Digital holographic microscopy system phase distortion correction method based on adaptive optics

Abstract

The invention belongs to the technical field of optical measurement, and particularly relates to a digital holographic microscopy system phase distortion correction method based on adaptive optics, which has the advantage that optical wave complex amplitude information can be acquired in a wide field by means of digital holographic microscopy, and uses a distortion phase image measured by a digital holographic microscopy system as input to correct phase distortion of the digital holographic microscopy system. And iterating the image by using an optimization algorithm until the image evaluation function converges, and obtaining a correction pattern for removing phase distortion. And uploading the correction pattern to a self-adaptive correction device and modulating the wavefront of the light wave to finally realize accurate compensation of phase distortion. The method can provide an in-situ, accurate and rapid phase distortion correction mode and means for the field of optical microscopic imaging, especially the field of quantitative phase imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and particularly relates to a method for correcting phase distortion of an optical system, and more particularly to a method for accurately and rapidly correcting phase distortion of a digital holographic microscopy system by introducing adaptive optical technology in the digital holographic microscopy system. Background Art

[0002] Due to its label-free and non-invasive characteristics, quantitative phase imaging technology can achieve high-contrast imaging and measurement of optically weakly absorbing samples (such as transparent biological cells, etc.). Currently, there are various implementation methods for quantitative phase imaging, including digital holographic microscopy, intensity transport equation, Fourier ptychography, and differential phase contrast microscopy, etc. Among them, digital holographic microscopy is based on the principle of light wave interference. An optical path structure is built to make the object light wave carrying sample information interfere with the reference light wave. A digital hologram is recorded using an image acquisition device, and then the complex amplitude of the object light wave is reconstructed by combining a computer and a numerical reconstruction algorithm. Compared with other quantitative phase imaging technologies, digital holographic microscopy has the advantages of wide field, real-time, and high measurement accuracy.

[0003] However, manufacturing defects of optical elements and construction errors of optical systems will cause system aberrations, and sample and environmental perturbations will also cause phase distortion of light waves, seriously affecting the quantitative phase imaging function of the digital holographic microscopy system. To address this problem, researchers first proposed a physical compensation method to correct the phase distortion of the digital holographic microscopy system. For example, by adding a liquid lens with a flexibly adjustable focal length in the optical path system, the parabolic phase distortion of light waves 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 two wavelengths. By subtracting the phase images corresponding to the two groups of wavelengths, the phase error is removed. The numerical compensation method is another method for removing phase distortion. For example, by using the principal component analysis method to analyze the distorted image, the distorted phase information can be obtained and specific distortion terms can be corrected. In addition, the researchers in Chinese Patent CN118444545A proposed a method of surface fitting modeling to achieve numerical compensation for phase distortion by solving an inverse problem.

[0004] Although the above methods can correct phase distortion, they all have deficiencies. The physical compensation method requires a high construction accuracy for the optical path system and can only correct specific types of distortion; while the numerical compensation method is a numerical post-processing method, which cannot correct distortion in real time and the data processing process is relatively complex. How to correct the phase distortion of the digital holographic microscopy system in-situ, rapidly, and accurately and achieve high-quality quantitative phase imaging remains an urgent problem to be solved. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] To solve the deficiencies of the prior art, the present invention proposes a method for correcting phase distortion in a digital holographic microscopy system. This method does not require a wavefront sensor and uses the model wavefront sensing method in adaptive optics to indirectly measure the distorted wavefront. Further, an adaptive correction device in the system is used to quickly, accurately, and real-time correct the optical field wavefront distortion.

[0007] Technical solution

[0008] The idea of the present invention is as follows: Relying on the advantage that digital holographic microscopy can measure the complex amplitude of light waves, using the measured distorted phase image of the system as input, the model wavefront sensing method is used to determine the optimal coefficients of Zernike polynomials and their correction patterns. The adaptive correction device realizes the compensation and correction of wavefront distortion by loading the correction pattern.

[0009] In a first aspect, a method for correcting phase distortion in a digital holographic microscopy system based on adaptive optics is provided, characterized in that the steps are as follows:

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

[0011] Step S2: Use the distorted phase image as input, and combine with an optimization algorithm to iterate the image until the image evaluation function converges, obtain the optimal coefficients of Zernike polynomials and calculate the corresponding Zernike phase, and superimpose a blazed grating on the Zernike phase distribution to obtain a correction pattern;

[0012] 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 realize the modulation of the distorted wavefront and remove the phase distortion;

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

[0014] Further, the preprocessing process in step S1 is: Extract a rectangular area containing sample information in the reconstructed phase image and set the phase values of this area to zero to form a distorted phase image.

[0015] Further, the digital hologram numerical reconstruction algorithms in step S1 and step S4 are based on scalar diffraction theory and the convolution method.

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

[0017] Further, the image evaluation function M in the 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] where x and y respectively represent the pixel coordinate values of the image in two orthogonal directions, represents the phase value of a single pixel, and X and Y respectively represent the total number of pixels.

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

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

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

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

[0027] Beneficial effects

[0028] For the phase distortion correction method of the digital holographic microscopy system based on adaptive optics proposed by the present invention, only an adaptive correction unit needs to be introduced into the digital holographic microscopy system. Combining the advantage that digital holographic microscopy can quickly measure the complex amplitude of light waves, the distorted phase image is fed back to the adaptive correction unit, where the data processing system quickly searches for the best Zernike coefficients and calculates the correction pattern, and the control system uploads the pattern to the correction device to realize the fast modulation of the wavefront, and finally effectively removes the phase distortion in the digital holographic microscopy system. This method can provide an effective implementation way for high-precision long-time quantitative phase imaging. Description of the drawings

[0029] Figure 1It is the optical path diagram of the phase aberration correction method for the digital holographic microscopy system based on adaptive optics involved in the present invention;

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

[0031] Figure 3(a) is the phase aberration correction result based on the hill climbing method in the embodiment of the present invention.

[0032] Figure 3(b) is the phase aberration correction result based on the stochastic parallel gradient descent method in the embodiment of the present invention.

[0033] Figure 3(c) is the phase aberration correction result based on the simulated annealing method in the embodiment of the present invention.

[0034] Figure 3(d) is the phase aberration correction result based on the particle swarm optimization algorithm in the embodiment of the present invention.

[0035] Figure 3(e) is the phase aberration correction result based on the genetic algorithm in the embodiment of the present invention.

[0036] Reference numerals:

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

[0038] Now, the present invention will be further described in combination with embodiments and the accompanying drawings:

[0039] Embodiment 1

[0040] A phase aberration correction method for a digital holographic microscopy system based on adaptive optics, the steps are as follows:

[0041] Step S1: Build a digital holographic microscopy system, use the system to capture a digital hologram containing sample information and aberration information, and after preprocessing, obtain a phase image containing only aberration phase information, that is, an aberration phase image;

[0042] The specific preprocessing process is: for the original phase image reconstructed by the numerical reconstruction algorithm, a rectangular area containing sample information is extracted in the reconstructed phase image and the phase values of this area are set to zero to form an aberration phase image.

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

[0044] Step S2: Use the distorted phase image obtained in Step S1 as the input, and combine it with an optimization algorithm to iteratively process the image until the image evaluation function converges, obtain the optimal Zernike polynomial coefficients, calculate the corresponding Zernike phase, and superimpose a blazed grating on the Zernike phase distribution to obtain a correction pattern;

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

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

[0047] (1)

[0048] 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:

[0049] (2)

[0050] (3)

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

[0052] 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;

[0053] The adaptive distortion correction unit 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 100 mm and 150 mm respectively. This adaptive distortion correction unit can effectively filter out other orders diffracted by the adaptive distortion correction unit and only retain the effective diffraction order.

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

[0055] Step S4: Use the digital holographic microscopy system containing the adaptive distortion correction unit to take the sample hologram again and perform numerical reconstruction on it to obtain the phase image after phase distortion correction.

[0056] Embodiment 2

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

[0058] The working process of implementing the phase aberration correction method by using the above system is as follows:

[0059] ① Aberration phase measurement: A laser beam with a wavelength of 632.8 nm emitted from the He-Ne laser 1 is collimated by the first lens 2 and then becomes a linearly polarized light with a polarization state of 45° through the first polarizer 3, and then is incident on the spatial light modulator 4. Only the wavefront of the p-polarization component will be modulated by the spatial light modulator 4. A blazed grating is loaded on the spatial light modulator 4, so that the outgoing light wave is divided into multiple diffraction orders. The +1st diffraction order contains the part of the light wave modulated by the spatial light modulator 4, and the 0th diffraction order contains the part of the light wave not modulated. Then, the reflected light wave is incident on a 4f system composed of the second lens 5, the light passing hole 6, and the third lens 7. The second lens 5 focuses the diffracted light wave on the rear focal plane. The light passing hole 6 only allows the +1st and 0th diffraction orders to pass through and filters out other orders. After passing through the third lens 7, the light wave is further collimated. The fourth lens 8 focuses the light wave at the rear focal plane of the microscopic objective lens 10 and is collimated again by the microscopic objective lens 10. The collimated light beam is incident on the coupling substrate 11 at a certain angle and is reflected. The sample to be measured 12 is placed on the upper surface of the coupling substrate 11. The p-polarization component carrying the sample information and the s-polarization component not carrying the 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 aberration background and the sample information, as Figure 2 shown.

[0060] ② Aberration correction pattern calculation: Based on the phase image measured by the system, the phase of the sample area is set to zero to form a new aberration phase image. According to the characteristics of the system phase aberration, several Zernike polynomials are selected, and the aberration phase image is iterated multiple times by using the hill climbing method, the stochastic parallel gradient descent method, the simulated annealing method, the particle swarm optimization algorithm, and the genetic algorithm until the image evaluation function converges, and finally the optimal coefficients of the Zernike polynomials are output. Further calculate the Zernike phase, and superimpose the Zernike phase with the blazed grating to obtain the final aberration 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 beam with the wavefront distortion removed passes through the subsequent components along the same path and carries the sample information. The image acquisition device takes another digital hologram and performs numerical reconstruction on it to obtain the 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 Figures 3(a)-3(e) shown

[0062] The method and system for correcting phase distortion of a digital holographic microscopy system based on adaptive optics provided by the present invention rely on the advantage of digital holographic microscopy to obtain the complex amplitude information of light waves in a wide field. Using the distorted phase image as the input, the image is iterated using an optimization algorithm until the image evaluation function converges, and a correction pattern for removing phase distortion is obtained. The adaptive correction device further modulates the light wavefront based on the correction pattern, and finally realizes the rapid compensation of phase distortion. This method can provide a way and means for in-situ, accurate and rapid correction of phase distortion in the field of optical microscopy imaging, especially in the field of quantitative phase imaging.

[0063] As mentioned above, only the specific preferred embodiments of the present invention are described, but the protection scope of the present invention is not limited thereto. The substitution may be the substitution of part of the structure, device, method steps, or the entire technical solution. Any equivalent substitution or change made according to the technical solution and inventive concept of the present invention should be covered within the protection scope 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: construct a digital holographic microscope system, and use the system to shoot a digital hologram containing sample information and distortion information, and after numerical reconstruction and preprocessing, obtain a distorted phase image containing only distortion phase information; Step S2: taking the distorted phase image as input, combining the optimization algorithm to iterate the image until the image evaluation function converges, obtaining the optimal coefficients of the Zernike polynomial and calculating the corresponding Zernike phase, and superimposing the blazed grating on the Zernike phase distribution to obtain a correction pattern; Step S3: constructing an adaptive distortion correction unit in the digital holographic microscopy system, and uploading the correction pattern to the adaptive distortion correction unit to modulate the distorted wavefront and remove phase distortion; Step S4: Use 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 phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to claim 1, characterized in that: The digital hologram numerical reconstruction algorithm in step S1 and step S4 is based on scalar diffraction theory and convolution method.

4. The phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to claim 1, characterized in that: 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 phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to claim 1, characterized in that: The image evaluation function M in step S2 is recorded as: (1) Among them, p is the phase mean of the distorted phase image, and q is the standard deviation of the distorted phase image, which can be expressed as: (2) (3) 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.

6. The phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to claim 1, characterized in that: 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.

7. The phase distortion correction method of a digital holographic microscopy system based on adaptive optics according to claim 6, characterized in that: The focal lengths of the two lenses are 100 mm and 150 mm respectively.

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

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

10. A system for implementing the phase distortion correction method of a digital holographic microscopy system based on adaptive optics as described in any one of claims 1 to 9.

Images