JPH10300627A - Optical fiber for detecting liquid and cable including it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the intrusion length of liquid into a long region by arranging a liquid absorbing resin around a core and providing an air gap between the liquid absorbing resin and the outer circumferential surface of the core. SOLUTION: With regard to the intrusion detection optical fiber 10 a core 12 coated with a clad 20. The core 12 is composed of an optical resin, e.g. quartz glass, and the clad 20 is composed of a basic material 22 mixed with a massive water absorbing resin 24. The basic material 22 is composed of an optical resin, e.g. quartz glass, similarly to the core 12 and the refractive index thereof is set lower than that of the core 12 so that a light propagating through the core 12 is totally reflected on the interface between the core 12 and the basic material 22 of the clad 20. When water intrudes at any point of the intrusion detection optical fiber 10, the water absorbing resin 24 absorbs the water to be swelled and an air gap 30 is filled. Since a light propagating through the core 12 leaks at the interface between the core 12 and the water absorbing resin 24, leakage can be detected for a long region by measuring the transmission loss of light due to the optical fiber 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid detecting optical fiber for detecting intrusion of liquid in a long region such as electric power, a signal, and water entering a communication cable, and a cable including the same.

[0002]

2. Description of the Related Art Conventionally, as a sensor for detecting inundation at a specific location, there is a sensor that utilizes an electrical short circuit or a decrease in insulation resistance due to inundation.

Further, as a sensor using an optical fiber,
There is one that detects inundation at the end of an optical fiber by using light reflection or light attenuation at an inundation point.

[0004]

However, any of the above-described sensors for detecting inundation detect inundation at a specific point. So, for example,
It is not possible to detect inundation over the entire communication cable with a single sensor.

Accordingly, the present invention has been made to solve the above-mentioned problems, and provides a liquid detecting optical fiber capable of detecting the intrusion of liquid into a long area and a cable including the same. The purpose is to do.

[0006]

In order to solve the above problems, a liquid detecting optical fiber according to the present invention has a liquid absorbing resin disposed around a core, the liquid absorbing resin and the core. A gap is interposed at least partially between the outer peripheral surface and the outer peripheral surface.

In the optical fiber for liquid detection according to the present invention, the bulk or granular liquid absorbing resin extends from the outer peripheral surface side to the inner peripheral surface side of the clad in the base material of the clad coated around the core. The liquid-absorbent resin is mixed to be continuous, and has a refractive index lower than the refractive index of the core in a non-absorbed state of liquid, and the refractive index increases in a liquid-absorbed state. .

Further, another optical fiber for liquid detection according to the present invention includes a cladding base material coated around a core,
The bulk or granular liquid absorbing resin is mixed so as to be continuous from the outer peripheral surface side to the inner peripheral surface side of the clad, and a concave portion is formed on the inner peripheral surface of the clad, so that the outer peripheral surface of the core and the outer peripheral surface of the clad are mixed. A gap is interposed at least partially between the inner peripheral surface and the inner peripheral surface.

In the optical fiber for liquid detection according to the present invention, the core is coated with an absorbing layer made of a powdery, fibrous or non-woven liquid absorbing resin, and a liquid is formed around the absorbing layer. A permeable protective layer is coated.

As the liquid absorbing resin, a starch-acrylic acid graft copolymer, a polyacrylate or a gelled vinyl acetate acrylate copolymer can be used.

In the cable according to the present invention, the above-mentioned liquid detecting optical fiber is bundled with at least one of an electric wire and an optical fiber, a protective tape is wound around the optical fiber, and And a protective layer made of resin.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical fiber for detecting inundation according to a first embodiment of the present invention will be described.

As shown in FIG. 1 and FIG. 2, the optical fiber 10 for detecting inundation has a cladding 20 coated around a core 12.

The core 12 is made of optical glass such as quartz glass or optical resin such as polymethyl methacrylate or polystyrene, and has a refractive index of usually about 1.5 to 1.3.

The clad 20 is formed by mixing a bulk or granular water-absorbent resin 24 into a base material 22. The base material 22 is made of optical glass such as quartz glass or optical resin such as polymethyl methacrylate or polystyrene similarly to the core 12, and its refractive index is set to be smaller than the refractive index of the core 12. The light propagating in the core 12 is totally reflected at the interface between the core 12 and the base material 22 of the clad 20. The water-absorbent resin 24 is made of a resin having a hydrophilic group, such as a starch-acrylic acid graft copolymer, a polyacrylate, or a gelled product of a vinyl acetate acrylate copolymer. The water-absorbent resin 24 is dispersed and mixed in the clad 20 in a volume ratio of 50% or more, and water on the outer peripheral surface of the clad 20 sequentially penetrates the mixed water-absorbent resin 24 to form the inner peripheral surface side. , The absorbent resin 24 is mixed so as to be continuous from the outer peripheral surface side to the inner peripheral surface side of the clad 20.

Further, by forming grooves along the axial direction at appropriate intervals in the circumferential direction on the inner peripheral surface of the clad 20, a plurality of grooves are formed between the core 12 and the clad 20. A void 30 is formed. The gap 30 can be formed by increasing the feeding speed of the core 12 more than usual or lowering the melting temperature of the clad 20 when the core 12 is coated with the clad 20 by extrusion. .

Next, the operation of the water immersion detecting optical fiber 10 will be described with reference to FIG.

First, when the optical fiber 10 is not immersed in water, the air gap 30 is usually filled with air, and the refractive index of the air is almost 1. Therefore, the light (OP _n-1 ) in the core 12 propagates while being totally reflected at the boundary between the core 12 and the clad 20 or at the boundary between the core 12 and the air in the gap 30.

If there is water in any part of the water detecting optical fiber 10 (see the water immersion portion H in FIG. 3), the water absorbent resin 24 absorbs water and swells or dissolves, and the void 3
Fill in zeros. Here, since the refractive index of the water-absorbent resin 24 that has absorbed water is usually close to the refractive index of water (1.33), the refractive index difference between the core 12 and the water-absorbent resin 24 is Is smaller than the refractive index difference between
The refractive index of the water-absorbing resin 24 that has absorbed water is larger than the refractive index of the core 12.

Therefore, when there is water, light (OP _n ) propagating through the core 12 leaks at the boundary surface between the core 12 and the water-absorbing resin 24. That is, if there is water in any part of the optical fiber 10 for detecting inundation, the transmission loss of the optical fiber 10 increases.

According to the immersion detecting optical fiber 10 configured as described above, the immersion detecting optical fiber 10 is provided in a predetermined long area, and light is emitted from one end side by a light emitting element or the like. The intensity of the light that enters and is emitted to the other end is measured by a light receiving element, and the optical fiber 1
If the light transmission loss due to 0 is measured, it is possible to obtain the effect that the inundation can be detected in the long area.

Further, since the transmission loss of light increases as the degree of flooding increases, it is also possible to know the degree of flooding based on the magnitude of the transmission loss of light.

Further, by measuring the backscattered light of the light propagating in the core 12 and determining the relationship between the distance from one end of the fiber 10 and the transmission loss of the light, the location where the transmission loss of the light is sharply reduced can be determined. It can be obtained as an inundation point.

Further, since the gap 30 is covered with the clad 20, dust and the like other than water do not enter between the core 12 and the clad 20.

The water-absorbent resin 24 has a refractive index lower than that of the core 12 in a water-absorbed state and increases in a water-absorbed state. , Can also detect inundation.

Next, an optical fiber 50 for detecting inundation according to a second embodiment of the present invention will be described.

As shown in FIGS. 4 and 5, the optical fiber 50 for detecting inundation has a core 52 covered with an absorbing layer 60 and a further outer periphery covered with a protective layer 70.

The core 52 is made of optical glass such as quartz glass or optical resin such as polymethyl methacrylate or polystyrene, and has a refractive index of usually about 1.5 to 1.3.

The absorbent layer 60 is formed by powdering the above-mentioned water-absorbing resin.
It is formed into a fibrous or nonwoven fabric.

The protective layer 70 is formed by foaming the resin into open cells and coating the resin, or by coating the resin in a mesh form, and the water outside passes through the open cell portions or the net holes. The protective layer 70 is formed so as to be transmitted to the inside of the protective layer 70.

According to the immersion detecting optical fiber 50 configured as described above, since the absorbing layer 60 is formed in a powdery, fibrous, or nonwoven fabric shape, at least a portion of the core 52 is not in contact with the absorbing layer 60. It is in contact. Therefore, in a state where the optical fiber 50 is not submerged, air is filled in a portion of the outer peripheral surface of the core 52 which is not in contact with the absorbing layer 60, and light in the core 52 is transmitted at a boundary between the core 52 and air. The light propagates while being totally reflected.

However, if any part of the water detecting optical fiber 50 is flooded, water permeates the protective layer 70 and reaches the absorbing layer 60 at the flooded point. When the water-absorbent resin absorbs water and swells, the water-absorbent resin comes into contact with the outer peripheral surface of the core 52.

Here, as in the case of the first embodiment, since the refractive index of the water-absorbing resin that has absorbed water is larger than the refractive index of air, the absorbent resin that has absorbed water and the core 52 have a larger refractive index.
Is smaller than the refractive index difference between the core 52 and the air, or the refractive index of the absorbent resin that has absorbed water is larger than the refractive index of the core 52.

Therefore, light propagating through the core 52 leaks at the interface between the core 52 and the water-absorbing resin at the flooded portion. That is, when the water is detected in the water detecting optical fiber 50, the transmission loss of the optical fiber 50 increases.

According to the optical fiber 50 for detecting inundation of the second embodiment configured as described above, the optical fiber 50 for detecting inundation is disposed in a predetermined long area, and light is emitted from one end thereof. When light is incident by an element or the like, and by measuring the intensity or the like of the light emitted to the other end side by a light receiving element, if the transmission loss of the light by the optical fiber 50 is measured, the light in the long area can be measured. The effect of being able to detect inundation can be obtained.

It is also possible to know the degree of flooding based on the magnitude of the light transmission loss.

Further, by measuring the backscattered light of the light propagating in the core 52 and determining the relationship between the distance from one end of the fiber 50 and the light transmission loss, the point where the light transmission loss is drastically reduced can be determined. It can be obtained as an inundation point.

The optical fiber for detecting inundation of the second embodiment uses an absorbing layer 60 made of a water-absorbing resin in the form of powder, fibrous or non-woven fabric, and its outer periphery is made of foamed resin or net-like. Since it is covered with the protective layer 70 made of resin, water easily penetrates into the inside, and the reactivity of detecting water entry is excellent.

Further, since the protective layer 70 is covered around the absorption layer 60, it is possible to effectively prevent dust other than water from entering the inside.

Next, a cable according to a third embodiment of the present invention will be described.

As shown in FIGS. 6 and 7, the cable 100 includes a core 110, a protective tape layer 120, and an external protective layer 130.

The core section 110 includes four electric wires 112.
Is twisted together with the immersion detecting optical fiber 118 having the same configuration as that of the first or second embodiment. Further, a protective tape is spirally wound around the core portion 110 to form a protective tape layer 120. Further, a protective layer 130 made of resin is extrusion-coated on the protective tape layer 120 to form an external protective layer 130.

According to the cable 100 of the third embodiment configured as described above, water enters the core portion 110 from the external protective layer 130 through the tape protective layer 120 at any part of the entire area of the cable 100. Then, this can be detected. Further, by measuring the backscattered light as described above, it is also possible to obtain the inundation point. Therefore, it is possible to detect inundation over the entire area of the cable 100 and to repair only the inundated portion as necessary.

In the third embodiment, the electric wire 1
Instead of 12, the core portion 110 may be formed by twisting optical fibers or by appropriately combining an electric wire and an optical fiber and twisting them.

In each of the above embodiments, if a resin (such as a highly oil-absorbing resin) that absorbs oil or other liquid and swells is used in place of the water-absorbing resin, water other than water can be used. Can be detected.

[0046]

As described above, according to the optical fiber for liquid detection of the present invention, the liquid absorbent resin is provided around the core, and the liquid absorbent resin is disposed between the liquid absorbent resin and the outer peripheral surface of the core. Since a void is interposed in at least a part of the liquid crystal, air normally fills the void when no liquid enters. Therefore, in this state, the light propagating in the core is totally reflected at the interface between the core and the air.

However, if a liquid enters the area where the optical fiber is installed, the absorbent resin absorbs the liquid and swells to fill the above-mentioned gap. Here, since the refractive index of the absorbent resin that has absorbed the liquid is greater than the refractive index of air, the refractive index difference between the absorbent resin that has absorbed the liquid and the core is greater than the refractive index difference between the core and air. The refractive index of the absorbent resin that has absorbed the liquid is smaller than that of the core or the refractive index of the core.

Therefore, in a state where no liquid enters,
Light that has been totally reflected at the interface between the core and air also leaks outside at the interface between the absorbent resin that has absorbed the liquid and the core when the liquid has entered. Therefore, if the optical transmission loss of the optical fiber is measured, it is possible to detect the intrusion of liquid in a long area, for example, the intrusion of water into a communication cable.

According to the optical fiber for liquid detection of the present invention, the base material of the clad coated around the core includes:
Lumpy or granular liquid absorbing resin is mixed so as to be continuous from the outer peripheral surface side to the inner peripheral surface side of the clad, and the liquid absorbing resin has a refractive index lower than the refractive index of the core in a liquid non-absorbing state. Since the liquid has a refractive index and the refractive index increases in a liquid absorbing state, light propagating in the core is totally reflected at a boundary surface between the core and the liquid absorbing resin in a state where no liquid enters.

When the liquid enters, the liquid absorbing resin absorbs the liquid and its refractive index increases. Therefore, light leaks to the outside at the boundary surface between the core and the resin that has absorbed the liquid.Therefore, comparing the light transmission loss between when the liquid does not enter and when it enters, the liquid in the long area Can be detected.

According to another liquid detecting optical fiber of the present invention, the core is covered with a clad mixed with a lump or granular liquid absorbing resin, and a concave portion is formed on the inner peripheral surface of the clad. As a result, a void is interposed at least in part between the outer peripheral surface of the core and the inner peripheral surface of the clad, so that air normally fills the void when no liquid enters. Therefore, in this state, the light propagating in the core is totally reflected at the interface between the core and the air.

However, if a liquid enters the area where the optical fiber is installed, the absorbent resin absorbs the liquid and swells to fill the above-mentioned gap. Here, since the refractive index of the absorbent resin that has absorbed the liquid is greater than the refractive index of air, the refractive index difference between the absorbent resin that has absorbed the liquid and the core is greater than the refractive index difference between the core and air. The refractive index of the absorbent resin that has absorbed the liquid is smaller than that of the core or the refractive index of the core.

Therefore, in a state where no liquid enters,
Light that has been totally reflected at the interface between the core and air also leaks outside at the interface between the absorbent resin that has absorbed the liquid and the core when the liquid has entered. Therefore, by comparing the light transmission loss when the liquid does not penetrate and when it penetrates, it is possible to detect the liquid intrusion in a long region.

Further, according to another liquid detecting optical fiber of the present invention, the periphery of the core is covered with an absorbing layer made of a powdery, fibrous or non-woven liquid absorbing resin, and the periphery of the absorbing layer is formed. Is coated with a protective layer through which liquid can penetrate, so that at least a part of the outer peripheral surface of the core is not in contact with the liquid absorbing resin, and is filled with air. Therefore, in this state, the light propagating in the core is totally reflected at the interface between the core and the air.

However, if a liquid enters the area where the optical fiber is installed, the absorbent resin absorbs the liquid and swells to come into contact with the outer peripheral surface of the core. Here, since the refractive index of the absorbent resin that has absorbed the liquid is greater than the refractive index of air, the refractive index difference between the absorbent resin that has absorbed the liquid and the core is greater than the refractive index difference between the core and air. Small or
The refractive index of the absorbent resin that has absorbed the liquid is larger than the refractive index of the core.

Therefore, in a state where no liquid enters,
Light that has been totally reflected at the interface between the core and air also leaks outside at the interface between the absorbent resin that has absorbed the liquid and the core when the liquid has entered. Therefore, by comparing the light transmission loss when the liquid does not penetrate and when it penetrates, it is possible to detect the liquid intrusion in a long region.

According to the cable of the present invention, the above-described liquid detecting optical fiber is bundled together with at least one of an electric wire and an optical fiber.
A protective tape is wrapped around the cable, and a resin protective layer is coated around the protective tape.If liquid such as water enters the protective layer and the protective tape of the cable, it can be detected. It is possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical fiber for detecting inundation of a first embodiment according to the present invention.

FIG. 2 is a sectional view showing an optical fiber for detecting inundation according to the first embodiment;

FIG. 3 is a diagram for explaining the operation of the above-mentioned water immersion detecting optical fiber.

FIG. 4 is a perspective view showing an optical fiber for detecting inundation of a second embodiment according to the present invention.

FIG. 5 is a cross-sectional view showing the optical fiber for water intrusion detection in the above.

FIG. 6 is a perspective view showing a cable according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing the cable of the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Water-immersion detection optical fiber 12 Core 20 Clad 24 Water-absorbing resin 30 Void

Claims (6)

[Claims] 1. A liquid, wherein a liquid absorbing resin is disposed around a core, and a void is interposed at least in part between the liquid absorbing resin and the outer peripheral surface of the core. Optical fiber for detection. 2. A bulk or granular liquid absorbing resin is mixed into a base material of a clad coated around a core so as to be continuous from the outer peripheral surface side to the inner peripheral surface side of the clad. An optical fiber for liquid detection, wherein the reactive resin has a refractive index lower than the refractive index of the core in a liquid non-absorbing state, and increases in a liquid absorbing state. 3. A bulk or granular liquid-absorbent resin is mixed into a base material of the clad coated around the core so as to be continuous from the outer peripheral surface side to the inner peripheral surface side of the clad, and An optical fiber for liquid detection, wherein a concave portion is formed on an inner peripheral surface of a clad, and a gap is interposed at least partially between an outer peripheral surface of the core and an inner peripheral surface of the clad. 4. An absorbent layer made of a powdery, fibrous or non-woven liquid-absorbent resin is coated around a core, and a liquid-permeable protective layer is coated around the absorbent layer. An optical fiber for detecting a liquid, comprising: 5. The liquid absorbent resin according to claim 5, wherein said liquid absorbing resin is starch-
The optical fiber for liquid detection according to any one of claims 1 to 4, wherein an acrylic acid graft copolymer, a polyacrylate or a gel of a vinyl acetate acrylate copolymer is used. 6. The optical fiber for liquid detection according to claim 1, which is bundled with at least one of an electric wire and an optical fiber, a protective tape is wound around the bundle, and further, the periphery thereof. A cable characterized in that a resin protective layer is coated on the cable.