JPH0599783A - Water entrance detection method and system device of optical fiber - Google Patents

Abstract

PURPOSE:To obtain a water entrance detection method and system device which can detect presence or absence of water entrance at a number of water entrance detection points with one optical fiber for detecting water entrance without requiring any special consideration in terms of operation. CONSTITUTION:Optical fiber parts 8 and 8' with a water-absorption inflation material 3 where the birefringence of an optical fiber 1 is changed by operating an inflation pressure absorbing water are placed at least one required water entrance detection point. A light pulse is transmitted repeatedly from a pulse light source 9 which is placed at one edge of the optical fiber 1 using light pulse testers a and b and at the same time any polarization constituent out of the reflection light is received selectively and birefringence change at the optical fiber parts 8 and 8' at a required position is detected by measuring change with time at a rear-scattering waveform from the optical fiber 1 which is away from a required water entrance detection point by a data-processing part, thus presence or absence of water entrance at the water entrance detection point to be observed is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting water ingress in an optical fiber facility and a system device used directly for implementing the method.

[0002]

2. Description of the Related Art In recent years, in order to improve the maintainability of optical fiber equipment,
The degassing of optical fiber cables is being promoted. In order to guarantee the long-term reliability of a non-gas optical fiber cable, that is, an optical fiber cable in which gas is not sealed in the cable, it is necessary to measure the amount of strain, which is a factor of deterioration of the optical fiber, and detect water immersion. In particular, at the connection point of the optical fiber cable, since bending strain is applied to the optical fiber for the sake of accommodating the extra length, deterioration due to water immersion is significant, and water immersion detection is indispensable. Conventionally, such a method of detecting water immersion has been performed by bending the optical fiber with a sensor using a water-swelling material to cause an increase in loss and detecting this with an optical pulse tester (Kasahara et al., 1990 IEICE Spring National Convention, B-878).

A conventional technique is shown in FIGS. FIG. 7 is a diagram showing a conventional sensor for detecting inundation using a water-absorptive expansive material, FIG. 8 is a diagram showing a conventional intrusion detection system device using the intrusion detection sensor of FIG. 7, and FIG. 9 is a diagram of FIG. It is a graph which shows the measurement result by a system unit. In the figure, A is a conventional water immersion detection sensor, α is a conventional water immersion detection system device using the sensor A, 1 is a water immersion detection optical fiber, 2,
2'is a convex pressing guide and a concave receiving guide for bending the optical fiber 1, 3 is a water-swellable material, 4, 5 are guides 2, 2'and a lid and a case for housing the water-swellable material 3, 6
Is an optical pulse tester, and 7 is a data processing unit.

FIG. 7 (a) is a view showing a state before water absorption of the water-swellable expansive material 3 before water immersion, and the optical fiber 1 is attached so as not to be bent. FIG. 7B is a diagram showing a state when the sensor A is flooded, and the water-absorptive expandable material 3 absorbs water and expands, whereby the optical fiber 1 is recessed by the convex pressing guide 2 and the concave receiving guide 2 ′. It is pressed against and bent, and a loss increase of about 2 dB or more occurs. Figure 8
Conventional Infiltration Detection System Device α Using the Sensor A
FIG. 4 is a diagram showing the above, in which one end of the water immersion detection optical fiber 1 to which a plurality of sensors A are attached is connected to an optical pulse tester 6.

The optical pulse tester 6 sends an optical pulse to the optical fiber to be measured, detects the backscattered light and Fresnel reflected light generated thereby, and detects the optical fiber 1 to be measured.
For detecting the loss distribution and the position of the break point of the water.
Used to detect changes in light loss at the installation point of the. FIG. 9 is a graph showing the measurement results by the system α in FIG. 8, where L1 shows the characteristics before water immersion and L2 shows the characteristics after water immersion, showing that the loss of the optical fiber 1 for water immersion detection changes due to water immersion. There is.

[0006]

However, the conventional water immersion detection system device α has the following drawbacks. First, in the sensor A for detecting water immersion, since it is necessary to add a predetermined bend to the optical fiber 1, it is necessary to secure the slack of the optical fiber 1 necessary for bending before and after the sensor A. Was very difficult. Secondly, there is a problem that the number of sensors A that can be installed in one optical fiber 1 for water detection is limited.

That is, since the presence or absence of water intrusion is detected by the increase in loss of the water inundation detecting optical fiber 1, when water is simultaneously infiltrated into a plurality of sensors A, the loss of the water inundation detecting optical fiber A is finally detected by the optical pulse tester 6. This is because the dynamic range (maximum measurable loss) of is exceeded and the state at a long distance can no longer be detected. In this regard, the present invention eliminates the drawbacks of the conventional sensor for detecting water immersion, does not require special work considerations, and detects the presence or absence of water leakage at a large number of water detection points with one optical fiber for water detection. An object of the present invention is to provide a detectable inundation detection method and its system device.

[0008]

The solution to the above-mentioned problems can be achieved by incorporating the following novel characteristic methods and constituent means of the present invention. That is, the first feature of the method of the present invention is to dispose an optical fiber component equipped with a means for absorbing water to change the birefringence of the optical fiber at at least one required inundation detection point, and one end of the optical fiber. The optical pulse is repeatedly transmitted from the light source installed in the light source and any polarized component of the reflected light is selectively received, and the temporal change in the backscattering waveform from the optical fiber distant from the required immersion detection point is temporally changed. Is detected to detect the change in birefringence in the optical fiber component at a required position, and to detect the presence or absence of water immersion at the water immersion detection point.

The second feature of the method of the present invention is the method for detecting water immersion in an optical fiber according to the first feature, wherein an optical pulse repeatedly sent from a light source installed at one end of the optical fiber is made into an arbitrary polarization state. Is.

The first feature of the device of the present invention is at least one.
An optical fiber wired up to two required inundation detection points, an optical fiber component having means for changing the birefringence of the optical fiber by absorbing water at the inundation detection point, and connected to one end of the optical fiber, An optical pulse tester that repeatedly transmits an optical pulse to one end and selectively receives any polarized component of the reflected light, and the time in the backscattering waveform from the optical fiber far from the water immersion detection point of interest. And a data processing unit that detects the presence or absence of water immersion at the detection point of interest by measuring a dynamic change, detects a birefringence change in the optical fiber component of interest, and detects the presence or absence of water intrusion.

The second feature of the device of the present invention is, in the first feature, an optical fiber flooding detection system device in which an optical pulse repeatedly transmitted from one end of the optical fiber is transmitted in an arbitrary polarization state.

A third feature of the device of the present invention is that the optical fiber component according to the first or second feature of the device is arranged around the optical fiber with a water-absorptive material whose volume expands by absorbing water. Then, when the optical fiber is flooded, the water-swellable expansive material absorbs water to cause lateral pressure on the optical fiber,
This is an optical fiber water immersion detection system device that can add bending or twisting.

[0013]

In the present invention, since the above-mentioned method and means are taken, the polarization state of the light pulse repeatedly transmitted from one end of the optical fiber and the backscattered light generated thereby is
It changes due to birefringence generated inside the optical fiber during transmission through the optical fiber. Therefore, by measuring only a specific polarization component when receiving the backscattered light, it is possible to detect a change in the polarization state inside the optical fiber, and thus a change in birefringence.

On the other hand, if the birefringence changes at an arbitrary point of the optical fiber due to water immersion, all the polarization states far from the arbitrary point change. Therefore, it is necessary to detect whether there is a change in this polarization state with time. Thus, the change in the birefringence of the optical fiber, that is, the water immersion at the water immersion detection point is detected.
In addition, the polarization state of the light pulse repeatedly sent from one end of the optical fiber can be set arbitrarily, so the relationship between the polarization states of the incident light and the backscattered light can be measured more accurately, and changes in the polarization state caused by flooding can be detected. can do.

Further, the data processing means accurately measures the change with time in the polarization state of the backscattered light, and thereby accurately detects the inundation at the inundation detection point.
Further, since the polarization state of the light pulse repeatedly transmitted from one end of the optical fiber can be arbitrarily set, the relation between the polarization states of the incident light and the backscattered light can be measured more accurately, and the polarization state of the backscattered light can be further measured by the data processing means. The change over time with respect to is accurately measured, thereby accurately detecting the inundation at the inundation detection point. Further, a water-absorbing expansive material is placed around the optical fiber, and when water is immersed around the optical fiber, the expansion of the water-absorbing expansive material causes lateral pressure, bending, or twisting to the optical fiber to cause birefringence of the optical fiber. It is possible to change.

[0016]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a system device according to this embodiment, and FIG.
(A) and (b) are graphs showing the distribution of the backscattered light of each optical fiber in the case where the polarization selecting part is not used and the case where the polarization selecting part is provided, and FIG. FIG. 4 is a graph showing changes, FIG. 4 is a diagram showing an example of an optical fiber component for detecting water immersion using a water-swellable material, and FIG. 5 is a diagram showing another example of the optical fiber component for detecting water immersion. In the figure, β is the water immersion detection system device of this embodiment, a is an optical pulse tester, 8 and 8 ′ are optical fiber components for water immersion detection applied to this embodiment, 9 is a pulse light source, and 10 is a light output / input unit. 1
Reference numeral 1 is a polarization selecting unit, and 12 is a light receiving unit. The same members as those in the conventional example are designated by the same reference numerals.

FIG. 4 is a diagram showing an optical fiber component 8 as an example in the present embodiment. (A) is a perspective view of the entire optical fiber component 8 and (b) is a line IVb-IVb in (a). FIG. The case 13 is provided with a hole 14 for guiding water inside and a pressing plate 16 attached to the lower surface of the water-absorbing expansive material 3 attached to the convex top surface of the lid 15. When flooded,
Water permeates the inside of the optical fiber component 8 through the hole 14,
It is absorbed by the water-swellable material 3. As a result, the water-absorptive material 3 expands, and lateral pressure is applied to the optical fiber 1 by the case 13 and the pressing plate 16 to change the polarization state of the optical fiber 1.

Further, if a hydrophilic treatment such as coating a hydrophilic material such as protein, starch, agar, gelatin or the like is applied to the inside of the hole 14 and the case 13, water can be more surely invaded. Further, FIG. 4 showing the optical fiber component 8 in the present embodiment shows the case where the inner surface of the case 13 and the surface of the pressing plate 16 are flat, but it is not necessary that both surfaces are flat surfaces, and curved surfaces are possible. There is no problem even if there is. In this case, since lateral pressure and bending are applied to the optical fiber 1, a larger change in the polarization state occurs in the optical fiber 1 and it becomes easier to detect water immersion.

5A and 5B are views showing an optical fiber component 8'as another example of the present embodiment. FIG. 5A is a perspective view with the lid 15 and the case 13 removed, and FIG. 'Is a Vb-Vb line sectional view before water absorption, and (c) is a Vb-Vb line sectional view after water absorption. The optical fiber component 8'in the present embodiment applies a twist to the optical fiber 1. Reference numeral 17 denotes an optical fiber twisting portion, and the optical fiber twisting portion 17 and the optical fiber 1 are fixed.

Due to the dimensional change of the water-swellable expansive material 3 due to water absorption, the optical fiber twisting portion 17 rotates and twists the optical fiber 1 as shown in the sectional views (b) and (c). Therefore, the polarization state of the optical fiber 1 changes, and the same effect as the optical fiber component 8 is produced. Also, FIG.
Then, the optical fiber 1 is fixed to the rotation center of the optical fiber twisting portion 17, but the optical fiber 1 may be arranged around the optical fiber twisting portion 17. With the structure in which the optical fiber 1 is twisted due to the expansion change of the water-absorbent expansive material 3 at the time of absorbing water, a change in the polarization state occurs and it becomes possible to detect water immersion.

The specification of this embodiment is such a concrete embodiment, and its operation will be described with reference to FIG. The optical fiber component 8 applies a lateral pressure to the optical fiber 1 when it is flooded, and the optical fiber component 8 ′ applies a twist to the optical fiber 1 when it is flooded. The pulsed substantially linearly polarized light emitted from the pulse light source 9 is incident on the water detection optical fiber 1 via the light output / input unit 10, and the backscattered light from the optical fiber 1 is the light output / input unit. 1
It is guided to the polarization selection unit 11 by 0. The polarization selection unit 1
1 transmits only an arbitrary polarized component of the backscattered light,
The transmitted light is received by the light receiving unit 12 and the amount of light is measured. The data processing unit 7 measures whether or not there is a change with time in the backscattered light in the optical fiber 1 behind each of the optical fiber components 8 and 8 ', and detects the birefringence change of the optical fiber 1 from the presence or absence of the change. The presence or absence of inundation at each inundation detection point is detected.

Next, the principle of the present invention will be described with reference to FIGS. FIG. 2A is a graph showing the backscattered light distribution of the optical fiber 1 in the case of using the normal optical pulse tester 6 that does not include the polarization selection unit 11 in FIG. As is apparent from this figure, the intensity of the backscattered light monotonically decreases in proportion to the length of the optical fiber 1. On the other hand, in the case of the optical pulse tester a including the polarization selecting unit 11, the result of measuring the backscattered light distribution of the optical fiber 1 is shown in FIG.
It shows in (b). In this case, as in the case of FIG. 2A, the intensity of the backscattered light decreases in proportion to the length of the optical fiber 1, but a large fluctuation is recognized instead of a monotonous decrease.

The cause is that the optical fiber 1 is locally subjected to a disturbance such as bending or twisting, or the polarization direction of the light transmitted through the inside of the optical fiber 1 changes due to the local dimensional nonuniformity. Due to. That is, when the polarization selection unit 11 that transmits only a specific polarization direction is used,
A large amount of light is measured in the case of backscattered light whose polarization direction matches that of the polarization selection unit 11, but only a small amount of light is measured in the case of orthogonal backscattered light. Therefore, fluctuations in the amount of backscattered light are observed due to the difference in length of the optical fiber 1, and the backscattered light distribution shown in FIG. 2B is obtained.

In the present embodiment, the optical fiber parts 8 and 8'apply a lateral pressure to the optical fiber 1 for detecting water immersion from the surroundings when the water is inundated to change the polarization direction of the light transmitted inside. Therefore, as shown in FIG. 3, in the backscattered light distribution of the optical fiber 1 farther from the optical fiber components 8 and 8 ′,
A change occurs before and after the inundation, and the presence or absence of the inundation can be detected by detecting the presence or absence of the change. As described above, the present embodiment does not require the increase in loss, which has been conventionally used, and thus has an advantage of being able to detect water immersion even in a long optical line.

Although the above description assumes the use of the pulsed light source 9 (for example, a laser diode) having the characteristic of substantially linearly polarized light, this is not always the case in reality. For example, when a non-polarized high-power light source such as a super luminescent diode is used, the incident light to the optical fiber 1 for detecting water immersion is non-polarized, and therefore the backscattered light from each part of the optical fiber 1 is unpolarized. Also becomes non-polarized, and the polarization state of the optical fiber 1 cannot be measured even if the polarization selector 11 is used. Even in such a case, the case where the change of the polarization state due to the water immersion can be detected will be described below.

(Second Embodiment) A second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is an overall configuration diagram of the system of this embodiment. In the figure, γ is the infiltration detection system device of this embodiment,
Reference numeral b is an optical pulse tester, and 18 is a polarizer. The polarizer 18 transmits only an arbitrary linearly polarized light component of the output of the pulse light source 9 in the non-polarized state. Therefore, it is possible to detect the change in the polarization state due to the water immersion, as in the first embodiment, which assumes that a linearly polarized light source is used.

[0027]

As described above, according to the present invention, an optical fiber component having means for changing the birefringence of an optical fiber by absorbing water is arranged at at least one of the water immersion detection points, and one end of the optical fiber is provided. While repeatedly sending an optical pulse, selectively receive any polarized component of the reflected light, and measure the temporal change in the backscattering waveform from the optical fiber far from the inundation detection point of interest,
By detecting the birefringence change in the optical fiber component of interest and detecting the presence or absence of water intrusion at the water intrusion detection point of interest, compared with the conventional detection method using a sensor using water-absorbing expansive material, In addition, since there is no increase in optical line loss or fluctuations in reflection after flooding, one optical fiber for flooding detection can detect the presence or absence of flooding at many flooding detection points.

Further, an optical fiber component having a means for changing the birefringence of the optical fiber by absorbing water is arranged at at least one of the water immersion detection points, and an optical pulse having an arbitrary polarization state is repeated from one end of the optical fiber. While sending out, it selectively receives any polarized component of the reflected light, measures the temporal change in the backscattering waveform from the optical fiber far from the inundation detection point of interest, and Since the change in birefringence is detected to detect the presence / absence of water intrusion at a water intrusion detection point of interest, it is possible to detect water intrusion accurately regardless of the type of pulse light source.

Further, it is possible to process the backscattered light information over time by the data processing unit and provide an accurate inundation detection system device. At the same time, it is possible to realize an economical inundation detection system device that can use an arbitrary pulse light source. Further, since the water absorbing expansive material whose volume expands by absorbing water is arranged around the optical fiber, the invading water is transmitted to the water absorbing expansive material, and it is possible to provide an optical fiber component capable of reliably detecting water infiltration. Excellent usefulness such as
Demonstrate convenience and economy.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a system of a first embodiment to which the present invention is applied.

FIG. 2 is a graph for explaining the principle of the present invention,
FIG. 6A is a graph showing the distribution of backscattered light of each optical fiber when the polarization selection unit is not used and FIG.

FIG. 3 is a graph showing a change in backscattered light distribution before and after flooding as above.

4A and 4B are views showing an example of an optical fiber component for water immersion detection using the water-absorptive expandable material of the present invention, FIG. 4A is a perspective view of the whole, and FIG. 4B is a sectional view taken along line IVb-IVb of FIG. 4A. It is a figure.

FIG. 5 is a diagram showing another example of the optical fiber component for detecting water in the same as above, (a) is a perspective view of the entire structure with the lid and case removed, and (b) is Vb- of (a) before water absorption. Vb line sectional view, (c) is a Vb-Vb line sectional view after water absorption.

FIG. 6 is an overall configuration diagram of a system device of a second embodiment to which the present invention is applied.

7A and 7B are cross-sectional views showing a conventional sensor for detecting water immersion using a water-absorbing expansive material. FIG.

FIG. 8 is a configuration diagram showing a conventional water infiltration detection system device using a conventional water infiltration detection sensor.

FIG. 9 is a graph showing measurement results of optical loss by a conventional system device.

[Explanation of symbols]

 A ... Inundation detection sensor of conventional example α ... Infiltration detection system device of conventional example β, γ ... Infiltration detection system device of this embodiment 1 ... Optical fiber 2 ... Convex pressing guide 2 '... Concave receiving guide 3 ... Water absorption expansion Material 4,15 ... Lid 5, 13 ... Case 6, a, b ... Optical pulse tester 7 ... Data processing unit 8, 8 '... Optical fiber component 9 ... Pulse light source 10 ... Light output input unit 11 ... Polarization selection unit 12 ... Light receiving part 14 ... Hole 16 ... Pressing plate 17 ... Optical fiber twisting part 18 ... Polarizer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shinichi Furukawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. An optical fiber component equipped with means for absorbing water to change the birefringence of the optical fiber is arranged at at least one required inundation detection point, and light is emitted from a light source installed at one end of the optical fiber. Repeatedly sends out pulses and selectively receives any polarized component of the reflected light,
Detect the birefringence change in the optical fiber parts at the required location by measuring the temporal change in the backscattering waveform from the optical fiber far from the required inundation detection point, and check the presence or absence of water at the inundation detection point. A method for detecting water ingress of an optical fiber, characterized in that 2. A method for detecting water immersion in an optical fiber according to claim 1, wherein an optical pulse repeatedly sent from a light source installed at one end of the optical fiber is set in an arbitrary polarization state. 3. An optical fiber wired to at least one required inundation detection point, an optical fiber component having means for changing birefringence of the optical fiber at the inundation detection point by absorbing water, and the optical fiber. An optical pulse tester that is connected to one end of the optical pulse and repeatedly transmits an optical pulse to the one end, and selectively receives an arbitrary polarization component of the reflected light, and the optical fiber far from the inundation detection point of interest. Of the optical fiber comprising a data processing means for detecting the presence or absence of water immersion at the detection point of interest by measuring the temporal change in the backscattering waveform from Flood detection system device 4. The optical fiber inundation detection system device according to claim 3, wherein the optical pulse tester sends the optical pulse repeatedly sent from one end of the optical fiber as an arbitrary polarization state. 5. An optical fiber component has a water absorbing expandable material whose volume expands by absorbing water disposed around the optical fiber, and when the optical fiber is submerged, the water absorbing expandable material absorbs water. 5. The optical fiber immersion detection system device according to claim 3, wherein lateral pressure, bending or twisting can be applied to the optical fiber.