Fiber-optic sensor based on cascaded superstructure fiber grating, measurement system, and method for simultaneous measurement of temperature and strain based on the measurement system

Abstract

The application discloses a fiber sensor based on a cascaded superstructure grating, which comprises at least one cascaded superstructure grating, and the cascaded superstructure grating is composed of two superstructure gratings spaced at a certain distance and engraved on the same fiber; the superstructure grating is composed of a series of modulation units of refractive index periodic modulation, and each modulation unit comprises an effective modulation area and a non-modulation interval area. The fiber sensor based on the cascaded superstructure grating provided by the application reduces the bandwidth of the characteristic peak of the transmission spectrum of the superstructure grating, improves the measurement precision of the wavelength moving amount of the characteristic peak, reduces the requirement on the bandwidth of a probe light source, and improves the measurement precision and stability. The application further discloses a measurement system comprising the fiber sensor based on the cascaded superstructure grating and a method for simultaneously measuring temperature and strain based on the measurement system.

Description

Technical Field

[0001] This application relates to fiber optic sensors and methods for measuring temperature and strain using fiber optic sensors, and more particularly to fiber optic sensors formed using gratings based on metastructures and methods for measuring temperature and strain. Background Technology

[0002] Fiber optic sensors use light as the carrier and optical fiber as the transmission medium to sense parameters such as strain, temperature, and vibration through changes in optical properties. They offer advantages such as resistance to electromagnetic interference, corrosion resistance, and small size. In structural health monitoring, they can monitor minute deformations and damage in bridges, dams, and buildings in real time, ensuring structural safety. They are widely used in aerospace, energy, and transportation fields, exhibiting high precision, long-term stability, and strong environmental adaptability. Superstructure fiber Bragg gratings (SBRs) are a type of fiber optic sensor, also known as sampling gratings, obtained by periodically sampling a uniform Bragg grating. When the sampling period reaches tens or hundreds of micrometers, the periodic sampling structure gives them not only the spectral characteristics of Bragg gratings but also the spectral features of long-period gratings. The unique spectral characteristics of SBRs allow them to be applied in multi-sensoring fields. Currently, there are three methods for using SBRs for dual-parameter temperature and strain sensing:

[0003] The first approach utilizes the changes in wavelength shift of the central Bragg peak and spacing of the sideband resonance peaks in the reflection spectrum of the superstructure fiber grating to achieve dual-parameter differentiation (Sanipatin B, Sánchez LA, Maldonado-Hurtado D, et al. Customized femtosecond laser-inscribed superstructure fiberBragg grating: A novel approach to decoupling temperature and strain[J]. Optics & Laser Technology, 2024, 177: 111083.). However, since the sensitivity of the central Bragg peak and the sideband resonance peak to temperature and strain is positively correlated and there is a linear correlation between the two, the decoupling error is extremely large, making it difficult to apply in practical industrial scenarios.

[0004] The second method relies on the shift in the center wavelength of the Bragg peak of a superstructure grating and the change in transmission intensity to achieve simultaneous temperature and strain measurement (Guan BO, Tam HY, Tao XM, et al. Simultaneous strain and temperature measurement using a superstructure fiber Bragg grating[J]. IEEE Photonics Technology Letters, 2000, 12(6): 675-677.). However, in practical applications, the change in transmission intensity is weak and easily affected by external interference, which limits the practical application of this method.

[0005] The third method utilizes the strain insensitivity of a specific loss peak in a superstructure grating to overcome the cross-sensitivity effect and simultaneously measure temperature and strain (Sengupta S, Ghorai SK, Biswas P. Design of superstructure fiber Bragg grating with efficient mode coupling for simultaneous strain and temperature measurement with low cross-sensitivity[J]. IEEE Sensors Journal, 2016, 16(22): 7941-7949.). This method can achieve high measurement accuracy, but its limitation lies in the excessively large bandwidth of the loss peak in the superstructure grating. The large shift in the center wavelength of the loss peak will affect the sensing accuracy, and the large bandwidth of the loss peak requires matching a large sweep bandwidth, which places high demands on the measurement system and is not conducive to cost reduction. Summary of the Invention

[0006] The purpose of this invention is to realize a high-precision single-grating fiber optic sensor capable of stably measuring both temperature and strain parameters.

[0007] To this end, this application proposes an optical fiber sensor based on a cascaded superstructure grating for achieving high-precision simultaneous measurement of strain and temperature. The sensor includes at least one cascaded superstructure grating, which is composed of two superstructure gratings spaced apart by a certain distance and etched on the same optical fiber. The superstructure grating is composed of a series of modulation units with periodically modulated refractive index, and each modulation unit includes an effective modulation region and a region without modulation interval.

[0008] In some embodiments, the modulation method of the modulation unit includes sinusoidal modulation and rectangular modulation.

[0009] In some embodiments, a plurality of cascaded superstructure gratings are included, wherein the plurality of cascaded superstructure gratings are etched on the same optical fiber, and any two of the cascaded superstructure gratings are spaced apart by a predetermined distance.

[0010] In some embodiments, the plurality of cascaded superstructure gratings are configured to have different initial Bragg peak center wavelengths and initial loss peak center wavelengths.

[0011] Other embodiments of this application provide a measurement system comprising a fiber optic sensor based on a cascaded superstructure grating as described in any one of the above claims, a light source module connected via an optical fiber to the input end of the fiber optic sensor based on the cascaded superstructure grating, and a spectral detection module connected via an optical fiber to the output end of the fiber optic sensor based on the cascaded superstructure grating.

[0012] In some embodiments, the light source module is a tunable swept-frequency laser or a spontaneously emitted light source. The spectral detection module is a spectral analyzer or a photodetector.

[0013] Other embodiments of this application provide a method for simultaneously measuring temperature and strain, using the measurement system described in any one of the preceding claims; the method includes the steps of: allowing the light output from the light source module to enter the fiber optic sensor based on a cascaded superstructure grating, and then transmitting the transmitted light into the spectral detection module to obtain the spectrum of the fiber optic sensor based on the cascaded superstructure grating; and recording the shift of the center wavelength of the Bragg peak in the spectrum. The amount of shift of the center wavelength of the loss peak The temperature change measured by the fiber optic sensor based on the cascaded superstructure grating is calculated. and strain change ;

[0014] (Formula 1)

[0015] in , , , These are the Bragg peak strain sensitivity, loss peak strain sensitivity, Bragg peak temperature sensitivity, and loss peak temperature sensitivity of the fiber optic sensor based on the cascaded superstructure grating, respectively. .

[0016] In some embodiments, the method for obtaining the Bragg peak temperature sensitivity and loss peak temperature sensitivity of the fiber optic sensor based on a cascaded superstructure grating is as follows: the fiber optic sensor based on the cascaded superstructure grating is pre-stretched and mounted on a micro-displacement platform within a temperature control device. The pre-stretching is kept constant. The temperature control device is used to calibrate the temperature sensitivity of the fiber optic sensor based on the cascaded superstructure grating. The center wavelengths of the Bragg peak and loss peak at different temperatures are recorded. The Bragg peak temperature sensitivity of the fiber optic sensor based on the cascaded superstructure grating is then obtained using a linear fitting method. Loss peak temperature sensitivity The method for obtaining the Bragg peak strain sensitivity and loss peak strain sensitivity of the fiber optic sensor based on the cascaded superstructure grating is as follows: Keeping the temperature of the temperature control device constant, the strain sensitivity of the fiber optic sensor based on the cascaded superstructure grating is calibrated using the micro-displacement platform. The center wavelengths of the Bragg peak and loss peak are recorded under different strains. The Bragg peak strain sensitivity of the fiber optic sensor based on the cascaded superstructure grating is then obtained through a linear fitting method. Loss peak strain sensitivity .

[0017] In some embodiments, for the fiber optic sensor based on cascaded superstructure gratings, which includes multiple cascaded superstructure gratings, each of the cascaded superstructure gratings is arranged at different test locations of the structure under test, and wavelength division multiplexing is used to achieve simultaneous measurement of strain and temperature at the multiple test locations.

[0018] In the embodiments of this application, the loss peak of the cascaded superstructure grating exhibits interference modulation, causing the original broadband loss peak to be modulated into numerous narrow peaks. This significantly reduces the bandwidth of the loss peak, decreases the measurement error of the center wavelength shift of the loss peak, and improves sensing accuracy. Therefore, the fiber optic sensor based on the cascaded superstructure grating provided by this invention improves the measurement accuracy of the characteristic peak wavelength shift by reducing the bandwidth of the characteristic peak of the superstructure grating's transmission spectrum, reduces the bandwidth requirements of the probe light source, and improves measurement accuracy and stability. Furthermore, it can reduce the bandwidth of the loss peak, relax the sweep frequency bandwidth limitation, and improve sensing measurement accuracy. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a cascaded superstructure grating in an optical fiber sensor based on a cascaded superstructure grating according to an embodiment of this application.

[0020] Figure 2 The transmission spectrum of the cascaded superstructure grating according to one embodiment of this application is shown.

[0021] Figure 3This is a comparison diagram of the transmission spectrum of the cascaded superstructure grating according to another embodiment of this application and the transmission spectrum of the superstructure grating.

[0022] Figure 4 This is a comparison diagram of the transmission spectrum of the cascaded superstructure grating and the transmission spectrum of the superstructure grating according to another embodiment of this application.

[0023] Figure 5 This is a schematic diagram of the structure of a measurement system including the fiber optic sensor based on a cascaded superstructure grating of this application.

[0024] Figure 6 This is a schematic diagram of the structure of a fiber optic sensor based on a cascaded superstructure grating, which includes multiple cascaded superstructure gratings according to an embodiment of this application.

[0025] Figure 7 This is a flowchart illustrating a method for simultaneously measuring temperature and strain of a structure under test using a fiber optic sensor based on a cascaded superstructure grating according to an embodiment of this application.

[0026] Figure 8 The flowchart shows the method for calibrating the temperature sensitivity and strain sensitivity of the fiber optic sensor based on the cascaded superstructure grating according to this application. Detailed Implementation

[0027] The present application will now be described in detail with reference to the accompanying drawings.

[0028] Figure 1 The figure shows a schematic diagram of the basic structure of a cascaded superstructure grating (CSFG) 100 in an optical fiber sensor based on a cascaded superstructure grating according to an embodiment of this application. As shown in the figure, the cascaded superstructure grating 100 in one embodiment consists of two superstructure gratings, abbreviated as SFG, namely the first superstructure grating, abbreviated as SFG1, and the second superstructure grating, abbreviated as SFG2, etched in the same optical fiber. The two superstructure gratings are spaced apart by a distance, namely the cascade spacing. The first or second superstructure grating can both be composed of a series of modulation units with periodically modulated refractive index, where the modulation period is the sampling period. Each modulation unit contains an effective modulation region. With no modulation interval region Each effective modulation region There are finer periodic variations in refractive index, such as sinusoidal or rectangular periodic variations.

[0029] In both the first and second superstructure gratings, there is coupling between the core fundamental mode and the cladding mode in the same direction. When the light wave passes through the first superstructure grating SFG1, some energy is coupled from the core to the cladding 20, and the remainder continues to propagate in the core 10; it then propagates a certain distance in the ungrated fiber 10. After passing through the second superstructure grating SFG2, the light wave propagating in the cladding 20 is coupled back to the fiber core 10. Due to the optical path difference between the light waves propagating in the fiber core 10 and the cladding 20, interference occurs in the fiber core 10, forming an effect similar to Mach-Zehnder interference. This modulates the loss peak in the original superstructure grating transmission spectrum, changing it from a broadband loss peak to several narrowband loss peaks.

[0030] The transmission spectrum (hereinafter referred to as the spectrum) of the cascaded superstructure grating 100 has similar characteristics to that of the superstructure grating and can still be analyzed using the transfer matrix method. The transfer matrix of the loss peak spectra of the first superstructure grating SFG1 and the second superstructure grating SFG2 can be obtained from the following equation. , It can be expressed as a general formula:

[0031]

[0032] in, The coupling coefficient between the core fundamental mode and the cladding mode transmission modes is denoted as . This represents the self-coupling coefficient of the fiber core fundamental mode. ,when hour, It is an imaginary number. These represent the first superstructure grating SFG1 and the second superstructure grating SFG2, respectively. When a light wave passes through the first superstructure grating and enters the cascaded gratingless region, the resulting optical path difference... As shown in the following formula:

[0033]

[0034] in, The propagation constant of the fiber core is denoted as . Let be the cladding propagation constant of the optical fiber. The loss peak spectral transfer matrix of the cascaded superstructure grating modulated by Mach-Zehnder interference can be calculated from the above two equations. for:

[0035]

[0036] set up , Indicates the distance the light wave travels. The field amplitude at that time. Therefore, the loss peak spectrum of the cascaded superstructure grating can be represented by the following transfer matrix:

[0037]

[0038] Assuming only one type of light wave enters from infinity, the initial conditions are: Therefore, the loss peak transmittance of the cascaded superstructure grating can be obtained as follows:

[0039] Let the transmittances of the Bragg peaks of the first superstructure grating SFG1 and the second superstructure grating SFG2 be respectively... , Therefore, the transmittance of the spectrum of the cascaded superstructure grating 100 is obtained:

[0040] Figure 2 The transmission spectrum of the cascaded superstructure grating is shown in Table 1. The grating parameters of the cascaded superstructure grating are shown in Table 1. The loss peaks in the transmission spectrum of the cascaded superstructure grating are modulated by the Mach-Zehnder interference effect, becoming several narrowband loss peaks, and the 3dB bandwidth is significantly reduced.

[0041] Table 1. Parameters of a cascaded superstructure grating sensor

[0042] Superstructure grating sensor parameters Specific values grating period 0.536μm Sampling period 322μm Modulation of refraction depth <![CDATA[1.8X10 -4 <!-- 4 -->]]> Cascade spacing 50mm Duty cycle 0.5 Number of samples 40

[0043] Figure 3 The diagram shows a comparison of the transmission spectra of the cascaded superstructure grating and the superstructure grating. The first superstructure grating SFG1 and the second superstructure grating SFG2, which are cascaded together, have identical grating parameters. The total length of the cascaded superstructure grating sensor is twice the total length of either the first superstructure grating SFG1 or the second superstructure grating SFG2. Figure 3 The parameters of the fiber optic sensor based on cascaded superstructure gratings in the table are consistent with those in Table 1, except for the cascade spacing. Figure 3 The cascading spacing of the fiber optic sensor based on cascaded superstructure gratings is 30mm. Figure 3 The loss peak of each superstructure grating in the cascaded superstructure grating is modulated into five narrowband loss peaks. The middle narrowband loss peak has the narrowest bandwidth, the lowest transmission intensity, and the highest loss. Compared with the first superstructure grating SFG1 or the first superstructure grating SFG2 with the same parameters, it can be seen that the bandwidth of the loss peak of the cascaded superstructure grating is significantly reduced, and the transmission intensity is also significantly reduced.

[0044] Figure 4 The image shows a comparison of the transmission spectra of a cascaded superstructure grating with those of a superstructure grating, using a different set of parameters. The cascading spacing of the cascaded superstructure grating is compared to... Figure 2 , Figure 3For cascaded superstructure gratings, the size is further reduced to 12 mm. The loss peak of the superstructure grating is modulated into a narrowband loss peak.

[0045] Figure 2 , Figure 3 , Figure 4 In the cascaded superstructure gratings, as the cascade spacing increases sequentially, the number of narrowband loss peaks in the transmission spectrum of the corresponding cascaded superstructure gratings increases sequentially, while the bandwidth of the loss peaks decreases sequentially. From Figure 2 , Figure 3 , Figure 4 As can be seen from the above, the loss peak bandwidth of the fiber optic sensor based on cascaded superstructure grating designed in this invention is significantly reduced compared to that of the superstructure grating; and different numbers and bandwidths of narrowband loss peaks can be designed by controlling the size of the cascade spacing; therefore, the fiber optic sensor designed in this invention is more conducive to reducing the error of the center wavelength shift of the loss peak, reducing the requirement for the bandwidth of the detection light source, and improving the sensing accuracy.

[0046] Figure 2 , Figure 3 , Figure 4 In the fiber optic sensor based on cascaded superstructure gratings, the first superstructure grating SFG1 and the second superstructure grating SFG2 in any cascaded superstructure grating have the same grating parameters. This only serves to demonstrate the transmission spectrum of the cascaded superstructure grating and does not limit the fiber optic sensor based on cascaded superstructure gratings and the method for simultaneous temperature and strain measurement. The grating parameters of the two cascaded superstructure gratings can be different.

[0047] Figure 5 The diagram shows a schematic of a measurement system including a fiber optic sensor based on a cascaded superstructure grating. Figure 5 As shown, the measurement system includes a fiber optic sensor 100 based on a cascaded superstructure grating, a light source module 200 connected to the input end of the fiber optic sensor based on the cascaded superstructure grating via an optical fiber, and a spectral detection module 300 connected to the output end of the fiber optic sensor 100 based on the cascaded superstructure grating via an optical fiber. Figure 5 In the measurement system, the light source module 200 can be a swept-frequency laser or a spontaneously emitted light source; the spectral detection module 300 can be a spectral analyzer or a photodetector. The swept-frequency laser output by the light source module 200 is processed by... Figure 5 The optical fiber shown transmits the light, and the transmitted light passes through... Figure 5When the cascaded superstructure grating in the fiber optic sensor 100 of the cascaded superstructure grating is cascaded, after the corresponding loss and modulation effects are generated, the transmission spectrum is output and displayed through the spectral detection module 300. The shift of the center wavelength of the Bragg peak and the shift of the center wavelength of the loss peak in the transmission spectrum are read. The corresponding temperature change and strain change can be obtained through matrix calculation.

[0048] Figure 6 The diagram illustrates multiple cascaded superstructure gratings (SFRs) arranged in series on the same optical fiber, according to this application, enabling monitoring of different test locations within the structure under test. For example, multiple cascaded superstructure gratings can be etched onto the same optical fiber, with a distance between any two cascaded superstructure gratings, thus forming a multi-point detection fiber optic sensor based on cascaded superstructure gratings. Figure 6 As shown, a first cascaded superstructure grating 101, a second cascaded superstructure grating 102, and a third cascaded superstructure grating 103, coupled in series via the same optical fiber, constitute a multi-point detection fiber optic sensor based on cascaded superstructure gratings. In some embodiments, the first cascaded superstructure grating 101, the second cascaded superstructure grating 102, and the third cascaded superstructure grating 103 are configured to have the same structure but different initial Bragg peak center wavelengths and initial loss peak center wavelengths. During use, they are respectively arranged on different test locations of the structure under test, thereby enabling multi-point detection. Similarly, this multi-point detection fiber optic sensor, together with the light source module 200 and the spectral detection module 300, constitute the measurement device, which can be combined using wavelength division multiplexing. Figure 7 The method shown enables simultaneous measurement of temperature and strain at the multiple test sites.

[0049] To clearly illustrate the method for simultaneously measuring temperature and strain based on a cascaded superstructure grating fiber optic sensor according to the invention, specific embodiments of the method will be further described below with reference to the accompanying drawings, but the scope of protection of the invention should not be limited thereto.

[0050] Figure 7 The figure shows a flowchart of a method for simultaneously measuring temperature and strain based on a cascaded superstructure grating fiber optic sensor. The method includes the following specific steps:

[0051] Step S11: First, the cascaded superstructure grating fiber optic sensor is mounted on the structure under test. The cascaded superstructure grating sensor is configured to be attached to or embedded in the detection area of ​​the structure under test.

[0052] Step S12: Connect the light source module 200 and the spectral detection module 300 to both sides of the cascaded superstructure grating fiber optic sensor 100, respectively. Turn on the light source module 200, and use the spectral detection module 300 to read the initial wavelength positions of the loss peak center wavelength and the Bragg peak center wavelength in the transmission spectrum of the cascaded superstructure grating fiber optic sensor 100, and record the initial temperature and strain values ​​at this time. , .

[0053] Step S13: When the temperature or strain of the measured part changes, it will cause the wavelength positions of the center wavelengths of the Bragg peak and the center wavelengths of the loss peak in the cascaded superstructure grating fiber optic sensor 100 to shift; the shifted center wavelength position of the Bragg peak in the cascaded superstructure grating fiber optic sensor 100 is read in real time by the spectral detection module 300. Position of the center wavelength of the first loss peak The wavelength shift at the center of the Bragg peak was calculated. Wavelength shift of the loss peak center .

[0054] Step S14: Finally, shift the center wavelength of the Bragg peak of the cascaded superstructure grating fiber optic sensor 100 by an amount of... The amount of wavelength shift at the center of the loss peak Substitute into the matrix equation to solve for the temperature change. and strain change .

[0055]

[0056] in, This refers to the temperature sensitivity of the Bragg peak center wavelength of the cascaded superstructure grating fiber optic sensor. It is the temperature sensitivity of the center wavelength of the loss peak; It is the strain sensitivity of the center wavelength of the Bragg peak. The above refers to the strain sensitivity at the center wavelength of the loss peak. .

[0057] The temperature change was calculated. and strain change Then, compare it with the initial temperature value recorded in step S12. and initial strain value Adding them together gives the changed temperature and strain. .

[0058] The detection error of the center wavelength shift of the Bragg peak in the transmission spectrum of the fiber optic sensor Detection error of the amount of wavelength shift at the center of the loss peak This results in errors in the calculated temperature change and strain change, specifically the error in the temperature change. And the error of the strain change It can be evaluated by the following formula:

[0059]

[0060] The cascaded superstructure grating fiber sensor proposed in this invention has a narrower loss peak bandwidth, which can greatly reduce the error in the shift of the center wavelength of the loss peak. This results in smaller errors in the calculated temperature and strain changes, thereby improving sensing accuracy.

[0061] Figure 6 The measurement system shown, based on a cascaded superstructure grating fiber optic sensor, can be combined using wavelength division multiplexing. Figure 7 The method shown enables simultaneous measurement of temperature and strain at multiple points. According to... Figure 7 The steps in the process involve recording the initial wavelength positions and the shifted wavelength positions of the Bragg peak and loss peak at different initial wavelengths, and calculating the temperature change and strain change using the above formulas; by observing the wavelengths of the Bragg peak and loss peak that have shifted in real time, the temperature change and strain change corresponding to different detection points are calculated.

[0062] Figure 8 The following is a method for calibrating temperature strain sensitivity using a cascaded superstructure grating. The specific steps are as follows:

[0063] Step S21: First, place the cascaded superstructured grating fiber optic sensor to be calibrated on a micro-displacement platform within a temperature control device for pre-stretching installation, i.e., installation with a known stretch applied. The temperature control device is, for example, a tube furnace, a semiconductor refrigeration device, a standard temperature control chamber, or other standard device with a known temperature. Connect the light source module and the spectral detection module to the two ends of the cascaded superstructured grating fiber optic sensor, respectively. Turn on the light source module and use the spectral detection module to read and record the initial wavelength positions of the center wavelengths of the loss peak and Bragg peak in the transmission spectrum of the cascaded superstructured grating in the fiber optic sensor.

[0064] Step S22: Keep the pre-stretched state of the optical fiber unchanged, and record the current temperature in the temperature control device as the initial temperature; by adjusting the temperature in the temperature control device, for example, by gradually increasing the temperature to gradually increase the temperature of the cascaded superstructure grating fiber sensor, and reading the center wavelength of the Bragg peak and the center wavelength of the loss peak at each temperature increase; record each temperature value and the positions of the center wavelength of the Bragg peak and the center wavelength of the loss peak read at that temperature value.

[0065] Step S23: Calculate the temperature sensitivity of the Bragg peak center wavelength of the cascaded superstructure grating fiber optic sensor using a linear fitting method, such as the least squares method. Temperature sensitivity to the center wavelength of the loss peak ;

[0066] Step S24: Restore the temperature control device to the initial temperature, record the current vernier position of the micro-displacement stage, and read and record the initial wavelength positions of the center wavelengths of the loss peak and the Bragg peak in the transmission spectrum of the cascaded superstructure grating in the cascaded superstructure grating fiber sensor through the spectral detection module.

[0067] Step S25: Keeping the temperature of the optical fiber constant, gradually move the micro-displacement stage to stretch the cascaded superstructure grating fiber sensor, and record the applied strain value and the corresponding wavelength shift of the Bragg peak center wavelength and the loss peak center wavelength; record the strain value and the corresponding wavelength position of the Bragg peak center wavelength and the loss peak center wavelength.

[0068] Step S26: Calculate the strain sensitivity of the center wavelength of the Bragg peak of the cascaded superstructure grating using a linear fitting method, such as the least squares method. Strain sensitivity relative to the center wavelength of the loss peak .

[0069] Currently, using the wavelength shift of the broadband loss peak and the central Bragg peak of a superstructured grating for temperature strain decoupling achieves high accuracy. However, the extremely large bandwidth of the broadband loss peak poses significant challenges for peak detection, further contributing to large errors in the wavelength shift of the broadband loss peak and consequently, large temperature strain decoupling errors. Simultaneously, the wider loss peak bandwidth increases the sweep bandwidth of spectrometers or other photodetectors, leading to reduced detection resolution and further increasing temperature strain decoupling errors. The cascaded superstructured grating sensor proposed in this invention reduces the 3dB bandwidth of the broadband loss peak in the transmission spectrum of the superstructured grating sensor, decreases the sweep bandwidth requirement, and improves the temperature strain decoupling accuracy of the sensor.

[0070] It should be understood that the above methods can be implemented with human intervention or entirely through automated control. Therefore, the above steps can be implemented in the form of computer software code and in reverse.

[0071] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention. Moreover, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A fiber-optic sensor based on cascaded superstructure fiber grating for high-precision simultaneous strain and temperature measurement, characterized in that: The device comprises at least one cascaded superstructure grating, which comprises a first superstructure grating and a second superstructure grating with a cascaded distance, and the first superstructure grating and the second superstructure grating are engraved on the same optical fiber; the first superstructure grating and the second superstructure grating are both composed of a series of refractive index periodic modulation units, each of the modulation units comprises an effective modulation area and a non-modulation interval area, and the cascaded distance is set so that when a light wave passes through the first superstructure grating, a first light wave part of the light wave is coupled from the fiber core to the cladding, and the remaining second light wave part of the light wave propagates in the unengraved grating fiber core for the cascaded distance and then passes through the second superstructure grating and propagates in the cladding, the first light wave part is coupled back to the fiber core from the cladding again, and the first light wave part and the second light wave part interfere with each other in the fiber core, so that the wideband loss peak in the transmission spectrum of the second superstructure grating becomes several narrowband loss peaks.

2. The fiber-optic sensor based on a cascaded superstructure fiber grating according to claim 1, characterized in that: The modulation mode of the modulation unit includes sinusoidal modulation and rectangular modulation.

3. The fiber-optic sensor based on a cascaded superstructure fiber grating according to claim 1, characterized in that: The multiple cascaded superstructure fiber gratings are arranged on the same optical fiber with a preset distance between any two of the cascaded superstructure fiber gratings.

4. The fiber-optic sensor based on a cascaded superstructure fiber grating according to claim 3, characterized in that: The multiple cascaded superstructure fiber gratings are configured to have different initial Bragg peak central wavelengths and initial loss peak central wavelengths.

5. A measurement system characterized by, The measurement system comprises the cascaded superstructure fiber grating-based optical fiber sensor, a light source module connected to an input end of the cascaded superstructure fiber grating-based optical fiber sensor via one end of an optical fiber, and a spectrum detection module connected to an output end of the cascaded superstructure fiber grating-based optical fiber sensor via the other end of the optical fiber.

6. The measurement system of claim 5, wherein: The light source module is a tunable swept laser or a spontaneous emission light source.

7. The measurement system of claim 5, wherein: The spectrum detection module is a spectrum analyzer or a photodetector.

8. A method of simultaneously measuring temperature and strain, characterized by: The method comprises the steps of The light source module outputs light into the cascaded superstructure grating-based optical fiber sensor, and the transmitted light enters the spectrum detection module to obtain the spectrum of the cascaded superstructure grating-based optical fiber sensor; and the movement amount of the Bragg peak center wavelength in the spectrum is recorded The movement amount of the loss peak center wavelength The temperature change amount measured by the cascaded superstructure grating-based optical fiber sensor is calculated by using formula 1 And the strain change amount ; (Formula 1) wherein 、 、 、 are the Bragg peak strain sensitivity, the loss peak strain sensitivity, the Bragg peak temperature sensitivity, the loss peak temperature sensitivity of the fiber sensor based on the cascaded superstructure grating, respectively, .

9. The method of simultaneously measuring temperature and strain of claim 8, wherein: The Bragg peak temperature sensitivity and the loss peak temperature sensitivity of the fiber sensor based on the cascaded superstructure grating are obtained by the following method: the fiber sensor based on the cascaded superstructure grating is pre-stretched and mounted on a micro-displacement platform in a temperature control device, the pre-stretching is kept unchanged, the temperature sensitivity of the fiber sensor based on the cascaded superstructure grating is calibrated by using the temperature control device, the corresponding Bragg peak center wavelength and loss peak center wavelength at different temperatures are recorded, and the Bragg peak temperature sensitivity of the fiber sensor based on the cascaded superstructure grating is obtained by a linear fitting method , the loss peak temperature sensitivity The Bragg peak strain sensitivity and the loss peak strain sensitivity of the fiber sensor based on the cascaded superstructure grating are obtained by the following method: the temperature of the temperature control device is kept unchanged, the strain sensitivity of the fiber sensor based on the cascaded superstructure grating is calibrated by using the micro-displacement platform, the corresponding Bragg peak center wavelength and loss peak center wavelength at different strains are recorded, and the Bragg peak strain sensitivity of the fiber sensor based on the cascaded superstructure grating is obtained by a linear fitting method , the loss peak strain sensitivity .

10. The method of simultaneously measuring temperature and strain of claim 8, wherein: For the cascaded superstructure fiber grating-based optical fiber sensor comprising multiple cascaded superstructure fiber gratings, each of the cascaded superstructure fiber gratings is arranged at a different measurement site of the structure to be measured, and the strain and temperature of multiple measurement sites are simultaneously measured by using wavelength division multiplexing.

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