Long-distance wavefront correction Fourier lamination imaging system

Abstract

The invention belongs to the field of space optical remote sensing, and provides a long-distance wavefront correction Fourier laminated imaging system, so as to improve the resolution and quality of long-distance imaging and solve the imaging problem under the influence of atmospheric turbulence and optical distortion in the traditional technology. The system is composed of an illumination subsystem and an imaging subsystem, the illumination subsystem generates a light source in a specific polarization state, the imaging subsystem comprises a Hartmann-Shack sensor, a deformable mirror, a spectroscope, a linear polarizer and other assemblies, and images are fused and reconstructed into high-resolution images through the Fourier lamination imaging technology; meanwhile, the Hartmann-Shack sensor monitors wavefront distortion in real time, and the deformable mirror carries out correction according to feedback information, so that the imaging quality is ensured. According to the invention, the distortion wavefront correction module is combined with the Fourier lamination imaging technology, so that atmospheric disturbance and system distortion in long-distance imaging are effectively overcome, and the adaptability and stability of the imaging system in a complex environment are improved.

Description

Technical Field

[0001] The invention relates to a long-distance wavefront correction Fourier stack imaging system, and belongs to the field of space optical remote sensing. Background Art

[0002] With the rapid development of optical imaging technology, the demand for long-distance high-resolution imaging is growing in many fields, especially in applications such as astronomical observation, national defense monitoring, and remote sensing detection. Traditional imaging systems are limited by the size and resolution of optical components and are difficult to meet the imaging requirements of ultra-high resolution and large field of view. In recent years, Fourier stack imaging technology, as an emerging computational imaging method, has gradually attracted widespread attention. This technology collects low-resolution images of objects from multiple angles and combines them with phase recovery algorithms to reconstruct high-resolution images, thereby effectively breaking through the diffraction limit of traditional imaging systems.

[0003] In the field of space optical remote sensing, the application of Fourier stack imaging technology has great potential. By performing multi-angle imaging of remote sensing objects, this technology can obtain rich frequency domain information, thereby achieving high-quality image reconstruction. This method can not only enhance the detail presentation of remote sensing images, but also reduce the impact of noise. Therefore, Fourier stack imaging technology has demonstrated extremely 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 acquisition field of view and long object distance, the phase recovery and reconstruction of the image are 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 the wavefront correction system is particularly important. Through real-time monitoring and compensation of atmospheric disturbances and optical system distortion through wavefront correction technology, the clarity and resolution of the imaging can be significantly improved, ensuring the acquisition of high-quality remote sensing images in a dynamically changing environment.

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

[0005] The present invention 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 that combines a wavefront correction optical system with a Fourier stack imaging (FP) method.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A long-distance wavefront correction Fourier stack imaging system of the present invention is composed of an illumination subsystem and an imaging subsystem;

[0008] The illumination subsystem includes a laser, a lens, a pinhole, and a linear polarizer, so that the light finally emitted by the laser is converted into a converging spherical wave in a linear polarization state to illuminate the sample to be tested. When the far-field condition is not met, the converging spherical wave illumination is used to approximate Fraunhofer diffraction;

[0009] The imaging subsystem includes a Hartmann-Shack sensor, a deformable mirror, a beam splitter, a linear polarizer, a lens, a CCD sensor, and an electric translation stage. The camera composed of the lens and the CCD sensor is moved by the electric translation stage so that the camera can collect corresponding low-resolution images at different positions.

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

[0011] The Hartmann-Shack sensor is used to detect the change of the wavefront after passing through atmospheric turbulence and optical system distortion in real time, and transmit the wavefront error information to the wavefront control system;

[0012] The deformable mirror is adjusted in real time according to the correction information fed back by the wavefront control system to correct the distortion, thereby compensating for the wavefront distortion and ensuring the wavefront quality during the imaging process;

[0013] The linear polarizer is fixed to the exit end of the spherical wave and the front end of the imaging lens respectively, ensuring that the light entering the CCD is the specific polarization light emitted by the laser, thereby reducing the interference of stray light;

[0014] The camera includes a lens and a CCD sensor, the lens is used to image the sample to be tested onto the CCD sensor, and the CCD sensor is used to record low-resolution images collected by the camera at different positions;

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

[0016] Compared with the prior art, the present invention has the following innovative features:

[0017] Fourier stacking imaging technology: This invention adopts Fourier stacking imaging technology to effectively improve the resolution and quality of long-distance remote sensing images through iterative fusion of multiple low-resolution images. This method acquires different spectral information by panning the camera to collect low-resolution images at different positions, and alternately iterates and fuses them in the spatial and frequency domains to achieve high-resolution remote sensing imaging. Compared with traditional imaging technology, this method has higher noise resistance and sub-diffraction limit imaging capabilities, and can overcome the influence of factors such as atmospheric turbulence at larger imaging distances.

[0018] Wavefront correction module: This invention introduces wavefront correction technology to monitor and compensate for the impact of atmospheric turbulence on imaging quality in real time. The wavefront sensor acquires real-time wavefront data and uses a deformable mirror 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: Add a linear polarizer at the place where the spherical wave emerges and in front of the camera 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 and improve the system's response to specific light waves, thereby enhancing the clarity and contrast of the imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A long-distance wavefront correction Fourier stack imaging system is proposed by the present invention.

[0021] Figure 2 It is the spot shift caused by the distorted wavefront passing through the Hartmann-Shack sensor.

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

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

[0024] Figure 5 The results of Fourier stack reconstruction under the simulated atmospheric turbulence. (a) is the degraded image of the low-resolution image at the center after being affected by atmospheric turbulence. (b) and (c) are the amplitude and phase of the high-resolution image reconstructed from the uncorrected degraded image sequence.

[0025] Figure 6Reconstruction of the Fourier stack system after the simulated distortion wavefront correction. (a) is the corrected image of the centrally degraded low-resolution image. (b) and (c) are the amplitude and phase of the high-resolution image reconstructed from the corrected low-resolution image sequence.

[0026] Figure 7 The SSIM values ​​of the images reconstructed by the Fourier stacking algorithm under different iteration numbers are the ideal, degraded, and corrected conditions. In the figure, 1-laser; 2-lens; 3-pinhole; 4-linear polarizer; 5-lens; 6-sample; 7-deformable 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 invention is based on Fourier stacking technology and a distortion wavefront correction system, and proposes a long-distance wavefront correction Fourier stacking imaging system. By combining Fourier stacking imaging technology with a distortion correction system, the problem of reduced imaging resolution caused by atmospheric disturbances and system distortion in long-distance imaging is solved. The system detects wavefront distortion in real time through a Hartmann-Shack sensor, corrects the wavefront using a deformable mirror, and then iteratively fuses low-resolution images through Fourier stacking imaging technology to achieve high-resolution long-distance imaging.

[0028] like Figure 1 As shown, the long-distance wavefront correction Fourier stack imaging system provided by the present invention is composed of an illumination subsystem and an imaging subsystem. The illumination subsystem includes a laser 1, a lens 2, a pinhole 3, a linear polarizer 4 and a lens 5. The imaging subsystem includes a deformable 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] Combination Figure 1 The wavefront correction optical remote sensing imaging method based on Fourier stack of the present invention comprises the following steps:

[0030] Step 1: Laser 1 emits laser light, which is converted into an emission spherical wave through lens 2 and pinhole 3. The emission spherical wave is converted into an emission spherical wave with polarization state through linear polarizer 4. The divergent spherical wave with polarization state is converted into a convergent spherical wave with polarization state through lens 5. Because the far-field condition cannot be met in the laboratory, it is necessary to use convergent spherical wave illumination 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 light wave irradiates the sample 6 to be tested, it is reflected by the sample to the deformable mirror, and the deformable mirror 7 reflects it to the beam splitter 9, which splits it into two beams of light. One beam of light is collected by the Hartmann-Shack sensor 8, and the other beam of light is collected by the CCD sensor 12 through the imaging lens 11. Step 3: The Hartmann-Shack sensor 8 is composed of a microlens array and a CCD sensor, such as Figure 2 As shown, when the wavefront is distorted, the light spot collected by the CCD sensor will shift, and the distorted wavefront information can be obtained based on the shift amount. The distorted wavefront signal collected by the Hartmann-Shack sensor 8 is transmitted to the computer 14, 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 reflector 7 is deformed, thereby correcting the distorted wavefront.

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

[0033] Step 5: Iteratively reconstruct the collected low-resolution images through the Fourier stack imaging algorithm. First, make an initial estimate of the target high-resolution sample function. Select the central low-resolution image as the initial guess and obtain its complex amplitude distribution. o (x0, y0), thus obtaining the high-resolution spectrum of the sample function O(u, v) = F{o(x0, y0)}.

[0034] Step 6: Calculate the light field distribution collected by the CCD. When the sample to be tested is imaged, it is first transformed by Fourier and then low-pass filtered by the optical system. It is 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 amplitude information of the estimated light field with the low-resolution intensity image actually collected by the camera while keeping its phase unchanged. The updated estimated light field is:

[0037]

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

[0039]

[0040] Step 9, iterative update until convergence. For all low-resolution images captured by the camera, repeat steps 6 to 8 as one iteration; repeat the iterative process until the algorithm converges, iteratively reconstructs the high-resolution spectrum 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, simulation was performed and the system parameters were set as follows: the laser wavelength was 632nm, the lens F / #10, the lens focal length was 75mm, the lens aperture was 7.5mm, the CCD sensor pixel size was 4.8μm, a 15×15 array of low-resolution images was collected, the moving step was 1.2mm, and the aperture overlap rate reached 84%.

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

[0043] Then, the Zernike polynomial simulation is used to generate images degraded by atmospheric turbulence to simulate the effect of turbulence on light propagation and study its effect 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, such as Figure 5 (a) shows the degraded image of the central low-resolution image. Figure 5 (b) and Figure 5 (c) is the amplitude and phase of the high-resolution image reconstructed from the uncorrected degraded image sequence.

[0044] The present invention simulates the correction effect of the deformable mirror on the distorted wavefront by correcting the Zernike coefficients. By slightly adjusting each Zernike coefficient, the corresponding image under the current Zernike coefficient is generated, and the new gradient is calculated. The corrected Zernike coefficients are obtained by using the Gaussian fitting method, and the distorted wavefront of the system is corrected by the corrected Zernike coefficients. Figure 6 (a) shows the corrected image of the center-degraded low-resolution image. Figure 6 (b) and Figure 6(c) The amplitude and phase of the high-resolution image reconstructed from the corrected low-resolution image sequence.

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

Claims

1. A long-distance wavefront-corrected Fourier stack imaging system, comprising an illumination subsystem and an imaging subsystem, wherein the illumination subsystem comprises a laser, a lens, a pinhole and a linear polarizer, and the imaging subsystem comprises a Hartmann-Shack sensor, a deformable mirror, a beam splitter, a linear polarizer, a lens, a CCD sensor and an electric translation stage; wherein: The laser light emitted by the laser is transformed into an outgoing spherical wave through a lens and a pinhole, and then transformed into a converging spherical wave through a lens; The Hartmann-Shack sensor is used to detect the wavefront changes after atmospheric turbulence and optical system distortion in real time, and transmit the wavefront error information to the wavefront control system; The deformable mirror is used to receive correction information fed back by the wavefront control system and make real-time adjustments to compensate for wavefront distortion, thereby ensuring the wavefront quality during the imaging process; The linear polarizer is respectively arranged at the spherical wave output end and the front end of the imaging lens to ensure that the light entering the CCD is laser specific polarization light, thereby reducing stray light interference; The camera includes a lens and a CCD sensor. The lens images the sample to be tested onto the CCD sensor, and the CCD sensor records low-resolution images collected at different positions. Through the Fourier stack imaging method, low-resolution images containing different spectral information are fused and reconstructed into high-resolution images.

2. A long-distance wavefront-corrected Fourier stack imaging system according to claim 1, characterized in that: The system uses Fourier stack imaging technology to collect low-resolution image sequences through camera scanning, and fuses low-resolution images containing different spectral information into high-resolution images.

3. The long-distance wavefront-corrected Fourier stack imaging system according to claim 1, characterized in that: The wavefront correction module monitors the wavefront changes in the optical system in real time through the Hartmann-Shack sensor. It decomposes the wavefront into multiple sub-wavefronts through the array lens and generates a spot array on the detector. By measuring and calculating the spot position offset, it obtains real-time information on the wavefront distortion of the optical system and transmits the distortion signal to the control system.

4. The long-distance wavefront-corrected Fourier stack imaging system according to claim 1, characterized in that: The wavefront correction module dynamically adjusts the deformable mirror according to the wavefront correction signal transmitted by the control system, dynamically changes its surface shape by adjusting the driving unit, and compensates for the wavefront distortion in the optical system in real time, thereby optimizing the imaging quality and reducing the aberration of the optical system.

5. The long-distance wavefront-corrected Fourier stack imaging system according to claim 1, characterized in that: A polarizing plate is set at the spherical wave output end and the front end of the camera to ensure that the light entering the CCD is the specific polarized light emitted by the laser, thereby effectively filtering out stray light and improving the contrast and clarity of the image.

6. The long-distance wavefront-corrected Fourier stack imaging system according to claim 1, characterized in that: By improving the traditional Fourier stacking 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 far-field Fourier stacking imaging technology is verified.

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