Optoacoustic endoscopic imaging probe, device and imaging method based on microsphere resonance in a tapered annular core fiber

Abstract

This invention discloses a photoacoustic endoscopic imaging probe, imaging device, and imaging method based on microsphere resonators within a tapered ring-core fiber. The probe includes a microsphere resonator based on a tapered ring-core fiber, a focusing lens, and a reflecting mirror. Double-clad fiber is used in the probe to achieve simultaneous transmission of excitation and probe light. The probe light propagates within the microsphere resonator based on the tapered ring-core fiber, forming a resonant cavity that receives the photoacoustic signal and converts it into modulated light output. This invention partially collapses the coupling region between the ring-core fiber and the double-clad fiber, forming a conical shape. This ensures efficient coupling of the probe light from the double-clad fiber to the ring-core fiber while reducing the impact of Fabry-Perot type reflections formed in the ring-core fiber on the photoacoustic signal detection process.

Description

Technical Field

[0001] This invention belongs to the technical field of endoscopic imaging, specifically relating to a photoacoustic endoscopic imaging probe, device, and imaging method based on microsphere resonance within a tapered annular fiber core. Background Technology

[0002] In recent years, photoacoustic imaging, a novel imaging technology based on the photoacoustic effect, has become a focus of research in the field of medical imaging technology. Photoacoustic imaging not only sensitively reflects the functional information of biological tissues but also utilizes the excellent penetrability of sound waves in tissues to achieve high spatial resolution and high optical contrast imaging of deep tissues. Photoacoustic endoscopy, as an important branch of photoacoustic imaging, enables non-invasive, high-resolution imaging of tissues and lesion areas within the body by miniaturizing the imaging probe.

[0003] Currently, photoacoustic endoscopic imaging systems commonly employ traditional piezoelectric transducers as the receiving element for ultrasonic signals, as shown in patent applications 202110386427.X, 202120312794.0, and 202310660241.8. However, traditional piezoelectric transducers have certain limitations: on the one hand, although they possess high energy conversion efficiency, their large size presents significant challenges for integration into endoscopic imaging probes; on the other hand, the detection bandwidth of a piezoelectric transducer is inversely proportional to its size, meaning that miniaturized piezoelectric transducers struggle to achieve ultra-wideband ultrasonic detection performance. Furthermore, miniaturization reduces the sensitivity of the piezoelectric transducer, thereby affecting the signal-to-noise ratio and resolution of the reconstructed image.

[0004] Another patent (application number: 202310127542.4, title: "An Omnidirectional Rotational Scanning Endoscopic Imaging Device Based on Fiber Optic Sensor") discloses a highly integrated and miniaturized endoscopic imaging device using a fiber optic sensor, capable of omnidirectional rotational scanning and effectively converting ultrasonically modulated optical signals into electrical signals for transmission. However, this endoscopic imaging probe still requires two optical fibers—one for transmitting excitation light and the other for transmitting signal light, involving two different wavelengths of light. This increases the complexity and cost of the system to some extent.

[0005] Given the limitations of the aforementioned traditional technologies, there is an urgent need to develop a new type of photoacoustic endoscopic imaging probe to overcome the shortcomings of existing technologies and achieve a more efficient, smaller, and high-performance photoacoustic endoscopic imaging system. Summary of the Invention

[0006] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a photoacoustic endoscopic imaging probe, device and imaging method based on microsphere resonance in a tapered ring core fiber. This invention forms a cone shape by incompletely collapsing the coupling region between the ring core fiber and the double-clad fiber. On the one hand, this can ensure the coupling efficiency of the probe light from the double-clad fiber to the ring core fiber. On the other hand, it can reduce the influence of Fabry-Perot reflection formed by the probe light in the ring core fiber on the photoacoustic signal detection process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered annular fiber, comprising: a microsphere resonator based on a tapered annular fiber, wherein the microsphere resonator comprises a double-clad fiber, a tapered annular fiber, and a solid microsphere, wherein the double-clad fiber and the tapered annular fiber are fused together at a sharp apex angle in a transition region, and the solid microsphere is disposed within the tapered annular fiber and embedded in the tapered region to ensure the stability of the microsphere resonator;

[0009] The double-clad optical fiber can simultaneously transmit two different wavelengths of light, used to transmit photoacoustic excitation light and photoacoustic probe light respectively; the ring-core optical fiber has a high-refractive-index inner ring core, used to confine the light energy within the ring core, and couple the probe light into the solid microsphere as an evanescent wave; the solid microsphere is used to confine the probe light that has reached the resonance condition within the microsphere, excite the whispering gallblade mode, and form a microsphere resonant cavity, which is used to receive the photoacoustic signal; the focusing lens is used to focus the excitation light, and after being reflected by the mirror, it illuminates the surface of biological tissue through the window.

[0010] As a preferred technical solution, the double-clad optical fiber includes a fiber core, an inner cladding covering the fiber core, and an outer cladding covering the inner cladding, which enables the probe light to propagate along the fiber core within the double-clad optical fiber and the excitation light to propagate along the inner cladding within the double-clad optical fiber.

[0011] As a preferred technical solution, the ring-core fiber has a low-refractive-index silica cladding, a high-refractive-index doped silica ring core, and an air hole. The ring-core fiber is used to confine light energy within a ring core of a few micrometers to excite evanescent waves. The probe light has two optical paths within the ring-core fiber: one part is coupled to the solid microsphere as an evanescent wave, and the other part is transmitted along the ring core to the end face and reflected back. To solve the interference caused by Fabry-Perot type reflection on the resonance peak formed by the microsphere resonator, the coupling region between the double-clad fiber and the ring-core fiber is thinned to form a tapered ring-core fiber. By controlling the size of the cone apex angle, the probe light is prevented from directly transmitting into the air hole, while also ensuring the coupling efficiency between the double-clad fiber and the ring-core fiber.

[0012] As a preferred technical solution, the solid microspheres are used to confine the probe light of the resonant wavelength within the solid microspheres to form a whispering-gallery mode resonant cavity; after the photoacoustic signal excited by the excitation light on the surface of the biological tissue is received by the solid microspheres, the refractive index and size of the solid microspheres change, causing the wavelength of the resonant probe light to shift, and outputting probe light modulated by the photoacoustic signal.

[0013] As a preferred technical solution, the excitation light transmitted through the annular fiber core needs to be focused by a focusing lens, reflected by a mirror, and then irradiated onto the surface of biological tissue through the window of the probe.

[0014] In a second aspect, the present invention provides an imaging device, including a control module, a light source module, an optical path module, a photoacoustic endoscopic imaging probe, and a data acquisition and image reconstruction module;

[0015] The control module is used to generate timing pulse signals to control the excitation light source and the detection light source;

[0016] The light source module includes an excitation light source and a detection light source, and the control module is connected to the excitation light source and the detection light source respectively; the excitation light source is a pulsed laser, used to generate photoacoustic signal excitation light, and the detection light source is a tunable diode laser, used to generate photoacoustic signal detection light;

[0017] The optical path module includes an optical isolator, a single-mode fiber circulator, a dichroic mirror, and a focusing lens; the optical isolator is used to isolate the returning stray light; the single-mode fiber circulator is used to separate the input probe light signal from the output modulated light signal; the dichroic mirror is a short-pass dichroic mirror, used to transmit the excitation light and reflect the probe light; the focusing lens is used to focus the probe light and the excitation light into the photoacoustic endoscopic imaging probe.

[0018] The photoacoustic endoscopic imaging probe includes a microsphere resonator based on a tapered ring fiber core, a focusing lens, and a reflecting mirror;

[0019] The data acquisition and image reconstruction module includes a photodetector, a data acquisition card, and a computer; the photodetector is used to convert the detection light modulated by the photoacoustic signal into an electrical signal and amplify it; the data acquisition card is used to acquire the amplified electrical signal and transmit it to the computer; the computer is used to reconstruct the photoacoustic image from the acquired data.

[0020] As a preferred technical solution, the control module adopts an FPGA development board.

[0021] Thirdly, the present invention provides an imaging method applied to the aforementioned imaging device, comprising the following steps:

[0022] Trigger signal generation: The control module generates a trigger signal to control the excitation light source to generate a photoacoustic signal to excite the light, and the detection light source generates a photoacoustic signal to detect the light;

[0023] Photoacoustic excitation and detection: The photoacoustic excitation light passes through an optical isolator and a dichroic mirror, while the photoacoustic detection light passes through a single-mode fiber circulator, is reflected by the dichroic mirror, and is then combined with the photoacoustic excitation light before entering the photoacoustic endoscopic imaging probe. The combined light enters the photoacoustic endoscopic imaging probe, where the excitation and detection light are transmitted in a microsphere resonator based on a tapered ring fiber core to form a resonant cavity. The mixed light that passes through the end face of the ring fiber core is focused by a focusing lens and reflected by a mirror, and finally illuminates the surface of the biological tissue to be imaged through a window.

[0024] Data acquisition and image reconstruction: The photoacoustic signal excited by the excitation light is received by a microsphere resonator based on a tapered ring fiber core, and the output photoacoustic signal modulates the light. The light then passes through a dichroic mirror and a single-mode fiber circulator and is sent to a photodetector. The photodetector converts the modulated light signal into an electrical signal and amplifies it. The amplified electrical signal is acquired by a data acquisition card and sent to a computer. Finally, the computer uses the acquired data for photoacoustic image reconstruction.

[0025] As a preferred technical solution, the specific steps of the photoacoustic detection are as follows:

[0026] The combined beam enters the photoacoustic endoscopic imaging probe. The probe light propagates in the core of the double-clad fiber, while the excitation light propagates in the inner cladding and reaches the tapered region between the double-clad fiber and the ring-core fiber. The excitation light continues to propagate along the silica cladding, and the probe light couples into the solid microsphere as an evanescent wave, exciting a whispering-gallery mode that confines the resonant wavelength light within the microsphere and propagates along its diameter. The probe light then couples out of the solid microsphere and returns to the core of the ring-core fiber.

[0027] As a preferred technical solution, the specific steps of data acquisition and image reconstruction are as follows:

[0028] The photoacoustic signal excited by the excitation light is received by the solid microsphere. The photoacoustic signal causes the resonant peak wavelength of the probe light in the microsphere to shift, and the probe light modulated by the photoacoustic signal is output. It then passes through a dichroic mirror and a single-mode fiber circulator and is sent to the photodetector.

[0029] The photodetector converts the modulated optical signal into an electrical signal and amplifies it. The amplified electrical signal is then acquired by the acquisition card and sent to the computer.

[0030] Finally, the computer uses the collected data to reconstruct the photoacoustic image.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. This invention uses a ring-core fiber to confine light energy within an extremely fine ring core to excite evanescent waves, which is beneficial for the probe light to couple into the solid microsphere as an evanescent wave, thereby improving the coupling efficiency of the probe light.

[0033] 2. This invention uses an internal microsphere resonator in an optical fiber as an ultrasonic transducer. Compared with traditional piezoelectric ultrasonic transducers, the size of the microsphere resonator is on the order of micrometers, which is more conducive to the miniaturization of the probe. It also has outstanding advantages such as high sensitivity and ultra-wide detection bandwidth.

[0034] 3. This invention is the first to use a microsphere resonator within an optical fiber as the ultrasonic transducer in a photoacoustic endoscopic imaging system, providing a photoacoustic endoscopic imaging method based on an optical whispering-gallery mode: A photoacoustic signal is excited, received using a microsphere resonator within a ring-core optical fiber, and modulated light is output. This modulated light is then converted to photoelectric signal using a photodetector, and finally, data is acquired. Using optical signal transmission significantly reduces interference from electromagnetic signals and enables ultra-wideband photoacoustic signal detection, thereby improving the signal-to-noise ratio and resolution of the photoacoustic image.

[0035] 4. This invention uses double-clad optical fiber to couple the excitation light and the probe light into a single optical fiber for transmission, resulting in a smaller probe size, a more compact structure, and better suitability for endoscopic imaging. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the photoacoustic endoscopic imaging probe structure based on microsphere resonance within a tapered annular fiber core, according to an embodiment of the present invention.

[0038] Figure 2 yes Figure 1 Cross-sectional view of the double-clad optical fiber in the photoacoustic endoscopic imaging probe.

[0039] Figure 3 yes Figure 1 Cross-sectional view of the ring-core optical fiber in the photoacoustic endoscopic imaging probe.

[0040] Figure 4 This is a schematic diagram of the imaging device according to an embodiment of the present invention;

[0041] Figure 5 This is a flowchart of the imaging method according to an embodiment of the present invention.

[0042] Explanation of icon numbers:

[0043] 1. Double-clad optical fiber; 2. Solid microsphere; 3. Ring-core optical fiber; 4. Focusing lens; 5. Mirror; 6. Outer cladding of double-clad optical fiber; 7. Inner cladding of double-clad optical fiber; 8. Core of double-clad optical fiber; 9. Cladding of ring-core optical fiber; 10. Ring core; 11. Air hole; 12. FPGA development board; 13. Excitation source; 14. Probe source; 15. Optical isolator; 16. Dichroic mirror; 17. Single-mode fiber circulator; 18. Photoacoustic endoscopic imaging probe; 19. Photodetector; 20. Data acquisition card; 21. Computer. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0045] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0046] In this application, unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or merely surface contact. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0047] like Figures 1-3 As shown in the figure, this embodiment discloses a photoacoustic endoscopic imaging probe based on microsphere resonator in tapered annular fiber core, comprising a microsphere resonator based on tapered annular fiber core, a focusing lens 4, and a reflector 5.

[0048] The microsphere resonator based on tapered ring-core fiber comprises a double-clad fiber 1, a tapered ring-core fiber 3, and a solid microsphere 2. The double-clad fiber 1 can simultaneously transmit two different wavelengths of light, used to transmit photoacoustic excitation light and photoacoustic probe light respectively. The ring-core fiber 3 has a high-refractive-index inner ring core, used to confine light energy within an extremely fine ring core, and couples the probe light into the barium titanate microsphere as an evanescent wave. The solid microsphere 2 can confine the probe light that has reached the resonance condition within the microsphere, excite the whispering-gallery mode, and form a microsphere resonant cavity for receiving photoacoustic signals.

[0049] The focusing lens 4 is used to focus the excitation light, which is then reflected by the mirror 5 and illuminated onto the surface of the biological tissue to be imaged through the window.

[0050] Furthermore, such as Figure 2 As shown, the double-clad optical fiber in the microsphere resonator includes a double-clad optical fiber core 8, a double-clad inner cladding 7 covering the core, and a double-clad outer cladding 6 covering the inner cladding. This enables the probe light to propagate along the double-clad optical fiber core 8 within the double-clad optical fiber, and the excitation light to propagate along the double-clad inner cladding 7 within the double-clad optical fiber.

[0051] Furthermore, the annular fiber 3 in the microsphere resonator includes an annular fiber cladding 9, an annular core 10, and an air hole 11. The annular fiber cladding 9 can be a low-refractive-index silica cladding; the annular core 10 can be a high-refractive-index annular core or a silica-doped annular core. The annular fiber 3 can confine light energy within a few micrometers of the annular core to excite evanescent waves. Since the probe light has two optical paths within the annular fiber, one part couples to the solid microsphere as an evanescent wave, and the other part is transmitted along the annular core to the end face and reflected back. To solve the interference caused by Fabry-Perot reflection (FP reflection) on the resonance peak formed by the microsphere resonator, the coupling region between the double-clad fiber and the annular fiber is thinned to form a tapered annular fiber. By controlling the size of the cone apex angle, the probe light can be prevented from directly transmitting into the air hole while ensuring the coupling efficiency between the double-clad fiber and the annular fiber.

[0052] Understandably, the cone apex angle is generally less than 9° and can be controlled according to actual needs.

[0053] Furthermore, the solid microsphere 2 in the microsphere resonator is used to confine the probe light of the resonant wavelength within the microsphere, forming a whispering-gallery mode resonant cavity. In a specific embodiment, the solid microsphere is configured as barium titanate microspheres. Due to the high refractive index of barium titanate, a high quality factor can be achieved with a small cavity size, resulting in high-sensitivity detection. Moreover, under the same structural conditions, materials with lower Young's modulus exhibit greater strain to ultrasonic stress (i.e., higher sensitivity). Using barium titanate microspheres can achieve a more significant refractive index change through microsphere deformation and photoelasticity, thereby generating a stronger modulated light signal in photoacoustic imaging.

[0054] Furthermore, the excitation light transmitted through the annular fiber core needs to be focused by the focusing lens 4, reflected by the reflecting mirror 5, and then irradiated onto the surface of the biological tissue to be imaged through the window.

[0055] Furthermore, the photoacoustic signal excited by the excitation light on the surface of biological tissue is received by barium titanate microspheres. The refractive index of the barium titanate microspheres changes, causing the wavelength of the resonant probe light to shift, and the output probe light modulated by the photoacoustic signal.

[0056] like Figure 2 As shown in the figure, this embodiment also discloses an imaging device for a photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered ring fiber core. The imaging device includes a control module, a light source module, an optical path module, a photoacoustic endoscopic imaging probe, and a data acquisition and image reconstruction module.

[0057] The control module is used to generate timing pulses to control the excitation light source 13 and the detection light source 14. In a specific embodiment, the control module adopts an FPGA development board 12. The FPGA development board acts as the control module to generate trigger signals to control the excitation light source to generate photoacoustic signal excitation light and the detection light source to generate photoacoustic signal detection light.

[0058] The light source module includes an excitation light source 13 and a detection light source 14. The excitation light source 13 is a pulsed laser used to generate photoacoustic signal excitation light. The detection light source 14 is a tunable diode laser with a tuning range of 1520-1570nm used to generate photoacoustic signal detection light.

[0059] The optical path module includes an optical isolator 15, a dichroic mirror 16, and a single-mode fiber circulator 17. The optical isolator 15 is used to isolate the returning stray light. The dichroic mirror 17 is a short-pass dichroic mirror with a cutoff wavelength range of 1180–1500 nm, used to transmit photoacoustic excitation light and reflect photoacoustic probe light. The single-mode fiber circulator 17 is used to separate the input probe light signal from the output modulated light signal.

[0060] The photoacoustic endoscopic imaging probe 18 includes a microsphere resonator based on a tapered ring fiber core, a focusing lens 4, and a reflecting mirror 5.

[0061] The data acquisition and image reconstruction module includes a photodetector 19, a data acquisition card 20, and a computer 21. The photodetector 19 is a balanced light receiver with adjustable gain and bandwidth, with a wavelength range of 900–1700 nm, used to convert the probe light modulated by the photoacoustic signal into an electrical signal and amplify it; the data acquisition card 20 is used to acquire the amplified electrical signal and transmit it to the computer; the computer 21 is used to reconstruct the photoacoustic image from the acquired data.

[0062] like Figure 5 As shown, the photoacoustic endoscopic imaging device based on microsphere resonance within a tapered annular fiber optic core, as described above, is further described in this invention. The invention also provides an imaging method for a photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered annular fiber optic core, comprising the following steps:

[0063] S1. Generating trigger signal: The FPGA development board 12, as a control module, generates a trigger signal to control the pulse excitation light source 13 to generate a photoacoustic signal to excite the light, and the tunable detection light source 14 generates a photoacoustic signal to detect the light.

[0064] S2. Photoacoustic Excitation and Detection: The photoacoustic excitation light passes through the optical isolator 15 and the dichroic mirror 16. The photoacoustic detection light passes through the single-mode fiber circulator 17, and after being reflected by the dichroic mirror 16, it is combined with the photoacoustic excitation light and enters the photoacoustic endoscope imaging probe 18. After entering the photoacoustic endoscope imaging probe 18, the detection light propagates in the double-clad fiber core 8, and the excitation light propagates in the inner cladding 7 of the double-clad fiber, reaching the tapered region between the double-clad fiber and the ring-core fiber. The excitation light continues to propagate along the silica cladding 9, and the detection light enters the silica ring core 10, coupling to the solid microsphere 2 as an evanescent wave, exciting the whispering gallblade mode, confining the resonant wavelength light in the microsphere, and propagating along the diameter of the microsphere. The detection light couples out of the solid microsphere 2 and returns to the silica ring core 10. The mixed light that passes through the end face of the ring-core fiber is focused by the focusing lens 4 and reflected by the reflecting mirror 5, and finally illuminates the surface of the biological tissue to be imaged through the window.

[0065] S3. Data Acquisition and Image Reconstruction: The photoacoustic signal excited by the excitation light is received by the solid microsphere 2. The ultrasonic wave causes the resonant peak wavelength of the probe light in the solid microsphere 2 to shift, and the probe light modulated by the photoacoustic signal is output. It then passes through the dichroic mirror 16 and the single-mode fiber circulator 17 and is sent to the photodetector 19. The photodetector 19 converts the modulated light signal into an electrical signal and amplifies it. The amplified electrical signal is then acquired by the acquisition card 20 and sent to the computer 21. The computer 21 reconstructs the photoacoustic image from the acquired data.

[0066] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0067] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered annular fiber core, characterized in that, include: A microsphere resonator based on a tapered ring core fiber is provided. The microsphere resonator consists of a double-clad fiber, a tapered ring core fiber, and a solid microsphere. The double-clad fiber and the tapered ring core fiber are fused together at a sharp cone apex angle in the transition region. The solid microsphere is disposed inside the tapered ring core fiber and embedded in the tapered region to ensure the stability of the microsphere resonator. The double-clad optical fiber can transmit two different wavelengths of light simultaneously, used to transmit photoacoustic excitation light and photoacoustic probe light respectively; the ring-core optical fiber has a high-refractive-index inner ring core, used to confine the light energy within the ring core, and to couple the probe light into the solid microsphere as an evanescent wave. The solid microspheres are used to confine the probe light that has reached the resonance condition within the microspheres, excite the whispering gallblade mode, and form a microsphere resonant cavity. The microsphere resonant cavity is used to receive photoacoustic signals. The focusing lens is used to focus the excitation light, which is then reflected by a mirror and irradiated onto the surface of biological tissue through a window. The ring-core fiber has a low-refractive-index silica cladding, a high-refractive-index doped silica ring core, and air holes. The ring-core fiber is used to confine light energy within a ring core of a few micrometers to excite evanescent waves. The probe light has two optical paths within the ring-core fiber: one part couples to the solid microsphere as an evanescent wave, and the other part propagates along the ring core to the end face and is reflected back. To address the interference caused by Fabry-Perot type reflections on the resonance peaks formed by the microsphere resonator, the coupling region between the double-clad fiber and the ring-core fiber is thinned to form a tapered ring-core fiber. By controlling the size of the cone apex angle, the probe light is prevented from directly propagating into the air holes while maintaining the coupling efficiency between the double-clad fiber and the ring-core fiber. The solid microspheres are used to confine the probe light of the resonant wavelength within the solid microspheres to form a whispering-gallery mode resonant cavity; The solid microspheres are configured as barium titanate microspheres. After the photoacoustic signal excited by the excitation light on the surface of the biological tissue is received by the barium titanate microspheres, the refractive index and size of the barium titanate microspheres change, causing the wavelength of the resonant probe light to shift, and outputting probe light modulated by the photoacoustic signal.

2. The photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered annular fiber core according to claim 1, characterized in that, The double-clad optical fiber includes a core, an inner cladding covering the core, and an outer cladding covering the inner cladding, which enables probe light to propagate along the core within the double-clad optical fiber and excitation light to propagate along the inner cladding within the double-clad optical fiber.

3. The photoacoustic endoscopic imaging probe based on microsphere resonance within a tapered annular fiber core according to claim 1, characterized in that, The excitation light transmitted through the annular fiber core needs to be focused by a focusing lens, reflected by a mirror, and then irradiated onto the surface of biological tissue through the probe window.

4. An imaging device, characterized in that, It includes a control module, a light source module, an optical path module, a photoacoustic endoscopic imaging probe as described in any one of claims 1-3, and a data acquisition and image reconstruction module; The control module is used to generate timing pulse signals to control the excitation light source and the detection light source; The light source module includes an excitation light source and a detection light source, and the control module is connected to the excitation light source and the detection light source respectively; the excitation light source is a pulsed laser, used to generate photoacoustic signal excitation light, and the detection light source is a tunable diode laser, used to generate photoacoustic signal detection light; The optical path module includes an optical isolator, a single-mode fiber circulator, a dichroic mirror, and a focusing lens; the optical isolator is used to isolate the returning stray light; the single-mode fiber circulator is used to separate the input probe light signal from the output modulated light signal; the dichroic mirror is a short-pass dichroic mirror, used to transmit the excitation light and reflect the probe light; the focusing lens is used to focus the probe light and the excitation light into the photoacoustic endoscopic imaging probe. The photoacoustic endoscopic imaging probe includes a microsphere resonator based on a tapered ring fiber core, a focusing lens, and a reflecting mirror; The data acquisition and image reconstruction module includes a photodetector, a data acquisition card, and a computer; the photodetector is used to convert the detection light modulated by the photoacoustic signal into an electrical signal and amplify it; the data acquisition card is used to acquire the amplified electrical signal and transmit it to the computer; the computer is used to reconstruct the photoacoustic image from the acquired data.

5. The imaging device according to claim 4, characterized in that, The control module uses an FPGA development board.

6. An imaging method, characterized in that, The imaging apparatus applied to any one of claims 4-5 comprises the following steps: Trigger signal generation: The control module generates a trigger signal to control the excitation light source to generate a photoacoustic signal to excite the light, and the detection light source generates a photoacoustic signal to detect the light; Photoacoustic excitation and detection: The photoacoustic excitation light passes through an optical isolator and a dichroic mirror, and the photoacoustic detection light passes through a single-mode fiber circulator, and then is reflected by the dichroic mirror and combined with the photoacoustic excitation light before entering the photoacoustic endoscopic imaging probe. The combined light enters the photoacoustic endoscopic imaging probe. The excitation light and the probe light are transmitted in a microsphere resonator based on a tapered ring fiber and form a resonant cavity. The mixed light that passes through the end face of the ring fiber is focused by the focusing lens and reflected by the reflecting mirror, and finally illuminates the surface of the biological tissue to be imaged through the window. Data acquisition and image reconstruction: The photoacoustic signal excited by the excitation light is received by a microsphere resonator based on a tapered ring fiber core, and the output photoacoustic signal modulates the light, which is then sent to a photodetector after passing through a dichroic mirror and a single-mode fiber circulator. The photodetector converts the modulated optical signal into an electrical signal and amplifies it. The amplified electrical signal is then acquired by the acquisition card and sent to the computer. Finally, the computer uses the acquired data to reconstruct the photoacoustic image.

7. The imaging method according to claim 6, characterized in that, The specific steps of the photoacoustic detection are as follows: The combined beam enters the photoacoustic endoscopic imaging probe. The probe light propagates in the core of the double-clad fiber, while the excitation light propagates in the inner cladding and reaches the tapered region between the double-clad fiber and the ring-core fiber. The excitation light continues to propagate along the silica cladding, and the probe light couples into the solid microsphere as an evanescent wave, exciting a whispering-gallery mode that confines the resonant wavelength light within the microsphere and propagates along its diameter. The probe light then couples out of the solid microsphere and returns to the core of the ring-core fiber.

8. The imaging method according to claim 6, characterized in that, The specific steps for data acquisition and image reconstruction are as follows: The photoacoustic signal excited by the excitation light is received by the solid microsphere. The photoacoustic signal causes the resonant peak wavelength of the probe light in the microsphere to shift, and the probe light modulated by the photoacoustic signal is output. It then passes through a dichroic mirror and a single-mode fiber circulator and is sent to the photodetector. The photodetector converts the modulated optical signal into an electrical signal and amplifies it. The amplified electrical signal is then acquired by the acquisition card and sent to the computer. Finally, the computer uses the collected data to reconstruct the photoacoustic image.

Images