A transceiver integrated optical fiber full-optical ultrasonic probe and a preparation method thereof

Abstract

This invention belongs to the field of ultrasonic transducer technology and discloses a transceiver integrated fiber optic all-optical ultrasonic probe and its fabrication method. The probe includes an optical fiber (1), a capillary tube (2), a plano-concave diaphragm (4), and a photoacoustic conversion layer (5). One end of the plano-concave diaphragm is concave, and the other end is planar, forming a closed FP cavity (3) with the optical fiber and capillary tube. The photoacoustic conversion layer can absorb the laser beam energy of the excitation light and convert it into ultrasonic waves, which are then emitted outwards to realize ultrasonic wave transmission. At the same time, the photoacoustic conversion layer can receive ultrasonic wave echoes and deform the plano-concave diaphragm according to the strength of the ultrasonic wave echoes, causing the cavity length of the FP cavity to change, thereby realizing the function of receiving and detecting sound waves. This invention utilizes a capillary tube and forms a plano-concave diaphragm at the end of the capillary tube, which on the one hand facilitates the miniaturization of the probe, and on the other hand significantly improves the reflection contrast of the FP cavity, thereby enhancing the detection performance.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic transducer technology, and more specifically, relates to a transceiver integrated fiber optic all-optical ultrasonic probe and its preparation method. Background Technology

[0002] A photoacoustic transducer is a device that converts light signals into ultrasonic signals through the photoacoustic effect. It features high-intensity, high-frequency, and wide-bandwidth ultrasound, making it promising for applications in ultrasound therapy and imaging. Furthermore, because photoacoustic transducers can be integrated into the end face of optical fibers, they offer flexibility, miniaturization, resistance to electromagnetic interference, and compatibility with other medical devices. Currently, most fiber-optic all-optical ultrasound transceivers employ a separate ultrasonic transmitting and receiving probe structure. However, this structure has drawbacks: the transmitting and receiving probes are not coaxial, resulting in an angle between the ultrasonic echo and the probe surface. When this structure is used for ultrasound imaging, additional correction processing of the received signal is required. Moreover, the structure lacks compactness, necessitating further encapsulation of the ultrasonic transmitting and receiving probes, further limiting the miniaturization of the entire transceiver.

[0003] Chinese patent CN111112035B discloses a transceiver integrated all-optical ultrasonic transceiver device and its fabrication method. While it also discloses a method for fabricating a miniaturized all-optical ultrasonic transceiver probe on the fiber end face, its specific structure involves inserting the optical fiber into a structured substrate and bonding a planar rigid substrate photoacoustic conversion film or a suspended photoacoustic conversion film to the other end of the structured substrate. The drawback of this method is that the miniaturization difficulty of the probe increases significantly as the size of the structured substrate decreases, and the stability of the bonding becomes highly challenging. Furthermore, when the device is used for receiving, both end faces of the FP cavity are planar, which is detrimental to improving the contrast of the FP cavity's reflection spectrum. This is why the patent specifically increases the contrast of the FP cavity by depositing a metal film on the inner wall of the FP cavity. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a transceiver integrated fiber optic all-optical ultrasonic probe and its fabrication method. Improvements are made to the structure of each component and their cooperative operation. A capillary tube is utilized, with a plano-concave diaphragm formed at its end. This facilitates probe miniaturization and significantly improves the reflection contrast of the FP cavity, thereby enhancing detection performance. Furthermore, the fabrication method is convenient; by controlling the amount of polymer drawn into the capillary tube, the thickness of the plano-concave diaphragm can be controlled, thus regulating the ultrasonic receiving response of the probe.

[0005] To achieve the above objectives, according to one aspect of the present invention, a transceiver integrated fiber optic all-optical ultrasonic probe is provided, characterized in that it comprises an optical fiber (1), a capillary tube (2), a plano-concave diaphragm (4), and a photoacoustic conversion layer (5) tightly connected to the planar end of the plano-concave diaphragm (4), wherein the optical fiber (1) is used to simultaneously transmit excitation light and probe light, and the excitation light can pass through the plano-concave diaphragm (4); one end of the plano-concave diaphragm (4) is concave and the other end is planar; the optical fiber (1) is inserted and fixed into the capillary tube (2) and cooperates with the plano-concave diaphragm (4) located at the end of the capillary tube (2), thereby forming a closed FP cavity (3); correspondingly, the two end faces of the FP cavity (3) are the output end face of the optical fiber (1) and the concave end face of the plano-concave diaphragm (4), respectively; the plano-concave diaphragm (4) can improve the reflection spectral contrast of the FP cavity;

[0006] The photoacoustic conversion layer (5) can absorb the laser beam energy of the excitation light and convert it into ultrasonic waves and emit them outward, realizing the function of transmitting ultrasonic waves in the integrated transceiver fiber optic all-optical ultrasonic probe. At the same time, the photoacoustic conversion layer (5) can receive ultrasonic echoes and deform according to the strength of the ultrasonic echoes, thereby causing the plano-concave diaphragm (4) to deform and the cavity length of the FP cavity (3) to change, thereby further affecting the returned detection light signal. By detecting the returned detection light signal, the function of receiving sound waves in the integrated transceiver fiber optic all-optical ultrasonic probe can be realized.

[0007] As a further preferred embodiment of the present invention, the plano-concave diaphragm (4) is obtained by drawing liquid polymer into the capillary tube (2) based on the capillary effect and then solidifying it;

[0008] The liquid polymer is capable of wetting the capillary; preferably, the polymer is polydimethylsilane (PDMS) or UV adhesive, preferably UV adhesive.

[0009] As a further preferred embodiment of the present invention, the inner diameter of the capillary (2) at the connection point with the optical fiber (1) is greater than or equal to the outer diameter of the optical fiber (1), and the difference between the two diameters is not greater than 1 mm.

[0010] The optical fiber (1) is a single double-clad optical fiber, wherein the core is used to transmit probe light and the inner cladding is used to transmit excitation light; or, the optical fiber (1) is an optical fiber bundle composed of multiple optical fibers, wherein one optical fiber in the optical fiber bundle is used to transmit probe light and the remaining optical fibers are used to transmit excitation light.

[0011] Preferably, the optical fiber (1) is a single double-clad optical fiber.

[0012] As a further preferred embodiment of the present invention, the capillary (2) is a single capillary or a combination capillary obtained by nesting multiple capillary tubes of matching sizes together.

[0013] The capillary tube (2) is made of glass, polymer or metal, preferably quartz.

[0014] As a further preferred embodiment of the present invention, the end of the capillary (2) is a plane perpendicular to its length direction;

[0015] The end of the capillary (2) is a plane perpendicular to its length direction, or an inclined plane that is not at a 90-degree angle to its length direction.

[0016] As a further preferred embodiment of the present invention, the photoacoustic conversion layer (5) is a composite film composed of a metal-based thin film or a light-absorbing micro / nano structure material and a flexible polymer, wherein the light-absorbing micro / nano structure material is a carbon-based micro / nano structure material, a metal-based micro / nano structure material, or a disulfide material with a micro / nano structure; the carbon-based micro / nano structure material is preferably selected from thin-film carbon nanotubes, carbon black particles, slag nanoparticles (CSNPs), graphene, or carbon fibers; the metal-based micro / nano structure material is preferably selected from metal nanoparticles, metal nanofilms, or metal nanoarrays; the disulfide material with a micro / nano structure is preferably selected from granular or sheet-like molybdenum disulfide or tungsten disulfide;

[0017] Preferably, the photoacoustic conversion layer (5) is a composite photoacoustic conversion layer composed of slag particles (CSNPs) and polydimethylsilane (PDMS).

[0018] As a further preferred embodiment of the present invention, for the photoacoustic conversion layer (5), the end face of the photoacoustic conversion layer (5) that is in close contact with the plano-concave diaphragm (4) is a plane, and the other end face is a convex surface, a concave surface, a parallel plane or an inclined plane, thereby obtaining a plano-convex, plano-concave, plano-flat or wedge-shaped structure.

[0019] Preferably, the photoacoustic conversion layer (5) has a plano-convex structure, which can act as a plano-convex acoustic lens to focus the ultrasonic waves emitted by the probe.

[0020] According to another aspect of the present invention, the present invention provides a method for manufacturing the above-mentioned transceiver integrated fiber optic all-optical ultrasonic probe, characterized by comprising the following steps:

[0021] (1) Place the substrate above the candle flame core and vapor-deposit candle ash particles (CSNPs);

[0022] (2) A capillary tube with an inner diameter matching the outer diameter of the optical fiber is vertically clamped on a displacement platform, and polymer droplets are dropped onto the CSNPs layer obtained in step (1), with the center of the droplets directly below the capillary tube. The displacement platform is adjusted so that the capillary tube descends to contact the substrate on which the CSNPs are attached. At this time, the polymer droplets will enter the capillary tube under the action of capillary effect and form a concave liquid surface. After the liquid surface stabilizes, it is cured to obtain a flat concave structure.

[0023] (3) After curing, the capillary is peeled off from the substrate with the CSNPs layer attached, and the plano-concave diaphragm fixedly connected to the capillary and the planar end of the plano-concave diaphragm are obtained.

[0024] (4) Immerse the plano-concave diaphragm located in the capillary into the defoamed liquid PDMS prepolymer, coat it with a layer of PDMS prepolymer, and then stand it vertically on another clean substrate so that the end coated with PDMS prepolymer is in direct contact with the substrate. Then cure it and demold it to obtain a composite photoacoustic conversion layer that is tightly attached to the end face of the capillary. Accordingly, the composite photoacoustic conversion layer is a planar structure, and the end face that is tightly attached to the plano-concave diaphragm is a plane, and the other end face is a plane parallel to it.

[0025] Alternatively, the plano-concave diaphragm located inside the capillary can be immersed in defoamed liquid PDMS prepolymer, coated with a layer of PDMS prepolymer, and then vertically suspended and cured to obtain a composite photoacoustic conversion layer that is tightly attached to the end face of the capillary. Accordingly, the composite photoacoustic conversion layer has a plano-convex structure, with the end face that is tightly attached to the plano-concave diaphragm being flat and the other end face being convex.

[0026] Alternatively, the plano-concave diaphragm located inside the capillary is immersed in defoamed liquid PDMS prepolymer, coated with a layer of PDMS prepolymer, and then placed on a clean substrate at a non-90° angle, so that the end coated with PDMS prepolymer is in direct contact with the substrate. After curing and demolding, a composite photoacoustic conversion layer tightly attached to the end face of the capillary is obtained. Accordingly, the composite photoacoustic conversion layer has a planar structure, with the end face tightly attached to the plano-concave diaphragm being a plane, and the other end face being a plane with a corresponding tilt angle.

[0027] Alternatively, the plano-concave diaphragm located inside the capillary is immersed in defoamed liquid PDMS prepolymer, coated with a layer of PDMS prepolymer, and then placed on a clean spherical base, with one end coated with PDMS prepolymer in direct contact with the spherical base. After curing and demolding, a composite photoacoustic conversion layer tightly attached to the end face of the capillary is obtained. Accordingly, the composite photoacoustic conversion layer has a planar structure, with the end face tightly attached to the plano-concave diaphragm being planar, and the other end face being a concave surface with the same radius of curvature as the base.

[0028] (5) Insert the optical fiber from the open end of the capillary tube. Adjust the initial cavity length of the FP cavity by controlling the insertion depth of the optical fiber. After adjusting the initial cavity length of the FP cavity, fix the optical fiber and the capillary tube to keep their relative positions fixed. This will give you a transceiver integrated fiber optic all-optical ultrasonic probe.

[0029] As a further preferred embodiment of the present invention, in step (1), the glass slide is specifically placed 1.5cm to 3cm above the candle flame core, and the vapor deposition time is 5-40s;

[0030] In step (4), the curing process specifically involves curing at 75℃~85℃ for 2h~4h.

[0031] In step (2), the polymer droplets are specifically UV adhesive droplets.

[0032] According to another aspect of the present invention, the present invention provides a transceiver integrated fiber optic all-optical ultrasonic probe, characterized in that it includes an optical fiber (1), a capillary tube (2), and an integrally formed plano-concave photoacoustic conversion layer, wherein the optical fiber (1) is used to transmit excitation light and probe light simultaneously; one end of the plano-concave photoacoustic conversion layer is concave and the other end is planar; the optical fiber (1) is inserted and fixed into the capillary tube (2) and cooperates with the plano-concave photoacoustic conversion layer located at the end of the capillary tube (2), thereby forming a closed FP cavity (3); correspondingly, the two end faces of the FP cavity (3) are the output end face of the optical fiber (1) and the concave end face of the plano-concave photoacoustic conversion layer, respectively; by setting the plano-concave end face of the plano-concave photoacoustic conversion layer, the reflection spectrum contrast of the FP cavity can be improved;

[0033] The plano-concave photoacoustic conversion layer can absorb the laser beam energy of the excitation light and convert it into ultrasonic waves and emit them outward, realizing the function of transmitting ultrasonic waves in the transceiver fiber optic all-optical ultrasonic probe. At the same time, the plano-concave photoacoustic conversion layer can receive ultrasonic echoes and deform according to the strength of the ultrasonic echoes, thereby changing the cavity length of the FP cavity (3), which further affects the back-transmitted probe light signal. By detecting the back-transmitted probe light signal, the function of receiving sound waves in the transceiver fiber optic all-optical ultrasonic probe can be realized.

[0034] Preferably, an additional photoacoustic conversion layer with a planar, convex, planar, or wedge-shaped structure is provided on the planar end face of the planar photoacoustic conversion layer.

[0035] Compared with existing technologies, the technical solution conceived in this invention utilizes a capillary tube. One end of the capillary tube is embedded with an optical fiber, while at the other end, a polymer is drawn into the capillary tube through capillary action and solidifies to form a plano-concave diaphragm. The optical fiber, capillary tube, and the concave surface of the plano-concave diaphragm work together to form a plano-concave (FP) cavity. The two reflective surfaces of this FP cavity are the end face of the optical fiber and the concave surface of the plano-concave diaphragm. This concave reflective surface significantly improves the reflection contrast of the FP cavity and also provides a certain degree of divergence for the excitation light, increasing the effective area of ​​the photoacoustic effect and enlarging the area of ​​the sound source. Furthermore, by nesting a capillary tube outside the optical fiber, this invention facilitates probe miniaturization. The probe in this invention can not only be used independently as an ultrasonic transmitting or detecting device, but also perform in-situ reception and detection of its own emitted ultrasonic echo signal, achieving self-transmission and self-reception functionality.

[0036] This invention constructs a plano-concave cavity (FP cavity) by setting a plano-concave structure (such as a plano-concave diaphragm or a plano-concave photoacoustic conversion layer), which can improve the reflectance spectral contrast of the FP cavity and give the probe better ultrasound detection performance. The transceiver integrated all-optical ultrasound probe of this invention is integrated on the end face of the optical fiber, combining flexibility and miniaturization, and is suitable for intravascular ultrasound imaging. The size of the capillary assembly matches the optical fiber, making the probe structure compact and stable.

[0037] The use of the aforementioned plano-concave structure not only improves the sensitivity of the ultrasonic probe, but also facilitates probe miniaturization, especially since the plano-concave structure in this invention can be fabricated based on the capillary effect. The transceiver-integrated all-optical ultrasonic probe of this invention is fabricated by drawing a polymer into one end of a capillary tube using the capillary effect to form a plano-concave polymer diaphragm. A photoacoustic conversion layer is then fabricated on the planar end of this diaphragm for ultrasonic transmission. Finally, the optical fiber and capillary tube are assembled, enabling simultaneous ultrasonic transmission and reception on a single optical fiber, making fabrication convenient. In other words, the plano-concave diaphragm can be formed by solidifying a liquid polymer drawn into a capillary tube through the capillary effect.

[0038] The existing technology CN111112035B uses a structured substrate to connect the diaphragm and optical fiber. One end of the substrate has the optical fiber inserted, and the other end connects to the planar diaphragm and the photoacoustic conversion film. A flat-flat FP cavity structure is formed between the end face of the optical fiber and the planar diaphragm. The outer diameter of the structured substrate determines the overall size of the device. If the wall thickness of the structured substrate is too small (the smaller the external dimensions), the contact area between the planar diaphragm and the structured substrate is less, making it difficult to adhere and form a stable device structure. In other words, in the prior art, the suspended membrane needs to be connected to the end face of the structured substrate. To form a stable device structure, the structured substrate and the suspended membrane must be tightly connected. Given that the inner dimensions of the structured substrate match the outer diameter of the optical fiber, the overall size of the device depends on the outer dimensions of the structured substrate. The larger the outer dimensions of the structured substrate, the larger the contact area between the suspended membrane and the structured substrate, resulting in a more robust device, but also a larger device size. Conversely, the smaller the outer dimensions of the structured substrate, the smaller the contact area between the structured substrate and the suspended membrane, making it more difficult to achieve a tight connection, which is detrimental to device miniaturization. However, this invention, based on the capillary effect, allows the plano-concave diaphragm and photoacoustic conversion layer formed through the capillary effect to form a very tight connection with the capillary (regardless of the capillary wall thickness), resulting in high stability and facilitating probe miniaturization.

[0039] Furthermore, since the mechanical properties of a plano-concave diaphragm are determined by parameters such as its thickness, diameter, and Young's modulus, the diameter of the plano-concave diaphragm is also determined when the inner diameter of the capillary is fixed. In this case, the thickness of the plano-concave diaphragm can be controlled by the amount of polymer absorbed (for example, the height of the liquid level rise can be controlled by controlling the amount of UV adhesive dropped onto the CSNPs layer). The thicker the plano-concave diaphragm, the smaller its diameter, or the larger its Young's modulus, the higher its frequency response. Based on this application, these parameters can be flexibly adjusted according to different practical needs, such as adjusting the ultrasonic receiving response frequency of the ultrasonic probe to meet the operating frequency requirements of different application scenarios.

[0040] Furthermore, for the transceiver integrated all-optical ultrasonic probe of the present invention, the plano-concave diaphragm and the photoacoustic conversion layer can also be made of the same material. For example, metal particles or carbon-based micro-nano particles used to absorb pulsed laser energy can be uniformly mixed with polymers, and then drawn into a capillary tube through capillary effect. The resulting plano-concave structure can serve as both the diaphragm of the FP cavity and the photoacoustic conversion layer, absorbing the energy of the excitation light and radiating ultrasonic waves through the photoacoustic effect. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the transceiver integrated all-optical ultrasonic probe provided in Embodiment 1 of the present invention.

[0042] Figure 2This is an experimental result diagram of the transceiver integrated all-optical ultrasonic probe obtained in Embodiment 1 of the present invention, showing the change of the probe light signal with the change of the distance between the probe surface and the glass plate surface (i.e., the change of the probe light intensity detected by the optical power meter when the distance between the probe and the reflective surface changes).

[0043] Figure 3 This is a schematic diagram of the transceiver integrated all-optical ultrasonic probe provided in Embodiment 2 of the present invention.

[0044] Figure 4 The diagram below shows the structure of the all-optical ultrasonic transceiver integrated with Comparative Example 1.

[0045] Figure 5 The image shows the reflection spectrum of the transceiver-integrated all-optical ultrasonic probe obtained in Comparative Example 1.

[0046] Figure 6 This is the reflection spectrum of the transceiver integrated all-optical ultrasonic probe obtained in Embodiment 1 of the present invention.

[0047] Figure 7 This is a schematic diagram of the structure of the all-optical ultrasonic transceiver integrated with the present invention.

[0048] The meanings of the labels in the figure are as follows: 1 is optical fiber, 2 is capillary, 3 is FP cavity, 4 is plano-concave diaphragm, 5 is photoacoustic conversion layer (corresponding to plano structure), 6 is outer capillary, and 7 is the protruding part of the photoacoustic conversion layer of plano-convex structure (i.e., the PDMS protruding part). Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0050] In summary, the transceiver integrated fiber optic all-optical ultrasonic probe of this invention, such as Figure 7 As shown, the device includes an optical fiber 1 for transmitting excitation and probe light, which is tightly connected from left to right. The optical fiber 1 is inserted into a capillary tube 2, and the two fit together tightly. At the right end of the capillary tube 2 is a plano-concave diaphragm 4 formed by the polymer being drawn into the capillary tube through the capillary effect and then solidified. The optical fiber 1, the capillary tube 2, and the plano-concave diaphragm 4 fit together to form a closed FP cavity 3. At the right end face of the plano-concave diaphragm and the capillary tube is a photoacoustic conversion layer 5 that is tightly connected.

[0051] This probe structure can generate and detect ultrasonic waves. Its operation is as follows: When emitting ultrasonic waves, the pulsed excitation light exits from the fiber end face, passes through the FP cavity 3 and the flat-concave diaphragm 4, and reaches the photoacoustic conversion layer 5 (the flat-concave diaphragm 4 is transparent to the excitation light, allowing it to pass through before reaching the photoacoustic conversion layer). The photoacoustic conversion layer 5 absorbs the energy of the pulsed laser and radiates ultrasonic waves through the photoacoustic effect. When detecting ultrasonic waves, the reflected ultrasonic signal exerts pressure on the photoacoustic conversion layer 5, which is then transmitted to the flat-concave diaphragm 4, causing it to deform. Considering that the exit end face of the fiber 1 and the concave surface of the flat-concave diaphragm 4 constitute the two reflecting end faces of the FP cavity, the deformation of the flat-concave diaphragm 4 due to pressure causes a change in the cavity length of the FP cavity, resulting in a corresponding change in the intensity of the detection light, thus achieving ultrasonic wave detection.

[0052] Of course, the plano-concave diaphragm 4 and the photoacoustic conversion layer 5 can also be combined to form an integrated plano-concave photoacoustic conversion layer.

[0053] Taking a composite photoacoustic conversion layer composed of CSNPs and PDMS as an example, the following is a specific embodiment:

[0054] Example 1

[0055] like Figure 1 As shown, the transceiver integrated all-optical ultrasonic probe in this embodiment includes: an optical fiber 1, a capillary (in this embodiment, it is formed by nesting an inner capillary 2 and an outer capillary 6), an air FP cavity 3, a plano-concave diaphragm 4, and a photoacoustic conversion layer 5. The optical fiber 1 is a double-clad optical fiber; the inner cladding transmits pulsed excitation light with a wavelength of 532 nm, and the core transmits probe light with a wavelength of 1550 nm. The outer diameter of the double-clad optical fiber is 0.245 mm. The inner capillary has an inner diameter of 0.25 mm, an outer diameter of 0.6 mm, and a length of 10 mm; the outer capillary has an inner diameter of 0.6 mm, an outer diameter of 1 mm, and a length of 6 mm. The optical fiber 1 is nested within the inner capillary 2, which is nested within the outer capillary 6. The other end of the outer capillary 6 is used to fabricate the plano-concave diaphragm 4 and the photoacoustic conversion layer 5. The specific fabrication process is as follows:

[0056] (1) Place the glass slide 2 cm above the candle flame core and vapor-deposit candle ash particles (CSNPs) for 15 s.

[0057] (2) The outer capillary is vertically clamped on the displacement platform, and a drop of UV adhesive is dropped onto the CSNPs layer prepared in step (1). The center of the droplet is directly below the capillary. The displacement platform is adjusted so that the outer capillary descends to contact the glass slide with the attached CSNPs. At this time, the UV adhesive will enter the outer capillary due to the capillary effect. The liquid surface is concave. The height of the liquid surface rise can be controlled by the amount of UV adhesive dropped on the CSNPs layer. After the liquid surface stabilizes, ultraviolet light is vertically irradiated above the outer capillary to cure the UV adhesive in the capillary, forming a flat-concave structure. The minimum thickness of the flat-concave structure is measured to be 0.455 mm.

[0058] (3) Peel the cured capillary off the glass slide with the CSNPs layer attached. You can see that the CSNPs are also stably attached to the UV glue and the end face of the capillary, forming a circular CSNPs layer area with the same outer diameter (1 mm) as the capillary.

[0059] (4) Immerse the candle ash layer area in the defoamed liquid PDMS prepolymer, coat it with a layer of PDMS, stand it vertically on a clean glass slide, with the PDMS-coated end in direct contact with the glass slide, and place it in an oven at 75°C for 4 hours to cure. Demolding will yield a composite photoacoustic conversion layer composed of CSNPs and PDMS that are tightly bonded to the capillary end face.

[0060] (5) Insert the inner capillary into the outer capillary, so that the distance between the insertion end of the inner capillary and the UV adhesive diaphragm is about 2mm. Then apply adhesive to the junction of the inner capillary and the outer capillary and cure it.

[0061] (6) Insert the double-clad optical fiber from the open end of the inner capillary. Adjust the initial cavity length of the FP cavity by controlling the insertion depth of the optical fiber. After adjusting the initial cavity length and reflection spectrum of the FP cavity (i.e., adjusting to the optimal position, at which point the contrast of the reflection spectrum of the FP cavity is the highest), apply adhesive to the junction of the optical fiber and the outer part of the inner capillary to solidify and form a stable probe structure. This completes the fabrication of the transceiver integrated all-optical ultrasonic probe.

[0062] The performance of the transceiver-integrated all-optical ultrasonic probe was characterized according to the parameters in the above embodiments. The excitation light, after passing through the coupler, enters the inner cladding of the double-clad fiber and propagates. After passing through the FP cavity and the plano-concave diaphragm, it reaches the photoacoustic conversion layer. The photoacoustic conversion layer absorbs the energy of the pulsed laser and generates ultrasonic waves through the photoacoustic effect. A glass plate perpendicular to the propagation direction is placed in the ultrasonic wave propagation path. The ultrasonic wave emitted by the probe undergoes total internal reflection at this glass plate, and the reflected ultrasonic wave propagates in the opposite direction to the emitted ultrasonic wave to the probe surface. The reflected ultrasonic signal exerts a vertical pressure on the probe surface. This pressure, after passing through the photoacoustic conversion layer 5, acts on the plano-concave diaphragm 4, causing the plano-concave diaphragm 4 to shift. This changes the cavity length of the FP cavity 3, leading to a change in the intensity of the probe light. Figure 2 The variation of the detected optical signal with the distance between the probe surface and the glass plate surface is shown. It can be seen that as the distance between the probe and the glass plate surface increases, the detected optical signal travels further in time and its amplitude decreases. The experimental results verify the feasibility of this transceiver-integrated all-optical ultrasonic probe.

[0063] Example 2

[0064] like Figure 3 As shown, the transceiver integrated all-optical ultrasonic probe in this embodiment includes: optical fiber 1, capillary tube 2, air FP cavity 3, plano-concave diaphragm 4, photoacoustic conversion layer 5, and PDMS protrusion 7 (the photoacoustic conversion layer 5 and the PDMS protrusion 7 together constitute a plano-convex photoacoustic conversion layer). Optical fiber 1 is a double-clad optical fiber; the inner cladding transmits pulsed excitation light with a wavelength of 532 nm, and the core transmits probe light with a wavelength of 1550 nm. The outer diameter of the double-clad optical fiber is 0.245 mm. The capillary tube has an inner diameter of 0.25 mm, an outer diameter of 0.7 mm, and a length of 10 mm. Optical fiber 1 is nested within capillary tube 2. The other end of capillary tube 2 is used to fabricate the plano-concave diaphragm 4 and the photoacoustic conversion layer 5. A PDMS plano-convex structure is located outside the photoacoustic conversion layer, serving as a thermal expansion layer and a focusing acoustic lens for photoacoustic conversion. The specific fabrication process is as follows:

[0065] (1) Place the glass slide 2cm above the candle flame core and vapor-deposit candle ash particles (CSNPs) for 20s.

[0066] (2) The outer capillary is vertically clamped on the displacement platform, and a drop of UV adhesive is dropped onto the CSNPs layer prepared in step (1). The center of the droplet is directly below the capillary. The displacement platform is adjusted so that the outer capillary descends to contact the glass slide with the attached CSNPs. At this time, the UV adhesive will enter the capillary due to the capillary effect, and the liquid surface is concave. The height of the liquid surface rise can be controlled by the amount of UV adhesive dropped on the CSNPs layer. After the liquid surface stabilizes, ultraviolet light is vertically irradiated above the outer capillary to cure the UV adhesive in the capillary, forming a flat-concave structure. The minimum thickness of the flat-concave structure is measured to be 0.6 mm.

[0067] (3) Peel the cured capillary off the glass slide with the CSNPs layer attached. You can see that the CSNPs are also stably attached to the UV glue and the end face of the capillary, forming a circular CSNPs layer area with the same outer diameter (0.7 mm) as the capillary.

[0068] (4) Immerse the area of ​​the candle ash layer in the defoamed liquid PDMS prepolymer, coat it with a layer of PDMS, stand it vertically on a clean glass slide, with the end coated with PDMS in direct contact with the glass slide, and place it in an oven at 75°C for 4 hours to cure.

[0069] (5) Peel the capillary off the glass to obtain a probe with a flat transmitting end face. Then immerse it in the defoamed liquid PDMS prepolymer, coat it with a small amount of PDMS, and place it in an oven at 75°C for 1 hour to cure. The PDMS end is suspended with the PDMS facing down. Under the action of the gravity of PDMS, a flat-convex PDMS structure is formed on the probe end face.

[0070] (6) Insert the double-clad optical fiber from the open end of the capillary tube. Adjust the initial cavity length of the FP cavity by controlling the insertion depth of the optical fiber. After adjusting the initial cavity length and reflection spectrum value of the FP cavity (i.e., adjusting to the optimal position, at which point the contrast of the reflection spectrum of the FP cavity is the highest), apply adhesive to the junction of the optical fiber and the outside of the capillary tube to solidify and form a stable probe structure. This completes the preparation of the transceiver integrated all-optical ultrasonic probe.

[0071] The performance of the transceiver-integrated all-optical ultrasonic probe was characterized according to the parameters in the above embodiments. The excitation light, after passing through a coupler, enters the inner cladding of a double-clad fiber and propagates through the FP cavity and plano-concave diaphragm before reaching the photoacoustic conversion layer. The photoacoustic conversion layer absorbs the energy of the pulsed laser and generates ultrasonic waves through the photoacoustic effect. A glass plate perpendicular to the propagation direction is placed along the ultrasonic wave's transmission path. The ultrasonic wave emitted by the probe undergoes total internal reflection at this glass plate, and the reflected ultrasonic wave propagates in the opposite direction to the emitted ultrasonic wave to the probe surface. The reflected ultrasonic signal exerts a vertical pressure on the probe surface. This pressure, after passing through the photoacoustic conversion layer 5, acts on the plano-concave diaphragm 4, causing the plano-concave diaphragm 4 to shift. This changes the cavity length of the FP cavity 3, leading to a change in the intensity of the detected light. Experimental results show that as the distance between the probe and the glass plate surface increases, the detected optical signal travels further in time and its amplitude decreases. The experimental results verify the feasibility of this transceiver-integrated all-optical ultrasonic probe.

[0072] Comparative Example 1

[0073] To analyze the effect of plano-concave diaphragms, the inventors designed this comparative example.

[0074] like Figure 4 As shown, the transceiver integrated all-optical ultrasonic probe in this comparative example includes an optical fiber 1, a capillary tube 2, an air FP cavity 3, and a photoacoustic conversion layer 5 tightly connected to the capillary end face, without a plano-concave diaphragm. The optical fiber 1 is a double-clad fiber; the inner cladding transmits pulsed excitation light with a wavelength of 532 nm, and the core transmits probe light with a wavelength of 1550 nm. The outer diameter of the double-clad fiber is 0.245 mm. The capillary has an inner diameter of 0.25 mm, an outer diameter of 2 mm, and a length of 10 mm. The optical fiber 1 is nested within the capillary tube 2, and the other end of the capillary tube 2 is used to bond the photoacoustic conversion layer 5. The specific fabrication process is as follows:

[0075] (1) Spin-coat a layer of PDMS prepolymer onto a clean glass slide, then place the glass slide 2.5cm directly above the flame core of the candle flame with the side of the PDMS spin-coated facing the flame direction, vapor-deposit candle ash particles CSNPs for 15s, and then place it in an oven at 75℃ for 4h to cure.

[0076] (2) Use a blade to peel off a piece of the cured CSNPs / PDMS composite photoacoustic film with an area of ​​2.2mm×2.2mm (flat structure), and use UV glue to bond it to the end face of the capillary. It can be used as a photoacoustic conversion film to emit ultrasound and FP cavity diaphragm to receive ultrasound.

[0077] (3) Insert the double-clad optical fiber into the open end of the capillary. The end face of the double-clad optical fiber and the photoacoustic conversion film form the two reflecting surfaces of the FP cavity. The reflection spectrum of the FP cavity length is adjusted by controlling the insertion depth of the optical fiber. After adjusting to the optimal position (when the contrast of the FP cavity reflection spectrum is the highest), apply adhesive to the outer junction of the double-clad optical fiber and the capillary to solidify and form a stable probe structure.

[0078] The transceiver-integrated all-optical ultrasonic probe prepared by this method has two planar reflective end faces of its FP cavity, and its reflection spectrum is as follows: Figure 5 As shown, the contrast ratio is approximately 6 dB. In contrast, the reflectance spectral contrast ratio in Example 1 exceeds 20 dB (e.g., Figure 6 As shown in the figure, the presence of a plano-concave diaphragm can improve the sensitivity of the ultrasonic probe.

[0079] In summary, it is easy to see that the transceiver integrated all-optical ultrasonic probe of the present invention, compared with previous achievements (Chinese Patent CN111112035B), not only has a greatly optimized manufacturing method, making the probe easier to miniaturize, but also, based on the unique plano-concave diaphragm structure formed by capillary effect, can greatly increase the contrast of the FP cavity reflection spectrum on the probe, thereby greatly improving the sensitivity of ultrasonic reception.

[0080] The above embodiments are merely examples. For instance, in addition to flat and flat-convex photoacoustic conversion layers, other shapes such as flat-concave and wedge-shaped (with inclined end faces) photoacoustic conversion layers can be used according to actual needs (this is because sound waves radiate along the normal direction of the end face, and different end face shape designs, such as convex, concave, planes parallel to the previous end face, and planes at a certain angle to the previous end face, can correspond to different sound wave radiation directions).

[0081] In addition, since the inner diameter of the capillary is generally no more than 2 mm, based on the present invention, the overall cross-sectional diameter of the probe can be as low as a few millimeters (taking Example 1 as an example, its maximum cross-sectional diameter corresponds to the outer diameter of the outer capillary, i.e., 1 mm), which fully meets the miniaturization requirements.

[0082] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A transceiver integrated fiber optic all-optical ultrasonic probe, characterized in that, The device includes an optical fiber (1), a capillary tube (2), a plano-concave diaphragm (4), and a photoacoustic conversion layer (5) tightly connected to the planar end of the plano-concave diaphragm (4). The optical fiber (1) is used to transmit excitation light and probe light simultaneously, and the excitation light can pass through the plano-concave diaphragm (4). One end of the plano-concave diaphragm (4) is concave, and the other end is planar. The optical fiber (1) is inserted into and fixed in the capillary tube (2) and cooperates with the plano-concave diaphragm (4) located at the end of the capillary tube (2), thereby forming a closed FP cavity (3). Correspondingly, the two end faces of the FP cavity (3) are the output end face of the optical fiber (1) and the concave end face of the plano-concave diaphragm (4), respectively. The plano-concave diaphragm (4) can improve the reflection spectrum contrast of the FP cavity. The photoacoustic conversion layer (5) can absorb the laser beam energy of the excitation light and convert it into ultrasonic waves and emit them outward, realizing the function of transmitting ultrasonic waves in the integrated fiber optic all-optical ultrasonic probe. At the same time, the photoacoustic conversion layer (5) can receive ultrasonic echoes and deform according to the strength of the ultrasonic echoes, thereby causing the plano-concave diaphragm (4) to deform and the cavity length of the FP cavity (3) to change, thereby further affecting the back-transmitted detection light signal. By detecting the back-transmitted detection light signal, the function of receiving sound waves in the integrated fiber optic all-optical ultrasonic probe can be realized. The plano-concave diaphragm (4) is obtained by drawing liquid polymer into the capillary tube (2) based on the capillary effect and then solidifying it; The liquid polymer is capable of wetting capillaries and is either polydimethylsilane (PDMS) or UV adhesive. The transceiver integrated fiber optic all-optical ultrasonic probe is manufactured according to a method including the following steps: (1) Place the substrate above the candle flame core and vapor deposit candle ash particles (CSNPs); (2) A capillary tube with an inner diameter matching the outer diameter of the optical fiber is vertically clamped on a displacement platform, and polymer droplets are dropped onto the CSNPs layer obtained in step (1), with the center of the droplets directly below the capillary tube. The displacement platform is adjusted so that the capillary tube descends to contact the substrate on which the CSNPs are attached. At this time, the polymer droplets will enter the capillary tube under the action of capillary effect and form a concave liquid surface. After the liquid surface stabilizes, it is cured to obtain a flat concave structure. (3) After curing, peel the capillary off the substrate with the CSNPs layer attached to it to obtain the plano-concave diaphragm fixedly connected to the capillary and the CSNPs layer connected to the planar end of the plano-concave diaphragm. (4) Immerse the plano-concave diaphragm located in the capillary into the defoamed liquid PDMS prepolymer, coat it with a layer of PDMS prepolymer and then cure it to obtain a composite photoacoustic conversion layer that is tightly attached to the end face of the capillary. (5) Insert the optical fiber from the open end of the capillary tube. Adjust the initial cavity length of the FP cavity by controlling the insertion depth of the optical fiber. After adjusting the initial cavity length of the FP cavity, fix the optical fiber and the capillary tube to keep their relative positions fixed. This will give you a transceiver integrated fiber optic all-optical ultrasonic probe.

2. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, The inner diameter of the capillary (2) at the connection point with the optical fiber (1) is greater than or equal to the outer diameter of the optical fiber (1), and the difference between the two diameters is no greater than 1 mm. The optical fiber (1) is a single double-clad optical fiber, wherein the core is used to transmit probe light and the inner cladding is used to transmit excitation light; or, the optical fiber (1) is an optical fiber bundle composed of multiple optical fibers, wherein one optical fiber in the optical fiber bundle is used to transmit probe light and the remaining optical fibers are used to transmit excitation light.

3. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, The capillary (2) is a single capillary or a combination capillary obtained by nesting multiple capillary tubes of matching size. The capillary (2) is made of glass, polymer or metal.

4. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, The capillary (2) is a single capillary or a combination capillary obtained by nesting multiple capillary tubes of matching size. The capillary tube (2) is made of quartz.

5. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, The end of the capillary (2) is a plane perpendicular to its length direction, or an inclined plane that is not at a 90-degree angle to its length direction.

6. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, The photoacoustic conversion layer (5) is a composite film composed of a metal-based thin film or a light-absorbing micro / nano structure material and a flexible polymer. The light-absorbing micro / nano structure material is a carbon-based micro / nano structure material, a metal-based micro / nano structure material, or a disulfide material with a micro / nano structure. The carbon-based micro / nano structure material is selected from thin-film carbon nanotubes, carbon black particles, slag nanoparticles (CSNPs), graphene, or carbon fibers. The metal-based micro / nano structure material is selected from metal nanoparticles, metal nanofilms, or metal nanoarrays. The disulfide material with a micro / nano structure is selected from granular or sheet-like molybdenum disulfide or tungsten disulfide.

7. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 6, characterized in that, The photoacoustic conversion layer (5) is a composite photoacoustic conversion layer composed of slag particles (CSNPs) and polydimethylsilane (PDMS).

8. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 1, characterized in that, For the photoacoustic conversion layer (5), the end face of the photoacoustic conversion layer (5) that is in close contact with the plano-concave diaphragm (4) is a plane, and the other end face is a convex surface, a concave surface, a parallel plane or an inclined plane, thereby obtaining a plano-convex, plano-concave, plano-flat or wedge-shaped structure.

9. The transceiver integrated fiber optic all-optical ultrasonic probe as described in claim 8, characterized in that, The photoacoustic conversion layer (5) has a plano-convex structure and can act as a plano-convex acoustic lens to focus the ultrasonic waves emitted by the probe.

10. The method for fabricating the transceiver integrated fiber optic all-optical ultrasonic probe as described in any one of claims 1-9, characterized in that, Includes the following steps: (1) Place the substrate above the candle flame core and vapor deposit candle ash particles (CSNPs); (2) A capillary tube with an inner diameter matching the outer diameter of the optical fiber is vertically clamped on a displacement platform, and polymer droplets are dropped onto the CSNPs layer obtained in step (1), with the center of the droplets directly below the capillary tube. The displacement platform is adjusted so that the capillary tube descends to contact the substrate on which the CSNPs are attached. At this time, the polymer droplets will enter the capillary tube under the action of capillary effect and form a concave liquid surface. After the liquid surface stabilizes, solidification is performed to obtain a plano-concave structure. (3) After curing, peel the capillary off the substrate with the CSNPs layer attached to it to obtain the plano-concave diaphragm fixedly connected to the capillary and the CSNPs layer connected to the planar end of the plano-concave diaphragm. (4) Immerse the plano-concave diaphragm located in the capillary into the defoamed liquid PDMS prepolymer, coat it with a layer of PDMS prepolymer and then cure it to obtain a composite photoacoustic conversion layer that is tightly attached to the end face of the capillary. (5) Insert the optical fiber from the open end of the capillary tube. Adjust the initial cavity length of the FP cavity by controlling the insertion depth of the optical fiber. After adjusting the initial cavity length of the FP cavity, fix the optical fiber and the capillary tube to keep their relative positions fixed. This will give you a transceiver integrated fiber optic all-optical ultrasonic probe.

11. The preparation method according to claim 10, characterized in that, In step (1), the substrate is specifically placed 1.5 cm to 3 cm above the candle flame core, and the vapor deposition time is 5-40 s; In step (4), the curing process specifically involves curing at 75°C to 85°C for 2 to 4 hours. In step (2), the polymer droplets are specifically UV adhesive droplets.

12. The preparation method according to claim 10, characterized in that, In step (4), the composite photoacoustic conversion layer has a planar structure. The end face that is in close contact with the plano-concave diaphragm is a plane, and the other end face is a plane parallel to it. The composite photoacoustic conversion layer is obtained by immersing the plano-concave diaphragm located in the capillary into the defoamed liquid PDMS prepolymer, coating it with a layer of PDMS prepolymer, and then vertically standing it on another clean substrate so that the end coated with PDMS prepolymer is in direct contact with the substrate. Then it is cured and demolded. Alternatively, the composite photoacoustic conversion layer has a plano-convex structure, with a planar end face that is in close contact with the plano-concave diaphragm and a convex end face; the composite photoacoustic conversion layer is obtained by immersing the plano-concave diaphragm located in the capillary into the defoamed liquid PDMS prepolymer, coating it with a layer of PDMS prepolymer, and then vertically suspending it for curing. Alternatively, the composite photoacoustic conversion layer has a planar structure, with one end face tightly attached to the plano-concave diaphragm being a plane, and the other end face being a plane with a corresponding tilt angle; the composite photoacoustic conversion layer is obtained by immersing the plano-concave diaphragm located in the capillary into a defoamed liquid PDMS prepolymer, coating it with a layer of PDMS prepolymer, and then placing it on another clean substrate at a non-90° tilt angle, so that the end coated with PDMS prepolymer is in direct contact with the substrate, then curing, and demolding. Alternatively, the composite photoacoustic conversion layer has a planar structure, with one end face that is in close contact with the plano-concave diaphragm being planar, and the other end face being concave with the same radius of curvature as the base. The composite photoacoustic conversion layer is obtained by immersing the plano-concave diaphragm located in the capillary into a defoamed liquid PDMS prepolymer, coating it with a layer of PDMS prepolymer, and then placing it on a clean spherical base, so that the end coated with PDMS prepolymer is in direct contact with the spherical base, and then curing and demolding.

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