance without causing any damage.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber manufacturing apparatus suitably used in the optical fiber manufacturing method of the present invention, and FIG. 2 shows the chlorine gas concentration added to the hydrocarbon compound and the obtained Figure 3 is a graph showing the relationship between the mechanical strength of the optical fiber obtained, and Figure 4 is a graph showing the relationship between the chlorine gas concentration added to the hydrocarbon compound and the hydrogen resistance properties of the obtained optical fiber. is a graph showing the concentration of chlorine gas added to a hydrocarbon compound and the stress fatigue resistance of the obtained optical fiber. 2 Optical fiber base material, CVD reactor.

Claims (2)

[Claims] (1) An optical fiber manufacturing method in which a raw material gas is thermally decomposed using residual heat from spinning the optical fiber to form a carbon film on the surface of the bare optical fiber, and the raw material gas is made by adding chlorine gas to a hydrocarbon compound. A method for manufacturing an optical fiber characterized by using (2) 0.3 per mole of hydrogen in the hydrocarbon compound
The method for manufacturing an optical fiber according to claim 1, characterized in that a raw material gas containing ~0.6 mole of chlorine is used.