A multimode optical fiber endoscopic imaging method and apparatus

Abstract

The application discloses a kind of multi-mode optical fiber endoscopic imaging device and method, device includes: laser;Quadrant piezoelectric ceramic tube;Single-mode optical fiber, near end is coupled with laser, far end passes through quadrant piezoelectric ceramic tube and forms coaxial structure;Supporting shell, for encapsulating coaxial structure;Multi-mode optical fiber coupler, with input port, output port and signal port, input port is coupled with the far end of single-mode optical fiber;Photodetector, connect with signal port;Camera, acquisition output port emitted speckle sequence;Host computer controller, control camera, the synchronous signal acquisition of photodetector, control quadrant piezoelectric ceramic tube to drive the far end of single-mode optical fiber on the fiber core end face of input port scanning excitation and generate continuous variation speckle sequence and emit from output port;Combination calibrated speckle sequence and measurement value reconstruct sample image.The application is superior to prior art in system integration, imaging speed, stability, operability and cost performance etc..

Description

Technical Field

[0001] This invention relates to the field of fiber optic imaging technology, and in particular to a multimode fiber optic endoscopic imaging method and apparatus. Background Technology

[0002] Optical fiber, as an ideal light-guiding medium, is widely used in biomedical imaging, industrial imaging, and other fields. Traditional fiber optic imaging uses single-mode fiber, where the fiber transmits image information as a single "pixel," requiring mechanical scanning or fiber bundle structures to achieve imaging, which limits probe size and imaging resolution. Multimode fiber, on the other hand, supports thousands of independently propagating modes, each containing a large amount of information capacity and degrees of freedom. It is hoped that complex image information can be transmitted using a single multimode fiber. In the biomedical field, multimode fiber imaging promises to provide a new solution for detailed exploration of deep tissues with sub-millimeter-level probes and micrometer-level resolution, and has received widespread attention and research in recent years.

[0003] However, in practical applications, multimode fiber itself does not support direct imaging like traditional lenses. On the one hand, the inherent modal dispersion and mode coupling characteristics of multimode fiber cause the incident image to lose its original spatial phase relationship, ultimately producing complex speckle patterns at the output end. These speckles, seemingly random, actually contain complete information about the light field. On the other hand, the transmission characteristics of multimode fiber are easily affected by environmental factors such as bending deformation, leading to changes in the output speckle, which further increases the imaging difficulty. To achieve multimode fiber imaging, researchers have been searching for effective solutions. Active modulation and random scanning techniques have shown some effectiveness in solving the image distortion problem caused by fiber mode coupling. Active modulation techniques use wavefront shaping to modulate the incident light field, enabling the fiber output end to form a focused spot for point-by-point scanning to achieve imaging. However, the optical system currently relied upon by this technique is relatively complex, and wavefront shaping techniques suffer from poor timeliness and cumbersome operation. On the other hand, random scanning techniques reconstruct the image by exciting a random speckle matrix and combining it with post-processing algorithms. Its optical path design is relatively simple and does not require real-time wavefront modulation. In recent years, with advancements in image reconstruction technologies such as compressed sensing theory and deep learning, random scanning fiber optic imaging has made significant progress in sampling efficiency and reconstruction quality. However, existing random scanning techniques still face challenges in achieving speckle modulation, including insufficient stability, speed limitations, and difficulty in integration. Traditional spatial light modulation techniques typically rely on spatial light modulators or digital micromirror devices (DMDs) as spatial encoders, capable of simultaneously modulating the intensity and phase of the light field to generate diverse random speckle sequences. Nevertheless, these techniques often suffer from drawbacks such as large system size, stringent requirements for optical path alignment accuracy, and limited modulation speed. As for other speckle modulation techniques, such as wavelength coding and time-domain coding, while they exhibit potential for high-speed modulation and easy integration, they are also constrained by limited modulated speckle capacity and high cost.

[0004] To address the problem of fiber optic deformation interference, researchers both domestically and internationally have proposed various methods, including near-end wavefront measurement, beacon coding, average speckle, and low-rank constraint. However, these methods still have limitations in terms of response speed, calibration accuracy, and environmental adaptability. By embedding optical fibers into rigid steel tubes to form rigid multimode fibers, the disturbance problem caused by fiber bending can be physically solved. However, because the optical modulation template and the probe optical path (which typically requires a beam splitter at the incident end to conduct reflected light signals) have not yet been miniaturized and integrated, the completely rigid probe is limited in imaging depth, making it difficult to meet the clinical needs for endoscopic imaging of complex and curved internal cavities. Summary of the Invention

[0005] This invention provides a multimode fiber endoscopic imaging method and device based on PZT-driven single-mode fiber scanning modulation light field, aiming to achieve miniaturization and rapid, stable imaging of the multimode fiber endoscopic imaging system.

[0006] The technical solution of the present invention is as follows: A multimode fiber optic endoscopic imaging device, comprising: A laser, used to output laser light; Four-zone piezoelectric ceramic tube; A single-mode optical fiber is coupled to a laser at its near end and passes through a four-segment piezoelectric ceramic tube at its far end, forming a coaxial structure. A supporting outer shell is used to encapsulate the aforementioned coaxial structure; A multimode fiber coupler has an input port, an output port, and a signal port. The input port is coupled to the far end of a single-mode fiber encapsulated in a support housing. A photodetector, connected to the signal port, is used to acquire the light intensity signal after it has been reflected by the sample, collected by the output port, and split by a multimode fiber coupler during imaging. The camera acquires the speckle sequence emitted from the output port for calibration of the speckle sequence before imaging. The host computer controller controls the synchronous acquisition of the camera and the signal acquisition of the photodetector. It controls the coordinated movement of each section of the four-segment piezoelectric ceramic tube to drive the far end of the single-mode fiber to scan on the fiber core end face of the input port, so that the laser is coupled into the multimode fiber from different positions, exciting and generating a continuously changing speckle sequence and emitting it from the output port; the sample image is reconstructed by combining the calibrated speckle sequence with the measured values.

[0007] Before imaging, the host computer controller controls the camera to pre-calibrate the speckle sequence; during imaging, the speckle emitted from the output port illuminates the sample to be tested, and the reflected light carrying the sample information returns through the output port and is output to the photodetector through the signal port; the host computer controller reconstructs the sample image based on the speckle sequence calibrated by the camera and the light intensity signal collected by the photodetector.

[0008] Preferably, in a static state, the far end of the single-mode fiber is perpendicularly aligned with the center of the fiber core end face of the input port, and the coupling distance between the far end of the single-mode fiber and the input port is adjustable.

[0009] More preferably, the fiber core end face of the input port is located at the waist of the single-mode fiber output end.

[0010] Preferably, the input port is connected to the support housing via a rigid housing through a threaded connection, so that the far end of the single-mode fiber is coupled to the input port; the multimode fiber between the input port and the output port is encapsulated in the rigid housing to form a rigid multimode fiber segment; the fiber of the signal port is encapsulated in the same flexible structure as the single-mode fiber, and the working length of the endoscope is adjusted by changing the length of the flexible fiber segment.

[0011] The rigid structure prevents multimode fiber from bending, ensuring stable transmission characteristics. The length of the rigid multimode fiber segment is designed to be the shortest length required to ensure sufficient mixing of multimode fiber modes, typically less than 10 cm.

[0012] More preferably, the length of the rigid multimode fiber segment is ≤10 cm.

[0013] The multimode fiber coupler is a 2×1 multimode fiber coupler.

[0014] Preferably, the host computer controller generates four voltage drive signals, which are respectively loaded into the four partitions of the four-part piezoelectric ceramic tube, driving each partition to move in coordination and drive the far end of the single-mode optical fiber to scan.

[0015] The present invention also provides a multimode fiber optic endoscopic imaging method based on the aforementioned device, comprising the following steps: (1) Scanning drive: The host computer controller controls the four-zone piezoelectric ceramic tube to drive the far end of the single-mode fiber to move along the predetermined scanning trajectory, thereby exciting the multimode fiber to generate different speckle patterns. (2) Pre-calibration: Before imaging, the host computer controller controls the camera to synchronously acquire M different speckle images emitted from the output port within a complete scanning cycle, which are used as the calibration speckle sequence; (3) Sample measurement: During imaging, the scanning is driven with the same configuration as in step (1) so that the speckle sequence illuminates the sample. The photodetector synchronously collects the light signal output from the signal port after being reflected by the sample, which is used as the measurement data. (4) Data preprocessing: The speckle image obtained in step (2) and the measurement values ​​obtained in step (3) are preprocessed to remove low-brightness speckles and high-correlation speckles, and the low-correlation speckle matrix and the corresponding measurement value vector are obtained. (5) Image reconstruction: Establish a mathematical model between the sample image, the low-correlation speckle matrix and the measurement value vector, and solve it through an optimization algorithm to reconstruct the sample image.

[0016] The predetermined scanning trajectory mentioned in step (1) is a spiral scan or a Lissajous scan.

[0017] The complete scan cycle of the spiral scan is 1 / 2 cycle corresponding to the modulation frequency. Within one complete scan cycle, the far end of the single-mode fiber completes the scanning process from the center of the fiber core end face of the input port to the edge and back to the center.

[0018] Preferably, in the spiral scanning driving method, the driving voltage signals applied to the four zones of the four-zone piezoelectric ceramic tube are as follows: in, and To load along x Voltage signals on the first and third sections of the directional movement; and To load along y Voltage signals on the 2nd and 4th sections of the directional movement; and This is the maximum voltage amplitude. , For driving frequency, The modulation frequency; For time.

[0019] In step (2), the camera's acquisition is triggered synchronously with the same trigger signal as the scanning drive in step (1).

[0020] In step (3), the signal acquisition of the photodetector is synchronously triggered by the same trigger signal as the scanning drive in step (1).

[0021] Preferably, in step (4), data preprocessing includes: (4-1) Calculate the mean of each speckle image and remove speckle images with a mean less than a preset threshold; (4-2) Perform correlation analysis on the retained speckle images and filter out speckle images whose normalized cross-correlation coefficient with the retained speckle images exceeds the set threshold; (4-3) Extract the measurement values ​​corresponding to the retained speckle image from the measurement value matrix to form the measurement value vector.

[0022] In step (4-1), the preset threshold for the mean is half of the maximum value among all speckle images.

[0023] In step (4-2), the threshold for the normalized cross-correlation coefficient is set to 0.7 to 0.8.

[0024] In step (4-2), starting from the second speckle image, the normalized cross-correlation coefficient between the current speckle image and all previously retained speckle images is calculated sequentially. The current speckle image is retained only when all normalized cross-correlation coefficients are lower than a set threshold.

[0025] Preferably, in step (5), the mathematical model is: in, A vector of measured values; It is a low-correlation speckle matrix; For sample images; For measuring noise.

[0026] Preferably, in step (5), the optimization algorithm is the compressed sensing reconstruction algorithm.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) PZT is used to drive single-mode fiber scanning to achieve modulation of multimode fiber output speckle. Compared with traditional spatial light modulation devices such as DMD, PZT is smaller (only a few hundred micrometers), has a higher response frequency (more than 1MHz), and is more cost-effective. The resulting benefits are a smaller imaging system, faster imaging speed, and lower cost. (2) The transmission of reflected light is achieved through a multimode fiber coupler, which overcomes the shortcomings of the traditional method of transmitting reflected light through a spatial beam splitter in terms of structural volume and optical path complexity, making the imaging system more integrated and the optical path more stable. (3) The overall optical path adopts all-fiber coupling and combines rigid multimode fiber with flexible fiber, which effectively overcomes the deformation interference of multimode fiber and ensures that the imaging probe is compatible with the operation of the internal cavity.

[0028] In summary, the technical solution of this invention is superior to existing solutions in terms of system integration, imaging speed, stability, operability, and cost-effectiveness. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a multimode fiber optic endoscopic imaging device that utilizes PZT to drive a single-mode fiber to scan and modulate the optical field, provided in an embodiment of the present invention. The specific symbols in the diagram are as follows: 1. Laser; 2. Single-mode fiber; 3. Support housing; 4. 4-section piezoelectric ceramic tube; 5. Steel housing; 6. Input port of 2×1 multimode fiber coupler; 7. Output port of 2×1 multimode fiber coupler; 8. Sample; 9. Signal port of 2×1 multimode fiber coupler; 10. Photodetector; 11. Camera; 12. Multifunction I / O card; 13. Host computer.

[0030] Figure 2 This is a schematic diagram illustrating the principle of driving a PZT-single-mode fiber scanner for spiral scanning, provided in an embodiment of the present invention.

[0031] Figure 3This is a schematic diagram of the actual scanning trajectory of the far end of a single-mode optical fiber recorded by a position detector in an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the multimode fiber output speckle image and correlation analysis results provided in an embodiment of the present invention.

[0033] Figure 5 This is a schematic diagram of the sample imaging effect provided in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0035] The overall structure of the multimode fiber optic endoscopic imaging device based on PZT-driven single-mode fiber scanning modulation light field provided in this embodiment of the invention is as follows: Figure 1 As shown, the laser output from laser 1 is coupled through single-mode fiber 2 to provide illumination for the imaging system. The distal end of single-mode fiber 2 passes through a four-segment piezoelectric ceramic tube 4 and is fixed at its end center to form a coaxial structure. This coaxial structure is encapsulated in a support housing 3, which is connected to a steel housing 5 encapsulating a 2×1 multimode fiber coupler via a threaded connection, allowing the distal end of single-mode fiber 2 to couple with the input port 6 of the 2×1 multimode fiber coupler. The host computer 13 controls each segment of the four-segment piezoelectric ceramic tube 4 to move collaboratively under external voltage, driving the distal end of single-mode fiber 2 to scan at high speed. This allows the laser to couple into the multimode fiber from different positions on the fiber core end face of the input port 6 of the 2×1 multimode fiber coupler, exciting different modes of coupling within the multimode fiber, thereby generating continuously varying speckle patterns at the output port 7 of the 2×1 multimode fiber coupler. Before imaging, the host computer 13 controls the camera 11 to pre-calibrate these speckle patterns. During imaging, these speckle patterns illuminate the sample 8. The light reflected from the surface of sample 8, carrying spatial structural information of the sample, is collected again by the output port 7 of the 2×1 multimode fiber coupler. After a specific coupling ratio, the light enters the signal port 9 of the 2×1 multimode fiber coupler and is transmitted to the photodetector 10. Under the control of the host computer 13, the light intensity signal is acquired. Finally, by combining the sample measurement data and the calibrated speckle sequence, the sample image is reconstructed using an algorithm.

[0036] In this embodiment, the single-mode fiber 2, the supporting shell 3, the four-segment piezoelectric ceramic tube 4, the steel shell 5, and the input port 6 of the 2×1 multimode fiber coupler are connected in a concentric structure. In a static state, the distal end of the single-mode fiber 2 is perpendicularly aligned with the core center of the input port 6 of the 2×1 multimode fiber coupler. The coupling distance between the distal end of the single-mode fiber 2 and the input port 6 of the 2×1 multimode fiber coupler is adjustable. The optimal distance is achieved by adjusting the end face of the multimode fiber to the position of the beam waist at the output end of the single-mode fiber. At this position, the diameter of the emitted beam from the single-mode fiber is the smallest, the light field energy is most concentrated, and the correlation between the resulting speckle sequences from the multimode fiber is the lowest, which is beneficial for imaging.

[0037] In this embodiment, the input port 6 to the output port 7 of the 2×1 multimode fiber coupler are encapsulated in a steel housing to form a rigid multimode fiber. This rigid structure prevents bending of the multimode fiber, ensuring stable transmission characteristics. The length of the rigid multimode fiber is designed to be the shortest length required to ensure sufficient mixing of multimode modes, typically less than 10 cm. Bending deformation of the signal-end fiber has no effect on imaging (because imaging only detects the total power of the emitted light from the signal end, without considering the speckle pattern). Therefore, the signal-end fiber and the single-mode fiber are encapsulated in the same flexible structure. By changing the length of this flexible fiber segment, the working length of the endoscope can be adjusted, ensuring that the endoscope can operate flexibly and perform imaging within narrow internal cavities.

[0038] In this embodiment, the specific steps for obtaining sample images using a multimode fiber optic endoscopic imaging device based on PZT-driven single-mode fiber scanning modulation light field are as follows: (A) The host computer 13 controls the multi-function I / O card 12 to generate four voltage drive signals, which are respectively connected to the four partitions of the PZT. These signals drive the coordinated movement of each partition, causing the far end of the single-mode fiber fixed in its center to scan at high speed, thus exciting the multi-mode fiber to generate different speckle patterns. This embodiment uses a helical scanning drive method, such as... Figure 2 As shown, the drive voltage signals applied to the four partitions of the PZT are as follows: (1) in, and To load along x Voltage signals on the first and third sections of the directional movement; and To load along y Voltage signals on the 2nd and 4th sections of the directional movement; and This is the maximum voltage amplitude. , For driving frequency, The modulation frequency.

[0039] One complete scan cycle is the modulation frequency. In the corresponding 1 / 2 cycle, the far end of the single-mode fiber completes the scanning process from the center of the multimode fiber core end face to the edge and back to the center. Figure 3 The data represents the actual scanning trajectory of the far end of a single-mode fiber driven by multiple repeated scans recorded by a position detector, demonstrating that PZT-driven single-mode fiber scanning exhibits excellent repeatability. Apart from helical scanning, other scanning methods, such as Lissajous scanning, as long as their essential principle is to drive a PZT to scan a single-mode fiber, thereby exciting a multimode fiber to generate different speckle patterns, should all fall within the scope of this invention.

[0040] (B) Before imaging, the host computer 13 controls the camera 11 to synchronously acquire the speckle sequence emitted from the output port 7 of the 2×1 multimode fiber coupler. Preferably, the host computer 13 controls the multifunction I / O card 12 to generate a square wave signal with a specific frequency and duty cycle as the camera's acquisition trigger signal. The frequency and duty cycle of the square wave signal can be fixed or variable. The camera uses a fixed exposure time at the rising edge of each square wave of the trigger signal. t Acquire speckle images. A total of [number] images were recorded during the complete scan cycle. M Different speckle images.

[0041] Random speckle scanning imaging requires low correlation between outgoing speckles. Figure 4 The multimode fiber speckle images excited by the helical scan shown in step (A) and their correlation analysis show that when the spacing between different scanning positions exceeds 5 micrometers, the normalized cross-correlation coefficient (ZNCC) between the excited speckles is less than 0.75, and the average ZNCC coefficient among all speckle images is less than 0.4, meeting the low correlation requirement for imaging. Since PZT scanning has high repeatability, and the camera acquisition trigger signal is strictly synchronized with the PZT drive signal, the speckle sequence calibrated by multiple scans also has high repeatability. In practice, the speckles excited by multiple repeated scans can be recorded and averaged to further improve the signal-to-noise ratio of the calibrated speckle images.

[0042] (C) During imaging, the output port 7 of the 2×1 multimode fiber coupler is aligned with the sample. Using the same configuration as in step (A), the single-mode fiber is driven again to scan and excite the speckle sequence to irradiate the sample. The light reflected from the sample surface is split by the coupler and enters the signal port 9 of the 2×1 multimode fiber coupler, which is then transmitted to the photodetector 10. The photodetector 10 converts the optical signal into a voltage signal and outputs it. The host computer 13 controls the multi-function I / O card 12 to synchronously acquire this voltage signal. Preferably, the multi-function I / O card 12 receives the same trigger signal as in step (A) as the acquisition trigger signal, and samples at a fixed sampling frequency on each rising edge of the square wave. f s Continuous data acquisition kA voltage signal k Based on exposure time t The relationship between the sampling rate and the sampling rate is as follows: k = f s × t During the complete scan cycle, a total of 10 data dimensions were obtained. M × k The matrix. The integral of each row of the matrix is ​​the measured value of the sample under the corresponding speckle pattern.

[0043] (D) Preprocess the speckle image obtained in step (B) and the measurement values ​​obtained in step (C). The specific steps are as follows: D1. Calculate the mean intensity (mean grayscale value) of each speckle image and discard speckle images with a mean less than a preset threshold, which is set to half the maximum value among the speckle image mean values. The discarded speckles are those excited when a single-mode fiber scans to the outer edge of the multimode fiber core end face. At this time, the laser is not fully coupled into the multimode fiber, so these speckles have low brightness and weak optical signals, which is not conducive to imaging.

[0044] D2. Perform correlation analysis on the retained speckle images to filter out highly correlated speckle images that are detrimental to image reconstruction. These speckles usually originate from scan positions that are close to each other. In this embodiment, the ZNCC coefficient is used to evaluate the correlation between two speckle images. Starting from the second speckle image, the ZNCC coefficient between it and the preceding speckle images is calculated sequentially. Only when the ZNCC coefficient between the speckle image and all preceding speckle images is lower than a set threshold is the speckle image retained. Conversely, if the ZNCC coefficient between the speckle image and any preceding speckle image is greater than the set threshold, the speckle image is filtered out. Empirically, the threshold for the ZNCC coefficient should be set between 0.7 and 0.8. All retained speckle images are arranged in order to form a low-correlation speckle matrix. .

[0045] D3. Sum the measured value matrix row by row, extract the measured values ​​corresponding to the low-correlation speckle sequences, and construct the measured value vector. ; (E) Creating sample images speckle matrix With the measured value vector Mathematical model between them: (2) in, This represents the noise introduced during measurement. The above model is solved using optimization algorithms, such as the commonly used compressed sensing reconstruction algorithm, to reconstruct the sample image. . Figure 5This is a schematic diagram illustrating the imaging effect of the resolution plate and checkerboard test sample provided in an embodiment of the present invention.

[0046] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multimode fiber optic endoscopic imaging device, characterized in that, include: A laser, used to output laser light; Four-zone piezoelectric ceramic tube; A single-mode optical fiber is coupled to a laser at its near end and passes through a four-segment piezoelectric ceramic tube at its far end, forming a coaxial structure. A supporting outer shell is used to encapsulate the aforementioned coaxial structure; A multimode fiber coupler has an input port, an output port, and a signal port. The input port is coupled to the far end of a single-mode fiber encapsulated in a support housing. A photodetector, connected to the signal port, is used to acquire the light intensity signal after it has been reflected by the sample, collected by the output port, and split by a multimode fiber coupler during imaging. The camera acquires the speckle sequence emitted from the output port for calibration of the speckle sequence before imaging. The host computer controller controls the synchronous acquisition of the camera and the signal acquisition of the photodetector. It controls the coordinated movement of each section of the four-segment piezoelectric ceramic tube to drive the far end of the single-mode fiber to scan on the fiber core end face of the input port, so that the laser is coupled into the multimode fiber from different positions, exciting and generating a continuously changing speckle sequence and emitting it from the output port; the sample image is reconstructed by combining the calibrated speckle sequence with the measured values.

2. The multimode fiber optic endoscopic imaging device according to claim 1, characterized in that, In a static state, the far end of the single-mode fiber is perpendicularly aligned with the center of the fiber core end face of the input port, and the coupling distance between the far end of the single-mode fiber and the input port is adjustable.

3. The multimode fiber optic endoscopic imaging device according to claim 1, characterized in that, The input port is connected to the supporting shell via a rigid shell through a threaded connection, so that the far end of the single-mode fiber is coupled to the input port; the multimode fiber between the input port and the output port is encapsulated in the rigid shell to form a rigid multimode fiber segment; the fiber of the signal port is encapsulated in the same flexible structure as the single-mode fiber.

4. A multimode fiber optic endoscopic imaging method based on the device according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Scanning drive: The host computer controller controls the four-zone piezoelectric ceramic tube to drive the far end of the single-mode fiber to move along the predetermined scanning trajectory, thereby exciting the multimode fiber to generate different speckle patterns. (2) Pre-calibration: Before imaging, the host computer controller controls the camera to synchronously acquire M different speckle images emitted from the output port within a complete scanning cycle, which are used as the calibration speckle sequence; (3) Sample measurement: During imaging, the scanning is driven with the same configuration as in step (1) so that the speckle sequence illuminates the sample. The photodetector synchronously collects the light signal output from the signal port after being reflected by the sample, which is used as the measurement data. (4) Data preprocessing: The speckle image obtained in step (2) and the measurement values ​​obtained in step (3) are preprocessed to remove low-brightness speckles and high-correlation speckles, and the low-correlation speckle matrix and the corresponding measurement value vector are obtained. (5) Image reconstruction: Establish a mathematical model between the sample image, the low-correlation speckle matrix and the measurement value vector, and solve it through an optimization algorithm to reconstruct the sample image.

5. The multimode fiber optic endoscopic imaging method according to claim 4, characterized in that, The predetermined scanning trajectory mentioned in step (1) is a spiral scan or a Lissajous scan.

6. The multimode fiber optic endoscopic imaging method according to claim 4, characterized in that, The camera's acquisition and the photodetector's signal acquisition are both triggered synchronously by the same trigger signal as the scanning drive in step (1).

7. The multimode fiber optic endoscopic imaging method according to claim 4, characterized in that, In step (4), data preprocessing includes: (4-1) Calculate the mean of each speckle image and remove speckle images with a mean less than a preset threshold; (4-2) Perform correlation analysis on the retained speckle images and filter out speckle images whose normalized cross-correlation coefficient with the retained speckle images exceeds the set threshold; (4-3) Extract the measurement values ​​corresponding to the retained speckle image from the measurement value matrix to form the measurement value vector.

8. The multimode fiber optic endoscopic imaging method according to claim 7, characterized in that, The preset threshold for the mean is half of the maximum value among all speckle images; the set threshold for the normalized cross-correlation coefficient is 0.7 to 0.

8.

9. The multimode fiber optic endoscopic imaging method according to claim 4, characterized in that, In step (5), the mathematical model is as follows: in, A vector of measured values; It is a low-correlation speckle matrix; For sample images; For measuring noise.

10. The multimode fiber optic endoscopic imaging method according to claim 4, characterized in that, In step (5), the optimization algorithm is the compressed sensing reconstruction algorithm.

Images