Long range wavefront correction fourier lithography system

Abstract

The present application belongs to the field of space optical remote sensing, and provides a long-distance wavefront correction Fourier stack imaging system to improve the resolution and quality of long-distance imaging and solve the imaging problem of traditional technology under the influence of atmospheric turbulence and optical distortion. The system is composed of an illumination subsystem and an imaging subsystem, wherein the illumination subsystem generates a light source with a specific polarization state, and the imaging subsystem includes Hartmann-Shack sensors, an anamorphic lens, a beam splitter, a linear polarizer and other components, which fuse and reconstruct the image into a high-resolution image through Fourier stack imaging technology. At the same time, the Hartmann-Shack sensor monitors the wavefront distortion in real time, and the anamorphic lens corrects according to the feedback information to ensure the imaging quality. The present application combines the distortion wavefront correction module with the Fourier stack imaging technology, effectively overcomes the atmospheric disturbance and system distortion in long-distance imaging, and improves the adaptability and stability of the imaging system in complex environments.

Description

TECHNICAL FIELD

[0001] The present application relates to a long-distance wavefront correction Fourier ptychographic imaging system, belonging to the field of space optical remote sensing. BACKGROUND

[0002] With the rapid development of optical imaging technology, the demand for long-distance high-resolution imaging is increasing in many fields, especially in astronomical observation, national defense monitoring and remote sensing detection. Traditional imaging systems are difficult to meet the requirements of ultra-high resolution and large field of view due to the limitations of the size and resolution of optical elements. In recent years, Fourier ptychographic imaging technology, as a new emerging computational imaging method, has gradually attracted widespread attention. This technology can reconstruct high-resolution images by collecting low-resolution images of objects at multiple angles and combining phase recovery algorithms, thus effectively breaking through the diffraction limit of traditional imaging systems.

[0003] In the field of space optical remote sensing, Fourier ptychographic imaging technology has great potential. By imaging remote sensing objects at multiple angles, this technology can obtain rich frequency domain information, thus realizing high-quality image reconstruction. This method not only enhances the detail presentation of remote sensing images, but also reduces the impact of noise. Therefore, Fourier ptychographic imaging technology has shown high feasibility and application value in space optical remote sensing. However, the challenges faced by long-distance imaging systems are more complex. Due to the large field of view and long distance of the collected images, the phase recovery and reconstruction process is easily affected by external factors such as atmospheric turbulence and system distortion, resulting in a decrease in imaging quality. In order to solve these problems, the introduction of a wavefront correction system is particularly important. Through wavefront correction technology, real-time monitoring and compensation of atmospheric disturbances and optical system distortions can significantly improve the clarity and resolution of imaging, ensuring high-quality remote sensing images in a dynamically changing environment.

[0004] In summary, the combination of Fourier ptychographic imaging technology and wavefront correction system can effectively cope with the multiple challenges in long-distance high-resolution imaging. This combination not only overcomes the influence of atmospheric disturbances, but also improves the imaging quality, thus meeting the needs of modern space optical remote sensing imaging. This innovative imaging scheme is expected to provide more efficient and accurate solutions for astronomical observation, national defense monitoring and remote sensing detection. SUMMARY

[0005] The present application aims to solve the challenges of traditional space optical remote sensing technology in improving image resolution and quality, and provides a high-performance long-distance remote sensing imaging system combining wavefront correction optical system and Fourier ptychographic (FP) method.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] The present application is a long-distance wavefront correction Fourier stack imaging system, which is composed of an illumination subsystem and an imaging subsystem;

[0008] The illumination subsystem comprises a laser, a lens, a pinhole and a linear polarizer, so that the light emitted by the laser is a converging spherical wave in linear polarization state to illuminate the sample to be measured, and the Fraunhofer diffraction is approximated by the converging spherical wave illumination when the far-field condition is not met;

[0009] The imaging subsystem comprises a Hartmann-Shack sensor, an anamorphic mirror, a beam splitter, a linear polarizer, a camera and a motorized translation stage, and the camera composed of the lens and the CCD sensor is moved by the motorized translation stage, so that the camera collects corresponding low-resolution images at different positions;

[0010] The laser emitted by the laser is focused by the lens, and then the high-order mode is filtered out by the pinhole to ensure the quality of the emitted spherical wave, and then the spherical wave is changed into a converging spherical wave by the lens;

[0011] The Hartmann-Shack sensor is used for real-time detection of the change of the wavefront after the atmospheric turbulence and the optical system distortion, and the wavefront error information is transmitted to the wavefront control system;

[0012] The anamorphic mirror adjusts in real time according to the correction information of the wavefront control system to compensate for the wavefront distortion and ensure the quality of the wavefront in the imaging process;

[0013] The linear polarizers are fixed at the exit end of the spherical wave and the front end of the imaging lens respectively, so as to ensure that the light entering the CCD is the specific polarized light emitted by the laser, thereby reducing the interference of stray light;

[0014] The camera comprises a lens and a CCD sensor, the lens is used for imaging the sample to be measured on the CCD sensor, and the CCD sensor is used for recording the low-resolution images collected by the camera at different positions;

[0015] The motorized translation stage is responsible for driving the camera to take pictures of the sample at different positions, and the low-resolution images containing different spectral information are fused and reconstructed into a high-resolution image by the Fourier stack imaging method;

[0016] Compared with the prior art, the present application has the following innovations:

[0017] Fourier ptychographic imaging technology: The present application adopts Fourier ptychographic imaging technology, which effectively improves the resolution and quality of remote sensing images through the iterative fusion of multiple low-resolution images. This method collects low-resolution images at different positions by shifting the camera, obtains different spectral information, and iteratively fuses in spatial and frequency domains, thereby realizing high-resolution remote sensing imaging. Compared with traditional imaging technology, this method has higher noise resistance and sub-diffraction limit imaging capability, and can overcome the influence of atmospheric turbulence and other factors at a larger imaging distance.

[0018] Wavefront correction module: The present application introduces wavefront correction technology to monitor and compensate the influence of atmospheric turbulence on imaging quality in real time. Real-time wavefront data is obtained through a wavefront sensor, and a deformable mirror is used for dynamic adjustment to compensate for the distortion of the optical system, ensuring clear and high-resolution images in long-distance imaging. This module significantly improves the adaptability and imaging stability of the system in complex environments.

[0019] Application of linear polarizer: A linear polarizer is added before the camera where the spherical wave exits to ensure that the light entering the camera is the light emitted by the laser. The linear polarizer can effectively filter out unnecessary stray light, improve the system's response to specific light waves, and enhance the clarity and contrast of the image. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A long-distance wavefront correction Fourier ptychographic imaging system is proposed for the present application.

[0021] Figure 2 The spot shift generated by the Hartmann-Shack sensor for the distorted wavefront.

[0022] Figure 3 The input high-resolution image amplitude and phase. (a) is the input high-resolution image amplitude, and (b) is the input high-resolution image phase.

[0023] Figure 4 The result of Fourier ptychographic reconstruction under ideal conditions. (a) is the original low-resolution image at the center position, and (b) and (c) are the reconstructed high-resolution image amplitude and phase under ideal conditions, respectively.

[0024] Figure 5 The Fourier ptychographic reconstruction result under the action of simulated atmospheric turbulence. (a) is the degraded image of the low-resolution image at the center position after the action of atmospheric turbulence. (b) and (c) are the high-resolution image amplitude and phase reconstructed by the degraded image sequence without correction.

[0025] Figure 6To simulate the Fourier stack system reconstruction after aberration wavefront correction. (a) is the image after correction of the low-resolution image of central degradation. (b) and (c) are the high-resolution image amplitude and phase reconstructed by the low-resolution image sequence after correction.

[0026] Figure 7 The SSIM values of the images reconstructed by the Fourier stack algorithm under the ideal condition, the degradation condition and the correction condition with different iteration numbers. In the figure, 1-laser; 2-lens; 3-needle hole; 4-linear polarizer; 5-lens; 6-sample; 7-deformation mirror; 8-Hartmann-Shack sensor; 9-beam splitter; 10-linear polarizer; 11-imaging lens; 12-CCD sensor; 13-electric translation stage; 14-computer. DETAILED DESCRIPTION

[0027] The present application is based on the Fourier stack technology and the aberration wavefront correction system, and proposes a long-distance wavefront correction Fourier stack imaging system. By combining the Fourier stack imaging technology with the aberration correction system, the problem of imaging resolution decline caused by atmospheric disturbance and system aberration in long-distance imaging is solved. The system detects the wavefront aberration in real time through the Hartmann-Shack sensor, corrects the wavefront by using the deformation mirror, and then iteratively fuses the low-resolution image through the Fourier stack imaging technology, so as to realize high-resolution long-distance imaging.

[0028] As shown in Figure 1 , the long-distance wavefront correction Fourier stack imaging system provided by the present application is composed of an illumination subsystem and an imaging subsystem. The illumination subsystem includes a laser 1, a lens 2, a needle hole 3, a linear polarizer 4 and a lens 5. The imaging subsystem includes a deformation mirror 7, a Hartmann-Shack sensor 8, a beam splitter 9, a linear polarizer 10, an imaging lens 11, a CCD sensor 12 and an electric translation stage 13.

[0029] In combination Figure 1 , the wavefront correction optical remote sensing imaging method based on the Fourier stack provided by the present application comprises the following steps:

[0030] Step 1, the laser 1 emits laser, which becomes a transmitting spherical wave through the lens 2 and the needle hole 3, the transmitting spherical wave becomes a transmitting spherical wave with a polarization state through the linear polarizer 4, and the divergent spherical wave with the polarization state becomes a convergent spherical wave with the polarization state through the lens 5. Because the far field condition cannot be met in the laboratory, the convergent spherical wave illumination is needed to eliminate the secondary phase factor caused by Fresnel diffraction, so that the light field distribution in front of the imaging lens is equivalent to the light field distribution in the far field.

[0031] Step 2, after the sample 6 is irradiated by the light wave, the reflected light is reflected by the deformable mirror 7 to the beam splitter 9, and the beam splitter 9 divides the light into two beams, one of which is collected by the Hartmann-Shack sensor 8, and the other is collected by the CCD sensor 12 through the imaging lens 11. Figure 2 As shown in FIG. 1, when the wavefront is distorted, the light spot collected by the CCD sensor will be offset, and the distortion of the wavefront information can be obtained according to the offset. The distorted wavefront signal collected by the Hartmann-Shack sensor 8 is transmitted to the computer 14, which is converted into a wavefront correction control signal by the control system and transmitted to the deformable mirror 7. Under the action of multiple driving units, the mirror surface of the deformable mirror 7 is deformed, thereby correcting the distorted wavefront.

[0032] Step 4, the camera composed of the imaging lens 11 and the CCD sensor 12 is fixed on the motorized two-dimensional translation stage 13, and the linear polarizer 10 is fixed in front of the camera. The images of the camera at different positions are collected by moving the motorized translation stage 13, and are transmitted to the computer 14 to obtain a batch of original low-resolution images.

[0033] Step 5, the collected low-resolution images are iteratively reconstructed by the Fourier ptychographic algorithm. First, the target high-resolution sample function is estimated. The central low-resolution image is selected as the initial guess, and the complex amplitude distribution o o (x0,y0) is obtained, so that the high-resolution spectrum of the sample function O(u,v) = F{o(x0,y0)} is obtained.

[0034] Step 6, calculate the light field distribution collected by the CCD. When the sample is imaged, it is first Fourier transformed, then low-pass filtered by the optical system, and then Fourier transformed and collected by the CCD. The corresponding light field distribution collected is:

[0035]

[0036] Step 7, update the light field amplitude. Replace the estimated light field amplitude information with the actual low-resolution intensity image collected by the camera, while keeping the phase unchanged, and obtain the updated estimated light field:

[0037]

[0038] Step 8, update the spectrum. Transform the updated and replaced light field to the frequency domain, update the corresponding sub-region and the corresponding pupil function in the frequency domain, and keep other regions unchanged. The update formula is as follows:

[0039]

[0040] Step 9, iteratively update to convergence. Repeat steps 6 to 8 as an iteration for all low-resolution images collected by the camera; repeat the iteration process until the algorithm converges, iteratively reconstructs the high-resolution spectral function of the sample, and obtains the complex amplitude information of the high-resolution sample through inverse Fourier transform.

[0041] In order to verify the feasibility of the above method, verification is carried out by simulation, and the system parameters are set as follows: the wavelength of the laser is 632 nm, the lens F / # is 10, the lens focal length is 75 mm, the lens aperture is 7.5 mm, the pixel size of the CCD sensor is 4.8 μm, the low-resolution image of a 15*15 array is collected, the moving step is 1.2 mm, and the aperture overlap rate reaches 84%.

[0042] First, a series of low-resolution image sequences containing different spectral information are generated, and the camera collects images at different positions, Figure 3 (a) and Figure 3 (b) are the input high-resolution image amplitude and phase, and the original low-resolution image sequence is generated by converting the input complex amplitude image to the frequency domain and intercepting the spectral information of different regions. Figure 4 (a) is the original low-resolution image at the center, Figure 4 (b) and Figure 4 (c) are the high-resolution image amplitude and phase iteratively reconstructed by the Fourier ptychographic algorithm under ideal conditions.

[0043] Then, the degraded images after the action of atmospheric turbulence are generated by Zernike polynomial simulation to simulate the influence of turbulence on light propagation and study its influence on imaging quality. First, the distorted phase distribution is simulated on the pupil plane by randomly generated Zernike coefficients, and then the pupil function is applied to the original low-resolution image sequence to simulate the wavefront distortion caused by atmospheric turbulence, as shown in Figure 5 (a) is the degraded image of the central low-resolution image, Figure 5 (b) and Figure 5 (c) are the high-resolution image amplitude and phase reconstructed by the degraded image sequence without correction.

[0044] The present application simulates the correction effect of the deformable mirror on the distorted wavefront by correcting the Zernike coefficients, generates the corresponding image under the current Zernike coefficient by slightly adjusting each Zernike coefficient, calculates the new gradient, obtains the corrected Zernike coefficient by using the Gaussian fitting method, and corrects the distorted wavefront of the system by the corrected Zernike coefficient. As shown in Figure 6 (a) is the corrected image of the central degraded low-resolution image, Figure 6 (b) and Figure 6(c) high resolution image amplitude and phase reconstructed from the corrected low resolution image sequence.

[0045] Figure 7 The SSIM values of the reconstructed high resolution images under ideal, atmospheric turbulence and distortion correction conditions are shown for different iteration numbers. It can be seen that the corrected low resolution image sequence can well reconstruct the high resolution image.

Claims

1. A long-distance wavefront correction Fourier ptychographic imaging system, comprising an illumination subsystem and an imaging subsystem, the illumination subsystem comprising a laser, a lens, a pinhole, and a linear polarizer, and the imaging subsystem comprising a Hartmann-Shack sensor, a deformable mirror, a beam splitter, a linear polarizer, a camera, and a motorized translation stage; wherein: the laser emits laser light which, after passing through the lens and the pinhole, becomes an outgoing spherical wave, and then, after passing through the lens, becomes a converging spherical wave; the Hartmann-Shack sensor is used to detect in real time the wavefront changes after atmospheric turbulence and optical system distortion, and to transmit wavefront error information to a wavefront control system; the deformable mirror is used to receive correction information fed back by the wavefront control system, and to adjust in real time to compensate for wavefront distortion, thereby ensuring the wavefront quality during imaging; the linear polarizers are respectively arranged at the outgoing end of the spherical wave and the front end of the imaging lens, to ensure that the light entering the CCD is a specific polarized light of the laser, thereby reducing stray light interference; the camera comprises a lens and a CCD sensor, the lens images the sample to be measured onto the CCD sensor, and the CCD sensor records low-resolution images collected at different positions; and the low-resolution images containing different spectral information are fused and reconstructed into a high-resolution image by a Fourier ptychographic imaging method. The system uses Fourier ptychographic imaging technology, acquires a low-resolution image sequence by camera scanning, and fuses and reconstructs the low-resolution images containing different spectral information into a high-resolution image. The wavefront correction module monitors in real time the wavefront changes in the optical system through the Hartmann-Shack sensor, decomposes the wavefront into multiple sub-wavefronts through an array lens, generates a spot array on a detector, obtains real-time information of the wavefront distortion in the optical system by measuring and calculating the position offset of the spots, and transmits the distortion signal to the control system. The wavefront correction module dynamically adjusts the deformable mirror according to the wavefront correction signal transmitted by the control system, dynamically changes the surface shape of the deformable mirror through the adjustment of a driving unit, compensates in real time for the wavefront distortion in the optical system, thereby optimizing the imaging quality and reducing the aberration of the optical system. A linear polarizer is arranged at the outgoing end of the spherical wave and the front end of the camera, to ensure that the light entering the CCD is a specific polarized light of the laser, thereby effectively filtering stray light and improving the contrast and clarity of the imaging. By improving the traditional Fourier ptychographic system and introducing an optical wavefront correction module, the influence of atmospheric turbulence on the imaging process is compensated, and the feasibility of combining the wavefront correction system with the long-distance Fourier ptychographic imaging technology is verified. ​ 2. The remote wavefront correction Fourier ptychographic imaging system of claim 1, wherein: ​ 3. The remote wavefront correction Fourier ptychographic imaging system of claim 1, wherein: ​ 4. The remote wavefront correction Fourier ptychographic imaging system of claim 1, wherein: ​ 5. The remote wavefront correction Fourier ptychographic imaging system of claim 1, wherein: ​ 6. The remote wavefront correction Fourier ptychographic imaging system of claim 1, wherein: ​

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