JP2715624B2 - Optical fiber for measurement - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber.

[Prior Art] Optical fibers are used not only for communication, such as long-distance transmission, but also for measurement.

Recently, it has become possible to measure the local temperature distribution with considerable accuracy using a single optical fiber. This optical fiber is made of plastic like the transmission optical fiber. Therefore, in temperature measurement, a polymer such as an ultraviolet curable resin, silicone, or polyimide, a metal such as aluminum or nickel, or a ceramic such as carbon, silicon nitride, or boron nitride is coated according to the application. Among them, ceramic is poor in ductility, so that it is applied to a very thin film, and serves the purpose of preventing permeation of water and hydrogen harmful to the optical fiber. However, since there is no protective effect for the thin films, they are usually supplied in the form of plastic coating on their outer periphery.

Further, the metal is easily corroded, and therefore, depending on the environment, the outer periphery may be covered with plastic in some cases.

[Problems to be Solved by the Invention] When an optical fiber is used for temperature measurement, it may be exposed to a high temperature depending on the use. In such a case, polyimide has tended to be used for plastics and aluminum has been used for metals. However, in the case of polyimide, the maximum temperature is about 300 ° C in long-term use even in an inert atmosphere. Considering separation due to the difference, it is considered that the limit is about 350 ° C. Therefore, when a temperature of 400 ° C. or more is measured for a long period of time, the optical fiber may be broken due to deterioration of the coating or the like.

Although heat-resistant polymers such as ladder polymers and polyborosiloxanes have recently been proposed, even if they withstand short-term use, they become brittle due to the volatilization of the organic groups in the side chains and lose their protective effect when exposed to long-term exposure. There is a tendency.

Therefore, if an optical fiber that can be used even when exposed to high temperatures for a long period of time can be provided, it will be possible to measure not only temperature but also magnetic fields, electric fields, velocities, angular velocities, chemical substances, images, etc. Is considered very large.

An object of the present invention is to provide a measurement optical fiber which can solve the above-mentioned conventional disadvantages and can be used even in a high-temperature atmosphere.

[Means for Solving the Problems] The measuring optical fiber of the present invention has a hermetically coated measuring optical fiber inserted in a metal tube, filled in the metal tube, and heated by a ceramic treatment. The fiber is fixed in the metal tube by an admixture of a substance having at least an inorganic molecule which is converted into a ceramic or semi-ceramic.

The metal tube can be made of a material selected from stainless steel, titanium, nickel, aluminum, and copper.

In addition, the admixture of the substance having the inorganic molecule in the skeleton,
A material selected from polysiloxane, polyborosiloxane, organopolysilsesquioxane, polysilane, and polytitanate can be mainly used.

[Operation] A structure in which an optical fiber is arranged inside a metal pipe is filled with an admixture of a substance having an inorganic molecule in a skeleton, and is ceramicized or semiceramicized by an appropriate method, and the optical fiber is fixed. The heat resistance of the optical fiber for use is greatly improved.

That is, the conventional optical fiber coated with polyimide becomes brittle at high temperature due to thermal degradation or oxidation degradation and loses its protective function, so that the mechanical strength is significantly reduced. Therefore, it cannot be used at 250 ° C. in air and at most 350 ° C. in an inert atmosphere. On the other hand, the optical fiber of the present invention is protected by a metal tube, and the inside of the tube is fixed with a ceramicized filler having excellent heat resistance, so that it can be used even in an atmosphere of 400 ° C. or more. .

As the optical fiber, a silica glass-based optical fiber is preferable. However, a multi-component glass having a composition which can be used at a high temperature may be used. The optical fiber includes not only a single fiber but also a bundle or an image guide having two or more fibers.

In manufacturing the measuring optical fiber of the present invention,
Hermetic coating of carbon, boron nitride, silicon nitride, metal, etc. is applied to prevent fiber breakage during the process and loss increase due to generation of hydrogen and the like.

These preliminary coatings may remain as they are in the final stage, may be changed to another substance by a chemical reaction, or may be volatilized. Examples of changes to other substances due to chemical reactions include the case where silicon is volatilized due to the volatilization of organic groups by high-temperature heat treatment, and the case where polyimide undergoes similar heat treatment to form a carbonized layer. This is the case when the metal reacts with the filling.

As the metal tube of the present invention, stainless steel, titanium,
Copper, aluminum, nickel and the like are applicable, but are not limited to these, and are included in the present invention regardless of a simple substance or an alloy. In addition, the case where a plurality of metal or alloy layers are used is also included.

The filler of the present invention may be a powder, a mixture of a powder and a liquid, or a liquid substance in some cases. A specific example is described below.

Examples of the powder include those obtained by treating the surface of an inorganic powder such as quartz, alumina, or carbon with an inorganic polymer such as organopolysiloxane (ladder polymer) or polyborosiloxane. Since these surface layers are ceramicized by a high-temperature heat treatment, they serve as a binder and can integrate the powder.

Examples of the mixture of the powder and the liquid include an inorganic powder such as quartz, alumina, and carbon dispersed in a liquid binder such as silicone oil. In these admixtures, the organic groups of the binder are volatilized by the heat treatment at a high temperature, and the binder is turned into ceramic and integrated.

Examples of the liquid material include polysilanes such as polydimethylsilane, polydiphenylsilane, ladder polysilane, and octasuracuban. Since these precursor monomers are liquid, they may be injected into the metal pipe at the monomer stage, or may be easily injected since they become liquid by heating before curing. Similarly, the above-mentioned organopolysilsesquioxane and polyborosiloxane can be easily injected since they become liquid before curing.

The optical fiber and the ceramic layer may or may not adhere. The ceramic layer is more advantageous in terms of heat conduction as it has no pores, but may contain pores to such an extent that the accuracy of the temperature measurement is not hindered.

[Examples] Hereinafter, the present invention will be described with reference to specific examples.

Example 1 After spinning a quartz glass optical fiber preform for measurement to an outer diameter of 125 μm by a drawing furnace, the outer periphery was coated with amorphous carbon by a thermal CVD method (0.1 μm in thickness).
Polyimide (Trenice 200 manufactured by Toray Industries, Inc.)
0) was coated to a thickness of 20 μm, and cured by passing through an electric furnace set at 500 ° C. Outer diameter of this coated optical fiber
It was inserted into a 0.9 mm, 0.1 mm thick stainless steel tube. Inside this tube, a silicone oil admixture with fused quartz powder (25
(Viscosity in ° C. = 100 poise).

Next, nitrogen gas was introduced into the tube to maintain it in a completely inert atmosphere, and then inserted into an electric furnace in a nitrogen gas atmosphere in the form of a tube, and heated in the following temperature profile (40
0 ° C, 10h hold → 3 ° C / min, temperature rise → 600 ° C, 48h hold). The optical fiber thus obtained was left in an atmosphere of about 400 ° C. for one month, and it was confirmed that the optical fiber operated normally.

Comparative Example 1 An optical fiber preform for quartz for measurement having an outer diameter of 12 was drawn by a drawing furnace.
After spinning to 5 μm, the outer periphery was coated with a polyimide having a thickness of 20 μm, and cured by passing through an electric furnace set at 500 ° C. As a result of leaving the coated optical fiber in an inert gas atmosphere at about 400 ° C., the fiber was broken after about one week.

Comparative Example 2 The coated optical fiber of Comparative Example 1 was inserted into a stainless steel tube having an outer diameter of 0.9 mm and a thickness of 0.1 mm. As a result of leaving the optical fiber-inserted metal tube in an inert gas atmosphere at about 400 ° C., the fiber was broken after about two weeks.

Comparative Example 3 The metal tube of Comparative Example 2 was filled with a hydrocarbon oil mixture containing quartz powder. As a result of leaving the optical fiber thus obtained in an inert gas atmosphere at about 400 ° C., rapid thermal decomposition of the hydrocarbon oil occurs, and the generated hydrogen gas diffuses into the optical fiber to cause the optical fiber to lose its properties. A significant increase in transmission loss and a break in the fiber was noted after about one week.

[Effects of the Invention] As described above, the measuring optical fiber of the present invention is protected by the metal tube, and the inside of the tube is fixed by the ceramicized filler having excellent heat resistance. It can also be used in applications exposed to a high-temperature atmosphere such as 400 ° C. or more. Therefore, not only temperature measurement, but also measurement of a magnetic field, an electric field, a velocity, an angular velocity, a chemical substance, an image, and the like at a high temperature becomes possible, and the industrial contribution is extremely large. In addition, since the measuring optical fiber of the present invention is subjected to hermetic coating on the fiber and then inserted into the metal tube, it is possible to prevent loss of the fiber due to breakage of the fiber or generation of hydrogen, etc. during the process of ceramicization. Can be.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroshi Kawakami 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Pref. Nippon Electric Cable Co., Ltd. (56) Reference Reference U)

Claims (3)

(57) [Claims] A measuring optical fiber provided with a hermetic coating is inserted into a metal tube, and at least inorganic molecules filled in the metal tube and ceramicized or semi-ceramicized by heat treatment are used as a skeleton. An optical fiber for measurement, wherein the fiber is fixed in the metal tube by an admixture of substances having the same. 2. The measuring optical fiber according to claim 1, wherein said metal tube is made of a material selected from stainless steel, titanium, nickel, aluminum and copper. 3. An admixture of the above-mentioned substance having an inorganic molecule in the skeleton is mainly composed of a material selected from polysiloxane, polyborosiloxane, organopolysilsesquioxane, polysilane and polytitanate. The measuring optical fiber according to claim 1.