CN117848681B - Active optical detection method based on annular spliced telescope - Google Patents
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Abstract
The application provides an active optical detection method based on an annular spliced telescope, which can be used for measuring inclination and translational errors Piston of the spliced telescope and is an important component for realizing co-phase adjustment and co-phase maintenance of the annular spliced telescope. The application not only can measure the inclination in the co-phase adjustment, but also can measure millimeter-sized Piston in the confocal adjustment and micrometer-sized Piston in the co-phase adjustment. The measurement system can also be used for tilt and Piston measurements while co-phase is maintained.
Description
Technical Field
The application belongs to the technical field of optical measurement, and particularly relates to an active optical detection method based on an annular spliced telescope.
Background
The huge solar telescope of China (CGST) is the big solar telescope plan of next generation that chinese sun physicist jointly proposed, and the primary mirror of CGST is the annular concatenation of adoption, and the external diameter of primary mirror is 8m, is spliced by 24 sub mirrors that are 1 meter wide. For a spliced telescope, the active optical technology of a spliced mirror surface is a key technology for realizing a scientific target, namely, co-phasing is finally realized. The co-phase adjustment is divided into three steps: the sub-mirrors are aligned, confocal and co-phased, so the active optical detection method of the split mirrors has the capability of detecting Tilt (Tip/Tilt) and translational error (Piston), and can measure in real time in the process of co-phase maintenance.
For a tiled telescope, SHWFS (Shack-Hartmann Wavefront Sensor) can be used to detect sub-mirror tilt errors. In 1994, chanan and the like improved the traditional SHWFS wavefront detection technology, redesigned the arrangement mode of the SHWFS microlens array, and positioned the microlens array at the exit pupil, which is equivalent to adding a pupil mask on which circular through photon apertures are distributed. The tilt error can be calculated by using the centroid position of the image point corresponding to the central sampling round hole, and the translation error of the sub-mirror can be calculated by using the cross correlation of the focal plane diffraction light spot image corresponding to the sampling round hole at the edge of the sub-mirror and the sample plate light spot image. However, most telescopes that have been commonly used today employ hexagonal tiling, so the corresponding pupil mask also takes the shape of a hexagon. For annular spliced telescopes, the traditional pupil mask is not suitable, so that a set of active optical detection method suitable for the annular spliced telescope needs to be designed.
Disclosure of Invention
The application provides an active optical detection method based on an annular spliced telescope, which not only can detect inclination at the same time, but also can detect translational errors from coarse to fine, and the detection precision can meet the co-phase requirement of the annular spliced telescope.
The technical scheme is as follows: an active optical detection method based on an annular spliced telescope specifically comprises the following steps:
Step 1: calculating Piston errors of inclination and millimeter magnitude by utilizing the position of the mass center of an image point corresponding to a sampling circular hole in the micro lens array, and realizing Piston detection in an alignment and confocal adjustment stage;
Step2: after confocal adjustment of the split lens is completed, 2 sampling round holes of the micro lens array corresponding to the edges of the sub lens are utilized to sequentially carry out broadband PSF detection by using broadband light with different coherent lengths, the maximum detection range of the method is about +/-30 mu m, and the highest detection precision can reach hundred nanometers;
step 3: after the Piston detected by the broadband PSF method is compensated, the Piston is measured by adopting a narrow-band PSF detection algorithm, the detection range is half wavelength, and the detection precision can reach the nanometer level.
Preferably SHWFS detects that the wavefront reconstruction using the mode method yields Z 2,Z3 and Z 4 which represent tilt and a wide range of Piston.
Preferably, the circumscribed circle of the microlens array corresponding to the sub-mirror is selected as a unit orthogonal circle domain of a Zernike polynomial, and in the ring sector, a2 nd term Zernike polynomial (2 x) and a3 rd term Zernike polynomial (2 y) are orthogonal, and a3 rd term Zernike polynomial (2 y) and a4 th term Zernike polynomialOrthogonalization, namely, satisfies:
Where S is the area of the ring sector and D represents the ring sector. Thus, using the mode wavefront reconstruction, Z 2,Z3 and Z 4, which represent tilt and a wide range of Piston, can be decoupled.
Compared with the prior art, the embodiment of the application has the beneficial effects that:
(1) The application can be used for the co-phase detection of the annular spliced telescope, which is important for the annular spliced telescope to realize co-phase adjustment and co-phase maintenance.
(2) The application can detect the inclination and translation errors of the sub-mirrors simultaneously, and can detect the translation errors from coarse to fine, namely, the same system can complete confocal adjustment and can complete cophase adjustment.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a diagram of a microlens array corresponding to a sub-mirror according to an embodiment of the present application;
FIG. 2 is a unit circle field diagram of a Zernike polynomial according to an embodiment of the present application;
Fig. 3 is an optical path diagram of a method for detecting a common phase according to an embodiment of the present application.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.
As shown in fig. 1 to 3, according to the characteristics of the CGST annular aperture, the microlens array of the active optical detection method adopts annular band distribution, and adopts circular light-passing holes, which can ensure the uniformity of the shape and size of the light spot imaged by each light-passing hole on the focal plane. The annular micro lens array is placed at the exit pupil plane of the split lens, the size of the sub aperture corresponding to the main lens is not larger than the atmospheric coherence length, the number of the sub apertures can be reasonably designed according to the whole size of the micro lens array, and the detection precision of the system is related to the equivalent focal length and the centroid extraction algorithm of the whole optical system. The CGST is provided with 16 sub-apertures in a planning mode in the micro-lens array corresponding to each sub-mirror, 2 sub-apertures are arranged at the edge of the micro-lens array, and the sub-apertures correspond to about 9.8cm on the main mirror, as shown in figure 1.
The inner sub-aperture can be used for tilt measurement of a split lens, piston measurement in a large range (mm magnitude) in a confocal adjustment stage, the edge sub-aperture can be used for Piston measurement in co-phase adjustment and co-phase maintenance, and based on the theoretical analysis, the following technical scheme is provided:
The specific operation steps of the co-phase detection scheme based on the invention are as follows:
Step 1: and calculating the Piston error of inclination and millimeter magnitude by utilizing the position of the mass center of the image point corresponding to the sampling round hole in the micro lens array, and realizing the Piston detection in the alignment and confocal adjustment stage.
For SHWFS detection, the modal wavefront reconstruction can be used to reconstruct Z 2,Z3 and Z 4, which represent tilt and a wide range of Piston. Because of the special form of annular splicing, the circumscribed circle of the microlens array corresponding to the sub-mirror is selected as a unit orthogonal circle domain of a Zernike polynomial, as shown in figure 2.
It was verified that in the ring sector, the 2 nd and 3 rd Zernike polynomials (2 x, 2 y) are orthogonal, and the 3 rd and 4 th Zernike polynomials (2 y, 4 th Zernike polynomials)Orthogonalization, namely, satisfies:
Where S is the area of the ring sector and D represents the ring sector. Thus, using the mode wavefront reconstruction, Z 2,Z3 and Z 4, which represent tilt and a wide range of Piston, can be decoupled.
Step2: after confocal adjustment is completed on the split lens, 2 sampling round holes corresponding to the edges of the sub-lens are utilized to sequentially carry out broadband PSF detection by using broadband light with different coherent lengths, the maximum detection range of the method is about +/-30 mu m, and the highest detection precision can reach hundred nanometers.
Step 3: and compensating the Piston detected by the broadband PSF method. And then, a narrow-band detection algorithm is adopted to measure Piston, the detection range of the method is half wavelength, and the detection precision can reach the nanometer level.
The wide-narrow PSF method is only one of the co-phase algorithms, and in practical application, the multi-wavelength PSF method can be used to detect Piston.
The method is used as an implementation case of a co-phase detection method on an 800mm spliced experimental system (formed by splicing 8 ring sector sphere sub-mirrors). FIG. 3 is a schematic diagram of a co-phase detection method, in which light sources are placed at the clear points of the tiled mirrors, and SHWFS is used to detect tip/tilt and pixel between sub-mirrors.
The annular micro lens array is placed at the exit pupil plane of the split lens, 7 circular sub apertures are arranged in each micro lens array corresponding to each sub lens, 2 circular sub apertures are arranged at the edge, 72 sub apertures are all arranged, the diameter of each sub aperture is 583 mu m, and the sub apertures correspond to about 5cm on the main lens.
The inner 7 sub-apertures are used to detect sub-mirrors tip/tilt and Piston of the confocal adjustment stage, and the edge 2 sub-apertures are used to detect Piston of the confocal adjustment stage. In the phase-sharing maintaining stage, piston is detected in real time by adopting two sub-apertures at the edge, and inclination is detected in real time by 7 sub-apertures in the interior. The equivalent focal length of the entire optical system is 6602mm.
(1) The tilt of the sub-mirror and Piston in millimeter magnitude can be measured by using the centroid offset of the internal 7 sub Kong Jingcheng image spots and using the mode wavefront reconstruction. And the amount of tilt corresponding to 1pixel on the detector was 0.085arcsecond, and the Piston corresponding to 1pixel was about 50 μm. SHWFS is mainly determined by the detection accuracy of the mass center, and the detection accuracy of the mass center can reach sub-pixels at present. Thus, the detection accuracy of the tilt can be better than 0.01arcsecond in theory, and the detection accuracy of the large-scale Piston can be better than 5 μm.
(2) After confocal adjustment is completed, the following broadband light with different coherent lengths is adopted to detect Piston in sequence: ① A filter with a central wavelength of 636nm and a bandwidth of 10nm (detection range of + -20 μm and scanning step length of 1 μm), a filter with a central wavelength of ② nm and a bandwidth of 80nm (detection range of + -1170 nm and scanning step length of 100 nm), a filter with a central wavelength of ③ of 515nm and a bandwidth of 230nm (detection range of + -432 nm and scanning step length of 40 nm).
(3) After the three broadband light detection modes are finished, the Piston is measured by adopting a narrowband detection algorithm, the center wavelength of the Piston is 610nm, the bandwidth of the Piston is 30nm, and the detection range is half wavelength (+ -152.5 nm).
In summary, not only can the tilt be detected simultaneously, but also the detection of the translational error from coarse to fine can be realized, and the detection precision can meet the co-phase requirement of the annular spliced telescope.
The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.
Claims (1)
1. An active optical detection method based on an annular spliced telescope, wherein a mirror surface of the annular spliced telescope is formed by splicing annular sector sub-mirrors, is characterized by comprising the following steps:
Step 1: calculating Piston errors of inclination and millimeter magnitude by utilizing the position of the mass center of an image point corresponding to a sampling circular hole in the micro lens array, and realizing Piston detection in an alignment and confocal adjustment stage;
Step 2: after confocal adjustment of the split lens is completed, 2 sampling round holes corresponding to the edges of the sub-lens are utilized to sequentially carry out broadband PSF detection by using broadband light with different coherent lengths, and the maximum detection range of the method is as follows 30The highest detection precision is hundred nanometers;
Step 3: after the Piston detected by the broadband PSF method is compensated, the Piston is measured by adopting a narrow-band PSF detection algorithm, the detection range of the method is half wavelength, and the detection precision is nano-scale;
SHWFS detection Piston, which uses a mode wavefront reconstruction to represent tilt and millimeter magnitude , And；
Selecting the circumcircle of the microlens array corresponding to the sub-mirror as the unit orthogonal circle domain of the Zernike polynomial, and selecting the 2 nd Zernike polynomial in the ring sector areaAnd term 3 Zernike polynomialsOrthogonalization, term 3 Zernike polynomialsAnd term 4 Zernike polynomialsOrthogonalization, namely, satisfies:
……（1）
wherein S is the area of the ring sector and D is the ring sector, so that the modal wavefront reconstruction can be decoupled into Piston, which is indicative of tilt and in the order of millimeters ，And。
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| CN106644105B (en) * | 2016-10-26 | 2019-04-30 | 深圳大学 | Wavefront sensor, detection method and system based on double helix point spread function |
| CN107966280B (en) * | 2017-11-21 | 2021-07-06 | 华东交通大学 | Photoelectric detection system applied to spliced telescope and rapid common-phase adjustment method thereof |
| EP3924711A4 (en) * | 2019-03-05 | 2022-12-07 | Gaston Daniel Baudat | System and method of wavefront sensing with engineered images |
| CN111551351B (en) * | 2020-06-09 | 2021-08-03 | 中国科学院长春光学精密机械与物理研究所 | Piston error detection system between adjacent splicing mirrors |
| CN113917686A (en) * | 2021-10-19 | 2022-01-11 | 中国科学院光电技术研究所 | Image-based splicing diffraction telescope splicing error parallel correction method |
| CN115901192A (en) * | 2022-12-23 | 2023-04-04 | 中国科学院西安光学精密机械研究所 | Optical system wavefront splicing detection method and device with real-time alignment function |
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