Raman temperature sensing apparatus and method for infrastructure security monitoring without calibration

Abstract

The present application relates to the field of distributed optical fiber sensing, and discloses a kind of infrastructure security monitoring oriented calibration-free Raman temperature sensing device and method.The device comprises: pulse laser, the pulse laser emitted by pulse laser is sequentially incident to first calibration fiber ring, second calibration fiber ring, third calibration fiber ring and sensing fiber after wavelength division multiplexer, the Raman backward stokes scattering light and Raman backward anti-stokes scattering light generated in sensing fiber are respectively detected by two ports of avalanche photodetector, and the output end of avalanche photodetector is connected with computer through data acquisition card;The present application directly fits out calibration curve by measuring the average intensity of Raman backward anti-stokes light signal and Raman backward stokes light signal at first calibration fiber ring, second calibration fiber ring and third calibration fiber ring, realizes temperature demodulation, avoids calibration process, and improves signal-to-noise ratio and temperature measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of distributed optical fiber sensing, specifically a calibration-free Raman temperature sensing device and method for infrastructure safety monitoring. Background Technology

[0002] With the rapid development of infrastructure, geotechnical structures are becoming increasingly complex, and engineering projects are growing in scale. The field of safety monitoring for major infrastructure projects is facing enormous challenges, requiring sensors with ever-increasing monitoring accuracy. However, conventional point-based, electronic sensing technologies are insufficient to meet the requirements of continuous, long-distance, and long-term safety monitoring of complex infrastructure. Compared to traditional electronic sensors, distributed fiber optic sensors offer advantages such as electrical insulation, corrosion resistance, intrinsic safety, high sensitivity, light weight, small size, and embeddability. Raman distributed fiber optic sensing technology, enabling real-time monitoring of distributed temperature along the fiber optic cable, has become a key area of ​​international research.

[0003] In traditional Raman distributed fiber optic sensing technology, calibration is required before measurement to demodulate distributed temperature information. Calibration necessitates placing the entire sensing fiber in a constant ambient temperature environment to obtain Raman signal intensity information at various locations along the fiber at that constant temperature. This method of calibrating by placing the entire sensing fiber in a constant ambient temperature environment presents two significant technical bottlenecks:

[0004] (1) During the calibration period, the system's laser, wavelength division multiplexer, avalanche photodetector and other devices will heat up as the usage time increases, resulting in a large error in the calibration temperature curve, which will ultimately affect the measurement accuracy of the system.

[0005] (2) When the optical fiber is bent or damaged at a certain point, the temperature demodulation result will have a serious measurement error at that point.

[0006] Therefore, it is necessary to improve the existing Raman distributed fiber optic sensing devices and temperature demodulation methods to solve the technical bottlenecks in the calibration and demodulation of existing Raman distributed fiber optic sensing systems, eliminate the complexity of the traditional calibration process, and thus improve the temperature measurement accuracy of the system. Summary of the Invention

[0007] This invention overcomes the shortcomings of existing technologies and aims to solve the following technical problem: provide a calibration-free Raman temperature sensing method for infrastructure safety monitoring to improve temperature measurement accuracy.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a calibration-free Raman temperature sensing device for infrastructure safety monitoring, comprising: a pulsed laser, a wavelength division multiplexer, a first calibration fiber ring, a second calibration fiber ring, a third calibration fiber ring, a sensing fiber, an avalanche photodetector, a data acquisition card, and a computer; the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are sequentially connected to the sensing fiber.

[0009] The pulsed laser emitted by the pulsed laser is sequentially incident on the first calibration fiber ring, the second calibration fiber ring, the third calibration fiber ring, and the sensing fiber after passing through a wavelength division multiplexer. The Raman backscattered Stokes light and the Raman backscattered anti-Stokes light generated in the sensing fiber are detected by the two ports of the avalanche photodetector, respectively. The output of the avalanche photodetector is connected to the computer through a data acquisition card.

[0010] The computer is used to calculate the temperature along the sensing fiber based on the average intensity of Raman backscattered Stokes light and Raman backscattered anti-Stokes light in the first calibration fiber ring, the second calibration fiber ring, the third calibration fiber ring and the sensing fiber, as well as the temperatures of the first calibration fiber ring, the second calibration fiber ring and the third calibration fiber ring.

[0011] The calculation unit obtains the following formula for calculating the temperature along the sensing fiber:

[0012]

[0013] Where Δv is the frequency shift of the Raman scattering signal, h is Planck's constant, k is Boltzmann's constant, T0' represents the calibration temperature, and F Back (T,L) represents the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered Stokes light signal intensity at position L, F Back (L) represents the ratio of the Raman backward Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity at position L.

[0014] F Back The formula for calculating (L) is:

[0015]

[0016] Where, Φ as [L1,L2] and Φ s [L1,L2] represents the first-order average difference between the average intensity of the Raman backscattered anti-Stokes light and the average intensity of the Raman backscattered Stokes light at the first and second calibration fiber loops, Φ as [L1,L2,L3] and Φ s[L1,L2,L3] represents the second-order average difference of the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered anti-Stokes light at the first, second, and third calibration fiber loops, respectively. L1, L2, and L3 represent the positions of the first, second, and third calibration fiber loops in the entire fiber, respectively. Φ as (L1) and Φ s (L1) The average intensity of Raman backscattered anti-Stokes light and Raman backscattered anti-Stokes light at the first calibration fiber loop, respectively.

[0017] The Φ as [L1,L2]、Φ as [L1,L2,L3]、Φ s [L1,L2]、Φ s The formulas for calculating [L1, L2, L3] are as follows:

[0018]

[0019]

[0020]

[0021]

[0022] in,

[0023]

[0024]

[0025] Where, Φ as (L2) and Φ s (L2) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the second calibration fiber loop, respectively. Φ as (L3) and Φ s (L3) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the third calibration fiber loop, respectively.

[0026] The temperatures of the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring remain constant.

[0027] The lengths of the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are at least twice the spatial length corresponding to the pulse width of the laser pulse.

[0028] The wavelength of the pulsed laser is 1550nm.

[0029] A calibration-free Raman distributed fiber optic temperature sensing method for infrastructure safety monitoring employs a device comprising a pulsed laser, a wavelength division multiplexer, a first calibration fiber ring, a second calibration fiber ring, a third calibration fiber ring, a sensing fiber, and an avalanche photodetector. The pulsed laser emitted by the pulsed laser is sequentially incident on the first calibration fiber ring, the second calibration fiber ring, the third calibration fiber ring, and the sensing fiber after passing through the wavelength division multiplexer. The Raman backscattered Stokes light and the Raman backscattered anti-Stokes light generated in the sensing fiber are detected by two ports of the avalanche photodetector, respectively. The method includes the following steps:

[0030] S1. Obtain the temperature values ​​of the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring, and calculate the calibration temperature value T0'.

[0031] S2. Obtain the average intensity of Raman back-Stokes scattered light and Raman back-anti-Stokes scattered light in the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring; at the same time, obtain the intensity of Raman back-Stokes scattered light and Raman back-anti-Stokes scattered light at each position in the sensing fiber.

[0032] S3. Calculate the temperature at various locations in the sensing fiber. The calculation formula is as follows:

[0033]

[0034] Where Δv is the frequency shift of the Raman scattering signal, h is Planck's constant, k is Boltzmann's constant, and F Back (T,L) represents the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered Stokes light signal intensity at position L, F Back (L) represents the ratio of the Raman backward Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity at position L;

[0035] F Back The formula for calculating (L) is:

[0036]

[0037] Where, Φ as [L1,L2] and Φ s [L1,L2] represents the first-order average difference between the average intensity of the Raman backscattered anti-Stokes light and the average intensity of the Raman backscattered anti-Stokes light at the first calibration fiber loop and the second calibration fiber loop, Φ as [L1,L2,L3] and Φ s[L1,L2,L3] represents the second-order average difference of the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered anti-Stokes light at the first, second, and third calibration fiber loops, respectively. L1, L2, and L3 represent the positions of the first, second, and third calibration fiber loops in the entire fiber, respectively. Φ as (L1) and Φ s (L1) The average intensity of Raman backscattered anti-Stokes light and Raman backscattered anti-Stokes light at the first calibration fiber loop, respectively.

[0038] The Φ as [L1,L2]、Φ as [L1,L2,L3]、Φ s [L1,L2]、Φ s The formulas for calculating [L1, L2, L3] are as follows:

[0039]

[0040]

[0041]

[0042]

[0043] in,

[0044]

[0045]

[0046] Where, Φ as (L2) and Φ s (L2) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the second calibration fiber loop, respectively. Φ as (L3) and Φ s (L3) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the third calibration fiber loop, respectively.

[0047] The formula for calculating the calibration temperature value T0' is:

[0048]

[0049] Where T1, T2, and T3 represent the average temperatures of the environments in which the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are located, respectively.

[0050] In summary, this invention provides a calibration-free Raman temperature sensing device and method for infrastructure safety monitoring. By measuring the average intensity of the Raman backscattered anti-Stokes light signal and the Raman backscattered Stokes light signal at the first, second, and third calibration fiber rings, the signal intensity calibration curves of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light are directly fitted. Using the Raman backscattered anti-Stokes light signal intensity and the Raman backscattered Stokes light signal intensity at the measurement location, along with the corresponding calibration curves, the temperature along the fiber optic cable is demodulated. This avoids the calibration process and eliminates demodulated temperature errors caused by operational mistakes or system errors during calibration. Compared with existing distributed fiber optic sensing methods, the calibration-free Raman temperature sensing method for infrastructure safety monitoring proposed in this invention has the following advantages:

[0051] (1) The calibration process of placing the entire optical fiber at a constant temperature before measurement was eliminated, thus optimizing the measurement time of the system;

[0052] (2) The signal-to-noise ratio of the system was optimized, which ultimately improved the sensing distance and temperature measurement accuracy of the system. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the sensing device used in an embodiment of the present invention;

[0054] In the diagram: 1: Pulsed laser, 2: Wavelength division multiplexer, 3: First calibration fiber ring, 4: Second calibration fiber ring, 5: Third calibration fiber ring, 6: Sensing fiber, 7: Avalanche photodetector, 8: Data acquisition card, 9: Computer. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Example 1

[0057] like Figure 1As shown, Embodiment 1 of the present invention provides a calibration-free Raman temperature sensing device for infrastructure safety monitoring, comprising: a pulsed laser 1, a wavelength division multiplexer 2, a first calibration fiber ring 3, a second calibration fiber ring 4, a third calibration fiber ring 5, a sensing fiber 6, an avalanche photodetector 7, a data acquisition card 8, and a computer 9; the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5 are sequentially connected to the sensing fiber 6.

[0058] The pulsed laser emitted by the pulsed laser 1 is sequentially incident on the first calibration fiber ring 3, the second calibration fiber ring 4, the third calibration fiber ring 5, and the sensing fiber 6 after passing through the wavelength division multiplexer 2. The Raman backscattered Stokes light and Raman backscattered anti-Stokes light generated in the sensing fiber 6 are detected by two ports of the avalanche photodetector 7. The output of the avalanche photodetector 7 is connected to the computer 9 via a data acquisition card 8. The data acquisition card 8 can be a high-speed data acquisition card, used for real-time acquisition of the Raman backscattered anti-Stokes light signal and the Raman backscattered Stokes light signal in the sensing fiber. The sensing fiber 6 has a nonlinear parameter greater than 10W. -1 km -1 Nonlinear optical fiber.

[0059] The computer 9 is used to calculate the temperature along the sensing fiber 6 based on the Raman back-stokes light intensity, Raman back-stokes anti-stokes light intensity, and the temperatures of the first calibration fiber ring 3, the second calibration fiber ring 4, the third calibration fiber ring 5, and the sensing fiber 6.

[0060] Specifically, in this embodiment, the temperatures of the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5 are kept constant.

[0061] Specifically, in this embodiment, the output end of the pulsed half-laser 1 is connected to port a of wavelength division multiplexer 2, ports b and c of wavelength division multiplexer 2 are respectively connected to the two input ends of avalanche photodetector 7, port d is connected to one end of the first calibration fiber ring 3, the other end of the first calibration fiber ring 3 is connected to one end of the second calibration fiber ring 4, the other end of the second calibration fiber ring 4 is connected to one end of the third calibration fiber ring 5, the other end of the third calibration fiber ring 5 is connected to one end of the sensing fiber 6, and the output end of avalanche photodetector 7 is connected to high-speed data acquisition card 8.

[0062] Furthermore, the pulsed laser 1 is a pulsed semiconductor laser with a wavelength of 1550nm. The wavelength division multiplexer has port a at the input, and ports b, c, and d at the output, with the following wavelengths: port a is 1550nm, port b is 1450nm, port c is 1650nm, and port d is 1550nm.

[0063] Specifically, in this embodiment, the lengths of the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are all at least twice the spatial length corresponding to the system laser pulse width.

[0064] The principle of distributed temperature demodulation of this invention is described below.

[0065] The calibration-free Raman temperature sensing device for infrastructure safety monitoring in this invention uses backscattering of Raman scattering for temperature demodulation. In the device, the position L of the optical fiber propagation is used as a reference point to acquire the Raman backscattering signal generated in the sensing fiber. The pulsed laser emitted by the 1550nm pulsed laser passes through a wavelength division multiplexer and enters the first calibration fiber ring, the second calibration fiber ring, the third calibration fiber ring, and the sensing fiber, exciting Raman scattering at various points along the entire fiber. During this process, the pulsed laser simultaneously excites a 1450nm Raman backscattering anti-Stokes scattering signal and a 1650nm Raman backscattering anti-Stokes scattering signal. The Raman backscattering signals excited at various points along the sensing fiber return to the wavelength division multiplexer and are output from its b and c ports, where they are detected by an avalanche photodetector. At this time, the intensity of the 1450nm Raman backscattering anti-Stokes scattering signal detected by the avalanche photodetector is:

[0066]

[0067] The intensity of the Raman backscattered Stokes light signal with a wavelength of 1650 nm detected in the avalanche photodetector is:

[0068]

[0069] The expressions for the temperature coefficients in equations (1) and (2) are as follows:

[0070]

[0071]

[0072] Where P is the incident power of the pulsed laser, and K as K sLet represent the coefficients related to the Raman backscattered anti-Stokes light signal and the Raman backscattered Stokes light signal with respect to the scattering cross section, respectively; S is the backscattering factor of the optical fiber; and v as v s Let α0 and α be the frequencies of the Raman backscattered anti-Stokes light signal and the Raman backscattered anti-Stokes light signal, respectively. as α s Δv represents the loss coefficients of the incident light signal, the Raman backscattered anti-Stokes light signal, and the Raman backscattered anti-Stokes light signal in the sensing fiber, respectively; h is Planck's constant; k is Boltzmann's constant; and T is the temperature of the sensing fiber.

[0073] Using formulas (1) and (2), the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered anti-Stokes light signal intensity is:

[0074]

[0075] Traditional Raman temperature demodulation requires placing the entire optical fiber at a constant ambient temperature T0. At a calibration temperature of T0, the Raman backscattered anti-Stokes light signal intensity at a wavelength of 1450 nm detected by an avalanche photodetector is:

[0076]

[0077] The Raman backscattered Stokes light signal intensity at a wavelength of 1650 nm along the entire optical fiber, detected by the avalanche photodetector, is:

[0078]

[0079] The expressions for the temperature coefficients in equations (6) and (7) are as follows:

[0080]

[0081]

[0082] Where P is the incident power of the pulsed laser, and K as K s Let represent the coefficients related to the Raman backscattered anti-Stokes light signal and the Raman backscattered Stokes light signal with respect to the scattering cross section, respectively; S is the backscattering factor of the optical fiber; and v as v s Let α0 and α be the frequencies of the Raman backscattered anti-Stokes light signal and the Raman backscattered anti-Stokes light signal, respectively. as α sThese are the loss coefficients of the incident light signal, the Raman backscattered anti-Stokes light signal, and the Raman backscattered anti-Stokes light signal in the sensing fiber, respectively. Δv is the frequency shift of the Raman scattering signal, h is Planck's constant, k is Boltzmann's constant, and T0 is the constant temperature measured during calibration.

[0083] Using formulas (6) and (7), the ratio of the Raman backward anti-Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity is:

[0084]

[0085] Calculate F using formulas (5) and (10). Back (T,L) and F Back Comparing (T0,L), we can obtain:

[0086]

[0087] From equation (11), the final temperature along the optical fiber can be expressed as:

[0088]

[0089] Where T represents the temperature at the location of the sensing fiber L during measurement, and T0 represents the ambient temperature during calibration. Back (T,L) represents the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered anti-Stokes light signal intensity generated at position L of the sensing fiber by the laser output from the pulsed laser during measurement. F Back (T0,L) represents the ratio of the intensity of the Raman back-stokes calibration light signal generated by the laser output from the pulsed laser at position L of the sensing fiber during calibration to the intensity of the Raman back-stokes calibration light signal, where k is the Boltzmann constant, Δv is the frequency shift of the Raman scattering signal, and h is the Planck constant.

[0090] Analysis of the formula reveals that the traditional Raman distributed fiber optic temperature demodulation method eliminates the influence of factors related to the scattering cross section, the backscattering factor of the fiber, the frequency of the Raman backscattered light signal, the incident light signal, and the loss coefficient of the Raman backscattered light signal in the sensing fiber by comparing the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered anti-Stokes light signal intensity during measurement with the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered light signal intensity during calibration. This allows for accurate demodulation of the temperature to be measured.

[0091] In this invention, a first calibration fiber ring, a second calibration fiber ring, and a third calibration fiber ring are respectively set at the front end of the sensing fiber 6. The length of each ring is at least twice the spatial length corresponding to the system laser pulse width. During measurement, only the temperature of the variable-temperature region (located at a different position from the first, second, and third calibration fiber rings) changes; the non-variable-temperature region of the entire fiber remains under a constant temperature environment. At this time, the scattered signal intensity at various locations along the entire fiber is directly measured. The average intensity of the Raman backscattered anti-Stokes light signal measured at the first, second, and third calibration fiber rings is recorded as Φ. as (L1), Φ s (L1), Φ as (L2), Φ s (L2), Φ as (L3) and Φ s (L3). L1, L2, and L3 represent the positions of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) on the entire fiber, respectively. The average intensity of the Raman backscattered Stokes light signal is related to the sampling rate of the acquisition card. If the sampling rate is 1.0 Gsa / s, that is, one point is collected every 0.1m, and if the length of a ring is 2.0m, then the above average intensity is the average of the intensities of 20 sampling points.

[0092] Based on the known positions of the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5, and the average intensity of the corresponding Raman backscattered anti-Stokes light signal and the average intensity of the Raman backscattered anti-Stokes light signal, corresponding interpolation polynomials can be constructed respectively, that is, the corresponding temperature calibration curves can be fitted. The fitting process is illustrated below by taking the construction of the Raman backscattered anti-Stokes light signal intensity calibration curve as an example.

[0093] The first-order mean difference of an interpolating polynomial is defined as:

[0094]

[0095] Therefore, we can conclude that:

[0096] Φ as (L)=Φ as (L1)+Φ as [L,L1](L-L1); (14)

[0097] The second-order mean difference of an interpolation polynomial is defined as:

[0098]

[0099] Therefore, we can conclude that:

[0100] Φ as [L,L1]=Φ as [L1,L2]+Φ as [L,L1,L2](L-L2); (16)

[0101] Following this logic, we can obtain equation (17):

[0102] Φ as [L,L1,L2]=Φ as [L1,L2,L3]+Φ as [L,L1,L2,L3](L-L3); (17)

[0103] Substituting equation (17) into equation (16), and then substituting equation (16) into equation (14), we get:

[0104]

[0105] Where, Φ as (L1) represents the average intensity of the Raman backscattered anti-Stokes light signal measured at the first calibration fiber loop, Φ as [L1,L2] represents the first-order average difference in the average intensity of the Raman backscattered anti-Stokes light signal at the first and second calibration fiber loops, Φ as [L1,L2,L3] represents the second-order average difference of the average intensity of the Raman backscattered anti-Stokes light signal at the first, second, and third calibration fiber loops, R n (L) represents the interpolation remainder.

[0106] For formula (18), let L = L1, or L = L2, or L = L3, then we can obtain:

[0107] R n (L) = 0; (19)

[0108] Therefore, the final fitted Raman backscattered anti-Stokes light signal intensity calibration curve can be expressed as:

[0109] Φ as (L)=Φ as (L1)+Φ as [L1,L2](L-L1)+Φ as [L1,L2,L3](L-L1)(L-L2); (20)

[0110] Similarly, the final fitted Raman backscattered Stokes light signal intensity calibration curve can be expressed as:

[0111] Φ s (L)=Φs (L1)+Φ s [L1,L2](L-L1)+Φ s [L1,L2,L3](L-L1)(L-L2); (21)

[0112] Where, Φ s (L1) represents the average intensity of the Raman backscattered Stokes light signal measured at the first calibration fiber loop, Φ s [L1, L2] represent the first-order average difference of the average intensity of the Raman backscattered Stokes light signal at the first and second calibration fiber loops, respectively, Φ s [L1,L2,L3] represents the second-order average difference of the average intensity of the Raman backscattered Stokes light signal at the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring.

[0113] Using formulas (20) and (21), the ratio of the Raman backward anti-Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity is:

[0114]

[0115] Then, the temperatures of the environments where the first, second, and third calibration fiber rings are located are measured multiple times, and the average values ​​are recorded as T1, T2, and T3, respectively. The average value can be taken as the calibration temperature T0' of the calibration fiber ring at this time, i.e.

[0116]

[0117] This invention simultaneously measures the intensity of the scattered signal at various locations along the entire optical fiber. Therefore, the coefficients related to the scattering cross-section, the backscattering factor of the optical fiber, the frequency of the Raman backscattered light signal, the incident light signal, and the loss coefficient of the Raman backscattered light signal in the sensing optical fiber are all the same at the same location. Thus, the final temperature demodulation result along the optical fiber can be expressed as follows:

[0118]

[0119] Where T0' represents the calibration temperature, T(L)' represents the temperature at position L of the sensing fiber during measurement, and F Back (T,L) represents the ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered anti-Stokes light signal intensity generated at position L of the sensing fiber by the laser output from the pulsed laser during measurement. F Back(L) represents the ratio of the Raman back-stokes calibration light signal intensity to the Raman back-stokes calibration light signal intensity generated at position L of the sensing fiber by the laser output from the pulsed laser, k is the Boltzmann constant, Δv is the frequency shift of the Raman scattering signal, and h is the Planck constant.

[0120] Therefore, in this embodiment, it is not necessary to place the entire sensing fiber at a constant temperature for calibration. It is only necessary to collect the Raman backward Stokes light signal intensity and Raman backward Stokes light signal intensity at the first calibration fiber ring, the second calibration fiber ring and the third calibration fiber ring during measurement, measure the current ambient temperature, and directly use formula (24) to demodulate the temperature at the sensing fiber L.

[0121] Specifically, it can be seen from formulas (20)-(22) that F Back The formula for calculating (L) is:

[0122]

[0123] Where, Φ as [L1,L2] and Φ s [L1,L2] represents the first-order average difference of the average intensity of the Raman backscattered anti-Stokes and Raman backscattered stokes light associated with positions L1 and L2, Φ as [L1,L2,L3] and Φ s [L1,L2,L3] represents the second-order average difference of the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered signal associated with the first calibration fiber ring, the first calibration fiber ring 4, and the first calibration fiber ring 5, respectively. L1, L2, and L3 represent the positions of the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5 in the entire fiber, respectively. Φ as (L1) and Φ s (L1) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light of the first calibration fiber ring 3, respectively.

[0124] Specifically, it can be seen from formulas (13) and (15) that the Φ as [L1,L2]、Φ as [L1,L2,L3]、Φ s [L1,L2]、Φ s The formulas for calculating [L1, L2, L3] are as follows:

[0125]

[0126]

[0127]

[0128]

[0129] in,

[0130]

[0131]

[0132] Where, Φ as (L2) and Φ s (L2) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light in the second calibration fiber ring 4, respectively. Φ as (L3) and Φ s (L3) represents the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light in the third calibration fiber ring 5, respectively.

[0133] Example 2

[0134] Embodiment 2 of the present invention provides a calibration-free Raman temperature sensing method for infrastructure safety monitoring, employing... Figure 1 The illustrated device is implemented by including the following steps:

[0135] S1. Obtain the temperature values ​​of the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5, and calculate the calibration temperature value T0';

[0136] S2. Obtain the average intensity Φ of the Raman backscattered Stokes light and the Raman backscattered anti-Stokes light at positions L1, L2, and L3 of the first calibration fiber ring 3, the second calibration fiber ring 4, and the third calibration fiber ring 5, respectively. s (L1), Φ as (L1), Φ s (L2), Φ as (L2), Φ s (L3) and Φ as (L3); Simultaneously acquire the Raman backscattered Stokes light and Raman backscattered anti-Stokes light intensity at each position in the sensing fiber 6;

[0137] S3. Calculate the temperature at each location in the sensing fiber 6 using the formulas (24)-(30) from Example 1.

[0138] Specifically, in this embodiment, the environments in which the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are located can be the same or different, but they all remain constant. When their temperatures are different, the formula for calculating the calibration temperature value T0' is as follows:

[0139]

[0140] Where T1, T2, and T3 represent the average temperatures of the environments in which the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are located, respectively.

[0141] In summary, this invention provides a calibration-free Raman temperature sensing device and method for infrastructure safety monitoring. By measuring the Raman backward anti-Stokes light signal intensity and the Raman backward Stokes light signal intensity at the first, second, and third calibration fiber rings, the calibration curve is directly fitted, avoiding the calibration process of placing the entire fiber at a constant temperature before measurement, thus optimizing the system's measurement time. Simultaneously, the signal-to-noise ratio of the system is optimized, ultimately improving the system's sensing distance and temperature measurement accuracy.

[0142] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calibration-free Raman temperature sensing device for infrastructure safety monitoring, characterized in that, include: A pulsed laser (1), a wavelength division multiplexer (2), a first calibration fiber ring (3), a second calibration fiber ring (4), a third calibration fiber ring (5), a sensing fiber (6), an avalanche photodetector (7), a data acquisition card (8), and a computer (9); the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) are connected to the sensing fiber (6) in sequence; The pulsed laser emitted by the pulsed laser (1) is sequentially incident on the first calibration fiber ring (3), the second calibration fiber ring (4), the third calibration fiber ring (5), and the sensing fiber (6) after passing through the wavelength division multiplexer (2). The Raman backscattered Stokes light and the Raman backscattered anti-Stokes light generated in the sensing fiber (6) are detected by the two ports of the avalanche photodetector (7) respectively. The output end of the avalanche photodetector (7) is connected to the computer (9) through the data acquisition card (8). The computer (9) is used to calculate the temperature along the line of the sensing fiber (6) based on the average intensity of the Raman back-stokes and Raman back-stokes in the first calibration fiber ring (3), the second calibration fiber ring (4), the third calibration fiber ring (5) and the sensing fiber (6), as well as the temperatures of the first calibration fiber ring (3), the second calibration fiber ring (4) and the third calibration fiber ring (5); The computer (9) calculates the temperature along the sensing fiber (6) using the following formula: ； in, The frequency shift of the Raman scattering signal, is Planck's constant. Boltzmann's constant, Indicates the calibration temperature. Indicates position L The ratio of the Raman backscattered anti-Stokes light signal intensity to the Raman backscattered Stokes light signal intensity at a given location. Indicates position L The ratio of the Raman backward Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity at the location; The calculation formula is: ； in, and This represents the first-order average difference between the average intensity of the Raman backscattered anti-Stokes light and the average intensity of the Raman backscattered Stokes light at the first and second calibration fiber loops. and The second-order mean difference represents the average intensity difference of the Raman backscattered anti-Stokes light and the Raman backscattered anti-Stokes light at the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring. L 1. L 2. L 3 represents the positions of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) in the entire optical fiber, respectively. and The values ​​represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the first calibration fiber ring (3), respectively.

2. The calibration-free Raman temperature sensing device for infrastructure safety monitoring according to claim 1, characterized in that, The , , , The calculation formulas are as follows: ； ； ； ； in, ； ； in, and Let represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the second calibration fiber loop (4), respectively. and These represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the third calibration fiber ring (5), respectively.

3. The calibration-free Raman temperature sensing device for infrastructure safety monitoring according to claim 1, characterized in that, The temperatures of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) remain constant.

4. A calibration-free Raman temperature sensing device for infrastructure safety monitoring according to claim 1, characterized in that, The lengths of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) are at least twice the spatial length corresponding to the pulse width of the pulse laser.

5. A calibration-free Raman temperature sensing device for infrastructure safety monitoring according to claim 1, characterized in that, The wavelength of the pulsed laser (1) is 1550 nm.

6. A calibration-free Raman temperature sensing method for infrastructure safety monitoring, characterized in that, The device used includes a pulsed laser (1), a wavelength division multiplexer (2), a first calibration fiber ring (3), a second calibration fiber ring (4), a third calibration fiber ring (5), a sensing fiber (6), and an avalanche photodetector (7). The pulsed laser emitted by the pulsed laser (1) is incident sequentially on the first calibration fiber ring (3), the second calibration fiber ring (4), the third calibration fiber ring (5), and the sensing fiber (6) after passing through the wavelength division multiplexer (2). The Raman backscattered Stokes light and the Raman backscattered anti-Stokes light generated in the sensing fiber (6) are detected by the two ports of the avalanche photodetector (7), including the following steps: S1. Obtain the temperature values ​​of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5), and calculate the calibration temperature value. ; S2. Obtain the average intensity of Raman back-stokes and Raman back-stokes in the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5); and simultaneously obtain the intensity of Raman back-stokes and Raman back-stokes at each position in the sensing fiber (6). S3. Calculate the temperature at each location in the sensing fiber (6). The calculation formula is as follows: ； in, The frequency shift of the Raman scattering signal, is Planck's constant. Boltzmann's constant, This represents the ratio of the Raman backscattered anti-Stokes light signal intensity at position L to the Raman backscattered Stokes light signal intensity. This represents the ratio of the Raman backward anti-Stokes calibration light signal intensity to the Raman backward Stokes calibration light signal intensity at position L; The calculation formula is: ； in, and This represents the first-order average difference between the average intensity of the Raman backscattered anti-Stokes light and the average intensity of the Raman backscattered Stokes light at the first calibration fiber loop and the second calibration fiber loop. and The second-order mean difference represents the average intensity difference of the Raman backscattered anti-Stokes light and the Raman backscattered anti-Stokes light at the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring. L 1. L 2. L 3 represents the positions of the first calibration fiber ring (3), the second calibration fiber ring (4), and the third calibration fiber ring (5) in the entire optical fiber, respectively. and The values ​​represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the first calibration fiber ring (3), respectively.

7. A calibration-free Raman temperature sensing method for infrastructure safety monitoring according to claim 6, characterized in that, The , , , The calculation formulas are as follows: ； ； ； ； in, ； ； in, and Let represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the second calibration fiber loop (4), respectively. and These represent the average intensity of the Raman backscattered anti-Stokes light and the Raman backscattered Stokes light at the third calibration fiber ring (5), respectively.

8. A calibration-free Raman temperature sensing method for infrastructure safety monitoring according to claim 6, characterized in that, Calibration temperature value The calculation formula is: ； in, These represent the average temperature of the environments in which the first calibration fiber ring, the second calibration fiber ring, and the third calibration fiber ring are located, respectively.

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