JPH07140045A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To enhance heat resistance by forming a sensing part under high temperature environment at an end of a glass based optical fiber having a carbon coat layer. CONSTITUTION:An optical fiber 1 comprises a glass optical fiber 2 comprising a core 2a having high refractive index applied with a clad 2b having low refractive index, a carbon coat layer 3 formed on it, and a polymer resin jacket 4 applied on it. The optical fiber 1 is then introduced, at an end part, into a vacuum tank and a thin functional film is deposited by sputtering, CVD, vacuum deposition, etc., in order to provide a sensing part. Although the optical fiber 1 is heated up to several hundreds degree Celsius in the vicinity of the end part, function of the fiber 1 is not damaged because the heat resistance is enhanced by the coat layer 3. This structure realize an optical fiber sensor excellent in heat resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor using an optical fiber useful for measuring physical quantities such as pressure, temperature, force and magnetic field, and chemical quantities such as pH, ions and oxygen.

[0002]

2. Description of the Related Art In recent years, physical quantities such as pressure and temperature or pH
An optical fiber sensor is often used as a method of remotely controlling and measuring the chemical amount of ions and ions. For example, as shown in FIG. 6, one of the optical fibers 31 and 31 is connected to the light source 34 and the detector 35, and the other is connected to the sensing unit 30.
Is placed in the object 36 to be measured to measure a required physical quantity or chemical quantity. In this case, one optical fiber 31 may receive the reflected light at the same time to measure the measured object 36. The sensing unit 30 has optical characteristics (light intensity, phase, frequency) corresponding to changes in physical quantity and chemical quantity.
A functional thin film having a variable thickness is used. Further, the measurement target 36 may be not only the inside of various industrial equipment but also the inside of a living body such as a blood vessel in the human body.

As shown in FIG. 5, the cross-sectional structure of the optical fiber 31 is such that a core 32a having a high refractive index is covered with a clad 32b having a low refractive index, and further, a jacket 33 made of a polymer material covers the core 32a. The core 32a and the clad 32b are made of transparent glass or transparent resin.

[0004]

The optical fiber sensor is
Since it does not use electricity, it has many advantages such as non-electric shock, low noise, non-induction, and lengthening, and many applied technologies in the industrial and medical fields are considered. Various sensing units of various methods and structures have been proposed and studied in order to measure and analyze physical quantities and chemical quantities. However, although the end of the optical fiber 31 and the sensing unit 30 need to be bonded (joined) with high precision and strength, the sensing unit 30 is generally a fine and complicated structure, and the joining method is extremely difficult. Is. In particular, the optical fiber 31 and the sensing unit 30
In the coupling process with or the process of forming a functional film with a minute thickness at the tip of the optical fiber 31, a high temperature environment of several hundreds of degrees or more is required, so not only the optical fiber having an organic compound core or clad The heat resistance of glass optical fibers is a major bottleneck. The present invention has been made in view of the above problems, and an object thereof is to provide an optical fiber sensor which has heat resistance and can be manufactured by various processes even in a high temperature environment of several hundred degrees or more. It is in.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an optical fiber sensor formed at the end of a glass optical fiber having a carbon coat layer under a high temperature environment. It is characterized in that it is provided with a sensing unit.

[0006]

When the optical fiber sensor is used as the above means, the carbon coat layer 3 formed around the glass optical fiber 2 is used.
Increases the bending strength of the optical fiber 1 itself and enhances the heat resistance. Therefore, by forming the sensing portion 11 (or the functional thin film 10 or the like) at the end of the optical fiber 1 on which the carbon coat layer 3 is formed, an optical fiber sensor having improved heat resistance and strength resistance can be obtained. . Also, the car
An optical fiber not having the boncoat layer 3 deteriorates in maximum strength and average strength when immersed in water, but even if the optical fiber having the carbon coat layer 3 is immersed in water, the maximum strength,
The average strength and the like hardly deteriorate. Therefore, the optical fiber sensor used as the above means can be an optical fiber sensor excellent in heat resistance, strength resistance, water resistance and the like.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional structural view of an optical fiber 1 used in the optical fiber sensor of the present invention. This optical fiber 1 is composed of a glass optical fiber 2 having a high refractive index core 2a and a low refractive index cladding 2b, and a carbon coat layer 3 covering the periphery thereof. It is covered with a polymer resin jacket 4.

As the glass optical fiber 2, for example, quartz glass is used, and the carbon coat layer 3 covering the glass optical fiber 2 is formed by thermally decomposing a hydrocarbon gas as described later. The hydrocarbon gas may be aliphatic, alicyclic, aromatic, or saturated or unsaturated hydrocarbon gas. For example, saturated hydrocarbon gas such as methane, ethane, propane, butane, benzene and toluene, and unsaturated hydrocarbon gas such as ethylene, propylene, butene and acetylene can be used.

The thermal decomposition temperature of the hydrocarbon gas is 5
It is a high temperature range of 00 ° C. or higher at which quartz glass can be drawn, but preferably 800 ° C. to 1800 ° C., particularly 1
It is 000 ° C to 1500 ° C. The higher the thermal decomposition temperature, the shorter the carbon film thickness can be formed.

The carbon film can be formed by the thermal decomposition of hydrocarbon gas, for example, by the thermal CVD method.
FIG. 2 is a schematic view of a CVD apparatus for forming the carbon coat layer 3 on the glass optical fiber 2. In this apparatus, a heating furnace for wire drawing 22 is installed under a base material supply section 21, a carbon coating reaction vessel 23 is installed further below, and an organic compound (jacket) coating apparatus 24 for curing by ultraviolet irradiation is further installed. It is arranged. That is, a glass (quartz glass) optical fiber preform is introduced into a high-temperature heating furnace 22 to be drawn, and then the glass optical fiber 2 is introduced into a CVD reaction vessel 23 and a hydrocarbon gas is introduced.
It is formed by causing a VD reaction.

The most effective method for forming a carbon film is
This is a method of thermally decomposing a hydrocarbon gas by utilizing the residual heat immediately after drawing the glass optical fiber 2. According to this apparatus, the drawing of the glass optical fiber 2 is performed at a high temperature exceeding 2000 ° C., so that the glass optical fiber 2 immediately after the drawing retains the heat necessary for the thermal decomposition of the hydrocarbon gas. Therefore, the carbon coat layer can be formed only by installing the CVD reaction container 23 directly below the heating furnace 22 for drawing and supplying the hydrocarbon gas.

More specifically, the coating of the carbon coat layer 3 is performed as follows. For example, a glass optical fiber 2 in which a base material composed of a germanium oxide doped quartz core and a pure quartz glass clad is drawn through a supply section 21 and a heating furnace 22 is inserted into a reaction vessel 23 and run, Raw material gas (for example, acetylene gas 10
0 cc / min) and diluent gas (eg, argon gas 400
cc / min), and the thermal CVD reaction is caused by the heat of the high temperature glass optical fiber 2 immediately after stretching which passes through the inside of the reaction vessel 23, and the carbon film 3 is deposited and formed on the surface of the glass optical fiber 2. You can

Next, an embodiment will be described in which the sensor portion is formed on the optical fiber 1 in which the carbon coat layer 3 is formed around the glass optical fiber 2. In FIG. 3 (A), the end portion of the optical fiber 1 on which the carbon coat layer 3 is formed is shown in FIG.
It is a schematic cross-sectional view of the state introduced into the interior 8a of. In this case, a sealing means 9 (for example, a grease sealant such as a silicon-based vacuum grease or the grease sealant) is provided around the end of the optical fiber 1.
(A combination of a sealing material and a spacer) is attached so that the inside 8a can be kept secret. Thus, as shown in FIG. 3B, the functional thin film 10 serving as a sensing portion can be formed on the end face of the optical fiber 1 with the end portion of the optical fiber 1 introduced into the vacuum chamber 8.

Specific means for forming the functional thin film 10 on the end face of the optical fiber 1 introduced into the vacuum chamber 8 includes a sputtering method, a CVD method, a vacuum deposition method, a molecular beam epitaxial method and an ion deposition method. Can be used. The type, method, and thickness of the functional thin film 10 may be appropriately selected depending on the purpose of sensing. When the functional thin film 10 is formed by such a method, the periphery of the tip of the optical fiber 1 inside the vacuum chamber 8 is exposed to a high temperature of several hundreds of degrees or more, but the optical fiber 1 is provided with the glass optical fiber 2 as described above. Since the carbon coat layer 3 is formed around the glass and the heat resistance is remarkably improved, the glass optical fiber 2 portion is not melted or the function of optical transmission is not impaired.

FIG. 4 shows an embodiment in which a sensor section 11 capable of detecting pressure is formed on the optical fiber 1 having a carbon coat layer 3 formed around the glass optical fiber 2.
The sensing unit 11 has the optical fiber 1 formed with a hole 14a.
A transparent plate 13 to which a frame spacer 12 to which a flexible reflective film (for example, a semiconductor film such as GaAs) 10 'is bonded and fixed is bonded and fixed is formed on a fixed plate 14 which is inserted and fixed to. The fixed plate 14, the transparent plate 13 and the transparent plate 1
Bonding with 2 can also be achieved by bonding with a resin curing agent, and particularly when bonding with a thermosetting resin, the optical fiber 1 has heat resistance because the carbon coat layer 3 is formed. Therefore, the frame space forming these sensing units 11
The bonding step of assembling the support 12, the transparent plate 13, the fixed plate 14 and the like is performed in a thermal environment of several hundred degrees, and even if the end of the optical fiber 1 is exposed to heat, thermal damage does not occur. .

The coating of the carbon coat layer 3 formed around the glass optical fiber 2 as described above increases the bending strength of the optical fiber 1 itself and enhances the heat resistance.
Therefore, by forming the sensing portion 11 (or the functional thin film 10) at the end portion of the optical fiber 1 on which the carbon coat layer 3 is formed, an optical fiber sensor with improved heat resistance and strength resistance can be obtained. Further, the optical fiber not having the carbon coat layer 3 deteriorates in maximum strength and average strength when immersed in water, but even if the optical fiber having the carbon coat layer 3 formed therein is immersed in water. Maximum strength, average strength, etc. hardly deteriorate. Therefore, the optical fiber sensor of the present invention can be an optical fiber sensor excellent in heat resistance, strength resistance, water resistance and the like.

[0017]

Since the optical fiber sensor of the present invention has the structure described in detail above, heat resistance can be dramatically improved in the process of connecting the optical fiber and the sensor section. Further, this optical fiber sensor can be a sensor in which the water resistance does not deteriorate even if the jacket of the organic compound is thermally damaged because the carbon coat layer has water resistance. Further, in forming the sensor portion of this optical fiber sensor, various processes (sputtering method, CVD method, vacuum deposition method, molecular beam epitaxial method,
Ion vapor deposition method, etc.)
It can be used even in the high temperature and high humidity environment during sensing.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a glass optical fiber used in an optical fiber sensor of the present invention.

FIG. 2 is a schematic view of a CVD apparatus for forming a carbon coat layer on a glass optical fiber.

FIG. 3 (A) is a schematic cross-sectional view showing a state in which an end of an optical fiber having a carbon coat layer is introduced into a vacuum chamber, and FIG. 3 (B) is an optical fiber having a functional film formed thereon. It is a figure which shows the front-end | tip part.

FIG. 4 shows an example of forming a sensing part in an optical fiber in which a carbon coat layer is formed around a glass optical fiber.

FIG. 5 is a schematic diagram of a case where one of the optical fibers is connected to a light source and a detector, and the other is connected to a sensing unit, and the sensor unit is placed in the object to be measured.

FIG. 6 is a cross-sectional structural view of a conventional glass optical fiber.

[Code clan]

DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Glass optical fiber 3 Carbon coat layer 4 Jacket 8 Vacuum tank 9 Sealing means 10 Functional thin film 11 Sensing part 12 Frame spacer 13 Transparent plate 14 Fixing plate 21 Base material supply part 22 Heating furnace for wire drawing 23 Carbon Coated Reactor

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G02B 6/02 A 7036-2K 6/44 331 7036-2K

Claims (1)

[Claims] 1. An optical fiber sensor comprising a glass-based optical fiber having a carbon coat layer and a sensing portion formed in a high temperature environment at an end portion thereof.