JP2710402B2 - Optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber coated with a carbon film,
By specifying the crystal structure of the carbon coating, the hydrogen resistance of the optical fiber is significantly 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 P ₂ O ₅ and GeO ₂ contained as dopants further increase. ,
Since B ₂ O _{3 and the} like 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, it has been found that the hydrogen resistance of the carbon fiber formed on the surface of the optical fiber varies greatly depending on the type of crystal structure, and it has been proposed that only the carbon film having a certain crystal structure be coated on the surface of the optical fiber. However, it was difficult to limit the crystal structure of the carbon coating.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide an optical fiber having sufficient hydrogen resistance by specifying the crystal structure of a carbon coating.

[Means for Solving the Problems] The optical fiber of the present invention has an apparent size Lc (00) on the (002) plane of the crystal lattice obtained by the X-ray diffraction method.
2) has a carbon coating of 15 mm or more as a solution.

 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 here is obtained by decomposing hydrocarbons, and has a (002) crystal lattice by X-ray diffraction.
The apparent size Lc (002) of the surface is 15 mm or more.

The following method can be used to calculate the apparent size Lc (002) on the (002) plane of the crystal lattice by the X-ray diffraction method.

The carbon coating 2 formed on the surface of the bare optical fiber 1 is irradiated with X-rays, and the X-ray diffraction of the carbon coating 2 is measured by a transmission method.

The X-ray generator used at this time is CuKα ray
An X-ray diffraction peak as shown in FIG. 2 was obtained using a source having an output of 35 kV and 15 mA as a radiation source. In FIG. 2, Ip
Represents the intensity of the diffraction peak, Ip _{/ 2} represents the intensity of the half of the Ip, and the width of the diffraction peak at Ip _{/ 2} and half width beta E. Then, from the half value width of the diffraction peak at 26.55 ° of the diffraction angle (2θ) corresponding to the (002) plane of the crystal of the carbon coating 2, Lc was calculated using the following formula (1) called Scherrer's formula.
(002).

Lc (002) = κλ / β 0 cosθ B ... (1) However Shikichu, κ = 1.0, λ: wavelength of X-rays used for the ^{_{measurement, β 0 = (βE 2 -βI}} 2) 1/2, βE: Half width (measured value), βI = 1.05 × 10 ⁻² rad, θ _B : Bragg angle.

As a method of coating such a carbon coating 2 on the surface of the bare optical fiber 1, for example, a hydrocarbon compound is thermally decomposed into radicals or ions, and this is deposited on the surface of the bare optical fiber 1 as a carbon coating 2. A CVD method or the like can be used. FIG. 3 shows an example of an optical fiber manufacturing apparatus suitably used for the thermal CVD method.

In FIG. 3, 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. This 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.
A resin liquid application device 8 and a curing device 9 are provided continuously below the heating furnace 5, and are provided on the carbon coating 2 formed on the surface of the bare optical fiber 1 in the heating furnace 5. The resin film 3 can be formed.

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 compound containing a carbon atom in its molecule and capable of depositing a carbon film by thermal decomposition or the like 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 a hydrocarbon compound is decomposed by a VD method or the like to form radicals or ions and deposited as a carbon coating 2 can be used. If the carbon coating 2 can be deposited on the surface of the bare optical fiber 1, the method can be used. Is not particularly limited.

Hereinafter, a test example for obtaining an appropriate value of Lc (002) will be described.

[Example] To obtain an appropriate value of Lc (002), bare optical fiber 1
The carbon coating 2 was formed on the surface under various conditions, and the relationship between the apparent size of the crystal lattice of the obtained optical fiber and the hydrogen resistance was examined.

(Production Example 1) An optical fiber production apparatus similar to that shown in FIG. 3 was prepared, and an optical fiber preform having an outer diameter of 30 mm and a core portion impregnated with GeO ₂ as a dopant was installed in the production apparatus. did.
The optical fiber preform was heated to 2000 ° C. and spun into a single mode fiber having an outer diameter of 125 μm at a spinning speed of 30 m / min.
Then, while heating the inside of the reaction tube to 1200 ° C., a benzene vapor 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 3 / min, and the surface of the bare optical fiber spun. Was formed with a carbon coating.

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 30%.
An optical fiber of 0 μm was used.

(Production Example 2) An optical fiber was produced in exactly the same manner as in Production Example 1 except that the temperature in the reaction tube was set to 1000 ° C and the raw material compound was changed to o-chloromethyltoluene.

(Production Example 3) An optical fiber was produced in exactly the same manner as in Production Example 1 except that ethylene was used as a raw material compound.

(Production Example 4) An optical fiber was produced in exactly the same manner as in Production Example 1, except that 1,2 dichloroethane was used as a raw material compound and the temperature inside the reaction tube was set at 1300 ° C.

(Production Example 5) An optical fiber was produced in exactly the same manner as in Production Example 1 except that the temperature of the reaction tube was set to 1500 ° C and the spinning speed was set to 15 m / min.

(Manufacturing Example 6) A differential evacuation device was connected above and below the device shown in FIG. 3 to reduce the pressure inside the reaction tube to generate argon plasma, and benzene vapor diluted to 5 vol% with argon gas was generated in the region. An optical fiber was manufactured in the same manner as in Production Example 1 except that the raw material compound was supplied and a carbon coating was deposited on the bare optical fiber surface by a plasma CVD method.

(Comparative Example 1) An optical fiber was manufactured in exactly the same manner as in Manufacturing Example 1, except that the raw material compound was 1,2 dichloroethylene and the temperature in the reaction tube was 900 ° C.

(Comparative Example 2) An optical fiber was manufactured in exactly the same manner as in Manufacturing Example 1, except that the raw material compound was 1,1,2,2 tetrachloroethane.

(Comparative Example 3) An optical fiber was manufactured in exactly the same manner as in Manufacturing Example 1, except that the temperature in the reaction tube was set to 1000 ° C and the spinning speed was set to 50 m / min.

(Test Example 1) Each of the optical fibers obtained in Production Examples 1 to 6 and Comparative Examples 1 to 3 was assembled into a bundle of about 1 mm and a diameter of about 150 mmφ, and this was hydrogenated at a hydrogen partial pressure of 10 atm and a temperature of 80 ° C. After being left in the pressure vessel for 48 hours, the amount of increase in transmission loss at a wavelength of 1.24 μm was measured.

(Test Example 2) After removing the resin coating of each of the optical fibers obtained in Production Examples 1 to 6 and Comparative Examples 1 to 3, 40 mg each of which was cut to a length of 40 mm was placed in a molding die. These were arranged and fixed using a collodion-alcohol solution to prepare a measurement sample having a width of 1 mm.

The X-ray diffraction of each of the measurement samples was measured using an X-ray generator (Rigaku Corporation, X-ray source: CuKα ray, output 35 kV, 15 mA). Then, the diffraction peak at a diffraction angle of 26.55 ° is defined as the peak at the (002) plane of the crystal lattice.
The apparent size Lc (002) of the crystal lattice was calculated from the half width of this peak using the above Scherrer's formula.

And the hydrogen resistance obtained in Test Example 1 and Test Example 2
The relationship between the carbon coating and the apparent size of the crystal lattice of the carbon coating obtained was examined. The results are shown in Table 1.

From Table 1, it was confirmed that when the apparent size Lc (002) of the crystal lattice of the carbon coating formed on the bare optical fiber surface was 15 ° or more, good hydrogen resistance was exhibited.

[Effect of the Invention] As described above, the optical fiber of the present invention has a carbon coating in which the apparent size Lc (002) on the (002) plane of the crystal lattice obtained by the X-ray diffraction method is 15 ° or more. Therefore, it exhibits sufficient hydrogen resistance for practical use.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the optical fiber of the present invention, FIG. 2 is a graph showing the peak of X-ray diffraction of the optical fiber of the present invention, and FIG. FIG. 2 is a schematic configuration diagram showing an example of a manufacturing apparatus suitably used at the time. 1 ... bare optical fiber, 2 ... carbon coating.

Claims (1)

(57) [Claims] 1. An optical fiber having a carbon coating having an apparent size Lc (002) of at least 15 ° on a (002) plane of a crystal lattice obtained by an X-ray diffraction method.