Optical fiber sensing device and method

Abstract

The purpose of the present disclosure is to provide a feature of a multi-point interferometric optical fiber sensor based on coherence area division multiplexing, wherein a multi-point sensor configuration can be achieved without complicating the device configuration and design.　The present disclosure is an optical fiber sensing device comprising a reference interferometer for producing a prescribed propagation delay time difference in continuous light, a sensor interferometer in which one of the optical paths of a plurality of Mach-Zehnder interferometers functions as a sensor unit, and a signal processing unit for performing signal processing using a light reception signal I(t) from reception of light transmitted through the sensor interferometer and a reference signal Iref-1(t) from reception of light transmitted through the reference interferometer, the signal processing unit calculating the cross-correlation Rj of a reference signal Iref-j(t) and the light reception signal I(t), and detecting a change in the jth sensor unit using a change in the cross-correlation Rj.

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, or 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, low-coherence 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 using 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 light emitted 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] 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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[0008] Substituting equation (5) into equation (3), in the region where τ>0, j (t)> is expressed as follows:

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[0009] 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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[0010] [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]

[0011] ​In a conventional multipoint interferometer type optical fiber sensor based on the 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.

[0012] 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]

[0013] The optical fiber sensing device of the present disclosure comprises: A light source that outputs continuous light; an optical coupler that branches the continuous light; The continuous light branched by the optical coupler is input, and a predetermined propagation delay time difference τ ref in the continuous light; The continuous light branched by the optical coupler is input, and the predetermined propagation delay time difference τ ref a sensor interferometer in which a plurality of Mach-Zehnder interferometers are connected to generate propagation delay time differences in the continuous light that correspond to integer multiples of and are different from each other, and one of the optical paths of the Mach-Zehnder interferometers functions as a sensor unit; The received light signal I(t) obtained by receiving the transmitted light of the sensor interferometer and the reference signal I(t) obtained by receiving the transmitted light of the reference interferometer ref-1 A signal processing unit that performs signal processing using (t); Equipped with The signal processing unit includes: The reference signal I ref-1 (t), the reference signal I corresponding to the jth (j is a natural number) sensor unit is ref―j Calculate (t), The received light signal I(t) and the reference signal I ref―jCross-correlation R of (t) j Calculate The cross-correlation R j The change in the j-th sensor unit is detected using the change in

[0014] The optical fiber sensing method of the present disclosure includes: Continuous light from the light source is branched, Predetermined propagation delay time difference τ ref The split continuous light is incident on a reference interferometer which generates a The predetermined propagation delay time difference τ ref the branched continuous light is input to a sensor interferometer, in which a plurality of Mach-Zehnder interferometers are connected to generate propagation delay time differences in the continuous light that correspond to integer multiples of and are different from each other, and one of the optical paths of the Mach-Zehnder interferometers functions as a sensor unit; A signal processing unit receives a light receiving signal I(t) obtained by receiving the transmitted light of the sensor interferometer and a reference signal I(t) obtained by receiving the transmitted light of the reference interferometer. ref-1 (t) an optical fiber sensing method for detecting a change in the sensor unit, The signal processing unit includes: The reference signal I ref-1 (t) is used to obtain the reference signal I ref―j Calculate (t), The received light signal I(t) and the reference signal I ref―j Cross-correlation R of (t) j Calculate The cross-correlation R j The change in the j-th sensor unit is detected using the change in Effect of the Invention

[0015] 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]

[0016] [Figure 1] 11 is a conceptual diagram of calculation of a phase XMj(t) of a reference signal in the present disclosure. FIG. [Diagram 2] FIG. 1 is a block diagram showing an apparatus configuration according to a first embodiment of the present disclosure. [Diagram 3] 1 is a flowchart showing an implementation procedure according to the first and second embodiments of the present disclosure. [Figure 4] FIG. 11 is a block diagram showing an apparatus configuration according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 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.

[0018] In the present disclosure, the optical signal transmitted through the interferometer of the sensor unit is received without using an interferometer on the light receiving side. Specifically, the optical fiber sensing device of the present disclosure provides a reference interferometer that passes through a different optical path from the interferometer of the sensor unit, and generates pseudo signals of each sensor unit before the temperature and strain change by signal processing using a signal obtained from the reference interferometer. In the present disclosure, this pseudo-generated signal is called a reference signal. The optical fiber sensing device of the present disclosure realizes a multi-point interferometer type optical fiber sensor without complicating the device configuration by calculating the cross-correlation between this reference signal and the received light signal obtained from the interferometer of the sensor unit.

[0019] When no interferometer is used in the light receiving section, the light receiving signal I(t) acquired for an optical path passing through N sensor sections (N is a natural number) is expressed by the following equation.

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[0020] By substituting equation (2) into equation (8), the received light signal I(t) is expressed as follows:

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[0021] Here, θ(t) is the phase of the continuous light from the light source, and the DC component is omitted in the second line of equation (9). In addition, the light intensity that passes through each sensor is sufficiently weak (a i <<1) It was assumed that the interference components between the lights transmitted through the sensor unit could be ignored.

[0022] On the other hand, the reference signal I obtained from the transmitted light of the reference interferometer ref―1 (t) is expressed as follows:

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[0023] Next, I ref―1 (t) is used to generate a pseudo reference signal before the temperature and strain change for the jth sensor part by numerical calculation. The delay time τ given to the optical path of the jth sensor part j τ j =M j τ ref (M j is a natural number), then θ(t)-θ(tMj τ ref ) as a phase component. Here, M j Phase X1(t) when =1, and M j Phase X in the case Mj (t) is defined as follows:

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[0024] X Mj (t) can be calculated using X1(t) according to the following formula:

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[0025] Figure 1 shows M j X according to equation (13) when >1 Mj This is an image of the calculation of (t). X Mj (t) is M j X1(t) on the time axis τ ref It is calculated by adding up the waveforms shifted by X. Mj Using (t), the pseudo reference signal I ref―Mj (t) is generated by the following formula:

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[0026] Next, I(t) and I ref―Mj Cross-correlation R of the cosine wave of (t) Mj Calculate R Mj is calculated by the following formula:

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[0027] Here, the coherence time of the continuous light from the light source is τ refIf it is assumed that the propagation delay times of the multiple sensor units are sufficiently short compared to and do not overlap with each other, the following equation is established.

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[0028] Therefore, τ j =M j τ ref Meet M j The cross-correlation R calculated for Mj Since the magnitude of changes depending on the temperature and distortion of the j-th sensor, R Mj By monitoring the change in , it is possible to sense the change in temperature and strain of the j-th sensor part. Similarly, for any i-th sensor part other than the j-th sensor part, τ i =M i τ ref Meet M i The cross-correlation R calculated for Mi By monitoring this, changes in temperature and strain can be sensed.

[0029] (Effects of the present disclosure) By using the present disclosure, it is possible to increase the number of sensor points in a multipoint interferometer type optical fiber sensor without adding an interferometer or receiver in the light receiving section. In addition, whereas it was necessary to design the interferometer in the sensor section and the interferometer in the light receiving section 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 section unnecessary, thereby simplifying the design of the light receiving section. As a result, multipoint sensing is possible with a single device configuration regardless of the number of sensor sections, and optical fiber sensing that is lower cost and more scalable than conventional methods can be realized.

[0030] The present disclosure will be described with reference to the accompanying drawings, in which two types of embodiments having different configurations of the sensor unit will be described.

[0031] (Embodiment 1) 2 is a block diagram showing the device configuration in this embodiment. A low-coherence light source 11 is used as the light source, and continuous light output from the low-coherence light source 11 is branched by an optical coupler 16 and input to a sensor interferometer 20 and a reference interferometer 30. The sensor interferometer 20 includes N sensor units 21#1 to 21#N. The optical receiver 13S receives light from the sensor interferometer 20. The optical receiver 13S receives light from the reference interferometer 30.

[0032] The reference interferometer 30 measures the propagation delay time difference between the optical paths as τ ref The Mach-Zehnder interferometer is configured as follows. The propagation delay time differences τ1 to τ N is τ ref , and multiple Mach-Zehnder interferometers are set to have no overlap (M j ≠M i (j ≠ i)). The low coherence light source 11 has a coherence time of τ ref Use something shorter than

[0033] In this embodiment, the sensor interferometer 20 has a chain-type configuration in which multiple Mach-Zehnder interferometers are connected in series using optical couplers 22#1 to 22#N and 23#1 to 23#N, and one optical path of each Mach-Zehnder interferometer of the sensor interferometer 20 is a sensor section 21#1 to 21#N.

[0034] 3 is a flowchart showing the implementation procedure in this embodiment. The implementation procedure includes an optical interference signal acquisition step S11, a reference signal phase calculation step S12, a phase connection step S13, a pseudo signal generation step S14, and a cross-correlation step S15. Note that, here, a case where sensing is performed for the j-th sensor unit 21#i among the multiple sensor units 21#1 to 21#N will be described.

[0035] In the optical interference signal acquisition step S11, two types of optical interferometers, the sensor interferometer 20 and the reference interferometer 30, are used to acquire the respective optical interference signals. Specifically, the continuous light transmitted through the sensor interferometer 20 and the continuous light transmitted through the reference interferometer 30 are received by individual optical receivers 13S and 13R, respectively, and converted into electrical signals. The received optical signals converted into electrical signals are each converted into digital signals by the A / D converter 14, and transferred to the signal processing unit 15.

[0036] The signal processing unit 15 calculates the optical interference signals of the sensor interferometer 20 and the reference interferometer 30 using the digital signals from the A / D converter 14. The digital signal obtained from the optical receiver 13S is the received light signal I(t), and the digital signal obtained from the optical receiver 13R is the received light signal I(t). ref―1 (t).

[0037] Next, in the reference signal phase calculation step S12, the signal processing unit 15 calculates the received light signal I obtained with respect to the reference interferometer 30 from among the two types of optical interference signals obtained in the optical interference signal acquisition step S11. ref―1 (t) is used to calculate the phase X1(t), which is the signal I ref―1 It can be calculated using the following formula using (t).

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[0038] Here, H[I ref―1 (t)] is I ref―1 (t) is the Hilbert transform of I ref―1 If (t) is expressed as in equation (10), then H[I ref―1 (t)] is expressed as follows:

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[0039] Next, in the phase connection step S13, X1(t) is calculated by the formula (13) Mj (t) is calculated. Here, M jis the propagation delay time difference between the optical paths in the interferometer of the j-th sensor unit 21#j, j As τ j =M j τ ref is a natural number that satisfies.

[0040] Next, in the pseudo signal generation step S14, a pseudo signal I ref―Mj Calculate (t).

[0041] Finally, in the cross-correlation step S15, the optical interference signal I(t) and the pseudo signal I ref―Mj Cross-correlation R of (t) Mj Calculate the R Mj The magnitude of the signal is monitored to detect changes in temperature and strain in the j-th sensor unit 21#j.

[0042] (Embodiment 2) In this embodiment, the implementation procedure is the same as in embodiment 1, but the device configuration used is different from that in embodiment 1. Fig. 4 is a block diagram showing the device configuration in this embodiment. A low-coherence light source 11 is used as the light source, and continuous light output from the low-coherence light source 11 is split by an optical coupler 16 and input to a sensor interferometer 20 and a reference interferometer 30.

[0043] The reference interferometer 30 measures the propagation delay time difference between the optical paths as τ ref The sensor interferometer 20 includes a plurality of sensor units 21 connected in parallel, and the propagation delay time τ of continuous light passing through the sensor interferometer 20 differs for each sensor unit 21. In this embodiment, the sensor interferometer 20 is configured by connecting optical fibers in a ladder shape using optical couplers 22#1 to 22#N and 23#1 to 23#N, and the optical path of each step of the ladder shape is sensor unit 21#1 to 21#N.

[0044] In the sensor interferometer 20 of FIG. 4, the delay time until the emitted light from the optical coupler 22#0 at the upper left end passes through each of the sensor units 21#1 to 21#N and enters the optical coupler 23#0 at the lower left end is τ ref, and the number of sensor units 21 is set to an integer multiple so that they do not overlap with each other (M j ≠M i (j≠i)). The continuous light transmitted through the sensor interferometer 20 and the continuous light transmitted through the reference interferometer 30 are received by individual photodetectors 13S and 13R, respectively, and converted into electrical signals. The received electrical signals are converted into digital signals by an A / D converter 14, and transferred to a signal processing unit 15. The low coherence light source 11 used in this device configuration has a coherence time of τ ref Use something shorter than

[0045] Other steps are performed according to the flowchart of FIG. 3, similarly to the first embodiment.

[0046] 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]

[0047] The present disclosure can be applied to the information and communications industry. [Explanation of symbols]

[0048] 11: Low coherence light source 12: High coherence light source 13:Receiver 14: A / D converter 15: Signal processing section 16, 22#0~22#N, 23#0~23#N, 32, 33: Optical coupler 20: Sensor interferometer 30: Reference interferometer

Claims

1. A light source that outputs continuous light; an optical coupler that branches the continuous light; The continuous light branched by the optical coupler is input, and a predetermined propagation delay time difference τ ｒｅｆ in the continuous light; The continuous light branched by the optical coupler is input, and the predetermined propagation delay time difference τ ｒｅｆ a sensor interferometer in which a plurality of Mach-Zehnder interferometers are connected to generate propagation delay time differences in the continuous light that correspond to integer multiples of and are different from each other, and one of the optical paths of the Mach-Zehnder interferometers functions as a sensor unit; A light receiving signal I(t) obtained by receiving the transmitted light of the sensor interferometer and a reference signal I(t) obtained by receiving the transmitted light of the reference interferometer ｒｅｆ－１ A signal processing unit that performs signal processing using (t); Equipped with The signal processing unit includes: The reference signal I ｒｅｆ－１ (t) is used to obtain the reference signal I corresponding to the j-th (j is a natural number) sensor unit. ｒｅｆ―ｊ (t) is calculated, The received light signal I(t) and the reference signal I ｒｅｆ―ｊ Cross-correlation R ｊ Calculate The cross-correlation R ｊ Using the change in Optical fiber sensing device.

2. The signal processing unit includes: The reference signal I ｒｅｆ－１ (t) to obtain the predetermined propagation delay time difference τ ｒｅｆ The phase X of the continuous light when １ (t) is calculated, The propagation delay time difference in the j-th sensor unit is τ ｒｅｆ M ｊ In the case of double, M ｊ X of pieces １ (t) to τ ｒｅｆ By adding up the waveforms shifted by one, the phase X corresponding to the j-th sensor unit is obtained. Ｍｊ (t) is calculated, The phase X Ｍｊ (t) is used to obtain the reference signal I corresponding to the j-th sensor unit. ｒｅｆ―ｊ Calculate (t); 2. The optical fiber sensing device according to claim 1.

3. The signal processing unit includes: The phase X Ｍｊ A cosine wave having a phase component of (t) is used as the reference signal I ｒｅｆ―ｊ (t) Using the cosine wave, the received light signal I(t) and the reference signal I ｒｅｆ―ｊ Cross-correlation R ｊ Calculate 3. The optical fiber sensing device according to claim 2.

4. The predetermined propagation delay time difference τ in the reference interferometer ｒｅｆ is longer than the coherence time of the continuous light.

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

5. The sensor interferometer 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 propagation delay time differences of the sensors included in the plurality of Mach-Zehnder interferometers are different from each other.

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

6. the sensor interferometer includes a plurality of sensor units connected in parallel, a propagation delay time of the continuous light passing through the sensor interferometer differs for each sensor unit; 6. The optical fiber sensing device according to claim 1.

7. The change in the sensor unit is a change in temperature or strain of the j-th sensor unit.

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

8. Continuous light from the light source is branched, Predetermined propagation delay time difference τ ｒｅｆ The split continuous light is incident on a reference interferometer which generates a The predetermined propagation delay time difference τ ｒｅｆ the branched continuous light is input to a sensor interferometer, in which a plurality of Mach-Zehnder interferometers are connected to generate propagation delay time differences in the continuous light that correspond to integer multiples of and are different from each other, and one of the optical paths of the Mach-Zehnder interferometers functions as a sensor unit; A signal processing unit receives a light receiving signal I(t) obtained by receiving the transmitted light of the sensor interferometer and a reference signal I(t) obtained by receiving the transmitted light of the reference interferometer. ｒｅｆ－１ (t) an optical fiber sensing method for detecting a change in the sensor unit, The signal processing unit includes: The reference signal I ｒｅｆ－１ (t) is used to obtain the reference signal I ｒｅｆ―ｊ (t) is calculated, The received light signal I(t) and the reference signal I ｒｅｆ―ｊ Cross-correlation R ｊ Calculate The cross-correlation R ｊ Using the change in Fiber optic sensing methods.

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