A macro fourier lamination imaging method with large equivalent aperture based on a pure phase spatial light modulator

Abstract

The application provides a macroscopic Fourier stack imaging method based on a pure phase spatial light modulator with a large equivalent aperture, which comprises the following steps: first, laser is emitted by a laser, and then a circular flat-top light is formed by beam expansion and shaping and is incident to the center of a target surface of a pure phase spatial light modulator; under the specific modulation of the pure phase spatial light modulator, the incident light field forms a specific exit light field; the exit light field is enlarged by an imaging lens, and then forms an illumination light field after far distance Fraunhofer diffraction propagation, and the illumination light field is irradiated to the surface of a target object and is collected by a small-aperture camera at a far distance to obtain low-resolution images of different spectral passbands of the target; and the collected low-resolution images are combined with a specific reconstruction algorithm to synthesize a large-range spectrum of the target, so that the resolution of the target is improved. The application can effectively improve the diffraction blur problem caused by the limited optical aperture in macroscopic imaging, and the system is simple and compact, does not need a high-precision displacement device for assistance, and can realize a larger equivalent aperture with a lower system load.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging technology, and particularly relates to a large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator. Background Technology

[0002] Fourier layered microscopy is a next-generation computational and quantitative phase imaging technique that combines phase retrieval and coherent synthetic aperture concepts. Its main principle involves using an LED array to generate multi-angle illumination, shifting the relative position between the target's spectrum and the camera aperture. Low-resolution images of different spectral passbands of the target are acquired through a small-aperture camera, and then phase retrieval is used to interferometrically synthesize a large-scale spectrum of the target, thereby improving its resolution. It primarily addresses the problem of the trade-off between resolution and field of view in traditional microscopy, offering advantages such as high resolution, large field of view, quantitative phase imaging, label-free operation, and low cost.

[0003] In recent years, an increasing number of Fourier layer imaging technologies have attempted to expand from the microscopic field to macroscopic and long-distance imaging in order to solve the diffraction blurring problem caused by the limited optical aperture in macroscopic long-distance imaging.

[0004] From a practical application perspective, macroscopic Fourier stacked imaging should be very suitable for small unmanned motion platforms with limited payload, such as drones, unmanned vehicles, and unmanned ships, because such platforms cannot carry bulky and expensive large-aperture imaging systems, and therefore their resolution will inevitably be limited by the limited optical aperture.

[0005] Currently, the mainstream macroscopic Fourier stack imaging methods at home and abroad can be divided into two categories: camera-scanning Fourier stack and laser-scanning Fourier stack.

[0006] Technical solution of existing technology 1

[0007] Camera-scanning Fourier stack:

[0008] The principle of the camera-scanning Fourier stacking method can be summarized as follows: Under coherent illumination, the object light of a target propagates through the far field and reaches the camera's aperture plane. Assuming this process satisfies the Fraunhofer diffraction condition, the camera's aperture plane can be considered the target object's spectral plane. Using a high-precision displacement stage to move the entire camera allows the camera aperture to perform a stacked scan on the object's spectral plane, allowing information from different positions in the object's spectrum to pass through. This yields multiple low-resolution images required by the Fourier stacking reconstruction algorithm. Then, phase retrieval is used to perform interferometry on the image plane to synthesize a large-scale spectrum of the target, thereby improving the target's resolution.

[0009] Technical solution of existing technology 2

[0010] Laser scanning Fourier transform stack:

[0011] The basic principle of the laser scanning Fourier stacking method is similar to that of the original Fourier stacking microscopy, except that the method of generating multi-angle coherent illumination light is different. It was first proposed by a research team at the Xi'an Institute of Optics and Precision Mechanics. Its core idea is to achieve a relative displacement between the target's spectrum and the camera aperture through variable-angle laser illumination, thereby acquiring low-resolution images of different spectral passbands required for high-resolution reconstruction. Then, phase retrieval methods are used to perform interference on the image plane to synthesize a large-scale spectrum of the target, thus improving the target's resolution.

[0012] Disadvantages of existing technologies one and two

[0013] Both existing macroscopic Fourier layered imaging methods require the assistance of high-precision displacement devices, and their imaging systems still need a large payload space to accommodate camera translation or illumination laser translation in order to obtain a sufficient equivalent aperture. This undoubtedly limits the application of macroscopic Fourier layered imaging methods on small unmanned moving platforms. Summary of the Invention

[0014] The purpose of this invention is to overcome the shortcomings of the existing technology and to achieve an active illumination imaging system with high compactness, low load requirements, and large equivalent aperture to meet the application needs of small unmanned motion platforms.

[0015] Like other macroscopic Fourier stacked imaging methods, the new method can effectively improve the diffraction blurring problem caused by the limited optical aperture in macroscopic imaging. Moreover, its system is simple and compact, does not require the assistance of high-precision displacement devices, and can achieve a larger equivalent aperture with lower system load.

[0016] The present invention adopts the following technical solution:

[0017] A large-equivalent-aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator includes the following steps:

[0018] S1. The laser is emitted by the laser, and after being expanded and shaped, it forms a flat-topped light that is incident on the center of the target surface of the pure phase spatial light modulator.

[0019] S2. Under the specific modulation of a pure phase spatial light modulator, the incident light field forms a specific outgoing light field;

[0020] S3. The emitted light field is magnified by the imaging lens, and after propagating through Fraunhofer diffraction over a long distance, it forms an illumination light field that illuminates the surface of the target object. A small aperture camera is used to collect low-resolution images of different spectral passbands of the target from a distance.

[0021] S4. By using the acquired low-resolution images and combining them with a specific reconstruction algorithm, a large-scale spectrum of the target is synthesized, thereby improving the target's resolution;

[0022] As a preferred embodiment of the present invention, the specific modulation of the pure phase spatial light modulator in step S2 is as follows: the phase distribution on the target surface of the pure phase spatial light modulator consists of all-zero phases superimposed with a fixed phase pattern block. The phase pattern block within the target surface undergoes translational motion within the circular flat-top light range, and different translational distances will modulate different emitted light fields. The formula describing the specific emitted light field formed by this specific modulation is:

[0023] ;

[0024] in, Let the coordinates be the spatial coordinates of the light field. The translation distance of the phase pattern block. It is a fixed component in the emitted light field, which does not change with the movement of the phase pattern block. The changing components in the emitted light field will change as the phase pattern block moves.

[0025] As a preferred embodiment of the present invention, the light field formed after the emitted light field propagates through long-distance Fraunhofer diffraction can be regarded as having a Fourier transform relationship with the original light field. Therefore, the illumination light field formed after diffraction propagation in step S3 is formally expressed as:

[0026] ;

[0027] in, To fix the light field components in the illumination light field, The light field components that vary with the translation of the phase pattern block in the illumination light field are called light field components. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

[0028] As a preferred embodiment of the present invention, the object light field formed by the reflection of the illumination light field onto the surface of the target object is formally represented as follows:

[0029] ;

[0030] in, The composition of the fixed object light field formed by a fixed illumination light field illuminating a target. The optical field components that vary with the translation of the phase pattern patch in the object's optical field. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

[0031] As a preferred embodiment of the present invention, the low-resolution image formed by the object light field being acquired at a distance by a small aperture camera is formally represented as follows:

[0032] ;

[0033] in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. The term representing the change in the object light field with modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation Let the point spread function and coherence transfer function of the imaging system be denoted as . It is an exponential constant.

[0034] As a preferred embodiment of the present invention, the reconstruction algorithm process in step S4 includes the following steps:

[0035] s1. Input multiple low-resolution images acquired;

[0036] s2. Initially guess the spectral information of the two object light fields;

[0037] s3. Based on the initial guess, calculate the th... The low-resolution light field corresponding to the image;

[0038] s4. Using the actual input of the first... The low-resolution image is used as an amplitude constraint to update the optical field amplitude.

[0039] s5. Return to the frequency domain and use the updated optical field amplitude to update the spectrum information of the two object optical fields simultaneously;

[0040] s6. Traverse all low-resolution images to complete one iteration update process;

[0041] s7. Repeat the iteration until convergence.

[0042] As a preferred embodiment of the present invention, the reconstruction algorithm is related to the acquisition model of the low-resolution image, and the forward imaging model of the system is written as follows:

[0043] ;

[0044] in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. This represents the term in the object light field that changes with the modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation. and They are respectively and The spectrum. and These are the point spread function and coherent transfer function of the imaging system, respectively.

[0045] As a preferred embodiment of the present invention, the reconstruction algorithm aims to solve the following optimization problem:

[0046]

[0047] When the spectrum When the reconstruction is completed, the inverse Fourier transform is used to obtain the required high resolution. information.

[0048] The present invention also provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method.

[0049] The present invention also provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to implement the method described thereon.

[0050] The beneficial effects of this invention are:

[0051] This invention does not require the assistance of a high-precision displacement device, and the system is simple and compact. It can achieve a large equivalent aperture with low system load, providing an active illumination imaging solution with high compactness, low load requirements, and large equivalent aperture for the application needs of small unmanned motion platforms. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the optical path of a large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator as described in Embodiment 1 of the present invention.

[0053] Figure 2 This is a flowchart of a specific reconstruction algorithm used in a large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator, as described in Embodiment 1 of the present invention.

[0054] Figure 3This is a comparison between the reconstruction and restoration results obtained by the large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator as described in Embodiment 1 of the present invention and the effect of the original image captured by the camera. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0056] Example 1

[0057] The optical path diagram of the large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator is shown below. Figure 1 As shown, the entire method includes the following steps:

[0058] S1. The laser is emitted by the laser, and after being expanded and shaped, it forms a flat-topped light that is incident on the center of the target surface of the pure phase spatial light modulator.

[0059] S2. Under the specific modulation of a pure phase spatial light modulator, the incident light field forms a specific outgoing light field;

[0060] S3. The emitted light field is magnified by the imaging lens, and after propagating through Fraunhofer diffraction over a long distance, it forms an illumination light field that illuminates the surface of the target object. A small aperture camera is used to collect low-resolution images of different spectral passbands of the target from a distance.

[0061] S4. By using the acquired low-resolution images and combining them with a specific reconstruction algorithm, a large-scale spectrum of the target is synthesized, thereby improving the target's resolution.

[0062] The specific modulation of the pure phase spatial light modulator in step S2 is as follows: the phase distribution on the target surface of the pure phase spatial light modulator consists of all zero phases superimposed with a fixed phase pattern block. The phase pattern block within the target surface undergoes translational motion within the circular flat-top light range, and different translational distances will modulate different emitted light fields. The formula describing the specific emitted light field formed by this specific modulation is:

[0063] ;

[0064] in, Let the coordinates be the spatial coordinates of the light field. The translation distance of the phase pattern block. It is a fixed component in the emitted light field, which does not change with the movement of the phase pattern block. The changing components in the emitted light field will change as the phase pattern block moves.

[0065] After the emitted light field propagates through long-distance Fraunhofer diffraction, the resulting light field and the original light field can be considered to be mutually Fourier transforms. Therefore, the illumination light field formed after diffraction propagation as described in step S3 can be formally expressed as:

[0066] ;

[0067] in, To fix the light field components in the illumination light field, The light field components that vary with the translation of the phase pattern block in the illumination light field are called light field components. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

[0068] When an illumination field shines on the surface of a target object, the reflected object light field can be formally represented as:

[0069] ;

[0070] in, The composition of the fixed object light field formed by a fixed illumination light field illuminating a target. The optical field components that vary with the translation of the phase pattern patch in the object's optical field. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

[0071] The low-resolution image formed by the object light field being acquired at a distance by a small aperture camera can be formally represented as:

[0072] ;

[0073] in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. This represents the term in the object light field that changes with the modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation. Let be the point spread function of the imaging system. It is an exponential constant.

[0074] The specific reconstruction algorithm process described in step S4 is as follows: Figure 2 As shown, it includes the following steps:

[0075] s1. Input multiple low-resolution images acquired. ;

[0076] in, Indicates the first Low-resolution image under secondary illumination light field modulation. This indicates the total number of low-resolution images.

[0077] s2. Initially guess the spectral information of the two object light fields:

[0078] ;

[0079] in, and They are respectively and The spectra of these two object light fields, Indicates the current loop number. This represents the positive Fourier transform.

[0080] s3. Based on the initial guess, calculate the th... The low-resolution light field corresponding to the image: ;

[0081] in, Indicates the first The low-resolution light field corresponding to the image. This represents the inverse Fourier transform. Let be the coherent transfer function of the imaging system. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation.

[0082] s4. Using the actual input of the first... The low-resolution image is used as an amplitude constraint to update the optical field amplitude: ;

[0083] in, This represents the updated light field.

[0084] s5. Return to the frequency domain, and then use the updated optical field amplitude to simultaneously update the spectral information of the two object optical fields: ;

[0085] in, and This represents the updated optical field spectrum information for the two objects.

[0086] s6. Iterate through all low-resolution images This completes one iteration update process;

[0087] s7. Repeat the iteration until convergence;

[0088] The specific reconstruction algorithm proposed in this invention is closely related to the acquisition model of low-resolution images. The forward imaging model of the system can be written as:

[0089] ;

[0090] in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. This represents the term in the object light field that changes with the modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation. and They are respectively and The spectrum. and These are the point spread function and coherent transfer function of the imaging system, respectively.

[0091] In fact, the purpose of the reconstruction algorithm is to solve the following optimization problem:

[0092]

[0093] When the spectrum Once reconstruction is complete, the required high-resolution image can be obtained using the inverse Fourier transform. information.

[0094] The core of the specific reconstruction algorithm proposed in this invention is to solve the above-mentioned optimization problem. Essentially, it is based on the original Fourier stacked reconstruction algorithm, which modifies the spectrum... The recovery process is embedded into the traditional alternating projection algorithm to achieve... and Synchronous reconstruction of information.

[0095] Figure 3 The paper presents a low-resolution original image acquired by a small-aperture camera and a reconstructed high-resolution image. The original low-resolution image shows that the scribe lines of the target are difficult to discern, while the reconstructed image is clearly distinguishable, and the speckle size is significantly reduced. This result demonstrates that the method proposed in this invention effectively improves the equivalent aperture of the system's imaging and achieves higher imaging resolution.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A large-equivalent-aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator, characterized in that, Includes the following steps: S1. The laser is emitted by the laser, and after being expanded and shaped, it forms a flat-topped light that is incident on the center of the target surface of the pure phase spatial light modulator. S2. Under the specific modulation of a pure phase spatial light modulator, the incident light field forms a specific outgoing light field; S3. The emitted light field is magnified by the imaging lens, and after propagating through Fraunhofer diffraction over a long distance, it forms an illumination light field that illuminates the surface of the target object. A small aperture camera is used to collect low-resolution images of different spectral passbands of the target from a distance. S4. By using the acquired low-resolution images and combining them with a specific reconstruction algorithm, a large-scale spectrum of the target is synthesized, thereby improving the target's resolution.

2. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 1, characterized in that, The specific modulation of the pure phase spatial light modulator in step S2 is as follows: the phase distribution on the target surface of the pure phase spatial light modulator is composed of all-zero phase superimposed with a fixed phase pattern block. The phase pattern block in the target surface undergoes translational motion within the circular flat-top light range. Different translational distances will modulate different output light fields. The formula describing the specific output light field formed by this specific modulation is: ； in, Let the coordinates be the spatial coordinates of the light field. The translation distance of the phase pattern block. It is a fixed component in the emitted light field, which does not change with the movement of the phase pattern block. The changing components in the emitted light field will change as the phase pattern block moves.

3. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 2, characterized in that, After the emitted light field propagates through long-distance Fraunhofer diffraction, the resulting light field and the original light field can be considered to have a Fourier transform relationship. Therefore, the illumination light field formed after diffraction propagation as described in step S3 can be formally expressed as: ； in, To fix the light field components in the illumination light field, The light field components that vary with the translation of the phase pattern block in the illumination light field are called light field components. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

4. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 3, characterized in that, When an illumination field shines on the surface of a target object, the reflected object light field is formally represented as: ； in, The composition of the fixed object light field formed by a fixed illumination light field illuminating a target. The optical field components that vary with the translation of the phase pattern patch in the object's optical field. Let the spatial coordinates of the light field be... The imaginary unit, The translation distance of the phase pattern block. The wavelength of the illumination light, The distance at which the illumination light diffracts and propagates.

5. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 4, characterized in that, The low-resolution image formed after the object light field is acquired at a distance by a small aperture camera is formally represented as: ； in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. The term representing the change in the object light field with modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation Let the point spread function and coherence transfer function of the imaging system be denoted as . It is an exponential constant.

6. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 1, characterized in that, The specific reconstruction algorithm process described in step S4 is as follows: s1. Input multiple low-resolution images acquired; s2. Initially guess the spectral information of the two object light fields; s3. Based on the initial guess, calculate the th... The low-resolution light field corresponding to the image; s4. Using the actual input of the first... The low-resolution image is used as an amplitude constraint to update the optical field amplitude. s5. Return to the frequency domain and use the updated optical field amplitude to update the spectrum information of the two object optical fields simultaneously; s6. Traverse all low-resolution images to complete one iteration update process; s7. Repeat the iteration until convergence.

7. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 6, characterized in that, The reconstruction algorithm is related to the acquisition model of low-resolution images. The forward imaging model of the system is written as follows: ； in, Indicates the first Low-resolution image under secondary illumination light field modulation. This represents a fixed term in the object light field. The term representing the change in the object light field with modulation of the illumination light field. Indicates the first Equivalent illumination wave vector under secondary illumination light field modulation and They are respectively and The spectrum, and These are the point spread function and coherent transfer function of the imaging system, respectively.

8. The large equivalent aperture macroscopic Fourier stacked imaging method based on a pure phase spatial light modulator according to claim 7, characterized in that, The purpose of the reconstruction algorithm is to solve the following optimization problem: When the spectrum When the reconstruction is completed, the inverse Fourier transform is used to obtain the required high resolution. information.

9. An electronic device, characterized in that, include: One or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method of any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed by a processor, cause the processor to perform the method described in any one of claims 1 to 8.

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