JP2581285B2 - Manufacturing method of heat resistant optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a heat-resistant optical fiber, and more particularly, to a method for improving a heat-resistant coating.

[Prior Art] Optical fibers have been used not only for communication but also for data processing and measurement. Among these data processing and measurement fields, there is an increasing demand for heat-resistant optical fibers that can withstand high temperatures, particularly for measurement systems in high-temperature environments, such as control systems for blast furnaces and geothermal power generation. Current optical fibers cannot sufficiently meet this demand.

That is, the surface of an optical fiber made of quartz glass is easily damaged as in the case of ordinary glass, so that the resin is coated and protected at the same time as the drawing. As a coating material for protecting the optical fiber, UV resin, silicone, or polyimide is usually used. However, the temperature that can be used for a long time among such coating materials is only 200 ° C. for polyimide.

Therefore, an optical fiber coated with metal, ceramic, or the like has been studied in order to be able to withstand a high temperature environment. However, optical fibers coated with metal tend to have microbend loss when a metal having excellent heat resistance is used, and have a poor heat resistance when a metal that prevents microbend loss is used. For example,
Although metal coatings such as Al can withstand high temperatures up to 500 ° C., there is a disadvantage that the difference in thermal expansion coefficient is large and the surface of the optical fiber is scratched and the strength is deteriorated.

On the other hand, ceramics are extremely weak in bending due to poor ductility, and several tens of
It was used as a coating of an extremely thin film having a thickness of 0 to 1000 °.

[Problems to be Solved by the Invention] As described above, in the related art, a low-loss optical fiber with excellent heat resistance that can be used in a high-temperature environment such as around a blast furnace or geothermal power cannot be manufactured. .

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art,
It is an object of the present invention to provide a method for manufacturing a heat-resistant optical fiber that can obtain an optical fiber that is stable for a long time even in a high-temperature environment.

[Means for Solving the Problems] In the method for producing a heat-resistant optical fiber of the present invention, a carbon coating is applied to an optical fiber obtained by heating and stretching a preform, and after coating an organometallic polymer thereon, The thermal hydrolysis is performed by applying an organic metal compound.

The organometallic polymer is preferably polytitanocarbosilane, and the organometallic compound is preferably (CH ₃ O) ₄ Si, (C ₂ H ₅ O) ₄ Si, or a mixture containing these.

[Action] During the coating process or in a high-temperature environment, hydrogen gas is generated by decomposition of residual methyl groups and the like contained in the organometallic polymer. Is prevented.

In addition, since the organic metal polymer has an inorganic substance as a skeleton and an organic substance added to a side chain, the organic metal polymer maintains flexibility and heat resistance between the inorganic substance and the organic substance. However, simply coating the optical fiber with the organometallic polymer tends to cause cracks in the coating layer because the coating surface is porous. Therefore, in the present invention, the optical fiber is further passed through an organometallic compound solution, the solution is impregnated in the porous material, and is thermally hydrolyzed through a high-temperature heating furnace. As a result, the organometallic polymer coating layer changes from a porous state to a glass state, so that cracks are eliminated. Therefore, the heat resistance and strength of the optical fiber can be significantly improved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an optical fiber drawing line for carrying out the method for producing a heat-resistant optical fiber according to the present invention.

A drawing furnace 3 spins the preform 1 by heating the preform 1 to a molten state. Reference numeral 4 denotes a carbon coating furnace, which supplies carbon material from the outside to the optical fiber 2 spun in the drawing furnace 3 to coat carbon by a thermal CVD method, a plasma CVD method, a sputtering method, or the like, thereby forming a fiber. Improve the long-term reliability of strength and transmission characteristics. Carbon material supplied from the outside is benzene + N _2.

Reference numeral 5 denotes a coating die in which polytitanocarbosilane which is an organometallic polymer serving as a material for further coating on the carbon coating is stored. Reference numeral 6 denotes a curing furnace for curing the coated coating material by UV (ultraviolet) or heating to fix the coating material to the fiber.

Reference numeral 7 denotes a coating die storing a mixed solution of tetramethoxysilane: methanol: H ₂ O, which is an organometallic compound for impregnating the organometallic polymer coating. Reference numeral 8 denotes a heating furnace for thermally hydrolyzing the organometallic compound impregnated in the organometallic polymer.

Reference numeral 9 denotes a turn pulley for switching the horizontal force applied to the optical fiber 10 to the direction of gravity in order to draw the wire from the furnace 3 in the direction of gravity at once.

Now, in the optical fiber drawing furnace having the above configuration,
Outer diameter φ30mm, 1.3μm band preform is heated and drawn
A method for manufacturing a 125 μm heat-resistant optical fiber will be described.

First, the preform 1 is spun in a drawing furnace 3 and then guided to a carbon coating furnace 4 where the guided optical fiber 2
Is passed through a high temperature (about 1200 ° C.) benzene + Ni gas atmosphere to coat the optical fiber 2 with carbon.

The optical fiber 2 coated with carbon is further coated with polytitanocarbosilane (filler zirconia) through a coating die 5 and then guided to a curing oven at 600 ° C. to be cured.

Next, the optical fiber obtained by curing the polytitanocarbosilane is passed through a coating die 7 and a mixture of tetramethoxysilane: methanol: H ₂ O = 1: 1: 1 is adjusted to pH 10 with NH ₄ OH and applied. After that, the mixture is guided to a heating furnace 8 at 800 ° C. to be thermally hydrolyzed, and wound around a bobbin via a turn pulley 9 at a speed of 30 m / min.

The outer diameter of the coated optical fiber 10 wound on the bobbin in this manner was 155 μm.

The transmission loss of this optical fiber was 0.36 dB / km at a wavelength of 1.3 μm, and no increase in loss due to the coating was observed.

Here, the carbon film is formed during the coating process or in a high-temperature environment of 500 ° C. or higher, hydrogen gas is generated by decomposition of residual methyl groups and the like contained in polytitanocarbosilane. This is to prevent diffusion into the fiber.

After coating with polytitanocarbosilane, a mixed solution is further applied to perform thermal hydrolysis for the following reason. At the stage of coating the optical fiber with polytitanocarboxylan, the surface of the coating was found to be porous by SEM. The coated optical fiber stopped at this stage is made of φ1.8 × φ1.4mm SUS (stainless steel)
When placed in a pipe and heated at 600 ° C for 24 hours to apply vibration to the pipe, the polytitanocarbosilane coating layer peels off,
Alternatively, a crack occurred and the optical fiber was disconnected.

Therefore, a tetramethoxysilane solution was passed through, the solution was impregnated in the porous material, and then passed through a high-temperature heating furnace 8 to form a glassy state, thereby preventing the occurrence of cracks in the polytyranocarbosilane coating layer.

The coated optical fiber produced in this way was
Heated at 60 ° C for 100 hours in a Φ1.4mm SUS pipe.
Even after heating, the loss increase was less than 0.1 dB / km, and there was no disconnection for vibration. Therefore, even when the coated optical fiber according to the present embodiment is used in a high-temperature environment such as around a blast furnace or geothermal power generation, it is possible to withstand the optical fiber without a cooling pipe.

[Effects of the Invention] As described above, according to the present invention, the organometallic polymer is applied on the carbon coating, and the optical fiber is coated by thermal hydrolysis of the organometallic compound. A heat-resistant high-strength optical fiber that is stable for a long time can be obtained even under the following conditions.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an optical fiber drawing furnace for carrying out the method for producing a heat-resistant optical fiber of the present invention. 1 ... preform, 2 ... fiber, 3 ... drawing furnace,
4 ... carbon coating furnace, 5 ... coating die, 6 ... curing furnace, 7 ... coating die, 8 ...
... heating furnace, 9 ... turn pulley, 10 ... optical fiber.

Claims (1)

(57) [Claims] An optical fiber obtained by heating and stretching a preform is coated with carbon, and after coating with an organic metal polymer, an organic metal compound is further applied to perform thermal hydrolysis. A method for producing a heat-resistant optical fiber, comprising: