Apparatus and method for detecting the optical axis consistency of a biconvex aspheric mirror

Abstract

The application discloses a device and method for detecting optical axis consistency of two-surface common large-aperture aspheric mirrors, and belongs to the technical field of optical part processing and detection. The device comprises an interferometer and two CGH compensators. In the interference detection light path, the optical axes of the two aspheric surfaces are introduced to the CGH compensators through precise adjustment and strict calibration, parallel light is emitted from the specific area of the CGH, and the interference fringes representing the included angle of the two CGH compensators are formed in the interferometer after being reflected by the other CGH, the number of the interference fringes is observed and counted, and the optical axis consistency deviation of the two aspheric surfaces is calculated. Compared with the traditional interference measurement method, the device has the advantages of high detection precision, few error sources and low detection cost.

Description

Technical Field

[0001] This invention relates to an apparatus and method for detecting the optical axis consistency of a two-sided aspherical mirror, belonging to the field of optical component processing and testing technology. Background Technology

[0002] In the field of aerospace optical remote sensing, the coaxial four-mirror optical system adopts an aspherical primary mirror and four mirrors integrated into one unit, which greatly reduces the complexity of the system, lightens the overall weight, and improves the installation efficiency. On the other hand, the integrated molding of the primary mirror and four mirrors restricts the freedom of subsequent optical system assembly and adjustment. During the mirror manufacturing process, the optical axis consistency of both needs to be strictly measured and controlled.

[0003] Currently, the main methods for measuring the optical axis angle of aspherical surfaces include the centering method, profile scanning method, interferometry method, and aberration-free method. The centering method determines the optical axis by finding the spherical center image reflected from the surface being measured by the light emitted from the autocollimating telescope. It is mainly suitable for measuring the optical axis of spherical lenses. When measuring aspherical surfaces, the optical axis is fitted by measuring the spherical center images returned from different annular zones of the aspherical surface. However, because the curvature radii at the vertices of different annular zones of the aspherical surface are relatively small, the baseline of the fitted optical axis is short, resulting in lower measurement accuracy. It is also not suitable for measuring the optical axis of large-aperture aspherical surfaces.

[0004] The profilometry method obtains the sagittal profile data of the mirror surface by scanning with a profilometry probe, and then calculates the optical axis deviation by data fitting. When measuring the optical axis consistency of two aspherical mirrors with one surface, this method requires scanning the surface shape of different mirrors twice under different mechanical references, which can easily introduce mechanical reference transmission errors. Furthermore, the diameter of the aspherical surface measured by this method is limited by the range of the profilometry instrument.

[0005] Interferometry utilizes a laser interferometer combined with compensating optical elements (plane mirrors, null compensators, or computational holograms (CGHs)) to measure the shape of aspherical surfaces. The aspherical optical axis is then traced to the compensating optical element, and a laser tracker or other measuring instrument is used to measure the deviation of the optical axis relative to a mechanical reference. The measurement accuracy is limited by the machining accuracy of the mechanical reference and the detection accuracy of the measuring instrument. The literature "Measurement of Optical Axis Consistency of Two Co-faced Aspherical Mirrors" proposes a method to measure the optical axis by measuring the angle between two CGHs in the interferometric detection optical path using a theodolite. This method eliminates the need to trace the mechanical reference, but it imposes limitations on mirror parameters and makes in-situ online measurement difficult. Summary of the Invention

[0006] The technical problem solved by the present invention is to overcome the shortcomings of the prior art. The present invention provides a device and method for detecting the optical axis of a two-sided aspherical mirror, which realizes the simultaneous measurement of surface shape and optical axis, and has the advantages of high detection accuracy, few error sources and low detection cost.

[0007] The technical solution of this invention is:

[0008] A device for detecting the optical axis consistency of a large-aperture aspherical mirror with two surfaces, comprising an interferometer and a CGH compensator;

[0009] The surfaces of the two-sided aspherical optical component to be tested are divided into aspherical optical surface M and aspherical optical surface N. The two CGH compensators are placed on the outside of aspherical optical surface M and aspherical optical surface N, respectively. An interferometer is placed on the other side of each of the two CGH compensators.

[0010] Each CGH compensator is divided into a zero-position test area, an alignment area, and a reference area. The zero-position test area is used to measure the surface shape error of the optical component, the alignment area is used for the auxiliary alignment of the interferometer and the CGH compensator, and the reference area is used to measure the included angle error between the two CGH compensators to obtain the included angle error of the optical axis of the optical component.

[0011] Preferably, the following conditions must be met before the device can be used for measurement:

[0012] Two interferometers emit standard spherical test light waves. The zero-point test area of ​​each CGH compensator shows corresponding interference fringes in the interferometer outside the CGH compensator. The number of interferometer fringes is less than 3.

[0013] Preferably, the distance from the CGH compensator to the nearest aspherical optical surface does not exceed the vertex radius of curvature of the aspherical optical surface.

[0014] Preferably, the diameter of the zero-position test area of ​​the CGH compensator is no greater than 100mm; the outer diameter of the alignment area is no greater than 135mm, and the difference between the inner and outer diameters is no less than 20mm; the diameter of the reference area is no less than 15% of the diameter of the zero-position test area.

[0015] Preferably, the manufacturing parameters of the CGH compensator are obtained by simulation design using the optical design software Zemax based on the geometric parameters of the optical components, the distance between the CGH compensator and the aspherical optical surface, the aperture of all areas of each CGH compensator, and the material of the CGH compensator, and the CGH compensator is manufactured according to the manufacturing parameters.

[0016] Preferably, the standard spherical test light wave emitted by the interferometer is modulated into a wavefront consistent with the surface of the aspherical optical component after passing through the zero-position test area of ​​the CGH compensator, which can form interferometric measurement conditions and realize the measurement of the surface shape error of the aspherical optical component.

[0017] Preferably, two interferometers sequentially emit standard spherical test light waves. After passing through the reference area of ​​the CGH compensator, the test light waves are modulated into standard plane light waves. After passing through the CGH compensator farthest from the interferometer, they self-collimate and return, forming interference fringes. The number of fringes in the two tests is counted to obtain the angle error between the two CGH compensators, which is the optical axis angle error of the optical component.

[0018] Preferably, the F-number of the interferometer's standard lens is less than the ratio of the distance from the CGH compensator next to the interferometer to the aperture of the alignment area.

[0019] A method for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces includes:

[0020] Based on the geometric parameters of the two-sided aspherical optical component to be tested, a device for detecting the optical axis consistency of a large-aperture aspherical mirror as described in claim 1 is designed; the CGH compensator and interferometer placed on one side of the aspherical optical surface M are respectively denoted as the first CGH compensator and the first interferometer, and the CGH compensator and interferometer placed on one side of the aspherical optical surface N are respectively denoted as the second CGH compensator and the second interferometer;

[0021] Based on the device, two interferometers emit standard spherical test light waves, and the positions of the two interferometers are adjusted respectively so that the alignment areas B of the first CGH compensator and the second CGH compensator appear corresponding interference fringes in the first interferometer and the second interferometer respectively, with the number of fringes being less than 3.

[0022] The position and tilt angle of the two-sided aspherical optical component under test are finely adjusted so that the zero-position test area of ​​the first CGH compensator appears with corresponding interference fringes in the first interferometer, the number of fringes is less than 3, and the primary coma of the wavefront measured by the first interferometer is less than 0.02; the surface shape error of the aspherical optical surface M is calculated.

[0023] Fine-tune the position and tilt angle of the second interferometer and the second CGH compensator so that the zero-position test area of ​​the second CGH compensator appears in the second interferometer with corresponding interference fringes. The number of fringes should be less than 3, and the primary coma of the wavefront measured by the second interferometer should be less than 0.02. Calculate the surface shape error of the aspherical optical surface N.

[0024] The number of interference fringes in the reference region of the first CGH compensator in the first interferometer is observed and counted, and the number of interference fringes in the reference region of the second CGH compensator in the second interferometer is calculated to obtain the optical axis angle error.

[0025] The advantages of this invention compared to the prior art are:

[0026] This invention achieves in-situ high-precision detection of the optical axis of a two-sided aspherical mirror by observing and statistically analyzing the interference fringes formed by the included angle of two CGH compensators. Compared with the traditional interferometry method for detecting the optical axis, which requires the introduction of a mechanical reference and the use of high-precision detection instruments such as theodolites, this invention has the advantages of fewer error sources and lower detection costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the surface shape to be detected according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram illustrating the detection of the optical axis angle in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram showing the distribution of each planned area of ​​the CGH compensator in an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings.

[0031] like Figure 1 As shown, the device in this invention includes: a first interferometer 1, a second interferometer 2, a first CGH compensator 3, and a second CGH compensator 4. The left and right surfaces of the two-sided aspherical optical component 5 to be tested are divided into an aspherical optical surface M and an aspherical optical surface N. The first CGH compensator 3 is placed on the left side of the aspherical optical surface M, and the second CGH compensator 4 is placed on the right side of the aspherical optical surface N. The first interferometer 1 is placed on the left side of the first CGH compensator 3, and the second interferometer 2 is placed on the right side of the second CGH compensator 4.

[0032] like Figure 3 As shown, based on the geometric parameters of the aspherical optical surfaces M and N and the positional relationship of the optical elements in the device, the first CGH compensator 3 and the second CGH compensator 4 are divided into different regions, including a zero-position test region A, an alignment region B, and a reference region C. Region A is used to measure the surface shape error of the two-sided aspherical optical component 5. The standard spherical test light wave emitted by the laser interferometer is modulated into a wavefront consistent with the surface of the aspherical optical component after passing through region A, thus forming the interferometric measurement conditions. The standard spherical test light wave emitted by the laser interferometer returns after self-collimation after passing through region B, forming interference fringes, which are used for auxiliary alignment of the laser interferometer and the CGH compensator. Region C is used to measure the angle between the first CGH compensator 3 and the second CGH compensator 4, such as... Figure 2As shown, the standard spherical test light wave emitted by the first interferometer 1 is modulated into a standard plane light wave after passing through region C. The light wave returns after being collimated by the CGH compensator 4, forming interference fringes in the first interferometer 1. The number of fringe roots N1 is counted. Similarly, the standard spherical test light wave emitted by the second interferometer 2 can be counted. The light wave emitted from surface region C of the second CGH compensator 4 is reflected by the first CGH compensator 3, forming the number of interference fringe roots N2 in the interferometer 2.

[0033] The interference fringes N1 and N2 are calculated as the optical axis angle θ according to the following formula.

[0034]

[0035] D1 and D2 are the diameters of surface regions C of the first CGH compensator 3 and the second CGH compensator 4, respectively, and λ is the laser wavelength of the interferometer.

[0036] The standard spherical test light wave emitted by the first interferometer 1 is modulated into a wavefront consistent with the theoretical aspherical optical surface M after passing through the test area A of the first CGH compensator 3. After reflection from the aspherical optical surface M, carrying its surface shape error information, the test light wave returns to the first interferometer 1 after passing through the test area A of the first CGH compensator 3 again, and interferes with the reference spherical light wave inside the first interferometer 1. The interferometer data acquisition and processing system can then calculate and inversely determine the surface shape error of the aspherical optical surface M. Similarly, the surface shape error of the aspherical optical surface N can be measured.

[0037] In the design of optical path parameters, the aperture of the CGH compensator test area A is affected by the distance L1 from the CGH compensator to the aspherical optical surface. This distance must be comprehensively evaluated based on the geometric parameters of the aspherical optical surface and the ease of fabrication of the CGH compensator. Generally, the distance L1 from the CGH compensator to the aspherical optical surface should not exceed the vertex curvature radius R of the aspherical optical surface. Within this range, the closer the distance L1 is to the aspherical optical surface, the larger the required aperture of the test area A. This distance should be chosen so that the aperture of the CGH compensator test area A does not exceed 100 mm. The distance L2 from the CGH compensator to the interferometer affects the minimum feature size of the CGH compensator. This distance should be chosen so that the minimum feature size is not less than 5 μm, which can be calculated in the optical design software Zemax. For reference, the outer aperture of the alignment area B should not exceed 135 mm, and the difference between the inner and outer apertures should not be less than 20 mm. The aperture of the reference area C should not be less than 15% of the aperture of the test area A.

[0038] When selecting the standard lens for the interferometer, the F-number of the standard lens should be less than the ratio of the distance L2 from the CGH compensator to the interferometer to the aperture of the alignment area B.

[0039] Simulation design is performed using the optical design software Zemax. The aperture, vertex radius of curvature, and aspheric coefficient of the aspheric optical surfaces M and N of the two aspheric optical parts to be tested are input, as well as the material, thickness, aperture of each region, and distance of the compensator from the optical part. The design parameters of the two compensators are obtained through simulation, and the corresponding compensators are manufactured.

[0040] based on Figure 1 The optical path and distance parameters were established to complete the design of this device.

[0041] The following detailed description is provided through an example. The aspherical optical surface M of the two-sided aspherical optical component 5 has a diameter of Φ500mm, a vertex radius of curvature R0 = 560mm, and an aspherical coefficient K = -0.88. The aspherical optical surface N has a diameter of Φ420mm, a vertex radius of curvature R0 = 1558mm, and an aspherical coefficient K = -3.

[0042] The first CGH compensator 3 and the second CGH compensator 4 are designed using the optical design software Zemax based on the geometric parameters of the aspherical optical surfaces M and N in the two-sided aspherical optical component 5 to be tested.

[0043] The laser wavelength is set to λ = 6.328e-4mm, the distance between the aspherical optical surface M and the CGH compensator 3 is 460mm, the distance between the CGH compensator 3 and the interferometer 1 is 190mm, and the material of the CGH compensator is fused silica with a thickness of 6.35mm.

[0044] The first CGH compensator 3 has a test area A with an aperture of 80mm. The even-order coefficients of the binary optical polynomial parameters in Binary2 format from the quadratic to the tenth order are 5.057E+001, -2.035E-002, 7.053E-006, -1.387E-009, and 1.104E-013, respectively.

[0045] The first CGH compensator 3 has an alignment area B with a diameter of 120mm. The even-order coefficients of the binary optical polynomial parameters in Binary2 format from the quadratic to the octagonal terms are -7.195E+004, 1.987E+003, -1.074E+002, and 5.878E+000, respectively.

[0046] The first CGH compensator has a reference region C aperture D1 = 20 mm. The even-order coefficients of the binary optical polynomial parameters in the Binary2 format from the quadratic to the quartic terms are -1.30E+003 and 3.448E-001, respectively.

[0047] The distance between the aspherical optical surface N and the second CGH compensator 4 is set to 1000mm, and the distance between the second CGH compensator 4 and the second interferometer 2 is set to 240mm. The material of the CGH compensator is fused silica with a thickness of 6.35mm.

[0048] The second CGH compensator 4 has a test area A with a diameter of 70mm. The even-order coefficients of the binary optical polynomial parameters from the quadratic to the tenth order are 6.184E+001, -3.051E-002, 7.361E-006, -2.237E-009, and 6.345E-013, respectively.

[0049] The second CGH compensator 4 has an alignment area B with a diameter of 115mm. The even-order coefficients of the binary optical polynomial parameters in Binary2 format from the quadratic to the octagonal terms are -8.213E+004, 2.156E+003, -1.129E+002, and 3.788E+000, respectively.

[0050] The second CGH compensator has a reference region C aperture D2 = 18 mm. The even-order coefficients of the binary optical polynomial parameters in the Binary2 format from the quadratic to the quartic terms are -1.50E+003 and 5.448E-001, respectively.

[0051] Based on the above optical path parameters, the first CGH compensator 3 and the second CGH compensator 4 were designed and manufactured. An interferometric detection optical path was then constructed for detection, including the following steps:

[0052] Step 1: The standard lenses of the first interferometer 1 and the second interferometer 2 have F-numbers of 1.5 and 2, respectively, and the initial detection optical path is constructed.

[0053] Step 2: Adjust the translation of the first interferometer 1 and the second interferometer 2 in the X / Y / Z directions respectively, so that the alignment area B of the first CGH compensator 3 and the second CGH compensator 4 appears as corresponding interference fringes in the first interferometer 1 and the second interferometer 2. The number of interferometer fringes should be less than 3. Figure 1 As shown, the rotational symmetry axis of the two-sided aspherical optical component is the X-axis, the Z-axis is the direction from the aspherical optical surface M to the aspherical optical surface N and perpendicular to the paper upwards, and the Y-axis can be determined according to the right-hand rule. The same coordinate system definition is used for all the following measurement steps.

[0054] Step 3: Fine-tune the translation and X / Y axis tilt of the two-sided aspherical optical component 5 in the X / Y / Z directions, so that the test area A of the first CGH compensator 3 shows corresponding interference fringes in the interferometer 1, such as... Figure 1As shown, the surface shape error of the aspherical optical surface M is measured using an interferometer data acquisition and processing system. The number of interferometer fringes must be less than 3, and the primary coma of the wavefront measured by the interferometer must be less than 0.02.

[0055] Step 4: Fine-tune the translation and X / Y axis tilt of the second interferometer 2 and the second CGH compensator 4 in the X / Y / Z directions, so that the test area A of the second CGH compensator 4 appears with corresponding interference fringes in the interferometer 2. Measure the surface shape error of the aspherical optical surface N using the interferometer data acquisition and processing system. The number of interferometer fringes should be less than 3, and the primary coma of the wavefront measured by the interferometer should be less than 0.02.

[0056] Step 5: Observe and count the number of interference fringes N1 = 5 in the surface region C of the first CGH compensator 3 in the first interferometer 1, and the number of interference fringes N2 = 4 in the surface region C of the second CGH compensator 4 in the second interferometer 2. Calculate the optical axis angle error θ according to the following formula.

[0057]

[0058] The angle corresponding to the five stripes is 13 seconds, and the angular resolution of one stripe is about 2 seconds, which realizes in-situ high-precision detection. Compared with the traditional interferometry method for detecting the optical axis, which requires the introduction of a mechanical reference and the use of high-precision detection instruments such as theodolites, it has the advantages of fewer error sources and lower detection cost.

[0059] The above description is only the best specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

[0060] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces, characterized in that, Including interferometers and CGH compensators; The surfaces of the two-sided aspherical optical component to be tested are divided into aspherical optical surface M and aspherical optical surface N. The two CGH compensators are placed on the outside of aspherical optical surface M and aspherical optical surface N, respectively. An interferometer is placed on the other side of each of the two CGH compensators. Each CGH compensator is divided into a zero-position test area, an alignment area, and a reference area. The zero-position test area is used to measure the surface shape error of the optical component. The alignment area is used for the auxiliary alignment of the interferometer and the CGH compensator. The reference area is used to measure the included angle error between the two CGH compensators to obtain the included angle error of the optical axis of the optical component. Two interferometers sequentially emit standard spherical test light waves. After passing through the reference area of ​​the CGH compensator, the test light waves are modulated into standard plane light waves. After passing through the CGH compensator farthest from the interferometer, they are collimated and return, forming interference fringes. The number of fringes in the two tests is counted to obtain the angle error between the two CGH compensators, which is the optical axis angle error of the optical component.

2. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 1, characterized in that, The following conditions must be met before the device can be used for measurement: Two interferometers emit standard spherical test light waves. The zero-point test area of ​​each CGH compensator shows corresponding interference fringes in the interferometer outside the CGH compensator. The number of interferometer fringes is less than 3.

3. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 1, characterized in that, The distance from the CGH compensator to the nearest aspherical optical surface does not exceed the vertex radius of curvature of that aspherical optical surface.

4. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 1, characterized in that, The diameter of the zero-point test area of ​​the CGH compensator shall not exceed 100mm; the outer diameter of the alignment area shall not exceed 135mm, and the difference between the inner and outer diameters shall not be less than 20mm; the diameter of the reference area shall not be less than 15% of the diameter of the zero-point test area.

5. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 4, characterized in that, Based on the geometric parameters of the optical components, the distance between the CGH compensator and the aspherical optical surface, the aperture of all areas of each CGH compensator, and the material of the CGH compensator, the optical design software Zemax is used for simulation design to obtain the manufacturing parameters of the CGH compensator, and the CGH compensator is manufactured according to the manufacturing parameters.

6. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 1, characterized in that, The standard spherical test light wave emitted by the interferometer is modulated into a wavefront consistent with the surface of the aspherical optical component after passing through the zero-position test area of ​​the CGH compensator, which can form the interferometric measurement conditions and realize the measurement of the surface shape error of the aspherical optical component.

7. The device for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces according to claim 1, characterized in that, The F-number of the interferometer's standard lens is less than the ratio of the distance from the CGH compensator next to the interferometer to the aperture of the alignment area.

8. A method for detecting the optical axis consistency of a large-aperture aspherical mirror with two concentric surfaces, characterized in that, include: Based on the geometric parameters of the two-sided aspherical optical component to be tested, design a device as described in claim 1 for detecting the optical axis consistency of a large-aperture two-sided aspherical mirror. The CGH compensator and interferometer placed on one side of the aspherical optical surface M are respectively referred to as the first CGH compensator and the first interferometer, and the CGH compensator and interferometer placed on one side of the aspherical optical surface N are respectively referred to as the second CGH compensator and the second interferometer. Based on the device, two interferometers emit standard spherical test light waves, and the positions of the two interferometers are adjusted respectively so that the alignment areas B of the first CGH compensator and the second CGH compensator appear corresponding interference fringes in the first interferometer and the second interferometer respectively, with the number of fringes being less than 3. The position and tilt angle of the two-sided aspherical optical component under test are finely adjusted so that the zero-position test area of ​​the first CGH compensator appears with corresponding interference fringes in the first interferometer, the number of fringes is less than 3, and the primary coma of the wavefront measured by the first interferometer is less than 0.02; the surface shape error of the aspherical optical surface M is calculated. Fine-tune the position and tilt angle of the second interferometer and the second CGH compensator so that the zero-position test area of ​​the second CGH compensator appears in the second interferometer with corresponding interference fringes. The number of fringes should be less than 3, and the primary coma of the wavefront measured by the second interferometer should be less than 0.

02. Calculate the surface shape error of the aspherical optical surface N. The number of interference fringes in the reference region of the first CGH compensator in the first interferometer is observed and counted, and the number of interference fringes in the reference region of the second CGH compensator in the second interferometer is calculated to obtain the optical axis angle error.

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