A fiber-optic ultrasonic sensor based on a spring resonator and a method of manufacturing the same

Abstract

The application discloses a spring resonator-based optical fiber ultrasonic sensor and a preparation method thereof, and comprises a single-mode optical fiber and a spring resonator. The single-mode optical fiber comprises a fiber core and a single-mode optical fiber end face, is used for receiving incident light, reflects on the single-mode optical fiber end face, obtains a first reflection light path, and transmits adjacent incident light to the spring resonator. The spring resonator comprises a ring-shaped base, a spring, a cylindrical waveguide and a micro disk, is used for receiving the adjacent incident light transmitted by the single-mode optical fiber, reflects on the end face of the micro disk, and obtains a second reflection light path. When an acoustic wave acts on the spring resonator, the optical path difference between the first reflection light path and the second reflection light path changes, an optical signal modulation is generated, and the acoustic wave is sensed. The application is used for solving the technical problems that the existing optical fiber ultrasonic sensor is too large in size, is not high in sensitivity and is complex in a preparation process, so that a small-sized, high-sensitivity and easy-to-manufacture optical fiber ultrasonic sensor is developed.

Description

Technical Field

[0001] This invention relates to the field of fiber optic ultrasonic sensor technology, specifically to a fiber optic ultrasonic sensor based on a spring resonator and its fabrication method. Background Technology

[0002] Fiber optic ultrasonic sensors detect ultrasonic waves by measuring parameters such as intensity, wavelength, phase, and polarization state of light transmitted within an optical fiber. Compared to traditional electrical ultrasonic transducers, fiber optic ultrasonic sensors can achieve high-sensitivity detection of broadband ultrasonic signals. Their excellent anti-interference capabilities and multiplexing properties effectively improve the reliability and efficiency of ultrasonic detection, making them highly promising for applications in underwater defense and security, biological imaging, non-destructive testing, and seismic physical model imaging. Currently, fiber optic ultrasonic sensors are classified into three types: functional, non-functional, and light-harvesting.

[0003] (1) Functional type

[0004] Optical fibers are highly sensitive to external information and are therefore often used as sensing elements, forming sensors that combine transmission and sensing capabilities. In addition to transmitting light, optical fibers can also change their phase, polarization state, and other optical properties under the influence of factors such as bending or phase transitions, enabling sensing functions.

[0005] (2) Non-functional type

[0006] This type of fiber optic ultrasonic sensor only has the function of transmitting light and is relatively lacking in sensing external signals. It achieves "sensing" external signals only through the physical properties of its functional components. This type of fiber is discontinuous, has low technical requirements, and is simple and inexpensive to implement. However, its sensitivity is relatively low, so it is suitable for some fields where high sensitivity is not required.

[0007] (3) Light-collecting type

[0008] These sensors use fiber optic probes, receiving optical signals reflected from the object being measured. The most typical application of light-harvesting ultrasonic sensors is the fiber laser Doppler velocimeter. Currently, fiber optic ultrasonic sensors are receiving increasing attention and have found successful applications in many fields.

[0009] The main applications of fiber optic ultrasonic sensors are as follows:

[0010] (1) Non-destructive testing technology

[0011] Non-destructive testing (NDT) refers to the inspection of intact structures and is very helpful in controlling material quality. Currently, ultrasonic testing is widely used in NDT. The propagation of ultrasonic waves within the object being tested reveals the material's structure and quality.

[0012] (2) Medical Imaging

[0013] Ultrasound waves can be transmitted and reflected within biological tissues, and the reflected information carries details about the organism. Analyzing the reflected ultrasound signals reveals specific information about the organism. Traditional PZT (photonic radiography) has been widely used in clinical medicine, offering good acquisition of information from the surface of organisms. However, traditional PZT devices are relatively large, making it impossible to acquire high-resolution images in very small biological spaces. Replacing PZT with a fiber optic ultrasound sensor allows for the acquisition of high-resolution biological information over small areas. To obtain high-resolution biological tissue information, a high-frequency ultrasound carrier with a wavelength below 1 mm is needed. This places demands on the size of the fiber optic ultrasound sensor. In 2014, a miniature fiber optic sensor based on nanotechnology was developed, offering twice the resolution of PZT and capable of generating highly compatible ultrasound images.

[0014] (3) Ultrasonic imaging of earthquake models

[0015] Earthquake models are scaled-down structures based on geological features, used to simulate the transmission of seismic waves. These simulations provide highly realistic earthquake information, with minimal impact from calculation methods and setup conditions. Compared to real-world environments, simulating earthquakes using seismic models is not only much cheaper but also provides a highly stable seismic wave transmission process. Furthermore, the models can be repeatedly simulated, significantly improving the reliability of the final results.

[0016] In recent years, there has been an increasing amount of research on fiber optic ultrasonic sensors, and broadband ultrasonic detection has been completed. However, existing fiber optic ultrasonic sensors still have technical problems such as excessive size, insufficient sensitivity, and complex fabrication process. Summary of the Invention

[0017] To overcome the shortcomings of existing technologies, this invention provides a fiber optic ultrasonic sensor based on a spring resonator and its fabrication method, which solves the technical problems of existing fiber optic ultrasonic sensors being too large, having low sensitivity, and having a complex fabrication process, thereby achieving the goal of developing a miniaturized, highly sensitive, and easy-to-manufacture fiber optic ultrasonic sensor.

[0018] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0019] A fiber optic ultrasonic sensor based on a spring resonator, characterized in that it comprises:

[0020] A single-mode optical fiber, including a fiber core and a single-mode fiber end face, is used to receive incident light, reflect it on the single-mode fiber end face to obtain a first reflected optical path, and transmit adjacent incident light to a spring resonator.

[0021] A spring resonator, comprising a ring base, a spring, a cylindrical waveguide, and a microdisk, is used to receive adjacent incident light transmitted from the single-mode optical fiber and reflect it on the end face of the microdisk to obtain a second reflected optical path.

[0022] When the sound wave acts on the spring resonator, the optical path difference between the first reflected optical path and the second reflected optical path changes, generating optical signal modulation to sense the sound wave.

[0023] In a preferred embodiment of the present invention, the spring resonator is fixedly connected to the end face of the single-mode fiber via the annular base, and the annular base is used to increase the contact area between the spring and the end face of the single-mode fiber; the cylindrical waveguide is coaxial with the fiber core and is used to support the micro disk, and together with the spring, is used to constrain the micro disk.

[0024] In a preferred embodiment of the present invention, the annular base and the micro disk are arranged opposite to each other by the spring, and the cylindrical waveguide is disposed between the end face of the single-mode fiber and the micro disk and is fixedly connected to the micro disk.

[0025] In a preferred embodiment of the present invention, the microdisk, the cylindrical waveguide, and the single-mode fiber end face together form an FP cavity; wherein, the length of the FP cavity changes under the action of acoustic waves.

[0026] In a preferred embodiment of the present invention, the spring is a variable pitch spring.

[0027] A method for fabricating a fiber optic ultrasonic sensor based on a spring resonator includes the following steps:

[0028] A single-mode optical fiber is provided, and the end of the single-mode optical fiber is cut to obtain a flat single-mode optical fiber end face.

[0029] The single-mode fiber is fixed on a displacement controller, and the end face of the single-mode fiber is immersed in a photoresist droplet using the displacement controller. Based on a preset three-dimensional model of a spring resonator, a spring resonator is printed on the end face of the single-mode fiber using two-photon polymerization 3D printing technology.

[0030] The printed single-mode fiber end face is removed, cleaned, and further cured to obtain the fiber optic ultrasonic sensor based on the spring resonator.

[0031] In a preferred embodiment of the present invention, the cutting of the end of the single-mode optical fiber includes:

[0032] After removing the coating layer from the single-mode fiber, the end of the single-mode fiber is cut using a fiber optic cleaver to obtain the end face of the single-mode fiber.

[0033] As a preferred embodiment of the present invention, when printing a spring resonator using two-photon polymerization 3D printing technology, the following is included:

[0034] A neodymium-doped yttrium aluminum garnet laser with a wavelength of 520-540 nm and a pulse width of 630-670 ps was used as the laser source, with a laser power range of 2.02-2.16 mW and an exposure time of 900-1100 milliseconds.

[0035] In a preferred embodiment of the present invention, cleaning the end face of a single-mode fiber includes:

[0036] The end face of the single-mode fiber is washed in anhydrous ethanol for 30-60 seconds to remove excess photoresist.

[0037] In a preferred embodiment of the present invention, further curing of the single-mode fiber end face includes:

[0038] Place the cleaned single-mode fiber end face under green light to cure for 10-15 minutes.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] (1) The fiber optic ultrasonic sensor of the present invention adopts a micro resonator structure of ring base + spring + cylindrical waveguide + micro disk, which makes it respond well at external frequencies from 50KHz to 400KHz and exhibits a wide frequency response.

[0041] (2) Compared with existing fiber optic ultrasonic sensors, the present invention exhibits lower temperature sensitivity and better temperature stability;

[0042] (3) The present invention directly processes the spring resonator on the end face of the single-mode fiber, thereby effectively ensuring the miniaturization of the fiber ultrasonic sensor.

[0043] (4) The fiber optic ultrasonic sensor of the present invention is based on a micron-level fine polymer cavity waveguide, a polymer microdisk-type reflective film structure, and incorporates a special structure of a polymer spring resonator, which effectively enhances the vibration sensitivity of this type of fiber optic ultrasonic sensor. At the same time, based on the low Young's modulus of polymer, it has ultra-high sensitivity to ultrasound. Combined with the two-photon polymerization process, it is easy to realize the repeated processing and manufacturing of this type of fiber optic sensor.

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0045] Figure 1 - is a structural diagram of the spring resonator according to an embodiment of the present invention;

[0046] Figure 2 - is a schematic diagram of the fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention;

[0047] Figure 3 - This is a schematic diagram of the fabrication process of the fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention;

[0048] Figure 4 - is the reflection spectrum of the fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention;

[0049] Figure 5 - is a power spectral density diagram of the output signal of the fiber optic ultrasonic sensor based on a spring resonator in air according to an embodiment of the present invention;

[0050] Figure 6 - This is the reflection spectrum of the fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention at 25℃-61℃;

[0051] Figure 7 - is a temperature response fitting diagram of a fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention;

[0052] Figure 8 - This is a step diagram illustrating the fabrication method of a fiber optic ultrasonic sensor based on a spring resonator according to an embodiment of the present invention.

[0053] Reference numerals in the attached figures: 1. Single-mode fiber; 2. Single-mode fiber end face; 3. Ring base; 4. Spring; 5. Cylindrical waveguide; 6. Microdisk; 7. Micro-displacement platform; 8. Positioning pin; 9. Displacement controller; 10. Glass slide; 11. Objective lens. Detailed Implementation

[0054] The fiber optic ultrasonic sensor based on a spring resonator provided by this invention includes: a single-mode fiber 1 and a spring resonator. The single-mode fiber 1 includes a fiber core and a single-mode fiber end face 2, used to receive incident light, reflect it at the single-mode fiber end face 2 to obtain a first reflected optical path, and transmit adjacent incident light to the spring resonator. The spring resonator includes a ring base 3, a spring 4, a cylindrical waveguide 5, and a microdisk 6, used to receive adjacent incident light transmitted from the single-mode fiber 1, reflect it at the end face of the microdisk 6 to obtain a second reflected optical path.

[0055] When the sound wave acts on the spring resonator, the optical path difference between the first and second reflected optical paths changes, generating optical signal modulation to sense the sound wave.

[0056] Furthermore, the spring resonator is fixedly connected to the single-mode fiber end face 2 via an annular base 3. The annular base 3 is used to increase the contact area between the spring 4 and the single-mode fiber end face 2. The cylindrical waveguide 5 is coaxial with the fiber core and is used to support the micro disk 6, and together with the spring 4, it is used to constrain the micro disk 6.

[0057] Specifically, by using a cylindrical waveguide 5 combined with a spring 4 to constrain the microdisk 6, the present invention can effectively improve the sensitivity of the spring resonator to sound waves.

[0058] Furthermore, the annular base 3 and the micro disk 6 are positioned opposite each other by a spring 4, and the cylindrical waveguide 5 is positioned between the single-mode fiber end face 2 and the micro disk 6 and is fixedly connected to the micro disk 6.

[0059] Furthermore, the microdisk 6, the cylindrical waveguide 5, and the single-mode fiber end face 2 together form an FP cavity;

[0060] The length of the FP cavity changes under the influence of sound waves.

[0061] Specifically, the cylindrical waveguide 5 mentioned above is coaxial with the fiber core, and another purpose is to serve as a waveguide for the FP cavity.

[0062] Furthermore, spring 4 is a variable pitch spring.

[0063] Specifically, the dimensions of the variable pitch spring are as follows: the pitch of the 0th turn is 5μm, the pitch of the 1st turn is 30μm, the pitch of the 2nd turn is 30μm, and the pitch of the 3rd turn is 5μm; the center line diameter of the spring helix is ​​60μm, and the cross-sectional diameter of the spring 4 is 5μm.

[0064] Furthermore, the outer diameter of the annular base 3 can be up to 125 μm and the inner diameter can be as small as 9 μm. When the inner diameter is 9 μm, the annular base 3 is connected to the cylindrical waveguide 5.

[0065] Furthermore, the ring width and height of the annular base 3 are 40μm and 5μm, respectively. The ring width of the annular base 3 is set to 40μm, which can ensure sufficient contact area between the spring 4 and the single-mode fiber end face 2, while not increasing the manufacturing cost of the fiber ultrasonic sensor too much. In addition, the reason for setting the height of the annular base 3 to 5μm is to save processing and manufacturing time and to keep the thickness consistent with that of the micro disk 6, which is more aesthetically pleasing overall.

[0066] Furthermore, the cylindrical waveguide 5 has a diameter of 9 μm and a length of 60 μm; the microdisk 6 has a radius of 40 μm and a thickness of 5 μm.

[0067] Specifically, the structure of the spring resonator and the principle of the fiber optic ultrasonic sensor are as follows: Figure 1 and Figure 2 As shown, the principle of this application is as follows: the microdisk 6 and the cylindrical waveguide 5 form an FP cavity with the single-mode fiber end face 2. The incident light is reflected multiple times on the end faces of the single-mode fiber end face 2 and the microdisk 6, forming multi-beam interference. The sound wave causes a change in the length of the FP cavity, and the optical path difference between two adjacent reflected beams changes, thereby causing optical signal modulation. A tunable laser is used as the light source, a circulator is used as the optical path connection, and a photodetector is used to convert the optical signal fed back by the sensor into an electrical signal. The amplified electrical signal is acquired by an oscilloscope, and the linear relationship between the sound pressure and the output voltage can be obtained, thereby realizing the sensing of sound waves.

[0068] The method for fabricating a fiber optic ultrasonic sensor based on a spring resonator provided by this invention, such as... Figure 8 As shown, it includes the following steps:

[0069] Step S1: Provide a single-mode fiber 1 and cut the end of the single-mode fiber 1 to obtain a flat single-mode fiber end face 2.

[0070] Step S2: Fix the single-mode fiber 1 on the displacement controller, and use the displacement controller 9 to immerse the end face 2 of the single-mode fiber in a photoresist droplet. According to the preset three-dimensional model of the spring resonator, use two-photon polymerization 3D printing technology to print the spring resonator on the end face 2 of the single-mode fiber.

[0071] Step S3: Take out the printed single-mode fiber end face 2, clean it and further solidify it to obtain a fiber optic ultrasonic sensor based on a spring resonator.

[0072] In step S1 above, when cutting the end of the single-mode fiber 1, the following steps are included:

[0073] After removing the coating layer from the single-mode fiber 1, the end of the single-mode fiber 1 is cut using a fiber optic cleaver to obtain the single-mode fiber end face 2.

[0074] In step S2 above, when printing the spring resonator using two-photon polymerization 3D printing technology, the following is included:

[0075] A neodymium-doped yttrium aluminum garnet laser with a wavelength of 520-540 nm and a pulse width of 630-670 ps was used as the laser source, with a laser power range of 2.02-2.16 mW and an exposure time of 900-1100 milliseconds.

[0076] Preferably, a neodymium-doped yttrium aluminum garnet laser with a wavelength of 532 nm and a pulse width of 650 ps is used as the laser source, and the exposure time is 1000 milliseconds.

[0077] In step S3 above, cleaning the single-mode fiber end face 2 includes:

[0078] Wash the single-mode fiber end face 2 in anhydrous ethanol for 30-60 seconds to remove excess photoresist.

[0079] Preferably, the washing time is 30 seconds.

[0080] In step S3 above, further curing of the single-mode fiber end face 2 includes:

[0081] Place the cleaned single-mode fiber end face 2 under green light to cure for 10-15 minutes.

[0082] Preferably, the curing time is 15 minutes, which is sufficient to increase the mechanical strength of the spring resonator.

[0083] Specifically, the specific fabrication process of the fiber optic ultrasonic sensor of the present invention is as follows:

[0084] Step 1, Fiber Pre-processing: The single-mode fiber 1, after removing the coating, is cut using a fiber cleaver to obtain a flat single-mode fiber end face 2. The cut single-mode fiber 1 is fixed to a displacement controller 9 using positioning pins 8. The displacement controller 9 is placed on a micro-displacement platform 7, and photoresist is dropped onto a glass slide 10 to form a photoresist droplet. Observation is performed using an objective lens 11. The displacement controller 9 controls the single-mode fiber end face 2 to slowly immerse itself into the photoresist droplet, ensuring sufficient 3D printing depth without touching the glass slide 10. The specific process is as follows... Figure 3 As shown. The photoresist is Green-A, manufactured by Microlight3D, a French company.

[0085] The second step, two-photon polymerization 3D printing: A 3D model of the spring resonator is constructed using 3D modeling software. After steps such as model slicing, printing path selection, and printing parameter settings, the spring resonator is directly printed on the end face 2 of a single-mode fiber using a commercial two-photon polymerization 3D printing system. A neodymium-doped yttrium aluminum garnet laser with a wavelength of 532 nm and a pulse width of 650 ps is used as the laser source, with a laser power range of 2.02-2.16 milliwatts and an exposure time of 1000 milliseconds.

[0086] The third step is cleaning and curing: the printed and removed single-mode fiber end face 2 is washed in anhydrous ethanol for 30 seconds to remove excess photoresist, and then cured under green light for 15 minutes to further enhance mechanical strength. Figure 3 The microscopic image shown in (b) illustrates an FP-type cavity with a surface diameter D and a cavity length L.

[0087] Example

[0088] Figure 4 The image shows the reflection spectrum of the fiber optic ultrasonic sensor of this application. Based on the free spectral range (FSR) in the image, the effective length of the FP cavity of the fiber optic ultrasonic sensor can be calculated to be 65.8 μm, and the radius of the microdisk 6 is 40 μm. The specific calculation process is as follows:

[0089] Depend on Figure 4 The distance between each pair of adjacent troughs can be calculated from the spectrum. Then, substituting the distance between each pair of adjacent troughs into Formula 1, the effective length can be obtained.

[0090]

[0091] In the formula, λ m and λ m+1 Let λ be the wavelength between two adjacent troughs, n be the refractive index of the waveguide, and L be the effective length.

[0092] Depend on Figure 4 As can be seen, there are 5 adjacent valleys in the reflectance spectrum. Therefore, 5 sets of data can be calculated, and the average is taken to obtain an effective length of 65.8 μm.

[0093] Figure 5 This image shows the power spectral density plots of the output signal of the fiber optic ultrasonic sensor of this application, measured in air at frequencies of (a) 50 kHz, (b) 200 kHz, and (c) 400 kHz, with the time-domain signal provided in the inset. The power spectral density was obtained by performing a Fast Fourier Transform (FFT) on the time-domain signal using MATLAB. Figure 5 As can be seen, the peak position of the power spectral density matches the frequency of the excitation sound wave, and its signal-to-noise ratio (SNR) is as high as 64.4dB, 70.0dB, and 52.8dB, respectively. Furthermore, this fiber optic ultrasonic sensor responds well in the external frequency range of 50kHz to 400kHz, exhibiting a wide frequency response.

[0094] Figure 6 This is the reflection spectrum of the fiber optic ultrasonic sensor of this application at 25℃-61℃, derived from... Figure 6 It can be seen that the reflectance spectrum exhibits a blue shift as the temperature increases. Figure 7 This is a temperature response fitting graph of a fiber optic ultrasonic sensor, derived from... Figure 7 As can be seen, the temperature sensitivity of this fiber optic ultrasonic sensor is -108.45 pm / ℃. The above experimental results show that the fiber optic ultrasonic sensor of this application exhibits low temperature sensitivity and good temperature stability.

[0095] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A fiber optic ultrasonic sensor based on a spring resonator, characterized in that, include: A single-mode optical fiber, including a fiber core and a single-mode fiber end face, is used to receive incident light, reflect it on the single-mode fiber end face to obtain a first reflected optical path, and transmit adjacent incident light to a spring resonator. A spring resonator, comprising a ring base, a spring, a cylindrical waveguide, and a microdisk, is used to receive adjacent incident light transmitted from the single-mode optical fiber and reflect it on the end face of the microdisk to obtain a second reflected optical path. When the sound wave acts on the spring resonator, the optical path difference between the first reflected optical path and the second reflected optical path changes, generating optical signal modulation to sense the sound wave.

2. The fiber optic ultrasonic sensor based on a spring resonator according to claim 1, characterized in that, The spring resonator is fixedly connected to the end face of the single-mode fiber via the annular base. The annular base is used to increase the contact area between the spring and the end face of the single-mode fiber. The cylindrical waveguide is coaxial with the fiber core and is used to support the micro disk, and together with the spring, it is used to constrain the micro disk.

3. The fiber optic ultrasonic sensor based on a spring resonator according to claim 2, characterized in that, The annular base and the micro disk are positioned opposite each other via the spring. The cylindrical waveguide is positioned between the end face of the single-mode fiber and the micro disk and is fixedly connected to the micro disk.

4. The fiber optic ultrasonic sensor based on a spring resonator according to any one of claims 1-3, characterized in that, The micro disk, the cylindrical waveguide, and the single-mode fiber end face together form an FP cavity; The length of the FP cavity changes under the influence of sound waves.

5. The fiber optic ultrasonic sensor based on a spring resonator according to any one of claims 1-3, characterized in that, The spring is a variable pitch spring.

6. A method for fabricating a fiber optic ultrasonic sensor based on a spring resonator, characterized in that, The fiber optic ultrasonic sensor is the fiber optic ultrasonic sensor as described in any one of claims 1-5, and the preparation method includes the following steps: A single-mode optical fiber is provided, and the end of the single-mode optical fiber is cut to obtain a flat single-mode optical fiber end face. The single-mode fiber is fixed on a displacement controller, and the end face of the single-mode fiber is immersed in a photoresist droplet using the displacement controller. According to the preset three-dimensional model of the spring resonator, the spring resonator is printed on the end face of the single-mode fiber using two-photon polymerization 3D printing technology. The printed single-mode fiber end face is removed, cleaned, and further cured to obtain the fiber optic ultrasonic sensor based on the spring resonator.

7. The method for fabricating a fiber optic ultrasonic sensor based on a spring resonator according to claim 6, characterized in that, When cutting the end of the single-mode fiber, the following steps are included: After removing the coating layer from the single-mode fiber, the end of the single-mode fiber is cut using a fiber optic cleaver to obtain the end face of the single-mode fiber.

8. The method for fabricating a fiber optic ultrasonic sensor based on a spring resonator according to claim 6, characterized in that, When printing spring resonators using two-photon polymerization 3D printing technology, the following are included: A neodymium-doped yttrium aluminum garnet laser with a wavelength of 520-540 nm and a pulse width of 630-670 ps was used as the laser source, with a laser power range of 2.02-2.16 mW and an exposure time of 900-1100 milliseconds.

9. The method for fabricating a fiber optic ultrasonic sensor based on a spring resonator according to claim 6, characterized in that, Cleaning the end face of a single-mode fiber includes: The end face of the single-mode fiber is washed in anhydrous ethanol for 30-60 seconds to remove excess photoresist.

10. The method for fabricating a fiber optic ultrasonic sensor based on a spring resonator according to claim 6, characterized in that, Further curing of the single-mode fiber end face includes: Place the cleaned single-mode fiber end face under green light to cure for 10-15 minutes.

Images