OPGW cable micro-bending identification method and system based on DPP-BOTDA

Abstract

The application provides an OPGW optical cable micro-bending identification method and system based on DPP-BOTDA, and relates to the field of distributed optical fiber sensing. The method comprises the following steps: acquiring a strain distribution curve of an OPGW optical cable along a line; extracting a cable space feature from the strain distribution curve, and determining an OPGW optical cable structure type based on the cable space feature; processing the strain distribution curve, and identifying a micro-bending area based on a processing result and the OPGW optical cable structure type. The application can realize distributed strain measurement with a centimeter-level spatial resolution, can identify early micro-bending which has not caused significant attenuation, and can realize early warning and accurate positioning of the micro-bending. The application can be integrated in an existing OPGW optical cable online monitoring system, is suitable for daily inspection, fault positioning and structure health monitoring of overhead transmission lines, and has important engineering application value and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing, specifically to a method and system for identifying microbends in OPGW optical cables based on DPP-BOTDA. Background Technology

[0002] Fiber-optic composite overhead ground wire (OPGW) cables are widely used in power transmission lines, and their operating status directly affects communication and power grid security. During long-term operation, the cables may be affected by mechanical stress, environmental disturbances, and other factors, resulting in hidden defects such as microbending and localized strain anomalies. Microbending typically occurs on a centimeter-scale or even smaller scale, leading to additional fiber loss and localized stress concentration, and is one of the key factors affecting cable reliability. However, traditional detection methods struggle to effectively identify microbending at such a small scale. For example, while Brillouin optical time-domain analysis (BOTDA) can achieve distributed strain measurement along the fiber, its traditional spatial resolution is typically on the meter level, which is insufficient for microbending identification. Different OPGW cable structures (such as central tube and stranded types) exhibit different strain response characteristics under stress. Therefore, it is necessary to propose a detection method with high spatial resolution to achieve microbending identification in optical cables. Summary of the Invention

[0003] In view of the above problems, this invention proposes a method and system for identifying microbends in OPGW optical cables based on DPP-BOTDA.

[0004] According to one aspect of the present invention, a method for identifying microbends in OPGW optical cables based on DPP-BOTDA is proposed, the method comprising:

[0005] Obtain the strain distribution curve along the OPGW optical cable;

[0006] The spatial characteristics of the optical cable are extracted from the strain distribution curve, and the OPGW optical cable structure type is determined based on the spatial characteristics of the optical cable.

[0007] The strain distribution curve is processed, and micro-bending regions are identified based on the processing results and the OPGW optical cable structure type.

[0008] Furthermore, obtaining the strain distribution curve along the OPGW optical cable includes:

[0009] Two sets of Brillouin time-domain signals corresponding to two optical pulses of different widths were acquired using a distributed optical fiber sensing system based on DPP-BOTDA.

[0010] Differential processing is performed on the two sets of Brillouin time-domain signals to obtain high spatial resolution differential time-domain signals;

[0011] Based on high spatial resolution differential time-domain signals of microwave sources at different output frequencies, a differential Lyon spectrum is constructed.

[0012] The Brillouin center frequency shift at each location point is obtained by fitting the differential distribution Brillouin spectrum, thus forming the Brillouin center frequency shift curve.

[0013] Based on the correspondence between Brillouin frequency shift and strain, the strain distribution curve along the optical cable is obtained.

[0014] Furthermore, the DPP-BOTDA-based distributed fiber optic sensing system includes a laser, a coupler, a first electro-optic modulator, a polarization controller, an erbium-doped fiber amplifier, a first circulator, a second electro-optic modulator, an adjustable attenuator, an isolator, a second circulator, a fiber Bragg grating filter, a photodetector, a data acquisition card, a pulse source, and a microwave source; wherein, the pulse source drives the first electro-optic modulator to generate two optical pulses of different widths, and the microwave source drives the second electro-optic modulator to perform frequency modulation; the output of the laser is connected to the input of the coupler, and the output of the coupler is connected to the inputs of the first and second electro-optic modulators respectively; the output of the first electro-optic modulator is connected to the input of the polarization controller, and the output of the polarization controller is connected to the erbium-doped fiber amplifier. The input of the fiber amplifier is connected, the output of the erbium-doped fiber amplifier is connected to port 1 of the first circulator, and port 2 of the first circulator is connected to one end of the fiber under test; the output of the second electro-optic modulator is connected to the input of the adjustable attenuator, the output of the adjustable attenuator is connected to the input of the isolator, and the output of the isolator is connected to the other end of the fiber under test; port 3 of the first circulator is connected to port 1 of the second circulator, port 2 of the second circulator is connected to the fiber grating filter, port 3 of the second circulator is connected to the input of the photodetector, and the output of the photodetector is connected to the data acquisition card; the output of the pulse source is connected to the modulation end of the first electro-optic modulator and the trigger end of the data acquisition card, respectively; the output of the microwave source is connected to the modulation end of the second electro-optic modulator.

[0015] Furthermore, the step of extracting the optical cable spatial features from the strain distribution curve and determining the OPGW optical cable structure type based on the optical cable spatial features includes:

[0016] Statistical features, spatial spectrum features, and periodic features are extracted from the strain distribution curve. When the statistical feature value of the strain distribution is less than a preset threshold and there is no dominant frequency component in the spatial spectrum features, it is determined to be a central tube type optical cable. When the strain distribution has periodic features and there is a dominant frequency component in the spatial spectrum features, it is determined to be a stranded type optical cable.

[0017] Furthermore, the statistical features include at least one of the following: mean, standard deviation, variance, and fluctuation range; the extraction of periodic features from the strain distribution curve includes: performing autocorrelation analysis on the strain distribution curve and extracting the spatial displacement corresponding to the peak value of the autocorrelation function.

[0018] Further, the process of processing the strain distribution curve and identifying the micro-bending region based on the processing result and the OPGW optical cable structure type includes:

[0019] Calculate the first derivative of the strain distribution to obtain the strain gradient; calculate the strain change amplitude within a local window to obtain the local change amplitude; when the strain gradient or local change amplitude exceeds its respective preset threshold, it is determined to be a micro-bending region; wherein, the preset threshold is determined according to the OPGW optical cable structure type: the preset threshold corresponding to the stranded optical cable is greater than the preset threshold corresponding to the central tube optical cable.

[0020] Furthermore, the method also includes: assessing the degree of microbending based on the spatial width and strain peak characteristics of the determined microbending region; the degree of microbending includes: mild, moderate and severe.

[0021] Furthermore, after obtaining the strain distribution curve, the strain distribution curve is subjected to a smoothing filter, which includes sliding window averaging or low-pass filtering.

[0022] According to another aspect of the present invention, a DPP-BOTDA-based OPGW optical cable micro-bend identification system is proposed, the system being used to implement the aforementioned DPP-BOTDA-based OPGW optical cable micro-bend identification method; the system includes:

[0023] The strain distribution acquisition module is configured to acquire the strain distribution curve along the OPGW optical cable.

[0024] The structural discrimination module is configured to extract the optical cable spatial features from the strain distribution curve and determine the OPGW optical cable structure type based on the optical cable spatial features.

[0025] The microbend identification module is configured to process the strain distribution curve and identify microbend regions based on the processing results and the OPGW optical cable structure type.

[0026] The beneficial technical effects of this invention are:

[0027] 1) Achieving centimeter-level high spatial resolution: This invention is based on differential pulse-pair Brillouin optical time-domain analysis (DPP-BOTDA) technology. By generating two optical pulses of different widths to form a differential pulse pair, the two sets of Brillouin time-domain signals are differentially processed, effectively eliminating the limitations of traditional BOTDA systems where pulse width and spatial resolution are mutually constrained. Compared to traditional Brillouin optical time-domain analyzers (whose spatial resolution is typically meter-level), this invention can achieve distributed strain measurement with centimeter-level spatial resolution, providing a data foundation for the precise positioning of micro-bending regions.

[0028] 2) Precise identification of micro-bending regions: Based on high spatial resolution strain distribution curves, this invention can detect local strain anomalies at the centimeter scale by calculating the strain gradient and the amplitude of strain change within a local window. When the strain gradient or the amplitude of local change exceeds a set threshold, the micro-bending region can be accurately identified. Compared with traditional detection methods based on optical power attenuation (which can only detect obvious losses caused by macroscopic bending), this invention can identify early micro-bending that has not yet caused significant attenuation, achieving early warning and precise location of micro-bending.

[0029] 3) First-ever achievement of optical cable structure type identification based on strain distribution: This invention is the first to propose using the statistical characteristics, spatial spectrum characteristics, and periodicity characteristics of distributed strain distribution to identify the structural type of OPGW optical cables. By analyzing the standard deviation, dominant frequency component, and periodicity characteristics of the strain distribution, it can effectively distinguish between central tube optical cables and stranded optical cables. Specifically, stranded optical cables exhibit obvious periodic fluctuations in strain distribution due to the presence of the stranding structure, while the strain distribution of central tube optical cables is relatively smooth. This invention fills the technological gap in optical cable structure identification based on strain distribution.

[0030] 4) Achieving Multifunctional Integrated Detection: This invention integrates micro-bend region identification and optical cable structure discrimination into the same detection system. Based on the strain distribution curve obtained from the same measurement, it simultaneously achieves both functions. The structure discrimination result can be used as prior information for micro-bend identification. Different detection thresholds are applied for different optical cable structure types: stranded optical cables, due to their larger normal stranding fluctuations, use a larger threshold to avoid false alarms; central tube optical cables use a smaller threshold to ensure sensitivity. This integrated design avoids repeated measurements and improves detection efficiency and accuracy.

[0031] 5) Applicable to Engineering-based Online Monitoring of OPGW Optical Cables: This invention is based on DPP-BOTDA technology, with pump and probe light injected from both ends of the optical fiber, enabling long-distance distributed measurement, with a single measurement distance reaching tens of kilometers. The entire detection process does not require interruption of the optical cable operation or the deployment of additional sensors; it can be completed using only the existing communication optical fibers in the OPGW optical cable. Therefore, this invention can be integrated into existing OPGW optical cable online monitoring systems and is suitable for daily inspection, fault location, and structural health monitoring of overhead transmission lines, possessing significant engineering application value and economic benefits. Attached Figure Description

[0032] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example, not limitation, in which:

[0033] Figure 1 This is a flowchart of the OPGW optical cable microbend identification method based on DPP-BOTDA as described in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure of a distributed optical fiber sensing system based on DPP-BOTDA in an embodiment of the present invention;

[0035] Figure 3 This is a differential schematic diagram of a distributed optical fiber sensing system based on DPP-BOTDA in an embodiment of the present invention.

[0036] Figure 4 This is an example diagram of the strain distribution of the central tube optical cable in an embodiment of the present invention;

[0037] Figure 5 This is an example diagram of strain distribution in a stranded optical cable according to an embodiment of the present invention;

[0038] Figure 6 This is a schematic diagram of the structure of the OPGW optical cable micro-bend identification system based on DPP-BOTDA as described in an embodiment of the present invention. Detailed Implementation

[0039] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0040] Those skilled in the art will recognize that embodiments of the present invention can be implemented as a system, apparatus, device, method, or computer program product. Therefore, this disclosure can be specifically implemented in the following forms: entirely hardware, entirely software (including firmware, resident software, microcode, etc.), or a combination of hardware and software. It should be understood herein that any number of elements in the accompanying drawings is for illustrative purposes only and not as a limitation, and any naming is for distinction only and has no limiting meaning.

[0041] This invention proposes a method for identifying microbends in OPGW optical cables based on DPP-BOTDA, such as... Figure 1 As shown, the method includes:

[0042] S1. Obtain the strain distribution curve along the OPGW optical cable;

[0043] S2. Extract the spatial characteristics of the optical cable from the strain distribution curve, and determine the OPGW optical cable structure type based on the spatial characteristics of the optical cable;

[0044] S3. Process the strain distribution curve and identify the micro-bending region based on the processing result and the OPGW optical cable structure type.

[0045] The method begins with S1, obtaining the strain distribution curve along the OPGW optical cable. This includes:

[0046] S11. Acquire two sets of Brillouin time-domain signals corresponding to two optical pulses of different widths using a distributed optical fiber sensing system based on DPP-BOTDA.

[0047] S12. Perform differential processing on the two sets of Brillouin time-domain signals to obtain high spatial resolution differential time-domain signals;

[0048] S13. Construct a differential Lyon spectrum based on high spatial resolution differential time-domain signals at different output frequencies of a microwave source.

[0049] S14. Fit the Brillouin spectrum of the differential distribution to obtain the Brillouin center frequency shift at each location point, and form the Brillouin center frequency shift curve.

[0050] S15. Based on the correspondence between Brillouin frequency shift and strain, the strain distribution curve along the optical cable is obtained.

[0051] According to an embodiment of the present invention, the distributed optical fiber sensing system based on DPP-BOTDA is the data acquisition module described in patent number CN202411411516.5, entitled "Tower Positioning System and Method Based on Differential Pulse Pair Brillouin Optical Time Domain Analyzer," such as... Figure 2As shown, it includes: a laser 1, a coupler 2, a first electro-optic modulator (EOM1) 3, a polarization controller (PS) 4, an erbium-doped fiber amplifier (EDFA) 5, a first circulator 6, a second electro-optic modulator (EDFA2) 7, an adjustable attenuator (VOA) 8, an isolator 9, a second circulator 10, a fiber grating filter (FBG) 11, a photodetector (PD) 12, a data acquisition card (DAQ) 13, a pulse source 14, and a microwave source 15; wherein, the output end of the laser 1 is connected to the input end of the 50:50 coupler 2, and the output end of the 50:50 coupler 2 is connected to the input ends of the first electro-optic modulator 3 and the second electro-optic modulator 7 respectively; the output end of the first electro-optic modulator 3 is connected to the input end of the polarization controller 4, and the output end of the polarization controller 4 is connected to the input end of the erbium-doped fiber amplifier 5. The output of the erbium-doped fiber amplifier 5 is connected to port 1 of the first circulator 6, and port 2 of the first circulator 6 is connected to one end of the fiber under test; the output of the second electro-optic modulator 7 is connected to the input of the adjustable attenuator 8, the output of the adjustable attenuator 8 is connected to the input of the isolator 9, and the output of the isolator 9 is connected to the other end of the fiber under test; port 3 of the first circulator 6 is connected to port 1 of the second circulator 10, port 2 of the second circulator 10 is connected to the fiber grating filter 11, port 3 of the second circulator 10 is connected to the input of the photodetector 12, and the output of the photodetector 12 is connected to the data acquisition card 13; the output of the pulse source 14 is connected to the modulation end of the first electro-optic modulator 3 and the trigger end of the data acquisition card 13, respectively; the output of the microwave source 15 is connected to the modulation end of the second electro-optic modulator 7.

[0052] Specifically, laser 1 employs a narrow linewidth distributed feedback laser to output continuous light. The light is split into pump light and probe light by coupler 2. The pump light is driven by pulse source 14 through first electro-optic modulator 3 to form a differential pulse pair, while the probe light is driven by microwave source 15 for frequency modulation. The pump light and probe light undergo stimulated Brillouin scattering in the optical fiber, and their gain spectra satisfy the Lorentz distribution. In the pump light path, the continuous light first enters the first electro-optic modulator 3, which generates two sets of optical pulse signals with different pulse widths under the drive of pulse source 14, forming a differential pulse pair. The difference between the two pulse widths is preferably controlled on the order of nanoseconds to achieve centimeter-level spatial resolution. The modulated optical pulses are polarized by polarization controller 4 to form an approximately random polarization distribution in the optical fiber, thereby reducing the influence of polarization-dependent noise. Subsequently, the optical pulses enter erbium-doped fiber amplifier 5 for power amplification. The peak power is optimized according to the measurement distance to ensure the Brillouin gain signal strength. The amplified pump light is injected into one end of the optical fiber under test (the fiber core inside the OPGW optical cable) through first circulator 6. In the probe light path, continuous light enters the second electro-optic modulator 7 and is frequency-modulated under the drive of the microwave source 15 to form a reference light signal with a certain frequency shift relative to the pump light. The output frequency of the microwave source 15 scans around the Brillouin frequency shift center, with a preferred scanning step size of 1~5MHz. The modulated probe light is adjusted by an adjustable attenuator 8 to avoid the influence of nonlinear effects on the measurement results, and is injected from the other end of the fiber under test through an isolator 9. In the fiber, the pump light and the probe light undergo stimulated Brillouin scattering, generating a Brillouin scattering signal containing strain information. This signal is extracted by the first circulator 6 and enters the second circulator 10 for path separation. The Brillouin signal is then filtered by a fiber optic grating filter 11 to remove irrelevant frequency components, retaining only the target sideband signal. The filtered light signal is converted into an electrical signal by a photodetector 12 and sampled at high speed by a data acquisition card 13. The data acquisition card 13 is synchronously triggered with the pulse source 14 to ensure consistency between time-domain sampling and light pulse propagation, thereby establishing a time-space mapping relationship and realizing distributed measurement along the fiber.

[0053] The above-mentioned distributed optical fiber sensing system based on DPP-BOTDA is constructed to perform high spatial resolution strain detection on the fiber core inside the OPGW optical cable and obtain the strain distribution curve along the OPGW optical cable. This includes: using pulse source 14 to drive the first electro-optic modulator 3 to generate two optical pulses of different widths, forming a differential pulse pair; acquiring the Brillouin time-domain signals corresponding to the two pulses; then, performing differential processing on the two sets of signals to obtain high spatial resolution differential time-domain signals; obtaining differential time-domain signals at different frequencies by adjusting the frequency of microwave source 15; constructing a differential Brillouin gain spectrum and performing spectral fitting to obtain the Brillouin center frequency shift at each location point; and obtaining the strain distribution curve along the optical fiber based on the correspondence between the Brillouin frequency shift and strain. Figure 3A differential schematic diagram of a distributed optical fiber sensing system based on DPP-BOTDA is shown.

[0054] If the Brillouin time-domain signals corresponding to the two pulses are collected, they are represented as follows: and High spatial resolution differential time domain signal is obtained through differential operations. Where z represents the spatial location point; v represents the sweep frequency; and the Brillouin center frequency shift at each spatial location is obtained by fitting the differential time-domain signals at different frequencies. Based on the linear relationship between Brillouin frequency shift and strain, the frequency shift distribution is converted into a strain distribution curve. The Brillouin frequency shift and strain satisfy the following linear relationship:

[0055] ;

[0056] In the formula, Represents the strain distribution curve; This represents the change in frequency shift at the Brillouin center at position z; Indicates the strain coefficient; Indicates the temperature coefficient; It represents the amount of temperature change.

[0057] Under conditions where the temperature change is small or has been compensated for, we have: .

[0058] Furthermore, to improve the signal-to-noise ratio, after obtaining the strain distribution curve, the strain distribution curve is smoothed and filtered, for example, by using sliding window averaging or low-pass filtering methods.

[0059] Then, step S2 is executed to extract the spatial characteristics of the optical cable from the strain distribution curve, and to determine the OPGW optical cable structure type based on the spatial characteristics. This includes: extracting statistical characteristics, spatial spectrum characteristics, and periodic characteristics from the strain distribution curve; when the statistical characteristic value of the strain distribution is less than a preset threshold and there is no dominant frequency component in the spatial spectrum characteristics, it is determined to be a central tube type optical cable; when the strain distribution has periodic characteristics and there is a dominant frequency component in the spatial spectrum characteristics, it is determined to be a stranded type optical cable.

[0060] According to an embodiment of the present invention, statistical and frequency domain analysis is performed on the global strain distribution to extract periodic features and distribution patterns, thereby enabling the identification of optical cable structures.

[0061] Before extracting the spatial characteristics of the optical cable, the strain distribution data can be preprocessed uniformly, including denoising, normalization, and trend term removal, in order to eliminate environmental influencing factors.

[0062] First, perform statistical analysis on the strain distribution to extract statistical characteristics, including at least one of the following: calculating the mean, standard deviation, variance, and fluctuation range. For a length of... In an optical cable segment, the strain distribution curve can be represented as a discrete sampling point sequence. The mean of the strain distribution reflects the overall strain level of the entire cable segment. The standard deviation is the core indicator for measuring the dispersion of the strain distribution; a smaller standard deviation indicates a more uniform strain distribution with less fluctuation, while a larger standard deviation indicates a more dispersed strain distribution with greater fluctuation. For central tube optical cables, due to their uniform structure, the standard deviation of their strain distribution is usually small. For stranded optical cables, due to the presence of the stranding structure, their strain distribution exhibits periodic fluctuations, resulting in a relatively large standard deviation. Variance, the square of the standard deviation, is also used to measure the dispersion of the strain distribution, and it has the same physical meaning as the standard deviation. The fluctuation range is defined as the difference between the maximum and minimum values ​​of the strain distribution, reflecting the overall variation amplitude of the strain distribution. The fluctuation range is sensitive to outliers and can quickly reflect the overall fluctuation of the strain distribution.

[0063] Then, the strain distribution is transformed in the frequency domain (e.g., by fast Fourier transform) to extract its spatial spectral characteristics. : k represents the spatial frequency, which is also the wave number, representing the number of strain oscillation cycles per unit length. For stranded optical cables, a significant dominant frequency component typically exists in their spectrum. , This corresponds to the stranding pitch of the optical cable; while the spectrum of the central tube type optical cable is characterized by low frequency and no obvious peak.

[0064] Then, autocorrelation analysis is performed on the strain distribution to extract the periodic characteristics of the strain distribution, which are the spatial displacements corresponding to the peak values ​​of the autocorrelation function. Specifically, the autocorrelation function is calculated according to the following formula: In the formula, This represents the offset of the same signal between two different times. When the autocorrelation function... There are obvious periodic peaks The fact that the strain distribution is periodic indicates that the structure is a layered stranded structure.

[0065] Based on the above characteristics, when the statistical characteristic value of the strain distribution is less than the preset threshold and there is no dominant frequency component in the spatial spectrum characteristics, it is determined to be a central tube type optical cable; when the strain distribution has periodic characteristics and there is a dominant frequency component in the spatial spectrum characteristics, it is determined to be a stranded type optical cable; otherwise, it is determined to be other structural types or the output cannot be identified. Figure 4 and Figure 5 Examples of strain distribution for central tube optical cables and stranded optical cables are given respectively.

[0066] Then, step S3 is executed to process the strain distribution curve and identify micro-bending regions based on the processing results and the OPGW optical cable structure type. This includes: calculating the first derivative of the strain distribution to obtain the strain gradient; calculating the strain change amplitude within a local window to obtain the local change amplitude; and determining a micro-bending region when the strain gradient or local change amplitude exceeds its corresponding preset threshold. The preset threshold is determined based on the OPGW optical cable structure type: the preset threshold for stranded optical cables is greater than the preset threshold for central tube optical cables.

[0067] According to an embodiment of the present invention, the strain distribution curve Local feature analysis is performed to extract strain gradient and abrupt change information, identifying microbending regions. A sliding scan is performed on the entire optical fiber segment using fixed-length windows (e.g., centimeter-level windows); the first-order difference of strain is calculated within each window to obtain the strain gradient distribution; simultaneously, the maximum strain change amplitude within the window is calculated; the corresponding region is identified as a microbending region when any of the following conditions are met: the local strain gradient exceeds a preset gradient threshold. The magnitude of local changes within the window exceeds a preset threshold. .

[0068] Specifically, the strain gradient is: ; in length of Within the sliding window, the local variation amplitude is: ; This indicates taking the maximum value. This indicates taking the minimum value.

[0069] Furthermore, the method also includes S4: assessing the degree of microbending based on the spatial width and strain peak characteristics of the determined microbending region; the degree of microbending includes: mild, moderate and severe.

[0070] According to an embodiment of the present invention, for each identified micro-bend region, the following two core feature parameters are extracted: 1) Spatial width W is defined as the extension range of the micro-bend region along the length of the optical cable. The specific calculation method is as follows: For continuously distributed micro-bend regions, the length between its starting position z_start and ending position z_end is defined as the spatial width, where z_start is the starting position where the strain gradient or local fluctuation amplitude first exceeds the threshold, and z_end is the ending position where it last falls below the threshold. 2) Strain peak value Defined as the maximum value of strain distribution within the microbending region; the strain peak reflects the maximum degree of deformation in the microbending region and is an important indicator for assessing the severity of microbending.

[0071] This embodiment is based on the spatial width W and the peak strain. The degree of slight bending is divided into three levels: mild, moderate, and severe.

[0072] 1) Judgment condition for mild micro-bending: spatial width W<W1 (e.g., W1=0.3m), and the strain peak < (e.g. =200με); the local strain corresponding to mild micro-bending changes slightly, and has no obvious influence on the optical fiber transmission performance, which belongs to acceptable construction or environmental fluctuation.

[0073] 2) Judgment condition for moderate micro-bending: spatial width W≥W1, and the strain peak ≤ < (e.g. 200με≤ <500με); the local strain corresponding to moderate micro-bending increases significantly, which may have caused certain additional loss to the optical fiber, but has not yet reached the critical value affecting communication or sensing functions.

[0074] 3) Judgment condition for severe micro-bending (any of the following conditions is satisfied): spatial width W≥W2 (e.g., W2=1.0m), and the strain peak ≥ (e.g. =500με); the ratio of strain peaks exceeds a preset ratio R_peak (e.g. / >3, wherein is the average strain in a normal area).

[0075] The local strain corresponding to severe micro-bending is serious, which may lead to too small bending radius of the optical fiber, significant signal attenuation or even interruption, and there is a risk of fiber breakage. Therefore, when severe micro-bending is detected, an alarm shall be issued immediately, on-site maintenance shall be arranged as soon as possible, the cause shall be identified and rectification measures shall be taken.

[0076] Experimental results have shown that the method of the present invention can accurately identify micro-bending positions within the centimeter scale, has higher spatial resolution and detection sensitivity than traditional BOTDA systems, and has certain robustness to measurement noise.

[0077] An embodiment of the present invention also provides a DPP-BOTDA-based micro-bending identification system for OPGW optical cables, wherein the system is configured to implement the DPP-BOTDA-based micro-bending identification method for OPGW optical cables described in the above embodiment; as Figure 6 shown, the system comprises:

[0078] a strain distribution acquisition module (610) configured to acquire a strain distribution curve along the OPGW optical cable;

[0079] a structure discrimination module (620) configured to extract optical cable spatial features from the strain distribution curve, and determine the structure type of the OPGW optical cable based on the optical cable spatial features;

[0080] The microbend identification module 630 is configured to process the strain distribution curve and identify microbend regions based on the processing results and the OPGW optical cable structure type.

[0081] The functions of the OPGW optical cable microbend identification system based on DPP-BOTDA described in this embodiment of the invention can be explained by the aforementioned OPGW optical cable microbend identification method based on DPP-BOTDA. Therefore, for the parts not described in detail in the system embodiment, please refer to the above method embodiment, and they will not be repeated here.

[0082] It should be noted that although several units, modules, or sub-modules are mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided and embodied by multiple modules.

[0083] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0084] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for identifying micro-bends in OPGW optical cables based on DPP-BOTDA, characterized in that, include: Obtaining the strain distribution curve along the OPGW optical cable includes: acquiring two sets of Brillouin time-domain signals corresponding to two optical pulses of different widths using a distributed optical fiber sensing system based on DPP-BOTDA; performing differential processing on the two sets of Brillouin time-domain signals to obtain high spatial resolution differential time-domain signals; constructing a differential Brillouin spectrum based on the high spatial resolution differential time-domain signals at different output frequencies of a microwave source; fitting the differential Brillouin spectrum to obtain the Brillouin center frequency shift at each location point, forming a Brillouin center frequency shift curve; and obtaining the strain distribution curve along the optical cable based on the correspondence between the Brillouin frequency shift and strain. Extracting spatial features of the optical cable from the strain distribution curve and determining the OPGW optical cable structure type based on these features includes: extracting statistical features, spatial spectrum features, and periodic features from the strain distribution curve; the statistical features include at least one of the following: mean, standard deviation, variance, and fluctuation range; extracting periodic features from the strain distribution curve includes: performing autocorrelation analysis on the strain distribution curve and extracting the spatial displacement corresponding to the peak value of the autocorrelation function; when the statistical feature value of the strain distribution is less than a preset threshold and there is no dominant frequency component in the spatial spectrum features, it is determined to be a central tube type optical cable; when the strain distribution has periodic features and there is a dominant frequency component in the spatial spectrum features, it is determined to be a stranded type optical cable. The strain distribution curve is processed, and micro-bending regions are identified based on the processing results and the OPGW optical cable structure type. This includes: calculating the first derivative of the strain distribution to obtain the strain gradient; calculating the strain change amplitude within a local window to obtain the local change amplitude; and determining a micro-bending region when the strain gradient or local change amplitude exceeds its corresponding preset threshold. The preset threshold is determined according to the OPGW optical cable structure type: the preset threshold for stranded optical cables is greater than the preset threshold for central tube optical cables.

2. The OPGW optical cable micro-bend identification method based on DPP-BOTDA according to claim 1, characterized in that, The DPP-BOTDA-based distributed optical fiber sensing system includes a laser (1), a coupler (2), a first electro-optic modulator (3), a polarization controller (4), an erbium-doped fiber amplifier (5), a first circulator (6), a second electro-optic modulator (7), an adjustable attenuator (8), an isolator (9), a second circulator (10), a fiber grating filter (11), a photodetector (12), a data acquisition card (13), a pulse source (14), and a microwave source (15). The pulse source (14) drives the first electro-optic modulator (3) to generate two optical pulses of different widths, and the microwave source (15) drives the second electro-optic modulator (7) to perform frequency modulation. The output of the laser (1) is connected to the input of the coupler (2), and the output of the coupler (2) is connected to the inputs of the first electro-optic modulator (3) and the second electro-optic modulator (7). The output of the first electro-optic modulator (3) is connected to the input of the polarization controller (4), and the output of the polarization controller (4) is connected to the input of the second electro-optic modulator (7). The output of the erbium-doped fiber amplifier (5) is connected to the input of the erbium-doped fiber amplifier (5), and the output of the erbium-doped fiber amplifier (5) is connected to port 1 of the first circulator (6). Port 2 of the first circulator (6) is connected to one end of the fiber under test. The output of the second electro-optic modulator (7) is connected to the input of the adjustable attenuator (8), and the output of the adjustable attenuator (8) is connected to the input of the isolator (9). The output of the isolator (9) is connected to the other end of the fiber under test. Port 3 of the first circulator (6) is connected to the input of the second circulator (7). The first port of the second circulator (10) is connected to the fiber optic filter (11), the second port of the second circulator (10) is connected to the input end of the photodetector (12), the output end of the photodetector (12) is connected to the data acquisition card (13); the output end of the pulse source (14) is connected to the modulation end of the first electro-optic modulator (3) and the trigger end of the data acquisition card (13) respectively; the output end of the microwave source (15) is connected to the modulation end of the second electro-optic modulator (7).

3. The OPGW optical cable micro-bend identification method based on DPP-BOTDA according to claim 1, characterized in that, The method further includes: assessing the degree of microbending based on the spatial width and strain peak characteristics of the determined microbending region; the degree of microbending includes: mild, moderate and severe.

4. The OPGW optical cable micro-bend identification method based on DPP-BOTDA according to claim 1, characterized in that, After obtaining the strain distribution curve, the strain distribution curve is subjected to a smoothing filter, which includes sliding window averaging or low-pass filtering.

5. An OPGW optical cable micro-bend identification system based on DPP-BOTDA, characterized in that, The system is used to implement the OPGW optical cable micro-bend identification method based on DPP-BOTDA as described in any one of claims 1 to 4; the system includes: The strain distribution acquisition module is configured to acquire the strain distribution curve along the OPGW optical cable. The structural discrimination module is configured to extract the optical cable spatial features from the strain distribution curve and determine the OPGW optical cable structure type based on the optical cable spatial features. The microbend identification module is configured to process the strain distribution curve and identify microbend regions based on the processing results and the OPGW optical cable structure type.

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