JPH0284603A - Sensor fiber - Google Patents

Abstract

PURPOSE:To allow the detection of a water infiltrating point by constituting a bar-shaped member adjacent to an optical fiber of a non-water-absorbent material and constituting wire-shaped members of a material having high water absorptive shrinkability. CONSTITUTION:The optical fiber 8 coated with a covering is fixed by bringing the fiber into tight contact with the non-water-absorbent bar-shaped member 9 in parallel therewith and spirally binding the fiber with the wire-shaped members 10 which shrink when the fiber absorbs water. Since the optical fiber 8 is not bent in this state, a propagation loss is not generated. On the other hand, the wire-shaped members 10 shrink to tighten the covering and the optical fiber 8 is bent to a wave shape when the water infiltrates this sensor fiber. Since the transmission loss is increased in this way, the point where the loss is generated is detected by detecting the increase with a backward scattering measuring machine, etc.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical fiber that detects the location of water intrusion or heating when water enters the optical cable or the temperature of the optical cable increases. .

[Prior art]

BACKGROUND OF THE INVENTION Optical transmission systems using optical fibers have become increasingly large in capacity, long distance, and highly reliable, and are now used everywhere, including not only terrestrial relay transmission but also submarine relay transmission.

By the way, when water enters an optical fiber cable or when the temperature of the optical cable increases, the optical loss of the optical fiber increases. In particular, water accelerates defect growth on the optical fiber surface, thereby shortening the lifetime of the optical fiber.

Therefore, it is necessary to prevent water intrusion and heating in the optical fiber cable as much as possible, but if the cable is damaged, it is necessary to immediately detect the location of water ingress and heating. There is a device that uses the swelling of water-absorbing polymers to detect water intrusion inside a cable.

Figure 7 shows the first conventional technology, which is a sensor fiber that utilizes the swelling of a water-absorbing polymer.
-OPTIC5ENSORFORDETECTING
WATERPENETORATION INTO0PT
ICALP+B[? E CABLES), Electronics Letters (ELECTRON) C3LETTE
R8), 10th h.

November 1983 Vol, 19No.
, 23, pp. 980-982), this sensor fiber has a V-groove structure (Periodlc V-groovestr.
(2) are arranged in parallel (or spirally) within a cable 4 via a multimode optical fiber 3, and a non-water-absorbing tape (or string) 5 is wrapped around it (Fig. 7). (a)). When water enters the cable 4, the water-absorbing swelling material 1 expands within the cable 4 and presses the multimode optical fiber 3 into the V-groove structure 2 (FIG. 7(b)). Therefore, the multimode optical fiber 3 is bent into a wave shape, increasing transmission loss. A backscatter measuring device detects the loss points, and the flooded areas are detected.

Figure 8 shows the second prior art, which shows a sensor fiber that utilizes the swelling of another water-absorbing polymer (optical fiber cable with submersion sensor fiber).
r cable vlth submersion 5
ensor['1bcr), 36th, International Wire and Cable Symposium Proceedings (International Wl, r
e & Cable Symposium! 1P
roceedings), 1987, I) p.
284-285). This sensor fiber is made by spirally winding a standard multimode optical fiber 3 around a water-absorbing swelling material 1 coated on an FRP tensile calot 6.
A string 7 having a high Young's modulus and low water-absorbing swelling property is wound spirally over the multi-mode optical fiber 3' so as to intersect with the multi-mode optical fiber 3'. When water enters the sensor fiber, the water-absorbing swelling material 1 expands and presses the multimode optical fiber 3 against the string 7. This bends the multimode optical fiber 3 and increases transmission loss. A backscatter measuring device detects the loss points, and the flooded areas are detected.

In addition, as a sensor fiber for measuring the temperature distribution in the optical axis direction, there is a sensor fiber that uses Lehre scattering of an optical fiber (Multi-point measurement technology using optical fiber, sensor technology, 19
June 1988 issue (Vol, 8No, 7, pp, 3l-34
).

[Problem to be solved by the invention]

However, in the first prior art, tension is applied to the sensor fiber itself when it is actually housed in a cable. This tension is applied to the water-absorbing swelling substance, inhibiting its swelling ability.
The drawback was that it could not adequately detect flooding.

Further, the second conventional technique requires a step of applying a water-absorbing swelling substance to the FRP tensile carrot. Furthermore, there is a drawback in that it is difficult to easily adjust the increase in loss per unit length of the sensor when it is submerged in water.

In addition, sensor fibers that measure temperature distribution using Lehre scattering in optical fibers detect temperature differences of several hundred degrees Celsius, which is high temperature, and it is difficult to measure temperature changes at low temperatures of 100 degrees Celsius or less. There was a drawback.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a sensor fiber that has high precision and reliability and is easy to manufacture.

[Means to solve the problem]

In order to achieve the above object, the sensor fiber according to the present invention includes an optical fiber covered with a coating, a rod-shaped member that has a higher Young's modulus than the coating and is adjacent to the optical fiber, and the rod-shaped member and the optical fiber are closely connected. It is configured to include a linear member that is spirally wound while being left in place.

In this case, the rod-shaped member is made of a material that is non-water-absorbing (or has a low thermal deformation rate), and the linear member is made of a material that is water-absorbing and shrinkable (heat-shrinkable).
Constructed of high-quality materials, it detects flooded areas (or heated areas).

In addition, the rod-shaped member is made of a material with high water-absorbing expansion property (or coefficient of thermal expansion), and the linear member is made of a material with non-water-absorbing property (or low coefficient of thermal deformation). Detect.

In this case, the rod-like member having a high coefficient of thermal expansion may be constructed of a non-water-absorbing pipe in which gas is intermittently filled in the axial direction.

[Effect]

Since the present invention is configured as described above, it is possible to reliably transmit physical changes (contraction, expansion, etc.) of a rod-like member or a wire-like member due to water (or heat) to an optical fiber with a simple structure. Can be done. Therefore, a sensor fiber with high precision and reliability can be obtained.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sensor fiber according to the present invention will be described below with reference to the accompanying drawings. In addition, in the description, the same reference numerals are used for the same elements, and redundant description will be omitted.

FIG. 1 is a perspective view showing an embodiment of a sensor fiber according to the present invention. This invention basically includes an optical fiber covered with a coating, a rod-like member, and a wire-like member. The bar member has a higher Young's modulus than the coating and is adjacent to the optical fiber. Moreover, the linear member is spirally wound with these rod-shaped members and the optical fiber in close contact with each other.

In FIG. 5A, a non-water-absorbing rod-like member 9 is tightly attached in parallel to an optical fiber 8 covered with a coating, and the optical fiber 8 is spirally wound with a linear member 10 having high water-absorbing and contracting properties.

In FIG. 4(b), a rod-shaped member 11 having a low thermal deformation rate is tightly attached in parallel to an optical fiber 8 covered with a coating, and the fiber is spirally wound with a linear member 12 having a high heat-shrinkability.

In the same figure (C), a non-water-absorbing rod-like member 11 with a small thermal deformation rate is closely attached in parallel to an optical fiber 8 covered with a coating, and these are connected to a linear member 10 with a high water-absorbing shrinkability and a non-water-absorbing rod-like member 11 with a high water-absorbing shrinkage property The wire members 12 are wound alternately in a spiral shape. In this case, two linear members (linear member 1 with high water absorption and contraction properties)
Instead of the linear member 12) having high water absorption shrinkability and high heat shrinkability, a single linear member having high water absorption shrinkability and high heat shrinkability may be used.

In the same figure (d), a non-water-absorbing rod-like member 13 with a high coefficient of thermal expansion is tightly attached in parallel to an optical fiber 8 covered with a coating, and a linear member 10 with a high water-absorbing shrinkage property and a low coefficient of thermal deformation is spirally attached. It is rolled. The rod-shaped member 13 having a high coefficient of thermal expansion is constituted by a non-water-absorbing pipe in which gas such as air is intermittently filled in the axial direction. In this case, the same effect can be obtained by using a material with a low coefficient of thermal deformation and high coefficient of water absorption and fat expansion for the rod-like member, and using a material with high heat-shrinkability and non-water-absorbing property for the linear member.

Figure (e) shows a non-water-absorbing coating with a Young's modulus higher than that of the coating applied to the optical fiber and a small thermal convexity between the optical fiber 8 and the rod-shaped member 13 in the sensor fiber of Figure (d). A rod-like member 14 is interposed between these members, and these are spirally wound with a linear member 10 having high water absorption and contraction properties.

In the same figure (f), the optical fiber 8 and the rod-like member 13 are wound around the non-water-absorbing rod-like member 14 as a central axis, and a linear member 10 with high water-absorbing and contracting properties is wound so as to fix them. It is spirally wound.

In FIG. 3(g), the non-water-absorbing rod-like member 14 in the sensor fiber shown in FIG. 4(e) is formed into a rectangular shape with a circular shape t14a provided on one side. A rod-shaped member 13 is housed in this circular groove 14a, and a linear member 10 having high water absorption and contraction properties is wound spirally so as to fix the rod-shaped member 13. With this structure, the depth of the groove can be adjusted so as to apply an external force to the optical fiber above a certain temperature.

Next, the operation of the sensor fiber according to the above embodiment will be explained. Since the above sensor fiber is basically the same in function as the sensor fiber shown in Figures (a) and (e), the function of the sensor fiber in Figures (a) and (e) will be explained below. .

FIG. 2 is a process diagram showing the operation of the sensor fiber of FIG. 1(a). The optical fiber 8 covered with a coating is tightly attached in parallel with a non-water-absorbing rod-shaped member 9, and is fixed by being spirally wound with a linear member 10 that contracts when water is absorbed (see figure (a)
)). In this state, the optical fiber 8 is not bent, so no transmission loss occurs. However, when water enters this sensor fiber, the linear member 10 contracts and the coating is tightened, causing the optical fiber 8 to bend into a wavy shape (as shown in the figure).
b)). In this case, since transmission loss increases, the location where the loss occurs can be detected using a backscattering measurement device or the like.

FIG. 3 is a process diagram showing the operation of the sensor fiber shown in FIG. 1(e). A non-water-absorbing rod-like member 14, which has a higher Young's modulus and a lower thermal deformation rate than the coating applied to the optical fiber, is placed between the tip fiber 8 covered with the coating and the rod-shaped member 13. Linear member 1o with high properties
is spirally wound (Fig. 3(a)). When heat is applied to this sensor fiber, the air layers 13a, 13a, . b)). In this case, the transmission loss increases, so
The location where the loss occurs can be detected using a backscatter measuring device or the like.

Next, an experimental system and experimental results for confirming the effects of the present invention will be explained based on FIGS. 4 to 6. FIG. 4 shows the relationship between time after flooding and transmission loss. The optical fiber 8 covered with a coating is tightly attached in parallel with a non-water-absorbing rod-like member 9, and is fixed by being wound helically with a linear member 10 that contracts when water is absorbed (FIG. 4(a)). The optical fiber 8 is a graded index fiber with a cladding diameter of 37,150 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 1%, coated with an ultraviolet curing resin (Young's modulus of 50 kg/mm2) and a finished diameter of 0.
It is applied at 25mm. This optical fiber 8 has an outer diameter of 0
, 4 m m s Young's modulus of 5300 kg/mm2 F
It was placed in parallel with an RPO rad (rod-shaped member) 9 and wound spirally with a water-absorbing and contractible linear member 10 at a pitch of 50 mm to create a 2 m sample. This sample was immersed in tap water at 20° C., and an increase in transmission loss was measured using an LED light source with a wavelength of 1.3 μm. According to this experiment,
It increased by 0.17 dB in about 20 seconds, making it possible to detect water intrusion. Note that when the coating was applied with a diameter of 0.4 mm, an increase in loss of 0°3 dB could be detected.

FIG. 5 shows the increase in transmission loss with respect to temperature changes. This optical fiber 8 includes a graded index fiber with a core diameter of 50 μm, a cladding diameter of 125 μm, a relative refractive index difference of 1%, and an ultraviolet curing resin (Young's modulus of 50 k).
g/mm2) with a finished diameter of 0.25 mm. The optical fiber 8 covered with the coating has an outer diameter of 0 with a small thermal deformation rate.
．． 4mm, FRP with Young's modulus of 5300kg/mm2.

A heat-shrinkable tube (linear member) 12, which shrinks when heated, is wound and fixed in a spiral manner (FIG. 5(a)).

This experiment was conducted for 2 hours per step, and at a temperature of 20°C-100°C.
The temperature was changed to −20° C., and an increase in transmission loss was measured using an LED light source with a wavelength of 1.3 μm. In this sensor fiber, the transmission loss suddenly increased when the temperature reached 80°C. In this case, since heat shrink tubing was used, losses did not decrease as the temperature decreased.

FIG. 6 shows the increase in transmission loss with respect to temperature changes. This optical fiber 8 includes a graded index fiber with a core diameter of 50 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 1%, and an ultraviolet curing resin (Young's modulus of 50
kg/mm2) with a finished diameter of 0.25 mm. Optical fiber 8 covered with coating and rod-shaped member 13
An FRP rod (rod-shaped member) with an outer diameter of 0.4 mm and a Young's modulus of 5300 kg/mm2 has a higher Young's modulus and a lower thermal deformation rate than the coating applied to the optical fiber.
14, and Kevlar thread (linear member) 10 having high water absorption and contraction properties is spirally wound at a pitch of 50 mm. This experiment was conducted for 2 hours per step and at 20°C-10°C.
The temperature was changed from 0°C to 20°C, and the increase in transmission loss was measured using an LED light source with a wavelength of 1.3 μm. The transmission loss increased by about 0.2 dB at 100°C. The transmission loss of this sensor fiber also decreased as the temperature decreased.

〔Effect of the invention〕

Since this invention is configured as explained above,
With a simple structure, it is possible to detect flooded areas and heated areas.

Further, since the combination of the rod-shaped member and the linear member allows the optical fiber to be reliably bent, the accuracy and reliability of the sensor can be improved.

In this case, by changing the Young's modulus of the optical fiber coating, the coating diameter, and the helical pitch of the linear member, it is possible to control the increase in transmission loss per unit length during immersion in water or heating.

In particular, when used in combination with a backscattering measuring device, it is possible to detect flooded locations and heated locations within the cable in the optical axis direction, which is effective for track maintenance.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the sensor fiber according to the present invention, Figs. 2 and 3 are process diagrams showing its operation, and Fig. 4 shows the relationship between time after submergence and transmission loss. FIGS. 5 and 6 are explanatory diagrams of experimental results showing the relationship; FIGS. 5 and 6 are explanatory diagrams of experimental results showing an increase in transmission loss with respect to temperature changes; FIG. 7 is a cross-section showing the sensor fiber according to the first prior art. figure,
FIG. 8 is a perspective view showing a sensor fiber according to the second prior art. 1... Water-absorbing swelling material 2... V-shaped groove structure 3... Multimode optical fiber 4... Cable 5... Tape 6... FRP tensile culotte 7... String 8... ...Optical fiber 9, 1. 13, 4... Rod-shaped member 10, 2... Linear member

Claims (1)

[Claims] 1. An optical fiber covered with a coating, a rod-shaped member having a higher Young's modulus than the coating and adjacent to the optical fiber, and a spirally formed optical fiber with the rod-shaped member and the optical fiber in close contact with each other. 1. A sensor fiber comprising a wound linear member, wherein the rod-shaped member is made of a non-water-absorbing material, and the linear member is made of a material with high water-absorbing and contracting properties. 2. An optical fiber covered with a coating, a rod-shaped member that has a Young's modulus higher than the coating and is adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. A sensor fiber comprising: the rod-shaped member being made of a material with a low thermal deformation rate, and the linear member being made of a material with high heat-shrinkability. 3. An optical fiber covered with a coating, a rod-shaped member that has a Young's modulus higher than the coating and is adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. A sensor fiber comprising: the rod-shaped member made of a non-water-absorbing material with a low thermal deformation rate, and the linear member made of a material with high water-absorbing shrinkability and high heat-shrinkability. 4. An optical fiber covered with a coating, a rod-shaped member having a Young's modulus higher than that of the coating and adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. A sensor fiber comprising: the rod-shaped member being made of a material with high water-absorbing and expanding properties; and the linear member being made of a non-water-absorbing material. 5. An optical fiber covered with a coating, a rod-shaped member having a Young's modulus higher than that of the coating and adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. A sensor fiber comprising: the rod-shaped member made of a material with a high coefficient of thermal expansion, and the linear member made of a material with a low coefficient of thermal deformation. 6. An optical fiber covered with a coating, a rod-shaped member that has a Young's modulus higher than the coating and is adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. The sensor fiber is characterized in that the rod-shaped member is made of a material with high water-absorbing expansion property and low thermal deformation rate, and the linear member is made of a non-water-absorbing material with high heat-shrinkability. 7. An optical fiber covered with a coating, a rod-shaped member that has a higher Young's modulus than the coating and is adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. The sensor fiber is characterized in that the rod-like member is made of a non-water-absorbing material with a high coefficient of thermal expansion, and the linear member is made of a material with a high water-absorbing shrinkage property and a low coefficient of thermal deformation. 8. An optical fiber covered with a coating, a rod-shaped member that has a higher Young's modulus than the coating and is adjacent to the optical fiber, and a linear member that is spirally wound while keeping the rod-shaped member and the optical fiber in close contact with each other. characterized in that the rod-shaped member is composed of a non-water-absorbing pipe in which gas is intermittently filled in the axial direction, and the linear member is composed of a material that has high water-absorbing shrinkage and a low thermal deformation rate. sensor fiber.