A large-aperture optical antenna common phase error detection system based on vortex light zero-position interference and its working method

Abstract

The present invention relates to a large-aperture optical antenna common phase error detection system based on vortex light zero-position interference and its working method, belonging to the field of optical precision testing for precision measurement. The plane wave of the present invention carries the common phase error information of the spliced ​​mirror, and the plane wave and the vortex light beam undergo zero-position interference in a CCD camera. A four-step phase shift method is used to obtain the spiral wavefront phase carrying the common phase error, and the spiral wavefront phase is demodulated to obtain the error information of the spliced ​​sub-mirrors. The translation error and tilt error are obtained respectively by the angle and curvature of the wavefront dislocation line, thereby achieving accurate analysis of the common phase error. The present invention uses the spiral wavefront dislocation line of the central reference mirror as the reference baseline, compares it with the spiral wavefront dislocation lines on all the spliced ​​sub-mirrors, and extracts the common phase error information of all the spliced ​​sub-mirrors. The method is simple and has high detection efficiency. The translation error and tilt error between the spliced ​​sub-mirrors can be obtained in real time.

Description

Technical Field

[0001] The present invention relates to a large-aperture optical antenna common-phase error detection system based on vortex light-like zero-position interference and a working method thereof, belonging to the technical field of optical precision testing for precision measurement. Background Art

[0002] With the continuous advancement of science and technology, large-aperture optical antennas are widely used in many important fields, including environmental monitoring, astronomical observation, and military reconnaissance. They are playing an increasingly important role in national security, space debris detection, and astronomical research. According to optical imaging system theory, when the observation wavelength is fixed, the spatial angular resolution of the optical system is inversely proportional to the aperture of the optical antenna. The larger the entrance pupil diameter of the optical imaging system, the smaller its angular resolution, the greater its light-gathering ability, the higher its resolution, and the closer it is to the diffraction limit. Increasing the aperture of the primary mirror of an optical antenna is an effective means of improving observation resolution and light-gathering ability. Therefore, countries around the world have invested heavily in the research and development of large-aperture optical antennas. The continuous increase in the primary mirror aperture poses significant challenges to the processing, testing, integrated assembly, and transportation of optical antennas.

[0003] Replacing a single primary mirror with a composite mirror composed of several sub-mirrors effectively addresses the aperture limitations of large telescopes. By dividing the entire mirror into multiple smaller mirrors, costs are reduced while also simplifying mirror processing, transportation, and assembly. By adjusting the positions of the individual sub-mirrors, the spliced ​​mirror forms a virtual, continuous, single primary mirror optical surface. This improves light-gathering capacity and resolving power while reducing the cost and quality of the telescope.

[0004] One of the key technologies in a spliced ​​primary mirror lies in the co-phasing between sub-mirrors. Due to their unique splicing structure, each sub-mirror inevitably experiences tilt error and axial (translation) error between them. This prevents the sub-mirrors from achieving optical confocal co-phasing, and the phases of the sub-mirrors cannot be guaranteed to be consistent. This co-phasing error introduces wavefront aberrations into the primary mirror, degrading image quality. The tilt and axial errors between the mirrors in a spliced ​​primary mirror are collectively referred to as co-phasing errors. Only by achieving strict co-phasing among all sub-mirrors can the maximum optical performance of a large aperture be truly realized.

[0005] In recent years, the problem of high-precision common-phase detection of spliced ​​mirrors has become a research hotspot. In order to solve the problem of detecting common-phase errors, researchers from various countries have conducted extensive research and proposed many effective detection methods. However, traditional common-phase error detection has various problems, and the detection process for more than two spliced ​​sub-mirrors is usually cumbersome and complicated. A single common-phase detection method is difficult to achieve large-scale, high-precision detection. Although the combination of multiple common-phase detection methods can achieve large-scale, high-precision detection, it not only makes the instrument structure more complex, but also leads to cumbersome and abnormal processes, making it difficult to achieve high-efficiency detection. Achieving optical common-phase detection with a large range, high precision, high efficiency, and a simple detection process is an extremely challenging task. Summary of the Invention

[0006] In response to the current significant demand and technical bottlenecks in the field of common-phase detection in large-aperture optical antennas, the present invention provides a large-aperture optical antenna common-phase error detection system and its working method based on vortex light zero-position interferometry, which has the advantages of large range, high precision, high efficiency and simple detection process, and provides a new research idea and technical approach for the online detection and assembly and adjustment testing of large-aperture optical antennas.

[0007] The present invention adopts the following technical solutions:

[0008] A large-aperture optical antenna common phase error detection system based on vortex light null-position interferometry includes a laser, a beam expander, a beam splitter A, a beam splitter B, a beam splitter C, a beam splitter D, a quarter-wave plate, a spiral phase plate, a lens group, a splicing mirror, a reflector, and a CCD camera;

[0009] The linearly polarized plane wave emitted by the laser first passes through the beam expander and is then divided into reference light and test light by beam splitter A. The reference light is converted into circularly polarized light by a quarter-wave plate and then passes through a spiral phase plate to generate a vortex beam. The vortex beam is then incident on beam splitter C, reflected by beam splitter C to the reflector, and then returns to the original path through beam splitter C and is incident on beam splitter D.

[0010] The test light is transmitted through beam splitter B and focused by the lens group, turning into a spherical wave and incident on the stitching mirror. By adjusting the front-to-back distance of the stitching mirror, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the stitching mirror, the light beam reflected from the surface of the stitching mirror passes through the lens group again and turns into a plane wave. This plane wave carries the common phase error information of the stitching mirror. The test light, i.e., the plane wave, enters the CCD camera through beam splitter D, and generates quasi-zero-position interference with the reference light, i.e., the vortex beam, in the CCD camera. The four-step phase shift method is used to obtain the phase of the spiral wavefront carrying the common phase error. Finally, the common phase error is accurately analyzed by demodulating the spiral wavefront phase.

[0011] Preferably, the reflector is arranged on a PZT displacement platform driven by piezoelectricity for phase shifting.

[0012] A method for detecting a common phase error of a large-aperture optical antenna based on vortex-light null-interference comprises the following steps:

[0013] (1) The linearly polarized plane wave emitted by the laser first passes through the beam expander and then is divided into reference light and test light by beam splitter A;

[0014] (2) The reference light is converted into circularly polarized light by a quarter-wave plate, and then passes through a spiral phase plate to generate a vortex beam. The vortex beam is then incident on beam splitter C, and is reflected by beam splitter C to the reflector, where it introduces a phase shift, and then returns along the original path through beam splitter C and is incident on beam splitter D.

[0015] (3) The test light is transmitted through beam splitter B and focused by the lens group, becoming a spherical wave and incident on the splicing mirror. By adjusting the front-to-back distance of the splicing mirror, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the splicing mirror, the light beam reflected from the surface of the splicing mirror passes through the lens group again and becomes a plane wave. This plane wave carries the common phase error information of the splicing mirror.

[0016] (4) The test light, i.e., the plane wave, and the reference light, i.e., the vortex beam, undergo zero-position interference in the CCD camera;

[0017] (5) The four-step phase shift method is used to obtain the phase of the spiral wavefront carrying the common phase error;

[0018] (6) The spiral wavefront phase is demodulated to obtain the error information of the spliced ​​sub-mirrors. The translation error and tilt error are obtained respectively through the angle and curvature of the wavefront dislocation line, thus achieving accurate analysis of the common phase error.

[0019] Preferably, the spliced ​​mirror includes a central reference mirror and a spliced ​​sub-mirror. After step (6), the translation error and tilt error information are used as feedback to guide the actuator to adjust the spliced ​​sub-mirror in real time until the spiral wavefront dislocation lines of the spliced ​​sub-mirror under dual-wavelength measurement are collinear with the central reference mirror, and the common phase error is corrected here.

[0020] Preferably, optical zero-position interference test is a relative measurement method, which has been widely used in the high-precision detection of optical components, wherein zero-position interference refers to that the phase difference between the reference wavefront and the test wavefront at any point in the interference region is zero or equal to a certain constant. Vortex light is a special light field with a spiral wavefront phase (positive helicoid), and the notable feature of the wavefront is that it is equiphase in the radial direction, so the vortex light and the plane wave are zero-position interference in each radial direction, and are quasi-zero-position interference in the entire interference region. During correction, a pair of central reference mirrors and spliced ​​sub-mirrors are first selected for correction, and correction is performed separately for multiple groups of central reference mirrors and spliced ​​sub-mirrors.

[0021] The electric field expression of a vortex beam with a topological charge of l propagating along the z direction is:

[0022] E v =E v ·exp(ilθ)exp(ikz) (1)

[0023] The electric field expression of a plane wave propagating along the z direction is:

[0024] E p =E p ·exp(ikz) (2)

[0025] The electric field expression of the plane wave carrying the common phase error of the splicing mirror propagating along the z direction is:

[0026] E error =E p ·exp{i[k(z+Δz)·cosδ]} (3)

[0027] Where i is the imaginary part, θ is the phase carried by the vortex light, k = 2π / λ, and z represents the transmission distance in the z direction;

[0028] Take E v =E p =E0, the zero-interference intensity of the vortex light and the plane wave captured by the CCD camera is:

[0029]

[0030] Among them, Δz is the translation error between the central reference mirror and the spliced ​​sub-mirror, and δ is the tilt error between the central reference mirror and the spliced ​​sub-mirror.

[0031] Preferably, a reference image is collected when the measured mirror is not loaded, and its light intensity expression is:

[0032] I0=a+bcosα (5)

[0033] Where a is the background light intensity, b is the modulation depth, and α is the unknown random phase;

[0034] The mirror under test is loaded and a four-step phase shift is introduced through the PZT displacement platform with a step length of The phase shift is 0, π, The following four light intensity images are obtained:

[0035]

[0036] In order to obtain the phase difference β, the four deformed intensity images are subtracted from the reference image to obtain four subtraction images:

[0037]

[0038] Where, It is a high-frequency phase and is considered as high-frequency noise. It is usually filtered out by mean filtering or low-pass frequency domain filtering. The filtered light intensity is squared to obtain:

[0039]

[0040] According to formula (8), the tangent expression of the phase difference is:

[0041]

[0042] The phase of the spiral wavefront is:

[0043]

[0044] Preferably, when the central reference mirror of the petal-shaped interference pattern and the spliced ​​sub-mirror have obvious dislocation and the interference pattern is curved in the radial direction, the dislocation is caused by the translation error, and the curvature is caused by the tilt error, that is, there are both translation error and tilt error, and the magnitude of the curvature is positively correlated with the tilt. Four phase-shifted interference patterns are collected by the camera, and the spiral wavefront phase with wavefront dislocation and curvature is obtained by the four-step phase shift method, as shown in formula (10) and Figure 5 , extract the spiral wavefront dislocation line construction function on the central reference mirror and the spliced ​​sub-mirror:

[0045] f(x)=Ax 3 +Bx 2 +Cx+D (11)

[0046] Establish a coordinate system, extract several data points from the spiral wavefront dislocation line on the central reference mirror and the spliced ​​sub-mirror, and calculate the values ​​of constants A, B, C, and D in formula (11). Alternatively, use a curve to fit the spiral wavefront dislocation line, and the fitted curve is formula (11);

[0047] The least square method is used to calculate the data points (x i ,y i The root mean square F(x) of the distance from the constructed straight line function (i=1,2,3,…,m) to the curve can be divided into m+1 segments according to a certain interval. The coordinates of the data points are extracted at the segmentation points. For places where the slope changes greatly, more data points can be extracted. The curvature evaluation function is calculated as follows:

[0048] g(x)=ax+b (12)

[0049] The curvature evaluation function is:

[0050]

[0051] When the function F(x) reaches the minimum value, the straight line function g(x) is used as the benchmark for tilt correction to adjust the curvature. F(x) is used as the curvature evaluation function value to quantify the size of the tilt error. The curvature evaluation function value is fed back to the actuator to perform tilt correction on the splicing mirror. The larger the F(x) value, the greater the curvature. When F(x) min When it approaches 0, the tilt error is considered to be corrected.

[0052] Preferably, after obtaining the spiral wavefront phase according to formula (10), the magnitude of the translation error Δz is quantified by calculating the angle Δθ between the dislocation line of the spliced ​​sub-mirror and the dislocation line of the central reference mirror. Δθ can be obtained based on the collected image, such as Figure 4 θ1, θ2, θ3 in:

[0053]

[0054] The angle value is fed back to the actuator to perform translation correction on the splicing mirror. When the angle value decreases to approach 0, it is considered that the translation error is corrected.

[0055] Preferably, the present invention adopts the basic principle of vortex light and plane wave interference, obtains the spiral wavefront phase carrying common phase error information through a four-step phase shift method, and extracts the wavefront dislocation line of the spiral wavefront, wherein the angle between the wavefront dislocation line of the central reference mirror and the spiral wavefront dislocation line of the spliced ​​sub-mirror is proportional to the translation error; the curvature of the spiral wavefront dislocation line is positively correlated with the tilt error. In the experimental operation, the tilt error is first corrected until the curvature of the spiral wavefront dislocation line tends to zero, and then the translation error is corrected until the angle between the wavefront dislocation line of the central reference mirror and the spiral wavefront dislocation line of the spliced ​​sub-mirror tends to zero. It can be considered that the common phase error of the large-aperture optical antenna is corrected. This detection scheme is simple and easy to implement, with the characteristics of high precision and fast measurement. At the same time, the manifestation of the common phase error is very intuitive and can be distinguished by the naked eye, which is of great value for the detection of the common phase error of high-precision large-aperture optical antennas.

[0056] The present invention uses the central sub-mirror in the spliced ​​mirror as a reference mirror, and then obtains the spiral wavefront dislocation line carrying the common phase error of the spliced ​​sub-mirrors through computer processing, establishes the mathematical relationship between the rotation angle and curvature of the spiral wavefront dislocation line and the translation error and tilt error in the common phase error, and then uses this theoretical model as a guide to design an optical path structure for high-precision detection of the common phase error of the spliced ​​sub-mirrors, and constructs a four-step phase-shift interference optical path of vortex light and plane wave.

[0057] Where the present invention is not exhaustive, please refer to the prior art.

[0058] The beneficial effects of the present invention are:

[0059] 1) From the perspective of zero-position interference between vortex light and plane waves, the present invention provides a new research idea and technical approach for common-phase error detection with large detection range, high detection accuracy and high detection efficiency, and provides a new and reliable guarantee system for the design and adjustment of spliced ​​optical antennas.

[0060] 2) The present invention uses the central spiral wavefront dislocation line (i.e., the spiral wavefront dislocation line of the central reference mirror) as the reference baseline, compares it with the spiral wavefront dislocation lines on all the spliced ​​sub-mirrors, and extracts the common-phase error information of all the spliced ​​sub-mirrors. The method is simple and has high detection efficiency. The translation error and tilt error between the spliced ​​sub-mirrors can be obtained in real time. There is no need to perform a separate common-phase calibration to record the initial relative error between the sub-mirrors. The spiral wavefront dislocation line always exists, and there is no dark stripe in the traditional common-phase detection method, which may make comparison difficult or information difficult to determine. The interference information, i.e., the spiral wavefront dislocation line, is clear, sharp, and easy to extract. The extracted spiral wavefront dislocation line angle and curvature are used to invert the common-phase error of adjacent sub-mirrors, which can avoid the introduction of additional sensor devices.

[0061] 3) The present invention can intuitively observe translation error and tilt error, which can be distinguished by the naked eye. The two errors are represented by the angle and curvature in the petal-shaped interference pattern. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 A schematic diagram of the system of the present invention;

[0063] Figure 2 is a flow chart of the common phase error extraction algorithm of the present invention;

[0064] Figure 3 The schematic diagram for solving the common phase error of the spliced ​​sub-mirrors is shown in Figure 1, where (a) shows the spliced ​​mirror surface viewed from a top-down perspective;

[0065] (b) The shape of the spiral wavefront dislocation line on the spliced ​​sub-mirror and the central reference mirror when the translation error exists;

[0066] (c) is the translation error between the splicing mirrors observed from the three-dimensional view;

[0067] (d) The shape of the spiral wavefront dislocation line on the spliced ​​sub-mirrors and the central reference mirror when the tilt error exists;

[0068] Figure 4 This is a flow chart for detecting translation errors between vortex light and plane wave zero-position interference;

[0069] Figure 5 This is a flow chart for detecting the tilt error of vortex light and plane wave quasi-zero-position interference;

[0070] In the figure, 1-laser, 2-beam expander, 3-beam splitter A, 4-beam splitter B, 5-beam splitter C, 6-beam splitter D, 7-1 / 4 wave plate, 8-spiral phase plate, 9-lens group, 10-splitting mirror, 11-reflecting mirror, 12-PZT displacement platform, 13-CCD camera. DETAILED DESCRIPTION

[0071] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, they will be described in detail below with reference to the accompanying drawings and specific embodiments, but are not limited thereto. Matters not fully described in the present invention shall be based on conventional techniques in the art.

[0072] Example 1:

[0073] A large-aperture optical antenna common phase error detection system based on vortex light zero-position interferometry, such as Figure 1 As shown, it includes a laser 1, a beam expander 2, a beam splitter A3, a beam splitter B 4, a beam splitter C 5, a beam splitter D 6, a 1 / 4 wave plate 7, a spiral phase plate 8, a lens group 9, a splicing mirror 10, a reflecting mirror 11 and a CCD camera 13;

[0074] The linearly polarized plane wave emitted by laser 1 first passes through beam expander 2, and then is split into reference light and test light by beam splitter A3. The reference light is converted into circularly polarized light by quarter-wave plate 7, and then passes through spiral phase plate 8 to generate a vortex beam. The vortex beam is then incident on beam splitter C5, reflected by beam splitter 5C to reflector 11, and then returns to the original path through beam splitter C5 and is incident on beam splitter D6.

[0075] The test light is transmitted through the beam splitter B4 and focused by the lens group 9, then becomes a spherical wave and is incident on the splicing mirror 10. By adjusting the front-to-back distance of the splicing mirror, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the splicing mirror, the light beam reflected from the surface of the splicing mirror 10 passes through the lens group 9 again and becomes a plane wave. The plane wave carries the common phase error information of the splicing mirror. The test light, i.e., the plane wave, enters the CCD camera 13 through the beam splitter D6, and generates quasi-zero-position interference with the reference light, i.e., the vortex beam, at the CCD camera 13. The four-step phase shift method is used to obtain the phase of the spiral wavefront carrying the common phase error. Finally, the accurate analysis of the common phase error is achieved by demodulating the spiral wavefront phase.

[0076] The reflector 11 is placed on a PZT displacement platform 12 driven by piezoelectricity for phase shifting.

[0077] Example 2:

[0078] A working method of a large-aperture optical antenna common phase error detection system based on vortex light zero-position interference, such as Figure 2-5 As shown, the following steps are included:

[0079] (1) The linearly polarized plane wave emitted by laser 1 first passes through beam expander 2 and then is divided into reference light and test light by beam splitter A;

[0080] (2) The reference light is converted into circularly polarized light by the quarter-wave plate 7, and then passes through the spiral phase plate 8 to generate a vortex beam. The vortex beam is then incident on the beam splitter C5, and is reflected by the beam splitter C5 to the reflector 11, where a phase shift is introduced. After that, the vortex beam returns along the original path through the beam splitter C5 and is incident on the beam splitter D6.

[0081] (3) The test light is transmitted through the beam splitter B4 and focused by the lens group 9, then becomes a spherical wave and is incident on the splicing mirror 10. By adjusting the front-to-back distance of the splicing mirror 10, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the splicing mirror, the light beam reflected from the surface of the splicing mirror passes through the lens group again and becomes a plane wave. This plane wave carries the common phase error information of the splicing mirror.

[0082] (4) The test light, i.e., the plane wave, and the reference light, i.e., the vortex beam, undergo zero-position interference in the CCD camera;

[0083] (5) The four-step phase shift method is used to obtain the phase of the spiral wavefront carrying the common phase error;

[0084] (6) The spiral wavefront phase is demodulated to obtain the error information of the spliced ​​sub-mirrors. The translation error and tilt error are obtained respectively through the angle and curvature of the wavefront dislocation line, thus achieving accurate analysis of the common phase error.

[0085] After step (6), the translation error and tilt error information are used as feedback to guide the actuator to adjust the spliced ​​sub-mirrors in real time until the spiral wavefront dislocation lines of the spliced ​​sub-mirrors under dual-wavelength measurement are collinear with the central reference mirror, and the common phase error is corrected here.

[0086] Example 3:

[0087] A working method of a large-aperture optical antenna common-phase error detection system based on vortex light-like zero-position interferometry is as described in Example 2, except that during calibration, a pair of central reference mirrors and spliced ​​sub-mirrors are first selected for calibration, and multiple groups of central reference mirrors and spliced ​​sub-mirrors are calibrated separately.

[0088] The electric field expression of a vortex beam with a topological charge of l propagating along the z direction is:

[0089] E v =E v ·exp(ilθ)exp(ikz) (1)

[0090] The electric field expression of a plane wave propagating along the z direction is:

[0091] E p =E p·exo(ikz) (2)

[0092] The electric field expression of a plane wave carrying the common phase error of the splicing mirror propagating along the z direction is:

[0093] E error =E p ·exp{i[k(z+Δz)·cosδ]} (3)

[0094] Where i is the imaginary part, θ is the phase carried by the vortex light, k = 2π / λ, and z represents the transmission distance in the z direction;

[0095] Take E v =E p =E0, the zero-interference intensity of the vortex light and the plane wave captured by the CCD camera is:

[0096]

[0097] Among them, Δz is the translation error between the central reference mirror and the spliced ​​sub-mirror, and δ is the tilt error between the central reference mirror and the spliced ​​sub-mirror.

[0098] Example 4:

[0099] A working method of a large-aperture optical antenna common phase error detection system based on vortex light-like zero-position interference is as described in Example 3, except that, from the interference pattern, the central reference mirror and the spliced ​​sub-mirrors at the edge of the petal-shaped interference pattern produce obvious dislocation and / or curvature. The spiral wavefront phase with wavefront dislocation and the spiral wavefront phase with wavefront curvature can be obtained by solving and restoring the four-step phase shift method, as shown in FIG. Figure 3 (b), 3(d);

[0100] When the mirror under test is not loaded, a reference image is collected and its light intensity expression is:

[0101] I0=a+bcosα (5)

[0102] Where a is the background light intensity, b is the modulation index, and α is the unknown random phase;

[0103] The mirror under test is loaded and a four-step phase shift is introduced through the PZT displacement platform with a step length of The phase shift is 0, π, The following four light intensity images are obtained:

[0104]

[0105] In order to obtain the phase difference β, the four deformed intensity images are subtracted from the reference image to obtain four subtraction images:

[0106]

[0107] Where, It is a high-frequency phase and is considered as high-frequency noise. It is usually filtered out by mean filtering or low-pass frequency domain filtering. The filtered light intensity is squared to obtain:

[0108]

[0109] According to formula (8), the tangent expression of the phase difference is:

[0110]

[0111] The phase of the spiral wavefront is:

[0112]

[0113] When the central reference mirror and the spliced ​​sub-mirror of the petal-shaped interference pattern have obvious dislocation and the interference pattern is curved in the radial direction, the dislocation is caused by the translation error, and the curvature is caused by the tilt error, that is, there are both translation error and tilt error, and the magnitude of the curvature is positively correlated with the tilt. The camera collects four phase-shifted interference patterns, and the spiral wavefront phase with wavefront dislocation and curvature is solved by the four-step phase shift method, as shown in formula (10), Figure 3 (d) and Figure 5 As shown, the function for extracting the spiral wavefront dislocation line on the central reference mirror and the spliced ​​sub-mirror is:

[0114] f(x)=Ax 3 +Bx 2 +Cx+D (11)

[0115] Establish a coordinate system, extract several data points from the spiral wavefront dislocation lines on the central reference mirror and the spliced ​​sub-mirror, and calculate the values ​​of constants A, B, C, and D in formula (11);

[0116] The least square method is used to calculate the data points (x i ,y i For example, the total curve length can be divided into 101 segments on the spiral wave front dislocation line, with 100 segmentation points, that is, m = 100. The coordinates of the data points are extracted at the segmentation points to construct the curvature evaluation function. The root mean square F(x) of the distance from the constructed straight line function is used as the curvature evaluation function, where the straight line function is:

[0117] g(x)=ax+b (12)

[0118] The curvature evaluation function is:

[0119]

[0120] When the function F(x) reaches the minimum value, the straight line function g(x) is used as the benchmark for tilt correction to adjust the curvature. F(x) is used as the curvature evaluation function value to quantify the size of the tilt error. The curvature evaluation function value is fed back to the actuator to perform tilt correction on the splicing mirror. The larger the F(x) value, the greater the curvature. When F(x) min When it approaches 0, the tilt error is considered to be corrected.

[0121] The specific process of solving F(x) is preferably:

[0122] A. Extract m data points (x i ,y i );

[0123] B. Use the point-to-line distance formula to calculate the distances between each of the m data points and the line ax+b (the result includes the two unknown quantities a and b).

[0124] C. Write the RMS formula for distance, F(x);

[0125] D. Take the partial derivative of a and b so that F'(x) is equal to 0. When F(x) reaches its minimum value, the values ​​of a and b are the values ​​in formula (12).

[0126] Example 5:

[0127] A working method of a large-aperture optical antenna common phase error detection system based on vortex light null-position interferometry is as described in Example 4, except that after the spiral wavefront phase is obtained according to formula (10), the magnitude of the translation error Δz is quantified by calculating the angle Δθ between the dislocation line of the spliced ​​sub-mirror and the dislocation line of the central reference mirror. Δθ can be obtained based on the collected image, as shown in FIG. Figure 3 (b) Figure 4 θ1, θ2, θ3 in:

[0128]

[0129] The angle value is fed back to the actuator to perform translation correction on the splicing mirror. When the angle value decreases to approach 0, it is considered that the translation error is corrected.

[0130] The present invention utilizes the basic principle of vortex light and plane wave interference. A four-step phase shift method is used to determine the spiral wavefront phase, which carries common-phase error information. The wavefront dislocation line of the spiral wavefront is extracted, where the angle between the wavefront dislocation line of the central reference mirror and the spiral wavefront dislocation line of the spliced ​​sub-mirrors is proportional to the translation error; the curvature of the spiral wavefront dislocation line is positively correlated with the tilt error. In experimental operation, the tilt error is first corrected until the curvature of the spiral wavefront dislocation line approaches zero. The translation error is then corrected until the angle between the wavefront dislocation line of the central reference mirror and the spiral wavefront dislocation line of the spliced ​​sub-mirrors both approach zero. This indicates that the common-phase error of large-aperture optical antennas has been corrected. This detection scheme is simple and easy to implement, featuring high precision and rapid measurement. Furthermore, the common-phase error is intuitive and can be discerned by the naked eye, making it valuable for detecting the common-phase error of high-precision, large-aperture optical antennas.

[0131] Figure 3 This method uses the spiral wavefront dislocation line of the central reference mirror as a reference baseline, compares it with the spiral wavefront dislocation lines on all the mirrors, and extracts the common-phase error information for all mirrors. This method is simple and efficient, and can determine the tilt and translation errors between mirrors in real time without requiring separate common-phase calibration to record the initial relative errors between mirrors. The spiral wavefront dislocation line is always present, without the dark streaks that can make comparison or information determination difficult as in traditional common-phase detection methods. The interference information, namely the spiral wavefront dislocation line, is clear, sharp, and easy to extract. The extracted angles and curvature of the spiral wavefront dislocation line are used to invert the common-phase error of adjacent mirrors, avoiding the need for additional sensors. This system not only offers high precision over a wide range, but most importantly, meets the future needs for efficient common-phase detection of multiple mirrors in a spliced ​​mirror.

[0132] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A large-aperture optical antenna common phase error detection system based on vortex light null-position interferometry, characterized in that: Including laser, beam expander, beam splitter A, beam splitter B, beam splitter C, beam splitter D, 1 / 4 wave plate, spiral phase plate, lens group, splicing mirror, reflector and CCD camera; The linearly polarized plane wave emitted by the laser first passes through the beam expander and is then divided into reference light and test light by beam splitter A. The reference light is converted into circularly polarized light by a quarter-wave plate and then passes through a spiral phase plate to generate a vortex beam. The vortex beam is then incident on beam splitter C, reflected by beam splitter C to the reflector, and then returns to the original path through beam splitter C and is incident on beam splitter D. The test light is transmitted through beam splitter B and focused by the lens group, then becomes a spherical wave and is incident on the stitching mirror. By adjusting the front-to-back distance of the stitching mirror, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the stitching mirror, the light beam reflected from the surface of the stitching mirror passes through the lens group again and becomes a plane wave. This plane wave carries the common phase error information of the stitching mirror. The test light, i.e., the plane wave, enters the CCD camera through beam splitter D, and generates quasi-zero-position interference with the reference light, i.e., the vortex beam, in the CCD camera.

2. The large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 1 is characterized in that: The reflector is arranged on a PZT displacement platform driven by piezoelectricity for phase shifting.

3. A method for detecting a common phase error of a large-aperture optical antenna based on vortex-light null-interference according to claim 1, characterized in that: The following steps are involved: (1) The linearly polarized plane wave emitted by the laser first passes through the beam expander and then is divided into reference light and test light by beam splitter A; (2) The reference light is converted into circularly polarized light by a quarter-wave plate, and then passes through a spiral phase plate to generate a vortex beam. The vortex beam is then incident on beam splitter C, and is reflected by beam splitter C to the reflector, where it introduces a phase shift, and then returns along the original path through beam splitter C and is incident on beam splitter D. (3) The test light is transmitted through beam splitter B and focused by the lens group, becoming a spherical wave and incident on the splicing mirror. By adjusting the front-to-back distance of the splicing mirror, when the curvature radius of the spherical wave is exactly equal to the curvature radius of the splicing mirror, the light beam reflected from the surface of the splicing mirror passes through the lens group again and becomes a plane wave. This plane wave carries the common phase error information of the splicing mirror. (4) The test light, i.e., the plane wave, and the reference light, i.e., the vortex beam, undergo zero-position interference in the CCD camera; (5) The four-step phase shift method is used to obtain the phase of the spiral wavefront carrying the common phase error; (6) The spiral wavefront phase is demodulated to obtain the error information of the spliced ​​sub-mirrors. The translation error and tilt error are obtained respectively through the angle and curvature of the wavefront dislocation line, thus achieving accurate analysis of the common phase error.

4. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 3 is characterized in that: The spliced ​​mirror includes a central reference mirror located in the center and a spliced ​​sub-mirror located at the edge. After step (6), the translation error and tilt error information are used as feedback to guide the actuator to adjust the spliced ​​sub-mirror in real time until the spiral wavefront dislocation lines of the spliced ​​sub-mirror under dual-wavelength measurement are collinear with the central reference mirror, and the common phase error is corrected here.

5. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 4 is characterized in that: The electric field expression of a vortex beam with a topological charge of l propagating along the z direction is: E v =E v ·exp(ilθ)exp(ikz) (1) The electric field expression of a plane wave propagating along the z direction is: E p =E p ·exp(ikz) (2) The electric field expression of the plane wave carrying the common phase error of the splicing mirror propagating along the z direction is: E error =E p ·exp{i[k(z+Δz)·cosδ]} (3) Where i is the imaginary part, θ is the phase carried by the vortex light, k = 2π / λ, and z represents the transmission distance in the z direction; Take E v =E p =E0, the zero-interference intensity of the vortex light and the plane wave captured by the CCD camera is: Among them, Δz is the translation error between the central reference mirror and the spliced ​​sub-mirror, and δ is the tilt error between the central reference mirror and the spliced ​​sub-mirror.

6. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 5 is characterized in that: When the mirror under test is not loaded, a reference image is collected and its light intensity expression is: I0=a+bcosα (5) Where a is the background light intensity, b is the modulation depth, and α is the unknown random phase; The mirror under test is loaded and a four-step phase shift is introduced through the PZT displacement platform with a step length of The phase shift is 0, π, The following four light intensity images are obtained: In order to obtain the phase difference β, the four deformed intensity images are subtracted from the reference image to obtain four subtraction images: Where, It is a high-frequency phase, which is regarded as high-frequency noise and is filtered out by averaging or low-pass frequency domain filtering; Square the filtered light intensity to obtain: According to formula (8), the tangent expression of the phase difference is: The phase of the spiral wavefront is:

7. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 6 is characterized in that: When the central reference mirror and the spliced ​​sub-mirror of the petal-shaped interferogram have obvious dislocations and the interferogram is curved in the radial direction, that is, there are both translation errors and tilt errors. The magnitude of the curvature is positively correlated with the tilt. The camera collects four phase-shifted interferograms, and the spiral wavefront phase with wavefront dislocation and curvature is solved by the four-step phase shift method. The spiral wavefront dislocation line on the central reference mirror and the spliced ​​sub-mirror is extracted to construct the function: f(x)=Ax 3 +Bx 2 +Cx+D (11) Establish a coordinate system, extract several data points from the spiral wavefront dislocation line on the central reference mirror and the spliced ​​sub-mirror, and calculate the values ​​of constants A, B, C, and D in formula (11). Alternatively, use a curve to fit the spiral wavefront dislocation line, and the fitted curve is formula (11); The least square method is used to calculate the data points (x i ,y i The root mean square F(x) of the distance from (i=1,2,3,…,m) to the constructed straight line function is used as the curvature evaluation function, where the straight line function is: g(x)=ax+b (12) The curvature evaluation function is: When the function F(x) reaches the minimum value, the straight line function g(x) is used as the benchmark for tilt correction to adjust the curvature. F(x) is used as the curvature evaluation function value to quantify the size of the tilt error. The curvature evaluation function value is fed back to the actuator to perform tilt correction on the splicing mirror. The larger the F(x) value, the greater the curvature. When F(x) min When it approaches 0, the tilt error is considered to be corrected.

8. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 7 is characterized in that: After obtaining the spiral wavefront phase according to formula (10), the magnitude of the translation error Δz is quantified by calculating the angle Δθ between the dislocation line of the spliced ​​sub-mirror and the dislocation line of the central reference mirror: The angle value is fed back to the actuator to perform translation correction on the splicing mirror. When the angle value decreases to approach 0, it is considered that the translation error is corrected.

9. The working method of the large-aperture optical antenna common phase error detection system based on vortex light null-interference according to claim 8 is characterized in that: During the experimental operation, the tilt error is first corrected until the curvature of the spiral wavefront dislocation line approaches zero, and then the translation error is corrected until the angles between the wavefront dislocation line of the central reference mirror and the spiral wavefront dislocation line of the spliced ​​sub-mirror approach zero, and the common phase error of the large-aperture optical antenna is corrected.

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