JP7424250B2 - Optical fiber strain measuring device and optical fiber strain measuring method - Google Patents

Description

The present invention relates to an optical fiber strain measuring device and an optical fiber strain measuring method using backward Brillouin scattered light.

With the development of optical fiber communications, distributed optical fiber sensing, in which optical fiber itself is used as a sensing medium, has been actively researched. In particular, optical fiber sensing that uses scattered light can sense a long-distance distribution, unlike an electric sensor that measures point by point, so it can measure physical quantities of the entire object to be measured.

In distributed optical fiber sensing, a light pulse (probe light) is input from one end of an optical fiber, and time-domain reflectometry (OTDR) is used to measure the light backscattered in the optical fiber with respect to the elapsed time from the probe light input. : Optical Time Domain Reflectmetry) is typical (for example, see Non-Patent Document 1).

Backscattering in optical fibers includes Rayleigh scattering, Brillouin scattering, and Raman scattering. An OTDR that uses natural Brillouin scattering as a measurement target is called a Brillouin OTDR (BOTDR) (for example, see Non-Patent Document 2). Note that in the following description, natural Brillouin scattering may be simply referred to as Brillouin scattering.

Brillouin scattering is observed as a frequency shifted by about several GHz toward the Stokes side and the anti-Stokes side with respect to the center frequency of the probe light incident on the optical fiber. The spectrum of Brillouin scattering is called a Brillouin gain spectrum (BGS). The frequency shift amount and spectral linewidth of BGS are respectively determined by the Brillouin Frequency Shift (BFS).
Shift) and Brillouin line width. The BFS and Brillouin linewidth differ depending on the material of the optical fiber and the wavelength (frequency) of the probe light incident on the optical fiber. For example, when a probe light with a wavelength of 1.55 μm is incident on a quartz-based single mode optical fiber, the BFS is about 11 GHz and the Brillouin linewidth is about 30 MHz.

It is known that BFS changes linearly at a rate of about 500 MHz/% with respect to optical fiber strain. When converted into tensile strain and temperature, this corresponds to 0.058 MHz/με and 1.18 MHz/°C, respectively.

In this way, BOTDR is capable of measuring strain and temperature distribution in the longitudinal direction of optical fibers, and is attracting attention as a monitoring technology for large buildings such as bridges and tunnels.

In BOTDR, generally, in order to measure the spectral waveform of Brillouin scattered light generated in an optical fiber, heterodyne detection with separately prepared reference light is performed. The intensity of Brillouin scattered light is about two to three orders of magnitude smaller than the intensity of Rayleigh scattered light used in general OTDR. For this reason, heterodyne detection is useful in improving the minimum light receiving sensitivity.

Since BOTDR handles information on the frequency spectrum distribution in the longitudinal direction of an optical fiber, it is necessary to acquire three-dimensional information of time, amplitude, and frequency. Here, the Brillouin scattered light is very weak as mentioned above, so even if heterodyne detection is applied, the signal-to-noise ratio (
S/N) cannot be secured. As a result, averaging processing is required to improve the S/N. Due to this averaging process and the above-mentioned three-dimensional information acquisition, it is difficult to shorten the measurement time with conventional BOTDR devices.

As a method of shortening the measurement time in a BOTDR device, a method using a self-delay interferometer has been proposed (see, for example, Patent Document 1). In this method, two-dimensional information of time and phase is obtained by measuring the frequency change of light as a phase difference of a beat signal obtained by coherently detecting backscattered light using a self-delay interferometer. Therefore, measurement time is reduced compared to conventional BOTDR devices that require acquisition of three-dimensional information.

Japanese Patent Application Publication No. 2016-191659

Yokogawa Technical Report, Vol. 49, No. 2 pages 56-58 T. Kurashima et al. , “Brillouin Optical-Fiber Time Domain Reflectmetry”, IEICE Trans. Commun. , VOL. E76-B, NO. 4, pp. 382-390 (1993)

In the conventional example described above, for example, an erbium doped fiber amplifier (EDFA) is used as an optical amplifier that amplifies backscattered light. The output of the EDFA includes amplified spontaneous emission (ASE) noise (hereinafter also referred to as ASE noise) generated by the EDFA itself.

This ASE noise is white noise (random noise). ASE noise remains white noise even after passing through a self-delay interferometer, and is expected to become approximately zero through the above-described averaging process.

However, in reality, when ASE noise passes through the self-delaying interferometer, weak noise having the same frequency as the frequency shift f _AOM given by the optical frequency shifter included in the self-delaying interferometer is generated. Since the noise caused by this ASE noise has the same frequency as the beat signal obtained by the Brillouin scattered light, it is impossible to remove it with a filter.

Compared to the signal level of the backscattered light generated near the near end of the optical fiber to be measured, where the probe light is input, the signal level of the backscattered light generated near the far end on the opposite side from the near end is smaller. . Therefore, as the length of the optical fiber increases, the influence of ASE noise on the signal level corresponding to the far end may become non-negligible.

This invention has been made in view of the above-mentioned problems. An object of the present invention is to provide an optical fiber strain measuring device and an optical fiber strain measuring method that can reduce the influence of ASE noise in BOTDR using a self-delaying interferometer.

In order to achieve the above-mentioned object, an optical fiber strain measuring device of the present invention includes a light source section, a light receiving/detecting section, and a signal processing section. The light source section includes a wavelength tunable light source and generates probe light. The light receiving and detecting section detects backscattered light generated by the probe light in the optical fiber to be measured, and generates a measurement signal. The signal processing section generates measurement result data including optical fiber strain data from the measurement signal. Here, the signal processing unit calculates the phase of the ASE noise based on the wavelength setting means that sets the wavelength of the probe light and instructs the variable wavelength light source, and the measurement result data corresponding to the section where there is no optical fiber, The apparatus includes a phase difference calculation means that calculates the phase of the probe light based on the measurement result data corresponding to the section where the optical fiber exists, and calculates the phase difference between the ASE noise and the probe light.

According to a preferred embodiment of this optical fiber strain measuring device, the signal processing section sequentially changes the wavelength of the probe light within a predetermined range, obtains the relationship between the wavelength of the probe light and the phase difference, and obtains the optimal Obtain the wavelength of the probe light that provides the phase difference.

The light receiving and detecting section also includes an optical splitter that branches the backscattered light into a first optical path and a second optical path, and a frequency shift of the beat frequency provided in either one of the first optical path and the second optical path. an optical frequency shifter that provides an optical frequency shifter, an optical delay device provided in either one of the first optical path and the second optical path, and a multiplexer that combines the lights propagating in the first optical path and the second optical path to generate combined light. , a balanced photodiode that generates a beat signal by heterodyne detection of the combined light, a local electric signal source that generates a local oscillation signal with the same frequency as the measurement signal, and a difference frequency signal between the measurement signal and the local oscillation signal. It is preferable to include a mixer and a low-pass filter for acquiring the signal as a measurement signal.

Furthermore, the optical fiber strain measurement method of the present invention includes a probe light generation process that generates a probe light, and a light reception detection process that generates a measurement signal by detecting backscattered light generated in the optical fiber to be measured by the probe light. and a signal processing process for generating measurement result data including optical fiber strain data from the measurement signal. In the signal processing process, the phase of ASE noise is calculated based on the measurement result data corresponding to the section without optical fiber, the phase of the probe light is calculated based on the measurement result data corresponding to the section with optical fiber, and the phase of ASE noise is calculated based on the measurement result data corresponding to the section with optical fiber. Calculate the phase difference between the noise and the probe light. The probe light generation process and the light reception/detection process are performed repeatedly by sequentially changing the wavelength of the probe light, and from the relationship between the acquired wavelength of the probe light and the phase difference, the probe light with the optimal phase difference is generated. Obtain the wavelength of

According to another embodiment of the optical fiber strain measurement method of the present invention, the probe light generation process generates the probe light, and the measurement signal is obtained by detecting the backscattered light generated by the probe light in the optical fiber to be measured. It is configured to include a light reception detection process for generating, and a signal processing process for generating measurement result data including optical fiber strain data from the measurement signal. In the signal processing process, the phase of ASE noise is calculated based on the measurement result data corresponding to the section without optical fiber, the phase of the probe light is calculated based on the measurement result data corresponding to the section with optical fiber, and the phase of ASE noise is calculated based on the measurement result data corresponding to the section with optical fiber. Calculate the phase difference between the noise and the probe light. The probe light generation process, photodetection process, and signal processing process are repeated by sequentially changing the wavelength of the probe light until an optimal phase difference is obtained.

According to the optical fiber strain measuring device and optical fiber strain measuring method of the present invention, the phase difference between the ASE noise and the probe light can be calculated, and the wavelength of the probe light can be set so that this phase difference is optimal. The influence of ASE noise on backscattered light can be reduced.

FIG. 1 is a schematic block diagram of an optical fiber strain measurement device. FIG. 2 is a schematic block diagram of a light source section included in the optical fiber strain measurement device. FIG. 2 is a schematic block diagram of a light separation unit included in the optical fiber strain measurement device. FIG. 2 is a schematic block diagram of a light receiving and detecting section included in the optical fiber strain measuring device. FIG. 2 is a schematic block diagram of a signal processing section included in the optical fiber strain measurement device. FIG. 3 is a schematic diagram showing the relationship between the frequency of probe light, phase difference, and temperature shift. FIG. 3 is a processing flow diagram for explaining a method of setting the optimum wavelength of probe light.

Embodiments of the present invention will be described below with reference to the drawings. Note that in each figure, the shape, size, and arrangement relationship of each component are merely shown schematically to the extent that the present invention can be understood. Further, although preferred configuration examples of the present invention will be described below, the numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following configuration examples or each drawing, and many changes and modifications can be made to achieve the effects of the present invention without departing from the scope of the configuration of the present invention. In addition, common or similar components in each figure are designated by the same reference numerals, and redundant explanation thereof will be omitted.

The optical fiber strain measuring device of the present invention will be explained with reference to FIGS. 1 to 5. FIG. 1 is a schematic block diagram of an optical fiber strain measuring device. 2 to 5 are schematic block diagrams of a light source section, a light separation section, a light reception/detection section, and a signal processing section, respectively, which are included in the optical fiber strain measurement device. Although an optical fiber strain measuring device and an optical fiber strain measuring method will be described here, it is possible not only to simply measure the strain of an optical fiber, but also to measure the temperature based on the strain of the optical fiber.

The optical fiber strain measurement device 100 includes, for example, a light source section 110, a light separation section 120, an optical fiber 130, a light reception/detection section 140, a signal processing section 150, and an output section 160.

The light source section 110 includes, for example, a variable wavelength light source 111, an optical pulse generator 112, a probe optical amplifier 113, and a timing controller 114. As the wavelength tunable light source 111, a conventionally known continuous light source such as a laser diode (LD) can be used. The wavelength of the continuous light generated by the wavelength tunable light source 111 is set to a predetermined wavelength according to an instruction from the signal processing unit 150. Further, the frequency of the electric pulse, the amplification factor in the probe optical amplifier 113, and the like may be configured to be adjustable according to instructions from the signal processing section 150, as necessary.

Continuous light generated by the wavelength tunable light source 111 is sent to an optical pulse generator 112. As the optical pulse generator 112, any suitable acousto-optic modulator (AOM) or electro-optic modulator (EOM) can be used.

The optical pulse generator 112 generates optical pulses from continuous light based on the electric pulses of a constant frequency generated by the timing controller 114. This optical pulse is sent to probe optical amplifier 113. The probe optical amplifier 113 adjusts the optical power of the optical pulse to generate probe light. The probe light passes through the optical separation section 120 and is sent to the optical fiber 130 to be measured.

Here, when the wavelength (frequency) of the continuous light generated by the variable wavelength light source 111 is changed, the phase of the probe light changes. When changing the phase of the probe light from -180° to +180°, the wavelength variable range of the variable wavelength light source 111 needs to be about several tens of nanometers (the frequency variable range is about several GHz).

The optical separation section 120 makes the probe light generated by the probe light generation section 110 enter the fiber 130 . Further, the backscattered light generated in the optical fiber 130 by the incident probe light is separated and extracted and sent to the light receiving/detecting section 140 .

The optical separation unit 120 includes, for example, an optical circulator 121, a backscattered optical amplifier 122, and an optical band pass filter (OBPF) 123.

As the optical circulator 121, a conventionally known three-port optical circulator can be used. The optical circulator 121 makes the probe light output from the probe light generation section 110 enter the optical fiber 130 to be measured, and also sends the backscattered light generated in the optical fiber 130 to the backscattered light amplifier 122 . Note that an optical coupler may be used instead of the optical circulator 121.

As the backscattered light amplifier 122, for example, an erbium-doped optical fiber amplifier (EDFA) is used. The backscattered light amplifier 122 amplifies the optical power of the backscattered light and inputs it to the OBPF 123.

The OBPF 123 separates and extracts one of the Stokes component and the anti-Stokes component of the natural Brillouin scattered light, in this example, only the Stokes component on the low frequency side, from the input backscattered light, passes it, and sends it to the light reception detection section 140 . Note that, in this example, the anti-Stokes component on the high frequency side of the natural Brillouin scattered light is not used.

As described above, it is known that the frequency of the Brillouin scattered light is different from the frequency of the probe light incident on the optical fiber 130. If a general single mode fiber is used as the optical fiber 130 and the frequency of the wavelength tunable light source 111 is 193.4 THz (equivalent to a wavelength of 1.55 μm), the difference between the frequency of the wavelength tunable light source 111 and the passband center frequency fBPF of the OBPF 123 is is approximately 11 GHz. That is, in this configuration example, the passband center frequency of the OBPF 123 is set to be 11 GHz lower than the frequency of the wavelength tunable light source 111.

On the other hand, it is known that the frequency of Rayleigh scattered light, which is other backscattered light, is approximately equal to the frequency of probe light. In the optical fiber strain measuring device 100 of the present invention, Rayleigh scattered light becomes an impediment to measurement. As mentioned above, the frequency difference between the Rayleigh scattered light and the Brillouin scattered light is about 11 GHz, so in order to remove the Rayleigh scattered light, the OBPF 123 has a pass band width of about 10 GHz as described above, and also has a pass band width of about 10 GHz. It is desirable that the rise (fall) of the band be steep.

The light receiving/detecting unit 140 detects backscattered light generated by the probe light in the optical fiber to be measured, and generates a measurement signal.

The light receiving and detecting section 140 includes, for example, an optical branching device 141, an optical delay device 142, an optical frequency shifter 143, a local electric signal source 144, a multiplexer 145, a balanced photodiode (PD) 146, and a beat signal amplifier. 147, a mixer 148, and a low pass filter (LPF) 149. In particular, the optical splitter 141, optical delay device 142, optical frequency shifter 143, local electric signal source 144, multiplexer 145, and balanced PD 146 constitute a self-delay heterodyne interferometer.

The optical splitter 141 branches the natural Brillouin scattered light separated and extracted by the OBPF 123 into a first optical path and a second optical path. In this configuration example, an optical delay device 142 is provided in the first optical path. Further, an optical frequency shifter 143 is provided on the second optical path.

The optical delay device 142 gives a delay of time τ to the first propagation light propagating on the first optical path. Furthermore, the optical frequency shifter 143 applies a frequency shift to the second propagation light propagating through the second optical path based on the local electric signal of frequency f _LO generated by the local electric signal source 144 . As the optical frequency shifter 143, for example, any suitable AOM can be used.

Local electrical signal source 144 generates a local electrical signal of frequency f _LO as described above. The generated local electrical signal is branched into two, one being sent to an optical frequency shifter 143 and the other being sent to a mixer 148.

The multiplexer 145 combines the first propagation light delayed by the optical delay device 142 and the second propagation light subjected to a frequency shift by the optical frequency shifter 143 to generate combined light. The combined light is sent to a balanced PD 146.

The balanced PD 146 performs heterodyne detection on the input multiplexed light to generate a beat signal. The beat signal is sent to beat signal amplifier 147. The beat signal amplifier 147 amplifies the input beat signal. The amplified beat signal is sent to mixer 148.

The mixer 148 performs homodyne detection on the amplified beat signal and the local electric signal to generate a homodyne signal. The LPF 149 removes the sum frequency component of the amplified beat signal and the local electric signal from the homodyne signal, and generates a measurement signal that is a difference frequency component. The measurement signal is sent to the signal processing section 150.

The signal processing section 150 includes, for example, an averaging processing means 151, a noise signal generation means 152, a measurement result data generation means 153, a phase difference calculation means 154, and a wavelength setting means 155. The signal processing section 150 generates measurement result data including optical fiber strain data based on the measurement signal received from the light reception/detection section 140.

The signal processing unit 150 can be configured with, for example, an FPGA (Field Programmable Gate Array). Alternatively, the signal processing unit 150 may be implemented by executing software. It should be noted that the storage means for storing the contents of each process can be of any suitable conventionally known configuration, so a description thereof will be omitted here.

The averaging processing means 151 performs averaging M times (M is an integer of 2 or more), that is, averaging processing. The number of times of this averaging corresponds to the number of electrical pulses generated by timing controller 114. The number of times M of averaging is set to any suitable number, but for example, when the length of the optical fiber 130 is 5 km, it can be set to about 4000 times.

The noise signal generation means 152 generates a noise signal based on the averaged data obtained by the averaging processing means 151. The noise signal is obtained from averaged data corresponding to a section with no optical fiber in a state where backscattered light is input to the backscattered light amplifier 122.

In the section where there is no optical fiber, the averaged data is only the ASE noise generated by the backscattered optical amplifier 122. Since this ASE noise has a low signal level, the averaged data in the section where there is no optical fiber is further averaged N times (N is an integer of 2 or more) to obtain noise data. The initial phase and amplitude of ASE noise are calculated from the noise data. Thereafter, a noise signal is generated using the calculated initial phase and amplitude.

The measurement result data generation means 153 subtracts the noise signal from the averaged data corresponding to the section where the optical fiber is present, and then generates measurement result data including strain data of the optical fiber. The processing in the measurement result data generation means 153 can utilize the conventionally known processing disclosed in Patent Document 1, for example. At this time, the position along the light propagation direction of the optical fiber 130 where the strain has occurred can be calculated from the elapsed time t from the incidence of the probe light to the detection of the strain and the propagation speed v of the light within the optical fiber 130. .

Here, when the frequency (wavelength) of the wavelength tunable light source 11 is changed, the phases of the probe light and the backscattered light change, but the phase of the ASE noise does not change. Therefore, by changing the frequency (wavelength) of the variable wavelength light source, the phase difference between the probe light and the ASE noise can be changed. Note that the frequency and wavelength of the wavelength tunable light source have a one-to-one correspondence. Furthermore, when the phase of the probe light changes, the phase of the backscattered light also changes by the same amount.

With reference to FIG. 6, the phase difference and temperature shift between the probe light and ASE noise when the frequency (wavelength) of the wavelength tunable light source is changed will be described. FIG. 6 is a schematic diagram showing the relationship between the frequency of the wavelength tunable light source, the phase difference, and the temperature shift. In FIG. 6, the frequency of the wavelength variable light source is plotted on the horizontal axis, the temperature shift (° C.) is plotted on the left axis, and the phase difference (°) is plotted on the right axis. Here, the temperature shift is the difference between the temperature obtained by the optical fiber strain measuring device and the accurate temperature obtained separately. Furthermore, in calculating the temperature shift, a noise signal is subtracted from the backscattered light.

As shown in FIG. 6, when the frequency (wavelength) of the wavelength tunable light source 111 changes, the phase difference (indicated by I in the figure) and the temperature shift (indicated by II in the figure) change. The temperature deviation remains even when the noise signal is subtracted. However, when the phase difference between the probe light and the ASE noise is +90°, the temperature shift becomes 0°C, which is optimal. In this way, since there is an optimal phase difference between the probe light and ASE noise, the frequency (wavelength) of the wavelength tunable light source 111 is set so that the optimal phase difference is achieved even when subtracting the noise signal. It is better to do so.

The phase difference calculation means 154 has a function of calculating the phase difference between backscattered light and ASE noise. Note that although the measurement result data generation means 153 subtracts the noise signal from the backscattered light, the phase difference calculation means 154 does not need to subtract the noise signal from the backscattered light.

The wavelength setting unit 155 has a function of setting the wavelength of the probe light and instructing the wavelength variable light source. In order to change the phase of the probe light, that is, the phase difference from -180° to +180°, the wavelength of the variable wavelength light source 111 is changed by about several tens of nanometers (the frequency is about several GHz). The wavelength setting means 155 sequentially changes the wavelength of the probe light within a predetermined range, so-called sweeping. If the amount of change in wavelength is increased, it becomes difficult to obtain an optimal phase difference, and if the amount of change in wavelength is decreased, the time required for sweeping becomes longer. For this reason, it is preferable to change the wavelength by an appropriate official amount of change depending on the allowable time for wavelength setting and the required measurement accuracy. The wavelength setting means obtains an optimal phase difference (+90° in the example of FIG. 6) from the set wavelength and the phase difference obtained for the set wavelength and is indicated by I in FIG. The variable wavelength light source 111 is set to the wavelength at which the phase difference is obtained.

The output unit 160 outputs the measurement result data generated by the signal processing unit 150. The output form of the measurement result data in the output unit 160 is not particularly limited, and includes, for example, output (display) to a display device such as a display, output (save) to a recording medium, and output to warning means such as an alarm. It can be done. The output unit 160 does not necessarily need to include a functional unit such as a display that supports such output formats, and may just include output terminals suitable for each output format.

With reference to FIG. 7, the process of obtaining the optimal wavelength of the probe light will be described. FIGS. 7A and 7B are flowcharts for explaining the process of acquiring the optimal wavelength of probe light. FIG. 7(A) shows the first embodiment, and FIG. 7(B) shows the second embodiment.

In the first embodiment shown in FIG. 7A, first, a wavelength is set and probe light is generated (S10). Next, backscattered light generated in the optical fiber 130 to be measured is detected by the probe light to obtain a measurement signal (S20). Next, it is determined whether the wavelength sweep is completed (S30). If the wavelength sweep is not completed (No), the wavelength is changed and set again (S10), and the measurement signal is acquired again (S20). This process is repeated until the wavelength sweep in a predetermined range is completed.

In the determination of S30, if the wavelength sweep is completed (Yes), the phase difference between the ASE noise and the probe light is calculated for each set wavelength for the acquired measurement signal (S40).

After that, the optimum wavelength is obtained from the obtained relationship between wavelength and phase difference (S50).

After obtaining the optimum wavelength, the wavelength of the variable wavelength light source 111 is set to the optimum wavelength, and normal measurements are performed.

Note that the process of calculating the phase difference for each set wavelength with respect to the acquired measurement signal, which is performed in S40, takes time. For this reason, as in the first embodiment described above, it is preferable to sweep the wavelengths and acquire measurement signals for a plurality of wavelengths, and then perform the phase difference calculation at once. However, the configuration is not limited to this.

In the second embodiment shown in FIG. 7(B), first, a wavelength is set and probe light is generated (S10). Next, backscattered light generated in the optical fiber 130 to be measured is detected by the probe light to obtain a measurement signal (S20). Next, the phase difference between the ASE noise and the probe light is calculated from the acquired measurement signal (S40).

Next, it is determined whether the calculated phase difference is the optimum phase difference (S45). If the phase difference is optimal (Yes), the wavelength at that time is acquired as the optimal wavelength (S50). Here, since the optimal phase difference is +90°, a configuration can be adopted in which the phase difference is determined to be optimal if it is within a few degrees around +90°.

If the phase difference is not optimal (No), the wavelength is changed and set again (S10), and the measurement signal is acquired again (S20). This process is repeated until the calculated phase difference becomes the optimum phase difference. After obtaining the optimum wavelength, the wavelength of the variable wavelength light source 111 is set to the optimum wavelength, and normal measurements are performed.

As explained above, according to the optical fiber strain measuring device and the optical fiber strain measuring method of the present invention, the wavelength (frequency) of the probe light is adjusted so that the phase difference between the probe light and ASE noise becomes an appropriate phase difference. By setting this, it is possible to perform a more accurate measurement than simply subtracting a noise signal based on ASE noise.

100 Optical fiber strain measurement device 110 Light source section 111 Tunable wavelength light source 112 Optical pulse generator 113 Probe optical amplifier 114 Timing controller 120 Optical separation section 121 Optical circulator 122 Backscattered optical amplifier 123 Optical bandpass filter (OBPF)
130 Optical fiber 140 Light receiving/detecting unit 141 Optical splitter 142 Optical delay unit 143 Optical frequency shifter 144 Local electric signal source 145 Multiplexer 146 Balanced photodiode (PD)
147 Beat signal amplifier 148 Mixer 149 Low pass filter (LPF)
150 Signal processing section 151 Averaging processing means 152 Noise signal generation means 153 Measurement result data generation means 154 Phase difference calculation means 155 Wavelength setting means 160 Output section

Claims (5)

a light source section that includes a wavelength tunable light source and generates probe light;
a light receiving and detecting unit that generates a measurement signal by detecting backscattered light generated in the optical fiber to be measured by the probe light;
a signal processing unit that generates measurement result data including strain data of the optical fiber from the measurement signal,
The signal processing section includes:
wavelength setting means for setting the wavelength of the probe light and instructing the wavelength variable light source;
The phase of the ASE noise is calculated based on the measurement signal corresponding to the section without the optical fiber, the phase of the probe light is calculated based on the measurement result data corresponding to the section with the optical fiber, and the phase of the ASE noise is calculated based on the measurement result data corresponding to the section with the optical fiber. and a phase difference calculation means for calculating a phase difference of the probe light. The signal processing section includes:
sequentially changing the wavelength of the probe light within a predetermined range;
The optical fiber strain measuring device according to claim 1, further comprising: acquiring a relationship between the wavelength of the probe light and the phase difference; and acquiring a wavelength of the probe light at which an optimal phase difference is obtained. The light receiving and detecting section includes:
an optical splitter that branches the backscattered light into a first optical path and a second optical path;
an optical frequency shifter that is provided in either the first optical path or the second optical path and provides a frequency shift of the beat frequency;
an optical delay device provided in either the first optical path or the second optical path;
a multiplexer that multiplexes light propagating through the first optical path and the second optical path to generate multiplexed light;
a balanced photodiode that heterodyne-detects the combined light and generates a beat signal;
a local electric signal source that generates a local signal having the same frequency as the measurement signal;
3. The optical fiber distortion measuring device according to claim 1, further comprising a mixer and a low-pass filter that obtain a difference frequency signal between the measurement signal and the local oscillation signal as a measurement signal. a probe light generation process that generates probe light;
a photodetection process of generating a measurement signal by detecting backscattered light generated in the optical fiber to be measured by the probe light;
a signal processing step of generating measurement result data including strain data of the optical fiber from the measurement signal,
The signal processing process includes:
Calculating the phase of ASE noise based on the measurement result data corresponding to the section where there is no optical fiber,
Calculating the phase of the probe light based on measurement result data corresponding to the section where the optical fiber is present,
Calculating the phase difference between the ASE noise and the probe light,
The probe light generation process and the light reception/detection process are repeatedly performed by sequentially changing the wavelength of the probe light,
An optical fiber strain measurement method characterized in that the wavelength of the probe light that provides an optimal phase difference is obtained from the obtained relationship between the wavelength of the probe light and the phase difference. a probe light generation process that generates probe light;
a photodetection process of generating a measurement signal by detecting backscattered light generated in the optical fiber to be measured by the probe light;
a signal processing step of generating measurement result data including strain data of the optical fiber from the measurement signal,
The signal processing process includes:
Calculating the phase of ASE noise based on the measurement result data corresponding to the section where there is no optical fiber,
Calculating the phase of the probe light based on measurement result data corresponding to the section where the optical fiber is present,
Calculating the phase difference between the ASE noise and the probe light,
An optical fiber strain measurement method characterized in that the probe light generation process, the light reception detection process, and the signal processing process are repeated by sequentially changing the wavelength of the probe light until an optimal phase difference is obtained. .

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