JP2596578B2 - Optical fiber immersion detection sensor - Google Patents

Description

The present invention relates to an optical fiber immersion detection sensor disposed inside, for example, a telecommunication cable or the like, and capable of accurately and quickly detecting the immersion accident of this kind of cable. About.

"Prior art and its problems" Generally, telecommunication cables such as power cables and communication cables are laid in transmission lines outside and inside the city and on the sea floor.

In such a cable, an alarm wire such as a bare wire, a paper insulated wire or a plastic insulated wire is wired along the longitudinal direction, and a cable that detects inundation by a partial short circuit of the alarm wire is used. Have been.

However, in the waterproof cable configured by arranging the alarm line, there is a problem that the flooded portion cannot be detected accurately and quickly because the above-described alarm line is used. In addition, there is a problem that the sensitivity of the alarm line for detecting inundation is low. Also, there is a problem that an alarm line using a metal conductor cannot be applied in a section where electromagnetic induction is present.

Also, in recent optical fiber cables, there is a problem that the alarm line itself cannot be used because the relay interval is long.

Under such circumstances, it has been desired to develop a waterlogging detection sensor that can be disposed inside the above-described telecommunication cable or the like.

[Means for Solving the Problems] The optical fiber immersion detection sensor according to the present invention covers a single-mode optical fiber with a water-absorbing tube, winds an expansion-suppressing string from above the water-absorbing tube, and covers the portion covered with the water-absorbing tube. The means for solving the problem is to form a water immersion sensor part, which is wound a plurality of times and fixed and has an initial bending loss of 0.01 to 1 dB, in at least one place of a single mode optical fiber serving as a waveguide.

[Operation] The optical fiber immersion detection sensor of the present invention has the following operation by the above configuration.

That is, in the event of a flood, the water absorbing tube absorbs the permeated water and expands its volume, whereby the bent portion of the optical fiber to which bending stress is applied in advance is further bent. Therefore, the increase in the transmission light loss due to the bending of the optical fiber is detected by measuring the reflected light such as the backscattered light of the light incident from the input end of the optical fiber, and the occurrence of the inundation accident and the occurrence position thereof are accurately and accurately detected. Can be detected quickly.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view showing an embodiment of the present invention, wherein reference numeral 1 denotes an optical fiber immersion detection sensor (hereinafter simply referred to as a sensor). This sensor 1 has an optical fiber 2
The water immersion sensor part 3 is formed in a part of. In the water immersion sensor section 3, a water absorbing tube 4 made of a water absorbing resin is attached to a part of the optical fiber 2, a string 5 is wound around the outer periphery of the water absorbing tube 4 at a constant pitch, and the attaching portion of the water absorbing tube 4 is further attached. It is configured to be fixed in a state of being wound several turns with a predetermined radius of curvature r. Although not shown, a plurality of immersion sensor units 3 are formed in the optical fiber 2 at appropriate intervals.

As the optical fiber 2, a single-mode optical fiber such as a quartz single-mode optical fiber, a multi-component single-mode optical fiber, or a plastics single-mode optical fiber is used. An optical fiber with a bare fiber coated with one or more layers of thermosetting silicone, urethane, UV-curable polymer, etc., or an optical fiber with this coated with nylon etc. is preferred. Used for

As the material of the water absorbing tube 4, a material whose volume becomes 5 times or more when absorbing water is used. Examples of suitable materials include polyvinyl chloride, polyethylene, EVA resin, and EVA resin.
Heat of EA resin, polyester resin, polyurethane, styrene-based thermoplastic elastomer (hereinafter abbreviated as TPE), olefin-based TPE, ester-based TPE, vinyl chloride-based TPE, amide-based TPE, diene-based TPE, ionomer-based TPE, etc. Polyacrylic acid-polyacrylic acid copolymer, polyvinyl alcohol-vinyl acetate copolymer, polyurethane, polyethylene oxide, starch graft copolymer, carboxymethyl cellulose (CMC) ) Are suitably used. Also, the thickness of the water absorbing tube 4 is
It is set appropriately in consideration of the water absorption capacity and the volume expansion coefficient of the water-absorbing resin.

The string 5 is made of a material that does not expand when immersed. For example, a string made of a synthetic resin such as polyester, a string made of a natural fiber such as cotton or silk, or a metal thread is used.

The radius of curvature r of the immersion sensor unit 3 is set so that the transmission loss (initial loss value) of the immersion sensor unit 3 is about 0.01 to 1 dB, and it is particularly preferable that the initial loss value is about 0.1 dB.

The sensor 1 is manufactured, for example, as follows. First, the water absorbing tube 4 is attached to a predetermined position of the optical fiber 2. As a method of mounting the water absorbing tube 4,
A method of forming the water-absorbent resin into a tube shape and inserting the tube into the optical fiber 2 or a method of applying a melt of the water-absorbent resin to a predetermined position of the optical fiber 2 so as to have a predetermined thickness is used. Next, the string 5 is wound around the outer periphery of the water absorbing tube 4. Next, the portion of the water absorbing tube 4 is
It is wound around several turns so that the transmission loss is about 0.1 dB, and is fixed by a method of applying an adhesive to a part in this state.

Further, the immersion sensor unit 3 is prepared as described above by using a single-mode optical fiber of a fixed size, and the single-mode optical fiber of the immersion sensor unit 3 is fusion-spliced to another single-mode optical fiber serving as a waveguide. For example, the sensor 1 can be connected in series with the sensor 1.

The sensor 1 configured as described above detects occurrence of a flood accident as follows. First, a flood accident occurs at one of the locations where the flood sensor unit 3 is installed, and this moisture permeates the water absorbing tube 4. By absorbing the permeated water, the water absorbing tube 4 undergoes volume expansion. On the other hand, in a portion where the string 5 wound around the outer periphery of the water absorbing tube 4 abuts, the expansion of the water absorbing tube 4 is suppressed. The portion 3 is deformed, and a portion having a radius of curvature smaller than a predetermined radius of curvature r occurs. In this portion, the loss of the transmission light transmitted through the optical fiber 2 increases, so that the loss of the transmission light increases. , The occurrence of a flood accident can be detected.

Next, an example of a flood detection system using the sensor 1 will be described with reference to FIG. Sensor 1 shown in this figure
Is constructed by providing a plurality of immersion sensor units 3 on an optical fiber 2. At the end of the sensor 1, a sensor 1
A water immersion detecting device 6 is connected to measure the time delay of the reflected light of the light incident on the inside and to measure the change in the received light level to detect the position where the optical fiber is bent.
The immersion detecting device 6 includes a light emitting unit 9 including a pulse generator 7 for inputting a light pulse from an input end of the optical fiber 2 and a light emitting element 8 such as an LD (laser diode) or an LED (light emitting diode); 2, a light detection unit 10 having a light emitting element such as an APD (avalanche photodiode) for receiving a reflected light pulse such as backscattered light, and a flow of a light pulse from the light emitting unit 9 and a reflected light pulse from the optical fiber 2. The optical directional coupler 11 controls the time delay of the reflected light pulse received by the light detection unit 10, and the display unit 13 displays the processing result. Things.

Next, a method of operating the inundation detection system having such a configuration will be described. First, one end of the sensor 1 is connected to the immersion detecting device 6, and then the other end of the sensor 1 is disposed all over the floor of a building or the like in which communication equipment is housed. This completes the flood detection system.

If, for example, a water intrusion accident occurs in the X area shown in this figure, water penetrates into the water infiltration sensor unit 3 disposed in the X area, and the water absorption tube 4 of the water infiltration sensor unit 3 absorbs and swells. Causes volume expansion. by this,
In the immersion sensor section 3 in the X section, the radius of curvature of the optical fiber 2 becomes smaller than the initial set value, and the transmission loss increases. The increase in loss due to the bending of the optical fiber 2 is detected by the immersion detecting device 6 based on a time delay of a reflected light pulse such as backscattered light returning to the input end of the optical fiber 2 and a change in light receiving level. And the inundation detection device 6
The calculation unit 12 analyzes the measurement data of the reflected light pulse to determine the distance from the input end of the optical fiber 2 to the position where the water intrusion occurs. Then, by displaying this data on the display unit 13, it is possible to detect a flood accident in the X area.

Next, in response to the occurrence of the inundation accident, immediately take countermeasures against the inundation accident in the area X.

In such an inundation detection system, at the position of the display unit 13 of the inundation detection device 6, an inundation accident in an area such as the X area where the inundation sensor unit 3 is provided in advance is accurately and promptly. It is possible to detect. The immersion detection system is not limited to the above example, and may have a configuration in which, for example, the sensor 1 is disposed in an electric communication cable together with another electric communication line or an optical fiber.

In this case, the sensor 1 is provided with a water-absorbing tube 4 that expands in volume when absorbing water to the optical fiber 2, winds a string 5 around the outer periphery of the water-absorbing tube 4, and further divides the portion of the water-absorbing tube 4 with a predetermined radius of curvature r. The immersion sensor section 3 having a winding configuration is formed at a plurality of locations of the optical fiber 2, and when the water penetrates into the immersion sensor section 3, the water absorption tube 4 is formed.
Causes volume expansion, while the string 5
Reduces the radius of curvature of the optical fiber 2 of the immersion sensor unit 3 from the initial set value by suppressing the expansion of the water absorption tube 4,
Since the increase in the transmission loss of the optical fiber 2 is used as the flood detection means, it is possible to lay the fiber over a longer distance as compared with the conventional flood detector using a metal conductor, and it is also possible to apply it in an area where electromagnetic induction exists. it can.

By the way, in a sensor that determines whether or not a water intrusion has occurred by increasing the loss of the optical fiber 2 as in this example, it is possible to determine the amount of increase in the loss of the optical fiber 2 at the time of detecting water intrusion so that the optical fiber 2 can be installed over a long distance. It is desirable that the size be as small as possible. Therefore, it is necessary that the amount of transmission loss increase due to the bending of the optical fiber can be controlled within a certain range. In general, the bending loss of a single-mode optical fiber is determined by the refractive index difference between the core and the clad, the core diameter, and the profile of the core. Therefore, in a single mode optical fiber, the controllability of transmission loss due to bending is poor. For example, if an optical fiber is pressed against a mandrel having a constant bending radius to cause bending, loss does not increase due to variations in fiber parameters. In some cases, the loss increases extremely. Therefore, by bending the optical fiber 2 in advance to a radius of curvature where the loss of the optical fiber 2 is likely to increase as in the above-described example, even if a single mode optical fiber is used, the transmission loss due to bending is reduced. Good controllability can be achieved.

The reason will be described with reference to FIG. FIG. 3 is a diagram for explaining an example of bending loss of a single mode optical fiber, where the horizontal axis is the bending radius (mm) of the optical fiber;
The vertical axis represents the bending loss (dB) on a logarithmic scale. The single mode optical fiber used had a mode field diameter of 10 μm, a cladding outer diameter of 125 μm, a refractive index difference (Δ) of 0.3%, and an effective cutoff wavelength (λce) of 1.15.
μm, and the measurement wavelength (λ) was 1.3 μm.

As is clear from this figure, the bending loss increases exponentially when the bending radius of the optical fiber is reduced. Further, in this figure, when it is estimated how much the bending loss changes with respect to a slight change in the bending radius of the horizontal axis, for example, the bending radius of the optical fiber is 17 mm, and the bending radius changes by ± 1 mm. If any, bending loss is ± 1
It shows a change of about 0 ^-3 dB / m, but the bending radius of the optical fiber is 1
If the bending radius changes by ± 1 mm at 0 mm, bending loss
It shows a change of about 1 dB / m. Therefore, in the case where a single mode optical fiber is used, a single mode optical fiber is provided with a bend so that the transmission loss is about 0.1 dB in advance, and the bend of the optical fiber is increased when water is absorbed. Even so, it is possible to sufficiently identify the increase in transmission loss.

Hereinafter, the working effects of the present invention will be clarified by showing examples.

(Example 1) Mode field diameter 10 μm, clad outer diameter 125 μm,
Thermosetting silicone (primary coating) diameter 400μm, nylon (secondary coating) diameter 0.9mm, refractive index difference 0.3%, effective cutoff wavelength 1.15μm, using a silica single-mode fiber core wire, thermoplastic for this optical fiber Attach a water absorbing tube with an outer diameter of 1.0 mm and a length of 500 mm made of a water absorbing resin made of a mixture of an elastomer and a polyacrylate based water absorbing material,
A plastic thread is wound around the outer circumference of the water-absorbing tube at a pitch of 50 mm.
A water immersion sensor portion was formed by winding a turn, and a sensor having the same configuration as that shown in FIG. 1 was prepared. In addition, the water-absorbing resin showed about 100-fold volume expansion after absorbing water. Also,
The initial loss value of this sensor was about 0.1 dB.

Next, the sensor was operated by immersing the sensor in water for 24 hours, and thereafter, a flooded portion was detected by a flooded water detecting device having the same configuration as that shown in FIG.
As a result, a loss increase of about 0.5 dB was detected at the position where the water immersion sensor was formed.

[Effects of the Invention] As described above, the optical fiber immersion detection sensor of the present invention covers a single-mode optical fiber with a water-absorbing tube on at least one location of the single-mode optical fiber serving as a waveguide. And a portion covered with a water-absorbing tube is wound and fixed a plurality of times to form a flood sensor having an initial bending loss of 0.01 to 1 dB.

This optical fiber flood detection sensor, in the event of a flood,
While the water absorption tube absorbs the water in the water sensor and the water absorption tube expands its volume, the expansion suppression string suppresses the volume expansion of the water absorption tube, causing the single mode optical fiber of the water sensor to bend further. To detect the increase in transmission light loss by measuring reflected light, such as backscattered light, of light incident from the input end of a single-mode optical fiber, and to accurately and quickly detect the occurrence of an inundation accident and its occurrence position. Can be.

In addition, since the water absorbing tube expands due to the penetration of moisture, causing the optical fiber to bend and increasing the transmission loss of the optical fiber, the water intrusion detection means is used. Long-distance laying is possible, and adaptation is possible even in sections where electromagnetic induction is present.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of the present invention, in which a perspective view of a sensor, FIG. 2 is a schematic configuration diagram for explaining an example of a flood detection system using the sensor of the present invention, and FIG. 6 is a graph for explaining an example of a relationship between a bending of an optical fiber and a transmission loss. 1 ... sensor, 2 ... optical fiber, 3 ... water sensor, 4 ... water absorption tube, 5 ... string.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroyuki Sawano 1440 Mutsuzaki, Sakura City, Chiba Prefecture Fujikura Electric Cable Co., Ltd. Sakura Plant (56) References JP-A-62-262805 (JP, A) 143237 (JP, U) Japanese Utility Model Showa 59-6756 (JP, U) Japanese Utility Model Showa 62-16673 (JP, Y2)

Claims (1)

(57) [Claims] A single-mode optical fiber is provided with a water-absorbing tube over at least one portion of the single-mode optical fiber, and an expansion-suppressing cord is wound over the water-absorbing tube to cover the single-mode optical fiber. An optical fiber immersion detection sensor, wherein an optical fiber portion is wound and fixed a plurality of times, and an immersion sensor portion is formed in advance so that an initial bending loss at this portion is 0.01 to 1 dB.