A dual microcavity fiber optic differential pressure sensor and its manufacturing, sensing measurement method

Abstract

The application discloses a double-microcavity optical fiber differential pressure sensor, which comprises a shell, a diaphragm, a fiber ferrule, an optical fiber and a pressure inlet; the shell comprises two symmetrical cylindrical metal bodies, among the two cylindrical metal bodies, the bottom surfaces close to each other are first bottom surfaces, and the bottom surfaces far away from each other are second bottom surfaces; the center of the first bottom surface is provided with a concave arc surface along the axis direction of the shell; the cavity wall surface of the shell of the double-microcavity optical fiber differential pressure sensor is an arc surface, which can effectively prevent the damage of the diaphragm caused by the excessive deformation of the diaphragm due to the excessive differential pressure value, and plays an overload protection role; the concave surface structure on the surface of the diaphragm can converge the reflected light of the diaphragm, and increase the reflected light intensity; the end surface of the optical fiber is located in a circular hole, which can increase the Fabry-Perot cavity length, improve the spatial frequency and demodulation accuracy; under the condition of the same cavity length, compared with other differential pressure sensors, the sensor of the application reduces the use amount of the pressure sensing medium and the response time of the sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a dual-microcavity fiber optic differential pressure sensor, its manufacturing process, and sensing and measurement methods. Background Technology

[0002] Differential pressure signals, as key characteristic parameters for liquid level and flow measurement, can intuitively reflect the liquid level state and flow velocity within pipelines. Real-time and accurate measurement of differential pressure signals is one of the most important requirements in industry, and differential pressure sensors are among the most common sensors in industry. Differential pressure sensors are mainly used to detect pressure differences in fluids at different locations, and their applications have penetrated into fields such as nuclear power system safety monitoring, petrochemical industry, biomedicine, and civil engineering. In today's industrial field, the most widely used differential pressure sensor is the electronic differential pressure sensor. Based on different sensing principles, electronic differential pressure sensors can be divided into several types, among which capacitive and resistive differential pressure sensors are more common. However, in long-term application, both capacitive and resistive differential pressure sensors have their own shortcomings. For example, capacitive differential pressure sensors, due to their sensing principle, inevitably suffer from problems such as distributed capacitance and parasitic capacitance, which affect their measurement accuracy and response speed. Resistive differential pressure sensors are sensitive to both temperature and pressure simultaneously, and are greatly affected by environmental cross-influences, limiting their measurement accuracy and stability.

[0003] Many industrial sectors (such as energy security, oil and gas storage, and nuclear power system safety monitoring) have an urgent need for differential pressure sensors that can withstand harsh environmental interference, provide high-precision and stable measurements, and are easy to embed. However, traditional electronic differential pressure sensors cannot operate stably and with high precision for extended periods in harsh and unfavorable environments, and they suffer from problems such as temperature drift, poor reliability, and difficulty in installation in confined spaces. In differential pressure measurement, traditional electronic differential pressure sensors are also prone to damage due to overload, resulting in poor reliability and repeatability. Therefore, it is urgent to develop a new type of differential pressure sensor that can solve these problems. Summary of the Invention

[0004] One of the objectives of this invention is, at least, to provide a dual-microcavity fiber optic differential pressure sensor and its manufacturing and sensing measurement methods to overcome the problems existing in the prior art. This sensor is characterized by being insensitive to temperature, resistant to strong electromagnetic interference, flame-retardant and explosion-proof, and having stable performance. It can work stably and with high precision in harsh and severe environments, and has unilateral overload protection capability and high reliability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention includes the following aspects.

[0006] A dual-microcavity fiber optic differential pressure sensor includes: a housing, a diaphragm, a fiber optic ferrule, an optical fiber, and a pressure port; the housing has an internal cavity structure, and the housing includes two symmetrically arranged cylindrical metal bodies, wherein the bottom surfaces of the two cylindrical metal bodies that are close to each other are the first bottom surface, and the bottom surfaces that are far apart from each other are the second bottom surface, and the center of the first bottom surface has a concave arc surface along the axis of the housing.

[0007] The diaphragm is disposed in the middle of the cavity and parallel to the second bottom surface; the second bottom surface is provided with optical fiber mounting holes and pressure-sensing holes communicating with the cavity along the direction of the housing axis; the optical fiber is located inside the optical fiber ferrule, the first ends of the two optical fiber ferrules pass through the optical fiber mounting holes respectively and are symmetrically disposed on the housing, the left and right sides of the diaphragm respectively form a Fabry-Perot cavity with the first end face of the optical fiber, and the pressure-sensing ports are symmetrically disposed at the pressure-sensing holes.

[0008] A circular hole is provided at the bottom of the arc surface, and the circular hole is coaxial with the optical fiber mounting hole. The portion between the diaphragm surface and the arc surface is a first microcavity, and the portion between the bottom of the arc surface and the bottom of the circular hole is a second microcavity. The end face of the optical fiber ferrule is flush with the end face of the optical fiber, and the first end face of the optical fiber ferrule is located at the bottom of the circular hole.

[0009] The dual-microcavity fiber optic differential pressure sensor of this invention inherits the advantages of traditional fiber optic differential pressure sensors, such as intrinsic insulation, low loss, anti-electromagnetic interference, and resistance to high temperature and high pressure. It can work stably and with high precision in harsh and severe environments. The center of the first bottom surface of the cylindrical metal body is provided with an inwardly concave arc surface along the direction of the shell axis, so that the shell cavity wall forms an arc surface structure. This can effectively prevent damage to the diaphragm caused by excessive deformation (plastic deformation) due to excessive differential pressure value, play a role in unilateral overload protection, and improve the reliability and repeatability of the sensor.

[0010] The second microcavity between the bottom of the arc surface and the bottom of the circular hole increases the Fabry-Perot cavity length. At this time, the fiber end face is located at the opening of the circular hole away from the arc surface, that is, the fiber end face is inside the hole of the metal body, which is beneficial to improve the spatial frequency and demodulation accuracy. Compared with other fiber optic differential pressure sensors, with the same cavity length, the dual microcavity fiber optic differential pressure sensor of the present invention can reduce the amount of silicone oil used, reduce the response time of the sensor, and effectively reduce the error caused by the thermal expansion of the pressure-sensing medium (such as silicone oil).

[0011] Preferably, annular plates are symmetrically arranged on the left and right sides of the diaphragm. The annular plates can hold the diaphragm; on the other hand, they are used to adjust the length of the Fabry-Perot cavity. After the arc surface is machined on the first bottom surface, the thickness of the annular plates can be adjusted according to the depth of the arc surface so that the length of the Fabry-Perot cavity meets the design requirements.

[0012] Preferably, the diaphragm is circular or cylindrical in shape. When the diaphragm is cylindrical, the thickness of the central region is greater than the thickness of the edge region. Setting the thickness of the central region to be greater than that of the edge region improves the reliability of the diaphragm and makes the central region less prone to damage during deformation.

[0013] Preferably, the diaphragm has concave surfaces symmetrically arranged on its left and right sides, with the concave surfaces located at the center of the diaphragm. These concave surfaces help to improve the intensity and spectral quality of the reflected light, thereby enhancing the demodulation effect of the dual-microcavity fiber optic differential pressure sensor.

[0014] Furthermore, the concave surface is spherical or nearly spherical. Setting the concave surface as spherical or nearly spherical enables the light reflected from the diaphragm to be reflected back to the optical fiber with a parallel light or focusing effect. Under the same cavity length and the same demodulation conditions, it can increase the intensity of reflected light, reduce the fluctuation of the reflected spectrum, improve the uniformity of light intensity, and thus improve the spectral quality.

[0015] Furthermore, the first end face of the optical fiber is located at the focal point of the concave surfaces on both sides of the diaphragm. Because the first end face of the optical fiber is located at the focal point of the concave surfaces on both sides of the diaphragm, it can receive more reflected light compared to other locations, thus improving spectral quality.

[0016] Furthermore, the diameter of the diaphragm is the same as the diameter of the shell, and the effective diameter d2 of the diaphragm is less than 10 cm; the length of the first microcavity is not greater than the length of the second microcavity, and the sum L of the lengths of the first and second microcavities satisfies 10 μm. <L<5cm。

[0017] In sensor manufacturing, the diaphragm functions to sense pressure and deform, thereby altering the cavity length, as well as to converge incident light and increase reflected light intensity. If the actual diaphragm material and processing technology meet the required precision and stability, the two sides of the diaphragm can be directly processed into curved surfaces or near-planar curved surfaces with infinite diameter. Alternatively, based on parameters such as cavity diameter and length range, the diaphragm sides can be designed in the desired shape to maximize reflected light intensity.

[0018] This invention also provides a method for manufacturing a dual-microcavity fiber optic differential pressure sensor, comprising the following steps:

[0019] Step 1: Pass the optical fiber through the fiber optic ferrule, making its end face extend beyond the end face of the fiber optic ferrule, and use high-temperature and high-pressure resistant adhesive to fix the optical fiber and the fiber optic ferrule.

[0020] Step 2: Cut off the portion of the optical fiber that extends beyond the fiber ferrule end face, and polish both the fiber end face and the fiber ferrule end face together.

[0021] Step 3: Drill a fiber optic mounting hole through the cylindrical metal body along the axial direction at the center of the cylindrical metal body, and drill a pressure hole through the cylindrical metal body at a certain distance from the axis of the cylindrical metal body.

[0022] Step 4: Use milling to machine an arc surface at the center of the first bottom surface of the cylindrical metal body;

[0023] Step 5: Pass the polished fiber optic ferrule through the fiber mounting hole of the cylindrical metal body, with the insertion direction from the second bottom surface to the first bottom surface; fill the bottom of the arc surface with low-temperature glass solder, use a sintering process to fix the fiber optic ferrule to the metal body, and polish the entire metal body.

[0024] Step 6: Drill a circular hole at the center of the bottom of the arc surface, with the first end face of the optical fiber at the bottom of the circular hole, and measure and record the distance between the first end face of the optical fiber and the first bottom surface of the metal body;

[0025] Step 7: Clamp the two annular plates on both sides of the diaphragm, and clamp the two metal bodies made in steps 3 to 6 on the surface of the annular plates, with the first bottom surface of the metal bodies adhering to the surface of the annular plates. At this time, the end face of the optical fiber is facing the center of the diaphragm. Use laser welding to weld the diaphragm, annular plates and metal bodies together, and ensure the sealing after welding.

[0026] Step 8: Weld the pressure interfaces to the pressure inlet holes on the left and right ends of the housing using laser welding, which will serve as the input ports for the pressure input medium.

[0027] If the actual processing accuracy and stability meet the requirements, steps one and two are omitted, and the optical fiber is directly inserted from the optical fiber mounting hole of the cylindrical metal body in step five.

[0028] The order of steps five and six can be interchanged. During the processing, a circular hole is first machined at the bottom of the arc surface, and then the optical fiber is inserted into the optical fiber mounting hole so that the first end face of the optical fiber is at the bottom of the circular hole.

[0029] In sensor manufacturing, fiber optic ferrules serve to protect the optical fiber and calibrate its position. However, if the actual manufacturing process requires sufficient precision and stability, fiber optic ferrules may not be necessary. Instead, a fiber optic mounting hole can be machined directly through the cylindrical metal body along its axial direction at the center, allowing the fiber to be inserted directly.

[0030] The present invention also provides a sensing and measurement method for a dual-microcavity fiber optic differential pressure sensor employing any of the above-described structures, comprising the following steps:

[0031] Step 1: Connect the two single-mode optical fibers to the spectral demodulator respectively. Without input pressure, use the demodulator to obtain the Fabry-Perot cavity lengths L1 and L2 on the left and right sides of the diaphragm respectively.

[0032] Step 2: Input two pressure values, P1 and P2, of different magnitudes into the differential pressure sensor through two pressure ports, and record the change in cavity length as ΔL. P差 ;

[0033] Step 3: Based on the change in cavity length ΔL P差 The formula corresponding to the pressure difference ΔP is:

[0034]

[0035] The difference ΔP between the two pressures experienced by the differential pressure sensor at this time is obtained.

[0036] In summary, by adopting the above technical solution, the present invention has at least the following beneficial effects:

[0037] By setting an inwardly concave arc surface at the center of the first bottom surface along the axis of the housing, the cavity wall of the housing forms an arc surface structure, which can effectively prevent damage to the diaphragm caused by excessive deformation (plastic deformation) due to excessive differential pressure, thus playing an overload protection role and improving the reliability and repeatability of the sensor.

[0038] By setting a circular hole at the center of the bottom of the arc surface, with the circular hole coaxial with the optical fiber mounting hole, the portion between the diaphragm surface and the bottom of the arc surface is the first microcavity, and the portion between the bottom of the arc surface and the bottom of the circular hole is the second microcavity; the optical fiber end face is located at the opening of the circular hole away from the arc surface (bottom of the circular hole), and the optical fiber end face is not flush with the inner wall of the metal body but is located inside the hole of the metal body, which can increase the length of the Fabry-Perot cavity, improve the spatial frequency and demodulation accuracy; compared with other optical fiber differential pressure sensors, with the same cavity length, the dual microcavity optical fiber differential pressure sensor of the present invention can reduce the amount of silicone oil used, reduce the response time of the sensor, and effectively reduce the error caused by the thermal expansion of the pressure-sensing medium (e.g., silicone oil).

[0039] By symmetrically setting concave surfaces at the center of both sides of the diaphragm, the concave surfaces are spherical or nearly spherical, and the light reflected by the diaphragm can be reflected back to the optical fiber with parallel light or focusing effect. Under the same cavity length and the same demodulation conditions, the intensity of reflected light can be increased, the fluctuation of the reflected spectrum can be reduced, the uniformity of light intensity can be improved, and thus the spectral quality can be improved. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the dual-microcavity fiber optic differential pressure sensor structure according to an exemplary embodiment of the present invention.

[0041] Figure 2This is a demodulation result diagram of the dual microcavity fiber optic differential pressure sensor of an exemplary embodiment of the present invention with a cavity length of 100 μm.

[0042] Figure 3 This is a demodulation result diagram of the dual microcavity fiber optic differential pressure sensor of an exemplary embodiment of the present invention with a cavity length of 200 μm.

[0043] Figure 4 This is an experimental result of the response time of a 200µm ordinary microcavity structure fiber optic differential pressure sensor.

[0044] Figure 5 This is an experimental result of the response time of the 200µm dual-microcavity fiber optic differential pressure sensor according to an exemplary embodiment of the present invention.

[0045] Figure 6 This is a graph showing the reflected light intensity of a dual-microcavity fiber optic differential pressure sensor according to an exemplary embodiment of the present invention.

[0046] Figure 7 This is a schematic diagram of a membrane structure according to another exemplary embodiment of the present invention.

[0047] Figure 8 This is a schematic diagram illustrating the manufacturing process of a dual-microcavity fiber optic differential pressure sensor according to an exemplary embodiment of the present invention.

[0048] The diagram is labeled as follows: 1-shell, 11-first bottom surface, 12-second bottom surface, 13-arc surface, 14-circular hole, 2-diaphragm, 3-ring plate, 4-fiber ferrule, 5-fiber, 6-pressure port, 7-first microcavity, 8-second microcavity. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so that the objectives, technical solutions, and advantages of the present invention will be clearer. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0050] Figure 1The present invention illustrates a dual-microcavity fiber optic differential pressure sensor structure, comprising a housing 1, a diaphragm 2, an annular plate 3, a fiber optic ferrule 4, an optical fiber 5, and a pressure port 6. The housing 1 has an internal cavity structure and includes two symmetrically arranged cylindrical metal bodies. The bottom surfaces of the two cylindrical metal bodies that are close to each other are designated as a first bottom surface 11, and the bottom surfaces that are far apart are designated as a second bottom surface 12. The diaphragm 2 is located in the center of the cavity and is parallel to the second bottom surface 12. An optical fiber mounting hole communicating with the cavity is provided at the center of the second bottom surface 12 along the axis of the housing. The fiber optic ferrule 4 passes through the optical fiber mounting hole, and the single-mode optical fiber 5 is located inside the fiber optic ferrule 4. The first end face of the optical fiber 5 is flush with the first end face of the fiber optic ferrule 4. The left and right sides of the diaphragm 2 respectively form Fabry-Perot cavities with the first end faces of the optical fiber 5. Without pressure, the Fabry-Perot cavities on the left and right sides of the diaphragm 2... The cavities are of equal length; a pressure-inducing hole is also provided on the second bottom surface 12 to connect the cavity, and a pressure-inducing port 6 is connected to the pressure-inducing hole. The pressure-inducing port 6 is separated from the fiber optic ferrule 4 by a certain distance. During the operation of the differential pressure sensor, the pressure-inducing port and the fiber optic ferrule do not interfere with each other; a concave arc surface 13 is provided at the center of the first bottom surface 11 along the axis of the housing. The shape and size of the arc surface 13 are determined according to the size of the diaphragm 2 and the shape of the diaphragm when it deforms. When the pressure difference between the left and right Fabry-Perot cavities of the diaphragm 2 reaches the threshold, the deformation of the diaphragm 2 reaches a certain degree and directly contacts the arc surface 13 of the Fabry-Perot cavity on the side with lower pressure. When the diaphragm 2 is in contact with the arc surface 13, the diaphragm 2 no longer deforms. Therefore, it can effectively prevent the damage to the diaphragm caused by excessive deformation (plastic deformation) due to excessive differential pressure value, play an overload protection role, and thus improve the reliability of the differential pressure sensor. Compared with traditional fiber optic differential pressure sensors, the arc surface 13 can reduce the volume of the Fabry-Perot cavity and the volume of the pressure-sensing medium under the same cavity length, thereby reducing the error caused by the thermal expansion of the pressure-sensing medium during the use of the differential pressure sensor, and thus reducing the measurement error of the sensor.

[0051] The diaphragm 2 is circular, with the same diameter as the housing 1. The diaphragm 2 is made of the same material as the housing 1, and both have the same coefficient of thermal expansion, which facilitates welding and ensures the sealing of the differential pressure sensor. The effective diameter d2 (the diameter occupied by the working part of the diaphragm) of the diaphragm 2 meets the requirement of d2<10cm, and the thickness h of the diaphragm 2 meets the requirement of h<10mm. The working wavelength λ of the optical fiber 5 is 1550nm. The pressure input medium of the pressure port 6 is air or silicone oil.

[0052] On the left and right sides of the diaphragm 2, annular pieces 3 are symmetrically arranged. The material of the annular piece 3 is the same as that of the diaphragm 2. The outer diameter of the annular piece 3 is equal to the diameter of the diaphragm 2, and the inner diameter is determined according to the design and processing requirements. The housing 1, the diaphragm 2 and the annular piece 3 are welded together by laser welding. On the one hand, the annular piece 3 is used to clamp the diaphragm 2; on the other hand, the annular piece 3 is used to adjust the cavity length of the Fabry-Perot cavity. After the arc surface 13 is machined on the first bottom surface 11, the thickness of the annular piece can be adjusted according to the depth of the arc surface 13, so that the cavity length of the Fabry-Perot cavity meets the design requirements.

[0053] As a preferred embodiment of the present invention, a circular hole 14 is further provided at the center of the bottom of the arc surface 13. The circular hole 14 is coaxial with the optical fiber installation hole, and the diameter d1 is not less than the diameter of the optical fiber installation hole, d1 < 5 cm. The depth of the circular hole 14 is determined according to the design requirements of the Fabry-Perot cavity. The end face of the first end of the optical fiber ferrule 4 is located at the position of the hole opening of the circular hole 14 away from the arc surface 13. When the circular hole 14 is provided at the center of the bottom of the arc surface 13, the end faces of the first ends of the optical fiber ferrule 4 and the optical fiber 5 are at the bottom of the circular hole 14, and the part between the surface of the diaphragm 2 and the arc surface 13 is the first microcavity 7 (when the circular hole 14 is not provided on the double-microcavity optical fiber differential pressure sensor, the first microcavity 7 is the original Fabry-Perot cavity). The part between the bottom of the arc surface 13 and the bottom of the circular hole 14 (the hole opening position of the circular hole away from the arc surface) is the second microcavity 8, and the length of the first microcavity 7 is not greater than the length of the second microcavity 8.

[0054] The second microcavity 8 formed by the circular hole 14 increases the Fabry-Perot cavity length. The first microcavity 7 and the second microcavity 8 are combined to form a new Fabry-Perot cavity. The sum L of the lengths of the first microcavity 7 and the second microcavity 8 satisfies 10um < L < 5 cm (when the circular hole 14 is not provided at the bottom of the arc surface 13, the lengths of the original Fabry-Perot cavities on the left and right sides of the diaphragm 2 also satisfy 10um < L < 5 cm). Increasing the Fabry-Perot cavity length through the second microcavity 8 is beneficial to improving the spatial frequency and the demodulation accuracy of the sensor; compared with the traditional optical fiber differential pressure sensor, under the same cavity length, the cavity volume of the differential pressure sensor of the present invention is smaller, so the usage amount of the pressure-sensing medium can be reduced, and the response time of the sensor can be reduced. Refer to Figure 4 、 Figure 5 , at the same 200um cavity length, the average response time of the optical fiber differential pressure sensor with a common microcavity structure is 0.128 s, and the average response time of the double-microcavity optical fiber differential pressure sensor of the present invention is 0.120 s. The double-microcavity optical fiber differential pressure sensor of the present invention has a faster response time. Figure 2 和 Figure 3 Figures and are respectively schematic diagrams of the demodulation results of the double-microcavity optical fiber differential pressure sensor at different cavity lengths. It can be seen that when the cavity length increases, the fluctuation of the reflection spectrum decreases, and the demodulation accuracy of the sensor increases.

[0055] In a preferred embodiment of the present invention, concave surfaces are symmetrically arranged on the left and right sides of the diaphragm 2, with the concave surfaces located at the center of the diaphragm 2. The concave surfaces are spherical or nearly spherical, and their dimensions (chord length and depth) are on the order of micrometers. The chord length and depth of the concave surfaces are determined according to the designed focal length of the concave mirror. The concave surfaces can reflect the reflected light from the diaphragm 2 back into the optical fiber 5 with parallel light or a focusing effect, which is beneficial for improving the intensity and uniformity of the reflected light, thereby reducing the fluctuation of the reflected spectrum and improving the spectral quality. When the first end face of the optical fiber is located at the focal point of the concave surfaces on both sides of the diaphragm (i.e., the focal length is equal to the length of the Fabry-Perot cavity), the reflected light intensity is strongest. (Reference) Figure 6 Under the same cavity length and demodulation conditions, the reflected light intensity of the concave diaphragm is significantly improved compared to the diaphragm without a concave structure. When the dual-microcavity fiber optic differential pressure sensor of this invention employs... Figure 1 When making the diaphragm shown, depending on the diaphragm material, processing precision, and stability requirements, the two sides or the center of the two sides of the diaphragm can be directly processed into arc surfaces, or the diameter of the arc surface can be made infinitely large so that the arc surface of the diaphragm becomes a near-planar structure.

[0056] refer to Figure 7 The dual-microcavity fiber optic differential pressure sensor of the present invention can also employ the diaphragm shown in the figure. The diaphragm has an overall cylindrical structure, with the thickness of the central region being greater than that of the edge region. Symmetrically arranged concave surfaces are located at the center of both sides of the diaphragm. These concave surfaces are spherical or nearly spherical, with dimensions on the order of micrometers. The chord length and depth of the concave surfaces are determined based on the designed focal length of the concave mirror. Because the thickness of the central region of the diaphragm is greater than that of the edge region, the concave surfaces do not affect the reliability of the diaphragm when it deforms due to differential pressure. During the use of the sensor, the appropriate materials for the housing and diaphragm can be selected according to the environment in which the sensor is used, making the sensor suitable for various harsh and severe environments (e.g., electromagnetic interference environments, high temperature and high pressure environments, flammable and explosive environments, etc.).

[0057] The manufacturing process of the dual-microcavity fiber optic differential pressure sensor of the present invention is as follows: Figure 8 As shown:

[0058] Step 1: Pass the optical fiber through the fiber optic ferrule, making its end face extend beyond the end face of the fiber optic ferrule, and use high-temperature and high-pressure resistant adhesive to fix the optical fiber and the fiber optic ferrule.

[0059] Step 2: Cut off the portion of the optical fiber that extends beyond the fiber ferrule end face, and polish both the fiber end face and the fiber ferrule end face together.

[0060] Step 3: At the center of the cylindrical metal body, a fiber optic mounting hole is machined along the axial direction, penetrating the cylindrical metal body. The diameter of the fiber optic mounting hole is slightly larger than the outer diameter of the fiber optic ferrule. A pressure-applying hole is also machined at a certain distance along the axis of the cylindrical metal body.

[0061] Step 4: Use milling to machine an arc surface at the center of the first bottom surface of the cylindrical metal body;

[0062] Step 5: Pass the polished fiber optic ferrule through the fiber mounting hole of the cylindrical metal body, with the insertion direction from the second bottom surface to the first bottom surface; fill the bottom of the arc surface with low-temperature glass solder, use a sintering process to fix the fiber optic ferrule to the metal body, and polish the entire metal body.

[0063] Step 6: Drill a circular hole at the center of the bottom of the arc surface, with the fiber end face at the bottom of the circular hole, and measure and record the distance between the first end face of the fiber and the first bottom surface;

[0064] Step 7: Clamp the two annular plates on both sides of the diaphragm, and clamp the two metal bodies made in steps 3 to 6 on the surface of the annular plates, with the first bottom surface of the metal bodies adhering to the surface of the annular plates. At this time, the end face of the optical fiber is facing the center of the diaphragm. Use laser welding to weld the diaphragm, annular plates and metal bodies together, and ensure the sealing after welding.

[0065] Step 8: Weld the pressure interfaces to the pressure inlet holes on the left and right ends of the housing using laser welding, which will serve as the input ports for the pressure input medium.

[0066] The differential pressure measurement process of the dual-microcavity fiber optic differential pressure sensor of the present invention is as follows:

[0067] 1. Connect the two single-mode optical fibers to the spectral demodulator respectively. Without input pressure, use the demodulator to obtain the Fabry-Perot cavity lengths L1 and L2 on the left and right sides of the diaphragm respectively.

[0068] 2. Two pressure values, P1 and P2, of different magnitudes are input into the dual-microcavity fiber optic differential pressure sensor through two pressure inlets. Because the two pressure values ​​are different, the diaphragm deforms under the influence of the differential pressure, bulging out on the side with the smaller pressure value. Therefore, the cavity lengths of the Fabry-Perot cavities on both sides of the diaphragm change, and the amount of change in cavity length is the same on both sides. This change in cavity length is denoted as ΔL. P差 ;

[0069] 3. Based on the change in cavity length ΔL P差 The formula corresponding to the pressure difference ΔP is:

[0070]

[0071] The difference in pressure ΔP between the two pressures acting on the differential pressure sensor can be calculated. In the formula, μ and E represent the Poisson's ratio and Young's modulus of the diaphragm, respectively, n is the refractive index of the pressure-sensing medium in the Fabry-Perot cavity, R is the radius of the Fabry-Perot cavity, and h is the thickness of the diaphragm. Based on this principle, dual-microcavity fiber optic differential pressure sensors with different sensitivities and measurement ranges can be designed by changing the diaphragm thickness and effective radius.

[0072] The above description is merely a detailed illustration of specific embodiments of the present invention and is not intended to limit the invention. Various substitutions, modifications, and improvements made by those skilled in the art without departing from the principles and scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-microcavity fiber optic differential pressure sensor, characterized in that, include: The shell (1), diaphragm (2), fiber optic ferrule (4), fiber (5) and pressure port (6); the shell (1) has a cavity structure inside, and the shell (1) includes two symmetrically arranged cylindrical metal bodies. Among the two cylindrical metal bodies, the bottom surface that is close to each other is the first bottom surface (11), and the bottom surface that is far away from each other is the second bottom surface (12). The center of the first bottom surface (11) is provided with an inwardly concave arc surface (13) along the axis of the shell. The diaphragm (2) is disposed in the middle of the cavity and parallel to the second bottom surface (12); the second bottom surface (12) is provided with optical fiber mounting holes and pressure holes communicating with the cavity along the direction of the housing axis; the optical fiber (5) is located inside the optical fiber ferrule (4), the first ends of the two optical fiber ferrules (4) pass through the optical fiber mounting holes respectively and are symmetrically disposed on the housing (1), the left and right sides of the diaphragm (2) form a Fabry-Perot cavity with the first end face of the optical fiber (5) respectively, and the pressure ports (6) are symmetrically disposed at the pressure holes; The bottom of the arc surface (13) is provided with a circular hole (14), which is coaxial with the optical fiber mounting hole. The part between the surface of the diaphragm (2) and the arc surface (13) is the first microcavity (7), and the part between the bottom of the arc surface (13) and the bottom of the circular hole (14) is the second microcavity (8). The end face of the optical fiber ferrule (4) is flush with the end face of the optical fiber (5), and the first end face of the optical fiber ferrule (4) is located at the bottom of the circular hole (14). Annular plates (3) are symmetrically arranged on the left and right sides of the diaphragm (2).

2. The dual-microcavity fiber optic differential pressure sensor according to claim 1, characterized in that, The diaphragm (2) is circular or the diaphragm (2) is cylindrical in shape.

3. The dual-microcavity fiber optic differential pressure sensor according to claim 2, characterized in that, When the diaphragm (2) is a cylindrical structure, the thickness of the central region of the diaphragm (2) is greater than the thickness of the edge region.

4. The dual-microcavity fiber optic differential pressure sensor according to any one of claims 1 to 3, characterized in that, The diaphragm (2) has concave surfaces symmetrically arranged on its left and right sides, and the concave surfaces are located at the center of the diaphragm (2).

5. The dual-microcavity fiber optic differential pressure sensor according to claim 4, characterized in that, The concave surface is a sphere or nearly a sphere.

6. The dual-microcavity fiber optic differential pressure sensor according to claim 4, characterized in that, The first end face of the optical fiber (5) is located at the focal point of the concave surfaces on both sides of the diaphragm (2).

7. The dual-microcavity fiber optic differential pressure sensor according to claim 4, characterized in that, The diameter of the diaphragm (2) is the same as the diameter of the shell (1), and the effective diameter d2 of the diaphragm (2) is less than 10 cm; the length of the first microcavity (7) is not greater than the length of the second microcavity (8), and the sum L of the lengths of the first microcavity (7) and the second microcavity (8) satisfies .

8. A method for manufacturing a dual-microcavity fiber optic differential pressure sensor, characterized in that, A method for manufacturing a dual-microcavity fiber optic differential pressure sensor according to any one of claims 1 to 7, comprising the following steps: Step 1: Pass the optical fiber through the fiber optic ferrule, making its end face extend beyond the end face of the fiber optic ferrule, and use high-temperature and high-pressure resistant adhesive to fix the optical fiber and the fiber optic ferrule. Step 2: Cut off the portion of the optical fiber that extends beyond the fiber ferrule end face, and polish both the fiber end face and the fiber ferrule end face together. Step 3: Drill a fiber optic mounting hole through the cylindrical metal body along the axial direction at the center of the cylindrical metal body, and drill a pressure hole through the cylindrical metal body at a certain distance from the axis of the cylindrical metal body. Step 4: Use milling to machine an arc surface at the center of the first bottom surface of the cylindrical metal body; Step 5: Pass the polished fiber optic ferrule through the fiber mounting hole of the cylindrical metal body, with the insertion direction from the second bottom surface to the first bottom surface; fill the bottom of the arc surface with low-temperature glass solder, use a sintering process to fix the fiber optic ferrule to the metal body, and polish the entire metal body. Step 6: Drill a circular hole at the center of the bottom of the arc surface, with the first end face of the optical fiber at the bottom of the circular hole, and measure and record the distance between the first end face of the optical fiber and the first bottom surface of the metal body; Step 7: Clamp the two annular plates on both sides of the diaphragm, and clamp the two metal bodies made in steps 3 to 6 on the surface of the annular plates, with the first bottom surface of the metal bodies adhering to the surface of the annular plates. At this time, the end face of the optical fiber is facing the center of the diaphragm. Use laser welding to weld the diaphragm, annular plates and metal bodies together, and ensure the sealing after welding. Step 8: Weld the pressure interfaces to the pressure inlet holes on the left and right ends of the housing using laser welding, which will serve as the input ports for the pressure input medium.

9. A sensing and measurement method for a dual-microcavity fiber optic differential pressure sensor, characterized in that, Using the dual-microcavity fiber optic differential pressure sensor as described in any one of claims 1 to 7, the sensing and measurement method of the dual-microcavity fiber optic differential pressure sensor includes the following steps: Step 1: Connect the two single-mode optical fibers to the spectral demodulator respectively. Without input pressure, use the demodulator to obtain the Fabry-Perot cavity lengths L1 and L2 on the left and right sides of the diaphragm respectively. Step 2: Input two pressure values, P1 and P2, of different magnitudes into the differential pressure sensor through two pressure ports, and record the change in cavity length. ; Step 3: Based on the change in cavity length Pressure difference The corresponding formula: The difference between the two pressures acting on the differential pressure sensor at this time is obtained. Where μ represents the Poisson's ratio of the diaphragm, E represents the Young's modulus of the diaphragm, n represents the refractive index of the pressure-sensitive medium in the Fabry-Perot cavity, R represents the radius of the Fabry-Perot cavity, and h represents the thickness of the diaphragm.

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