Signal detection device and optical fiber characteristic measuring device

Abstract

To provide a signal detector, etc., which can separately detect each amplitude of a time division signal having an amplitude changing in time division.SOLUTION: A signal detector 1 comprises: a multiplication unit 13 that multiplies a measurement signal MS by a reference signal RS; a filter processing unit 16 that performs filtering on the multiplication result of the multiplication unit 13; an internal memory 17 that stores the internal state of the filter processing unit 16; and a memory 18 that stores the processing result of the filter processing unit 16. The filter processing unit 16 performs filtering using the internal state stored in the internal memory 17. The internal memory 17 switches a region to and from which the internal state is written and read by the filter processing unit 16, in accordance with an index signal IS that indicates the type of amplitude of the time division signal included in the measurement signal MS. The memory 18 switches the region in which the processing results of the filter processing unit 16 is stored, in accordance with the index signal IS.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a signal detection device and an optical fiber characteristic measuring device. [Background technology]

[0002] A lock-in amplifier is generally a signal detection device that includes a multiplier that multiplies a measurement signal by a reference signal, and a low-pass filter that extracts the direct current (DC) component of the signal multiplied by the multiplier, and detects a specific signal contained in the measurement signal. Such lock-in amplifiers have the characteristic of being able to detect minute signals buried in noise with high sensitivity. There are two types of lock-in amplifiers: analog types in which the multiplier and low-pass filter are realized by analog circuits, and digital types in which the multiplier and low-pass filter are realized by digital circuits.

[0003] The following Patent Documents 1 and 2 disclose an optical fiber characteristic measuring device equipped with a lock-in amplifier. This optical fiber characteristic measuring device detects the temperature distribution and strain distribution in the longitudinal direction of the optical fiber by detecting Brillouin scattered light generated by incident light on the optical fiber. The Brillouin scattered light generated within the optical fiber is extremely weak, and a lock-in amplifier is used to detect such weak Brillouin scattered light with high sensitivity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-159387 A [Patent Document 2] Patent Publication No. 2022-014178 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, as described above, a conventional lock-in amplifier extracts a DC component from a signal obtained by multiplying a measurement signal by a reference signal using a low-pass filter. For this reason, for example, it is not possible to separate and detect the amplitudes of a signal (time-shared signal) whose frequency is the same as that of the reference signal and whose amplitude changes in a time-shared manner. Even if a measurement signal containing such a time-shared signal is input to a conventional lock-in amplifier, the conventional lock-in amplifier can only obtain one output in which the time-shared signal has been subjected to low-pass filtering.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide a signal detection device that can separate and detect each amplitude of a time-division signal whose amplitude changes in a time-division manner, and an optical fiber characteristic measuring device equipped with the signal detection device. [Means for solving the problem]

[0007] In order to solve the above problem, a signal detection device (1, 2) according to a first aspect of the present invention comprises a multiplication unit (13) that multiplies a measurement signal (MS) and a reference signal (RS), a filter processing unit (16) that performs filter processing on a multiplication result of the multiplication unit, a first memory unit (17) that stores an internal state of the filter processing unit, and a second memory unit (18) that stores a processing result of the filter processing unit, wherein the filter processing unit performs the filter processing using the internal state stored in the first memory unit, the first memory unit switches an area where the internal state is written and read by the filter processing unit according to an index signal (IS) that indicates the type of amplitude of a time division signal (DS) included in the measurement signal, and the second memory unit switches an area where the processing result of the filter processing unit is stored according to the index signal.

[0008] Furthermore, a signal detection device according to a second aspect of the present invention is the signal detection device according to the first aspect, further comprising a first conversion unit (11) that converts the measurement signal into a digital signal, a second conversion unit (12) that converts the reference signal into a digital signal, a detection unit (15) that detects the timing at which the index signal changes, and a resampling unit (14) that resamples the multiplication result of the multiplication unit at the timing detected by the detection unit.

[0009] Furthermore, a signal detection device according to a third aspect of the present invention is a signal detection device according to the first or second aspect, further comprising a measurement signal input terminal (T11) to which the measurement signal is input, a reference signal input terminal (T12) to which the reference signal is input, and an index signal input terminal (T13) to which the index signal is input.

[0010] Furthermore, a signal detection device according to a fourth aspect of the present invention is the signal detection device according to the first aspect, further comprising a first generator (21) that generates the reference signal based on a start trigger signal (TS) that defines the start timing of the time division signal, and generates a timing signal (TM) that indicates the division timing of the time division signal, and a second generator (22) that generates the index signal based on the timing signal.

[0011] Furthermore, a signal detection device according to a fifth aspect of the present invention is the signal detection device according to the fourth aspect, wherein the first generation unit generates the reference signal as a digital signal, a first conversion unit (11) that converts the measurement signal into a digital signal, and a resampling unit (14) that resamples a multiplication result of the multiplication unit at a division timing indicated by the timing signal.

[0012] Furthermore, a signal detection device according to a sixth aspect of the present invention is a signal detection device according to the fourth or fifth aspect, further comprising a measurement signal input terminal (T11) to which the measurement signal is input, and a start trigger signal input terminal (T14) to which the start trigger signal is input.

[0013] Further, a signal detection device according to a seventh aspect of the present invention is the signal detection device according to any one of the first to sixth aspects, wherein the filter processing unit performs processing using an infinite impulse response low-pass filter as the filtering process.

[0014] An optical fiber characteristic measuring device (MD) according to one aspect of the present invention includes a first optical branching unit (32) that branches a frequency-modulated modulated light (L1) into a pump light (LP) and a reference light (LR), a second optical branching unit (36) that inputs the pump light to one end of a test optical fiber (FUT) and outputs Brillouin scattered light (LS) generated within the test optical fiber, a first detection unit (39) that detects interference light between the Brillouin scattered light and the reference light output from the second optical branching unit, and an analysis unit (40) that determines a Brillouin gain spectrum, which is the spectrum of the Brillouin scattered light, from a detection signal (S1) output from the first detection unit. The signal detection device comprises a second detection unit (41) that detects a second harmonic component having a frequency twice the modulation frequency of the modulated light contained in the Brillouin gain spectrum obtained by the analysis unit, and a measurement unit (42) that measures characteristics of the measured optical fiber based on the Brillouin gain spectrum obtained by the analysis unit and the second harmonic component detected by the second detection unit, wherein the second detection unit comprises a signal detection device according to any one of the first to seventh aspects, in which the Brillouin gain spectrum obtained by the analysis unit is input as the measurement signal, and the second detection unit detects the second harmonic component by the reference signal having a frequency twice the modulation frequency of the modulated light. Effect of the Invention

[0015] According to the present invention, there is an advantage that it is possible to separate and detect the amplitudes of time-division signals whose amplitudes change in a time-division manner. [Brief description of the drawings]

[0016] [Figure 1] 1 is a block diagram showing a configuration of a main part of a signal detection device according to a first embodiment of the present invention. [Diagram 2] 2 is a diagram showing an example of a signal input to the signal detection device according to the first embodiment of the present invention; FIG. [Diagram 3] FIG. 2 is a diagram showing an example of a memory map of the signal detection device according to the first embodiment of the present invention. [Figure 4] FIG. 11 is a block diagram showing a configuration of a main part of a signal detection device according to a second embodiment of the present invention. [Diagram 5] 1 is a block diagram showing a configuration of a main part of an optical fiber characteristic measuring device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a signal detection device and an optical fiber characteristic measuring device according to embodiments of the present invention will be described in detail with reference to the drawings. First, an overview of the embodiments of the present invention will be described, and then each embodiment of the present invention will be described in detail.

[0018] 〔overview〕 The embodiment of the present invention is to enable separate detection of the amplitude of each of the time-division signals whose amplitude changes in a time-division manner. For example, in an optical fiber characteristic measuring device, when pulsed light is sequentially input to an optical fiber, it is possible to enable separate detection of the amplitude of each of the time-division signals obtained by detecting weak Brillouin scattered light sequentially output from the optical fiber.

[0019] A lock-in amplifier detects a minute signal buried in noise with high sensitivity by extracting a direct current component from a signal obtained by multiplying a measurement signal by a reference signal using a low-pass filter. When extracting a frequency f component contained in a measurement signal in a lock-in amplifier, the signal of frequency f is used as a reference signal. When such a reference signal is multiplied by a measurement signal, a direct current component (DC component) and a double wave component (2f component) are obtained. In a conventional lock-in amplifier, only the obtained direct current component (DC component) is extracted by a low-pass filter, thereby detecting a minute signal buried in noise with high sensitivity. It is also possible to obtain a double wave component (2f component) by using a high-pass filter instead of a low-pass filter.

[0020] When a measurement signal containing a time-division signal whose amplitude changes in a time-division manner is input to such a conventional lock-in amplifier, the conventional lock-in amplifier only produces one output that is the time-division signal that has been subjected to low-pass filtering. Therefore, the conventional lock-in amplifier cannot detect the amplitudes of the time-division signals separately.

[0021] A signal detection device according to an embodiment of the present invention includes a multiplication unit that multiplies a measurement signal by a reference signal, a filter processing unit that performs a filter process on the multiplication result of the multiplication unit, a first storage unit that stores an internal state of the filter processing unit, and a second storage unit that stores the processing result of the filter processing unit. The filter processing unit performs the filter process using the internal state stored in the first storage unit. The first storage unit switches an area where the internal state is written and read by the filter processing unit according to an index signal that indicates the type of amplitude of a time-division signal included in the measurement signal. The second storage unit switches an area where the processing result of the filter processing unit is stored according to the index signal. This makes it possible to separate and detect the amplitudes of each of the time-division signals whose amplitudes change in a time-division manner.

[0022] [Signal detection device] First embodiment Fig. 1 is a block diagram showing the main components of a signal detection device according to a first embodiment of the present invention. As shown in Fig. 1, the signal detection device 1 of this embodiment includes an ADC (analog / digital conversion unit) 11 (first conversion unit), an ADC 12 (second conversion unit), a multiplication unit 13, a resampling unit 14, a change point detection unit 15 (detection unit), a filter processing unit 16, an internal memory 17 (first storage unit), and a memory 18 (second storage unit).

[0023] A measurement signal MS, a reference signal RS, and an index signal IS are input to the signal detection device 1. The signal detection device 1 uses the reference signal RS and the index signal IS to separate and detect the amplitude of each of the time division signals DS (see FIG. 2(a)) included in the measurement signal MS. The signal detection device 1 includes a measurement signal input terminal T11 to which the measurement signal MS is input, a reference signal input terminal T12 to which the reference signal RS is input, an index signal input terminal T13 to which the index signal IS is input, and an output terminal T20 to which the detected amplitude is output.

[0024] FIG. 2 is a diagram showing an example of a signal input to the signal detection device according to the first embodiment of the present invention. FIG. 2(a) is a diagram showing an example of a measurement signal MS, FIG. 2(b) is a diagram showing an example of a reference signal RS, and FIG. 2(c) is a diagram showing an example of an index signal IS. As shown in FIG. 2(a), the measurement signal MS is an analog signal including a time-division signal DS whose amplitude changes in a time-division manner. The time-division signal DS shown in FIG. 2(a) is a signal whose amplitude changes sequentially from A1 to A3 every two periods, and is a weak signal on which noise is superimposed. The frequency of the time-division signal DS is, for example, several to several tens of MHz.

[0025] As shown in Fig. 2(b), the reference signal RS is an analog signal having the same frequency as the time division signal DS included in the measurement signal MS and synchronized with the time division signal DS. As shown in Fig. 2(c), the index signal IS is a signal indicating the type of the amplitude of the time division signal DS included in the measurement signal MS and is a signal synchronized with the time division signal DS. The index signal IS illustrated in Fig. 2(c) indicates that the type of the amplitude A1 of the time division signal DS is "1", the type of the amplitude A2 of the time division signal DS is "2", and the type of the amplitude A3 of the time division signal DS is "3". The index signal IS is a multi-bit (e.g., 16-bit) digital signal.

[0026] In the example shown in FIG. 2, for the sake of simplicity, the time division signal DS has three amplitudes (amplitudes A1, A2, and A3), but the time division signal DS may have two amplitudes or four or more amplitudes. If the index signal IS is 16 bits, the number of amplitudes of the time division signal DS that can be detected by the signal detection device 1 is a maximum of 65536 (=2 16 Types).

[0027] The ADC 11 converts the measurement signal MS input from the measurement signal input terminal T11 into a digital signal. The ADC 12 converts the reference signal RS input from the reference signal input terminal T12 into a digital signal. The multiplier 13 multiplies the measurement signal MS converted into a digital signal by the ADC 11 by the reference signal RS converted into a digital signal by the ADC 12. The sampling frequency of the ADCs 11 and 12 is, for example, several hundred MHz.

[0028] The resampler 14 resamples the multiplication result of the multiplier 13 every time the timing signal TM is output from the change point detector 15. The first reason for providing the resampler 14 is that the processing timing after the resampler 14 can be aligned with the time division timing of the time division signal DS, making the processing easier. The second reason for providing the resampler 14 is that since what is ultimately detected by the signal detector 1 is the direct current component (DC component) contained in the multiplication result of the multiplier 13, there is no problem even if high frequency components are lost by resampling. The sampling frequency (resampling frequency) in the resampler 14 is, for example, several to several tens of MHz. The resampler 14 also performs aliasing noise countermeasures such as low-pass filter processing that passes frequency components equal to or lower than 1 / 2 the resampling frequency on the original data (the multiplication result of the multiplier 13) before thinning out the data.

[0029] The change point detection unit 15 detects the timing at which the index signal IS changes. Specifically, the change point detection unit 15 detects a change in the value of the index signal IS, and when the change is detected, outputs a timing signal TM at that timing. As described above, the resampling unit 14 resamples the multiplication result of the multiplication unit 13 every time a timing signal TM is output from the change point detection unit 15. For this reason, it can be said that the resampling unit 14 resamples the multiplication result of the multiplication unit 13 at the timing detected by the change point detection unit 15.

[0030] The filter processing unit 16 performs a filter process on the multiplication result of the multiplication unit 13 resampled by the resample unit 14. For example, the filter processing unit 16 performs a process using an infinite impulse response (IIR) low-pass filter as the above filter process. The filter processing unit 16 can also perform a process using a finite impulse response (FIR) low-pass filter as the above filter process. When an infinite impulse response low-pass filter is used, the internal state quantity can be reduced compared to when a finite impulse response low-pass filter is used. Therefore, in consideration of the processing load in the filter processing unit 16 and the capacity of the internal memory 17, it is preferable to use an infinite impulse response low-pass filter rather than a finite impulse response low-pass filter.

[0031] The internal memory 17 is a memory that stores the internal state of the filter processing unit 16. The internal memory 17 switches an area where the internal state is written and read by the filter processing unit 16 in response to the index signal IS. The memory 18 is a memory that stores the processing results of the filter processing unit 16. The memory 18 switches an area where the processing results of the filter processing unit 16 are stored in response to the index signal IS.

[0032] Fig. 3 is a diagram showing an example of a memory map of the signal detection device according to the first embodiment of the present invention. Fig. 3(a) is a diagram showing a memory map of the internal memory 17, and Fig. 3(b) is a diagram showing a memory map of the memory 18. As shown in Figs. 3(a) and 3(b), the internal memory 17 and the memory 18 are each provided with three areas according to the type of amplitude (amplitudes A1, A2, A3) of the time division signal DS.

[0033] 3(a) is an area where the internal state is written and read by the filter processing unit 16 when, for example, the index signal IS is "1." Area R12 is an area where the internal state is written and read by the filter processing unit 16 when, for example, the index signal IS is "2." Area R13 is an area where the internal state is written and read by the filter processing unit 16 when, for example, the index signal IS is "3."

[0034] 3(b), an area R21 is an area in which the processing result of the filter processing unit 16 is stored when, for example, the index signal IS is "1." An area R22 is an area in which the processing result of the filter processing unit 16 is stored when, for example, the index signal IS is "2." An area R23 is an area in which the processing result of the filter processing unit 16 is stored when, for example, the index signal IS is "3."

[0035] That is, when filter processing is performed on the time-division signal DS whose amplitude is A1 shown in Fig. 2(a), the internal state stored in the area R11 shown in Fig. 3(a) is used, and the processing result is stored in the area R21 shown in Fig. 3(b). When filter processing is performed on the time-division signal DS whose amplitude is A2 shown in Fig. 2(a), the internal state stored in the area R12 shown in Fig. 3(a) is used, and the processing result is stored in the area R22 shown in Fig. 3(b). When filter processing is performed on the time-division signal DS whose amplitude is A3 shown in Fig. 2(a), the internal state stored in the area R13 shown in Fig. 3(a) is used, and the processing result is stored in the area R23 shown in Fig. 3(b).

[0036] 3, the number of areas provided in the internal memory 17 and the memory 18 corresponds to the number of types of amplitude of the time division signal DS. When the number of types of amplitude of the time division signal DS becomes huge, the number of areas provided in the internal memory 17 and the memory 18 also becomes huge. In such a case, it is possible to deal with it by increasing the capacity of the internal memory 17 and the memory 18.

[0037] Next, the operation of the signal detection device 1 in the above configuration will be described. When the operation of the signal detection device 1 starts, a measurement signal MS, a reference signal RS, and an index signal IS are input from a measurement signal input terminal T11, a reference signal input terminal T12, and an index signal input terminal T13, respectively. Note that the time division signal DS, the reference signal RS, and the index signal IS included in the measurement signal MS are synchronized with each other.

[0038] A measurement signal MS input from a measurement signal input terminal T11 is converted into a digital signal by the ADC 11, and a reference signal RS input from a reference signal input terminal T12 is converted into a digital signal by the ADC 12. The measurement signal MS and reference signal RS converted into digital signals are multiplied by a multiplication unit 13.

[0039] On the other hand, index signal IS input from index signal input terminal T13 is input to change point detection unit 15, which detects a change in its value. When change point detection unit 15 detects a change in value, it outputs a timing signal TM to resample unit 14. Furthermore, index signal IS is input to internal memory 17 and memory 18, and an area for storing the internal state of filter processing unit 16 and an area for storing the processing result of filter processing unit 16 are respectively set.

[0040] For example, suppose that the index signal IS input from the index signal input terminal T13 is "1." At this time, for example, an area R11 of the internal memory 17 shown in Fig. 3(a) is set as an area for storing the internal state of the filter processing unit 16. Also, for example, an area R21 of the memory 18 shown in Fig. 3(b) is set as an area for storing the processing result of the filter processing unit 16.

[0041] The multiplication result of the multiplication unit 13 is input to the resampling unit 14 and resampled at the timing of the timing signal TM output from the change point detection unit 15. The multiplication result of the multiplication unit 13 resampled by the resampling unit 14 is input to the filtering unit 16 and subjected to filtering. Specifically, in the filtering unit 16, processing is performed by an infinite impulse response low-pass filter, and processing is performed to extract direct current components (DC components).

[0042] When the internal state is stored in the area of ​​the internal memory 17 set by the index signal IS (here, area R11 shown in FIG. 3(a)), the filter processing unit 16 reads out the internal state and performs the above-mentioned filter processing. The internal state of the filter processing unit 16 is sequentially written into the area of ​​the internal memory 17 set by the index signal IS (here, area R11 shown in FIG. 3(a)).

[0043] The processing result (extracted direct current component (DC component)) of the filter processing unit 16 is stored in an area of ​​the memory 18 set by the index signal IS (here, area R21 shown in FIG. 3(b)). The extracted direct current component (DC component) indicates the magnitude of the amplitude A1 shown in FIG. 2(a).

[0044] Next, suppose that index signal IS input from index signal input terminal T13 changes from "1" to "2." Then, this change in value is detected by change point detection unit 15, which outputs timing signal TM to resample unit 14. Then, in resample unit 14, the multiplication result from multiplication unit 13 is resampled at the timing of timing signal TM.

[0045] Furthermore, in response to a change in the index signal IS, a new area for storing the internal state of the filter processing unit 16 and a new area for storing the processing result of the filter processing unit 16 are respectively set. Specifically, when the index signal IS changes to "2", for example, an area R12 of the internal memory 17 shown in Fig. 3(a) is newly set as an area for storing the internal state of the filter processing unit 16. Furthermore, for example, an area R22 of the memory 18 shown in Fig. 3(b) is newly set as an area for storing the processing result of the filter processing unit 16.

[0046] The multiplication result of the multiplication unit 13 resampled by the resample unit 14 is input to the filter processing unit 16 for filtering. If an internal state is stored in an area of ​​the internal memory 17 set by the index signal IS (here, area R12 shown in FIG. 3(a)), the filter processing unit 16 reads out the internal state and performs the above filtering process. The internal state of the filter processing unit 16 is written sequentially into an area of ​​the internal memory 17 set by the index signal IS (here, area R12 shown in FIG. 3(a)).

[0047] The processing result (extracted direct current component (DC component)) of the filter processing unit 16 is stored in an area of ​​the memory 18 set by the index signal IS (here, area R22 shown in FIG. 3(b)). Note that the extracted direct current component (DC component) indicates the magnitude of the amplitude A2 shown in FIG. 2(a).

[0048] Next, suppose that index signal IS input from index signal input terminal T13 changes from "2" to "3." Then, this change in value is detected by change point detection unit 15, which outputs timing signal TM to resample unit 14. Then, in resample unit 14, the multiplication result from multiplication unit 13 is resampled at the timing of timing signal TM.

[0049] Furthermore, in response to a change in the index signal IS, a new area for storing the internal state of the filter processing unit 16 and a new area for storing the processing result of the filter processing unit 16 are respectively set. Specifically, when the index signal IS changes to "3", for example, an area R13 of the internal memory 17 shown in Fig. 3(a) is newly set as an area for storing the internal state of the filter processing unit 16. Furthermore, for example, an area R23 of the memory 18 shown in Fig. 3(b) is newly set as an area for storing the processing result of the filter processing unit 16.

[0050] The multiplication result of the multiplication unit 13 resampled by the resample unit 14 is input to the filter processing unit 16 for filtering. If an internal state is stored in an area of ​​the internal memory 17 set by the index signal IS (here, area R13 shown in FIG. 3(a)), the filter processing unit 16 reads out the internal state and performs the above filtering. The internal state of the filter processing unit 16 is written sequentially into an area of ​​the internal memory 17 set by the index signal IS (here, area R13 shown in FIG. 3(a)).

[0051] The processing result (extracted direct current component (DC component)) of the filter processing unit 16 is stored in an area of ​​the memory 18 set by the index signal IS (here, area R23 shown in FIG. 3(b)). The direct current component (DC component) extracted here indicates the magnitude of the amplitude A3 shown in FIG. 2(a).

[0052] Thereafter, similarly, each time the value of the index signal IS changes, the multiplication result of the multiplication unit 13 is resampled at that timing, and an area for storing the internal state of the filter processing unit 16 and an area for storing the processing result of the filter processing unit 16 are set. Here, if an area according to the value of the index signal IS has already been set, that area is set as the area for storing the internal state of the filter processing unit 16 and the area for storing the processing result of the filter processing unit 16. On the other hand, if an area according to the value of the index signal IS has not been set, an area for storing the internal state of the filter processing unit 16 and an area for storing the processing result of the filter processing unit 16 are newly set.

[0053] For example, suppose that the value of the index signal IS changes to "1" again. Then, for example, the area R11 of the internal memory 17 shown in FIG. 3(a) and the area R21 of the memory 18 shown in FIG. 3(b) are set as an area for storing the internal state of the filter processing unit 16 and an area for storing the processing result of the filter processing unit 16, respectively. On the other hand, suppose that the value of the index signal IS becomes a new value of "4". Then, for example, an area other than the areas R11 to R13 of the internal memory 17 shown in FIG. 3(a) is newly set as an area for storing the internal state of the filter processing unit 16. Also, for example, an area other than the areas R21 to R23 of the memory 18 shown in FIG. 3(b) is newly set as an area for storing the processing result of the filter processing unit 16.

[0054] By carrying out the above processing, values ​​indicating the magnitudes of the amplitudes A1, A2, and A3 of the time division signal DS shown in Fig. 2(a) are stored in different areas of the memory 18. For example, the value indicating the magnitude of the amplitude A1 is stored in an area R21 of the memory 18, the value indicating the magnitude of the amplitude A2 is stored in an area R22 of the memory 18, and the value indicating the magnitude of the amplitude A3 is stored in an area R23 of the memory 18 (see Fig. 3(b)).

[0055] The values ​​stored in different areas of the memory 18 can be read out, for example, by specifying a read address for the memory 18. The value read out from the memory 18 is output from the output terminal T20 of the signal detection device 1. In this way, the amplitudes of the time division signals DS included in the measurement signal MS are separately detected.

[0056] As described above, this embodiment includes the multiplication unit 13 that multiplies the measurement signal MS by the reference signal RS, and the filter processing unit 16 that performs a filter process on the multiplication result of the multiplication unit 13. The internal memory 17 that stores the internal state of the filter processing unit 16, and the memory 18 that stores the processing result of the filter processing unit 16. The filter processing unit 16 performs the filter process using the internal state stored in the internal memory 17. The internal memory 17 switches the area where the internal state is written and read by the filter processing unit 16 according to the index signal IS that indicates the type of the amplitude of the time division signal DS included in the measurement signal MS. The memory 18 switches the area where the processing result of the filter processing unit 16 is stored according to the index signal IS. This makes it possible to separate and detect the amplitudes of the time division signals DS whose amplitudes change in a time division manner.

[0057] Second Embodiment Fig. 4 is a block diagram showing the main configuration of a signal detection device according to a second embodiment of the present invention. In Fig. 4, the same blocks as those shown in Fig. 1 are given the same reference numerals. As shown in Fig. 4, the signal detection device 2 of this embodiment is configured by omitting the ADC 12 and the change point detection unit 15 of the signal detection device 1 shown in Fig. 1 and adding a reference signal generation unit 21 (first generation unit) and an index signal generation unit 22 (second generation unit).

[0058] A measurement signal MS and a start trigger signal TS are input to the signal detection device 2. The start trigger signal TS is a signal that specifies the start timing of a time division signal DS included in the measurement signal MS. The signal detection device 2 generates a reference signal RS and an index signal IS from the start trigger signal TS, and uses the generated reference signal RS and index signal IS to separate and detect the amplitudes of each of the time division signals DS (see FIG. 2(a)) included in the measurement signal MS.

[0059] The signal detection device 2 of this embodiment is based on the premise that the frequency of the time division signal DS, the period in which the amplitude of the time division signal DS changes, and the type of the amplitude of the time division signal DS are known. Note that the signal detection device 2 does not include the reference signal input terminal T12 and the index signal input terminal T13 shown in Fig. 1, and is provided with a start trigger signal input terminal T14 to which a start trigger signal TS is input.

[0060] The reference signal generating unit 21 starts generating a reference signal RS at the timing when the start trigger signal TS is input from the start trigger signal input terminal T14. The reference signal RS generated by the reference signal generating unit 21 is a digital signal having the same frequency as the frequency of the known time division signal DS. The reference signal generating unit 21 generates a timing signal TM every time a period during which the amplitude of the known time division signal DS changes has elapsed since the start trigger signal TS was input. This timing signal TM is a signal indicating the division timing of the time division signal DS, and is input to the resampling unit 14 and the index signal generating unit 22. The timing signal TM can be said to be the same signal as the timing signal TM output from the change point detecting unit 15 in the first embodiment.

[0061] The index signal generator 22 generates an index signal IS based on the timing signal TM generated by the reference signal generator 21. For example, consider a case where the amplitude type of the known time division signal DS is "3." In this case, the index signal generator 22 generates an index signal IS that changes from "1," "2," "3," "1," "2," ... each time the timing signal TM is output from the reference signal generator 21, similar to the index signal IS shown in Fig. 2(c).

[0062] The operation of the signal detection device 2 in the above configuration is basically the same as that of the signal detection device 1 of the first embodiment, except that the reference signal RS and the index signal IS are generated inside the signal detection device 2 based on the start trigger signal TS. Therefore, here, the operation of the signal detection device 2 will be briefly described.

[0063] When the operation of the signal detection device 2 is started, a measurement signal MS and a start trigger signal TS are input from a measurement signal input terminal T11 and a start trigger signal input terminal T14, respectively. Note that the time division signal DS included in the measurement signal MS and the start trigger signal TS are synchronized.

[0064] The measurement signal MS input from the measurement signal input terminal T11 is converted into a digital signal by the ADC 11. The start trigger signal TS input from the start trigger signal input terminal T14 is input into the reference signal generating unit 21. This causes the reference signal generating unit 21 to start generating a reference signal RS as a digital signal at the timing when the start trigger signal TS is input. The measurement signal MS converted into a digital signal and the reference signal RS generated by the reference signal generating unit 21 are multiplied by the multiplier unit 13.

[0065] Furthermore, in the reference signal generating unit 21, a timing signal TM is generated every time a period in which the amplitude of the time division signal DS changes after the start trigger signal TS is input. This timing signal TM is input to the resampling unit 14 and also to the index signal generating unit 22. When the timing signal TM is input to the resampling unit 14, the resampling unit 14 resamples the multiplication result of the multiplication unit 13 at the timing of the timing signal TM. On the other hand, when the timing signal TM is input to the index signal generating unit 22, the index signal generating unit 22 generates an index signal IS.

[0066] The multiplication result of the multiplication unit 13, which has been resampled by the resample unit 14, is input to the filter processing unit 16 and subjected to filtering. Meanwhile, the index signal IS generated by the index signal generation unit 22 is input to the internal memory 17 and the memory 18, and an area for storing the internal state of the filter processing unit 16 and an area for storing the processing result of the filter processing unit 16 are set, respectively, in the same manner as in the first embodiment.

[0067] Each time the reference signal generator 21 generates a timing signal TM, the value of the index signal IS generated by the index signal generator 22 changes. This sequentially switches between an area in the internal memory 17 that stores the internal state of the filter processor 16 and an area in the memory 18 that stores the processing result of the filter processor 16. By performing such processing, values ​​indicating the magnitudes of the amplitudes A1, A2, and A3 of the time division signal DS shown in Fig. 2(a) are stored in different areas of the memory 18, similarly to the first embodiment.

[0068] In this embodiment as well, the values ​​stored in different areas of the memory 18 can be read out, for example, by specifying a read address for the memory 18. The value read out from the memory 18 is output from the output terminal T20 of the signal detection device 2. In this way, the amplitudes of the time division signals DS included in the measurement signal MS are separately detected.

[0069] As described above, this embodiment includes a multiplication unit 13 that multiplies the measurement signal MS by the reference signal RS, and a filter processing unit 16 that performs filtering on the multiplication result of the multiplication unit 13. Also includes an internal memory 17 that stores the internal state of the filter processing unit 16, and a memory 18 that stores the processing result of the filter processing unit 16. In addition, this embodiment includes a reference signal generation unit 21 that generates a reference signal RS based on a start trigger signal TS and also generates a timing signal TM, and an index signal generation unit 22 that generates an index signal IS based on the timing signal TM.

[0070] Then, the filter processing unit 16 performs filtering using the internal state stored in the internal memory 17. The internal memory 17 switches the area in which the internal state is written and read by the filter processing unit 16, according to the index signal IS generated by the index signal generating unit 22. The memory 18 switches the area in which the processing result of the filter processing unit 16 is stored, according to the index signal IS generated by the index signal generating unit 22. This makes it possible to separate and detect the amplitudes of the time-division signals DS whose amplitudes change in a time-division manner.

[0071] Furthermore, in this embodiment, the reference signal RS and the index signal IS are generated inside the signal detection device 2 based on a start trigger signal TS input from the outside. This makes it possible to reduce the number of signals input to the signal detection device 2 compared to the number of signals input to the signal detection device 1, and also to reduce noise and jitter. Such a signal detection device 2 can be expected to have higher performance than the signal detection device 1.

[0072] [Optical fiber characteristic measuring device] Fig. 5 is a block diagram showing the main components of an optical fiber characteristic measuring device according to one embodiment of the present invention. As shown in Fig. 5, the optical fiber characteristic measuring device MD of this embodiment includes a signal generating section 30, a light source section 31, an optical branching section 32 (first optical branching section), a pulsing section 33, an optical delay section 34, an optical amplifying section 35, an optical branching section 36 (second optical branching section), an optical amplifying section 37, a multiplexing section 38, an optical detecting section 39 (first detecting section), a frequency analyzing section 40 (analyzing section), a second harmonic component detecting section 41 (second detecting section), and a measuring section 42.

[0073] The optical fiber characteristic measuring device MD of this embodiment is an optical fiber characteristic measuring device using the so-called BOCDR (Brillouin Optical Correlation Domain Reflectometry) method, which measures the characteristics of the optical fiber FUT to be measured based on the Brillouin scattered light LS obtained by injecting a pump pulse light P into the optical fiber FUT to be measured. The pump pulse light P is a pulsed pump light LP that is a continuous light to which frequency modulation has been applied. The Brillouin scattered light LS is backscattered light generated by Brillouin scattering in the optical fiber FUT to be measured.

[0074] Any optical fiber FUT to be measured can be used depending on the wavelength of the pump pulse light P. In this embodiment, the length of the optical fiber FUT to be measured is longer than the interval dm between correlation peaks, and multiple correlation peaks exist in the optical fiber FUT to be measured.

[0075] The signal generating unit 30 generates a modulated signal Sm supplied to the light source unit 31, a pulsed signal Sp supplied to the pulsing unit 33, and a start trigger signal TS supplied to the second harmonic component detecting unit 41. The modulated signal Sm is a signal for outputting a frequency-modulated continuous light L1 (modulated light) from the light source unit 31. The frequency (modulation frequency fm) of the modulated signal Sm is swept within a predefined frequency range. The pulsed signal Sp is a signal for pulsating the pump light LP as continuous light. The start trigger signal TS is a signal for causing the second harmonic component detecting unit 41 to start detecting the second harmonic component contained in the Brillouin gain spectrum obtained by the frequency analyzing unit 40.

[0076] The light source unit 31 includes a light source 31a and a drive signal generating unit 31b, and outputs a frequency-modulated continuous light L1 using a modulation signal Sm output from the signal generating unit 30. The light source 31a includes a semiconductor laser element such as a distributed feedback laser diode (DFB-LD), and outputs a frequency-modulated continuous light L1 in response to a drive signal D1 output from the drive signal generating unit 31b. The drive signal generating unit 31b uses the modulation signal Sm output from the signal generating unit 30 to generate a drive signal D1 for outputting the frequency-modulated continuous light L1 from the light source 31a.

[0077] The optical branching unit 32 branches the continuous light L1 output from the light source unit 31 into a pump light LP and a reference light LR having a predefined intensity ratio (for example, 1:1). The pulsing unit 33 pulses the pump light LP branched by the first optical branching unit 32 using a pulsed signal Sp output from the signal generating unit 30. The reason for providing such a pulsing unit 33 is to obtain pulsed pump light P used in the time gating method.

[0078] The optical delay unit 34 delays the pump light LP (pump pulse light P) pulsed by the pulsating unit 33 by a predetermined time. The optical delay unit 34 includes, for example, an optical fiber of a predetermined length. The delay time can be adjusted by changing the length of the optical fiber. The reason for providing such an optical delay unit 34 is to locate the zero-order correlation peak, whose position does not move even when the modulation frequency fm is swept, outside the measured optical fiber FUT.

[0079] The optical amplifier 35 amplifies the pump pulse light P that has passed through the optical delay unit 34. The optical amplifier 35 includes an optical amplifier such as an EDFA (Erbium Doped Fiber Amplifier), and amplifies the pump pulse light P at a predetermined amplification factor.

[0080] The optical branching unit 36 ​​has a first port, a second port, and a third port. The first port is connected to the optical amplifier 35. The second port is connected to the measured optical fiber FUT. The third port is connected to the optical amplifier 37. The optical branching unit 36 ​​outputs the pump pulse light P input from the first port to the second port. Also, the optical branching unit 36 ​​outputs the Brillouin scattered light LS from the measured optical fiber FUT input from the second port to the third port. For example, an optical circulator can be used as such an optical branching unit 36.

[0081] The optical amplifier 37 amplifies the Brillouin scattered light LS output from the third port of the optical branching unit 36. Like the optical amplifier 35, the optical amplifier 37 includes an optical amplifier such as an EDFA, and amplifies the Brillouin scattered light LS output from the third port of the optical branching unit 36 ​​at a predetermined amplification factor.

[0082] The multiplexing unit 38 combines the Brillouin scattered light LS amplified by the optical amplifier 37 with the reference light LR branched by the optical branching unit 32. The multiplexing unit 38 also branches the combined light into two lights with a predefined intensity ratio (for example, 1:1) and outputs them to the optical detection unit 39. Each of the two lights branched by the multiplexing unit 38 contains, for example, 50% of the backscattered light from the measured optical fiber FUT and 50% of the reference light. For example, an optical coupler can be used as this multiplexing unit 38.

[0083] The optical detection unit 39 performs optical heterodyne detection by causing interference between the Brillouin scattered light LS and the reference light LR contained in the two lights output from the multiplexing unit 38. The optical detection unit 39 includes, for example, a balanced photodiode consisting of two photodiodes (PD: Photo Diode) 39a and 39b, and a multiplexer 39c. The photodiodes 39a and 39b receive the two lights output from the multiplexing unit 38, respectively. The received light signals of the photodiodes 39a and 39b are input to the multiplexer 39c. A detection signal S1, which is an interference signal (beat signal) indicating the frequency difference between the Brillouin scattered light LS and the reference light LR, is output from the multiplexer 39c.

[0084] The frequency analysis unit 40 performs frequency analysis of the detection signal S1 output from the optical detection unit 39. That is, the frequency analysis unit 40 obtains a Brillouin gain spectrum from the detection signal S1 output from the optical detection unit 39. The frequency analysis unit 40 includes, for example, a spectrum analyzer (ESA: Electrical Spectrum Analyzer). The frequency analysis unit 40 captures the detection signal S1 output from the optical detection unit 39 during a period defined by a time gate method. This makes it possible to measure the characteristics of the measured optical fiber FUT without any problems even if multiple correlation peaks exist in the measured optical fiber FUT.

[0085] Instead of the spectrum analyzer, the frequency analysis unit 40 may be configured to include a time axis measurement device such as an oscilloscope and a converter that performs a fast Fourier transform (FFT). The frequency analysis unit 40 configured in this way converts the time-continuous data acquired by the time axis measurement device into spectrum data by the converter.

[0086] The second harmonic component detection unit 41 converts the Brillouin gain spectrum output from the frequency analysis unit 40 into a digital signal, and then detects the second harmonic component contained in the Brillouin gain spectrum. Here, the second harmonic component is a component having a frequency (2fm) that is twice the modulation frequency fm of the continuous light L1. The reason for detecting such a second harmonic component is to remove noise superimposed on the Brillouin gain spectrum obtained by the frequency analysis unit 40 and to suppress baseline fluctuations, thereby enabling stable measurement to be performed in a shorter time than in the past.

[0087] This second harmonic component indicates the intensity at the frequency (2fm) of the Brillouin gain spectrum obtained by the frequency analysis unit 40, and its magnitude varies depending on the position in the measured optical fiber FUT at which the Brillouin gain spectrum was obtained. For example, when the Brillouin gain spectrum obtained by the frequency analysis unit 40 is obtained at a position where a correlation peak appears, the magnitude of the second harmonic component becomes the largest.

[0088] The second harmonic component detection unit 41 includes the signal detection device 2 shown in Fig. 4. The signal detection device 2 receives the Brillouin gain spectrum determined by the frequency analysis unit 40 as the measurement signal MS, and also receives the start trigger signal TS output from the signal generation unit 30. When the start trigger signal TS is input, the signal detection device 2 generates a reference signal RS and an index signal IS having a frequency twice the modulation frequency of the modulated light, and detects the second harmonic component.

[0089] The measurement unit 42 measures the characteristics of the optical fiber FUT under test based on the Brillouin gain spectrum converted into a digital signal by the second harmonic component detection unit 41 and the second harmonic component detected by the second harmonic component detection unit 41. Specifically, the measurement unit 42 performs digital processing using the Brillouin gain spectrum converted into a digital signal by the second harmonic component detection unit 41 and the second harmonic component detected by the second harmonic component detection unit 41 to obtain a peak frequency of the Brillouin gain spectrum. Then, the measurement unit 42 obtains a Brillouin frequency shift amount from the obtained peak frequency, and converts this Brillouin frequency shift amount into the magnitude of strain applied to the optical fiber FUT under test or a temperature change. The measurement unit 42 may include a display unit that displays the second harmonic component detected by the second harmonic component detection unit 41 or the measured characteristics (e.g., strain distribution) of the optical fiber FUT under test. The display unit is, for example, a liquid crystal display or an organic EL (Electro Luminescence) display device.

[0090] In this embodiment, first, the frequency-modulated continuous light L1 is split into pump light LP, reference light, and LR, and the pump light LP is converted into pump pulse light P, which is then input from one end of the optical fiber FUT to obtain Brillouin scattered light LS generated in the optical fiber to be measured. Next, the interference light between the Brillouin scattered light LS and the reference light LR is detected to obtain a Brillouin gain spectrum, which is the spectrum of the Brillouin scattered light. Then, a signal detection device detects a second harmonic component having a frequency twice the modulation frequency of the modulated light contained in the obtained Brillouin gain spectrum, and the characteristics of the optical fiber to be measured are measured based on the obtained Brillouin gain spectrum and the detected second harmonic component. This allows stable measurement to be performed in a shorter time than before.

[0091] Although the signal detection device and the optical fiber characteristic measuring device according to the embodiment of the present invention have been described above, the present invention is not limited to the above embodiment and can be freely modified within the scope of the present invention. For example, the second harmonic component detection unit 41 (see FIG. 5) of the optical fiber characteristic measuring device MD described in the above embodiment includes the signal detection device 2 of the second embodiment shown in FIG. 4. However, the second harmonic component detection unit 41 may also include the signal detection device 1 of the first embodiment shown in FIG. 1. [Explanation of symbols]

[0092] 1,2 Signal detection device 11,12 ADC 13 Multiplication section 14 Resample section 15 Change point detection section 16 Filter processing section 17 Internal Memory 18 Memory 21 Reference signal generation section 22 Index signal generator 32 Optical branching section 36 Optical branching section 39 Light detection unit 40 Frequency Analysis Section 41 Double wave component detector 42 Measuring part DS time division signal FUT Optical fiber under test IS Index Signal L1 Continuum LP pump light LR reference light LS Brillouin scattered light MD Optical Fiber Characteristics Measurement Device MS measurement signal RS reference signal S1 detection signal T11 Measurement signal input terminal T12 Reference signal input terminal T13 Index signal input terminal T14 Start trigger signal input terminal TS Start Trigger Signal TM Timing Signal

Claims

1. a multiplication unit that multiplies the measurement signal by a reference signal; a filter processing unit that performs a filter process on a multiplication result of the multiplication unit; a first storage unit that stores an internal state of the filtering unit; A second storage unit that stores a processing result of the filtering unit; Equipped with The filtering unit performs the filtering process by using the internal state stored in the first storage unit, the first storage unit switches an area in which the internal state is written and read by the filter processing unit in response to an index signal indicating a type of amplitude of a time-division signal included in the measurement signal; the second storage unit switches an area in which the processing result of the filtering unit is stored in response to the index signal. Signal detection device.

2. a first conversion unit for converting the measurement signal into a digital signal; A second conversion unit that converts the reference signal into a digital signal; a detection unit that detects a timing when the index signal changes; a resampler that resamples a multiplication result of the multiplier at the timing detected by the detector; The signal detection device according to claim 1 , comprising:

3. a measurement signal input terminal to which the measurement signal is input; a reference signal input terminal to which the reference signal is input; an index signal input terminal to which the index signal is input; The signal detection device according to claim 2 , comprising:

4. a first generating unit that generates the reference signal based on a start trigger signal that defines a start timing of the time division signal, and generates a timing signal that indicates a division timing of the time division signal; a second generator for generating the index signal based on the timing signal; The signal detection device according to claim 1 , comprising:

5. The first generator generates the reference signal as a digital signal; a first conversion unit for converting the measurement signal into a digital signal; a resampler unit that resamples a multiplication result of the multiplier unit at a division timing indicated by the timing signal; The signal detection device according to claim 4 , comprising:

6. a measurement signal input terminal to which the measurement signal is input; a start trigger signal input terminal to which the start trigger signal is input; The signal detection device according to claim 5 , comprising:

7. 2. The signal detection device according to claim 1, wherein the filter processing unit performs the filtering process using an infinite impulse response low-pass filter.

8. a first optical branching unit that branches the frequency-modulated light into a pump light and a reference light; a second optical branching unit for inputting the pump light into one end of the optical fiber under test and outputting Brillouin scattered light generated within the optical fiber under test; a first detector that detects interference light between the Brillouin scattered light and the reference light output from the second optical branching unit; an analysis unit that determines a Brillouin gain spectrum, which is a spectrum of the Brillouin scattered light, from the detection signal output from the first detection unit; a second detection unit that detects a second harmonic component having a frequency twice the modulation frequency of the modulated light included in the Brillouin gain spectrum obtained by the analysis unit; a measurement unit that measures characteristics of the test optical fiber based on the Brillouin gain spectrum obtained by the analysis unit and the second harmonic component detected by the second detection unit; Equipped with the second detection unit includes the signal detection device according to any one of claims 1 to 7, wherein the Brillouin gain spectrum determined by the analysis unit is input as the measurement signal, and the second detection unit detects the second harmonic component by the reference signal having a frequency twice the modulation frequency of the modulated light. Optical fiber characteristic measuring device.

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