Optical fiber sensing method, optical fiber sensor, and program

Abstract

It mitigates the impact of noise, which can cause measurement errors. [Solution] The method includes the following steps: creating frequency spectrum sequences that are shifted to the lower frequency side and frequency spectrum sequences that are shifted to the higher frequency side by a predetermined number of shift points, based on the frequency spectrum of the divided section to be corrected; performing cross-correlation processing on each of the frequency spectrum sequences that are shifted to the lower frequency side and the frequency spectrum sequences that are shifted to the higher frequency side to obtain the result of the cross-correlation function; calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences that are shifted to the lower frequency side and the higher frequency side; calculating the average Lag value that maximizes the average value of the results of the cross-correlation function; and, if the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold, replacing the reference Lag value with the average Lag value.

Description

[Technical Field]

[0001] The present invention relates to an optical fiber sensing method, an optical fiber sensor, and a program that can be used in Optical Frequency Domain Reflectometry (OFDR) used for maintenance and management of social infrastructure, etc. [Background Art]

[0002] As a measurement algorithm for OFDR, one disclosed in Non-Patent Document 1 is known. In the technique disclosed in Non-Patent Document 1, a reference signal and a measurement signal are acquired, each acquired signal is subjected to fast Fourier transform, divided at constant frequency intervals, then subjected to inverse Fourier transform, and a cross-correlation function is acquired for each divided section. A Lag value at which the cross-correlation coefficient is maximized is obtained for each divided section, and a strain value is determined according to the Lag value. [Prior Art Documents] [Non-Patent Documents]

[0003] [Non-Patent Document 1] "Cryogenic temperature measurement using Rayleigh backscattering spectra shift by OFDR", IEEE Photon. Technol. Lett., vol. 26, no. 11, pp. 1150-1153, Jun. 2014. [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, in the measurement algorithm disclosed in the aforementioned Non-Patent Document 1, when the measurement resolution is increased and the amount of change in strain is increased, the similarity between the reference signal and the measurement signal decreases, which causes measurement errors and creates the problem that appropriate strain cannot be calculated.

[0005] Distortion is calculated by determining the amount of shift in the Rayleigh scattered light spectrum using a cross-correlation function. When the measurement resolution is high, the correlation coefficient decreases as the number of points to which the cross-correlation function is applied decreases. Also, when the amount of change in distortion is large, the amount of shift in the Rayleigh scattered light spectrum increases, and as highly similar signals and new signals are swapped by the amount of the shift, it becomes difficult to obtain correlation, and the correlation coefficient decreases.

[0006] In this way, as the measurement resolution is increased and the amount of distortion change increases, the correlation peak becomes buried in noise, and the noise is mistaken for an incorrect peak. As a result, an incorrect result is calculated, and a measurement error occurs.

[0007] This invention has been made in view of the above-mentioned problems. The object of this invention is to provide an optical fiber sensing method, an optical fiber sensor, and a program that can mitigate the effects of noise, even in situations where conventional methods would cause measurement errors due to noise overload. [Means for solving the problem]

[0008] To achieve the above-mentioned objectives, the optical fiber sensing method of this invention includes the following steps: dividing the reference signal and measurement signal obtained by frequency domain optical reflectometry by a frequency width ΔX, performing cross-correlation processing of the reference signal and measurement signal with respect to the frequency spectrum of the divided section to be corrected as a reference to calculate the Lag value as the reference Lag value; creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points Shift_Point with respect to the frequency spectrum of the divided section to be corrected as a reference; and creating a frequency spectrum sequence that is shifted to the higher frequency side by the aforementioned number of shift points Shift_Point with respect to the frequency spectrum of the divided section to be corrected as a reference. The method includes the following steps: performing cross-correlation processing on each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side to obtain the result of a cross-correlation function; calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side; calculating the Lag value that maximizes the average value of the results of the cross-correlation function as the average Lag value; and, if the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold, replacing the reference Lag value with the average Lag value.

[0009] Furthermore, the optical fiber sensor of this invention includes a processing unit to which a reference signal and a measurement signal obtained by frequency-domain optical reflectometry are input, a means for dividing the reference signal and measurement signal obtained by frequency-domain optical reflectometry by a frequency width ΔX, and performing cross-correlation processing of the reference signal and the measurement signal with respect to the frequency spectrum of the divided section to be corrected as a reference to calculate the Lag value as the reference Lag value, a means for creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points Shift_Point with respect to the frequency spectrum of the divided section to be corrected as a reference, and a means for creating a frequency spectrum sequence that is shifted to the higher frequency side by the aforementioned number of shift points Shift_Point with respect to the frequency spectrum of the divided section to be corrected The system includes means for creating a frequency spectrum sequence, means for performing cross-correlation processing on each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequence shifted to the higher frequency side to obtain the result of a cross-correlation function, means for calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequence shifted to the higher frequency side, means for calculating the Lag value that maximizes the average value of the results of the cross-correlation function as the average Lag value, and means for replacing the reference Lag value with the average Lag value if the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold.

[0010] Furthermore, the program of this invention provides a processing unit to which a reference signal and a measurement signal obtained by frequency-domain optical reflectometry are input. The program provides means for dividing the reference signal and measurement signal obtained by frequency-domain optical reflectometry into a frequency width ΔX, and calculating the Lag value as the reference Lag value by performing cross-correlation processing of the reference signal and the measurement signal with respect to the frequency spectrum of the divided section to be corrected. It also provides means for creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points Shift_Point with respect to the frequency spectrum of the divided section to be corrected. The system functions as a means for creating a frequency spectrum sequence, a means for performing cross-correlation processing on each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side to obtain the result of a cross-correlation function, a means for calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side, a means for calculating the Lag value that maximizes the average value of the results of the cross-correlation function as the average Lag value, and a means for replacing the reference Lag value with the average Lag value if the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold. [Effects of the Invention]

[0011] According to the optical fiber sensing method, optical fiber sensor, and program of this invention, by averaging the results of cross-correlation processing, it is possible to measure peaks that would normally be buried in noise. This reduces the impact of noise in situations where conventional methods would result in measurement errors due to noise overload. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of an optical fiber sensor. [Figure 2] Figure (1) shows the processing flow of the optical fiber sensing method. [Figure 3] Figure (2) shows the processing flow of the optical fiber sensing method. [Figure 4] This is a schematic diagram to explain the averaging process. [Figure 5] The measurement results are shown in the figure. [Figure 6] This figure shows the results of the cross-correlation process. [Modes for carrying out the invention]

[0013] The embodiments of this invention will be described below with reference to the figures, but the shapes, sizes, and arrangements of each component are only shown in a general manner to the extent that the invention can be understood. Furthermore, preferred configuration examples of this invention will be described below, but these are merely examples. Therefore, this invention is not limited to the following embodiments, and many changes or modifications can be made to achieve the effects of this invention without departing from the scope of the configuration of this invention.

[0014] The OFDR type optical fiber sensor will be explained with reference to Figure 1. Figure 1 is a schematic diagram of the optical fiber sensor.

[0015] The optical fiber sensor comprises a frequency-swept light source 10, a 1:99 splitter 11, a main interferometer 20, an auxiliary interferometer 30, a polarizing beam splitter 40, an optical fiber to be measured 50, and an optical signal acquisition unit 60.

[0016] Light generated by the frequency-swept light source 10 is sent to the 1:99 splitter 11. The 1:99 splitter 11 splits the light generated by the frequency-swept light source 10 into two. One of the two branches from the 1:99 splitter 11 is sent to the main interference system 20, and the other is sent to the auxiliary interference system 30.

[0017] The main interferometer system 20 comprises a 1:99 branching unit 21, a circulator 22, and a 50:50 branching unit 23. The light sent to the main interferometer system 20 is split into two branches by the 1:99 branching unit 21. One of the two beams split by the 1:99 branching unit 21 is sent to the circulator 22. The other of the two beams split by the 1:99 branching unit 21 is sent to the 50:50 branching unit 23.

[0018] The circulator 22 has first to third ports. Light input to the first port is output from the second port, light input to the second port is output from the third port, and light input to the third port is output from the first port.

[0019] Light sent from the 1:99 branching unit 21 is input to the first port of the circulator 22 and output from the second port. An optical fiber 50 to be measured is connected to the second port of the circulator 22. Light output from the second port of the circulator 22 is incident into the optical fiber 50. Rayleigh scattered light generated in the optical fiber 50 propagates through the optical fiber 50 in a direction opposite to the incident direction, and is sent to the main interferometer system 20. The Rayleigh scattered light sent to the main interferometer system 20 is input to the second port of the circulator 22 and output from the third port. Light output from the third port of the circulator 22 is sent to the 50:50 branching unit 23.

[0020] The 50:50 branching unit 23 multiplexes the light sent from the 1:99 branching unit 21 and the light sent from the circulator 22.

[0021] The light multiplexed by the 50:50 branching unit 23 is sent to a polarizing beam splitter 40. The polarizing beam splitter 40 splits input light into light components in two orthogonal polarization directions, and sends each of the light components to an optical signal acquisition unit 60.

[0022] The auxiliary interference system 30 is comprised of a first 50:50 splitter 31, a delay optical fiber 32, and a second 50:50 splitter 33. Light sent to the auxiliary interference system 30 is split into two at the first 50:50 splitter 31. One of the two branches from the first 50:50 splitter 31 is sent to the second 50:50 splitter 33. The other branch from the first 50:50 splitter 31 is sent to the delay optical fiber 32. The light sent to the delay optical fiber 32 is delayed for a certain period of time before being sent to the second 50:50 splitter 33.

[0023] The second 50:50 splitter 33 combines the light sent from the first 50:50 splitter 31 with the light sent from the delay optical fiber 32. The light combined in the second 50:50 splitter 33 is sent to the optical signal acquisition unit 60.

[0024] The optical signal acquisition unit 60 is comprised of first to third photoelectric converters 61-1 to 61-3, an analog-to-digital converter (ADC) 62, and a processing unit 63.

[0025] The two beams of light separated by the polarizing beam splitter 40 are incident on the first and second photoelectric converters 61-1 and 61-2, respectively. The light combined at the second 50:50 splitter 33 of the auxiliary interferometer 30 is incident on the third photoelectric converter 61-3. The first to third photoelectric converters 61-1 to 61-3 convert the incident light into analog electrical signals. The analog electrical signals generated by the first to third photoelectric converters 61-1 to 61-3 are sent to the ADC 62. The ADC 62 converts the analog electrical signals into digital electrical signals and sends them to the arithmetic processing unit 63.

[0026] The arithmetic processing unit 63 is a device that has the function of processing digital electrical signals, and apart from the functional means implemented by the arithmetic processing unit 63, it can be any suitable conventional known configuration, such as a personal computer (PC). Similarly, apart from the functional means implemented by the arithmetic processing unit 63, the optical fiber sensor, including the frequency sweep light source 10, the 1:99 branching unit 11, the main interference system 20, the auxiliary interference system 30, the polarizing beam splitter 40, the optical fiber to be measured 50, and the optical signal processing unit 60, can also be any suitable conventional known configuration. Therefore, a detailed explanation of the aspects that can be of conventional known configuration is omitted.

[0027] The following processes are performed when the arithmetic processing unit 63 executes a program stored in a storage device of any choice. That is, the arithmetic processing unit 63 is equipped with functional means to perform the following processes.

[0028] The processing in the arithmetic processing unit 63 will be explained with reference to Figures 2 to 4. Figures 2 and 3 are diagrams showing the processing flow of the optical fiber sensing method. Figure 2(A) is a flowchart of the demodulation process, Figure 2(B) is a flowchart of the strain conversion process, Figure 3 is a flowchart of the averaging process, and Figure 4 is a schematic diagram for explaining the averaging process.

[0029] The processing in the arithmetic processing unit 63 includes a demodulation process (step 100 (hereinafter, step will be denoted as S)) and a distortion conversion process (S200).

[0030] The demodulation process S100 is performed on the signal sent to the arithmetic processing unit 63. The demodulation process S100 includes the following steps S101 to S109.

[0031] First, in S101, the signal acquired from the auxiliary interference system 30 (hereinafter also referred to as the reference signal) is subjected to a Hilbert transform to calculate the phase of the reference signal.

[0032] Next, in S102, the phase of the reference signal calculated in S101 is unwrapped. The phase calculated in S101 repeatedly changes from -π to +π. At this time, there is a discontinuity where the phase changes from +π to -π. Therefore, if an unwrapping process is applied, for example, by adding +2π each time the phase changes from +π to -π, the phase of the reference signal is converted into a continuous phase.

[0033] Next, in S103, phases are extracted from the continuous phases obtained in S102 at arbitrary phase intervals so that the phases are equally spaced. The storage positions on the array corresponding to these extracted phases are recorded. These storage positions on the array correspond to time t.

[0034] Next, in S104, the signal from the main interferometer (hereinafter also referred to as the measurement signal) is extracted. In this step, the storage position signal recorded in S103 is extracted from the two measurement signals output from the main interferometer and split into two by the polarizing beam splitter 40.

[0035] Next, in S105, for each of the two measurement signals split by the polarizing beam splitter 40, the signals extracted in S104 are spline-interpolated to match the number of data points of the original signal.

[0036] Next, in S106, the measurement signal that was spline-interpolated in S105 is subjected to a Fast Fourier Transform.

[0037] Next, in S107, the frequency spectrum obtained by the Fast Fourier Transform in S106 is divided into segments with a constant frequency width ΔX, starting from the low-frequency side. This frequency width ΔX corresponds to the spatial resolution in OFDR.

[0038] Next, in S108, an inverse fast Fourier transform is performed on each of the data points that were divided in S107.

[0039] Next, in S109, the two signals obtained by the inverse fast Fourier transform in S108 are subjected to polarization diversity processing and demodulated into a single signal.

[0040] The demodulation process S100 (S101-S109) described above is performed on the reference signal and the measurement signal, respectively.

[0041] The reference signal and measurement signal, which have undergone the demodulation process S100, are then subjected to the distortion conversion process S200.

[0042] The distortion conversion process S200 includes processes S201 to S203.

[0043] In S201, cross-correlation processing is performed. In cross-correlation processing, the correlation coefficient is calculated for each Lag value when the reference signal and the measured signal are shifted (the Lag value is changed) for the same divided interval obtained in the division processing in S107.

[0044] In S202, the Lag value at which the cross-correlation is greatest for each partitioned interval is obtained, and the intervals are sorted accordingly.

[0045] In S203, the Lag value is converted into distortion for each division interval. This allows the distortion for each division interval to be calculated.

[0046] Furthermore, the demodulation process S100 (S101-S109) and the distortion conversion process S200 (S201-S203) described above can be any preferred conventional known configuration.

[0047] Here, if the measurement resolution is increased and the amount of distortion change is increased, the peak obtained by cross-correlation processing of the reference signal and the measurement signal (correlation peak) becomes buried in noise, and the noise is mistaken for an incorrect peak. As a result, an incorrect result is calculated, and a measurement error occurs.

[0048] In light of this situation, the present invention performs the averaging process S300 between the strain conversion processes S202 and S203, or after the processing of S203. Therefore, the optical fiber sensing method, optical fiber sensor, and program of this invention are characterized by having an algorithm for the averaging process S300.

[0049] First, in S301, a data column List is prepared. The data column List may be all the data of the reference signal and the measurement signal, or it may be data extracted by any extraction method. Here, it is assumed that the data column List contains N (N is an integer of 1 or more) data for the division intervals to be corrected.

[0050] The parameter z (where z is an integer between 1 and N, inclusive) is set as a parameter for scanning the data list, and z=1. Additionally, the number of data point shifts, Shift_num (Shift_num is an integer greater than or equal to 1), is set as an arbitrary value. Furthermore, the number of data points N_Point (N_Point is an integer greater than or equal to 1) included in the frequency width ΔX is divided by the number of shifts, Shift_num, to obtain the number of shift points, Shift_Point (=N_Point / Shift_num). The loop count n is set to Shift_num / 2.

[0051] Next, in S302, let m be the z-th value of the data column List.

[0052] Furthermore, in S303, a loop variable i (where i is an integer between 1 and n, inclusive) is set to i=1. Also, a storage column Average_Data is created, and the m-th Lag value calculated in S202 is assigned to the Average_Data column.

[0053] Next, in S310, frequency spectrum sequences are created that are shifted to lower frequencies by Shift_Points and shifted to higher frequencies by Shift_Points, using the m-th frequency spectrum as a reference. Cross-correlation processing is then performed on each of these frequency spectrum sequences. The average value of the cross-correlation function results calculated for each frequency spectrum sequence and the cross-correlation function result calculated for the reference frequency spectrum is obtained. The Lag value (also called the average Lag value) that has the maximum correlation coefficient among these averaged cross-correlation function results is calculated. If the difference between the obtained average Lag value and the Lag value calculated for the reference frequency spectrum (also called the reference Lag value) is greater than a threshold, the Lag value of the m-th frequency spectrum is replaced with the average value of the Lag values.

[0054] Specifically, S310 comprises steps S311 to S320.

[0055] In S311, (i × Shift_Point) data points are concatenated from the end of the (m-1)th frequency spectrum, and {N_Point - (i × Shift_Point)} data points are concatenated from the beginning of the mth frequency spectrum. This creates a frequency spectrum sequence that is shifted to the lower frequency side by (i × Shift_Point) points from the mth frequency spectrum.

[0056] Next, in S312, {N_Point-(i×Shift_Point)} data points are joined together from the end of the m-th frequency spectrum and (i×Shift_Point) data points are joined from the beginning of the (m+1)-th frequency spectrum. This creates a frequency spectrum sequence that is shifted to a higher frequency side by (i×Shift_Point) points from the m-th frequency spectrum.

[0057] Next, in S313, the frequency spectrum sequence shifted to the lower frequency side created by the processing in S311 and the frequency spectrum sequence shifted to the higher frequency side created by the processing in S312 are subjected to OFDR processing, and the results of the cross-correlation function are obtained by sequentially performing the processes in S108, S109, and S201.

[0058] Next, in S314, the result of the cross-correlation function obtained by processing in S313 is added to the storage column Average_Data.

[0059] Next, in S315, it is determined whether the loop variable i matches the loop count n (i=n or not).

[0060] If the result of the S315 check is No, that is, if i is less than n, then in S316, 1 is added to the loop variable i, and i+1 is used as the new i, and the process from S311 to S315 is repeated.

[0061] On the other hand, if the result of the determination in S315 is Yes, that is, if i is equal to n, then the processing for the desired number of frequency spectra is considered complete, and in S317, the storage column Average_Data, which is the sum of the results of the cross-correlation function, is divided by the number of frequency spectra, 2n+1. Here, the results of the cross-correlation function added to the storage column Average_Data are 1 calculated from the reference frequency spectrum, n calculated from frequency spectrum columns shifted to the lower frequency side, and n calculated from frequency spectrum columns shifted to the higher frequency side, for a total of 2n+1 results.

[0062] Next, in S318, the Lag value (average Lag value) that maximizes the result of the cross-correlation function is calculated from the averaged Average_Data obtained in S317.

[0063] Next, in S319, it is determined whether the difference between the average Lag value newly obtained in S318 and the m-th Lag value (reference Lag value) is less than or equal to a predetermined threshold.

[0064] If the result of the judgment in S319 is No, that is, if the difference is greater than the threshold, then in S320, the reference Lag value is replaced with the average Lag value calculated in S318, and the process proceeds to S331.

[0065] On the other hand, if the result of the determination in S319 is Yes, that is, if the difference is less than or equal to the threshold, the process proceeds directly to S331.

[0066] Next, in S331, it is determined whether processing has been performed on all N (where N is an integer greater than or equal to 1) data points to be corrected (i.e., whether z=N or not).

[0067] If the result of the determination in S331 is No, that is, if the number of processed data z is less than N, then in S332, 1 is added to the parameter z, and z+1 is used as the new z, and the processing from S302 to S321 is repeated.

[0068] On the other hand, if the result of the determination in S331 is Yes, that is, if the number of processed data points z is equal to N, the averaging process is terminated, as it is assumed that the averaging process has been completed for all the division intervals to be corrected.

[0069] As described above, this invention averages the results of cross-correlation processing. As a result, it is possible to measure peaks that would normally be buried in noise. This reduces the impact of noise in situations where conventional methods would cause measurement errors due to noise overload.

[0070] The measurement results obtained by the optical fiber sensor of this invention will be explained with reference to Figure 5. Figure 5 is a diagram showing the measurement results. In Figure 5, the horizontal axis represents the distance from the input end of the measuring optical fiber (Distance) [unit: m], and the vertical axis represents the strain (Strain) [unit: με].

[0071] Figures 5(A) and (B) show the measurement results when six levels of strain are applied at 1000 με intervals to an 8-9 m section of the measurement optical fiber. Figure 5(A) shows the result without S300 averaging, and Figure 5(B) shows the result with S300 averaging.

[0072] As shown in Figure 5(A), without averaging, strains up to 4000 με can be measured accurately, but strains greater than 4000 με, in this case 5000 με and 6000 με, cannot be measured accurately, resulting in measurement errors.

[0073] On the other hand, as shown in Figure 5(B), when averaging is performed, strains up to 6000 με can be measured accurately.

[0074] Referring to Figure 6, the cross-correlation processing obtained by the optical fiber sensor of this invention will be explained. Figure 6 is a diagram showing the results of the cross-correlation processing. Figure 6(A) shows the case where the averaging processing in S300 is not performed, and Figure 6(B) shows the case where the averaging processing in S300 is performed.

[0075] As shown in Figure 6(A), without averaging, the noise is high and the peaks are buried.

[0076] On the other hand, as shown in Figure 6(B), when averaging is applied, the noise is reduced and the peaks become clearly visible.

[0077] By incorporating this averaging algorithm, it becomes possible to measure distortions that are difficult to measure with conventional methods. [Explanation of symbols]

[0078] 10 Frequency Sweep Light Source 11, 21 1:99 branching point 20. Main Interferometer 22 Circulator 23, 31, 33 50:50 branching point 30 Auxiliary Interferometry 32 Optical fibers for delay 40 Polarizing Beam Splitter 50 optical fibers 60 Optical signal acquisition unit 61 Photoelectric Converter 62 ADC 63 Arithmetic Processing Unit

Claims

1. The process involves dividing the reference signal and measurement signal obtained by frequency domain optical reflectometry into segments with a frequency width ΔX, and then using the frequency spectrum of the segment to be corrected as a reference to perform cross-correlation processing on the reference signal and measurement signal to calculate the reference Lag value. The process of creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points (Shift_Point), based on the frequency spectrum of the division section to be corrected. The process of creating a frequency spectrum sequence that is shifted towards the higher frequency side by the number of shift points Shift_Point, based on the frequency spectrum of the division section to be corrected. The process of performing cross-correlation processing on the frequency spectrum sequence shifted to the lower frequency side and the frequency spectrum sequence shifted to the higher frequency side, and obtaining the result of the cross-correlation function, The process of calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side, The process of calculating the average Lag value as the Lag value that maximizes the average of the results of the cross-correlation function, and If the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold, the process of replacing the reference Lag value with the average Lag value is performed. A fiber optic sensing method comprising [a specific feature / feature].

2. A processing unit that receives the reference signal and measurement signal obtained by frequency-domain optical reflectometry is, A means for dividing the reference signal and measurement signal obtained by frequency domain optical reflectometry into sections with a frequency width ΔX, and calculating the Lag value as the reference Lag value by performing cross-correlation processing on the reference signal and measurement signal using the frequency spectrum of the section to be corrected as the reference. A means for creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points, Shift_Point, based on the frequency spectrum of the division section to be corrected. Means for creating a frequency spectrum sequence that is shifted towards the higher frequency side by the number of shift points Shift_Point, based on the frequency spectrum of the division section to be corrected. Means for performing cross-correlation processing on the frequency spectrum sequence shifted to the lower frequency side and the frequency spectrum sequence shifted to the higher frequency side, and obtaining the result of the cross-correlation function. Means for calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side. A means for calculating the average Lag value as the Lag value that maximizes the average of the results of the cross-correlation function, and If the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold, the means for replacing the reference Lag value with the average Lag value. A fiber optic sensor equipped with the following features.

3. A processing unit that receives the reference signal and measurement signal obtained by frequency-domain optical reflectometry is configured to accept these signals. A means for dividing the reference signal and measurement signal obtained by frequency domain optical reflectometry into sections with a frequency width ΔX, and calculating the Lag value as the reference Lag value by performing cross-correlation processing on the reference signal and measurement signal using the frequency spectrum of the section to be corrected as the reference. A means for creating a frequency spectrum sequence that is shifted to the lower frequency side by a predetermined number of shift points, Shift_Point, based on the frequency spectrum of the division section to be corrected. Means for creating a frequency spectrum sequence that is shifted towards the higher frequency side by the number of shift points Shift_Point, based on the frequency spectrum of the division section to be corrected. Means for performing cross-correlation processing on the frequency spectrum sequence shifted to the lower frequency side and the frequency spectrum sequence shifted to the higher frequency side to obtain the result of the cross-correlation function, Means for calculating the average value of the results of the cross-correlation function calculated for each of the frequency spectrum sequences shifted to the lower frequency side and the frequency spectrum sequences shifted to the higher frequency side. A means for calculating the average Lag value as the Lag value that maximizes the average of the results of the cross-correlation function, and If the difference between the average Lag value and the reference Lag value is greater than a predetermined threshold, the means for replacing the reference Lag value with the average Lag value. A program designed to function as such.

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