A transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device and its fabrication method

Abstract

This invention belongs to the field of photoacoustic transduction technology, specifically relating to a transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device. The device includes a fiber optic photoacoustic transducer and a fiber optic hydrophone. The fiber optic photoacoustic transducer comprises a nanosecond pulsed laser, a lens, a fan-in / fan-out module, and a dual-core optical fiber. A trapezoidal slot is formed on one side of the dual-core optical fiber, and an absorption layer is uniformly filled within the slot. Each core of the dual-core optical fiber is an independent single-mode fiber, and one of the single-mode fibers is connected to the nanosecond pulsed laser via the fan-in / fan-out module. The nanosecond pulsed laser has a wavelength of 532 nm, a pulse width of 10-200 ns, a repetition frequency of 1-100 kHz, and a power of 400-800 mW. This invention integrates the transmission and reception of ultrasonic signals onto a single optical fiber, achieving integrated transmission and reception simultaneously. In the optical path, the acoustic signal generated by the transducer does not affect the hydrophone.

Description

Technical Field

[0001] This invention belongs to the field of photoacoustic transduction technology, specifically relating to an integrated fiber optic photoacoustic transducer and fiber optic hydrophone device and its preparation method. Background Technology

[0002] Ultrasound refers to sound waves with frequencies exceeding 20,000 Hz. These sound waves possess strong penetrating power, thus offering broad application prospects in medicine, machinery, and national defense. An acoustic transducer is an instrument that converts energy; its main function is to convert one form of energy into mechanical energy, thereby exciting ultrasonic signals through mechanical vibration. Traditional transducers include mechanical transducers, capacitive transducers, piezoelectric transducers, and magnetostrictive transducers, etc. However, these transducers generally suffer from drawbacks such as large size, high power consumption, and limited application flexibility. With increasingly demanding application requirements, photoacoustic transducers have gradually come into focus.

[0003] The photoacoustic effect refers to the phenomenon where sound waves are generated when a material is irradiated with light of periodically modulated intensity. When a material is irradiated with light, the absorption of light causes changes in its internal temperature, resulting in short-term changes in the structure and volume of certain regions within the material. When a material is irradiated with a pulsed light source, it also undergoes periodic volume expansion and contraction in accordance with the frequency of the pulsed light, thus generating sound wave signals that propagate outward. Ultrasonic waves generated based on the photoacoustic effect generally have frequencies above MHz, thus constituting a high-frequency ultrasonic wave. Currently, photoacoustic transducers are mainly divided into two categories: spatial light-excited photoacoustic transducers and fiber optic photoacoustic transducers. The former is simple to design and easy to manufacture, but its optical path is complex, its operating state is unstable, its size is not small, and its excitation point is fixed, making flexible arrangement impossible. The latter has a compact structure, good stability, strong resistance to electromagnetic interference, and can be flexibly arranged, but generally, this type of photoacoustic transducer is made by coating the surface of optical fibers with photoacoustic materials, so the signal is relatively divergent, its directionality is low, and some materials have excessive absorption loss for laser light, resulting in low excitation efficiency.

[0004] Since fiber optic photoacoustic transducers can generate sound waves underwater, instruments capable of receiving these signals are naturally needed, leading to the emergence of hydrophones. A hydrophone is an underwater instrument that receives sound waves, converting underwater sound signals into processable signals for target detection, identification, and location. Hydrophones can be categorized based on their sensing principles, including piezoelectric, magnetostrictive, and fiber optic types. Early hydrophones relied primarily on the energy coupling of electric and magnetic fields for underwater acoustic detection, but these methods had limitations in signal detection distance, power supply, and electromagnetic interference. With technological advancements, they have become insufficient to meet application requirements in many aspects. The advent of fiber optics has had a profound impact on the world, and as a component of fiber optic sensing technology, fiber optic hydrophones represent a new future for underwater acoustic signal detection.

[0005] Numerous fiber optic transducer and hydrophone structures have been proposed in domestic and international research, each with its own advantages and disadvantages. In the existing technology "Development of an optical fiber hydrophone with fiber Bragg grating," Nobuaki Takahashi et al. utilized a Bragg fiber grating (FBG) to modulate laser light within the fiber under acoustic pressure, constructing a fiber optic hydrophone. This hydrophone can monitor the phase and amplitude of the sound field in real time, with a dynamic range of approximately 70 dB, and can operate within the sound wave frequency range of 1 kHz to 3 MHz without signal distortion. In the existing technology "CuInS2, Quantum Dot and Polydimethylsiloxane Nanocomposites for Al1-Optical Ultrasound and Photoacoustic Imaging," Semyon Bodian et al. coated the end of an optical fiber with a nanocomposite material composed of CuInS2 quantum dots and medical-grade polydimethylsiloxane (CIS-PDMS), fabricating a photoacoustic transducer. This transducer can generate an acoustic pressure exceeding 3.5 MPa, with a corresponding bandwidth of 18 MHz. However, using CuInS2 quantum dots to prepare the absorption layer significantly increases the fabrication cost and difficulty of the transducer. Chinese patent CN110339992A proposes a photo-induced ultrasonic transducer based on transition metal sulfides and its fabrication method. This transducer, from bottom to top, consists of a light absorption layer composed of carbon nanotubes and transition metal sulfide composite particles, and a thermoelastic expansion layer composed of PDMS. In this design, the transition metal sulfides improve the light absorption efficiency of the absorption layer, thus increasing the sound wave intensity to some extent. Chinese patent CN117824816A proposes a high-pressure resistant fiber optic hydrophone based on a fiber grating structure. This transducer uses two fiber gratings to wind a small-sized solid polycarbonate cylinder, giving the hydrophone both high sensitivity and high-pressure resistance.

[0006] In the above design, the fiber optic hydrophone and fiber optic transducer exist independently and can only perform a single function. However, in reality, if it were possible to achieve integrated underwater sound wave transmission and reception, this device would have a much broader range of applications. Summary of the Invention

[0007] The purpose of this invention is to provide a fiber optic photoacoustic transducer and fiber optic hydrophone device and manufacturing method that integrates the transmission and reception of ultrasonic signals on a single optical fiber, achieving integrated transmission and reception, and the transmission and reception can be carried out simultaneously. In the optical path, the acoustic signal generated by the transducer will not affect the hydrophone.

[0008] The specific technical solution adopted by this invention is as follows:

[0009] A transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device includes a fiber optic photoacoustic transducer and a fiber optic hydrophone. The fiber optic photoacoustic transducer includes a nanosecond pulsed laser, a lens, a fan-in and fan-out module, and a dual-core fiber. A trapezoidal slot is formed on one side of the dual-core fiber, and an absorption layer is uniformly filled in the trapezoidal slot. Each fiber core in the dual-core fiber is an independent single-mode fiber, and one of the single-mode fibers is connected to the nanosecond pulsed laser through the fan-in and fan-out module.

[0010] The nanosecond pulsed laser has a wavelength of 532nm, a pulse width of 10-200ns, a repetition frequency of 1-100kHz, and a power of 400-800mW. After being focused by a lens, the nanosecond pulsed laser is coupled into a dual-core optical fiber and a fan-in / fan-out module.

[0011] The trapezoidal groove is right-angled, with one side of the right-angled side of the trapezoidal groove serving as the input end of a nanosecond pulse laser. The hypotenuse and the top surface of the trapezoidal groove are reflective surfaces, which are coated with a metal reflective film.

[0012] The metal reflective film includes gold nanoparticles, which are used to absorb light irradiation energy, with a resonance absorption peak of 530-535 nm.

[0013] The fiber optic hydrophone includes a fiber optic circulator, a narrow-linewidth single-wavelength laser, a photodetector, a fiber optic 1×2 coupler, a thin-walled elastic tube, and a Faraday rotating mirror. The hydrophone adopts a fiber optic Michelson interference structure. The single-mode fiber is connected to the core of the dual-core fiber on the side without the trapezoidal slot. Another single-mode fiber is connected to the fiber optic circulator. The fiber optic circulator outputs two single-mode fibers, which are respectively connected to the narrow-linewidth single-wavelength laser and the photodetector.

[0014] The two single-mode optical fibers output by the 1×2 fiber coupler are respectively wound and connected to the thin-walled elastic tube, and both single-mode optical fibers output by the 1×2 fiber coupler are connected to the Faraday rotating mirror.

[0015] The single-mode optical fibers have a uniform core diameter, and the ratio of the wall thickness of the thin-walled elastic tube to the radius of the single-mode optical fiber is less than 1 / 10.

[0016] The narrow-linewidth single-wavelength laser has a center wavelength of 1550nm, an output power of 12.2mW, and a linewidth of 1.2kHz.

[0017] A method for fabricating an integrated fiber optic photoacoustic transceiver and fiber optic hydrophone device, the method comprising the following steps:

[0018] S1: Clean the surface of the dual-core optical fiber connected to the fan-in and fan-out modules, and use a femtosecond laser to engrave a smooth right-angled trapezoidal groove on the side of the dual-core optical fiber. The depth of the trapezoidal groove is exactly the position where the fiber core A in the dual-core optical fiber is cut off.

[0019] S2: Place the dual-core optical fiber in a magnetron sputtering instrument, deposit a metal reflective film on the top and bottom surfaces and the inclined surfaces of the trapezoidal groove, and uniformly mix the prepared PDMS polymer with the light-absorbing material to form a photoacoustic medium.

[0020] S3: Immerse the engraved dual-core optical fiber into the mixture, use the liquid tension to fill the trapezoidal groove with the mixture, then take out the dual-core optical fiber, remove the excess liquid acousto-optic material on the surface, and heat to solidify the mixture to form an absorption layer.

[0021] S4: On the single-mode fiber side of the fan-in fan-out module, adjust the position of the nanosecond pulse laser, lens, and quartz fiber so that the input laser can be stably coupled into the single-mode fiber A corresponding to the core A of the dual-core fiber.

[0022] S5: The laser beam enters the absorption layer through the optical fiber. The light irradiation energy is absorbed and converted into heat energy. Then, due to the thermoelastic effect of the absorption layer, it undergoes elastic expansion. When a pulsed laser is used as the light source, the heat generated is also modulated by the time interval of the pulse. During the interval between the transmission of two pulses, the absorption layer will contract due to the loss of heat. During the expansion and contraction of the material, ultrasonic waves are generated in the liquid environment.

[0023] When sound waves can propagate stably in the surrounding liquid medium, it means that the structure has become stable and the fiber optic photoacoustic transducer has been successfully fabricated.

[0024] S6: Connect port a of the fiber optic circulator to the narrow linewidth single-wavelength laser, and port b to the single-mode fiber B of the fan-in fan-out module. This single-mode fiber corresponds to core B in the dual-core fiber. Connect port c to the photodetector. Connect core B of the dual-core fiber to the single-mode fiber by core welding. Connect a 1×2 fiber coupler after the single-mode fiber.

[0025] S7: The two branches of the 1×2 fiber optic coupler serve as the reference arm and the sensing arm of the Michelson interference structure in the hydrophone. The sensing arm part is enhanced by wrapping the single-mode fiber around a thin-walled elastic tube, while the other branch serves as the reference arm and is not processed.

[0026] S8: Connect the ends of the reference arm and the sensing arm to the Faraday rotating mirror respectively, and encapsulate the hydrophone part with sound-transparent material.

[0027] S9: After all optical paths are working properly, test the hydrophone to see if it is functioning correctly. When the hydrophone can receive sound wave signals normally, it means that the fiber optic hydrophone is ready.

[0028] By combining a fiber optic optical transducer with a fiber optic hydrophone using a dual-core optical fiber and corresponding fan-in / fan-out modules, it is possible to achieve integrated transmission and reception, and the transmission and reception of acoustic signals can be carried out simultaneously without crosstalk between signals.

[0029] The technical effects achieved by this invention are as follows:

[0030] The present invention provides a transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device and preparation method, which combines a fiber optic hydrophone and a fiber optic photoacoustic transducer to achieve integrated sound wave transmission and reception, and the sound reception and transmission can be carried out simultaneously without crosstalk between them; adopting a reflective structure, the entire sensing structure does not form a loop, so the dry end and wet end can be remotely controlled; and the structure is simple, if damaged, only the underwater part needs to be replaced.

[0031] The present invention provides an integrated fiber optic photoacoustic transducer and fiber optic hydrophone device and its fabrication method, which can achieve integrated sound wave transmission and reception. It has a certain improvement in application scope compared with other similar devices. By using optical fiber as the carrier for transmitting light and exciting sound waves, compared with the photoacoustic transducer of spatial light, the structure is simpler, smaller, easier to integrate, and more flexible in application scenarios. Compared with traditional electroacoustic transducers, the use of optical fiber as the carrier for photoacoustic transducer has greatly reduced its size and greatly improved its anti-electromagnetic interference capability, enabling it to be applied to a wider range of fields. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the fiber optic photoacoustic transducer section of an embodiment of the present invention;

[0034] Figure 3 This is a partial schematic diagram of the fiber optic hydrophone according to an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the fiber optic hydrophone part of an embodiment of the present invention.

[0036] The attached diagram lists the components represented by each number as follows:

[0037] 1. Nanosecond pulsed laser; 2. Fan-in / fan-out module; 3. Dual-core fiber; 4. Fiber circulator; 5. Narrow linewidth single-wavelength laser; 6. Photodetector; 7. Absorption layer; 8. Fiber 1×2 coupler; 9. Metal reflective film; 10. Gold nanoparticles; 11. Thin-walled elastic tube; 12. Faraday rotation mirror. Detailed Implementation

[0038] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0039] Example 1:

[0040] like Figures 1-4 As shown, a transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device includes a fiber optic photoacoustic transducer and a fiber optic hydrophone. The fiber optic photoacoustic transducer includes a nanosecond pulsed laser 1, a lens, a fan-in fan-out module 2, and a dual-core fiber 3. A trapezoidal slot is opened on one side of the dual-core fiber 3, and an absorption layer 7 is uniformly filled in the trapezoidal slot. Each fiber core in the dual-core fiber 3 is an independent single-mode fiber, and one of the single-mode fibers is connected to the nanosecond pulsed laser 1 through the fan-in fan-out module 2.

[0041] Among them, the composite material of thermal expansion matrix material filled with uniformly distributed light-absorbing material in the trapezoidal groove serves as the absorption layer 7. Based on the light-absorbing material absorbing the excitation laser and converting light energy into heat energy, after the pulsed light enters the absorption layer 7, the light irradiation energy is absorbed by the absorption layer and converted into heat energy, causing its thermoelastic expansion, thereby converting the pulsed laser into an ultrasonic pulse.

[0042] The nanosecond pulsed laser 1 has a wavelength of 532nm, a pulse width of 10-200ns, a repetition frequency of 1-100kHz, and a power of 400-800mW. After being focused by a lens, the nanosecond pulsed laser 1 is coupled into the dual-core fiber 3 and the fan-in and fan-out module 2.

[0043] The ratio of PDMS matrix to curing machine used is 5:1, 10:1 or 20:1;

[0044] In this method, the irradiation energy of the laser, based on the resonant absorption of gold nanoparticles 10, is converted into heat energy. This heat energy is then absorbed by the PDMS matrix material of the absorption layer, causing it to expand thermoelastically. When a pulsed laser is used as the light source, the generated heat is also modulated by the pulse time interval. During the interval between two pulses, the absorption layer 7 contracts due to heat loss. During this expansion and contraction, an ultrasonic pulse signal is generated, which is also modulated by the pulsed laser source. Based on the Michelson interferometric fiber optic hydrophone, the narrow-linewidth single-wavelength laser used for detection is split into two beams after passing through a 1×2 fiber coupler 8. One beam enters the reference arm, and the other enters the sensing arm. When the acoustic signal acts on the sensing arm, the thin-walled elastic tube 11 expands and contracts under the influence of the acoustic wave, causing a change in the fiber length of the sensing arm. This alters the phase difference between the two arms, which is ultimately reflected in the reflected light intensity signal.

[0045] The trapezoidal slot is right-angled, with one side of the right-angled side of the trapezoidal slot serving as the input end of the nanosecond pulse laser 1. The hypotenuse and the upper bottom surface of the trapezoidal slot are reflective surfaces, and a metal reflective film 9 is coated on the reflective surface.

[0046] The metal reflective film 9 includes gold nanoparticles 10, which are used to absorb light irradiation energy, with a resonant absorption peak at 530-535 nm. Quantum dots, carbon nanotubes, and optical dyes can also be used as light-absorbing materials.

[0047] The fabrication process of the microlens fiber optic photoacoustic transducer is described below with reference to embodiments and accompanying drawings:

[0048] Turn on the nanosecond pulse laser 1, calibrate the position of the light source and lens, determine the optimal position for placing the optical fiber, and ensure that the laser can be stably coupled into the single-mode fiber A of the dual-core fiber.

[0049] Use fiber strippers to remove the coating from the middle section and end of the dual-core fiber 3. Clean the fiber surface with anhydrous ethanol. Use a fiber cleaver to cut the end of the fiber after removing the coating to ensure that the fiber end face is flat.

[0050] A right-angled trapezoidal groove is obtained by etching one side of the core A of the dual-core fiber 3 using a femtosecond laser. The top surface faces down. The size of the trapezoidal groove is designed to be a smooth right-angled trapezoidal groove with an upper base of about 20μm, a lower base of about 40μm, and a depth of about 36μm. The right-angled side is close to the fan-in and fan-out module 2, i.e. the laser incident end.

[0051] The etched optical fiber, with its trapezoidal groove facing the target, is placed in a magnetron sputtering instrument. The instrument is then activated to deposit a 300nm metal reflective film 9 on the top and inclined surfaces of the trapezoidal groove as a reflector. This reflects the perpendicularly incident light into the remaining absorption layer 7, improving the utilization rate of the laser.

[0052] A mixture of PDMS and light-absorbing materials was used as the absorbing material. PDMS has a high coefficient of thermal expansion, while the light-absorbing material has a high absorption capacity for light radiation energy at a specific wavelength, thus greatly improving the photoacoustic conversion efficiency. The PDMS matrix and curing agent were mixed in a ratio of 10:1 as the matrix material, and about 10% of the mass of the matrix material was added to form nano-gold particles with a particle size of 40-60 nm. The mixture was homogenized using an ultrasonic oscillator to complete the pre-preparation of the liquid absorbing layer material.

[0053] Under a microscope, a micro-manipulation robotic arm is used to control the dual-core optical fiber 3, immersing its trapezoidal groove into the absorption layer 7 material. Liquid tension is used to fill the trapezoidal groove with the liquid absorption layer 7 material. The robotic arm is then raised and cleaned with anhydrous ethanol to remove excess material. The optical fiber is kept horizontal and heated to solidify the absorption layer 7 material into a photoacoustic absorption layer 7.

[0054] Weld the fabricated dual-core optical fiber 3 to the fan-in / fan-out module 2, ensuring that the fiber cores are aligned during welding.

[0055] A nanosecond pulsed laser 1 is set up, and the laser is allowed to enter the core A of the dual-core optical fiber 3 through the fan-in and fan-out modules 2. The middle section of the quartz optical fiber generates stable ultrasonic waves that can be detected in the liquid environment, thus completing the fabrication of the microlens fiber photoacoustic transducer.

[0056] like Figure 1-4 As shown, the fiber optic hydrophone includes a fiber optic circulator 4, a narrow-linewidth single-wavelength laser 5, a photodetector 6, a fiber optic 1×2 coupler 8, a thin-walled elastic tube 11, and a Faraday rotating mirror 12. The hydrophone adopts a fiber optic Michelson interference structure. The single-mode fiber is connected to the core of the dual-core fiber 3 on the side without the trapezoidal slot, and another single-mode fiber is connected to the fiber optic circulator 4. The output of the fiber optic circulator 4 consists of two single-mode fibers that are connected to the narrow-linewidth single-wavelength laser 5 and the photodetector 6, respectively.

[0057] The two single-mode optical fibers output by the 1×2 fiber coupler 8 are respectively wound and connected to the thin-walled elastic tube 11, and both single-mode optical fibers output by the 1×2 fiber coupler 8 are connected to the Faraday rotating mirror 12.

[0058] Hydrophones are encapsulated using sound-permeable rubber materials. Common encapsulation materials include polyurethane elastomers, neoprene rubber, and butyl rubber.

[0059] A hydrophone structure is set in the sensing arm of the photodetector 6. When the sound wave signal being measured acts on the hydrophone structure, the length of the optical fiber in the sensing arm changes, so the phase difference between the two arms changes, and is ultimately reflected in the light intensity signal detected by the photodetector 6.

[0060] The core diameter of the single-mode fiber is uniform, and the ratio of the wall thickness of the thin-walled elastic tube 11 to the radius of the single-mode fiber is less than 1 / 10. This avoids generating unnecessary interference signals.

[0061] The narrow-linewidth single-wavelength laser 5 has a center wavelength of 1550nm, an output power of 12.2mW, and a linewidth of 1.2kHz.

[0062] The Michelson interferometer structure is used to make hydrophones. Because of the reflection structure, the sensitivity of the hydrophone is greatly improved. Alternatively, other structures such as the Sagnac interferometer structure, the MZ interferometer structure, or fiber optic gratings can also be used.

[0063] Thin-walled elastic tube 11 was used to make the sensing arm of the hydrophone. There are many types of thin-walled elastic tubes. By definition, tubes whose wall thickness to tube radius ratio is less than 1 / 10 can be called thin-walled tubes. All tubes made of elastic materials can be called elastic tubes. Common materials include PE, PU, ​​PVC, TPE, etc.

[0064] Example 2:

[0065] A method for fabricating an integrated fiber optic photoacoustic transceiver and fiber optic hydrophone device, the method comprising the following steps:

[0066] S1: Clean the surface of the dual-core optical fiber 3 connected to the fan-in fan-out module 2, and use a femtosecond laser to engrave the dual-core optical fiber 3. Engrav a smooth right-angled trapezoidal groove on the side of the dual-core optical fiber 3. The depth of the trapezoidal groove is exactly the position where the fiber core A in the dual-core optical fiber 3 is cut off.

[0067] S2: Place the dual-core optical fiber 3 in a magnetron sputtering instrument, deposit a metal reflective film 9 on the top and bottom surfaces and the inclined surfaces of the trapezoidal groove, and uniformly mix the prepared PDMS polymer with the light-absorbing material to form a photoacoustic medium.

[0068] S3: Immerse the engraved dual-core optical fiber 3 into the mixture, use the liquid tension to fill the trapezoidal groove with the mixture, then take out the dual-core optical fiber 3, remove the excess liquid acousto-optic material on the surface, and heat the mixture to solidify and form the absorption layer 7.

[0069] S4: On the single-mode fiber side of the fan-in fan-out module 2, adjust the position of the nanosecond pulse laser 1, the lens, and the quartz fiber so that the input laser can be stably coupled into the single-mode fiber A corresponding to the core A of the dual-core fiber 3.

[0070] S5: The laser beam enters the absorption layer 7 through the optical fiber. The light irradiation energy is absorbed and converted into heat energy. Then, due to the thermoelastic effect of the absorption layer 7, it undergoes elastic expansion. When a pulsed laser is used as the light source, the heat generated is also modulated by the time interval of the pulse. During the interval between the transmission of two pulses, the absorption layer 7 will contract due to the loss of heat. During the expansion and contraction of the material, ultrasonic waves are generated in the liquid environment.

[0071] When sound waves can propagate stably in the surrounding liquid medium, it means that the structure has become stable and the fiber optic photoacoustic transducer has been successfully fabricated.

[0072] S6: Connect port a of fiber optic circulator 4 to narrow linewidth single-wavelength laser 5, and port b to single-mode fiber B of fan-in fan-out module 2. This single-mode fiber corresponds to core B in dual-core fiber 3. Connect port c to photodetector 6. Connect core B of dual-core fiber 3 to single-mode fiber by core welding. Connect a fiber optic 1×2 coupler 8 after single-mode fiber.

[0073] S7: The two branches of the fiber optic 1×2 coupler 8 serve as the reference arm and the sensing arm of the Michelson interference structure in the hydrophone. The sensing arm part is enhanced by winding the single-mode fiber around the thin-walled elastic tube 11, while the other branch serves as the reference arm and is not processed.

[0074] S8: Connect the ends of the reference arm and the sensing arm to the Faraday rotating mirror 12 respectively, and encapsulate the hydrophone part with sound-transparent material.

[0075] S9: After all optical paths are working properly, test the hydrophone to see if it is functioning correctly. When the hydrophone can receive sound wave signals normally, it means that the fiber optic hydrophone is ready.

[0076] By using a dual-core optical fiber 3 and a corresponding fan-in / fan-out module 2, the fiber optic optical acoustic transducer and the fiber optic hydrophone are combined to achieve integrated transmission and reception, and the transmission and reception of acoustic signals can be carried out simultaneously without crosstalk between signals.

[0077] For the integrated fiber-optic photoacoustic transceiver and hydrophone prepared according to the above steps, the nanosecond pulse laser 1 emits laser light, which enters the core A of the dual-core fiber 3 through the fan-in and fan-out module 2. The absorption layer 7 absorbs the pulse light and expands and contracts, generating mechanical vibration and producing ultrasonic waves. The continuous light emitted by the narrow linewidth single-wavelength laser 5 enters the core B of the dual-core fiber 3 through the fan-in and fan-out module 2 and is continuously transmitted into the subsequent hydrophone section. The single-wavelength laser is split into two beams after passing through the fiber 1×2 coupler 8. One beam enters the reference arm and the other enters the sensing arm. When the acoustic signal acts on the sensing arm, the thin-walled elastic tube 11 expands and contracts under the action of the acoustic wave, which at the same time causes the fiber length of the sensing arm to change. Therefore, the phase difference between the two arms changes and is finally reflected in the reflected light intensity signal and detected by the photodetector 6.

[0078] Example 3:

[0079] Based on Examples 1-2, the light-absorbing material in the fiber optic photoacoustic transducer can be replaced with other absorbing materials:

[0080] Following steps S1-S4 in Example 2:

[0081] PDMS matrix and curing agent were mixed in a ratio of 20:1 to form the matrix material. Multi-arm carbon nanotubes with a diameter of about 10-20 nm were added, with a mass equivalent to about 10% of the matrix material. The mixture was then homogenized using an ultrasonic oscillator to complete the pre-preparation of the liquid absorption layer material.

[0082] Under a microscope, a micro-manipulation robotic arm is used to control the dual-core optical fiber 3, immersing its trapezoidal groove into the absorption layer material. Liquid tension is used to fill the trapezoidal groove with liquid absorption layer material. The robotic arm is then raised and cleaned with anhydrous ethanol to remove excess material. The optical fiber is kept horizontal and heated to solidify the absorption layer 7 material into photoacoustic absorption layer 7.

[0083] Weld the fabricated dual-core optical fiber 3 to the fan-in / fan-out module 2, ensuring that the fiber cores are aligned during welding.

[0084] A nanosecond pulsed laser 1 is set up, and the laser is allowed to enter the core A of the dual-core optical fiber 3 through the fan-in and fan-out modules 2. The middle section of the quartz optical fiber generates stable ultrasonic waves that can be detected in the liquid environment, thus completing the fabrication of the microlens fiber photoacoustic transducer.

[0085] The manufacturing process of the hydrophone part is carried out according to steps S6-S9 in Example 1.

[0086] The above embodiments provide a set of specific component parameters:

[0087] The dual-core optical fiber used in the above embodiments has a core diameter of 8.2 / 125, is based on an all-quartz optical fiber structure, has an 8.2μm core diameter, a 125μm cladding diameter, and a 62.5μm core-to-core spacing.

[0088] The gold nanoparticles 10 use particles with a diameter of 50 nm, and the corresponding absorption peak of the nanoparticles is at the position of 535 nm.

[0089] Multi-walled carbon nanotubes have a diameter of approximately 10-20 nm and an absorption rate of up to 99.5% in the ultraviolet and visible light bands, as well as 98% in the slightly longer wavelength bands and the far-infrared band.

[0090] The narrow-linewidth single-wavelength laser 5 has a center wavelength of 1550nm, an output power of 12.2mW, and a linewidth of 1.2kHz.

[0091] In Examples 1 and 2, the wavelength of nanosecond pulsed laser 1 is 532nm, its pulse width is 50ns, its repetition frequency is 10kHz, and its average power is 400-800mW.

[0092] In Example 3, the nanosecond pulse laser 1 has a wavelength of 1550nm, a pulse width of 50ns, a repetition frequency of 10kHz, and an average power of 300-600mW.

[0093] Thin-walled elastic tube 11 is a PE tube with an inner radius of 23mm, an outer radius of 25mm, a Young's modulus of 2.5GPa, and a Poisson's ratio of 0.37.

[0094] The encapsulation material used in this paper is JA-2 castable polyurethane sound-permeable rubber, which has good sound transmission, as well as low water permeability and water absorption.

[0095] The trapezoidal grooves on the side of the dual-core optical fiber 3 can be made by engraving the end face of the optical fiber with a femtosecond laser processing instrument, or by etching the optical fiber with a chemical reagent that can corrode glass (such as hydrofluoric acid) to make the grooves, or by polishing the side of the optical fiber. Any method that allows the pulsed laser to enter the absorption layer 7 is acceptable.

[0096] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device, characterized in that: The device includes a fiber optic photoacoustic transducer and a fiber optic hydrophone. The fiber optic photoacoustic transducer includes a nanosecond pulsed laser (1), a lens, a fan-in fan-out module (2), and a dual-core fiber (3). A trapezoidal slot is provided on one side of the dual-core fiber (3), and an absorption layer (7) is uniformly filled in the trapezoidal slot. Each fiber core in the dual-core fiber (3) is an independent single-mode fiber, and one of the single-mode fibers is connected to the nanosecond pulsed laser (1) through the fan-in fan-out module (2). The nanosecond pulse laser (1) has a wavelength of 532nm, a pulse width of 10-200ns, a repetition frequency of 1-100kHz, and a power of 400-800mW. The nanosecond pulse laser (1) is coupled into the dual-core fiber (3) and the fan-in and fan-out module (2) after being focused by a lens. The trapezoidal groove is right-angled, and one side of the right-angled side of the trapezoidal groove is the input end of the nanosecond pulse laser (1). The hypotenuse and the top surface of the trapezoidal groove are reflective surfaces, and a metal reflective film (9) is coated on the reflective surface. The metal reflective film (9) includes gold nanoparticles (10), which are used to absorb light irradiation energy and have a resonance absorption peak of 530-535 nm. The fiber optic hydrophone includes a fiber optic circulator (4), a narrow linewidth single-wavelength laser (5), a photodetector (6), a fiber optic 1×2 coupler (8), a thin-walled elastic tube (11), and a Faraday rotating mirror (12). The fiber optic hydrophone adopts a fiber optic Michelson interference structure. The single-mode fiber is connected to the core of the dual-core fiber (3) on the side without the trapezoidal slot. Another single-mode fiber is connected to the fiber optic circulator (4). The fiber optic circulator (4) outputs two single-mode fibers, which are respectively connected to the narrow linewidth single-wavelength laser (5) and the photodetector (6). The fiber optic 1×2 coupler (8) outputs two single-mode optical fibers which are respectively wound and connected to the thin-walled elastic tube (11). Both single-mode optical fibers output by the fiber optic 1×2 coupler (8) are connected to the Faraday rotating mirror (12). The ratio of the wall thickness of the thin-walled elastic tube (11) to the radius of the single-mode optical fiber is less than 1 / 10.

2. The fiber optic photoacoustic transceiver and fiber optic hydrophone device according to claim 1, characterized in that: The single-mode optical fibers have a uniform core diameter.

3. The fiber optic photoacoustic transceiver and fiber optic hydrophone device according to claim 1, characterized in that: The narrow linewidth single-wavelength laser (5) has a center wavelength of 1550nm, an output power of 12.2mW, and a linewidth of 1.2kHz.

4. A method for fabricating a transceiver integrated fiber optic photoacoustic transducer and fiber optic hydrophone device, characterized in that: The preparation method includes the following steps: S1: Clean the surface of the dual-core fiber (3) connected to the fan-in fan-out module (2), and use a femtosecond laser to carve the dual-core fiber (3) to carve a smooth right-angled trapezoidal groove on the side of the dual-core fiber (3). The depth of the trapezoidal groove is just enough to cut off the fiber core A in the dual-core fiber (3). S2: Place the dual-core optical fiber (3) in a magnetron sputtering instrument, deposit a metal reflective film (9) on the top and bottom surfaces and the inclined surfaces of the trapezoidal groove, and uniformly mix the prepared PDMS polymer with the light-absorbing material to form a photoacoustic medium; S3: Immerse the engraved dual-core optical fiber (3) into the mixture, use the liquid tension to fill the trapezoidal groove, then take out the dual-core optical fiber (3), remove the excess liquid acousto-optic material on the surface, and heat the mixture to solidify and form an absorption layer (7). S4: On the single-mode fiber side of the fan-in fan-out module (2), adjust the position of the nanosecond pulse laser (1), lens and quartz fiber so that the input laser can be stably coupled into the single-mode fiber A corresponding to the core A of the dual-core fiber (3). S5: The laser enters the absorption layer (7) through the transmission of the optical fiber. The light irradiation energy is absorbed and converted into heat energy. Then, due to the thermoelastic effect of the absorption layer (7), elastic expansion occurs. When a pulsed laser is used as the light source, the heat generated will also be modulated by the time interval of the pulse. During the gap between the transmission of two pulses, the absorption layer (7) will shrink due to the loss of heat. During the expansion and contraction of the material, ultrasonic waves are generated in the liquid environment. When sound waves can propagate stably in the surrounding liquid medium, it means that the structure has become stable and the fiber optic photoacoustic transducer has been successfully fabricated. S6: Connect port a of the fiber circulator (4) to the narrow linewidth single-wavelength laser (5), and port b to the single-mode fiber B of the fan-in fan-out module (2). The single-mode fiber corresponds to the core B in the dual-core fiber (3). Port c is connected to the photodetector (6). The core B of the dual-core fiber (3) is connected to the single-mode fiber by core welding. A fiber 1×2 coupler (8) is connected to the single-mode fiber. S7: The two branches of the 1×2 fiber coupler (8) serve as the reference arm and the sensing arm of the Michelson interference structure in the hydrophone. The sensing arm part is enhanced by wrapping the single-mode fiber around the thin-walled elastic tube (11), while the other branch serves as the reference arm without any processing. S8: Connect the ends of the reference arm and the sensing arm to the Faraday rotating mirror (12) respectively, and encapsulate the hydrophone part with sound-transparent material; S9: After all optical paths are working properly, test the hydrophone to see if it is functioning correctly. When the hydrophone can receive sound wave signals normally, it means that the fiber optic hydrophone is ready.

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