JP2825843B2 - Optical fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber having a carbon coating, and specifies the electrical resistance of the carbon coating to improve the mechanical strength and hydrogen resistance of the optical fiber. It has been improved.

[Prior art and its problems] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to molecular vibration of hydrogen molecules diffused into the fiber increases, and further, P ₂ O ₅ , Ge contained as a dopant is contained.
Since O ₂ , B ₂ O _3, etc. react with hydrogen and are taken into the fiber glass as OH groups, there is a problem that transmission loss due to absorption of OH groups increases.

To cope with such adverse effects, a method of filling a liquid composition having a hydrogen absorbing ability into an optical cable (Japanese Patent Application No.
No. 251808) is considered, but the effect is insufficient, and the structure becomes complicated, which is economically problematic.

In order to solve such problems, it has recently been announced that a carbon film can be formed on the surface of an optical fiber by a chemical vapor deposition method (hereinafter abbreviated as a CVD method), thereby improving the hydrogen resistance of the optical fiber. ing.

However, such a carbon coating is not always suitable for practical use, and has a disadvantage that the hydrogen resistance and the mechanical strength vary.

The present invention has been made in order to solve the above-mentioned problem, and specifies the electric resistance value of a carbon coating obtained by pyrolysis of a hydrocarbon or a halogenated hydrocarbon on a bare silica glass optical fiber. It is an object of the present invention to provide an optical fiber exhibiting sufficient hydrogen resistance and mechanical strength.

[Means for Solving the Problems] The optical fiber of the present invention has a carbon coating obtained by pyrolysis of a hydrocarbon or a halogenated hydrocarbon on a bare silica glass optical fiber, and has an electric resistance of 5 kΩ / cm or more and 20 kΩ or more.
/ cm or less.

[Action] It has been found that as the electrical resistance value of the carbon coating decreases, the hydrogen resistance of the optical fiber improves. On the other hand, it was found that the mechanical strength of the optical fiber also improved as the electrical resistance of the carbon coating increased.

Therefore, by keeping the electrical resistance of the carbon coating constant, an optical fiber having both hydrogen resistance and mechanical strength can be obtained.

 Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of the optical fiber of the present invention.
In the figure, reference numeral 1 denotes a bare optical fiber. The bare optical fiber 1 is made of glass such as quartz-based glass and multi-component glass. A carbon coating 2 is provided on the bare optical fiber 1. A resin coating 3 is further provided on the carbon coating 2 as needed.

The carbon coating 2 is obtained by obtaining a hydrocarbon or a halogenated hydrocarbon and has an electric resistance of 5 kΩ / cm or more.
It is less than 0 kΩ / cm. As the electrical resistance of the carbon coating 2 decreases, the hydrogen resistance of the optical fiber improves, while the mechanical strength decreases. Therefore, by limiting the electrical resistance of the carbon coating 2 to a certain range, the mechanical strength is reduced. And an optical fiber having excellent hydrogen resistance. As will be described later in detail in Examples, it was found that the carbon coating 2 having an electric resistance value of 5 kΩ / cm or more and less than 20 kΩ / cm had excellent hydrogen resistance. Electric resistance value is 20
When it is more than kΩ / cm, although the mechanical strength is sufficient,
It is not preferable because the hydrogen resistance is reduced. On the other hand, if the electric resistance is less than 5 kΩ / cm, the hydrogen resistance is sufficient, but the mechanical strength is undesirably reduced. Therefore, in order for the carbon coating 2 to have both the hydrogen resistance property and the mechanical strength, its electric resistance value should be 5 kΩ / cm or more and 20 kΩ / cm.
It is necessary to be less than.

In order to measure the electric resistance of the carbon coating 2, a normal electric resistance measuring method such as a four-terminal method can be used.

Examples of a method for forming such a carbon coating 2 on the surface of the bare optical fiber 1 include a thermal CVD method in which hydrocarbons or halogenated hydrocarbons are thermally decomposed into radicals or ions, and the radicals or ions are deposited as the carbon coating 2. Can be used. FIG. 2 shows an example of an optical fiber manufacturing apparatus suitably used for the thermal CVD method.

In FIG. 2, reference numeral 1 denotes a bare optical fiber. The bare optical fiber 1 is obtained by heating and spinning an optical fiber preform (not shown) in an optical fiber spinning furnace 4. The bare optical fiber 1 is spun and provided at a lower stage of the optical fiber spinning furnace 4. The heating furnace 5 is supplied. The heating furnace 5 is for forming a carbon coating 2 on the surface of the bare optical fiber 1 spun in the upper optical fiber spinning furnace 4 by a thermal CVD method, in which a CVD reaction proceeds. It comprises a substantially cylindrical reaction tube 6 to be heated and a heating element 7 for heating the reaction tube 6. A source compound supply pipe 6a for supplying a source compound into the reaction tube 6 is provided at an upper portion of the reaction tube 6, and an exhaust pipe 6b for exhausting unreacted gas and the like is provided at a lower portion.
Are attached respectively. The reaction tube 6 and the heating element 7 for heating the reaction tube 6 can be appropriately selected depending on the heating temperature and the like, and a resistance heating furnace, an induction heating furnace, an infrared heating furnace, or the like can be used. It is also possible to use one that generates plasma using high frequency or microwaves to ion-decompose the raw material compound.
In addition, a resin liquid application device 8 and a curing device 9 are provided continuously below the heating furnace 5, and the carbon coating 2 formed on the surface of the bare optical fiber 1 in the heating furnace 5 is provided. The resin film 3 can be formed on the substrate.

Using the above apparatus, a carbon coating 2 is applied to the surface of the bare optical fiber 1.
And the resin film 3 are formed by the following steps.

The optical fiber preform is heated and spun in the optical fiber spinning furnace 4, and inserted into a heating furnace 5, a resin liquid coating device 8, and a curing device 9 provided at a lower stage of the optical fiber spinning furnace 4. It is supplied so as to travel at a predetermined linear speed on the upper side.
Then, the heating element 7 is heated to heat the inside of the reaction tube 6 to a predetermined temperature, and the raw material compound is supplied into the reaction tube 6 from the raw material supply tube 6a. As the raw material compound, a hydrocarbon or a halogenated hydrocarbon is used, and a compound that precipitates a carbon film by thermal decomposition can be used. In addition, this raw material compound can be supplied in the form of a gas in the reaction tube 6, or diluted with an inert gas or the like.

The raw material compound is thermally decomposed in the reaction tube 6 to form radicals or ions, which are deposited on the bare optical fiber surface, whereby a carbon coating can be formed.

Thus, the optical fiber having the carbon coating 2 formed on its surface is introduced into the resin liquid coating device 8 provided at the lower stage, and then inserted into the curing device 9 for curing the resin liquid. An ultraviolet-curable resin liquid or a thermosetting resin liquid for forming a protective coating layer is applied to the bare optical fiber 1 inserted into the resin liquid coating device 8, and then suitable for the applied resin liquid. The resin film 3 is formed by curing in a curing device 9 having curing conditions.

In order to coat the surface of the bare optical fiber 1 with the carbon coating 2, besides using the thermal CVD method as described above, the plasma C
A method in which hydrocarbons or halogenated hydrocarbons are decomposed by VD or the like to form radicals or ions and deposited as the carbon coating 2 can be used.

Hereinafter, an example for limiting the appropriate range of the electric resistance value of the carbon coating 2 will be described.

[Examples] In order to limit the appropriate range of the electric resistance value of the carbon coating, a carbon coating was formed on the bare optical fiber surface under various conditions,
The relationship between the electrical resistance value of the obtained optical fiber, the hydrogen resistance, and the mechanical strength was examined.

Example 1 An apparatus for manufacturing an optical fiber similar to that shown in FIG. 2 was prepared, and an external device having a core portion made of quartz glass doped with GeO ₂ and a clad portion made of quartz glass was prepared in this manufacturing device. An optical fiber preform having a diameter of 30 mm was installed. This optical fiber preform is heated to 2000 ° C and the outer diameter is 125μ at a spinning speed of 30m / min.
m of single mode fiber. Next, 12
While heating to 00 ° C., a 1,1,1 trichloroethane gas diluted with argon gas to about 5 vol% as a raw material compound for forming a carbon film is supplied at a flow rate of about 5 l / min, and an exhaust pressure of −4 mmH ₂ is supplied from an exhaust port. The carbon fiber was formed on the bare optical fiber surface while evacuating with O to remove unreacted gas and by-products.

In addition, a urethane acrylate resin liquid (Young's modulus 70 kg / mm ² , elongation 60
%) And applying a resin liquid to the surface of the optical fiber, and then curing the resin liquid with an ultraviolet lamp to obtain an outer diameter of about 25%.
An optical fiber of 0 μm was obtained for 1 km.

The optical fiber obtained in this manner was sampled as 1 m samples from the spinning start and end ends, and after removing the resin coating of these sample fibers, the electrical resistance of the carbon coating was measured using a digital multimeter. Each sample fiber had a value of 10 kΩ / cm.

(Example 2) An optical fiber was manufactured in exactly the same manner as in Example 1 except that benzene was used as the raw material compound.

The electrical resistance of the carbon coating was measured in exactly the same manner as in Example 1, and was found to be 18 kΩ / cm at both the start and end.

(Example 3) Ethane was used as a raw material compound, and the temperature in the reaction tube was adjusted to 13
An optical fiber was manufactured in exactly the same manner as in Example 1 except that the temperature was changed to 00 ° C.

The electrical resistance of the carbon film was measured in exactly the same manner as in Example 1, and was found to be 7 kΩ / cm at both the start and end.

(Example 4) An optical fiber was manufactured in exactly the same manner as in Example 1 except that the spinning speed was changed to 50 m / min.

The electrical resistance of the carbon coating was measured in exactly the same manner as in Example 1, and was found to be 18 kΩ / cm at both the start and end.

(Comparative Example 1) The spinning speed was 60 m / min, and the temperature in the reaction tube was 1100 ° C.
An optical fiber was manufactured in exactly the same manner as in Example 1 except that the above conditions were satisfied.

When the electrical resistance of the carbon coating was measured in exactly the same manner as in Example 1, it was 22 kΩ / cm at both the start end and the end end.

(Comparative Example 2) The raw material compound was dichloromethane, and the temperature in the reaction tube was
An optical fiber was manufactured in exactly the same manner as in Example 1 except that the temperature was changed to 1100 ° C.

When the electrical resistance of the carbon coating was measured in exactly the same manner as in Example 1, it was 30 kΩ / cm at both the start end and the end end.

(Comparative Example 3) The spinning speed was 10 m / min, and the temperature in the reaction tube was 1300 ° C.
An optical fiber was manufactured in exactly the same manner as in Example 1 except that the above conditions were satisfied.

The electrical resistance of the carbon coating was measured in exactly the same manner as in Example 1, and was found to be 3 kΩ / cm at both the start and end.

Test Example 1 Each of the optical fibers obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was sampled at a length of 700 m, and the optical transmission loss of the sample fibers at a wavelength of 1.24 μm was measured. Then, after leaving each of these sample fibers in a hydrogen pressurized vessel at a hydrogen partial pressure of 1 atm and a temperature of 80 ° C. for 100 hours, the wavelength was again 1.24 μm.
The optical transmission loss at m was measured, and the increase in the transmission loss was measured.

 The results are shown in Table 1.

(Test Example 2) Each of the optical fibers obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was tested with a test number of 20, a gauge length of 3 m, and a strain rate of 30 cm / min. A Weibull plot of the strength was performed, and the tensile strength at a 50% probability of breaking was measured. The results are shown in Table 1.

Further, a carbon coating was formed on the surface of the bare optical fiber under various conditions, and the relationship between the electric resistance of the carbon coating and its hydrogen resistance was plotted. The results are shown together with the results of Comparative Examples 1 to 3.

FIG. 4 is a graph showing the relationship between the electrical resistance of the carbon coating and the mechanical strength of the optical fiber.

From Table 1 and FIG. 3, it was confirmed that the optical fiber having the carbon coating having an electric resistance value of less than 20 kΩ / cm had a small increase in transmission loss and was excellent in hydrogen resistance.

From Table 1 and FIG. 4, the electric resistance value is 5 kΩ / cm.
An optical fiber having the above carbon coating has a high breaking strength,
It was confirmed that the mechanical strength was high.

From these results, the electric resistance value is 5 kΩ / cm or more and 20 kΩ / cm
It was confirmed that an optical fiber having a carbon coating of less than 30% was excellent in hydrogen resistance and mechanical strength.

[Effects of the Invention] As described above, the optical fiber of the present invention is provided with a carbon coating obtained by thermally decomposing a hydrocarbon or a halogenated hydrocarbon on a bare silica glass optical fiber, and Since the electric resistance value is 5 kΩ / cm or more and less than 20 kΩ / cm, it exhibits hydrogen resistance and mechanical strength sufficient for practical use.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one example of the optical fiber of the present invention, FIG. 2 is a schematic structural view showing one example of an optical fiber manufacturing apparatus suitably used for manufacturing the optical fiber of the present invention, and FIG. FIG. 4 is a graph showing the relationship between the electrical resistance of the carbon coating and the hydrogen resistance of the optical fiber, and FIG. 4 is a graph showing the relationship between the electrical resistance of the carbon coating and the mechanical strength of the optical fiber. 1 ... bare optical fiber, 2 ... carbon coating.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shinji Araki 144 Sakura-shi, Sakura-shi, Chiba Fujikura Electric Wire Co., Ltd. Sakura Plant (56) References JP-A-61-267711 (JP, A)

Claims (1)

(57) [Claims] A carbon coating obtained by thermally decomposing a hydrocarbon or a halogenated hydrocarbon is provided on a bare silica glass optical fiber, and the carbon coating has an electric resistance value of 5 kΩ / cm or more and less than 20 kΩ / cm. An optical fiber, characterized in that: