Asymmetric multi-resonant optical fiber sensor and preparation method thereof

Abstract

The invention discloses an asymmetric multi-resonant optical fiber sensor and a preparation method thereof, and belongs to the technical field of optical fiber sensors. The sensor comprises a diaphragm, a sleeve, a capillary tube and an optical fiber. The diaphragm comprises a device layer; the reflecting end of the device layer is a plane and is provided with a reflecting layer; the middle part of the input end of the device layer is provided with a deformation area, a plurality of resonance areas are arranged around the periphery of the deformation area, the plurality of resonance areas are adjacent in pairs, the heights of the input surfaces of the adjacent resonance areas are different, and the heights of the input surfaces of all the resonance areas are greater than the height of the input surface of the deformation area; the periphery of the diaphragm is fixed at one end of the sleeve, and the diaphragm reflecting layer faces the interior of the sleeve; one end of the capillary tube is inserted into the sleeve and fixedly connected to the reflecting end of the diaphragm; one end of the optical fiber faces the diaphragm deformation area, is inserted into the capillary and is fixed in the capillary. According to the invention, acoustic signal detection in a wider frequency range is realized through the diaphragm with the three-dimensional asymmetric structure, and the sensitivity and the stability of the sensor can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensors, in particular to an asymmetric multi-resonance optical fiber sensor and a preparation method thereof. Background Art

[0002] Traditional Fabry-Perot (FP) sensors usually adopt a symmetrical structural design, which has a natural advantage in fiber interference and resonance. The symmetrical structure can form a stable optical path in the cavity, making the interference fringes clear and the resonance frequency clear, so it has been widely used in the field of fiber optic sensing. However, this symmetrical design also brings certain limitations.

[0003] First, due to the symmetry of the structure, traditional FP sensors usually exhibit a single frequency response at the resonant frequency, and this single resonant frequency may not be ideal in certain application scenarios. For example, in the field of acoustics, the sensor needs to respond to sound waves of different frequencies, and the single-frequency resonant response limits its detection sensitivity to sound signals in a wider frequency range, especially when it is necessary to cover a wide-band sound field from low frequency to high frequency at the same time. In addition, the frequency response characteristics of the traditional symmetrical FP structure also limit the dynamic range of the sensor, making it impossible to effectively capture small frequency changes, making it difficult to achieve high-precision audio detection in complex acoustic environments.

[0004] Secondly, most traditional FP sensors adopt a planar structure, which has a weak anti-interference ability when facing changes in the external environment and is easily affected by factors such as ambient temperature and pressure. The limitations of the planar structure are also reflected in its insufficient sensitivity to sound waves in different directions, which makes the sensor's omnidirectional response to the sound field poor and cannot meet the needs of high-precision acoustic measurement. Therefore, how to improve the sensitivity and stability of the sensor in a wide frequency range by optimizing the structural design has become a key issue in improving traditional FP sensors. Summary of the invention

[0005] The purpose of the present invention is to provide an asymmetric multi-resonance optical fiber sensor and a preparation method thereof, which can realize acoustic signal detection in a wider frequency range through a diaphragm with a three-dimensional asymmetric structure, thereby improving the sensitivity and stability of the sensor. The technical solution adopted by the present invention is as follows.

[0006] In one aspect, the present invention provides an asymmetric multi-resonance optical fiber sensor, comprising a diaphragm, a sleeve, a capillary tube and an optical fiber;

[0007] The diaphragm includes a device layer; the reflection end of the device layer is planar and is provided with a reflection layer; a deformation area is provided in the middle of the input end of the device layer, and a plurality of resonance areas are arranged around the outer periphery of the deformation area. The plurality of resonance areas are adjacent to each other in pairs, and the heights of the input surfaces of adjacent resonance areas are different, and the heights of the input surfaces of all resonance areas are greater than the height of the input surface of the deformation area;

[0008] The periphery of the diaphragm is fixed to one end of the sleeve, and the reflection layer of the diaphragm faces the inside of the sleeve;

[0009] One end of the capillary is inserted into the sleeve and fixedly connected to the reflection end of the diaphragm;

[0010] One end of the optical fiber is inserted into the capillary and fixed in the capillary. The axial projection of the optical fiber is located in the deformation area of the device layer, and there is an optical transmission interval between the end of the optical fiber and the reflection layer.

[0011] In the above technical solution, the plurality of resonance areas with different surface heights and the deformation area with a concave middle part provided on the diaphragm constitute an asymmetric multi-resonance structure of the sensor. A Fabry-Perot interference cavity is formed between the optical fiber and the reflection layer of the diaphragm. When the diaphragm undergoes a small deformation under the action of sound pressure, the central area and the peripheral areas with different thicknesses respectively generate resonance responses in different frequency bands, forming a multi-band resonance characteristic, expanding the frequency response range of the sensor, and enabling the sensor to respond to broadband acoustic signals with high sensitivity. As the diaphragm deforms, the cavity length of the Fabry-Perot interference cavity changes, and 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 interference cavity, the sound pressure values of different frequencies can be calculated, so as to realize the high-precision measurement of multi-band acoustic signals. The specific detection and calculation process can adopt the existing technology, which is not the content concerned by the present invention and will not be elaborated.

[0012] Optionally, the diaphragm further includes a support layer and a connection layer. The support layer and the connection layer are annularly arranged around the periphery of the reflection end of the device layer and project outside the plurality of resonance areas. 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 sleeve is fixedly connected to the support layer.

[0013] Further, the outer diameter of the capillary is adapted to the inner diameter of the support layer so that the two fit together, and glue can be applied to the outer wall of the capillary to bond it to the inner wall of the support layer.

[0014] Optionally, the optical fiber adopts a single-mode optical fiber, and the reflection layer is a gold material attached to the surface of the reflection end of the diaphragm and can be formed by vacuum ion sputtering technology. Other metal materials with high reflection performance can also be used as the material of the reflection layer.

[0015] In the above technical solution, the setting of the support layer can achieve the mechanical support of the sleeve and the capillary tube for the diaphragm and the optical fiber, ensuring the structural stability of the overall sensor. The sleeve is made of glass material.

[0016] Optionally, the deformation area is a square groove, and the outer edges of the multiple resonance areas enclose a square. The groove shape of the deformation area can also be set as other shapes such as circular or triangular to meet the detection requirements of different scenarios. The shape enclosed by the outer edges of the multiple resonance areas can also be other shapes.

[0017] Optionally, among the multiple resonance areas, the surface heights of any two are different.

[0018] As an implementation manner of different thickness levels of the resonance area: among the multiple resonance areas, starting from one of the resonance areas, the surface height of the resonance area increases or decreases in sequence.

[0019] Preferably, among the multiple resonance areas, starting from one of the resonance areas, the surface height of the resonance area increases or decreases by the same height value in sequence.

[0020] As another implementation manner of different thickness levels of the resonance area: all the resonance areas are arranged at intervals of high and low according to the surface height on the outer periphery of the deformation area.

[0021] Preferably, in the order of the surface height values of the resonance areas from large to small, the difference in the surface height values between any two adjacent resonance areas with adjacent surface height values is equal. This setting can simplify the logical operation when the sensor is actually applied to detection.

[0022] Optionally, the optical fiber uses a single-mode optical fiber, and the reflective layer is a gold material attached to the reflective end surface of the diaphragm.

[0023] Optionally, the thickness of the deformation area is 1-3 microns, and the ratio of the area of the deformation area to the sum of the areas of the deformation area and the resonance area is less than 1 / 16. It can improve the sensitivity of the fiber optic sensor while keeping the main resonance frequency changing little. The smaller thickness of the deformation area can also improve the sensitivity of the sensor.

[0024] Preferably, the inner diameter of the sleeve is equal to the outer diameter of the capillary tube, the outer diameter of the sleeve is slightly larger than its inner diameter, and the outer diameter of the capillary tube is much larger than its inner diameter. As a feasible implementation manner, the outer diameter of the sleeve is 4 mm, the inner diameter is 3 mm; the outer diameter of the capillary tube is 3 mm, the inner diameter is 0.135 mm; the length of the optical fiber outside the capillary tube is 2 mm - 3 mm.

[0025] In the second aspect, the present invention provides a preparation method for the asymmetric multi-resonance fiber optic sensor described in the first aspect, including preparing the diaphragm, and the preparation process of the diaphragm includes:

[0026] Coat the SOI wafer with a photoresist layer and perform a baking process;

[0027] 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 shape of the reflecting end surface of the diaphragm;

[0028] 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 surface heights of multiple resonance regions and deformation regions until the multiple resonance regions and deformation regions are obtained, completing the preparation of the diaphragm.

[0029] The above-mentioned layer-by-layer etching can be carried out from shallow to deep, that is, finally etching out the groove of the deformation region, or from deep to shallow, that is, first etching out the groove of the deformation region.

[0030] 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 surface heights and shapes of the deformation region and multiple resonance regions;

[0031] For the silicon substrate layer of the SOI wafer, using the multi-step deep reactive ion etching process to etch, and layer by layer etch according to the surface heights of multiple resonance regions and deformation regions until the multiple resonance regions and deformation regions are obtained, includes:

[0032] According to the different surface heights of the deformation region and multiple resonance regions, divide the etching process of the silicon substrate layer into etching operation processes of multiple height levels;

[0033] In the order from shallow to deep, successively use the corresponding mask plates to perform the etching operation processes of each height level on the silicon substrate layer of the SOI crystal, and successively obtain multiple resonance regions and deformation regions;

[0034] Among them, for each height level, the etching operation process includes: coating the 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 resonance region with the same surface height, or according to the surface height difference between the resonance region to be etched and the adjacent deformation region, or according to the depression depth of the deformation region, completing the etching of the current height level, and obtaining the corresponding resonance region or deformation region.

[0035] As another implementation manner of the etching operation, optionally, the number of the upper mask plates is multiple, and they are respectively made according to the different surface heights and shapes of the deformation region and the multiple resonance regions;

[0036] For the silicon substrate layer of the SOI wafer, the deep reactive ion etching process is used for etching. According to the surface heights of the multiple resonance regions and the deformation region, layer-by-layer etching is performed until the multiple resonance regions and the deformation region are obtained, including:

[0037] According to the different surface heights of the deformation region and the multiple resonance regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0038] In the order from deep to shallow, the etching operation processes of each height level are sequentially performed on the silicon substrate of the SOI crystal by using the corresponding mask plates, and the deformation region and the multiple resonance regions are sequentially obtained;

[0039] 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 deformation region or resonance region to be etched, and completing the etching of the current height level to obtain the corresponding deformation region or resonance region.

[0040] Optionally, the preparation method further includes assembling the sensor, specifically including:

[0041] Fix the sleeve 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 sleeve, and use an ultraviolet lamp to irradiate to fixedly connect the diaphragm and the sleeve;

[0042] Cut out the optical fiber with the required length, remove the coating of the optical fiber and clean the bare fiber;

[0043] Insert the bare fiber into the inner hole of the capillary, apply UV glue at both ends of the capillary, and use an ultraviolet lamp to irradiate to relatively fix the optical fiber and the capillary;

[0044] Align the optical fiber with the center of the deformation region of the diaphragm, place the capillary with the optical fiber inserted into the sleeve and fix it on the surface of the reflection end of the diaphragm to obtain the asymmetric multi-resonant fiber optic sensor.

[0045] Beneficial effects

[0046] The asymmetric multi-resonant fiber optic sensor of the present invention, through the combined design of the deformation region with a central depression and the multi-resonant region with a graded thickness on the periphery, not only improves the overall frequency response characteristics but also enhances the sensitivity of the sensor in broadband detection. It provides a new solution for broadband acoustic monitoring, enabling the fiber optic sensor to exhibit excellent adaptability in fields such as high-precision acoustic monitoring, environmental noise analysis, and industrial noise monitoring;

[0047] The preparation method of the present invention designs the etching operation process according to the structural characteristics of the diaphragm. By cooperating with different mask plates, the layer-by-layer etching of the multi-thickness resonant region and the deformation region can be achieved, which can ensure the realization of the high-sensitivity and wide-frequency response range characteristics 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, enabling the optical fiber to be stably embedded without damaging the diaphragm, and further improving the durability of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The following shows the schematic structural diagram of the fiber optic sensor in the embodiment of the present invention;

[0049] Figure 2 The following shows the three-dimensional schematic diagram of the diaphragm of the fiber optic sensor in the embodiment of the present invention;

[0050] Figure 3 The following shows Figure 2 the planar schematic diagram of the diaphragm in

[0051] Figure 4 The following shows the schematic diagram of the diaphragm preparation process of the fiber optic sensor in the embodiment of the present invention, which includes process (A), process (B), process (C), process (D), and process (E);

[0052] Figure 5 The following shows the three-dimensional schematic diagram of the diaphragm preparation result of the fiber optic sensor in the embodiment of the present invention;

[0053] Figure 6 The following shows the planar schematic diagram of the diaphragm preparation result of the fiber optic sensor in the embodiment of the present invention;

[0054] Figure 7 The following shows the schematic diagram of the deformation result of the diaphragm in the fiber optic sensor of the present invention under an external ultrasonic signal;

[0055] Figure 8 The following shows the schematic diagram of the frequency response curve simulation of the fiber optic sensor in the embodiment of the present invention;

[0056] In the figure, 1 - diaphragm, 11 - silicon-based bottom layer, 12 - silicon oxide layer, 13 - silicon substrate bottom layer, 14 - reflection layer, 2 - sleeve, 3 - capillary tube, 4 - optical fiber. DETAILED DESCRIPTION OF THE INVENTION

[0057] 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.

[0058] Embodiment 1

[0059] This embodiment introduces an asymmetric multi-resonant fiber optic sensor, including a diaphragm 1, a sleeve 2, a capillary 3, and an optical fiber 4;

[0060] As Figure 2 and Figure 3 shown, the diaphragm 1 includes a device layer, which can be processed from the silicon substrate layer of an SOI crystal. One side of the device layer is the reflection end and the other side is the input end; the reflection end of the device layer is a plane and is provided with a reflection layer 14; a deformation area is provided in the middle of the input end of the device layer, such as the area e in Figure 2 , and a plurality of resonant areas are arranged around the periphery of the deformation area, such as the areas a, b, c, and d in Figure 2 ; the plurality of resonant areas are adjacent to each other in pairs, the heights of the input surfaces of adjacent resonant areas are different, and the heights of the input surfaces of all resonant areas are greater than the height of the input surface of the deformation area;

[0061] The periphery of the diaphragm 1 is fixed to one end of the sleeve 2, and the reflection layer 14 of the diaphragm 1 faces the inside of the sleeve 2;

[0062] One end of the capillary 3 is inserted into the sleeve 2 and fixedly connected to the reflection end of the diaphragm 1;

[0063] One end of the optical fiber 4 is inserted into the capillary 3 and fixed in the capillary 3. The axial projection of the optical fiber 4 is located in the deformation area of the device layer, and there is an optical transmission interval between the end of the optical fiber 4 and the reflection layer 14.

[0064] In this embodiment, the plurality of resonant areas with different top surface heights and the deformation area with a concave middle provided on the diaphragm constitute the asymmetric multi-resonant structure of the sensor. The sleeve is used to form a stable support structure, and the capillary is used to protect the optical fiber inserted therein to ensure its alignment with the deformation area of the diaphragm and realize an accurate optical fiber interference measurement path. The end face of the optical fiber and the gold-plated surface at the center of the diaphragm form a Fabry-Perot interference cavity for detecting acoustic signals. The single-mode optical fiber emits incident light. As the diaphragm deforms, the cavity length of the Fabry-Perot interference 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 interference cavity, different frequency sound pressure values can be calculated, thereby realizing high-precision measurement of multi-band acoustic signals.

[0065] When the diaphragm undergoes a slight deformation under the action of sound pressure, the central region and the peripheral regions with different thicknesses generate resonant responses in different frequency bands respectively, forming a multi-band resonance characteristic, expanding the frequency response range of the sensor, and enabling the sensor to respond to broadband acoustic signals with high sensitivity.

[0066] It should be noted that Figure 2 and Figure 3 show the structures of multiple resonant regions and deformation regions on the device layer in the diaphragm of the present invention. At the same time, this structure can also be directly used as the diaphragm of an optical fiber resonator, and assembled with a sleeve, a capillary tube, and an optical fiber to obtain an asymmetric multi-resonant optical fiber sensor. Specifically, a sleeve with a radial cross-section adapted to the shape of the periphery of the diaphragm is selected, and the periphery of one end of the sleeve is fixedly connected to the outer edge of the multi-resonant region of the device layer. In addition, the sensor of the present invention can also be extended at the periphery of the multi-resonant region on the diaphragm to facilitate the assembly of the sleeve and the capillary tube, and make the overall structure of the optical fiber sensor more stable.

[0067] Embodiment 2

[0068] Based on Embodiment 1, as Figure 2 and Figure 3 , in the optical fiber sensor of this embodiment, the diaphragm only includes a device layer made of silicon material. On this device layer, the deformation region e is a square groove, and there are 4 resonant regions, and their outer edges enclose a square. The groove shape of the deformation region can also be set to other shapes such as triangles and circles, and the shape enclosed by the outer edges of multiple resonant regions can also be other shapes to meet the detection requirements of different frequency band range scenarios.

[0069] As Figure 2 , in this embodiment, among multiple resonant regions, the surface heights of any two of them, that is, the heights where the top surfaces are located, are different.

[0070] Specifically, among the four resonant regions a, b, c, and d, all resonant regions are arranged at intervals of high and low according to the surface height on the periphery of the deformation region.

[0071] Sort the four resonant regions a, b, c, and d according to the magnitude of the surface height values. In this embodiment, it can be set that the difference in the surface height values between any two adjacent resonant regions with adjacent surface height values is equal. When the sensor is actually applied to detection, this structural design can simplify the corresponding logical operations. Of course, it can also be set that the difference in the surface height values between any two resonant regions with increasing or decreasing thickness is not unique, and the corresponding detection and calculation can also be completed.

[0072] Regarding Figure 2 and Figure 3For the diaphragm shown, a square glass sleeve is selected for the sleeve, and the radial cross-section of the sleeve corresponds to the outer shape of the four resonant regions a, b, c, and d. The peripheral portion of the inner wall at one end of the sleeve is adhesively bonded to the peripheral portion of the diaphragm, and further, the capillary and the optical fiber are assembled to obtain the entire asymmetric fiber optic sensor.

[0073] Example 3

[0074] Different from Example 2, in this example, among the multiple resonant regions around the deformation region, starting from one of the resonant regions, the surface height of the resonant regions increases or decreases in sequence.

[0075] Similarly, in order to simplify the calculation in practical applications, in this example, it is set that among the multiple resonant regions, starting from one of the resonant regions, the surface height of the resonant regions increases or decreases by the same height value in sequence.

[0076] Example 4

[0077] Based on Example 1, the asymmetric fiber optic sensor of this example is as Figure 1 shown, which includes a diaphragm, a sleeve, a 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 annularly arranged at the peripheral portion of the reflection end of the device layer and project onto the outer periphery of the 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 end surface of one end of the sleeve is fixedly connected to the support layer, and its inner diameter is adapted to the outer diameter of the capillary, and the outer diameter of the capillary is adapted to the inner diameter of the support layer so as to be able to fit together to achieve a supporting effect. On this basis, glue can be applied to the outer wall of the capillary to bond it to the inner wall of the support layer, further improving the stability of the mechanism while providing support.

[0078] The entire diaphragm in this example 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 substrate layer 11 of the SOI crystal.

[0079] As Figure 5 and Figure 6 , on the device layer, the deformation region e is a square groove, and there are 4 resonant regions, and their outer edges enclose a square. The groove shape of the deformation region can also be set to other shapes such as triangles and circles, and the shape enclosed by the outer edges of the multiple resonant regions can also be other shapes.

[0080] As Figure 6 , in this example, among the multiple resonant regions, the surface heights of any two, that is, the heights where the top surfaces are located, are different. Specifically, among the four resonant regions a, b, c, and d, all the resonant regions are arranged at intervals of high and low according to the surface height on the outer periphery of the deformation region.

[0081] If the four resonant regions a, b, c, and d are sorted according to the surface height values from large to small, in this embodiment, it can be set that the difference in the surface height values between any two adjacent resonant regions with adjacent surface height values is equal, or it can also be set that the surface height difference between any two resonant regions with increasing or decreasing thickness is not unique.

[0082] The thickness of the deformation region of the device layer is relatively thin, which can improve the sensitivity, and the peripheral region forms a multi-band response structure. In this embodiment, the thickness of the deformation region of the device layer is 1-3 microns, and the ratio of the area of the deformation region to the sum of the areas of the deformation region and the resonant region is less than 1 / 16. It can improve the sensitivity of the fiber optic sensor while keeping the main resonance frequency changing little, and the relatively small thickness of the deformation region can also improve the sensitivity of the sensor.

[0083] The inner diameter of the sleeve is equal to the outer diameter of the capillary, the outer diameter of the sleeve is slightly larger than its inner diameter, and the outer diameter of the capillary is much larger than its inner diameter. For example, the outer diameter of the sleeve 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. It can be adjusted according to needs.

[0084] Example 5

[0085] Different from Example 4, in this embodiment, among the multiple resonant regions, among the multiple resonant regions around the deformation region, starting from one of the resonant regions, the surface height of the resonant regions increases or decreases in sequence. And, among the multiple resonant regions, starting from one of the resonant regions, the surface height of the resonant regions increases or decreases by the same height value in sequence.

[0086] 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 surface of the reflective end of the diaphragm, and the sleeve is made of glass. The number of resonant regions is not limited to 4 and can be flexibly set according to the needs of the multi-band range.

[0087] Example 6

[0088] Reference Figure 4 As shown, this embodiment introduces the preparation method of the asymmetric multi-resonant fiber optic sensor in Examples 1 - 4. The method includes preparing the diaphragm, and the preparation process of the diaphragm includes:

[0089] Coating a photoresist layer on the SOI wafer and performing a baking treatment;

[0090] After coating the photoresist layer and baking the SOI wafer, align it with the mask plate and place it into the exposure machine for exposure and development processing. Then, perform post-baking processing on the exposed and developed SOI wafer. Among them, the mask plate includes an upper mask plate and a lower mask plate, which are used to etch the silicon substrate layer and the silicon-based substrate layer of the SOI wafer respectively. 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.

[0091] For the exposed area of the silicon-based substrate layer of the SOI wafer, use reactive ion etching 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 a multi-step deep reactive ion etching process to etch, and etch layer by layer according to the surface heights of multiple resonant regions and deformation regions until the multiple resonant regions and deformation regions are obtained, completing the preparation of the diaphragm.

[0092] Since multiple resonant regions and deformation regions with different surface heights 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 resonant regions, and each mask plate is made according to the different surface heights and shapes of the deformation regions and multiple resonant regions.

[0093] The above layer-by-layer etching can be carried out from shallow to deep layer by layer, that is, finally etching out the groove of the deformation region, or from deep to shallow layer by layer, that is, first etching out the groove of the deformation region. Specifically:

[0094] As an etching operation method, for the silicon substrate layer of the SOI wafer, using a multi-step deep reactive ion etching process to etch, and etching layer by layer according to the surface heights of multiple resonant regions and deformation regions until the multiple resonant regions and deformation regions are obtained, includes:

[0095] According to the different surface heights of the deformation regions and multiple resonant regions, divide the etching process of the silicon substrate layer into etching operation processes of multiple height levels;

[0096] In the order from shallow to deep, 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 resonant regions and deformation regions in turn;

[0097] Among them, for each height level, the etching operation process includes: coating a photoresist on the surface of the current silicon substrate layer, transferring the pattern to be etched to the photoresist layer by using a mask plate corresponding to the current height level, and controlling the etching depth according to the surface height difference between the resonant region to be etched and the adjacent surface height resonant region, or according to the surface height difference between the resonant region to be etched and the adjacent deformation region, or according to the depression depth of the deformation region, so as to complete the etching of the current height level and obtain the corresponding resonant region or deformation region.

[0098] As another etching operation method, for the silicon substrate layer of the SOI wafer, the deep reactive ion etching process is used for etching multiple times. Etching layer by layer according to the surface heights of multiple resonant regions and deformation regions until the multiple resonant regions and deformation regions are obtained, including:

[0099] According to the different surface heights of the deformation region and multiple resonant regions, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0100] In the order from deep to shallow, use the corresponding mask plates to perform the etching operation processes of each height level on the silicon substrate layer of the SOI crystal, and obtain the deformation region and multiple resonant regions in sequence;

[0101] Among them, for each height level, the etching operation process includes: coating a 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, and controlling the etching depth according to the surface height of the deformation region or resonant region to be etched, so as to complete the etching of the current height level and obtain the corresponding deformation region or resonant region.

[0102] After the diaphragm is prepared, according to the structures of the sensors introduced in Embodiments 1 to 5, assemble the diaphragm with the sleeve, capillary and optical fiber, and then the asymmetric multi-resonant fiber sensor is obtained.

[0103] Embodiment 7

[0104] Based on Embodiment 6, taking Figure 1 the shown asymmetric multi-resonant sensor as the preparation target, referring to Figure 4 , the preparation process of this embodiment includes the following steps:

[0105] S1, select or prepare an SOI crystal with an appropriate area size and shape, such as Figure 5 the shown circular SOI wafer substrate;

[0106] S2, manufacture mask plates for etching resonant regions and deformation regions with different thicknesses;

[0107] S3, as Figure 4In step (A), the SOI wafer is placed on a spin coater, a photoresist layer is uniformly coated on the silicon substrate 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;

[0108] S4, after accurately aligning the wafer covered with photoresist with the lower mask plate, placing it into an exposure machine, irradiating the transparent area of ​​the mask plate with ultraviolet light to cause a photochemical reaction on the surface of the photoresist to form a projection of the mask plate pattern, after exposure, using a developer to remove the photoresist area that has reacted, retaining the pattern structure of the unexposed area, and then post-baking to enhance the adhesion and tolerance of the developed photoresist layer to ensure that it effectively protects the required pattern area during the deep etching process;

[0109] S5, such as Figure 4 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 4 In step (C), the silicon oxide layer is etched and cleaned. After the silicon oxide layer is cleaned, the required graphic structure of the sensor reflective end can be accurately transferred to the wafer to form the target microstructure of the diaphragm reflective end;

[0110] S6, such as Figure 4 In step (D), the silicon substrate layer of the SOI crystal is finely processed by using the multiple deep reactive ion etching DRIE processes described in Example 6, and the precise structure of different thickness areas is achieved through step-by-step photolithography and etching, such as: first, photoresist is coated on the surface of the silicon substrate layer and the upper mask pattern is used for photolithography to define the etching area of ​​each layer, and then the peripheral areas with decreasing thickness are formed in sequence by controlling the etching depth. After each layer is etched, the upper mask is replaced and photolithography is performed again to limit the etching depth of the next layer. Finally, the deepest etching is performed in the central area to form a thin groove area for the main frequency response;

[0111] S7, such as Figure 4 In step (E), vacuum sputtering technology is used to perform metal coating on the bottom surface of the silicon substrate layer, that is, the surface of the silicon substrate layer exposed at the reflective end of the diaphragm. By sputtering the metal target in a vacuum environment, gold atoms are uniformly deposited on the surface of the diaphragm to form a highly reflective gold film layer, thereby achieving precise processing of the asymmetric multi-resonance structure diaphragm;

[0112] S8, fix the sleeve vertically on the bracket, and evenly apply a small amount of UV glue on its end surface. Then, with the help of a microscope, accurately align and fit the membrane to the sleeve end surface, so that the sleeve end surface is closely attached to the surface of the silicon substrate layer, that is, the support layer. Use a UV curing lamp to irradiate 360° for 10 minutes to complete the initial bonding and fixing of the membrane and the sleeve;

[0113] S9. Process the SMF optical fiber, remove its coating layer and clean the bare fiber, and cut it to a length 2 to 3 millimeters longer than the capillary length. After threading the bare fiber into the capillary, apply a small amount of UV glue to both ends of the capillary and irradiate it with an ultraviolet lamp for 10 minutes to preliminarily fix the optical fiber to the capillary;

[0114] S10. Align and assemble the two cured components obtained after S8 and S9 on a three-dimensional adjustment rack to ensure precise alignment of each component 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 for measuring and responding to sound signals of different frequencies.

[0115] For the fabricated fiber optic sensor, the initial cavity length of the Fabry-Perot interferometric cavity is optimized and adjusted 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 end of the single-mode optical fiber of the fiber optic sensor to an sm155 fiber grating sensing demodulator and performing real-time spectral adjustment on the reflected light. Specifically:

[0116] Fix the uncured fiber optic sensor on a three-dimensional adjustment rack, gradually adjust the position of the sensor in the X, Y, and Z axis directions of each axis through the fine adjustment rack, and connect the demodulator to a computer to observe the change of the interference spectrum in real time 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 subsequent detection stability and high sensitivity.

[0117] In this embodiment, the COMSOL multi-physics simulation software is used to perform simulation analysis on the asymmetric multi-resonant fiber optic sensor. The simulation experiment adopts the acoustic-solid coupling condition, and the boundary of the diaphragm is set as a fixed constraint to simulate the acoustic response in the actual working environment. The deformation and frequency response characteristics of the asymmetric multi-resonant diaphragm under the action of an external acoustic signal are analyzed through the simulation software, and the results are as Figure 7 and Figure 8 shown, where Figure 7 is the deformation effect of the diaphragm structure under the ultrasonic signal, Figure 8 is the frequency response characteristic of the fiber optic sensor.

[0118] From Figure 7 and Figure 8 it can be seen that the structural design of the asymmetric multi-resonant fiber optic sensor of the present invention and the corresponding preparation method enable the central groove region to obtain a larger deformation amplitude under the action of sound pressure, thereby significantly improving the sensitivity and frequency selectivity of the sensor. These design schemes enable the sensor to have broadband response ability and high sensitivity and can accurately detect multi-band acoustic signals.

[0119] 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 rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims. All of these are within the protection scope of the present invention.

Claims

1. An asymmetric multi-resonance optical fiber sensor, comprising a diaphragm, a sleeve, a capillary and an optical fiber; wherein: The diaphragm comprises a device layer; the reflection end of the device layer is a plane and is provided with a reflection layer; a deformation zone is provided in the middle of the input end of the device layer, and a plurality of resonance zones are provided around the periphery of the deformation zone, the plurality of resonance zones are adjacent to each other, the input surfaces of adjacent resonance zones are at different heights, and the input surfaces of all resonance zones are at a height greater than the input surface of the deformation zone; The periphery of the diaphragm is fixed to one end of the sleeve, and the reflective layer of the diaphragm faces the inside of the sleeve; One end of the capillary is inserted into the sleeve and fixedly connected to the reflective end of the diaphragm; One end of the optical fiber is inserted into the capillary and fixed in the capillary, the axial projection of the optical fiber is located in the deformation zone of the device layer, and there is a light transmission interval between the end of the optical fiber and the reflection layer.

2. The asymmetric multi-resonance optical fiber sensor according to claim 1, characterized in that: The diaphragm also includes a supporting layer and a connecting layer, which are annularly arranged around the reflective end of the device layer and projected onto the periphery of multiple resonance regions. The upper and lower surfaces of the connecting layer are respectively fixedly connected to the supporting layer and the device layer; the end surface of one end of the sleeve is fixedly connected to the supporting layer.

3. The asymmetric multi-resonance optical fiber sensor according to claim 2, characterized in that: The outer diameter of the capillary is adapted to the inner diameter of the support layer.

4. The asymmetric multi-resonance optical fiber sensor according to claim 1, characterized in that: The deformation zone is a square groove, and the outer edges of the multiple resonance zones form a square.

5. The asymmetric multi-resonance optical fiber sensor according to claim 4, characterized in that: Any two of the plurality of resonance regions have different surface heights.

6. The asymmetric multi-resonance optical fiber sensor according to claim 5, characterized in that: Among the multiple resonance regions, starting from one of the resonance regions, the surface heights of the resonance regions increase or decrease in sequence.

7. The asymmetric multi-resonance optical fiber sensor according to claim 6, characterized in that: Among the multiple resonance regions, starting from one of the resonance regions, the surface heights of the resonance regions increase or decrease in sequence by the same height value.

8. The asymmetric multi-resonance optical fiber sensor according to claim 5, characterized in that: All the resonance areas are arranged at high and low intervals on the periphery of the deformation area according to the surface height.

9. The asymmetric multi-resonance optical fiber sensor according to claim 8, characterized in that: According to the order of the surface height values ​​of the resonance regions from large to small, the difference in the surface height values ​​between any two resonance regions with adjacent surface height values ​​is equal.

10. The asymmetric multi-resonance optical fiber sensor according to any one of claims 1 to 9, 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 sleeve is made of glass.

11. The asymmetric multi-resonance optical fiber sensor according to any one of claims 1 to 9, characterized in that: The thickness of the deformation zone is 1-3 microns, and the ratio of the area of ​​the deformation zone to the sum of the areas of the deformation zone and the resonance zone is less than 1 / 16.

12. The asymmetric multi-resonance optical fiber sensor according to claim 11, characterized in that: The outer diameter of the sleeve 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.

13. The method for preparing the asymmetric multi-resonance optical fiber 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 surface heights of the multiple resonance zones and deformation zones, the etching is performed layer by layer until the multiple resonance zones and deformation zones 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 surface heights and shapes of the deformation region and the 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 deformation regions are etched layer by layer according to the surface height of the multiple resonance regions and deformation regions, including: According to the different surface heights of the deformation zone and the plurality of resonance zones, the etching process of the silicon substrate layer is divided into etching operation processes of a plurality of 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, and multiple resonance areas and deformation areas are obtained 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 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 deformation area, or according to the depression depth of the deformation area, to complete the etching of the current height level and obtain the corresponding resonance area or deformation area.

15. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, which are respectively made according to different surface heights and shapes of the deformation region and the 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 deformation regions are etched layer by layer according to the surface height of the multiple resonance regions and deformation regions, including: According to the different surface heights of the deformation zone and the plurality of resonance zones, the etching process of the silicon substrate layer is divided into etching operation processes of a plurality of height levels; In order from deep to shallow, the corresponding mask plates are used in sequence to perform etching operation processes of various height levels on the silicon substrate layer of the SOI crystal, so as to obtain a deformation zone and a plurality of resonance zones 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 deformation area or resonance area to be etched, completing the etching of the current height level, and obtaining the corresponding deformation area 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 sleeve on the bracket, apply UV glue on its end surface, align and fit the reflective end of the diaphragm to the end surface of the sleeve, and use ultraviolet light to irradiate the diaphragm and the sleeve to fix the connection; 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 capillary, and irradiate with ultraviolet light to fix the optical fiber and the capillary relatively; The optical fiber is aligned with the center of the deformation zone of the diaphragm, and the capillary through which the optical fiber is passed is placed in the sleeve and fixed to the reflective end surface of the diaphragm to obtain the asymmetric multi-resonance optical fiber sensor.

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