CN114323310B - High-resolution Hartmann wavefront sensor - Google Patents

Abstract

The invention discloses a high-resolution Hartmann wavefront sensor. The number of pixels of an image sensor corresponding to a single sub-aperture is set to a total of 4 pixels in a 2×2 array, and through the optimal design of the focal length of the microlens, the Ha The sub-aperture sampling spatial resolution of the Terman wavefront sensor reaches the double-pixel level and maintains measurement accuracy. The invention solves the key problems of low pixel utilization rate and redundant image data of the image sensor in the traditional Hartmann wavefront sensor technical scheme, improves the pixel utilization rate to nearly 100%, and improves the spatial resolution of the Hartmann wavefront sensor at the same time To the near-pixel level, and at the same spatial resolution, the pixel demand and image data volume of Hartmann wavefront sensors are reduced by more than an order of magnitude, providing a feasible technical solution for the development of ultra-high spatial resolution Hartmann wavefront sensors. In addition The extremely small pixel requirements can also be used to develop ultra-high-speed Hartmann wavefront sensors.

Description

A High Resolution Hartmann Wavefront Sensor

technical field

The invention belongs to the technical field of optical engineering, and relates to a device for detecting wavefront distortion of light beams, in particular to a high-resolution Hartmann wavefront sensor.

Background technique

The Hartmann wavefront sensor is a widely used beam wavefront distortion measurement device. Because of its simple structure, fast speed, high precision, and good environmental adaptability, it is widely used in adaptive optics, optical detection, and flow field measurement. Fields continue to be successfully applied.

The structure of a typical Hartmann wavefront sensor can be referred to an optical wavefront sensor disclosed in the Chinese Patent Application Publication (Application No. 98112210.8, Publication No. CN1245904). The wavefront is divided into sub-apertures, and a processing method similar to mathematical calculus is used in the wavefront measurement. It only needs to measure the size of the oblique aberration in each sub-aperture, and the wavefront aberration of the entire aperture can be restored with a specific restoration algorithm. The oblique aberration component in the sub-aperture is determined according to the far-field spot centroid shift obtained by focusing the light wave through the microlens. The Hartmann wavefront sensor generally uses an array image sensor (such as a CCD or CMOS camera) to detect the microlens array. An array of spots formed on the focal plane.

According to the detection principle, the detection spatial resolution of the Hartmann wavefront sensor is limited by the segmentation density of the microlens array, and it is necessary to delineate a certain area of pixels for each sub-spot on the image sensor as the sub-aperture. Due to this limitation, the spatial resolution of the Hartmann wavefront sensor is difficult to reach near-pixel level, and the image sensor needs to have a certain pixel resolution for imaging of all sub-spot arrays. Therefore, the Hartmann wavefront sensor has high requirements for the pixel resolution of the image sensor, but the utilization rate is low. In the ultra-high-speed wavefront detection scene, a large amount of high-resolution image data severely limits the actual measurement speed.

Aiming at the problem of spatial resolution and pixel utilization of the Hartmann wavefront sensor, Ragazzoni first proposed a concept of Pyramid wavefront sensing technology in 1996 (Ragazzoni R.Pupil plan wavefrontsensing with an oscillating prism[J]. J. Mod. Opt., 1996, 43:289-293). The sensor uses the quadrangular pyramid as a two-dimensional dichroic prism, cooperates with the lens group to realize the pupil division and imaging of the incident beam, divides the four-quadrant area on the detector to detect the wavefront slope of different pupil apertures, and then completes the wavefront detection , which has the advantages of large dynamic range of wavefront measurement, high sensitivity, and flexible sampling partition methods. Theoretically, each wavefront slope sampling point of the quadrangular pyramid sensor only needs four pixels, which can realize high-resolution wavefront detection. However, the quadrangular pyramidal wavefront sensor still has problems such as beam focus position control, high-precision processing requirements for the edges and apex angles of the quadrangular pyramid, and solving fitting models, which limits the wide application of the quadrangular pyramidal wavefront sensor.

With the continuous extension of application fields, the demand for high-performance wavefront sensors is increasingly strong, and new wavefront sensor technologies with high spatial resolution, high pixel utilization, light energy utilization and high-speed detection potential are bound to have better applications prospect.

Contents of the invention

The technical problem to be solved by the present invention is: to overcome the deficiencies of the existing Hartmann wavefront sensor in terms of resolution and pixel utilization, through the corresponding design of specific sub-apertures and pixels, combined with the selection of the focal length of the microlens array, the Hartmann The spatial resolution of the Mamwave front sensor is increased to 2 pixel size levels, and the pixel utilization rate is almost 100%.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a high-resolution Hartmann wavefront sensor, mainly composed of a microlens array and an array-type image sensor, the microlens array is covered on the photosensitive chip of the array-type image sensor, and the The incident beam to be measured is divided into a sub-aperture array, that is, a thin beam array and focused. The photosensitive chip of the array image sensor is placed under the microlens array, and the distance between the two is the focal length of the microlens array. Beam intensity distribution information to be measured, each sub-aperture only corresponds to a total of 4 image sensor pixels in a 2×2 arrangement, the center-to-center spacing of pixel areas corresponding to adjacent sub-apertures is twice the size of a single pixel, and the focal length f range of the microlens array is L _p ² /λ≤f≤4L _p ² /λ, where L _p is the pixel width size, λ is the probe beam wavelength, according to the light intensity signal value of the 2×2 array pixels corresponding to each sub-aperture, the current sub-aperture corresponds to Spot centroid data of narrow beam focus:

Among them, I ₁ , I ₂ , I ₃ , and I ₄ represent the pixel gray values of the upper left, upper right, lower left, and lower right of the 2×2 array image sensor pixels, and calculate the centroid of the light spot in each sub-aperture according to the above centroid calculation formula Finally, based on the spot centroid data of all effective sub-apertures, the wavefront distortion information of the entire beam to be measured can be reconstructed using the Hartmann wavefront sensor wavefront restoration algorithm.

Further, the array image sensor has photosensitive pixels arranged in a two-dimensional array, and may be a CCD sensor camera, a CMOS sensor camera, a PDA detector, or the like.

Further, the 4 image sensor pixels in the 2×2 arrangement can be a single physical pixel of the image sensor, or a single numerical pixel in the output image of the image sensor after the pixel combination function. At this time, the size of a single numerical pixel is It is an integer multiple of the size of a single physical pixel of the sensor.

Further, the effective sub-aperture refers to the sub-aperture whose corresponding spot centroid data participates in the wavefront restoration calculation, which may be a sub-aperture completely covered by the incident beam, or a sub-aperture partially covered by the incident beam.

Compared with the prior art, the present invention has the following advantages: the detection of each sub-aperture in the method of the present invention only needs 2×2 total 4 pixels, and under the same pixel resolution of the image sensor, it can divide more sub-apertures than the prior art The number of sub-aperture arrays can achieve higher wavefront sampling resolution; secondly, a single sub-aperture of the present invention only needs 4 pixels, and under the same number of sub-aperture arrays, the number of image sensor pixels required for wavefront detection Compared with the existing technology, it can be reduced by at least one order of magnitude, and image pixel number compression is very important for realizing real-time high-speed wavefront measurement; finally, through a specific focal length design, the 4 pixels corresponding to each sub-aperture of the present invention have effective light intensity information Therefore, the image sensor pixels used for wavefront detection in the present invention theoretically have light intensity data, and the pixel utilization rate can reach 100%, which is at least 2 times higher than that of the prior art. Therefore, the present invention can theoretically realize extremely high-resolution wavefront detection and extremely high image sensor pixel utilization, and also has the technical potential of extremely high-speed wavefront detection, which will have important application value in high-performance wavefront detection scenarios. The present invention uses every 2×2 pixels on the image sensor as a position sensor, and turns the image sensor into a large-scale position sensor array. This application method is also an innovation for the image sensor.

Description of drawings

Fig. 1 is the schematic structural diagram of the high-resolution Hartmann wavefront sensor of the present invention;

Fig. 2 is a sub-aperture segmentation design diagram of a high-resolution Hartmann wavefront sensor in Embodiment 1 of the present invention;

3 is a schematic diagram of randomly generated distorted wavefront distribution in Embodiment 1 of the present invention;

4 is a spot image on a high-resolution Hartmann wavefront sensor parallel cursor timing image sensor in Embodiment 1 of the present invention;

Fig. 5 is the light spot image on the image sensor of the high-resolution Hartmann wavefront sensor under the incident light beam containing the distorted wavefront in Embodiment 1 of the present invention;

6 is a schematic diagram of the 23rd-order aberration mode coefficients (white columnar data) of the restored wavefront measured by the high-resolution Hartmann wavefront sensor in Embodiment 1 of the present invention and the aberration mode coefficients (black columnar data) forming the input wavefront ;

7 is a schematic diagram of a wavefront restored by a high-resolution Hartmann wavefront sensor in Embodiment 1 of the present invention;

FIG. 8 is a schematic diagram of an error wavefront between a restored wavefront of a wavefront sensor and an input wavefront in Embodiment 1 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

Fig. 1 is the schematic structural diagram of the high-resolution Hartmann wavefront sensor of the present invention. After the sub-apertures of the microlens array of the light beam to be measured are divided, they are respectively focused on the photosensitive chip of the image sensor to form an array of light spots. Each microlens or sub-aperture The aperture corresponds to the 2×2 pixel area on the photosensitive chip of the image sensor. Figure 2 shows the sub-aperture segmentation diagram of the high-resolution Hartmann wavefront sensor designed in Embodiment 1 of the present invention. The input wavelength λ of the light beam to be measured is set to 635nm, the pupil is circular, and the wavefront sensor adopts a 12×12 aperture. Segmentation (grid lines in the figure). For the convenience of calculation, the sub-apertures that are completely covered by the light beam and full of light energy are selected as effective sub-apertures, which are represented by solid-line grids in the figure; the sub-apertures of the dotted-line grids are set as invalid sub-apertures, which do not participate in the calculation of wavefront restoration. The sub-figure in the upper right corner of Figure 2 shows that each sub-aperture corresponds to 2×2 pixels of the image sensor. The pixel size L _p of the image sensor is 14 μm, which directly corresponds to the size of each microlens and sub-aperture is 28 μm×28 μm, which is a single Twice the physical pixel size, the focal length f of the microlens array is 1.5L _p ² /λ within the required range of L _p ² /λ≤f≤4L _p ² /λ, which is about 926 μm. Under the division of 12×12 sub-apertures, the pixel resolution required for complete sampling of spot array image information is 28×28. It can be seen that the wavefront sensor in Embodiment 1 requires very little pixel resources of the image sensor.

In order to test the aberration measurement capability of the high-resolution Hartmann wavefront sensor of Embodiment 1, the wavefront distortion of the input beam is composed of the first 23-order Zernike aberration modes, and the coefficients of the 23-order Zernike aberration modes of this group are randomly generated and distributed Satisfying the Kolmogonov turbulence model, the generated random wavefront is shown in Figure 3, with a PV value of 2.8874λ and an RMS value of 0.4861λ. The light spot image on the parallel cursor timing image sensor of the high-resolution Hartmann wavefront sensor is shown in Figure 4. The light spot array picture is very different from the light spot array picture of the conventional Hartmann wavefront sensor. There is no independent sub- The spot image, with data for each pixel in the pupil area, demonstrates the high pixel utilization of the high-resolution Hartmann wavefront sensor of the present invention. In the calibration state, the initial x and y direction centroid positions x _cali and y _cali of the light spot in each sub-aperture can be obtained by the following formula:

分别代表标定状态下单个子孔径对应2×2排列图像传感器像素中左上、右上、左下和右下的像素灰度值。in,

Respectively represent the pixel gray values of the upper left, upper right, lower left and lower right of the pixels of the 2×2 array image sensor corresponding to a single sub-aperture in the calibration state.

The present invention only involves a new method for realizing high resolution to the wavefront slope, and has no special requirements for the mathematical process of reconstructing the wavefront after obtaining the wavefront slope information, so the present invention can be adapted to various types of Hartmann wavefront sensor wave pre-recovery algorithm. Embodiment 1 The Hartmann wavefront sensor uses the mode method to restore the wavefront, and according to the sub-aperture segmentation arrangement and the set 23-order Zernike aberration mode, the centroid offset or slope data of the light spot in the sub-aperture can be constructed according to the classical mode method Computes the restoration matrix of the aberration mode coefficients, which can be generated in advance as a system configuration.

Under the input of the light beam containing the wavefront distortion to be measured in Embodiment 1, the spot image on the high-resolution Hartmann wavefront sensor image sensor is shown in Figure 5, and there is an obvious change in pixel information compared with the calibration. Through the spot image, the centroid positions xc and _yc in the x and y directions of each sub-aperture under the input of the beam _containing the wavefront distortion to be measured can be obtained by the following centroid calculation formula:

Wherein, I ₁ , I ₂ , I ₃ , and I ₄ respectively represent the gray values of the upper left, upper right, lower left, and lower right pixels in the 2×2 array of image sensor pixels. Subtract the x _c , y _c of the light spot in each sub-aperture from the corresponding initial position x _cali , y _cali during calibration to obtain the centroid shift or wavefront of the light spot in each sub-aperture under the input of the wavefront distortion to be measured slope data. Finally, based on the spot centroid offset data in all effective sub-apertures, the Hartmann wavefront sensor mode restoration algorithm and restoration matrix can be used to calculate the Zernike aberration mode coefficient components of the input wavefront distortion, as shown in Figure 6. The 23rd-order aberration mode coefficient (white columnar data) obtained by the wavefront sensor measurement in Fig. 6 agrees well with the aberration mode coefficient (black columnar data) forming the input wavefront, indicating that the high-resolution Hartmann The wavefront sensor makes accurate measurements of the input aberration components. Further use the restored aberration mode coefficients to reconstruct the wavefront distortion information of the entire beam to be measured, as shown in FIG. 7 . The size and distribution of the restored wavefront in Fig. 7 are highly consistent with the input wavefront, and the agreement between the PV value and the RMS value is as high as 99% and 98%. The error wavefront between the restored wavefront and the input wavefront is shown in Figure 8. The PV value and RMS value of the error wavefront are only 0.08λ and 0.0122λ respectively, which proves again that the wavefront sensor can accurately restore the distortion of the input wavefront. distributed. Example 1 shows that the proposed high-resolution Hartmann wavefront sensor can achieve accurate restoration of wavefront distortion when each sub-aperture only corresponds to a total of 4 pixels of 2×2, and the sub-aperture size is twice the physical pixel size, the spatial resolution of the Hartmann wavefront sensor is increased to the order of two pixels.

The above is only a specific implementation mode in the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technology can understand the conceivable transformation or replacement within the technical scope disclosed in the present invention. All should be covered within the scope of the present invention.

Claims (4)

1. A high-resolution Hartmann wavefront sensor is characterized in that: it is mainly composed of a microlens array and an array image sensor, and the microlens array is covered on the array image sensor photosensitive chip, and the incident beam to be measured is divided The photosensitive chip of the array image sensor is placed under the microlens array, and the distance between the two is the focal length of the microlens array, which is used to detect the intensity distribution information of the beam to be measured after the microlens array is divided and focused , each sub-aperture only corresponds to a total of 4 image sensor pixels in a 2×2 arrangement, the center-to-center spacing of pixel areas corresponding to adjacent sub-apertures is twice the size of a single pixel, and the focal length f range of the microlens array is L _p ² /λ≤f≤ 4L _p ² /λ, where L _p is the pixel width size, λ is the wavelength of the probe beam, according to the light intensity signal value of the 2×2 array pixels corresponding to each sub-aperture, the centroid of the focused spot of the thin beam corresponding to the current sub-aperture can be obtained data:

Among them, I ₁ , I ₂ , I ₃ , and I ₄ represent the pixel gray values of the upper left, upper right, lower left, and lower right of the 2×2 array image sensor pixels, and calculate the centroid of the light spot in each sub-aperture according to the above centroid calculation formula Finally, based on the spot centroid data of all effective sub-apertures, the conventional Hartmann wavefront sensor wavefront restoration algorithm can be used to reconstruct the wavefront distortion information of the entire beam to be measured. 2. A kind of high-resolution Hartmann wavefront sensor according to claim 1, is characterized in that: described array type image sensor has the photosensitive pixel of two-dimensional array arrangement, can be CCD sensor camera, CMOS sensor camera , PDA detector. 3. A kind of high-resolution Hartmann wavefront sensor according to claim 1, is characterized in that: described 2 * 2 arranges 4 image sensor pixels altogether, can be single physical pixel of image sensor, also can be The image sensor outputs a single numerical pixel in the image after the pixel combination function. At this time, the size of a single numerical pixel is an integer multiple of the size of a single physical pixel of the sensor. 4. A kind of high-resolution Hartmann wavefront sensor according to claim 1, is characterized in that: described effective sub-aperture refers to the sub-aperture that corresponding light spot centroid data participates in wavefront restoration calculation, can be by A sub-aperture completely covered by the incident beam may also be a sub-aperture partially covered by the incident beam.

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