A Compensation Method for Brillouin Frequency Shift and Power Temperature Strain Coefficients

Abstract

The present invention discloses a method for compensating Brillouin frequency shift and power temperature strain coefficients, belonging to the technical field of optical fiber sensing. The present invention proposes a theoretical derivation method to respectively obtain the relationships between Brillouin frequency shift and power temperature coefficient and strain, and between Brillouin frequency shift and power strain coefficient and temperature; uses this variation relationship to compensate the Brillouin frequency shift and power temperature strain coefficients; and respectively uses the uncompensated and compensated Brillouin sensing coefficients to simultaneously measure temperature and strain. The results show that there are certain differences in the temperature and strain obtained by the two measurement methods, and the temperature difference gradually increases with the increase of the strain in the environment where the optical fiber is located, and the strain difference gradually increases with the increase of the temperature change amount in the environment where the optical fiber is located. Therefore, in actual sensing measurements, the above method can be used to compensate the Brillouin frequency shift and power temperature strain coefficients, which is beneficial to improving the accuracy of simultaneous temperature and strain measurement, and realizes the dynamic change of the Brillouin sensing coefficient with the environment where the sensing optical fiber is located, which is of great significance for distributed optical fiber sensing based on Brillouin scattering.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensing, and particularly to a compensation method for Brillouin frequency shift and power temperature strain coefficients. Background Art

[0002] In addition to the traditional advantages such as high precision, corrosion resistance, and anti-interference, the distributed optical fiber sensing technology based on Brillouin scattering can also achieve long-distance continuous measurement of temperature and strain, and has higher measurement accuracy and spatial resolution compared with other types of optical fiber distributed sensing technologies. Therefore, it has become a research hotspot. It has outstanding technical advantages and broad application prospects in application fields such as power equipment monitoring, submarine cable fault point location, and health status monitoring of major infrastructure construction projects.

[0003] Brillouin frequency shift (BFS) and Brillouin power, as two important parameters of optical fiber sensing, both have a linear relationship with the changes in temperature and strain. Using this relationship, the changes in the environment where the sensing optical fiber is located can be estimated. Although relevant experimental measurements and theoretical derivations have accurately given the temperature and strain coefficients of BFS and power, the obtained sensing coefficients are limited to separately considering the temperature or strain changes in the environment where the optical fiber is located, ignoring the temperature and strain cross-sensitivity problem. In order to improve the measurement accuracy, it is necessary to study the changes in the Brillouin sensing coefficients under the simultaneous action of temperature and strain and compensate for them. Summary of the Invention

[0004] The purpose of the present invention is to provide a compensation method for Brillouin frequency shift and power temperature strain coefficients in order to improve the accuracy of simultaneous temperature and strain measurement.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] Step 1: Obtain the relationship between the Brillouin frequency shift temperature coefficient and the change in strain ε: Brillouin frequency shift strain coefficient and the change in temperature ΔT: Brillouin power temperature coefficient and the change in ε: Brillouin power strain coefficient and the relationship with ΔT:

[0007] Step 2: When ΔT = 0°C and ε = 0 με in the relationship described in Step 1, obtain the uncompensated and Use the uncompensated Brillouin frequency shift and power temperature strain coefficients and the observed changes in Brillouin frequency shift and power to estimate the temperature and strain of the environment where the sensing optical fiber is located;

[0008] Step 3: Substitute the estimated reference values of the environmental temperature and strain of the sensing optical fiber obtained in Step 2 into the relationship obtained in Step 1 to compensate for the Brillouin frequency shift and the temperature and strain coefficients of power, and obtain the true values of the temperature and strain of the environment where the sensing optical fiber is located.

[0009] The present invention provides a method for compensating the Brillouin frequency shift and the temperature and strain coefficients of power. Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: realizing the dynamic change of the Brillouin sensing coefficient with the environment where the sensing optical fiber is located, which is beneficial to improving the accuracy of simultaneous measurement of temperature and strain. Description of the Drawings

[0010] Figure 1 It is a graph showing the relationship between the Brillouin frequency shift temperature coefficient and strain.

[0011] Figure 2 It is a graph showing the relationship between the change amount of the Brillouin frequency shift and the change amount of temperature, where the strain increases by 20 με for every 1 °C increase in temperature.

[0012] Figure 3 It is a graph showing the relationship between the Brillouin frequency shift strain coefficient and temperature.

[0013] Figure 4 It is a graph showing the relationship between the change amount of the Brillouin frequency shift and strain, where the change amount of temperature increases by 1 °C for every 20 με increase in strain.

[0014] Figure 5 It is a graph showing the relationship between the Brillouin power temperature coefficient and strain.

[0015] Figure 6 It is a graph showing the relationship between the change amount of the Brillouin power and the change amount of temperature, where the strain increases by 20 με for every 1 °C increase in temperature.

[0016] Figure 7 It is a graph showing the relationship between the Brillouin power strain coefficient and temperature.

[0017] Figure 8 It is a graph showing the relationship between the change amount of the Brillouin power and strain, where the change amount of temperature increases by 1 °C for every 20 με increase in strain.

[0018] Figure 9 It is a graph showing the relationship between the change amount of temperature and strain obtained when simultaneously measuring temperature and strain using the uncompensated and compensated Brillouin sensing coefficients.

[0019] Figure 10 It is a graph showing the relationship between the change amount of strain and temperature obtained when simultaneously measuring temperature and strain using the uncompensated and compensated Brillouin sensing coefficients. Detailed Embodiment

[0020] The present invention will be further described in detail below in conjunction with the accompanying drawings and through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments.

[0021] The present invention Figure 1 The relationship between the Brillouin frequency shift temperature coefficient and strain shown is carried out according to the following method. In the derivation process, T0 = 20 °C and ε0 = 0 με are involved.

[0022] The Brillouin frequency shift BFS can be expressed as

[0023]

[0024] where n is the refractive index of the optical fiber; V a is the sound velocity in the optical fiber; λ is the wavelength of the incident light; θ is the scattering angle. For ordinary silica optical fibers, the scattered light mainly occurs in the backward direction, so θ = π.

[0025] V a can be expressed as

[0026]

[0027] where E is Young's modulus; μ is Poisson's ratio; ρ is the density of the optical fiber material.

[0028] n, V a , E, μ, ρ are all functions of temperature T and strain ε. Substituting Equation (2) into Equation (1) can further express BFS as

[0029]

[0030] where n(T, ε), E(T, ε), μ(T, ε) and ρ(T, ε) can be expressed as

[0031]

[0032] When the changes in T and ε are small, perform a Taylor expansion of Equation (3) at the points T = T0 and ε = ε0, and obtain

[0033]

[0034] where ΔT = T - T0 is the temperature change amount relative to the reference temperature T0, with the unit of °C; Δε = ε - ε0 is the strain change amount relative to the reference strain ε0, with the unit of με. Equation (5) can be further expressed as

[0035]

[0036] where δv B is the Brillouin frequency shift change amount; is the temperature coefficient of Brillouin frequency shift, with the unit of MHz / ℃; is the strain coefficient of Brillouin frequency shift, with the unit of MHz / με.

[0037] From Equations (5) and (6), we can obtain which is expressed as

[0038]

[0039] where

[0040] Then Equation (7) can be further expressed as

[0041]

[0042] where n T is the temperature coefficient of refractive index; ρ T is the temperature coefficient of density; E T is the temperature coefficient of Young's modulus; μ T is the temperature coefficient of Poisson's ratio.

[0043] When T = T0,

[0044] From Equation (9), to obtain the influence of ε on it is necessary to derive in detail the relationships between n(T0, ε), ρ(T0, ε), E(T0, ε) and μ(T0, ε) and ε. From Equation (4), when T = T0, the relationships between n(T0, ε), ρ(T0, ε), E(T0, ε) and μ(T0, ε) and ε are as follows

[0045]

[0046] where

[0047] Under the premise of the derivation (T = T0), n ε , ρ ε , E ε and μ e in Equation (11) can be expressed as

[0048]

[0049] where

[0050] Substituting Equations (12) and (14) into Equation (13), we can obtain

[0051]

[0052] Substituting Equations (12) and (15) into Equation (11), we can obtain

[0053]

[0054] Substituting Equation (10) and Equation (16) into Equation (9) gives Relationship with Δη

[0055]

[0056] At this time, the BFS is expressed as

[0057] In Equation (17), Δη = ε - ε0, and ε0 = 0με, so Δη = ε. When ε = ε0, Substituting Equation (18) into Equation (17) gives Relationship with ε is as Figure 1 shown. Through fitting calculation, the change trend of under different ε is obtained: From Figure 1 it can be seen that gradually increases with the increase of ε, and when the order of magnitude of strain is 10 5 με, it will cause a large change. The results show that under normal circumstances, ε has little influence on .

[0058] The present invention Figure 2 The relationship diagram of the change of the Brillouin frequency shift variation with the change of the temperature variation shown is obtained from Equation (18), where for every 1°C increase in temperature, the strain increases by 20με. From Figure 2 it can be found that when considering the influence of ε (0 - 1600με) on , the relationship between δv B and ΔT and the relationship between δv and ΔT without considering the influence of ε on B are roughly the same, and the difference between the two δv B varies within the range of approximately 0 - 1MHz. The results show that the compensated also has little influence on δv B . Therefore, when using the Brillouin frequency shift temperature coefficient, there is no need to compensate it according to the actual strain borne by the optical fiber.

[0059] The present invention Figure 3 The relationship between the Brillouin frequency shift strain coefficient and the temperature shown is carried out according to the following method. T0 = 20°C and ε0 = 0με involved in the derivation process.

[0060] can be expressed as

[0061]

[0062] Among them,

[0063] Equation (19) can be expressed as

[0064]

[0065] where n ε is the refractive index strain coefficient; ρ ε is the density strain coefficient; E ε is the Young's modulus strain coefficient; μ ε is the Poisson's ratio strain coefficient.

[0066] In order to obtain the relationship between T and it is necessary to derive in detail and obtain the relationships between n(T, ε0), ρ(T, ε0), E(T, ε0) and μ(T, ε0) and T. When ε = ε0, substituting Equation (10) and Equation (12) into Equation (4) gives

[0067]

[0068] Finally, substituting Equation (15) and Equation (22) into Equation (21) gives the relationship between and ΔT

[0069]

[0070] At this time, BFS is expressed as

[0071] When T = T0, Substituting Equation (24) into Equation (23) can obtain the relationship between and ΔT as Figure 3 shown. Through fitting calculation, the relationship between under different ΔT is obtained: From Figure 3 it can be obtained that gradually increases with the increase of ΔT, and when the order of magnitude of ΔT is 10 5 it will cause a large change in. The results show that the influence of ΔT on is small.

[0072] The present invention Figure 4 The relationship diagram of the change of the Brillouin frequency shift shown with respect to strain is obtained from Equation (24), where for every 20 με increase in strain, the temperature change increases by 1 °C. From Figure 4 it can be found that when considering the influence of ΔT (0 - 80 °C) on the relationship between δv B and ε and when not considering the influence of ΔT on the relationship between δvB The relationship with ε is roughly the same, and the difference between the two δv B varies approximately in the range of 0 - 1 MHz. The results show that after compensation, the influence on δv B is also very small. Therefore, when using the Brillouin frequency shift strain coefficient, there is no need to compensate it according to the actual temperature borne by the optical fiber.

[0073] The present invention Figure 5 The relationship between the Brillouin power temperature coefficient and strain shown is carried out according to the following method. During the derivation process, T0 = 20 °C and ε0 = 0 με are involved.

[0074] According to the Rayleigh scattering power expression, similarly, the expression of the optical fiber Brillouin power can be obtained

[0075] P B = PSα B cW / 2n (25)

[0076] Among them, P is the peak value of the incident pulsed light power; S is the Brillouin scattering backward capture coefficient; α B is the Brillouin scattering loss coefficient; W is the pulse width.

[0077] S and α B can be expressed as

[0078] S = (λ / n) 2 / 4πA eff (26)

[0079]

[0080] Among them, A eff is the effective core area of the optical fiber; K is the Boltzmann constant; T is the absolute temperature.

[0081] n, ρ, V a are all functions of T and ε. Substituting equations (26) and (27) into equation (25), the Brillouin power can be further expressed as

[0082]

[0083] When T and ε change slightly, performing a Taylor expansion of equation (28) at the point of T = T0 and ε = ε0, we get

[0084]

[0085] Equation (29) can be further expressed as

[0086]

[0087] Among them, δPB is the Brillouin power change; is the Brillouin power temperature coefficient, with the unit of % / °C; is the Brillouin power strain coefficient, with the unit of % / με.

[0088] From equations (29) and (30), we can obtain which is expressed as

[0089]

[0090] Substitute the relevant parameters of equations (10) and (16) into equation (31), and we can get the relationship between

[0091]

[0092] At this time, the Brillouin power is expressed as

[0093] In equation (32), Δε = ε - ε0, and ε0 = 0 με, so Δε = ε. When ε = ε0, Substitute equation (33) into equation (32), and we can get the relationship between Figure 5 and ε is as shown in . Through fitting calculation, the change trend of under different ε is obtained: Figure 5 It can be concluded that gradually decreases as ε increases, and when ε changes in the range of (0 - 1600 με) the change range of

[0094] is 0.31 - -0.18 % / °C. Figure 6 The relationship diagram of the change of the Brillouin power change amount shown in the present invention with respect to the change of the temperature change amount is obtained from equation (33), where for every 1 °C increase in temperature, the strain increases by 20 με. From Figure 6 it can be found that when considering the influence of ε on the relationship between δP B and ΔT and when not considering the influence of ε on the relationship between δP B and ΔT differ greatly, and the difference between the two δP B varies in the range of approximately 0 - -40 %. The results show that the compensated also has a great influence on δP B . Therefore, when using the Brillouin power temperature coefficient, it is necessary to compensate it according to the actual strain borne by the optical fiber.

[0095] The present invention Figure 7The relationship between the Brillouin power strain coefficient and temperature shown is carried out as follows. During the derivation process, T0 = 20°C and ε0 = 0 με are involved.

[0096] It can be expressed as

[0097]

[0098] Substitute the relevant parameters of Equation (15) and Equation (22) into Equation (34), and we can get And the relationship with ΔT

[0099]

[0100] At this time, the Brillouin power is expressed as

[0101] When T = T0, Substitute Equation (36) into Equation (35), and we can get And the relationship with ΔT is as Figure 7 Shown. Through fitting calculation, the change trend of under different ΔT: From Figure 7 It can be obtained that Gradually decreases with the increase of ΔT, and ΔT will cause A large change in.

[0102] The present invention Figure 8 The relationship diagram of the change of the Brillouin power variation with strain shown is obtained from Equation (36), where for every 20 με increase in strain, the temperature change increases by 1°C. From Figure 8 It can be found that when considering the influence of ΔT (0 - 80°C) on The relationship between δP B And ε and when not considering the influence of T on The relationship between δP B And ε is significantly different, and the difference between the two δP B Varies within the range of approximately 0 - -40%. The results show that the compensated Has a great influence on δP B Therefore, when using the Brillouin power strain coefficient, it needs to be compensated according to the actual temperature borne by the optical fiber.

[0103] In practical applications, changes in T or ε usually cause simultaneous changes in BFS and Brillouin power, resulting in the cross-sensitivity problem of T and ε in the Brillouin optical fiber sensing system. The changes in BFS and Brillouin power due to ε and T are represented by the matrix equation

[0104]

[0105] It can be seen from Equation (37) that the estimation of T and ε requires the use of the sensing coefficients of BFS and Brillouin power. When Δε and ΔT can be determined conversely through the matrix equation. The Δε r and ΔT r solved by using Equation (38) are regarded as the measured reference values.

[0106]

[0107] Among them, Δε r and ΔT r respectively represent the strain and temperature reference values of the estimated environment where the sensing optical fiber is located, δv B is the change in Brillouin frequency shift, and δP B is the change in Brillouin power.

[0108] The compensated and The Δε t and ΔT t solved by using Equation (39) are regarded as the measured true values.

[0109]

[0110] Among them, Δε t and ΔT t respectively represent the strain and temperature true values of the estimated environment where the sensing optical fiber is located.

[0111] Therefore, when measuring T and ε simultaneously, Δε t -Δε r is the strain error generated by the two measurement methods, and ΔT t -ΔT r is the temperature error generated by the two measurement methods, which can be respectively expressed as

[0112]

[0113] In order to more intuitively observe the influence of the compensated Brillouin sensing coefficient on the measurement of ΔT and Δε, four groups of data of δv B = 10, δP B = 0.1, δv B = 20, δP B = 0.2, δv B = 30, δP B = 0.3, δv B = 40, δP B = 0.4 are given for quantitative description. The Δε r and ΔT rSubstitute into Equations (17), (23), (32), and (35) to obtain the compensated Brillouin coefficient, and then use Equation (41) to obtain Δε t and ΔT t . The Δε t and ΔT t obtained by using the compensated Brillouin coefficient and the Δε r and ΔT r obtained by using the uncompensated Brillouin coefficient have an obvious gap. The reason for this gap is that the strain affects the temperature coefficient, and the temperature coefficient is in dynamic change different from the previous constant; the strain coefficient also changes with the change of temperature.

[0114] The present invention Figure 9 The temperature difference E obtained when simultaneously measuring temperature and strain by using the uncompensated and compensated Brillouin sensing coefficients shown ΔT The relationship diagram of the change with ε is obtained by fitting the results of the above 4 groups of data. From Figure 9 it can be seen that as the ε of the environment where the optical fiber is located increases, E ΔT also becomes larger and larger, which indicates that the ΔT t measured by using the compensated Brillouin coefficient is r larger than the ΔT measured by using the uncompensated Brillouin coefficient.

[0115] The present invention Figure 10 The relationship diagram of the change of the strain difference E obtained when simultaneously measuring temperature and strain by using the uncompensated and compensated Brillouin sensing coefficients shown Δε with ΔT is obtained by fitting the results of the above 4 groups of data. From Figure 9 it can be seen that the Δε t measured by using the compensated Brillouin coefficient is r smaller than the Δε measured by using the uncompensated Brillouin coefficient, and as the ΔT of the environment where the optical fiber is located increases, E Δε also becomes larger and larger.

[0116] The compensation method for the Brillouin frequency shift and the power temperature strain coefficient described in the present invention can improve the sensing accuracy when simultaneously measuring temperature and strain, and is of great significance to the distributed sensing technology based on Brillouin scattering.

[0117] The above is only one implementation manner of the present invention, not all or the only implementation manner. Any equivalent transformation of the technical solution of the present invention adopted by those of ordinary skill in the art by reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. A compensation method for Brillouin frequency shift and power temperature strain coefficients, which can improve the accuracy of simultaneous temperature and strain measurement, is characterized in that, Including the following steps: Step 1: Obtain the temperature coefficient of Brillouin frequency shift and its variation relationship with strain ε: Brillouin frequency shift strain coefficient and its relationship with the temperature change ΔT: Brillouin power temperature coefficient and its variation relationship with ε: Brillouin power strain coefficient and its relationship with ΔT: Step 2: When the relationship described in Step 1 sets ε = 0 με, the uncompensated Brillouin frequency shift temperature coefficient is obtained and the Brillouin power temperature coefficient When the relationship described in Step 1 sets ΔT = 0 °C, the uncompensated Brillouin frequency shift strain coefficient is obtained and the Brillouin power strain coefficient Based on Equation (1), the strain and temperature reference values of the environment where the sensing optical fiber is located can be estimated where, Δε r and ΔT r represent the strain and temperature reference values of the estimated environment where the sensing optical fiber is located respectively, δv B is the change in Brillouin frequency shift, and δP B is the change in Brillouin power; Step 3: Substitute the estimated environmental temperature and strain reference values of the sensing optical fiber obtained in Step 2 into the relationship obtained in Step 1 to compensate the Brillouin frequency shift and the power temperature and strain coefficients. From the formula Obtain the compensated Brillouin frequency shift temperature coefficient From the formula Obtain the compensated Brillouin frequency shift strain coefficient From the formula Obtain the compensated Brillouin power temperature coefficient And from the formula Obtain the compensated Brillouin power strain coefficient Then, based on Equation (2), obtain the true temperature and strain values of the environment where the sensing optical fiber is located; Among them, Δε t and ΔT t respectively represent the true values of the strain and temperature of the environment where the sensing optical fiber is located.

2. The compensation method for Brillouin frequency shift and power temperature strain coefficient according to claim 1, characterized in that: The relationship between the Brillouin frequency shift temperature coefficient and strain in Step 1 can be obtained through the following derivation process. In the derivation process, T0 = 20°C and ε0 = 0 με are involved, and the Brillouin frequency shift BFS is expressed as where n is the refractive index of the optical fiber; V a is the sound velocity in the optical fiber; λ is the wavelength of the incident light; θ is the scattering angle. For ordinary silica optical fibers, the scattered light mainly occurs in the backward direction, so θ = π, and V a is expressed as where E is Young's modulus; μ is Poisson's ratio; ρ is the density of the optical fiber material, and n, V a , E, μ, and ρ are all functions of temperature T and strain ε. Substituting Equation (4) into Equation (3), we get where n(T, ε), E(T, ε), μ(T, ε), and ρ(T, ε) can be expressed as When T and ε change slightly, perform a Taylor expansion of Equation (5) at the points T = T0 and ε = ε0, and we get where ΔT = T - T0 is the temperature change amount relative to the reference temperature T0, with the unit of °C; Δε = ε - ε0 is the strain change amount relative to the reference strain ε0, with the unit of με. Equation (7) is further expressed as Among them, δv B is the change in Brillouin frequency shift; is the temperature coefficient of Brillouin frequency shift, with the unit of MHz / °C; is the strain coefficient of Brillouin frequency shift, with the unit of MHz / με, which can be obtained from Equations (7) and (8) is expressed as Among them, Then Equation (9) is further expressed as where n T is the refractive index temperature coefficient; ρ T is the density temperature coefficient; E T is the Young's modulus temperature coefficient; μ T is the Poisson's ratio temperature coefficient, when T = T0 As can be seen from Equation (11), to obtain the influence of ε on it is necessary to deduce in detail the relationships between n(T0, ε), ρ(T0, ε), E(T0, ε) and μ(T0, ε) and ε. From Equation (6), when T = T0, the relationships between n(T0, ε), ρ(T0, ε), E(T0, ε) and μ(T0, ε) and ε are as follows where When T = T0, n in Equation (13) ε , ρ ε , E ε and μ ε are expressed as where Substitute Equation (14) and Equation (16) into Equation (15) to obtain Substitute Equation (14) and Equation (17) into Equation (13) to obtain Substituting Equation (12) and Equation (18) into Equation (11) gives Relationship with Δε At this time, BFS is expressed as In Equation (19), Δε = ε - ε0, and ε0 = 0με, so Δε = ε. When ε = ε0, Substituting Equation (20) into Equation (19), we can obtain The relationship between and ε. Through fitting calculations, we obtained the variation trend under different ε values:

3. A compensation method for Brillouin frequency shift and power temperature strain coefficient according to claim 1, characterized in that: The relationship between the Brillouin frequency shift strain coefficient and the temperature change ΔT in the first step can be obtained through the following derivation process. In the derivation process, T0 = 20°C and ε0 = 0 με are involved. It can be expressed as where Then Equation (21) is expressed as Among them, n ε is the refractive index strain coefficient; ρ ε is the density strain coefficient; E ε is the Young's modulus strain coefficient; μ ε is the Poisson's ratio strain coefficient. In order to obtain the relationship between T and , it is necessary to derive in detail and obtain the relationships between n(T, ε0), ρ(T, ε0), E(T, ε0) and μ(T, ε0) and T. When ε = ε0, substituting Equation (12) and Equation (14) into Equation (6) gives Finally, substituting Equation (17) and Equation (24) into Equation (23), we can obtain The relationship with ΔT At this time, BFS is expressed as When T = T0, Substituting Equation (26) into Equation (25) gives the relationship between and ΔT. Through fitting calculations, the relationships for different ΔT are obtained as follows:

4. A compensation method for Brillouin frequency shift and power temperature strain coefficient according to claim 1, characterized in that: The relationship between the Brillouin power temperature coefficient and strain in Step 1 can be obtained through the following derivation process. In the derivation process, T0 = 20°C and ε0 = 0 με are involved, and the expression of the fiber optic Brillouin power is P B = PSα B cW / 2n (27) where P is the peak power of the incident pulsed light; S is the Brillouin scattering backward capture coefficient; α B is the Brillouin scattering loss coefficient; c is the speed of light; W is the pulse width, and S and α B are expressed as S = (λ / n) 2 / 4πA eff (28) Among them, A eff is the effective core area of the optical fiber; K is the Boltzmann constant; T is the absolute temperature, and n, ρ, V a are all functions of T and ε. Substituting Equation (28) and Equation (29) into Equation (27), the Brillouin power can be further expressed as When T and ε change slightly, perform a Taylor expansion of Equation (30) at the points T = T0 and ε = ε0, and we get Equation (31) is further expressed as Among them, δP B is the Brillouin power change amount; is the Brillouin power temperature coefficient, with the unit of % / °C; is the Brillouin power strain coefficient, with the unit of % / με, which can be obtained from Equations (31) and (32) as expressed as Substituting the relevant parameters of Equation (12) and Equation (18) into Equation (33), we can obtain and the relationship of Δε At this time, the Brillouin power is expressed as In Equation (34), Δε = ε - ε0, and ε0 = 0με, so Δε = ε. When ε = ε0, Substituting Equation (35) into Equation (34), we can obtain The relationship between and ε. Through fitting calculations, the changing trends under different ε values are obtained as follows: Trends of change:

5. A compensation method for Brillouin frequency shift and power temperature strain coefficient according to claim 1, characterized in that: The relationship between the Brillouin power strain coefficient and the temperature change ΔT in the first step can be obtained through the following derivation process. In the derivation process, T0 = 20°C and ε0 = 0 με are involved. can be expressed as Substituting the relevant parameters of Equation (17) and Equation (24) into Equation (36), we can obtain Relationship with ΔT At this time, the Brillouin power is expressed as When T = T0, Substituting Equation (38) into Equation (37), we can obtain The relationship with ΔT. Through fitting calculations, at different ΔT The changing trend:

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