Asymmetric multi-resonance optical fiber sensor and preparation method thereof

Abstract

The present invention discloses an asymmetric multi-resonance optical fiber sensor and a preparation method thereof, belonging to the technical field of optical fiber sensors. The sensor includes a diaphragm, a sleeve, a capillary tube and an optical fiber; the diaphragm includes a device layer; the reflective end of the device layer is a plane and is provided with a reflective layer; a deformation zone is provided in the middle of the input end of the device layer, and multiple resonance zones are provided around the periphery of the deformation zone. The multiple resonance zones are adjacent to each other, and the input surfaces of adjacent resonance zones are at different heights, and the heights of the input surfaces of all resonance zones are greater than the height of the input surfaces of the deformation zones; 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 tube is inserted into the sleeve and fixedly connected to the reflective end of the diaphragm; one end of the optical fiber faces the deformation zone of the diaphragm and is inserted into the capillary tube and fixed in the capillary tube. The present invention realizes acoustic signal detection in a wider frequency range through a diaphragm with a three-dimensional asymmetric structure, which can improve the sensitivity and stability of the sensor.

Description

Technical Field

[0001] The present 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 typically employ a symmetrical design, which offers inherent advantages in fiber interference and resonance. This symmetrical structure creates a stable optical path within the cavity, resulting in clear interference fringes and a well-defined resonant frequency, making it widely used in fiber optic sensing. However, this symmetrical design also presents certain limitations.

[0003] First, due to the symmetry of the structure, traditional FP sensors typically exhibit a single-frequency response at the resonant frequency, which may not be ideal in certain application scenarios. For example, in the field of acoustics, sensors need to respond to sound waves of different frequencies, and a single-frequency resonant response limits their detection sensitivity to acoustic signals within a wider frequency range, especially when a broadband sound field needs to be covered simultaneously, from low to high frequencies. 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 acoustic detection in complex acoustic environments.

[0004] Secondly, most traditional FP sensors utilize a planar structure, which has weak immunity to environmental fluctuations and is susceptible to factors such as ambient temperature and pressure. This limitation also manifests itself in insufficient sensitivity to sound waves from different directions, resulting in poor omnidirectional response to the sound field and an inability to meet the demands of high-precision acoustic measurements. Therefore, optimizing the structural design to improve the sensor's sensitivity and stability across a wide frequency range has become a key issue in improving traditional FP sensors. Summary of the Invention

[0005] The present invention aims to provide an asymmetric multi-resonance optical fiber sensor and its fabrication method, which utilizes a diaphragm with a three-dimensional asymmetric structure to detect acoustic signals over a wider frequency range, thereby improving the sensitivity and stability of the sensor. The present invention employs the following technical solutions.

[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 reflective end of the device layer is flat and provided with a reflective 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, wherein the plurality of resonance zones are adjacent to each other, and the input surfaces of adjacent resonance zones are located at different heights, and the input surfaces of all resonance zones are located at a height greater than the input surface of the deformation zone;

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

[0009] One end of the capillary tube is inserted into the sleeve and fixedly connected to the reflective 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 zone of the device layer, and there is a light transmission gap between the end of the optical fiber and the reflective layer.

[0011] In the above technical solution, multiple resonance regions with different surface heights and a concave deformation region in the middle set 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 diaphragm reflective layer. When the diaphragm undergoes a slight deformation under the action of sound pressure, the central area and the peripheral areas of different thicknesses respectively produce resonant responses in different frequency bands, forming a multi-band resonance characteristic, which expands the frequency response range of the sensor and enables 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. This change in cavity length causes the optical path difference of the reflected light to change. By detecting the optical path difference of the interference cavity, the sound pressure values of different frequencies can be calculated, thereby achieving high-precision measurement of multi-band acoustic signals. The specific detection and calculation process can adopt existing technology. It is not the focus of this invention and will not be described in detail.

[0012] Optionally, 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 fixedly connected to the supporting layer and the device layer respectively; the end face of one end of the sleeve is fixedly connected to the supporting layer.

[0013] Furthermore, 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 make it adhere to the inner wall of the support layer.

[0014] Optionally, the optical fiber is a single-mode optical fiber, and the reflective layer is a gold material attached to the reflective end surface of the diaphragm, which can be formed by vacuum ion sputtering technology. The reflective layer can also be made of other metal materials with high reflective properties.

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

[0016] Optionally, the deformation zone is a square groove, and the outer edges of the multiple resonant zones form a square. The groove of the deformation zone can also be configured as a circle, triangle, or other shape to accommodate the detection requirements of different scenarios. The shape formed by the outer edges of the multiple resonant zones can also be other shapes.

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

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

[0019] Preferably, among the multiple resonance regions, starting from one resonance region, the surface heights of the resonance regions increase or decrease in sequence by the same height value.

[0020] As another implementation method of different thickness levels of the resonance regions: all the resonance regions are arranged at different heights on the periphery of the deformation region according to the surface height.

[0021] Preferably, in descending order of the surface height values of the resonance regions, the difference in surface height values between any two adjacent resonance regions is equal. This setting can simplify the logical operation of the sensor in actual detection applications.

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

[0023] Optionally, the thickness of the deformation zone is 1-3 microns, and the ratio of the deformation zone area to the sum of the deformation zone and resonant zone areas is less than 1 / 16. This can improve the sensitivity of the optical fiber sensor while maintaining a small change in the main resonant frequency. A smaller thickness of the deformation zone can also improve the sensitivity of the sensor.

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

[0025] In a second aspect, the present invention provides a method for preparing the asymmetric multi-resonance optical fiber sensor according to the first aspect, comprising preparing the diaphragm, wherein the preparation process of the diaphragm comprises:

[0026] Coating a photoresist layer on the SOI wafer and performing a baking process;

[0027] The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the surface of the reflective end of the diaphragm;

[0028] 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 for etching, and according to the surface height of the multiple resonance regions and deformation regions, the etching is carried out layer by layer until the multiple resonance regions and deformation regions are obtained, thereby completing the preparation of the diaphragm.

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

[0030] As an etching operation implementation mode, optionally, the number of the upper mask plates is multiple, and they are respectively made according to different surface heights and shapes of the deformation region and the multiple resonance regions;

[0031] 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:

[0032] According to the different surface heights of the deformation zone and the multiple resonance zones, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0033] In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and deformation regions in turn;

[0034] 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 resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent 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 resonant area or deformation area.

[0035] As another etching operation implementation mode, optionally, there are multiple upper mask plates, each of which is manufactured according to different surface heights and shapes of the deformation region and the multiple resonance regions;

[0036] The silicon substrate layer of the SOI wafer is etched using multiple deep reactive ion etching processes, and etching layer by layer according to the surface heights of the multiple resonance regions and the deformation regions until the multiple resonance regions and the deformation regions are obtained, including:

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

[0038] 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, thereby obtaining a deformation zone and multiple resonance zones in turn;

[0039] 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.

[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 the reflective end of the diaphragm and stick it to the end face of the sleeve, and use UV light to irradiate the diaphragm and sleeve to fix the connection;

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

[0043] Insert the bare fiber into the inner hole of the capillary, apply UV glue on both ends of the capillary, and irradiate with UV light to fix the fiber and capillary relatively;

[0044] The optical fiber is aligned with the center of the deformation zone of the diaphragm, and the capillary tube through which the optical fiber is passed is placed in a sleeve and fixed to the reflective end surface of the diaphragm to obtain the asymmetric multi-resonance optical fiber sensor.

[0045] Beneficial effects

[0046] The asymmetric multi-resonant fiber sensor of this invention combines a centrally recessed deformation zone with peripheral multi-resonant zones of graded thickness, enhancing not only its overall frequency response but also its sensitivity in broadband detection. This provides a novel solution for broadband acoustic monitoring, making it highly adaptable in applications such as high-precision acoustic monitoring, environmental noise analysis, and industrial noise monitoring.

[0047] The fabrication method of the present invention designs the etching process based on the structural characteristics of the diaphragm. By using different mask plates, layer-by-layer etching of the multi-thickness resonance and deformation zones is achieved, ensuring the sensor's high sensitivity and wide frequency response range. Furthermore, the nested protective design of the optical fiber and capillary tube ensures accurate centering of the sensor diaphragm and secure assembly, allowing the optical fiber to be stably embedded without damaging the diaphragm, further enhancing the structural durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 FIG2 is a schematic diagram of the structure of an optical fiber sensor according to an embodiment of the present invention;

[0049] Figure 2 FIG2 is a three-dimensional schematic diagram of a diaphragm of an optical fiber sensor according to an embodiment of the present invention;

[0050] Figure 3 Shown Figure 2 Schematic diagram of the middle diaphragm;

[0051] Figure 4 FIG2 is a schematic diagram of a process for preparing a diaphragm of an optical fiber sensor according to an embodiment of the present invention, which includes steps (A), (B), (C), (D), and (E);

[0052] Figure 5 It is a three-dimensional schematic diagram of the preparation result of the membrane of the optical fiber sensor in the embodiment of the present invention;

[0053] Figure 6 It is a schematic plan view of the preparation result of the membrane of the optical fiber sensor in the embodiment of the present invention;

[0054] Figure 7 FIG2 is a schematic diagram showing the deformation of the diaphragm in the optical fiber sensor of the present invention under an external ultrasonic signal;

[0055] Figure 8 FIG2 is a schematic diagram of a frequency response curve simulation of an optical fiber sensor according to an embodiment of the present invention;

[0056] In the figure, 1-diaphragm, 11-silicon base layer, 12-silicon oxide layer, 13-silicon substrate layer, 14-reflection layer, 2-casing, 3-capillary tube, 4-optical fiber. DETAILED DESCRIPTION

[0057] The following is further described in conjunction with the accompanying drawings and specific embodiments. The embodiments mentioned are merely exemplary descriptions of the present invention, used to illustrate the present invention, and should not be understood as limiting the present invention. In the absence of any conflict, the various embodiments of the present invention and their technical features may be combined with each other.

[0058] Example 1

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

[0060] like Figure 2 and Figure 3 As shown, the diaphragm 1 includes a device layer, which can be processed from a silicon substrate layer of an SOI crystal. One side of the device layer is a reflection end and the other side is an input end. The reflection end of the device layer is flat and is provided with a reflection layer 14. A deformation zone is provided in the middle of the input end of the device layer, as shown in FIG. Figure 2 There are multiple resonance regions around the deformation region, such as Figure 2 Regions a, b, c, and d in the figure; multiple resonance regions are adjacent to each other, the input surfaces of adjacent resonance regions are at different heights, and the heights of the input surfaces of all resonance regions are greater than the height of the input surface of the deformation region;

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

[0062] One end of the capillary tube 3 is inserted into the sleeve 2 and fixedly connected to the reflective 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 zone of the device layer, and there is a light transmission gap between the end of the optical fiber 4 and the reflective layer 14 .

[0064] In this embodiment, multiple resonance zones with different top surface heights and a concave deformation zone in the middle provided on the diaphragm constitute an asymmetric multi-resonance 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, ensuring that it is aligned with the deformation zone of the diaphragm, thereby realizing an accurate fiber interference measurement path. A Fabry-Perot interferometer cavity is formed between the end face of the optical fiber and the gold-plated surface in the center of the diaphragm for detecting acoustic signals. The single-mode optical fiber emits incident light. As the diaphragm deforms, the cavity length of the Fabry-Perot interferometer 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 in the interference cavity, the sound pressure values of different frequencies 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 area and the peripheral areas of different thicknesses produce resonant responses in different frequency bands, forming multi-band resonance characteristics, 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 The structure of multiple resonant and deformable zones on the device layer of the diaphragm of the present invention is shown. This structure can also be directly used as a diaphragm for a fiber resonator, assembled with a sleeve, capillary tube, and optical fiber to produce an asymmetric multi-resonant fiber sensor. Specifically, a sleeve with a radial cross-section that matches the shape of the diaphragm's perimeter is selected, with one end of the sleeve secured to the outer edge of the multi-resonant zone of the device layer. Furthermore, the sensor of the present invention can also be designed with an extension around the perimeter of the multi-resonant zone on the diaphragm to facilitate assembly of the sleeve and capillary tube, and to enhance the overall stability of the fiber sensor structure.

[0067] Example 2

[0068] Based on Example 1, Figure 2 and Figure 3 In this embodiment of the optical fiber sensor, the diaphragm comprises only a device layer fabricated on silicon. Within this device layer, the deformation region e is a square groove, and there are four resonant regions, whose outer edges form a square. The grooves in the deformation regions can also be shaped like triangles or circles, and the outer edges of the multiple resonant regions can also form other shapes to accommodate detection requirements in different frequency ranges.

[0069] like Figure 2 In this embodiment, among the multiple resonance regions, the surface heights, that is, the heights of the top surfaces, of any two of them are different.

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

[0071] The four resonant regions a, b, c, and d are sorted by their surface height values. In this embodiment, the difference between any two adjacent resonant regions with the same surface height value can be set to be equal. This structural design can simplify the corresponding logical operations when the sensor is actually used for detection. Of course, the difference between any two resonant regions with increasing or decreasing thickness can also be set to be non-unique, and the corresponding detection and calculation can still be completed.

[0072] against Figure 2 and Figure 3The diaphragm shown in the figure uses a square glass sleeve with a radial cross-section corresponding to the outer shape of the four resonance zones a, b, c, and d. The inner wall of one end of the sleeve is bonded to the periphery of the diaphragm, and the capillary and optical fiber are further assembled to obtain the entire asymmetric optical fiber sensor.

[0073] Example 3

[0074] Different from the second embodiment, in this embodiment, among the multiple resonance regions surrounding the deformation region, starting from one of the resonance regions, the surface heights of the resonance regions increase or decrease in sequence.

[0075] Similarly, in order to simplify calculations in practical applications, this embodiment is configured such that, in a plurality of resonance regions, starting from one resonance region, the surface heights of the resonance regions are sequentially increased or decreased by the same height value.

[0076] Example 4

[0077] Based on Example 1, the asymmetric optical fiber sensor of this embodiment is as follows Figure 1 As shown, it includes a diaphragm, a sleeve, a capillary tube, and an optical fiber. The diaphragm includes a device layer, a connection layer, and a support layer. The support and connection layers are annularly arranged around the reflective end of the device layer and project onto 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 end face 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 tube, which in turn is adapted to the inner diameter of the support layer, so that they can fit together and provide support. Furthermore, glue can be applied to the outer wall of the capillary tube 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 embodiment can be made based on SOI crystal, and the device layer, the connection layer and the support layer correspond to the silicon substrate layer 13, the silicon oxide layer 12 and the silicon base layer 11 of the SOI crystal respectively.

[0079] like Figure 5 and Figure 6 On the device layer, the deformation zone e is a square groove, and there are four resonant zones, whose outer edges form a square. The groove shape of the deformation zone can also be set to other shapes such as triangles and circles, and the shape formed by the outer edges of multiple resonant zones can also be other shapes.

[0080] like Figure 6 In this embodiment, the surface heights of any two of the multiple resonant regions are different. Specifically, among the four resonant regions a, b, c, and d, all resonant regions are arranged at different heights around the deformation region.

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

[0082] The thin deformation zone of the device layer improves sensitivity, while the peripheral region forms a multi-band response structure. In this embodiment, the deformation zone thickness of the device layer is 1-3 microns, and the ratio of the deformation zone area to the sum of the deformation zone and resonant zone areas is less than 1 / 16. This improves the sensitivity of the optical fiber sensor while maintaining a small change in the main resonant frequency. A thin deformation zone also improves sensor sensitivity.

[0083] The inner diameter of the cannula is equal to the outer diameter of the capillary, but slightly larger than its inner diameter, while the outer diameter of the capillary is much larger than its inner diameter. For example, the outer diameter of the cannula is 4mm and the inner diameter is 3mm; the outer diameter of the capillary is 3mm and the inner diameter is 0.135mm; the length of the optical fiber outside the capillary is 2mm-3mm. This can be adjusted as needed.

[0084] Example 5

[0085] Unlike Example 4, in this embodiment, among the multiple resonant regions, the surface heights of the resonant regions surrounding the deformation region sequentially increase or decrease starting from one of the resonant regions. Furthermore, among the multiple resonant regions, the surface heights of the resonant regions sequentially increase or decrease by the same height value starting from one of the resonant regions.

[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 reflective end surface of the diaphragm, and the sleeve can be made of glass. The number of resonance zones is not limited to four and can be flexibly set according to the needs of multiple frequency bands.

[0087] Example 6

[0088] refer to Figure 4 As shown, this embodiment introduces a method for preparing the asymmetric multi-resonance optical fiber sensor in Examples 1 to 4. The method includes preparing the membrane. The preparation process of the membrane includes:

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

[0090] The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the surface of the reflective end of the diaphragm;

[0091] 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 for etching, and according to the surface height of the multiple resonance regions and deformation regions, the etching is carried out layer by layer until the multiple resonance regions and deformation regions are obtained, thereby completing the preparation of the diaphragm.

[0092] Since multiple resonance 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 required upper mask plates should adapt to the number of resonance regions, and each mask plate is made according to the different surface heights and shapes of the deformation region and multiple resonance regions.

[0093] The above-mentioned etching can be performed layer by layer from shallow to deep, that is, the groove of the deformation zone is etched out last, or from deep to shallow, that is, the groove of the deformation zone is etched out first.

[0094] As an etching operation mode, the silicon substrate layer of the SOI wafer is etched using multiple deep reactive ion etching processes, and etching layer by layer according to the surface height of the multiple resonance regions and the deformation region until the multiple resonance regions and the deformation region are obtained, including:

[0095] According to the different surface heights of the deformation zone and the multiple resonance zones, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0096] In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and deformation regions in turn;

[0097] 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 resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent 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 resonant area or deformation area.

[0098] As another etching operation, the silicon substrate layer of the SOI wafer is etched using multiple deep reactive ion etching processes, and etching layer by layer according to the surface height of the multiple resonance regions and deformation regions until the multiple resonance regions and deformation regions are obtained, including:

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

[0100] 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, thereby obtaining a deformation zone and multiple resonance zones in turn;

[0101] 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.

[0102] After the membrane is prepared, the membrane is assembled with the sleeve, capillary tube and optical fiber according to the structure of the sensor described in Examples 1 to 5 to obtain an asymmetric multi-resonance optical fiber sensor.

[0103] Example 7

[0104] Based on Example 6, Figure 1 The asymmetric multi-resonance sensor shown is the preparation target, reference Figure 4 The preparation process of this embodiment includes the following steps:

[0105] S1, select or prepare a SOI crystal of appropriate size and shape, such as Figure 5 The circular SOI wafer substrate shown;

[0106] S2, making a mask for etching the resonance region and deformation region with different thicknesses;

[0107] S3, such as Figure 4In step (A), the SOI wafer is placed on a spin coater, a photoresist layer is uniformly coated on the silicon base layer, and the photoresist layer is pre-baked at 90-100°C for 1-2 minutes to remove the solvent in the photoresist and enhance its stability during the exposure process;

[0108] S4, after precisely aligning the wafer covered with photoresist with the lower mask, the wafer is placed into an exposure machine, and ultraviolet light is irradiated on the transparent area of the mask to cause a photochemical reaction on the surface of the photoresist, forming a projection of the mask pattern. After exposure, a developer is used to remove the reacted photoresist area, while retaining the pattern structure of the unexposed area. Post-baking is then performed to enhance the adhesion and tolerance of the developed photoresist layer, thereby ensuring that it effectively protects the desired 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 pattern structure of the sensor reflective end can be accurately transferred to the wafer, forming 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 using the multiple deep reactive ion etching (DRIE) processes described in Example 6. Accurate structures of regions of varying thickness are achieved through step-by-step photolithography and etching. For example, photoresist is first coated on the surface of the silicon substrate layer and photolithography is performed using an upper mask pattern to define the etching area for each layer. Subsequently, by controlling the etching depth, peripheral regions of decreasing thickness are sequentially formed. After each layer is etched, the upper mask is replaced and photolithography is performed again to define the etching depth of the next layer. Finally, the deepest etching is performed in the central region to form a thin groove region for the main frequency response.

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

[0112] S8: Fix the cannula vertically to the bracket and evenly apply a small amount of UV glue to its end surface. Then, under the guidance of a microscope, precisely align and attach the diaphragm to the cannula end surface, ensuring that the cannula end surface is closely attached to the surface of the silicon substrate layer, also known as the support layer. Use a UV curing lamp to irradiate 360° for 10 minutes to achieve the initial bonding and fixation of the diaphragm and cannula.

[0113] S9, process the SMF fiber, remove its coating and clean the bare fiber, and cut it to a length 2 to 3 mm longer than the capillary length. After inserting the bare fiber into the capillary, apply a small amount of UV glue to both ends of the capillary and irradiate it with a UV lamp for 10 minutes to complete the initial fixation of the fiber and the capillary.

[0114] S10, align and assemble the two cured components obtained after S8 and S9 on a three-dimensional adjustment frame to ensure that each component is precisely aligned to achieve an effective acoustic conduction path. A Fabry-Perot interferometer cavity is formed between the end face of the single-mode optical fiber and the gold-plated surface of the diaphragm to measure and respond to sound signals of different frequencies.

[0115] The initial cavity length of the fabricated fiber optic sensor's Fabry-Perot interferometer cavity is optimized and adjusted based on the optimal interference spectrum observed in real time to ensure the sensor's optimal frequency response and sensitivity. The optimal interference spectrum is obtained by connecting the fiber optic sensor's single-mode fiber end to an SM155 fiber Bragg grating sensor interrogator and performing real-time spectral adjustment on the reflected light. Specifically:

[0116] The uncured fiber optic sensor is mounted on a three-dimensional adjustment frame. The sensor's position is gradually adjusted along each of the three axes (X, Y, and Z) using a fine-tuning mechanism. A demodulator connected to a computer monitors the interferometric spectrum in real time until the contrast reaches the optimal position. The cavity length at this point is recorded and used as the sensor's initial reference length to ensure stability and high sensitivity in subsequent measurements.

[0117] In this embodiment, COMSOL multi-physics simulation software is used to simulate and analyze the asymmetric multi-resonant fiber optic sensor. The simulation experiment adopts the acoustic-solid coupling condition and sets the diaphragm boundary 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 external acoustic signals are analyzed by simulation software. The results are as follows: Figure 7 and Figure 8 As shown, Figure 7 is the deformation effect of the diaphragm structure under ultrasonic signal, Figure 8 is the frequency response characteristic of the optical fiber sensor.

[0118] Depend on Figure 7 and Figure 8 As can be seen, the asymmetric multi-resonant fiber sensor structure and corresponding fabrication method of the present invention enable the central groove region to achieve a greater deformation amplitude under the action of sound pressure, thereby significantly improving the sensor's sensitivity and frequency selectivity. These design solutions provide the sensor with broadband response and high sensitivity, enabling accurate detection of acoustic signals across multiple frequency bands.

[0119] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. An asymmetric multi-resonance optical fiber sensor comprising a diaphragm, a sleeve, a capillary tube, and an optical fiber; characterized by: The diaphragm includes a device layer; the reflective end of the device layer is flat and provided with a reflective 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, wherein the plurality of resonance zones are adjacent to each other, and the input surfaces of adjacent resonance zones are located at different heights, and the input surfaces of all resonance zones are located 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 interior of the sleeve; One end of the capillary tube 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 gap between the end of the optical fiber and the reflective layer.

2. The asymmetric multi-resonance optical fiber sensor according to claim 1, wherein: 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 fixedly connected to the supporting layer and the device layer respectively; the end face 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, wherein: The outer diameter of the capillary tube is adapted to the inner diameter of the supporting layer.

4. The asymmetric multi-resonance optical fiber sensor according to claim 1, wherein: 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, wherein: 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 resonance region, the surface heights of the resonance regions increase or decrease in sequence.

7. The asymmetric multi-resonance optical fiber sensor according to claim 6, wherein: 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, wherein: 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, wherein: According to the order of the surface height values of the resonance regions from large to small, the differences in the surface height values between any two resonance regions with adjacent surface height values are 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, wherein: 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 process of preparing the diaphragm includes: Coating a photoresist layer on the SOI wafer and performing a baking process; The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which respectively etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the shape of the surface of the input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the surface of the reflective end of the diaphragm; For the exposed area of the silicon base layer of the SOI wafer, reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is 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 for etching, and according to the surface height of the multiple resonance regions and deformation regions, the etching is carried out layer by layer until the multiple resonance regions and deformation regions are obtained, thereby completing the preparation of the diaphragm.

14. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, each of which is 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 multiple resonance zones, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels; In order from shallow to deep, the corresponding mask plates are used to perform etching operations of different height levels on the silicon substrate layer of the SOI crystal, thereby obtaining multiple resonance regions and deformation 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 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 resonant area to be etched and the adjacent surface height resonant area, or according to the surface height difference between the resonant area to be etched and the adjacent 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 resonant area or deformation area.

15. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, each of which is 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 multiple resonance zones, 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, thereby obtaining a deformation zone and multiple resonance zones 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 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 the assembly of sensors, including: Fix the sleeve on the bracket, apply UV glue on its end face, align the reflective end of the diaphragm and stick it to the end face of the sleeve, and use UV light to irradiate the diaphragm and sleeve to fix the connection; Cut the required length of optical fiber, remove the coating and clean the bare fiber; Insert the bare fiber into the inner hole of the capillary, apply UV glue on both ends of the capillary, and irradiate with UV light to fix the fiber and capillary relatively; The optical fiber is aligned with the center of the deformation zone of the diaphragm, and the capillary tube through which the optical fiber is passed is placed in a sleeve and fixed to the reflective end surface of the diaphragm to obtain the asymmetric multi-resonance optical fiber sensor.

Images