Double-coating-layer sound wave sensibilization optical fiber and application

Abstract

The invention provides a double-coating-layer sound wave sensitization optical fiber. The double-coating-layer sound wave sensitization optical fiber sequentially comprises a fiber core, a wrapping layer, a first coating layer and a second coating layer from inside to outside. The first coating layer and the second coating layer are made of acrylic resin or epoxy resin materials, the Young modulus of the second coating layer is smaller than that of the first coating layer, and the Poisson's ratio of the second coating layer is higher than that of the first coating layer. The invention also provides an application of the double-coating acoustic wave sensibilization optical fiber in preparation of an optical fiber sensor. The optical fiber structure is modeled, the influence rule of the Poisson's ratio, Young modulus and other parameters of the coating layer material on the optical fiber sound wave detection sensitivity is analyzed, the appropriate material is screened out according to the influence rule, the novel optical fiber with the optimized coating layer structure is prepared, and the sound wave detection sensitivity of the optical fiber can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a double-coated acoustic wave sensitization optical fiber and its application. Background Art

[0002] Fiber-optic distributed acoustic sensing (DAS) technology based on phase-sensitive optical time-domain reflectometer (Φ-OTDR) uses the phase change of light waves when propagating in optical fibers to provide more information. Φ-OTDR sensors have attracted widespread attention due to their advantages such as non-invasiveness, high resolution, high precision, real-time monitoring and wide measurement range. They can play a role in various sensing and monitoring occasions, such as optical fiber communication networks, engineering structure monitoring, environmental monitoring, biomedical applications and other fields, providing technical support and solutions for scientific research and engineering practice, and have broad application prospects.

[0003] The Φ-OTDR system consists of a laser, an optical modulator, an optical fiber, etc. The continuous light wave emitted by the narrow linewidth laser light source is modulated into a sequence of optical pulses by the modulator, the optical pulses are amplified by the erbium-doped fiber amplifier, and then injected into the sensing fiber through a circulator. The back-scattered Rayleigh light generated by the light propagating in the optical fiber is output through the circulator, then received by the photodetector, and collected by the acquisition card. The output of the Φ-OTDR system is a back-scattered Rayleigh curve reflecting time and signal strength. By analyzing and demodulating this curve, changes in the external environment can be reflected.

[0004] At present, in order to reduce noise and improve the sensitivity of the Φ-OTDR system, researchers have proposed many methods. From the perspective of optical fiber structure optimization, Sun Qizhen's team at Huazhong University of Science and Technology developed a hollow cylindrical structure for acoustic wave transduction in 2020 to improve the sensitivity of acoustic wave detection. In the flat frequency response range of 500Hz to 5kHz, the high sensitivity of the device is higher than -112dB (re rad / μPa). In the same year, Rao Yunjiang and others from the University of Electronic Science and Technology proposed, manufactured, and tested a cladding softened fiber (CSF) with a cladding Young's modulus lower than that of a standard single-mode optical fiber (SSMF). When the phosphorus doping concentration is 0.48WT% and the cladding diameter is 80μm, the phase sensitivity of CSF is 22% and 54% higher than that of non-phosphorus-doped optical fiber with a cladding diameter of 80μm and SSMF, respectively. However, the sensitivity improvement of the above scheme is limited.

[0005] Most DAS systems use Figure 1The standard single-mode optical fiber shown in the figure consists of three parts: the core (first layer), the cladding (second layer) and the coating (third layer). Among them, the refractive index of the core is greater than the refractive index of the cladding, and the core and the cladding together form a waveguide structure. The coating is a protective layer of the optical fiber, which plays a role in increasing the mechanical properties and bending resistance of the optical fiber. At present, the mainstream coatings include acrylic resin coatings, polyimide coatings, silicone rubber coatings and metal coatings. Optical fibers with suitable coating materials are selected according to the requirements of different uses, different environments and different fields. However, the coatings of various materials are mostly for the purpose of protecting the core and cladding, and do not enhance their sensitivity in sensing. In fact, many materials will reduce the sensitivity of acoustic wave detection.

[0006] In addition, for sensing systems using fiber interferometers or fiber distributed sensing, the coating of existing optical fibers causes the external strain to be attenuated when it is transmitted to the fiber core, resulting in a decrease in the fiber sensing capability, and ultimately a decrease in the acoustic wave detection sensitivity of the DAS. Therefore, not only for DAS systems, but also for most optical fiber sensing systems, improving the acoustic wave detection sensitivity of the optical fiber itself is also a key technical issue that needs to be solved urgently. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a double-coated acoustic wave sensitization optical fiber and its application. By modeling the optical fiber structure, analyzing the influence of parameters such as the Poisson's ratio and Young's modulus of the coating material on the acoustic wave detection sensitivity of the optical fiber, and thereby screening out suitable materials to prepare a new optical fiber with an optimized coating structure, the acoustic wave detection sensitivity of the optical fiber can be significantly improved.

[0008] The present invention adopts the following technical solutions to solve the above technical problems:

[0009] A double-coated acoustic wave sensitization optical fiber comprises, from the inside to the outside, a core, a cladding, a first coating layer and a second coating layer; the first coating layer and the second coating layer are made of acrylic resin or epoxy resin material, and the Young's modulus of the second coating layer is smaller than that of the first coating layer, and the Poisson's ratio of the second coating layer is higher than that of the first coating layer.

[0010] As one of the preferred embodiments of the present invention, when the acrylic resin material is used as the coating material, its Young's modulus is in the range of 1.5 to 3 GPa, and its Poisson's ratio is in the range of 0.35 to 0.4.

[0011] As one of the preferred embodiments of the present invention, when the epoxy resin material is used as the coating material, its Young's modulus is in the range of 1 to 3 GPa, and its Poisson's ratio is in the range of 0.2 to 0.4.

[0012] As one of the preferred embodiments of the present invention, the radius of the core is 2 to 5 μm.

[0013] As one of the preferred embodiments of the present invention, the radius of the "core+cladding" structure after being coated with the cladding is 61-64 μm.

[0014] As one of the preferred embodiments of the present invention, in the optical fiber structure, the radius of the "core+cladding+first coating layer" structure after coating the first coating layer is 120-180 μm.

[0015] As one of the preferred embodiments of the present invention, in the optical fiber structure, the radius of the structure of "core+cladding+first coating layer+second coating layer" after coating the second coating layer is 146.9-201.5 μm.

[0016] As one of the preferred embodiments of the present invention, when the Young's modulus of the first coating layer is 2.5 Gpa, the Poisson's ratio is 0.35, and the thickness is 117.5 μm, and the Young's modulus of the second coating layer is 2 Gpa, the Poisson's ratio is 0.4, and the thickness is 21.5 μm, the phase sensitivity of the optical fiber is 1.8351, which is an increase of 102.89% to 167.43% compared to the phase sensitivity of the standard single-mode fiber.

[0017] An application of the above double-coated acoustic wave sensitization optical fiber in the preparation of optical fiber sensors, wherein the optical fiber sensors include but are not limited to Φ-OTDR sensors.

[0018] The advantages of the present invention compared to the prior art are:

[0019] The present invention models the optical fiber structure, analyzes the influence of the parameters such as the Poisson's ratio and Young's modulus of the coating material on the acoustic wave detection sensitivity of the optical fiber, and selects suitable acrylic resin and epoxy resin materials to prepare a new optical fiber with an optimized coating structure, which can significantly improve the phase sensitivity and acoustic wave detection sensitivity of the optical fiber (which is proportional to the phase sensitivity). At the same time, it has been experimentally verified that when a two-layer coating structure is set, and the Young's modulus of the outer coating structure (i.e., the second coating) is smaller than the Young's modulus of the inner coating (i.e., the first coating), and the Poisson's ratio of the outer coating structure is higher than that of the inner coating, the sensitivity is higher; in addition, within a certain range, the greater the thickness of the outer coating, the higher the sensitivity of the optical fiber, and when the size of the outer coating is constant, the thicker the inner coating, the higher the sensitivity of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the cross-section structure of a standard single-mode optical fiber;

[0021] Figure 2 It is a schematic diagram of the cross-sectional structure of the double-coated acoustic wave sensitization optical fiber in Examples 1 to 5 of the present invention;

[0022] Figure 3 is a schematic diagram of the force principle of the optical fiber cross section in Experimental Example 1;

[0023] Figure 4 is a result diagram of the effect of the change of Young's modulus of the first coating layer on the sensitivity in Experimental Example 1;

[0024] Figure 5 is a result diagram of the effect of the change of the Young's modulus of the second coating layer on the sensitivity in Experimental Example 1;

[0025] Figure 6 is a graph showing the effect of the change in radius of the first coating layer on sensitivity in Experimental Example 1;

[0026] Figure 7 This is a graph showing the effect of the change in radius of the second coating layer on sensitivity in Experimental Example 1. DETAILED DESCRIPTION

[0027] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0028] Example 1

[0029] A double-coated acoustic wave sensitization optical fiber of this embodiment, such as Figure 2 As shown, from the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer.

[0030] Among them, the first coating layer and the second coating layer are both made of acrylic resin material, and the acrylic resin Young's modulus of the first coating layer structure is 1.6Gpa, and the Poisson's ratio is 0.35, and the acrylic resin Young's modulus of the second coating layer is 1.5Gpa, and the Poisson's ratio is 0.38.

[0031] At the same time, in this embodiment, the core radius is 2μm, and the radius of the core surface after being coated with cladding, first coating layer and second coating layer in sequence is 61μm, 120μm and 146.9μm respectively, that is, the thickness of cladding, first coating layer and second coating layer are 59μm, 59μm and 26.9μm respectively.

[0032] Example 2

[0033] A double-coated acoustic wave sensitization optical fiber of this embodiment, such as Figure 2 As shown, from the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer.

[0034] Among them, the first coating layer is made of epoxy resin material, and the second coating layer is made of acrylic resin material. The epoxy resin Young's modulus of the first coating layer structure is 2Gpa, and the Poisson's ratio is 0.3. The acrylic resin Young's modulus of the second coating layer structure is 1.5Gpa, and the Poisson's ratio is 0.35.

[0035] At the same time, in this embodiment, the core radius is 3μm, and the radius of the core surface after being successively coated with cladding, first coating layer and second coating layer are 62μm, 125μm and 150μm respectively, that is, the thickness of cladding, first coating layer and second coating layer are 59μm, 63μm and 25μm respectively.

[0036] Example 3

[0037] A double-coated acoustic wave sensitization optical fiber of this embodiment, such as Figure 2 As shown, from the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer.

[0038] Among them, the first coating layer is made of epoxy resin material, and the second coating layer is made of acrylic resin material. The epoxy resin Young's modulus of the first coating layer structure is 2.5Gpa, and the Poisson's ratio is 0.35. The acrylic resin Young's modulus of the second coating layer structure is 2Gpa, and the Poisson's ratio is 0.4.

[0039] At the same time, in this embodiment, the core radius is 4.1μm, and the radius of the core surface after being successively coated with the cladding, the first coating layer and the second coating layer are 62.5μm, 180μm, and 201.5μm, respectively, that is, the thickness of the cladding, the first coating layer and the second coating layer are 58.4μm, 117.5μm, and 21.5μm, respectively.

[0040] Example 4

[0041] A double-coated acoustic wave sensitization optical fiber of this embodiment, such as Figure 2 As shown, from the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer.

[0042] Among them, the first coating layer is made of acrylic resin material, and the second coating layer is made of epoxy resin material. The Young's modulus of the epoxy resin in the first coating layer structure is 3Gpa, and the Poisson's ratio is 0.38. The Young's modulus of the epoxy resin in the second coating layer structure is 1Gpa, and the Poisson's ratio is 0.4.

[0043] At the same time, in this embodiment, the core radius is 4.25μm, and the radius of the core surface after being coated with cladding, first coating layer and second coating layer in sequence is 63μm, 160μm and 200μm respectively, that is, the thickness of cladding, first coating layer and second coating layer are 58.75μm, 97μm and 40μm respectively.

[0044] Example 5

[0045] A double-coated acoustic wave sensitization optical fiber of this embodiment, such as Figure 2 As shown, from the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer.

[0046] Among them, the first coating layer and the second coating layer are both made of epoxy resin material, and the epoxy resin Young's modulus of the first coating layer structure is 3Gpa, and the Poisson's ratio is 0.3, and the epoxy resin Young's modulus of the second coating layer is 2Gpa, and the Poisson's ratio is 0.4.

[0047] At the same time, in this embodiment, the core radius is 5μm, and the radius of the core surface after being coated with cladding, first coating layer and second coating layer in sequence is 64μm, 180μm and 201.5μm respectively, that is, the thickness of cladding, first coating layer and second coating layer are 59μm, 116μm and 21.5μm respectively.

[0048] Experimental Example 1

[0049] This experimental example is used to explore the influence of coating material parameters such as Poisson's ratio, Young's modulus, and bulk modulus on the sensitivity of optical fiber acoustic wave detection.

[0050] 1. The influence of Poisson's ratio, Young's modulus and bulk modulus on standard single-mode optical fiber

[0051] A typical optical fiber ( Figure 1 ) consists of a core, cladding, and coating. Usually, this glass waveguide is first coated with a soft elastomer and then a plastic, polymer, or metal sheath to maintain the strength of the fiber. In this experiment, the composition and geometry of the optical fiber remain unchanged. The various parameters of a typical commercial (ITT) single-mode optical fiber are shown in Table 1.

[0052] Table 1 Typical commercial (ITT) single-mode fiber parameters

[0053] Fiber Core Cladding Coating Element <![CDATA[SiO2+GeO2(0.1%)]]> <![CDATA[95%SiO2+5%B2O3]]> Acrylate Radius size (μm) 4.1 62.5 122.5 Young's modulus, E(GPa) 72.45 64.14 2.079 Poisson's ratio, μ 0.17 0.149 0.35～0.4 <![CDATA[Photoelastic coefficient, P 11 > 0.126 / / <![CDATA[Photoelastic coefficient, P 12 > 0.27 / / Refractive index, n 1.458 / /

[0054] Note: The radius of the cladding in Table 1 specifically refers to the radius size of the "core + cladding" structure after the cladding is applied, and the radius of the coating layer is similar.

[0055] like Figure 1 In the cross section of a single-mode fiber shown in , the core is considered to be elastically uniform, its radius is R1, Young's modulus is E1, and Poisson's ratio is μ1. It is covered by another elastic material, the cladding radius is R2 ("core + cladding" structure radius), Young's modulus is E2, and Poisson's ratio is μ2. Similarly, the coating radius is R3 ("core + cladding + coating" structure radius), Young's modulus is E3, and Poisson's ratio is μ3.

[0056] The phase sensitivity of the optical fiber is Therefore, the higher the phase sensitivity of the optical fiber, the greater the phase change obtained when a unit load is applied per unit length.

[0057] Assume that Figure 1The pressure P applied by the standard optical fiber shown is 1Pa, as Figure 3 As shown in the figure, when the optical fiber has no coating layer, the absolute value of its phase sensitivity is 0.2723, which is used as a reference value. At the same time, in the following simulations, it is assumed that the radial stress applied to the enhanced optical fiber is 1Pa.

[0058] Referring to Table 1, for common standard single-mode optical fibers, the absolute value of their phase sensitivity is 0.6862 to 0.9045, which is 152% to 232% higher than the phase sensitivity of optical fibers without coatings. For optical fibers with a general three-layer structure, when the Poisson's ratio and Young's modulus of the coating material remain unchanged, the thicker the coating, the higher the phase sensitivity of the optical fiber; when the Poisson's ratio and radius of the coating material remain unchanged, the smaller the Young's modulus of the coating, the lower the phase sensitivity of the optical fiber; when the Young's modulus and radius of the coating material remain unchanged, the larger the Poisson's ratio of the coating, the lower the phase sensitivity of the optical fiber.

[0059] 2. Influence of Poisson's ratio and Young's modulus on the optical fiber with double-layer coating structure of the present invention

[0060] The acoustic wave sensitizing optical fiber with a double-layer coating structure of the present invention comprises, from the inside to the outside, a core, a cladding, a first coating layer and a second coating layer; the first coating layer and the second coating layer are made of acrylic resin or epoxy resin material, and the Young's modulus of the second coating layer is smaller than the Young's modulus of the first coating layer, and the Poisson's ratio of the second coating layer is higher than the Poisson's ratio of the first coating layer.

[0061] First, in this experiment, the radii of the four layers of the optical fiber core, cladding, first coating layer and second coating layer in the optical fiber are fixed, and the optimal Young's modulus and Poisson's ratio of the first coating layer are selected; then, after determining the Young's modulus and Poisson's ratio of the first coating layer, the optimal material of the second coating layer is selected. In the following simulation, unless otherwise specified, the radius of the fixed optical fiber core and cladding remains unchanged (core radius 4.1μm, cladding radius 62.5μm), and the materials of the two do not change, E1=72.45GPa, μ1=0.17, E2=64.14GPa, μ2=0.149.

[0062] This experimental example first simulates the relationship between the Young's modulus of the first coating layer and the phase sensitivity of the optical fiber at different Poisson's ratios when the radii of the optical fiber core, cladding, first coating layer and second coating layer remain unchanged and R4 is set to 300 μm and the pressure P = 1N.

[0063] The results are as follows Figure 4As shown in the figure, when the Young's modulus of the second coating layer is 2.079GPa, the Young's modulus E3 of the first coating layer increases from 10kPa to 10GPa, and when μ3=0.3, 0.35, and 0.4, the curve first rises sharply to a certain value and then slowly decreases; when μ3=0.45 and 0.499, the curve drops sharply to a certain value and then slowly decreases, so materials with relatively low Poisson's ratio and Young's modulus are selected. Combined with the performance parameters of commonly used materials, two materials, acrylate and epoxy resin, are selected, and their simulation results are shown in Table 2.

[0064] Table 2 Simulation results when acrylate and epoxy resin are used as the first coating layer

[0065] Acrylate Epoxy resin Young's modulus, E(GPa) 1.5～3 1～3 Poisson's ratio, μ 0.35～0.4 0.2～0.4 Phase sensitivity 0.8773～1.1555 0.8773～1.6725

[0066] It can be seen that when "acrylate or epoxy resin" is used as the first coating material, the phase sensitivity of the optical fiber is higher than that of the original coating fiber. Therefore, the following simulation fixes the inner coating layer to use "epoxy resin or acrylate material", and because the Young's modulus and Poisson's ratio of these two materials usually vary in different applications and conditions, the following simulation assumes that "the Young's modulus of the first coating material is 2GPa and the Poisson's ratio is 0.3".

[0067] Next, simulation is performed with the radius of the optical fiber core, cladding, first coating layer and second coating layer unchanged, E3 = 2 GPa, μ3 = 0.3. Relationship between Young's modulus of the second coating layer and optical fiber phase sensitivity at different Poisson's ratios under pressure P = 1N.

[0068] The results are as follows Figure 5 As shown in Figure 3, when the Young's modulus E3 of the first coating layer is 2 GPa and the Poisson's ratio μ3 is 0.3, the Young's modulus E4 of the second coating layer increases from 10 kPa to 10 GPa, and the phase sensitivity of the optical fiber decreases monotonically, so the material with relatively low Poisson's ratio and Young's modulus is still selected. When the above two materials are used as the second coating layer, the simulation results are shown in Table 3.

[0069] Table 3 Simulation results when acrylate and epoxy resin are used as the second coating layer

[0070]

[0071]

[0072] It is known from calculation that when other structural parameters are the same, "the Young's modulus of the second coating layer is less than that of the first coating layer, and the Poisson's ratio is higher than that of the first coating layer", the phase sensitivity of the optical fiber is higher, so the following simulations assume that "the Young's modulus of the first coating layer E2 = 2.5GPa, Poisson's ratio μ2 = 0.35", "the Young's modulus of the second coating layer E3 = 2GPa, Poisson's ratio μ2 = 0.4". When the radius of each layer of the optical fiber structure remains unchanged, the phase sensitivity of the optical fiber reaches 1.1077, which is 22.47% to 61.43% higher than the phase sensitivity of the standard single-mode single fiber.

[0073] Through the above example analysis, it can be seen that reducing the Young's modulus of the optical fiber coating, and the Young's modulus of the first coating layer is higher than that of the second coating layer, and the Poisson's ratio is lower than that of the second coating layer, can significantly improve the acoustic sensitivity of the optical fiber, that is, the acoustic sensitization optical fiber with a double coating structure can be used as an effective means to improve the phase sensitivity and acoustic detection sensitivity of the optical fiber distributed acoustic wave sensing system.

[0074] 3. Influence of Bulk Modulus on the Double-Layer Coating Structure Optical Fiber of the Present Invention

[0075] The material of the four-layer structure of the enhanced optical fiber, its Young's modulus and Poisson's ratio are fixed, and the optimal radius of the first and second coating layers are selected when the core and cladding radii remain unchanged. Specifically, within a certain range, the larger the radius of the second coating layer, the higher the phase sensitivity of the optical fiber, and when the size of the second coating layer is constant, the thicker the first coating layer, the higher the phase sensitivity of the optical fiber.

[0076] The materials of the four layers of the optical fiber core, cladding, first coating layer and second coating layer in the optical fiber have been determined, and the optimal coating layer geometry has been selected. In the following simulation, unless otherwise specified, the radius of the fixed optical fiber core and cladding remains unchanged (core radius 4.1μm, cladding radius 62.5μm), and the four layers of materials do not change, E1 = 72.45GPa, μ1 = 0.17, E2 = 64.14GPa, μ2 = 0.149, E3 = 2.5GPa, μ3 = 0.35, E4 = 2GPa, μ4 = 0.4.

[0077] When the pressure P is 1N and the radius R4 of the second coating layer is 0.5mm, the relationship between the radius of the first coating layer and the phase sensitivity of the optical fiber is as follows: Figure 6 As shown in the figure, when the radius of the first coating layer increases from 62.5 μm to 0.5 mm, the phase sensitivity curve increases monotonically and the slope gradually increases. This shows that when the size of the second coating layer is fixed, the thicker the first coating layer, the higher the phase sensitivity of the optical fiber.

[0078] The materials and dimensions of the core, cladding, and first coating layer are fixed, where R3 = 65 μm. Figure 7The figure shows the relationship between the radius of the second coating layer and the phase sensitivity of the optical fiber when the pressure P = 1N. The radius of the second coating layer increases from 65μm to 0.52mm, and the phase sensitivity curve increases monotonically, but the slope of the curve increases from R4 = 65μm to R4 = 201.5μm, and then decreases, and when R4 = 146.9μm, it has exceeded the phase sensitivity of the standard single-mode optical fiber. Therefore, the radius of the second coating layer is best between 146.9μm and 201.5μm, and a larger size should be selected as much as possible.

[0079] A layer of acrylic ester material or epoxy resin material with a small Young's modulus is thickly coated on the outer layer of the optical fiber cladding as the first coating layer, and a layer of acrylic ester material or epoxy resin with a smaller Young's modulus is thinly coated on the outer layer of the first coating layer as the second coating layer, and the Poisson's ratio of the second coating layer material is higher than that of the first coating layer. At this time, the phase sensitivity of the optical fiber can be significantly improved. Assuming E3 = 2.5GPa, μ3 = 0.35, R3 = 180μm (single layer thickness 117.5μm), E4 = 2GPa, μ4 = 0.4, R4 = 201.5μm (single layer thickness 21.5μm), the phase sensitivity of the optical fiber reaches 1.7979, which is 98.77% to 162.01% higher than the phase sensitivity of the standard single-mode single fiber.

[0080] In addition, it should be noted that the specific calculation method of the phase sensitivity of the present invention is as follows:

[0081] For a cylinder, the strain can be obtained by the following Lame solution:

[0082]

[0083] For m-layer optical fiber, the constant A in the formula i , B i and C i Determined by boundary conditions.

[0084] (1) The radial stress outside the mth layer is equal to the pressure, then:

[0085] σ Rm (r=R m )=-P.

[0086] (2) At the boundary r = r i At , the radial stress of the (i-1)th layer is equal to the radial stress of the i-th layer, then:

[0087]

[0088] (3) At the boundary r = r, the radial displacement of the (i-1)th layer should match the radial displacement of the i-th layer, then:

[0089]

[0090] The radial displacement is:

[0091]

[0092] (4) The total axial force exerted by the end pressure of the composite structure is equal to the stress σ of each layer z The integral sum of , then:

[0093]

[0094] Among them, S i is the cross-sectional area of ​​the i-th layer of material.

[0095] (5) Away from the two ends, the axial strain is equal between the layers, then:

[0096] ε z1 =ε z2 =... =ε zm .

[0097] Combining the above equations, we can get a set of linear equations, from which the pressure sensitivity is calculated as:

[0098]

[0099] Therefore, the phase sensitivity is:

[0100]

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A double-coated acoustic wave sensitization optical fiber, It is characterized in that From the inside to the outside, it includes a core, a cladding, a first coating layer and a second coating layer; the first coating layer and the second coating layer are made of acrylic resin or epoxy resin material, and the Young's modulus of the second coating layer is smaller than the Young's modulus of the first coating layer, and the Poisson's ratio of the second coating layer is higher than the Poisson's ratio of the first coating layer.

2. The double-coated acoustic wave sensitization optical fiber according to claim 1, It is characterized in that When the acrylic resin material is used as a coating material, its Young's modulus ranges from 1.5 to 3 GPa, and its Poisson's ratio ranges from 0.35 to 0.

4.

3. The double-coated acoustic wave sensitization optical fiber according to claim 1, It is characterized in that When the epoxy resin material is used as a coating material, its Young's modulus ranges from 1 to 3 GPa, and its Poisson's ratio ranges from 0.2 to 0.

4.

4. The double-coated acoustic wave sensitization optical fiber according to claim 1, It is characterized in that The radius of the fiber core is 2-5 μm.

5. The double-coated acoustically-sensitized optical fiber according to claim 1, It is characterized in that The radius of the "core+cladding" structure after being coated with the cladding is 61-64 μm.

6. The double-coated acoustically-sensitized optical fiber according to claim 1, It is characterized in that The radius of the "core+cladding+first coating layer" structure after coating the first coating layer is 120-180 μm.

7. The double-coated acoustically-sensitized optical fiber according to claim 1, It is characterized in that The radius of the structure of "core+cladding+first coating layer+second coating layer" after coating the second coating layer is 146.9-201.5 μm.

8. The double-coated acoustic wave sensitization optical fiber according to any one of claims 1 to 7, It is characterized in that When the Young's modulus of the first coating layer is 2.5 Gpa, the Poisson's ratio is 0.35, and the thickness is 117.5 μm, and the Young's modulus of the second coating layer is 2 Gpa, the Poisson's ratio is 0.4, and the thickness is 21.5 μm, the phase sensitivity of the optical fiber is 1.8351, which is an increase of 102.89% to 167.43% compared with the phase sensitivity of the standard single-mode single fiber.

9. Use of the double-coated acoustic wave sensitization optical fiber as claimed in any one of claims 1 to 8 in the preparation of an optical fiber sensor.

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