A fiber-optic fabry-perot ultrasonic sensor and a method of manufacturing the same

Abstract

The application relates to a fiber Fabry-Perot ultrasonic sensor and a manufacturing method thereof. On the basis of a traditional quartz diaphragm, a double-sided groove type quartz diaphragm is prepared by using photoetching and hydrofluoric acid etching technology, the central thickness of the quartz diaphragm is reduced, the quartz diaphragm can generate a larger deformation amount when subjected to ultrasonic waves, the sensor is more sensitive and accurate in capturing partial discharge signals, the sensor sensitivity is improved, meanwhile, the inherent frequency of the diaphragm is improved, the frequency detection range of the sensor is increased, meanwhile, the multiple rectangular grooves arranged on the quartz diaphragm connect the air inside and outside the Fabry-Perot cavity, the measurement error of the sensor caused by the expansion of the gas in the cavity after temperature rise is avoided, the external environment gas can enter the Fabry-Perot cavity, the change of the environment gas can be judged by using the change of the refractive index of different gases, double-parameter sensing is realized, the whole device has the advantages of simple structure, good overall stability, long service period, low manufacturing cost and suitability for practical use.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic sensing technology, and in particular to a fiber optic Fabry-Perot ultrasonic sensor and its manufacturing method. Background Technology

[0002] Fiber optic Fabry-Perot ultrasonic sensors are an important component of online partial discharge monitoring systems. They determine the presence of partial discharge by detecting the ultrasonic signals generated synchronously during partial discharge and are widely used in fault monitoring of electrical cable equipment.

[0003] Existing fiber optic Fabry-Perot sensors suffer from a trade-off between detection sensitivity and frequency detection range, making it difficult to simultaneously achieve high sensitivity and a wide detection range. Their simple structure prevents structural adjustments for specific application scenarios, hindering the acquisition of more accurate sensing results. Furthermore, the use of sealed cavities as Fabry-Perot chambers means that as temperatures rise, the air inside the chamber expands, compressing the chamber and potentially causing changes in its length, affecting the final detection results and leading to false alarms. Additionally, existing fiber optic Fabry-Perot sensors can only detect a single parameter, resulting in low utilization of detection equipment. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this invention is to overcome the contradiction between detection sensitivity and frequency detection range in existing fiber optic Fabry-Perot sensors, making it difficult to simultaneously achieve high sensitivity and wide detection range; the sensor structure is simple and cannot be adjusted for application scenarios to obtain more accurate sensing results; moreover, existing fiber optic Fabry-Perot sensors mostly use a sealed cavity as the Fabry-Perot cavity, and when the temperature rises, the air inside the Fabry-Perot cavity expands, and the expanding gas compresses the cavity, which may cause changes in the cavity length, affecting the final detection result and causing false alarms; and existing fiber optic Fabry-Perot sensors can only detect a single parameter, resulting in low utilization of the detection equipment. This invention provides a fiber optic Fabry-Perot ultrasonic sensor and its manufacturing method, which can reduce the influence of temperature on the ultrasonic sensor detection results, balance the pressure difference inside and outside the Fabry-Perot cavity, and provide conditions for dual-parameter measurement.

[0005] To address the aforementioned technical problems, this invention provides a fiber optic Fabry-Perot ultrasonic sensor, comprising:

[0006] A quartz diaphragm, wherein a first groove is provided at one end of the quartz diaphragm and a plurality of second grooves are provided at the other end;

[0007] A quartz tube has a third groove and a fourth groove along its length. The third groove and the fourth groove are interconnected. When the quartz diaphragm is connected to the quartz tube, the cavity formed by the quartz diaphragm and the third groove is connected to the outside through the second groove, allowing outside gas to enter the cavity.

[0008] A single-mode optical fiber is disposed in the fourth groove, and the end face of the single-mode optical fiber adjacent to the quartz diaphragm constitutes two reflecting surfaces of the Fabry-Perot cavity.

[0009] In one embodiment of the present invention, the quartz tube includes a first quartz tube, a second quartz tube, and a third quartz tube, all of which are cylindrical. The first quartz tube is sleeved on a single-mode optical fiber, the second quartz tube is sleeved on the first quartz tube, and the third quartz tube is sleeved on the second quartz tube. The single-mode optical fiber, the first quartz tube, and the second quartz tube are located on the same side at one end in the same plane and together with the third quartz tube form the third groove.

[0010] In one embodiment of the present invention, a first anti-reflection film is provided on the end face of the single-mode optical fiber adjacent to the third groove, and a second anti-reflection film is provided on the end face of the quartz film connected to the quartz tube.

[0011] In one embodiment of the present invention, the quartz diaphragm is cylindrical and is coaxially arranged with the quartz tube.

[0012] In one embodiment of the present invention, the first groove is coaxially disposed on a quartz diaphragm.

[0013] In one embodiment of the present invention, a plurality of second grooves are symmetrically arranged with the center of the end face as the center.

[0014] A method for fabricating a fiber optic Fabry-Perot ultrasonic sensor as described in any of the above claims includes the following steps:

[0015] Insert the single-mode fiber into the first quartz tube so that the plane at one end of the single-mode fiber is flush with the plane at one end of the first quartz tube, and fix the single-mode fiber on the first quartz tube.

[0016] The second quartz tube is fitted onto the first quartz tube, so that the end of the first quartz tube and the single-mode optical fiber are flush with one end of the second quartz tube, and the second quartz tube is fixed on the first quartz tube.

[0017] The assembly of the fixed first quartz tube, second quartz tube and single-mode optical fiber is inserted into the third quartz tube, so that one end of the third quartz tube and the other end of the assembly are far apart to form a third groove, and the third quartz tube is fixed on the second quartz tube.

[0018] The end of the quartz diaphragm with the second groove is tightly fitted to the third quartz tube, so that the quartz diaphragm and the third groove of the quartz tube form a cavity, and the third quartz tube and the quartz diaphragm are fixed together at the fitting point.

[0019] In one embodiment of the invention, the depth of the third groove formed by the third quartz tube and the assembly is adjusted using a microscope.

[0020] A method for fabricating a quartz diaphragm for a fiber optic Fabry-Perot ultrasonic sensor as described above, characterized by comprising the following steps:

[0021] A layer of photoresist is evenly coated on the quartz film and then dried until it solidifies.

[0022] Based on the shape and position of the first and second grooves, a photoresist area other than the pattern corresponding to the first groove is photolithographically etched on one end face of the quartz film, and a photoresist area other than the pattern corresponding to the second groove is photolithographically etched on the other end face of the quartz film.

[0023] The quartz film after photolithography is washed away, in which the photoresist in the unlithographic areas is washed away, exposing the quartz, while the photoresist in the lithographic areas remains on the quartz film.

[0024] The rinsed quartz film is acid-washed, and the areas on the two end faces of the quartz film that are not covered by photoresist are etched to obtain the first groove and the second groove respectively. At the same time, the acid washing time is controlled until the depth of the first groove and the second groove reaches the predetermined depth, and then the quartz film is removed.

[0025] Clean the acid-washed quartz membrane thoroughly.

[0026] In one embodiment of the present invention, a developing solution is used to rinse the quartz film after photolithography.

[0027] The technical solution of the present invention has the following advantages compared with the prior art:

[0028] This invention discloses a fiber optic Fabry-Perot ultrasonic sensor and its fabrication method. The sensor comprises a quartz diaphragm, a quartz tube, and a single-mode optical fiber. Grooves are formed on the outer surface of the quartz diaphragm to reduce its central thickness. When subjected to ultrasonic waves, the quartz diaphragm exhibits greater deformation compared to ordinary quartz diaphragms, improving the sensor's sensitivity and making its capture of partial discharge signals more sensitive and accurate. The unique structure of the quartz diaphragm increases the sensor's natural frequency, expanding its frequency detection range. Simultaneously, the grooves on the quartz diaphragm and quartz tube form a cavity, and multiple grooves on the end face of the quartz diaphragm connect the cavity to the external space. This prevents gas expansion within the cavity from compressing the quartz diaphragm when the external temperature rises, thus avoiding damage. The change in the length of the cavity affects the final detection result; and when the sensor is applied to environments with different pressures, the pressure inside and outside the cavity remains consistent, and no pressure difference is generated on both sides of the quartz diaphragm, thus broadening the sensor's applicability. Simultaneously, gas from the external environment can enter the cavity through grooves on the quartz diaphragm. Therefore, when the device is in different gas environments, the refractive index inside the Fabry-Perot cavity will differ from the refractive index of air at standard pressure. According to the Fabry-Perot interference principle, the change in refractive index inside the cavity will change the intensity of the interference light. The detection result of the ambient gas can be obtained based on the change in light intensity, thus broadening the sensor's application range. The ultrasonic sensor of this invention has a simple structure, good overall stability, long service life, and low manufacturing cost, making it suitable for practical use. Attached Figure Description

[0029] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0030] Figure 1 This is a schematic diagram of the overall structure of the fiber optic Fabry-Perot ultrasonic sensor in a preferred embodiment of the present invention;

[0031] Figure 2 yes Figure 1 The exploded view of the fiber optic Fabry-Perot ultrasonic sensor is shown.

[0032] Figure 3 yes Figure 1 The diagram shows the structure of the quartz tube in the fiber optic Fabry-Perot ultrasonic sensor.

[0033] Figure 4 yes Figure 1 The image shows a cross-sectional view of a fiber optic Fabry-Perot ultrasonic sensor.

[0034] Figure 5 yes Figure 1 The diagram shows a structural schematic of one end face of the quartz diaphragm of the fiber optic Fabry-Perot ultrasonic sensor.

[0035] Figure 6 yes Figure 1 A schematic diagram of the structure of the other end face of the quartz diaphragm of the fiber optic Fabry-Perot ultrasonic sensor.

[0036] Figure 7 This is a schematic diagram of a photolithographic region (shaded area) of the method for fabricating the quartz diaphragm of the fiber optic Fabry-Perot ultrasonic sensor in Example 3.

[0037] Figure 8 This is a schematic diagram of another photolithographic region (shaded area) of the method for fabricating the quartz film of the fiber optic Fabry-Perot ultrasonic sensor in Example 3.

[0038] Explanation of reference numerals in the accompanying drawings: 1. Quartz film; 11. First groove; 12. Second groove; 13. Second anti-reflection film; 2. Quartz tube; 21. Third groove; 22. Fourth groove; 23. First quartz tube; 24. Second quartz tube; 25. Third quartz tube; 3. Single-mode optical fiber; 31. First anti-reflection film. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0040] Example 1

[0041] Reference Figures 1-6 As shown, a fiber optic Fabry-Perot ultrasonic sensor of the present invention includes:

[0042] Quartz diaphragm 1, one end of quartz diaphragm 1 is provided with a first groove 11, and the other end is provided with a plurality of second grooves 12;

[0043] Quartz tube 2 has a third groove 21 and a fourth groove 22 along its length. The third groove 21 and the fourth groove 22 are interconnected. When the quartz diaphragm 1 is connected to the quartz tube 2, the cavity formed by the quartz diaphragm 1 and the third groove 21 is connected to the outside through the second groove 12, allowing outside gas to enter the cavity.

[0044] A single-mode fiber 3 is disposed in the fourth groove 22. The end face of the single-mode fiber 3 adjacent to the quartz diaphragm 1 constitutes the two reflecting surfaces of the Fabry-Perot cavity.

[0045] Specifically, one end of the quartz diaphragm 1 with the second groove 12 is connected to one end of the quartz tube 2 with the third groove 21. The connected quartz diaphragm 1 and the third groove 21 form an internal cavity, and the second groove 12 on the quartz diaphragm 1 connects the cavity to the outside.

[0046] It is conceivable that the second groove 12 on the end face of the quartz diaphragm 1 can serve as an air passage, connecting the air inside and outside the Fabry-Perot cavity. When the temperature rises, the air inside the Fabry-Perot cavity expands, and the expanded gas can be discharged through the second groove 12, avoiding the expansion gas from compressing the quartz diaphragm 1 and causing changes in cavity length, which would affect the sensing effect. This reduces the impact of temperature changes on the test results. At the same time, when the sensor is in different gas environments, the ambient gas enters the cavity through the second groove 12. Based on the difference in gas refractive index, the spectral shift is achieved, and the composition of the ambient gas is determined, realizing dual-parameter sensing and improving the sensor utilization rate. In addition, the connection between the air inside and outside the Fabry-Perot cavity allows the sensor to be used in environments with different pressures, which can expand the application range of the sensor.

[0047] Furthermore, the quartz tube 2 includes a first quartz tube 23, a second quartz tube 24, and a third quartz tube 25, all of which are cylindrical. The first quartz tube 23 is sleeved on the single-mode optical fiber 3, the second quartz tube 24 is sleeved on the first quartz tube 23, and the third quartz tube 25 is sleeved on the second quartz tube 24. The single-mode optical fiber 3, the first quartz tube 23, and the second quartz tube 24 are located on the same side at one end, in the same plane, and together with the third quartz tube 25, form a third groove 21. It is conceivable that all components in the ultrasonic sensor, except for the anti-reflective coating, are made of quartz. Quartz is stable, heat-resistant, and resistant to electromagnetic interference. It can avoid minor deformations caused by differences in thermal expansion coefficients and thermo-optical coefficients between different materials, effectively improving the stability of the sensor structure. At the same time, quartz is inexpensive, saving on sensor manufacturing costs.

[0048] Specifically, the following manufacturing dimensions can be used: the diameter of the single-mode optical fiber 3 is 0.125 mm; the outer diameter of the first quartz tube 23 is 1.8 mm and the inner diameter is 0.126 mm; the outer diameter of the second quartz tube 24 is 2.78 mm and the inner diameter is 1.81 mm; the outer diameter of the third quartz tube 25 is 3.5 mm and the inner diameter is 3 mm. The above is only one manufacturing dimension provided, but it is not limited to this manufacturing dimension. The specific dimensions of each component in the device can be determined according to actual needs and circumstances.

[0049] Furthermore, a first anti-reflection film 31 is provided on the end face of the single-mode optical fiber 3 adjacent to the third groove 21, and a second anti-reflection film 13 is provided on the end face of the quartz diaphragm 1 connected to the quartz tube 2.

[0050] It is conceivable that the distance between the end face of the single-mode fiber 3 with the first anti-reflection coating 31 and the end face of the quartz diaphragm 1 with the second anti-reflection coating 13 is the original cavity length of the Fabry-Perot cavity. It is also conceivable that placing anti-reflection coatings on the two reflecting surfaces of the Fabry-Perot cavity of the ultrasonic sensor can match the reflectivities of the two reflecting surfaces.

[0051] Furthermore, the quartz diaphragm 1 is cylindrical and coaxially arranged with the quartz tube 2. The quartz diaphragm 1 structure, with a first groove 11 and a second groove 12 respectively on its two end faces, reduces the center thickness of the quartz diaphragm 1. Under the same intensity of sound pressure, the center deformation of the double-grooved quartz diaphragm 1 is higher than that of a traditional circular quartz diaphragm of the same radius and thickness, which can improve the sensitivity of the sensor.

[0052] It is conceivable that traditional circular quartz diaphragms present a trade-off between sensitivity and natural frequency; improving one inevitably requires sacrificing the other. However, the double-grooved quartz diaphragm 1 of this invention, with its unique structure, simultaneously improves both the sensor's sensitivity and natural frequency. By adjusting the dimensional parameters, when the natural frequency of the quartz diaphragm 1 of this invention matches that of a traditional circular quartz diaphragm, the sensitivity of the fiber optic Fabry-Perot ultrasonic sensor based on the double-grooved quartz diaphragm 1 is approximately 3.5 times that of the fiber optic Fabry-Perot ultrasonic sensor based on a traditional circular quartz diaphragm. Furthermore, the natural frequency of the double-grooved quartz diaphragm 1 is higher than that of a traditional circular quartz diaphragm of the same radius and thickness. A higher natural frequency allows for a wider range of forced vibration frequencies, thus the fiber optic Fabry-Perot ultrasonic sensor based on the double-grooved quartz diaphragm 1 has a broader frequency detection range.

[0053] Furthermore, the first groove 11 is coaxially disposed on the quartz diaphragm 1. The first groove 11 can be a circular groove, but is not limited to a circular groove, and its shape and size can be designed and adjusted according to different needs. It is conceivable that setting the groove on the outer surface of the quartz diaphragm 1 reduces the center thickness of the quartz diaphragm 1. When the quartz diaphragm 1 is subjected to ultrasonic waves, it can generate a larger deformation than a general quartz diaphragm 1, which can improve the sensitivity of the sensor and make the sensor more sensitive and accurate in capturing partial discharge signals. The unique structure of the quartz diaphragm 1 increases the inherent frequency of the sensor and increases the frequency detection range of the sensor.

[0054] Furthermore, multiple second grooves 12 are symmetrically arranged with the center of their respective end faces as the center. The second grooves 12 can be rectangular grooves, but are not limited to rectangular grooves; their shape and size can be designed and adjusted according to different needs.

[0055] Working process: The end of the quartz diaphragm 1 in the ultrasonic sensor with the first groove 11 is placed directly opposite the ultrasonic source. When the ultrasonic waves generated by the ultrasonic source act on the quartz diaphragm 1, the quartz diaphragm 1 deforms. At this time, the distance between the end face of the quartz diaphragm 1 with the second anti-reflection film 13 and the end face of the single-mode optical fiber 3 with the first anti-reflection film 31 changes, and the length of the cavity changes. According to the Fabry-Perot interference principle, the change in the Fabry-Perot cavity length will change the intensity of the interference light, and the ultrasonic detection result can be obtained based on the change in light intensity. Since the second groove 12 on the outer surface of the double-grooved quartz diaphragm 1 reduces the thickness at the center of the quartz diaphragm 1, when the same sound pressure acts on the quartz diaphragm 1, the deformation of the quartz diaphragm 1 will be greater than that of a traditional circular quartz diaphragm, thus enhancing the sensitivity of the detection device.

[0056] It is conceivable that the ultrasonic sensor could be placed in a container filled with SF6 at 3 atmospheres. The SF6 gas enters the Fabry-Perot cavity through the second groove 12 on the quartz diaphragm 1, balancing the pressure difference on both sides of the quartz diaphragm 1 and avoiding the limitations of sensor application caused by pressure imbalance on both sides of the quartz diaphragm 1. Furthermore, when the Fabry-Perot cavity is filled with SF6 at 3 atmospheres, the refractive index within the Fabry-Perot cavity will differ from the refractive index of air at standard pressure. According to the Fabry-Perot interference principle, the change in refractive index within the cavity will change the intensity of the interference light. Based on the change in light intensity, the detection result of the ambient gas can be obtained, thus broadening the application range of the sensor.

[0057] Example 2

[0058] Reference Figures 1-6 As shown, a method for fabricating a fiber optic Fabry-Perot ultrasonic sensor as described in any of the above-mentioned embodiments includes the following steps:

[0059] Insert the single-mode fiber 3 into the first quartz tube 23 so that the plane at one end of the single-mode fiber 3 is flush with the plane at one end of the first quartz tube 23, and fix the single-mode fiber 3 on the first quartz tube 23.

[0060] The second quartz tube 24 is fitted onto the first quartz tube 23, so that one end of the first quartz tube 23 and the single-mode optical fiber 3 are flush with one end of the second quartz tube 24, and the second quartz tube 24 is fixed onto the first quartz tube 23.

[0061] The assembly of the fixed first quartz tube 23, second quartz tube 24 and single-mode optical fiber 3 is inserted into the third quartz tube 25, so that one end of the third quartz tube 25 and the other end of the assembly are far apart to form a third groove 21, and the third quartz tube 25 is fixed on the second quartz tube 24.

[0062] One end of the quartz diaphragm 1 with the second groove 12 is tightly fitted to the third quartz tube 25, so that the quartz diaphragm 1 and the third groove 21 of the quartz tube 2 form a cavity, and the third quartz tube 25 and the quartz diaphragm 1 are fixed together at the fitting point. It should be noted that when welding the mating surfaces of the quartz diaphragm 1 and the third quartz tube 25, it is necessary to ensure that the end faces of the quartz diaphragm 1 and the third quartz tube 25 are parallel to each other after welding, so as to ensure that the quartz diaphragm 1 is subjected to uniform force.

[0063] Furthermore, the depth of the third groove 21 formed by the third quartz tube 25 and the assembly is adjusted using a microscope. When connecting the fixed assembly of the first quartz tube 23, the second quartz tube 24, and the single-mode optical fiber 3 to the third quartz tube 25, a microscope can be used for observation, and the assembly can be slowly moved until the distance between one end of the third quartz tube 25 and the end of the assembly flush with it reaches a predetermined distance.

[0064] It is conceivable that the connection of the various components of the quartz tube 2 can be achieved by CO2 laser welding, which can avoid loosening of the connection caused by the external environment and improve the service life and detection accuracy of the sensor.

[0065] Example 3

[0066] Reference Figures 1-8 As shown, a method for fabricating a quartz diaphragm for a fiber optic Fabry-Perot ultrasonic sensor, as described above, is characterized by comprising the following steps:

[0067] A layer of photoresist is evenly coated on the quartz film 1, and the photoresist is dried until it solidifies.

[0068] Based on the shape and position of the first groove 11 and the second groove 12, a photoresist area other than the pattern corresponding to the first groove 11 is photolithographically etched on one end face of the quartz film 1, and a photoresist area other than the pattern corresponding to the second groove 12 is photolithographically etched on the other end face of the quartz film 1.

[0069] The quartz film 1 after photolithography is completed is rinsed, in which the photoresist in the unlithographic area is washed away, exposing the quartz, while the photoresist in the lithographic area remains on the quartz film 1.

[0070] The quartz film 1 after rinsing is acid-washed. The areas on the two end faces of the quartz film 1 that are not covered by photoresist are etched to obtain the first groove 11 and the second groove 12 respectively. At the same time, the acid washing time is controlled until the depth of the first groove 11 and the second groove 12 reaches the predetermined depth, and then the quartz film 1 is taken out.

[0071] Clean the acid-washed quartz membrane 1 thoroughly.

[0072] Furthermore, the quartz film 1 after photolithography is completed is rinsed with a developing solution.

[0073] Specifically, a circular quartz film with a diameter of 3.5 mm and a thickness of 70 micrometers can be used. A 50-micrometer-thick layer of photoresist is evenly coated on one end face of the quartz film 1 and dried until solidified. A 50-micrometer-thick layer of photoresist is also evenly coated on the other end face of the quartz film 1 and dried until solidified. SU8-2050 photoresist can be used. A circular pattern with a diameter of 1.5 mm and four rectangular patterns with a length of 0.75 mm and a width of 50 micrometers are drawn using graphic design software. The drawn pattern is then imported into the lithography machine, which performs photolithography on the photoresist coated on both end faces of the quartz film 1 according to the imported pattern. Specifically, on one end face of the quartz film 1, the photoresist area excluding the circular pattern is lithographically etched according to the imported circular pattern; on the other end face of the quartz film 1, the photoresist area excluding the rectangular patterns is lithographically etched. The quartz film is then subjected to photolithography. 1. Rinse the quartz film 1 in the developing solution. It is conceivable that the photoresist areas lithographically processed by the lithography machine do not react with the developing solution, while the photoresist areas not lithographically processed by the lithography machine are washed away by the developing solution after contact, exposing the quartz. The rinsed quartz film 1 is then immersed in hydrofluoric acid. The two end faces of the quartz film 1 are etched by the hydrofluoric acid to form corresponding first grooves 11 and second grooves 12, and the acid washing time is controlled until the depth of the etched grooves reaches 40 micrometers. Specifically, the exposed circular and rectangular quartz areas are etched by hydrofluoric acid to form corresponding circular grooves (first groove) and rectangular grooves (second groove). It is important to note that the acid washing time must be controlled. Once the depth of the circular and rectangular grooves reaches the predetermined depth, the quartz film 1 is removed. The above is only one possible manufacturing shape and size, but it is not limited to this manufacturing shape and size. The specific shape and size of each part can be determined according to actual needs and circumstances.

[0074] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A fiber optic Fabry-Perot ultrasonic sensor, characterized in that, include: A quartz diaphragm, one end of which has a first groove and the other end has multiple second grooves; a quartz tube, along its length, has a third groove and a fourth groove, which are interconnected. When the quartz diaphragm is connected to the quartz tube, the cavity formed by the quartz diaphragm and the third groove is connected to the outside through the second grooves, allowing outside gas to enter the cavity; a single-mode optical fiber, disposed in the fourth groove, the end face of the single-mode optical fiber adjacent to the quartz diaphragm forming two reflecting surfaces of the Fabry-Perot cavity; The quartz tube includes a first quartz tube, a second quartz tube, and a third quartz tube, all of which are cylindrical. The first quartz tube is sleeved on a single-mode optical fiber, the second quartz tube is sleeved on the first quartz tube, and the third quartz tube is sleeved on the second quartz tube. The single-mode optical fiber, the first quartz tube, and the second quartz tube are located on the same side at one end in the same plane and together with the third quartz tube form the third groove. A first anti-reflection film is provided on the end face of the single-mode optical fiber adjacent to the third groove, and a second anti-reflection film is provided on the end face of the quartz film connected to the quartz tube. The quartz diaphragm is cylindrical and is coaxially arranged with the quartz tube; The first groove is coaxially disposed on the quartz diaphragm; Multiple second grooves are symmetrically arranged with the center of the end face as the center.

2. A method for manufacturing a fiber optic Fabry-Perot ultrasonic sensor as described in claim 1, characterized in that: The procedure includes the following steps: inserting a single-mode optical fiber into a first quartz tube, making the plane of one end of the single-mode optical fiber flush with the plane of one end of the first quartz tube, and fixing the single-mode optical fiber onto the first quartz tube; fitting a second quartz tube onto the first quartz tube, making the ends of the first quartz tube and the single-mode optical fiber flush with one end of the second quartz tube, and fixing the second quartz tube onto the first quartz tube; inserting the fixed assembly of the first quartz tube, the second quartz tube, and the single-mode optical fiber into a third quartz tube, making one end of the third quartz tube and the end of the assembly flush with each other to form a third groove, and adjusting the depth of the third groove formed by the third quartz tube and the assembly using a microscope, and then fixing the third quartz tube onto the second quartz tube; tightly fitting the end of a quartz diaphragm with the second groove to the third quartz tube, so that the quartz diaphragm and the third groove of the quartz tube form a cavity, and fixing the third quartz tube and the quartz diaphragm together at the fitting point.

3. A method for fabricating a quartz diaphragm in the fabrication method of the fiber optic Fabry-Perot ultrasonic sensor as described in claim 2, characterized in that: The process includes the following steps: uniformly coating a layer of photoresist onto a quartz film and drying the photoresist until it solidifies; based on the shape and position of the first and second grooves, photoresist areas other than those corresponding to the first groove are photolithographically etched on one end face of the quartz film, and photoresist areas other than those corresponding to the second groove are photolithographically etched on the other end face of the quartz film; rinsing the photolithographically etched quartz film with a developing solution, wherein the photoresist in the un-photolithographic areas is washed away, exposing the quartz, while the photoresist in the photolithographic areas remains on the quartz film; acid-washing the rinsed quartz film, wherein the areas on both end faces of the quartz film not covered by photoresist are etched to obtain the first and second grooves respectively, while controlling the acid-washing time until the depth of the first and second grooves reaches a predetermined depth, and then removing the quartz film; and finally cleaning the acid-washed quartz film.

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