Multispectral holographic imaging system and imaging method

Abstract

The invention discloses a multispectral holographic imaging system and an imaging method. The system comprises a multi-wavelength light source module which is composed of a plurality of light source assemblies which are independently driven and have different wavelengths; the optical fiber coupling module is composed of a plurality of optical fiber bundles which are connected with the emergent end face of the light source assembly and used for restraining optical signals of the light source assembly as point light sources. Light signals of the light source assembly are constrained to the light emitting area to form an equivalent point light source; the image acquisition module comprises a sample jig and an image sensor which are coaxially arranged with the emergent end face of the optical fiber bundle, and the image sensor is used for acquiring spectral interferograms of the object light and the reference light; and the control processing module is used for sequentially controlling the switching of each wavelength light source assembly, analyzing and processing a plurality of spectral interferograms, and reconstructing the three-dimensional morphology of the sample through an angular spectrum diffraction algorithm. The problems of aberration, field depth limitation, view limitation, complex structure, high cost, resolution limitation and the like in the traditional microscopic imaging technology can be solved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of optical imaging technology, and in particular to a multispectral holographic imaging system and imaging method. Background Art

[0002] Traditional microscopy relies primarily on optical lenses for focusing and imaging. These lenses inevitably introduce aberrations, which compromise image quality. Traditional microscopes also have a limited depth of field, making it difficult to image thick samples in their entirety. Furthermore, the field of view is typically small, necessitating image stitching to obtain a larger field of view. High-resolution microscopes typically require complex optical systems and expensive lenses, increasing equipment costs.

[0003] At present, holographic imaging has become an important high-resolution imaging technology for electron microscopes. Holographic imaging can reconstruct the three-dimensional information of an object by recording the interference pattern of light waves. Although traditional holographic imaging methods (such as off-axis digital holography) can provide high-resolution imaging, they also have some problems. Traditional holographic imaging has high requirements for light sources, requiring light sources with high coherence and stability, and high requirements for the precision of optical components. The precision and stability of optical components such as beam splitters and reflectors directly affect the imaging quality. Any slight structural error may cause distortion of the interference fringes. There is a correlation between resolution and imaging field of view, making it difficult to achieve high resolution and wide field of view at the same time.

[0004] Multispectral imaging technology can provide information about a sample at multiple wavelengths, which is important for sample classification and analysis. Traditional multispectral imaging technology usually requires complex optical systems and multiple lenses, increasing the complexity and cost of the equipment.

[0005] In summary, although traditional microscopy and holographic imaging technologies have made significant progress in their respective fields, they still have some limitations. Summary of the Invention

[0006] In response to the above-mentioned shortcomings of the existing technology, this application provides a multispectral holographic imaging system and imaging method that can achieve low-cost, lightweight, high-resolution multispectral microscopic imaging. It solves the problems existing in traditional microscopic imaging technology, such as aberrations, depth of field limitations, field of view limitations, complex structure, high cost, and limited resolution.

[0007] In a first aspect, an embodiment of the present application provides a multispectral holographic imaging system, comprising:

[0008] Multi-wavelength light source module, consisting of multiple independently driven light source components of different wavelengths;

[0009] an optical fiber coupling module, composed of a plurality of optical fiber bundles, the optical fiber bundles being connected to the output end face of the light source assembly and being used to constrain the optical signal of the light source assembly to be a point light source;

[0010] Used to constrain the light output area of the light signal of the light source assembly to form an equivalent point light source;

[0011] An image acquisition module, comprising a sample fixture and an image sensor coaxially arranged with the output end face of the optical fiber bundle, wherein the image sensor is used to collect a spectral interference pattern of the object light and the reference light;

[0012] The control and processing module is used to control the switching of each wavelength light source component in a sequential manner, analyze and process multiple spectral interference patterns, and reconstruct the three-dimensional morphology of the sample through the angular spectrum diffraction algorithm.

[0013] As a preferred solution, the optical fiber bundle includes a multimode optical fiber bundle or a single-mode optical fiber, and a plurality of the optical fiber bundle arrays are formed to couple the optical signals of the light source components of each wavelength to the same fixed output end face, and constrain the light output area to form an equivalent point light source;

[0014] The exit end face of the optical fiber bundle is fixed and perpendicular to the working plane of the image sensor.

[0015] As a preferred solution, the sample fixture has an adjustable spacing mechanism for achieving:

[0016] Independent adjustment of the working distance Z1 between the sample and the output end face of each wavelength light source assembly;

[0017] Independent adjustment of the imaging distance Z2 between the sample and the photosensitive surface of the image sensor.

[0018] As a preferred solution, the spectral response range of the image sensor covers the wavelengths of all light source components, and no optical lens is provided at the front end.

[0019] As a preferred solution, the multi-wavelength light source module includes at least four light source components with different wavelengths, and the wavelength range includes ultraviolet, visible light or near-infrared bands.

[0020] As a preferred solution, the pixel size of the image sensor is less than 2.5 μm, and the spectral response range covers the wavelength band of the light source assembly.

[0021] As a preferred solution, the light source assembly includes any one of a laser diode, a light emitting diode and a superluminescent diode.

[0022] In a second aspect, the present application provides a multispectral holographic imaging method, which uses the system provided in the first aspect, including the steps of:

[0023] By sequentially controlling the light source components of each wavelength to light up in sequence, the optical fiber coupling module constrains the light signals emitted by each wavelength light source component to be emitted as a point light source;

[0024] Controlling the image sensor to collect spectral interference patterns of object light and reference light scattered by the sample at various wavelengths;

[0025] By fusing multiple spectral interference patterns using the angular spectrum diffraction theory algorithm, the three-dimensional morphology and spectral characteristics of the sample are reconstructed based on the phase differences of multiple spectral interference patterns.

[0026] As a preferred solution, the angular spectrum diffraction algorithm includes:

[0027] Perform angular spectrum diffraction calculation on the spectral interference pattern corresponding to each wavelength to obtain the initial phase distribution;

[0028] Scattering noise and coherent noise are suppressed by weighted fusion algorithm to improve imaging robustness;

[0029] The material components are classified based on the differences in absorption characteristics at different wavelengths.

[0030] As a preferred solution, before collecting the spectral interferogram, the following is also included:

[0031] According to the thickness of the sample, the sample fixture is controlled to adjust the distance Z1 between the sample and the emission end face of the light source assembly and the distance Z2 between the sample and the photosensitive surface of the image sensor to make the obtained spectral interference pattern clear.

[0032] In summary, the multispectral holographic imaging system and imaging method provided by the present application are characterized by a multi-wavelength light source module composed of a plurality of independently driven light source components of different wavelengths; a fiber coupling module composed of a plurality of fiber bundles, which are connected to the output end face of the light source component and are used to constrain the light signal of the light source component to be a point light source; and a method for constraining the light signal of the light source component to a light output area to form an equivalent point light source; an image acquisition module comprising a sample fixture and an image sensor coaxially arranged with the output end face of the fiber bundle, the image sensor being used to collect the spectral interference pattern of the object light and the reference light; a control and processing module being used to sequentially control the switching of each wavelength light source component, analyze and process multiple spectral interference patterns, and reconstruct the three-dimensional morphology of the sample through an angular spectrum diffraction algorithm. This system can achieve low-cost, lightweight, high-resolution multispectral microscopic imaging. It can solve the problems of aberration, depth of field limitation, field of view limitation, complex structure, high cost, and limited resolution existing in traditional microscopic imaging technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of a module of a multispectral holographic imaging system provided in this application;

[0034] Figure 2 A schematic structural diagram of another multispectral holographic imaging system provided in this application;

[0035] Figure 3 A schematic structural diagram of another multispectral holographic imaging system provided in this application;

[0036] Figure 4 A schematic structural diagram of another multispectral holographic imaging system provided in this application;

[0037] Figure 5 A schematic structural diagram of another multispectral holographic imaging system provided in this application;

[0038] Figure 6 A schematic diagram of a multispectral holographic imaging method provided in this application;

[0039] Figure 7 A schematic diagram of the mechanical structure of a multispectral holographic imaging system provided in this application;

[0040] Figure 8 A schematic diagram of a logic block diagram of a multispectral holographic imaging method provided in this application;

[0041] Figure 9 It is a multispectral hologram collected and obtained in this application.

[0042] In the picture:

[0043] 10. Multi-wavelength light source module; 20. Fiber coupling module; 30. Image acquisition module; 40. Control and processing module; 11. Light source assembly; 12. Support frame; 13. Multi-spectral light source switching device; 21. Fiber bundle; 22. Output end face; 31. Sample fixture; 32. Image sensor; 33. Mechanical module. DETAILED DESCRIPTION

[0044] The present application will be described in further detail below in conjunction with the accompanying drawings and examples. It will be understood that the specific embodiments described herein are merely intended to explain the present application and are not intended to limit the present application. It should also be noted that, for ease of description, only portions, rather than all, of the structures relevant to the present application are shown in the accompanying drawings. Various modifications and variations can be made in the present application without departing from the spirit or scope of the present application, which will be apparent to those skilled in the art. Therefore, the present application is intended to cover modifications and variations of the present application that fall within the scope of the corresponding claims (technical solutions claimed for protection) and their equivalents. It should be noted that the embodiments provided in the present application examples can be combined with each other without contradiction.

[0045] Figure 1 This is a module diagram of a multispectral holographic imaging system provided in this application. Figure 2 This is a schematic diagram of the structure of another multispectral holographic imaging system provided in this application. Figure 3 This is a schematic diagram of another multispectral holographic imaging system provided in this application, refer to Figure 1-Figure 3The multi-spectral holographic imaging system provided in the embodiment of the present application includes a multi-wavelength light source module 10, a fiber coupling module 20, an image acquisition module 30 and a control and processing module 40. Among them, the multi-wavelength light source module 10 is composed of a plurality of independently driven light source components 11 of different wavelengths. The fiber coupling module 20 is composed of a plurality of fiber bundles 21, and the fiber bundle 21 is connected to the output end face of the light source component 11, and is used to constrain the light signal of the light source component 11 to be a point light source. The image acquisition module 30 includes a sample fixture 31 and an image sensor 32 arranged coaxially with the output end face of the fiber bundle 21, and the image sensor 32 is used to collect the spectral interference pattern of the object light and the reference light. The control and processing module 40 is used to control the switching of each wavelength light source component 11 in time sequence, analyze and process multiple spectral interference patterns, and reconstruct the three-dimensional morphology of the sample through the angular spectrum diffraction algorithm.

[0046] The multispectral holographic imaging system provided by this application does not have an optical lens in the imaging light path. Through the coordinated action of the multi-wavelength light source module 10, the fiber coupling module 20, and the image acquisition module 30, high-resolution, wide-field imaging can be achieved. It is not affected by the aberrations of traditional optical lenses, and the entire system is simpler, lighter, and lower in cost. Specifically, it includes:

[0047] refer to Figure 2 and Figure 3 The multi-wavelength light source module 10 utilizes a modular design and consists of multiple independently controllable light source assemblies 11. Each light source assembly 11 integrates a specific wavelength light source and a supporting driver unit, enabling independent and precise adjustment of optical power. The control processing module 40 sequentially controls the light source assemblies 11, sequentially connecting them to the optical path and activating them. This system enables multi-wavelength time-sharing imaging, thereby completing high-precision multispectral image acquisition.

[0048] Optionally, the light source assembly 11 includes, but is not limited to, a laser diode (LD), a light emitting diode (LED), or a superluminescent light emitting diode (SLD). Different substances have different absorption and scattering characteristics at different wavelengths. This application can obtain spectral information of the target at multiple wavelengths by selecting appropriate wavelengths based on the characteristics of the sample, providing richer color and material characteristic data while reducing noise.

[0049] The fiber coupling module 20 is constructed from a precisely arranged multi-fiber bundle 21. By precisely matching the fiber core size to the light source's exit surface, it effectively limits the beam divergence angle and the light exit area of the light source entering the optical path, thereby precisely adjusting the position of the light exit surface of the light source assembly 11 and the end face of the coupled fiber. The fiber bundle transmits the light source into the imaging optical path and constrains the light exit area so that the light source within the optical path can emit light similar to a point source. This helps improve the spatial coherence of the light source, ensuring that the incident angle and incident position of each wavelength remain unchanged, thereby enhancing the quality of holographic imaging. This module can effectively enhance the fringe contrast of multispectral holographic imaging and is particularly suitable for phase-sensitive imaging applications.

[0050] Optional, reference Figure 3 , the optical fiber bundle 21 includes a multimode optical fiber bundle or a single-mode optical fiber, and is composed of an array of multiple optical fiber bundles 21, which are used to couple the optical signals of each wavelength light source component to the same fixed exit end face 22, and constrain the light-emitting area to form an equivalent point light source. Among them, the exit end face position of the optical fiber bundle 21 is fixed and perpendicular to the working plane of the image sensor 32. The present application couples optical signals of multiple wavelengths into a bundle to the same fixed exit end face 22 through a multimode optical fiber or a single-mode optical fiber, and the light-emitting surface of the coupled optical fiber is fixed on the axis of the imaging optical path, so that the irradiation angle and position of each wavelength of light are the same each time, avoiding the introduction of spectral distortion and uncertainty errors due to angle deviation and position deviation.

[0051] The control processing module 40 can be implemented as an integrated circuit (IC), a processor, a microprocessor, or the like, such as a central processing unit (CPU), or can also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The control processing module 40 stores a control program for controlling the multi-wavelength light source module 10, the fiber coupling module 20, and the image acquisition module 30.

[0052] Optionally, the image acquisition module 10 includes a high-resolution image sensor, which includes but is not limited to a CMOS color camera, a CCD color camera, a standard RGB color camera, etc. The high-resolution image sensor can record the holographic image after interference. It is installed in the imaging path of the sample and connected to the control processing module 40 for image acquisition and transmission. The spectral response range of the image sensor 32 covers the wavelengths of all light source components 11, and no optical lens is provided at the front end. Among them, the optical lens refers to an optical element with focusing, collimation, imaging or splitting functions.

[0053] The pixel size of the image sensor 32 is less than 2.5 μm, and the spectral response range covers the wavelength band of the light source component, for example, 380-1100 nm. In other words, the corresponding spectrum of the image sensor includes all wavelength bands of the multi-spectral light source.

[0054] It should be noted that the image sensor records the intensity distribution of the interference image and performs phase recovery based on the intensity image. Figure 2 and Figure 3 The incident light is scattered by the sample M under test, generating a random phase that depends on the non-uniformity of the sample M and the wavelength of the radiation. Therefore, monochromatic images at different wavelengths have different speckle patterns. During the phase intermediate process, the multi-wavelength monochromatic images are synthesized to enhance the sample features and average the speckle noise, thereby improving the contrast of the useful interference pattern, reducing noise, and achieving higher reconstruction accuracy.

[0055] Figure 4 This is a schematic diagram of the structure of another multispectral holographic imaging system provided in this application. Figure 5 This is a schematic diagram of the structure of another multispectral holographic imaging system provided by this application. Based on the above embodiment, refer to Figure 4 and Figure 5 The sample fixture 31 has an adjustable spacing mechanism for realizing: independent adjustment of the working distance Z1 between the sample M and the emission end face of each wavelength light source assembly 11; and independent adjustment of the imaging distance Z2 between the sample M and the photosensitive surface of the image sensor 32.

[0056] Specific implementations of the adjustment mechanism include, but are not limited to, thread adjustment, guide rail adjustment, and an electrically controlled translation stage. The light source assembly 11, target sample M, and image sensor 32 are arranged on the same axis, with the target sample M at a distance Z1 from the light source assembly 11 and a distance Z2 from the image sensor 32. The distance Z1 between the sample M on the sample fixture 31 and the emission end face of the light source assembly 11 at each wavelength, as well as the distance Z2 between the sample M on the sample fixture 31 and the photosensitive surface of the image sensor 32, are automatically adjusted based on acquisition needs.

[0057] In some embodiments, reference Figure 4The sample is close to the illuminating surface of the point light source, and Z2 > Z1, causing the sample M to scatter near the point light source. As the spherical waves emitted by the point light source are amplified during propagation, they interfere with the reference light, resulting in more details being recorded on the image sensor. The advantage of this method is that the influence of twin images is very small, but the disadvantage is that the imaging field of view is limited.

[0058] In some embodiments, reference Figure 5 , for example, the adjustment range of Z1 and Z2 satisfies: Z1>80mm, Z2 takes a value between 0mm and 1mm, and maintains the technical effect of Z2<Z1, realizing imaging aberration control, field of view optimization, etc. It should be noted that, according to the absorption response and phase response of the sample, the smaller Z2 is, the more conducive it is to image reconstruction. When Z2 is small enough, the equivalent numerical aperture (NA) of the system is close to 1. However, when Z2 becomes smaller, the low-frequency response becomes smaller, which is not conducive to phase recovery. Therefore, the distance Z1 between the target sample M and the light source assembly 11 and the distance Z2 between the target sample M and the image sensor 32 need to be reasonably adjusted according to the situation of the sample M. Generally, Z2>0.3mm, and Z1>80mm.

[0059] The equivalent numerical aperture (NA) is an important parameter used to measure the light collection capability or resolution in an optical system. The smaller the equivalent numerical aperture (NA), the weaker the system's light collection capability and resolution.

[0060] The imaging field of view of this system depends on the spot size of the incident light reaching the sample and the size of the effective photosensitive surface of the image sensor. It should be noted that the application sets the spot area of the incident light to be larger than the photosensitive surface size of the image sensor. Figure 5 When Z1 is set to be much larger than Z2, the equivalent magnification of the system is 1, and the target surface size of the image sensor 32 is the imaging field of view of the system. At this time, due to the larger imaging field of view, compared with the existing technology, rapid imaging of large samples can be achieved without sample scanning and field of view stitching.

[0061] Continue to refer Figure 5 The multi-wavelength light source module 10 includes at least four light source assemblies 11 with different wavelengths, covering the ultraviolet, visible, or near-infrared bands, for example, a wavelength range of 280 nm to 1100 nm. In some embodiments, multiple light source assemblies 11 are arranged in an array, with wavelengths covering the visible light range of 400 nm to 700 nm. Multiple adjacent wavelengths can also be spaced ≥ 30 nm apart to ensure spectral separation and reduce crosstalk.

[0062] In an embodiment of the present application, the specific wavelength light source assembly, sample, and image sensor involved in imaging are placed on the same axis. After the light source enters the optical path and acts on the sample, the light carrying the sample information and the unaffected reference light propagate in the same direction and interfere with each other. The resulting holographic interference image is directly recorded by the image sensor, eliminating the need for traditional optical lenses and reducing the impact of aberrations on imaging quality. The distance from the sample to the light source assembly and the distance from the image sensor are adjustable, optimizing the imaging effect. A high-resolution image sensor is used to record the holographic interference image, and an image reconstruction algorithm is run on a computer to achieve multispectral topography reconstruction of the sample. By combining a multispectral light source and an image sensor, holographic interference patterns of multiple wavelengths can be collected, reducing noise. By analyzing the phase and amplitude changes of holographic images of different wavelengths, the object's topography information can be reconstructed more accurately. A control processing module is used as the control and calculation unit to achieve image acquisition and data processing. Together, these constitute a multispectral holographic imaging system without an optical lens in the imaging optical path. It has the characteristics of high resolution, wide field of view, low cost, and lightweight, and is suitable for a variety of microscopic imaging applications.

[0063] Based on the same inventive concept, an embodiment of the present invention provides a multispectral holographic imaging method, Figure 6 This is a flow chart of a multispectral holographic imaging method provided in this application, refer to Figures 1-6 The multispectral holographic imaging system provided by the above embodiment is used to realize the three-dimensional morphology reconstruction of the sample. The multispectral holographic imaging method includes the following steps:

[0064] S101 , the control processing module lights up each wavelength light source component in sequence through timing control, and the optical fiber coupling module constrains the optical signal emitted by each wavelength light source component to be emitted as a point light source.

[0065] S102 : The control processing module controls the image acquisition module to acquire spectral interference patterns of the object light and the reference light scattered by the sample at various wavelengths.

[0066] S103, the control processing module fuses multiple spectral interference patterns through angular spectrum diffraction theory, and reconstructs the three-dimensional morphology and spectral characteristics of the sample based on the phase difference of the multiple spectral interference patterns.

[0067] Specifically, refer to Figure 2 and Figure 3The control processing module 40 controls the light sources of corresponding wavelengths in the multiple light source components 21 to light up, and constrains the light into a point through the optical fiber bundle 21 to be incident on the image sensor 32. The incident light irradiation direction, the sample M, and the image sensor 32 are on the same axis. The incident light is scattered on the sample M. This part of the light carrying phase and amplitude information is called object light, and the light around the object that is not disturbed is called reference light. The object light and the reference light propagate in the same direction and interfere with each other. The image sensor 32 records the holographic image after interference, that is, the spectral interference pattern. The control processing module 40 switches and lights up the light source components 11 of different wavelengths in sequence. The light of the corresponding wavelength enters the holographic optical path and acts on the sample M to interfere. The image sensor 32 collects multiple spectral interference images. The multiple spectral interference images are recorded and transmitted to the computing unit of the control processing module 40. The control processing module 40 reconstructs the true multi-spectral morphological image of the sample and has a higher color reproduction degree through the angular spectrum diffraction algorithm.

[0068] Based on the above embodiment, the angular spectrum diffraction algorithm executed by the control processing module 40 includes:

[0069] Step S1: performing angular spectrum diffraction calculation on the spectral interference pattern corresponding to each wavelength to obtain an initial phase distribution.

[0070] Step S2: Suppress scattered noise and coherent noise through a weighted fusion algorithm to improve the robustness of imaging. Robustness refers to the ability of a system to maintain its functionality and performance in the face of abnormal inputs, parameter changes, or external interference.

[0071] Step S3: classify the material components based on the differences in absorption characteristics at each wavelength.

[0072] Specifically, the image sensor 32 records the intensity distribution of the interference image and performs phase recovery based on the intensity image. The incident light emitted by the light source assembly 11 of the embodiment of the present application is a spherical wave. When the sample M is far enough from the light source, the incident light beam reaching the sample M is approximately a plane wave. The intensity of the reconstructed image based on the interference pattern is recorded as:

[0073] I(x,y,z)=∫∫H(x',y′)·G(x-x',y-y',z)dx'dy';

[0074] Where G(xx′,yy′,z) represents the propagation function from any point A′ on the hologram to the observation point A. (x,y,x) is the spatial position of the observation point A, and (x′,y′,z′) is the spatial position of the corresponding A′ on the hologram. This application uses angular spectrum diffraction theory to perform system modeling and image reconstruction, and obtains the diffraction field of the holographic interference pattern reconstruction as:

[0075]

[0076] Among them, the angular spectrum A of the hologram hologram (α,β)=A ref (α,β)+A obj (α,β).

[0077] For spherical waves, r0 is the reference light propagation distance, r1 is the object light propagation distance, A ref (α, β) is the reference light angular spectrum, A obj (α, β) is the object angular spectrum.

[0078] For a plane wave, A ref (α,β)=δ(α-α0)δ(β-β0),A obj (α,β)=δ(α-α1)δ(β-β1).

[0079] Where (α0, β0) is the reference light spatial frequency, (α1, β1) is the object light spatial frequency. δ is the Dirac function, α and β are the two components of the spatial frequency, which describe the wave number of the light wave in the x and y directions. λ is the wavelength.

[0080] In another embodiment of the present application, multispectral holographic imaging can also record the information of the sample at multiple wavelengths based on the different absorption and scattering characteristics of the sample for light of different wavelengths. After further processing the data, different material components in the same sample can be identified and classified.

[0081] On the basis of the above embodiment, before collecting the spectral interference pattern in step S102, the multispectral holographic imaging method further includes: controlling the sample fixture 31 to adjust the distance Z1 between the sample M and the output end face of the light source assembly 11 and the distance Z2 between the sample M and the photosensitive surface of the image sensor 32 according to the sample thickness, so as to obtain a clear spectral interference pattern.

[0082] Continue to refer Figure 2 and Figure 3 As shown, the present embodiment dynamically adjusts the working distance Z1 between the sample M and the emission end face of the light source assembly 11, as well as the detection distance Z2 between the sample M and the photosensitive surface of the image sensor 32, based on the actual thickness of the sample to be tested, by precisely manipulating the displacement mechanism of the sample fixture 31. By establishing a correlation model between distance parameters and interferometric imaging quality, closed-loop feedback control is used to optimize the Z1 and Z2 values in real time, ensuring optimal spectral interference fringe contrast. Ultimately, a high-definition, high-resolution spectral interferogram is obtained, laying the foundation for subsequent accurate analysis of the sample's true multispectral topography.

[0083] In summary, the multispectral holographic imaging method proposed in this paper leverages fiber bundle transmission constraints and multispectral information to improve phase retrieval quality, analyze material properties, and suppress noise and interference. This simplifies the optical system, reducing hardware complexity and cost, thereby increasing the system's accessibility and application scope.

[0084] Compared with the existing technology, the multispectral holographic imaging method proposed in the present invention has a lens-free design that simplifies the optical path and eliminates the influence of aberrations and multiple reflections of traditional optical lenses on imaging quality. There is no depth of field limitation, and thick samples can be imaged as a whole, providing more comprehensive sample information. By coupling the light source and the optical fiber, there is no structural deviation when switching between multiple wavelengths, and the incident angle and irradiation position of the light source remain consistent each time. The optical fiber output end face constrains the light-emitting area to achieve high coherence while reducing light energy loss. Multispectral imaging suppresses noise and interference, and multi-wavelength images are integrated with high-quality phase reconstruction. The spectral information provides an analytical basis for sample classification and analysis.

[0085] The technical advantage lies in its lensless design, which eliminates the constraints of traditional optical lenses, optimizing the field of view without reducing the optical aperture (NA), resulting in better image quality. The lack of depth of field allows for full-scale imaging of thick samples, making it suitable for microscopic imaging of a wide range of complex samples. The wide field of view eliminates the need for stitching, improving imaging efficiency. Fiber-optic bundle coupling is used to transmit and constrain optical signals, ensuring coherence and light energy utilization while preventing angular and positional deviations caused by spectral switching, which can affect the uniformity and consistency of multispectral images and lead to spectral distortion, compromising image quality.

[0086] Some specific embodiments are listed below for explanation.

[0087] Example 1:

[0088] Figure 7 This is a schematic diagram of the mechanical structure of a multispectral holographic imaging system provided in this application, refer to Figure 8 The system includes multiple light source components 11, a support frame 12, a multi-spectral light source switching device 13, an optical fiber bundle ( Figure 6 ), a sample fixture 31, an image sensor 32, a mechanical module 33 and a control processing module (not shown in the figure).

[0089] Combine Figure 2 and Figure 6The source component 11 uses multiple laser diode (LD) light sources with different wavelengths. Each LD is equipped with an independent drive unit and can independently adjust the output light power. Multiple optical fiber bundles 21 couple multiple LDs into a bundle. The output end face is on the optical axis of the imaging light path, in the same direction as the sample fixture 31 and the image sensor 32. By sequentially lighting the light source components 11 (LD) of different wavelengths, the light source components 11 (LD) of different wavelengths are sequentially imaged in the optical path through the optical fiber bundle. Because the optical fiber output surface constrains the light source's light output area, the light source entering the imaging light path is approximately a point light source.

[0090] Light emitted from the light source assembly 11 passes through a fiber optic bundle before reaching the sample fixture 31. This fixture secures the sample under test and is adjustable in the Z direction, perpendicular to the horizontal plane. The image sensor 32 is a high-resolution digital sensor, either a CCD or CMOS camera, without any lens on the front end. The camera is mounted in the imaging path of the sample. A mechanical module 33 can be manually or automatically switched to adjust the image sensor 32 in the horizontal X and Y directions, aligning the image sensor 32's photosensitive surface with the light transmitted through the sample to ensure the recording of a complete interference image. The image sensor 32 records the captured spectral interference pattern and transmits it to the control and processing module.

[0091] It should be noted that, in this embodiment, in order to make the sample closer to the image sensor 32 , the light source assembly 11 is provided to illuminate the sample M from bottom to top, and the sample M is placed above the sample fixture 31 .

[0092] refer to Figure 3 The sample fixture 31 is made of high-transmittance uniform-thickness glass with a thickness of 1.2 mm. The distance Z1 from the sample M to the exit end face 22 of the light source assembly 11 is 80 mm, and Z2 is 2.2 mm. The distance from the sample fixture 31 to the image sensor 32 is 1 mm.

[0093] Imaging process: By controlling the light source assembly 11 (LD) to light up in sequence, the light beam emitted by the light source assembly 11 is coupled through the optical fiber bundle 21 to form the incident light. The sample M is placed on the sample fixture 31 in the direction of the incident light. The image sensor 32 is located above the sample fixture 31 in the direction of the incident light. After the incident light passes through the sample, it interferes with the reference light. The position of the image sensor 32 in the X and Y directions on the horizontal plane is pre-adjusted so that the image sensor 32 is aligned with the imaging light path. The image sensor 32 records the interference image. The image sensor 32 collects the interference image of the corresponding spectrum and transmits it to the control processing module. After receiving the image, the control processing module turns off the current light source, lights up the light source assembly 11 of the next wavelength, and collects the interference image again. The above steps are repeated until all the preset wavelength interference images are collected, and then all light sources are turned off. The control processing module calculates the phase information of the sample through angular spectrum diffraction from all the spectral interference patterns and reconstructs the sample topography image.

[0094] Example 2

[0095] Furthermore, the embodiment can be optimized as follows Figure 3 As shown, the light source component 11 of the device can be a plurality of laser diodes LD of different wavelengths, and each light source corresponds to a single-mode optical fiber. The function of the single-mode optical fiber is to constrain the light output area. The light source and the optical fiber are coupled together and installed on the mechanical module 33. The output end face of the optical fiber bundle is parallel to the optical axis of the imaging light path. The image sensor 32 can be switched manually or automatically so that it can be adjusted in the horizontal X and Y directions so that the photosensitive surface of the image sensor 32 is aligned with the light passing through the sample, and the light of the corresponding wavelength is incident on the imaging system to ensure that a complete interference image is recorded. The light source component 11 illuminates the sample M from bottom to top, and the sample M is placed above the sample fixture 31. The image sensor 32 records the collected spectral interference pattern and transmits it to the control processing module.

[0096] The imaging process is similar and will not be described again here.

[0097] Example 3

[0098] Furthermore, the embodiment is optimized to Figure 4 and Figure 5 As shown, for an array of light source assemblies, each light source is guided and consolidated into one location via fiber bundles. Multiple bundles are then fixed to the same exit end face 22. The end planes of each fiber bundle 21 are aligned at the same height. Due to the divergence angle of the light emitted from the fiber end face, at a certain distance, the light emitted by each fiber optic cable strikes the sample as a plane wave, with a fixed angle of incidence and position. Light sources of different wavelengths are sequentially illuminated within the optical path to produce interference imaging.

[0099] The system's field of view (FOV) depends on the size of the light spot projected onto the sample and the size of the photosensitive surface of the image sensor 32. Generally, the size of the light spot projected onto the image sensor 32 should be larger than the photosensitive surface of the image sensor 32. The spot radius of the laser beam emitted through a single-mode fiber after propagating a distance z is calculated using the following formula:

[0100]

[0101] Where 2w0 is the mode field diameter of the optical fiber. The available core diameter is approximately 3 μm, λ is the wavelength, and n=1 is the refractive index. Assume that the effective photosensitive surface size of the image sensor 32 is (3.674×2.760) mm. 2 For light of λ=405nm, the light spot propagating onto the image sensor 32 covers the diagonal size of the image sensor 32, and is set. Figure 4 In the figure, Z1+Z2 should be at least 26.8 mm. This setting can obtain a clear spectral interference pattern, which is conducive to reconstructing the sample morphology image.

[0102] Example 4

[0103] Figure 8 This is a logic block diagram of a multispectral holographic imaging method provided in this application. Figure 9 This is the multi-spectral hologram collected and obtained by this application. Figure 7-Figure 9 In this example, four light source components with different wavelengths are used, and the wavelengths are 402±5nm, 488±5nm, 524±5nm, and 635±5nm. It should be noted that the number and wavelength of the light source components are only the specific implementation content of this embodiment and are not restrictive.

[0104] The working distance Z1 between the sample M and the emission end face of each wavelength light source assembly 11, and the imaging distance Z2 between the sample M and the photosensitive surface of the image sensor 32 satisfy the relationship: Z1+Z2=82.2mm. Figure 9 By using the multispectral holographic imaging system and the multispectral holographic imaging method provided in the embodiments of the present application, a clear spectral interference pattern can be obtained.

[0105] It should be noted that transparent or translucent objects have a very low absorption rate for light. Due to the difference between the internal refractive index and the external environment refractive index, after the light acts on the object and is scattered, the main information is recorded in the phase of the light. This application adopts lensless holographic imaging technology. For transparent or translucent objects, it directly records the interference pattern of object light and reference light, and then calculates the true information of the measured sample through a reconstruction algorithm. The lensless design has no depth of field limitation and can perform overall imaging of thick samples, with a large field of view, high resolution, and low cost.

[0106] The multispectral holographic imaging system and imaging method provided in the embodiments of this application combine the advantages of lensless imaging and multispectral imaging, enabling high-resolution, wide-field-of-view, and low-cost multispectral imaging. By eliminating the aberrations of traditional optical lenses, providing wide-field imaging without depth-of-field limitations, and achieving high-resolution and multispectral imaging, they overcome the shortcomings of existing technologies and possess significant innovative significance and application value.

[0107] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and the features of the various embodiments of the present invention may be partially or completely coupled or combined with each other, and may cooperate with each other in various ways and be technically driven. It is possible for those skilled in the art to make various obvious changes, readjustments, combinations and substitutions without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A multispectral holographic imaging system, characterized in that: include: Multi-wavelength light source module, consisting of multiple independently driven light source components of different wavelengths; an optical fiber coupling module, composed of a plurality of optical fiber bundles, the optical fiber bundles being connected to the output end face of the light source assembly and being used to constrain the optical signal of the light source assembly to be a point light source; Used to constrain the light output area of the light signal of the light source assembly to form an equivalent point light source; An image acquisition module, comprising a sample fixture and an image sensor coaxially arranged with the output end face of the optical fiber bundle, wherein the image sensor is used to collect a spectral interference pattern of the object light and the reference light; The control and processing module is used to control the switching of each wavelength light source component in a sequential manner, analyze and process multiple spectral interference patterns, and reconstruct the three-dimensional morphology of the sample through the angular spectrum diffraction algorithm.

2. The system according to claim 1, wherein: The optical fiber bundle includes a multimode optical fiber bundle or a single-mode optical fiber, and is composed of a plurality of optical fiber bundle arrays, which are used to couple the optical signals of the light source components of each wavelength to the same fixed output end face and constrain the light output area to form an equivalent point light source; The exit end face of the optical fiber bundle is fixed and perpendicular to the working plane of the image sensor.

3. The system according to claim 1, wherein: The sample fixture has an adjustable spacing mechanism for achieving: The working distance Z1 between the sample and the output end face of each wavelength light source assembly is adjusted independently; The imaging distance Z2 between the sample and the photosensitive surface of the image sensor is adjusted independently.

4. The system according to claim 1, wherein: The spectral response range of the image sensor covers the wavelengths of all light source components, and no optical lens is provided at the front end.

5. The system according to claim 1, wherein: The multi-wavelength light source module includes at least four light source components with different wavelengths, and the wavelength range includes ultraviolet, visible light or near-infrared bands.

6. The system according to claim 5, characterized in that The pixel size of the image sensor is less than 2.5 μm, and the spectral response range covers the wavelength band of the light source component.

7. The system according to claim 1, wherein: The light source assembly includes any one of a laser diode, a light emitting diode and a superluminescent diode.

8. A multispectral holographic imaging method, using the system according to any one of claims 1 to 7, characterized in that: Including steps: By sequentially controlling the light source components of each wavelength to light up in sequence, the optical fiber coupling module constrains the light signals emitted by each wavelength light source component to be emitted as a point light source; Controlling the image sensor to collect spectral interference patterns of object light and reference light scattered by the sample at various wavelengths; By fusing multiple spectral interference patterns using the angular spectrum diffraction theory algorithm, the three-dimensional morphology and spectral characteristics of the sample are reconstructed based on the phase differences of multiple spectral interference patterns.

9. The method according to claim 8, characterized in that Angular spectrum diffraction algorithms include: Perform angular spectrum diffraction calculation on the spectral interference pattern corresponding to each wavelength to obtain the initial phase distribution; Scattering noise and coherent noise are suppressed by weighted fusion algorithm to improve imaging robustness; The material components are classified based on the differences in absorption characteristics at different wavelengths.

10. The method according to claim 8, characterized in that: Before collecting the spectral interferogram, it also includes: According to the thickness of the sample, the sample fixture is controlled to adjust the distance Z1 between the sample and the emission end face of the light source assembly and the distance Z2 between the sample and the photosensitive surface of the image sensor to make the obtained spectral interference pattern clear.

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