Optical fiber end face integrated microcavity sonic sensor

Abstract

The invention relates to the technical field of ultrasonic sensors, and discloses an optical fiber end face integrated micro-cavity sonic sensor which comprises a seven-core optical fiber, two light propagation waveguides, a coupling waveguide, a supporting assembly, a micro disc, a light emitter and a photoelectric detector, the two light propagation waveguides are arranged on the end face of the seven-core optical fiber, the coupling waveguide is arranged between the two light propagation waveguides, and the supporting assembly is arranged on the end face of the seven-core optical fiber. A supporting assembly is arranged on the end face of the seven-core optical fiber, a micro disc is arranged on the top of the supporting assembly, and the first fiber core and the second fiber core are connected with an external light emitter and an external photoelectric detector respectively. The wavelength of the laser output by the light emitter is locked at the linear slope of the micro-disk harmonic peak, the radius and the effective refractive index of the micro-disk are changed through the action of ultrasonic waves on the micro-disk and vibration, the harmonic peak drifts and the intensity of the output laser is changed, and then the ultrasonic waves are detected; compared with the prior art, ultrasonic waves are detected through a micro-disk resonance and laser sideband locking method, and the problem of electromagnetic interference can be effectively avoided by utilizing the optical principle.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic sensors, and particularly to an optical fiber end-face integrated microcavity acoustic wave sensor. Background Art

[0002] With the continuous development of technology, ultrasonic sensors are increasingly applied in fields such as non-destructive testing, medical diagnosis, underwater detection, and meteorological detection. By virtue of the penetration characteristics of ultrasonic waves, relevant information can be obtained through ultrasonic wave reflection and other situations without directly contacting the object to be measured, realizing non-contact detection and having a wide application range, being unaffected by factors such as the material, color, and transparency of the object to be measured. Moreover, it has high precision and can accurately measure physical quantities such as distance, speed, and liquid level. At the same time, it has low production cost, is easy to install and maintain, and has high safety, and is basically harmless to the human body in application scenarios such as medical diagnosis.

[0003] Existing sensors are mainly traditional piezoelectric ultrasonic sensors, which achieve the sensing function through the piezoelectric effect of piezoelectric materials; when the piezoelectric material is subjected to the pressure of ultrasonic waves, an electrical signal will be generated, and the position, image, etc. information can be restored by demodulating the electrical signal to achieve the detection effect; however, the electrical signal generated by the existing piezoelectric ultrasonic sensors during operation is relatively weak and is easily affected by the external electromagnetic environment, resulting in noise, distortion, etc. in the detected signal, which is not conducive to the accurate analysis and subsequent processing of ultrasonic signals, and its accuracy will be reduced when used in some complex industrial environments with strong electromagnetic interference, places with dense electrical equipment, etc.

[0004] In view of this, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the deficiencies of the above-mentioned existing technology, the purpose of the present invention is to provide an optical fiber end-face integrated microcavity acoustic wave sensor, aiming to solve the problem that the piezoelectric ultrasonic sensors in the existing technology are easily affected by the external electromagnetic environment, resulting in poor detection accuracy.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: An optical fiber end-face integrated microcavity acoustic wave sensor, comprising: A seven-core optical fiber; Two optical propagation waveguides, arranged on the end face of the seven-core optical fiber; the two optical propagation waveguides are respectively connected to the first core and the second core of the seven-core optical fiber; A coupling waveguide, arranged between the two optical propagation waveguides for connecting the two optical propagation waveguides; A support assembly, arranged on the end face of the seven-core optical fiber; A microdisk is disposed on the support assembly such that the microdisk is located on one side of the coupling waveguide; the microdisk and the coupling waveguide are arranged at intervals to form a resonant micro-ring; when ultrasonic waves act on the microdisk, the resonance condition changes, which can cause the output laser intensity to change; An optical transmitter is disposed at one end of the seven-core optical fiber away from the optical propagation waveguide; the optical transmitter is connected to the first core; A photodetector is disposed at one end of the seven-core optical fiber away from the optical propagation waveguide; the photodetector is connected to the second core.

[0007] Furthermore, it further includes: A fixing platform is disposed on the end face of the seven-core optical fiber; the fixing platform is located on the side of the coupling waveguide away from the microdisk, and the fixing platform is connected to the coupling waveguide for supporting the coupling waveguide.

[0008] Furthermore, the support assembly includes: A conical platform is disposed on the end face of the seven-core optical fiber; the microdisk is disposed on the conical platform.

[0009] Furthermore, a cylindrical platform is disposed at the top of the conical platform, the microdisk is located on the cylindrical platform, and the diameter of the microdisk is larger than the diameter of the cylindrical platform.

[0010] Furthermore, a micro-ring is disposed on the surface of the microdisk, and the bottom of the microdisk is in an inverted conical shape.

[0011] Furthermore, the optical propagation waveguide includes: Two tapered waveguides are disposed on the end face of the seven-core optical fiber; Two bent waveguides are respectively disposed at the tops of the two tapered waveguides; the coupling waveguide is connected to the two bent waveguides so that the two tapered waveguides are in communication.

[0012] Furthermore, the coupling waveguide is in a cuboid shape or a cylindrical shape, and the thickness or diameter of the coupling waveguide is smaller than the diameter of the bent waveguide so that the connection between the bent waveguide and the coupling waveguide is in a tapered shape.

[0013] Furthermore, the thickness or diameter of the coupling waveguide gradually decreases from both ends to the center.

[0014] Furthermore, the coupling waveguide is spaced 200 nm from the microdisk.

[0015] Furthermore, the optical propagation waveguide, the coupling waveguide, the support assembly, and the microdisk are all made of a photosensitive material with a refractive index of 1.54.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: In the present invention, two optical propagation waveguides are provided on the end face of a seven-core optical fiber. The two optical propagation waveguides are respectively connected to the first core and the second core of the seven-core optical fiber. A coupling waveguide is provided between the two optical propagation waveguides. A support assembly is provided on the end face of the seven-core optical fiber. A microdisk is provided on the top of the support assembly. The microdisk cooperates with the coupling waveguide. The first core and the second core are respectively connected to an external optical transmitter and a photodetector. The laser wavelength output by the optical transmitter is locked at the linear slope of the resonance peak of the microdisk. By the action of ultrasonic waves on the microdisk, the vibration changes its radius and effective refractive index, resulting in the drift of the resonance peak and the change of the output laser intensity, and then the ultrasonic waves are detected. Compared with the prior art, in this application, the ultrasonic waves are detected through the action of the microdisk resonance and the coupling waveguide. By using the optical principle, the problem of electromagnetic interference can be effectively avoided. At the same time, the integrated design is adopted to reduce the volume, and it has the advantages of strong anti-electromagnetic interference ability, compact structure and easy integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 It is a schematic diagram of the optical propagation waveguide structure of the present invention.

[0019] Figure 3 It is a schematic top view structure diagram of the acoustic wave sensor of the present invention.

[0020] Figure 4 It is a sine response test diagram of the acoustic wave sensor of the present invention.

[0021] Figure 5 It is a pulse time-domain signal diagram of the acoustic wave sensor of the present invention.

[0022] Figure 6 It is a frequency-domain signal diagram of the acoustic wave sensor of the present invention.

[0023] The numbers in the figure are marked as: 1, seven-core optical fiber; 2, optical propagation waveguide; 21, tapered waveguide; 22, bent waveguide; 3, coupling waveguide; 4, support assembly; 5, microdisk; 51, micro-ring; 6, fixed platform. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the following further elaborates the present invention with reference to the accompanying drawings and by way of examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0026] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "mounted", "connected" and "coupled" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In view of the deficiencies of the prior art, the present embodiment provides an optical fiber end-face integrated microcavity acoustic wave sensor, which is specifically as follows: As shown in the attached Figure 1 and the attached Figure 3 As shown, an optical fiber end-face integrated microcavity acoustic wave sensor includes a seven-core optical fiber 1, two optical propagation waveguides 2, a coupling waveguide 3, a support assembly 4, a microdisk 5, an optical transmitter and a photodetector; two optical propagation waveguides 2 are arranged on the end face of the seven-core optical fiber 1, and the two optical propagation waveguides 2 are respectively connected to the first core and the second core of the seven-core optical fiber 1. A coupling waveguide 3 is arranged between the two optical propagation waveguides 2, and the coupling waveguide 3 is used to connect the two optical propagation waveguides 2 to realize the transmission of light; a support assembly 4 is arranged on the end face of the seven-core optical fiber 1, and a microdisk 5 is arranged on the top of the support assembly 4. The microdisk 5 is arranged at an interval and cooperates with the coupling waveguide 3 to form a resonant micro-ring. The output laser wavelength of the optical transmitter is locked at the linear slope of the resonant peak of the microdisk 5. By applying ultrasonic waves to the microdisk 5, the vibration changes its radius and effective refractive index, resulting in the drift of the resonant peak and the change of the output laser intensity, and then the ultrasonic waves are detected. The first core and the second core are respectively connected to an external optical transmitter and a photodetector; by the action of ultrasonic waves on the microdisk 5, the light intensity output by the coupling waveguide 3 can be changed, and then the ultrasonic waves can be detected; compared with the prior art, in this application, the ultrasonic waves are detected through the resonance effect of the microdisk 5. By using the optical principle, the problem of electromagnetic interference can be effectively avoided. At the same time, the integrated design is adopted to reduce the volume, and it has the advantages of strong anti-electromagnetic interference ability, compact structure and easy integration.

[0028] Among them, the seven-core optical fiber 1 refers to a composite optical fiber structure with seven independent cores, which can be specifically drawn from glass materials to achieve multi-channel optical signal transmission; the core diameter is 9 μm, the core pitch is 42 μm, and the cladding diameter is 150 μm. One of the cores is in the center of the optical fiber, and the other six cores are evenly distributed around it at an angle of 60°. The optical propagation waveguide 2 refers to a light guiding structure arranged on the end face of the optical fiber, which can be specifically made of a photosensitive material formed by 3D printing to ensure that the optical signal is transmitted along a predetermined path. The coupling waveguide 3 refers to a light guiding component connecting two optical propagation waveguides 2, which can be specifically a rectangular or cylindrical waveguide structure to achieve optical path closure and energy coupling. The support assembly 4 refers to a bearing structure for fixing the microdisk 5, which can be specifically a combination of a conical platform and a cylindrical platform to maintain the spatial position stability of the microdisk 5. The microdisk 5 refers to an optical microcavity with acoustic wave sensitivity characteristics, which can be specifically processed from a high refractive index material. The drift of the resonance peak of the microdisk 5 caused by ultrasonic waves changes the intensity of the laser output. The optical transmitter refers to a laser signal generating device, which can be specifically a tunable laser, and the detection light is input through the first core. The photodetector refers to a light signal receiving device, which can be specifically an avalanche photodiode, and the modulated output light is received through the second core.

[0029] Specifically, the laser emitted by the optical transmitter is transmitted to the optical propagation waveguide 2 through the first core. The working wavelength of the laser is locked at the linear slope of the resonance peak of the microdisk 5, and the laser enters the microdisk 5 through the coupling waveguide 3. When the acoustic wave acts on the microdisk 5, its vibration changes the radius and effective refractive index of the microdisk 5. The combined action of various factors causes the resonance condition to change, and the output light intensity changes. The light that satisfies the resonance condition forms a standing wave in the microdisk 5, and the remaining optical signals return to the second optical propagation waveguide 2 through the coupling waveguide 3. The photodetector receives the light intensity change signal through the second core, and this change corresponds to the acoustic wave vibration parameters. The support assembly 4 ensures that the distance between the microdisk 5 and the coupling waveguide 3 is constant, avoiding over-coupling and under-coupling.

[0030] Compared with the prior art, the traditional piezoelectric sensor converts acoustic waves into electrical signals through piezoelectric materials, while this solution uses the optical microcavity resonance effect to achieve acousto-optic conversion. Piezoelectric sensors are prone to generate electrical noise in an electromagnetic interference environment, and the all-optical path structure of this solution eliminates electromagnetic sensitivity. Traditional sensors require conductive lines to transmit signals, and this solution realizes lossless signal transmission through optical fibers.

[0031] Through the above technical solution, the present application realizes the all-optical detection of acoustic signals, eliminates the influence of electromagnetic interference on signal quality. The physical isolation design of the optical propagation channel reduces signal crosstalk and improves detection accuracy. The evanescent wave coupling mechanism between the microdisk 5 and the waveguide enhances the acoustic wave sensitivity and improves the weak signal detection ability. The non-contact structure avoids mechanical wear and extends the service life of the sensor. The independent optical emission and reception components ensure the stability of the signal modulation process and improve the reliability of the measurement results.

[0032] In one embodiment of the present application, as shown in the appendix Figure 1 The fiber end-face integrated microcavity acoustic wave sensor further includes a fixing platform 6, and the fixing platform 6 is arranged on the end face of the seven-core optical fiber 1; the fixing platform 6 is located on the side of the coupling waveguide 3 away from the microdisk 5, and the fixing platform 6 is connected to the coupling waveguide 3 for supporting the coupling waveguide 3.

[0033] Among them, the fixing platform 6 is also a support structure constructed of photosensitive material. Specifically, it can be prepared by 3D printing process using a photosensitive resin material with the same refractive index as the coupling waveguide 3. Its function is to provide an anchor point for the coupling waveguide 3 in the area away from the microdisk 5, and form a multi-point support system through physical connection to enhance mechanical stability. Among them, the side of the coupling waveguide 3 away from the microdisk 5 refers to the non-functional area where the coupling waveguide 3 has no sensing relationship with the microdisk 5. This position selection can avoid the interference of the fixing platform 6 on the acoustic wave vibration transmission path of the microdisk 5, and at the same time offset the waveguide deformation caused by the vibration of the microdisk 5 through mechanical balance.

[0034] Specifically, when an external vibration or the microdisk 5 is displaced under the action of an acoustic wave, the fixing platform 6 absorbs the vibration energy through the rigid connection with the end face of the seven-core optical fiber 1, and suppresses the displacement of the coupling waveguide 3 in the direction perpendicular to the optical fiber axis. Since the fixing platform 6 only acts on the non-working end of the waveguide, the transmission path of the optical signal at the gap between the coupling waveguide 3 and the microdisk 5 will not generate additional loss due to the intervention of the support structure, and the spacing distance between the coupling waveguide 3 and the microdisk 5 can be kept constant. Thus, the coupling efficiency of the optical signal between the coupling waveguide 3 and the microdisk 5 remains stable, avoiding the problems of optical phase mutation or power attenuation caused by waveguide position offset.

[0035] Through the above technical solution, the present application can effectively suppress the optical path difference fluctuation caused by the mechanical deformation of the coupling waveguide 3, ensure that the coupling strength of the optical signal between the coupling waveguide 3 and the microdisk 5 remains stable, reduce the signal modulation error caused by structural instability, and improve the signal-to-noise ratio and phase consistency of the acoustic wave detection signal.

[0036] In one embodiment of the present application, as shown in the appendix Figure 1 The support assembly 4 includes a tapered platform, the tapered platform is arranged on the end face of the seven-core optical fiber 1, and the microdisk 5 is arranged on the top of the tapered platform.

[0037] The conical platform refers to a three-dimensional structure whose top cross-sectional dimension is smaller than that of the bottom cross-sectional dimension. Specifically, a photosensitive material can be used to form a geometric shape with controllable taper through 3D printing technology. The bottom is connected to the end face of the seven-core optical fiber 1, and the external stress is dispersed by expanding the contact area to enhance the bonding strength between the support component 4 and the end face of the optical fiber. The microdisk 5 is arranged on the conical platform, which means that the disk-shaped optical microcavity with acoustic wave sensitivity is fixed to the top plane of the conical platform. The microdisk 5 and the conical platform are integrated components and can be produced by 3D printing. The axially symmetrical gradient cross-sectional shape of the conical platform is used to provide a uniform support force for the microdisk 5, thereby suppressing the position displacement of the microdisk 5 caused by temperature changes or mechanical vibrations.

[0038] Specifically, the geometric structure of the conical stage adapts to the spatial distribution of the end face of the seven-core optical fiber 1 through a shape that is wide at the bottom and narrow at the top, achieving maximum contact between the support component 4 and the end face of the optical fiber in a limited area, reducing the risk of deformation of the support structure caused by high-frequency vibration during the acoustic wave sensing process. The tapered cross-section design of the conical stage can optimize the internal stress distribution of the support component 4, disperse the stress concentration area through changes in cross-sectional dimensions when subjected to external loads, and avoid local fracture or deformation. The microdisk 5 is positioned by the top plane of the conical stage, and the central axis of the conical stage coincides with the center of the microdisk 5, ensuring that the spacing between the microdisk 5 and the coupling waveguide 3 remains uniformly changed under the action of acoustic waves, avoiding fluctuations in the light field coupling efficiency due to tilt or offset of the support structure.

[0039] Through the above technical solution, the present application can significantly reduce the deformation risk of the support component 4 due to external interference, suppress the influence of the position offset of the micro-disk 5 on the light field coupling efficiency, and thus improve the stability of the light signal modulation during the acoustic wave sensing process. The conical platform structure enhances the anti-vibration ability of the support component 4 by optimizing the mechanical distribution characteristics, and can still maintain the precise spacing between the micro-disk 5 and the coupling waveguide 3 under strong electromagnetic interference or temperature fluctuation environments, ensuring that the acoustic wave signal is accurately converted into a light intensity signal through the light field coupling change, thereby improving the reliability of the sensor detection results.

[0040] In this embodiment, a cylindrical stage is disposed on the top of the conical stage, the microdisk 5 is located on the top of the cylindrical stage, and the diameter of the microdisk 5 is greater than the diameter of the cylindrical stage.

[0041] The cylindrical platform refers to a columnar structure extending from the top, and its diameter can be set to micrometer level to adapt to the size of the microdisk 5, and a secondary support structure is formed by combining with the conical platform. The diameter of the microdisk 5 is larger than the diameter of the cylindrical platform, which means that the edge of the microdisk 5 exceeds the outer edge of the cylindrical platform to form a suspended area, which can be achieved through a 3D printing process, so that the contact area between the bottom surface of the microdisk 5 and the cylindrical platform is concentrated in the center.

[0042] Specifically, the frustum provides the basic support stiffness as the main carrier, and the top cylindrical platform forms a secondary support interface. When the microdisk 5 deforms under the action of sound waves, the stepped support structure disperses the longitudinal stress through the bottom surface of the frustum, and the cylindrical platform contacts the central area of the microdisk 5 to form a point support. The difference in diameter between the suspended part at the edge of the microdisk 5 and the cylindrical platform forms a buffer area, which can absorb the transverse displacement energy during the sound wave vibration process and avoid stress concentration at the edge of the support interface. This structural design enables the microdisk 5 to maintain stable contact and vibrate freely during the sound wave detection process, thus ensuring the detection accuracy of the resonant wavelength change during the optical signal modulation process.

[0043] In one embodiment of the present application, as shown in the attached Figure 1 figure, a micro-ring 51 is provided on the surface of the microdisk 5, and the bottom of the microdisk 5 is arranged in an inverted cone shape.

[0044] Specifically, through the Comsol simulation software, the size of the micro-ring 51 is determined to have a high quality factor and improve the sensitivity.

[0045] In one embodiment of the present application, as shown in the attached Figure 1 and the attached Figure 2 figure, the optical propagation waveguide 2 includes two tapered waveguides 21 and two bent waveguides 22. The tapered waveguides 21 are arranged on the end face of the seven-core optical fiber 1, and the two bent waveguides 22 are respectively arranged on the tops of the two tapered waveguides 21, and the coupling waveguide 3 is connected to the two bent waveguides 22 so that the two tapered waveguides 21 are connected.

[0046] Among them, the tapered waveguide 21 refers to a waveguide structure with a gradually changing cross-sectional size. Specifically, a photosensitive material can be used to process a tapered optical waveguide channel with a gradually changing taper through a 3D printing process, which is used for spatially constraining and energy converging of optical signals. The bent waveguide 22 refers to an optical transmission channel with an arc-shaped geometric shape. Specifically, a 3D printing technology can be used to form an arc-shaped waveguide structure with a preset curvature radius in the photosensitive material, which is used for directionally guiding the optical wave propagation path. The coupling waveguide 3 refers to an optical interface for connecting different waveguides. Specifically, a continuous transition connection structure can be made of a photosensitive material of the same material as the bent waveguide 22, which is used to establish a closed optical path and form an optical field interference condition.

[0047] The bottom diameter of the tapered waveguide 21 is 14 μm, the top diameter is 4 μm, and the height is 85 μm. The bending radius of the bent waveguide 22 is 30 μm, and the cross-sectional diameter is 4 μm. The coupling waveguide 3 is 24 μm long, and the width gradually narrows from both sides, and the narrowest part is 1 μm wide. The distance between the coupling waveguide 3 and the fixed platform 6 is 0 μm, and the distance from the microdisk 5 is 200 nm. The outer diameter of the microdisk 5 is 40 μm, the inner diameter is 36 μm, and the height is 5 μm.

[0048] Specifically, the tapered waveguide 21 disposed at the end face of the seven-core optical fiber 1 utilizes its geometric gradient characteristics to confine the divergent optical field within the core diameter range, reducing the energy loss of the optical signal during free-space transmission. The curved waveguide 22 controls the optical waveguide path through a precisely designed radius of curvature, causing the optical signal to turn in a predetermined direction and form a closed loop. The coupled waveguide 3 integrates two curved waveguides 22 into a continuous optical path through a low-loss connection method, establishing the phase matching condition required for optical field interference between the tapered waveguides 21. This combined waveguide structure constructs an electromagnetic interference-resistant optical sensing path through the triple effects of spatial confinement, path control, and optical path closure, replacing the easily interfered circuit system in traditional piezoelectric sensors.

[0049] Compared with the prior art, traditional piezoelectric sensors rely on electrical signals to transmit ultrasonic information. In this solution, through the synergistic effect of the tapered waveguide 21 and the curved waveguide 22, the vibration of the microdisk 5 caused by ultrasonic waves is converted into the phase modulation amount of the optical signal, and the acoustic wave information is demodulated using the principle of optical interference. In the prior art, the transmission of electrical signals is vulnerable to the electromagnetic environment. This solution adopts a full-optical path transmission method, eliminating the coupling path of electromagnetic interference to the sensing signal from the physical mechanism.

[0050] Through the above technical solution, this application effectively solves the problems of signal noise and distortion in traditional piezoelectric ultrasonic sensors caused by the vulnerability of the electrical signal conduction path to electromagnetic interference, realizes the stable transmission of ultrasonic information using the physical characteristics of optical waveguides, and can still maintain the integrity of the sensing signal in a strong electromagnetic interference environment. The closed design of the optical propagation path enhances the stability of optical field interference and improves the corresponding accuracy between acoustic wave vibration information and optical phase modulation, providing a reliable solution for ultrasonic detection in complex electromagnetic environments.

[0051] In this embodiment, the coupled waveguide 3 is in the shape of a cuboid or a cylinder. The thickness and width of the coupled waveguide 3 are smaller than the diameter of the curved waveguide 22, so that the connection between the curved waveguide 22 and the coupled waveguide 3 is in a tapered shape.

[0052] Among them, the cuboid or cylinder shape means that the cross-sectional shape of the coupled waveguide 3 is a regular geometric form, and it can be specifically realized by 3D printing technology.

[0053] Specifically, when the optical signal is transmitted from the curved waveguide 22 to the coupled waveguide 3, due to the tapered change in the cross-sectional size at the connection, the optical field is gradually confined to a smaller transmission channel. During this process, the optical wave mode realizes the readjustment of energy distribution through the smooth transition of the waveguide structure, avoiding the mode mismatch caused by traditional right-angle connections or sudden size changes. The continuous gradient of the optical field in the tapered region enables most of the energy to be effectively transferred to the coupled waveguide 3, thereby reducing the energy loss caused by reflection or scattering and improving the coupling efficiency of the acoustic wave signal to the optical signal conversion.

[0054] Through the above technical solution, the present application solves the problems of optical signal transmission loss and insufficient coupling efficiency at the connection between the bent waveguide 22 and the coupling waveguide 3, realizes the efficient conversion of optical wave modes and low-loss transmission, thereby improving the sensitivity of the acoustic wave sensor for detecting weak signals.

[0055] In this embodiment, the thickness of the coupling waveguide 3 gradually decreases from both ends to the center.

[0056] This design forms a transition with the adjacent waveguide through the thicker regions at both ends, reducing the optical reflection at the connection. At the same time, in the central region, the confinement ability of the waveguide to the optical field is enhanced through the thickness reduction.

[0057] Specifically, when the optical signal enters the coupling waveguide 3 from the bent waveguide 22, due to the larger cross-sectional area at both ends, the optical field distribution matches the mode field of the bent waveguide 22, effectively suppressing the reflection loss. As the optical field propagates towards the center, the cross-sectional area of the coupling waveguide 3 gradually decreases, and the optical field energy is confined to the surface region of the coupling waveguide 3, enhancing its interaction with the microdisk 5. When the acoustic wave causes the deformation of the microdisk 5, the change in the distance between the coupling waveguide 3 and the microdisk 5 leads to a change in the resonance condition, and the optical field energy distribution is adjusted accordingly. This structure improves the modulation depth and sensitivity of the optical signal, avoiding the problem that the electrical signal in the traditional piezoelectric sensor is vulnerable to electromagnetic interference.

[0058] Through the above technical solution, the present application realizes the efficient coupling and stable transmission of optical signals, reduces the reflection loss and noise interference, enables the acoustic wave detection process to be unaffected by the electromagnetic environment, and is applicable to high-precision acoustic wave sensing in industrial strong electromagnetic interference scenarios.

[0059] In an embodiment of the present application, as shown in the appendix Figure 3 The coupling waveguide 3 is spaced 200 nm from the microdisk 5.

[0060] Specifically, the optical field in the coupling waveguide 3 forms an evanescent wave during transmission and extends to the surface region of the microdisk 5 through the precisely controlled spacing distance. When an external acoustic wave acts on the microdisk 5, the nanoscale mechanical vibration generated on its surface will periodically change the distribution state of the evanescent field, thereby modulating the phase or intensity of the optical signal. The fixed spacing distance avoids the vibration damping effect caused by mechanical contact, enabling the microdisk 5 to freely respond to the acoustic wave frequency. At the same time, this distance is controlled within the effective action range of the optical field, ensuring both sufficient interaction intensity and preventing interference to signal modulation caused by random gap changes due to environmental vibration.

[0061] Through the above technical solution, the present application realizes the efficient and stable coupling of optical signals and acoustic wave signals, enhances the modulation depth of the optical field on the premise of ensuring the free vibration of the microdisk 5, and effectively improves the detection sensitivity of the sensor to external acoustic waves and the anti-environmental interference ability.

[0062] In this embodiment, the optical propagation waveguide 2, the coupling waveguide 3, the support component 4, and the microdisk 5 are all made of a photosensitive material with a refractive index of 1.54.

[0063] Specifically, the optical propagation waveguide 2 and the fiber core can use photosensitive materials with different refractive indices, which can avoid reflection losses caused by sudden changes in the refractive index at the interface during the input and output of optical signals, thereby improving the coupling efficiency. The tapered design of the coupling waveguide 3 combined with the refractive index matching of the material can ensure the stable phase characteristics of the optical signal during transmission and avoid modal distortion caused by refractive index differences. The support component 4 and the microdisk 5 use the same material, which can avoid introducing additional optical path difference noise due to material refractive index differences when the microdisk 5 generates mechanical vibrations under acoustic wave excitation, thereby improving the stability of signal detection.

[0064] Compared with the prior art, traditional piezoelectric ultrasonic sensors rely on electrical signal conversion, and their piezoelectric materials are vulnerable to electromagnetic interference. In this solution, a fully photosensitive material system is adopted to completely avoid the influence of the electromagnetic environment through optical signal transmission. In addition, in the prior art, different components often use heterogeneous material splicing, resulting in scattering or reflection losses of optical signals due to refractive index mismatch at the interface. In this solution, the optical parameters between components are continuously matched through material unity, reducing optical losses at the source.

[0065] Through the above technical solutions, this application can effectively eliminate the optical signal loss caused by material heterogeneity and improve the overall transmission efficiency of the optical waveguide system. At the same time, the all-optical signal transmission mechanism avoids the defect that traditional electrical signals are vulnerable to electromagnetic interference and can still maintain stable acoustic wave detection accuracy in a strong electromagnetic environment.

[0066] The working principle of the fiber optic ultrasonic sensor of this application is based on the micro-ring resonance principle, where the coupling waveguide 3 and the microdisk 5 form a resonant micro-ring. The light emitted from the first fiber core of the seven-core fiber 1 enters the optical propagation waveguide 2, and the light travels along the optical propagation waveguide 2. When the light transmitted from the coupling waveguide 3 is coupled into the microdisk 5 and satisfies the resonance condition, resonance occurs, and the light that does not satisfy the resonance condition is output from the corresponding optical propagation waveguide 2. Only the light with an optical path equal to an integer multiple of the wavelength can resonate, and the resonance wavelength satisfies the following expression: mλ=n eff L; where m is a positive integer representing the wave number of the optical whispering gallery mode; λ represents the resonance wavelength of the optical whispering gallery mode with wave number m, and n eff is the effective refractive index of the material; L is the path length of the light propagating in the resonant cavity.

[0067] The free spectral range FSR of the resonance wavelength can be calculated by the following expression: ; where λ represents the resonance wavelength, and neff where \(n_{eff}\) is the effective refractive index of the material and \(R\) is the radius of the microdisk 5.

[0068] The principle of ultrasonic sensing is that when ultrasonic waves propagate to the microdisk 5, the ultrasonic waves will change the effective refractive index and the radius of the microdisk 5, thereby causing changes in the resonant wavelength \(\lambda\) and the free spectral range FSR. By locking the laser wavelength at the point where the slope of the resonant wavelength is the largest, the output intensity modulated by optical resonance is collected by a photodetector, and the ultrasonic signal is converted into a detectable optical intensity signal. By demodulating the corresponding optical intensity, the ultrasonic signal intensity and frequency information can be effectively demodulated.

[0069] The prepared ultrasonic sensor is applied to the experimental device for analyzing the ultrasonic response characteristics of the ultrasonic sensor. Among them, the experimental device mainly consists of two parts: ultrasonic generation and ultrasonic sensing demodulation. The ultrasonic generation part is to drive a piezoelectric transducer to generate ultrasonic waves by a signal generator. The ultrasonic sensing demodulation part consists of an optical fiber ultrasonic sensor, a tunable laser, a photodetector, and an oscilloscope. Since ultrasonic waves are easy to propagate and have low loss in water, the test is carried out in a water-filled water tank.

[0070] As shown in the appendix Figure 4 Using the above experimental device, the sinusoidal response characteristics of the ultrasonic sensor can be tested. The piezoelectric transducer is placed 3 cm in front of the ultrasonic sensor. Turn on the signal generator, set the output frequency to 1 MHz, the drive voltage to 20 Vpp, the waveform to a sine wave, and drive the piezoelectric transducer to emit ultrasonic waves. The ultrasonic waves propagate through the medium water and reach the ultrasonic sensor. The ultrasonic waves change the effective refractive index and radius of the microdisk 5 of the ultrasonic sensor, resulting in a change in the resonant wavelength. The light intensity output by the laser also changes accordingly. The optical signal is detected by the photodetector and converted into an electrical signal, which is received and displayed by the oscilloscope. Figure 4 is a 1 MHz sinusoidal signal received by the sensor and displayed on the oscilloscope. The results show that the fiber optic ultrasonic sensor has the characteristic of accurately detecting a single sinusoidal ultrasonic wave.

[0071] As shown in the appendix Figure 5 and the appendix Figure 6 Using the above experimental device, the pulse response characteristics of the fiber optic ultrasonic sensor can be tested. The piezoelectric transducer is placed 3 cm in front of the ultrasonic sensor. Turn on the signal generator, set the output frequency to 1 MHz, the drive voltage to 20 Vpp, the waveform to a sine wave and excited in the form of a pulse, and emit a pulse signal every 1 ms to drive the piezoelectric transducer to emit ultrasonic waves. The ultrasonic waves propagate through the medium water and reach the ultrasonic sensor. The ultrasonic waves change the effective refractive index and radius of the microdisk 5 of the ultrasonic sensor, resulting in a change in the resonant wavelength. The light intensity output by the laser also changes accordingly. The optical signal is detected by the photodetector and converted into an electrical signal, which is received and displayed by the oscilloscope. Figure 5It is a 1MHz pulse signal received by the sensor and displayed on the oscilloscope. Fourier transform is performed on this signal to convert the time-domain pulse signal into a frequency-domain signal, as shown in the appendix Figure 6 The figure shows that the response is maximum at 1MHz in the frequency-domain result, indicating that the fiber optic ultrasonic sensor has the performance of accurately detecting a single pulse ultrasonic wave.

[0072] After considering the specification and practicing the disclosed solutions herein, those skilled in the art will readily conceive of other embodiments of the present invention. The present invention is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include well-known common general knowledge or conventional technical means in the technical field not disclosed in this solution. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the claims.

Claims

1. An optical fiber end-face integrated microcavity acoustic wave sensor, characterized in that, Comprising: Seven-core optical fiber; Two optical propagation waveguides, disposed on the end face of the seven-core optical fiber; the two optical propagation waveguides are respectively connected to the first core and the second core of the seven-core optical fiber; Coupling waveguide, disposed between the two optical propagation waveguides for connecting the two optical propagation waveguides; Support assembly, disposed on the end face of the seven-core optical fiber; Microdisk, disposed on the support assembly such that the microdisk is located on one side of the coupling waveguide; the microdisk and the coupling waveguide are arranged at intervals to form a resonant micro-ring; when ultrasonic waves act on the microdisk, resulting in a change in the resonance condition, the output laser intensity can be changed; Optical transmitter, disposed at one end of the seven-core optical fiber away from the optical propagation waveguide; the optical transmitter is connected to the first core; Optoelectronic detector, disposed at one end of the seven-core optical fiber away from the optical propagation waveguide; the optoelectronic detector is connected to the second core.

2. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 1, wherein It further comprises: Fixed stage, disposed on the end face of the seven-core optical fiber; the fixed stage is located on one side of the coupling waveguide away from the microdisk, and the fixed stage is connected to the coupling waveguide for supporting the coupling waveguide.

3. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 1, wherein The support assembly includes: Conical stage, disposed on the end face of the seven-core optical fiber; the microdisk is disposed on the conical stage.

4. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 3, characterized in that, A cylindrical stage is provided at the top of the conical stage, the microdisk is located on the cylindrical stage, and the diameter of the microdisk is larger than the diameter of the cylindrical stage.

5. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 1, characterized in that, A micro-ring is provided on the surface of the microdisk, and the bottom of the microdisk is in an inverted conical shape.

6. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 1, characterized in that, The optical propagation waveguide includes: Two tapered waveguides, disposed on the end face of the seven-core optical fiber; Two bent waveguides, respectively disposed on the tops of the two tapered waveguides; the coupling waveguide is connected to the two bent waveguides so that the two tapered waveguides are in communication.

7. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 6, wherein The coupling waveguide is in a cuboid shape or a cylindrical shape, and the thickness and width of the coupling waveguide are both smaller than the diameter of the bent waveguide, so that the connection between the bent waveguide and the coupling waveguide is in a tapered shape.

8. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 7, characterized in that, The thickness of the coupling waveguide gradually decreases from both ends to the center.

9. The fiber end face integrated microcavity acoustic wave sensor according to claim 1, wherein The coupling waveguide is spaced 200 nm from the microdisk.

10. The integrated microcavity acoustic wave sensor for optical fiber end face according to claim 1, wherein The optical propagation waveguide, the coupling waveguide, the support assembly, and the microdisk are all made of a photosensitive material with a refractive index of 1.54.

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