Optical fiber end face integrated microcavity acoustic wave sensor

Abstract

The application relates to the technical field of ultrasonic sensors and discloses a kind of optical fiber end face integrated microcavity acoustic wave sensors, including seven-core optical fiber, two light propagation waveguides, coupling waveguide, support assembly, microdisk, light emitter and photodetector, the end face of seven-core optical fiber is provided with two light propagation waveguides, coupling waveguide is arranged between two light propagation waveguides, the end face of seven-core optical fiber is provided with support assembly, the top of support assembly is provided with microdisk, first fiber core and second fiber core are connected with external light emitter and photodetector respectively;Light emitter outputs laser wavelength lock at the linear slope of microdisk resonance peak, through ultrasonic wave acting on microdisk, vibration changes its radius and effective refractive index, causes resonance peak drift and output laser intensity change, and then detects ultrasonic wave;Compared with the prior art, the application detects ultrasonic wave by the method of microdisk resonance and laser lock sideband, and can effectively avoid the problem of electromagnetic interference by using optical principle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic sensors, in particular to a fiber end face integrated microcavity acoustic wave sensor. BACKGROUND

[0002] With the continuous development of science and technology, ultrasonic sensors are increasingly applied to non-destructive testing, medical diagnosis, underwater detection and meteorological detection fields. With the penetration characteristics of ultrasonic waves, relevant information can be obtained through ultrasonic wave reflection without direct contact with the measured object, realizing non-contact detection and having a wide range of applications, and being not affected by the material, color and transparency of the measured object. 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 manufacturing cost, is easy to install and maintain, and has high safety, and is basically harmless to the human body in medical diagnosis and other application scenarios.

[0003] The existing sensor is mainly a traditional piezoelectric ultrasonic sensor, which realizes the sensing function through the piezoelectric effect of piezoelectric material. When the piezoelectric material is subjected to ultrasonic pressure, an electric signal is generated, and the position, image and other information can be restored by demodulating the electric signal to realize the detection effect. However, the electric signal generated by the existing piezoelectric ultrasonic sensor during operation is relatively weak, and is easily disturbed by the external electromagnetic environment, resulting in noise, distortion and other problems of the detected signal, which is not conducive to accurate analysis and subsequent processing of the ultrasonic signal. In some complex industrial environments with strong electromagnetic interference, electrical equipment intensive places and the like, the accuracy thereof will be reduced.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the above problems in the prior art, the present application aims to provide a fiber end face integrated microcavity acoustic wave sensor, which aims to solve the problem that the piezoelectric ultrasonic sensor in the prior art is easily disturbed by the external electromagnetic environment, resulting in poor detection accuracy.

[0006] The technical scheme adopted by the present application to solve the technical problems is as follows:

[0007] A fiber end face integrated microcavity acoustic wave sensor comprises:

[0008] a seven-core optical fiber;

[0009] two optical propagation waveguides arranged on the end face of the seven-core optical fiber, and the two optical propagation waveguides are connected with the first fiber core and the second fiber core of the seven-core optical fiber, respectively;

[0010] a coupling waveguide arranged between the two optical propagation waveguides and used for connecting the two optical propagation waveguides;

[0011] a support assembly arranged on the end surface of the seven-core fiber;

[0012] a microdisk arranged on the support assembly so that the microdisk is located on one side of the coupling waveguide; the microdisk is arranged apart from the coupling waveguide to form a resonant micro-ring; when an ultrasonic wave acts on the microdisk, the resonant condition changes, which can cause the output laser intensity to change;

[0013] a light emitter arranged at one end of the seven-core fiber away from the light propagation waveguide; the light emitter is connected to the first fiber core;

[0014] a photodetector arranged at one end of the seven-core fiber away from the light propagation waveguide; the photodetector is connected to the second fiber core.

[0015] Further, it also includes:

[0016] a fixing table arranged on the end surface of the seven-core fiber; the fixing table is located on the side of the coupling waveguide away from the microdisk, and the fixing table is connected to the coupling waveguide to support the coupling waveguide.

[0017] Further, the support assembly includes:

[0018] a tapered table arranged on the end surface of the seven-core fiber; the microdisk is arranged on the tapered table.

[0019] Further, the top of the tapered table is provided with a cylindrical table, and the microdisk is located on the cylindrical table, and the diameter of the microdisk is greater than the diameter of the cylindrical table.

[0020] Further, the surface of the microdisk is provided with a micro-ring, and the bottom of the microdisk is in the shape of an inverted cone.

[0021] Further, the light propagation waveguide includes:

[0022] two tapered waveguides arranged on the end surface of the seven-core fiber;

[0023] two curved waveguides arranged on the top of the two tapered waveguides respectively; the coupling waveguide is connected to the two curved waveguides to make the two tapered waveguides communicate with each other.

[0024] Further, the coupling waveguide is in the shape of a rectangular prism or a cylinder, and the thickness or diameter of the coupling waveguide is smaller than the diameter of the curved waveguide, so that the connection between the curved waveguide and the coupling waveguide is tapered.

[0025] Further, the thickness or diameter of the coupling waveguide gradually decreases from both ends to the center.

[0026] Further, the coupling waveguide is spaced 200nm from the microdisk.

[0027] Further, the light propagation waveguide, the coupling waveguide, the support assembly and the microdisk are made of photosensitive material with a refractive index of 1.54.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] In the present application, two light propagation waveguides are arranged on the end face of the seven-core optical fiber, the two light propagation waveguides are connected with the first fiber core and the second fiber core of the seven-core optical fiber respectively, a coupling waveguide is arranged between the two light propagation waveguides, a support assembly is arranged on the end face of the seven-core optical fiber, a microdisk is arranged on the top of the support assembly, the microdisk cooperates with the coupling waveguide, the first fiber core and the second fiber core are connected with the external light emitter and the photoelectric detector respectively; the light emitter outputs laser whose wavelength is locked at the linear slope of the microdisk resonance peak, through the effect of ultrasonic wave on the microdisk, the vibration changes the radius and effective refractive index of the microdisk, resulting in resonance peak drift and output laser intensity change, and then the ultrasonic wave is detected; compared with the prior art, the present application detects the ultrasonic wave through the cooperation of the microdisk resonance and the coupling waveguide, uses the optical principle, can effectively avoid the problem of electromagnetic interference, at the same time, uses integrated design to reduce the volume, has the advantages of strong anti-electromagnetic interference ability, compact structure and easy integration. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the present application.

[0031] Figure 2 It is a schematic diagram of the light propagation waveguide structure of the present application.

[0032] Figure 3 It is a schematic diagram of the top view structure of the sound wave sensor of the present application.

[0033] Figure 4 It is a sine response test diagram of the sound wave sensor of the present application.

[0034] Figure 5 It is a pulse time domain signal diagram of the sound wave sensor of the present application.

[0035] Figure 6 It is a frequency domain signal diagram of the sound wave sensor of the present application.

[0036] The number in the figure indicates that: 1, seven-core optical fiber; 2, light propagation waveguide; 21, tapered waveguide; 22, curved waveguide; 3, coupling waveguide; 4, support assembly; 5, microdisk; 51, micro ring; 6, fixed table. DETAILED DESCRIPTION

[0037] For the purposes of the present invention, the technical solutions and effects, the following will be further described in detail with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present invention and not to limit the present invention.

[0038] In the description of the present application, 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" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can be explicitly or implicitly included one or more features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0039] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] In view of the deficiencies of the prior art, the present embodiment provides an optical fiber end face integrated microcavity acoustic wave sensor, which can be specifically referred to as follows:

[0041] As shown in FIG. 1, the optical fiber end face integrated microcavity acoustic wave sensor comprises an optical fiber 1, a microcavity 2 and a sensing layer 3. Figure 1 As shown in FIG. 1, the optical fiber end face integrated microcavity acoustic wave sensor comprises an optical fiber 1, a microcavity 2 and a sensing layer 3. Figure 3As shown, a kind of optical fiber end face integrated microcavity acoustic wave sensor includes seven-core optical fiber 1, two light propagation waveguides 2, coupling waveguide 3, support assembly 4, microdisk 5, light emitter and photodetector;Two light propagation waveguides 2 are provided on the end face of seven-core optical fiber 1, two light propagation waveguides 2 are connected with the first fiber core and the second fiber core of seven-core optical fiber 1 respectively, coupling waveguide 3 is provided between two light propagation waveguides 2, and coupling waveguide 3 is used to connect two light propagation waveguides 2 to realize the transmission of light;Support assembly 4 is provided on the end face of seven-core optical fiber 1, microdisk 5 is provided on the top of support assembly 4, microdisk 5 is arranged with coupling waveguide 3 and cooperates with each other to form resonant microloop, the linear slope of the laser wavelength output by light emitter is locked at the resonant peak of microdisk 5, ultrasonic wave acts on microdisk 5, vibration changes its radius and effective refractive index, leading to resonant peak drift and output laser intensity change, and then detecting ultrasonic wave;

[0042] The first fiber core and the second fiber core are connected with external light emitter and photodetector respectively;Through the action of ultrasonic wave on microdisk 5, the light intensity output by coupling waveguide 3 can be changed, and then ultrasonic wave is detected;Compared with the prior art, the present application detects ultrasonic wave through the resonant action of microdisk 5, uses optical principle, can effectively avoid the problem of electromagnetic interference, at the same time, adopts integrated design to reduce the volume, has the advantages of strong anti-electromagnetic interference ability, compact structure and easy integration.

[0043] Wherein, seven-core optical fiber 1 refers to a composite optical fiber structure with seven independent cores, which can be made of glass material and realize multi-channel optical signal transmission;The core diameter is 9 μm, the core distance 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 at an angle of 60°. Light propagation waveguide 2 refers to a light guide structure provided on the end face of the optical fiber, which can be made of 3D printing light-sensitive material to ensure that the light signal is transmitted along the predetermined path. Coupling waveguide 3 refers to a light guide component connecting two light propagation waveguides 2, which can adopt rectangular or cylindrical waveguide structure to realize light path closure and energy coupling. Support assembly 4 refers to a bearing structure for fixing microdisk 5, which can adopt a combination of conical table and cylindrical table to maintain the spatial position stability of microdisk 5. Microdisk 5 refers to an optical microcavity with acoustic wave sensitive characteristics, which can be processed by high refractive index material. The drift of resonant peak of microdisk 5 caused by ultrasonic wave makes the intensity of laser output change. Light emitter refers to a laser signal generating device, which can be a tunable laser, and the first fiber core is used to input probe light. Photodetector refers to a light signal receiving device, which can be an avalanche photodiode, and the second fiber core is used to receive modulated output light.

[0044] Specifically, the laser emitted by the light emitter is transmitted to the light propagation waveguide 2 through the first core, the laser working wavelength is locked at the linear slope of the resonance peak of the micro disk 5, and the laser enters the micro disk 5 through the coupling waveguide 3. When the acoustic wave acts on the micro disk 5, the vibration changes the radius and effective refractive index of the micro disk 5, and various factors jointly cause the resonance condition to change, and the output light intensity changes. The light satisfying the resonance condition forms a standing wave in the micro disk 5, and the remaining light signals return to the second light propagation waveguide 2 through the coupling waveguide 3. The photodetector receives the light intensity change signal through the second core, and the change corresponds to the acoustic wave vibration parameter. The support assembly 4 ensures that the distance between the micro disk 5 and the coupling waveguide 3 is constant, avoiding over-coupling and under-coupling.

[0045] Compared with the prior art, the traditional piezoelectric sensor converts the acoustic wave into an electric signal through a piezoelectric material, while the present scheme realizes acousto-optic conversion by utilizing the optical microcavity resonance effect. The piezoelectric sensor is prone to produce electrical noise in an electromagnetic interference environment, and the all-optical structure of the present scheme eliminates electromagnetic sensitivity. The traditional sensor needs a conductive circuit to transmit signals, and the present scheme realizes lossless signal transmission through an optical fiber.

[0046] Through the above technical scheme, the present application realizes all-optical detection of the acoustic wave signal, eliminating the influence of electromagnetic interference on the signal quality. The physical isolation design of the light propagation channel reduces signal crosstalk and improves detection accuracy. The evanescent wave coupling mechanism of the micro disk 5 and the waveguide enhances the acoustic wave sensitivity and improves the weak signal detection capability. The non-contact structure avoids mechanical wear and tear, prolonging the service life of the sensor. The independent light emitting and receiving components ensure the stability of the signal modulation process and improve the reliability of the measurement results.

[0047] In an embodiment of the present application, as shown in the accompanying drawings, the optical fiber end face integrated microcavity acoustic wave sensor further comprises a fixing table 6 arranged on the end face of the seven-core optical fiber 1; the fixing table 6 is located on the side of the coupling waveguide 3 away from the micro disk 5, and the fixing table 6 is connected with the coupling waveguide 3 for supporting the coupling waveguide 3. Figure 1 The fixing table 6 is also a support structure made of photosensitive material, which can be made of photosensitive resin material with the same refractive index as the coupling waveguide 3 by 3D printing process. Its function is to provide an anchoring point for the coupling waveguide 3 away from the micro disk 5, and form a multi-point support system through physical connection to enhance mechanical stability. The side of the coupling waveguide 3 away from the micro disk 5 refers to the non-functional area of the coupling waveguide 3 that has no sensing relationship with the micro disk 5. The selection of this position can avoid interference of the fixing table 6 with the acoustic wave vibration transmission path of the micro disk 5, and at the same time offset the waveguide deformation caused by the vibration of the micro disk 5 through mechanical balance.

[0048]

[0049] ​Specifically, when the external vibration or the micro-disk 5 is displaced by the sound wave, the fixed 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 fixed 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 micro-disk 5 will not cause additional loss due to the intervention of the support structure, and the spacing distance between the coupling waveguide 3 and the micro-disk 5 can be kept constant. Therefore, the coupling efficiency between the coupling waveguide 3 and the micro-disk 5 is stable, and the problems of light phase mutation or power attenuation caused by waveguide position deviation are avoided.

[0050] Through the above technical solution, the present application can effectively suppress the optical path difference fluctuation of the coupling waveguide 3 caused by mechanical deformation, ensure the coupling strength between the coupling waveguide 3 and the micro-disk 5 to be stable, reduce the signal modulation error caused by structural instability, and improve the signal-to-noise ratio and phase consistency of the sound wave detection signal.

[0051] In an embodiment of the present application, as shown in the accompanying drawings, Figure 1 The support assembly 4 includes a conical platform, which is arranged on the end face of the seven-core optical fiber 1, and the micro-disk 5 is arranged on the top of the conical platform.

[0052] The conical platform refers to a three-dimensional structure with a top cross-sectional size smaller than a bottom cross-sectional size, which can be formed by 3D printing technology using photosensitive materials to process a geometric shape with controllable taper, and the bottom is connected with the end face of the seven-core optical fiber 1 to disperse external stress by expanding the contact area and enhance the bonding strength between the support assembly 4 and the end face of the optical fiber. The micro-disk 5 arranged on the conical platform means that the disc-shaped optical microcavity with sound wave sensitive characteristics is fixed on the top plane of the conical platform, and the micro-disk 5 and the conical platform are integrated components, which can be made by 3D printing. By utilizing the axially symmetrical tapered cross-sectional shape of the conical platform, uniform support force is provided for the micro-disk 5 to suppress the position deviation of the micro-disk 5 caused by temperature change or mechanical vibration.

[0053] Specifically, the geometric structure of the conical platform is adapted to the spatial distribution of the end face of the seven-core optical fiber 1 through the form of the bottom wide and the top narrow, which realizes the maximum contact between the support assembly 4 and the end face of the optical fiber in a limited area, and reduces the risk of deformation caused by high-frequency vibration of the support structure during the sound wave sensing process. The tapered cross-sectional design of the conical platform can optimize the internal stress distribution of the support assembly 4, disperse the stress concentration area by changing the cross-sectional size when bearing external load, and avoid local fracture or deformation. The micro-disk 5 is positioned through the top plane of the conical platform, the central axis of the conical platform coincides with the center of the micro-disk 5, which ensures that the spacing distance between the micro-disk 5 and the coupling waveguide 3 remains uniform under the action of the sound wave, and avoids the fluctuation of the light field coupling efficiency caused by the tilt or deviation of the support structure.

[0054] By the technical solution, the deformation risk of the support assembly 4 caused by external interference can be significantly reduced, the influence of the position deviation of the micro disk 5 on the light field coupling efficiency is inhibited, and the stability of the light signal modulation in the acoustic wave sensing process is improved. The tapered table structure enhances the anti-vibration capability of the support assembly 4 by optimizing the mechanical distribution characteristics, and the micro disk 5 and the coupling waveguide 3 can still maintain the accurate spacing in a strong electromagnetic interference or temperature fluctuation environment, so that the acoustic wave signal is accurately converted into the light intensity signal through the light field coupling change, and the reliability of the sensor detection result is improved.

[0055] In the embodiment, the top of the tapered table is provided with a cylindrical table, the micro disk 5 is located at the top of the cylindrical table, and the diameter of the micro disk 5 is greater than the diameter of the cylindrical table.

[0056] The cylindrical table refers to a columnar structure extending at the top, and the diameter thereof can be set to microns to adapt to the size of the micro disk 5, and a two-stage support structure is formed by being combined with the tapered table. The micro disk 5 diameter greater than the cylindrical table diameter means that the edge of the micro disk 5 is suspended outside the cylindrical table, and the 3D printing process can be used to make the contact area between the bottom surface of the micro disk 5 and the cylindrical table concentrated at the center.

[0057] Specifically, the tapered table serves as a main bearing to provide basic support stiffness, and the top cylindrical table forms a secondary support interface. When the micro disk 5 is deformed due to the action of the acoustic wave, the stepped support structure disperses the longitudinal stress through the bottom surface of the tapered table, and the cylindrical table contacts the center area of the micro disk 5 to form a point support. The suspended part of the edge of the micro disk 5 and the diameter difference of the cylindrical table form a buffer area, which can absorb the transverse displacement energy in the acoustic wave vibration process, so as to avoid stress concentration at the edge of the support interface. This structure design makes the micro disk 5 maintain stable contact and be able to vibrate freely during the acoustic wave detection process, thereby ensuring the detection accuracy of the resonant wavelength change in the light signal modulation process.

[0058] In an embodiment of the present application, as shown in FIG. 1, the surface of the micro disk 5 is provided with a micro ring 51, and the bottom of the micro disk 5 is arranged in an inverted tapered shape. Figure 1

[0059] Specifically, the size of the micro ring 51 is determined by using the comsol simulation software, so that the micro ring 51 has a high quality factor and improves the sensitivity.

[0060] In an embodiment of the present application, as shown in FIG. 1, the surface of the micro disk 5 is provided with a micro ring 51, and the bottom of the micro disk 5 is arranged in an inverted tapered shape. Figure 1 Figure 2 As shown in FIG. 1 and FIG. 2, the light propagation waveguide 2 includes two tapered waveguides 21 and two curved waveguides 22, the tapered waveguides 21 are arranged on the end face of the seven-core optical fiber 1, the two curved waveguides 22 are arranged at the top of the two tapered waveguides 21 respectively, and the coupling waveguide 3 is connected with the two curved waveguides 22, so that the two tapered waveguides 21 are connected in communication.

[0061] ​​The taper waveguide 21 refers to a waveguide structure with gradually changing cross-sectional dimensions, which can be formed by 3D printing technology using photosensitive materials to process the taper gradually changing optical waveguide channel for spatial constraint and energy convergence of optical signals. The curved waveguide 22 refers to an optical transmission channel with an arc-shaped geometry, which can be formed by 3D printing technology to form an arc-shaped waveguide structure with a preset curvature radius in photosensitive materials for directional guidance of the light wave propagation path. The coupling waveguide 3 refers to an optical interface for connecting different waveguides, which can be made of the same material as the curved waveguide 22 to form a continuous transition connection structure for establishing a closed optical path and forming an optical field interference condition.

[0062] The taper waveguide 21 has a bottom diameter of 14 μm, a top diameter of 4 μm, and a height of 85 μm. The curved waveguide 22 has a bending radius of 30 μm and a cross-sectional diameter of 4 μm. The coupling waveguide 3 has a length of 24 μm and a width that gradually narrows from both sides to a width of 1 μm at the narrowest point. The coupling waveguide 3 is 0 μm away from the fixed table 6 and 200 nm away from the microdisk 5. The microdisk 5 has an outer diameter of 40 μm, an inner diameter of 36 μm, and a height of 5 μm.

[0063] Specifically, the taper waveguide 21 set at the end face of the seven-core optical fiber 1 uses its geometrically varying characteristics to constrain the divergent light field within the core diameter range, reducing the energy loss of the optical signal during free-space transmission. The curved waveguide 22 controls the light waveguide path by precisely designing the curvature radius, causing the optical signal to turn in a predetermined direction and form a closed loop. The coupling waveguide 3 integrates the 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 taper waveguides 21. This combined waveguide structure achieves an anti-electromagnetic interference optical sensing path through spatial constraint, path control, and optical path closure, replacing the easily disturbed circuit system in traditional piezoelectric sensors.

[0064] Compared with the prior art, the traditional piezoelectric sensor relies on electrical signals to transmit ultrasonic wave information, while the present scheme converts the microdisk 5 vibration caused by ultrasonic waves into the phase modulation amount of optical signals through the synergistic effect of the taper waveguide 21 and the curved waveguide 22, and realizes the demodulation of acoustic wave information using the principle of optical interference. The electrical signal transmission in the prior art is easily affected by the electromagnetic environment, and the present scheme uses an all-optical transmission method to eliminate the coupling path of electromagnetic interference on the sensing signal from a physical mechanism.

[0065] By the technical solution, the application effectively solves the problems of signal noise and distortion caused by the fact that the electrical signal transmission path of the traditional piezoelectric ultrasonic sensor is susceptible to electromagnetic interference, and realizes stable transmission of ultrasonic wave information by using the physical characteristics of the optical waveguide, so that the integrity of the sensing signal can be maintained in a strong electromagnetic interference environment. The closed design of the light propagation path enhances the stability of the light field interference and improves the corresponding accuracy of the sound wave vibration information and the light phase modulation, thereby providing a reliable solution for ultrasonic detection in a complex electromagnetic environment.

[0066] In this embodiment, the coupling waveguide 3 is in the shape of a cuboid or a cylinder, and the thickness and width of the coupling waveguide 3 are smaller than the diameter of the curved waveguide 22, so that the connection between the curved waveguide 22 and the coupling waveguide 3 is tapered.

[0067] In this embodiment, the coupling waveguide 3 is in the shape of a cuboid or a cylinder, and the thickness and width of the coupling waveguide 3 are smaller than the diameter of the curved waveguide 22, so that the connection between the curved waveguide 22 and the coupling waveguide 3 is tapered.

[0068] Specifically, when the optical signal is transmitted from the curved waveguide 22 to the coupling waveguide 3, the optical field is gradually constrained into a smaller transmission channel due to the tapering change of the cross-sectional size at the connection. In this process, the energy distribution is re-adjusted through the smooth transition of the waveguide structure, avoiding the mode mismatch caused by the traditional right-angle connection or size mutation. The continuous gradual change of the optical field in the tapered region enables most of the energy to be effectively transferred to the coupling waveguide 3, thereby reducing the energy loss caused by reflection or scattering and improving the coupling efficiency of the conversion of the sound wave signal to the optical signal.

[0069] By the technical solution, the application solves the problems of light signal transmission loss and insufficient coupling efficiency at the connection between the curved waveguide 22 and the coupling waveguide 3, realizes efficient conversion and low-loss transmission of the optical wave mode, and thereby improves the sensitivity of the sound wave sensor to weak signal detection.

[0070] In this embodiment, the thickness of the coupling waveguide 3 gradually decreases from both ends to the center.

[0071] This design forms a transition with the adjacent waveguide through the thicker regions at both ends, reduces the light reflection at the connection, and at the same time enhances the constraint ability of the waveguide to the optical field through the thickness reduction in the central region.

[0072] Specifically, when the optical signal enters the coupling waveguide 3 from the curved waveguide 22, the light field distribution matches the mode field of the curved waveguide 22 due to the large cross-sectional area at both ends, effectively suppressing the reflection loss. As the light field propagates to the center, the cross-sectional area of the coupling waveguide 3 gradually decreases, and the light field energy is confined to the surface area of the coupling waveguide 3, enhancing the interaction between the coupling waveguide 3 and the microdisk 5. When the acoustic wave causes the microdisk 5 to deform, the change in the distance between the coupling waveguide 3 and the microdisk 5 causes the resonance condition to change, and the light field energy distribution adjusts accordingly. This structure improves the modulation depth and sensitivity of the optical signal, and avoids the problem of electrical signals being easily affected by electromagnetic interference in traditional piezoelectric sensors.

[0073] Through the above technical solutions, the present application realizes efficient coupling and stable transmission of optical signals, reduces reflection loss and noise interference, makes the acoustic wave detection process not affected by the electromagnetic environment, and is suitable for high-precision acoustic wave sensing in industrial strong electromagnetic interference scenes.

[0074] In an embodiment of the present application, as shown in the accompanying drawings, Figure 3 The coupling waveguide 3 and the microdisk 5 are separated by 200 nm.

[0075] Specifically, the light field in the coupling waveguide 3 forms an evanescent wave during transmission and extends to the surface area of the microdisk 5 through a precisely controlled separation distance. When external acoustic waves act on the microdisk 5, the nanoscale mechanical vibration of its surface will periodically change the distribution state of the evanescent field, thereby modulating the phase or intensity of the optical signal. The fixed separation distance avoids the vibration damping effect caused by mechanical contact, allowing the microdisk 5 to freely respond to acoustic frequencies. At the same time, the distance is controlled within the effective range of the light field, ensuring sufficient interaction strength and preventing random gap changes caused by environmental vibration from interfering with signal modulation.

[0076] Through the above technical solutions, the present application realizes efficient and stable coupling of optical signals and acoustic signals, enhances the light field modulation depth under the premise of ensuring the free vibration of the microdisk 5, and effectively improves the detection sensitivity and environmental interference resistance of the sensor to external acoustic waves.

[0077] In the present embodiment, the optical propagation waveguide 2, the coupling waveguide 3, the support assembly 4, and the microdisk 5 are all made of photosensitive material with a refractive index of 1.54.

[0078] Specifically, the light propagation waveguide 2 and the core can adopt light-sensitive materials with different refractive indexes, which can avoid reflection loss caused by interface refractive index mutation during input and output of the optical signal, thereby improving the coupling efficiency. The tapered design of the coupling waveguide 3 combined with the material refractive index matching can ensure that the optical signal maintains stable phase characteristics during transmission, avoiding mode distortion caused by refractive index difference.

[0079] Compared with the prior art, the traditional piezoelectric ultrasonic sensor relies on electrical signal conversion, and the piezoelectric material is susceptible to electromagnetic interference, while the present scheme adopts an all-optical material system, which completely avoids the influence of electromagnetic environment through optical signal transmission. In addition, different components in the prior art are often spliced with heterogeneous materials, resulting in scattering or reflection loss of the optical signal at the interface due to refractive index mismatch, while the present scheme realizes continuous matching of optical parameters between components through material uniformity, thereby reducing optical loss from the root.

[0080] Through the above technical solutions, the present 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 the traditional electrical signal is susceptible to electromagnetic interference, and can still maintain stable acoustic detection accuracy in a strong electromagnetic environment.

[0081] The working principle of the optical fiber ultrasonic sensor of the present application is based on the micro-ring resonance principle, in which the coupling waveguide 3 and the micro-disk 5 form a resonant micro-ring. The light emitted from the first core of the seven-core optical fiber 1 enters the light propagation waveguide 2, and the light is transmitted along the light propagation waveguide 2. When the light transmitted from the coupling waveguide 3 couples into the micro-disk 5 and meets the resonance condition, resonance occurs, and the light that does not meet the resonance condition is output from the corresponding light propagation waveguide 2. Only light with an optical path equal to an integer multiple of the wavelength can resonate, and the resonance wavelength satisfies the following expression:

[0082] mλ=n eff L;

[0083] Wherein, 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 a wave number of m, n eff is the effective refractive index of the material; L is the path length of the light propagating in the resonant cavity.

[0084] The free spectral range FSR of the resonance wavelength can be calculated by the following expression:

[0085] ;

[0086] Wherein λ represents the resonance wavelength, n effis the effective refractive index of the material, and R is the radius of the microdisk.

[0087] The principle of ultrasonic sensing is that when ultrasound waves propagate to the microdisk 5, they alter the effective refractive index and radius of the microdisk, resulting in changes in the resonant wavelength λ and free spectral range (FSR). By locking the laser wavelength to the point where the slope of the resonant wavelength is maximum, the output intensity modulated by optical resonance is collected by a photodetector, converting the ultrasonic signal into a detectable light intensity signal. By demodulating the corresponding light intensity, the ultrasonic signal intensity and frequency information can be effectively demodulated.

[0088] The prepared ultrasonic sensor was used in an experimental setup to analyze its ultrasonic response characteristics. The experimental setup primarily consists of two components: ultrasound generation and ultrasonic sensor demodulation. The ultrasound generation component uses a signal generator to drive a piezoelectric transducer to generate ultrasonic waves. The ultrasonic sensor demodulation component consists of a fiber-optic ultrasonic sensor, a tunable laser, a photodetector, and an oscilloscope. Because ultrasonic waves propagate easily in water and have low loss, the test was conducted in a water-filled tank.

[0089] As attached Figure 4 As shown, the experimental setup described above can be used to test the sinusoidal response characteristics of an ultrasonic sensor. Place the piezoelectric transducer 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, and the waveform to a sinusoidal wave, and drive the piezoelectric transducer to emit ultrasonic waves. The ultrasonic waves propagate through the water medium and reach the ultrasonic sensor. The ultrasonic waves change the effective refractive index and radius of the ultrasonic sensor microdisk 5, causing the resonant wavelength to shift. The light intensity of the laser output also changes accordingly. The optical signal is detected by a photodetector, converted into an electrical signal, and received and displayed by an oscilloscope. Figure 4 The 1MHz sinusoidal signal received by the sensor is displayed on the oscilloscope. The results show that the fiber optic ultrasonic sensor has the characteristics of accurately detecting single sinusoidal ultrasonic waves.

[0090] As attached Figure 5 and attached Figure 6 As shown, the experimental setup described above can be used to test the pulse response characteristics of a fiber-optic ultrasonic sensor. A piezoelectric transducer is placed 3 cm in front of the ultrasonic sensor. The signal generator is turned on, with an output frequency of 1 MHz and a drive voltage of 20 Vpp. The waveform is pulsed with a sinusoidal wave, emitting a pulse signal every 1 ms, driving the piezoelectric transducer to emit ultrasonic waves. The ultrasonic waves propagate through the water medium and reach the ultrasonic sensor. The ultrasonic waves alter the effective refractive index and radius of the ultrasonic sensor microdisk 5, causing the resonant wavelength to change. The light intensity of the laser output also changes accordingly. The optical signal is detected by a photodetector, converted into an electrical signal, and received and displayed by an oscilloscope. Figure 5The 1 MHz pulse signal received by the sensor is shown on the oscilloscope. The time domain pulse signal is converted to a frequency domain signal by taking the Fourier transform of the time domain signal, as shown in FIG. 8. The frequency domain result shows that the response is maximum at 1 MHz. This indicates that the fiber optic ultrasound sensor has the ability to accurately detect a single pulse of ultrasound. Figure 6

[0091] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the aspects disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the application being indicated by the following claims.​

Claims

1. An optical fiber end-face integrated microcavity acoustic wave sensor, characterized in that: include: Seven-core optical fiber; Two light propagation waveguides are provided on the end face of the seven-core optical fiber; the two light propagation waveguides are respectively connected to the first fiber core and the second fiber core of the seven-core optical fiber; A coupling waveguide, disposed between the two light propagation waveguides, for connecting the two light propagation waveguides; A support assembly is provided on the end face of the seven-core optical fiber; A microdisk is disposed on the support assembly so that the microdisk is located on one side of the coupling waveguide; the microdisk and the coupling waveguide are spaced apart to form a resonant microring; when ultrasonic waves act on the microdisk, the resonance condition changes, thereby causing the output laser intensity to change; A light emitter is provided at one end of the seven-core optical fiber away from the light propagation waveguide; the light emitter is connected to the first fiber core; a photoelectric detector, disposed at an end of the seven-core optical fiber away from the light propagation waveguide; the photoelectric detector is connected to the second fiber core; a fixing platform disposed on an end face of the seven-core optical fiber and rigidly connected to the end face of the seven-core optical fiber; the fixing platform is located on a side of the coupling waveguide away from the microdisk, where the side of the coupling waveguide away from the microdisk refers to a non-functional area where the coupling waveguide has no sensing relationship with the microdisk; the fixing platform is connected to the coupling waveguide to support the coupling waveguide; the diameter of the microdisk is larger than the diameter of the fixing platform; A micro-ring is provided on the surface of the micro-disk, and the bottom of the micro-disk is in an inverted cone shape.

2. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 1, characterized in that: The support assembly comprises: The conical platform is arranged on the end face of the seven-core optical fiber; and the micro-disk is arranged on the conical platform.

3. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 2, characterized in that: A cylindrical platform is provided on 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.

4. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 1, characterized in that: The light propagation waveguide comprises: Two tapered waveguides are provided on the end face of the seven-core optical fiber; Two curved waveguides are respectively arranged on the top of the two tapered waveguides; the coupling waveguide is connected to the two curved waveguides so that the two tapered waveguides are connected.

5. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 4, characterized in that: The coupling waveguide is in a rectangular parallelepiped or cylindrical shape, and the thickness and width of the coupling waveguide are both smaller than the diameter of the curved waveguide, so that the connection between the curved waveguide and the coupling waveguide is tapered.

6. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 5, characterized in that: The thickness of the coupling waveguide gradually decreases from both ends to the center.

7. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 1, characterized in that: The coupling waveguide is spaced 200 nm apart from the microdisk.

8. The optical fiber end-face integrated microcavity acoustic wave sensor according to claim 1, characterized in that: The light propagation waveguide, coupling waveguide, supporting component and micro-disk are all made of a photosensitive material with a refractive index of 1.54.

Images