JPH07120627A - Optical fiber for temperature detection and its manufacture - Google Patents

Abstract

PURPOSE:To reduce light loss, extend the light transmitting distance of an optical fiber, and detect an abnormal temperature of a linear long material over a long length by providing a core having a color changing core part containing a thermosensitive color changing material in the center part, and a clad provided on the outer circumference of the core. CONSTITUTION:An optical fiber 11 is formed out of a core 11a, a color changing core part 11b containing a thermosensitive color changing material formed in the center part part of the core 11a and changing to a color whose light absorption is easily changed to a specified wavelength of the light from a light source by a temperature rise, a clad provided on the outer circumference of the core 11a, and a sheath 11d provided on the outer circumference of the clad 11c. Since the area capable of propagating light without passing the color changing core part 11b is formed when such a color changing core part 11b containing the thermosensitive color changing material is formed in the center part of the core 11a, the light propagated without passing the color changing core part 11b is increased, and the light loss by light absorption is reduced, and the light transmitting distance of the optical fiber 11 can be extended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting optical fiber applied to the temperature detection of a long linear object such as an electric wire and a method for manufacturing the same.

[0002]

2. Description of the Related Art Various types of means have been developed as means for detecting the temperature of an object to be detected. When the object to be detected is a long linear object, a so-called lumped constant type temperature sensor such as a semiconductor temperature sensor is used. In order to detect the temperature of the linear long object with the sensor, a plurality of temperature sensors must be arranged along the linear elongated object, and a large number of temperature sensors are required. Since the circuit that processes the output of the temperature sensor also becomes complicated, the overall configuration becomes complicated, and there is the inconvenience that malfunction is likely to occur due to the influence of noise.

Therefore, conventionally, a distributed constant type temperature sensor using an optical fiber has been proposed as a suitable means for detecting the temperature of a linear long object. The change in backscattered light due to the temperature rise of the fiber is detected to detect an abnormal temperature of a linear elongated object.In this case, the backscattered light from the optical fiber is weak in the first place, so the change is detected. In order to do so, a detection means with a complicated and expensive structure is required.

On the other hand, similarly, as a means for temperature detection using an optical fiber, as described in Japanese Utility Model Publication No. 62-3761, a temperature-sensitive color-developing layer is provided on the outer periphery of the core of the optical fiber as a color change with temperature. Is being done.

That is, as shown in FIGS. 6 (a) and 6 (b),
The temperature-sensitive coloring layer 1b is provided on the outer periphery of the core 1a, the clad 1c is provided on the outer periphery of the temperature-sensitive coloring layer 1b, and the sheath 1c is further provided on the outer periphery thereof to form the optical fiber 1. The wavelength change of the light emitted from the optical fiber is detected by the attenuation effect due to the absorption of the light of a specific wavelength by the temperature-sensitive color developing layer 1b which is made incident by the light from the white light source or the like.

[0006]

However, when the temperature-sensitive coloring layer 1b is provided on the outer periphery of the core 1a as described above, it is not necessary to detect weak light as much as backscattered light, but light loss is large, There is also a limit to the optical transmission distance of the optical fiber, and if the linear long object that is the target of temperature detection becomes too long, the emitted light of the optical fiber becomes too weak and abnormal temperature cannot be detected sufficiently. There is a point.

That is, as shown by the arrows in FIGS. 6A and 6B, the light incident on the optical fiber 1 is generally the core 1
Although the light propagates while being totally reflected at the boundary surface between the a and the clad 1c, the temperature-sensitive color developing layer 1b causes the light to be reflected by the temperature-sensitive color developing layer 1b, at which time a part of the light is absorbed (or As the optical fiber 1 becomes longer, the optical loss increases as the optical fiber 1 becomes longer.

Further, as shown in FIG. 7, it is described in the above-mentioned publication that a plurality of stripes of the temperature-sensitive color forming layer 1e are provided on the outer periphery of the core 1a. Because almost no light propagates without hitting,
After all, the light loss becomes large.

Therefore, the present invention has been made in order to solve the above problems, and aims to reduce the optical loss and extend the optical transmission distance of the optical fiber, and to extend the length of the optical fiber as compared with the conventional one. It is intended to detect an abnormal temperature of a linear long object.

[0010]

An optical fiber for temperature detection according to the present invention comprises a core having a color-changing core portion containing a temperature-sensitive color-changing material in its central portion, and a clad provided on the outer periphery of this core. It is characterized by that.

As a manufacturing method thereof, a core material containing a thermochromic material is poured into a hollow pipe, and after the core material is cured, the cured core material is taken out from the hollow pipe to form a discolored core portion. It is preferable that a core made of a core material is formed on the outer periphery of the discolored core portion, and a clad is formed on the outer periphery of the core. A first step of forming a core by pouring a core material having a refractive index higher than that of the resin tube into a resin tube as a clad, and a temperature-sensitive color changing material for the core material in the resin tube after the first step. It is effective to include a second step of forming a discolored core portion by pouring a mixture of

After that, the resin tube may be removed and a material having a large difference in refractive index from the air layer or the core may be replaced with the clad.

[0013]

In the present invention, for example, when a temperature-sensitive color changing material that changes from colorless to green at 100 ° C. is used, it is colorless at room temperature, so that when white light enters, the emitted light is white, When the color-changing core changes to green due to a temperature rise, light other than the green component of the white light is absorbed when passing through this color-changing core, and the color (wavelength) of the emitted light changes with respect to the incident light. To do.

On the other hand, when red light is made incident, the red light passing through the discolored core that has changed color to green is absorbed, so that the intensity of emitted light is attenuated and becomes smaller than the intensity of incident light.

Therefore, the abnormal temperature of the linear elongated object can be detected by detecting the color (wavelength) change or the intensity change of the emitted light.

At this time, since the color-changing core portion is provided at the center of the core as compared with the case where the color-changing layer is provided on the outer periphery of the core as in the conventional case, the total reflection at the core-clad boundary surface does not pass through the color-changing core portion. The amount of light that propagates repeatedly is increased, the optical loss due to absorption in the color-changing core portion is reduced, and the optical transmission distance can be increased.

[0017]

FIG. 1 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing the configuration of an applied device, and FIGS. 3 and 4 are operation explanatory diagrams.

In FIG. 2 showing an apparatus to which the present embodiment is applied, 11 is an optical fiber arranged along a linear elongated object such as an electric wire (not shown), and 12 is a light incident end of the optical fiber 11. To provide white light or monochromatic light to the optical fiber 11
The light source 13 incident on the light receiving portion 13 is a light receiving portion including a light receiving element such as a photodiode or a phototransistor, and is provided at the light emitting end of the optical fiber 11 and outputs a light receiving signal according to the intensity of the emitted light.

At this time, when the light source 12 is a monochromatic light source, a light emitting element such as a red LED or a green LED may be used.

The optical fiber 11 is constructed in detail as shown in FIG. 1, and includes a core 11a and a core 11a.
Provided on the outer periphery of the core 11a, and a color-changing core portion 11b including a temperature-sensitive color-changing material which is formed in the central portion of the core 11a and whose color changes to a color whose light absorption easily changes with respect to a specific wavelength of light from the light source 12 due to temperature rise. It is composed of a clad 11c and a sheath 11d provided on the outer periphery of the clad 11c.

At this time, when the color-changing core portion 11b containing the temperature-sensitive color-changing material is formed only in the central portion of the core 11a, the first step is, for example, a clad 11c made of a fluororesin having an inner diameter of 2 mm and an outer diameter of 3 mm. Core 1 by pouring transparent silicone into a resin tube as a syringe
1a is formed, and as the subsequent second step, the color-changing core portion 11b may be formed by pouring silicone containing a temperature-sensitive color-changing material into a resin tube using a syringe.

At this time, the silicone A poured into the resin tube in the first step is rubbed by the inner wall surface of the tube as shown in FIG. The poured silicone B containing the temperature-sensitive color changing material smoothly advances in the portion corresponding to the central portion of the core 11a as shown in 3 (b), and as a result, the structure shown in FIG. 1 is obtained.

However, in the above-mentioned first step and second step, since the same silicone is poured, there is no boundary between the silicone A containing no temperature-sensitive color changing material after the silicone is cured and the silicone B containing it.

After the second step described above, the resin tube may be removed and the clad 11c may be replaced with a material having a large difference in refractive index from the air layer or the core 11a.

By the way, the combination of the light from the light source 12 and the temperature-sensitive color changing material is preferably as shown in Table 1, for example. In addition to the white light, the light source 12 receives monochromatic light such as red light, green light and yellow light. It is preferable to use, and as the temperature-sensitive color changing material, as shown in Table 1, it is preferable to use a material that develops, discolors, or erases color at high temperature.

[0026]

[Table 1]

Table 1 shows the color of the emitted light before and after the color change and the amount of the emitted light when the color of the temperature-sensitive color-changing material changes (for example, changes from colorless to red) while using the incident light of each color. In particular, the emitted light quantity represents the change in light quantity after color change with reference to the color before change. For example, “small green” means that the light quantity of the green component is smaller than before change, and “green large” “Indicates that the light amount of the green component increases more than before the change.

In Table 1, "before change" means the state at room temperature, and "after color change" means the state at a high temperature of, for example, 60 ° C or higher.

The material of the temperature-sensitive color changing material to be dispersed in the core 11a of the optical fiber 11 may be selected such that the light absorption changes before and after the color change in relation to the light source 12, for example, red light is used for the light source 12. In such a case, it is desirable to use one that reversibly changes from colorless or red, which normally does not absorb in that wavelength range, to green, black, or another color that absorbs red light,
Specifically, the materials shown in Table 2 may be used. As shown in Table 2, PSD-R (fluorane-based leuco compound), lauryl gallate, and toluene are used as the materials that change color from colorless to red as the temperature rises. It may be used, but is not particularly limited to the materials shown in Table 2.

[0030]

[Table 2]

Now, considering the range in which the incident light to the optical fiber 11 does not pass through the discolored core portion 11b at the center of the core 11a when propagating in the optical fiber 11, FIG.
As shown in (a) and (b), a position where light is incident on the point P0 using the light source 12 or other light guide,
The point P1 is a position where a light ray at the maximum angle that does not hit the color changing core portion 11b first hits the outer wall of the core 11a, and the point P2 is a position where a light ray at the minimum angle that does not hit the color changing core portion 11b hits the outer wall of the core 11a first, When the point O is the center of the core 11a, r is the radius of the color changing core portion 11b, R is the radius of the core 11a, and d is the distance from the center O to the light incident position P0, the incident angle δ of the incident light is given by Given by. However, φ and θ in Equation 1 are given by Equations 2 and 3, respectively.

[0032]

[Equation 1]

[0033]

[Equation 2]

[0034]

[Equation 3]

Then, by rearranging the formulas 1 to 3, the incident angle δ is expressed by the formula 4, and FIG.
In terms of a circle in the cross section of the optical fiber 11 shown in (c), the incident angle δ is φ ≦ δ ≦ (π−θ), (π + θ) ≦ δ ≦
When in the range of (2π−φ), light propagates without passing through the color-changing core portion 11b.

[0036]

[Equation 4]

As described above, when the color-changing core portion 11b containing the temperature-sensitive color-changing material is formed only in the central portion of the core 11a, light can be propagated without passing through the color-changing core portion 11b specified by the incident angle δ of the equation (4). Since a large area is formed, a large amount of light propagates without passing through the color-changing core portion 11b, and light loss due to light absorption in the color-changing core portion 11b is reduced as compared with the conventional case where a coloring layer is provided on the outer periphery of the core. As a result, the optical transmission distance of the optical fiber 11 can be extended, and it becomes possible to detect an abnormal temperature of a linear long object over a longer length than before, and an environment with a lot of electromagnetic noise. It can also be used underneath or in an environment where there is a risk of explosion.

As another embodiment, as shown in FIG. 5, a plastic optical fiber 15 is used as an optical fiber, and a portion of the core of the plastic optical fiber 15 having a length L corresponding to a temperature detection range is used. However, the above-mentioned temperature-sensitive color changing material may be dispersed, and in this case, there is an advantage that the temperature rise in an unnecessary portion is not detected as compared with the one shown in FIG.

As another method of forming the color-changing core portion 11b, a core material such as silicone containing a temperature-sensitive color-changing material is poured into a hollow pipe such as a glass tube or a vinyl chloride pipe, and this core material is used. After curing, the cured core material is taken out from the hollow pipe to form the color-changing core portion 11b, and the core 1 made of the core material is formed on the outer periphery of the color-changing core portion 11b.
1a is formed, and then the cladding 11 is formed on the outer periphery of the core 11a.
You may make it form c.

[0040]

As described above, according to the temperature detecting optical fiber of the present invention, since the color changing core portion including the temperature sensitive color changing material is formed only in the center portion of the core, the light propagating without passing through the color changing core portion is formed. As a result, the optical loss can be reduced, the optical transmission distance of the optical fiber can be extended compared to the conventional one, and it becomes possible to detect abnormal temperatures of long linear objects over longer lengths, and abnormal temperatures of electric wires, etc. It can be used in an environment with a lot of electromagnetic noise or an environment in which there is a risk of explosion, and has a wide range of application.

Also, an optical fiber having a color-changing core portion in the central portion of the core can be manufactured by the method according to the second or third aspect.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is an overall schematic configuration diagram of an embodiment.

FIG. 3 is a diagram illustrating the operation of the embodiment.

FIG. 4 is a diagram illustrating the operation of the embodiment.

FIG. 5 is a schematic view of another embodiment.

FIG. 6 is a schematic view of a conventional example.

FIG. 7 is an operation explanatory diagram of a conventional example.

[Explanation of symbols]

 11 optical fiber 11a core 11b discolored core portion 11c clad 15 plastic optical fiber

Claims (3)

[Claims] 1. An optical fiber for temperature detection, comprising a core having a color-changing core portion containing a temperature-sensitive color-changing material in a central portion, and a clad provided on the outer periphery of the core. 2. A core material containing a thermochromic material is poured into a hollow pipe, and after the core material is cured, the cured core material is taken out from the hollow pipe to form a discolored core portion, and then the discolored core portion is formed. A method of manufacturing an optical fiber for temperature detection, comprising forming a core made of a core material on the outer periphery of the core, and forming a clad on the outer periphery of the core. 3. A first step of forming a core by pouring a core material having a refractive index larger than that of the resin tube into a resin tube as a clad, and the core material in the resin tube after the first step. And a second step of forming a color-changing core portion by pouring a mixture of a temperature-sensitive color-changing material into the method of manufacturing an optical fiber for temperature detection.