Optical fiber characteristic measurement system and humidity measurement method

Abstract

Easily measure humidity with high spatial resolution. [Solution] The optical fiber characteristic measurement system 1 according to this disclosure comprises an optical fiber 20 having a wet portion and a dry portion, and an optical fiber characteristic measurement device 10 capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber 20. The optical fiber characteristic measurement device 10 measures humidity based on a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet portion, and a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry portion.

Description

Technical Field

[0001] The present disclosure relates to an optical fiber characteristic measurement system and a humidity measurement method.

Background Art

[0002] Conventionally, techniques for measuring humidity using optical fibers have been studied.

[0003] For example, Patent Document 1 discloses a technique for measuring humidity based on a wet-bulb temperature obtained from the temperature of a portion of an optical fiber sensor covered with a moisture retention material and a dry-bulb temperature obtained from the temperature of an uncovered portion, among optical fiber sensors housed in a breathable container disposed near a road.

[0004] For example, Patent Document 2 discloses a technique for measuring humidity using a Rayleigh frequency shift.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technique described in Patent Document 1 measures humidity using an optical fiber sensor disposed in a breathable container disposed near a road, so the position for measuring humidity cannot be changed. Also, the technique described in Patent Document 1 has a spatial resolution of about 1 m at the measurement position when measuring humidity, and humidity cannot be measured with high spatial resolution.

[0007] The technology described in Patent Document 2 measures humidity using Rayleigh frequency shift. However, since Rayleigh frequency shift can only measure relative temperature, it is necessary to measure absolute temperature using another method before measuring humidity. Therefore, measuring humidity is time-consuming.

[0008] Therefore, the purpose of this disclosure is to provide an optical fiber characteristic measurement system and a humidity measurement method that can easily measure humidity with high spatial resolution. [Means for solving the problem]

[0009] Some embodiments of optical fiber characteristic measurement systems include an optical fiber having a wet portion and a dry portion, and an optical fiber characteristic measurement device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber, wherein the optical fiber characteristic measurement device measures humidity based on a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet portion, and a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry portion. Such an optical fiber characteristic measurement system makes it possible to easily measure humidity with high spatial resolution.

[0010] In an optical fiber characteristic measurement system according to one embodiment, the optical fiber characteristic measurement device may measure a first temperature, which is the temperature of the wet part, based on the first Brillouin frequency shift, measure a second temperature, which is the temperature of the dry part, based on the second Brillouin frequency shift, and measure the humidity based on the temperature difference obtained by subtracting the first temperature from the second temperature, and the second temperature. This makes it possible to measure humidity based on the temperature measured based on the Brillouin frequency shift.

[0011] In one embodiment of the optical fiber characteristic measurement system, the optical fiber characteristic measurement device may control the position for measuring the first Brillouin frequency shift and the second Brillouin frequency shift by adjusting the modulation frequency of the light emitted from the optical fiber. This makes it possible to continuously change the position for measuring humidity with high spatial resolution.

[0012] In one embodiment of the optical fiber characteristic measurement system, the range of the wet area may be within the range of the spatial resolution when the optical fiber characteristic measurement device measures the Brillouin frequency shift. This allows the range of the wet area to be limited to a narrow range.

[0013] In an optical fiber characteristic measurement system according to one embodiment, the distance from the location of the wet section where the first Brillouin frequency shift is measured to the location of the dry section where the second Brillouin frequency shift is measured may be less than or equal to a predetermined distance. This allows the first and second temperatures to be measured at a close distance.

[0014] In an optical fiber characteristic measurement system according to one embodiment, the optical fiber may have a plurality of wet areas. This allows for easy measurement of humidity at multiple locations.

[0015] In one embodiment of the optical fiber characteristic measurement system, the optical fiber characteristic measurement device may be a device that measures the characteristics of the optical fiber using the BOCDR method or the BOCDA method. This allows the position for measuring humidity to be controlled with high spatial resolution.

[0016] A humidity measurement method according to some embodiments includes a fiber optic cable having a wet portion and a dry portion, and a fiber optic cable characteristic measurement device capable of measuring the Brillouin frequency shift of the Brillouin scattered light from the fiber optic cable. The humidity measurement method in the fiber optic cable characteristic measurement system includes measuring a first Brillouin frequency shift that is the Brillouin frequency shift in the wet portion, measuring a second Brillouin frequency shift that is the Brillouin frequency shift in the dry portion, and measuring humidity based on the first Brillouin frequency shift and the second Brillouin frequency shift. According to such a humidity measurement method, it is possible to easily measure humidity with high spatial resolution.

Advantages of the Invention

[0017] According to the present disclosure, it is possible to provide a fiber optic cable characteristic measurement system and a humidity measurement method capable of easily measuring humidity with high spatial resolution.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing a schematic configuration of a fiber optic cable characteristic measurement system according to an embodiment. [Figure 2] It is a diagram showing a schematic configuration of the fiber optic cable characteristic measurement device of FIG. 1. [Figure 3] It is a diagram showing a state where the Brillouin frequency shift is measured in a fiber optic cable characteristic measurement system according to an embodiment.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0020] FIG. 1 is a diagram showing a schematic configuration of a fiber optic cable characteristic measurement system 1 according to an embodiment. The fiber optic cable characteristic measurement system 1 includes a fiber optic cable characteristic measurement device 10, a fiber optic cable 20, and absorbent cotton 30.

[0021] The optical fiber characteristic measuring device 10 is a device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber 20. The Brillouin scattered light includes a Brillouin gain spectrum. The Brillouin gain spectrum includes a frequency component of about 11 GHz. The optical fiber characteristic measuring device 10 can measure the Brillouin frequency shift, which is the shift amount of the peak of the Brillouin gain spectrum.

[0022] The optical fiber characteristic measuring device 10 may be a device that measures the characteristics of the optical fiber 20 to be measured, for example, by a Brillouin optical correlation domain reflectometer (BOCDR) method.

[0023] The optical fiber 20 may be a normal optical fiber used for measurements such as those by the BOCDR method. The optical fiber 20 may be attached to and installed on a measurement object that measures humidity, for example. The measurement object may be, for example, a building, a road, a bridge, a dam, a tunnel, an aircraft, or the like.

[0024] The optical fiber 20 has a wet part and a dry part. The wet part is the part of the optical fiber 20 covered with moisture. The dry part is the part of the optical fiber 20 not covered with moisture.

[0025] FIG. 1 shows an example in which the wet part is covered with absorbent cotton 30 containing moisture. Note that this is just an example, and the wet part may be covered with moisture by any method. For example, the wet part may be covered with any material that retains moisture. Note that the position of the wet part can be easily changed, for example, by changing the position of the absorbent cotton 30.

[0026] The optical fiber characteristic measuring device 10 can measure the temperature at any position of the optical fiber 20 with high spatial resolution by measuring the Brillouin frequency shift. The spatial resolution when the optical fiber characteristic measuring device 10 measures the temperature at any position of the optical fiber 20 is, for example, about 10 cm.

[0027] The range of the wet area of ​​the optical fiber 20 may be within the range of the spatial resolution when the optical fiber characteristic measuring device 10 measures the Brillouin frequency shift. For example, if the spatial resolution is about 10 cm, the range of the wet area may be about 10 cm.

[0028] The dry section of the optical fiber characteristic measuring device 10, where temperature is measured by measuring the Brillouin frequency shift, may be any position other than the wet section, but it is preferable that it be adjacent to the wet section. Therefore, it is preferable that the distance from the wet section to the dry section is less than or equal to a predetermined distance. The predetermined distance may be approximately the same as the spatial resolution when the optical fiber characteristic measuring device 10 measures the Brillouin frequency shift. For example, if the spatial resolution is approximately 10 cm, the predetermined distance may be approximately 10 cm to 30 cm.

[0029] Figure 2 shows a schematic configuration of the optical fiber characteristic measurement device 10. In this embodiment, the case in which the optical fiber characteristic measurement device 10 measures the characteristics of the optical fiber 20 using the BOCDR method will be explained as an example.

[0030] The optical fiber characteristic measuring device 10 comprises a laser light source 111, a laser light source driver 112, a first optical coupler 113, an optical switch 114, a delay fiber 115, a polarization scrambler 116, a circulator 117, a scattered light amplifier 118, a second optical coupler 119, a photodiode 120, an RF (Radio Frequency) signal amplifier 121, and a frequency analyzer 122.

[0031] The laser light source 111 outputs laser light. The laser light source 111 may be, for example, a laser diode. The laser light source 111 is capable of outputting frequency-modulated laser light. The laser light output by the laser light source 111 is frequency-modulated by the laser light source driver 112.

[0032] The laser light source 111 outputs frequency-modulated laser light to the first optical coupler 113.

[0033] The laser light source driver 112 frequency modulates the laser light output by the laser light source 111 by supplying a sinusoidal signal to the laser light source 111. The laser light source driver 112 may be any circuit configuration capable of frequency modulating the laser light output by the laser light source 111.

[0034] The first optical coupler 113 splits the laser light supplied from the laser light source 111 into pump light and reference light. The first optical coupler 113 outputs the pump light to the optical switch 114. The first optical coupler 113 outputs the reference light to the second optical coupler 119.

[0035] The optical switch 114 chops the pump light supplied from the first optical coupler 113 to generate pulsed light. The optical switch 114 outputs the pulsed pump light to the delay fiber 115.

[0036] The delay fiber 115 delays the pump light supplied from the optical switch 114 and outputs it to the polarization scrambler 116.

[0037] The polarization scrambler 116 depolarizes the polarization state of the pump light supplied from the delay fiber 115 and outputs it to the circulator 117.

[0038] The circulator 117 emits the pump light supplied from the polarization scrambler 116 into the optical fiber 20. When the pump light is emitted into the optical fiber 20, the optical fiber 20 generates Brillouin scattered light. The circulator 117 outputs the Brillouin scattered light incident from the optical fiber 20 to the scattered light amplifier 118.

[0039] The scattered light amplifier 118 amplifies the Brillouin scattered light supplied from the circulator 117 and outputs it to the second optical coupler 119. The scattered light amplifier 118 may be, for example, an erbium-doped fiber amplifier (EDFA).

[0040] The second optical coupler 119 combines the Brillouin scattered light supplied from the scattered light amplifier 118 with the reference light supplied from the first optical coupler 113 and outputs it to the photodiode 120.

[0041] The photodiode 120 receives the combined light supplied from the second optical coupler 119 and performs heterodyne detection. The photodiode 120 converts the received light into an electrical signal and outputs it to the RF signal amplifier 121.

[0042] The RF signal amplifier 121 amplifies the electrical signal supplied from the photodiode 120 and outputs it to the frequency analyzer 122.

[0043] The frequency analyzer 122 performs frequency analysis on the electrical signal supplied from the RF signal amplifier 121, that is, the electrical signal corresponding to the light combined by the second optical coupler 119.

[0044] The electrical signal supplied to the frequency analyzer 122 from the RF signal amplifier 121 includes a Brillouin gain spectrum due to Brillouin scattering. The Brillouin gain spectrum includes frequency components around 11 GHz.

[0045] The frequency analyzer 122 measures the Brillouin frequency shift, which is the amount of peak shift in the Brillouin gain spectrum. The Brillouin frequency shift is first dependent on the temperature of the optical fiber 20.

[0046] The optical fiber characteristic measuring device 10 can control the position at which the Brillouin frequency shift is measured by adjusting the modulation frequency of the light emitted from the optical fiber 20. The optical fiber characteristic measuring device 10 adjusts the modulation frequency of the light emitted from the optical fiber 20 by changing the frequency of the sinusoidal signal supplied by the laser light source driver 112 to the laser light source 111.

[0047] The position z for measuring the Brillouin frequency shift is expressed, for example, by the following equations (1) and (2). The position z for measuring the Brillouin frequency shift is the position reached by a distance z from one end of the optical fiber 20 connected to the optical fiber characteristic measuring device 10 to the other end of the optical fiber 20.

number

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[0048] The optical fiber characteristic measuring device 10 can continuously change the position z at which the Brillouin frequency shift is measured by adjusting the modulation frequency.

[0049] Next, we will explain the process by which the optical fiber characteristic measuring device 10 measures humidity.

[0050] The optical fiber characteristic measuring device 10 emits pump light into the optical fiber 20 with the modulation frequency adjusted so that the position for measuring the Brillouin frequency shift is the position of the wet area, and measures the Brillouin frequency shift in the wet area. Hereafter, the Brillouin frequency shift in the wet area may be referred to as the "first Brillouin frequency shift".

[0051] The optical fiber characteristic measuring device 10 emits pump light into the optical fiber 20 with the modulation frequency adjusted so that the position for measuring the Brillouin frequency shift is at the dry section, and measures the Brillouin frequency shift in the dry section. Hereafter, the Brillouin frequency shift in the dry section may be referred to as the "second Brillouin frequency shift".

[0052] When measuring the Brillouin frequency shift in the dry region, it is preferable to adjust the modulation frequency so that the distance from the wet region to the dry region is less than or equal to a predetermined distance.

[0053] Figure 3 shows an example of how the optical fiber characteristic measurement system 1 measures the first Brillouin frequency shift BFS1, which is the Brillouin frequency shift in the wet area, and the second Brillouin frequency shift BFS2, which is the Brillouin frequency shift in the dry area.

[0054] The optical fiber characteristic measuring device 10 measures the humidity of the wet area based on the measured first Brillouin frequency shift and second Brillouin frequency shift. The humidity measurement will be described in more detail below.

[0055] The Brillouin frequency shift is firstly dependent on the temperature at the location where the Brillouin frequency shift is being measured in the optical fiber 20. Therefore, the optical fiber characteristic measuring device 10 can calculate the temperature of the wet part as an absolute temperature based on the measured first Brillouin frequency shift. In other words, the optical fiber characteristic measuring device 10 can measure the temperature of the wet part as an absolute temperature based on the first Brillouin frequency shift. Furthermore, the optical fiber characteristic measuring device 10 can calculate the temperature of the dry part as an absolute temperature based on the measured second Brillouin frequency shift. In other words, the optical fiber characteristic measuring device 10 can measure the temperature of the dry part as an absolute temperature based on the second Brillouin frequency shift.

[0056] Hereafter, the temperature of the wet part may be referred to as the "first temperature," and the temperature of the dry part may be referred to as the "second temperature."

[0057] The optical fiber characteristic measuring device 10 can calculate humidity based on the temperature difference obtained by subtracting the temperature of the wet part (first temperature) from the temperature of the dry part (second temperature), and the temperature of the dry part (second temperature). In other words, the optical fiber characteristic measuring device 10 can measure humidity based on the temperature difference obtained by subtracting the temperature of the wet part (first temperature) from the temperature of the dry part, and the temperature of the wet part.

[0058] <Multiple wet areas> The optical fiber 20 may have multiple wet areas. In this case, the optical fiber characteristic measuring device 10 can measure the humidity of each of the multiple wet areas by adjusting the modulation frequency. Since the humidity of each of the multiple wet areas can be measured simply by adjusting the modulation frequency, the optical fiber characteristic measuring system 1 can efficiently measure the humidity at multiple locations.

[0059] According to the optical fiber characteristic measurement system 1 of one embodiment described above, it is possible to easily measure humidity with high spatial resolution. More specifically, the optical fiber characteristic measurement system 1 comprises an optical fiber 20 having a wet part and a dry part, and an optical fiber characteristic measurement device 10 capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber 20. The optical fiber characteristic measurement device 10 measures humidity based on a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet part, and a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry part. Thus, since the optical fiber characteristic measurement device 10 is a device that measures Brillouin frequency shifts, it can easily measure the first Brillouin frequency shift, which is the Brillouin frequency shift in the wet part, and the second Brillouin frequency shift, which is the Brillouin frequency shift in the dry part, with high spatial resolution. The optical fiber characteristic measurement device 10 can then measure humidity based on the first and second Brillouin frequency shifts measured with high spatial resolution. Therefore, according to the optical fiber characteristic measurement system 1 of one embodiment, it is possible to easily measure humidity with high spatial resolution.

[0060] It will be apparent to those skilled in the art that this disclosure can be implemented in other predetermined forms besides the embodiments described above without deviating from its spirit or essential features. Therefore, the prior description is illustrative and not limiting. The scope of the disclosure is defined not by the prior description but by the added claims. Any modifications within their equivalent scope are incorporated therein.

[0061] For example, the arrangement and number of each component described above are not limited to those shown in the above description and drawings. The arrangement and number of each component may be configured arbitrarily, as long as it can achieve its function.

[0062] For example, although the optical fiber characteristic measuring device 10 has been described as measuring the Brillouin frequency shift of the optical fiber 20 using the BOCDR method, it is not limited to this. The optical fiber characteristic measuring device 10 may also measure the Brillouin frequency shift of the optical fiber 20 using, for example, the Brillouin Optical Correlation Domain Analysis (BOCDA) method.

[0063] Some embodiments of the present disclosure are described below. However, it should be noted that the embodiments of the present disclosure are not limited to these. [Note 1] An optical fiber having a wet portion and a dry portion, An optical fiber characteristic measuring device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber, A fiber optic characteristic measurement system comprising, The optical fiber characteristic measuring device is an optical fiber characteristic measuring system that measures humidity based on a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet part, and a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry part. [Note 2] In the optical fiber characteristic measurement system described in Appendix 1, The optical fiber characteristic measuring apparatus is, Based on the first Brillouin frequency shift, the first temperature, which is the temperature of the wet area, is measured. Based on the second Brillouin frequency shift, the second temperature, which is the temperature of the dry part, is measured. An optical fiber characteristic measurement system that measures humidity based on the temperature difference obtained by subtracting the first temperature from the second temperature, and the second temperature. [Note 3] In the optical fiber characteristic measurement system described in Appendix 1 or 2, The optical fiber characteristic measuring device is an optical fiber characteristic measuring system that controls the position for measuring the first Brillouin frequency shift and the second Brillouin frequency shift by adjusting the modulation frequency of the light emitted from the optical fiber. [Note 4] In the optical fiber characteristic measurement system described in any one of the appendices 1 to 3, The range of the wet area is within the range of the spatial resolution when the optical fiber characteristic measuring device measures the Brillouin frequency shift, in an optical fiber characteristic measuring system. [Note 5] In the optical fiber characteristic measurement system described in any one of the appendices 1 to 4, An optical fiber characteristic measurement system in which the distance from the location of the wet part where the first Brillouin frequency shift is measured to the location of the dry part where the second Brillouin frequency shift is measured is less than or equal to a predetermined distance. [Note 6] In the optical fiber characteristic measurement system described in any one of the appendices 1 to 5, The optical fiber is an optical fiber characteristic measurement system having a plurality of the aforementioned wet portions. [Note 7] In the optical fiber characteristic measurement system described in any one of the appendices 1 to 6, The optical fiber characteristic measurement device is an optical fiber characteristic measurement system, which is a device that measures the characteristics of the optical fiber using the BOCDR method or the BOCDA method. [Note 8] A method for measuring humidity in an optical fiber characteristic measurement system comprising an optical fiber having a wet portion and a dry portion, and an optical fiber characteristic measurement device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber, The steps include measuring a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet area, The steps include measuring a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry portion, A step of measuring humidity based on the first Brillouin frequency shift and the second Brillouin frequency shift, A method for measuring humidity, including the following. [Note 9] In the humidity measurement method described in Appendix 8, The step of measuring the humidity is, A step of measuring a first temperature, which is the temperature of the wet part, based on the first Brillouin frequency shift, A step of measuring a second temperature, which is the temperature of the dry part, based on the second Brillouin frequency shift, A step of measuring the humidity based on the temperature difference obtained by subtracting the first temperature from the second temperature, and the second temperature. A method for measuring humidity, including the following. [Note 10] In the humidity measurement method described in Appendix 8 or 9, The step of measuring the first Brillouin frequency shift involves controlling the position at which the first Brillouin frequency shift is measured by adjusting the modulation frequency of the light emitted from the optical fiber. A humidity measurement method comprising the step of measuring the second Brillouin frequency shift, wherein the position for measuring the second Brillouin frequency shift is controlled by adjusting the modulation frequency of the light emitted from the optical fiber. [Note 11] In the humidity measurement method described in any one of the appendices 8 to 10, A humidity measurement method wherein the range of the humid area is within the range of the spatial resolution when the optical fiber characteristic measuring device measures the Brillouin frequency shift. [Note 12] In the humidity measurement method described in any one of the appendices 8 to 11, A humidity measurement method wherein the distance from the location of the wet part where the first Brillouin frequency shift is measured to the location of the dry part where the second Brillouin frequency shift is measured is less than or equal to a predetermined distance. [Note 13] In the humidity measurement method described in any one of the appendices 8 to 12, A humidity measurement method comprising the optical fiber having a plurality of the aforementioned wet parts. [Note 14] In the humidity measurement method described in any one of the appendices 8 to 13, A humidity measurement method comprising an optical fiber characteristic measuring device that measures the characteristics of the optical fiber using the BOCDR method or the BOCDA method. [Explanation of symbols]

[0064] 1. Optical Fiber Characterization System 10 Optical fiber characteristic measurement device 20 Fiber Optics 30 cotton balls 111 Laser light 112 Laser light source driver 113 First Optical Coupler 114 Optical switch 115 Delay Fiber 116 Polarization Scrambler 117 Circulator 118 Scattered Light Amplifier 119. Second Optical Coupler 120 Photodiodes 121 RF Signal Amplifier 122 Frequency analyzer

Claims

1. An optical fiber having a wet portion and a dry portion, An optical fiber characteristic measuring device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber, A fiber optic characteristic measurement system comprising, The optical fiber characteristic measuring device is an optical fiber characteristic measuring system that measures humidity based on a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet part, and a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry part.

2. In the optical fiber characteristic measurement system according to claim 1, The optical fiber characteristic measuring apparatus is, Based on the first Brillouin frequency shift, the first temperature, which is the temperature of the wet area, is measured. Based on the second Brillouin frequency shift, the second temperature, which is the temperature of the dry part, is measured. An optical fiber characteristic measurement system that measures humidity based on the temperature difference obtained by subtracting the first temperature from the second temperature, and the second temperature.

3. In the optical fiber characteristic measurement system according to claim 1, The optical fiber characteristic measuring device is an optical fiber characteristic measuring system that controls the position for measuring the first Brillouin frequency shift and the second Brillouin frequency shift by adjusting the modulation frequency of the light emitted from the optical fiber.

4. In the optical fiber characteristic measurement system according to claim 1, The range of the wet area is within the range of the spatial resolution when the optical fiber characteristic measuring device measures the Brillouin frequency shift, in an optical fiber characteristic measuring system.

5. In the optical fiber characteristic measurement system according to claim 1, An optical fiber characteristic measurement system in which the distance from the location of the wet part where the first Brillouin frequency shift is measured to the location of the dry part where the second Brillouin frequency shift is measured is less than or equal to a predetermined distance.

6. In the optical fiber characteristic measurement system according to claim 1, The optical fiber is an optical fiber characteristic measurement system having a plurality of the aforementioned wet portions.

7. In the optical fiber characteristic measurement system according to claim 1, The optical fiber characteristic measurement device is an optical fiber characteristic measurement system, which is a device for measuring the characteristics of the optical fiber by the BOCDR method or the BOCDA method.

8. A method for measuring humidity in an optical fiber characteristic measurement system comprising an optical fiber having a wet portion and a dry portion, and an optical fiber characteristic measurement device capable of measuring the Brillouin frequency shift of Brillouin scattered light from the optical fiber, The steps include measuring a first Brillouin frequency shift, which is the Brillouin frequency shift in the wet area, The steps include measuring a second Brillouin frequency shift, which is the Brillouin frequency shift in the dry portion, A step of measuring humidity based on the first Brillouin frequency shift and the second Brillouin frequency shift, A method for measuring humidity, including the following.

9. In the humidity measurement method described in claim 8, The step of measuring the humidity is, A step of measuring a first temperature, which is the temperature of the wet part, based on the first Brillouin frequency shift, A step of measuring a second temperature, which is the temperature of the dry part, based on the second Brillouin frequency shift, A step of measuring the humidity based on the temperature difference obtained by subtracting the first temperature from the second temperature, and the second temperature. A method for measuring humidity, including the following.

10. In the humidity measurement method described in claim 8, The step of measuring the first Brillouin frequency shift involves controlling the position for measuring the first Brillouin frequency shift by adjusting the modulation frequency of the light emitted from the optical fiber. A humidity measurement method comprising the step of measuring the second Brillouin frequency shift, wherein the position for measuring the second Brillouin frequency shift is controlled by adjusting the modulation frequency of the light emitted from the optical fiber.

11. In the humidity measurement method described in claim 8, A humidity measurement method wherein the range of the humid area is within the range of the spatial resolution when the optical fiber characteristic measuring device measures the Brillouin frequency shift.

12. In the humidity measurement method described in claim 8, A humidity measurement method wherein the distance from the location of the wet part where the first Brillouin frequency shift is measured to the location of the dry part where the second Brillouin frequency shift is measured is less than or equal to a predetermined distance.

13. In the humidity measurement method described in claim 8, A humidity measurement method comprising the optical fiber having a plurality of the aforementioned wet parts.

14. In the humidity measurement method described in claim 8, The aforementioned optical fiber characteristic measuring device is a device for measuring the characteristics of the optical fiber by the BOCDR method or the BOCDA method, and the humidity measurement method is also described.

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