Phase distortion correction method for digital holographic microscopy system based on adaptive optics

Abstract

The present invention belongs to the field of optical measurement technology, specifically to a method for correcting phase distortion in a digital holographic microscopy system based on adaptive optics. Leveraging the advantage of digital holographic microscopy in acquiring complex amplitude information of light waves over a wide field, the method uses the distorted phase image measured by the digital holographic microscopy system as input, iterates the image using an optimization algorithm until the image evaluation function converges, and obtains a correction pattern for removing phase distortion. The correction pattern is uploaded to an adaptive correction device and the light wavefront is modulated, ultimately achieving accurate compensation for phase distortion. This method can provide a method and means for in-situ, accurate, and rapid phase distortion correction in the field of optical microscopy, particularly quantitative phase imaging.

Description

Technical Field

[0001] The present invention belongs to the field of optical measurement technology, and specifically relates to a method for correcting phase distortion of an optical system, and more particularly to a method for introducing adaptive optics technology into a digital holographic microscopy imaging system to achieve accurate and rapid correction of phase distortion of the digital holographic microscopy system. Background Art

[0002] Quantitative phase imaging technology, due to its label-free and non-invasive properties, can achieve high-contrast imaging and measurement of optically weakly absorbing samples (such as transparent biological cells). Currently, there are many ways to implement quantitative phase imaging, including digital holographic microscopy, intensity transfer equations, Fourier stacking microscopy, and differential phase contrast. Among them, digital holographic microscopy is based on the principle of light wave interference. It constructs an optical path structure to cause interference between the object light wave carrying sample information and the reference light wave. The digital hologram is recorded using an image acquisition device, and then combined with a computer and numerical reconstruction algorithm to achieve the reconstruction of the complex amplitude of the object light wave. Compared with other quantitative phase imaging techniques, digital holographic microscopy has the advantages of wide field, real-time, and high measurement accuracy.

[0003] However, manufacturing defects in optical components and errors in the construction of the optical system can cause system aberrations. Sample and environmental disturbances can also cause distortion in the lightwave phase, seriously affecting the quantitative phase imaging capabilities of digital holographic microscopy systems. To address this issue, researchers first proposed a physical compensation method to correct the phase distortion of digital holographic microscopy systems. For example, by adding a liquid lens with a flexibly adjustable focal length to the optical path system, parabolic phase distortion of lightwaves can be effectively removed. Another physical compensation method is the double exposure method. For example, Chinese patent CN114001643A proposes a double exposure method based on dual wavelengths, which removes phase errors by subtracting the phase images corresponding to the two sets of wavelengths. Numerical compensation is another method for removing phase distortion. For example, by analyzing the distorted image using principal component analysis, the distortion phase information can be obtained and specific distortion terms can be corrected. In addition, researchers in Chinese patent CN118444545A proposed a surface fitting modeling method that achieves numerical compensation for phase distortion by solving an inverse problem.

[0004] Although the aforementioned methods can correct phase distortion, they all have drawbacks. Physical compensation methods require high optical system construction precision and can only correct specific types of distortion. Numerical compensation methods, on the other hand, are numerical post-processing methods that cannot correct distortion in real time and require complex data processing. How to quickly and accurately correct phase distortion in digital holographic microscopy systems in situ and achieve high-quality quantitative phase imaging remains an urgent problem. Summary of the Invention

[0005] Technical problems to be solved

[0006] In order to address the shortcomings of the existing technology, the present invention proposes a method for correcting the phase distortion of a digital holographic microscopy system. This method does not require a wavefront sensor, but uses the model wavefront sensing method in adaptive optics to achieve indirect measurement of the distorted wavefront, and further uses the adaptive correction device in the system to quickly, accurately and in real time correct the light field wavefront distortion.

[0007] Technical Solution

[0008] The idea of the present invention is to take advantage of the fact that digital holographic microscopy can measure the complex amplitude of light waves, use the distorted phase image measured by the system as input, and use the model wavefront sensing method to determine the optimal coefficients of the Zernike polynomials and their correction patterns. The adaptive correction device can compensate and correct the wavefront distortion through the loaded correction pattern.

[0009] In a first aspect, a method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics is provided, characterized by the following steps:

[0010] Step S1: Build a digital holographic microscopy imaging system and use the system to capture a digital hologram containing sample information and distortion information. After numerical reconstruction and preprocessing, a distorted phase image containing only distortion phase information is obtained.

[0011] Step S2: Using the distorted phase image as input, the image is iterated in combination with an optimization algorithm until the image evaluation function converges, the optimal coefficients of the Zernike polynomial are obtained, and the corresponding Zernike phase is calculated. The blazed grating is superimposed on the Zernike phase distribution to obtain a correction pattern;

[0012] Step S3: Building an adaptive distortion correction unit in the digital holographic microscopy system, uploading the correction pattern to the adaptive distortion correction unit to modulate the distorted wavefront and remove phase distortion;

[0013] Step S4: using a digital holographic microscope system containing an adaptive distortion correction unit to photograph the sample hologram again and perform numerical reconstruction on it to obtain a phase image after phase distortion correction.

[0014] Furthermore, the preprocessing process in step S1 is: extracting a rectangular area containing sample information in the reconstructed phase image and setting the phase value of the area to zero to form a distorted phase image.

[0015] Furthermore, the digital hologram numerical reconstruction algorithm in step S1 and step S4 is based on scalar diffraction theory and convolution method.

[0016] Furthermore, the optimization algorithm in step S2 is one or more of the following: hill climbing method, stochastic parallel gradient descent method, simulated annealing method, particle swarm optimization algorithm and genetic algorithm.

[0017] Furthermore, the image evaluation function M in step S2 is composed of

[0018] (1)

[0019] Calculated; where p is the phase mean of the distorted phase image, q represents the standard deviation of the distorted phase image, and the specific expression is:

[0020] (2)

[0021] (3)

[0022] Among them, x and y represent the pixel coordinate values of the image in two orthogonal directions, Represents the phase value of a single pixel, and X and Y represent the total number of pixels.

[0023] Furthermore, the adaptive distortion correction unit in step S3 is composed of an adaptive correction device and a 4f system, wherein the 4f system includes two lenses and a filter hole, and the focal lengths of the two lenses are 100 mm and 150 mm respectively.

[0024] Furthermore, the adaptive correction device in step S3 is a phase-type spatial light modulator.

[0025] Furthermore, the target surface of the adaptive correction device in step S3 is conjugate with the target surface of the image acquisition device.

[0026] In a second aspect, a system for implementing the above-mentioned phase distortion correction method is provided.

[0027] Beneficial effects

[0028] This paper proposes a method for correcting phase distortion in digital holographic microscopy systems based on adaptive optics. This method simply incorporates an adaptive correction unit into the system. Taking advantage of digital holographic microscopy's ability to rapidly measure the complex amplitude of light waves, the distorted phase image is fed back to the adaptive correction unit. A data processing system rapidly searches for the optimal Zernike coefficients and calculates a correction pattern. The control system then uploads this pattern to the correction device, enabling rapid modulation of the wavefront. Ultimately, this method effectively removes phase distortion in the digital holographic microscopy system. This method provides an effective approach for high-precision, long-term quantitative phase imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is a light path diagram of the phase distortion correction method of the digital holographic microscopy system based on adaptive optics involved in the present invention;

[0030] Figure 2 This is the phase imaging result without distortion correction in the embodiment of the present invention.

[0031] FIG3( a ) is a phase distortion correction result based on the hill climbing method in an embodiment of the present invention.

[0032] FIG3( b ) is a phase distortion correction result based on the stochastic parallel gradient descent method in an embodiment of the present invention.

[0033] FIG3( c ) is a phase distortion correction result based on the simulated annealing method in an embodiment of the present invention.

[0034] FIG3( d ) is a phase distortion correction result based on the particle swarm algorithm in an embodiment of the present invention.

[0035] FIG3( e ) is a phase distortion correction result based on a genetic algorithm in an embodiment of the present invention.

[0036] Reference numerals:

[0037] In the figure: 1-He-Ne laser, 2-first lens, 3-polarizer 1, 4-spatial light modulator, 5-second lens, 6-light aperture, 7-third lens, 8-fourth lens, 9-beam splitter prism, 10-microscope objective lens, 11-coupling substrate, 12-sample to be measured, 13-fifth lens, 14-Wollaston prism, 15-polarizer 2, 16-image acquisition device. DETAILED DESCRIPTION

[0038] The present invention will now be further described with reference to the embodiments and accompanying drawings:

[0039] Example 1

[0040] A method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics, comprising the following steps:

[0041] Step S1: Building a digital holographic microscope system, using the system to capture a digital hologram containing sample information and distortion information, and obtaining a phase image containing only distortion phase information, i.e., a distortion phase image, after preprocessing;

[0042] The specific preprocessing process is as follows: for the original phase image reconstructed by the numerical reconstruction algorithm, a rectangular area containing sample information is extracted from the reconstructed phase image and the phase value of the area is set to zero to form a distorted phase image.

[0043] As an optional implementation, the digital hologram numerical reconstruction algorithm is implemented based on scalar diffraction theory and convolution algorithm.

[0044] Step S2: Using the distorted phase image obtained in step S1 as input, the image is iterated in combination with the optimization algorithm until the image evaluation function converges, the optimal coefficients of the Zernike polynomial are obtained, and the corresponding Zernike phase is calculated. The blazed grating is superimposed on the Zernike phase distribution to obtain a correction pattern;

[0045] The optimization algorithm is one or more of hill climbing, stochastic parallel gradient descent, simulated annealing, particle swarm optimization and genetic algorithm to achieve optimization.

[0046] As an optional implementation, the image evaluation function M is recorded as:

[0047] (1)

[0048] Where p is the phase mean of the distorted phase image, and q represents the standard deviation of the distorted phase image. The specific expression is:

[0049] (2)

[0050] (3)

[0051] Among them, x and y represent the pixel coordinate values of the image in two orthogonal directions, Represents the phase value of a single pixel, and X and Y represent the total number of pixels.

[0052] Step S3: Building an adaptive distortion correction unit in the digital holographic microscopy system, uploading the correction pattern to the adaptive distortion correction unit to modulate the distorted wavefront and remove phase distortion;

[0053] The adaptive distortion correction unit (ADC) consists of an adaptive correction device and a 4f system. The 4f system includes two lenses and a filter aperture. The focal lengths of the two lenses can be 100mm and 150mm, respectively. This ADC effectively filters out other diffraction orders generated by the ADC, retaining only the effective diffraction orders.

[0054] The adaptive correction device is a phase-type spatial light modulator. The target surface of the adaptive correction device is conjugate with the target surface of the image acquisition device. This design allows the wavefront corrected by the adaptive correction device and free of distortion to be directly imaged onto the image acquisition device.

[0055] Step S4: using a digital holographic microscope system containing an adaptive distortion correction unit to photograph the sample hologram again and perform numerical reconstruction on it to obtain a phase image after phase distortion correction.

[0056] Example 2

[0057] The present invention relates to an optical system of a phase distortion correction method of a digital holographic microscopy system based on adaptive optics. Figure 1 As shown, it includes: a He-Ne laser 1, a first lens 2, a polarizer 3, a spatial light modulator 4, a second lens 5, a light hole 6, a third lens 7, a fourth lens 8, a beam splitter prism 9, a microscope objective 10, a coupling substrate 11, a sample to be measured 12, a fifth lens 13, a Wollaston prism 14, a polarizer 2 15, and an image acquisition device 16.

[0058] The workflow of the phase distortion correction method implemented using the above system is as follows:

[0059] ① Distortion phase measurement: A 632.8nm laser beam emitted from a He-Ne laser 1 is collimated by a first lens 2 and then passes through a polarizer 3, becoming a linearly polarized beam with a polarization state of 45°. The beam is then incident on a spatial light modulator 4, where only the p-polarization component of the wavefront is modulated by the spatial light modulator 4. A blazed grating is applied to the spatial light modulator 4, splitting the outgoing light wave into multiple diffraction orders. The +1 order diffraction order contains the light wave modulated by the spatial light modulator 4, while the 0th order diffraction order contains the unmodulated light wave. The reflected light wave then enters a 4f system consisting of a second lens 5, a light aperture 6, and a third lens 7. The second lens 5 focuses the diffracted light wave onto the back focal plane. The light aperture 6 allows only the +1 and 0th order diffraction orders to pass through, filtering out all other orders. The light wave is further collimated by the third lens 7. The fourth lens 8 focuses the light wave at the rear focal plane of the microscope objective 10, and is collimated again by the microscope objective 10. The collimated light beam is incident on the coupling substrate 11 at a certain angle and is reflected. The sample 12 to be measured is placed on the upper surface of the coupling substrate 11. The p-polarization component carrying sample information and the s-polarization component not carrying sample information are collimated by the fifth lens 13. The Wollaston prism 14 separates the two orthogonal polarization components at a certain angle. After passing through the second polarizer 15, the two light beams carrying the same polarization component interfere in the overlapping area and the interference fringes are collected by the image acquisition device 16 to form a digital hologram. The digital hologram collected by the system is numerically reconstructed to obtain a phase image containing the distorted background and sample information, such as Figure 2 shown.

[0060] ② Distortion Correction Pattern Calculation: Based on the phase image measured by the system, a phase zeroing operation is performed on the sample area to form a new distorted phase image. Based on the characteristics of the system's phase distortion, several Zernike polynomials are selected. Multiple iterations of the distorted phase image are performed using hill climbing, stochastic parallel gradient descent, simulated annealing, particle swarm optimization, and genetic algorithms until the image evaluation function converges. The optimal coefficients of the Zernike polynomials are ultimately output. The Zernike phase is further calculated and superimposed with the blazed grating to obtain the final distortion correction pattern.

[0061] ③ Adaptive distortion correction: The control system uploads the distortion correction pattern to the spatial light modulator 4, so that the distorted wavefront of the p-polarization component is compensated by the Zernike phase. The light beam without wavefront distortion passes through the subsequent elements along the same path and carries the sample information. The image acquisition device takes another digital hologram and numerically reconstructs it to obtain a phase image. Since the target surface of the spatial light modulator 4 and the target surface of the image acquisition device 16 are conjugate, the reconstructed phase image removes the background distortion and only contains the effective information of the sample, such as Figure 3(a)-Figure 3(e) shown.

[0062] The present invention provides a method and system for correcting phase distortion in a digital holographic microscopy system based on adaptive optics. Leveraging the wide-field acquisition of complex amplitude information of light waves by digital holographic microscopy, the method uses a distorted phase image as input and utilizes an optimization algorithm to iterate the image until the image evaluation function converges, generating a correction pattern for removing phase distortion. The adaptive correction device further modulates the light wavefront based on the correction pattern, ultimately achieving rapid compensation for phase distortion. This method provides a means and method for in-situ, accurate, and rapid phase distortion correction in the field of optical microscopy, particularly quantitative phase imaging.

[0063] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The replacement may be a replacement of a portion of a structure, device, or method step, or it may be a complete technical solution. Any equivalent replacement or modification based on the technical solution and inventive concept of the present invention shall be covered by the scope of protection of the present invention.

Claims

1. A phase distortion correction method for a digital holographic microscopy system based on adaptive optics, characterized in that Here are the steps: Step S1: Build a digital holographic microscope system and use the system to capture a digital hologram containing sample information and distortion information. After numerical reconstruction and preprocessing, a distorted phase image containing only distortion phase information is obtained. Step S2: Using the distorted phase image as input, the image is iterated in combination with an optimization algorithm until the image evaluation function converges, the optimal coefficients of the Zernike polynomial are obtained, and the corresponding Zernike phase is calculated. The blazed grating is superimposed on the Zernike phase distribution to obtain a correction pattern; The image evaluation function M Denoted as: (1) in, p is the phase mean of the distorted phase image, q is the standard deviation of the distorted phase image, denoted as: (2) (3) in, x and y Represents the pixel coordinate values of the image in two orthogonal directions, φ x,y Represents the phase value of a single pixel, X and Y Respectively represent the total number of pixels; Step S3: Build an adaptive distortion correction unit in the digital holographic microscopy system, upload the correction pattern to the adaptive distortion correction unit to modulate the distorted wavefront and remove the phase distortion; the adaptive distortion correction unit consists of an adaptive correction device and 4 f System composition, the 4 f The system consists of two lenses and a filter aperture; Step S4: using a digital holographic microscope system containing an adaptive distortion correction unit to photograph the sample hologram again and perform numerical reconstruction on it to obtain a phase image after phase distortion correction.

2. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, characterized in that: The preprocessing process in step S1 is: extracting a rectangular area containing sample information in the reconstructed phase image and setting the phase value of the area to zero to form a distorted phase image.

3. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, wherein: The digital hologram numerical reconstruction algorithm in step S1 and step S4 is based on scalar diffraction theory and convolution method.

4. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, wherein: The optimization algorithm in step S2 is one or more of the following: hill climbing algorithm, stochastic parallel gradient descent algorithm, simulated annealing algorithm, particle swarm algorithm and genetic algorithm.

5. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, wherein: The focal lengths of the two lenses are 100 mm and 150 mm respectively.

6. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, wherein: The adaptive correction device in step S3 is a phase-type spatial light modulator.

7. The method for correcting phase distortion of a digital holographic microscopy system based on adaptive optics according to claim 1, wherein: The target surface of the adaptive correction device in step S3 is conjugate with the target surface of the image acquisition device.

8. A system for implementing the phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to any one of claims 1 to 7.

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