Optical fiber sensing device and method

Abstract

The present disclosure relates to a multi-point interferometer type optical fiber sensor based on coherence domain division multiplexing, and the objective thereof is to provide a technology that enables an increase in the number of sensor points without complicating the device configuration or design.　The optical fiber sensing device of the present disclosure comprises an optical fiber sensor system provided with a plurality of sensor units having different propagation delay times, a first light source for outputting incident light to the optical fiber sensor system, a second light source for outputting local light to be combined with light transmitted through the optical fiber sensor system, and a signal processing unit for detecting a change in an optical fiber using a received light signal I(t) obtained by combining the transmitted light and the local light, wherein, if τi is an inter-optical-path propagation delay time difference for an i-th sensor unit, a change in the i-th sensor unit is obtained using an autocorrelation between an optical intensity I(t) of the sensor unit and a signal I(t+τi) obtained by offsetting the optical intensity I(t) by a time τi.

Description

[Technical field]

[0001] The present disclosure relates to the field of optical fiber sensing technology. [Background technology]

[0002] An optical fiber sensor is a general term for a system and measurement technology that uses optical fiber as a sensor medium to sense changes in physical quantities such as temperature and strain by associating them with changes in light intensity, frequency, and phase. One type of optical fiber sensor is an interferometric optical fiber sensor. An interferometric optical fiber sensor uses one optical path of a Mach-Zehnder interferometer as the sensor unit, and performs sensing by utilizing the phenomenon in which the intensity of an interference signal changes due to changes in the optical path length of the sensor unit caused by temperature or strain.

[0003] Multipoint interferometer optical fiber sensors have also been developed, which connect multiple interferometer optical fiber sensors to separate and detect the signals from each sensor. Multipoint interferometer optical fiber sensors are classified into time domain division multiplexing, wavelength domain division multiplexing, and coherence domain division multiplexing, depending on the division multiplexing method used for multiple sensor signals. Among these, the coherence domain division multiplexing method is characterized by its ability to constantly monitor each sensor signal and its ability to achieve multipoint sensor operation without using special optical devices such as wavelength division optical couplers.

[0004] An overview of a multipoint interferometer-type optical fiber sensor using the coherence domain division multiplexing method is as described in Non-Patent Document 1. Specifically, continuous light is incident on a sensor unit to which multiple Mach-Zehnder interferometers are connected, and the transmitted light is optically branched to separate and detect signals with a light-receiving Mach-Zehnder interferometer corresponding to each sensor unit. At this time, the propagation delay time difference between the optical paths of the multiple interferometers used in the sensor unit is designed to be different from one another, and the propagation delay time difference between the optical paths of the light-receiving interferometer is designed to be equal to the propagation delay time difference between the optical paths of the interferometers in the corresponding sensor unit.

[0005] Let N be the number of sensor parts (N is a natural number), E0(t) be the complex electric field amplitude of the continuous light output from the low-coherence light source, and E i (t) is the time average of the light intensity detected by the jth (j=1 to N) photodetector. j (t)> is expressed by the following equation.

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[0006] The propagation delay time and the optical phase change due to the change in temperature or strain in the i-th sensor are respectively expressed as τ i , Δθ i Then, E i (t) and j (t)> can be written as follows:

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[0007] Γ(τ) is the autocorrelation function of E0(t) and is defined as follows:

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[0008] If the coherence time of E0(t) is short enough for the possible values ​​of τ, then Γ(τ) can be considered as

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[0009] Substituting equation (5) into equation (3), in the region where τ>0, j (t)> is expressed as follows:​​​

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[0010] Therefore, the time average of the light intensity detected by the jth receiver is j (t)> is the optical phase change Δθ at the sensor part where the propagation delay time difference of the interferometer matches j In other words, it is possible to separate and detect the signals of the individual sensor parts for each light receiver. j is the temperature change ΔT at the jth sensor part j and strain change Δε j The following equation holds true for

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[0011] Here, C T and C. ε are the proportionality constants for the temperature change and the strain change, respectively. T Or C ε By determining the above and substituting equation (7) into equation (6), the change in temperature or strain at the corresponding sensor part can be measured. [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] JL Brooks, RH Wentworth, RC Youngquist, M. Tur, BYKim, and HJ Shaw, “Coherence Multiplexing of Fiber-Optic Interferometric Sensors,” J. Lightw. Technol., Vol. LT-3, No. 5, pp. 1062-1072, 1985. Summary of the Invention [Problem to be solved by the invention]

[0013] ​ In a multipoint interferometer type optical fiber sensor based on the conventional coherence domain division multiplexing method, it is necessary to prepare a Mach-Zehnder interferometer and a photoreceiver in the light receiving section for each sensor section, which means that the device configuration becomes more complex and expensive as the number of sensor sections increases.In addition, it is necessary to design the propagation delay time difference between the optical paths of the interferometers prepared in the light receiving section to match the propagation delay time difference between the optical paths of the interferometers in the corresponding sensor sections, which is not necessarily easy.

[0014] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide a technology that enables multi-point sensor deployment in a multi-point interferometer-type optical fiber sensor based on a coherence domain division multiplexing method without complicating the device configuration and design. [Means for solving the problem]

[0015] The optical fiber sensing device of the present disclosure comprises: an optical fiber sensor system including a plurality of sensor units having different propagation delay times; a first light source that outputs light incident on the optical fiber sensor system; a second light source that outputs local light to be multiplexed with the transmitted light of the optical fiber sensor system; a signal processing unit that detects a change in an optical fiber using a received light signal I(t) obtained by multiplexing the transmitted light and the local light; Equipped with The propagation delay time difference between the optical paths of the i-th sensor unit is τ i In this case, the light intensity I(t) of the sensor unit and the light intensity I(t) are calculated by dividing the light intensity I(t) by the time τ i The signal I(t+τ i ) is used to determine the change in the i-th sensor unit.

[0016] The optical fiber sensing method of the present disclosure includes: Incident light from a first light source is incident on an optical fiber sensor system including a plurality of sensor units having different propagation delay times; local light from a second light source is combined with transmitted light from the optical fiber sensor system; a signal processing unit detecting a change in an optical fiber by using a received light signal I(t) obtained by multiplexing the transmitted light and the local light, The propagation delay time difference between the optical paths of the i-th sensor unit is τ i In this case, the light intensity I(t) of the sensor unit and the light intensity I(t) are calculated by dividing the light intensity I(t) by the time τ i The signal I(t+τ i ) is used to determine the change in the i-th sensor unit. Effect of the Invention

[0017] According to the present disclosure, it is possible to provide multiple sensor units without using an interferometer on the light receiving side, and it is possible to perform multi-point sensing with a single device configuration regardless of the number of sensor units. Therefore, the present disclosure makes it possible to provide multiple sensors without complicating the device configuration and design in a multi-point interferometer type optical fiber sensor based on a coherence domain division multiplexing method. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a conceptual diagram of a method for calculating an autocorrelation function in the present disclosure. [Diagram 2] FIG. 2 is a conceptual diagram of a calculation result of an autocorrelation function in the present disclosure. [Diagram 3] 1 is a block diagram showing an apparatus configuration according to a first embodiment of the present disclosure. [Figure 4] FIG. 11 is a block diagram showing a device configuration according to a second embodiment of the present disclosure. [Diagram 5] 4 shows an example of the relationship between the coherence time and the propagation delay time of a sensor unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0020] The optical fiber sensing device of the present disclosure is an optical fiber sensing device that uses two types of light sources, detects changes in the optical fiber by inputting continuous light output from a first light source into the optical fiber and multiplexing the light transmitted through the optical fiber with local light output from a second light source. The optical fiber is an optical fiber sensor system including a plurality of sensor parts with different propagation delay times.

[0021] The optical fiber sensing device of the present disclosure includes a first light source that outputs incident light to the optical fiber sensor system, a second light source that outputs local light to be multiplexed with transmitted light from the optical fiber sensor system, and a light receiver that receives the multiplexed light of the transmitted light and the local light. The incident light and the local light are both continuous light. The optical fiber sensing device of the present disclosure transmits incident light output from the first light source through the optical fiber sensor system, and measures the light intensity of the multiplexed light obtained by multiplexing the transmitted light from the optical fiber sensor system and the local light.

[0022] In the present disclosure, transmitted light after passing through multiple sensor units is combined with local light and coherently detected all at once using a single photoreceiver, and the signals from each sensor unit are separated and detected by performing digital autocorrelation processing on the signals obtained by the coherent detection.

[0023] The complex electric field amplitude of the local light is E lo (t), the signal I(t) obtained by coherent detection is expressed as follows:

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[0024] In this case, the local light intensity is sufficiently strong compared to the transmitted light intensity of each sensor, and the interference component between the transmitted lights of the sensor parts can be ignored. i (t) is defined as follows:

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[0025] Next, calculate the autocorrelation function R(τ) of I(t). Figure 1 shows an image of how R(τ) is calculated. R(τ) is calculated as a function of τ, which is the time integral of the product of I(t) and the waveform I(t+τ), which is I(t) shifted by an arbitrary time τ from I(t). R(τ) can be calculated by digital signal processing based on the following formula.

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[0026] In addition, here, I0(t) is compared with I i (t) is weak enough (a i <<1), I i (t)I j (t) (i and j are any natural numbers from 1 to N, i ≠ j) can be ignored. The first term of equation (11) is calculated as follows:

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[0027] If the coherence time of the local light is long enough for a given value of τ, then E * lo (t)Elo (t+τ) and its complex conjugate can be regarded as constants independent of t. Furthermore, by applying equations (4) and (5), equation (12) can be expressed as follows.

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[0028] Similarly, the second term of equation (11) is calculated as follows:

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[0029] The waveform of R(τ) calculated from the above is shown in Figure 2. R(τ) is τ=0,τ1,...τ N and has a peak at τ=τ i The peak intensity of cosΔθ i In other words, the intensity of each peak of R(τ) changes according to the change in temperature or strain of each sensor part. i The relationship between the temperature or strain change of the i-th sensor part and the proportional constant C T , C ε By determining the above, it is possible to measure the change in each peak intensity of R(τ) in correspondence with the change in temperature or strain of each sensor portion.

[0030] Therefore, in the optical fiber sensing device of the present disclosure, the propagation delay time difference between the optical paths of the i-th sensor unit is τ i In this case, the light intensity I(t) of the sensor unit and the light intensity I(t) are calculated by dividing the light intensity I(t) by the time τ i The signal I(t+τ i ) is used to determine the change in the i-th sensor unit.

[0031] By using the present disclosure, it is possible to multiply the sensor unit in a multipoint interferometer type optical fiber sensor without adding an interferometer or a receiver in the light receiving unit. In addition, while it was necessary to design the interferometer in the sensor unit and the interferometer in the light receiving unit so that the propagation delay time difference between the optical paths was equal in the conventional interferometer, the use of the present disclosure makes the interferometer in the light receiving unit unnecessary, and therefore the design of the light receiving unit can be simplified. As a result, multipoint sensing is possible with a single device configuration regardless of the number of sensor units, and optical fiber sensing that is lower in cost and more scalable than conventional ones can be realized. Hereinafter, an embodiment of the present disclosure will be described with reference to the attached drawings. Two types of embodiments with different configurations of the sensor unit will be described.

[0032] (Embodiment 1) 3 is a block diagram showing the device configuration in this embodiment. A low-coherence light source 11 is used as the first light source, and a high-coherence light source 12 is used as the second light source. The high-coherence light source 12 functions as a local light source that outputs local light. The local light in this disclosure uses high-coherence light, which has a longer coherence time than the low-coherence light from the low-coherence light source 11 and is also longer than the optical propagation delay time of any sensor unit 21. The optical fiber sensor system 20 has a chain-type configuration in which multiple Mach-Zehnder interferometers 21 are connected in series using an optical coupler 22, and one optical path in each Mach-Zehnder interferometer serves as the sensor unit 21.

[0033] Continuous light from the low-coherence light source 11 is incident on the optical fiber sensor system 20, and the low-coherence light after passing through the chain-type optical fiber sensor system 20 is multiplexed with the high-coherence light from the high-coherence light source 12 by the optical coupler 16 and converted into an analog electrical signal by the optical receiver 13. The received light signal converted into an electrical signal is converted into a digital signal by the A / D converter 14 and transferred to the signal processing unit 15. The signal processing unit 15 uses the received light signal I(t) converted into a digital signal to calculate the autocorrelation function R(τ) according to equation (11).

[0034] R(τ) is τ=0,τ1,...τ NWhen observing the change in temperature or strain of the sensor unit 21#i (i is an arbitrary integer from 1 to N) in FIG. 3, τ=τ i The change in peak intensity is monitored. Peak intensity change cosΔθ i The relationship in equation (7) is applied to measure the change in temperature or strain in the sensor unit 21#i.

[0035] In this embodiment, optical fibers having different fiber lengths are used for each sensor unit 21#i, and the propagation delay time difference |τ j -τ i The minimum value of |(j≠i) is designed to be longer than the coherence time of the low-coherence light source 11, and the propagation delay time τ j The maximum value of max{τ1,τ2,...τ N} is designed to be shorter than the coherence time of the high coherence light source 12.

[0036] (Embodiment 2) 4 is a block diagram showing the configuration of the device in this embodiment. A low-coherence light source 11 is used as the first light source, and a high-coherence light source 12 is used as the second light source. The high-coherence light source 12 functions as a local light source that outputs local light. The optical fiber sensor system 20 includes a plurality of sensor units 21 connected in parallel, and the propagation delay time τ of the coherence light passing through the optical fiber sensor system 20 differs for each sensor unit 21. In this embodiment, the optical fiber sensor system 20 is configured by connecting optical fibers in a ladder shape using an optical coupler 22, and the optical path of each step of the ladder shape is defined as a sensor unit 21#i.

[0037] Continuous light from a low-coherence light source 11 is incident on an optical fiber sensor system 20, and the continuous light after passing through the ladder-type optical fiber sensor system 20 is multiplexed with local light from a high-coherence light source 12 by an optical coupler 16 and converted into an electrical signal by an optical receiver 13. The received light signal converted into an electrical signal is converted into a digital signal by an A / D converter 14 and transferred to a signal processing unit 15. The signal processing unit 15 calculates an autocorrelation function R(τ) according to equation (11) using the received light signal I(t) converted into a digital signal.

[0038] R(τ) is τ=0,τ1,...τ N When observing the change in temperature or strain of the sensor unit 21#i (i is an arbitrary integer from 1 to N) in FIG. 4, τ=τ i The change in peak intensity is monitored. Peak intensity change cosΔθ i The relationship in equation (7) is applied to measure the change in temperature or strain in the sensor unit 21#i.

[0039] Figure 5 shows an example of the relationship between the coherence time and the propagation delay time of the sensor. C1 , the local light coherence time τ C2 In this embodiment, the optical fiber sensor system 20 has a propagation delay time difference |τ between the optical paths passing through the sensor units 21#i. j -τ i The minimum value of |(j≠i) is the coherence time τ of the low-coherence light source 11. C1 and the maximum propagation delay time of the optical path passing through each sensor unit 21#i is set to be longer than the maximum propagation delay time max{τ1, τ2, . . . τ N} is the coherence time τ of the high coherence light source 12 C2 Design it to be shorter than

[0040] Furthermore, the signal processing unit 15 of the present disclosure can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network. [Industrial Applicability]

[0041] The present disclosure can be applied to the information and communications industry. [Explanation of symbols]

[0042] 11: Low coherence light source 12: High coherence light source 13:Receiver 14: A / D converter 15: Signal processing section 16, 22: Optical coupler 20: Optical fiber sensor system 21: Mach-Zehnder interferometer

Claims

1. an optical fiber sensor system including a plurality of sensor units having different propagation delay times; a first light source that outputs light incident on the optical fiber sensor system; a second light source that outputs local light having a longer coherence time than the incident light, the local light being combined with the transmitted light of the optical fiber sensor system; a signal processing unit that detects a change in an optical fiber using a received light signal I(t) obtained by multiplexing the transmitted light and the local light; Equipped with The signal processing unit is configured to detect a propagation delay time difference between the optical paths of the i-th sensor unit as τ ｉ In this case, the light intensity I(t) of the sensor unit is expressed as I(t) and the light intensity I(t) is expressed as I(t) over time τ ｉ The signal I(t+τ ｉ ) and calculate an autocorrelation function R(τ i ) with the i-th sensor unit, and the change in the autocorrelation function R(τ i ) is regarded as the change in the i-th sensor unit. Optical fiber sensing device.

2. The propagation delay time difference τ between the optical paths of the incident light passing through the i-th sensor unit ｉ is shorter than the coherence time of the local light, The propagation delay time difference τ between the optical paths of the incident light passing through the j-th (j is a natural number other than i) sensor unit ｊ The difference in the propagation delay time difference between the optical paths compared to |τ ｉ - τ ｊ | is longer than the coherence time of the incident light, 2. The optical fiber sensing device according to claim 1.

3. the optical fiber sensor system includes a plurality of Mach-Zehnder interferometers connected in series; the sensor unit is one of the optical paths in the Mach-Zehnder interferometer, The optical path propagation delay time differences τ of the sensor units included in the plurality of Mach-Zehnder interferometers are different from each other.

3. The optical fiber sensing device according to claim 1 or 2.

4. the optical fiber sensor system includes a plurality of sensor units connected in parallel; a propagation delay time τ of the incident light passing through the optical fiber sensor system differs for each sensor unit; 4. The optical fiber sensing device according to claim 1.

5. The change in the sensor unit is a change in temperature or strain of the i-th sensor unit.

5. The optical fiber sensing device according to claim 1.

6. Incident light from a first light source is incident on an optical fiber sensor system including a plurality of sensor units having different propagation delay times; local light from a second light source having a longer coherence time than the incident light is multiplexed with the transmitted light of the optical fiber sensor system; a signal processing unit detecting a change in an optical fiber by using a received light signal I(t) obtained by multiplexing the transmitted light and the local light, The signal processing unit is configured to detect a propagation delay time difference between the optical paths of the i-th sensor unit as τ ｉ In this case, the light intensity I(t) of the sensor unit is expressed as I(t) and the light intensity I(t) is expressed as I(t) over time τ ｉ The signal I(t+τ ｉ ) and calculate an autocorrelation function R(τ i ) with the i-th sensor unit, and the change in the autocorrelation function R(τ i ) is regarded as the change in the i-th sensor unit. Fiber optic sensing methods.

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