Sensing optical fiber and its fabrication method

Abstract

This invention provides a sensing optical fiber and its fabrication method. The sensing optical fiber includes an optical fiber body and a multilayer coating layer disposed on the outer side of the optical fiber body. The multilayer coating layer includes a heat-resistant layer and at least two buffer layers. The at least two buffer layers are sequentially disposed between the optical fiber body and the heat-resistant layer from the inside out. All buffer layers are made of silicone resin. Along the arrangement direction from the optical fiber body to the heat-resistant layer, the elastic modulus of each buffer layer increases sequentially, and the coefficient of thermal expansion of each buffer layer decreases sequentially. Each buffer layer has a different Poisson's coefficient. The sensing optical fiber and its fabrication method of this invention enable the optical fiber to be highly sensitive to pressure changes under high temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a sensing optical fiber and its manufacturing method. Background Technology

[0002] Fiber optic sensing is a sensing technology that utilizes the scattering of light as it propagates through optical fibers. Fiber optic sensing based on Brillouin scattering can simultaneously measure temperature and strain along a continuous path. However, conventional optical fibers are unusable at temperatures above 200°C. In high-temperature and high-pressure environments, optical fibers with higher temperature resistance, greater pressure sensitivity, and lower transmission loss are required for temperature or pressure sensing in special environments such as oil and gas wells.

[0003] Optical fiber consists of a core, cladding, and coating. Specifically, the cladding is located between the core and the coating, and the coating, as the outermost layer of the optical fiber, protects the core and cladding to enable normal transmission. To allow optical fibers to operate at temperatures above 200°C, existing optical fiber coatings typically use polyimide coatings to withstand these high temperatures.

[0004] However, the coating layer uses a polyimide coating, which is not sensitive enough to pressure. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a sensing optical fiber and its fabrication method, which enables the optical fiber to be highly sensitive to pressure changes even under high temperature conditions.

[0006] This invention provides a sensing optical fiber, comprising an optical fiber body and a multilayer coating layer disposed on the outer side of the optical fiber body. The multilayer coating layer includes a heat-resistant layer and at least two buffer layers. The at least two buffer layers are disposed sequentially from the inside to the outside between the optical fiber body and the heat-resistant layer. All buffer layers are silicone resin material layers. Along the arrangement direction from the optical fiber body to the heat-resistant layer, the elastic modulus of each buffer layer increases sequentially, and the coefficient of thermal expansion of each buffer layer decreases sequentially. Each buffer layer has a different Poisson's coefficient.

[0007] Optionally, at least two buffer layers include a first buffer layer and a second buffer layer arranged adjacent to each other along the arrangement direction from the optical fiber body to the heat-resistant layer. The elastic modulus of the heat-resistant layer is greater than that of the second buffer layer, and the coefficient of thermal expansion of the heat-resistant layer is less than that of the second buffer layer.

[0008] Optionally, each buffer layer is a silicone resin layer, and the heat-resistant layer is a polyimide resin layer.

[0009] Optionally, the elastic modulus of the second buffer layer is 10 times greater than that of the first buffer layer.

[0010] Optionally, the elastic modulus of the first buffer layer is 5-50 MPa, and the coefficient of thermal expansion is 30-50 × 10⁻⁶. -5 / ℃; the elastic modulus of the second buffer layer is 800-1200MPa, and the coefficient of thermal expansion is 5-7×10. -5 / ℃; the elastic modulus of the heat-resistant layer is greater than or equal to 2GPa, and the coefficient of thermal expansion is 2-4×10. -5 / ℃.

[0011] Optionally, the outer diameter of the buffer layer is greater than or equal to 150 μm; the outer diameter of the sensing fiber is greater than or equal to 160 μm; the sensing fiber can withstand a temperature greater than or equal to 200℃, a strain intensity greater than or equal to 100 KPsi, and a Brillouin dispersion frequency shift-pressure coefficient greater than or equal to -0.901 MHz / MPa.

[0012] Optionally, the optical fiber body includes a core layer and a cladding layer, with the cladding layer disposed between the core layer and the buffer layer, and both the core layer and the cladding layer being made of quartz material.

[0013] Optionally, the fiber body is a single-mode fiber with a cladding diameter of 125±1μm, and the fiber body attenuation at a wavelength of 1550nm is less than or equal to 0.5dB / km.

[0014] This invention provides a method for fabricating a sensing optical fiber, the method comprising:

[0015] Provide optical fiber preforms;

[0016] The optical fiber preform is melted and softened before being drawn into fibers to form the optical fiber body;

[0017] The multi-layer coating is sequentially applied to the outer layer of the optical fiber body, and the coating is then cured.

[0018] The sensing fiber is pulled and wound up.

[0019] Optionally, the optical fiber preform is melt-softened and then drawn into fibers, specifically including:

[0020] According to the formula

[0021] Δ V =αcos(R1-R0+π / 2)

[0022] Adjust the speed of the transmission optical fiber preform; where Δ V The value is the adjustment value for the transmission fiber preform speed, α is the correction coefficient, R1 is the actual cladding diameter, and R0 is the target cladding diameter.

[0023] Optionally, the drawing process adopts a low-speed steady-speed traction method, and the traction speed is 15-50m / min.

[0024] Optionally, the multilayer coating is applied by pressure coating, whereby the coating material is applied to the outer layer of the optical fiber body through a feeding section, a pipe, a transition section, and a mold to form a multilayer coating. The feeding section contains the coating material, the pipe is connected between the feeding section and the transition section, and the mold is located in the transition section and distributed on the outer side of the optical fiber body along the same axis as the optical fiber body.

[0025] Optionally, the inner diameter of the pipe is 6-10mm, and 4-6 through holes for the coating material to pass through are evenly provided between the transition section and the mold.

[0026] Optionally, the coating layer includes a first buffer layer, a second buffer layer, and a heat-resistant layer arranged sequentially from the inside out; the coating viscosity of the first buffer layer is 2500-4000 mPa·s; the coating viscosity of the second buffer layer is 1500-3000 mPa·s; the coating viscosity of the heat-resistant layer is 6000-8000 mPa·s; and the coating pressure of the first buffer layer, the second buffer layer, and the heat-resistant layer is 0.05-0.2 MPa.

[0027] Optionally, both the first and second buffer layers are cured by ultraviolet light, and the two layers are cured separately; the heat-resistant layer is cured by heat curing.

[0028] Optionally, the power of the ultraviolet light source is 0.5-2KW, and the irradiation energy obtained by the sensing fiber is 200-500mj / cm². 2 The curing degree is 85%-95%, and the thickness ratio of the first buffer layer and the second buffer layer after curing is 1:1.5-2. The thickness of the first buffer layer and the second buffer layer is greater than or equal to 12.5μm.

[0029] Optionally, the polyimide resin solid content of the heat-resistant layer is 15-25%, the thermosetting temperature is 150-400℃, the heating furnace adopts a staged heating method, and the thickness of the heat-resistant layer after curing is 5-20μm.

[0030] Optional, the take-up tension is 40-70g.

[0031] This invention provides a sensing optical fiber and its fabrication method. The sensing optical fiber includes an optical fiber body and a multilayer coating layer disposed on the outer side of the optical fiber body. The multilayer coating layer includes a heat-resistant layer and at least two buffer layers. The at least two buffer layers are sequentially disposed between the optical fiber body and the heat-resistant layer from the inside out. All buffer layers are made of silicone resin. Along the arrangement direction from the optical fiber body to the heat-resistant layer, the elastic modulus of each buffer layer increases sequentially, and the coefficient of thermal expansion of each buffer layer decreases sequentially. Each buffer layer has a different Poisson's coefficient. The sensing optical fiber and its fabrication method of this invention enable the optical fiber to be highly sensitive to pressure changes under high temperature conditions. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of the sensing optical fiber provided in an embodiment of the present invention;

[0034] Figure 2 This is a schematic flowchart illustrating the method for fabricating a sensing optical fiber according to an embodiment of the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] 100-Sensing fiber optic cable;

[0037] 110 - Optical fiber body;

[0038] 120 - Coating layer;

[0039] 111-Core layer;

[0040] 112-cladding;

[0041] 121-Buffer layer;

[0042] 122 - Temperature-resistant layer;

[0043] 1211 - First Buffer Layer;

[0044] 1212 - Second buffer layer. Detailed Implementation

[0045] To make the above-mentioned objectives, features, and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and 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.

[0046] Optical fiber consists of a core, cladding, and coating. Specifically, the cladding is located between the core and the coating, and the coating, as the outermost layer of the optical fiber, protects the core and cladding to enable normal transmission. To allow optical fibers to operate at temperatures above 200°C, existing optical fiber coatings typically use polyimide coatings to withstand these high temperatures.

[0047] However, the coating layer uses a polyimide coating, which is not sensitive enough to pressure.

[0048] To address the aforementioned problems, this invention provides a sensing optical fiber and its fabrication method. The sensing optical fiber comprises an optical fiber body and multiple coating layers. The elastic modulus of the multiple coating layers increases sequentially, the coefficient of thermal expansion decreases sequentially, and they have different Poisson coefficients. This results in a higher influence of external pressure on the sound field and effective refractive index within the optical fiber body, enabling the sensing optical fiber to be more sensitive to pressure changes even under high temperature conditions.

[0049] The specific content of the present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0050] Optical fiber consists of a core, cladding, and coating. Specifically, the cladding is positioned between the core and the coating, while the coating, as the outermost layer, protects the core and cladding to ensure proper transmission. To enable optical fibers to operate at temperatures above 200°C, existing fiber coatings typically use polyimide coatings to withstand these high temperatures. However, polyimide coatings are not sufficiently sensitive to pressure.

[0051] The sensing optical fiber and its manufacturing method provided by this invention include an optical fiber body and a multilayer coating layer disposed on the outside of the optical fiber body. The multilayer coating layer includes a heat-resistant layer and at least two buffer layers. The at least two buffer layers include a first buffer layer and a second buffer layer. The elastic modulus of the first buffer layer, the second buffer layer and the heat-resistant layer increase sequentially, the coefficient of thermal expansion decreases sequentially, and they have different Poisson coefficients. This makes the influence of external pressure on the sound field and effective refractive index inside the optical fiber body relatively high, so that the sensing optical fiber can be more sensitive to pressure changes under high temperature conditions.

[0052] To enable optical fibers to operate at temperatures above 200°C, existing fiber coatings typically use pure polyimide. However, its high elastic modulus leads to significant transmission loss, and continuous production over long lengths is challenging. According to Lamé's theorem, an optical fiber can be viewed as a multi-layered sleeve structure. Existing ordinary silica optical fibers generally use two coating materials, with adjacent coatings having similar coefficients of thermal expansion and Poisson's ratios. External pressure has a relatively low impact on the acoustic field and effective refractive index within the fiber core, resulting in insufficient Brillouin frequency shift-pressure sensitivity in sensing fibers, thus failing to simultaneously possess both high-temperature resistance and low-loss characteristics.

[0053] Figure 1 This is a schematic diagram of the structure of the sensing optical fiber provided in an embodiment of the present invention. Figure 1 As shown, the sensing fiber 100 includes an optical fiber body 110 and a multilayer coating layer 120 disposed on the outside of the optical fiber body 110. The multilayer coating layer 120 includes a heat-resistant layer 122 and at least two buffer layers 121.

[0054] The optical fiber body 110 serves as the inner structure of the sensing optical fiber 100. It utilizes the scattering effect generated when light propagates within the optical fiber body 110 to transmit signals and perform sensing, featuring high resolution, wide testing range, and high measurement accuracy. The multilayer coating layer 120, disposed on the outer side of the optical fiber body 110, serves as the outer structure of the sensing optical fiber 100, protecting the inner optical fiber body 110 from damage by the external environment.

[0055] Furthermore, when the sensing fiber 100 is used in special environments such as oil and gas wells, where temperatures can typically reach above 200°C, the multilayer coating 120, including a heat-resistant layer 122 and at least two buffer layers 121, can protect the fiber optic body 110 through the heat-resistant layer 122, allowing it to function normally even at temperatures above 200°C. The buffer layers 121 also ensure that the transmission and sensing functions of the fiber optic body 110 are not affected.

[0056] Specifically, at least two buffer layers 121 are sequentially disposed between the optical fiber body 110 and the heat-resistant layer 122 from the inside out. All buffer layers 121 are made of silicone resin material. Along the arrangement direction from the optical fiber body 110 to the heat-resistant layer 122, the elastic modulus of each buffer layer 121 increases sequentially, and the coefficient of thermal expansion of each buffer layer 121 decreases sequentially. Each buffer layer 121 has a different Poisson coefficient.

[0057] It should be noted that the light scattering produced by the interaction between the incident light wave and the elastic sound wave within the medium is Brillouin scattering. Due to acousto-optic modulation, the center frequency of the backscattered Brillouin light will shift from the center frequency of the incident light wave, which is called the Brillouin frequency shift. The Brillouin frequency shift can be expressed by the formula:

[0058] v B =2n eff v α / λ0

[0059] Where, ν B For Brillouin frequency shift, n eff λ is the effective refractive index of the fiber body (110), λ0 is the pump light wavelength, and ν α For longitudinal sound speed, and ν α This can be expressed by a formula:

[0060]

[0061] Where E is the Young's modulus of the optical fiber, γ is the Poisson's ratio, and ρ is the density.

[0062] When the temperature or pressure in the fiber body 110 changes, the longitudinal sound velocity and effective refractive index of the fiber body 110 can be affected, causing the Brillouin frequency to change linearly. This allows the temperature or pressure information of the surrounding mirrors of the fiber body 110 to be demodulated.

[0063] Since at least two buffer layers 121 are sequentially disposed between the optical fiber body 110 and the heat-resistant layer 122 from the inside out, and the buffer layers 121 are all made of silicone resin material; along the arrangement direction from the optical fiber body 110 to the heat-resistant layer 122, the elastic modulus of each buffer layer 121 increases sequentially, and the coefficient of thermal expansion of each buffer layer 121 decreases sequentially. Each buffer layer 121 has a different Poisson's coefficient. The difference in the coefficient of thermal expansion, elastic modulus and Poisson's ratio of the materials between different layers makes the influence of external pressure on the sound field and effective refractive index inside the optical fiber body 110 relatively high, resulting in a strong change in the Brillouin frequency shift of the sensing optical fiber 100. Under the action of the heat-resistant layer 122, the sensing optical fiber 100 can be made more sensitive to pressure changes under high temperature conditions.

[0064] Optionally, at least two buffer layers 121 include a first buffer layer 1211 and a second buffer layer 1212 arranged adjacent to each other along the arrangement direction from the optical fiber body 110 to the heat-resistant layer 122. The elastic modulus of the heat-resistant layer 122 is greater than that of the second buffer layer 1212, and the coefficient of thermal expansion of the heat-resistant layer 122 is less than that of the second buffer layer 1212.

[0065] Specifically, because the elastic modulus of the heat-resistant layer 122 is greater than that of the second buffer layer 1212, and the coefficient of thermal expansion of the heat-resistant layer 122 is smaller than that of the second buffer layer 1212, on the one hand, the external pressure can have a greater impact on the sound field and effective refractive index inside the optical fiber body 110, resulting in a stronger change in the Brillouin frequency shift of the sensing optical fiber 100, and thus making the sensing optical fiber 100 more sensitive to pressure changes. On the other hand, the elastic modulus of the heat-resistant layer 122 is greater than that of the buffer layer 121, making the stiffness of the heat-resistant layer 122 relatively greater than that of the buffer layer 121. During the process of sequentially coating the buffer layer 121 and the heat-resistant layer 122, the stiffness of the outer layer can be gradually increased, making the processing more convenient.

[0066] Optionally, each buffer layer 121 is a silicone resin layer, and the heat-resistant layer 122 is a polyimide resin layer. Specifically, since each buffer layer 121 is a silicone resin layer, it can have a lower surface tension. Furthermore, the heat resistance, water resistance, and air permeability of silicone resin are superior to those of general organic resins, giving the buffer layer 121 better heat resistance, water resistance, and air permeability. Because the heat-resistant layer 122 is a polyimide resin layer, polyimide has a high temperature resistance of up to 400℃, a thermal decomposition temperature of up to 520℃, and a long-term operating temperature of up to 350℃. In special environments such as oil and gas wells, it can better protect the inner optical fiber body 110 and the buffer layer 121 from external environmental influences and damage, ensuring the normal operation of the sensing optical fiber 100.

[0067] Optionally, the elastic modulus of the second buffer layer 1212 is greater than 10 times that of the first buffer layer 1211. Specifically, because the elastic modulus of the second buffer layer 1212 is 10 times greater than that of the first buffer layer 1211, on the one hand, the greater the difference in elastic modulus between the first buffer layer 1211 and the second buffer layer 1212, the greater the impact of external pressure on the acoustic field and effective refractive index within the optical fiber body 110, resulting in a more intense Brillouin frequency shift change in the sensing optical fiber 100, and thus making the sensing optical fiber 100 more sensitive to pressure changes. On the other hand, the stiffness of the second buffer layer 1212 can be significantly greater than that of the first buffer layer 1211, so that the second buffer layer 1212 can better resist breakage damage during long-distance processing, thereby enabling the sensing optical fiber 100 to be processed over long distances.

[0068] As an optional implementation, the elastic modulus of the first buffer layer 1211 is 5-50 MPa, and the coefficient of thermal expansion is 30-50 × 10⁻⁶. -5 / ℃; the elastic modulus of the second buffer layer 1212 is 800-1200MPa, and the coefficient of thermal expansion is 5-7×10. -5 / ℃; the elastic modulus of the heat-resistant layer 122 is greater than or equal to 2GPa, and the coefficient of thermal expansion is 2-4×10. -5 / ℃.

[0069] Specifically, the elastic modulus of the first buffer layer 1211 is 5-50 MPa, and its coefficient of thermal expansion is 30-50 × 10⁻⁶. -5 / ℃, which can prevent the elastic modulus of the first buffer layer 1211 from being too small and the coefficient of thermal expansion from being too large, thus making the first buffer layer 1211 more prone to breakage. At the same time, it can prevent the elastic modulus of the first buffer layer 1211 from being too large and the coefficient of thermal expansion from being too small, thus making the stiffness of the first buffer layer 1211 smaller. After the optical fiber body 110 comes into contact with the first buffer layer 1211, the stress and strain will be smaller, thereby reducing the damage to signal transmission in the optical fiber body 110.

[0070] Because the elastic modulus of the second buffer layer 1212 is 800-1200 MPa and the coefficient of thermal expansion is 5-7 × 10⁻⁶ MPa. -5 / ℃ can give the second buffer layer 1212 greater rigidity, thus enabling it to withstand greater fracture strength during long-distance processing, so that the sensing fiber 100 can be manufactured over long distances.

[0071] Since the elastic modulus of the heat-resistant layer 122 is greater than or equal to 2 GPa, its coefficient of thermal expansion is 2-4 × 10⁻⁴. -5 / ℃ can make the heat-resistant layer 122 more rigid under the high temperature of special external environment, so as to avoid the heat-resistant layer 122 from breaking.

[0072] Optionally, the outer diameter of the buffer layer 121 is greater than or equal to 150 μm; the outer diameter of the sensing fiber 100 is greater than or equal to 160 μm; the length of the sensing fiber 100 is greater than or equal to 20 km; the sensing fiber 100 can withstand a temperature greater than or equal to 200℃, a strain intensity greater than or equal to 100 KPsi, and a Brillouin dispersion frequency shift-pressure coefficient greater than or equal to -0.901 MHz / MPa. Since the outer layer of the optical fiber body 110 is sequentially provided with a first buffer layer 1211, a second buffer layer 1212 and a heat-resistant layer 122, and the elastic modulus and thermal expansion coefficients of the first buffer layer 1211, the second buffer layer 1212 and the heat-resistant layer 122 are all different, the external pressure has a high impact on the sound field and effective refractive index inside the optical fiber body 110, resulting in a strong change in the Brillouin frequency shift of the sensing optical fiber 100. Compared with the conventional sensing optical fiber 100 which only has one layer of polyimide resin, the pressure sensitivity is increased by more than 21%, which makes the sensing optical fiber 100 more sensitive to pressure changes under high temperature conditions.

[0073] Optionally, the optical fiber body 110 includes a core layer 111 and a cladding layer 112, with the cladding layer 112 disposed between the core layer 111 and the buffer layer 121. Both the core layer 111 and the cladding layer 112 are made of quartz. Specifically, since the optical fiber body 110 includes a core layer 111 and a cladding layer 112, and the cladding layer 112 is disposed between the core layer 111 and the buffer layer 121, the cladding layer 112 can further protect the internal core layer 111 to prevent damage to the core layer 111 during signal transmission. Because both the core layer 111 and the cladding layer 112 are made of quartz, the optical fiber body 110 can have better signal transmission capabilities.

[0074] Optionally, the fiber body 110 is a single-mode fiber, the cladding 112 has a diameter of 125±1μm, and the attenuation of the fiber body 110 at a wavelength of 1550nm is less than or equal to 0.5dB / km. Because the fiber body 110 is a single-mode fiber, the cladding 112 has a diameter of 125±1μm, and the attenuation of the fiber body 110 at a wavelength of 1550nm is less than or equal to 0.5dB / km, the signal transmission loss in the fiber body 110 can be reduced during the sensing and signal transmission process of the sensing fiber 100.

[0075] This invention provides a method for manufacturing a sensing optical fiber 100, which is used to manufacture the sensing optical fiber 100. Figure 2 This is a schematic flowchart illustrating the fabrication method of the sensing optical fiber provided in an embodiment of the present invention. Figure 2 As shown, the method for manufacturing the sensing fiber 100 includes:

[0076] Step S101: Provide optical fiber preforms.

[0077] Step S102: After the optical fiber preform is melted and softened, it is drawn into fiber to form the optical fiber body 110.

[0078] Step S103: The multilayer coating layer 120 is sequentially coated onto the outer layer of the optical fiber body 110, and the coating layer 120 is cured.

[0079] Step S104: Pull and retract the sensing fiber optic cable 100.

[0080] Optionally, the optical fiber preform is melt-softened and then drawn into fibers, specifically including:

[0081] According to the formula

[0082] Δ V =αcos(R1-R0+π / 2)

[0083] Adjust the speed of the transmission optical fiber preform; where Δ V The value is the adjustment value for the transmission fiber preform speed, α is the correction coefficient, R1 is the actual cladding 112 diameter, and R0 is the target cladding 112 diameter.

[0084] Specifically, during the process of melting, softening, and drawing the optical fiber preform, the speed of the optical fiber preform is adjusted according to the relationship between the target cladding 112 diameter, the actual cladding 112 diameter, the speed of the optical fiber preform, and the cladding 112 diameter, so that the diameter of the cladding 112 after drawing reaches the target cladding 112 diameter, so that the processed optical fiber body 110 can transmit and sense normally.

[0085] Optionally, the fiber drawing process employs a low-speed, steady-speed traction method, with a traction speed of 15-50 m / min. Specifically, because the fiber drawing process uses a low-speed, steady-speed traction method with a traction speed of 15-50 m / min, it can ensure that the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 are heated uniformly during the curing process, thereby making the performance of the sensing fiber 100 more stable.

[0086] Specifically, after being cleaned with hydrofluoric acid, a gaseous material such as silicon-germanium is introduced into the glass tube. Under high temperature conditions, the gaseous material reacts chemically with the inner wall of the glass tube to form an optical fiber preform. The optical fiber preform is then melted and softened before being drawn into fibers to form the optical fiber body 110. Subsequently, multiple coating layers 120 are sequentially coated onto the outer layer of the optical fiber body 110, and the coating layers 120 are cured to form the sensing optical fiber 100. Because the elastic modulus, coefficient of thermal expansion, and Poisson's ratio are different among the multiple coating layers, the external pressure has a significant impact on the sound field and effective refractive index within the optical fiber body 110, resulting in a strong change in the Brillouin frequency shift of the sensing optical fiber 100, thus making the sensing optical fiber 100 highly sensitive to pressure changes.

[0087] Optionally, the multilayer coating layer 120 is coated by pressure coating. The coating material is coated onto the outer layer of the optical fiber body 110 through a feeding section, a pipe, a transition section and a mold to form the multilayer coating layer 120. The feeding section contains the coating material, the pipe is connected between the feeding section and the transition section, and the mold is located in the transition section and is distributed on the outside of the optical fiber body 110 along the same axis as the optical fiber body 110.

[0088] Specifically, the coating material is placed in the feeding section and transferred to the transition section through the pipeline. When the optical fiber body 110 passes through the mold in the transition section, the coating material in the transition section is coated onto the outer layer of the optical fiber body 110 through the mold, thereby forming the first buffer layer 1211, the second buffer layer 1212 and the heat-resistant layer 122 in sequence.

[0089] Optionally, the inner diameter of the pipe is 6-10mm, and 4-6 through holes for the coating material to pass through are evenly arranged between the transition section and the mold. Specifically, since the inner diameter of the pipe is 6-10mm and 4-6 through holes for the coating material to pass through are evenly arranged between the transition section and the mold, the problem of abnormal flow of the coating material during the coating process caused by the change of the inner diameter of the sensing fiber 100 can be reduced, and air can be fully discharged to ensure that no bubbles are generated in the first buffer layer 1211, the second buffer layer 1212 and the heat-resistant layer 122 after coating.

[0090] As an optional implementation, the coating layer 120 includes a first buffer layer 1211, a second buffer layer 1212, and a heat-resistant layer 122 arranged sequentially from the inside out; the coating viscosity of the first buffer layer 1211 is 2500-4000 mPa·s; the coating viscosity of the second buffer layer 1212 is 1500-3000 mPa·s; the coating viscosity of the heat-resistant layer 122 is 6000-8000 mPa·s; the coating pressure of the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 is 0.05-0.2 MPa, which makes the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 more facilitating flow during the coating process, so that the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 are better coated on the outer layer of the optical fiber body 110.

[0091] Optionally, the first buffer layer 1211 and the second buffer layer 1212 are both cured by ultraviolet light curing, and the two layers are cured separately; the heat-resistant layer 122 is cured by thermosetting.

[0092] Specifically, since both the first buffer layer 1211 and the second buffer layer 1212 are cured using ultraviolet light, on the one hand, automated machine operation can be used to reduce costs and time; on the other hand, no solvent evaporation occurs during the curing process, preventing air pollution. Furthermore, curing the first buffer layer 1211 and the second buffer layer 1212 separately improves their curing effect. Because the heat-resistant layer 122 is cured using thermosetting, the cured heat-resistant layer 122 exhibits better temperature resistance, oil resistance, and aging resistance.

[0093] Optionally, the power of the ultraviolet light source is 0.5-2KW, and the irradiation energy obtained by the sensing fiber 100 is 200-500mj / cm². 2 The curing degree is 85%-95%. After curing, the thickness ratio of the first buffer layer 1211 and the second buffer layer 1212 is 1:1.5-2, and the thickness of the first buffer layer 1211 and the second buffer layer 1212 is greater than or equal to 12.5μm.

[0094] Optionally, the polyimide resin solid content of the heat-resistant layer 122 is 15-25%, the thermosetting temperature is 150-400℃, the heating furnace adopts a staged heating method, and the thickness of the heat-resistant layer 122 after curing is 5-20μm.

[0095] Optionally, the take-up tension is 40-70g. Specifically, because the take-up tension is 40-70g, the sensing fiber 100 can proceed normally during the take-up process, thus avoiding the adverse effects of external tension on the take-up process.

[0096] As can be seen from the above, the working process of the sensing optical fiber 100 and its manufacturing method provided by the present invention is roughly as follows: The sensing optical fiber 100 is formed by providing an optical fiber preform, melting and softening the optical fiber preform and then drawing it into a fiber body 110, and then sequentially coating the outer layer of the fiber body 110 with multiple coating layers 120, and then curing the coating layers 120 to form the sensing optical fiber 100.

[0097] The sensing optical fiber 100 includes an optical fiber body 110 and a multilayer coating layer 120 disposed on the outside of the optical fiber body 110. The optical fiber body 110 includes a core layer 111 and a cladding layer 112. The multilayer coating layer 120 includes a heat-resistant layer 122 and at least two buffer layers 121. The at least two buffer layers 121 include a first buffer layer 1211 and a second buffer layer 1212, and are disposed sequentially from the inside to the outside between the optical fiber body 110 and the heat-resistant layer 122.

[0098] Specifically, along the arrangement direction from the optical fiber body 110 to the heat-resistant layer 122, the elastic modulus of the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 increase sequentially, while the coefficients of thermal expansion of the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 decrease sequentially. Furthermore, the first buffer layer 1211, the second buffer layer 1212, and the heat-resistant layer 122 have different Poisson coefficients. This results in a higher influence of external pressure on the sound field and effective refractive index within the optical fiber body 110, leading to a strong change in the Brillouin frequency shift of the sensing optical fiber 100. This makes the sensing optical fiber 100 more sensitive to pressure changes even under high-temperature conditions.

[0099] The sensing optical fiber and its fabrication method provided by this invention include an optical fiber body and a multilayer coating layer disposed on the outer side of the optical fiber body. The multilayer coating layer includes a heat-resistant layer and at least two buffer layers, which are sequentially disposed between the optical fiber body and the heat-resistant layer from the inside out. All buffer layers are made of silicone resin. Along the arrangement direction from the optical fiber body to the heat-resistant layer, the elastic modulus of each buffer layer increases sequentially, and the coefficient of thermal expansion of each buffer layer decreases sequentially. Each buffer layer has a different Poisson's coefficient. The sensing optical fiber and its fabrication method of this invention enable the optical fiber to be highly sensitive to pressure changes even under high-temperature conditions.

[0100] In the description of this invention, it should be understood that the terms "center," "length," "width," "thickness," "top," "bottom," "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "inner," "outer," "axial," and "circumferential," etc., used to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the indicated position or component must have a specific orientation, or a specific structure and operation, and therefore should not be construed as a limitation of this invention.

[0101] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0102] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0103] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0104] 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 sensing optical fiber, characterized in that, It includes an optical fiber body and a multilayer coating layer disposed on the outside of the optical fiber body; The optical fiber body includes a core layer and a cladding layer, the cladding layer being disposed between the core layer and the multilayer coating layer; the optical fiber body is a single-mode optical fiber, the diameter of the cladding layer is 125±1μm, and the attenuation of the optical fiber body at a wavelength of 1550nm is less than or equal to 0.5dB / km. The multilayer coating includes a first buffer layer, a second buffer layer, and a heat-resistant layer. The first buffer layer and the second buffer layer are sequentially disposed between the optical fiber body and the heat-resistant layer from the inside out. Along the arrangement direction from the optical fiber body to the heat-resistant layer, the elastic modulus of the first buffer layer, the second buffer layer, and the heat-resistant layer increases sequentially, and the coefficient of thermal expansion of the first buffer layer, the second buffer layer, and the heat-resistant layer decreases sequentially. The first buffer layer, the second buffer layer, and the heat-resistant layer have different Poisson coefficients to improve the sensitivity of the sensing optical fiber to pressure changes. The sensing optical fiber can withstand temperatures greater than or equal to 200℃, strain strength greater than or equal to 100KPsi, and Brillouin dispersion frequency shift-pressure coefficient greater than or equal to -0.901MHz / Mpa; the elastic modulus of the second buffer layer is greater than 10 times that of the elastic modulus of the first buffer layer. The core layer and cladding are both made of quartz, the first buffer layer and the second buffer layer are both silicone resin layers, and the heat-resistant layer is a polyimide resin layer.

2. The sensing optical fiber according to claim 1, characterized in that, The elastic modulus of the first buffer layer is 5-50 MPa, and the coefficient of thermal expansion is 30-50 × 10⁻⁶. -5 / ℃; The elastic modulus of the second buffer layer is 800-1200 MPa, and the coefficient of thermal expansion is 5-7 × 10⁻⁶. -5 / ℃; The heat-resistant layer has an elastic modulus greater than or equal to 2 GPa and a coefficient of thermal expansion of 2-4 × 10⁻⁴. -5 / ℃.

3. The sensing optical fiber according to claim 2, characterized in that, The outer diameter of the buffer layer is greater than or equal to 150 μm; The outer diameter of the sensing fiber is greater than or equal to 160 μm.

4. A method for fabricating a sensing optical fiber, characterized in that, The method for fabricating the sensing optical fiber according to any one of claims 1-3 includes: Provide optical fiber preforms; The optical fiber preform is melted and softened before being drawn into fibers to form the optical fiber body; The multilayer coating is sequentially applied to the outer layer of the optical fiber body, and the coating is then cured. The sensing fiber is pulled and wound up; The step of drawing the optical fiber preform into fibers after melting and softening specifically includes: According to the formula D V =αcos(R1-R0+π / 2) Adjust the speed at which the optical fiber preform is transmitted; wherein, the Δ V To transmit the adjustment value of the optical fiber preform speed, α is a correction coefficient, R1 is the actual cladding diameter, and R0 is the target cladding diameter; The coating layer comprises a first buffer layer, a second buffer layer, and a heat-resistant layer arranged sequentially from the inside out; the coating viscosity of the first buffer layer is 2500-4000 mPa·s. The viscosity of the second buffer layer is 1500-3000 mPa·s; The coating viscosity of the heat-resistant layer is 6000-8000 mPa·s; The coating pressure of the first buffer layer, the second buffer layer, and the heat-resistant layer is 0.05-0.2 MPa.

5. The method for fabricating the sensing optical fiber according to claim 4, characterized in that, The drawing process uses a low-speed, steady-speed traction method, with a traction speed of 15-50 m / min.

6. The method for fabricating a sensing optical fiber according to claim 5, characterized in that, The multilayer coating is applied by pressure coating, whereby the coating material is applied to the outer layer of the optical fiber body through a feeding section, a pipe, a transition section, and a mold to form multiple coating layers. The feeding section contains a coating material, the pipe connects the feeding section and the transition section, the mold is located in the transition section and is distributed on the outside of the optical fiber body along the same axis as the optical fiber body.

7. The method for fabricating a sensing optical fiber according to claim 6, characterized in that, The inner diameter of the pipe is 6-10mm, and 4-6 through holes for the coating material to pass through are evenly arranged between the transition section and the mold.

8. The method for manufacturing a sensing optical fiber according to claim 7, characterized in that, Both the first buffer layer and the second buffer layer are cured by ultraviolet light curing, and the two layers are cured separately; The heat-resistant layer is cured by thermosetting.

9. The method for fabricating a sensing optical fiber according to claim 8, characterized in that, The ultraviolet light source has a power of 0.5-2KW, and the sensing fiber receives irradiation energy of 200-500mJ / cm². 2 The curing degree is 85%-95%, and the thickness ratio of the first buffer layer to the second buffer layer after curing is 1:1.5-2. The thickness of the first buffer layer and the second buffer layer is greater than or equal to 12.5μm.

10. The method for fabricating a sensing optical fiber according to claim 9, characterized in that, The polyimide resin solid content of the heat-resistant layer is 15-25%, the thermosetting temperature is 150-400℃, the heating furnace adopts a staged heating method, and the thickness of the heat-resistant layer after curing is 5-20μm.

11. The method for fabricating a sensing optical fiber according to claim 10, characterized in that, The take-up tension is 40-70g.

Images