An IQ demodulation-based BOTDR signal processing method, device and system

Abstract

The application relates to an IQ demodulation-based BOTDR signal processing method, device and system. The method mainly comprises the following steps: performing fast Fourier transform on the coherent time-domain signal of the collected whole optical fiber to obtain the Brillouin scattering spectrum of the time-domain signal; performing sliding digital filtering on the Brillouin scattering spectrum by using a digital filter, and then performing inverse fast Fourier transform on the filtered signal to obtain time-domain signals of different frequencies; and performing IQ demodulation on the time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and the Brillouin phase spectrum of the signal. The application breaks the inherent contradiction between the frequency accuracy and the spatial resolution in the traditional STFT-BOTDR scheme, and realizes high-performance sensing by taking into account the frequency accuracy and the spatial resolution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, in particular to a BOTDR signal processing method, device and system based on IQ demodulation. BACKGROUND

[0002] With the continuous development of the global information age, sensors have become an important part of the Internet of Things due to their intelligent sensing ability of the surrounding environment. Optical fiber sensors have been widely concerned due to their small transmission loss, anti-electromagnetic interference, corrosion resistance, high sensitivity, and adaptability to harsh environments. Among them, the distributed optical fiber sensing system regards each point on the optical fiber link as a sensing unit, and the optical fiber itself is also a signal transmission carrier, so it can realize distributed continuous measurement along the length of the optical fiber. Due to its excellent technical solution and low cost, distributed sensors have been applied in many fields such as oil pipelines, bridges, dams, tunnels, power lines, housing construction, aircraft, earthquake warning, and border defense. It is an ideal distributed measurement tool that combines intelligence and environmental protection.

[0003] Brillouin Optical Time Domain Reflectometry (BOTDR) utilizes the self-Brillouin scattering effect in optical fiber to realize distributed temperature / stress sensing. Due to its simple single-end optical injection sensing system structure, it can still work normally when the optical fiber is broken, and the system maintenance cost is low, so it is widely used in large-scale structure health detection.

[0004] There are two main methods for Brillouin scattering spectrum measurement in traditional BOTDR sensing system, one is the curve fitting method based on microwave frequency sweeping, and the other is the time-frequency analysis method based on direct measurement of time-domain signal. The curve fitting method based on microwave frequency sweeping uses a microwave source or a frequency mixer to perform frequency sweeping in the optical or electrical domain in the Brillouin scattering frequency band, and then uses a narrow-band filter to obtain the "power-distance" curve of each frequency scanning point in the Brillouin scattering spectrum. Finally, through curve fitting and data processing, the Brillouin scattering spectrum of each sampling point along the fiber can be obtained. Since this scheme requires frequency sweeping measurement, the measurement speed of the sensing system is greatly limited. In order to improve the measurement speed, researchers have proposed the time-frequency analysis method based on direct measurement of time-domain signal. The most common method is the Brillouin scattering spectrum demodulation scheme based on short-time Fourier transform (STFT), namely STFT-BOTDR. Compared with the frequency sweeping method for obtaining Brillouin scattering spectrum, the time-frequency analysis method divides the time-domain curve into equal-length sub-data segments along the fiber length according to the spatial resolution requirement, and then performs Fourier transform on each sub-data segment to obtain the corresponding frequency spectrum as the Brillouin scattering spectrum of the data segment. Finally, the Brillouin scattering spectrum of the whole fiber can be restored by splicing the Brillouin scattering spectrum of each sub-data segment. Compared with the microwave frequency sweeping scheme, this scheme does not require frequency sweeping and has an advantage in measurement speed. However, this scheme also has some limitations. In order to ensure a high spatial resolution of the sensing system, the length of the sub-data segment must be short. However, a shorter sub-data segment length will result in lower frequency accuracy after Fourier transform, which will reduce the temperature and stress resolution of the measurement. Therefore, the frequency accuracy of the Brillouin scattering spectrum in the time-frequency analysis scheme and the spatial resolution of the sensing system are mutually restricted, and there is an inherent contradiction. In addition, in order to ensure sufficient frequency accuracy, a sufficient number of zeros are usually added at the end of the sub-data segment to improve the frequency resolution after Fourier transform, but this will significantly increase the computational complexity of data processing. Therefore, there are still many problems to be solved in STFT-BOTDR.

[0005] To solve the above problems, researchers have conducted a lot of research work. In 2012, Professor Zhang Xuping's research group of Nanjing University proposed a quadratic time-frequency analysis method (QTFA) based on Choi-Williams distribution (CWD). Compared with the traditional STFT method, the measurement accuracy of Brillouin frequency shift (BFS) can be improved by 3 times. However, the calculation complexity of CWD is much higher than that of STFT, and the measurement speed is greatly limited. In 2018, Professor Cheng Linghao's research group of Jinan University proposed a frequency spectrum analysis method based on an autoregressive model (AR model) to evaluate the Brillouin scattering spectrum. Compared with the traditional STFT method, the measurement accuracy can be improved by 5 times under the condition that the data length is not too short. However, this scheme needs to extend the data length by zero padding at the end of the data segment to improve the measurement accuracy. In 2022, the research group also proposed a Brillouin frequency measurement method based on instantaneous frequency analysis. The collected Brillouin gain spectrum (BGS) is subjected to inverse Fourier transform, and the instantaneous Brillouin frequency is calculated on the time domain curve to extract BFS. Compared with the traditional STFT scheme, this scheme reduces the data processing complexity while ensuring the same frequency accuracy and spatial resolution, achieving a 122-fold improvement in measurement speed. However, this scheme still needs to zero-pad at the end of the data segment, which still limits its measurement speed to some extent. Therefore, the existing technical solutions still cannot completely solve the problem of mutual restriction of spatial resolution, frequency accuracy, and data complexity in the STFT-BOTDR system.

[0006] In addition, similar to the Brillouin optical time domain analyzer BOTDA, the BOTDR system based on coherent detection can also realize the measurement of Brillouin phase spectrum (BPS), providing another effective means for environmental temperature / stress measurement. In addition, compared with the Brillouin gain spectrum BGS, BPS also shows unique sensing advantages, such as being unaffected by pump pulse power fluctuations. BPS can also be combined with BGS to improve accuracy and expand the dynamic strain measurement range. The traditional STFT demodulation scheme can realize the demodulation of BPS, but it is also limited by the mutual restriction of frequency accuracy and spatial resolution, and the zero-padding method at the end of the sub-data segment will cause BPS demodulation distortion. Therefore, the traditional STFT scheme still has many problems in demodulating BPS. And there are few existing research works on BPS measurement based on BOTDR sensing system, which still needs further exploration.

[0007] Therefore, how to overcome the defects of the prior art and solve at least part of the above technical problems is a difficult problem to be solved in the technical field. SUMMARY

[0008] In view of the defects in the prior art or the need for improvement: for the Brillouin scattering spectrum demodulation scheme based on short-time Fourier transform (STFT), a shorter sub-data segment length can ensure a higher spatial resolution of the sensing system, but the frequency accuracy of the STFT spectrum is low, and the temperature and stress resolution is limited. The method of zero padding at the tail end of the sub-data segment can improve the frequency accuracy to a certain extent, but this method greatly increases the computational complexity of data processing. Therefore, the traditional BOTDR system urgently needs a data processing method that can achieve high frequency accuracy and high spatial resolution. In addition, the measurement of BPS in the BOTDR system is less, and further research is needed.

[0009] The present application provides a BOTDR signal processing method, device and system based on IQ demodulation, which uses In-phase Quadrature (IQ) demodulation algorithm to replace the traditional STFT method to calculate the Brillouin scattering spectrum, selects a wider digital filter to ensure the spatial resolution of the system, and simultaneously slides the filter window to improve the frequency accuracy. The present application proposes and experimentally verifies the application of the IQ demodulation algorithm in the BOTDR system, breaks the inherent contradiction between frequency accuracy and spatial resolution in the traditional STFT-BOTDR scheme, realizes high-performance sensing that takes into account both frequency accuracy and spatial resolution, and paves the way for its wider application in engineering fields. In addition, the present application can also realize the measurement of BPS with high spatial resolution and high frequency accuracy through the IQ demodulation algorithm, providing a new means for temperature / stress measurement of the traditional BOTDR system.

[0010] The present application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a BOTDR signal processing method based on IQ demodulation, comprising:

[0012] Performing fast Fourier transform on the coherent time-domain signal of the collected whole section of optical fiber to obtain the Brillouin scattering spectrum of the time-domain signal;

[0013] Performing sliding digital filtering on the Brillouin scattering spectrum using a digital filter, and then performing inverse fast Fourier transform on the filtered signal to obtain time-domain signals of different frequencies;

[0014] Performing IQ demodulation on the time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and the Brillouin phase spectrum of the signal.

[0015] In some embodiments, the step of performing IQ demodulation on time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and Brillouin phase spectrum of the signal specifically includes:

[0016] By multiplying time-domain signals of different frequencies by two orthogonal reference signals of the same frequency, the I-channel and Q-channel signals are obtained.

[0017] The I-channel and Q-channel signals are filtered by a low-pass filter to obtain a low-pass filtered signal. The Brillouin scattering intensity and Brillouin scattering phase at each position are obtained based on the low-pass filtered signal.

[0018] The Brillouin scattering intensity and Brillouin scattering phase of the entire optical fiber are obtained by combining the Brillouin scattering intensity and Brillouin scattering phase of different filter center frequencies.

[0019] In some embodiments, performing a fast Fourier transform on the acquired coherent time-domain signal of the entire optical fiber to obtain the Brillouin scattering spectrum of the time-domain signal specifically includes:

[0020] The coherent time-domain signal I(t) acquired by the oscilloscope after removing the DC component is expressed as:

[0021]

[0022] Where ρ is the photoelectric conversion efficiency, ν is the frequency of the scattered light, t is the duration of the time-domain signal, and E B and E represents the light field signal intensity and initial phase of the Brillouin scattered light. L and The intensity and phase of the intrinsic light's optical field signal;

[0023] Performing a Fast Fourier Transform on the coherent time-domain signal I(t) of the entire optical fiber, the Brillouin scattering spectrum of the time-domain signal is expressed as follows:

[0024] f(ν)=∫I(t)·e -jνt dt;

[0025] Where e -jνt It is a complex signal that has undergone time-frequency conversion.

[0026] In some embodiments, after performing sliding digital filtering on the Brillouin scattering spectrum using a digital filter, an inverse fast Fourier transform is performed on the filtered signal to obtain time-domain signals of different frequencies, wherein the time-domain signals of different frequencies are represented as: I ν (t).

[0027] In some embodiments, multiplying time-domain signals of different frequencies by two orthogonal reference signals of the same frequency to obtain I-channel and Q-channel signals specifically includes:

[0028] I ν (t) multiplying the I and Q signals respectively by two orthogonal reference signals of the same frequency as them, to obtain I and Q signals:

[0029]

[0030] and Q signals:

[0031]

[0032] In some embodiments, the filtering the I and Q signals by the low-pass filter to obtain a low-pass filtered signal specifically comprises:

[0033] filtering the I signal by the low-pass filter to obtain an I low-pass filtered signal:

[0034]

[0035] filtering the Q signal by the low-pass filter to obtain a Q low-pass filtered signal:

[0036]

[0037] In some embodiments, the obtaining the Brillouin scattering intensity and the Brillouin scattering phase at each position according to the low-pass filtered signal specifically comprises:

[0038] the Brillouin scattering intensity G B at each position is represented as:

[0039]

[0040] the Brillouin scattering phase at each position is represented as:

[0041]

[0042] In a second aspect, the present application further provides an IQ demodulation-based BOTDR signal processing device for implementing the IQ demodulation-based BOTDR signal processing method of the first aspect, and the device comprises:

[0043] at least one processor; and a memory connected to the at least one processor in communication; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the processor to execute the IQ demodulation-based BOTDR signal processing method of the first aspect.

[0044] In a third aspect, the application further provides an IQ demodulation-based BOTDR signal processing system, which applies the IQ demodulation-based BOTDR signal processing method as described in the first aspect, and comprises a fast Fourier transform module, an inverse fast Fourier transform module and an IQ demodulation module, wherein:

[0045] The fast Fourier transform module is configured to perform fast Fourier transform on the collected coherent time-domain signal of the whole optical fiber to obtain a Brillouin scattering spectrum of the time-domain signal.

[0046] The inverse fast Fourier transform module is configured to perform inverse fast Fourier transform on the filtered signal after the digital filter is used to perform sliding digital filtering on the Brillouin scattering spectrum to obtain time-domain signals of different frequencies.

[0047] The IQ demodulation module is configured to perform IQ demodulation on the time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and the Brillouin phase spectrum of the signal.

[0048] In a fourth aspect, the application further provides a non-volatile computer storage medium, which stores computer executable instructions, and the computer executable instructions are executed by one or more processors to complete the IQ demodulation-based BOTDR signal processing method as described in the first aspect.

[0049] Compared with the prior art, the application has the beneficial effects that the application provides an IQ demodulation-based BOTDR signal processing method, device and system, uses the IQ demodulation algorithm to replace the traditional STFT method to calculate the Brillouin scattering spectrum, selects a relatively wide digital filter to ensure the spatial resolution of the system, and simultaneously uses the sliding filter window to improve the frequency accuracy. The application proposes and experimentally verifies the application of the IQ demodulation algorithm in the BOTDR system, breaks the inherent contradiction between the frequency accuracy and the spatial resolution in the traditional STFT-BOTDR scheme, realizes the high-performance sensing that takes into account the frequency accuracy and the spatial resolution, and paves the way for the application in a wider engineering application field. In addition, the application can also realize the measurement of the BPS that takes into account the high spatial resolution and the high frequency accuracy through the IQ demodulation algorithm, and provides a new means for the temperature / stress measurement of the traditional BOTDR system. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments of the application. Obviously, the drawings described below are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0051] Figure 1A flow chart of an IQ demodulation-based BOTDR signal processing method provided for an embodiment of the present application is shown in FIG. 1.

[0052] Figure 2 An IQ demodulation and STFT demodulation principle comparison diagram provided for an embodiment of the present application is shown in FIG. 2.

[0053] Figure 3 A phase demodulation BOTDR system structure diagram based on IQ demodulation provided for an embodiment of the present application is shown in FIG. 3.

[0054] Figure 4 A Brillouin scattering spectrum and Brillouin phase spectrum using IQ demodulation and a Brillouin scattering spectrum and Brillouin phase spectrum using STFT demodulation comparison diagram provided for an embodiment of the present application is shown in FIG. 4.

[0055] Figure 5 A Brillouin scattering spectrum and Brillouin phase spectrum using STFT demodulation with sub-data segment tail end zero padding provided for an embodiment of the present application is shown in FIG. 5.

[0056] Figure 6 A module diagram of an IQ demodulation-based BOTDR signal processing system provided for an embodiment of the present application is shown in FIG. 6.

[0057] Figure 7 A structure diagram of an IQ demodulation-based BOTDR signal processing device provided for an embodiment of the present application is shown in FIG. 7. DETAILED DESCRIPTION

[0058] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These are all within the scope of the present application. It should be noted that, if there is no conflict, each feature in the embodiments of the present application can be combined with each other, and all within the scope of protection of the present application. In addition, although the functional modules may be divided in the device diagram, and the logical order may be shown in the flow chart, in some cases, the steps shown or described may be different from the module division in the device or the order of execution in the flow chart.

[0059] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as understood by those skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as there is no conflict.

[0060] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0061] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0062] Example 1:

[0063] like Figure 1 As shown in the figure, this embodiment of the invention provides a BOTDR signal processing method based on IQ demodulation, which includes the following steps.

[0064] Step 100: Perform a Fast Fourier Transform on the coherent time-domain signal of the entire optical fiber to obtain the Brillouin scattering spectrum of the time-domain signal.

[0065] Step 200: After performing sliding digital filtering on the Brillouin scattering spectrum using a digital filter, perform an inverse fast Fourier transform on the filtered signal to obtain time-domain signals of different frequencies. It should be noted that this embodiment uses a digital filter with a large bandwidth to ensure the spatial resolution of the sensing system, while simultaneously improving the spectral accuracy of the Brillouin scattering spectrum through frequency window sliding.

[0066] Step 300: Perform IQ demodulation on time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and Brillouin phase spectrum of the signals. Specifically, this step includes: multiplying the time-domain signals of different frequencies by two orthogonal reference signals of the same frequency to obtain I-path and Q-path signals; inputting the I-path and Q-path signals into a low-pass filter to obtain a low-pass filtered signal; obtaining the Brillouin scattering intensity and Brillouin scattering phase at each position based on the low-pass filtered signal; and obtaining the Brillouin scattering spectrum and Brillouin phase spectrum of the entire optical fiber by combining the Brillouin scattering intensity and Brillouin scattering phase at the center frequencies of different filters.

[0067] Based on the above steps, the embodiment provides an IQ demodulation-based BOTDR signal processing method, which uses an IQ demodulation algorithm to replace a conventional STFT method to calculate a Brillouin scattering spectrum, selects a relatively wide digital filter to ensure system spatial resolution, and simultaneously slides a filter window to improve frequency accuracy. The application proposes and experimentally verifies the application of the IQ demodulation algorithm in a BOTDR system, breaks the inherent contradiction between frequency accuracy and spatial resolution in a conventional STFT-BOTDR scheme, realizes high-performance sensing that takes into account both frequency accuracy and spatial resolution, and paves the way for the application in a wider engineering field. In addition, the application can also realize BPS measurement that takes into account both high spatial resolution and high frequency accuracy through the IQ demodulation algorithm, and provides a new means for temperature / stress measurement of a conventional BOTDR system.

[0068] Reference Figure 2 As shown in the figure, Figure 2 (a) in the figure shows a signal processing flow of a BOTDR sensing system based on an IQ demodulation algorithm. In some embodiments, a coherent time-domain signal I(t) collected by an oscilloscope after filtering out a direct current component is represented as:

[0069]

[0070] where p is an optical-electric conversion efficiency, v is a frequency of scattered light, t is a time duration of a time-domain signal, E B and are a light field signal intensity and an initial phase of Brillouin scattered light, E L and are a light field signal intensity and a phase of intrinsic light.

[0071] Fast Fourier Transform (FFT) is performed on the coherent time-domain signal I(t) of the entire optical fiber, and a Brillouin scattering spectrum of the time-domain signal is represented as:

[0072] f(v) = ∫I(t)·e -jνt dt(2).

[0073] where e -jνt is a complex signal of time-frequency conversion.

[0074] The Brillouin scattering spectrum is in a Lorentz line shape, and after sliding digital filtering of the Brillouin scattering spectrum is performed by using a digital filter, inverse Fast Fourier Transform (IFFT) is performed on the filtered signal to obtain time-domain signals of different frequencies, where the time-domain signals of different frequencies are represented as I ν (t).

[0075] Finally, the time domain signals of each frequency are IQ demodulated to obtain the amplitude (Brillouin scattering spectrum) and phase (Brillouin phase spectrum) of the signal.

[0076] In some embodiments, for IQ demodulation, first, the I ν (t) is multiplied by two orthogonal reference signals of the same frequency, respectively, to obtain an I channel signal:

[0077]

[0078] and a Q channel signal:

[0079]

[0080] After obtaining the I channel and Q channel signals, the two signals are input into a low-pass filter for filtering. Specifically, the I channel signal is input into a low-pass filter for filtering to obtain an I channel low-pass filtered signal:

[0081]

[0082] The Q channel signal is input into a low-pass filter for filtering to obtain a Q channel low-pass filtered signal:

[0083]

[0084] The Brillouin scattering intensity G B (t) at each position can be represented as:

[0085]

[0086] The Brillouin scattering phase at each position can be represented as:

[0087]

[0088] Finally, the Brillouin scattering spectrum and the Brillouin phase spectrum of the entire optical fiber can be obtained by combining the Brillouin scattering intensities of different filter center frequencies. It should be noted that the bandwidth of the digital filter needs to be properly set, otherwise the spatial resolution of the sensing system will be affected. The larger the bandwidth of the digital filter, the higher the spatial resolution of the sensing system. Therefore, we set a digital filter with a larger bandwidth to ensure the spatial resolution of the sensing system, and improve the spectral accuracy of the Brillouin scattering spectrum by sliding the frequency window.

[0089] Figure 2 (b) in the above equation (1) is the signal processing flow of the BOTDR sensing system based on the traditional STFT demodulation algorithm. The time window is taken as a sub-data segment for the coherent detection time domain signal in equation (1), and the Brillouin scattering spectrum at the position of the sub-data segment can be obtained by performing FFT on the sub-data segment, which can be represented as:

[0090] STFT(t,f) = ∫I(τ)h(τ-t)e -j2πfτ dτ(9);

[0091] Where h(τ-t) is the time window function. By sliding the time window, the Brillouin scattering spectrum at each position along the fiber length can be obtained. By combining the Brillouin scattering spectrum at each position, the Brillouin scattering spectrum of the whole fiber can be restored. It should be noted that if a wider time window is selected in the STFT, the frequency resolution is higher, but the time resolution is lower. If a narrower time window is selected, the time resolution is higher, but the frequency resolution is lower. Therefore, in order to facilitate comparison, we set the same spatial resolution in the two demodulation methods to compare the difference in frequency accuracy.

[0092] Figure 3 The structure diagram of the phase demodulation BOTDR system based on the IQ demodulation provided by the present application, that is, the BOTDR system device diagram adopted in the present embodiment, since the signal processing will not change the sensing system, the system is essentially a conventional STFT-BOTDR system. The narrow linewidth laser, that is, the light source, is divided into two paths through the optical coupler 1: signal light and reference light. In the signal light path, the signal light is modulated into optical pulses through the semiconductor optical amplifier (the semiconductor optical amplifier is connected to an arbitrary waveform generator), and then the optical power is amplified in the erbium-doped fiber amplifier. Finally, the amplifier spontaneous emission noise is filtered out through the band-pass filter, and after passing through the circulator 1, the signal light is injected into the sensing optical fiber to generate spontaneous Brillouin scattering. The scattered light enters the optical coupler 2. In the reference light path, the reference light passes through the polarization controller and the electro-optic modulator (the electro-optic modulator is connected to a microwave source) to realize the double-sideband frequency shift with carrier suppression, and then enters the optical Bragg grating through the circulator 2 to filter out the Stokes sideband. Finally, after passing through the polarization scrambler to suppress the polarization-dependent noise, the reference light enters the optical coupler 2 to beat with the scattered light. The beat signal is converted into an electrical signal through the photodetector, and then collected by the oscilloscope and processed.

[0093] Figure 4 The comparison diagram for restoring the Brillouin scattering spectrum and the Brillouin phase spectrum by using the BOTDR system of the IQ demodulation scheme and the conventional STFT demodulation scheme proposed by the present application. Both schemes ensure the same 4m spatial resolution. Figure 4 (a) in FIG. 4 is the Brillouin scattering spectrum restored by the IQ demodulation scheme. The filter range of the digital filter is 50MHz to 350MHz, and the filter bandwidth is 40MHz, which meets the required 4m spatial resolution. The sliding interval is 5MHz, so the frequency accuracy of the Brillouin scattering spectrum is 5MHz, and the total number of frequency points of the spectrum is 60 points. Figure 4 (b) in FIG. 4 is the Brillouin phase spectrum restored by the IQ demodulation scheme, and the frequency accuracy is also 5MHz. Figure 4(c) in FIG. 6 is the Brillouin scattering spectrum restored by the STFT demodulation scheme, and since the sampling rate of the oscilloscope acquisition is 1 GSa / s, 4m spatial resolution corresponds to the length of each sub-data segment of 40 sampling points, the frequency accuracy is 25 MHz, the measured spectral range is 0-500 MHz, and the total number of frequency points is 20 points. Figure 4 (d) in FIG. 6 is the Brillouin phase spectrum restored by the STFT demodulation scheme, and the frequency accuracy is also 25 MHz. Therefore, it can be seen that under the condition of ensuring the same spatial resolution, the frequency accuracy of the IQ demodulation is determined by the sliding interval of the digital filter, and higher frequency accuracy can be achieved compared with the traditional STFT scheme. This fully verifies the high-performance sensing capability of the phase demodulation BOTDR sensing system based on the IQ demodulation algorithm, which simultaneously realizes high spatial resolution and high frequency accuracy.

[0094] Figure 5 The traditional STFT scheme demodulates the Brillouin scattering spectrum and the Brillouin phase spectrum with zero padding at the tail end of the sub-data segment, as shown in FIG. 7. Each sub-data segment is zero-padded to 200 sampling points, corresponding to a frequency accuracy of 5 MHz. As shown in (a) in FIG. 7, the number of frequency points of the spectrum after zero padding is equivalent to that of the IQ demodulation scheme. However, the Brillouin phase spectrum demodulated after zero padding cannot restore the correct phase, as shown in (b) in FIG. 7. Therefore, compared with the traditional STFT scheme, the BOTDR sensing system based on the IQ demodulation algorithm can also realize sensing with high spatial resolution and high frequency accuracy. Figure 5 Figure 5

[0095] In summary, the BOTDR sensing system based on the STFT algorithm demodulation has the problem that the spatial resolution, frequency accuracy and data complexity are mutually restricted, which needs to be solved. The embodiment of the present application provides a BOTDR signal processing method based on IQ demodulation, which realizes high-performance sensing of the BOTDR sensing system with high spatial resolution and high sensing accuracy by using the IQ demodulation algorithm, breaks through the limitation of spatial resolution and sensing accuracy of the traditional STFT-BOTDR system, and greatly improves the application ability of the Brillouin sensor in the actual engineering application scene of high-precision measurement. Although the STFT-BOTDR system can improve the measurement accuracy while ensuring the spatial resolution by means of sub-data segment zero padding, this scheme cannot realize the measurement of the Brillouin phase spectrum. The embodiment of the present application utilizes the IQ demodulation to realize the measurement of the distributed Brillouin phase spectrum, which provides a new sensing means for the temperature / stress measurement of the BOTDR sensor. Therefore, the present application has a broader application prospect.

[0096] Embodiment 2:

[0097] This embodiment 2 provides a specific implementation scheme on the basis of embodiment 1, and compares and illustrates the traditional scheme.

[0098] ​​The embodiment builds an implementation system as shown in Figure 3 The laser outputs 1550nm narrow linewidth laser, which is divided into two paths (signal light and reference light) through the optical coupler: in the signal light path, the signal light is modulated into optical pulses through the semiconductor optical amplifier, and then the optical power is amplified in the erbium-doped fiber amplifier, and finally the amplified spontaneous emission noise is filtered out through the band-pass filter to inject the sensing optical fiber to generate spontaneous Brillouin scattering, and the scattered light enters the optical coupler 2; in the reference light path, the reference light realizes double-sideband frequency shift with carrier suppression through the polarization controller and the electro-optic modulator, and then enters the optical ring through the optical ring, and the Stokes sideband is filtered out through the optical Bragg grating, and finally the polarization-dependent noise is suppressed through the polarization scrambler to enter the optical coupler 2 and beat with the scattered light. The beat signal enters the photodetector to complete the photoelectric conversion, and then is collected by the oscilloscope and subjected to subsequent signal processing.

[0099] The collected time domain signal is obtained by FFT to obtain the whole section of the Brillouin scattering spectrum, and then the digital filter is used for sliding filtering of the Brillouin scattering spectrum, and the IFFT is performed on the filtered signal to obtain the time domain signal at different frequencies, and finally the amplitude (Brillouin scattering spectrum) and phase (Brillouin phase spectrum) of each frequency time domain signal are restored through IQ demodulation, as shown in (a) of Figure 4 , (b) of Figure 4 , the Brillouin scattering spectrum and the Brillouin phase spectrum with a frequency accuracy of 5MHz and a spatial resolution of 4m at the tail end of the 2km sensing optical fiber are successfully measured. The measurement accuracy of the STFT demodulation scheme with the same spatial resolution is 25MHz, as shown in (c) of Figure 4 , (d) of Figure 4 .

[0100] The Brillouin scattering spectrum and the Brillouin phase spectrum of the sub-data segment of the STFT-BOTDR sensing system are zero-padded to 200 sampling points, as shown in (a) of Figure 5 , (b) of Figure 5 . Although the frequency accuracy of the Brillouin scattering spectrum is improved to 5MHz, the Brillouin phase spectrum cannot be restored, while the BOTDR system based on IQ demodulation can realize phase demodulation with high spatial resolution and high frequency accuracy, and has better sensing performance.

[0101] In summary, the embodiment provides an IQ demodulation-based BOTDR signal processing method, which uses an IQ demodulation algorithm to replace a conventional STFT method to calculate Brillouin scattering spectrum, selects a wide digital filter to ensure system spatial resolution, and realizes frequency accuracy improvement by sliding a filter window. The application proposes and experimentally verifies the application of the IQ demodulation algorithm in the BOTDR system, breaks the inherent contradiction between frequency accuracy and spatial resolution in the conventional STFT-BOTDR scheme, realizes high-performance sensing considering frequency accuracy and spatial resolution, and paves the way for wider engineering application. In addition, the application can also realize BPS measurement considering high spatial resolution and high frequency accuracy by the IQ demodulation algorithm, and provides a new means for temperature / stress measurement of the conventional BOTDR system.

[0102] Embodiment 3

[0103] Based on the IQ demodulation-based BOTDR signal processing method provided in the above embodiment 1, the embodiment 3 of the application further provides an IQ demodulation-based BOTDR signal processing system, as shown in Figure 6 The system includes a fast Fourier transform module, an inverse fast Fourier transform module and an IQ demodulation module, wherein: the fast Fourier transform module is used to perform fast Fourier transform on the collected coherent time-domain signal of the whole optical fiber to obtain the Brillouin scattering spectrum of the time-domain signal; the inverse fast Fourier transform module is used to perform inverse fast Fourier transform on the filtered signal after the Brillouin scattering spectrum is slidingly digitally filtered by a digital filter to obtain time-domain signals of different frequencies; and the IQ demodulation module is used to perform IQ demodulation on the time-domain signals of different frequencies to obtain the Brillouin scattering spectrum and the Brillouin phase spectrum of the signal.

[0104] The specific functions of the modules of the above system correspond to the introduction of the method steps in the embodiment 1, and thus will not be repeated here.

[0105] In addition, based on the IQ demodulation-based BOTDR signal processing method provided in the above embodiment 1, the application further provides an IQ demodulation-based BOTDR signal processing device that can be used to implement the above method and system, as shown in Figure 7 The device architecture schematic diagram of the embodiment of the application. The IQ demodulation-based BOTDR signal processing device of the embodiment includes one or more processors 21 and a memory 22. Among them, Figure 7 The processor 21 is taken as an example.

[0106] The processor 21 and the memory 22 can be connected through a bus or other means, Figure 7 The connection through the bus is taken as an example.

[0107] The memory 22, as a non-volatile computer readable storage medium, can be used to store non-volatile software programs, non-volatile computer executable programs and modules, such as the BOTDR signal processing method based on IQ demodulation in Embodiment 1. The processor 21 performs various functional applications and data processing of the BOTDR signal processing device based on IQ demodulation by running the non-volatile software programs, instructions and modules stored in the memory 22, that is, implements the BOTDR signal processing method based on IQ demodulation in Embodiment 1.

[0108] The memory 22 can include a high-speed random access memory, and can also include a non-volatile memory, for example, at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state memory device. In some embodiments, the memory 22 can optionally include a memory disposed remotely with respect to the processor 21, and these remote memories can be connected to the processor 21 through a network. Examples of the above-mentioned network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0109] The program instructions / modules are stored in the memory 22, and when executed by one or more processors 21, the BOTDR signal processing method based on IQ demodulation in Embodiment 1 described above is executed, for example, the above-described Figure 1 each step shown.

[0110] The above product can execute the method provided in the embodiments of the present application, and has the corresponding functional modules and beneficial effects of the method. Technical details not described in detail in the embodiments can be referred to the method provided in the embodiments of the present application.

[0111] It should be noted that the above-described device embodiments are only schematic, and the units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or distributed on multiple network units. Part or all of the modules can be selected according to actual needs to achieve the purpose of the embodiments of the present application.

[0112] Through the above description of the embodiments, those skilled in the art can clearly understand that the embodiments can be implemented by means of software plus a general hardware platform, and of course can also be implemented by hardware. Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by a computer program instructing related hardware, and the program can be stored in a computer readable storage medium. When the program is executed, it can include the processes of the above-mentioned embodiment methods. The storage medium can be a magnetic disc, an optical disc, a read-only memory (ROM) or a random access memory (RAM), etc.

[0113] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit it; under the idea of the present application, the technical features of the above examples or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An IQ demodulation-based BOTDR signal processing method, characterized by, The method comprises the following steps: The coherent time domain signal of the collected whole fiber is subjected to fast Fourier transform to obtain the Brillouin scattering spectrum of the time domain signal, including: subjecting the coherent time domain signal collected by the oscilloscope and filtered of the direct current component to fast Fourier transform is represented as: ； wherein is the photoelectric conversion efficiency, is the frequency of the scattered light, is the duration of the time domain signal, and is the optical field signal strength and initial phase of the Brillouin scattered light, and is the optical field signal strength and phase of the intrinsic light; Coherent time domain signal of an entire optical fiber The Fourier transform is performed rapidly, and the Brillouin scattering spectrum of the time domain signal is expressed as: ； wherein is a complex signal that is time-frequency converted; The time-domain signals of different frequencies are obtained by inverse fast Fourier transform of the filtered signals after sliding digital filtering of the Brillouin scattering spectrum by using a digital filter ; The method comprises the following steps: The method comprises the following steps: will be described below. respectively multiplied by two orthogonal reference signals of the same frequency, to obtain an I channel signal: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: Brillouin scattering intensity at each position is expressed as: ； Brillouin scattering phase at each position is expressed as: 。 2. An IQ demodulation-based BOTDR signal processing apparatus for implementing the IQ demodulation-based BOTDR signal processing method of claim 1, characterized by The method comprises the following steps: The method comprises the following steps:

3. An IQ demodulation-based BOTDR signal processing system applying the IQ demodulation-based BOTDR signal processing method of claim 1, characterized by, The method comprises the following steps: The method comprises the following steps: The system comprises a fast Fourier transform module, an inverse fast Fourier transform module and an IQ demodulation module, wherein: The fast Fourier transform module is configured to perform fast Fourier transform on the coherent time-domain signal of the whole optical fiber to obtain the Brillouin scattering frequency spectrum of the time-domain signal; 4. A non-transitory computer storage medium, comprising, The inverse fast Fourier transform module is configured to perform inverse fast Fourier transform on the filtered signal after performing sliding digital filtering on the Brillouin scattering frequency spectrum by using a digital filter to obtain the time-domain signal of different frequencies; The IQ demodulation module is configured to perform IQ demodulation on the time-domain signal of different frequencies to obtain the Brillouin scattering frequency spectrum and the Brillouin phase spectrum of the signal. The computer storage medium stores computer executable instructions, and the computer executable instructions are executed by one or more processors to complete the BOTDR signal processing method based on IQ demodulation.

Images