A multi-resonance frequency FP sensor and its preparation method

Abstract

The present invention aims to provide a multi-resonance frequency (FP) sensor and its preparation method, belonging to the field of optical fiber sensor technology. The sensor comprises a diaphragm, a first capillary, a second capillary, and an optical fiber; the diaphragm comprises a device layer; a reflective layer is provided on the reflective end surface of the device layer, a boss is provided in the middle of the input end, and multiple resonant regions are arranged around the periphery of the boss, with each adjacent resonant region having different thicknesses, and the boss thickness being greater than the thickness of all resonant regions; the periphery of the diaphragm is fixed to one end of the first capillary, with the reflective layer facing the interior of the first capillary; one end of the second capillary is inserted into the first capillary and fixed to the reflective end of the diaphragm; one end of the optical fiber is inserted into the second capillary and fixed therein, with the axial projection of the optical fiber located at the boss, and a light transmission gap is provided between the end of the optical fiber and the reflective layer. The present invention can overcome the limitations of multi-resonance optical fiber sensors in terms of sensitivity and frequency adjustment, achieving more efficient signal detection and response.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, in particular to a multi-resonance frequency FP sensor and a preparation method thereof. Background Art

[0002] With the continuous development of fiber optic sensing technology, Fabry-Perot (FP) sensors have been widely used in acoustic signal detection, vibration monitoring, and environmental monitoring. FP sensors offer advantages such as high sensitivity, low power consumption, and long-distance transmission, and are widely used in structural health monitoring, noise detection, and acoustic signal analysis. However, traditional FP sensors typically rely on a single resonant frequency, which presents significant performance bottlenecks in environments with complex or multi-frequency acoustic signals. Because they are only sensitive to signals within a specific frequency range, FP sensors with a single frequency response tend to lose accuracy and sensitivity when processing multi-band acoustic waves, limiting their effectiveness in changing environments.

[0003] Existing research mainly focuses on how to improve the frequency response range of FP sensors, but there are still some shortcomings. First, many studies have expanded the frequency response range by changing the shape or material of the diaphragm. However, these methods often find it difficult to achieve a balance between the stability and sensitivity of multiple resonance peaks at the same time. Secondly, due to the mutual influence and difficulty in adjustment between multiple resonance peaks in existing designs, the unevenness of frequency response is still one of the main problems affecting sensor performance. In addition, although multi-band design can expand the scope of use, existing research still faces great challenges in accurately controlling the distribution of resonant frequencies and ensuring independent response of each frequency band. Therefore, how to effectively widen the frequency response range and ensure that each frequency band has sufficient signal sensitivity and stability remains a key problem in current research. Summary of the Invention

[0004] The present invention aims to provide a multi-resonance frequency FP sensor and its fabrication method. By achieving multiple resonant frequencies, this sensor overcomes the limitations of multi-resonance fiber optic sensors in terms of sensitivity and frequency adjustment, enabling more efficient signal detection and response. The present invention employs the following technical solutions.

[0005] In one aspect, the present invention provides a multi-resonance frequency FP sensor, comprising a diaphragm, a first capillary tube, a second capillary tube, and an optical fiber;

[0006] The diaphragm includes a device layer, one end of the device layer is an input end, and the other end is a reflection end; the reflection end surface of the device layer is a plane and is provided with a reflection layer; a boss is provided in the middle of the input end of the device layer, and a plurality of resonance regions are provided around the periphery of the boss, wherein the plurality of resonance regions are adjacent to each other, the device layer thicknesses of adjacent resonance regions are different, and the device layer thickness of the boss portion is greater than the device layer thickness of all resonance regions;

[0007] The periphery of the diaphragm is fixed to one end of the first capillary tube, and the reflective layer faces the interior of the first capillary tube;

[0008] One end of the second capillary tube is inserted into the first capillary tube and fixedly connected to the reflective end of the diaphragm;

[0009] One end of the optical fiber is inserted into the second capillary and fixed in the second capillary, the axial projection of the optical fiber is located in the reflection layer area corresponding to the boss portion, and there is a light transmission gap between the end of the optical fiber and the reflection layer.

[0010] In the above technical solution, multiple resonant regions of varying thickness and a central projection on the diaphragm form a multi-resonant sensor structure. A Fabry-Perot interferometer cavity is formed between the optical fiber and the diaphragm's reflective layer. The optical fiber transmits incident light toward the reflective layer and receives reflected light from the Fabry-Perot interferometer cavity. When sound pressure acts on the diaphragm surface, the diaphragm deforms, while the optical fiber attached to the capillary tube does not shift. Consequently, the length of the Fabry-Perot cavity changes. The optical path difference of the reflected light caused by this change in cavity length can be used to calculate the ultrasonic sound pressure. In this process, because the diaphragm's resonant regions have different thicknesses, their maximum deformation occurs at different frequencies. This deformation also causes deformation of the central projection, resulting in multiple resonant peaks in the diaphragm's frequency response. Deformation in the resonant regions indirectly reflects the deformation at the central projection of the diaphragm. This means that the center of the diaphragm experiences greater deformation, and therefore greater sensitivity, at multiple frequencies. This improves sensitivity in the multi-resonant frequency response.

[0011] Optionally, the boss is cylindrical, the resonant region is in the shape of a sector ring arranged around the boss, and all resonant regions are spliced together to form a circular ring shape surrounding the boss. That is, in this embodiment, the sensitive area of the diaphragm is a circle. In addition, other shapes such as a square can also be set.

[0012] Optionally, the central angles of the resonance regions of the sector rings are equal and the input surface areas are equal, which can facilitate simulation during sensor design and calculation during practical application.

[0013] Optionally, thicknesses of any two of the multiple resonance regions are different.

[0014] As an implementation method of different thickness levels of the resonance regions: among the multiple resonance regions, starting from one resonance region, the thickness of the resonance regions increases or decreases in sequence.

[0015] Preferably, among the multiple resonance regions, starting from one resonance region, the thickness of the resonance regions increases or decreases by the same height value in sequence.

[0016] As another implementation method of different thickness levels of the resonance regions: all the resonance regions are arranged at different heights on the periphery of the boss according to the surface height.

[0017] Preferably, in descending order of the thickness values of the resonance regions, the thickness difference between any two adjacent resonance regions of the same thickness value is equal. This setting can simplify the logical operation of the sensor when it is actually used for detection.

[0018] Optionally, the diaphragm further includes a supporting layer and a connecting layer, the supporting layer and the connecting layer are annular, connected to the periphery of the reflective end of the device layer, and projected onto the periphery of the multiple resonance regions, wherein the upper and lower surfaces of the connecting layer are respectively fixedly connected to the supporting layer and the device layer;

[0019] The end face of one end of the first capillary is fixedly connected to the support layer, and the outer diameter of the second capillary is adapted to the inner diameter of the support layer and the first capillary, so that the outer wall of the second capillary is respectively fitted with the inner wall of the support layer and the inner wall of the first capillary. At the same time, glue can be applied on the outer wall of the second capillary to make it adhere to the inner wall of the support layer.

[0020] Optionally, the optical fiber is a single-mode optical fiber, and the reflective layer is a gold material attached to the reflective end surface of the diaphragm, which can be formed by vacuum ion sputtering technology. The reflective layer can also be made of other metal materials with high reflective properties.

[0021] In the above technical solution, the provision of the support layer can achieve mechanical support for the first capillary tube and the capillary tube to the diaphragm and the optical fiber, thereby ensuring the overall structural stability of the sensor.

[0022] Optionally, the ratio of the area of the boss region to the sum of the areas of the boss and the resonant region is less than 1 / 4. Because a larger boss area leads to a higher lowest resonant peak among the multiple resonant regions, the resonant frequency range corresponding to the multiple resonant regions becomes smaller, making the multi-peak phenomenon less noticeable. Therefore, a reasonable combination of the boss and resonant region areas can ensure that the FP sensor has a wider frequency response range and higher sensitivity within the frequency response range corresponding to each resonant region.

[0023] Preferably, the inner diameter of the first capillary tube is equal to the outer diameter of the second capillary tube, the outer diameter of the first capillary tube being slightly larger than its inner diameter, and the outer diameter of the second capillary tube being much larger than its inner diameter. As a feasible embodiment, the outer diameter of the first capillary tube is 4 mm and the inner diameter is 3 mm; the outer diameter of the capillary tube is 3 mm and the inner diameter is 0.135 mm; and the length of the optical fiber outside the capillary tube is 2 mm to 3 mm.

[0024] In a second aspect, the present invention provides a method for preparing the multi-resonance frequency FP sensor according to the first aspect, comprising preparing the diaphragm. The diaphragm preparation process includes:

[0025] Coating a photoresist layer on the SOI wafer and performing a baking process;

[0026] The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the surface of the reflective end of the diaphragm;

[0027] For the exposed area of the silicon base layer of the SOI wafer, reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is further etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching, and according to the thickness of the multiple resonance regions and bosses, the etching is carried out layer by layer until the multiple resonance regions and bosses are obtained, thereby completing the preparation of the diaphragm.

[0028] The above-mentioned layer-by-layer etching can be from shallow to deep layer-by-layer etching, that is, etching the boss first, or from deep to shallow layer-by-layer etching, that is, etching the boss last.

[0029] As an etching operation implementation mode, optionally, there are multiple upper mask plates, each of which is made according to different thicknesses and shapes of the boss and the multiple resonance regions;

[0030] The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the thickness of the multiple resonance regions and the bosses to obtain the multiple resonance regions and the bosses, including:

[0031] According to the different thicknesses of the bosses and the multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0032] In order from deep to shallow, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and bosses in sequence;

[0033] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent boss, or according to the surface height of the boss, to complete the etching of the current height level and obtain the corresponding resonant area or boss.

[0034] As another embodiment of the etching operation, optionally, there are multiple upper mask plates, each of which is made according to different thicknesses and shapes of the boss and the multiple resonance regions;

[0035] The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the thickness of the multiple resonance regions and the bosses to obtain the multiple resonance regions and the bosses, including:

[0036] According to the different thicknesses of the bosses and the multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0037] In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining a boss and multiple resonance regions in sequence;

[0038] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, transferring the pattern on the mask plate of the corresponding height level to the photoresist layer, controlling the etching depth according to the surface height of the boss or resonance area to be etched, completing the etching of the current height level, and obtaining the corresponding boss or resonance area.

[0039] Optionally, the preparation method further includes assembling the sensor, specifically including:

[0040] Fix the first capillary tube on the bracket, apply UV glue on its end surface, align and attach the reflective end of the diaphragm to the end surface of the first capillary tube, and irradiate with ultraviolet light to firmly connect the diaphragm and the first capillary tube;

[0041] Cut the required length of optical fiber, remove the coating and clean the bare fiber;

[0042] Insert the bare fiber into the inner hole of the capillary, apply UV glue on both ends of the second capillary, and irradiate with UV light to fix the optical fiber and the second capillary relatively;

[0043] The optical fiber is aligned with the center of the diaphragm boss, and the second capillary tube through which the optical fiber is passed is placed into the first capillary tube and fixed to the reflective end surface of the diaphragm to obtain the multi-resonance FP optical fiber sensor.

[0044] Beneficial effects

[0045] The multi-resonance frequency FP sensor of the present invention, through a combination of a boss and a multi-resonance zone with graded thickness, ensures that the response areas of multiple resonant frequencies can cover signals from multiple different frequency bands, significantly broadening the sensor's operating frequency range and improving its application performance in multi-band measurements. This avoids the limitation of traditional sensors that rely on a single resonant frequency, and the sensor can simultaneously respond to signals from multiple frequency bands, greatly improving its flexibility, accuracy, response speed, and applicability in complex environments. This structure can effectively enhance the sensor's overall performance, especially when capturing acoustic signals across complex and wide frequency ranges, and promote the development of fiber optic sensor technology in a wider range of application scenarios.

[0046] The fabrication method of the present invention designs the etching process based on the structural characteristics of the diaphragm. By using different mask plates, the multi-level resonant region and bosses are etched layer by layer, ensuring the sensor's high sensitivity and wide frequency response range. Furthermore, the nested protective design of the optical fiber and capillary tube ensures the centering accuracy and assembly security of the sensor diaphragm, allowing the optical fiber to be stably embedded without damaging the diaphragm, further enhancing the structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 FIG2 is a schematic diagram of the structure of a multi-resonance frequency FP sensor in one embodiment of the present invention;

[0048] Figure 2 The present invention is shown Figure 1 Schematic diagram of the 3D structure of the diaphragm of the multi-resonance frequency FP sensor;

[0049] Figure 3 FIG2 is a schematic structural diagram of a multi-resonance frequency FP sensor in another embodiment of the present invention;

[0050] Figure 4 Shown Figure 3 Schematic diagram of the diaphragm structure of the multi-resonance frequency FP sensor;

[0051] Figure 5 Shown Figure 4 Schematic diagram of the middle diaphragm from a top-down perspective;

[0052] Figure 6 FIG2 is a schematic diagram of the process for preparing a diaphragm of a multi-resonance frequency FP sensor according to an embodiment of the present invention;

[0053] In the figure, 1-diaphragm, 11-silicon base layer, 12-silicon oxide layer, 13-silicon substrate layer, 14-reflection layer, 2-first capillary, 3-second capillary, 4-optical fiber, 5-resonance region, 6-boss. DETAILED DESCRIPTION

[0054] The following is further described in conjunction with the accompanying drawings and specific embodiments. The embodiments mentioned are merely exemplary descriptions of the present invention, used to illustrate the present invention, and should not be understood as limiting the present invention. In the absence of any conflict, the various embodiments of the present invention and their technical features may be combined with each other.

[0055] Example 1

[0056] This embodiment introduces an asymmetric multi-resonance frequency FP optical fiber sensor, including a diaphragm 1, a first capillary 2, a second capillary 3 and an optical fiber 4. Figure 1 As shown;

[0057] refer to Figures 1 to 6 The diaphragm 1 includes a device layer, which can be processed from a silicon substrate layer of an SOI crystal. One end of the device layer is an input end, and the other end is a reflection end. The reflection end face of the device layer is a plane and is provided with a reflection layer 14. A boss 6 is provided in the middle of the input end of the device layer, and a plurality of resonance regions 5 are provided around the periphery of the boss. The plurality of resonance regions are adjacent to each other, and the device layer thicknesses of adjacent resonance regions are different, and the device layer thickness of the boss portion is greater than the device layer thickness of all resonance regions.

[0058] The periphery of the diaphragm is fixed to one end of the first capillary 2, and the reflective layer faces the interior of the first capillary;

[0059] One end of the second capillary tube 3 is inserted into the first capillary tube and fixedly connected to the reflective end of the diaphragm;

[0060] One end of the optical fiber 4 is inserted into the second capillary and fixed in the second capillary. The axial projection of the optical fiber is located in the reflective layer area corresponding to the boss portion. There is a light transmission gap between the end of the optical fiber and the reflective layer.

[0061] In this embodiment, multiple resonant regions of varying thickness and a central projection on the diaphragm form the sensor's multi-resonant FP structure. A first capillary tube provides support, while a second capillary protects the optical fiber passing through it, ensuring alignment between the fiber and the diaphragm projection, enabling accurate fiber interferometry measurement. A Fabry-Perot interferometer cavity is formed between the end face of the optical fiber and the reflective layer at the center of the diaphragm, used for acoustic signal detection.

[0062] When sound pressure acts on the surface of the diaphragm, the diaphragm will deform. Since the thickness of each resonance zone of the diaphragm is different, the maximum deformation of each resonance zone also occurs at different frequencies. When the resonance zone is deformed, the center boss 6 will also be deformed. Therefore, the frequency response of the diaphragm will have multiple resonance peaks. At multiple frequencies, the center boss of the diaphragm will have a larger deformation, that is, it has a higher sensitivity.

[0063] During detection, when the optical fiber emits incident light, the cavity length of the Fabry-Perot interferometer cavity changes as the diaphragm deforms. This change in cavity length causes the optical path difference of the reflected light to change. By detecting the optical path difference of the reflected light in the interferometer cavity, the sound pressure values at different frequencies can be calculated, thereby achieving high-precision measurement of multi-band acoustic signals.

[0064] Example 2

[0065] Based on Example 1, Figure 1 and Figure 2 In the multi-resonance frequency FP sensor of this embodiment, the diaphragm only includes a device layer made of silicon material. On the device layer, the boss is a cylinder, and there are four resonant regions, which are fan-shaped and surround the outer circumference of the boss, and their outer edges form a circle.

[0066] The bosses can also be square or other shapes, but a circular shape is more conducive to consistent deformation response across multiple resonant zones, facilitating logical operations during simulation and testing. The outer edges of the multiple resonant zones can also be formed in other shapes, and their number can be adjusted as needed to accommodate testing requirements across different frequency ranges.

[0067] Figure 2 The multiple resonance regions and boss structures on the device layer of the membrane in this embodiment are shown. Based on this membrane structure, when assembled with the first capillary, the second capillary and the optical fiber, as shown in FIG. Figure 1 A first capillary tube with an inner ring shape and dimensions that match the perimeter of the diaphragm device layer can be selected, with one end of the first capillary tube fixedly attached to the sidewall of the multi-resonance region of the device layer to provide support. A second capillary tube and optical fiber are then assembled to form the complete multi-resonance frequency FP sensor.

[0068] like Figure 2 In this embodiment, the device layer thicknesses, i.e., the heights of the top surfaces, of any two of the multiple resonance regions are different, and all the resonance regions are arranged at different heights on the periphery of the boss according to the surface heights.

[0069] To further simplify simulation during sensor design and computation during detection, the four resonant regions of the diaphragm can be configured in this embodiment to have the same surface height difference between any two adjacent resonant regions. This allows the resonant frequency range widths corresponding to each resonant region to be more consistent with the ideal state. Of course, the surface height difference between any two resonant regions with increasing or decreasing thicknesses can also be set to be non-unique, and the corresponding detection calculations can still be completed.

[0070] Example 3

[0071] What is different from the second embodiment is that in this embodiment, among the multiple resonance regions around the boss, starting from one of the resonance regions, the thickness of the device layer of the resonance region increases or decreases in sequence.

[0072] Similarly, in order to simplify calculations in practical applications, this embodiment is configured such that, in a plurality of resonance regions, starting from one resonance region, the thickness of the resonance regions increases or decreases by the same height value in sequence.

[0073] Example 4

[0074] In order to facilitate the assembly of the entire multi-resonance frequency FP sensor, make the overall structure of the optical fiber sensor more stable, and make the diaphragm have better resonance response performance, this embodiment has an extension area of the device layer body on the periphery of the multi-resonance region on the diaphragm, such as Figure 5 As shown, the diaphragm as a whole can still be designed to be circular or in other shapes.

[0075] Specifically, based on Example 1, the multi-resonance frequency FP sensor of this embodiment is as follows Figures 3 to 5 As shown, it includes a diaphragm, a first capillary, a second capillary, and an optical fiber. The diaphragm includes a device layer, a connecting layer, and a support layer. The support layer and the connecting layer are annular and connected to the periphery of the reflective end of the device layer and projected onto the periphery of multiple resonant regions. The upper and lower surfaces of the connecting layer are fixedly connected to the support layer and the device layer, respectively. The inner diameter of the first capillary is adapted to the outer diameter of the second capillary, and the outer diameter of the second capillary is adapted to the inner diameter of the support layer, so that they can fit together and provide support. Glue can be applied to the outer wall of the second capillary to bond it to the inner wall of the support layer, providing support and further improving the stability of the mechanism.

[0076] The entire diaphragm in this embodiment can be made based on SOI crystal, and the device layer, the connection layer and the support layer correspond to the silicon substrate layer 13, the silicon oxide layer 12 and the silicon base layer 11 of the SOI crystal respectively.

[0077] like Figure 4 and Figure 5 On the device layer, the boss is cylindrical, with four resonant regions, whose outer edges form a circle. The boss can also be set to other shapes such as polygons, and the shape of the outer edges of the multiple resonant regions and the number of resonant regions can also be other shapes.

[0078] like Figure 6 In this embodiment, the device layer thickness, i.e., the height of the top surface, of any two of the multiple resonant regions is different. Specifically, all resonant regions can be arranged at intervals around the periphery of the boss according to their surface heights. Alternatively, the four resonant regions can be arranged in descending order of thickness, with the surface height difference between any two adjacent resonant regions being equal. Alternatively, the surface height difference between any two resonant regions with increasing or decreasing thicknesses can be non-unique.

[0079] The boss area of the device layer should be within a certain range, such as no more than 1 / 4 of the total resonant area of the diaphragm, so as to achieve a wider overall resonant frequency range of the sensor while ensuring the boss's response sensitivity to the deformation of each resonant area.

[0080] The inner diameter of the first capillary tube is equal to the outer diameter of the second capillary tube, with the outer diameter of the first capillary tube slightly larger than its inner diameter, and the outer diameter of the second capillary tube much larger than its inner diameter. For example, the outer diameter of the first capillary tube is 4 mm and the inner diameter is 3 mm; the outer diameter of the second capillary tube is 3 mm and the inner diameter is 0.135 mm; the length of the optical fiber outside the second capillary tube is 2 mm to 3 mm. This can be adjusted as needed.

[0081] Example 5

[0082] Unlike Example 4, in this embodiment, among the multiple resonant regions, the thickness of the device layer corresponding to each resonant region increases or decreases sequentially, starting from one of the resonant regions. Furthermore, among the multiple resonant regions, the thickness of each resonant region increases or decreases sequentially, starting from one of the resonant regions, by the same height value.

[0083] In summary, in Examples 1 to 5, the optical fiber can be a single-mode optical fiber, the reflective layer can be a gold material attached to the reflective end surface of the diaphragm, and the first and second capillaries are both made of glass. The number of resonant zones is not limited to four and can be flexibly set to meet the needs of multiple frequency bands.

[0084] Example 6

[0085] refer to Figure 4 As shown, this embodiment introduces a method for preparing the asymmetric multi-resonance frequency FP optical fiber sensor in Examples 1 to 5. The method includes preparing the diaphragm. The preparation process of the diaphragm includes:

[0086] Coating a photoresist layer on the SOI wafer and performing a baking process;

[0087] The SOI wafer coated with a photoresist layer and baked is aligned with the mask and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask includes an upper mask and a lower mask, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask corresponds to the shape of the surface of the reflective end of the diaphragm;

[0088] For the exposed area of the silicon base layer of the SOI wafer, reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is continuously etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching, and according to the device layer thickness corresponding to the multiple resonance regions and the boss area, the etching is carried out layer by layer until the multiple resonance regions and bosses are obtained, thereby completing the preparation of the diaphragm.

[0089] Since multiple resonance regions and bosses of different thicknesses need to be prepared on the silicon substrate layer, when etching the silicon substrate layer of the SOI wafer, the number of required upper mask plates should adapt to the number of resonance regions, and each mask plate is made according to the different thicknesses and shapes of the bosses and multiple resonance regions.

[0090] The above-mentioned etching can be performed layer by layer from deep to shallow, that is, the protrusion is etched out last, or from shallow to deep, that is, the protrusion is etched out first.

[0091] As an etching operation mode, the silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and the device layer thickness corresponding to the multiple resonance regions and the boss area is etched layer by layer until the multiple resonance regions and the boss area are obtained, including:

[0092] According to the different thicknesses of the device layers of the bosses and multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0093] In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining a boss and multiple resonance regions in sequence;

[0094] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent boss, or according to the top surface height of the boss, to complete the etching of the current height level and obtain the corresponding resonant area or boss.

[0095] As another etching operation, the silicon substrate layer of the SOI wafer is etched using multiple deep reactive ion etching processes, and etching layer by layer according to the device layer thickness of the multiple resonance regions and the bosses until the multiple resonance regions and the bosses are obtained, including:

[0096] According to the different thicknesses of the device layers of the bosses and multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0097] In order from deep to shallow, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and bosses in sequence;

[0098] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, transferring the pattern on the mask plate of the corresponding height level to the photoresist layer, controlling the etching depth according to the surface height of the boss or resonance area to be etched, completing the etching of the current height level, and obtaining the corresponding boss or resonance area.

[0099] After the membrane is prepared, the membrane is assembled with the first capillary, the second capillary and the optical fiber according to the structure of the multi-resonance frequency FP sensor described in Examples 1 to 5 to obtain the multi-resonance frequency FP sensor.

[0100] Example 7

[0101] Based on Example 6, Figure 3 The multi-resonance frequency FP sensor shown is the preparation target, reference Figure 6 The preparation process of this embodiment includes the following steps:

[0102] S1, select or prepare a SOI crystal of appropriate size and shape, such as Figure 6 The circular SOI wafer substrate shown in step (a);

[0103] S2, making a mask for etching resonance regions and bosses of different thicknesses;

[0104] S3, such as Figure 6 In step (a), the SOI wafer is placed on a spin coater, a photoresist layer is uniformly coated on the silicon base layer, and the photoresist layer is pre-baked at 90-100° C. for 1-2 minutes to remove the solvent in the photoresist and enhance its stability during the exposure process;

[0105] S4, after precisely aligning the wafer covered with photoresist with the lower mask, the wafer is placed into an exposure machine. Ultraviolet light is irradiated on the transparent area of the mask to cause a photochemical reaction on the surface of the photoresist, forming a projection of the mask pattern. After exposure, a developer is used to remove the reacted photoresist area, while retaining the pattern structure of the unexposed area. A post-bake is then performed to enhance the adhesion and durability of the developed photoresist layer, thereby ensuring that it effectively protects the desired pattern area during the deep etching process;

[0106] S5, such as Figure 6 In step (b), for the silicon base layer of the SOI wafer, reactive ion etching (RIE) technology is used to gradually etch until the silicon oxide layer is exposed, and then continue as follows. Figure 6In step (c), the silicon oxide layer is etched and cleaned. After the silicon oxide layer is cleaned, the required pattern structure of the sensor reflective end can be accurately transferred to the wafer, forming the target microstructure of the diaphragm reflective end;

[0107] S6, such as Figure 6 In step (d), the silicon substrate layer of the SOI crystal is finely processed using the multiple deep reactive ion etching (DRIE) processes described in Example 6. Accurate structures of regions of varying thickness are achieved through step-by-step photolithography and etching. For example, first, photoresist is coated on the surface of the silicon substrate layer and photolithography is performed using an upper mask pattern to define the etching region for each layer. Subsequently, by controlling the etching depth, peripheral regions of decreasing thickness are sequentially formed. After each layer is etched, the upper mask is replaced and photolithography is performed again to define the etching depth of the next layer. The shallowest layer is etched in the central region to form the aforementioned boss.

[0108] S7, such as Figure 6 In step (e), vacuum sputtering is used to metallize the bottom surface of the silicon substrate, i.e., the surface of the silicon substrate exposed at the reflective end of the diaphragm. By sputtering a metal target in a vacuum environment, gold atoms are uniformly deposited on the diaphragm surface to form a highly reflective gold film, thus achieving precise processing of the asymmetric multi-resonant structure diaphragm.

[0109] S8. Fix the first capillary tube vertically to the bracket and evenly apply a small amount of UV glue to its end face. Then, using a microscope, precisely align and attach the membrane to the end face of the first capillary tube, ensuring that the inner wall of the first capillary tube closely adheres to the remaining silicon base layer and silicon oxide layer, i.e., the outer wall of the connecting layer and the supporting layer. Irradiate the membrane with a UV curing lamp at 360° for 10 minutes to achieve a preliminary bond between the membrane and the first capillary tube.

[0110] S9, process the SMF fiber, remove its coating, and then gently wipe the fiber with a dust-free paper soaked in alcohol to thoroughly remove coating residue. Use a precision cutting tool to cut the fiber to a length 2 to 3 mm longer than the length of the second capillary. Make sure the fiber end face is cut flat and smooth without defects to provide a good optical interface for subsequent assembly. Insert the bare fiber into the second capillary, ensuring that the fiber end face is aligned with the center of the tube. Apply a small amount of UV glue to both ends of the second capillary and irradiate it with a UV lamp for 10 minutes to complete the initial fixation of the fiber and the second capillary.

[0111] S10, align and assemble the two cured components obtained after S8 and S9 on a three-dimensional adjustment frame to ensure that each component is precisely aligned to achieve an effective acoustic conduction path. A Fabry-Perot interferometer cavity is formed between the end face of the single-mode optical fiber and the gold-plated surface of the diaphragm to measure and respond to sound signals of different frequencies.

[0112] The initial cavity length of the fabricated fiber optic sensor's Fabry-Perot interferometer cavity is optimized and adjusted based on the optimal interference spectrum observed in real time to ensure the sensor's optimal frequency response and sensitivity. The optimal interference spectrum is obtained by connecting the fiber optic sensor's single-mode fiber end to an SM155 fiber Bragg grating sensor interrogator and performing real-time spectral adjustment on the reflected light. Specifically:

[0113] The uncured fiber optic sensor is mounted on a three-dimensional adjustment frame. The sensor's position is gradually adjusted along each of the three axes (X, Y, and Z) using a fine-tuning mechanism. A demodulator connected to a computer monitors the interferometric spectrum in real time until the contrast reaches the optimal position. The cavity length at this point is recorded and used as the sensor's initial reference length to ensure stability and high sensitivity in subsequent measurements.

[0114] After the initial curing, the assembled optical fiber FP sensor is placed in a temperature-controlled box and adjusted to an appropriate temperature to ensure that the UV glue is completely cured at that temperature, thereby enhancing the structural stability and anti-interference ability of the entire sensor.

[0115] After the sensor structure is solidified, a frequency response test is performed to ensure that the sensor can detect multiple resonant frequencies and that the response areas of multiple resonant frequencies can cover signals in different frequency bands, thereby ensuring that the sensor product has high sensitivity, response speed, and application capabilities in complex environments.

[0116] Experiments have shown that the multi-resonance frequency FP sensor fabricated according to this invention can effectively improve signal detection sensitivity and frequency response. In particular, in scenarios requiring simultaneous detection of signals in multiple frequency bands, the sensor offers greater flexibility and high-precision performance, overcoming the limitations of traditional fiber optic sensors that rely solely on a single resonant frequency.

[0117] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. A multi-resonance frequency FP sensor, characterized in that: comprising a diaphragm, a first capillary tube, a second capillary tube and an optical fiber; The diaphragm includes a device layer, one end of the device layer is an input end, and the other end is a reflection end; the reflection end surface of the device layer is a plane and is provided with a reflection layer; a boss is provided in the middle of the input end of the device layer, and a plurality of resonance regions are provided around the periphery of the boss, wherein the plurality of resonance regions are adjacent to each other, the device layer thicknesses of adjacent resonance regions are different, and the device layer thickness of the boss portion is greater than the device layer thickness of all resonance regions; The periphery of the diaphragm is fixed to one end of the first capillary tube, and the reflective layer faces the interior of the first capillary tube; One end of the second capillary tube is inserted into the first capillary tube and fixedly connected to the reflective end of the diaphragm; One end of the optical fiber is inserted into the second capillary and fixed in the second capillary, the axial projection of the optical fiber is located in the reflection layer area corresponding to the boss portion, and there is a light transmission gap between the end of the optical fiber and the reflection layer.

2. The multi-resonance frequency FP sensor according to claim 1, characterized in that: The boss is cylindrical, the resonance zone is in the shape of a sector ring arranged around the boss, and all the resonance zones are spliced into a circular ring shape surrounding the boss.

3. The multi-resonance frequency FP sensor according to claim 2, characterized in that: The central angles of the resonance regions of the sector rings are equal, and the input surface areas are equal.

4. The multi-resonance frequency FP sensor according to claim 1, wherein: Any two of the plurality of resonance regions have different thicknesses.

5. The multi-resonance frequency FP sensor according to claim 4, characterized in that: Among the multiple resonance regions, starting from one resonance region, the thickness of the resonance regions increases or decreases in sequence.

6. The multi-resonance frequency FP sensor according to claim 5, characterized in that: Among the multiple resonance regions, starting from one resonance region, the thickness of the resonance regions increases or decreases by the same height value in sequence.

7. The multi-resonance frequency FP sensor according to claim 4, characterized in that: All the resonance areas are arranged at different heights on the periphery of the boss according to the surface height.

8. The multi-resonance frequency FP sensor according to claim 7, characterized in that: According to the order of the thickness values of the resonance regions from large to small, the thickness differences between any two resonance regions with adjacent thickness values are equal.

9. The multi-resonance frequency FP sensor according to any one of claims 1 to 8, characterized in that: The diaphragm further includes a support layer and a connection layer, the support layer and the connection layer are annular, connected to the periphery of the reflective end of the device layer, and projected onto the periphery of the multiple resonance regions, wherein the upper and lower surfaces of the connection layer are respectively fixedly connected to the support layer and the device layer; The end face of one end of the first capillary is fixedly connected to the support layer, and the outer diameter of the second capillary is adapted to the inner diameters of the support layer and the first capillary, so that the outer wall of the second capillary is respectively in contact with the inner wall of the support layer and the inner wall of the first capillary.

10. The multi-resonance frequency FP sensor according to claim 1, characterized in that: The optical fiber is a single-mode optical fiber, the reflective layer is a gold material attached to the reflective end surface of the diaphragm, and the first capillary is made of glass.

11. The multi-resonance frequency FP sensor according to any one of claims 1 to 8, characterized in that: The ratio of the area of the boss region to the sum of the areas of the boss and the resonance region is less than 1 / 4.

12. The multi-resonance frequency FP sensor according to claim 11, characterized in that: The inner diameter of the first capillary tube is equal to the outer diameter of the second capillary tube. The outer diameter of the first capillary tube is slightly larger than the inner diameter thereof, and the outer diameter of the second capillary tube is much larger than the inner diameter thereof.

13. The method for preparing the multi-resonance frequency FP sensor according to any one of claims 1 to 12, characterized in that: The process of preparing the diaphragm includes: Coating a photoresist layer on the SOI wafer and performing a baking process; The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the surface of the reflective end of the diaphragm; For the exposed area of the silicon base layer of the SOI wafer, reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is further etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching, and according to the thickness of the multiple resonance regions and bosses, the etching is carried out layer by layer until the multiple resonance regions and bosses are obtained, thereby completing the preparation of the diaphragm.

14. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, each made according to different thicknesses and shapes of the boss and the multiple resonance regions; The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the thickness of the multiple resonance regions and the bosses to obtain the multiple resonance regions and the bosses, including: According to the different thicknesses of the bosses and the multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels; In order from deep to shallow, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and bosses in sequence; Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent boss, or according to the surface height of the boss, to complete the etching of the current height level and obtain the corresponding resonant area or boss.

15. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, each made according to different thicknesses and shapes of the boss and the multiple resonance regions; The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the thickness of the multiple resonance regions and the bosses to obtain the multiple resonance regions and the bosses, including: According to the different thicknesses of the bosses and the multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels; In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining a boss and multiple resonance regions in sequence; Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, transferring the pattern on the mask plate of the corresponding height level to the photoresist layer, controlling the etching depth according to the surface height of the boss or resonance area to be etched, completing the etching of the current height level, and obtaining the corresponding boss or resonance area.

16. The preparation method according to any one of claims 13 to 15, characterized in that: It also includes the assembly of sensors, including: Fix the first capillary tube on the bracket, apply UV glue on its end surface, align and attach the reflective end of the diaphragm to the end surface of the first capillary tube, and irradiate with ultraviolet light to firmly connect the diaphragm and the first capillary tube; Cut the required length of optical fiber, remove the coating and clean the bare fiber; Insert the bare fiber into the inner hole of the second capillary, apply UV glue on both ends of the second capillary, and irradiate with UV light to fix the optical fiber and the second capillary relatively; The optical fiber is aligned with the center of the diaphragm boss, and the second capillary tube through which the optical fiber is passed is placed into the first capillary tube and fixed to the reflective end surface of the diaphragm to obtain the multi-resonance FP optical fiber sensor.

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