Wavefront Mosaic Detection Method and Device for an Optical System with Real-Time Alignment Function

Abstract

The present invention provides a method and device for detecting wavefront stitching of an optical system with a real-time alignment function, which are used to solve the technical problem of low wavefront detection accuracy of existing large-aperture optical systems. The detection method of the present invention is as follows: adjusting the optical system to be measured according to the interference fringes detected by the CCD detector, and aligning and correcting in real time the wavefront information of the optical system to be measured obtained by the Hartmann wavefront sensor measurement; realizing wavefront reconstruction of the optical system to be measured for the images collected by the Hartmann wavefront sensor through an improved Southwell model wavefront reconstruction algorithm; according to the wavefront phase information of different sub-apertures obtained by the Hartmann wavefront sensor, first redistributing the data with overlapping regions of two adjacent sub-apertures to non-overlapping regions, and then using a maximum likelihood estimation scanning stitching algorithm to realize the stitching of sub-apertures, so as to obtain the fitted full-aperture wavefront data of the optical system to be measured, greatly improving the wavefront detection accuracy of the large-aperture optical system.

Description

Technical Field

[0001] The present invention relates to wavefront detection technology, and in particular, to a wavefront stitching detection method and device for an optical system with a real-time alignment function. Background Art

[0002] As a main optoelectronic detection device for applications such as astronomical observation and laser communication, in order to achieve higher imaging resolution and detection sensitivity, the aperture of optical telescopes is getting larger and larger. Therefore, higher requirements are put forward for the processing means and high-precision detection technology of optical telescopes, and the image quality evaluation of the optical system of optical telescopes has become a current research hotspot.

[0003] Currently, the in-situ metrology requirements of large-aperture telescopes for multi-scene, low-latency, and high-integration have become important technical difficulties in optical detection systems. For the problem of high-precision wavefront detection of optical systems, the current traditional detection method for system alignment and adjustment is the interference autocollimation detection method. The spherical light wave emitted by the interferometer is reflected by the optical system and the standard flat mirror and then returns to the interferometer along the original path to complete the autocollimation detection. This method has the characteristics of simplicity, high efficiency, and high precision. However, as the aperture of the optical system continues to increase, the processing of large-aperture standard flat mirrors is difficult, the weight is heavy, and the handling is difficult. The self-gravity deformation of the standard flat mirror leads to unstable performance, which limits the application of this method in the detection of large-aperture space optical systems. Subsequently, the industry proposed to use a Shack-Hartmann wavefront sensor to collect the phase information of the incident light to calculate the wavefront of the optical system. The Shack-Hartmann wavefront sensor generates a focusing pattern through a microlens array and analyzes the offset of the centroid of the sub-spot to restore the phase distribution of the wavefront to be measured. The Shack-Hartmann wavefront detector has a simple structure, fast calculation speed, high light energy utilization rate, and is suitable for weak light detection. All technologies are mature. However, the manufacturing of large microlens arrays is difficult, costly, and time-consuming. Limited by the size of the microlens array, it is impossible to detect the wavefront of large-aperture optical systems. Therefore, for the wavefront detection of large-aperture optical systems, the sub-aperture stitching detection technology came into being, and the sub-aperture stitching interference detection technology that combines the sub-aperture stitching technology and the interference detection technology has become an effective means to solve the wavefront detection of large-aperture optical systems.

[0004] Chinese Patent CN110082073 A, "Device and Method for Adjusting Tilt of Plane Mirror in Transmitted Wavefront of Sub-Aperture Stitching Detection Optical System", can adjust the tilt amount of the plane mirror through an autocollimator at the sub-aperture position, reduce the tilt error of the sub-aperture surface shape, and ultimately improve the accuracy of the transmitted wavefront of the sub-aperture stitching detection optical system; the interferometric measurement method has high test accuracy, and it can intuitively judge whether data is collected by the sparsity of the fringes. Its combination with the stitching detection method of the plane mirror has good application prospects. However, interferometric measurement is easily affected by factors such as air disturbance and environmental vibration, and is limited in applications outside the laboratory environment, such as at the installation site of optical telescopes. Chinese Patent CN101493375 A, "Stitching Detection Device Based on Small Aperture Circular Hartmann-Shack Wavefront Sensor", designs a simple and efficient stitching detection system, uses a global optimization stitching algorithm to solve the absolute stitching parameters of the wavefront slope map relative to the reference sub-wavefront slope map, reduces error accumulation and error transfer in multi-frame scanning, and improves stitching accuracy; compared with interferometric measurement, the Hartmann wavefront sensor has strong anti-environmental interference ability, but when making system measurements, more human judgment is required for data result collection. Chinese Patent CN108151888 A, "Method for Error Decoupling of a Scanning Hartmann Detection Device", uses an optical tube array to stitch and detect a large-aperture optical system. By introducing error decoupling based on slope Zernike polynomial fitting, it eliminates the mechanical motion error of the optical tube array during the scanning detection process and realizes the wavefront detection of the large-aperture optical system; however, pointing error will inevitably be introduced during the scanning process of the optical tube array, affecting the wavefront detection accuracy of the optical system. In summary, the current sub-aperture stitching interferometric detection technology has problems such as limited installation and application of optical telescopes, the need for human judgment in data collection, and the introduction of pointing error during the scanning of the optical tube array, resulting in low wavefront detection accuracy of large-aperture optical systems. Summary of the Invention

[0005] The object of the present invention is to solve the technical problems existing in the current sub-aperture stitching interferometric detection technology, such as limited installation and application of optical telescopes, the need for human judgment in data collection, and the introduction of pointing error during the scanning of the optical tube array, which leads to low wavefront detection accuracy of large-aperture optical systems, and to provide a wavefront stitching detection method and device for an optical system with a real-time alignment function.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A wavefront stitching detection method for an optical system with a real-time alignment function, characterized in that it includes the following steps:

[0008] 1】The laser beam that has been expanded and collimated is split into two paths. One path is the reference beam, and the other path is the detection beam. The detection beam is incident on the optical system to be measured. The wavefront of the optical system to be measured is scanned through sub-apertures to obtain an object light beam carrying the phase information of the current sub-aperture of the optical system to be measured. The object light beam carrying the phase information of the current sub-aperture of the optical system to be measured is split into two paths. One path is combined with the reference beam and then incident on the CCD detector, and the other path is incident on the Hartmann wavefront sensor.

[0009] 2】The CCD detector and the Hartmann wavefront sensor simultaneously detect the wavefront phase information of the current sub-aperture of the optical system to be measured. According to the interference fringes detected on the target surface of the CCD detector, the translation, tilt, and higher-order aberrations of the optical system to be measured are adjusted to achieve real-time alignment between the phase information of the current sub-aperture of the optical system to be measured and the detection image of the Hartmann wavefront sensor.

[0010] 3】Wavefront reconstruction is performed on the image of the current sub-aperture of the optical system to be measured collected by the Hartmann wavefront sensor through an improved Southwell model wavefront reconstruction algorithm.

[0011] The improved Southwell model wavefront reconstruction algorithm uses the slopes at the four grid points (i, j-1), (i, j+1), (i-1, j), and (i+1, j) around the grid point (i, j) to estimate the phase value at the grid point (i, j).

[0012] 4】Each sub-aperture of the optical system to be measured is scanned one by one along an s-shaped trajectory. For each scanned sub-aperture, steps 2 - 3 are repeated until the scanning trajectory traverses the entire clear aperture of the optical system to be measured to collect the wavefront aberrations at different positions and obtain the wavefront reconstruction of each sub-aperture of the optical system to be measured.

[0013] 5】Full-aperture wavefront stitching is performed on the wavefront reconstruction information of each sub-aperture of the optical system to be measured obtained in step 4. If there is no overlapping area between adjacent sub-apertures, the improved maximum likelihood estimation scanning stitching algorithm is directly used to achieve the stitching of adjacent sub-apertures. If there is an overlapping area between adjacent sub-apertures, the data in the overlapping area is first redistributed to the non-overlapping area, and then the improved maximum likelihood estimation scanning stitching algorithm is used to achieve the stitching of adjacent sub-apertures. The fitted full-aperture wavefront data W of the optical system to be measured obtained by the improved maximum likelihood estimation scanning stitching algorithm is:

[0014]

[0015] where, A p is the Zernike polynomial coefficient, Z p is the p-th term of the Zernike polynomial, p = 4, 5, … m, ρ ais the radius coordinate of the measurement point in polar coordinates, and θ a is the angular coordinate of the measurement point in polar coordinates.

[0016] Furthermore, in step 3, the phase value φ of the grid point (i, j) i,j is calculated by the following formula:

[0017]

[0018] where σ i,j-1 σ i,j+1 σ i-1,j σ i+1,j respectively represent the data templates of the grid points (i, j - 1), (i, j + 1), (i - 1, j), and (i + 1, j). If the measurement point is within the grid array, the value of the corresponding grid point is 1; if the measurement point is outside the grid array, the value of the corresponding grid point is 0; is the distance between the grid points (i, j - 1) and (i, j), is the distance between the grid points (i, j) and (i, j + 1), is the distance between the grid points (i - 1, j) and (i, j), is the distance between the grid points (i, j) and (i + 1, j); is the slope value of the grid point (i, j) in the horizontal direction, is the slope value of the grid point (i, j - 1) in the horizontal direction, is the slope value of the grid point (i, j + 1) in the horizontal direction, is the slope value of the grid point (i, j) in the vertical direction, is the slope value of the grid point (i - 1, j) in the vertical direction, is the slope value of the grid point (i + 1, j) in the vertical direction.

[0019] Furthermore, in step 5, the improved maximum likelihood estimation scanning and stitching algorithm is as follows:

[0020] The j-th phase data D measured under the i-th sub-aperture ij is:

[0021]

[0022] where D ij a is the polynomial decomposition data, and Z 1 Z 2 Z 3 are the first, second, and third terms of the Zernike polynomial respectively, and P i is the translation coefficient on the i-th sub-aperture, Txi is the tilt coefficient in the x direction on the i-th sub-aperture, Ty i is the tilt coefficient in the y direction on the i-th sub-aperture, and residuals represents the residual;

[0023] Since the smaller the difference between the j-th phase data D ij measured under the i-th sub-aperture and the polynomial decomposition data D ij a , the better the simulation effect is proved. When the difference approaches 0, the fitting result reaches the best. Therefore, in order to solve the full-aperture wavefront coefficient of the optical system to be measured, it is equivalent to solving the equation:

[0024]

[0025] where u represents the number of sub-aperture measurements, and v represents the number of data on the i-th sub-aperture;

[0026] By the radius coordinate ρ a of the measurement point in polar coordinates and the angular coordinate θ a of the measurement point in polar coordinates, the Zernike polynomials Z 4 , Z 5 , Z 6 ... Z m , Z 1 , Z 2 , Z 3 in different modes can be obtained. Written in matrix form for the i-th sub-aperture as follows:

[0027]

[0028] Performing least squares calculation on the above equation can obtain the full-aperture wavefront Zernike polynomial coefficients A p of the optical system to be measured, that is, A 4 ~A m in the matrix. Furthermore, the fitted full-aperture wavefront data of the optical system to be measured is calculated as:

[0029]

[0030] Furthermore, step 2 is specifically as follows:

[0031] Block the detection optical path of the Hartmann wavefront sensor, adjust the object light optical path and the reference optical path to interfere, and make it present on the target surface of the CCD detector for detection; cancel the block of the detection optical path of the Hartmann wavefront sensor, and according to the interference fringes, finely adjust the translation amount, tilt amount and higher-order aberration of the current sub-aperture of the optical system to be measured in real time, so as to adjust the relative position of the incident light aperture on the Hartmann wavefront sensor, make the phase information of the current sub-aperture of the optical system to be measured be aligned with the Hartmann wavefront sensor in real time, and eliminate the error introduced by optical transmission.

[0032] Further, step 5 is specifically as follows:

[0033] Allocate the phase data measured by two adjacent sub-apertures to 3 data groups according to the two non-overlapping parts and the overlapping part of the two sub-apertures respectively, and then splice the 3 data groups through the maximum likelihood estimation scanning splicing algorithm to obtain the splicing data of the two sub-apertures. By analogy, the fitted full-aperture wavefront data W of the optical system to be measured is obtained;

[0034] Or, divide the phase data measured by two adjacent sub-apertures into 2 data groups according to two different overlapping methods, and respectively splice the 2 data groups under the two different overlapping methods through the maximum likelihood estimation scanning splicing algorithm to obtain the fitted wavefronts W 1 and W 2 for W 1 、W 2 take the average to obtain the splicing data of the two sub-apertures. By analogy, the fitted full-aperture wavefront W of the optical system to be measured is obtained.

[0035] Further, in step 4, when using the improved maximum likelihood estimation scanning splicing algorithm to realize the splicing of sub-apertures, it is necessary to use the method of multiple averaging processing during the measurement of each sub-aperture to suppress noise.

[0036] To implement the above-mentioned wavefront splicing detection method for an optical system with a real-time alignment function, the present invention also provides a wavefront splicing detection device for an optical system with a real-time alignment function, which is characterized in that it includes a laser, a beam expanding and collimating system, a first beam splitting prism, a first plane mirror, a detection unit, a CCD detector, a Hartmann wavefront sensor, a small plane mirror and a computer; the emitted light of the laser is incident on the first beam splitting prism through the beam expanding and collimating system for beam splitting, forming a detection beam and a reference beam;

[0037] The first plane mirror is vertically located on the optical path of the reference beam of the first beam splitting prism; the reference beam is reflected by the first plane mirror and then enters the first beam splitting prism again;

[0038] The detection unit includes a second beam splitter prism, a second plane mirror, and a second converging lens that are sequentially arranged on the detection light path of the detection beam of the first beam splitter prism; the optical system to be measured is located on the outgoing light path of the second converging lens, and the small plane mirror is vertically located on the outgoing light path of the optical system to be measured, and is used to realize the scanning of each sub-aperture of the optical system to be measured by moving the small plane mirror, and to realize the alignment and correction of the phase information of the current sub-aperture of the optical system to be measured by the CCD detector and the Hartmann wavefront sensor by adjusting the angle of the small plane mirror.

[0039] The detection beam is incident on the optical system to be measured after passing through the second beam splitter prism, the second plane mirror, and the second converging lens in sequence. After the outgoing light of the optical system to be measured is reflected by the small plane mirror, the reflected light completes the scanning of the current sub-aperture of the optical system to be measured, and forms an object light beam carrying the phase information of the current sub-aperture of the optical system to be measured; the object light beam enters the second beam splitter prism after passing through the second converging lens and the second plane mirror in sequence; after passing through the second beam splitter prism, it is divided into two paths, one path enters the first beam splitter prism to be combined with the reference beam and then is incident on the CCD detector, and the other path is incident on the Hartmann wavefront sensor; the output ends of the CCD detector and the Hartmann wavefront sensor are respectively connected to a computer, and the interference fringes detected on the target surface of the CCD detector and the focused pattern generated by the microlens array of the Hartmann wavefront sensor are transmitted to the computer, and the alignment of the phase information of the current sub-aperture of the optical system to be measured with the focused pattern is realized according to the interference fringe information, the wavefront of the current sub-aperture obtained by the Hartmann wavefront sensor during alignment is reconstructed, and then the wavefront reconstruction information of each sub-aperture is spliced to obtain the wavefront data of the full aperture of the optical system to be measured.

[0040] Further, the beam expanding and collimating system includes a microscopic objective lens and a first converging lens that are sequentially arranged along the outgoing light path of the laser; the outgoing light of the first converging lens is incident on the first beam splitter prism.

[0041] The beneficial effects of the present invention compared with the prior art are as follows:

[0042] 1. The method for detecting the wavefront splicing of an optical system with a real-time alignment function provided by the present invention introduces a Hartmann wavefront sensor and an interference measurement system into the wavefront detection optical path, can detect and correct the wavefront in real time through interference fringes, and can transiently image on the target surface of the Hartmann wavefront sensor, overcoming the problem that the Hartmann wavefront sensor cannot be internally adjusted, and greatly improving the wavefront detection accuracy of a large-aperture optical system.

[0043] 2. The method for detecting the wavefront splicing of an optical system with a real-time alignment function provided by the present invention proposes an improved Southwell wavefront reconstruction algorithm, which can solve the situation where the length and width of each sub-aperture are different, the result is closer to the real wavefront data, the reconstructed wavefront is more accurate, and its application is also more extensive.

[0044] 3. The wavefront stitching detection method of the optical system with real-time alignment function provided by the present invention performs wavefront data stitching processing through an improved maximum likelihood estimation stitching method. When stitching sparse sub-aperture wavefronts where the processed sub-apertures do not overlap, it can conveniently guide the alignment and adjustment. When performing wavefront stitching processing for adjacent sub-apertures with overlapping regions, it can accurately describe the wavefront distribution of the system, and has high flexibility and versatility.

[0045] 4. The wavefront stitching device of the optical system with real-time alignment function provided by the present invention has a simple structure and convenient operation. Combining the high sensitivity of the interference measurement system and the measurement stability advantage of the Hartmann wavefront sensor, it can achieve more accurate wavefront testing, which is of great significance for realizing high-precision wavefront detection of large-aperture telescopes.

[0046] 5. When the wavefront stitching device of the optical system with real-time alignment function provided by the present invention is applied to wavefront stitching detection of a large-aperture optical system, at each sub-aperture measurement position, the sparsity of the interference fringes can be used to intuitively feedback the adjustment angle of the small plane mirror. After obtaining the sparse fringe distribution, the Hartmann wavefront sensor is used to measure the wavefront at the position of this sub-aperture, which is of great significance for realizing high-precision wavefront detection of large-aperture telescopes. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic structural diagram of the wavefront stitching detection device of the optical system with real-time alignment function of the present invention;

[0048] Figure 2 is the real-time interference fringe pattern of different aberration combinations in step 2 of the wavefront stitching detection method of the present invention;

[0049] Figure 3 is the detection diagram of the Hartmann wavefront sensor in step 2 of the detection method of the present invention;

[0050] Figure 4 is a schematic diagram of the improved Southwell algorithm model in step 3 of the detection method of the present invention;

[0051] Figure 5 is the sub-aperture scanning trajectory diagram in step 4 of the detection method of the present invention;

[0052] Figure 6Schematic diagrams of two sub-aperture data processing methods for the stitching algorithm of the large-aperture imaging system in step 5 of the measurement method of the present invention; among them, a is one data processing method, in which the phase data measured by two sub-apertures are respectively assigned to 3 data groups according to the non-overlapping part and the overlapping part of the two sub-apertures; b is another data processing method, in which the phase data measured by two sub-apertures are divided into data groups according to two different overlapping methods.

[0053] The specific reference numerals are as follows:

[0054] 1 - Laser; 2 - Microscope objective; 3 - First converging lens; 4 - First plane mirror; 5 - First beam splitter prism; 6 - Second beam splitter prism; 7 - Second plane mirror; 8 - CCD detector; 9 - Hartmann wavefront sensor; 10 - Second converging lens; 11 - Optical system to be measured; 12 - Small plane mirror. Specific embodiments

[0055] To make the advantages and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] An optical system wavefront stitching detection device with a real-time alignment function, as Figure 1 shown, includes a laser 1, an expanding and collimating system, a first beam splitter prism 5, a first plane mirror 4, a detection unit, a CCD detector 8, a Hartmann wavefront sensor 9, a small plane mirror 12, and a computer 13. In this embodiment, the laser 1 uses a He-Ne laser with a wavelength of 633 nm. The expanding and collimating system is composed of a microscope objective 2 and a first converging lens 3, which can achieve a 3-fold beam expansion effect on the laser spot. The optical system 11 to be measured includes a plane mirror and an off-axis parabolic mirror arranged in sequence, which are respectively applicable to a transmissive optical system and a reflective optical system. The small plane mirror 12 in the present invention is used to scan each sub-aperture of the optical system 11 to be measured along an s-shaped trajectory, so that the scanning traverses the entire clear aperture of the optical system 11 to be measured. At the same time, by adjusting the angle of the small plane mirror 12, the alignment between the phase information of the current sub-aperture of the optical system 11 to be measured and the Hartmann wavefront sensor 9 can be achieved.

[0057] The positional relationship and working principle of each optical device are as follows: The emitted light of the laser 1 sequentially passes through the microscopic objective lens 2 and the first converging lens 3 and then enters the first beam splitting prism 5 for beam splitting, forming a detection beam and a reference beam. The first plane mirror 4 is vertically located on the optical path of the reference beam of the first beam splitting prism 5. The reference beam is reflected by the first plane mirror 4 and then enters the first beam splitting prism 5 again. The detection unit includes a second beam splitting prism 6, a second plane mirror 7, and a second converging lens 10 that are sequentially arranged on the optical path of the detection beam of the first beam splitting prism 5; the optical system 11 to be measured is located on the emitted light path of the second converging lens 10, and the small plane mirror 12 is vertically located on the emitted light path of the optical system 11 to be measured, and is used to realize the scanning of each sub-aperture of the optical system 11 to be measured by the translation of the small plane mirror 12, and at the same time, the alignment and correction of the phase information of the current sub-aperture of the optical system 11 to be measured are realized by adjusting the azimuth and pitch angles of the small plane mirror 12. The detection beam sequentially passes through the second beam splitting prism 6, the second plane mirror 7, and the second converging lens 10 and then enters the optical system 11 to be measured. The emitted light of the optical system 11 to be measured is reflected by the small plane mirror 12, and the reflected light scans the optical system 11 to be measured, forming an object light beam carrying the phase information of the current sub-aperture of the optical system 11 to be measured; the object light beam carrying the phase information of the current sub-aperture of the optical system 11 to be measured sequentially passes through the second converging lens 10 and the second plane mirror 7 and enters the second beam splitting prism 6; it is split into two paths by the second beam splitting prism 6. One path enters the first beam splitting prism 5, is combined with the reference beam and then enters the CCD detector 8, and the other path enters the Hartmann wavefront sensor 9; the output ends of the CCD detector 8 and the Hartmann wavefront sensor 9 are respectively connected to the computer 13, and the interference fringes detected on the target surface of the CCD detector 8 and the focusing pattern generated by the microlens array of the Hartmann wavefront sensor 9 are transmitted to the computer 13. The alignment of the phase information of the current sub-aperture of the optical system 11 to be measured and the focusing pattern is realized according to the interference fringe information, the wavefront of the current sub-aperture obtained by the Hartmann wavefront sensor 9 during alignment is reconstructed, and then the wavefront reconstruction information of each sub-aperture is spliced to obtain the wavefront data of the full aperture of the optical system 11 to be measured.

[0058] Based on the above-described wavefront stitching detection device for an optical system with a real-time alignment function, the present invention provides a method for detecting the wavefront stitching of an optical system with a real-time alignment function, which specifically includes the following steps:

[0059] 1】The emitted light of the laser 1 is incident on the first beam splitting prism 5 for beam splitting after passing through the microscope objective 2 and the first converging lens 3 in sequence, forming two beams of light. One is the reference beam, and the other is the detection beam. The detection beam passes through the second beam splitting prism 6, the second plane mirror 7, and the second converging lens 10 in sequence and then is incident on the optical system 11 to be measured. The emitted light of the optical system 11 to be measured is reflected by the small plane mirror 12, and the reflected light scans the wavefront of the optical system 11 to be measured through sub-apertures, obtaining an object light beam carrying the phase information of the current sub-aperture of the optical system 11 to be measured. The object light beam carrying the phase information of the current sub-aperture of the optical system 11 to be measured passes through the second converging lens 10 and the second plane mirror 7 in sequence and enters the second beam splitting prism 6. It is split into two paths by the second beam splitting prism 6. One path enters the first beam splitting prism 5, is combined with the reference beam, and then is incident on the CCD detector 8, and the other path is incident on the Hartmann wavefront sensor 9.

[0060] 2】Real-time alignment of the phase information of the optical system 11 to be measured and the detection image of the Hartmann wavefront sensor 9

[0061] The CCD detector 8 and the Hartmann wavefront sensor 9 simultaneously detect the wavefront phase information of the optical system 11 to be measured. The interference fringes detected on the target surface of the CCD detector 8 can reflect the phase of the optical system 11 to be measured in real time. As Figure 2 shown, it is the real-time interference fringe pattern of spherical aberration, coma, and astigmatism under different aberration combinations. The image of the optical system 11 to be measured detected by the Hartmann wavefront sensor 9 is as Figure 3 shown. According to the interference fringes detected on the target surface of the CCD detector 8, the translation amount, tilt amount, and higher-order aberrations of the current sub-aperture of the optical system 11 to be measured are adjusted to achieve real-time alignment between the phase information of the optical system 11 to be measured and the image detected on the Hartmann wavefront sensor 9 for compensation and correction. The specific alignment process is as follows: First, block the beam entering the Hartmann wavefront sensor 9, and adjust the object light beam carrying the phase information of the current sub-aperture of the optical system 11 to be measured so that it interferes with the reference beam. The interfered light is presented on the target surface of the CCD detector 8 for detection, generating interference fringes. Then, cancel the block of the incident beam on the Hartmann wavefront sensor 9, and finely adjust the relative position of the optical system detection device in real time through the interference fringes to accurately adjust the relative position of the incident light aperture on the Hartmann wavefront sensor 9, realizing the real-time alignment function and eliminating the error introduced by optical transmission, and improving the detection accuracy of the Hartmann wavefront sensor 9.

[0062] 3】Wavefront reconstruction of the current sub-aperture image of the optical system 11 to be measured

[0063] Wavefront reconstruction is performed on the image of the current sub-aperture of the optical system 11 to be measured collected by the Hartmann wavefront sensor 9 through an improved Southwell model wavefront reconstruction algorithm. Currently, the wavefront reconstruction algorithms are mainly the modal method and the zonal method. To handle the situation where the length and width of the sub-aperture are inconsistent and the effective data is not square, the present invention proposes an improved Southwell wavefront reconstruction algorithm. As Figure 4 shown, it is a schematic diagram of the improved Southwell algorithm model, which uses the slopes at the four grid points (i, j-1), (i, j+1), (i-1, j), and (i+1, j) around the grid point (i, j) to estimate the phase value at the grid point (i, j). In the improved algorithm of the Southwell wavefront reconstruction algorithm, a data template σ i,j is used. When σ i,j =1, the phase point (i, j) has a value; while when σ i,j =0, the phase point has no value. In the improved algorithm of the Southwell wavefront reconstruction algorithm, data templates σ i,j-1 , σ i,j+1 , σ i-1,j , and σ i+1,j are respectively introduced for the grid points (i, j-1), (i, j+1), (i-1, j), and (i+1, j). If the measurement point is within the grid lattice, the value of the corresponding grid point is 1, and if the measurement point is outside the grid lattice, the value of the corresponding grid point is 0. Let be the distance between the grid points (i, j-1) and (i, j), be the distance between the grid points (i, j) and (i, j+1), be the distance between the grid points (i-1, j) and (i, j), be the distance between the grid points (i, j) and (i+1, j); be the slope value in the horizontal direction of the grid point (i, j), be the slope value in the horizontal direction of the grid point (i, j-1), be the slope value in the horizontal direction of the grid point (i, j+1), be the slope value in the vertical direction of the grid point (i, j), be the slope value in the vertical direction of the grid point (i-1, j), be the slope value in the vertical direction of the grid point (i+1, j), and φ i,j be the phase value of the grid point (i, j). Then, there are the following relationships between them:

[0064]

[0065] Combining equations (1), (2), (3), and (4), the phase value φ i,j of the grid point (i, j) can be obtained as:

[0066]

[0067] Among them,

[0068] if there is no invalid data or no marked points in the slope data matrix composed of and the length and width of the sub-aperture are the same, then the grid points at the four corners of the matrix have k i,j = 2, the grid points on the four sides have k i,j = 3, and the grid points inside have k i,j = 4. The improved Southwell algorithm of the present invention is closer to the true wavefront data when solving the situation where the length and width of each sub-aperture are different.

[0069] 4] Scan each sub-aperture of the optical system 11 to be measured

[0070] To achieve the stitching measurement of the large-aperture wave aberration, as Figure 5 shown, move the small plane mirror 12 to scan each sub-aperture of the optical system 11 to be measured along an S-shaped trajectory one by one; for each scanned sub-aperture, repeat steps 2 - step 3 until the scanning trajectory traverses the entire clear aperture of the optical system 11 to be measured, so as to collect the wave aberrations at different positions and obtain the wavefront reconstruction of each sub-aperture of the optical system 11 to be measured;

[0071] 5] Complete the full-aperture wavefront stitching of the optical system 11 to be measured

[0072] In order to accurately stitch different sub-apertures of the optical system 11 to be measured to obtain the full-aperture wavefront phase of the optical system 11 to be measured, the present invention uses an improved maximum likelihood estimation method to accurately describe the wavefront distribution of the system. The traditional maximum likelihood estimation method is mainly used for the coefficient aperture without overlapping regions between sub-apertures. The improved maximum likelihood estimation scanning stitching algorithm of the present invention can achieve stitching when there are overlapping regions between sub-apertures. In the present invention, if there is no overlapping region between adjacent sub-apertures, the improved maximum likelihood estimation scanning stitching algorithm is directly used to achieve the stitching of adjacent sub-apertures; if there is an overlapping region between adjacent sub-apertures, two data processing methods are used to first redistribute the data in the overlapping region to the non-overlapping region, and then the improved maximum likelihood estimation scanning stitching algorithm is used to achieve the stitching of adjacent sub-apertures. As Figure 6 shown, Figure 6In it, a is a data processing method, which distributes the phase data measured by two adjacent sub-apertures to three data groups ①②③ according to two non-overlapping parts and an overlapping part of the two sub-apertures respectively, and then splices the three data groups through an improved maximum likelihood estimation scanning splicing algorithm to obtain the spliced data of the two sub-apertures. By analogy, the fitted full-aperture wavefront data W of the optical system 11 to be measured is obtained; Figure 6 In it, b is another data processing method, which divides the phase data measured by two adjacent sub-apertures into two data groups ①② according to two different overlapping methods, and respectively splices the two data groups under the two different overlapping methods through the maximum likelihood estimation scanning splicing algorithm to obtain the fitted wavefronts W 1 and W 2 For W 1 、W 2 Take the mean value to obtain the spliced data of the two sub-apertures. By analogy, the fitted full-aperture wavefront W of the optical system 11 to be measured is obtained. According to these two data processing methods, the versatility of splicing is increased when using the improved maximum likelihood estimation scanning splicing algorithm to solve the fitted wavefront of the optical system 11 to be measured. The spliced wavefront when it is on the sparse aperture can conveniently guide the alignment, while the wavefront with an overlapping area on the full aperture can accurately describe the wavefront distribution of the system.

[0073] The specific improved maximum likelihood estimation scanning splicing algorithm is as follows:

[0074] The j-th phase data D measured under the i-th sub-aperture ij is:

[0075]

[0076] Among them, D ij a is the polynomial decomposition data, Z 1 、Z 2 、Z 3 、Z p are respectively the first term, the second term, the third term and the p-th term of the Zernike polynomial, p = 4, 5,... m, P i is the translation coefficient on the i-th sub-aperture, Tx i is the tilt coefficient in the x direction on the i-th sub-aperture, Ty i is the tilt coefficient in the y direction on the i-th sub-aperture, A p is the Zernike polynomial coefficient, residuals represents the residual, ρ a is the radius coordinate of the measurement point in polar coordinates, θ a is the angular coordinate of the measurement point in polar coordinates.

[0077] Since the difference between the j-th phase data D measured under the i-th sub-aperture ij and the polynomial decomposition data D ij a is smaller, it proves that the simulation effect is better. When the difference approaches 0, the fitting result reaches the best. Therefore, in order to solve the full-aperture wavefront coefficient of the optical system 11 to be measured, it is equivalent to solving the equation:

[0078]

[0079] where u represents the number of sub-aperture measurements, and v represents the number of data on the i-th sub-aperture.

[0080] By the radius coordinate ρ of the measurement point in polar coordinates a and the angular coordinate θ of the measurement point in polar coordinates a the Zernike polynomials Z in different modes can be obtained 4 , Z 5 , Z 6 ... Z m , Z 1 , Z 2 , Z 3 For the i-th sub-aperture, it can be written in matrix form as follows:

[0081]

[0082] By performing least-squares calculation through formula (8), the full-aperture wavefront Zernike polynomial coefficients A of the optical system 11 to be measured can be obtained p , that is, A in the matrix 4 ~A m , and then the fitting full-aperture wavefront data of the optical system 11 to be measured is calculated as:

[0083]

[0084] It should be noted that when using the improved maximum likelihood estimation scanning and stitching algorithm to realize the stitching of sub-apertures, the method of multiple averaging processing needs to be used during the measurement of each sub-aperture to suppress noise.

[0085] A method for detecting wavefront stitching of an optical system with a real-time alignment function provided by the present invention introduces a Hartmann wavefront sensor 9 and an interference measurement system into the wavefront detection optical path, which can detect and correct the wavefront in real time through interference fringes, and can also transiently image the target surface of the Hartmann wavefront sensor 9, overcoming the problem that the Hartmann wavefront sensor 9 cannot be adjusted internally, and greatly improving the wavefront detection accuracy. When applying this test system to the wavefront stitching detection of a large-aperture optical system, at each sub-aperture measurement position, the sparsity of the interference fringes can be used to intuitively feedback the adjustment angle of the small plane mirror 12. After obtaining the sparse fringe distribution, the Hartmann wavefront sensor 9 is used to measure the wavefront at the position of this sub-aperture. Its device structure is simple and the operation is convenient. Combining the high sensitivity of the interference measurement system and the advantages of the measurement stability of the Hartmann wavefront sensor 9, more accurate wavefront testing can be realized, which has important significance for the realization of high-precision wavefront detection of large-aperture telescopes.

[0086] As described above, it is only used to illustrate the technical solution of the present invention, rather than to limit it. For those of ordinary professional skills in the art, the specific technical solution recorded in the above embodiments can be modified, or some of the technical features can be equivalently replaced, and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A method for detecting wavefront stitching of an optical system with real-time alignment function, characterized in that, it includes the following steps: 1] Split the expanded and collimated laser into two paths: a reference beam and a detection beam; the detection beam is incident on the optical system to be measured (11), and its wavefront is scanned through sub-apertures to obtain an object light beam carrying the phase information of the current sub-aperture of the optical system to be measured (11); divide the object light beam into two paths, one path is combined with the reference beam and then incident on the CCD detector (8), and the other path is incident on the Hartmann wavefront sensor (9); 2] The CCD detector (8) and the Hartmann wavefront sensor (9) simultaneously detect the wavefront phase information of the current sub-aperture of the optical system to be measured (11); according to the interference fringes detected on the target surface of the CCD detector (8), adjust the translation amount, tilt amount and higher-order aberration of the current sub-aperture of the optical system to be measured (11), so that the phase information of the current sub-aperture of the optical system to be measured (11) is aligned in real time with the detection image of the Hartmann wavefront sensor (9); 3] Perform wavefront reconstruction on the image of the current sub-aperture of the optical system to be measured (11) collected by the Hartmann wavefront sensor (9) through an improved Southwell model wavefront reconstruction algorithm; The improved Southwell model wavefront reconstruction algorithm is to use the slopes at the four grid points (i, j-1), (i, j+1), (i-1, j), (i+1, j) around the grid point (i, j) to estimate the phase value at the grid point (i, j); 4] Scan each sub-aperture of the optical system to be measured (11) one by one along an s-shaped trajectory. For each scanned sub-aperture, repeat steps 2 to 3 until the scanning trajectory traverses the entire clear aperture of the optical system to be measured (11) to collect wavefront aberrations at different positions and obtain the wavefront reconstruction of each sub-aperture of the optical system to be measured (11); 5] Perform full-aperture wavefront stitching on the wavefront reconstruction information of each sub-aperture of the optical system to be measured (11) obtained in step 4. If there is no overlapping area between adjacent sub-apertures, directly use the improved maximum likelihood estimation scanning stitching algorithm to achieve the stitching of adjacent sub-apertures; if there is an overlapping area between adjacent sub-apertures, first redistribute the data in the overlapping area to the non-overlapping area, and then use the improved maximum likelihood estimation scanning stitching algorithm to achieve the stitching of adjacent sub-apertures; the fitted full-aperture wavefront data W of the optical system to be measured (11) obtained by the improved maximum likelihood estimation scanning stitching algorithm is: Among them, A p is the Zernike polynomial coefficient, Z p is the p-th term of the Zernike polynomial, where p = 4, 5, … m, ρ a is the radius coordinate of the measurement point in polar coordinates, and θ a is the angular coordinate of the measurement point in polar coordinates.

2. A method for detecting wavefront stitching of an optical system with real-time alignment function according to claim 1, characterized in that: In step 3, the phase value φ of the grid point (i, j) i,j is calculated by the following formula: Among them, σ i,j-1 、σ i,j+1 、σ i-1,j 、σ i+1,j represent the data templates of grid points (i, j - 1), (i, j + 1), (i - 1, j), and (i + 1, j) respectively. If the measurement point is within the grid matrix, the value of the corresponding grid point is 1; if the measurement point is outside the grid matrix, the value of the corresponding grid point is 0; is the distance between grid points (i, j - 1) and (i, j), is the distance between grid points (i, j) and (i, j + 1), is the distance between grid points (i - 1, j) and (i, j), is the distance between grid points (i, j) and (i + 1, j); is the slope value in the horizontal direction of grid point (i, j), is the slope value in the horizontal direction of grid point (i, j - 1), is the slope value in the horizontal direction of grid point (i, j + 1), is the slope value in the vertical direction of grid point (i, j), is the slope value in the vertical direction of grid point (i - 1, j), is the slope value in the vertical direction of grid point (i + 1, j).

3. A method for detecting wavefront stitching of an optical system with real-time alignment function according to claim 2, characterized in that: In step 5, the improved maximum likelihood estimation scanning stitching algorithm is: The j-th phase data D measured under the i-th sub-aperture ij is as follows: Among them, D ij a is the polynomial decomposition data, and Z 1 , Z 2 , Z 3 are the first, second, and third terms of the Zernike polynomial respectively. P i is the translation coefficient on the i-th sub-aperture, Tx i is the tilt coefficient in the x-direction on the i-th sub-aperture, Ty i is the tilt coefficient in the y-direction on the i-th sub-aperture, and residuals represents the residual; Since the difference between the j-th phase data D measured under the i-th sub-aperture ij and the polynomial decomposition data D ij a is smaller, it proves that the simulation effect is better. When the difference approaches 0, the fitting result reaches the best. Therefore, in order to solve the full-aperture wavefront coefficient of the optical system (11) to be measured, it is equivalent to solving the equation: where u represents the number of sub-aperture measurements, and v represents the number of data on the i-th sub-aperture; By measuring the radius coordinate ρ of the measurement point in polar coordinates a and the angular coordinate θ of the measurement point in polar coordinates a the Zernike polynomials Z in different modes can be obtained 4 , Z 5 , Z 6 ... Z m , Z 1 , Z 2 , Z 3 , which can be written in matrix form for the i-th sub-aperture as follows: Performing least squares calculation on the above formula can obtain the full-aperture wavefront Zernike polynomial coefficients A of the optical system (11) to be measured p , that is, A in the matrix 4 ~A m , and then calculate the fitted full-aperture wavefront data of the optical system (11) to be measured as follows:

4. A method for detecting wavefront stitching of an optical system with real-time alignment function according to claim 3, characterized in that: Step 2 is specifically: Block the detection optical path of the Hartmann wavefront sensor (9), adjust the object light optical path and the reference optical path to interfere, and make it present on the target surface of the CCD detector (8) for detection; cancel the blocking of the detection optical path of the Hartmann wavefront sensor (9), and fine-tune the translation amount, tilt amount, and higher-order aberration of the current sub-aperture of the optical system to be measured (11) in real time according to the interference fringes, so as to adjust the relative position of the incident light aperture on the Hartmann wavefront sensor (9), align the phase information of the current sub-aperture of the optical system to be measured (11) with the real time of the Hartmann wavefront sensor (9), and eliminate the error introduced by optical transmission.

5. A method for detecting wavefront stitching of an optical system with real-time alignment function according to claim 4, characterized in that: Step 5 is specifically: The phase data measured by two adjacent sub-apertures are respectively assigned to 3 data groups according to two non-overlapping parts and an overlapping part of the two sub-apertures, and then the 3 data groups are stitched by the maximum likelihood estimation scanning stitching algorithm to obtain the stitching data of the two sub-apertures. By analogy, the fitted full-aperture wavefront data W of the optical system to be measured (11) is obtained; Alternatively, the phase data measured by two adjacent sub-apertures are divided into two data groups according to two different overlapping methods, and the stitching of the two data groups under the two different overlapping methods is respectively realized through the maximum likelihood estimation scanning stitching algorithm, so as to obtain the fitted wavefronts W 1 and W 2 . For W 1 and W 2 , the mean value is calculated to obtain the stitching data of the two sub-apertures, and so on, so as to obtain the fitted full-aperture wavefront W of the optical system (11) to be measured.

6. A method for detecting wavefront stitching of an optical system with real-time alignment function according to any one of claims 1-5, characterized in that: In step 4, when using the improved maximum likelihood estimation scanning stitching algorithm to realize the stitching of sub-apertures, it is necessary to use the method of multiple averaging processing during the measurement of each sub-aperture to suppress noise.

7. An apparatus for detecting wavefront stitching of an optical system with real-time alignment function, which is used to implement a method for detecting wavefront stitching of an optical system with real-time alignment function according to any one of claims 1-6, characterized in that: It includes a laser (1), a beam expanding and collimating system, a first beam splitting prism (5), a first plane mirror (4), a detection unit, a CCD detector (8), a Hartmann wavefront sensor (9), a small plane mirror (12) and a computer (13); the light emitted from the laser (1) is incident on the first beam splitting prism (5) through the beam expanding and collimating system for beam splitting, forming a detection beam and a reference beam; The first plane mirror (4) is vertically located on the optical path of the reference beam of the first beam splitting prism (5); the reference beam is reflected by the first plane mirror (4) and then enters the first beam splitting prism (5) again; The detection unit includes a second beam splitting prism (6), a second plane mirror (7) and a second converging lens (10) arranged in sequence on the detection beam optical path of the first beam splitting prism (5); the optical system to be measured (11) is located on the outgoing optical path of the second converging lens (10), and the small plane mirror (12) is vertically located on the outgoing optical path of the optical system to be measured (11), and is used to scan each sub-aperture of the optical system to be measured (11) through its translation, and to align and correct the phase information of the current sub-aperture of the optical system to be measured (11) by the CCD detector (8) and the Hartmann wavefront sensor (9) by adjusting the angle of the small plane mirror (12); The detection beam is incident on the optical system to be measured (11) successively through the second beam splitter prism (6), the second plane mirror (7), and the second converging lens (10). After the light emitted from the optical system to be measured (11) is reflected by the small plane mirror (12), the reflected light scans the current sub-aperture of the optical system to be measured (11), forming an object light beam carrying the phase information of the current sub-aperture of the optical system to be measured (11); the object light beam enters the second beam splitter prism (6) successively through the second converging lens (10) and the second plane mirror (7); it is split into two paths by the second beam splitter prism (6). One path enters the first beam splitter prism (5), is combined with the reference beam and then incident on the CCD detector (8), and the other path is incident on the Hartmann wavefront sensor (9); the output ends of the CCD detector (8) and the Hartmann wavefront sensor (9) are respectively connected to the computer (13), and the interference fringes detected on the target surface of the CCD detector (8) and the focused pattern generated by the microlens array of the Hartmann wavefront sensor (9) are transmitted to the computer (13). According to the interference fringe information, the alignment of the phase information of the current sub-aperture of the optical system to be measured (11) and the focused pattern is realized. The wavefront of the current sub-aperture obtained by the Hartmann wavefront sensor (9) during alignment is reconstructed, and then the wavefront reconstruction information of each sub-aperture is spliced to obtain the wavefront data of the full aperture of the optical system to be measured (11).

8. An optical system wavefront stitching detection device with a real-time alignment function according to claim 7, characterized in that: The beam expanding and collimating system includes a microscopic objective lens (2) and a first converging lens (3) arranged successively along the output optical path of the laser (1); the light emitted from the first converging lens (3) is incident on the first beam splitter prism (5).

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