CN210893429U - Defocusing type light field camera wavefront sensor - Google Patents
Defocusing type light field camera wavefront sensor Download PDFInfo
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- CN210893429U CN210893429U CN201921390305.2U CN201921390305U CN210893429U CN 210893429 U CN210893429 U CN 210893429U CN 201921390305 U CN201921390305 U CN 201921390305U CN 210893429 U CN210893429 U CN 210893429U
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Abstract
The utility model discloses a wavefront sensor of out of focus type light field camera, include: the converging lens is used for converging the wavefront to be measured; the micro lens array is used for dividing light spots formed by the converging lens converging the wavefront to be measured, and comprises a plurality of micro lens units; the CCD detector is used for receiving light spot array information formed by dividing light spots by the micro lens array, and the distance between the micro lens array and the CCD detector is equal to the focal length of the micro lens unit; the micro lens array is positioned at the focal distance from the convergent lens by the defocusing amount fdefcousAt least one of (1) and (b); the defocusing amount is fdefcousN is corresponding to one microlens unit in the microlens arrayThe number of pixels of the CCD detector, f is the focal length of the micro-lens unit, and r represents the number of the micro-lens units occupied by the light spots of the equivalent sub-aperture.
Description
Technical Field
The utility model relates to a wavefront detection field, in particular to wavefront sensor of out of focus type light field camera.
Background
Adaptive optics, which is a novel optical technology developed in recent decades, uses optoelectronic devices to measure dynamic errors of wavefronts in real time, and calculates and controls the dynamic errors through a high-speed computer system, so that active devices correct the wavefronts in real time. The adaptive optics enables the optical system to have the capability of automatically adapting to the change of external conditions and keeping a good working state, and has important application in the fields of high-resolution imaging and laser transmission.
Wavefront sensors are an important component of adaptive optics systems, where adaptive optics technology performs wavefront sensing primarily by measuring the first derivative (slope) or the second derivative (curvature) of the wavefront distortion. The shack-Hartmann sensor is the most widely used wavefront sensor at present, and utilizes a micro-lens array to divide incident wavefront, measure the average slope of the wavefront in each sub-aperture and further recover the wavefront aberration. The shack-Hartmann sensor has the advantages of compact structure, high light energy utilization rate, capability of working on a continuous or pulse target and the like, but also has the defects of smaller dynamic range, insufficient weak light detection capability, difficulty in adjusting the spatial resolution of wavefront measurement and the like. Ragazzoni in 1996 proposed a pyramid wavefront sensor whose basic principle is that a beam is split after focusing on the pyramid vertex, and the local slope of the wavefront is calculated from the intensity difference between four sub-pupil images on the detection plane. The rectangular pyramid wave-front sensor has higher spatial resolution than a Hartmann sensor, and has more prominent sensitivity and weak light detection capability in closed-loop correction.
In addition, Clare and Lane in New Zealand in 2003 proposed a method of placing a microlens array at the back focal plane of an objective lens and performing wavefront sensing in conjunction with a CCD photodetector. However, the wavefront detection method in the prior art has the problems that only relatively rough wavefront measurement can be performed due to the fact that the aperture of the microlens has a certain size (usually, several times of the diffraction limit) and the measurement accuracy of the wavefront sensor of the light field camera is limited by the signal saturation phenomenon, and the application of the wavefront detection method in the adaptive optics technology is limited to a certain extent.
SUMMERY OF THE UTILITY MODEL
The present invention aims at solving at least one of the technical problems in the related art to a certain extent. Therefore, the utility model discloses an aim at provide a out of focus type light field camera wavefront sensor of big visual field, big dynamic range, high measurement accuracy, simple structure, the adaptation optical development trend of agreeing with.
The utility model provides a defocusing type light field camera wavefront sensor, include:
the converging lens is used for converging the wavefront to be measured;
the micro lens array is used for dividing light spots formed by the converging lens converging the wavefront to be measured, and comprises a plurality of micro lens units;
the CCD detector is used for receiving light spot array information formed by dividing light spots by the micro lens array, and the distance between the micro lens array and the CCD detector is equal to the focal length of the micro lens unit;
the micro lens array is positioned at the focal distance from the convergent lens by the defocusing amount fdefcousAt least one of (1) and (b); the defocusing amount is fdefcousN is the number of pixels of the CCD detector corresponding to one microlens unit in the microlens array, f is the focal length of the microlens unit, and r is the number of microlens units occupied by the light spots of the equivalent sub-aperture.
The optical matching system is arranged at the input end of the convergent lens and is used for matching the wavefront to be measured to the convergent lens.
The device further comprises a processing module, wherein the processing module is used for recombining the light spot array to obtain an equivalent sub-aperture image, calculating the local slope of the measured wavefront through the equivalent sub-aperture image, and then calculating each order Zernike aberration coefficient of the measured wavefront by using a reconstruction matrix to obtain the phase distribution of the measured wavefront.
Further, the F-number of the microlens element is an integral multiple of the F-number of the condensing lens.
Furthermore, the size of the CCD detector pixel is matched with the aperture of a single micro-lens element,
further, the aperture of the micro lens unit is integral multiple of the size of the CCD detector pixel.
Further, the focal lengths of all the microlens units in the microlens array are equal, the filling factor of the microlens units is greater than 99%, the transmittance of the microlens units is greater than 99%, and the distance between the microlens array and the CCD detector is equal to the focal length of the microlens units.
Further, the microlens array is a refractive microlens array or a reflective microlens array or a binary diffraction element.
The utility model discloses an adopt the technical means that the microlens array defocuses, overcome and exist among the prior art and have certain size (be the several times of diffraction limit usually) because of the microlens aperture, and light field camera wavefront sensor's measurement accuracy receives the restriction of signal saturation phenomenon, and lead to carrying out comparatively rough wavefront measurement technical problem, realized carrying out the measurement of big visual field, big dynamic range, high measurement accuracy with simple structure's optical system to the wavefront.
Drawings
Fig. 1 is a schematic structural diagram of a wavefront sensor of an out-of-focus light field camera according to the present invention;
fig. 2 is a cross-sectional view of the wavefront sensor of the defocusing type light field camera of the present invention;
fig. 3 is a schematic structural diagram of data reconstruction of the wavefront sensor of the defocusing type light field camera according to the present invention;
fig. 4 is the utility model discloses a structural diagram that defocusing amount of microlens array of defocusing type light field camera wavefront sensor calculated.
FIG. 5A is a diagram of a test of an input wavefront to be tested;
FIG. 5B is a schematic diagram of the Zernike polynomial coefficients of the input wavefront to be measured;
FIG. 6A is a diagram of a conventional light field camera reconstructing a wavefront to be measured;
FIG. 6B is a schematic diagram of the distribution of Zernike polynomial coefficients for wavefront reconstruction in a prior art light field camera;
fig. 7A is a detection diagram of the defocused light field camera wavefront sensor reconstructing the wavefront to be detected of the present invention;
fig. 7B is a distribution diagram of Zernike polynomial coefficients of the wavefront sensor of the defocusing light field camera according to the present invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a defocus type wavefront sensor of a light field camera according to the present invention. The device specifically comprises an optical matching system 1, a converging lens 2, a micro-lens array 3 and a CCD detector 4. Wherein the microlens array 3 includes a plurality of identical microlens units arranged in a same plane at a certain period. The output surface of the optical matching system 1 coincides with the front focal plane of the convergent lens 2, and the micro lens array 3 is located near the back focal plane of the convergent lens 2 and has a certain defocusing amount. The optical matching system 1 is used for pre-modulating the wavefront to be measured, for example, modulating the wavefront to be measured into parallel light and irradiating the parallel light to the converging lens 2. The F-number (i.e. the reciprocal of the relative aperture) of the microlens elements in the microlens array 3 is smaller than that of the converging lens 2 to ensure the full utilization of the pixels under the microlenses without aliasing of the data, and the distance between the CCD detector 4 and the microlens array 3 is equal to the focal length of the microlenses. Wavefront distortion to be measured forms light spots with a certain area on the micro-lens array 3 through the optical matching system 1 and the converging lens 2, and the micro-lens array 3 divides the light spots and images the light spots on the CCD detector 4 to form a light spot array. The equivalent sub-aperture image can be obtained by recombining the image received by the CCD detector 4, after the local slope of the measured wavefront is calculated, each order Zernike aberration coefficient of the measured wavefront is calculated by utilizing a reconstruction matrix, so that the phase distribution of the measured wavefront is obtained.
For convenience of description and without loss of generality of conclusion, the two-dimensional form of the light field camera is taken as an example to illustrate a specific implementation method for realizing wavefront detection by using geometric optics.
Referring to fig. 2, fig. 2 is a cross-sectional view of a defocused wavefront sensor of an optical field camera according to the present invention. As shown in fig. 2, the light passing through the front focal point a of the converging lens 2 passes through the converging lens 2 and the microlens array 3 in sequence, and after being refracted, is irradiated onto the CCD detector 4, and illuminates one pixel on the CCD detector 4. Wherein the propagation directions of the light rays passing through the point A after being refracted by the micro lens are parallel to each other no matter how the incident direction of the light rays is changed. I.e. the relative position of the picture element illuminated on the CCD detector 4 and the microlens element of the corresponding microlens array 3 is fixed.
In other modified embodiments, the converging lens 2 can be replaced by other lens structures designed according to the difference of application scenes, so as to obtain higher wavefront measurement sensitivity or larger wavefront sensing field of view. The detection field of view can be enlarged by a lens group as in the large-field adaptive optics technology; or the system size can be reduced by using a telephoto lens structure.
In the present embodiment, the micro-transmission mirror array is a refractive micro-lens array, and in other modified embodiments, other element arrays that implement the function of the micro-lens array, such as a reflective micro-lens array, or a binary diffractive element, may be adopted.
In other modified embodiments, an object image conjugate system is added between the microlens array and the CCD detector to flexibly adjust the spatial resolution of the wavefront sensing and reduce the assembly difficulty of the light field camera
Referring to fig. 3, fig. 3 is a schematic structural diagram of data reconstruction of a defocus type wavefront sensor of a light field camera according to the present invention. Describing by combining a plurality of microlens units of the microlens array 3, the pixel 1 in the pupil image of each microlens unit is recombined into an image according to the arrangement sequence of the microlens units in the microlens array 3, and the recombined image represents the light spot of the light wave in a certain area at the entrance pupil on the focal plane, which is equivalent to the sub-aperture image of the hartmann detector. The local slope of the incident distorted wavefront can be calculated by using a centroid algorithm, and phase information contained in the wavefront distortion is recovered.
For further explanation of the data reconstruction process, it is assumed that the microlens array 3 is a lens array with 300 rows and 400 columns, i.e. the microlens array 3 contains 1.2w microlens elements, and each microlens element is disposed opposite to 30 × 30 pixels, 30 × 30 sub-aperture images can be extracted, each sub-aperture image is 300 × 400 pixels, the sub-aperture image of the central angle is the pixel value of the central position of each microlens sequentially extracted, and a new image of 300 × 400 is formed by splicing the sub-aperture images sequentially.
Further, we extract the pixel value of the pixel No. 1 of the microlens element at the (0, 0) position, that is, the pixel value of the sub-aperture image (0, 0) position, and the pixel value of the pixel No. 1 of the microlens element at the (0, 1) position, that is, the pixel value of the sub-aperture image (0, 1) position, and so on, until all the pixel values of the pixel No. 1 of the microlens element are extracted. And so on, extracting the pixel value of the rest pixels in all the microlens units to generate the sub-aperture images of the rest pixels.
And phase information contained in the wavefront to be detected can be recovered through Zernike aberration coefficient calculation.
Referring to fig. 4, fig. 4 is a schematic structural diagram of calculating the defocus amount of the microlens array of the wavefront sensor of the defocus light field camera according to the present invention. The wavefront measurement accuracy of the wavefront sensor of the light field camera is generally determined by the aperture of the microlens unit in the microlens array 3, and the smaller the aperture of the microlens unit, the higher the slope measurement accuracy. However, in practical application, the aperture of the microlens unit is usually hundreds of microns, the area of a light spot on the focal plane behind the convergent lens 2 is far smaller than the size of the microlens unit, and the light field camera cannot accurately sense the centroid offset. The area of the spot is thus enlarged by placing the microlens array 3 behind the back focal plane of the condenser lens 2. That is, a defocus amount is introduced to match the spot area on the back focal plane of the convergent lens 2 with the size of the microlens unit cell, so that the light field camera can accurately sense the centroid shift.
The defocusing amount is set according to the principle that the spot area of the equivalent sub-aperture on the micro-lens array is larger than the aperture of the micro-lens element, which can be specifically expressed as fdefcousWhere n is the number of CCD pixels under a single microlens, f is the focal length of the microlens, and r represents the number of microlenses occupied by the spot of the equivalent sub-aperture, and the range of values is usually 2 to 4.
In this example, the defocus amount calculated according to the method can ensure that the light spot in the equivalent sub-aperture covers a plurality of micro-lenses, and the measurement accuracy of the wavefront sensor of the light field camera is improved.
The invention utilizes the combination of the convergent lens, the micro-lens array and the CCD detector, solves the defects of poor linearity and low wavefront measurement precision of the wavefront sensor of the light field camera by optimally designing the optical structure, and constructs the wavefront sensor with large view field, large dynamic range, high measurement precision and simple structure.
The abscissa and ordinate of each of the following figures are explained below by way of analysis. The left ordinate and the bottom abscissa in fig. 5A, 6A, and 7A are used to represent the spatial coordinates of the wavefront, and the right ordinate represents the Zernike polynomial coefficients. And 5B, 6B, and 7B, the ordinate represents the Zernike polynomial coefficients, and the abscissa represents the Zernike polynomial orders.
Referring to fig. 5A-5B, fig. 5A is a diagram illustrating a test of an input wavefront to be tested, and fig. 5B is a diagram illustrating Zernike polynomial coefficients of the input wavefront to be tested corresponding to fig. 5A.
Fig. 6A-6B are also shown, in which fig. 6A is a diagram illustrating a test result of wavefront reconstruction of a conventional light field camera, and fig. 6B is a diagram illustrating Zernike polynomial coefficients of the wavefront reconstruction result corresponding to fig. 6A. The wavefront is detected and reconstructed with the existing light field camera, and the reconstruction result is shown in fig. 6A. As shown in fig. 6B, the Zernike polynomial coefficient obtained by wavefront reconstruction with the existing light field camera is greatly different from the input wavefront distortion Zernike polynomial coefficient, and the measurement accuracy is low.
Referring to fig. 7A-7B, fig. 7A is a diagram illustrating the wavefront reconstruction result of the field-of-view camera, and fig. 7B is a diagram illustrating the Zernike polynomial coefficients of the wavefront reconstruction result corresponding to fig. 7A. As shown in fig. 7B, the Zernike polynomial coefficient obtained by wavefront reconstruction with the defocus line light field camera substantially matches the input wavefront distortion Zernike polynomial coefficient, and the measurement accuracy is high. Compared with the existing wavefront detection method, the wavefront detection method based on the defocusing type light field camera provided by the invention has an obvious optimization effect on the measurement precision.
While the preferred embodiments of the present invention have been described, the present invention is not limited to the embodiments, and those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and such equivalent modifications or substitutions are intended to be included within the scope of the present invention as defined by the appended claims.
Claims (8)
1. A wavefront sensor for an out-of-focus light field camera, comprising:
the converging lens is used for converging the wavefront to be measured;
the micro lens array is used for dividing light spots formed by the converging lens converging the wavefront to be measured, and comprises a plurality of micro lens units;
the CCD detector is used for receiving light spot array information formed by dividing light spots by the micro lens array, and the distance between the micro lens array and the CCD detector is equal to the focal length of the micro lens unit;
the micro lens array is positioned at the focal distance from the convergent lens by the defocusing amount fdefcousAt least one of (1) and (b); the defocusing amount is fdefcousN is the number of pixels of the CCD detector corresponding to one microlens unit in the microlens array, f is the focal length of the microlens unit, and r is the number of microlens units occupied by the light spots of the equivalent sub-aperture.
2. The wavefront sensor of claim 1 further including an optical matching system disposed at the input end of the converging lens for matching the wavefront to be measured to the converging lens.
3. The wavefront sensor according to claim 1, further comprising a processing module, wherein the processing module is configured to recombine the spot array to obtain an equivalent sub-aperture image, calculate a local slope of the measured wavefront through the equivalent sub-aperture image, and calculate each order of Zernike aberration coefficient of the measured wavefront by using a reconstruction matrix to obtain a phase distribution of the measured wavefront.
4. The wavefront sensor of claim 1 with the F-number of the microlens element being less than the F-number of the converging lens.
5. The wavefront sensor of claim 1 with the CCD detector pixel size matched to the aperture of a single microlens element.
6. The wavefront sensor of claim 5 with the aperture of the microlens element being an integer multiple of the CCD detector pixel size.
7. The wavefront sensor of claim 1 with each microlens element in the microlens array having equal focal lengths, the microlens element having a fill factor greater than 99% and a transmittance greater than 99%.
8. The wavefront sensor of claim 1 with the microlens array being a refractive microlens array or a reflective microlens array or a binary diffractive element.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110487425A (en) * | 2019-08-26 | 2019-11-22 | 中国人民解放军国防科技大学 | A kind of wavefront sensing methods and its device based on defocus type light-field camera |
| CN114323310A (en) * | 2021-12-28 | 2022-04-12 | 中国科学院光电技术研究所 | High-resolution Hartmann wavefront sensor |
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2019
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110487425A (en) * | 2019-08-26 | 2019-11-22 | 中国人民解放军国防科技大学 | A kind of wavefront sensing methods and its device based on defocus type light-field camera |
| CN114323310A (en) * | 2021-12-28 | 2022-04-12 | 中国科学院光电技术研究所 | High-resolution Hartmann wavefront sensor |
| CN114323310B (en) * | 2021-12-28 | 2023-05-26 | 中国科学院光电技术研究所 | High-resolution Hartmann wavefront sensor |
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