Airspace fiber cavity ring-down temperature / strain double-parameter sensing method and device

Abstract

The invention discloses a spatial domain fiber cavity ring-down temperature / strain double-parameter sensing method and device, and the method comprises the steps: obtaining the peak amplitude variation and peak wavelength variation of a sensing device at different temperatures, and the peak amplitude variation and peak wavelength variation under different strains during initial calibration; based on the peak amplitude variation and the peak wavelength variation at different temperatures, obtaining corresponding temperature sensitivity during calibration; based on the peak amplitude variation and the peak wavelength variation under different strains, obtaining corresponding strain sensitivity during calibration; the method comprises the following steps: establishing a matrix equation about temperature sensitivity and strain sensitivity, extracting actual peak amplitude change and peak wavelength change from an optical fiber ring-down ring loss spectrum measured by a sensing device, substituting the actual peak amplitude change and peak wavelength change into the matrix equation, and solving to realize demodulation calculation of double parameters of temperature and strain.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a method for sensing the dual parameters of ring-down temperature and strain in a spatial fiber optic cavity. Background Technology

[0002] Fiber Bragg grating (FBG) sensors, as a key component of modern sensing technology, have been widely used in temperature monitoring and strain measurement due to their wavelength encoding characteristics, good compatibility, low cost, and strong multiplexing capabilities, making them a research focus. Traditional demodulation techniques primarily convert temperature or strain changes caused by external factors into Bragg wavelength shifts or optical power changes for measurement. Common methods include optical spectral analysis, optical edge filter detection, tunable filtering, wavelength-tunable light source demodulation, and interferometric scanning. Optical spectral analysis utilizes a spectrometer and broadband light source for spectral observation. Scholars such as Zhang Ying, Kim DG, Liu J, and Qi YF have used this method for temperature and strain measurement. However, this method suffers from problems such as large equipment size, high cost, slow response, and low resolution, severely limiting its application in practical engineering. Optical edge filter detection utilizes the linear conversion characteristics of optical edge filters to convert the Bragg wavelength shift of the fiber grating into optical power changes. Yan Liqin, Ma Weichao, and others have used this method for temperature and strain measurement, but further improvement of the measurement resolution is difficult due to limitations imposed by factors such as the signal-to-noise ratio. Tunable filtering methods employ tunable fiber optic narrowband filters for scanning filtering. Zheng Lilin, Zhang Xiuyong, and others have used this method to implement fiber optic strain sensing. However, this method suffers from poor demodulation repeatability and slow scanning speed, limiting its practical applications. Wavelength-tunable light source demodulation methods achieve wavelength demodulation by detecting the beat frequency signal, offering the advantage of being unaffected by light source fluctuations. Gagliardi G, Krarup O, and other researchers have significantly improved the resolution of FBG-based temperature sensors using this method, but it requires expensive equipment, leading to a substantial increase in system cost. Interferometric scanning methods detect wavelength changes by measuring the optical phase change of the interference signal. Jiang JJ, Yao QQ, Xu Ye, and other researchers have proposed fiber optic grating temperature strain demodulation techniques based on this method. However, this technology is not suitable for practical engineering scenarios due to the large size of the equipment and its susceptibility to environmental interference.

[0003] With the continuous development of fiber optic sensing technology, traditional fiber grating demodulation techniques are no longer sufficient to meet practical needs. Against this backdrop, fiber ring fading technology has gradually become a research hotspot. In the field of temperature sensing, in 2006, Wang CJ first proposed a fiber grating temperature sensing system based on time-domain fiber ring fading technology. This system utilizes fiber gratings to achieve temperature sensing, avoiding the use of expensive spectrometers and reducing external interference. However, it suffers from problems such as difficulty in balancing optical pulse parameters, low duty cycle, and low signal-to-noise ratio. In 2019, Qin C proposed a fiber grating temperature sensing system based on chaotic correlation fiber ring fading. This system transforms wavelength drift measurement into ring fading time measurement, offering advantages such as high sensitivity and fast response speed. However, its reliance on complex equipment significantly increases costs. In 2022, Tian XZ's team proposed a fiber ring fading temperature sensor integrating FBG and microwave photonics-assisted technology. This sensor effectively utilizes the duty cycle, possessing high sensitivity and resolution, but it also faces problems such as expensive equipment, complex structure, and limited measurement range. In the field of strain sensing, in 2007, Ni N proposed a novel fiber long-period grating cavity ring-down strain sensor, which exhibits high sensitivity and resolution. In 2015, Silva S's team proposed a strain sensing system based on time-domain fiber ring-down technology; in 2022, Wu K proposed a high-resolution strain sensor combining time-domain fiber ring-down technology. Both sensors demonstrate high sensitivity and resolution. In the same year, Xiao YY proposed a fiber ring-down CFBG strain sensor based on overlapping spectrum demodulation technology, effectively expanding the measurement range. However, traditional fiber ring-down fiber grating strain sensing technology requires equipment such as pulsed lasers, resulting in high costs and limiting its widespread application.

[0004] Furthermore, fiber Bragg grating sensors face several technical challenges in practical applications, the most significant being the cross-sensitivity to temperature and strain. Because the wavelength of a fiber Bragg grating is sensitive to both temperature and strain, it becomes difficult to distinguish between them simply by measuring wavelength changes. This problem limits the application of fiber Bragg grating sensors in fields requiring precise temperature and strain measurements. To address this issue, in 2010, Hu Ji proposed a novel sensor head design utilizing a metal cylinder to resolve the cross-sensitivity to temperature and strain. In 2012, Triollet S et al. achieved simultaneous temperature and strain measurement using a sensor combination of an overlapping long-period fiber Bragg grating and a Bragg grating. In 2023, Jia Ruoyi employed a dual-grating method to demodulate the temperature / strain dual-parameter matrix by monitoring changes in two Bragg wavelengths. However, these methods are limited by the spectrometer and its resolution, are expensive, have low demodulation accuracy, and poor practicality.

[0005] Therefore, it is necessary to design a sensor with a simple and compact structure, low equipment cost, good stability, and high demodulation accuracy, which does not require pulse modulation / microwave modulation, high-speed photoelectric detection, or rapid data acquisition. Summary of the Invention

[0006] In view of the above-mentioned prior art, the present invention provides a spatial fiber cavity ring-down temperature / strain dual-parameter sensing method, which mainly solves the technical problems existing in the above-mentioned background art.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows: The first aspect of the present invention provides a spatial fiber cavity ring-down temperature / strain dual-parameter sensing device, the sensing device including a tunable laser, a fiber circulator, a first fiber coupler, a first optical polarization controller, a fiber ring-down ring, a frequency shifter, and a balanced detector. The fiber optic ring decay loop is formed by connecting a second fiber coupler, a fiber grating, a third fiber coupler, and a second optical polarization controller to form a closed loop. The tunable laser is connected to the first port of the fiber optic circulator, the second port of the fiber optic circulator is connected to the first port of the first fiber optic coupler, and the third port of the fiber optic circulator is connected to the balanced detector. The second port of the first fiber coupler is connected to the first optical polarization controller, the third port of the first fiber coupler is connected to the balanced detector, and the fourth port of the first fiber coupler is connected to the frequency shifter. The first optical polarization controller is connected to the first port of the second optical fiber coupler, the second port of the second optical fiber coupler is connected to the fiber grating, the fiber grating is connected to the second port of the third optical fiber coupler, the first port of the third optical fiber coupler is connected to the second optical polarization controller, and the second optical polarization controller is connected to the third port of the second optical fiber coupler. The third port of the third fiber optic coupler is connected to the frequency shifter; The frequency shifter and the balance detector are connected to an external terminal via a data acquisition instrument.

[0008] Optionally, the splitting ratio of the first fiber coupler is 50:50.

[0009] Optionally, the second and third fiber couplers have the same splitting ratio, and the splitting ratio is not less than 99:1.

[0010] A second aspect of the present invention provides a method for sensing the dual parameters of ring-down temperature and strain in a spatial fiber cavity, the sensing method being implemented based on the sensing device described in any of the preceding claims, the sensing method comprising the following steps: During the initial calibration, the peak amplitude and peak wavelength changes of the sensing device at different temperatures, as well as the peak amplitude and peak wavelength changes under different strains, are obtained. Based on the changes in peak amplitude and peak wavelength at different temperatures, the temperature sensitivity corresponding to the calibration is obtained; Based on the changes in peak amplitude and peak wavelength under different strains, the strain sensitivity corresponding to the calibration is obtained. A matrix equation for temperature sensitivity and strain sensitivity is established. Based on the fiber ring-down loss spectrum measured by the sensing device, the actual peak amplitude change and peak wavelength change are extracted and substituted into the matrix equation. After solving, the demodulation calculation of temperature and strain dual parameters is realized.

[0011] Optionally, during initial calibration, the peak amplitude variation and peak wavelength variation of the sensing device at different temperatures are acquired, specifically including: When there is no strain and the initial ambient temperature of the fiber grating in the sensing device remains constant, the wavelength of the tunable laser is scanned to measure the loss spectrum of the fiber ring-down loop, and the initial values ​​of the temperature peak amplitude and temperature peak wavelength under this state are extracted. By changing the ambient temperature, repeat the above operations of obtaining wavelength, measuring loss spectrum and extracting peak amplitude and peak wavelength under each new temperature condition to obtain the change in peak amplitude and peak wavelength corresponding to different temperatures.

[0012] Optionally, during initial calibration, the peak amplitude change and peak wavelength change of the sensing device under different strains are obtained, specifically including: An initial small strain is applied to the fiber grating in the sensing device at a reference temperature, and the wavelength of the tunable laser is scanned to measure the loss spectrum of the fiber ring-down loop. The initial values ​​of the strain peak amplitude and strain peak wavelength in this state are extracted. By changing the applied strain, repeat the above operations of obtaining wavelength, measuring loss spectrum and extracting peak amplitude and peak wavelength under each new strain condition to obtain the change in peak amplitude and peak wavelength corresponding to different strains.

[0013] Optionally, the temperature sensitivity during calibration can be obtained based on the changes in peak amplitude and peak wavelength at different temperatures, specifically including: Based on the changes in peak amplitude and peak wavelength at different temperatures, as well as the initial values ​​of peak amplitude and peak wavelength at the reference temperature, calculate the changes in peak amplitude and peak wavelength at each temperature. The change in peak amplitude at each temperature is linearly fitted with the corresponding temperature change. The sensitivity of the peak amplitude to temperature change is determined by the linear relationship obtained from the fitting, i.e., the first temperature sensitivity coefficient. The change in peak wavelength at each temperature is linearly fitted with the corresponding change in temperature. The sensitivity of the peak wavelength to temperature change is determined by the linear relationship obtained from the fitting, which is the second temperature sensitivity coefficient.

[0014] Optionally, based on the changes in peak amplitude and peak wavelength under different strains, the strain sensitivity corresponding to the calibration is obtained, specifically including: Based on the changes in peak amplitude and peak wavelength under different strains, as well as the initial values ​​of peak amplitude and peak wavelength under the reference strain, calculate the changes in peak amplitude and peak wavelength of strain under each strain. The change in peak amplitude under each strain is linearly fitted with the corresponding change in strain. The sensitivity of the peak amplitude of strain to change with strain is determined by the linear relationship obtained by the fitting, i.e., the first strain temperature sensitivity coefficient. The change in peak wavelength under each strain is linearly fitted with the corresponding change in strain. The sensitivity of the peak wavelength to strain change is determined by the linear relationship obtained from the fitting, which is the second strain temperature sensitivity coefficient.

[0015] Optionally, a matrix equation is constructed that includes a first temperature sensitivity coefficient, a second temperature sensitivity coefficient, a first strain temperature sensitivity coefficient, a second strain temperature sensitivity coefficient, an actual peak amplitude change, and an actual peak wavelength change. When temperature and strain act simultaneously, the loss spectrum of the fiber ring-down loop is measured using the obtained wavelength, and the actual peak amplitude change and actual peak wavelength change under this state are obtained from it. The actual peak amplitude change and actual peak wavelength change are substituted into the above matrix equation, and the actual temperature and actual strain are obtained by solving the matrix equation, thereby realizing the demodulation calculation of temperature and strain dual parameters.

[0016] The beneficial effects of the present invention are as follows: (1) The use of spatial fiber ring decay technology can not only avoid wavelength demodulation and the use of expensive spectrometers, but also the use of continuous light as the light source does not require pulse modulation, fast detection and high-speed demodulation, thus having the advantages of simple structure and low cost.

[0017] (2) By using an optical fiber ring-down loop, the continuous laser is repeatedly cyclically attenuated in the optical fiber ring to amplify the effect of external parameters on the fiber grating. Therefore, the difference in the coefficient of the fiber grating transmission intensity and wavelength change response to temperature and strain can be greatly improved, thereby increasing the sensitivity of the sensor demodulation.

[0018] (3) Spatial fiber ring fading is essentially co-path interference. Differential detection is used to cancel DC noise, thus it has high signal-to-noise ratio, high stability, high measurement accuracy and high resolution.

[0019] (4) By using the method of establishing a mathematical model demodulation matrix, the influence of temperature and strain on the measurement results can be effectively separated, avoiding the problem of mutual interference between the two in the traditional method, and improving the accuracy and reliability of the measurement. Attached Figure Description

[0020] Figure 1 This is a structural block diagram of the sensing device in the embodiments of this application; Figure 2 This is a flowchart of the sensing method of the present invention; Figure 3 This is a schematic diagram showing the position of the laser wavelength in the transmission spectrum of a fiber optic grating; Figure 4 These are curves showing the change in loss with wavelength under different temperatures and strains. The solid line represents the curve of loss changing with wavelength at different temperatures, while the dashed line represents the curve of loss changing with wavelength under different strains.

[0021] Explanation of icon numbers: 1. Tunable laser; 2. Fiber circulator; 3. First fiber coupler; 4. First optical polarization controller; 5. Fiber ring decay ring; 5-1. Second fiber coupler; 5-2. Fiber grating; 5-3. Third fiber coupler; 5-4. Second optical polarization controller; 6. Frequency shifter; 7. Balanced detector; 8. Data acquisition instrument; 9. External terminal. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. In the following description, the expression "some embodiments" refers to a subset of all possible embodiments; however, it should be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0023] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0024] It should be understood that the present invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Furthermore, the terminology used herein is intended only to describe particular embodiments and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “compose” and / or “comprising,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0025] It should also be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "inner," "outer," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0026] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Optional embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0027] Please refer to the attached document. Figure 1 The first aspect of the present invention provides a spatial fiber cavity ring-down temperature / strain dual-parameter sensing device, the sensing device comprising a tunable laser 1, a fiber circulator 2, a first fiber coupler 3, a first optical polarization controller 4, a fiber ring-down ring 5, a frequency shifter 6, and a balanced detector 7. The fiber optic ring 5 is formed by connecting the second fiber coupler 5-1, the fiber grating 5-2, the third fiber coupler 5-3, and the second optical polarization controller 5-4 to form a closed loop. The tunable laser 1 is connected to the first port of the fiber optic circulator 2, the second port of the fiber optic circulator 2 is connected to the first port of the first fiber optic coupler 3, and the third port of the fiber optic circulator 2 is connected to the balanced detector 7. The second port of the first fiber optic coupler 3 is connected to the first optical polarization controller 4, the third port of the first fiber optic coupler 3 is connected to the balanced detector 7, and the fourth port of the first fiber optic coupler 3 is connected to the frequency shifter 6. The first optical polarization controller 4 is connected to the first port of the second fiber coupler 5-1, the second port of the second fiber coupler 5-1 is connected to the fiber grating 5-2, the fiber grating 5-2 is connected to the second port of the third fiber coupler 5-3, the first port of the third fiber coupler 5-3 is connected to the second optical polarization controller 5-4, and the second optical polarization controller 5-4 is connected to the third port of the second fiber coupler 5-1. The third port of the third fiber optic coupler 5-3 is connected to the frequency shifter 6; The frequency shifter 6 and the balance detector 7 are respectively connected to the external terminal 9 through the data acquisition instrument 8.

[0028] In one or more embodiments of this application, the splitting ratio of the first fiber coupler 3 is 50:50.

[0029] This 50:50 splitting ratio ensures that the two beams propagating clockwise and counterclockwise maintain equal intensity. This equal intensity results in a more stable interference signal when the two beams circulate within the subsequent fiber ring-down loop 5 and eventually interfere, avoiding the problem of reduced signal-to-noise ratio caused by excessive intensity differences between the two beams. Simultaneously, the balanced intensity distribution also facilitates more accurate reception and processing of the frequency-shifted interference differential signal by the balanced detector 7, reducing measurement errors caused by uneven intensity and thus improving the accuracy of the entire sensing device in detecting the loss spectrum of the fiber ring-down loop 5.

[0030] In one or more embodiments of this application, the second fiber coupler 5-1 and the third fiber coupler 5-3 have the same splitting ratio, and the splitting ratio is not less than 99:1, and the reflectivity of the fiber grating 5-2 is not greater than 10%.

[0031] When light enters the fiber ring-down loop 5, the second fiber coupler 5-1 transmits most of the light (not less than 99%) to the fiber grating 5-2, with only a small portion (not more than 1%) leaking out. The light passing through the fiber grating 5-2 is then subjected to similar beam splitting by the third fiber coupler 5-3, ensuring that most of the light continues to circulate within the loop while a small portion leaks out. The fiber grating 5-2, with a reflectivity of no more than 10%, reflects only a small amount of light as it passes through, allowing most of the light to transmit and participate in the loop's circulation process.

[0032] This configuration significantly reduces energy loss during light circulation within the fiber ring-down loop 5, allowing the light to undergo multiple cycles of attenuation within the loop. This amplifies the effects of external temperature and strain on the fiber grating 5-2. Since most of the light is retained within the loop, the transmission intensity and wavelength changes in the fiber grating 5-2 caused by temperature or strain variations are accumulated multiple times, making the peak amplitude and peak wavelength changes in the loss spectrum more pronounced, thereby improving the sensing device's sensitivity to these changes.

[0033] Specifically, the output frequency of tunable laser 1 is The continuous light is passed through fiber optic circulator 2 and then... The first fiber coupler 3 splits the light into two beams, one propagating clockwise and the other counterclockwise. The clockwise beam exits from the second port of the first fiber coupler 3, passes through the first optical polarization controller 4, and enters the fiber ring-down loop 5 for circulation. The counterclockwise beam exits from the fourth port of the first fiber coupler 3, first passes through the frequency shifter 6 to change its frequency from... v become Then it enters the fiber optic ring-down loop 5. The light, circulating clockwise, completes one revolution per cycle. The light remains within the fiber optic ring 5 and continues to circulate; only... Light leaks from the third fiber coupler 5-3, and is frequency-shifted by the frequency shifter 6 to change the frequency. become Then it reaches the first fiber coupler 3. The counter-clockwise circular light, similarly, only [a certain amount] per complete circle. The light leaks from the second fiber coupler 5-1 and returns to the first fiber coupler 3 via the first optical polarization controller 4. When the coherence length of the laser is less than the cavity length of the ring-down cavity, the same number of cycles and the same frequency... When two beams of light with opposite paths occur, frequency shift interference will be generated at the first fiber coupler 3, and the frequency shift interference differential signal will be received by the balanced detector 7.

[0034] The frequency-shifting interferometric differential signal is acquired using data acquisition instrument 8, and then subjected to Fourier fast transform using LabVIEW software on an external terminal 9, such as an external computer, to obtain the ring-down signal. The peak value is extracted and subjected to exponential fitting to attenuate the light intensity to... The distance of time transmission is defined as the fading distance. When fiber Bragg grating 5-2 is subjected to external forces (such as temperature and strain), its light intensity loss increases, its ringing-off becomes faster, and its ringing-off distance becomes shorter. The ringing-off distance after external forces is defined as... Thus, the loss after external action is obtained. ,in The cavity length of fiber optic ring 5 is given.

[0035] See Figures 2-4The second aspect of the present invention provides a method for sensing the dual parameters of ring-down temperature and strain in a spatial fiber cavity, the sensing method being implemented based on the sensing device described in any of the preceding claims, the sensing method comprising the following steps: S1. During the initial calibration, obtain the peak amplitude change and peak wavelength change of the sensing device at different temperatures, as well as the peak amplitude change and peak wavelength change under different strains. S2. Based on the changes in peak amplitude and peak wavelength at different temperatures, obtain the temperature sensitivity corresponding to the calibration. S3. Based on the changes in peak amplitude and peak wavelength under different strains, obtain the strain sensitivity corresponding to the calibration. S4. Establish matrix equations for temperature sensitivity and strain sensitivity. Based on the loss spectrum of the fiber ring-down loop 5 measured by the sensing device, extract the actual peak amplitude change and peak wavelength change from it, substitute them into the matrix equations, and solve to realize the demodulation calculation of temperature and strain dual parameters.

[0036] In one or more embodiments of this application, during initial calibration, the peak amplitude variation and peak wavelength variation of the sensing device at different temperatures are obtained, specifically including: When there is no strain and the initial ambient temperature of the fiber grating 5-2 in the sensing device remains constant, the wavelength of the tunable laser 1 is scanned to measure the loss spectrum of the fiber ring-down ring 5, and the initial value of the temperature peak amplitude under this state is extracted. and initial value of peak wavelength at temperature ; By changing the ambient temperature, repeating the above steps of obtaining wavelength, measuring loss spectrum, and extracting peak amplitude and peak wavelength under each new temperature condition, the change in peak amplitude corresponding to different temperatures can be obtained. and peak wavelength variation .

[0037] During initial calibration, it is first ensured that the fiber grating 5-2 is not subjected to strain and is under a stable initial ambient temperature. The wavelength of the tunable laser 1 is scanned to obtain the relationship curve of the loss of the fiber ring-down ring 5 as a function of wavelength, i.e., the loss spectrum. The initial values ​​of the temperature peak amplitude and the temperature peak wavelength under this state are extracted and used as the benchmark for subsequent comparison. Then, the ambient temperature of the fiber grating 5-2 is gradually changed. Under each new temperature condition, the state of no strain is kept unchanged, and the above operations of scanning wavelength, measuring loss spectrum and extracting corresponding peak amplitude and peak wavelength are repeated to obtain the change in peak amplitude and peak wavelength relative to the initial values ​​at different temperatures.

[0038] This implementation process, by controlling a single variable (changing only the temperature while maintaining a strain-free state), accurately isolates the independent influence of temperature on the characteristics of the fiber Bragg grating 5-2, avoiding measurement deviations caused by strain interference. By acquiring peak value variation data at different temperatures, reliable experimental data is provided for subsequent linear fitting to obtain the temperature sensitivity, ensuring the accuracy of the temperature sensitivity parameters.

[0039] Furthermore, based on the changes in peak amplitude and peak wavelength at different temperatures, as well as the initial values ​​of peak amplitude and peak wavelength at the reference temperature, the change in peak amplitude at each temperature is calculated. and the change in wavelength of the temperature peak ; The change in peak amplitude at each temperature and the corresponding temperature change A linear fit is performed, and the sensitivity of the temperature peak amplitude to temperature change is determined by the linear relationship obtained from the fit, i.e., the first temperature sensitivity coefficient. ; The change in peak wavelength at each temperature is linearly fitted to the corresponding temperature change. The sensitivity of the peak wavelength to temperature change, i.e., the second temperature sensitivity coefficient, is determined by the linear relationship obtained from the fitting. .

[0040] Specifically, this involves calculating the change in peak amplitude at each temperature relative to the initial value, i.e., the change in peak amplitude. Simultaneously calculate the change in temperature relative to the initial temperature, i.e., the temperature change. Similarly, calculate the change in peak wavelength at each temperature relative to the initial value, i.e., the change in peak wavelength. .

[0041] The obtained multiple peak amplitude changes Corresponding to the corresponding temperature change One-to-one correspondence, based on temperature change The horizontal axis represents the change in peak amplitude. A scatter plot is drawn with the vertical axis as the ordinate. A straight line reflecting the changing trends of both values ​​is obtained through linear fitting. The slope of this line represents the sensitivity of the peak amplitude to temperature, i.e., the first temperature sensitivity coefficient. The mathematical expression for this straight line is:

[0042] in, Indicates the amount of temperature change. It is a constant.

[0043] Using the same method, the variation of each peak wavelength was... and the corresponding temperature change By mapping the data one-to-one and plotting a scatter plot, a linear fit is performed to obtain another straight line. The slope of this line represents the sensitivity of the peak wavelength to temperature, i.e., the second temperature sensitivity coefficient. The mathematical expression for this straight line is:

[0044] in, It is a constant.

[0045] In one or more embodiments of this application, during initial calibration, the peak amplitude change and peak wavelength change of the sensing device under different strains are obtained, specifically including: An initial small strain is applied to the fiber grating 5-2 in the sensing device at a reference temperature. The wavelength of the tunable laser 1 is scanned to measure the loss spectrum of the fiber ring-down ring 5, and the initial value of the strain peak amplitude under this state is extracted. and initial value of strain peak wavelength ; By changing the applied strain, repeating the above operations of obtaining the wavelength, measuring the loss spectrum, and extracting the peak amplitude and peak wavelength under each new strain condition, the change in peak amplitude corresponding to different strains can be obtained. and peak wavelength variation .

[0046] By keeping the temperature constant and only changing the strain magnitude, the effect of strain on the characteristics of the fiber Bragg grating 5-2 can be isolated. The peak amplitude and peak wavelength of the fiber Bragg grating 5-2 change systematically with strain. Under constant temperature, this change is solely caused by strain, ensuring that the acquired peak variation data accurately reflects the effect of strain. This operation provides reliable data support for subsequent linear fitting to obtain the strain sensitivity, guaranteeing the accuracy of the strain sensitivity parameters.

[0047] Furthermore, based on the change in peak amplitude under different strains and peak wavelength variation To obtain the strain sensitivity corresponding to the calibration, specifically including: Based on the changes in peak amplitude and peak wavelength under different strains, and the initial value of peak amplitude under the reference strain. and initial value of peak wavelength Calculate the change in peak strain amplitude at each strain. and the change in peak strain wavelength ; The change in peak amplitude under each strain With the corresponding strain change A linear fit is performed, and the sensitivity of the strain peak amplitude to strain variation is determined by the linear relationship obtained from the fit, i.e., the first strain temperature sensitivity coefficient. ; The change in peak wavelength under each strain A linear fit is performed with the corresponding strain change, and the sensitivity of the strain peak wavelength to strain change, i.e., the second strain temperature sensitivity coefficient, is determined by the linear relationship obtained from the fit. .

[0048] Specifically, the change in peak amplitude relative to the initial value is calculated for each strain, i.e., the change in peak amplitude. Simultaneously, the change in strain at each strain relative to the initial small strain is calculated, i.e., the strain change; similarly, the change in peak wavelength at each strain relative to the initial value is calculated, i.e., the peak wavelength change. .

[0049] The obtained multiple peak amplitude changes Each of these corresponds to a specific strain change, with the strain change as the abscissa and the peak amplitude change as the ordinate. A scatter plot is drawn with the vertical axis as the ordinate. A straight line reflecting the changing trends of both is obtained through linear fitting. The slope of this line is the sensitivity of the peak amplitude to strain, which is the first strain sensitivity coefficient. The mathematical expression for this straight line is:

[0050] in, Indicates the amount of temperature change. constant Using the same method, the variation of each peak wavelength was... By mapping each strain change to its corresponding value and plotting a scatter plot, a linear fit is performed to obtain another straight line. The slope of this line represents the sensitivity of the peak wavelength to strain, which is the second strain sensitivity coefficient. The mathematical expression for this straight line is:

[0051] in, It is a constant.

[0052] In one or more embodiments of this application, a matrix equation is constructed that includes a first temperature sensitivity coefficient, a second temperature sensitivity coefficient, a first strain temperature sensitivity coefficient, a second strain temperature sensitivity coefficient, an actual peak amplitude change, and an actual peak wavelength change. When temperature and strain act simultaneously, the loss spectrum of the fiber ring-down loop 5 is measured using the obtained wavelength, and the actual peak amplitude change and actual peak wavelength change under this state are obtained from it. The actual peak amplitude change and actual peak wavelength change are substituted into the above matrix equation, and the actual temperature and actual strain are obtained by solving the matrix equation, thereby realizing the demodulation calculation of temperature and strain dual parameters.

[0053] Specifically, the wavelength of the laser is scanned under the simultaneous effects of temperature and strain to measure the loss spectrum of the fiber ring-down ring 5, extracting its peak wavelength and peak amplitude, and measuring the corresponding actual peak amplitude change. and actual peak wavelength variation Its actual peak amplitude variation The expression is:

[0054] Actual peak wavelength variation The expression is:

[0055] The resulting matrix equation is:

[0056]

[0057]

[0058] and All of these are constants. By solving the above matrix, the temperature and strain parameters can be demodulated.

[0059] Additionally, it should be noted that the transmission spectrum of fiber optic grating 5-2 exhibits a "concave" (i.e., a reflection band), such as... Figure 3 As shown, the point of lowest transmittance (center of the stopband). The wavelength is the Bragg wavelength, determined by the grating period and the effective refractive index. and The area between these points is the low-transmission region (linear operating region). By adjusting the wavelength of the tunable laser 1 in this embodiment, the continuous wavelength of the light emitted by the tunable laser 1 is positioned within the linear operating region of the fiber optic grating 5-2. When external parameters change, the transmission spectrum of the fiber optic grating 5-2 shifts overall, and the transmission intensity changes linearly with the external parameters, causing the additional loss introduced by the fiber optic grating 5-2 to also change linearly. The loss spectrum of the fiber ring-down ring 5 is measured under temperature and strain conditions, and its peak wavelength and peak amplitude are extracted. The response coefficient matrix is ​​decoupled, achieving dual-parameter sensing of temperature and strain. Based on this, the sensing method provided by this patent can be applied to fiber optic sensing scenarios where temperature and strain are mutually sensitive or require simultaneous detection.

[0060] The above are merely specific embodiments of the present invention, but 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 technical scope disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A spatial fiber cavity ring-down temperature / strain dual-parameter sensing device, characterized in that, The sensing device includes a tunable laser, a fiber optic circulator, a first fiber optic coupler, a first optical polarization controller, a fiber optic ring-down loop, a frequency shifter, and a balanced detector. The fiber optic ring decay loop is formed by connecting the second fiber coupler, fiber grating, third fiber coupler 5-3, and second optical polarization controller to form a closed loop. The tunable laser is connected to the first port of the fiber optic circulator, the second port of the fiber optic circulator is connected to the first port of the first fiber optic coupler, and the third port of the fiber optic circulator is connected to the balanced detector. The second port of the first fiber coupler is connected to the first optical polarization controller, the third port of the first fiber coupler is connected to the balanced detector, and the fourth port of the first fiber coupler is connected to the frequency shifter. The first optical polarization controller is connected to the first port of the second optical fiber coupler, the second port of the second optical fiber coupler is connected to the fiber grating, the fiber grating is connected to the second port of the third optical fiber coupler, the first port of the third optical fiber coupler is connected to the second optical polarization controller, and the second optical polarization controller is connected to the third port of the second optical fiber coupler. The third port of the third fiber optic coupler is connected to the frequency shifter; The frequency shifter and the balance detector are connected to an external terminal via a data acquisition instrument.

2. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing device according to claim 1, characterized in that, The splitting ratio of the first fiber coupler is 50:

50.

3. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing device according to claim 2, characterized in that, The second and third fiber couplers have the same splitting ratio, and the splitting ratio is not less than 99:

1.

4. A method for dual-parameter sensing of ring-down temperature and strain in a spatial fiber optic cavity, characterized in that, The sensing method is implemented based on the sensing device as described in any one of claims 1-3, and the sensing method includes the following steps: During the initial calibration, the peak amplitude and peak wavelength changes of the sensing device at different temperatures, as well as the peak amplitude and peak wavelength changes under different strains, are obtained. Based on the changes in peak amplitude and peak wavelength at different temperatures, the temperature sensitivity corresponding to the calibration is obtained; Based on the changes in peak amplitude and peak wavelength under different strains, the strain sensitivity corresponding to the calibration is obtained. A matrix equation for temperature sensitivity and strain sensitivity is established. Based on the fiber ring-down loss spectrum measured by the sensing device, the actual peak amplitude change and peak wavelength change are extracted and substituted into the matrix equation. After solving, the demodulation calculation of temperature and strain dual parameters is realized.

5. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing method according to claim 4, characterized in that, During initial calibration, the peak amplitude change and peak wavelength change of the sensing device at different temperatures are obtained, specifically including: When there is no strain and the initial ambient temperature of the fiber grating in the sensing device remains constant, the wavelength of the tunable laser is scanned to measure the loss spectrum of the fiber ring-down loop, and the initial values ​​of the temperature peak amplitude and temperature peak wavelength under this state are extracted. By changing the ambient temperature, repeat the above operations of obtaining wavelength, measuring loss spectrum and extracting peak amplitude and peak wavelength under each new temperature condition to obtain the change in peak amplitude and peak wavelength corresponding to different temperatures.

6. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing method according to claim 5, characterized in that, During initial calibration, the peak amplitude change and peak wavelength change of the sensing device under different strains are obtained, specifically including: An initial small strain is applied to the fiber grating in the sensing device at a reference temperature, and the wavelength of the tunable laser is scanned to measure the loss spectrum of the fiber ring-down loop. The initial values ​​of the strain peak amplitude and strain peak wavelength in this state are extracted. By changing the applied strain, repeat the above operations of obtaining wavelength, measuring loss spectrum and extracting peak amplitude and peak wavelength under each new strain condition to obtain the change in peak amplitude and peak wavelength corresponding to different strains.

7. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing method according to claim 6, characterized in that, Based on the changes in peak amplitude and peak wavelength at different temperatures, the temperature sensitivity corresponding to the calibration is obtained, specifically including: Based on the changes in peak amplitude and peak wavelength at different temperatures, as well as the initial values ​​of peak amplitude and peak wavelength at the reference temperature, calculate the changes in peak amplitude and peak wavelength at each temperature. The change in peak amplitude at each temperature is linearly fitted with the corresponding temperature change. The sensitivity of the peak amplitude to temperature change is determined by the linear relationship obtained from the fitting, i.e., the first temperature sensitivity coefficient. The change in peak wavelength at each temperature is linearly fitted with the corresponding change in temperature. The sensitivity of the peak wavelength to temperature change is determined by the linear relationship obtained from the fitting, which is the second temperature sensitivity coefficient.

8. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing method according to claim 7, characterized in that, Based on the changes in peak amplitude and peak wavelength under different strains, the strain sensitivity corresponding to the calibration is obtained, specifically including: Based on the changes in peak amplitude and peak wavelength under different strains, as well as the initial values ​​of peak amplitude and peak wavelength under the reference strain, calculate the changes in peak amplitude and peak wavelength of strain under each strain. The change in peak amplitude under each strain is linearly fitted with the corresponding change in strain. The sensitivity of the peak amplitude of strain to change with strain is determined by the linear relationship obtained by the fitting, i.e., the first strain temperature sensitivity coefficient. The change in peak wavelength under each strain is linearly fitted with the corresponding change in strain. The sensitivity of the peak wavelength to strain change is determined by the linear relationship obtained from the fitting, which is the second strain temperature sensitivity coefficient.

9. The spatial fiber cavity ring-down temperature / strain dual-parameter sensing method according to claim 8, characterized in that, A matrix equation is constructed that includes a first temperature sensitivity coefficient, a second temperature sensitivity coefficient, a first strain temperature sensitivity coefficient, a second strain temperature sensitivity coefficient, an actual peak amplitude change, and an actual peak wavelength change. When temperature and strain act simultaneously, the loss spectrum of the fiber ring-down loop is measured using the obtained wavelength, and the actual peak amplitude change and actual peak wavelength change under this state are obtained from it. The actual peak amplitude change and actual peak wavelength change are substituted into the above matrix equation, and the actual temperature and actual strain are obtained by solving the matrix equation, thereby realizing the demodulation calculation of temperature and strain dual parameters.

Images