Water ingress detection device

Abstract

A water ingress detection device 3 comprises a connection part 31 in which an end surface of a first optical fiber core 41a and an end surface of a second optical fiber core 41b face each other. The connection part 31 includes a change part 32, which is a space into which water enters when water ingress occurs and from which the water is drained when the water ingress ceases, and in which the refractive index of light changes depending on whether or not water ingress has occurred. Light is input to the first optical fiber core 41a, and the distance between the two end surfaces in the connection part 31 is set so that the intensity of reflected light due to reflection of the light on the two end surfaces varies depending on whether or not water ingress has occurred in the change part 32.

Description

Water immersion detection device

[0001] The present disclosure relates to a water immersion detection device.

[0002] In an optical access network, it is known that when the connection part of an optical fiber is immersed in water for a long time, it may cause a failure. There is a technique for detecting water immersion in the connection part of an optical fiber (Patent Documents 1-2).

[0003] In Patent Document 1, it is disclosed that when the water-absorbing material in the water immersion detection module of the connection part of an optical fiber absorbs water and expands, bending is added to the optical fiber, and the loss due to leakage light increases. Patent Document 1 detects water immersion without opening the closure by increasing the loss of the test light to a certain threshold value or more.

[0004] Patent Document 2 discloses measuring the wavelength variation period of the Fresnel reflectance when sending optical pulses while changing the wavelength at the connection part of optical fibers connected with a gap. Patent Document 2 detects water immersion by detecting the refractive index change in the gap of the connection part.

[0005] Japanese Unexamined Patent Application Publication No. 2010-212767, Japanese Unexamined Patent Application Publication No. 3-296679

[0006] In Patent Document 1, once the water-absorbing material in the water immersion detection module expands, the water does not return to its original state even if the water leaks out from the closure. The water immersion detection module needs to be replaced every time water immersion is detected. Maintenance work increases.

[0007] In Patent Document 2, since measurement with multiple wavelengths is required, multiple light sources or a wavelength-variable laser having a certain band is required. The cost of the water immersion detection system increases.

[0008] The present disclosure has been made in view of the above circumstances, and the object of the present disclosure is to provide a technique capable of reducing the burden in detecting water immersion in the connection part of an optical fiber.

[0009] A water ingress detection device according to one aspect of the present disclosure includes a connection portion that abuts the end face of a first optical fiber core with the end face of a second optical fiber core, the connection portion being a space into which water enters when water ingress occurs and into which the invaded water drains when the water ingress is resolved, and which includes a variable portion in which the refractive index of light changes depending on whether or not water is ingress, light is input to the first optical fiber core, and the distance between the two end faces at the connection portion is set such that the intensity of the reflected light at the two end faces differs depending on whether or not water is ingress at the variable portion.

[0010] This disclosure provides a technology that can reduce the burden of detecting water ingress at optical fiber connection points.

[0011] Figure 1 is a diagram illustrating the system configuration of the test system of the present disclosure. Figure 2 is a diagram illustrating the closure in the non-submerged and submerged states. Figure 3 is a diagram illustrating the interior of the closure of the present disclosure in the non-submerged state. Figure 4 is a diagram illustrating the interior of the closure of the present disclosure in the submerged state. Figure 5 is a diagram illustrating the reflection of light in the change section of the present disclosure. Figure 6 is a diagram illustrating an example of light intensity detected by the OTDR in the present disclosure. Figure 7 is a diagram illustrating the interior of a modified closure in the non-submerged state. Figure 8 is a diagram illustrating the interior of a modified closure in the submerged state. Figure 9 is a diagram illustrating the reflection of light in the change section of a modified example. Figure 10 is a diagram illustrating an example of light intensity detected by the OTDR in a modified example.

[0012] Embodiments of this disclosure will be described below with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals and their descriptions are omitted.

[0013] (Test System) The test system 1 shown in Figure 1 includes an OTDR (Optical Time Domain Reflectometer) 2 and a closure 3.

[0014] The OTDR2 emits an optical pulse into one of the optical fibers 41a in the first optical fiber bundle 4a, and evaluates the characteristics of the optical fiber 41a and the optical fibers connected to it from the light intensity of the reflected light and the time it took for that light intensity to be detected. The OTDR2 is installed, for example, in a telecommunications building. The OTDR2 makes it possible to inspect the optical fiber 41a from a remote location.

[0015] Closure 3 houses the connector for joining optical fibers. Closure 3 connects the first optical fiber bundle 4a and the second optical fiber bundle 4b. Closure 3 is installed in places where flooding is possible, such as underground.

[0016] In this disclosure, the closure 3 includes a mechanism for detecting water ingress into the closure 3. The closure 3 may be referred to as a water ingress detection device. The test system 1 shown in Figure 1 includes one closure 3, but multiple closures 3 may be provided in the direction of extension of the optical fiber.

[0017] As shown in Figure 2(a), the closure 3 is installed in an environment where flooding is possible, such as underground. Under normal conditions, water does not enter the inside of the closure 3.

[0018] On the other hand, depending on the environment surrounding closure 3, water may enter closure 3, as shown in Figure 2(b). In this case, water will enter the interior of closure 3. When the water in the surrounding environment of closure 3 drains away, the water that has entered the interior of closure 3 will also drain away.

[0019] The closure 3 will be explained with reference to Figure 3. Figure 3 is a cross-sectional view of the closure 3, taken from a plane passing through the direction of extension of the optical fiber bundle 4.

[0020] The closure 3 comprises a connecting portion 31, a changing portion 32, and a housing 33. The connecting portion 31 and the changing portion 32 are housed in the housing 33.

[0021] The connection portion 31 brings together the end face of the first optical fiber core 41a of the first optical fiber bundle 4 and the end face of the second optical fiber core 41b of the second optical fiber bundle 4b. Here, the distance between the end face of the first optical fiber core 41a and the end face of the second optical fiber core 41b is d.

[0022] Generally, optical fiber connections are performed in the field, such as outdoors. The closure 3 of this disclosure accommodates optical fiber cores in the field so that the distance between the end faces of the optical fiber cores is a specified distance d. For example, the closure 3 has a notch structure (not shown) at the end face of each optical fiber core, and each optical fiber core is pushed in and fixed so that the distance between the end faces is a specified distance d.

[0023] The connection section 31 connects the end face of one optical fiber core 41a of the first optical fiber bundle 4a to the end face of one optical fiber core 41b of the second optical fiber bundle 4b such that the distance between them is distance d. The other cores are connected by any other method.

[0024] The connection section 31 is a space into which water enters when flooding occurs and into which the water that entered drains when the flooding is resolved, and includes a change section 32 in which the refractive index of light changes depending on whether or not there is flooding.

[0025] In this disclosure, the variable section 32 is filled with air before flooding and after the water has drained from the flooding, as shown in Figure 3. During flooding, the variable section 32 is filled with water, as shown in Figure 4. After the water from the flooding has drained from the variable section 32 returns to the same state as before flooding. The closure 3 can continue to be used even after flooding.

[0026] The refractive index of light within the changing section 32 differs depending on whether the changing section 32 is filled with air or water. Since the distance d in the changing section 32 is on the order of 10 μm or less, the light intensity detected by OTDR2 may not be detectable with sufficient error between the water-immersed and non-water-immersed states.

[0027] Therefore, the distance d between the two end faces at the connection section 31 is set such that when light is input to the first optical fiber core 41a, the intensity of the reflected light from the two end faces differs depending on whether or not water is immersed in the change section 32. The reflected intensity only needs to be such that a difference in the light intensity measured by OTDR2 can be recognized between when water is immersed and before water is immersed or after the water has drained.

[0028] Figure 5 shows the state of the connection part 31 when light 21 is incident on the first optical fiber core 41a from the OTDR2. The light 21 incident on the first optical fiber core 41a may become reflected light 22a that is reflected off the end face of the first optical fiber core 41a on the OTDR2 side of the connection part 31. Alternatively, the light incident on the first optical fiber core 41a may pass through the end face of the connection part 31 on the OTDR2 side and become reflected light 22b that is reflected off the end face of the second optical fiber core 41b on the opposite side of the connection part 31 from the OTDR2.

[0029] OTDR2 measures the light intensity of the reflected light 21 from the reflected light 22a and reflected light 22b.

[0030] In this case, if the reflected light 22a and the reflected light 22b interfere with each other and resonate, specifically if the phase difference between the reflected light 22a and the reflected light 22b is an even multiple of π, then a strong reflected light is detected in OTDR2. On the other hand, if the reflected light 22a and the reflected light 22b interfere with each other and weaken each other, specifically if the phase difference between the reflected light 22a and the reflected light 22b is an odd multiple of π, then a weak reflected light is detected in OTDR2.

[0031] "Strong light" and "weak light" can be relative indicators of each other. "Strong light" can mean stronger than when the light is weakening each other due to interference, and "weak light" can mean weaker than when the light is strengthening each other due to interference.

[0032] Alternatively, "strong light" and "weak light" may indicate whether the light intensity is stronger or weaker than a predetermined threshold. "Strong light" may mean that the reflected light intensity is stronger than a predetermined value, and "weak light" may mean that the reflected light intensity is weaker than a predetermined value. Here, the threshold may be predetermined based on the optical fiber arrangement, etc.

[0033] In this disclosure, the distance d is set such that the reflected light from the two end faces (1) reinforces each other when not submerged and weakens each other when submerged, or (2) weakens each other when not submerged and reinforces each other when submerged.

[0034] Referring to Figure 6, an example of the reflected light intensity detected by OTDR2 will be explained. The upper graph in Figure 6 shows the case where the reflected light 22a and reflected light 22b reinforce each other due to the change unit 32, and the lower graph shows the case where the reflected light 22a and reflected light 22b weaken each other due to the change unit 32. The dashed lines in the vertical direction indicate the position of the change unit 32.

[0035] At the distance corresponding to the change section 32, both the upper and lower graphs detect the reflected light generated by the change section 32, thus forming a convex shape on the upper side. The upper graph forms a larger convex shape than the lower graph.

[0036] Test system 1 pre-measures the light intensity of reflected light when closure 3 is submerged and when it is not, and stores the upper and lower graphs. Test system 1 evaluates whether the waveform measured during the optical fiber core test corresponds to the upper or lower graph, and determines whether closure 3 is submerged or not. If a threshold for determining submerged or not is predetermined, test system 1 compares the convex shape of the waveform measured during the optical fiber core test with the threshold to determine whether closure 3 is submerged or not.

[0037] If the distance d between the two end faces is set such that (1) the reflected light from the two end faces reinforces each other when not submerged and weakens each other when submerged, the upper graph in Figure 6 shows the case when not submerged, and the lower graph shows the case when submerged. If the distance d between the two end faces is set such that (2) the reflected light from the two end faces weakens each other when not submerged and strengthens each other when submerged, the upper graph in Figure 6 shows the case when submerged, and the lower graph shows the case when not submerged.

[0038] Next, we will explain the specific method for calculating the distance d. Here, we will show the method for calculating the distance d between the two end faces when the reflected light from the two end faces (1) reinforces each other when not submerged and weakens each other when submerged.

[0039] Equation (1) shows the conditions when reflected light 22a and reflected light 22b reinforce each other. Equation (2) shows the conditions when reflected light 22a and reflected light 22b cancel each other out.

[0040] From Equations (1) and (2), it is derived that the distance d, in which the reflected light 22a and the reflected light 22b reinforce each other when not immersed in water and weaken each other when immersed in water, satisfies Equations (3) and (4).

[0041] A specific example of the distance d will be described. Here, the refractive index of air n = 1 and the refractive index of water n' = 1.3.

[0042] The case where the wavelength of the light incident on the first optical fiber core 41a of the OTDR 2 is 1.55 μm will be described. When m = 9 and l = 12, d = 6.58 μm.

[0043] The case where the wavelength of the light incident on the first optical fiber core 41a of the OTDR 2 is 1.65 μm will be described. When m = 9 and l = 12, d = 7.00 μm.

[0044] For example, when the distance d = 7.00 μm, if the wavelength of the light incident on the OTDR 2 is 1.65 μm and the superimposed wavelength of the communication service is 1.55 μm, the superimposed wavelength of 1.55 μm of the communication service passes through the changing portion 32. Therefore, test light can be superimposed on the light for communication services using one optical fiber core.

[0045] The test system 1 detects the presence or absence of water immersion in the closure 3 with the OTDR 2 without going to the installation position of the closure 3. Since the closure 3 can be used even after water has drained out after water immersion, the burden in detecting water immersion at the connection portion of the optical fiber is reduced.

[0046] (Modified Example) In the modified example, the case where the changing portion 32 includes a first layer and a second layer in the extending direction of the optical fiber core will be described. When not immersed in water, one of the first layer and the second layer is formed of air and the other is formed of a medium other than air. The medium other than air is formed of a medium that does not absorb water. The medium other than air does not change in size regardless of the presence or absence of water immersion.

[0047] In the example shown in FIG. 7, the variable section 32 includes an air layer 32a on the side of the first optical fiber core 41a and a solid medium layer 32b on the side of the second optical fiber core 41b when not immersed in water. When the closure 3 is immersed in water, as shown in FIG. 8, the air layer 32a on the side of the first optical fiber core becomes an aqueous layer 32a'. The solid medium layer 32b is formed of, for example, a solid matching agent.

[0048] FIG. 7 illustrates a case where the air layer 32a is provided closer to the OTDR 2 and the solid medium layer 32b is provided farther from the OTDR 2, but the present invention is not limited thereto. A solid medium layer may be provided closer to the OTDR 2 and an air layer may be provided farther from the OTDR 2. Also, the variable section 32 may be formed of three or more layers.

[0049] FIG. 9 shows the state of the connection section 31 when light 21 is incident on the first optical fiber core 41a in a modified example. In the modified example, in addition to the reflected lights 22a and 22b shown in FIG. 5, a reflected light 22c is generated when light 21 is incident on the first optical fiber core 41a. The reflected light 22c is detected when the light incident on the first optical fiber core 41a passes through the end face on the OTDR 2 side of the connection section 31 and is reflected at the boundary between the two layers of the variable section 32.

[0050] The OTDR 2 measures the light intensity of the reflected light of the light 21 from the reflected lights 22a, the reflected light 22b, and the reflected light 22c.

[0051] At this time, when the reflected lights 22a, the reflected light 22b, and the reflected light 22c reinforce each other due to interference, specifically, when the phase differences between the reflected light 22a and the reflected light 22b and between the reflected light 22a and the reflected light 22c are each an even multiple of π, a strong reflected light is detected. On the other hand, when the reflected lights 22a, the reflected light 22b, and the reflected light 22c weaken each other due to interference, specifically, when the phase differences between the reflected light 22a and the reflected light 22b and between the reflected light 22a and the reflected light 22c are each an odd multiple of π, a weak reflected light is detected.

[0052] Referring to Figure 10, an example of the reflected light intensity detected by OTDR2 will be explained. The upper graph in Figure 6 shows the case where reflected light 22a, reflected light 22b, and reflected light 22c reinforce each other due to the change unit 32, while the lower graph shows the case where reflected light 22a, reflected light 22b, and reflected light 22c weaken each other due to the change unit 32. The dashed lines in the vertical direction indicate the position of the change unit 32.

[0053] At the distance corresponding to the change section 32, both the upper and lower graphs detect the reflected light generated by the change section 32, thus forming a convex shape on the upper side. The upper graph forms a larger convex shape than the lower graph.

[0054] In the upper graph, the dashed line represents the light intensity of the reflected light in this disclosure. Because the variable section 32 is formed in two layers, it is possible to detect stronger reflected light compared to when it is formed in one layer, making it easier for the OTDR2 to detect the presence or absence of water ingress.

[0055] Next, we will explain the specific method for calculating the distance d. In the modified example, the thickness of the air layer 32a of the first layer is d1, and the thickness of the solid medium layer 32b of the second layer is d2. Here, we will show the method for calculating the distances d1 and d2 when the reflected light from the two end faces (1) reinforces each other when not submerged and weakens each other when submerged.

[0056] Equations (5) and (6) show the conditions under which reflected light 22a, reflected light 22b, and reflected light 22c reinforce each other. Equations (7) and (8) show the conditions under which reflected light 22a, reflected light 22b, and reflected light 22c destructively cancel each other out.

[0057]

[0058]

[0059] From equations (5) to (8), the distances d1 and d2 when reflected light 22a, reflected light 22b, and reflected light 22c reinforce each other when not submerged and weaken each other when submerged can be derived from equations (9) to (12). Equations (9) to (12) can be derived from equations (5) to (8), respectively.

[0060]

[0061] Let's explain a specific example of distances d1 and d2. Here, the refractive index of air is n1 = 1.0, the refractive index of water is n1' = 1.3, and the refractive index of the solid matching agent is n2 = 1.9.

[0062] OTDR2 explains the case where the wavelength of light incident on the first optical fiber core 41a is 1.55 μm. When m=9, l=17, m'=12, and l'=31, d1=6.58 μm and d2=7.95 μm.

[0063] OTDR2 explains the case where the wavelength of light incident on the first optical fiber core 41a is 1.65 μm. When m=6, l=10, m'=8, and l'=12, d1=4.49 μm and d2=1.95 μm.

[0064] In the modified example, since the modified portion 32 is formed in two layers, the interference effect is greater and the detection accuracy is improved compared to the case where it is formed in one layer as in the present disclosure.

[0065] This disclosure is not limited to the embodiments described above, and numerous modifications are possible within the scope of its essence.

[0066] 1 Test system 2 OTDR 3 Closure 4 Optical fiber bundle 31 Connection part 32 Modification part 33 Housing 41 Optical fiber core

Claims

1. A flood detection device comprising a connection portion that abuts the end face of a first optical fiber core with the end face of a second optical fiber core, wherein the connection portion is a space into which water enters when flooding occurs and into which the entered water drains when the flooding is resolved, and which includes a variable portion in which the refractive index of light changes depending on whether or not there is flooding, and the distance between the two end faces at the connection portion is set such that when light is input to the first optical fiber core, the intensity of the reflected light at the two end faces differs depending on whether or not there is flooding in the variable portion.

2. The flood detection device according to claim 1, wherein the reflected light from the two end faces reinforces each other when not submerged and weakens each other when submerged, or weakens each other when not submerged and reinforces each other when submerged.

3. The immersion detection device according to claim 1, wherein the distance between the two end faces satisfies formulas (1) and (2).

4. The immersion detection device according to claim 1, wherein the modified section comprises a first layer and a second layer in the direction of extension of the optical fiber core, and in the absence of immersion, one of the first layer and the second layer is formed of air and the other is formed of a medium other than air.

Images