Optical multi-point focusing method based on NSGA2-R algorithm

Abstract

The invention belongs to the technical field of optical imaging and light control, and relates to an optical multi-point focusing method based on an NSGA2-R algorithm, which is characterized in that laser emitted by a laser source (1) is conjugated to a spatial light modulator (SLM), the spatial light modulator (5) modulates the laser irradiated on the spatial light modulator (5), and then the laser is conjugated to a rear plane of a first microscope objective (9); the first microscope objective (9) gathers the laser to the front surface of the scattering medium (10), the laser passing through the scattering medium (10) is received by the second microscope objective (11), and the laser is received by the camera (12) after passing through the second microscope objective (11); a computer (13) connected with the camera (12) and the spatial light modulator (5) generates a wavefront phase mask through an NSGA2-R algorithm on the computer (13), the spatial light modulator (5) modulates the laser through the wavefront phase mask, and the optimal laser focus intensity and uniformity of laser multi-point focusing are obtained at the camera (12).

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging and light manipulation, and specifically relates to an optical multi-point focusing method based on the NSGA2-R algorithm, which is used to achieve multi-point focusing through a scattering medium and is suitable for optical capture, optogenetics, fluorescence imaging and other fields. Background Art

[0002] Optical focusing and imaging have wide applications in biomedical imaging, optical manipulation, optical communications and other fields. However, the presence of scattering media (such as biological tissue, fog, and frosted glass) will seriously interfere with the propagation of light. Traditional optical focusing methods are difficult to achieve multi-point focusing in scattering media, resulting in blurred imaging and low focusing efficiency. In recent years, wavefront shaping technology based on genetic algorithms (GA) has been proposed to improve the focusing quality in scattering media. However, most of these methods can only achieve single-point focusing, and the optimization efficiency is low, which makes it difficult to meet the needs of multi-point focusing and large-range scanning. In addition, multi-point focusing requires the simultaneous optimization of multiple objectives (such as focus intensity and uniformity), which places higher requirements on the global search capability and optimization efficiency of the algorithm, and existing technologies often cannot meet the requirements. Summary of the invention

[0003] The technical problem to be solved by the present invention is: how to achieve high-quality multi-point focusing in a scattering medium.

[0004] The technical solution adopted by the present invention is: an optical multi-point focusing method based on the NSGA2-R algorithm, wherein the laser light emitted by a laser source (1) is conjugated to a spatial light modulator (SLM), the spatial light modulator (5) modulates the laser light irradiated thereon and then conjugates it to the rear plane of a first microscope objective lens (9), the first microscope objective lens (9) focuses the laser light to the front surface of a scattering medium (10), the laser light passing through the scattering medium (10) is received by a second microscope objective lens (11), and the laser light passing through the second microscope objective lens (11) is received by a camera (12); a computer (13) connected to the camera (12) and the spatial light modulator (5) generates a wavefront phase mask through the NSGA2-R algorithm thereon, the spatial light modulator (5) modulates the laser light using the wavefront phase mask, and the optimal laser focus intensity and uniformity of the laser multi-point focusing are obtained at the camera (12).

[0005] The computer (13) connected to the camera (12) and the spatial light modulator (5) generates a wavefront phase mask through the NSGA2-R algorithm thereon, and the spatial light modulator (5) modulates the laser using the wavefront phase mask, including the following contents:

[0006] Step 1: Initially, the computer (13) generates a set of random wavefront phase masks as the initial population of the NSGA2-R algorithm, each wavefront phase mask represents a wavefront modulation scheme, each wavefront phase mask generates a set number of focuses on the camera (12), the set number is greater than or equal to 3, and the camera (12) feeds back the number of focuses and the focus intensity of the received laser to the computer (13);

[0007] Step 2: The NSGA2-R algorithm establishes the focus enhancement function f1 of the focus point and the uniformity coefficient function f2 between the focus points, evaluates the performance of the wavefront phase mask, and brings the focus number and focus intensity fed back by the camera (12) into the focus enhancement function f1 of the focus point and the uniformity coefficient function f2 between the focus points. The larger the value of the calculated focus enhancement function f1 of the focus point, the better the performance of the wavefront phase mask, and the smaller the value of the uniformity coefficient function f2 between the focus points, the better the performance of the wavefront phase mask.

[0008] Step 3, the NSGA2-R algorithm performs non-dominated sorting and crowding distance calculation on the population according to the evaluation result of the performance of the wavefront phase mask, and selects out excellent wavefront phase masks, that is, the function value of the focus enhancement function f1 of the focus point is used as the horizontal coordinate, the function value of the uniformity coefficient function f2 between the focus points is used as the vertical coordinate, and a rectangular coordinate system is established with the focus enhancement function f1 function value and the uniformity coefficient function f2 function value between the focus points as 0 as the origin, and the distance between the coordinate points corresponding to the uniformity coefficient function f2 function value between the focus points and the uniformity coefficient function f2 function value between the focus points corresponding to the wavefront phase mask is used as the crowding distance, and an excellent wavefront phase mask is selected according to the performance of the wavefront phase mask and the crowding distance;

[0009] Step 4: The NSGA2-R algorithm performs a crossover operation on the screened wavefront phase mask, and maps a phase wavefront mask to a chromosome in the NSGA2-R algorithm. The phase of a single pixel on the SLM corresponds to the gene of the chromosome. The number of pixels and the number of genes are made consistent, and half of the number of genes in any two chromosomes are crossed. A multi-point crossover method is adopted, and a dynamic mutation rate R is introduced. The mutation rate is dynamically adjusted according to the number of iterations, thereby dynamically changing the phase of the wavefront phase mask to balance the global search capability and the local optimization capability, generate a new population, and obtain a set of new wavefront phase masks. The new wavefront phase mask is loaded onto the spatial light modulator (5) to modulate the laser, and the camera (12) feeds back the number of focal points and focal intensity of the received laser to the computer (13);

[0010] Step 5, repeating steps 2 to 4, each repetition is an iteration, and the process is repeated until a preset number of iterations is reached, or the focus intensity and uniformity are no longer significantly improved, and an optimal wavefront phase mask is obtained, wherein the focus intensity is no longer significantly improved, which means that the absolute value of the difference between the uniformity coefficient function f2 function value before and after the iteration is less than the focus intensity setting value, and the uniformity is no longer significantly improved, which means that the uniformity coefficient function f2 function value between the focus points before and after the iteration is less than the uniformity setting value. The laser light emitted by the laser source (1) is conjugated to the spatial light modulator (5), which means that the laser light emitted by the laser source (1) passes through the half-wave plate (2) and is conjugated to the spatial light modulator (5) in free space through a conjugated system composed of a first lens (3) and a second lens (4); the conjugated to the rear plane of the first microscope objective lens (9) means that the laser light modulated by the spatial light modulator (5) passes through the third lens (6), the aperture stop (7), and the fourth lens (8) in sequence, and is conjugated to the rear plane of the first microscope objective lens (9).

[0011] The focus enhancement function f1 of the focus point is:

[0012]

[0013] Where M is the total number of foci, I avg is the average intensity of M foci, I m is the intensity of the mth focus; the uniformity coefficient function f2 between the focus points is

[0014]

[0015] Among them, σ m is the standard deviation of the focus intensity.

[0016] The calculation formula of the dynamic mutation rate R is:

[0017] R (n) =R0×(R end / R0) n / D

[0018] Where R0 is the initial mutation rate, R end is the final mutation rate, D is the attenuation factor, and n is the number of iterations. In the multi-point crossover method, the basic structure of the wavefront phase mask is kept unchanged during the crossover process, and only the local area of ​​the wavefront phase mask is cross-combined.

[0019] The beneficial effects of the present invention are as follows: the present invention proposes an optical multi-point focusing method based on the NSGA2-R algorithm, taking the established optical system as a model, and realizing high-quality multi-point focusing in a scattering medium by dynamically adjusting the mutation rate of an improved non-dominated sorting genetic algorithm (NSGA2-R). The method can generate a focus with high brightness and uniformity in the initial focusing stage, and further optimize the focusing effect by dynamically adjusting the mutation rate, thereby significantly improving the focusing efficiency and uniformity.

[0020] The present invention has high focusing efficiency: through the NSGA2-R algorithm of dynamic mutation rate, the efficiency and uniformity of multi-point focusing are significantly improved. The present invention has strong adaptability: it is suitable for a variety of scattering medium environments and has low requirements for the optical system. The present invention has multi-point focusing capability: it can generate multiple high-brightness focal points at the same time, and is suitable for applications such as optical capture and fluorescence imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a model diagram of an optical system of the present invention;

[0022] Figure 2 This is a flow chart of obtaining an optimal wavefront phase mask according to the present invention;

[0023] Figure 3 It is the crossover and mutation principle diagram of the present invention;

[0024] Figure 4 It is a multi-point focusing effect diagram;

[0025] Figure 5 It is the curve of focus intensity enhancement and uniformity coefficient changing with the number of iterations. DETAILED DESCRIPTION

[0026] In order to better understand the technology of the present invention, the present invention is further described below in conjunction with the accompanying drawings:

[0027] like Figure 1 As shown, the optical experimental system of the present invention includes the following main components:

[0028] The laser source 1 uses a continuous wave laser with a wavelength of 632.8nm to provide a stable light source; the laser source 1 emits laser light, which passes through the half-wave plate 2 and is conjugated to the spatial light modulator 5 in free space by a conjugate system composed of a first lens 3 and a second lens 4, and irradiates a 1080×1080 pixel area on the spatial light modulator 5. The computer 13 generates a group of random wavefront phase masks (including phase information capable of modulating the laser, and the size of the wavefront phase mask is consistent with that of the spatial light modulator) as the initial population, each mask (wavefront phase mask) represents a possible wavefront modulation scheme, and the wavefront phase mask is used to be loaded onto the spatial light modulator 5, and is used for the spatial light modulator 5 to modulate the laser. The modulated laser passes through the third lens 6, the aperture diaphragm 7, and the fourth lens 8 in sequence, and is conjugated to the rear plane of the first microscope objective lens 9. The first microscope objective lens 9 focuses the laser onto the front surface of the scattering medium 10, wherein the aperture diaphragm 7 functions to filter out the light of the first order of diffraction; after passing through the scattering medium 8, the laser is received by the second microscope objective lens 11, and then by the camera 12. The camera 12 extracts the intensity information of the speckle as a feedback signal received by the computer 13, and the camera 12 measures the intensity and uniformity of the laser focus after passing through the scattering medium 10;

[0029] like Figure 2 As shown, the optimization process of the NSGA2-R algorithm is as follows:

[0030] Initialize the population: Computer 13 generates a set of wavefront phase masks as the initial population and loads them onto the spatial light modulator. Each mask contains 1080×1080 pixels, that is, 108×108 modulation units, and one modulation unit corresponds to 10×10 pixels on the SLM. The number of wavefront phase masks in the initial population is N. The randomly generated initial population can provide sufficient diversity for the algorithm to ensure that the optimization process can cover a wider solution space. The diverse initial population helps to avoid the algorithm from falling into the local optimal solution, thereby improving the global optimization capability.

[0031] Multi-objective optimization function construction: The computer 13 receives the laser focus intensity value from the camera 12, and constructs a feedback function including a focus intensity enhancement function f1 and a uniformity coefficient function f2, which is used to evaluate the performance of each wavefront phase mask. The optimization function is as follows:

[0032] (1) Focus point intensity enhancement function f1:

[0033]

[0034] Among them I avg is the average intensity of M foci, M is the number of foci, I m is the intensity of the mth focus. The goal of this function is to maximize the total intensity of all focuses, thereby improving the focusing efficiency.

[0035] (2) Uniformity coefficient function f2 between focus points:

[0036]

[0037] Where M is the number of foci, σ m is the standard deviation of the focal intensity, I m is the intensity of the mth focus. The goal of this function is to minimize the inhomogeneity of the focus intensity and ensure that all focuses have similar intensities.

[0038] By optimizing both the focus intensity and uniformity, the NSGA2-R algorithm is able to achieve high-quality multi-point focusing in scattering media. The optimization function not only considers the total intensity of the focus, but also the uniformity between the focuses, thus achieving stable multi-point focusing in complex scattering environments.

[0039] Non-dominated sorting: The computer performs non-dominated sorting on the initial population based on the results of the optimization function to screen out excellent wavefront phase masks.

[0040] Crowding distance calculation: The computer calculates the crowding distance of each wavefront phase mask to ensure the diversity of the population. Crossover and mutation operations: The computer 13 selects the population through steps 3 and 4, and then performs pairwise crossover and dynamic mutation operations on the wavefront phase masks in the population, such as Figure 3 As shown, a phase wavefront mask is mapped to a chromosome in the NSGA2-R algorithm, the phase of a single pixel on the SLM corresponds to the gene of the chromosome, the number of pixels and the number of genes are made consistent, and half of the number of genes in any two chromosomes are crossed; a new chromosome is generated, and the gene on the chromosome is mutated from "1" to "0" or from "0" to "1". After completing these two processes, a brand new chromosome is generated, that is, a brand new wavefront phase mask population, and the number of phase masks is consistent with the number before the crossover mutation operation.

[0041] Iterative optimization: Repeating the above three steps is an iterative optimization. This process is repeated until the preset number of iterations is reached or the focus intensity and uniformity are no longer significantly improved, and the optimal phase mask is obtained. The computer 13 loads the optimal wavefront phase mask onto the spatial light modulator 5 for the spatial light modulator 5 to modulate the laser. The modulated laser passes through the third lens 6, the aperture diaphragm 7, and the fourth lens 8 in sequence, and is conjugated to the back plane of the first microscope objective 9. The first microscope objective 9 focuses the laser on the front surface of the scattering medium 10, wherein the aperture diaphragm 7 is used to filter out the first order of diffraction light; after passing through the scattering medium 8, the laser is received by the second microscope objective 11 and then by the camera 12. The camera 12 extracts the intensity information of the speckle as a feedback signal received by the computer 13. The camera 12 measures the focus intensity and uniformity of the laser after passing through the scattering medium 10.

[0042] The present invention is described in further detail below in conjunction with the embodiments:

[0043] Implementation plan 1:

[0044] This implementation aims to achieve high-quality multi-point focusing through scattering media using the NSGA2-R algorithm, verify the optimization capability of this method in terms of focus intensity and uniformity, and compare it with the traditional method (GA algorithm).

[0045] Prior conditions: The laser source 1 uses a continuous wave laser with a wavelength of 632.8nm to provide a stable light source; the laser source 1 emits laser light and passes through the half-wave plate 2, which is conjugated to the spatial light modulator 5 in free space by the conjugate system composed of the first lens 3 and the second lens 4, and irradiates the 1080×1080 pixel area on the spatial light modulator 5. The computer 13 generates a set of random wavefront phase masks (including phase information that can modulate the laser, and the size of the wavefront phase mask is consistent with the spatial light modulator) as the initial population, each mask represents a possible wavefront modulation scheme, and the wavefront phase mask is used to load onto the spatial light modulator 5 for the spatial light modulator 5 to modulate the laser light. The modulated laser light passes through the third lens 6, the aperture stop 7, the fourth lens 8 in sequence, and is conjugated to the back plane of the first microscope objective 9. The first microscope objective 9 focuses the laser light on the front surface of the scattering medium 10. Surface, where the aperture diaphragm 7 is used to filter out the diffraction first-order light; the laser passes through the scattering medium 8 and is received by the second microscope objective 11, and then by the camera 12. The camera 12 extracts the intensity information of the speckle as a feedback signal and is received by the computer 13. The camera 12 measures the intensity and uniformity of the laser focus after passing through the scattering medium 10; the parameter settings in the NSGA2-R algorithm are as follows: the population number N is 50, the number of iterations n is 600 times, the number of focus points M is 16, the initial mutation rate R0 in the dynamic mutation rate R is 0.01, and the final mutation rate R end The attenuation factor D is 250, and the phase mask resolution is 1080 × 1080 pixels.

[0046] Multi-point focus contrast effect Figure 4 As shown, Figure 4 (a) shows the focusing diagram of 16 points under the NSGA2-R algorithm. It can be seen that the intensity uniformity of each focus is good. Figure 4 (b) shows a focused image of 16 points under the GA algorithm, and it can be seen that the focus uniformity is very poor. These images are all obtained by camera 12.

[0047] In summary, it can be seen that the performance of NASGA2-R algorithm is better than that of GA algorithm in terms of multi-point focusing.

[0048] Implementation Plan 2:

[0049] This implementation scheme aims to verify the superior optical multi-point focusing performance of the NSGA2-R algorithm through the focus intensity enhancement and uniformity coefficient variation curves with the number of iterations.

[0050] Prior conditions: The laser source 1 uses a continuous wave laser with a wavelength of 632.8nm to provide a stable light source; the laser source 1 emits laser light and passes through the half-wave plate 2, which is conjugated to the spatial light modulator 5 in free space by the conjugate system composed of the first lens 3 and the second lens 4, and irradiates the 1080×1080 pixel area on the spatial light modulator 5. The computer 13 generates a set of random wavefront phase masks (including phase information that can modulate the laser, and the size of the wavefront phase mask is consistent with the spatial light modulator) as the initial population, each mask represents a possible wavefront modulation scheme, and the wavefront phase mask is used to load onto the spatial light modulator 5 for the spatial light modulator 5 to modulate the laser light. The modulated laser light passes through the third lens 6, the aperture stop 7, the fourth lens 8 in sequence, and is conjugated to the back plane of the first microscope objective 9. The first microscope objective 9 focuses the laser light on the front surface of the scattering medium 10. Surface, where the aperture diaphragm 7 is used to filter out the first-order diffraction light; the laser passes through the scattering medium 8 and is received by the second microscope objective 11, and then by the camera 12. The camera 12 extracts the intensity information of the speckle as a feedback signal and is received by the computer 13. The camera 12 measures the intensity and uniformity of the laser focus after passing through the scattering medium 10; the parameter settings in the NSGA2-R algorithm are as follows: the population number N is 50, the number of iterations n is 600 times, the number of focus points M is 8, the initial mutation rate R0 in the dynamic mutation rate R is 0.01, and the final mutation rate is R end The attenuation factor D is 250, and the phase mask resolution is 1080 × 1080 pixels.

[0051] The curves of focus intensity enhancement and uniformity coefficient changing with the number of iterations are shown in Figure 5 As shown, Figure 5 (a) is the focus intensity enhancement curve under the NSGA2-R algorithm. Figure 5 (b) is the focus intensity uniformity coefficient under the NSGA2-R algorithm; as the iteration proceeds, the focus intensity enhancement increases, while the focus intensity uniformity coefficient remains at 100; at the 300th iteration, the focus intensity is enhanced to 551, at which time the focus intensity uniformity coefficient decreases; after the iterative optimization is completed, the focus enhancement reaches a maximum value of 583, while the uniformity coefficient is only 1.5. These images are obtained by computer 13.

[0052] In summary, after the iterative optimization is completed, the focus can maintain high intensity enhancement and uniformity.

Claims

1. An optical multi-point focusing method based on NSGA2-R algorithm, characterized in that: The laser light emitted by the laser source (1) is conjugated to the spatial light modulator (5). The spatial light modulator (5) modulates the laser light irradiated thereon and then conjugates it to the rear plane of the first microscope objective lens (9). The first microscope objective lens (9) focuses the laser light on the front surface of the scattering medium (10). The laser light passing through the scattering medium (10) is received by the second microscope objective lens (11). The laser light passing through the second microscope objective lens (11) is received by the camera (12). A computer (13) connected to the camera (12) and the spatial light modulator (5) generates a wavefront phase mask through the NSGA2-R algorithm thereon. The spatial light modulator (5) modulates the laser light using the wavefront phase mask, and obtains the optimal laser focus intensity and uniformity of the laser multi-point focusing at the camera (12).

2. The optical multi-point focusing method based on the NSGA2-R algorithm according to claim 1, characterized in that: The computer (13) connected to the camera (12) and the spatial light modulator (5) generates a wavefront phase mask through the NSGA2-R algorithm thereon, and the spatial light modulator (5) modulates the laser using the wavefront phase mask, including the following contents: Step 1: Initially, the computer (13) generates a set of random wavefront phase masks as the initial population of the NSGA2-R algorithm, each wavefront phase mask represents a wavefront modulation scheme, each wavefront phase mask generates a set number of focuses on the camera (12), the set number is greater than or equal to 3, and the camera (12) feeds back the number of focuses and the focus intensity of the received laser to the computer (13); Step 2: The NSGA2-R algorithm establishes the focus enhancement function f1 of the focus point and the uniformity coefficient function f2 between the focus points, evaluates the performance of the wavefront phase mask, and brings the focus number and focus intensity fed back by the camera (12) into the focus enhancement function f1 of the focus point and the uniformity coefficient function f2 between the focus points. The larger the value of the calculated focus enhancement function f1 of the focus point, the better the performance of the wavefront phase mask, and the smaller the value of the uniformity coefficient function f2 between the focus points, the better the performance of the wavefront phase mask. Step 3, the NSGA2-R algorithm performs non-dominated sorting and crowding distance calculation on the population according to the evaluation result of the performance of the wavefront phase mask, and selects out excellent wavefront phase masks, that is, the function value of the focus enhancement function f1 of the focus point is used as the horizontal coordinate, the function value of the uniformity coefficient function f2 between the focus points is used as the vertical coordinate, and a rectangular coordinate system is established with the focus enhancement function f1 function value and the uniformity coefficient function f2 function value between the focus points as 0 as the origin, and the distance between the coordinate points corresponding to the uniformity coefficient function f2 function value between the focus points and the uniformity coefficient function f2 function value between the focus points corresponding to the wavefront phase mask is used as the crowding distance, and an excellent wavefront phase mask is selected according to the performance of the wavefront phase mask and the crowding distance; Step 4: The NSGA2-R algorithm performs a crossover operation on the screened wavefront phase mask, and maps a phase wavefront mask to a chromosome in the NSGA2-R algorithm. The phase of a single pixel on the SLM corresponds to the gene of the chromosome. The number of pixels and the number of genes are made consistent, and half of the number of genes in any two chromosomes are crossed. A multi-point crossover method is adopted, and a dynamic mutation rate R is introduced. The mutation rate is dynamically adjusted according to the number of iterations, thereby dynamically changing the phase of the wavefront phase mask to balance the global search capability and the local optimization capability, generate a new population, and obtain a set of new wavefront phase masks. The new wavefront phase mask is loaded onto the spatial light modulator (5) to modulate the laser, and the camera (12) feeds back the number of focal points and focal intensity of the received laser to the computer (13); Step 5, repeat steps 2 to 4, each repetition is an iteration, and this process is repeated continuously until the preset number of iterations is reached, or the focus intensity and uniformity are no longer significantly improved, and the optimal wavefront phase mask is obtained, the focus intensity is no longer significantly improved means that the absolute value of the difference between the uniformity coefficient function f2 function values ​​before and after the iteration is less than the focus intensity setting value, and the uniformity is no longer significantly improved means that the uniformity coefficient function f2 function value between the focus points before and after the iteration is less than the uniformity setting value.

3. The optical multi-point focusing method based on the NSGA2-R algorithm according to claim 2, characterized in that: The laser light emitted by the laser source (1) is conjugated to the spatial light modulator (5), which means that the laser light emitted by the laser source (1) passes through the half-wave plate (2) and is then conjugated to the spatial light modulator (5) in free space through a conjugated system composed of a first lens (3) and a second lens (4); the laser light conjugated to the rear plane of the first microscope objective lens (9) means that the laser light modulated by the spatial light modulator (5) passes through a third lens (6), an aperture stop (7), and a fourth lens (8) in sequence and is conjugated to the rear plane of the first microscope objective lens (9).

4. The optical multi-point focusing method based on the NSGA2-R algorithm according to claim 3, characterized in that: The focus enhancement function f1 of the focus point is: Where M is the total number of foci, I avg is the average intensity of M foci, I m is the intensity of the mth focus; the uniformity coefficient function f2 between the focus points is Among them, σ m is the standard deviation of the focus intensity.

5. The optical multi-point focusing method based on the NSGA2-R algorithm according to claim 3, characterized in that: The calculation formula of the dynamic mutation rate R is R (n) =R0×(R end / R0) n / D Where R0 is the initial mutation rate, R end is the final mutation rate, D is the decay factor, and n is the number of iterations.

6. The optical multi-point focusing method based on the NSGA2-R algorithm according to claim 3, characterized in that: During the crossover process of the multi-point crossover method, the basic structure of the wavefront phase mask is kept unchanged, and only the local area of ​​the wavefront phase mask is cross-combined.

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