JPH06656B2 - Method for manufacturing radiation resistant optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention relates to a radiation-resistant light used for an optical fiber cable or the like used in nuclear-related equipment or nuclear reprocessing equipment, which is expected to be exposed to a high radiation dose. The present invention relates to a fiber manufacturing method.

"Prior Art" Pure silica core optical fibers are used as optical fibers used in optical cables and the like used under high radiation dose. This optical fiber has excellent radiation resistance characteristics as compared with a normal optical fiber doped with GeO ₂ . FIG. 2 shows an example of such a pure silica core optical fiber. This optical fiber comprises a bare optical fiber consisting of a core 1 and a clad 2 made of pure quartz, a primary coating layer 3 made of a modified silicone resin, and a secondary buffer coating layer 4 made of a plastic material such as nylon. It consists of

[Problems to be Solved by the Invention] However, even in such a conventional pure silica core optical fiber having good radiation resistance, the radiation dose is 10 ⁶
When it becomes R or more, SiO ₂ in the optical fiber is destroyed by radiation to generate a defect Si—O, and hydrogen gas reacts with this to generate an OH group. As the source of hydrogen gas at this time, it is considered that the hydrogen gas was occluded in quartz of the optical fiber and the one generated by the primary coating layer or the secondary buffer coating layer being decomposed by radiation. When the number of OH groups in the fiber increases, the absorption of light by the OH groups makes it impossible to use optical communication in the 1.3 μm band.

The present invention has been made in view of the above circumstances, by suppressing the formation of OH groups in the optical fiber to be used in a high radiation dose of more than 10 ⁶ R, suppressing light absorption by OH group, 10 ⁶ R or 1.3μ even under the radiation dose of
The purpose is to enable optical communication in the m band.

"Means for Solving the Problem" In the present invention, therefore, the bare optical fiber is heated with helium gas, and hydrogen in the bare optical fiber is replaced with helium by passing through a pressurized gas atmosphere. Forming a coating layer on the surface of the wire with a substance that does not allow hydrogen gas to pass through was used as a means for solving the problem.

"Action" Residual hydrogen in the bare optical fiber is heated in helium gas,
It is replaced with helium by pressurization, and by forming a coating layer on the surface of this bare optical fiber with a substance that does not allow hydrogen gas to pass, defective Si-O is generated in the optical fiber under high radiation of 10 ⁶ R or more. Even if it occurs, since the hydrogen bonded to Si—O does not exist in the optical fiber, no OH group is generated and absorption of light in the 1.3 μm band by the OH group is suppressed.

Hereinafter, the method for producing the radiation resistant optical fiber of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of a manufacturing apparatus used in the method of manufacturing a radiation resistant optical fiber according to the present invention. Reference numeral 11 in FIG.
Is a bare optical fiber. The bare optical fiber is obtained by melting and spinning an optical fiber preform (not shown) in a spinning furnace 12. The bare optical fiber 11 is spun and is provided in the lower stage of the spinning furnace 12 without breaking the airtightness. It is sent to the heating and pressurizing treatment furnace 13. The heating / pressurizing treatment furnace 13 is for replacing the residual hydrogen in the bare optical fiber 11 spun in the spinning furnace 12 with helium by heating and pressurizing in the helium gas. A heating pressurizing pipe 14 for heating and pressurizing the wire 11 and a heat-resistant 15 for heating the heating pressurizing pipe 14 are provided, and a helium gas supply pipe 14a for supplying helium gas into the heating pressurizing pipe 14 and the helium gas. A helium gas exhaust pipe 14b for exhausting the gas is attached. A CVD furnace 16 is provided below the heating / pressurizing processing furnace 13 so as to keep airtightness. The CVD furnace 16 is for forming a carbon coating on the surface of the bare optical fiber 11 from which residual hydrogen has been removed and replaced with helium gas, by a CVD method in the upper heating and pressure treatment furnace 13. is there. Then, the CVD furnace 16 is a CV that forms a carbon coating on the bare optical fiber 11 by promoting a CVD reaction inside the CVD furnace 16.
It is composed of a D reaction tube 17 and a heating element 18 for heating the CVD reaction tube 17. A raw material compound supply pipe 17a for supplying a raw material compound to the CVD reaction pipe 17 is provided on the upper portion of the CVD reaction pipe 17, and an exhaust pipe 17b for exhausting reaction gas and the like between the CVD reaction pipe 17 is provided on the lower portion thereof. Each is installed. Further, a resin liquid coating device 19 and a thermosetting device 20 are continuously provided below the CVD furnace 16 so that a protective coating layer can be formed on the carbon coating formed in the CVD furnace 16. It has become.

A method of manufacturing a radiation resistant optical fiber according to the manufacturing method of the present invention using the above apparatus will be described below. First, the silica-based optical fiber preform is melt-spun in the spinning furnace 12 to form the bare optical fiber 11. This silica-based optical fiber preform contains a small amount of hydrogen that inevitably remains during the production of the preform, and the bare optical fiber 11 therefore also contains a small amount of hydrogen. Then, the bare optical fiber 11 is provided with a heating and pressurizing treatment furnace 1 which is sequentially provided in a lower stage of the spinning furnace 12.
3, CVD furnace 16, resin coating device 19, heat curing device 20
And is supplied so as to run at a predetermined speed on these central axes. Here, in the heating / pressurizing treatment furnace 13, the helium gas is supplied from the helium gas supply pipe 14a to heat the heating element 15 to generate heat. As the heating temperature,
The temperature is preferably about 500 to 1200 ° C. At this time, the pressure of the helium gas in the heating / pressurizing tank 14 is kept high by adjusting the supply rate of the helium gas and the exhaust amount from the helium gas exhaust pipe 14b. The hydrogen gas remaining in the bare optical fiber 11 is easily removed and replaced by helium gas by such heat and pressure treatment. Further, as the helium gas supplied here, a highly pure helium gas in an absolutely dry state is suitable. The bare optical fiber 11 from which the residual hydrogen has been removed in this way
Is inserted into the lower CVD furnace 16 while maintaining airtightness to form a carbon film. The raw material compound for forming the carbon coating is supplied from the raw material compound supply pipe 17a to the CVD reaction tube 1
7 and the CVD reaction tube 17 is heated by the heating element 18. The raw material compound supplied from the raw material supply pipe 17a is not particularly limited as long as it is a compound that thermally decomposes to form a carbon film, but from the viewpoint of the properties and the formation rate of the carbon film to be formed, a hydrocarbon having 15 or less carbon atoms. Alternatively, halogenated hydrocarbons are suitable. These raw material compounds may be supplied in a gas state or diluted with an inert gas and supplied. The supply rate is appropriately selected depending on the kind of the raw material compound and the heating temperature, but normally 0.2 to 1.0 / min is suitable. The heating temperature of the heating element 18 is appropriately selected depending on the kind of the above-mentioned feed compound, but is usually 400 to 12
It is about 00 ° C. In this way, the raw material compound is pyrolyzed in the CVD furnace 16 to form a carbon coating having a hydrogen permeation inhibiting ability on the surface of the bare optical fiber 11. The bare optical fiber 11 having the carbon coating formed on the surface thereof is introduced into the resin coating device 19 installed in the lower stage, and then inserted into the thermosetting device 20. In the resin coating device 19, a thermosetting resin or the like for forming a protective coating layer is coated on the surface of the bare optical fiber 11, and then the resin is heat-treated in the thermosetting device 20 to be cured.

Further, although the carbon coating is used as the substance having the hydrogen permeation inhibiting ability, the substance having the hydrogen permeation inhibiting ability used in the production method of the present invention is not limited to this, and examples thereof include silicon carbide. .

[Example 1] A heating / pressurizing furnace and a CVD furnace are provided in a lower stage of a spinning furnace for spinning a bare optical fiber from an optical fiber base material so as to keep airtightness, and a resin liquid coating device and thermosetting are further provided in the lower stage. The same apparatus as that shown in FIG. 1 was used to construct a radiation resistant optical fiber manufacturing apparatus. A graphite furnace was used as the heating and pressurizing furnace. Further, the reaction tube of the CVD furnace was a quartz tube, and heating was performed by an electric furnace (kanthal wire). A die spot was used as the resin coating device, and a thermosetting resin liquid was heated therein using a Kanthal wire in the thermosetting device.

Outer diameter 20 having a core portion made of pure quartz in the spinning furnace
mm base material for optical fiber is installed, the optical fiber base material is heated at 2200 ° C., and the outer diameter is 12 at a spinning speed of 60 m / min.
It was spun into a 5 μm optical fiber. Along with this, the heating and pressurizing furnace was heated to 500 ° C., and the dew point was −
High-purity helium gas at 90 ° C. or lower was supplied to maintain the pressure inside the heating and pressurizing tube at 1.5 × 10 ⁵ Pa. Further, while heating the inside of the CVD furnace to 400 ° C., teraalkylsilane vapor as a raw material gas was supplied at 0.2 / min. Then, the bare optical fiber is run in a heating and pressurizing furnace and a CVD furnace to remove hydrogen gas remaining inside the bare optical fiber and replace it with helium gas. Was coated. Then, the optical fiber is inserted into the die spot in which the silicone resin solution is sealed, the silicone resin solution is applied on the carbon coating, and the silicone resin solution is heated to 300 ° C. by an electric furnace (kanthal wire) in a thermosetting device. The resin was cured and used as a protective coating layer to form an optical fiber having an outer diameter of 400 μm.

1.3 μm using the optical fiber thus obtained
When optical communication in the band was performed, communication was possible even under radiation of 10 ⁶ R without absorption of light by the OH group.

Furthermore, it was confirmed that optical communication in the 1.3 μm band is possible with the above optical fiber even under the radiation of 10 ⁸ R, and that it has radiation resistance.

[Example 3] The spinning speed of the optical fiber preform was 70 m / min, the temperature of the heating / pressurizing furnace was 1100 ° C, the pressure was 1.8 x 10 ⁵ Pa, and the tetraalkylsilane vapor was supplied at 0.3 / min. A carbon coating was formed on the surface of the bare optical fiber in exactly the same manner as in Steam Example 1 except for the above.

Then, the bare optical fiber on which the carbon coating was formed was inserted into a die spot in which the urethane acrylate resin liquid was sealed, and the urethane acrylate resin liquid was applied onto the carbon coating. Then, ultraviolet rays were irradiated by a mercury lamp in an ultraviolet curing device to obtain an optical fiber having an outer diameter of 300 μm.

Using the optical fiber thus obtained, 10 ⁶ R
When optical communication was performed in the 1.3 μm band under the radiation, it was confirmed that the communication was possible and that it had radiation resistance.

Even if the radiation dose was further increased, no increase in transmission loss due to the OH group was observed, and stable communication was possible up to 10 ⁸ R.

[Advantages of the Invention] As described above, in the method for manufacturing the radiation resistant optical fiber, the bare optical fiber is heated by helium gas, and hydrogen in the bare optical fiber is changed to helium by passing through a pressurized gas atmosphere. Since the coating layer is formed on the surface of the bare optical fiber by substituting hydrogen gas, it is used under high radiation and SiO
_{Since 2} even if defective Si-O are destroyed by radiation, hydrogen gas combined with this to be generated OH groups due to the absence in the optical fiber, does not occur absorption of light by OH groups, 10 ⁶ Even under high radiation above R,
Optical communication in the 1.3 μm band becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber manufacturing apparatus used for carrying out the method of manufacturing a radiation resistant optical fiber of the present invention, and FIG. 2 is a schematic view showing an example of a conventional radiation resistant optical fiber. FIG. 11 ... Bare optical fiber 13 ... Heating / pressurizing treatment furnace 14 ... Heating / pressurizing tube 15 ... Heating element 16 ... CVD furnace 17 ... CVD reaction tube 18 ... Heating element

Claims (1)

[Claims] 1. A silica-based optical fiber preform containing hydrogen is spun into a bare optical fiber, and the bare optical fiber is heated by helium gas and passed through a pressurized gas atmosphere to obtain the bare optical fiber. A method for producing a radiation-resistant optical fiber, which comprises replacing hydrogen in the inside with helium, and then forming a coating layer on the bare surface of the optical fiber with a substance that does not allow hydrogen to pass therethrough.