Multi-resonant-frequency FP sensor and preparation method thereof

Abstract

The invention aims to provide a multi-resonant-frequency FP sensor and a preparation method thereof, and belongs to the technical field of optical fiber sensors. The sensor comprises a diaphragm, a first capillary tube, a second capillary tube and an optical fiber. The diaphragm comprises a device layer; a reflecting layer is arranged on the end face of the reflecting end of the device layer, a boss is arranged in the middle of the input end, a plurality of resonance areas are arranged around the periphery of the boss, every two resonance areas are adjacent, the thicknesses of the adjacent resonance areas are different, and the thickness of the boss is larger than that of all the resonance areas. The periphery of the diaphragm is fixed at one end of the first capillary, and the reflecting layer faces the interior of the first capillary; one end of the second capillary is inserted into the first capillary and fixed at the reflecting end of the diaphragm; one end of the optical fiber is inserted into and fixed in the second capillary, the axial projection of the optical fiber is located at the boss, and an optical transmission interval is arranged between the end of the optical fiber and the reflecting layer. According to the invention, the limitation of a multi-resonant optical fiber sensor in the aspects of sensitivity and frequency adjustment can be overcome, and more efficient signal detection and response are realized.

Description

Technical Field

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

[0002] With the continuous development of optical fiber sensing technology, Fabry-Perot (FP) sensors have been widely used in acoustic signal detection, vibration monitoring, and environmental monitoring. FP sensors have advantages such as high sensitivity, low power consumption, and long-distance transmission, and are widely used in fields such as structural health monitoring, noise detection, and acoustic signal analysis. However, traditional FP sensors usually operate relying on a single resonant frequency, which makes them face obvious performance bottlenecks in environments with complex or multi-frequency acoustic signals. Since they are only sensitive to signals in a specific frequency range, FP sensors with single-frequency response are prone to losing accuracy and sensitivity when dealing with multi-band sound waves, limiting their application effects in variable environments.

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

[0004] The purpose of the present invention is to provide a multi-resonant frequency FP sensor and a preparation method thereof, which, on the basis of realizing multi-resonant frequencies, overcome the limitations of multi-resonant fiber sensors in terms of sensitivity and frequency adjustment, and achieve more efficient signal detection and response. The technical solutions adopted by the present invention are as follows.

[0005] On the one hand, the present invention provides a multi-resonant frequency FP sensor, including a diaphragm, a first capillary, a second capillary, 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 end face of the reflection end 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 resonant regions are arranged around the outer periphery of the boss. The plurality of resonant regions are adjacent to each other in pairs, the thickness of the device layer at the adjacent resonant region parts is different, and the thickness of the device layer at the boss part is greater than the thickness of the device layer at all resonant region parts;

[0007] The peripheral part of the diaphragm is fixed to one end of the first capillary, and the reflective layer faces the inside of the first capillary;

[0008] One end of the second capillary is inserted into the first capillary 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 reflective layer area corresponding to the boss part, and there is an optical transmission gap between the end of the optical fiber and the reflective layer.

[0010] In the above technical solution, multiple resonance areas with different thicknesses and the central boss provided on the diaphragm constitute a multi-resonance structure of the sensor, and a Fabry-Perot interference cavity is formed between the optical fiber and the reflective layer of the diaphragm. The optical fiber emits incident light to the reflective layer and receives the reflected light reflected by the Fabry-Perot interference cavity. When the sound pressure acts on the surface of the diaphragm, the diaphragm will deform, while the optical fiber fixedly connected to the capillary will not displace. Therefore, the cavity length of the FP cavity will change, and then the sound pressure value of the ultrasonic wave can be calculated by using the optical path difference of the reflected light caused by the change in the cavity length of the Fabry-Perot interference cavity. During this process, since the thicknesses of the resonance areas of the diaphragm in the present invention are different, their respective maximum deformation amounts also occur at different frequencies. When deforming, the central boss will also be driven to deform. Therefore, multiple resonance peaks will appear in the frequency response of the diaphragm. When the resonance area deforms, it can indirectly reflect the deformation amount at the central boss of the diaphragm, that is, there is a large deformation and thus a large sensitivity at the center of the diaphragm at multiple frequencies, enabling the present invention to achieve an improvement in sensitivity under multi-resonance frequency response.

[0011] Optionally, the boss is cylindrical, and the shape of the resonance area is a fan-shaped ring arranged around the boss. All the resonance areas are spliced into a circular ring shape surrounding the boss. That is, in this embodiment, the sensitive area of the diaphragm is a circle. In addition, it can also be set to other shapes such as a square.

[0012] Optionally, the central angles of the fan-shaped ring resonance areas are equal, and the input surface areas are equal. This is convenient for simulation during sensor design and calculation during actual application.

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

[0014] As an embodiment of different thickness levels of the resonance area: among the multiple resonance areas, starting from one of the resonance areas, the thickness of the resonance area increases or decreases in sequence.

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

[0016] As another implementation of different thickness levels in the resonance region: all resonance regions are arranged at intervals of high and low according to the surface height on the outer periphery of the boss.

[0017] Preferably, in the order of decreasing thickness values of the resonance regions, the thickness difference between any two adjacent resonance regions with adjacent thickness values is equal. This setting can simplify the logical operation when the sensor is actually applied to detection.

[0018] Optionally, 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 reflection end of the device layer, and projected on the outer periphery of a plurality of resonance regions, wherein the upper and lower surfaces of the connection layer are fixedly connected to the support layer and the device layer respectively;

[0019] One end face of the first capillary is fixedly connected to the support layer. 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 to the outer wall of the second capillary to bond it 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 surface of the reflection end of the diaphragm, which can be formed by vacuum ion sputtering technology. Other metal materials with high reflection performance can also be used as the material of the reflective layer.

[0021] In the above technical solutions, the setting of the support layer can realize the mechanical support of the first capillary and the capillary to the diaphragm and the optical fiber, and ensure the structural stability of the overall sensor.

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

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

[0024] In the second aspect, the present invention provides a method for manufacturing the multi-resonant frequency FP sensor described in the first aspect, including manufacturing the diaphragm, and the manufacturing process of the diaphragm includes:

[0025] Coat the SOI wafer with a photoresist layer and perform a baking process;

[0026] Align the SOI wafer coated with the photoresist layer and baked with a mask plate, then place it into an exposure machine for exposure and development processing, and then perform a post-baking process on the exposed and developed SOI wafer; wherein, the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon-based substrate layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the surface shape of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the surface shape of the reflection end of the diaphragm;

[0027] For the exposed area of the silicon-based substrate layer of the SOI wafer, use the reactive ion etching method to etch until the silicon oxide layer is exposed, continue to etch and clean the silicon oxide layer, and perform metal coating on the area exposed after cleaning the silicon oxide layer to obtain the reflection layer; for the silicon substrate layer of the SOI wafer, use the multi-step deep reactive ion etching process to etch, and layer by layer etch according to the thicknesses of the multiple resonance regions and the boss until the multiple resonance regions and the boss are obtained to complete the preparation of the diaphragm.

[0028] The above layer-by-layer etching can be carried out from shallow to deep layer by layer, that is, first etch out the boss, or from deep to shallow layer by layer, that is, finally etch out the boss.

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

[0030] For the silicon substrate layer of the SOI wafer, use the multi-step deep reactive ion etching process to etch, and layer by layer etch according to the thicknesses of the multiple resonance regions and the boss until the multiple resonance regions and the boss are obtained, including:

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

[0032] In the order from deep to shallow, use the corresponding mask plates in turn to perform the etching operation processes of each height level on the silicon substrate layer of the SOI crystal, and obtain multiple resonance regions and bosses in turn;

[0033] 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 to be etched to the photoresist layer by using the mask plate corresponding to the current height level, and controlling the etching depth according to the surface height difference between the resonance region to be etched and the adjacent surface resonance region, or according to the surface height difference between the resonance region to be etched and the adjacent boss, or according to the surface height of the boss, and complete the etching of the current height level to obtain the corresponding resonance region or boss.

[0034] As another implementation manner of the etching operation, optionally, the number of the upper mask plates is multiple, which are respectively made according to the different thicknesses and shapes of the convex platform and the multiple resonant regions;

[0035] For the silicon substrate layer of the SOI wafer, the deep reactive ion etching process is used for etching multiple times. According to the thicknesses of the multiple resonant regions and the convex platform, layer-by-layer etching is performed until the multiple resonant regions and the convex platform are obtained, including:

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

[0037] In the order from shallow to deep, the etching operation processes of each height level are sequentially performed on the silicon substrate layer of the SOI crystal by using the corresponding mask plates, and the convex platform and the multiple resonant regions are sequentially obtained;

[0038] Among them, for each height level, the etching operation process includes: coating photoresist on the surface of the current silicon substrate layer, 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 convex platform or resonant region to be etched, and completing the etching of the current height level to obtain the corresponding convex platform or resonant region.

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

[0040] Fix the first capillary on the bracket, apply UV glue on its end face, align and attach the reflection end of the diaphragm to the end face of the first capillary, and use an ultraviolet lamp to irradiate to fixedly connect the diaphragm and the first capillary;

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

[0042] Insert the bare fiber into the inner hole of the capillary, apply UV glue at both ends of the second capillary, and use an ultraviolet lamp to irradiate to relatively fix the optical fiber and the second capillary;

[0043] Align the optical fiber with the center of the convex platform of the diaphragm, place the second capillary with the optical fiber inserted into the first capillary and fix it on the surface of the reflection end of the diaphragm to obtain the multi-resonant FP optical fiber sensor.

[0044] Beneficial effects

[0045] The multi-resonant frequency FP sensor of the present invention, through the combined design of a boss and a multi-resonant region with a graded thickness on the periphery, ensures that the response regions of multiple resonant frequencies can cover signals in multiple different frequency bands, so as to significantly broaden the working frequency range of the sensor, improve the application performance of the FP sensor in multi-band measurement, avoid the limitation of traditional sensors relying only on a single resonant frequency, and the sensor can simultaneously respond to signals in multiple frequency bands, greatly improving the flexibility, accuracy, response speed of the sensor and its application ability in complex environments. Especially when it is necessary to capture acoustic signals in a complex and wide frequency range, this structure can effectively improve the overall performance of the sensor and promote the development of fiber optic sensor technology in more diverse application scenarios.

[0046] The preparation method of the present invention designs the etching operation process according to the structural characteristics of the diaphragm, and realizes the layer-by-layer etching of the multi-thickness resonant region and the boss by cooperating with different mask plates, which can ensure the realization of the characteristics of high sensitivity and wide frequency response range of the sensor. At the same time, the nested protection design of the optical fiber and the capillary tube, etc., enables the present invention to ensure the central positioning accuracy and assembly firmness of the sensor diaphragm, enables the optical fiber to be stably embedded without damaging the diaphragm, and further improves the stability of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The following shows a schematic structural diagram of the multi-resonant frequency FP sensor in an embodiment of the present invention;

[0048] Figure 2 The following shows the present invention Figure 1 A schematic three-dimensional structure diagram of the diaphragm of the multi-resonant frequency FP sensor;

[0049] Figure 3 The following shows a schematic structural diagram of the multi-resonant frequency FP sensor in another embodiment of the present invention;

[0050] Figure 4 The following shows Figure 3 A schematic structure diagram of the diaphragm of the multi-resonant frequency FP sensor;

[0051] Figure 5 The following shows Figure 4 A schematic plan view of the diaphragm from a top view angle;

[0052] Figure 6 The following shows a schematic diagram of the diaphragm preparation process of the multi-resonant frequency FP sensor in an embodiment of the present invention;

[0053] In the figure, 1 - diaphragm, 11 - silicon-based bottom layer, 12 - silicon oxide layer, 13 - silicon substrate bottom layer, 14 - reflection layer, 2 - first capillary tube, 3 - second capillary tube, 4 - optical fiber, 5 - resonant region, 6 - boss. DETAILED DESCRIPTION OF THE INVENTION

[0054] The following further describes in conjunction with the accompanying drawings and specific embodiments. The described embodiments are only exemplary descriptions of the present invention for clarifying the present invention and should not be construed as limitations on the present invention. Without conflict, the various embodiments of the present invention and their technical features can be combined with each other.

[0055] Embodiment 1

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

[0057] Referring to Figures 1 to 6 , the diaphragm 1 includes a device layer, which can be processed from the silicon substrate layer of an SOI crystal. One end of the device layer is the input end, and the other end is the reflection end; the end face of the reflection end 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 resonant regions 5 are arranged around the outer periphery of the boss. The plurality of resonant regions are adjacent to each other in pairs, the thickness of the device layer at the adjacent resonant regions is different, and the thickness of the device layer at the boss part is greater than the thickness of the device layer at all resonant regions;

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

[0059] One end of the second capillary 3 is inserted into the first capillary and fixedly connected to the reflection 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 reflection layer area corresponding to the boss part, and there is an optical transmission interval between the end of the optical fiber and the reflection layer.

[0061] In this embodiment, the plurality of resonant regions with different thicknesses and the middle boss provided on the diaphragm constitute the multi-resonant FP structure of the sensor. The first capillary is used for support, and the second capillary is used to protect the optical fiber inserted therein to ensure the alignment of the optical fiber with the boss area of the diaphragm and realize an accurate optical fiber interference measurement path. The end face of the optical fiber and the surface of the reflection layer at the center of the diaphragm form a Fabry-Perot interference cavity for detecting acoustic signals.

[0062] When the sound pressure acts on the surface of the diaphragm, the diaphragm will deform. Since the thicknesses of the resonant regions of the diaphragm are different, the maximum deformations of the resonant regions also occur at different frequencies. When the resonant regions deform, the central boss 6 will also deform. Therefore, multiple resonant peaks will appear in the frequency response of the diaphragm, and the central boss of the diaphragm will have a large deformation at multiple frequencies, that is, it has a high sensitivity.

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

[0064] Embodiment 2

[0065] Based on Embodiment 1, as Figure 1 and Figure 2 In the multi-resonant frequency FP sensor of this embodiment, the diaphragm only includes a device layer made of silicon material. On this device layer, the boss is a cylinder, and there are 4 resonant regions, which are respectively fan-shaped rings wound around the outer periphery of the boss, and their outer edges enclose a circle.

[0066] In addition, the shape of the boss can also be set to other shapes such as square, etc. However, a circle is more friendly to the deformation response consistency of the multi-resonant regions, which is convenient for simulation and logical operations during detection. The shape enclosed by the outer edges of multiple resonant regions can also be other shapes, and the number can also be adjusted according to needs to meet the detection requirements of different frequency band range scenarios.

[0067] Figure 2 Shows the multiple resonant regions and the boss structure on the device layer of the diaphragm in this embodiment. Based on this diaphragm structure, when assembling with the first capillary, the second capillary, and the optical fiber, as Figure 1 , a first capillary with an inner ring shape and size adapted to the peripheral shape of the diaphragm device layer can be selected, so that one end of the first capillary is fixedly connected to the side wall of the multi-resonant region of the device layer to play a supporting role. Further assemble the second capillary and the optical fiber to obtain the entire multi-resonant frequency FP sensor.

[0068] As Figure 2 In this embodiment, among the multiple resonant regions, the device layer thicknesses of any two of them, that is, the heights of the top surfaces, are different, and all the resonant regions are arranged at intervals of high and low according to the surface height around the outer periphery of the boss.

[0069] In order to further simplify the simulation during sensor design and the operations during detection, for the four resonant regions in the diaphragm, in this embodiment, it can be set that the surface height difference between any two adjacent resonant regions with adjacent surface height sizes is equal, then the width of the resonant frequency range corresponding to each resonant region is more consistent with the ideal state. Of course, it can also be set that the surface height difference between any two resonant regions with increasing or decreasing thickness is not unique, and the corresponding detection calculations can still be completed.

[0070] Embodiment 3

[0071] Different from Embodiment 2, in the multiple resonant regions around the boss in this embodiment, starting from one of the resonant regions, the device layer thickness of the resonant regions increases or decreases in sequence.

[0072] Similarly, for simplifying the calculations during actual applications, in this embodiment, among multiple resonant regions, starting from one of the resonant regions, the thickness of the resonant regions increases or decreases by the same height value in sequence.

[0073] Embodiment 4

[0074] For facilitating the assembly of the entire multi-resonant frequency FP sensor, making the overall structure of the fiber optic sensor more stable, and enabling the diaphragm to have better resonant response performance, in this embodiment, an extension region of the device layer body is provided at the periphery of the multi-resonant regions on the diaphragm. As Figure 5 shown, the overall diaphragm can still be designed as circular or other shapes.

[0075] Specifically, based on Embodiment 1, the multi-resonant frequency FP sensor of this embodiment is as Figures 3 to 5 shown, and it includes a diaphragm, a first capillary, a second capillary, and an optical fiber; wherein the diaphragm includes a device layer, a connection layer, and a support layer. The support layer and the connection layer are annular, connected to the periphery of the reflection end of the device layer, and projected outside the periphery of multiple resonant regions. The upper and lower surfaces of the connection 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 as to be able to fit together to achieve a supporting effect. Here, glue can be applied to the outer wall of the second capillary to bond it to the inner wall of the support layer, further enhancing the stability of the mechanism while providing support.

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

[0077] As Figure 4 and Figure 5 shown, on the device layer, the boss is a cylinder, there are 4 resonant regions, and their outer edges enclose a circle. The boss can also be set as other shapes such as polygons, and the shape enclosed by the outer edges of multiple resonant regions and the number of resonant regions can also be other shapes.

[0078] As Figure 6 shown, among multiple resonant regions in this embodiment, the thickness of the device layer, that is, the height where the top surface is located, is different for any two of them. Specifically, it can be set that all resonant regions are arranged at intervals of high and low according to the surface height on the periphery of the boss, or it can be set that for the four resonant regions, they are sorted according to the thickness value from large to small, and the surface height difference between any two adjacent resonant regions with adjacent thickness values is equal. It can also be set that the surface height difference between any two resonant regions with increasing or decreasing thickness is not unique.

[0079] The area of the boss in the device layer should be within a certain range. For example, the area of the boss should not be greater than 1 / 4 of the total resonant area of the diaphragm, which can broaden the overall resonant frequency range of the sensor while ensuring the response sensitivity of the boss to the deformation of each resonant region.

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

[0081] Example 5

[0082] Different from Example 4, in this example, among multiple resonant regions, among the multiple resonant regions around the boss, starting from one of the resonant regions, the thickness of the device layer corresponding to the resonant regions increases or decreases in sequence. And among the multiple resonant regions, starting from one of the resonant regions, the thickness of the resonant regions increases or decreases by the same height value in sequence.

[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 both the first capillary and the second capillary are made of glass. The number of resonant regions is not limited to 4 and can be flexibly set according to the needs of multiple frequency bands.

[0084] Example 6

[0085] Reference Figure 4 As shown, this example introduces the preparation method of the asymmetric multi-resonant frequency FP optical fiber sensor in Examples 1 - 5. The method includes preparing the diaphragm, and the preparation process of the diaphragm includes:

[0086] Coat a photoresist layer on the SOI wafer and perform a baking treatment.

[0087] Align the SOI wafer coated with the photoresist layer and baked with the mask plate and place it in an exposure machine for exposure and development treatment, and then perform a post-baking treatment on the exposed and developed SOI wafer; wherein, the mask plate includes an upper mask plate and a lower mask plate, respectively etching the silicon substrate layer and the silicon-based substrate layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the input end surface of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the reflective end surface of the diaphragm.

[0088] For the exposed area of the silicon-based bottom layer of the SOI wafer, reactive ion etching is used for etching until the silicon oxide layer is exposed. Then, the silicon oxide layer is continuously etched and cleaned. After the silicon oxide layer is cleaned, metal coating is performed on the exposed area to obtain the reflection layer. For the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching. According to the device layer thickness corresponding to multiple resonance regions and the boss regions, etching is performed layer by layer until the multiple resonance regions and the bosses are obtained, and the preparation of the diaphragm is completed.

[0089] Since multiple resonance regions with different thicknesses and bosses need to be prepared on the silicon substrate layer, when etching the silicon substrate layer of the SOI wafer, the number of upper mask plates required 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 layer-by-layer etching can be performed from deep to shallow layer by layer, that is, the bosses are etched out finally, or from shallow to deep layer by layer, that is, the bosses are etched out first. Specifically:

[0091] As an etching operation method, for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching. According to the device layer thickness corresponding to multiple resonance regions and the boss regions, etching is performed layer by layer until the multiple resonance regions and the bosses are obtained, including:

[0092] According to the different device layer thicknesses 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 the order from shallow to deep, the corresponding mask plates are used in turn to perform the etching operation processes of each height level on the silicon substrate layer of the SOI crystal, and the bosses and multiple resonance regions are obtained in turn;

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

[0095] As another etching operation method, for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used for etching. According to the device layer thickness corresponding to multiple resonance regions and the bosses, etching is performed layer by layer until the multiple resonance regions and the bosses are obtained, including:

[0096] According to the different device layer thicknesses 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] According to the order from deep to shallow, using the corresponding mask plates in sequence, perform the etching operation process of each height level on the silicon substrate layer of the SOI crystal, and obtain multiple resonant regions and bosses in sequence;

[0098] Among them, for each height level, the etching operation process includes: coating photoresist on the surface of the current silicon substrate layer, 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 resonant region to be etched, completing the etching of the current height level, and obtaining the corresponding boss or resonant region.

[0099] After the diaphragm is prepared, according to the structures of the multi-resonant frequency FP sensors introduced in Embodiments 1 to 5, assemble the diaphragm with the first capillary, the second capillary, and the optical fiber, and then the multi-resonant frequency FP sensor is obtained.

[0100] Embodiment 7

[0101] Based on Embodiment 6, taking Figure 3 the shown multi-resonant frequency FP sensor as the preparation target, referring to Figure 6 , the preparation process of this embodiment includes the following steps:

[0102] S1, select or obtain an SOI crystal with an appropriate area size and shape, such as Figure 6 the circular SOI wafer substrate shown in process (a) in

[0103] S2, fabricate mask plates for etching resonant regions and bosses with different thicknesses;

[0104] S3, as in Figure 6 process (a) in , place the SOI wafer on a spin coater, uniformly coat a photoresist layer on the silicon substrate layer, perform pre-baking on the photoresist layer 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, precisely align the wafer covered with photoresist with the lower mask plate and then place it in an exposure machine. Through ultraviolet light irradiating the transparent area of the mask plate, cause a photochemical reaction on the surface of the photoresist to form a projection of the mask plate pattern. After exposure, use a developer to remove the reacted photoresist area and retain the graphic structure of the unexposed area. Subsequently, perform post-baking to enhance the adhesion and tolerance of the developed photoresist layer to ensure that it effectively protects the required graphic area during the deep etching process;

[0106] S5, as in Figure 6 process (b) in , for the silicon substrate layer of the SOI wafer, adopt the reactive ion etching (RIE) technology to gradually etch until the silicon oxide layer is exposed, and continue as in Figure 6In step (c), the silicon oxide layer is etched and cleaned. After the silicon oxide layer is cleaned, the required graphic structure at the reflection end of the sensor can be accurately transferred to the wafer, forming the target microstructure at the diaphragm reflection end;

[0107] S6, as in Figure 6 In step (d), for the silicon substrate layer of the SOI crystal, the multi-step deep reactive ion etching (DRIE) process introduced in Example 6 is used for fine processing. Precise structures in different thickness regions are achieved through successive photolithography and etching. For example: First, a photoresist is coated on the surface of the silicon substrate layer and lithographed using an upper mask pattern to define the etching regions for each layer. Subsequently, by controlling the etching depth, peripheral regions with decreasing thickness are formed in sequence. After each layer of etching is completed, the upper mask is replaced and lithography is performed again to define the etching depth for the next layer. And the shallowest etching is performed in the central region to form the boss;

[0108] S7, as in Figure 6 In step (e), vacuum sputtering technology is used to deposit a metal film on the bottom surface of the silicon substrate layer, that is, the surface of the silicon substrate layer exposed at the diaphragm reflection end. By sputtering a metal target in a vacuum environment, gold atoms are evenly deposited on the diaphragm surface to form a highly reflective gold film layer. Thus, the precise processing of the asymmetric multi-resonant structure diaphragm is achieved;

[0109] S8, vertically fix the first capillary on the bracket and evenly apply a small amount of UV glue on its end face. Subsequently, under the assistance of a microscope, accurately align and attach the diaphragm to the end face of the first capillary, so that the inner wall of the first capillary is closely attached to the remaining silicon-based substrate layer and the silicon oxide layer, that is, the outer walls of the connection layer and the support layer. Use an ultraviolet curing lamp to irradiate for 10 minutes at 360° to preliminarily bond and fix the diaphragm to the first capillary;

[0110] S9, process the SMF optical fiber, remove its coating layer, then gently wipe the optical fiber with a lint-free paper dipped in alcohol to thoroughly remove the coating residues. Use a precision cutting tool to cut the optical fiber to a length 2 to 3 millimeters longer than the length of the second capillary, and make the end face of the optical fiber cut flat to ensure it is smooth and defect-free, providing a good optical interface for subsequent assembly. Insert the bare optical fiber into the second capillary, ensure that the end face of the optical fiber is aligned with the center inside the tube, apply a small amount of UV glue to both ends of the second capillary, and irradiate with an ultraviolet lamp for 10 minutes to preliminarily fix the optical fiber to the second capillary;

[0111] S10, align and assemble the two cured components obtained after S8 and S9 on a three-dimensional adjustment rack, ensure that all components are accurately positioned, so as to achieve an effective acoustic conduction path. A Fabry - Perot interferometric cavity is formed between the end face of the single-mode optical fiber and the gold-plated surface of the diaphragm, which is used to measure and respond to sound signals of different frequencies.

[0112] The fabricated fiber optic sensor optimizes and adjusts the initial cavity length of its Fabry-Perot interferometric cavity according to the optimally observed interference spectrum in real time to ensure the best frequency response and sensitivity of the sensor. The acquisition of the optimally observed interference spectrum is achieved by connecting the single-mode fiber end of the fiber optic sensor to an sm155 fiber grating sensing demodulator and performing real-time spectral adjustment on the reflected light. Specifically:

[0113] Fix the uncured fiber optic sensor on a three-dimensional adjustment frame, gradually adjust the position of the sensor in the X, Y, and Z axes directions through the fine adjustment frame, and observe the change of the interference spectrum in real time through the demodulator connected to the computer until the contrast reaches the optimal position. The cavity length at this time is recorded and used as the initial reference length of the sensor to ensure the subsequent detection stability and high sensitivity.

[0114] After preliminary curing, place the assembled fiber optic FP sensor in a temperature control box and adjust it to an appropriate temperature to ensure that the UV glue is completely cured at this temperature, thereby enhancing the structural stability and anti-interference ability of the entire sensor.

[0115] After the sensor structure is cured, perform a frequency response test to ensure that the sensor can detect multiple resonant frequencies and the response regions of multiple resonant frequencies can cover signals in different frequency bands to ensure that the sensor product has high sensitivity, response speed, and application ability in complex environments.

[0116] Experiments prove that the multi-resonant frequency FP sensor fabricated according to the present invention can effectively improve the sensitivity and frequency response ability of signal detection. Especially in scenarios where it is necessary to detect signals in multiple frequency bands simultaneously, the sensor can provide more flexible and high-precision performance, overcoming the limitations of traditional fiber optic sensors that rely only on a single resonant frequency.

[0117] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. These all fall within the protection scope of the present invention.

Claims

1. A multi-resonance frequency FP sensor, characterized in that: It includes a diaphragm, a first capillary tube, a second capillary tube and an optical fiber; The diaphragm comprises a device layer, one end of the device layer is an input end, and the other end is a reflection end; the end surface of the reflection end 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, and the plurality of resonance regions are adjacent to each other, the device layer thicknesses at adjacent resonance regions are different, and the device layer thickness at the boss is greater than the device layer thickness at all resonance regions; The peripheral portion 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 is inserted into the first capillary 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 interval 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, characterized in that: 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 of the resonance regions, 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 of the resonance regions, 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 difference between any two resonance regions with adjacent thickness values ​​is equal.

9. The multi-resonance frequency FP sensor according to any one of claims 1 to 8, characterized in that: The diaphragm also includes a support layer and a connection layer, the support layer and the connection layer are annular, connected to the periphery of the reflection end of the device layer, and projected on the periphery of 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 surface 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 fitted 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 method comprises preparing the diaphragm, wherein the preparation process of the diaphragm comprises: Coating a photoresist layer on the SOI wafer and performing a baking process; Aligning the SOI wafer coated with a photoresist layer and baked with a mask plate and placing them into an exposure machine for exposure and development, and then performing a post-baking process on the SOI wafer after exposure and development; wherein the mask plate includes an upper mask plate and a lower mask plate, respectively etching 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 reflection 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 continuously etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is subjected to metal coating treatment to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used to etch, and according to the thickness of the multiple resonance zones and bosses, the etching is performed layer by layer until the multiple resonance zones 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, which are respectively made according to different thicknesses and shapes of the bosses and multiple resonance regions; The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and the multiple resonance regions and bosses are etched layer by layer according to the thickness of the multiple resonance regions and 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 various height levels on the silicon substrate layer of the SOI crystal, so as to obtain 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, transferring the pattern to be etched to the photoresist layer using a mask plate corresponding to the current height level, and controlling the etching depth according to the surface height difference between the resonance area to be etched and the adjacent surface height resonance area, or according to the surface height difference between the resonance 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 resonance area or boss.

15. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, which are respectively made according to different thicknesses and shapes of the bosses and multiple resonance regions; The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and the multiple resonance regions and bosses are etched layer by layer according to the thickness of the multiple resonance regions and 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 various height levels on the silicon substrate layer of the SOI crystal, so as to obtain a boss and a plurality of resonance regions in turn; 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 assembling the sensor, specifically including: Fix the first capillary 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, and use ultraviolet light to irradiate to fix the connection between the diaphragm and the first capillary; Cut the required length of optical fiber, remove the coating of the optical fiber and clean the bare fiber; Insert the bare fiber into the inner hole of the capillary, apply UV glue on both ends of the second capillary, and fix the optical fiber and the second capillary relatively by irradiating with ultraviolet light; 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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