Grating sensor for photoacoustic imaging, photoacoustic probe and photoacoustic imaging device

Abstract

The invention discloses a grating sensor for photoacoustic imaging, a photoacoustic probe and a photoacoustic imaging device, a grating structure is processed by adopting a three-dimensional photoetching process, and the design of an external solid structure and an internal periodic structure is combined, so that the external solid structure and a plurality of cavity areas form a remarkable refractive index difference; therefore, the resonance effect of the grating is enhanced. In the ultrasonic detection process, a periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert ultrasonic pressure into an optical signal, and the optical signal is further converted into an electric signal for photoacoustic imaging. Compared with a traditional ultrasonic sensor, the ultrasonic sensor provides higher sensitivity and wider bandwidth, can achieve clearer and more accurate imaging effect in high-resolution imaging, and effectively avoids the phenomenon that in the prior art, an ultrasonic sensor is poor in imaging effect in high-resolution imaging. In addition, a significant refractive index difference is formed by adopting two-photon processing and ultraviolet curing, so that the sound spectrum detection capability of photoacoustic endoscopic imaging is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic imaging, in particular to a grating sensor, a photoacoustic probe and a photoacoustic imaging device for photoacoustic imaging. Background Art

[0002] Photoacoustic Imaging (PAI), as an emerging biomedical imaging technology, combines the high resolution of optical imaging with the high penetration of ultrasound imaging in deep biological tissues, and has developed rapidly in recent years. The basic principle of photoacoustic imaging is that when biological tissue is irradiated by pulsed laser, the absorber in the tissue absorbs the laser energy and expands instantly due to heat, generating ultrasonic signals. By receiving these signals through ultrasonic sensors and combining signal processing and image reconstruction technology, images of light absorption distribution in tissues can be generated. This makes photoacoustic imaging have broad application prospects in disease detection, tissue analysis, and molecular imaging. In photoacoustic imaging, the performance of ultrasound detectors plays a key role in imaging quality.

[0003] Traditional ultrasonic transducers mainly work based on piezoelectric materials, converting pressure signals into electrical signals through the piezoelectric effect. However, with the development of technology, piezoelectric micro-machined ultrasonic transducers (PMUT) as a new type of transducer based on piezoelectric materials have gradually been widely studied. PMUT is prepared using micro-nano manufacturing technology and has the characteristics of high compatibility with integrated circuit technology, small size, light weight, low power consumption, high integration and flexible design. Its basic structure includes a vibrating film and upper and lower electrodes. Although PMUT has significant advantages, due to its small size and narrow working bandwidth, it is difficult to obtain multi-scale information, which limits its application in high-resolution imaging.

[0004] In order to solve the shortcomings of PMUT in bandwidth and sensitivity, people gradually turn their attention to ultrasonic sensors based on optical technology. For example, phase-shifted fiber Bragg grating (FBG) is a high-resolution fiber sensor that shows great potential in static and dynamic strain measurement due to its narrow bandwidth spectral characteristics and excellent dynamic strain detection capabilities. However, phase-shifted FBG also has certain limitations in practical applications, such as the need to be equipped with a high-performance, narrow-linewidth tunable laser, which significantly increases the system cost; at the same time, its performance is easily affected by environmental factors (such as temperature and humidity), resulting in decreased sensitivity and stability.

[0005] To overcome these limitations, ultrasonic sensors based on waveguide technology have been further explored. Previous studies have shown that polymer-based Bragg grating (BGW) ultrasonic detectors can be prepared by electron beam lithography and DUV lithography. However, such BGW structures still have the problem of low resolution. To address this problem, Goraus et al. designed a polymer SR-BG waveguide using 3D laser lithography and improved the system resolution by using high-order reflection modes. The main feature of the SR-BG structure is that the width of the waveguide varies periodically along the propagation direction, and direct fiber coupling is achieved by patterning the SR-BG on a high-column waveguide. This design shows good construction prospects in on-chip optical devices and tunable sensor applications. However, such polymer gratings usually rely on periodic modulation of low refractive index differences, and long gratings are required to achieve high sensitivity, which makes their miniaturization and high-sensitivity detection difficult.

[0006] In summary, the ultrasonic sensors in the related art have technical problems of poor imaging effects when applied to high-resolution imaging due to narrow working bandwidth, low refractive index difference, low resolution, low sensitivity and other reasons. Summary of the invention

[0007] The main purpose of the present invention is to propose a grating sensor, a photoacoustic probe and a photoacoustic imaging device for photoacoustic imaging, aiming to at least solve the technical problem in the related art that ultrasonic sensors have poor imaging effects when used for high-resolution imaging.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] According to a first aspect of the present invention, a grating sensor for photoacoustic imaging is provided, wherein the grating sensor comprises at least one grating structure processed by a three-dimensional photolithography process; the grating structure comprises an external solid structure and an internal periodic structure, the internal periodic structure is provided with a plurality of cavity regions linearly arranged at a preset period, and a refractive index difference is formed between the external solid structure and the plurality of cavity regions; wherein, when the grating sensor performs ultrasonic detection, the internal periodic structure and the external solid structure produce a resonance effect based on the refractive index difference, so as to convert the optical signal caused by ultrasonic pressure into an electrical signal for photoacoustic imaging.

[0010] On the basis of the first aspect, the three-dimensional photolithography process includes a two-photon polymerization process and a curing process; the internal periodic structure is formed by irradiating a target irradiation area of ​​a liquid photosensitive resin material with a femtosecond laser pulse adopted by the two-photon polymerization process, so that the target irradiation area triggers a molecular polymerization reaction; the multiple cavity areas in the internal periodic structure are formed based on non-target irradiation areas in the photosensitive resin material; the external entity structure is formed by curing the remaining liquid photosensitive resin material in the multiple cavity areas and the surface layer of the internal periodic structure through the curing process; wherein the two-photon polymerization process is used to form a first refractive index for the internal periodic structure, and the curing process is used to form a second refractive index for the external entity structure, and the refractive index difference is the difference between the first refractive index and the second refractive index.

[0011] Based on the first aspect, the curing process includes an ultraviolet light curing process; a solid filler is arranged in the non-target irradiation area, and the solid filler is formed by irradiating the remaining liquid photosensitive resin material with ultraviolet light adopted by the ultraviolet light curing process, triggering the remaining liquid photosensitive resin material to be cured; the external entity structure is formed by curing the remaining liquid photosensitive resin material in the multiple cavity areas and the internal periodic structure surface layer with ultraviolet light adopted by the ultraviolet light curing process.

[0012] Based on the first aspect, the photosensitive resin material includes photoresist or polydimethylsiloxane.

[0013] Based on the first aspect, a plurality of linearly arranged solid regions are formed on the surface of the external solid structure, and the plurality of solid regions and the plurality of cavity regions are staggered in the length direction of the grating structure, and an adjacent solid region and a cavity region form a resonance region; wherein the refractive index difference formed between the solid region and the cavity region in each resonance region is equal.

[0014] Based on the first aspect, the grating parameters of the grating structure include: waveguide width of 1.4-1.6μm, corrugation depth of 140-150nm, period size of 500-600nm, and number of periods of 90-110; wherein, the grating parameters are determined by simulating the simulated grating structure during the FDTD simulation process.

[0015] On the basis of the first aspect, during the FDTD simulation process, the grating parameters match the resonant frequency of the excitation light of the target wavelength and satisfy the narrow resonance at the resonant frequency; wherein the target wavelength is 1500-1600nm.

[0016] On the basis of the first aspect, when the internal periodic structure is processed by the two-photon polymerization process, the femtosecond laser pulse is focused by an oil model objective lens to immerse the photosensitive resin material on the glass sheet, and a galvanometer processing method is used to irradiate from top to bottom according to a preset processing path; wherein, the processing path is determined by a three-dimensional model file, the three-dimensional model file is determined based on the simulated grating structure, and the three-dimensional model file includes the geometric features of the external entity structure and the internal periodic structure.

[0017] A second aspect of the present invention provides a photoacoustic probe, comprising a probe body and a grating sensor for photoacoustic imaging as described in the first aspect, wherein the grating sensor is integrated into the probe body.

[0018] A third aspect of the present invention is a photoacoustic imaging device, characterized in that it comprises a photoacoustic imaging processor and the photoacoustic probe as described in the second aspect, wherein an output end of the photoacoustic probe is electrically connected to the photoacoustic imaging processor.

[0019] The grating sensor, photoacoustic probe and photoacoustic imaging device for photoacoustic imaging of the present invention use a three-dimensional photolithography process to process the grating structure, and combine the design of the external entity structure and the internal periodic structure, so that the external entity structure and the multiple cavity areas form a significant refractive index difference, thereby enhancing the resonance effect of the grating. During the ultrasonic detection process, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic pressure into an optical signal, and further convert it into an electrical signal for photoacoustic imaging. Compared with traditional ultrasonic sensors, the present invention provides higher sensitivity and a wider bandwidth, and can achieve clearer and more accurate imaging effects in high-resolution imaging, effectively avoiding the phenomenon that the ultrasonic sensor in the prior art has poor imaging effects in high-resolution imaging. In addition, two large refractive index differences are formed by two-photon processing and ultraviolet light curing to achieve miniaturization and high-sensitivity detection, thereby improving the acoustic spectrum detection capability of photoacoustic endoscopic imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A three-dimensional schematic diagram of a grating sensor provided in an embodiment of the present application;

[0022] Figure 2 A schematic diagram of the internal structure of the grating sensor provided in the embodiment of the present application;

[0023] Figure 3 It is a perspective view of the grating sensor in the embodiment of the present application.

[0024] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0025] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0026] It should be noted that related terms such as "first", "second", etc. can be used to describe various components, but these terms do not limit the components. These terms are only used to distinguish one component from another component. For example, without departing from the scope of the present invention, a first component can be referred to as a second component, and the second component can also be referred to as a first component similarly. The term "and / or" refers to any one or more combinations of related items and description items.

[0027] See also Figure 1 , Figure 2 and Figure 3 An embodiment of the present application provides a grating sensor for photoacoustic imaging, the grating sensor comprising at least one grating structure 1 processed by a three-dimensional photolithography process.

[0028] Specifically, the grating structure 1 includes an external entity structure 10 with two layers and an internal periodic structure 20. The internal periodic structure 20 is provided with a plurality of cavity regions 201 linearly arranged at a preset period. The external entity structure 10 and the plurality of cavity regions 201 form a refractive index difference.

[0029] The value of the refractive index difference is generally greater than or equal to 0.01, which can significantly enhance the resonance effect, so that when the grating sensor performs ultrasonic detection, the internal periodic structure 20 and the external solid structure 10 produce a periodic resonance effect based on the refractive index difference, so as to convert the optical signal caused by the ultrasonic pressure into an electrical signal for photoacoustic imaging.

[0030] Therefore, the grating sensor for photoacoustic imaging of the present invention uses a three-dimensional photolithography process to process the grating structure, and combines the design of the external entity structure and the internal periodic structure, so that the external entity structure forms a significant refractive index difference with multiple cavity regions, thereby enhancing the resonance effect of the grating. During the ultrasonic detection process, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic pressure into a light signal, and further convert it into an electrical signal for photoacoustic imaging. Compared with traditional ultrasonic sensors, the present invention provides higher sensitivity and a wider bandwidth, and can achieve clearer and more accurate imaging effects in high-resolution imaging, effectively avoiding the phenomenon that ultrasonic sensors in the prior art have poor imaging effects in high-resolution imaging.

[0031] In an optional implementation manner of this embodiment, the three-dimensional photolithography process includes a two-photon polymerization process and a curing process, and the internal periodic structure and the external entity structure are formed respectively through the two-photon polymerization process and the curing process.

[0032] In the first stage of processing, a two-photon polymerization process is used to form an internal periodic structure. Specifically, the internal periodic structure can be formed by irradiating a target irradiation area of ​​a liquid photosensitive resin material (e.g., photoresist) with a femtosecond laser pulse used in the two-photon polymerization process, so that the target irradiation area triggers a molecular polymerization reaction, and the multiple cavity areas in the internal periodic structure are formed based on non-target irradiation areas in the photosensitive resin material.

[0033] In the second stage of processing, a curing process is used to form an external entity structure. Specifically, after an internal periodic structure has been processed by a two-photon polymerization process, on this basis, since multiple cavity areas (for example, rectangular cavities) are still filled with uncured liquid photoresist after the structure processing is completed, the internal periodic structure is in a coexistence state of entity and liquid. The internal periodic structure in the coexistence state is processed by a curing process, that is, the remaining liquid photosensitive resin material in the multiple cavity areas and the surface layer of the internal periodic structure are cured (in this way, the refractive index of the periodic area inside the structure changes, and a high refractive index difference is formed between the outside and the inside), and finally an external entity structure is formed on the basis of the internal periodic structure.

[0034] It can be seen that through the two-photon polymerization process, the curing process (UV curing process) combined with the photoresist, the internal periodic structure forms a first refractive index (1.52-1.53), and the external entity structure forms a second refractive index (1.53-1.54), that is, the UV curing (external) refractive index can reach 1.53-1.54, the two-photon polymerization reaches 1.52-1.53, and the refractive index difference (the difference between the first refractive index and the second refractive index) reaches more than 0.01. The high refractive index difference formed can further effectively enhance the optical resonance effect and improve the conversion efficiency of the photoacoustic signal, thereby achieving higher sensitivity and clearer imaging effects in photoacoustic imaging.

[0035] In an optional implementation of this embodiment, the curing process includes an ultraviolet curing process. In the second stage of processing, ultraviolet light of the ultraviolet curing process is used to irradiate the remaining liquid photosensitive resin material in the plurality of cavity regions, triggering the remaining liquid photosensitive resin material (photoresist) to undergo a curing reaction for curing, and ultraviolet light is irradiated to the surface layer of the internal periodic structure to undergo a curing reaction for curing, thereby forming an external entity structure.

[0036] Specifically, by adopting the UV curing process, the curing reaction of the remaining liquid photosensitive resin material can be quickly triggered to ensure the integrity and uniformity of the external entity structure, while strengthening the surface layer of the internal periodic structure. This changes the refractive index of the periodic region inside the structure, forming a high refractive index difference between the outside and the inside. This innovative structure realizes the organic combination of external and internal periodic refractive index modulation through two-photon polymerization technology and UV curing, further improving the stability, sensitivity and photoacoustic signal conversion efficiency of the grating sensor, and meeting the needs of high-resolution photoacoustic imaging.

[0037] It should be noted that the photosensitive resin material includes photoresist or polydimethylsiloxane, and may also be a material with a relatively small Young's modulus.

[0038] In an optional implementation of the present embodiment, a plurality of linearly arranged solid regions 101 are formed on the surface of the external solid structure 10, and the plurality of solid regions 101 and the plurality of cavity regions 201 are staggered in the length direction of the grating structure 1, and an adjacent solid region 101 and a corresponding cavity region 201 form a resonance region.

[0039] Specifically, each resonance region is composed of a solid region 101 and its corresponding cavity region 201, and an optical resonance effect is generated between the two through a refractive index difference. In addition, the refractive index difference formed by the solid region and the cavity region in each resonance region is equal, indicating that the optical properties and resonance frequency of each resonance region are uniform, thereby ensuring that the response of the photoacoustic sensor is consistent and efficient, and can effectively enhance the optical resonance effect of the grating structure, improve the sensitivity and conversion efficiency of the sensor to ultrasonic pressure changes, and achieve higher resolution and more accurate photoacoustic imaging.

[0040] In an optional implementation manner of the present embodiment, grating parameters of optimal sensitivity of the grating structure include: waveguide width of 1.4-1.6μm, corrugation depth of 140-150nm, period size of 500-600nm, and number of periods of 90-110; wherein, the grating parameters are determined by simulating the simulated grating structure during FDTD (Finite-Difference Time-Domain) simulation.

[0041] During the FDTD simulation process, the MODE Solutions module of Lumerical software was used to simulate and optimize the selected grating parameters multiple times, that is, the waveguide width, internal waveguide depth, grating period and grating length were continuously optimized until the parameter combination could just resonate to the resonant frequency of the excitation light of the target wavelength (e.g., 1500-1600nm), and at the same time, it was also necessary to satisfy the narrow resonance at the resonant frequency, so as to obtain a high Q value (Quality Factor) to ensure that the grating structure can achieve high sensitivity and wide bandwidth performance in photoacoustic imaging.

[0042] It should be noted that according to the simulation results, the Q value can be calculated to be on the order of 105. The structure was successfully processed on-chip using a two-photon three-dimensional lithography machine. After experimental testing, the on-chip single-two-photon grating for photoacoustic endoscopic imaging has high sensitivity and small size, which is conducive to the next step of biological tissue imaging and then as a photoacoustic endoscope.

[0043] In an optional implementation of this embodiment, after the simulation process is completed, a 3D model is performed based on the simulated grating structure determined in the simulation process using a 3D tool such as SolidWorks, and a corresponding 3D model file (which may be an STP format file) is exported. In this way, after the 3D model file is obtained, the process processing method can be written for the structure to be processed, such as whether to process the border, the processing direction, etc. That is, the internal periodic structure and the external solid structure can be processed by two-photon polymerization process based on the three-dimensional model file: first, photoresist is dripped on one side of the glass substrate, and after the glass sheet is fixed, a femtosecond laser pulse of a laser device (wavelength 780nm, maximum power 50mW, repetition frequency 80MHz) is focused through an oil model objective (magnification can be 63 times) to immerse the photosensitive resin material (photoresist, IP-Dip, Nanoscribe GmbH) on the glass sheet. Then, the processing steps are determined by the Nanoscribe software, and a galvanometer processing method is used to irradiate from top to bottom according to the preset processing path, at a scanning speed of 100000c and a laser energy setting of 40 values. Finally, ultraviolet light curing is used to control the distance between the ultraviolet light and the sample and the irradiation time to achieve curing of different intensities (generally speaking, the distance is 1-2cm and the irradiation time is about 1min). In this way, a complete single-two-photon grating is processed, that is, both the internal and external structures are completed.

[0044] It should be noted that photoresist is a high refractive index material. Since photoresist can only polymerize when the intensity of the focused voxel is stronger than the threshold intensity, the writing speed and laser power are optimized to obtain high resolution. The faster the speed, the shorter the processing time. The laser energy needs to be properly controlled. If it is too large, the structure will be broken down due to overexposure, and it will feel burnt to the naked eye. If it is too small, the structure may not be visible on the wafer after the final development.

[0045] In an optional implementation of this embodiment, the processed grating structure can be ultrasonically detected. The sample can be placed in a protective cover in advance to protect the fiber core from breaking, and then the protective cover is placed in a funnel filled with pure water, and the ultrasonic transducer is placed at the bottom of the funnel, in full contact with the water, so as to generate ultrasound for sound penetration, and two optical fibers are used to connect the two ends of the sample. The transmitted optical signal is detected by the PD and recorded by the oscilloscope. If the signal does not meet expectations, it can be adjusted from two aspects: 1. Change the structural parameters and reprocess; 2. Adjust the processing method, such as changing the laser energy and scanning speed, so as to detect the ability of the probe to detect ultrasonic signals. In addition, after verifying the detection capability of the grating, it needs to be encapsulated with a low-refractive index UV-curing adhesive such as NOA1315 to facilitate subsequent use in photoacoustic endoscopic imaging.

[0046] An embodiment of the present application further provides a photoacoustic probe, comprising a probe body and the grating sensor for photoacoustic imaging of the above embodiment, wherein the grating sensor is integrated in the probe body.

[0047] An embodiment of the present application further provides a photoacoustic imaging device, comprising a photoacoustic imaging processor and the photoacoustic probe of the above embodiment, wherein an output end of the photoacoustic probe is electrically connected to the photoacoustic imaging processor.

[0048] The grating sensor, photoacoustic probe and photoacoustic imaging device for photoacoustic imaging of the present invention use a three-dimensional photolithography process to process the grating structure, and combine the design of the external entity structure and the internal periodic structure, so that the external entity structure and the multiple cavity areas form a significant refractive index difference, thereby enhancing the resonance effect of the grating. During the ultrasonic detection process, the periodic resonance effect caused by the refractive index difference of the grating structure can efficiently convert the ultrasonic pressure into an optical signal, and further convert it into an electrical signal for photoacoustic imaging. Compared with traditional ultrasonic sensors, the present invention provides higher sensitivity and a wider bandwidth, and can achieve clearer and more accurate imaging effects in high-resolution imaging, effectively avoiding the phenomenon that the ultrasonic sensor in the prior art has poor imaging effects in high-resolution imaging. In addition, two large refractive index differences are formed by two-photon processing and ultraviolet light curing to achieve miniaturization and high-sensitivity detection, thereby improving the acoustic spectrum detection capability of photoacoustic endoscopic imaging.

[0049] In addition, the present invention processes the waveguide directly on the chip to realize a single-double photon grating structure. This structure is not only smaller in size, easy to process, cheap, and has good repeatability, but also has a very high Q value. It can replace the traditional piezoelectric ultrasonic transducer and has a sensitivity that is 1 to 2 orders of magnitude higher than that of the traditional piezoelectric ultrasonic transducer. It is also 1 to 2 orders of magnitude higher than the Q value of some current optical resonators. In addition, the grating structure of the present invention is controllable and can be designed according to different needs, and the processed structure has excellent performance in theory.

[0050] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0051] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A grating sensor for photoacoustic imaging, characterized in that: The grating sensor includes at least one grating structure processed by a three-dimensional photolithography process; The grating structure includes an external entity structure and an internal periodic structure, wherein the internal periodic structure is provided with a plurality of cavity regions linearly arranged according to a preset period, and a refractive index difference is formed between the external entity structure and the plurality of cavity regions; When the grating sensor performs ultrasonic detection, the internal periodic structure and the external solid structure produce a resonance effect based on the refractive index difference to convert the optical signal caused by ultrasonic pressure into an electrical signal for photoacoustic imaging.

2. The grating sensor for photoacoustic imaging according to claim 1, characterized in that: The three-dimensional photolithography process includes a two-photon polymerization process and a curing process; The internal periodic structure is formed by irradiating a target irradiation area of ​​a liquid photosensitive resin material with a femtosecond laser pulse used in the two-photon polymerization process, so that the target irradiation area triggers a molecular polymerization reaction; The plurality of cavity regions in the internal periodic structure are formed based on non-target irradiation regions in the photosensitive resin material; The external entity structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and the surface layer of the internal periodic structure through the curing process; The two-photon polymerization process is used to form a first refractive index for the internal periodic structure, the curing process is used to form a second refractive index for the external entity structure, and the refractive index difference is the difference between the first refractive index and the second refractive index.

3. The grating sensor for photoacoustic imaging according to claim 2, characterized in that: The curing process includes an ultraviolet light curing process; A solid filler is provided in the non-target irradiation area, and the solid filler is formed by irradiating the remaining liquid photosensitive resin material with ultraviolet light adopted by the ultraviolet light curing process, triggering the remaining liquid photosensitive resin material to be cured; The external entity structure is formed by curing the remaining liquid photosensitive resin material in the plurality of cavity regions and the surface layer of the internal periodic structure by ultraviolet light used in the ultraviolet light curing process.

4. The grating sensor for photoacoustic imaging according to claim 3, characterized in that: The photosensitive resin material includes photoresist or polydimethylsiloxane.

5. The grating sensor for photoacoustic imaging according to claim 3, characterized in that: A plurality of linearly arranged solid regions are formed on the surface of the external solid structure, the plurality of solid regions and the plurality of cavity regions are staggered in the length direction of the grating structure, and one of the adjacent solid regions and one of the corresponding cavity regions form a resonance region; Wherein, the refractive index difference formed by the solid area and the cavity area in each of the resonance areas is equal.

6. The grating sensor for photoacoustic imaging according to claim 2, characterized in that: The grating parameters of the grating structure include: waveguide width of 1.4-1.6 μm, corrugation depth of 140-150 nm, period size of 500-600 nm, and period number of 90-110; The grating parameters are determined by simulating the simulated grating structure during the FDTD simulation process.

7. The grating sensor for photoacoustic imaging according to claim 6, characterized in that: During the FDTD simulation, the grating parameters match the resonant frequency of the excitation light of the target wavelength and satisfy the narrow resonance at the resonant frequency; Wherein, the target wavelength is 1500-1600nm.

8. The grating sensor for photoacoustic imaging according to claim 6, characterized in that: When the internal periodic structure is processed by the two-photon polymerization process, the femtosecond laser pulse is focused by an oil-molded objective lens to immerse the photosensitive resin material on the glass sheet, and irradiates from top to bottom according to a preset processing path by a galvanometer processing method; Wherein, the processing path is determined by a three-dimensional model file, the three-dimensional model file is determined based on the simulated grating structure, and the three-dimensional model file includes geometric features of the external entity structure and the internal periodic structure.

9. A photoacoustic probe, characterized in that: The invention comprises a probe body and a grating sensor for photoacoustic imaging according to any one of claims 1 to 8, wherein the grating sensor is integrated in the probe body.

10. A photoacoustic imaging device, characterized in that: It comprises a photoacoustic imaging processor and the photoacoustic probe as claimed in claim 9, wherein the output end of the photoacoustic probe is electrically connected to the photoacoustic imaging processor.

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