Distributed strain measurement device, measurement method and detection method

Abstract

The invention provides a distributed strain measurement device, a measurement method and a detection method, and the measurement device comprises a laser, an optical switch, a light splitting device, a photoelectric detector, a signal processing unit, a fiber grating and a signal modulation unit. The laser is used for emitting continuous optical signals; the optical switch is used for modulating the continuous optical signal into a pulse optical signal; the fiber bragg grating is used for reflecting the pulse light signal to obtain a reflected light signal; the light splitting device is used for guiding the pulsed light to the fiber bragg grating and receiving a reflected light signal; the photoelectric detector is used for detecting time-varying information of the light intensity of the reflected light signal and converting the information into a first electric signal; the signal processing unit is used for generating a modulation signal to modulate the continuous light wavelength emitted by the laser; the signal processing unit is used for receiving the first electric signal and processing the electric signal according to the modulation signal to output a strain result. The measuring device provided by the invention is not influenced by the spectral width of the light source, the number of the cascading gratings is large, and the measuring space range is large.

Description

Technical Field

[0001] This disclosure generally relates to the field of strain measurement technology, and specifically to a distributed strain measurement device, measurement method, and detection method. Background Technology

[0002] With the rapid development of fiber optic sensing and fiber optic communication technologies, fiber Bragg gratings have become highly promising passive fiber optic devices and are being used more and more widely. Distributed fiber optic sensing technology is a technology that uses optical fibers to sense and monitor environmental parameters. By densely arranging sensing units in the optical fibers, and with the support of signal processing, it is possible to monitor parameter changes at multiple locations in the environment in real time, such as temperature, pressure, and vibration.

[0003] In the field of distributed fiber Bragg grating sensing, multiple fiber Bragg gratings are typically cascaded together, and distributed measurement is achieved by demodulating the change in the center wavelength of each fiber Bragg grating. On the one hand, this application method requires that the wavelengths of each cascaded grating do not overlap, but the limited spectral width of the light source restricts the number of cascaded gratings. On the other hand, in most fiber Bragg grating sensing applications, the measured physical quantity is the overall average of its variation over the entire grating region, which cannot be applied to measurements with high spatial resolution requirements, such as crack detection. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a distributed strain measurement device, measurement method and detection method to solve the above problems.

[0005] The first aspect of this application provides a distributed strain measurement device, comprising a laser, an optical switch, a beam splitter, a photodetector, and a signal processing unit connected in sequence. The beam splitter is further connected to a fiber optic grating, and the signal processing unit and the laser are connected through a signal modulation unit. The laser is used to emit continuous optical signals; The optical switch is used to modulate the continuous optical signal into a pulsed optical signal; The fiber grating is used to reflect the pulsed light signal to obtain a reflected light signal, and the reflected light signal is used to reflect strain information; The beam splitter is used to guide the pulsed light to the fiber optic grating and to receive the reflected light signal; The photodetector is used to detect the change in the intensity of the reflected light signal over time and convert it into a first electrical signal; The signal modulation unit is used to generate a modulation signal to modulate the continuous light wavelength emitted by the laser; The signal processing unit is used to receive the first electrical signal and process the electrical signal according to the modulation signal to output a strain result, the strain result including strain location and strain magnitude.

[0006] According to the technical solution provided in the embodiments of this application, the laser is a wavelength-tunable laser; the optical switch is a high-speed optical switch with a response time on the order of picoseconds.

[0007] According to the technical solution provided in the embodiments of this application, the beam splitting device is a beam splitting prism or a circulator; the fiber grating is a long weak fiber grating or a cascaded array of weak fiber gratings.

[0008] According to the technical solution provided in the embodiments of this application, the photodetector is a balanced detector.

[0009] According to the technical solution provided in the embodiments of this application, the signal processing unit adopts a lock-in amplification algorithm, and combines the modulation signal and the light intensity change at the strain position to determine the relative position of the center wavelength of the laser and the center wavelength of the fiber optic grating, so as to expand the strain measurement range.

[0010] According to the technical solution provided in the embodiments of this application, a display unit is also included. The display unit is connected to the signal processing unit and is used to receive the strain result and display it.

[0011] A second aspect of this application provides a distributed strain measurement method, based on the distributed strain measurement device described above, the measurement method comprising: S1: Turn on the laser to control the laser to emit a continuous optical signal; the initial spectrum of the continuous optical signal has a wavelength region that overlaps with the initial spectrum of the fiber grating; S2: Turn on the optical switch to modulate the continuous optical signal into the pulsed optical signal and transmit it to the beam splitter; S3: Adjust the beam splitter to guide the pulsed light signal to the fiber optic grating, and transmit it to the photodetector after receiving the reflected light signal; S4: The photodetector is activated to detect the reflected light signal, and the converted first electrical signal is transmitted to the signal processing module so that the signal processing unit generates a strain result based on the first electrical signal and the modulation signal.

[0012] A third aspect of this application provides a distributed strain detection method, based on the distributed strain measurement device described above, the detection method comprising: S100: Receive the first electrical signal and acquire the modulation signal; S200: Based on the information of light intensity changing with time in the first electrical signal, determine the correspondence between time parameters and physical positions on the fiber optic grating, and then identify the strain position; S300: Combine the modulation signal to process the light intensity change information corresponding to the strain position in the first electrical signal, and associate the magnitude of the light intensity change with the magnitude of the strain. S400: Integrate the strain location and strain magnitude to obtain the strain result, and output it externally.

[0013] According to the technical solution provided in the embodiments of this application, step S200 includes: The time information of the change in light intensity in the first electrical signal is analyzed to extract the first duration and obtain the first velocity; the first duration is the duration corresponding to the change in light intensity, and the first velocity is the transmission speed of the optical signal in the fiber optic grating. The strain position is obtained based on the product of the first velocity and the first duration; wherein, the starting time point of the light intensity change corresponds to the starting position of the strain, and the ending time point of the light intensity change corresponds to the ending position of the strain.

[0014] According to the technical solution provided in the embodiments of this application, step S300 includes: The modulation signal is invoked to determine the continuous variation pattern and period of the laser wavelength; The light intensity change information at the strain position is synchronously demodulated with the modulation signal using a lock-in amplification method to obtain the amplitude information of the light intensity change. The amplitude information is used to call a preset database to obtain the strain magnitude; the preset database includes multiple pre-stored amplitude values ​​and strain values ​​corresponding to each amplitude value.

[0015] Compared with existing technologies, the advantages of this application are as follows: The distributed strain measurement device of this application emits a continuous optical signal from a laser, which is modulated into pulsed light by an optical switch. The pulsed light is then guided to a fiber optic grating by a beam splitter. The reflected light is converted into an electrical signal containing information on the time-varying intensity of the light by a photodetector. The signal processing unit then combines the signal with the modulation signal to output the strain result. This structure does not rely on the strict differentiation of the wavelengths of each grating, breaking through the limitation of the spectral width of the light source on the number of cascaded gratings, and can increase the number of cascaded gratings to expand the measurement range. At the same time, the information on the time-varying intensity of the light can accurately locate the strain position, realizing local strain measurement, and solving the problem that existing technologies can only obtain the overall average strain and cannot meet the requirements of high spatial resolution. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1This is a schematic diagram of the distributed strain measurement device provided in Example 1; Figure 2 A flowchart illustrating the steps of the distributed strain measurement method provided in Example 2; Figure 3 Here is a flowchart of the steps of the distributed strain detection method provided in Example 3; Figure 4 The impulse response diagram is shown without strain. Figure 5 The pulse response diagram after applying strain; Figure 6 The graph shows the relationship between strain magnitude (wavelength) and pulse intensity. Figure 7 This diagram illustrates the relative position of the laser's center wavelength and the fiber grating's center wavelength for a lock-in amplification algorithm.

[0017] Reference numerals: 10, laser; 20, optical switch; 30, beam splitter; 40, fiber optic grating; 50, photodetector; 60, signal modulation unit; 70, signal processing unit; 80, display unit. Detailed Implementation

[0018] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] Example 1 Please refer to Figure 1 This embodiment provides a distributed strain measurement device, including a laser 10, an optical switch 20, a beam splitter 30, a photodetector 50 and a signal processing unit 70 connected in sequence. The beam splitter 30 is also connected to a fiber optic grating 40, and the signal processing unit 70 and the laser 10 are connected through a signal modulation unit 60. The laser 10 is used to emit continuous optical signals; The optical switch 20 is used to modulate the continuous optical signal into a pulsed optical signal; The fiber grating 40 is used to reflect the pulsed light signal to obtain a reflected light signal, and the reflected light signal is used to reflect strain information; The beam splitter 30 is used to guide the pulsed light to the fiber optic grating 40 and to receive the reflected light signal; The photodetector 50 is used to detect the information of the change in the intensity of the reflected light signal over time and convert it into a first electrical signal; The signal modulation unit 60 is used to generate a modulation signal to modulate the continuous light wavelength emitted by the laser 10; The signal processing unit 70 is used to receive the first electrical signal and process the electrical signal according to the modulation signal to output a strain result, the strain result including strain location and strain magnitude.

[0021] Specifically, laser 10, as the core light source, continuously emits a stable, continuous optical signal, which provides the basic optical carrier for subsequent pulse modulation and strain detection. Optical switch 20 is electrically connected to laser 10, and its function is to modulate the continuous optical signal emitted by laser 10 into a pulsed optical signal. By converting continuous light into pulses, the transmission time of the optical signal in fiber Bragg grating 40 corresponds to its physical position, providing a time-dimensional reference for subsequently locating the specific location of strain, thus solving the problem of accurate local strain positioning in traditional technologies. Beam splitter 30 is electrically connected to optical switch 20, and it plays a bidirectional guiding role in the optical path: on the one hand, it efficiently guides the pulsed optical signal output by optical switch 20 to fiber Bragg grating 40, ensuring that the optical signal can accurately act on the sensing unit used for sensing; on the other hand, when fiber Bragg grating 40 receives external strain, it reflects a reflected optical signal carrying strain information. Beam splitter 30 receives this reflected optical signal and transmits it to the photodetector, achieving efficient bidirectional transmission of the optical signal. The fiber optic grating 40, as a sensing unit that directly senses strain, has a grating period that changes with external strain, leading to changes in the intensity of its reflected light signal. Therefore, the reflected light signal contains rich strain information and is the core information carrier for strain detection. The photodetector 50, electrically connected to the beam splitter 30, is responsible for detecting the reflected light signal, focusing on capturing the information about the change in light intensity over time, and converting this change into a first electrical signal that is easy to process. This "change in light intensity over time" includes both the time difference caused by different strain locations and the amplitude difference in light intensity caused by different strain magnitudes, providing raw electrical signal data for subsequent signal processing.

[0022] The signal modulation unit 60 is electrically connected to the laser 10. Its function is to generate a specific modulation signal, which acts on the laser 10 to dynamically modulate the wavelength of the continuous light emitted by the laser 10. Through wavelength modulation, the output wavelength of the laser can dynamically correspond to the reflection characteristics of the fiber grating 40. Even when multiple gratings are cascaded, strain signals at different locations can be distinguished by dynamically adjusting the wavelength. This overcomes the strict limitation of non-overlapping grating wavelengths in traditional technology, thereby supporting a larger number of cascaded gratings and expanding the measurement spatial range.

[0023] The signal processing unit 70 is electrically connected to the signal modulation unit 60 and the photodetector 50, respectively. It receives the first electrical signal output by the photodetector 50 and combines it with the modulation signal generated by the signal modulation unit 70 to perform comprehensive processing on the first electrical signal. By analyzing the change in light intensity over time in the first electrical signal and combining it with the wavelength change information reflected by the modulation signal, it finally outputs a strain result containing the strain location and strain magnitude. The strain location is determined based on the correspondence between the transmission time and velocity of the pulsed light, while the strain magnitude is determined based on the correlation analysis between the amplitude of light intensity change and the strain, thus achieving accurate measurement of distributed strain.

[0024] Furthermore, the laser 10 is a wavelength-tunable laser; the optical switch 20 is a high-speed optical switch with a response time on the order of picoseconds.

[0025] Specifically, compared to fixed-wavelength lasers, wavelength-tunable lasers can flexibly adjust the wavelength of the output continuous optical signal within a certain range. This characteristic allows for a more flexible dynamic matching with the reflection characteristics of fiber gratings, avoiding signal confusion caused by wavelength overlap when the number of cascaded gratings increases. The picosecond-level response time indicates that the optical switch 20 can modulate the continuous optical signal into an extremely narrow pulse signal. The shorter pulse width results in higher temporal differentiation of the reflected light signals at different positions during transmission within the fiber grating 40. Through this extremely narrow pulse modulation, the correspondence between the transmission time and physical position of the optical signal within the fiber grating 40 becomes more precise, enabling more accurate location of strain. This solves the problem of high spatial resolution measurement that is difficult to achieve in traditional technologies due to wider pulse widths, making it particularly suitable for scenarios with extremely high requirements for local strain localization, such as crack detection.

[0026] Furthermore, the beam splitting device 30 is a beam splitting prism or a circulator; the fiber grating 40 is a long weak fiber grating or a cascaded array of weak fiber gratings 40.

[0027] Specifically, the beam splitter separates the optical path through the principles of light refraction and reflection, while the circulator achieves directional transmission of the optical signal based on polarization characteristics. Although their principles differ, both ensure that the pulsed optical signal enters the fiber grating 40 with low loss, while accurately guiding the reflected optical signal carrying strain information into the photodetector 50, avoiding signal distortion caused by optical path crosstalk. Both beam splitting devices 30 ensure the accuracy of strain measurement, especially in complex optical paths with multiple cascaded gratings, effectively reducing signal interference and further supporting the expansion of the measurement range.

[0028] Specifically, weak fiber gratings have low reflectivity. This characteristic ensures that when multiple gratings are cascaded, the reflected light from the preceding grating does not excessively attenuate the incident light from the following grating, avoiding the limitation on the number of cascades caused by signal attenuation in traditional strong-reflection grating cascades. Long weak fiber gratings can achieve distributed strain measurement over long fiber regions, and their continuously distributed grating structure can capture subtle strain changes along the fiber length. Meanwhile, cascaded weak fiber grating arrays, through the orderly arrangement of multiple independent weak gratings, can precisely target specific monitoring points. Both types can meet the measurement requirements for high spatial resolution.

[0029] Furthermore, the photodetector 50 is a balanced detector.

[0030] Specifically, in this embodiment, the photodetector 50 uses a balanced detector, which can effectively suppress common-mode noise, such as signal disturbances caused by light source intensity fluctuations and ambient light interference.

[0031] Furthermore, it also includes a display unit 80, which is connected to the signal processing unit 70 and is used to receive and display the strain results.

[0032] Specifically, the display unit 80, as a human-computer interaction device, can present the strain position and strain magnitude output by the signal processing unit 70 in an intuitive form, such as numerical values, icons, or images. In distributed strain measurement scenarios, especially when there are many cascaded gratings and a large measurement space, staff can monitor the strain status at each location in real time through the display unit 80 without relying on complex backend data analysis processes.

[0033] Example 2 Please refer to Figure 2 This embodiment provides a distributed strain measurement method based on the distributed strain measurement device described in Embodiment 1. The measurement method includes: S1: Turn on the laser 10 to control the laser 10 to emit a continuous optical signal; the initial spectrum of the continuous optical signal has a wavelength overlap region with the initial spectrum of the fiber grating 40; S2: Turn on the optical switch 20 to modulate the continuous optical signal into the pulsed optical signal and transmit it to the beam splitter 30; S3: Adjust the beam splitter 30 to guide the pulsed light signal to the fiber optic grating 40, and transmit it to the photodetector 50 after receiving the reflected light signal; S4: The photodetector 50 is activated to detect the reflected light signal, and the converted first electrical signal is transmitted to the signal processing module so that the signal processing unit 70 generates a strain result based on the first electrical signal and the modulation signal.

[0034] Specifically, the measurement method provided in this embodiment is actually a method for personnel to operate the measuring device, used to illustrate how to perform distributed strain measurement through the measuring device, wherein the detailed working process of each component is the same as in Embodiment 1. In step S4, the operator visually obtains the strain location and strain magnitude through the display unit 80.

[0035] Example 3 Please refer to Figure 3 This embodiment provides a distributed strain detection method based on the distributed strain measurement device described in Embodiment 1. The detection method includes: S100: Receive the first electrical signal and acquire the modulation signal.

[0036] S200: Based on the information of light intensity changing with time in the first electrical signal, determine the correspondence between the time parameter and the physical position on the fiber optic grating 40, and then identify the strain position; S300: Combine the modulation signal to process the light intensity change information corresponding to the strain position in the first electrical signal, and associate the magnitude of the light intensity change with the magnitude of the strain. S400: Integrate the strain location and strain magnitude to obtain the strain result, and output it externally.

[0037] Specifically, the detection method provided in this embodiment is the process of signal processing by the signal processing unit 70, so the execution subject of steps S100-S400 is the signal processing unit 70.

[0038] Specifically, in step S100, a first electrical signal transmitted by the photodetector 50 is first received, which contains information about the change in intensity of reflected light over time; simultaneously, a modulation signal generated by the signal modulation unit 60 is acquired. In step S200, based on the information about the change in light intensity over time in the first electrical signal, a correspondence between the time parameter and the physical position on the fiber optic grating 40 is established; since the propagation speed of pulsed light in the optical fiber is known, the specific location of strain occurrence can be accurately located by analyzing the time differences of light intensity changes, i.e., the strain position is obtained. In step S300, the light intensity change information corresponding to the strain position is processed in conjunction with the modulation signal; by analyzing the correlation between the light intensity change amplitude and the wavelength modulation law of the laser 10, the magnitude of the light intensity change is converted into the corresponding strain value, i.e., the strain magnitude is obtained. In step S400, the strain position and strain magnitude are integrated to form a complete strain result and output to the display unit 80.

[0039] Further, step S200 includes: S201: Analyze the time information of the change in light intensity in the first electrical signal, extract the first duration and obtain the first speed; the first duration is the duration corresponding to the change in light intensity, and the first speed is the transmission speed of the light signal in the fiber optic grating 40. S202: The strain position is obtained based on the product of the first velocity and the first duration; wherein, the starting time point of the light intensity change corresponds to the starting position of the strain, and the ending time point of the light intensity change corresponds to the ending position of the strain.

[0040] Specifically, in step S200, the time information of the change in light intensity in the first electrical signal is first analyzed, focusing on extracting the first duration corresponding to the change in light intensity, that is, the time interval from the start of the change in light intensity to the end of the change. Simultaneously, the first velocity is obtained, that is, the transmission speed of the light signal in the fiber optic grating, which is a pre-defined known value. Next, by calculating the product of the first velocity and the first duration, the physical location of the strain on the fiber optic grating 40 is determined. This embodiment, through the conversion logic between time and position, utilizes the time delay characteristic of pulsed light transmission in optical fiber, overcoming the limitation of relying on grating wavelength to distinguish position in traditional technologies. This allows for precise location of the specific range of local strain even in long, weak fiber optic gratings or multi-cascaded weak grating arrays, significantly improving spatial resolution, and is particularly suitable for detecting local strains such as cracks.

[0041] Further, step S300 includes: S301: Call the modulation signal to determine the continuous variation law and variation period of the wavelength of laser 10; S302: Using the lock-in amplification method, the light intensity change information at the strain position is synchronously demodulated with the modulation signal to obtain the amplitude information of the light intensity change; S303: Based on the amplitude information, a preset database is invoked to obtain the strain magnitude; the preset database includes multiple pre-stored amplitude values ​​and strain values ​​corresponding to each amplitude value.

[0042] Specifically, in step S300, the modulation signal generated by the signal modulation unit 60 is first invoked to analyze the continuous variation law and variation period of the laser 10 wavelength, clarifying the dynamic adjustment characteristics of the laser 10 output wavelength over time. Then, using the modulation signal as a reference, the light intensity change information is synchronously demodulated with the modulation signal to filter out noise interference unrelated to the modulation law and extract the light intensity change amplitude information reflecting the effect of strain. This process fully utilizes the lock-in amplification algorithm's ability to enhance weak signals, accurately capturing subtle changes in light intensity even in multi-grating cascade scenarios where optical signal attenuation is significant. Finally, the signal processing unit 70 invokes a preset database based on the obtained amplitude information; this database pre-stores a large number of correspondences between amplitude values ​​and strain values ​​obtained through calibration experiments, i.e., the amplitude data of reflected light intensity changes corresponding to different strain magnitudes acting on fiber optic gratings. By matching the amplitude information with the pre-stored data in the database, the strain magnitude corresponding to the current light intensity change can be determined, achieving accurate conversion from optical signal characteristics to physical quantities.

[0043] Example 4 To facilitate understanding of the technical solution of the present invention, this embodiment is illustrated through specific examples.

[0044] In this embodiment, the laser 10 is a tunable laser with a center wavelength of 1550nm and a tuning range of 0.05nm; the pulsed light generated by the optical switch 20 has a full width at half maximum (FWHM) of 2.355ps; the beam splitter 30 is a circulator with an operating wavelength of 1525nm~1570nm; the fiber grating 40 is a long, weak fiber grating with a center wavelength of 1550nm and a length of 15cm; the functions of the signal modulation unit 60 and the signal processing unit 70 are implemented by a lock-in amplifier; and the photodetector 50 is a balanced detector.

[0045] Specific process: The continuous optical signal emitted by the tunable laser is modulated into a pulsed optical signal by optical switch 20. The pulsed optical signal is then split by a circulator and enters a long, weak fiber grating. After being reflected by the long, weak fiber grating, the pulsed optical signal carries strain information and passes through the circulator again as a reflected optical signal. A balanced detector then detects the change in light intensity over time. When the long, weak fiber grating experiences zero external strain, the reflected pulse response is as follows: Figure 4 As shown, the light intensity changes slowly within the grating range; when a strain of 1 cm in length and 400 με is applied at a position 1 cm from the start of the long, weak fiber grating, the reflected pulse response is as follows. Figure 5As shown, the impulse response exhibits an energy dip in a certain region, approximately at 100 ps. Time calculations indicate this corresponds to the location where strain was applied, at 1 cm. This means that applying localized strain to a long, weak fiber grating results in an energy change that matches the shape of the grating's reflection spectrum. Figure 6 As shown, the signal modulation unit 60 generates a modulation signal to modulate the tunable laser, causing its wavelength to change continuously. At the same time, the signal processing unit 70 uses the modulation signal to process the light intensity information, determines the relative position of the center wavelength of the long weak fiber grating and the center wavelength of the tunable laser, obtains the strain magnitude by searching a preset database, and finally displays the strain position and strain magnitude on the display unit 80.

[0046] Furthermore, the signal processing unit 70 employs a lock-in amplification algorithm to determine the relative position of the center wavelength of the laser 10 and the center wavelength of the fiber optic grating 40 by combining the modulation signal and the light intensity change at the strain position, thereby expanding the strain measurement range.

[0047] Specifically, the lock-in amplification algorithm, based on the principle of synchronous detection, uses the modulation signal of the signal modulation unit 60 as a reference to extract weak light intensity changes related to the modulation frequency from the noise. By capturing the light intensity change pattern synchronized with the modulation signal, this algorithm can accurately determine the relative position of the wavelength. Even with significant wavelength shifts and weak reflected light, it can still extract effective information, transforming strain signals that were originally outside the detection range into analyzable data, thus overcoming the range limitations imposed by wavelength shift in traditional measurements. (Reference) Figure 7 , Figure 7 The horizontal axis in the upper figure represents the wavelength, the vertical axis in the lower figure represents the intensity of the pulsed light signal, and the vertical axis in the lower figure represents the lock-in amplification modulation intensity value. When the lock-in amplification modulation value is positive, the center wavelength of the laser 10 is located to the left of the center wavelength of the fiber optic grating 40. When the lock-in amplification modulation value is negative, the center wavelength of the laser 10 is located to the right of the center wavelength of the fiber optic grating 40. Figure 7 The diagram shows that different strains cause changes in the wavelength of the grating reflection at the strain location, and Figure 6 This shows the energy change of the pulse at a certain location after applying different strains (i.e., changes in the grating wavelength). Figure 6 The relationship between intensity and wavelength is not one-to-one; one intensity corresponds to two wavelengths, i.e., strain. Therefore, a different approach is adopted. Figure 7 The positive or negative demodulation value of the lock-in amplification algorithm shown indicates the relative positional relationship between the fiber grating 40 and the center wavelength of the laser 10, thereby expanding the measurement range.

[0048] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A distributed strain measurement device, characterized in that, The system includes a laser (10), an optical switch (20), a beam splitter (30), a photodetector (50), and a signal processing unit (70) connected in sequence. The beam splitter (30) is also connected to a fiber optic grating (40). The signal processing unit (70) and the laser (10) are also connected through a signal modulation unit (60). The laser (10) is used to emit continuous light signals; The optical switch (20) is used to modulate the continuous optical signal into a pulsed optical signal; The fiber grating (40) is used to reflect the pulsed light signal to obtain a reflected light signal, which is used to reflect strain information; The beam splitter (30) is used to guide the pulsed light to the fiber optic grating (40) and to receive the reflected light signal; The photodetector (50) is used to detect the information of the change in the intensity of the reflected light signal over time and convert it into a first electrical signal; The signal modulation unit (60) is used to generate a modulation signal to modulate the continuous light wavelength emitted by the laser (10); The signal processing unit (70) is used to receive the first electrical signal and process the electrical signal according to the modulation signal to output a strain result, the strain result including strain location and strain magnitude.

2. The distributed strain measurement device according to claim 1, characterized in that, The laser (10) is a wavelength-tunable laser; the optical switch (20) is a high-speed optical switch with a response time on the order of picoseconds.

3. The distributed strain measurement device according to claim 2, characterized in that, The beam splitting device (30) is a beam splitting prism or a circulator; the fiber grating (40) is a long weak fiber grating or a cascaded array of weak fiber gratings (40).

4. The distributed strain measurement device according to claim 3, characterized in that, The photodetector (50) is a balanced detector.

5. The distributed strain measurement device according to claim 4, characterized in that, The signal processing unit (70) uses a lock-in amplification algorithm to determine the relative position of the center wavelength of the laser (10) and the center wavelength of the fiber optic grating (40) by combining the modulation signal and the light intensity change at the strain position, so as to expand the strain measurement range.

6. The distributed strain measurement device according to claim 5, characterized in that, It also includes a display unit (80), which is connected to the signal processing unit (70) and is used to receive and display the strain results.

7. A distributed strain measurement method, characterized in that, Based on the distributed strain measurement device as described in any one of claims 1-6, the measurement method includes: S1: Turn on the laser (10) to control the laser (10) to emit a continuous optical signal; the initial spectrum of the continuous optical signal has a wavelength region that overlaps with the initial spectrum of the fiber grating (40); S2: Turn on the optical switch (20) to modulate the continuous optical signal into the pulsed optical signal and transmit it to the beam splitter (30). S3: Adjust the beam splitter (30) to guide the pulsed light signal to the fiber optic grating (40) and transmit it to the photodetector (50) after receiving the reflected light signal. S4: The photodetector (50) is turned on to detect the reflected light signal and the converted first electrical signal is transmitted to the signal processing module so that the signal processing unit (70) generates a strain result based on the first electrical signal and the modulation signal.

8. A distributed strain detection method, characterized in that, Based on the distributed strain measurement device as described in any one of claims 1-6, the detection method includes: S100: Receive the first electrical signal and acquire the modulation signal; S200: Based on the information of light intensity changing with time in the first electrical signal, determine the correspondence between the time parameter and the physical position on the fiber optic grating (40), and then identify the strain position; S300: Combine the modulation signal to process the light intensity change information corresponding to the strain position in the first electrical signal, and associate the magnitude of the light intensity change with the magnitude of the strain. S400: Integrate the strain location and strain magnitude to obtain the strain result, and output it externally.

9. The distributed strain detection method according to claim 8, characterized in that, Step S200 includes: The time information of the change in light intensity in the first electrical signal is analyzed, the first duration is extracted and the first speed is obtained; the first duration is the duration corresponding to the change in light intensity, and the first speed is the transmission speed of the optical signal in the fiber optic grating (40); The strain position is obtained based on the product of the first velocity and the first duration; wherein, the starting time point of the light intensity change corresponds to the starting position of the strain, and the ending time point of the light intensity change corresponds to the ending position of the strain.

10. The distributed strain detection method according to claim 8, characterized in that, Step S300 includes: The modulation signal is invoked to determine the continuous variation law and variation period of the wavelength of the laser (10); The light intensity change information at the strain position is synchronously demodulated with the modulation signal using a lock-in amplification method to obtain the amplitude information of the light intensity change. The amplitude information is used to call a preset database to obtain the strain magnitude; the preset database includes multiple pre-stored amplitude values ​​and strain values ​​corresponding to each amplitude value.

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