Layered large-view-field light field wavefront sensor and use method thereof

Abstract

The invention discloses a layer-oriented large-view-field light field wavefront sensor and a use method thereof, and belongs to the technical field of wavefront detection, and the layer-oriented large-view-field light field wavefront sensor comprises a variable diaphragm, a liquid zoom converging lens, a liquid zoom microlens array, a high-precision array electric displacement table, a CCD camera and a high-precision camera electric displacement table. By changing the position of the variable diaphragm, the effective focal length of the converging lens, the effective focal length of the micro-lens array, the placement position of the micro-lens array and the placement position of the CCD camera, wavefront aberration detection at different conjugate positions can be realized. Meanwhile, based on the special optical structure of the light field sensor, wavefront information of multiple beacons in the view field can be collected at a time, so that the detection view field range is enlarged, and lamellar large-view-field wavefront sensing is finally achieved. According to the invention, the problem of layer-oriented large-view-field wavefront error detection is solved, and large-view-field wavefront sensing of different layers is realized through simple optical zooming on the premise of not increasing the complexity of the optical structure of the optical field sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of wavefront detection, and in particular relates to a layer-wise large-field-of-view light field wavefront sensor and a method for using the same. Background Art

[0002] The imperfect optical structure, individual differences and physiological activity characteristics of the human eye will introduce wavefront aberrations (introducing wavefront aberrations will cause wavefront distortion), which limits the high-resolution observation of the fundus structure of the human eye by traditional imaging equipment. The imaging system based on adaptive optics can detect wavefront aberrations through wavefront sensors, drive the adaptive optical system, compensate for wavefront distortion, and obtain high-resolution fundus imaging results of the human eye. Large-field-of-view and high-precision wavefront aberration detection is a prerequisite for large-field-of-view and high-resolution imaging. However, traditional large-field-of-view wavefront detection technology needs to rely on multiple wavefront sensors to perform wavefront detection on different field-of-view beacons respectively, resulting in a complex optical system structure and high cost. Traditional light field sensors can realize the simultaneous acquisition of multi-field-of-view wavefront information by placing a microlens array on the focal plane, which is a simple and low-cost method to achieve large-field-of-view wavefront detection.

[0003] However, traditional light field sensors can only detect the accumulated wavefront aberrations at fixed positions, and then reconstruct the wavefront aberrations of the preset layer through a complex tomographic inversion algorithm. The detection accuracy and efficiency are seriously affected by the preset layer and the number of guide stars: when the actual aberration distribution does not match the preset layer position, the wavefront aberration detection error increases significantly; when there are fewer guide stars and they fail to fully cover the preset layer field of view, the tomographic inversion algorithm efficiency is improved but the wavefront aberration detection error increases significantly; that is, the traditional light field sensor wavefront detection method can only detect the large-field wavefront aberrations accumulated at fixed positions. Its detection accuracy and efficiency are limited by the tomographic inversion algorithm, the preset layer position and the number of guide stars, and it is impossible to achieve simple and efficient detection of large-field wavefront aberrations of different layers. Summary of the invention

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: a layered large field of view light field wavefront sensor, comprising: a variable aperture, a liquid zoom convergence lens, a liquid zoom microlens array, a high-precision array electric translation stage, a CCD camera and a high-precision camera electric translation stage, wherein the variable aperture is located at the front focal plane of the liquid zoom convergence lens, the liquid zoom microlens array is located at the back focal plane of the liquid zoom convergence lens, the CCD camera is located at the back focal plane of the liquid zoom microlens array, the liquid zoom microlens array is fixed on the high-precision array electric translation stage, and the CCD camera is fixed on the high-precision camera electric translation stage.

[0005] A method for using a layer-wise large-field-of-view light field wavefront sensor, used for the layer-wise large-field-of-view light field wavefront sensor, comprising:

[0006] Step 1: Under ideal parallel light source illumination conditions, collect multi-beacon light field images at different focal lengths, segment the light field images according to the beacon positions in the field of view, reassemble the sub-field light field images obtained after segmentation to obtain sub-field reassembled images, and calculate the centroid position of the sub-field reassembled images as the centroid position calibrated under aberration-free input conditions;

[0007] Step 2: According to the field of view to be detected, adjust the focal length of the layer to the large field of view light field wavefront sensor;

[0008] Step 3: The large-field-of-view multi-beacon light waves containing wavefront aberrations are imaged after passing through the layer focused by step 2 to the large-field-of-view light field wavefront sensor. After the light field image is collected, the light field image is segmented according to the calibrated beacon position, the segmented sub-field-of-view images are reassembled, and the centroid position of the reassembled sub-field-of-view images is calculated to obtain the centroid position calculated under the aberration input condition;

[0009] Step 4: Calculate the centroid offset using the centroid position calibrated under the aberration-free input condition obtained in step 1 and the centroid position calculated under the aberration-containing input condition obtained in step 3, calculate the wavefront slope through the centroid offset, and obtain the wavefront aberration of each sub-field of view after wavefront restoration calculation of the wavefront slope;

[0010] Step 5: Using the sub-field wavefront aberrations obtained in step 4, perform Zernike mode decomposition on the sub-field wavefront aberrations to obtain the Zernike coefficients of the sub-field wavefront aberrations. Then, directly calculate the Zernike coefficients of the large field wavefront aberrations through the large field wavefront reconstruction matrix corresponding to the working focal length of the large field light field wavefront sensor of the current layer to obtain the wavefront aberration estimate of the current layer.

[0011] The present invention has the following beneficial effects:

[0012] 1. The layer-wise large-field-of-view light field wavefront sensor of the present invention changes the conjugate position of the light field sensor by adjusting the focal length of the liquid lens, thereby realizing flexible detection of wavefront aberrations of different layers by one light field sensor, thereby reducing the influence of the actual aberration distribution on the aberration detection method of the light field wavefront sensor.

[0013] 2. The layer-wise large-field-of-view light field wavefront sensor of the present invention directly detects the wavefront aberrations of different layers, thereby reducing the dependence of the light field wavefront sensor on the tomographic inversion algorithm and the number of guide stars.

[0014] 3. The layer-wise large-field wavefront aberration detected by the present invention can directly drive the wavefront corrector of the adaptive optical system conjugated to different layers to compensate for the wavefront distortion and realize large-field high-resolution tomography. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1Schematic diagram of the structure of a layer-wise large field of view light field wavefront sensor, wherein 1-variable aperture, 2-liquid zoom focusing lens, 3-liquid zoom microlens array, 4-high-precision array electric translation stage, 5-CCD camera, 6-high-precision camera electric translation stage;

[0016] Figure 2 It is a schematic diagram of the operation of the layer-wise large field of view optical field wavefront sensor when it is conjugated at different positions, wherein 1-variable diaphragm, 2-liquid zoom focusing lens, 3-liquid zoom microlens array, 4-high-precision array electric translation stage, 5-CCD camera, 6-high-precision camera electric translation stage;

[0017] Figure 3 It is the footprint diagram of the sub-field of view corresponding to the same beacon in the large field of view wavefront when the layer-wise large field of view light field wavefront sensor is conjugated at different positions, where the star is the position of the beacon light wave in the field of view to be detected;

[0018] Figure 4 Schematic diagram of light field image reconstruction in the central sub-field of view. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] like Figure 1 As shown, the layered large field of view light field wavefront sensor of the present invention is composed of a variable aperture 1, a liquid zoom converging lens 2, a liquid zoom microlens array 3, a high-precision array electric displacement stage 4, a CCD camera 5 and a high-precision camera electric displacement stage 6. Among them, the variable aperture 1 is located at the front focal plane of the liquid zoom converging lens 2, and is conjugate to the wavefront position to be detected, and its light aperture is determined by the position of the beacon at the edge of the field of view. The liquid zoom converging lens 2 is conjugate to the entrance pupil position of the optical system, and its focal length can be freely adjusted. The liquid zoom microlens array 3 is located at the back focal plane of the liquid zoom converging lens 2, and the relative apertures of the two are consistent. The CCD camera 5 is located at the back focal plane of the liquid zoom microlens array 3, and the liquid zoom microlens array 3 is fixed on the high-precision array electric displacement stage 4. The position of the high-precision array electric displacement stage 4 is controlled to ensure that the liquid zoom microlens array 3 is located at the back focal plane of the liquid zoom converging lens 2. The CCD camera 5 is fixed on a high-precision camera electric displacement stage 6 , and the position of the high-precision camera electric displacement stage 6 is controlled to ensure that the CCD camera 5 is located at the back focal plane of the liquid zoom microlens array 3 .

[0021] The working process of the layer-wise large field of view light field wavefront sensor of the present invention is as follows:

[0022] The multi-beacon light waves carrying the wavefront information in a large field of view pass through the variable aperture 1 to reach the liquid zoom convergence lens 2, and are focused on different positions on the liquid zoom microlens array 3 after passing through the liquid zoom microlens array 2. The focused light rays diverge after passing through the liquid zoom microlens array 3, and are finally imaged at different positions of the CCD camera 5, thereby realizing the simultaneous detection of the wavefront aberrations of multiple beacons in a large field of view.

[0023] like Figure 2 As shown, the wavefront to be detected is conjugate to the front focal plane of the liquid zoom convergence lens 2, and the wavefront errors of different layers can be detected by changing the focal length of the liquid zoom convergence lens 2. In order to avoid aliasing of the recombined sub-spot images, the relative apertures of the liquid zoom convergence lens 2 and the liquid zoom microlens array 3 need to be kept consistent; in order to avoid aliasing of the sub-field beacon images, the liquid zoom microlens array 3 needs to be placed on the back focal plane of the liquid zoom convergence lens 2. Therefore, when changing the conjugate position of the wavefront to be detected, it is necessary to synchronously control the high-precision array electric displacement stage 4 and the high-precision camera electric displacement stage 6 to synchronously change the position of the liquid zoom microlens array 3 and the position of the CCD camera 5, so that the liquid zoom microlens array 3 is always located at the back focal plane of the liquid zoom convergence lens 2, and the CCD camera 5 is always located at the back focal plane of the liquid zoom microlens array 3.

[0024] like Figure 3 As shown in the figure, when the wavefront to be detected of the layer-wise large field of view optical field wavefront sensor is conjugated at different positions, the positions of the beacon light waves of different fields of view change synchronously in the field of view to be detected. When the large field of view wavefront aberration is a different Zernike mode, according to the position of the sub-field of view in the large field of view, the aberration at the corresponding position is decomposed according to the Zernike polynomial to obtain the Zernike mode coefficients of each sub-field of view, and the relationship matrix between the sub-field of view Zernike mode coefficients and the large field of view Zernike mode is established. The large field of view wavefront reconstruction matrix at the current conjugate position can be obtained by inverting the relationship matrix.

[0025] The collected light field image can be segmented according to the beacon position to obtain light field images of different sub-fields. Figure 4 As shown, taking the central sub-viewing field light field image as an example, the sub-viewing field light field image can be reorganized according to the microlens and pixel positions in the liquid zoom microlens array 3 corresponding to the sub-viewing field (that is, the Kth pixel under each microlens of the liquid zoom microlens array 3 corresponding to the current sub-viewing field is extracted to form the Kth virtual sub-aperture), and the virtual sub-aperture spot array diagram is obtained, and then the centroid position and centroid offset of the virtual sub-aperture spot are solved to realize the sub-viewing field wavefront aberration detection. After obtaining the sub-viewing field wavefront aberration estimation, the large-viewing field wavefront aberration can be directly inverted through the large-viewing field wavefront reconstruction matrix at the current conjugate position. Figure 4In the figure, M and N represent the indexes of the liquid zoom microlenses in the horizontal and vertical directions respectively, and the index of the center microlens is (M=2, N=2). Assuming that each microlens contains 3×3 pixels, the pixel values ​​are represented by the characters AI in sequence, and the subscript index indicates that the current pixel is the pixel under the microlens in the Nth row and the Mth column.

[0026] In the layer-wise large field of view wavefront aberration detection based on the layer-wise large field of view light field wavefront sensor, it is first necessary to calibrate the ideal plane wave calibration centroid position according to the field of view to be detected and the beacon light position, that is, the steps are as follows:

[0027] Step 1: Under ideal parallel light source illumination conditions, collect multi-beacon light field images at different focal lengths, segment the multi-beacon light field images according to the beacon positions in the field of view, reassemble the sub-field of view light field images obtained after segmentation to obtain sub-field of view reassembled images, and calculate the centroid position of the sub-field of view reassembled images as the calibration centroid, that is, the centroid position calibrated under aberration-free input conditions;

[0028] Step 2: According to the field of view to be detected, adjust the focal length of the layer to the large field of view light field wavefront sensor. Specifically: according to the position of the wavefront to be detected, adjust the focal length of the liquid zoom convergence lens 2 so that its front focal plane is conjugate with the position of the wavefront to be detected, adjust the focal length of the liquid zoom microlens array 3 so that its relative aperture is consistent with the relative aperture of the liquid zoom convergence lens 2, control the movement of the high-precision array electric displacement stage 4 to make the liquid zoom microlens array 3 located at the back focal plane of the liquid zoom convergence lens 2, and control the movement of the high-precision camera electric displacement stage 6 to make the CCD camera 5 located at the back focal plane of the liquid zoom microlens array 3. After the above operations, the CCD camera 5 collects a light field image containing the wavefront aberration of the field of view to be detected.

[0029] Step 3: The large-field-of-view multi-beacon light waves containing wavefront aberrations are imaged after passing through the layer focused by step 2 toward the large-field-of-view light field wavefront sensor. After collecting the light field image, the light field image is segmented according to the calibrated beacon positions, the segmented sub-field-of-view images are reassembled, and the centroid position of the reassembled sub-field-of-view images is calculated to obtain the centroid position under the influence of aberrations, that is, the centroid position calculated under the input condition containing aberrations.

[0030] Step 4: Calculate the center of mass offset using the center of mass position calibrated under the aberration-free input condition obtained in step 1 and the center of mass position calculated under the aberration-containing input condition obtained in step 3. Calculate the wavefront slope through the center of mass offset. Obtain the wavefront aberration of each sub-field of view after the wavefront slope is subjected to wavefront restoration calculation.

[0031] Step 5: Using the sub-field wavefront aberrations obtained in step 4, perform Zernike mode decomposition on each sub-field wavefront aberration to obtain the Zernike coefficient of each sub-field wavefront aberration, and then directly calculate the Zernike coefficient of the large field wavefront aberration through the large field wavefront reconstruction matrix corresponding to the working focal length of the large field light field wavefront sensor of the current layer, and the wavefront aberration estimate of the current layer can be obtained.

[0032] Optionally, in practical applications of multi-layer conjugate adaptive optical systems, the layer-wise large-field-of-view light field wavefront sensor of the present invention can be used to detect wavefront aberrations layer by layer based on the principle of distance from the pupil plane from near to far, and the wavefront corrector conjugated to different layers can perform closed-loop correction on the wavefront aberrations, thereby obtaining large-field-of-view high-resolution tomographic imaging results.

[0033] In summary, the measurement of wavefront aberrations of different layers by the layer-wise large field of view light field wavefront sensor is realized.

Claims

1. A layer-wise large field of view light field wavefront sensor, characterized in that: include: A variable aperture (1), a liquid zoom converging lens (2), a liquid zoom microlens array (3), a high-precision array electric displacement stage (4), a CCD camera (5) and a high-precision camera electric displacement stage (6), wherein the variable aperture (1) is located at the front focal plane of the liquid zoom converging lens (2), the liquid zoom microlens array (3) is located at the back focal plane of the liquid zoom converging lens (2), the CCD camera (5) is located at the back focal plane of the liquid zoom microlens array (3), the liquid zoom microlens array (3) is fixed on the high-precision array electric displacement stage (4), and the CCD camera 5 is fixed on the high-precision camera electric displacement stage (6).

2. The layer-wise large field of view light field wavefront sensor according to claim 1, characterized in that: The light waves of multiple beacons carrying the wavefront information in a large field of view pass through the variable aperture (1) to reach the liquid zoom convergence lens (2), and are focused on different positions on the liquid zoom microlens array (3) after passing through the liquid zoom convergence lens (2). The focused light rays diverge after passing through the liquid zoom microlens array (3), and are finally imaged at different positions of the CCD camera 5, thereby realizing the simultaneous detection of the wavefront aberrations of multiple beacons in a large field of view.

3. The layer-wise large field of view light field wavefront sensor according to claim 1, characterized in that: The variable diaphragm (1) is located on the front focal plane of the liquid variable focus convergence lens (2) and is conjugate to the position of the wavefront to be detected. The light aperture is determined by the position of the beacon at the edge of the field of view.

4. The layer-wise large-field-of-view light field wavefront sensor according to claim 1, characterized in that: The liquid variable focus converging lens (2) is conjugate to the entrance pupil position of the optical system, and its focal length can be freely adjusted.

5. The layer-wise large-field-of-view light field wavefront sensor according to claim 1, characterized in that: The liquid zoom microlens array (3) is located at the rear focal plane of the liquid zoom converging lens (2), and the relative apertures of the liquid zoom microlens array (3) and the liquid zoom converging lens (2) are consistent.

6. The layer-wise large-field-of-view light field wavefront sensor according to claim 1, characterized in that: The liquid zoom microlens array (3) is fixed on a high-precision array electric displacement stage (4), and the position of the high-precision array electric displacement stage (4) is controlled to ensure that the liquid zoom microlens array (3) is located at the back focal plane of the liquid zoom convergence lens (2).

7. The layer-wise large-field-of-view light field wavefront sensor according to claim 1, characterized in that: The CCD camera (5) is fixed on a high-precision camera electric displacement stage (6), and the position of the high-precision camera electric displacement stage (6) is controlled to ensure that the CCD camera (5) is located at the back focal plane of the liquid zoom microlens array (3).

8. A method for using a layer-wise large-field-of-view light field wavefront sensor, used for the layer-wise large-field-of-view light field wavefront sensor according to any one of claims 1 to 7, characterized in that: include: Step 1: Under ideal parallel light source illumination conditions, collect multi-beacon light field images at different focal lengths, segment the light field images according to the beacon positions in the field of view, reassemble the sub-field light field images obtained after segmentation to obtain sub-field reassembled images, and calculate the centroid position of the sub-field reassembled images as the centroid position calibrated under aberration-free input conditions; Step 2: According to the field of view to be detected, adjust the focal length of the layer to the large field of view light field wavefront sensor; Step 3: The large-field-of-view multi-beacon light waves containing wavefront aberrations are imaged after passing through the layer focused by step 2 to the large-field-of-view light field wavefront sensor. After the light field image is collected, the light field image is segmented according to the calibrated beacon position, the segmented sub-field-of-view images are reassembled, and the centroid position of the reassembled sub-field-of-view images is calculated to obtain the centroid position calculated under the aberration input condition; Step 4: Calculate the centroid offset using the centroid position calibrated under the aberration-free input condition obtained in step 1 and the centroid position calculated under the aberration-containing input condition obtained in step 3, calculate the wavefront slope through the centroid offset, and obtain the wavefront aberration of each sub-field of view after wavefront restoration calculation of the wavefront slope; Step 5: Using the sub-field wavefront aberrations obtained in step 4, perform Zernike mode decomposition on the sub-field wavefront aberrations to obtain the Zernike coefficients of the sub-field wavefront aberrations. Then, directly calculate the Zernike coefficients of the large field wavefront aberrations through the large field wavefront reconstruction matrix corresponding to the working focal length of the large field light field wavefront sensor of the current layer to obtain the wavefront aberration estimate of the current layer.

9. The method for using the layer-wise large-field-of-view light field wavefront sensor according to claim 8, characterized in that: In step 2, adjusting the focal length of the layer toward the large field of view light field wavefront sensor comprises: adjusting the focal length of the liquid zoom convergence lens (2) according to the position of the wavefront to be detected so that its front focal plane is conjugate with the position of the wavefront to be detected, adjusting the focal length of the liquid zoom microlens array (3) so that its relative aperture is consistent with the relative aperture of the liquid zoom convergence lens (2), controlling the movement of the high-precision array electric displacement stage (4) so ​​that the liquid zoom microlens array (3) is located at the back focal plane of the liquid zoom convergence lens (2), and controlling the movement of the high-precision camera electric displacement stage (6) so that the CCD camera (5) is located at the back focal plane of the liquid zoom microlens array (3); after the above operations, the CCD camera 5 collects a light field image containing the wavefront aberration of the field of view to be detected.

10. The method for using the layer-wise large-field-of-view light field wavefront sensor according to claim 8, characterized in that: The method further includes step 6: using the layer-wise large-field-of-view light field wavefront sensor, detecting the wavefront aberration layer by layer according to the principle of distance from the pupil plane from near to far, and performing closed-loop correction on the wavefront aberration by a wavefront corrector conjugated to different layers, thereby obtaining a large-field-of-view high-resolution tomographic imaging result.

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