Sub-aperture stitching interferometry apparatus and method for optical freeform surfaces

Abstract

This invention discloses a sub-aperture stitching interferometric measurement device and method for optical freeform surfaces. The device includes a laser interferometer, a variable phase compensator, and a multi-axis motion stage for motion control of the mirror under test. The variable phase compensator consists of two freeform surface mirrors and two wedges, used to achieve phase compensation with a large dynamic range for each sub-aperture. The system automatically adjusts the compensation phase of the sub-apertures using a weighted stochastic gradient descent algorithm and performs in-situ measurement of the compensation phase using a micro-translation misalignment measurement method. The system can realize three measurement modes: full aperture coverage stitching measurement, sub-aperture coverage stitching measurement, and comprehensive measurement. This invention enables high-precision measurement of flexible, complex optical freeform surfaces (such as gull-wing surfaces).

Description

Technical Field

[0001] This invention belongs to the field of optical interferometry, specifically a sub-aperture splicing interferometric measurement device and method for optical freeform surfaces. Background Technology

[0002] Optical freeform surfaces, due to their large degree of freedom in surface design and excellent aberration correction capabilities, are increasingly widely used in numerous fields. However, high-precision surface shape measurement of freeform surfaces presents a significant challenge. Interferometry stands out among various methods due to its high precision and non-contact technical advantages. For traditional interferometric devices, because the freeform surface deviates from the standard sphere, the reflected light beam will form dense fringes with the reference light. When the deviation is large, the fringes become too dense to resolve, exceeding the dynamic range of the interferometer. Researchers have attempted to solve this problem by introducing various phase compensators. However, phase compensators are typically designed for a specific object and are not easily transferred to the measurement of other components, leading to increased measurement costs.

[0003] To address the adaptability issues of phase compensation, variable phase compensators have emerged. These compensators achieve variable phase compensation through state-variable optical devices or programmable surface compensators. Common variable phase compensators include spatial light modulators (SLMs), deformable mirrors (DMs), and rotating CGH phase plates. These compensators have two problems: First, they cannot provide full-range compensation for complex surfaces with alternating positive and negative spherical aberrations and large dynamic ranges, such as gull-wing surfaces; second, in-situ measurement of the compensated phase over a large dynamic range is very difficult, and the measurement accuracy of the compensated phase will affect the correction phase of each sub-aperture and the stitching accuracy of the measured phase. Therefore, the composition scheme and in-situ measurement method of variable phase compensators are very important in interferometric measurement techniques for optical freeform surfaces. Summary of the Invention

[0004] The purpose of this invention is to provide a sub-aperture splicing interferometric measurement device and method for optical freeform surfaces, so as to solve the problems of large dynamic range phase compensation and in-situ measurement of variable phase compensators.

[0005] The technical solution to achieve the purpose of this invention is: an optical freeform surface sub-aperture splicing interferometric measurement device, the device comprising a laser interferometer, a variable phase compensator and a mirror to be measured arranged sequentially along the optical axis, wherein the mirror to be measured is placed on a multi-axis motion stage;

[0006] The laser interferometer is used to generate test light for optical freeform surface interferometry.

[0007] The variable phase compensator is used to compensate for the wavefront phase of each sub-aperture, so that each sub-aperture obtains sparse interference fringes.

[0008] The multi-axis motion stage is used to control the multi-axis motion of the mirror under test.

[0009] Furthermore, the variable phase compensator includes a double freeform mirror and a double wedge plate arranged along the optical axis; wherein, the double freeform mirror is close to the laser interferometer and includes a first freeform mirror and a second freeform mirror arranged sequentially along the optical axis; the double wedge plate includes a first wedge plate and a second wedge plate arranged sequentially along the optical axis;

[0010] The double freeform mirror has a planar-freeform surface structure, and the equation of the freeform surface shape is:

[0011] z = A(xy) 2 +x 3 )+Dx+E

[0012] In the formula, z is the coordinate of the optical axis, with the rightward direction being positive; x is the coordinate perpendicular to the z-axis and parallel to the paper, with the upward direction being positive; y is the coordinate perpendicular to the optical axis and perpendicular to the paper, with the outward direction being positive; A, D, and E are all freeform surface coefficients.

[0013] The two freeform mirrors are placed perpendicular to the optical axis, with the two freeform surfaces facing each other, and initially coaxial. If the first freeform mirror is translated in the positive x-direction from its initial state, and the second freeform mirror is translated in the negative x-direction from its initial state, phase compensation for positive spherical aberration is achieved; conversely, phase compensation for negative spherical aberration is achieved. The magnitude of the spherical aberration compensation is related to the relative translation of the two freeform mirrors, specifically f = 1 / 4Ad(n) l -1), where f is the magnitude of the spherical aberration compensation, d is the relative translation, and n l The refractive index of the material is used. When the first freeform mirror is translated from the positive x-direction to the negative x-direction, and the second freeform mirror is translated from the negative x-direction to the positive x-direction, the phase compensation achieves the transition from positive spherical aberration to negative spherical aberration.

[0014] The double wedges are placed perpendicular to the optical axis and can rotate independently around the optical axis to compensate for astigmatism. They can also tilt as a whole in the x and y directions to compensate for coma.

[0015] The multi-axis motion stage enables the mirror under test to translate in the x, y, and z directions, as well as rotate in the x and z directions.

[0016] An optical freeform surface sub-aperture stitching interferometry method, the method comprising the following steps:

[0017] Step 1: Perform global measurement sub-aperture division for the mirror to be tested;

[0018] Step 2: Measure sequentially according to the divided sub-apertures, and use the weighted stochastic gradient descent algorithm to obtain the sparse interference fringe pattern of each sub-aperture, thereby realizing the automatic adjustment of the sub-aperture compensation phase.

[0019] Step 3: Obtain the measurement phase and compensation phase for each sub-aperture;

[0020] Step 4: Correct the measured phase of each sub-aperture and perform global least squares stitching to obtain the phase to be measured.

[0021] Furthermore, step 3, obtaining the measurement phase and compensation phase of each sub-aperture, specifically includes:

[0022] Step 3-1: Measure the i-th sub-aperture after phase compensation to obtain the phase data S1(i) of the sub-aperture;

[0023] Step 3-2: Perform four micro-translation misalignment measurements on the current i-th sub-aperture to obtain the phase data S2(i), S3(i), S4(i) and S5(i) of the four sub-apertures.

[0024] Let the center coordinates of S1(i) be [x1(i) y1(i) z1(i)], then the center coordinates of the other four sub-measuring apertures are [x1(i)+Δ y1(i) z2(i)], [x1(i)-Δ y1(i) z3(i)], [x1(i) y1(i)+Δ z4(i)] and [x1(i) y1(i)-Δ z5(i)], respectively;

[0025] Step 3-3: Using S1(i), S2(i), S3(i), S4(i), and S5(i) and the least squares method, fit the compensation phase P(i), specifically including:

[0026] Solve for x in the following equation using the least squares method:

[0027] S = Mx,

[0028] In the formula, S represents the sub-aperture data from 5 measurements, and M represents the surface Z to be measured. TS Compensation phase Z P And alignment error Z align The Zernike fitting polynomial matrix, where x represents the coefficients of the corresponding polynomial, is as follows:

[0029] S=[S1(i),S2(i),S3(i),S4(i),S5(i)],

[0030] M = [Z TS Z P Z align ],

[0031] x = [x TS ,x P ,x align ],

[0032] In the formula, x TS ,x P and x align These are the polynomial coefficients of the surface to be measured, the compensated phase, and the alignment error, respectively.

[0033] Based on the coefficient x, solve for the compensation phase P(i) of the i-th sub-aperture:

[0034]

[0035] In the formula, n is the number of Zernike terms used to fit the compensation phase of each sub-aperture;

[0036] Step 3-4: Repeat steps 3-1 to 3-3 until the measurement phase and compensation phase of all sub-apertures are obtained.

[0037] Further, step 4, which involves correcting the measurement phase of each sub-aperture and performing global least-squares stitching to obtain the phase to be measured, specifically includes:

[0038] Step 4-1: Calculate the corrected sub-aperture phase using the measured phase S1(i) and the compensation phase P(i) of each sub-aperture.

[0039] Step 4-2, for all corrected sub-aperture phases The phase to be measured is obtained by global least squares splicing.

[0040] Furthermore, during global least-squares stitching in step 4-2, the sub-aperture stitching mode is as follows:

[0041] Full aperture coverage measurement stitching mode: The test light covers the entire aperture of the mirror under test. The variable phase compensator is adjusted to make sparse fringes appear in the local sub-aperture region. The position of the local sub-aperture where the fringes appear is continuously changed until all sub-apertures are traversed to complete the measurement of the full aperture mirror under test and perform least squares stitching to obtain the complete phase under test.

[0042] Or sub-aperture coverage measurement splicing mode: the test light only covers a part of the mirror under test. By continuously adjusting the variable phase compensator and the state of the mirror under test, the measurement of the full aperture mirror under test is completed and the least squares splicing process is performed to obtain the complete phase under test.

[0043] Alternatively, a comprehensive measurement mode can be used: First, the full aperture coverage measurement stitching mode is used to perform a global measurement of the mirror under test. When a certain area cannot produce sparse fringes, the sub-aperture coverage measurement stitching mode is used to measure the sub-area separately. After completing the measurement of the full aperture mirror under test, the full aperture coverage measurement stitching result is stitched together with the sub-aperture coverage measurement result to obtain the complete phase under test.

[0044] Compared with existing technologies, the present invention has the following significant advantages: 1) The variable phase compensator can achieve phase compensation with a large dynamic range through the lateral translation, rotation and tilt of the components, including compensating phases for positive and negative spherical aberrations with different radii of curvature, which can realize the measurement of complex gull-wing surfaces; 2) The compensation phase can be directly calculated by multiple micro-translation misalignment measurements of a single sub-aperture without the need to add an additional measurement optical path, effectively reducing the complexity of the system; 3) Three measurement modes can be adopted respectively: full aperture coverage measurement splicing, sub-aperture coverage measurement splicing and sub-aperture comprehensive measurement splicing, to realize a flexible and high-precision optical freeform surface interferometry measurement scheme, which has very good application prospects.

[0045] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a sub-aperture splicing interferometry device for optical freeform surfaces in one embodiment.

[0047] Figure 2 The image shows the interference fringe pattern of the automatic phase adjustment process for sub-aperture compensation in one embodiment. Figures (a), (b), (c), and (d) are the initial interference pattern after sub-aperture interference pattern optimization, the visible fringe interference pattern, the sparse fringe interference pattern, and the near-zero fringe interference pattern, respectively.

[0048] Figure 3 This is a sub-aperture planning diagram for five micro-translational misalignment measurements of the sub-aperture in one embodiment.

[0049] Figure 4 The figure shows the interference fringe pattern of five micro-translation misalignment measurements of the sub-apertures in one embodiment. Figures (a), (b), (c), (d), and (e) are the interference patterns of the five sub-apertures S1(i), S2(i), S3(i), S4(i), and S5(i), respectively.

[0050] Figure 5 This is a diagram showing the calculated sub-aperture compensation phase results in one embodiment.

[0051] Figure 6 This is a diagram of the phase result to be measured after least-squares splicing of the sub-aperture in one embodiment. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0053] In one embodiment, combined Figure 1 An optical freeform surface sub-aperture splicing interferometric measurement device is provided. The device includes a laser interferometer A, a variable phase compensator B, and a mirror D to be measured arranged sequentially along the optical axis, wherein the mirror D to be measured is placed on a multi-axis motion stage C; here, the mirror to be measured can be other optical freeform surfaces.

[0054] The laser interferometer A is used to generate test light for optical freeform surface interferometry.

[0055] Preferably, the laser interferometer A is a Thyman-Green structure or Fizeau structure interferometer.

[0056] The variable phase compensator B is used to compensate for the wavefront phase of each sub-aperture, so that each sub-aperture obtains sparse interference fringes.

[0057] The multi-axis motion stage C is used to control the multi-axis motion of the mirror D under test.

[0058] Further, in one embodiment, the variable phase compensator B includes two freeform mirrors (B1, B2) and two wedges (B3, B4) arranged along the optical axis; wherein, the two freeform mirrors (B1, B2) are close to the laser interferometer A and include a first freeform mirror B1 and a second freeform mirror B2 arranged sequentially along the optical axis; the two wedges (B3, B4) include a first wedge B3 and a second wedge B4 arranged sequentially along the optical axis;

[0059] The double freeform mirrors (B1, B2) have a planar-freeform surface structure, and the equations of the freeform surface shape are as follows:

[0060] z = A(xy) 2 +x 3 )+Dx+E

[0061] In the formula, z is the coordinate of the optical axis, with the rightward direction being positive; x is the coordinate perpendicular to the z-axis and parallel to the paper, with the upward direction being positive; y is the coordinate perpendicular to the optical axis and perpendicular to the paper, with the outward direction being positive; A, D, and E are all freeform surface coefficients.

[0062] The two freeform mirrors (B1, B2) are placed perpendicular to the optical axis and the two freeform surfaces are positioned opposite each other, initially coaxial. If the first freeform mirror B1 is translated in the positive x-direction from its initial state, and the second freeform mirror B2 is translated in the negative x-direction from its initial state, phase compensation for positive spherical aberration is achieved; conversely, phase compensation for negative spherical aberration is achieved. The magnitude of the spherical aberration compensation is related to the relative translation of the two freeform mirrors (B1, B2), specifically f = 1 / 4Ad(n l -1), where f is the magnitude of the spherical aberration compensation, d is the relative translation, and n l The refractive index of the material; when the first freeform mirror B1 is translated from the positive x direction to the negative x direction, and the second freeform mirror B2 is translated from the negative x direction to the positive x direction, the phase compensation realizes the transition from positive spherical aberration to negative spherical aberration;

[0063] The double wedge plates (B3, B4) are placed perpendicular to the optical axis and can rotate independently around the optical axis to compensate for astigmatism. They can also tilt as a whole in the x and y directions to compensate for coma.

[0064] The multi-axis motion stage C enables the mirror D under test to translate in the x, y, and z directions and rotate in the x and z directions.

[0065] In one embodiment, an optical freeform surface sub-aperture stitching interferometry method is provided, the method comprising the following steps:

[0066] Step 1: Perform global measurement sub-aperture division for the mirror to be tested;

[0067] Step 2: Measure sequentially according to the divided sub-apertures, and use the weighted stochastic gradient descent algorithm to obtain the sparse interference fringe pattern of each sub-aperture, thereby realizing the automatic adjustment of the sub-aperture compensation phase.

[0068] Step 3: Obtain the measurement phase and compensation phase for each sub-aperture;

[0069] Step 4: Correct the measured phase of each sub-aperture and perform global least squares stitching to obtain the phase to be measured.

[0070] Furthermore, in one embodiment, step 2, which involves using a weighted stochastic gradient descent algorithm to obtain the sparse interference fringe pattern of the sub-aperture and achieve automatic adjustment of the compensation phase, specifically includes:

[0071] The relative translation δ of the two freeform mirrors (B1, B2) in the variable phase compensator B, the rotation α1 and α2 of each wedge in the double wedges (B3, B4), and the overall tilt β1 and β2 are used as variables, and the weighted stochastic parallel gradient descent algorithm is used for optimization control to make the sub-aperture stripes sparser.

[0072] Furthermore, in one embodiment, step 3, obtaining the measurement phase and compensation phase of each sub-aperture, specifically includes:

[0073] Step 3-1: Measure the i-th sub-aperture after phase compensation to obtain the phase data S1(i) of the sub-aperture;

[0074] Step 3-2: Perform four micro-translation misalignment measurements on the current i-th sub-aperture to obtain the phase data S2(i), S3(i), S4(i) and S5(i) of the four sub-apertures.

[0075] Let the center coordinates of S1(i) be [x1(i) y1(i) z1(i)], then the center coordinates of the other four sub-measuring apertures are [x1(i)+Δ y1(i) z2(i)], [x1(i)-Δ y1(i) z3(i)], [x1(i) y1(i)+Δ z4(i)] and [x1(i) y1(i)-Δ z5(i)], respectively;

[0076] Step 3-3: Using S1(i), S2(i), S3(i), S4(i), and S5(i) and the least squares method, fit the compensation phase P(i), specifically including:

[0077] Solve for x in the following equation using the least squares method:

[0078] S = Mx,

[0079] In the formula, S represents the sub-aperture data from 5 measurements, and M represents the surface Z to be measured. TS Compensation phase Z P And alignment error Z align The Zernike fitting polynomial matrix, where x represents the coefficients of the corresponding polynomial, is as follows:

[0080] S=[S1(i),S2(i),S3(i),S4(i),S5(i)],

[0081] M = [Z TS Z P Z align ],

[0082] x = [x TS ,x P ,x align ],

[0083] In the formula, x TS ,x P and x align These are the polynomial coefficients of the surface to be measured, the compensated phase, and the alignment error, respectively.

[0084] Based on the coefficient x, solve for the compensation phase P(i) of the i-th sub-aperture:

[0085]

[0086] In the formula, n is the number of Zernike terms used to fit the compensation phase of each sub-aperture;

[0087] Step 3-4: Repeat steps 3-1 to 3-3 until the measurement phase and compensation phase of all sub-apertures are obtained.

[0088] Furthermore, in one embodiment, step 4, which involves correcting the measurement phase of each sub-aperture and performing global least-squares stitching to obtain the phase to be measured, specifically includes:

[0089] Step 4-1: Calculate the corrected sub-aperture phase using the measured phase S1(i) and the compensation phase P(i) of each sub-aperture.

[0090] Step 4-2, for all corrected sub-aperture phases The phase to be measured is obtained by global least squares splicing.

[0091] Furthermore, in one embodiment, during global least-squares stitching in step 4-2, the sub-aperture stitching mode is as follows:

[0092] Full aperture coverage measurement stitching mode: The test light covers the entire aperture of the mirror under test. The variable phase compensator is adjusted to make sparse fringes appear in the local sub-aperture region. The position of the local sub-aperture where the fringes appear is continuously changed until all sub-apertures are traversed to complete the measurement of the full aperture mirror under test and perform least squares stitching to obtain the complete phase under test.

[0093] Or sub-aperture coverage measurement splicing mode: the test light only covers a part of the mirror under test. By continuously adjusting the variable phase compensator and the state of the mirror under test, the measurement of the full aperture mirror under test is completed and the least squares splicing process is performed to obtain the complete phase under test.

[0094] Alternatively, a comprehensive measurement mode can be used: First, the full aperture coverage measurement stitching mode is used to perform a global measurement of the mirror under test. When a certain area cannot produce sparse fringes, the sub-aperture coverage measurement stitching mode is used to measure the sub-area separately. After completing the measurement of the full aperture mirror under test, the full aperture coverage measurement stitching result is stitched together with the sub-aperture coverage measurement result to obtain the complete phase under test.

[0095] Exemplarily, in one embodiment, the sub-aperture splicing interferometry apparatus and method for optical freeform surfaces of the present invention are further verified and described. In this example, the interferometer is a Thyman-Green laser interferometer. In the variable phase compensator, the dimensionless coefficients of the freeform surface mirror are: A = 12, D = -4, E = 0. The freeform surface mirror is made of polymethyl methacrylate (PMMA), with an aperture of 34 mm and a center thickness of 5 mm. The wedge plate has a wedge angle of 8°, an aperture of 50.8 mm, and is made of K9 glass. The gull-wing type freeform surface to be measured, such as... Figure 1 It is placed on the five-dimensional electronic control console.

[0096] Figure 2 (a) is the interferogram of the i-th sub-aperture measurement without phase compensation module adjustment. It can be seen that the fringes are indistinguishable in most areas of the sub-aperture, making phase measurement impossible. The relative translation δ of the two freeform mirrors (B1, B2) in the variable phase compensator (B), the rotation α1 and α2 of the rotating wedges (B3, B4), and the overall tilt β1 and β2 are used as variables, and a weighted stochastic parallel gradient descent algorithm is used for optimization control. The optimization process is as follows: Figure 2 As shown in (b), (c), and (d), it can be seen that the fringes of the sub-aperture gradually become sparser, and the entire phase compensation process takes 10 seconds.

[0097] After adaptive aberration compensation is completed for the i-th sub-aperture, multiple measurements are performed to obtain the phase data and compensated aberrations for the sub-aperture. The five-measurement plan for each sub-aperture is as follows: Figure 3 As shown, the shaded area represents the central sub-aperture S1(i). The overlap ratio between S1(i) and the four surrounding sub-apertures is set to 0.85. The interferograms of the five sub-apertures S1(i), S2(i), S3(i), S4(i), and S5(i) are shown below. Figure 4 As shown in (a), (b), (c), (d), and (e), the compensated phase P(i) of the sub-aperture is calculated using the phase data of these five sub-apertures and the formula described above, as follows. Figure 5 As shown. The corrected phase of the sub-aperture can be obtained using the calculated compensation phase and the measured phase S1(i) of the sub-aperture.

[0098] After completing the measurements of all sub-apertures, a global least-squares stitching technique is applied to the sub-aperture data to obtain the phase to be measured, such as... Figure 6 As shown, this invention enables high-precision measurement of flexible, complex optical freeform surfaces (such as gull-wing surfaces).

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, equivalent changes, and alterations made based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An optical freeform surface subaperture stitching interferometer apparatus, characterized in that, The device comprises a laser interferometer (A), a variable phase compensator (B) and a mirror to be measured (D) arranged in sequence along the optical axis, wherein the mirror to be measured (D) is placed on a multi-axis motion platform (C); The laser interferometer (A) is used for generating test light for optical free-form surface interferometry; The variable phase compensator (B) is used for compensating the wavefront phase of each sub-aperture, so that each sub-aperture obtains sparse interference fringes; The multi-axis motion platform (C) is used for controlling the multi-axis motion of the mirror to be measured (D); The variable phase compensator (B) comprises double free-form mirrors (B1, B2) and double wedge plates (B3, B4) arranged along the optical axis; wherein the double free-form mirrors (B1, B2) are close to the laser interferometer (A) and comprise a first free-form mirror (B1) and a second free-form mirror (B2) arranged in sequence along the optical axis; the double wedge plates (B3, B4) comprise a first wedge plate (B3) and a second wedge plate (B4) arranged in sequence along the optical axis; The double free-form mirrors (B1, B2) are plane-free-form structure, and the free-form surface equation is: z = A(xy 2 + x 3 ) + Dx + E wherein z is the coordinate in the direction of the optical axis, and the right direction is positive; x is the coordinate perpendicular to the z-axis and parallel to the paper plane, and the upward direction is positive; y is the coordinate perpendicular to the optical axis and the paper plane, and the outward direction perpendicular to the paper plane is positive; A, D and E are free-form surface coefficients; The double free-form surface mirrors (B1, B2) are arranged opposite to each other and perpendicular to the optical axis, and the initial state is coaxial; if the first free-form surface mirror (B1) is translated from the initial state to the positive direction of x, and the second free-form surface mirror (B2) is translated from the initial state to the negative direction of x, then the phase compensation of positive spherical aberration is realized; on the contrary, the phase compensation of negative spherical aberration is realized; the size of the spherical aberration compensation is related to the relative translation amount of the double free-form surface mirrors (B1, B2), and is specifically f=1 / 4Ad(n l -1), wherein f is the size of the spherical aberration compensation, d is the relative translation amount, n l is the material refractive index; when the first free-form surface mirror (B1) is translated from the positive direction of x to the negative direction, and the second free-form surface mirror (B2) is translated from the negative direction of x to the positive direction, the compensation phase realizes the transition from positive spherical aberration to negative spherical aberration. The double wedge plates (B3, B4) are placed perpendicular to the optical axis and can be independently rotated around the optical axis to realize compensation of astigmatism, and can be tilted in the x and y directions as a whole to realize compensation of coma; The multi-axis motion platform (C) realizes the translation of the mirror to be measured (D) in the x, y and z directions and the rotation of the mirror to be measured (D) in the x and z directions.

2. The subaperture coUimated interferometry apparatus for optical freeform surfaces of claim 1, wherein, The laser interferometer (A) is a Teyman-Green structure or a Fizeau structure interferometer.

3. Subaperture stitching interferometry method for optical freeform surfaces based on the interferometry apparatus according to any one of claims 1 to 2, characterized in that The method comprises the following steps: Step 1: global measurement sub-aperture division is performed on the mirror to be measured; Step 2: measurement is sequentially performed according to the divided sub-apertures, and a weight random gradient descent algorithm is used to obtain sparse interference fringe patterns of the sub-apertures, so as to realize automatic adjustment of the compensation phase of the sub-apertures; Step 3: measurement phases and compensation phases of the sub-apertures are obtained; Step 4: the measurement phases of the sub-apertures are corrected, and global least square stitching is performed to obtain a measured phase.

4. The method of claim 3, wherein, In step 2, the weight random gradient descent algorithm is used to obtain the sparse interference fringe patterns of the sub-apertures, so as to realize automatic adjustment of the compensation phase, and specifically includes: The relative translation δ of the double free-form mirrors (B1, B2) in the variable phase compensator (B), the rotation α1 and α2 of each wedge plate in the double wedge plates (B3, B4), and the overall tilt β1 and β2 are taken as variables, and a weight random parallel gradient descent algorithm is used for optimization control, so that the sub-aperture fringes become sparse.

5. The method of claim 3, wherein, In step 3, the measurement phases and the compensation phases of the sub-apertures are obtained, and specifically includes: Step 3-1: the i-th sub-aperture after phase compensation is measured to obtain the phase data S1(i) of the sub-aperture; Step 3-2: four micro-translation misalignment measurements are performed on the current i-th sub-aperture to obtain four sub-measurement sub-aperture phase data S2(i), S3(i), S4(i) and S5(i); The center coordinates of the remaining four sub-measurement sub-apertures are [x1(i)+Δy1(i)z2(i)], [x1(i)-Δy1(i)z3(i)], [x1(i)y1(i)+Δz4(i)], and [x1(i)y1(i)-Δz5(i)] respectively, wherein S1(i) is the center coordinate of [x1(i)y1(i)z1(i)]; Step 3-3, using S1(i), S2(i), S3(i), S4(i) and S5(i) and the least square method, fitting the compensation phase P(i), specifically including: Solve x in the following formula by using the least square method: S=Mx, In the formula, S is the sub-aperture data of 5 measurements, M is the surface to be measured Z TS , the compensation phase Z P , and the Zernike fitting polynomial matrix of the alignment error Z align , x is the coefficient corresponding to the polynomial, and specifically: S=[S1(i),S2(i),S3(i),S4(i),S5(i)], M = [Z TS ,Z P ,Z align ], x = [x TS ,x P ,x align ], where x TS , x P , and x align are polynomial coefficients of the surface to be measured, the compensation phase, and the alignment error, respectively. Based on the coefficient x, solve the compensation phase P(i) of the i-th sub-aperture: In the formula, n is the number of Zernike terms used to fit the compensation phase of each sub-aperture; Step 3-4, repeat steps 3-1 to 3-3 until the measurement phase and the compensation phase of all sub-apertures are obtained.

6. The method of claim 5, wherein, Step 4 corrects the measurement phase of each sub-aperture and performs global least square stitching to obtain the to-be-measured phase, specifically including: Step 4-1, calculate the corrected sub-aperture phase using the measured phase S1(i) and the compensation phase P(i) for each sub-aperture Step 4-2, for all corrected sub-aperture phases The measured phase is obtained by global least square stitching.

7. The method of claim 6, wherein, In step 4-2, the sub-aperture stitching mode is: Full-aperture coverage measurement stitching mode: the test light covers the full-aperture to-be-measured mirror, the variable phase compensator is adjusted to make sparse fringes appear in the local sub-aperture region, the local sub-aperture position where the fringes appear is changed constantly until all sub-apertures are traversed to complete the measurement of the full-aperture to-be-measured mirror and the least square stitching processing is performed to obtain the complete to-be-measured phase; Or sub-aperture coverage measurement stitching mode: the test light only covers part of the to-be-measured mirror, the state of the variable phase compensator and the to-be-measured mirror is adjusted constantly until the measurement of the full-aperture to-be-measured mirror is completed and the least square stitching processing is performed to obtain the complete to-be-measured phase; Or comprehensive measurement mode: first, the full-aperture coverage measurement stitching mode is used to globally measure the to-be-measured mirror, when sparse fringes cannot appear in a certain region, the sub-aperture coverage measurement stitching mode is used to measure the region alone, after the measurement of the full-aperture to-be-measured mirror is completed, the full-aperture coverage measurement stitching result and the sub-aperture coverage measurement result are stitched to obtain the complete to-be-measured phase.

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