OFDR System

Abstract

This disclosure aims to improve the measurement accuracy in an OFDR system at distances that are integer multiples of the delay length of the reference interferometer. [Solution] This disclosure provides a data processor for processing a measurement interferometer signal measured using an OFDR, wherein the phase χ of a reference interferometer signal generated using the same optical frequency sweep light source as the measurement interferometer signal is used to process the phase χ of the reference interferometer signal corresponding to the measurement distance. P Calculate the phase χ P This is a data processor that linearizes the measurement interferometer signal using [a specific method / tool].

Description

[Technical Field]

[0001] This disclosure relates to an OFDR system. [Background technology]

[0002] One method for measuring optical reflectance is optical frequency domain reflectometry (OFDR) (see, for example, Patent Document 1). In OFDR, the optical frequency swept light emitted from an optical frequency swept light source is split into two, and the measurement interferometer signal generated by the interference between the signal light reflected and disturbed by the object being measured and one of the reference beams is analyzed to identify the reflection peak caused by the object being measured, thereby measuring the distance to the object.

[0003] In Patent Document 1, the measurement interferometer signal was linearized based on the phase of the reference interferometer signal, and the linearized measurement interferometer signal was subjected to an FFT (Fast Fourier Transform). In this case, the further the reflection position of the measurement interferometer signal deviated from the delay length of the reference interferometer, the blurred the OFDR spectrum became and the accuracy decreased. As a countermeasure, Patent Document 1 calculated an interferometer signal with a delay length that was an integer multiple of the delay length of the reference interferometer, and linearized the measurement interferometer signal from its phase. The linearization method in Patent Document 1 is called the coherence compensation method. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 4917640 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the coherence compensation method described in Patent Document 1, linearization is optimal at positions that are integer multiples of the delay length of the reference interferometer. However, the OFDR spectrum becomes blurred and the width of the reflection peak widens as the position moves away from an integer multiple of the delay length of the reference interferometer. For this reason, when the delay length is 30m, optimization is possible at 60m, 90m, 120m, etc., but the measurement accuracy deteriorates at 45m, 75m, etc. Thus, the coherence compensation method described in Patent Document 1 has the problem that the measurement accuracy of strain and temperature distribution decreases as the position moves away from an integer multiple of the delay length of the reference interferometer.

[0006] This disclosure aims to improve the measurement accuracy in an OFDR system at distances that are integer multiples of the delay length of the reference interferometer. [Means for solving the problem]

[0007] To achieve the above objectives, the OFDR system of this disclosure is A light source (11) that emits light swept by optical frequency, A reference interferometer (14) that generates a reference interferometer signal using the aforementioned optical frequency sweep light, A measuring interferometer (13) measures a measuring interferometer signal by combining the signal light reflected or scattered by the object to be measured (100) from the optical frequency sweep light with a reference light, A data processor (17) of the present invention linearizes the measurement interferometer signal using the reference interferometer signal, It is equipped with.

[0008] The OFDR system of this disclosure may include an AD converter (16) that converts the reference interferometer signal and the measurement interferometer signal into digital signals at the same time interval.

[0009] The data processor of the present disclosure performs the method of the present disclosure. Specifically, the data processor of the present disclosure is a method performed by a data processor that processes a measurement interferometer signal measured using an OFDR, using the phase χ of a reference interferometer signal generated using the same optical frequency sweep light source as the measurement interferometer signal, and the phase χ of the reference interferometer signal corresponding to the measurement distance. PCalculate the phase χ P Use it to linearize the measured interferometer signal.

[0010] The delay of the reference interferometer is L ref At this time, the data processor When the delay is L ref Calculate the phase χ of the reference interferometer signal, The delay L of the reference interferometer corresponding to the measured distance P The delay time τ at P Calculate, Using the phase χ, the phase χ at the delay time τ P Calculate the phase χ at P Calculate, The phase χ P By calculating the value of the measured interferometer signal at the time when the phase χ is equally spaced, the linearization of the measured interferometer signal may be performed.

[0011] The measured distance is longer than the delay L in the reference interferometer signal. The data processor uses the integrated phase obtained by integrating the phase χ on the time axis to calculate the phase χ ref For this reason, the linearization method of the present disclosure can be referred to as a phase integration method. For example, the data processor can calculate the phase χ using Equation (7) described later. P Calculate. P

[0012] The data processor may calculate the OFDR spectrum of the measured interferometer signal using the value of the measured interferometer signal at the time when the phase χ is equally spaced. At this time, the data processor can perform arbitrary processing using the OFDR spectrum of the measured interferometer signal. For example, the data processor may calculate the distance of the reflection point using the peak position of the OFDR spectrum of the measured interferometer signal. P

[0013] The measurement object may be an optical fiber. In this form, the data processor uses the delay L P As the delay L​​ref It can be set to a half-integer multiple of the delay length L. The data processor controls the delay length L. P 1 / 2L centered around ref The range of h may be used as the strain measurement section to calculate the distribution of at least one of the reflections and strains in the optical fiber in the longitudinal direction of the optical fiber.

[0014] Furthermore, the above disclosures can be combined as much as possible. [Effects of the Invention]

[0015] According to this disclosure, in an OFDR system, measurement accuracy can be improved at distances that are integer multiples of the delay length of the reference interferometer. [Brief explanation of the drawing]

[0016] [Figure 1] An example of the OFDR system described herein is shown. [Figure 2] An example of the measurement interferometer signal S and the reference interferometer signal is shown. [Figure 3] An example of a method for linearizing a measurement interferometer signal S using the coherence compensation method is shown. [Figure 4] An example of a phase Φ is shown. [Figure 5] An example of a continuous phase χ(t,τref) is shown. [Figure 6] An example of a partition of the continuous phase χ(t,τref) is shown. [Figure 7] An example of time ni is shown. [Figure 8] An example of calculating the value of the measured interferometer signal S at time ni is shown. [Figure 9] An example of a reflection peak is shown. [Figure 10] An example of the phase χ(t,τref) quantity relative to the A / D index is shown. [Figure 11] An example of the time variation of the value obtained by subtracting a cubic function from χ(t,τref) is shown. [Figure 12] An example of the integral phase Φ(t) is shown. [Figure 13] An example of a method for linearizing the measurement interferometer signal S using the phase integration method of this embodiment is shown. [Figure 14] An example of the phase χP = χ(t,τP) at the delay time τP is shown. [Figure 15] The following are examples of measurement results for each peak when χp is set to an integer multiple of the reference interferometer delay length using the linearization method of this disclosure, where (a) shows approximately 60m, (b) shows approximately 75m, and (c) shows approximately 85m. [Figure 16] The following are examples of the measurement results of each peak when χp is set to a half-integer multiple of the reference interferometer delay length using the linearization method of this disclosure, where (a) shows approximately 60m, (b) shows approximately 75m, and (c) shows approximately 85m. [Figure 17] An example of the OFDR system of this embodiment is shown. [Figure 18] This is an explanatory diagram of the reflection distribution R(z). [Figure 19] This is an explanatory diagram of the strain measurement category data Rd(h). [Figure 20] This is an explanatory diagram for the processing of strain measurement data Rd(h). [Figure 21] This is an explanatory diagram of the waveform Md(h) for strain measurement category h. [Figure 22] This is an explanatory diagram of the segmented waveform Md(h) when compression strain is applied. [Figure 23] This is an explanatory diagram of the segmental waveform Md(h) when strain is applied in the extension direction. [Figure 24] This is an explanatory diagram of the cross-phase correlation Sh(m) between the reference waveform Mdref(h) and the segmented waveform Md(h). [Figure 25] This is an example of the distribution of the maximum value of the cross-correlation Sh(m). [Figure 26] This is an explanatory diagram illustrating an example of measuring the strain temperature distribution in this embodiment. [Modes for carrying out the invention]

[0017] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0018] (First embodiment) Figure 1 shows an example of the OFDR system of this embodiment. The OFDR system of this embodiment linearizes the measurement interferometer signal S using a software linearization method. For example, the OFDR system includes an optical frequency sweep light source 11, a measurement interferometer 13, a reference interferometer 14, an AD converter 16, and a data processing unit 17.

[0019] The frequency-swept light emitted from the frequency-swept light source 11 is split by the coupler 12 to the reference interferometer 14 and the measurement interferometer 13. The reference interferometer 14 uses the frequency-swept light to measure a constant delay length L. ref The measuring interferometer 13 generates and outputs a corresponding reference interferometer signal. The measuring interferometer 13 irradiates the object to be measured 100 with optical frequency sweep light and outputs a measuring interferometer signal obtained by combining the signal light reflected or scattered by the object to be measured 100 with the reference light.

[0020] The AD converter 16 simultaneously samples the reference interferometer signal and the measurement interferometer signal S at equal time intervals. As a result, the digital signals of the reference interferometer signal and the measurement interferometer signal S are output from the AD converter 16 to the data processing unit 17. The data processing unit 17 analyzes the reference interferometer signal and the measurement interferometer signal S from the AD converter 16.

[0021] In this embodiment, a constant delay length L ref The measurement interferometer signal S is linearized using the corresponding reference interferometer signal. Therefore, even if the relationship between the optical frequency and time of the optical frequency sweep light is nonlinear, this nonlinearity can be canceled out.

[0022] The configuration of the reference interferometer 14 is arbitrary, but for example, the optical frequency sweep light is split by the coupler 41, the split light is reflected by different mirrors 42A and 42B, the reflected light from these mirrors 42A and 42B is combined by the coupler 41, and the combined light is received by the photodetector 43. As a result, the reference interferometer 14 has a delay length L which is the difference between the optical path length from the coupler 41 to mirror 42A and the optical path length from the coupler 41 to mirror 42B. ref The free spectral range is determined by (=C / (2L) ref It functions as an interferometer with (where C is the speed of light). The photodetector 43 outputs a reference interferometer signal whose strength repeatedly changes each time the optical frequency of the light sweeping light is swept through the frequencies of the above free spectral range.

[0023] The configuration of the measuring interferometer 13 is arbitrary, but for example, the optical frequency sweep light is split into a measurement light and a reference light by a coupler 31A, the measurement light is shone onto the object to be measured 100 from the collimator lens 33, the signal light reflected or scattered by the object to be measured 100 is combined with the reference light by a coupler 31B, and the combined light is received by a photodetector 34. As a result, the photodetector 34 is located at a distance L from the object to be measured 100. Z A measurement interferometer signal S is output, which has a reflection peak at the corresponding position on the OFDR spectrum. Here, the distance L z This refers to the optical path length from the interference origin, where the frequency of the OFDR spectrum is 0 (i.e., the position where the optical path length of the signal light and the optical path length of the reference light coincide), to the object being measured, 100.

[0024] Figure 2 shows an example of the measurement interferometer signal S and the reference interferometer signal. The AD converter 16 simultaneously samples the measurement interferometer signal S and the reference interferometer signal at equal time intervals. The reciprocal of the time interval is the sampling frequency f. s This is the result. If the optical frequency sweep speed is V [Hz / s], then the distance L max The frequency of the measured interferometer signal is V × 2L max / c. To sample this signal, V × (2L max / c) <f s The condition / 2 must be satisfied. In other words, the shorter the sampling time interval, the further away the measurement can be performed.

[0025] (Linearization of the measurement interferometer signal S) Figure 3 shows an example of a method for linearizing the measurement interferometer signal S. The data processor 17 linearizes the measured interferometer signal S using the reference interferometer signal. Specifically, the data processor 17 performs the following procedure. S11: In this embodiment, since the AD converter 16 samples at equal time intervals, the sampling position (Index) is proportional to the sampling time t. The data processor 17 uses the value of the reference interferometer signal for each sampling time t to calculate the phase Φ for each sampling time t. S12: Unwrap phase Φ to create a continuous phase χ(t,τ) ref Calculate ) where t is the sampling time, τ ref χ(t,τ) is the delay time of the reference interferometer 14. ref ) is the delay time τ ref This represents the value at sampling time t of the continuous phase obtained by unwrapping the reference interferometer signal output by the reference interferometer 14. S13: Continuous phase χ(t,τ) ref The time interval is divided into equal phase segments, and the time ni at which the phases are equally spaced is calculated. S14: The value of the measurement interferometer signal S at each sampling time t is corrected to the value of the measurement interferometer signal S at each time ni. This results in a linearized measurement interferometer signal S LN We seek.

[0026] (Procedure S11) The data processor 17 performs an FFT on the reference interferometer signal, sets the negative frequency components to zero, and then performs an inverse FFT. The phase Φ can be calculated from the obtained value (complex number). The data processor 17 may also calculate the phase Φ from the reference interferometer signal using Hilbert transforms or the like.

[0027] Figure 4 shows an example of the phase Φ. The phase Φ is expressed by the following equation. (Math 1) Φ(t) = tan -1 (Im(t) / Re(t)) (1)

[0028] (Procedure S12) The data processor 17 unwraps Φ and creates a continuous phase χ(t,τ) as shown in Figure 5. ref ) calculate.

[0029] (Procedure S13) As shown in Figure 6, the data processor 17 is χ(t,τ ref The time ) is divided into equal parts, and the time ni corresponding to the division point is calculated. As a result, time ni is a real number, not an integer.

[0030] (Procedure S14) The data processor 17 corrects the sampling time t to the time ni of the measurement interferometer signal S. LN The data processor 17 calculates the value of the measurement interferometer signal S at each time point ni, as shown in Figure 7. This gives the linearized measurement interferometer signal S LN It is possible to find this.

[0031] Here, the value of the measurement interferometer signal S corresponding to time ni is, for example, as shown in Figure 8, when time n5 is the sampling time t=5.4, the value of the measurement interferometer signal S at t=5, S(5), and the value of the measurement interferometer signal S at t=6, S(6). As a result, the data processor 17 calculates the value of the measurement interferometer signal S(5.4) at t=5.4 as S LN (5) can be calculated as (5).

[0032] (OFDR spectrum calculation) The data processor 17 processes the linearized measurement interferometer signal S. LN Perform an FFT on this. This allows us to calculate the OFDR spectrum with corrected phase spacing.

[0033] (Principles of this disclosure) Figure 9 shows an example of a reflection peak obtained from the OFDR spectrum. The data processor 17 processes the measured interferometer signal S LNThe distance L of the reflection point can be calculated using the peak position of the OFDR spectrum. In this case, the distance L of the reflection point is equal to the delay length L of the reference interferometer 14. ref If it is the same, then the measurement interferometer signal S LN The peaks are well linearized, resulting in sharp peaks with widths comparable to the FFT resolution.

[0034] However, L ref Reflection peaks located far from the source become broad peaks due to the coherence effect of the optical frequency sweep light source 11. In the coherence compensation method of Patent Document 1, the distance L of the reflection point is the delay length L. ref When it is an integer multiple of S, the measured interferometer signal S LN Because it is well linearized, a sharp peak is obtained, similar to Figure 9. However, the distance L of the reflection point is the delay length L. ref As the value moves away from an integer multiple of the value, the reflection peak becomes a broader peak.

[0035] Here, if the phase of the light swept by the optical frequency is Φ(t), then the phase of the reference interferometer signal is χ(t,τ). ref ) is expressed by the following formula.

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[0036] When the optical frequency of the reference interferometer signal is swept sinusoidally, as shown in Figure 10, the phase χ(t,τ) ref ) changes cubically. χ(t,τ) ref Fit ) with a cubic function, and χ(t,τ ref Subtracting the cubic function from , we see that it changes slowly with respect to the A / D Index, as shown in Figure 11. Therefore, it can be said that the phase Φ(t) also changes slowly with respect to the A / D Index, i.e., the sampling time t. For this reason, equation (2) can be approximated as equation (3).

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[0037] Integrating equation (3) yields equations (4) and (5). In this disclosure, the phase Φ(t) obtained by equation (5) is referred to as the integral phase.

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[0038] On the other hand, the delay length of the reference interferometer 14 is L P The delay time τ of the reference interferometer 14 at that time P This can be calculated using the following formula. (Math 6) τ P =2n F L P / c (6) However, n F is the refractive index of the optical fiber, and c is the speed of light.

[0039] Then, the data processor 17 uses the following equation to calculate the delay length L P Phase χ of the interferometer signal output from the reference interferometer 14 P =χ(t,τ P ) can be calculated, where t0 is the sampling start time.

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[0040] Therefore, the data processor 17 has a delay length L. ref From the reference interferometer signal, a reference interferometer signal with an arbitrary delay length can be calculated. Therefore, in this disclosure, the delay length L ref The measurement distance L P The phase χ(t,τ) is lengthened. ref Using the integral phase obtained by integrating ) on the time axis, the phase χ P =χ(t,τ P Specifically, the data processor 17 uses equation (7) to calculate the desired delay length L. P Phase χ(t,τ) P The data processor 17 calculates the desired delay length L using the graph of the integral phase Φ(t) as shown in Figure 12, instead of or in conjunction with the calculation of equation (7).P Phase χ(t,τ) P You may also calculate ).

[0041] (Linearization method of measurement interferometer signal S in this disclosure) Figure 13 shows an example of a method for linearizing the measurement interferometer signal S according to this embodiment. S21: In this disclosure, the user can specify in advance the desired delay length L. P The data is input to the data processor 17. The data processor 17 then processes L P The corresponding delay time τ P =2n F L P Calculate / C S11 and S12: In this disclosure as well, the data processor 17 uses the reference interferometer signal to perform continuous phase χ(t,τ ref ) calculate. S22: The data processor 17 uses equation (7) to calculate the delay time τ P Phase χ(t,τ) P This calculates the delay time τ shown in Figure 14. P Phase χ(t,τ) P ) can be obtained. S23: The data processor 17 processes the phase χ(t,τ) P ) is divided equally by phase, and the phase phase χ(t,τ P Calculate the time ni at which the intervals between ) become equal. S24: The data processor 17 calculates the value of the measurement interferometer signal S at time ni. This results in the linearized measurement interferometer signal S LN You can obtain this.

[0042] (OFDR spectrum calculation) The data processor 17 processes the measurement interferometer signal S. LN The FFT is performed on this. This gives the measured interferometer signal S LN The OFDR spectrum of the measured interferometer signal S can be calculated. The data processor 17 processes the measured interferometer signal S. LN The distance to the reflection point is calculated using the peak position of the OFDR spectrum.

[0043] In this embodiment, the measured interferometer signal SLN is the same as linearly rising using the reference interferometer 14 set to L ref where L P is set. Therefore, according to this embodiment, by calculating the OFDR spectrum using the measurement interferometer signal S LN , the distance to the reflection point at the position of the desired delay extension L P can be calculated with high precision, and thus the distance to the measurement object 100 can be measured with high precision.

[0044] (Second Embodiment) In this embodiment, when the delay extension L ref is 30 m and the measurement object 100 is a combined optical fiber in which optical fibers of 60 m, 15 m, and 10 m are connected in series, an example of observing the reflection from the connection point in the measurement object 100 will be described. In this connection, peaks are detected at around 60 m, around 75 m, and around 85 m, respectively.

[0045] FIG. 15 shows an example of the measurement result of the OFDR spectrum in which χ is set to an integer multiple of the delay extension L ref using the linear rising method of the present disclosure for comparison with Patent Document 1. Since the peak around 60 m is twice the delay extension L ref , as shown in FIG. 15(a), the reflection peak is sharp. However, as shown in FIGS. 15(b) and 15(c), the reflection peaks around 75 m and around 85 m, which are different from the integer multiple of the delay extension L ref , are broader than the peak shown in FIG. 15(a).

[0046] FIG. 16 shows an example of the measurement result of the OFDR spectrum in which the desired χ is set using the linear rising method of the present disclosure. In this embodiment, the desired delay extension L P is set to 60 m, 75 m, and 85 m, the phase χ(t,τ P ) is calculated, and the OFDR spectrum is calculated using this. FIG. 16(a) shows the case when the delay extension L P is 60 m, FIG. 16(b) shows the case when the delay extension L P is 75 m, and FIG. 16(c) shows the case when the delay extension L PThis is the OFDR spectrum when the frequency is set to 85m. As shown in these OFDR spectra, it can be seen that the reflection peaks around 60m, as well as around 75m and 85m, are observed with sharp shapes without widening.

[0047] Therefore, it can be seen that by using the linearization method of the measurement interferometer signal S of this disclosure, the measurement accuracy in an OFDR system can be improved at distances that are integer multiples of the delay length of the reference interferometer.

[0048] This disclosure enables improvement of measurement accuracy in OFDR systems at distances that are integer multiples of the delay length L of the reference interferometer, thus improving the measurement accuracy at distances that are integer multiples of the delay length L ref Measurement accuracy can be improved at any distance longer than the specified distance. For example, the data processor 17 can calculate at least one of the reflection and strain in the optical fiber. The data processor 17 may use the strain of the optical fiber to calculate temperature, shape, etc. The data processor 17 may also calculate the distribution of at least one of the reflection and strain in the optical fiber along the longitudinal direction of the optical fiber.

[0049] (Third embodiment) Figure 17 shows an example of the OFDR system of this embodiment. In the OFDR system of this embodiment, the object to be measured 100 is an optical fiber, and the strain distribution in the longitudinal direction of the optical fiber is measured using the software linearization method. In this embodiment, the longitudinal distance of the optical fiber 100 is denoted as z. In this embodiment as well, the linearized measurement interferometer signal S is used, similar to the first embodiment. LN We seek.

[0050] (Procedure S31) As shown in Figure 18, the data processor 17 processes the linearized measurement interferometer signal S. LN The FFT is performed to calculate the phase distribution R(z), which is the phase distribution in the longitudinal direction of the optical fiber. In Figure 18, the real part of R(z) is shown by the solid and dashed lines, and as shown by the dashed line, R(z) is a complex number.

[0051] (Procedure S32) As shown in Figure 19, the data processor 17 divides the phase distribution R(z) into strain measurement sections h of length D. The length D of the strain measurement section h is referred to as the section length D. Divided strain measurement section data R d (h) contains N RD There are several R(z) data points.

[0052] (Procedure S33) As shown in Figure 20, the data processor 17 is R d (h) is padded with 0. This results in the length of the section D after 0 padding. z Distortion measurement data R dz (h) is obtained. To speed up the FFT, R dz The number of data points in (h) should be a power of 2.

[0053] (Procedure S34) As shown in Figure 21, the data processor 17 processes strain measurement section data R dz (h) is subjected to the inverse FFT, and its real part is obtained as a piecewise waveform M d Let (h) be the case.

[0054] (Procedure S35) As shown in Figure 21, the data processor 17 processes the segmented waveform M at a certain time. d (h) See waveform M dref Let (h) be the case.

[0055] (Procedure S36) The data processor 17 uses the reference waveform M dref (h) The segmented waveform M when strain is applied d The change in (h) is calculated. Specifically, the data processor 17 calculates the change in the segmented waveform M d Calculate the frequency shift amount in waveform (h).

[0056] When a compressive strain is applied to the strain measurement area, as shown in Figure 22, R d (h) is dense. Therefore, the piecewise waveform M calculated by its inverse FFT is d(h) will shift to the high-frequency side. Conversely, if a strain in the extension direction is applied, as shown in Figure 23, R d (h) becomes coarse, and the segmented waveform M d (h) will shift to the lower frequency side. Therefore, by calculating this shift amount, we can determine the degree of expansion or contraction of the strain measurement section.

[0057] Reference waveform M dref (h) From the segmented waveform M d The amount of shift to (h) is generally the cross-correlation S between the two. h A method is used to calculate (m). For example, as shown in Figure 24, the data processor 17 uses the following equation to calculate the cross-correlation S h Find the value of m that maximizes (m).

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[0058] Strain measurement category data R d (h) is the phase data of the interference signal when light reflected from strain measurement section h interferes with the measurement interferometer 13. Therefore, if the optical path length of strain measurement section h is extended by half a wavelength due to stretching, the phase that was rotating within this optical path length will rotate another full turn. Here, the refractive index n of the optical fiber F Using the wavelength λ of the signal light, the optical path length for half a wavelength is expressed by the following equation. (Math 9) λ / (2n F ) (9)

[0059] This is the inverse FFT, which is a piecewise waveform M d From the perspective of (h), the frequency increases by one. In other words, the piecewise waveform M d (h) has shifted by 1, S h (m) is maximized when m=1. From this, the division length D z is λ / (2n F )When it stretches, m=1. Therefore, the data processor 17 can calculate the amount of strain ε in strain measurement section h using the following equation. Here, ρ is the photoelastic coefficient (≒0.8).

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[0060] (Fourth embodiment) This disclosure provides a desired delay length L P This can be set to any value. Therefore, the measurement interferometer signal S in the third embodiment LN When determining the desired delay length L corresponding to z, P This can be used. In this embodiment, in such cases, the desired delay length L P We will consider how to configure this.

[0061] Figure 25 shows the cross-correlation S h An example of the distribution of the maximum value of (m) is shown. Figure 25(a) shows the delay length L of 30m when the optical fiber of the object being measured, 100, is 150m. ref Using the delay length L P to L ref Examples are shown where the settings are integer multiples of 60m, 90m, 120m, and 150m. Figure 25(b) shows the delay length L of 30m when the optical fiber of the object being measured 100 is 150m. ref Using the delay length L P to L ref Examples of setting the distance to 45m, 60m, 75m, 90m, 105m, 120m, 135m, and 150m, which are half-integer multiples of the given value, are shown.

[0062] S h The maximum value of (m) indicates the degree of cross-correlation; a larger maximum value indicates a more accurate measurement. Desired delay length L P delay length L ref In the example shown in Figure 24(a), where the delay length L is set to an integer multiple of the specified value, ref At the intermediate position, the cross-correlation strength drops to nearly 90%. Desired delay length L P delay length L ref In the example shown in Figure 25(b), where the setting is a half-integer multiple of , the cross-correlation strength remains above 95% across the entire range. Therefore, the desired delay length L P delay length L refBy setting it to a half-integer multiple, it becomes possible to accurately calculate the frequency shift amount in each strain measurement section h.

[0063] (Fifth embodiment) Referring to Figure 26, the distribution measurement range is L ref An example of measuring the strain temperature distribution when it is twice the value will be described. The data processor 17 has a delay length L ref Set to a half-integer multiple of and delay length L P 1 / 2L centered around ref The OFDR spectrum is calculated using the range of h as one strain measurement segment.

[0064] Specifically, the strain measurement category h is as follows: • The first strain measurement section at h=1 (L P =L ref ): 0 ≤ z ≤ 5 / 4L ref • Second strain measurement section (L) at h=2 P = 3 / 2L ref ): 5 / 4L ref ≤z ≤ 7 / 4L ref • Third strain measurement category (L) at h=3 P =2L ref ): 7 / 4L ref ≤z ≤ 2L ref

[0065] The data processor 17 may calculate the OFDR spectrum of the three regions using the following method. Procedure S51: The data processor 17 sets the desired delay length L. P delay length L ref Set the parameters and calculate the OFDR spectrum. From that OFDR spectrum, calculate 0~5 / 4L. ref Extract the range up to that point.

[0066] Procedure S52: The data processor 17 sets the desired delay length L P Delay length 3 / 2L ref Set to and use equation (7) L P = 3 / 2L ref The phase χ(t,τ) at this point P) calculate. Next, the data processor 17 processes the phase χ(t,τ P The measured interferometer signal S is linearized, and the OFDR spectrum is calculated. Next, the data processor 17 calculates 5 / 4L from the OFDR spectrum. ref ~7 / 4L ref Extract the range up to that point.

[0067] Procedure S53: The data processor 17 sets the desired delay length L. P Delay length 2L ref Set to and use equation (7) L P =2L ref The phase χ(t,τ) at this point P ) calculate. Next, the data processor 17 processes the phase χ(t,τ P The measured interferometer signal S is linearized, and the OFDR spectrum is calculated. Next, the data processor 17 calculates 7 / 4L from the OFDR spectrum. ref Extract the following section.

[0068] The data processor 17 combines the OFDR spectra of these three regions to form a combined OFDR spectrum. As described in the fourth embodiment, the combined OFDR spectrum is well linearized in almost all regions. By calculating the strain and temperature distribution from this combined OFDR spectrum, highly accurate strain and temperature distributions can be measured.

[0069] The data processing unit 17 of the present invention 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. The program of this disclosure is a program for realizing a computer as each functional unit of the data processing unit 17 of this disclosure, and is a program for causing the computer to execute each step of the method executed by the data processing unit 17 of this disclosure. [Explanation of Symbols]

[0070] 11: Optical frequency sweep light source 12: Coupler 13: Measuring interferometer 14: Reference Interferometer 16: AD converter 17: Data Processing Unit 31A, 31B: Coupler 33: Collimator lens 34:Receiver 35: Miller 41: Kapra 42A, 42B: Miller 43:Receiver 100: Object to be measured

Claims

1. A data processor that processes measurement interferometer signals measured using OFDR (Optical Frequency Domain Reflectometry), Using the phase χ of the reference interferometer signal generated using the same optical frequency sweep light source as the measurement interferometer signal, the phase χ of the reference interferometer signal corresponding to the measurement distance is used. Ｐ Calculate, The phase χ Ｐ The measurement interferometer signal is linearized using the above method. Data processor.

2. The measurement distance is the delay length L in the reference interferometer signal. ｒｅｆ Longer than, Using the integrated phase obtained by integrating the aforementioned phase χ on the time axis, the phase χ Ｐ To calculate The data processor according to claim 1.

3. A light source that emits light swept by optical frequency, A reference interferometer that generates a reference interferometer signal using the aforementioned optical frequency sweep light, A measuring interferometer measures a measuring interferometer signal by combining the aforementioned optical frequency sweep light with a reference light, thereby combining the signal light reflected or scattered by the object to be measured. A data processor according to claim 1 or 2, which linearizes the measurement interferometer signal using the reference interferometer signal, An OFDR system equipped with [this feature].

4. The delay length of the aforementioned reference interferometer is L. ｒｅｆ And, The aforementioned data processor is The delay length is L ｒｅｆ Calculate the phase χ of the reference interferometer signal at that time. The delay length L of the reference interferometer corresponding to the measurement distance Ｐ Delay time τ Ｐ Calculate, Using the phase χ, the delay time τ Ｐ of the phase χ Ｐ is calculated, The phase χ Ｐ The measurement interferometer signal is linearized by calculating the value of the measurement interferometer signal at times when the intervals are equal. The OFDR system according to claim 3.

5. The data processor uses the following equation to determine the phase χ Ｐ To calculate The OFDR system according to claim 4. [Math C1] However, ｒｅｆ t is the delay time of the reference interferometer, and t is the sampling time.

6. The aforementioned data processor is The phase χ Ｐ Using the values ​​of the measurement interferometer signal at times when the intervals are equal, the OFDR spectrum of the measurement interferometer signal is calculated. The distance to the reflection point is calculated using the peak position of the OFDR spectrum of the aforementioned measurement interferometer signal. The OFDR system according to claim 4.

7. The object to be measured is an optical fiber, The data processor has a delay length L. Ｐ The delay length L ｒｅｆ Set to a half-integer multiple of The OFDR system according to claim 4.

8. The data processor has a delay length L. Ｐ 1 / 2L centered around ｒｅｆ Using the range of h as the strain measurement section, the distribution of at least one of the reflections and strains in the optical fiber along the longitudinal direction of the optical fiber is calculated. The OFDR system according to claim 7.

9. The system includes an AD converter that converts the reference interferometer signal from the reference interferometer and the measurement interferometer signal from the measurement interferometer into digital signals at the same time interval. The OFDR system according to claim 3.

10. A method performed by a data processor that processes a measurement interferometer signal measured using an OFDR (Optical Frequency Domain Reflectometer), Using the phase χ of the reference interferometer signal generated using the same optical frequency sweep light source as the measurement interferometer signal, the phase χ of the reference interferometer signal corresponding to the measurement distance is used. Ｐ Calculate, The phase χ Ｐ The measurement interferometer signal is linearized using the above method. method.

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