Omnidirectional Fabry-Perot sensor and preparation method thereof

Abstract

The invention discloses an omnidirectional Fabry-Perot sensor and a manufacturing method thereof in the technical field of acoustic sensing, and aims to solve the problem that the directivity of an existing sensing mechanism is limited. The sensor comprises a sound sensitive element, a capillary tube, an insertion core and an optical fiber. The sound sensitive element is formed by coupling a plurality of diaphragms with a central diaphragm through a connecting column; one end of the capillary tube is fixedly connected with the sound sensitive element, and the other end is connected with the ferrule; the insertion core is used for coaxially fixing the optical fiber with high precision; an optical fiber penetrates through and is fixed to the insertion core, and the end face of the insertion end of the optical fiber is flush with the end face of the insertion core. A gap is formed between the end face of the optical fiber and the sound sensitive element to form a Fabry-Perot cavity. According to the structure, the compactness of a single sensor is kept, meanwhile, omnidirectional acoustic signal detection is achieved, and the problems that the directivity of a traditional Fabry-Perot sensor is limited, and the size of a multi-sensor array is large are effectively solved.

Description

Technical Field

[0001] This invention relates to an omnidirectional Fabry-Perot sensor and its manufacturing method, belonging to the field of acoustic sensing technology. Background Technology

[0002] As one of the core means of modern information sensing, fiber optic sensing technology plays an increasingly important role in key areas such as acoustic detection, structural health monitoring, and environmental parameter sensing due to its unique advantages such as resistance to electromagnetic interference, corrosion resistance, and the ability to achieve distributed measurement. Within this technological system, Fabry-Perot fiber optic sensors, with their compact structure, high sensitivity, fast response speed, low power consumption, and support for long-distance signal transmission, have become the mainstream solution for achieving high-precision capture of acoustic waves, vibration, and pressure signals. They are widely used in scenarios such as real-time health diagnosis of large structures (e.g., bridges, buildings, aircraft), localization and characteristic analysis of industrial noise sources, and micro-disturbance monitoring in complex environments (e.g., oil and gas pipelines, power facilities).

[0003] The current performance and application scope of Fabry-Perf sensors face a critical bottleneck: their sensing mechanism suffers from significant directional limitations. This inherent directional dependence means that the sensor can only effectively detect acoustic signals or vibrations in specific directions, leading to blind spots in applications requiring omnidirectional sensing (such as sound source localization). Traditional solutions typically employ multiple sensor arrays for spatial signal detection, but this approach results in large system size, complex structure, demodulation difficulties, and low device integration, severely restricting its practical value in portable and embedded systems. Therefore, overcoming the directional constraints of single-point sensors and achieving high-sensitivity detection of multi-directional signals through a single device has become a crucial research hotspot for expanding the applications of Fabry-Perf sensors in acoustic monitoring, fault diagnosis, and other fields. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of limited directionality of traditional Fabry-Perot sensors and the large size of multi-sensor arrays.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention proposes an omnidirectional Fabry-Perot sensor, comprising an acoustic sensing element, a housing, a capillary tube, a ferrule, and an optical fiber; The acoustic sensing element includes a central diaphragm and several outer diaphragms coupled to the central diaphragm via connecting posts; The housing is used to encapsulate the entire structure of the acoustic sensing element; One end of the capillary is fixedly connected to the bottom of the housing of the acoustic sensing element, and the other end is connected to the insert. The optical fiber passes through and is coaxially fixed to the ferrule, and its insertion end face is flush with the end face of the ferrule. The end face of the optical fiber and the bottom surface of the central diaphragm of the acoustic sensing element form a gap, constituting a Fabry-Perot cavity.

[0006] The aforementioned technical solution integrates several outer diaphragms and couples them to a central diaphragm, enabling the sensor to perceive acoustic signals from different directions in all directions. When a sound wave is incident from a specific direction, the corresponding outer diaphragm preferentially deforms, and its central displacement is transmitted to the central diaphragm through the connecting post, exhibiting directional selectivity. The central diaphragm integrates the mechanical displacements from various directions and converts them into changes in the cavity length of the Fabry-Perot cavity, thereby outputting multi-directional acoustic information through a single interference signal, achieving integrated sensing of multiple signals. Furthermore, the spatial independence of each outer diaphragm ensures the ability to distinguish acoustic signals from different directions, while the unified modulation of the central diaphragm avoids the complex demodulation problems of multi-sensor arrays, exhibiting spatial decoupling characteristics.

[0007] Furthermore, the outer diaphragm is integrated onto the outer shell.

[0008] Furthermore, a connecting layer is provided around the middle of the outer shell, through which the outer shell is connected to the central diaphragm.

[0009] Furthermore, the bottom of the outer casing has a hollow ring structure; the protruding end face of the optical fiber is parallel and coaxial with the bottom of the outer casing of the acoustic sensing element.

[0010] In the above technical solution, a Fabry-Perot cavity is formed between the fiber end face fixed inside the ferrule and the bottom surface of the square diaphragm at the center of the acoustic sensing element. When external acoustic waves excite the diaphragm to generate the aforementioned various vibration modes, the optical interference characteristics of the Fabry-Perot cavity change accordingly with each resonant frequency, thereby achieving efficient detection and response to acoustic signals of different frequencies.

[0011] Furthermore, the outer membrane is a circular membrane, and the central membrane is a central square membrane.

[0012] In the above technical solution, the frequency response characteristics in all directions can be optimized by precisely controlling parameters such as the diameter and thickness of the circular diaphragm and the stiffness of the connecting pillars. Finally, the central square diaphragm serves as a shared sensing unit, converting multiple mechanical displacements into a single interference signal output, achieving effective spatial acoustic signal resolution while maintaining system compactness. This design, through the optimization of geometric parameters (such as diaphragm curvature and connecting pillar dimensions), provides a new solution for positioning and monitoring in complex acoustic environments.

[0013] Furthermore, the capillary is a capillary glass tube with an outer diameter equal to the diameter of the hollow annular structure and an inner diameter that matches the outer diameter of the ferrule. The ferrule is made of ceramic material, and the optical fiber is a single-mode optical fiber.

[0014] Secondly, this invention proposes a method for fabricating an omnidirectional Fabry-Perot sensor, comprising: Remove the coating layer from the optical fiber, peel it off, and wipe it clean to obtain the pretreated optical fiber. Prepare the acoustic sensing element; Assemble the ferrule and process the fiber end face so that the fiber end face is flush with the end face of the ferrule; The acoustic sensing element and the ferrule containing the optical fiber are assembled into a sensor body; The assembled sensor body is placed in a constant temperature device for heat treatment to obtain the finished sensor.

[0015] Furthermore, the acoustic sensing element is integrally fabricated using two-photon polymerization 3D printing technology, comprising: Obtain a three-dimensional model of the acoustic sensing element; Generate 3D printing instructions based on the 3D model; Based on the three-dimensional printing instructions, a femtosecond laser is used to perform precise focusing scanning on a substrate coated with liquid photosensitive resin. The resin is then cured point by point at the focal point through the two-photon polymerization effect, forming a three-dimensional structure prototype encapsulated in uncured resin. The uncured resin of the three-dimensional structure prototype was washed away to obtain an independent microstructure; The microstructure is subjected to critical point drying treatment to obtain a one-piece molded acoustic sensing element.

[0016] Among the above technical solutions, two-photon polymerization (TPP) 3D printing technology utilizes a high-precision femtosecond laser focused within a photosensitive resin material. Computer-controlled scanning of the laser focus along a precise three-dimensional path solidifies the resin point-by-point, ultimately producing a film with complex micro-nano scale structures in a single, high-precision process. This technology achieves sub-micron resolution, ensuring precise control of the geometric dimensions of each substructure and excellent consistency of the overall structure, which is crucial for achieving the expected omnidirectional response.

[0017] Furthermore, the assembly of the ferrule and processing of the fiber end face includes: Inject thermosetting adhesive into the ferrule and insert the pre-treated optical fiber into the ferrule. Heating allows the adhesive to initially cure and fix the optical fiber; Remove excess fiber and perform multi-stage polishing on the fiber end face.

[0018] Furthermore, assembling the acoustic sensing element and the ferrule containing the optical fiber into a sensor body includes: The housing of the fabricated acoustic sensing element is glued and fixed to one end of the capillary tube; The fiber optic ferrule is assembled onto the other side of the capillary tube, and ultraviolet light is used to cure the connection.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention utilizes two-photon polymerization 3D printing technology to integrally fabricate a multi-diaphragm coupled acoustic sensing element. This design enables the sensor to collect vibration information from all directions, achieving spatial dead-zone-free detection on a single device, to some extent achieving the effect of a sensor array. This not only significantly broadens the application scenarios of the sensor but also breaks through the limitation of traditional Fabry-Perot sensors, which can only detect in the positive direction.

[0020] Thanks to this structure, the sensor can simultaneously respond to acoustic or vibration signals from multiple directions, thereby significantly improving the flexibility, accuracy, and sensitivity of measurements in applications such as positioning and imaging. In particular, by using ceramic ferrules to fix the optical fiber and combining end-face processing techniques including precision grinding, we ensure that the Fabry-Perot cavity optical interface has high quality and high stability, which is key to obtaining a high signal-to-noise ratio and reliable signal response.

[0021] In complex signal scenarios, this innovative structural design, combined with high-precision manufacturing and assembly processes, can significantly improve the overall performance of the sensor. This research will strongly promote the application and development of high-performance fiber optic Fabry-Perot sensors in a wider range of fields. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the overall structure of an omnidirectional Fabry-Perot sensor. Figure 2 for Figure 1 The diagram shows the structure of the acoustic sensing element of the Fabry-Perot sensor. Figure 3 for Figure 1 The diagram shows the external structure of the acoustic sensing element of the Fabry-Perot sensor. Figure 4 for Figure 1 The image shows a top view of the acoustic sensing element of the Fabry-Perot sensor. The components are: 1. Acoustic sensing element; 2. Glass sleeve; 3. Ceramic ferrule; 4. Single-mode optical fiber; 5. Circular diaphragm; 6. Connecting post; 7. Central square diaphragm; 8. Acoustic sensing element shell; 9. Connecting layer; 10. Hollow ring; 11. Fabry-Perot cavity. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use.

[0025] Example 1: This example provides an omnidirectional Fabry-Perot sensor, such as... Figure 1 As shown, it mainly includes an acoustic sensing element 1, a glass sleeve 2, a ceramic ferrule 3, and a single-mode optical fiber 4. One end of the glass sleeve 2 is fixedly connected to the bottom of the acoustic sensing element shell 8 of the acoustic sensing element 1. The ceramic ferrule 3 is fixedly connected to the single-mode optical fiber 4, with the single-mode optical fiber 4 passing through and coaxially fixed to the ceramic ferrule 3, and its insertion end face is flush with the end face of the ceramic ferrule 3. The glass sleeve 2 and the ceramic ferrule 3 are fixedly connected after assembly, wherein the outer diameter of the glass sleeve 2 is equal to the diameter of the hollow ring 10, and the inner diameter is adapted to the outer diameter of the ceramic ferrule 3. A gap is formed between the end face of the single-mode optical fiber 4 and the bottom surface of the central diaphragm 7 of the acoustic sensing element 1, forming a Fabry-Perot cavity 11.

[0026] In this embodiment, the acoustic sensing element 1 is integrally formed using two-photon polymerization 3D printing technology. This acoustic sensing element 1 employs an innovative four-directional detection structure design, as shown below. Figure 2 and Figure 4 As shown. The surface of the acoustic sensing element 1 has four symmetrically distributed circular diaphragms 5, which are coupled to the central square diaphragm 7 via precisely designed connecting posts 6. The external structure of the acoustic sensing element 1 is as follows. Figure 3 As shown, the entire structure is encapsulated by a housing 8 for the acoustic sensing element, and a specially designed connecting layer 9 ensures a reliable connection between the housing 8 and the central square diaphragm 7. The bottom of the housing 8 is a hollow ring 10. This four-way symmetrical layout allows each circular diaphragm 5 to independently respond to sound pressure signals in a specific direction. Its displacement is transmitted to the central square diaphragm 7 through the connecting post 6, and finally converted into a Fabry-Perot interference signal output, realizing omnidirectional sound detection. During operation, the single-mode fiber 4 emits incident light towards the central square diaphragm 7 and receives the reflected light reflected by the Fabry-Perot interference cavity. By detecting the optical path difference of the reflected light caused by the change in the cavity length of the interference cavity under the action of the acoustic signal, the sound pressure information of the sound wave can be obtained.

[0027] The working principle of this embodiment is as follows: When sound pressure acts on the four-way symmetrical acoustic sensing element 1, sound waves from different directions will preferentially cause the corresponding circular diaphragms 5 to deform. Since the single-mode optical fiber 4 fixed by the ceramic ferrule 3 remains stationary, the displacement of each circular diaphragm 5 is transmitted to the central square diaphragm 7 through the connecting post 6, causing a directional change in the length of the Fabry-Perot cavity. Increasing the radius of the circular diaphragm 5 can improve sensitivity but reduce the resonant frequency, while increasing its thickness will lead to a decrease in sensitivity and an increase in frequency; increasing the radius or length of the connecting post 6 will both cause a decrease in sensitivity and an increase in frequency; increasing the thickness of the central square diaphragm 7 will also reduce sensitivity, but it is necessary to ensure that it has sufficient structural strength to avoid mechanical reliability problems due to excessive thinness. By precisely designing the size, thickness, and length of the circular diaphragm 5 and the connecting post 6, independent control of sensitivity and frequency response in each direction can be achieved, enabling a single sensor to have omnidirectional acoustic detection capability, effectively solving the problem of limited directionality in traditional Fabry-Perot sensors.

[0028] Example 2: This example provides an omnidirectional Fabry-Perot sensor with adjustable directionality. Based on Example 1, this example optimizes the directionality design of the acoustic sensing element 1. The core improvement lies in enhancing the sensor's directional response capability by setting multiple circular diaphragms 5 on the acoustic sensing element housing 8.

[0029] In this embodiment, the number and spatial arrangement of the circular diaphragms 5 can be flexibly configured according to actual needs. In particular, the upper and lower parts separated by the connecting layer 9 can use different numbers and arrangements of circular diaphragms 5. As the number of circular diaphragms 5 increases, the directional attenuation of the sensor gradually decreases. However, when the number exceeds a certain threshold, the deformation of each diaphragm will be limited due to the excessive number of connection points between the connecting post 6 and the central square diaphragm 7, which will reduce the overall sensitivity.

[0030] The working principle of this embodiment is as follows: each circular diaphragm 5 can independently respond to a sound pressure signal in a specific direction, and its displacement is transmitted to the central diaphragm 7 through the connecting post 6. When the number of circular diaphragms 5 increases, the sensor can cover more incident directions, but too many connection points will restrict the free deformation of each diaphragm. Therefore, in this embodiment, by configuring different numbers and spatial arrangements of circular diaphragms 5, a trade-off can be made between directional response and sensitivity to adapt to different detection scenarios.

[0031] Example 3: This example provides a method for fabricating an omnidirectional Fabry-Perot sensor. The specific steps are as follows: 1) Single-mode fiber pretreatment: First, the single-mode fiber 4 is pretreated by using specialized tools to remove the coating layer from its exterior. Then, the surface of the single-mode fiber 4 is carefully wiped with cleaning material to ensure complete removal of any residue. Finally, the end face of the single-mode fiber 4 is processed using precision cutting equipment to achieve the required flatness and smoothness, preparing it for subsequent assembly processes.

[0032] 2) Fabrication of the acoustic sensing element: An acoustic sensing element 1 with a special structure was fabricated using advanced 3D printing technology. The complex three-dimensional structure of the acoustic sensing element 1 was constructed by precisely controlling a laser beam to perform three-dimensional shaping on a photosensitive material. This structure underwent rigorous quality inspection to ensure that its geometry and dimensions met the design requirements.

[0033] 3) Ceramic ferrule assembly and single-mode fiber end-face treatment, including: Glue application and fiber insertion: Use a precision dispensing machine to inject an appropriate amount of thermosetting adhesive into the inner hole of the ceramic ferrule 3. Carefully insert the pretreated single-mode optical fiber 4 into the glued ceramic ferrule 3.

[0034] Preliminary curing and cutting: After ensuring the single-mode fiber 4 is centered, use a heating table to heat the area of ​​the ceramic ferrule 3 to preliminarily cure the thermosetting adhesive and fix the single-mode fiber 4. After the adhesive has preliminarily cured, use a fiber optic cleaver to cut off the excess fiber extending out of the ceramic ferrule 3.

[0035] Precision Grinding: The ceramic ferrule 3, with the single-mode fiber 4 fixed to it, is mounted onto a precision fiber polishing machine. The end face of the single-mode fiber 4 is then polished in multiple stages using polishing sandpaper or grinding discs with mesh counts increasing from low to high (e.g., 600 grit, 1200 grit, 2000 grit, 3000 grit, or higher). This process aims to gradually remove the unevenness of the end face caused by dicing and obtain a highly flat, smooth end face of the single-mode fiber 4 that is perpendicular to the fiber axis. This is crucial for forming a high-quality Fabry-Perot interferometer cavity.

[0036] 4) Sensor body assembly, including: Apply an appropriate amount of UV adhesive evenly to the base connection surface of the acoustic sensing element 1 and one end connection surface of the glass sleeve 2, then precisely align and bond the acoustic sensing element 1 and the glass sleeve 2, and use a UV curing lamp for initial curing.

[0037] The ceramic ferrule 3 is inserted into the other end of the glass sleeve 2, and its position is precisely adjusted to ensure that the polished flat end face of the single-mode fiber 4 is strictly parallel and coaxial with the bottom surface of the central square membrane 7 structure of the acoustic sensing element 1, thus forming the initial Fabry-Perot cavity.

[0038] Apply an appropriate amount of UV adhesive evenly to the outer connection surfaces of the glass sleeve 2 and the ceramic ferrule 3 with the fixed single-mode optical fiber 4, and perform preliminary curing using a UV curing lamp.

[0039] 5) Thermal Curing Enhancement: Place the pre-assembled and cured Fabry-Perot sensor into a temperature-controlled chamber and adjust it to the specific temperature required for complete UV adhesive curing, maintaining this temperature for a sufficient time. This step ensures deep curing of the UV adhesive, greatly enhancing the overall stability and long-term reliability of the sensor's mechanical structure.

[0040] 6) Conduct comprehensive performance testing on the finished sensor. Use professional testing equipment to test its spatial response characteristics and verify whether it meets the design requirements for directionality. Simultaneously test its operational stability under various environmental conditions to ensure it meets practical application needs.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An omnidirectional Fabry-Perot sensor, characterized in that, Includes acoustic sensing elements, housing, capillary tube, ferrule, and optical fiber; The acoustic sensing element includes a central diaphragm and several outer diaphragms coupled to the central diaphragm via connecting posts; The housing is used to encapsulate the entire structure of the acoustic sensing element; One end of the capillary is fixedly connected to the bottom of the housing of the acoustic sensing element, and the other end is connected to the insert. The optical fiber passes through and is coaxially fixed to the ferrule, and its insertion end face is flush with the end face of the ferrule. The end face of the optical fiber and the bottom surface of the central diaphragm of the acoustic sensing element form a gap, constituting a Fabry-Perot cavity.

2. The omnidirectional Fabry-Perot sensor according to claim 1, characterized in that, The outer diaphragm is integrated onto the outer shell.

3. The omnidirectional Fabry-Perot sensor according to claim 1, characterized in that, A connecting layer is provided around the middle of the outer shell, through which the outer shell is connected to the central diaphragm.

4. The omnidirectional Fabry-Perot sensor according to claim 1, characterized in that, The bottom of the housing is a hollow ring structure; the protruding end face of the optical fiber is parallel and coaxial with the bottom of the housing of the acoustic sensing element.

5. The omnidirectional Fabry-Perot sensor according to claim 1, characterized in that, The outer membrane is a circular membrane, and the central membrane is a square membrane.

6. The omnidirectional Fabry-Perot sensor according to claim 4, characterized in that, The capillary tube is a capillary glass tube with an outer diameter equal to the diameter of the hollow ring structure and an inner diameter that matches the outer diameter of the ferrule. The ferrule is made of ceramic material, and the optical fiber is a single-mode optical fiber.

7. A method for fabricating an omnidirectional Fabry-Perot sensor according to any one of claims 1 to 6, characterized in that, include: Remove the coating layer from the optical fiber, peel it off, and wipe it clean to obtain the pretreated optical fiber. Prepare the acoustic sensing element; Assemble the ferrule and process the fiber end face so that the fiber end face is flush with the end face of the ferrule; The acoustic sensing element and the ferrule containing the optical fiber are assembled into a sensor body; The assembled sensor body is placed in a constant temperature device for heat treatment to obtain the finished sensor.

8. The method for fabricating an omnidirectional Fabry-Perot sensor according to claim 7, characterized in that, The acoustic sensing element is fabricated in one piece using two-photon polymerization 3D printing technology, including: Obtain a three-dimensional model of the acoustic sensing element; Generate 3D printing instructions based on the 3D model; Based on the aforementioned 3D printing instructions, a femtosecond laser is used to perform precise focusing scanning on a substrate coated with liquid photosensitive resin. Through the two-photon polymerization effect, the resin is cured point by point at the focal point, forming a 3D structure prototype encapsulated in uncured resin. The uncured resin of the three-dimensional structure prototype was washed away to obtain an independent microstructure; The microstructure is subjected to critical point drying to obtain a one-piece molded acoustic sensing element.

9. The method for fabricating an omnidirectional Fabry-Perot sensor according to claim 7, characterized in that, The assembly of the ferrule and processing of the fiber end face include: Inject thermosetting adhesive into the ferrule and insert the pre-treated optical fiber into the ferrule. Heating allows the adhesive to initially cure and fix the optical fiber; Remove excess fiber and perform multi-stage polishing on the fiber end face.

10. The method for fabricating an omnidirectional Fabry-Perot sensor according to claim 7, characterized in that, The assembly of the acoustic sensing element and the ferrule containing the optical fiber into a sensor body includes: The housing of the fabricated acoustic sensing element is glued and fixed to one end of the capillary tube; The fiber optic ferrule is assembled onto the other side of the capillary tube, and ultraviolet light is used to cure the connection.

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