High-sensitivity multi-core fiber sensor probe with concave micro-pyramid structure and preparation method thereof

Abstract

This invention provides a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure and its fabrication method. It involves processing an integrated concave microconical structure at the end of a multi-core fiber, utilizing the central core and circumferentially arranged peripheral cores to construct independent axial and multi-lateral external cavity Fabry-Perot interferometer systems. This allows a single probe to perform synchronous detection of multi-dimensional parameters, eliminating assembly deviations at the source and improving overall structural stability. Simultaneously, the aforementioned concave microconical multi-core fiber, in conjunction with an optical beam splitter, achieves isolated transmission of multiple interference signals. Data is then analyzed via a multi-channel signal demodulation system, effectively suppressing crosstalk and ensuring independent, synchronous, and accurate detection data. Ultimately, this achieves low-crosstalk, high-stability integrated multi-dimensional high-precision sensing, overcoming the shortcomings of traditional technologies and enabling widespread application in dynamic monitoring scenarios for various precision structures.

Description

Technical Field

[0001] This invention relates to the field of mechanical engineering technology, and in particular to a high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure and its fabrication method. Background Technology

[0002] Fiber optic sensing technology, with its advantages of small size, strong resistance to electromagnetic interference, long-distance transmission, and suitability for detection in confined spaces, has been widely used in the measurement of parameters such as displacement, distance, morphology, pressure, and temperature. Especially in confined spaces such as micro-holes, microcavities, narrow slits, and complex internal wall structures, traditional electrical or mechanical probes often suffer from problems such as large size, difficulty in penetration, and significant disturbance to the measured environment. Fiber optic probes, on the other hand, are more suitable for achieving miniaturization and high-precision detection.

[0003] Most existing fiber optic sensing probes use single-core optical fibers or unidirectional measurement structures, typically only acquiring information in a single axial direction. When it is necessary to simultaneously acquire axial distance and gap or displacement information in multiple lateral directions, multiple optical fibers, multiple probes, or additional mechanical scanning mechanisms are often required. This approach not only increases the system size and assembly difficulty but also reduces the probe's integration, making it unsuitable for multidimensional measurements in confined spaces. To improve the light emission mode of fiber optic probes, existing research has attempted to fabricate microlenses, tilted end faces, or other surface microstructures on the fiber end face to alter the light propagation direction and enhance the echo signal. However, these approaches mostly focus on altering the morphology of the outer surface of the end face, resulting in relatively simple structures that make it difficult to simultaneously achieve axial linear light emission and lateral directional light emission within a single fiber. Particularly in multi-core fibers, there remains a lack of compact and easily fabricated methods for establishing multiple independent measurement channels using different cores and performing distance detection in different directions. Furthermore, in existing side-emitting optical solutions, the beam typically needs to pass through the sidewall of a cylindrical fiber, which easily leads to additional refraction and divergence, resulting in decreased return coupling efficiency and reduced interference fringe contrast, thus affecting measurement accuracy and signal stability. These problems are even more pronounced for multi-core fiber optic probes with multi-channel parallel demodulation.

[0004] Therefore, it is necessary to propose a new multi-core fiber optic sensing probe structure, which constructs a microstructure at a specific angle inside the fiber end, enabling the central fiber core to achieve axial measurement and the outer fiber cores to achieve measurement in different transverse directions. This approach improves optical path coupling efficiency and interference signal quality while ensuring probe miniaturization, in order to meet the sensing requirements of multidimensionality, high sensitivity, and high integration. Summary of the Invention

[0005] The purpose of this invention is to provide a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure and its fabrication method, addressing the technical problems of insufficient integration, single measurement direction, complex structure, and difficulty in acquiring multi-channel information in existing fiber optic end-face sensing probes for multi-dimensional displacement / distance detection. This sensing probe is based on a multi-core fiber, constructing a 45° conical cavity microstructure inside the fiber end. This allows the central and peripheral fiber cores to form external Fabry-Pérot interferometric measurement channels with different light output directions, thereby achieving distance information acquisition in multiple axial and lateral directions on a single fiber probe. It features a compact structure, high integration, rich measurement dimensions, and ease of miniaturization.

[0006] To address the aforementioned technical problems, this invention first provides a high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure, comprising: The concave microtapered multi-core optical fiber has a concave microtapered structure formed at its first end. The fiber comprises one central core and N-1 peripheral cores, where N is a positive integer greater than 3. The peripheral cores are evenly distributed around the central core circumferentially. The first probe light transmitted through the central core is axially emitted from the bottom surface of the concave microtapered structure, using the bottom surface as a reflection reference, and forms an axial external cavity Fabry-Perot interferometer with the axial reflection interface to be measured. The second probe light transmitted through each peripheral core is radially emitted from the sidewall of the corresponding concave microtapered structure, using the sidewall as a reflection reference, and forms N-1 independent transverse external cavity Fabry-Perot interferometers with the corresponding transverse reflection interfaces to be measured. An optical beam splitter, connected to the second-end optical path of a concave microtapered multi-core fiber, is used to separate multiple Fabry-Perot interference signals transmitted by N cores in the concave microtapered multi-core fiber into N independent transmission optical paths. The signal demodulation system, connected to the optical path of the optical beam splitter, is used to demodulate the Fabry-Perot interference signals corresponding to each transmission optical path and obtain real-time Fabry-Perot cavity length data in the axial and radial directions.

[0007] Preferably, the concave microconical structure is an embedded conical cavity, the bottom surface of which is the central fiber core end face of the concave microconical multi-core optical fiber, and the N-1 peripheral fiber core end faces of the concave microconical multi-core optical fiber are correspondingly arranged on the conical sidewall of the embedded conical cavity.

[0008] Preferably, the end face of the central fiber core is a planar light-emitting structure and is perpendicular to the central axis of the concave microtapered multi-core fiber.

[0009] Preferably, the tapered sidewall is provided with N-1 tilted deflection reflective surfaces corresponding to the outer fiber cores at the positions of each outer fiber core end face, and each tilted deflection reflective surface forms a 45° angle with the central axis of the concave microtapered multi-core optical fiber.

[0010] Preferably, the optical beam splitter is precisely coupled to the central fiber core and N-1 peripheral fiber cores in a one-to-one correspondence; the signal demodulation system is provided with multiple independent demodulation channels, each of which is used to demodulate the Fabry-Perot interference signal corresponding to each transmission optical path simultaneously or in a predetermined sequence.

[0011] Accordingly, the present invention also provides a method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure, the method comprising the following steps: S10: Select a multi-core optical fiber containing one central core and at least three peripheral cores, strip the coating layer from the end of the multi-core optical fiber, and after cutting and end-face polishing, identify the core distribution of the multi-core optical fiber and establish a processing coordinate system. S20: Fix the pre-processed multi-core optical fiber, establish the reference relationship between its optical fiber axis and the direction of movement, detect the core distribution information of the multi-core optical fiber end face, and mark the processing area. S30 involves microstructuring the internal structure of the multi-core optical fiber end face to form a concave microconical structure. S40, optical finishing process is performed on the concave microconical structure to reduce the surface roughness of its bottom and sidewalls; S50, the concave microconical structure is cleaned and tested sequentially to verify its structural morphology, coaxial alignment and overall structural integrity, and to produce concave microconical multi-core optical fiber; S60 connects one end of the concave microtapered multi-core fiber away from the concave microtapered structure to one end of the optical beam splitter, and simultaneously connects the other end of the optical beam splitter to the signal demodulation system, thus assembling a high-sensitivity multi-core fiber sensing probe with a concave microtapered structure.

[0012] Preferably, step S30 specifically includes: performing material removal processing on the interior of the fiber end face from the outside to the inside in a layer-by-layer ring scanning manner, while simultaneously reducing the scanning radius to obtain an embedded conical cavity.

[0013] Preferably, step S30 specifically includes: using a directional bevel precision cutting method, locally removing material from the interior of the fiber end face along a preset 45° direction, and combining this with circumferential rotation processing to achieve circumferential symmetrical structure forming, thereby preparing an embedded conical cavity.

[0014] Preferably, the concave microconical structure is an embedded conical cavity, the bottom surface of the embedded conical cavity is the central fiber core end face of the concave microconical multi-core optical fiber, and N-1 peripheral fiber core end faces in the concave microconical multi-core optical fiber are correspondingly arranged on the conical sidewall of the embedded conical cavity. The central fiber core end face is a planar light-emitting structure and is perpendicular to the central axis of the concave microtapered multi-core fiber. The tapered sidewalls are provided with N-1 tilted deflection reflection surfaces corresponding to the positions of the outer fiber core end faces, and each tilted deflection reflection surface forms a 45° angle with the central axis of the concave microtapered multi-core fiber.

[0015] Preferably, in step S40, a hydrofluoric acid etching process is used to perform chemical smoothing and optical finishing on the concave microconical structure; or a femtosecond laser or precision polishing method is used to perform secondary finishing on the local surface of the concave microconical structure.

[0016] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure and its fabrication method. It utilizes an integrated concave microconical structure fabricated at the end of a multi-core fiber, and employs a central core and circumferentially arranged peripheral cores to construct independent axial and multi-lateral external cavity Fabry-Perot interferometer systems. This allows a single probe to perform synchronous detection of multi-dimensional parameters, eliminating assembly deviations at the source and improving overall structural stability. Simultaneously, the aforementioned concave microconical multi-core fiber, in conjunction with an optical beam splitter, achieves isolated transmission of multiple interference signals. The data is then analyzed via a multi-channel signal demodulation system, effectively suppressing crosstalk and ensuring independent, synchronous, and accurate detection data. Ultimately, this achieves low-crosstalk, high-stability integrated multi-dimensional high-precision sensing, overcoming the shortcomings of traditional technologies and enabling widespread application in dynamic monitoring scenarios for various precision structures. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the concave microtapered multi-core optical fiber provided in Embodiment 1. Figure 2 This is a schematic diagram showing the connection between the concave microconical multi-core fiber, the optical beam splitter, and the signal demodulation system in the high-sensitivity multi-core fiber sensing probe with the concave microconical structure provided in Embodiment 1. Figure 3 This is a photograph of the concave microtapered multi-core optical fiber taken under a high-resolution electron microscope, as provided in Example 1. In the attached diagram: 10—Concave microtapered multi-core optical fiber; 101—Embedded tapered cavity; 11—Central fiber core; 12—Outer fiber core; 21—Axial reflection interface to be tested; 22—Transverse reflection interface to be tested; 30—Optical beam splitter; 40—Signal demodulation system; 41—Signal acquisition card; 42—Host computer. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Existing fiber optic interferometric sensing probes mostly employ single-core fibers or unidirectional measurement structures, failing to achieve integrated detection in both axial and lateral directions. Multidirectional measurement scenarios require multiple fibers or combinations of independent probes, resulting in large system size and low integration. Furthermore, existing fiber endface microstructure solutions struggle to simultaneously achieve axial linear light output from the central core and lateral directional light output from the outer cores within a single multi-core fiber. The curved sidewalls of the fiber also easily cause lateral light divergence, leading to reduced return coupling efficiency and poor Fabry-Perot interferometric signal quality. To address these shortcomings, this invention integrates axial and lateral multidirectional measurement functions into a single multi-core fiber probe, effectively reducing probe size and improving system integration. By incorporating a 45° conical cavity structure at the fiber end, a composite light output effect of axial light output from the central core and lateral directional light output from the outer cores is achieved. A planar light-emitting surface is also incorporated to optimize lateral light output performance and improve return coupling efficiency, ultimately significantly enhancing the accuracy and operational stability of multi-channel Fabry-Perot interferometric measurements.

[0020] The technical solution of this application will now be described in conjunction with specific embodiments.

[0021] Example 1: The core of the high-sensitivity multi-core fiber optic sensing probe with concave micro-conical structure provided in Embodiment 1 consists of a concave micro-conical multi-core fiber 10, an optical beam splitter 30, and a signal demodulation system 40. In this embodiment 1, a concave micro-conical multi-core fiber 10 with a core number of N=5 is preferably used. The concave micro-conical multi-core fiber 10 includes one central fiber core 11 and four peripheral fiber cores 12 that are circumferentially and symmetrically distributed around the central fiber core 11, which meets the design requirement of N>3. It can realize five-dimensional full coverage detection in four-way lateral + axial directions and is suitable for the synchronous acquisition of multi-dimensional displacement, gap, and attitude parameters under complex working conditions.

[0022] like Figure 1 As shown, the core sensing unit of the high-sensitivity multi-core fiber optic sensing probe with an inverted concave microconical structure provided in Embodiment 1 is a five-core multi-core fiber with an inverted concave microconical structure processed at the top. Its AA cross section clearly shows the fiber core distribution structure inside the fiber. The single fiber integrates one central fiber core 11 and four circumferentially symmetrically arranged peripheral fiber cores 12. The end face of the central fiber core 11 is located in the bottom plane area of ​​the concave microconical structure, and the end faces of the four peripheral fiber cores 12 are evenly arranged on the conical sidewall of the concave microconical structure.

[0023] Specifically, the first probe light transmitted by the central fiber core 11 can be emitted vertically along the fiber axis through the bottom plane structure (end face of the central fiber core 11) of the concave microconical structure. The first probe light is reflected back into the central fiber core 11 after hitting the axial reflection interface 21 (preferably made of polyimide film) in front of the fiber end face, thus forming a stable axial external cavity Fabry-Perot interference optical path. At the same time, the second probe light transmitted by the four peripheral fiber cores 12 can be precisely deflected by the tilted deflection reflection surface of the sidewall of the concave microconical structure and emitted radially along the fiber. The second probe light is reflected back to the original peripheral fiber core 12 after hitting the transverse reflection interface 22 (preferably made of polyimide film) in the corresponding direction, forming four independent transverse external cavity Fabry-Perot interference optical paths. Finally, the axial and four transverse multi-dimensional synchronous sensing and detection are integrated on a single fiber probe, completely breaking through the limitation of traditional fiber probes that measure in one direction.

[0024] In this embodiment 1, the inner side of the end of the aforementioned concave microtapered multi-core optical fiber 10 is formed with an embedded conical cavity 101 (i.e., a concave microtapered structure). This embedded conical cavity 101 is completely embedded inside the end face of the optical fiber, without any external protrusions, ensuring the miniaturization and compactness of the probe. The area of ​​the embedded conical cavity 101 corresponding to the central fiber core 11 is a flat planar structure perpendicular to the central axis of the optical fiber, which ensures that the laser in the central fiber core 11 is emitted in a straight line along the optical fiber axis without deflection and with low loss. The emitted laser and the front-end axial reflection interface 21 form an external cavity Fabry-Perot interferometer. By demodulating the cavity length change data of this interferometer, the axial distance and axial displacement change information between the sensing probe and the external measured interface can be accurately obtained, realizing high-precision axial ranging and deformation detection.

[0025] In this embodiment 1, the region of the embedded conical cavity 101 corresponding to the four peripheral fiber cores 12 is a smooth conical inclined surface structure with an angle of 45° to the central axis of the optical fiber. This angle is the optimal deflection angle, which can realize the efficient lateral deflection and emission of the laser emitted from the peripheral fiber cores 12. Each peripheral fiber core 12 corresponds to an independent lateral measurement orientation. After the laser emitted from each peripheral fiber core 12 is reflected by the external reflection interface in the corresponding direction, it accurately returns to the original peripheral fiber core 12 and forms an independent external cavity Fabry-Perot interferometer. By synchronously demodulating the four lateral interference signals, distance data in different circumferential lateral directions can be obtained. Through multi-channel data joint analysis, multi-dimensional parameters such as lateral displacement, eccentricity offset, attitude tilt, and small changes in circumferential gap during probe operation can be further calculated, which greatly improves the comprehensiveness and accuracy of sensing detection.

[0026] To further optimize the lateral light output quality and reduce optical signal loss, in this embodiment 1, flat planar light output surfaces are precisely machined on the outer wall of the multi-core fiber corresponding to the light output positions of the four outer cores 12, replacing the arc sidewall structure of traditional optical fibers. This effectively eliminates the problems of beam divergence and large scattering loss caused by arc sidewall light output, significantly improves the collimation of the lateral light output of the outer cores 12, increases the return coupling efficiency, effectively improves the spectral intensity and fringe contrast of each lateral Fabry-Perot interference signal, and ensures the stability and high precision of the multi-channel detection signal.

[0027] In this embodiment 1, the optical beam splitter 30 adopts a dedicated beam splitting device that is precisely coupled to the five groups of fiber cores of the five-core multi-core optical fiber. It can accurately split and couple the five interference optical signals transmitted by the five fiber cores in a single multi-core optical fiber into five independent transmission optical paths, avoiding crosstalk between the optical signals of each channel and ensuring the independence of multi-channel signal transmission.

[0028] In this embodiment 1, the signal demodulation system 40 is equipped with five independent signal demodulation channels, which can realize synchronous demodulation or time-division demodulation of the five optical interference signals according to the detection requirements, accurately extract the cavity length change data of each external cavity Fabry-Perot interference signal, and finally integrate to obtain multi-dimensional detection results in the axial and four-way transverse directions.

[0029] like Figure 2 The diagram shown is a schematic of the connection between the concave microcone multi-core fiber 10, the optical beam splitter 30, and the signal demodulation system 40 in the high-sensitivity multi-core fiber optic sensing probe with concave microcone structure provided in Embodiment 1. The entire multi-dimensional fiber optic interferometric sensing and detection system is mainly composed of a front-end fiber optic probe, an optical beam splitter 30, and a signal demodulation system 40 connected in sequence. The signal demodulation system 40 specifically includes two major hardware functional units: a signal acquisition card 41 and a host computer 42. The front-end fiber optic probe is a concave microtapered multi-core fiber 10 fabricated in Embodiment 1. As the core sensing unit of the system, the concave microtapered structure at its end can couple with the interface under test to form five independent Fabry-Perot interferometer cavities. The generated multi-channel interference light signals are transmitted back along the original path of the concave microtapered multi-core fiber 10. After receiving the composite light signal, the optical beam splitter 30 disassembles and separates the multi-coupling optical paths, outputting five independent single-channel optical signals. The separated interference light signals are connected to the signal acquisition card 41 of the signal demodulation system 40, where the signal acquisition card 41 completes photoelectric conversion, real-time signal acquisition, and noise reduction preprocessing. The preprocessed effective data is further transmitted to the host computer 42. Relying on the interference signal demodulation algorithm and cavity length data analysis model built into the host computer 42, the real-time calculation and data analysis of the multi-channel signals are completed, ultimately realizing high-precision real-time monitoring and data output of the axial and lateral multi-dimensional displacement, distance, and attitude parameters of the measured object.

[0030] Specifically, the testing principle of the high-sensitivity multi-core fiber optic sensing probe with concave microconical structure in Example 1 is as follows: First, the first probe light transmitted by the central fiber core 11 is emitted perpendicularly along the fiber axis through the end face of the central fiber core 11, and then reflected back to the central fiber core 11 after hitting the axial reflection interface 21 of the polyimide film material to be tested, forming a stable axial external cavity Fabry-Perot interference optical path. The second probe light transmitted by the four peripheral fiber cores 12 is precisely deflected radially by a tapered inclined plane at a 45° angle to the central axis of the fiber, and then irradiates the transverse reflection interface 22 of the polyimide film material to be tested in the corresponding direction, and then folds back and couples to the original peripheral fiber core 12 to form four independent transverse external cavity Fabry-Perot interference optical paths. Secondly, the five interferometric optical signals are transmitted back along the original optical fiber to the dedicated optical beam splitter 30, which is coupled to each of the five fiber cores. After being precisely split into five independent transmission optical paths, they are connected to the five independent channels of the signal demodulation system 40. Synchronous demodulation or time-division demodulation can be selected. The signal acquisition card 41 first completes photoelectric conversion, real-time acquisition and noise reduction preprocessing, and then transmits the effective data to the host computer 42. Relying on the built-in interferometric signal demodulation algorithm and cavity length data analysis model, the cavity length change data of the axial interferometric cavity is demodulated to obtain axial distance and displacement information. The four transverse interferometric signals are simultaneously demodulated to obtain different circumferential transverse distance data. Through multi-channel data joint analysis, multi-dimensional parameters such as transverse displacement, eccentric offset, attitude tilt and small changes in circumferential gap are further calculated. Finally, the five-dimensional full coverage synchronous high-precision real-time monitoring and data output of the measured object in the axial and four transverse directions are realized. After the entire probe is calibrated and calibrated in multiple dimensions by a standard displacement calibration device, it can stably realize multi-dimensional high-precision interferometric detection.

[0031] This embodiment 1 also discloses the complete fabrication process of the high-sensitivity multi-core fiber optic sensing probe with the above-mentioned concave microconical structure. The fabrication device used specifically includes a fiber clamping mechanism, a five-dimensional precision displacement platform, a fiber rotation mechanism, a high-magnification microscopic imaging system, a femtosecond laser processing system, an end face polishing device, a side wall finishing device, and a post-processing cleaning device. The various mechanisms work together to achieve high-precision integrated processing of the microstructure.

[0032] Furthermore, the fiber clamping mechanism can stably clamp multi-core fibers, preventing fiber swaying and displacement during processing and ensuring axial processing stability; the five-dimensional precision displacement platform can precisely adjust the relative spatial position of the fiber and the laser processing focus to meet the micron-level precision processing requirements; the fiber rotation mechanism can achieve precise circumferential positioning and step-by-step rotation processing of the fiber, ensuring the circumferential symmetry of the peripheral microstructure; the microscopic imaging system is used to observe the fiber end face core distribution in real time and monitor the microstructure processing progress, achieving full-process visualized precision processing; the femtosecond laser processing system is the core processing unit, used for high-precision shaping of the fiber end face with an embedded 45° conical cavity; the end face polishing device is used for fiber end face pretreatment and flattening; the side wall finishing device is used for precision shaping of the peripheral planar light-emitting surface; the post-processing cleaning device can thoroughly remove micro-debris and surface residual contaminants generated during processing, ensuring the optical performance of the fiber optic probe.

[0033] The specific fabrication process of the concave microtapered multi-core optical fiber 10 provided in this embodiment 1 is as follows: Step (1) Multi-core fiber preprocessing: First, a multi-core fiber preprocessing process is performed. A five-core multi-core fiber is selected, the protective coating layer at the fiber end is stripped, and the fiber end is flatly cut using a precision fiber cleaver. Then, a preliminary polishing process is completed using an end-face polishing device to obtain a flat, clean, and burr-free initial fiber end face. After preprocessing, the spatial distribution position, distribution radius, and circumferential angle parameters of the central fiber core 11 and the four peripheral fiber cores 12 are identified and calibrated using a high-magnification microscopic imaging system to establish a precise three-dimensional processing coordinate system, providing a precise positioning reference for subsequent microstructure processing.

[0034] Step (2) End face positioning and processing benchmark establishment: Then, the end face positioning and processing benchmark establishment work is carried out. The pre-processed multi-core optical fiber is firmly installed in the optical fiber clamping mechanism. The benchmark correspondence between the optical fiber central axis and the moving direction of the five-dimensional precision displacement platform is calibrated. The optical fiber end face is observed in real time through the microscopic imaging system to accurately determine the coaxial position of the central fiber core 11 and the circumferential distribution parameters of the peripheral fiber core 12. The calibration of the femtosecond laser processing focus is completed simultaneously to ensure that the central plane of the embedded conical cavity 101 to be processed is strictly coaxial with the central fiber core 11, and the circumferential distribution position of the 45° inclined plane on the periphery is accurately matched with the four peripheral fiber cores 12, so as to prevent the abnormal light output problem caused by structural misalignment.

[0035] Step (3) Processing of 45° conical cavity embedded in end face: After completing the benchmark calibration, the precision processing of 45° conical cavity embedded in end face is carried out by femtosecond laser processing system. In this embodiment, the layer-by-layer ring scanning processing method is preferred. The quartz material inside the fiber end face is removed layer by layer from the outside to the inside, and the laser scanning radius is reduced step by step at the same time to form a concave conical cavity structure inside the fiber end. During the processing, the geometric shape and size of the conical cavity are precisely controlled by precisely adjusting the three process parameters of laser scanning layer spacing, number of single-layer scanning and focal depth. Finally, the area of ​​the conical cavity corresponding to the central fiber core 11 retains a complete vertical plane structure, and the area corresponding to the four peripheral fiber cores 12 is formed into a regular conical inclined surface with a 45° angle to the fiber axis, so as to ensure the optical conditions of the central fiber core 11 axial straight light output and the peripheral fiber cores 12 lateral deflection light output. In another optional processing method, a directional bevel precision cutting process can be used to directionally remove the internal material of the fiber end along a preset 45° deflection angle. Combined with the equally divided rotation positioning of the fiber rotation mechanism, the circumferential symmetrical structure processing can be completed, and a composite embedded conical cavity 101 with a central plane and a 45° bevel on the periphery can also be prepared.

[0036] Step (4) Optical finishing of the end face: After the rough machining of the conical cavity is completed, the optical finishing of the fiber end is carried out. In this embodiment, a diluted hydrofluoric acid chemical smoothing process is used to etch and remove the step-like microstructures and surface microparticle residues generated by laser processing, effectively reducing the surface roughness of the microstructure and improving the surface smoothness and flatness of the conical plane and the inclined plane. For areas with local processing defects, low-energy femtosecond laser point finishing or end face polishing device can be used to assist in the finishing process, further optimizing the interface optical quality, ensuring that the central plane area is flat and defect-free, forming a high-quality axial interference cavity, while ensuring that the scattering loss of the 45° conical inclined plane is extremely low, meeting the optical requirements of transverse light output and return coupling.

[0037] Step (5) Processing of peripheral planar light-emitting surfaces: Subsequently, processing of peripheral planar light-emitting surfaces is carried out. Based on the circumferential distribution positions of the four peripheral fiber cores 12 as calibrated by the microscopic system, a composite process of femtosecond laser local planar cutting combined with micromechanical grinding and polishing is adopted to process four flat planar light-emitting surfaces at corresponding positions on the outer sidewall of the optical fiber. This ensures that the planar light-emitting surfaces are precisely matched with the transverse light-emitting path after the peripheral fiber cores are deflected at 1245°, thereby minimizing the beam divergence angle, reducing sidewall optical loss, and significantly improving the signal quality and detection sensitivity of the transverse interference channel.

[0038] Step (6) Cleaning and Structural Inspection: After all microstructures are fabricated, the fiber optic probe is systematically cleaned and its structure is inspected. Ultrapure water and anhydrous ethanol are used sequentially to ultrasonically clean the probe, thoroughly removing processing debris, dust, and surface organic contaminants. After cleaning, the probe is allowed to air dry. Subsequently, a high-powered microscope and a confocal profilometer are used to conduct a comprehensive inspection of the probe's end face structure and the side wall light-emitting surface. The integrity of the composite structure of the embedded conical cavity 101, the coaxiality of the central plane and the fiber core, and the alignment accuracy of the outer inclined surface and the light-emitting surface are verified to ensure that each microstructure is dimensionally regular, has a good surface, and exhibits excellent consistency.

[0039] like Figure 3 As shown, the concave microcone structure processed in Example 1 has a regular morphology, clear outline, and symmetrical structure, with no processing defects or damage. The overall depth of the concave microcone structure is marked as 23.96 μm, which directly verifies that the preparation process can achieve micron-level high-precision microstructure processing, with excellent controllability of structure forming, and the processing accuracy fully meets the requirements of precision fiber optic sensing probes, and can stably achieve multi-dimensional high-precision interferometric detection.

[0040] Step (7) Assembly of the high-sensitivity multi-core fiber optic sensing probe with concave microconical structure: After the structure is qualified, the processed concave microconical multi-core fiber 10 is precisely coupled and connected to the optical beam splitter 30 and the signal demodulation system 40 respectively to complete the optical path debugging and system assembly, and obtain the high-sensitivity multi-core fiber optic sensing probe with concave microconical structure; Finally, the entire high-sensitivity multi-core fiber optic sensing probe is calibrated in multiple dimensions by a standard displacement calibration device to calibrate the cavity length-displacement response parameters of each channel in the axial and transverse directions, eliminate system errors, and complete the preparation and debugging of the entire high-sensitivity multi-core fiber optic sensing probe.

[0041] Compared with existing technologies, the high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure and its fabrication method provided by the present invention have the following technical advantages: (1) A 45° conical cavity microstructure is constructed inside the end of a single multi-core fiber, so that the central fiber core 11 and the outer fiber core 12 form light output paths in different directions, thereby realizing distance measurement in multiple directions in the axial and transverse directions within a single probe, which improves the sensing dimension and information acquisition capability. (2) By utilizing the natural spatial distribution characteristics of multi-core optical fibers, multiple independent measurement channels can be integrated into the same optical fiber probe, which significantly reduces the probe size and system complexity, and is beneficial for miniaturization, integration and application in confined spaces. (3) By setting a 45° inclined light-emitting structure at the corresponding position of the outer fiber core 12 and further processing the outer wall into multiple planar light-emitting surfaces, the lateral light-emitting divergence can be effectively reduced, the echo coupling capability can be enhanced, and the Fabry-Perot interference signal intensity and fringe contrast can be improved. (4) The external cavity Fabry-Perot interference signal of each core channel of the multi-core fiber can be independently demodulated by the optical beam splitter 30 and the multi-channel signal demodulation system 40, which facilitates multi-directional, high-resolution and high-consistency displacement / distance detection. (5) The preparation method takes into account both the microstructure forming accuracy and processing efficiency, and is suitable for constructing a highly consistent end face embedded 45° conical cavity structure, which has the potential for further engineering and mass production.

[0042] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0043] The above embodiments merely illustrate implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure, characterized in that, include: The first end of the concave microtapered multi-core optical fiber has a concave microtapered structure. The concave microtapered multi-core optical fiber comprises one central core and N-1 peripheral cores, where N is a positive integer greater than 3. The peripheral cores are uniformly distributed around the central core circumferentially. The first probe light transmitted through the central core is emitted axially through the bottom surface of the concave microtapered structure. Using the bottom surface of the concave microtapered structure as a reflection reference, it forms an axial external cavity Fabry-Perot interferometer with the axial reflection interface to be tested. The second probe light transmitted through each peripheral core is emitted radially through the sidewall of the corresponding concave microtapered structure. Using the sidewall of the concave microtapered structure as a reflection reference, it forms N-1 independent transverse external cavity Fabry-Perot interferometers with the corresponding transverse reflection interface to be tested. An optical beam splitter is connected to the second end optical path of the concave microtapered multi-core optical fiber and is used to separate multiple Fabry-Perot interference signals transmitted by N cores in the concave microtapered multi-core optical fiber into N independent transmission optical paths. The signal demodulation system is connected to the optical path of the optical beam splitter and is used to demodulate the Fabry-Perot interference signals corresponding to each of the transmission optical paths to obtain real-time Fabry-Perot cavity length data in the axial and radial directions.

2. The high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure according to claim 1, characterized in that, The concave microconical structure is an embedded conical cavity. The bottom surface of the embedded conical cavity is the central fiber core end face of the concave microconical multi-core optical fiber. The N-1 peripheral fiber core end faces of the concave microconical multi-core optical fiber are correspondingly arranged on the conical sidewall of the embedded conical cavity.

3. The high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure according to claim 2, characterized in that, The central fiber core end face is a planar light-emitting structure and is perpendicular to the central axis of the concave microtapered multi-core optical fiber.

4. The high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure according to claim 2, characterized in that, The tapered sidewall is provided with N-1 tilted deflecting reflective surfaces corresponding to the outer fiber cores at the respective positions of the outer fiber cores. Each tilted deflecting reflective surface forms a 45° angle with the central axis of the concave microtapered multi-core optical fiber.

5. The high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure according to claim 1, characterized in that, The optical beam splitter is precisely coupled to the central fiber core and N-1 peripheral fiber cores in a one-to-one correspondence; the signal demodulation system is provided with multiple independent demodulation channels, each of which is used to demodulate the Fabry-Perot interference signal corresponding to each of the transmission optical paths simultaneously or in a predetermined sequence.

6. A method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure, characterized in that, The method includes the following steps: S10, Select a multi-core optical fiber containing one central core and at least three peripheral cores, remove the coating layer from the end of the multi-core optical fiber, and after cutting and end-face polishing, identify the core distribution of the multi-core optical fiber and establish a processing coordinate system. S20, fix the pre-processed multi-core optical fiber, establish the reference relationship between its optical fiber axis and the direction of movement, detect the core distribution information of the end face of the multi-core optical fiber, and mark the processing area. S30, perform microstructure processing on the internal structure of the multi-core optical fiber end face to form a concave microconical structure; S40, perform optical finishing on the concave microconical structure to reduce the surface roughness of its bottom and sidewalls; S50, the concave microconical structure is cleaned and inspected in sequence to verify its structural morphology, coaxial alignment and overall structural integrity, and to obtain the concave microconical multi-core optical fiber. S60, connect one end of the concave microtapered multi-core optical fiber away from the concave microtapered structure to one end of the optical beam splitter, and simultaneously connect the other end of the optical beam splitter to the signal demodulation system to assemble a high-sensitivity multi-core optical fiber sensing probe with a concave microtapered structure.

7. The method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure according to claim 6, characterized in that, The S30 step specifically includes: performing material removal processing on the interior of the optical fiber end face from the outside to the inside in a layer-by-layer ring scanning manner, while simultaneously reducing the scanning radius to obtain an embedded conical cavity.

8. The method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microcone structure according to claim 6, characterized in that, The S30 step specifically includes: using a directional bevel precision cutting method, locally removing material from the interior of the fiber end face along a preset 45° direction, and combining this with circumferential rotation processing to achieve circumferential symmetrical structure forming, thus preparing an embedded conical cavity.

9. The method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure according to claim 7 or 8, characterized in that, The concave microconical structure is an embedded conical cavity. The bottom surface of the embedded conical cavity is the central fiber core end face of the concave microconical multi-core optical fiber. The N-1 peripheral fiber core end faces of the concave microconical multi-core optical fiber are correspondingly arranged on the conical sidewall of the embedded conical cavity. The central fiber core end face is a planar light-emitting structure and is perpendicular to the central axis of the concave microtapered multi-core fiber. The tapered sidewall is provided with N-1 tilted deflection reflection surfaces corresponding to the outer fiber cores at the positions of each of the outer fiber core end faces. Each tilted deflection reflection surface forms a 45° angle with the central axis of the concave microtapered multi-core fiber.

10. The method for fabricating a high-sensitivity multi-core fiber optic sensing probe with a concave microconical structure according to claim 6, characterized in that, In step S40, the concave microconical structure is chemically smoothed and optically refined using a hydrofluoric acid etching process; or a secondary finishing process is performed on a local surface of the concave microconical structure using either femtosecond laser or precision polishing.

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