A phase sensitive optical time domain reflectometer, measurement method and readable storage medium

Abstract

The application provides a phase-sensitive optical time domain reflectometer, a measurement method and a readable storage medium, wherein a signal generation circuit of the phase-sensitive optical time domain reflectometer is configured to generate a radio frequency signal to drive an optical intensity modulator to modulate probe light, so that two groups of frequency division multiplexing sequences with differences can be used to synchronously detect a sensing optical fiber to be measured, a differential unfolding algorithm is combined to accurately solve a phase change amount in adjacent sampling intervals, and then demodulation results corresponding to different frequency parts are respectively unfolded to obtain unfolded phase results, so that the problem of large strain phase folding is solved and a large strain range is recovered, and further, the unfolded phase results are rearranged and combined in time sequence through time sequence interleaving processing of the unfolded phase results, so that a high sampling rate and a distortion-free reconstruction result are reconstructed, and therefore, the application can realize accurate measurement of high frequency response and large strain range dynamic strain.

Description

Technical Field

[0001] This invention relates to the field of optical measurement and sensing technology, and in particular to a phase-sensitive optical time-domain reflectometer, a measurement method, and a readable storage medium. Background Technology

[0002] A phase-sensitive optical time-domain reflectometer (Φ-OTDR) is a distributed sensing technology based on the Rayleigh scattering principle of optical fibers. It can be used to detect dynamic strains such as vibrations and acoustic waves at different locations along an optical fiber. Its basic principle is as follows: a coherent optical pulse is injected into the single-mode fiber under test. During the propagation of the pulse in the fiber, scattering occurs due to the non-uniformity of the refractive index distribution. The portion propagating backward along the incident direction is called backscattered light. This backscattered light corresponds in time to the propagation distance of the optical pulse in the fiber. When the fiber is locally subjected to external disturbances (such as changes in fiber diameter, refractive index, or length caused by strain), its optical path changes, resulting in a change in the phase of the backscattered light. By comparing the phase differences at certain distances along the fiber at different detection times, the dynamic disturbance can be detected, located, and quantified. With its long-distance sensing and high spatial resolution continuous distributed measurement capabilities, the Φ-OTDR system has been widely used in vibration monitoring and safety early warning of critical infrastructure such as bridges, tunnels, oil and gas pipelines, and power lines.

[0003] However, existing phase-sensitive optical time-domain reflectometers have limitations in practical applications, including limited high-frequency response and large strain range measurement capabilities.

[0004] The maximum sampling rate of traditional phase-sensitive optical time-domain reflectometers is strictly limited by the length of the optical fiber. To ensure the accuracy of pulse signal positioning along the line, the pulse repetition period must be greater than the time required for light to travel round trip in the sensing fiber. This necessitates the use of lower pulse repetition frequencies in long-distance sensing applications, resulting in a very low maximum detectable vibration frequency, which cannot meet the needs of high-frequency dynamic monitoring in applications such as bridges, large structures, or high-speed railways. Although technologies such as frequency-division multiplexing (FDM) exist to improve the equivalent sampling rate by interleaving pulses of different frequencies, traditional methods are easily limited by the sensitivity and bias differences of different frequency light. Direct time interleaving can cause signal waveform distortion.

[0005] Traditional phase-sensitive optical time-domain reflectometers demodulate phase information using the arctangent function, limiting their output range to -π to π. When external strain or disturbance is large, causing the phase change between two adjacent sampling points to exceed 2π, phase folding (or "phase entanglement") occurs. Phase folding severely distorts the demodulated phase value, making it unable to accurately reflect the true strain magnitude. This prevents the system from being applied to scenarios with large strain ranges, greatly limiting its industrial application scope.

[0006] Existing solutions typically address only one of the limitations in high-frequency response and large strain range measurement, and it is difficult to achieve both high-frequency response and large strain range simultaneously without adding complex hardware or significantly increasing costs. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] This invention provides a phase-sensitive optical time-domain reflectometer, a measurement method, and a readable storage medium, which can solve the problems of limited high-frequency response capability and limited measurement of large strain range without increasing complex hardware or significantly increasing costs, and realize accurate measurement of high-frequency response and dynamic strain with large strain range.

[0009] In a first aspect, embodiments of the present invention disclose a phase-sensitive optical time-domain reflectometer, comprising: a continuous laser, an optical coupler, an optical intensity modulator, a signal generation circuit, an optical amplifier, an optical circulator, a sensing fiber under test, a polarization coherent receiving module, and a signal acquisition and processing module; the continuous laser is configured to generate continuous laser light and incident it onto the optical coupler; the optical coupler is configured to split the continuous laser light into local light and probe light, and incident them onto the polarization coherent receiving module and the optical intensity modulator, respectively; the signal generation circuit is configured to generate a radio frequency signal to drive the optical intensity modulator to modulate the probe light to obtain a pulsed laser light, and incident the pulsed laser light onto the optical amplifier, wherein the radio frequency signal is composed of two or more frequency division multiplexing sequences, and the number of divisions and the repetition period of each frequency division multiplexing sequence are different; the optical amplifier is configured to incident the signal... The pulsed laser is amplified and then incident on an optical circulator. The optical circulator guides the pulsed laser to the optical fiber under test to generate backscattered Rayleigh light in the fiber. The optical circulator also guides the backscattered Rayleigh light to a polarization coherent receiver module to beat the backscattered light and the local light in the polarization coherent receiver module to obtain a beat frequency signal. The signal acquisition and processing module is configured to sample the beat frequency signal to obtain detection results corresponding to different frequency components. The detection results of different frequency components are then demodulated to obtain demodulation results with phase folding risk. The demodulation results are processed according to a preset differential defolding algorithm to obtain defolded phase results. The defolded phase results are then time-interleaved to obtain the reconstruction result.

[0010] The first aspect of the present invention has at least the following beneficial effects: Since the signal generation circuit is configured to generate a radio frequency signal to drive the optical intensity modulator to modulate the probe light, it is possible to synchronously detect the optical fiber under test using two sets of frequency division multiplexing sequences with differences. Combined with the differential defolding algorithm, the phase change within adjacent sampling intervals can be accurately solved. Then, the demodulation results corresponding to different frequency parts are defolded to obtain the defolded phase results, thereby solving the large strain phase folding problem and restoring the large strain range. Furthermore, by performing time-series interleaving processing on the defolded phase results, the previously dispersed but phase-folded defolded phase results are rearranged and combined in a precise time order, thereby reconstructing a high sampling rate, distortion-free strain signal, i.e., obtaining the reconstruction result. Therefore, the embodiments of the present invention can solve the problems of limited high-frequency response capability and limited large strain range measurement, and realize the accurate measurement of high-frequency response and large strain range dynamic strain.

[0011] Secondly, this invention discloses a measurement method applied to a phase-sensitive optical time-domain reflectometer (OTDR). The OTD includes: a continuous laser, an optical coupler, an optical intensity modulator, a signal generation circuit, an optical amplifier, an optical circulator, a sensing fiber under test, a polarization coherence receiving module, and a signal acquisition and processing module. The measurement method includes: obtaining local light and probe light based on the continuous laser; generating a radio frequency (RF) signal, and modulating the probe light based on the RF signal to obtain a pulsed laser, wherein the RF signal is composed of two or more frequency division multiplexing (FDM) sequences, and each FDM sequence has a different division number and repetition period; and amplifying the power of the pulsed laser. The system processes and acquires backscattered Rayleigh light based on the amplified pulsed laser light. The backscattered Rayleigh light and local light are then beat-frequencyd to obtain a beat-frequency signal. This beat-frequency signal is sampled to obtain detection results corresponding to different frequency components. These detection results are then demodulated separately to obtain demodulation results with phase folding risk. The demodulation results are processed according to a preset differential defolding algorithm to obtain defolded phase results. The defolded phase results are then subjected to time-series interleaving to obtain reconstruction results. The time-series interleaving is used to measure the high-frequency response, and the reconstruction results are used to map the measurement results of the high-frequency response and the large-strain dynamic strain.

[0012] The second aspect of the present invention has at least the following beneficial effects: A pulsed laser is obtained by modulating the probe light with radio frequency signals of different frequency division numbers and group repetition periods. Backscattered Rayleigh light is then acquired based on the amplified pulsed laser, and beat frequency is performed using local light as a reference. The beat frequency signal is sampled to obtain detection results corresponding to different frequency components. The detection results of different frequency components are then demodulated to obtain demodulation results. The demodulation results are processed using a differential defolding algorithm to obtain defolded phase results, thereby solving the large strain phase folding problem and restoring the large strain range. Furthermore, the defolded phase results are time-interleaved to rearrange and combine the previously dispersed but phase-folded defolded phase results according to a precise time sequence, thereby reconstructing a high-sampling-rate, distortion-free strain signal, i.e., obtaining the reconstruction result. Therefore, the embodiments of the present invention can solve the problems of limited high-frequency response capability and limited large strain range measurement, achieving accurate measurement of high-frequency response and large strain range dynamic strain.

[0013] Thirdly, embodiments of the present invention disclose a readable storage medium storing computer-executable instructions for causing a computer to perform the measurement method as described in the second aspect of the embodiments above. Therefore, it has the same beneficial effects as the second aspect of the embodiments above, and will not be repeated here.

[0014] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the description, claims and drawings. Attached Figure Description

[0015] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0016] Figure 1 This is a schematic diagram of the architecture of a phase-sensitive optical time-domain reflectometer provided in an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the steps of the measurement method provided in the embodiment of the present invention;

[0018] Figure 3 This is a detailed flowchart of step S500 provided in one embodiment of the present invention;

[0019] Figure 4 This is a detailed flowchart of step S510 provided in one embodiment of the present invention;

[0020] Figure 5 This is a detailed flowchart of step S520 provided in one embodiment of the present invention;

[0021] Figure 6 This is a schematic diagram of the architecture of a phase-sensitive optical time-domain reflectometer provided in a specific example of the present invention;

[0022] Figure 7 This is a schematic diagram of a frequency division multiplexing sequence provided in a specific example of the present invention;

[0023] Figure 8 This is a schematic diagram illustrating the variation of the phase standard deviation obtained after demodulation of all frequency pulses as a function of a 10km sensing fiber distance, provided in a specific example of the present invention.

[0024] Figure 9 This is a time-domain waveform diagram after direct interleaving and compensation, provided as a specific example of the present invention;

[0025] Figure 10 The power spectral density diagram after direct interleaving and compensation is provided as a specific example of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] It should be noted that although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0028] Phase-sensitive optical time-domain reflectometry (Φ-OTDR) is a distributed sensing technology based on the Rayleigh scattering principle of optical fibers. It can be used to detect dynamic strains such as vibrations and acoustic waves at different locations along an optical fiber. Its basic principle is as follows: a coherent optical pulse is injected into the single-mode fiber under test. During the propagation of the pulse in the fiber, scattering occurs due to the non-uniformity of the refractive index distribution. The portion propagating backward along the incident direction is called backscattered light. This backscattered light corresponds in time to the propagation distance of the optical pulse in the fiber. When the fiber is locally subjected to external disturbances (such as changes in fiber diameter, refractive index, or length caused by strain), its optical path changes, resulting in a change in the phase of the backscattered light. By comparing the phase differences at certain distances along the fiber at different detection times, the dynamic disturbance can be detected, located, and quantified. With its long-distance sensing and high spatial resolution continuous distributed measurement capabilities, Φ-OTDR systems have been widely used in vibration monitoring and safety early warning of critical infrastructure such as bridges, tunnels, oil and gas pipelines, and power lines.

[0029] Φ-OTDR quantitatively reconstructs external disturbance information by demodulating the phase of the backscattered Rayleigh light. Phase extraction typically relies on the arctangent function, which is inherently a multivalued function. To ensure demodulation consistency, it is usually assumed that the phase change between two adjacent sampling times is within the range of -π to π, thus creating a boundary for the phase change between adjacent samples. When the phase change caused by external strain exceeds this boundary, the demodulated phase will exhibit folding, leading to severe waveform distortion. This is the fundamental reason why traditional Φ-OTDR struggles to accurately measure large strain signals.

[0030] Without violating phase constraints, shortening the adjacent sampling interval can reduce the phase change under the same strain conditions, thus alleviating the phase folding problem to some extent. Frequency division multiplexing (FDM) is an effective means of shortening the sampling interval. The method involves using optical pulses of different frequencies to probe the optical fiber, with the receiver using a bandpass filter to distinguish the backscattered Rayleigh light of each frequency component. By interleaving optical pulses of different frequencies into the fiber under test and then interleaving them in the order they were injected after demodulation, the equivalent sampling rate of the distributed optical fiber sensing system can be improved. However, the detection results of different frequency components often exhibit differences in sensitivity and bias (even with the same applied strain signal, the phase amplitude and bias obtained from different frequency optical pulses will differ). Therefore, the demodulation results of each frequency must be defolded separately before interleaving. If interleaving is performed before defolding, more defolding errors will occur due to differences in sensitivity and bias. Thus, the strain measurement range of frequency division multiplexing distributed optical fiber sensing (DAS) is still limited to the measurement range of a single-frequency DAS.

[0031] Currently, although frequency division multiplexing (FDM) technology can improve the frequency response range of distributed optical fiber sensing (DAS) to some extent, its strain range remains limited, severely restricting the ability of phase-sensitive optical time-domain reflectometers to measure high-frequency, large-strain signals. Existing technical solutions often only improve a single indicator in frequency response or strain range, and there is a lack of compatibility between different solutions, making it difficult to achieve simultaneous improvement of these two performance indicators.

[0032] To address the above problems, this invention provides a phase-sensitive optical time-domain reflectometer, comprising: a continuous laser, an optical coupler, an optical intensity modulator, a signal generation circuit, an optical amplifier, an optical circulator, a sensing fiber under test, a polarization coherent receiving module, and a signal acquisition and processing module; the continuous laser is configured to generate continuous laser light and incident it onto the optical coupler; the optical coupler is configured to split the continuous laser light into local light and probe light, and incident them onto the polarization coherent receiving module and the optical intensity modulator, respectively; the signal generation circuit is configured to generate a radio frequency signal to drive the optical intensity modulator to modulate the probe light to obtain a pulsed laser, and incident the pulsed laser light onto the optical amplifier, wherein the radio frequency signal is composed of two or more frequency division multiplexing sequences, and the frequency division number and repetition period of each set of frequency division multiplexing sequences are different; the optical amplifier is configured to... The pulsed laser is amplified and then incident on an optical circulator. The optical circulator guides the pulsed laser to the optical fiber under test to generate backscattered Rayleigh light in the fiber. The optical circulator also guides the backscattered Rayleigh light to a polarization coherent receiver module to beat the backscattered light and the local light in the polarization coherent receiver module to obtain a beat frequency signal. The signal acquisition and processing module is configured to sample the beat frequency signal to obtain detection results corresponding to different frequency components. The detection results of different frequency components are then demodulated to obtain demodulation results with phase folding risk. The demodulation results are processed according to a preset differential defolding algorithm to obtain defolded phase results. The defolded phase results are then time-interleaved to obtain the reconstruction result.

[0033] Since the signal generation circuit is configured to generate radio frequency signals to drive the optical intensity modulator to modulate the probe light, it is possible to synchronously detect the optical fiber under test using two sets of frequency division multiplexing sequences with differences. Combined with the differential defolding algorithm, the phase change within adjacent sampling intervals can be accurately solved. Then, the demodulation results corresponding to different frequency parts are defolded to obtain the defolded phase results, thereby solving the large strain phase folding problem and restoring the large strain range. Furthermore, by performing time-series interleaving processing on the defolded phase results, the previously scattered but phase-folded defolded phase results are rearranged and combined in a precise time order, thereby reconstructing a high sampling rate, distortion-free strain signal, i.e., obtaining the reconstruction result. Therefore, the embodiments of the present invention can solve the problems of limited high-frequency response capability and limited large strain range measurement, and realize the accurate measurement of high-frequency response and large strain range dynamic strain.

[0034] Specifically, traditional Φ-OTDR strain measurements are limited by phase folding. Phase folding occurs when the phase change between adjacent sampling points exceeds ±π. Actual strain is typically limited to tens of microstrains. Once the strain amplitude becomes too large, the demodulation results immediately become distorted. This invention, however, uses a differential defolding algorithm to calculate and correct the integer number of phase folds. This means the system's measurement range is no longer limited by ±π, allowing for dynamic strain measurement of large strain ranges, theoretically extending to phase changes of hundreds or thousands of π. In practical applications, this means the ability to accurately measure large-amplitude strain events ranging from hundreds to thousands of microstrains or even higher, such as large-strain measurements over long distances and in complex environments, like bridge structural health monitoring and railway security.

[0035] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0036] Reference Figure 1 , Figure 1 This is a schematic diagram of the architecture of a phase-sensitive optical time-domain reflectometer provided in an embodiment of the present invention. Figure 1 In one example, this invention provides a phase-sensitive optical time-domain reflectometer, whose device architecture includes: a continuous laser, an optical coupler, an optical intensity modulator, a signal generation circuit, an optical amplifier, a sensor link under test, a polarization coherent receiving module, and a signal acquisition and processing module.

[0037] Specifically, continuous laser light is generated by a continuous laser generator. An optical coupler splits the continuous laser light into local light and probe light, which are then incident on a polarization coherent receiving module and an optical intensity modulator, respectively. A signal generation circuit generates an radio frequency signal to drive the optical intensity modulator to modulate the probe light, resulting in pulsed laser light. The pulsed laser light is then incident on an optical amplifier. The optical amplifier amplifies the power of the incident pulsed laser light and then incident the amplified pulsed laser light onto an optical circulator. The optical circulator guides the pulsed laser light into the optical fiber under test to generate pulses in the optical fiber. The backscattered Rayleigh light is generated, and the optical circulator is also used to guide the backscattered Rayleigh light to the polarization coherent receiving module so that the backscattered Rayleigh light and the local light beat in the polarization coherent receiving module to obtain the beat frequency signal. The signal acquisition and processing module samples the beat frequency signal to obtain the detection results corresponding to different frequency components. Then, the detection results of different frequency components are demodulated to obtain the demodulation results. The demodulation results are processed according to the preset differential defolding algorithm to obtain the defolded phase result. The defolded phase result is time-interleaved to obtain the reconstruction result.

[0038] Specifically, since the signal generation circuit is configured to generate radio frequency signals to drive the optical intensity modulator to modulate the probe light, it is possible to synchronously detect the optical fiber under test using two sets of frequency division multiplexing sequences with different characteristics. Combined with the differential defolding algorithm, the phase change within adjacent sampling intervals can be accurately calculated. Then, the demodulation results corresponding to different frequency parts are defolded to obtain the defolded phase results, thereby solving the large strain phase folding problem and restoring the large strain range. Furthermore, by performing time-series interleaving processing on the defolded phase results, the previously scattered but phase-folded defolded phase results are rearranged and combined in a precise time order, thereby reconstructing a high sampling rate, distortion-free strain signal, i.e., obtaining the reconstruction result. Therefore, the embodiments of the present invention can solve the problems of limited high-frequency response capability and limited large strain range measurement, and realize the accurate measurement of high-frequency response and large strain range dynamic strain.

[0039] It should be noted that further adjustments can be made using correction algorithms tailored to different frequency sensitivities and bias differences to effectively suppress waveform distortion and improve measurement accuracy. Compared to traditional Φ-OTDR, this invention not only overcomes the limitations of sensing distance on frequency response range but also significantly expands the strain measurement range, making it particularly suitable for large strain measurement scenarios in long-distance, complex environments such as bridge structural health monitoring and railway security.

[0040] Specifically, the signal acquisition and processing module includes a computer, and the differential defolding algorithm and timing interleaving processing are both completed by the computer as post-processing steps.

[0041] It is understood that the differential defolding algorithm and timing interleaving processing of the present invention are both performed by the computer as post-processing steps, rather than relying on complex or expensive special hardware modules. Therefore, it can solve the problems of limited high-frequency response capability and limited measurement of large strain range without increasing complex hardware or significantly increasing costs, and realize accurate measurement of high-frequency response and large strain range dynamic strain.

[0042] It is understood that the device architecture proposed in this invention can maintain the same hardware configuration as the traditional phase-sensitive optical time-domain reflectometer, without the need for additional components. Vibration measurement under high-frequency response and large strain conditions can be achieved simply through signal modulation and demodulation, thus avoiding additional cost increases. In addition, the device architecture proposed in this invention is simple and easy to operate. It can directly calculate the phase change within adjacent sampling intervals without prior knowledge of the vibration signal, and correctly defold the demodulation results of different frequency components, significantly improving the accuracy and reliability of the system in large dynamic range strain measurement.

[0043] Furthermore, the phase-sensitive optical time-domain reflectometer of this invention can reconstruct strain signals under high sampling rates through time-series interleaving processing, while the recovery of large strain signals can be performed independently. The two are compatible with each other, enabling the system to simultaneously achieve high-frequency response and large strain range measurement on the same platform.

[0044] Specifically, all optical and electronic devices involved in the embodiments of the present invention can be selected from conventional standard devices in the field of optical measurement and sensing technology, which have strong feasibility and engineering application value.

[0045] Understandable, Figure 1 The architecture shown does not constitute a limitation on the phase-sensitive optical time-domain reflectometer architecture of the present invention, nor on the measurement method.

[0046] Based on the aforementioned phase-sensitive optical time-domain reflectometer, the measurement method of this invention is proposed, referring to... Figure 2 , Figure 2 This is a schematic diagram of the steps of the measurement method provided in the embodiment of the present invention. Figure 2 In the examples, the measurement methods include:

[0047] Step S100: Obtain local light and probe light based on continuous laser;

[0048] Step S200: A radio frequency signal is generated, and the probe light is modulated based on the radio frequency signal to obtain a pulsed laser. The radio frequency signal is composed of two or more frequency division multiplexing sequences, and the number of divisions and the repetition period of each frequency division multiplexing sequence are different.

[0049] Step S300: The pulsed laser is amplified, and the back Rayleigh scattering light is obtained based on the amplified pulsed laser. The back Rayleigh scattering light and the local light are beat frequency matched to obtain the beat frequency signal.

[0050] Step S400: Sample the beat frequency signal to obtain the detection results of different frequency components, and then demodulate the detection results of different frequency components to obtain the demodulation results with phase folding risk.

[0051] Step S500: The demodulation result is processed according to the preset differential defolding algorithm to obtain the defolded phase result;

[0052] Step S600: Perform time-series interleaving processing on the defolded phase results to obtain the reconstruction results. The time-series interleaving processing is used to realize the measurement of high-frequency response, and the reconstruction results are used to map the accurate measurement results of high-frequency response and large strain dynamic strain.

[0053] The phase-sensitive optical time-domain reflectometer of this invention modulates the probe light with radio frequency signals of different division numbers and repetition periods to obtain pulsed laser light. Then, based on the amplified pulsed laser light, backscattered Rayleigh light is acquired, and beat frequency is performed using local light as a reference. The beat frequency signal is sampled to obtain detection results corresponding to different frequency components. The detection results of different frequency components are then demodulated to obtain demodulated results. A differential defolding algorithm is used to process the demodulated results to obtain defolded phase results, thereby solving the large strain phase folding problem and restoring the large strain range. Furthermore, the defolded phase results are time-interleaved to rearrange and combine the previously dispersed but phase-folded defolded phase results according to a precise time sequence, thereby reconstructing a high-sampling-rate, distortion-free strain signal, i.e., obtaining the reconstructed result. Therefore, this invention can solve the problems of limited high-frequency response capability and limited large strain range measurement, achieving accurate measurement of high-frequency response and large strain range dynamic strain.

[0054] It is understandable that radio frequency signals consist of two or more frequency division multiplexing sequences with different frequency division numbers and repetition periods.

[0055] Furthermore, the combination of frequency division multiplexing sequences can be extended to have any number of frequency divisions and the same number of group repetition periods as the frequency division multiplexing sequence.

[0056] Furthermore, the frequency division multiplexing sequence has a preset number of frequency divisions and the group repetition period corresponding to the same frequency component is greater than the time required for the light incident on the optical fiber under test to travel to and from the optical fiber under test to avoid signal confusion.

[0057] The differential defolding algorithm of this invention relies on secondary differential division using different group repetition periods to extract the minimum phase change. Each group of frequency division multiplexed sequences needs its own unique group repetition period, different from other groups. Therefore, the number of groups in the frequency division multiplexed sequence must be consistent with the number of group repetition periods in the frequency division multiplexed sequence. The number of frequency divisions determines how many independent measurement channels are in each group of frequency division multiplexed sequences, thus affecting the total sampling rate after the final signal interleaving. These differences are designed to achieve flexibility in sequence modulation without affecting the differential defolding algorithm.

[0058] Specifically, an optical coupler is used to split the continuous laser into local light and probe light, which are then incident on the polarization coherence receiving module and the optical intensity modulator, respectively. A signal generation circuit generates an radio frequency signal to drive the optical intensity modulator to modulate the probe light, resulting in pulsed laser light, which is then incident on an optical amplifier. The optical amplifier amplifies the power of the incident pulsed laser light and then incident the amplified pulsed laser light onto an optical circulator. The optical circulator guides the pulsed laser light into the fiber under test to generate backscattering Rayleigh scattering within the fiber. The optical circulator is also used to guide the backscattered Rayleigh light into the polarization coherent receiving module, so that the backscattered Rayleigh light and the local light beat in the polarization coherent receiving module to obtain the beat frequency signal; the signal acquisition and processing module samples the beat frequency signal to obtain the detection results corresponding to different frequency components, and then demodulates the detection results of different frequency components to obtain the demodulation results. The demodulation results are processed according to the preset differential defolding algorithm to obtain the defolded phase result. The defolded phase result is then subjected to time-series interleaving to obtain the reconstruction result.

[0059] Reference Figure 3 , Figure 3 This is a detailed flowchart of step S500 provided in one embodiment of the present invention. Figure 3 In the example, step S500 includes:

[0060] Step S510: Perform secondary differential processing based on the demodulation results of the two sets of frequency division multiplexing sequences and their corresponding frequency components to obtain the minimum phase change amount representing the phase change amount within the minimum sampling interval. The minimum phase change amount is used to cancel the confusion caused by phase folding within the same time period.

[0061] Step S520: The demodulation results of each frequency component are processed according to the minimum phase change to obtain the defolded phase result.

[0062] Specifically, by performing time difference on the demodulation result of a certain frequency component in the first set of two frequency division multiplexing sequences, the phase change within the repetition period of the first set of sequences is obtained; by performing time difference on the demodulation result of a certain frequency component in the second set of sequences, the phase change within the repetition period of the second set of sequences is obtained; then, further differential operations are performed on the phase change within the two different periods to obtain the phase change along the fiber within the minimum sampling interval.

[0063] Reference Figure 4 , Figure 4 This is a detailed flowchart of step S510 provided in one embodiment of the present invention, including:

[0064] Step S511: Select one frequency component from each of the two sets of frequency division multiplexing sequences, and perform differential operation on the demodulation results corresponding to the selected frequency components to obtain the first phase change and the second phase change corresponding to the two sets of frequency division multiplexing sequences respectively.

[0065] Step S512: Perform a differential operation based on the first phase change and the second phase change to obtain the minimum phase change.

[0066] It should be noted that the quadratic difference algorithm is the core technical means to solve the phase folding problem under large strain. This algorithm utilizes the characteristics of two frequency division multiplexed sequences with different group frequencies and repetition periods. First, it calculates the phase change within each long period. Then, it performs further differential operations on the phase changes of the two different time intervals to accurately extract the minimum phase change within the minimum sampling interval. This minimum phase change can be used as a reliable calibration benchmark to calculate the number of folds in the long-period phase change. Finally, it achieves defolding processing of the demodulation results of all frequency components, thereby recovering the true large strain range phase and achieving the beneficial effect of expanding the dynamic measurement range of the system.

[0067] Reference Figure 5 , Figure 5 This is a detailed flowchart of step S520 provided in one embodiment of the present invention, including:

[0068] Step S521: Based on the minimum phase change, calculate the number of phase folding cycles that occur in the demodulation results of each frequency component within their respective repetition periods.

[0069] Step S522: Defolding is performed sequentially on the demodulation results of each frequency component according to the number of folding turns to obtain the defolded phase result.

[0070] Specifically, step S522 includes the following steps: multiplying the number of folds by 2π and adding it to the demodulation result corresponding to the number of folds to obtain the defolded phase result, which is used to map the true phase of dynamic strain with large strain range.

[0071] It should be noted that defolding is a key step in solving the problem of large strain range measurement in this invention. Its function is to eliminate phase folding and restore the true phase of the signal. Specifically, this process uses the minimum phase change within the minimum sampling interval obtained by the aforementioned quadratic difference as a reliable benchmark to calculate and correct the phase ambiguity (i.e., the number of folds) caused by large external strain in the demodulation results of each frequency component, which is an integer multiple of 2π. By multiplying the number of folds by 2π and adding it back to the corresponding demodulation result, the system can accurately recover the true, undistorted phase change of the sensing fiber under test within the long period sampling interval, obtaining the defolded phase result. This enables accurate measurement of dynamic strain with large strain range, significantly expanding the dynamic measurement range of the system.

[0072] Specifically, step S600 includes:

[0073] Step S610: The defolded phase results of each frequency component are rearranged according to the time sequence of the measurement to obtain the reconstruction result. The rearrangement process is used to reconstruct the continuous strain signal within the minimum sampling interval to achieve accurate measurement of dynamic strain in high-frequency response.

[0074] Understandably, time-series interleaving is a key step in achieving the high-frequency response of the system in this invention, and it is performed after the core defolding process. Its function is to rearrange and recombine multiple independently recovered phase results of various frequency components that are scattered due to frequency division multiplexing, according to their precise time sequence when injected into the fiber. Through this method, the system synthesizes and reconstructs a continuous, high-density strain signal sequence with a minimum sampling interval from the low sampling rate signal originally limited by the round-trip time of the sensing fiber under test, thus enabling the accurate measurement and reconstruction of the high-frequency dynamic strain response. This effectively overcomes the limitation of fiber length on the system response frequency, significantly improves the system's effective sampling rate, thereby achieving accurate measurement of high-frequency dynamic strain, while avoiding signal distortion caused by direct interleaving in traditional FDM.

[0075] Example 1:

[0076] To illustrate the differential defolding algorithm and the time-series interleaving process in the embodiments of the present invention, specific examples are provided below:

[0077] Reference Figure 6 , Figure 6 This is a schematic diagram of the architecture of a phase-sensitive optical time-domain reflectometer provided in a specific example of the present invention. Figure 6In the example, the phase-sensitive optical time-domain reflectometer includes a continuous laser, an optical coupler, an optical intensity modulation and control unit, a signal generation circuit, an optical amplifier, a sensing fiber under test, a polarization coherent receiving module, and a signal acquisition circuit. A continuous-wave laser generates laser light that is incident on the input of an optical coupler. The optical coupler splits the laser light into two branches: a local path and a probe path. The local path is input to the input of a polarization coherent receiver module, while the probe path is incident on the input of an optical intensity modulation control unit. A signal generation circuit module generates an RF signal that is input to the optical intensity modulation control unit. The optical intensity modulation control unit modulates the continuous-wave laser light into two different frequency-division multiplexed sequences, which are then incident on the input of an optical amplifier. The optical amplifier amplifies the power of the pulsed laser sequence and incident it on an optical circulator. The optical circulator incident the pulsed laser sequence onto the fiber optic link under test. Rayleigh backscattered light generated in the fiber optic link under test is incident on the input of the polarization coherent receiver module through the optical circulator. The polarization coherent receiver module converts the beat frequency result of the local light and the backscattered Rayleigh light into an electrical signal and outputs it to a signal acquisition and processing module. The signal acquisition and processing module samples the backscattered Rayleigh signal and demodulates the detection results of different frequency components. Subsequently, a frequency is selected from each of the two frequency division multiplexing sequences, and its phase change at different time intervals is calculated. This phase change is then further differentiald to obtain the phase change within smaller time intervals. By accumulating the phase changes at each sampling interval, the number of folds in the phase result for each frequency can be calculated, and the foldless phase result can be recovered in reverse. Finally, the recovered phase results from different frequencies are interleaved sequentially to obtain a dynamic strain signal at a high sampling rate, thereby achieving strain measurement with high-frequency response and a large dynamic range.

[0078] Specifically, the continuous laser is a narrow linewidth single-frequency laser with a nominal output frequency of 1550.12nm, an output linewidth of 100Hz, and an output power of 20mW.

[0079] The optical coupler is a polarization-maintaining optical coupler with a nominal beam split of 90:10. 90% of the beam is incident on the light intensity modulation control unit as the probe light, and 10% of the beam is incident on the input of the polarization coherent receiver module as the local oscillator light, which is used to beat the back Rayleigh scattering signal and amplify it.

[0080] The light intensity modulation control unit uses a 1550nm intensity modulator with an extinction ratio greater than 25dB, an insertion loss less than 5dB, and an operating wavelength of 1530-1610nm. Its input is a polarization-maintaining jumper, and its output is a single-mode jumper.

[0081] The signal generation circuit is an arbitrary waveform generator with a nominal sampling rate of 1.25 GSa / s, an analog bandwidth of 500 MHz, and a storage capacity of 64 MSa. It has two independent output channels and one synchronous trigger channel. One independent output channel of the arbitrary waveform generator will generate an orthogonal frequency division multiplexing (OFDM) intensity-coded sequence. The RF pulse sequence used in this embodiment consists of two sets of OFDM sequences. These two sets of OFDM sequences have different division ratios and repetition periods, but their adjacent sampling intervals are the same. The OFDM sequences used in this example are as follows: Figure 7 As shown, it contains two different sets of frequency division multiplexing sequences, which are interleaved in time. The first set of frequency division multiplexing sequences { The frequency reuse number of} is =3, each pulse width is 1μs The frequency sweep ranges for the frequency components are 30-80MHz, 80-130MHz, and 130-180MHz, respectively. The pulse repetition interval is =150μs, sampling interval T=50μs between pulses. Second group of frequency division multiplexing sequences { Frequency reuse number =4, each pulse width is 1μs The frequency sweep ranges are 180-230MHz, 230-280MHz, 280-330MHz, and 330-380MHz, respectively, and the repetition interval of the same frequency pulses is... =200μs, sampling interval T=50μs between pulses. The repetition interval of pulses of the same frequency is greater than the round-trip time of light in the sensing fiber. A complete pulse sequence period... The duration is 600 μs. The RF output amplitude of the arbitrary waveform generator is 250 mV.

[0082] The optical amplifier is a pulsed fiber erbium-doped fiber amplifier with a nominal operating wavelength of 1550.12nm, a maximum input peak optical power of 1dBm, an output peak optical power of 1000mW, and a noise figure of 4.5dB.

[0083] The optical circulator is a single-mode optical circulator with a nominal insertion loss of less than 1.0 dB, an isolation of more than 60 dB, and a return loss of more than 50 dB. Port 1 of the optical circulator is connected to an optical amplifier, which guides the pulsed laser sequence through port 2 into the optical fiber of the sensor under test.

[0084] The sensing fiber under test is a G.652.D single-mode fiber with a nominal sensing distance of about 50.0 km and a transmission loss of less than 0.2 dB / km@1550 nm. The pulsed laser sequence excites Rayleigh scattering along the path in the single-mode fiber, and part of the scattered light propagates in the opposite direction along the fiber to form a Rayleigh backscattering signal.

[0085] The optical bridge and polarization diversity module are integrated into the polarization coherent receiver module. It employs an optical mixer with an integrated polarization beamsplitter and a 90° optical bridge, with a nominal operating wavelength of 1520~1625nm, an insertion loss of 7.0dB for the signal path, 10.0dB for the local path, and a phase angle of 85°~95° between the in-phase component (I path) and the quadrature component (Q path). The optical mixer separates the local oscillator light from the signal light, performing optical interference with phase differences of 0° and 90° respectively. Simultaneously, it performs orthogonal polarization beam splitting on the input light, ensuring that signals with different polarization states can interfere and superimpose with the local oscillator light. The generated I and Q path interference signals are output to the back-end balanced photodetector, achieving efficient coherent detection and polarization diversity.

[0086] The photodetector is integrated into the polarization coherent receiver module. A balanced photodetector is selected, with a nominal operating wavelength of 1200~1700nm, a 3dB bandwidth of DC-400MHz, a detector responsivity of 0.85A / W@1300nm, and a transimpedance gain of 10kV / A. The balanced photodetector converts the coherently superimposed interference light field into an electrical signal. Differential amplification effectively suppresses local oscillator DC noise and common-mode noise, while enhancing the beat frequency signal, achieving high-sensitivity coherent detection.

[0087] The signal acquisition circuit consists of a high-speed digital acquisition card and a computer. The high-speed acquisition card is programmable, with a nominal analog bandwidth of 400MHz, a sampling rate of 1GSa / s, and a resolution of 16 bits. The acquisition card is set to single-record acquisition mode and runs continuously throughout the test, with a cumulative acquisition time of 0.6 seconds. The computer, acting as the host computer, uses Matlab software to complete subsequent data processing. The acquisition card is also set to single-record acquisition mode and runs continuously throughout the test, with a cumulative acquisition time of 20 milliseconds. The computer performs subsequent data processing, including signal pulse compression and demodulation, defolding operations at different frequencies, and interleaving operations at different frequencies.

[0088] The specific process of the differential defolding algorithm and time-series interleaving processing is as follows: First, the detection results of different frequency components are pulse-compressed, and then subjected to temporal and spatial differential operations to obtain { }{ The detection results of the sequence at different locations and times in the optical fiber, where The detection results are recorded as , The detection results are recorded as , The detection results are recorded as ; The detection results are recorded as , The detection results are recorded as , The detection results are recorded as , The detection results are recorded as Detection results at the same frequency at different times can be differentially eliminated to remove the initial phase offset; therefore, { The phase change within a 3T interval can be obtained by differentiating the phase results in the previous step.

[0089]

[0090]

[0091]

[0092]

[0093] Similarly, { The phase change within a 4T interval can be obtained by differentiating the phase results in the previous step.

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] By taking the difference between each pair of phase changes at different sampling intervals, the adjacent sampling intervals can be obtained. The internal phase change, i.e.

[0100]

[0101]

[0102]

[0103]

[0104] Since the same time interval exists in both sampling intervals, the folding that occurs within that same time interval will cancel each other out, requiring only a change in the sampling interval. No phase folding occurs within the time interval, so the phase obtained is the true phase. The number of folds can be calculated by accumulating the phase changes over the time interval and comparing them with the original phase; for the number of folds at time 7T:

[0105]

[0106] The Round[·] operator performs integer division. The foldless phase can be recovered by reversing the number of folds and adding it back.

[0107]

[0108] Finally, all the foldless phases of different frequencies are interleaved according to the order in which they are driven into the optical fiber to obtain the final result. This means completing the measurement of high-frequency, large dynamic range strain signals:

[0109]

[0110] Example 2:

[0111] To illustrate the working effect of the embodiments of the present invention, specific examples are provided below:

[0112] Reference Figure 8 , Figure 8 This is a schematic diagram illustrating the variation of the phase standard deviation obtained after demodulation of all frequency pulses as a function of a 10km sensing fiber optic distance, provided in a specific example of the present invention. Figure 8 The examples demonstrate the effective detection capability of the present invention within a 10km range.

[0113] To further verify the system's ability to sense external strain, refer to Figure 9 , Figure 9 This is a time-domain waveform diagram after direct interleaving and compensation, provided as a specific example of the present invention. Figure 9 The time-domain waveforms after applying a 2kHz single-frequency sinusoidal signal of 65nε to the end of the sensing fiber and then directly interleaving and compensating are shown. The time-domain waveforms obtained by direct interleaving using the traditional unwrap method have large fluctuations. The embodiments of the present invention can correctly defold the phase results of different frequencies and restore good waveforms.

[0114] Figure 10 The power spectral density diagram after direct interleaving and compensation is provided as a specific example of the present invention. The power spectral density obtained by direct interleaving after using the traditional unwrap method has a large noise floor, making it difficult to distinguish the frequency of the applied vibration signal. It can be seen that the embodiment of the present invention can significantly suppress the noise floor rise of waveform distortion and reconstruct the high-frequency dynamic strain signal stably and accurately, verifying its applicability and effectiveness in large strain and broadband sensing scenarios.

[0115] Furthermore, one embodiment of the present invention provides a readable storage medium storing computer-executable instructions that are executed by a processor or controller, for example, by a processor in the above-described device or apparatus embodiments, such that the processor performs the measurement method described in the above-described embodiments.

[0116] It will be understood by those skilled in the art that all or some of the steps and systems in the methods disclosed above can be implemented as software, firmware, hardware, and suitable combinations thereof. Some or all of the physical components can be implemented as software executed by a processor, such as a central processing unit, digital signal processor, or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible to a computer. Furthermore, as is known to those skilled in the art, communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

[0117] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A phase sensitive optical time domain reflectometer, characterized in that, The method comprises the following steps: a continuous laser, an optical coupler, an optical intensity modulator, a signal generation circuit, an optical amplifier, an optical circulator, a to-be-measured sensing optical fiber, a polarization coherent receiving module, and a signal acquisition and processing module; the continuous laser is configured to generate continuous laser and incident to the optical coupler; the optical coupler is configured to divide the continuous laser into local light and probe light, and respectively incident to the polarization coherent receiving module and the optical intensity modulator; the signal generation circuit is configured to generate a radio frequency signal to drive the optical intensity modulator to modulate the probe light to obtain pulsed laser, and the pulsed laser is incident to the optical amplifier, wherein the radio frequency signal is composed of two or more groups of frequency division multiplexing sequences, and the frequency division number and group repetition period of each group of frequency division multiplexing sequences are different; the optical amplifier is configured to perform power amplification processing on the incident pulsed laser, and the pulsed laser after power amplification processing is incident to the optical circulator, wherein the optical circulator is used to guide the pulsed laser to be incident to the to-be-measured sensing optical fiber to generate backscattering Rayleigh scattering light in the to-be-measured sensing optical fiber, and the optical circulator is also used to guide the backscattering Rayleigh scattering light to be incident to the polarization coherent receiving module to perform beat frequency on the backscattering Rayleigh scattering light and the local light in the polarization coherent receiving module to obtain beat frequency signals; the signal acquisition and processing module is configured to sample and process the beat frequency signals to obtain detection results corresponding to different frequency components, demodulate the detection results of different frequency components respectively to obtain demodulation results of the phase folding risk, perform second difference processing on the demodulation results corresponding to two groups of frequency division multiplexing sequences and their frequency components to obtain minimum phase change amount representing the phase change amount in the minimum sampling interval, the minimum phase change amount is used to offset the confusion caused by phase folding in the same time period, and the demodulation results of each frequency component are processed according to the minimum phase change amount to obtain unfolded phase results, and the unfolded phase results are subjected to time interleaving processing to obtain reconstruction results.

2. The phase sensitive optical time domain reflectometer of claim 1, wherein, The signal acquisition and processing module comprises a computer, and the difference unfolding algorithm and the time interleaving processing are completed by the computer as post-processing steps.

3. A method of measurement applied to a phase sensitive optical time domain reflectometer, the phase sensitive optical time domain reflectometer comprising: The method comprises the following steps: based on continuous laser to obtain local light and probe light; generate a radio frequency signal, and modulate the probe light based on the radio frequency signal to obtain pulsed laser, wherein the radio frequency signal is composed of two or more groups of frequency division multiplexing sequences, and the frequency division number and group repetition period of each group of frequency division multiplexing sequences are different; perform power amplification processing on the pulsed laser, obtain backscattering Rayleigh scattering light based on the pulsed laser after amplification processing, and perform beat frequency on the backscattering Rayleigh scattering light and the local light to obtain beat frequency signals; The beat signal is sampled to obtain detection results corresponding to different frequency components, and the detection results of different frequency components are demodulated respectively to obtain demodulation results with a risk of phase folding; According to the demodulation results corresponding to the two groups of frequency division multiplexing sequences and their frequency components, secondary difference processing is performed to obtain a minimum phase change amount representing a phase change amount within a minimum sampling interval, and the minimum phase change amount is used to offset confusion caused by phase folding within the same time period; According to the minimum phase change amount, the demodulation results of each frequency component are processed to obtain unfolded phase results; The unfolded phase results are subjected to time sequence interleaving processing to obtain reconstruction results, wherein the time sequence interleaving processing is used to realize measurement of high-frequency response, and the reconstruction results are used to map measurement results of high-frequency response and large strain range dynamic strain.

4. The measurement method according to claim 3, characterized in that, The secondary difference processing of the demodulation results corresponding to the two groups of frequency division multiplexing sequences and their frequency components to obtain a minimum phase change amount representing a phase change amount within a minimum sampling interval comprises: A frequency component is selected from each of the two groups of frequency division multiplexing sequences, and difference operation is performed on the demodulation results corresponding to the selected frequency components to obtain a first phase change amount and a second phase change amount corresponding to the two groups of frequency division multiplexing sequences respectively; Difference operation is performed on the first phase change amount and the second phase change amount to obtain the minimum phase change amount.

5. The measurement method according to claim 3, characterized in that, The processing of the demodulation results of each frequency component according to the minimum phase change amount to obtain the unfolded phase results comprises: Based on the minimum phase change amount, the number of folding cycles of the demodulation results corresponding to each frequency component within their respective repetition periods is calculated; The demodulation results of each frequency component are sequentially unfolded according to the number of folding cycles to obtain the unfolded phase results.

6. The measurement method according to claim 5, characterized in that, The sequential unfolding processing of the demodulation results of each frequency component according to the number of folding cycles comprises: The number of folding cycles is multiplied by 2π and added to the demodulation results corresponding to the number of folding cycles to obtain the unfolded phase results, which are used to map the true phase of large strain range dynamic strain.

7. The measurement method according to claim 3, characterized by, The time sequence interleaving processing of the unfolded phase results to obtain reconstruction results comprises: The unfolded phase results of each frequency component are rearranged according to the time sequence relationship of measurement to obtain the reconstruction results, and the rearrangement processing is used to reconstruct continuous strain signals within a minimum sampling interval to realize measurement of high-frequency response dynamic strain.

8. The measurement method according to claim 3, characterized by, The frequency division multiplexing sequence has a preset number of frequency division numbers, and the group repetition period corresponding to the same frequency component is greater than the time required for light incident on the to-be-measured sensing optical fiber to return to the to-be-measured sensing optical fiber to avoid signal confusion.

9. A readable storage medium, characterized by, The readable storage medium stores computer executable instructions for causing a computer to execute the measurement method of any one of claims 3 to 8.

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