A system and method for detecting aspheric surface shape based on polarized light wavefront modulation

Abstract

The present invention relates to a system and method for detecting the shape of an aspheric surface based on polarized light wavefront modulation. The system comprises a coaxially arranged laser interferometer, a first aperture stop, a polarizing beam splitter prism, a quarter-wave plate, an aspheric surface to be measured, and a coaxially arranged half-wave plate, a second aperture stop, and a spatial light modulator. The laser interferometer emits a spherical wavefront, which, after passing through the first aperture stop and the polarizing beam splitter prism, changes its polarization state to a horizontal linear polarization state. After passing through the quarter-wave plate, the polarization state changes to a circular polarization state. The wavefront is reflected on the aspheric surface to be measured. After passing through the quarter-wave plate, the reflected light changes to a vertical linear polarization state. The reflected light is reflected on the polarizing beam splitter film of the polarizing beam splitter prism, and then changes to a horizontal linear polarization state after passing through the half-wave plate. After passing through the second aperture stop, the wavefront is modulated by the spatial light modulator. The modulated light returns along the original optical path to form interference fringes, which are analyzed by the laser interferometer to obtain measurement data. Compared with the existing technology, the present invention has the advantages of not requiring additional compensation components, being easy to adjust and test, and having strong versatility.

Description

Technical Field

[0001] The present invention relates to the technical field of optical aspheric surface shape detection, and in particular to an aspheric surface shape detection system and method based on polarized light wavefront modulation. Background Art

[0002] Aspheric optical elements have a variable radius of curvature, and their refractive and transmission properties are superior to traditional spherical optical elements. They can effectively correct image distortion and eliminate coma, which helps to greatly improve imaging quality and system resolution. In order to improve imaging quality, reduce structural size or the number of components, reduce weight, simplify the assembly process, and reduce overall manufacturing costs, aspheric surfaces have been increasingly widely used in various astronomical, military, civil, and medical fields. Interferometric surface shape detection is the most commonly used high-precision aspheric surface shape detection method. The traditional compensator processing in the interferometric detection method is costly and difficult. When there are a large number of aspheric surfaces in an optical system, it is often necessary to process a different compensator for each different aspheric surface. This has poor versatility, long detection cycles, and high costs. Therefore, the demand for compensators that can achieve adaptive aberration compensation for different aspheric surfaces in surface shape detection is becoming increasingly urgent.

[0003] As a programmable light field manipulation device, a spatial light modulator (SLM) can, under the control of an applied signal, alter the amplitude, polarization state, or phase of the spatial light distribution. It can also convert incoherent light into coherent light, writing specific information into the light field to achieve wavefront modulation. SLMs have been widely developed in fields such as AR / VR holographic displays, micro-nanolithography, and biomedicine. Due to their high resolution and simple control, they hold great promise for aspheric surface shape detection. Designing a compensator based on a SLM can meet the needs of high-precision surface shape detection for aspheric components with varying profile parameters.

[0004] Existing aspheric SLM (spatial light modulator) detection methods are affected by the resolution and optical path design of the spatial light modulator, which limits their detection accuracy and the difficulty of system adjustment. In addition, some high-precision reflective spatial light modulator optical paths require oblique incidence and off-axis adjustment, or additional compensation elements must be designed into the system to achieve surface shape detection. This limits its versatility and cannot well reflect the characteristics of the spatial light modulator as an adaptive compensator.

[0005] After searching, Chinese invention patent publication number CN107421436 B discloses an aspheric interferometry measurement method based on a spatial light modulator reference surface, including establishing an aspheric interferometry measurement system based on the spatial light modulator reference surface, and calculating the wavefront aberration of the test beam by ray tracing; the aspheric interferometry measurement system includes a laser 4, a collimating objective lens 3, a beam splitter 6, a reference mirror 5, a partial compensator 7, an aspheric surface to be measured 8, an imaging objective lens 2, and a CCD detector 1; an SLM is used as a reference mirror of the aspheric interferometry measurement system, which is defined as an SLM reference mirror 5; the parallel light formed by the laser emitted by the laser 4 after passing through the collimating objective lens 3 is projected onto the beam splitter 6, and is divided into two light beams after passing through the beam splitter 6; one light beam returns to the beam splitter 6 after passing through the SLM reference mirror 5, and this light beam is defined as a reference beam. In the reference beam, the SLM reference mirror 5 performs phase shifting on the parallel light formed after collimating the collimating objective lens 3. The invention relates to a method for the measurement of the surface error of the aspheric surface 8 by the SLM reference mirror 5. The method comprises the following steps: first, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; second, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; third, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fourth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fourth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fifth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fifth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fifth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; fifth, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; sixth ... seventh, the phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; eighth, the phase modulation of the reference beam wavefront by

[0006] How to realize aspheric surface shape detection without compensation components has become a technical problem that needs to be solved. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide an aspheric surface shape detection system and method based on polarized light wavefront modulation.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] According to one aspect of the present invention, there is provided an aspheric surface shape detection system based on polarized light wavefront modulation, the system comprising a coaxially arranged laser interferometer, a first aperture stop, a polarization beam splitter prism, a quarter-wave plate, and an aspheric surface to be measured, as well as a coaxially arranged half-wave plate, a second aperture stop, and a spatial light modulator;

[0010] The laser interferometer emits a spherical wavefront, which passes through the first aperture diaphragm and the polarization splitter prism in sequence and changes its polarization state to a horizontal linear polarization state. After passing through a quarter-wave plate, the polarization state changes to a circular polarization state. The wavefront is reflected on the aspheric surface to be measured. After passing through the quarter-wave plate, the polarization state of the reflected light changes to a vertical linear polarization state. The wavefront is reflected on the polarization splitter film of the polarization splitter prism and changes its polarization state to a horizontal linear polarization state after passing through a half-wave plate. The wavefront passes through the second aperture diaphragm and is modulated by a spatial light modulator. The modulated light returns to the laser interferometer along the original optical path, forming interference fringes, which are analyzed by the laser interferometer to obtain measurement data.

[0011] Preferably, the modulated light is returned along the original optical path as follows: the modulated light passes through the second aperture stop and the half-wave plate, becomes a vertical linear polarization state, is reflected on the beam splitter film of the polarization beam splitter prism, passes through the 1 / 4 wave plate after reflection, becomes a circular polarization state, is reflected again on the aspheric surface to be measured, and the reflected light passes through the 1 / 4 wave plate, the polarization beam splitter prism and the first aperture stop for the last time, and the polarization state becomes the horizontal linear polarization state and returns to the laser interferometer to form interference fringes.

[0012] Preferably, the interference factor of the laser interferometer is set to 0.25.

[0013] Preferably, the system further comprises a computer, which is connected to the phase modulation signal input port of the spatial light modulator.

[0014] Preferably, the computer simulation calculates the phase modulation distribution of the spatial light modulator, converts it into a grayscale image, and inputs the grayscale image into the spatial light modulator as an input signal; and the light field control software is deployed on the computer.

[0015] More preferably, the method for obtaining the grayscale image is as follows: a computer uses the profile parameters of the aspheric surface to be measured as the detection target in optical simulation software, determines the distance and position between each component, simulates and calculates the phase modulation distribution of the spatial light modulator, and converts it into a grayscale image.

[0016] Preferably, the first aperture stop is placed at the convergence point of the spherical wave emitted by the laser interferometer.

[0017] The second aperture stop is placed between the spatial light modulator and the half-wave plate, that is, at the point where the convergent spot of the spherical wave emitted by the laser interferometer is the smallest after passing through the half-wave plate for the first time.

[0018] Preferably, after the spherical wave emitted by the laser interferometer is reflected by the aspheric surface to be measured for the first time and passes through the 1 / 4 wave plate, if the optical axis of the 1 / 4 wave plate is not aligned, a portion of the spherical wave will pass through the polarization beam splitter prism, and a light spot will appear on the first aperture stop. The bracket paddle of the 1 / 4 wave plate is rotated until the light spot on the first aperture stop gradually darkens and disappears.

[0019] According to another aspect of the present invention, a method for detecting an aspheric surface shape based on polarized light wavefront modulation is provided, the method comprising:

[0020] Step S1, optical simulation software determines the distance and position between each component using the profile parameters of the aspheric surface to be measured as the detection target;

[0021] Step S2, optical simulation software calculates the phase modulation distribution of the spatial light modulator and converts it into a grayscale image;

[0022] Step S3: Establish a detection optical path based on the distance and position between the components in step S1. If a light spot appears on the first aperture stop, rotate the bracket of the quarter-wave plate until the light spot on the first aperture stop gradually darkens and disappears.

[0023] Step S4: After the positions of the optical elements are preliminarily adjusted, the grayscale image of step S2 is input as an input signal to the spatial light modulator to collect the surface error data of the aspheric surface to be measured.

[0024] Preferably, the process of collecting the surface error data of the aspheric surface to be measured in step S4 includes: fine-tuning the pitch, azimuth and relative distance between the aspheric surface to be measured and the spatial light modulator, while observing the changes in the interference fringes collected by the laser interferometer until they converge to stable interference fringes, collecting measurement data, and obtaining the surface error data of the aspheric surface to be measured.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The present invention uses components such as wave plates, polarization beam splitters, and spatial light modulators to form a coaxial detection optical path. This eliminates the need for off-axis oblique incidence of the light beam. Based on the principle of polarization, it can effectively avoid beam splitting and aliasing. Therefore, it does not require the processing of additional compensation components. The optical path assembly and detection are simple, the detection system has a large tolerance range, and is easy to adjust.

[0027] 2) The present invention combines a spatial light modulator with computer simulation to achieve free programming of the spatial light modulator, uses the spatial light modulator as an adaptive compensator, and utilizes the polarization principle to perform wavefront modulation on the detection system, thereby maximizing the adaptive compensation capability of the spatial light modulator and improving the versatility of the surface detection method.

[0028] 3) For the spatial light modulator, the present invention does not require the light beam to be incident off-axis at an angle. Instead, it only requires coarse adjustment of the distance from the convergence point of the spherical wave emitted by the laser interferometer to the central vertex of the aspheric surface to be measured to a computer simulation value, and then fine adjustment of the pitch, azimuth and relative distance between the aspheric surface to be measured and the spatial light modulator until the interference fringes converge to a stable state. The measurement result can be obtained, which is simple to adjust and convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the optical path structure of the aspheric surface shape detection system of the present invention;

[0030] Figure 2 Calculate optimized aspheric surface detection optical path diagram for optical simulation software;

[0031] Figure 3 Schematic diagram of the process of the aspheric surface detection method of the present invention;

[0032] In the accompanying drawings, 1 is a laser interferometer, 2 is a first aperture stop, 3 is a polarization beam splitter prism, 4 is a quarter wave plate, 5 is an aspheric surface to be measured, 6 is a half wave plate, 7 is a second aperture stop, 8 is a spatial light modulator, and 9 is a computer. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0034] This embodiment relates to an aspheric surface shape detection system based on polarized light wavefront modulation. The system includes a connected laser interferometer 1, a first aperture stop 2, a polarization beam splitter prism 3, a quarter-wave plate 4, an aspheric surface to be measured 5, a half-wave plate 6, a second aperture stop 7, a spatial light modulator 8, and a computer 9. The laser interferometer 1, the first aperture stop 2, the polarization beam splitter prism 3, the quarter-wave plate 4, and the aspheric surface to be measured 5 are coaxially arranged, and the polarization beam splitter prism 3, the half-wave plate 6, the second aperture stop 7, and the spatial light modulator 8 are coaxially arranged.

[0035] like Figure 1The optical path of the aspheric surface shape detection system is as follows: the laser interferometer 1 emits a spherical wavefront, which changes to a horizontal linear polarization state after passing through the first aperture diaphragm 2 and the polarization beam splitter prism 3, changes to a circular polarization state after passing through the 1 / 4 wave plate 4, and is reflected on the aspheric surface to be measured 5. The reflected light changes to a vertical linear polarization state after passing through the 1 / 4 wave plate 4, and is reflected on the polarization beam splitter film of the polarization beam splitter prism 3. It then changes to a horizontal linear polarization state after passing through the half-wave plate 6, and is modulated by the spatial light modulator 8 after passing through the second aperture diaphragm 7. The light after the reflection returns along the original optical path, and the return process is as follows: it passes through the second aperture diaphragm 7 and the half-wave plate 6, becomes a vertical linear polarization state, is reflected on the beam splitting film of the polarization beam splitter prism 3, passes through the 1 / 4 wave plate 4 after reflection, becomes a circular polarization state, and is reflected again on the aspheric surface 5 to be measured. The reflected light passes through the 1 / 4 wave plate 4, the polarization beam splitter prism 3 and the first aperture diaphragm 2 for the last time, and the polarization state becomes the light of the horizontal linear polarization state and returns to the laser interferometer 1, forming interference fringes, which are analyzed by the laser interferometer 1 to obtain measurement data.

[0036] The horizontal resolution of the computer 9 should reach 4000 pixels or above, and it should be equipped with optical simulation software for Figure 1 The detection optical path structure is configured to set the parameters of each component, and the phase modulation distribution of the spatial light modulator 8 is calculated by simulation and converted into a grayscale image.

[0037] The spatial light modulator 8 is installed with light field control software and is connected to the computer 9 via a data line. The grayscale image of the computer 9 is input as an input signal into the spatial light modulator 8 via the light field control software.

[0038] The spatial light modulator 8 is combined with the computer 9 to realize free programming of the spatial light modulator 8. The spatial light modulator 8 is used as an adaptive compensator to modulate the wavefront of the detection system using the polarization principle, so aspheric surface detection can be achieved without additional compensation elements.

[0039] The interference factor of laser interferometer 1 is set to 0.25.

[0040] The first aperture stop 2 is placed at the convergence point of the spherical wave emitted by the laser interferometer 1, and the second aperture stop 7 is placed between the spatial light modulator 8 and the half-wave plate 6, that is, the convergence spot of the spherical wave emitted by the laser interferometer 1 is smallest after passing through the various components in the optical system and passing through the half-wave plate 6 for the first time.

[0041] Before setting up the detection optical path, the computer 9 uses the profile parameters of the aspheric surface to be tested as the detection target in the optical simulation software. Figure 1Determine the distance and position between each component, simulate and calculate the phase modulation distribution of the spatial light modulator 8 and convert it into a grayscale image, connect the computer 9 to the phase modulation signal input port of the spatial light modulator 8 through a data line, and input the grayscale image as an input signal into the spatial light modulator 8 through the light field control software.

[0042] This embodiment also relates to a method for detecting aspheric surface shape based on polarized light wavefront modulation, taking an even-order aspheric surface as an example. Figure 3 The process of measuring the surface error of an aspheric surface using the method of the present invention is as follows:

[0043] 1) ZEMAX optical simulation software uses the profile parameters of the aspheric surface to be tested as the detection target to determine the distance and position between each component: perform optical path simulation in ZEMAX sequence mode on computer 9, set the parameters of components such as wave plate, polarization beam splitter prism and aspheric surface to be tested, set the spatial light modulator 8 to Zernike Fringe Phase polynomial diffraction surface, set the evaluation function with the 37 coefficients of the polynomial as variables for optimization, and obtain the aspheric surface detection optical path diagram after ZEMAX calculation optimization, as shown in Figure 1. Figure 2 shown.

[0044] The first aperture stop 2 is placed at the convergence point of the spherical wave emitted by the laser interferometer 1; the second aperture stop 7 is placed between the spatial light modulator 8 and the half-wave plate 6, that is, the point where the convergence spot of the spherical wave emitted by the laser interferometer 1 is smallest after passing through the various components in the optical system and passing through the half-wave plate 6 for the first time.

[0045] 2) Optical simulation software calculates the phase modulation distribution of spatial light modulator 8 and converts it into a grayscale image: The phase modulation distribution is obtained by summing the optimized Zernike Fringe Phase polynomials. Based on the pixel size and resolution of the spatial light modulator 8 used, a quantized discrete distribution set by grayscale levels of 0-255 bits within the phase modulation range of [0, 2π] is calculated. The phase modulation amount applied to each pixel is calculated and wrapped within [0, 2π]. This is converted to the corresponding grayscale level to generate a grayscale image with the same resolution as the spatial light modulator.

[0046] 3) Set up the test optical path according to the component positions set by ZEMAX. Install the even-order aspheric surface to be tested and the spatial light modulator 8 on the six-dimensional adjustment mount. If a light spot appears on the first aperture stop 2, rotate the bracket of the quarter-wave plate 4 until the light spot on the first aperture stop 2 gradually darkens and disappears.

[0047] 4) The grayscale image is input as an input signal to the spatial light modulator 8 through the light field control software, and measurement data is collected: After the positions of the optical components are initially adjusted, the input signal calculated corresponding to the even-order aspheric surface to be measured is loaded onto the spatial light modulator 8, and the pitch, azimuth, and relative distance between the even-order aspheric surface to be measured and the spatial light modulator 8 are fine-tuned. At the same time, the changes in the interference fringes collected by the laser interferometer 1 are observed until they converge to stable straight fringes. The measurement data is collected, and the surface error data of the aspheric surface 5 to be measured is obtained.

[0048] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. An aspheric surface shape detection system based on polarized light wavefront modulation, characterized in that: The system includes a coaxially arranged laser interferometer (1), a first aperture stop (2), a polarization beam splitter prism (3), a quarter-wave plate (4), and an aspheric surface to be measured (5), as well as a coaxially arranged half-wave plate (6), a second aperture stop (7), and a spatial light modulator (8); The laser interferometer (1) emits a spherical wavefront, which passes through the first aperture diaphragm (2) and the polarization beam splitter prism (3) in sequence, and the polarization state changes to a horizontal linear polarization state. After passing through the quarter wave plate (4), the polarization state changes to a circular polarization state. The wavefront is reflected on the aspheric surface (5) to be measured. After passing through the quarter wave plate (4), the polarization state of the reflected light changes to a vertical linear polarization state. The wavefront is reflected on the polarization beam splitter film of the polarization beam splitter prism (3). After passing through the half wave plate (6), the polarization state changes to a horizontal linear polarization state. After passing through the second aperture diaphragm (7), the wavefront is modulated by the spatial light modulator (8). The modulated light returns to the laser interferometer (1) along the original optical path, forms interference fringes, and is analyzed by the laser interferometer (1) to obtain measurement data. The modulated light returns along the original optical path as follows: the modulated light passes through the second aperture diaphragm (7) and the half-wave plate (6), changes to a vertical linear polarization state, is reflected on the beam splitting film of the polarization beam splitter prism (3), passes through the quarter-wave plate (4) after reflection, changes to a circular polarization state, is reflected again on the aspheric surface to be measured (5), and the reflected light passes through the quarter-wave plate (4), the polarization beam splitter prism (3) and the first aperture diaphragm (2) for the last time, and the polarization state changes to a horizontal linear polarization state, and returns to the laser interferometer (1), forming interference fringes.

2. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, characterized in that: The interference factor of the laser interferometer (1) is set to 0.

25.

3. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, characterized in that: The system further comprises a computer (9), which is connected to the phase modulation signal input port of the spatial light modulator (8).

4. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 3, characterized in that: The computer (9) simulates and calculates the phase modulation distribution of the spatial light modulator (8), converts it into a grayscale image, and inputs the grayscale image into the spatial light modulator (8) as an input signal; the light field control software is deployed on the computer (9).

5. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 4, characterized in that: The method for obtaining the grayscale image is specifically as follows: a computer (9) uses the profile parameters of the aspheric surface (5) to be tested as a detection target in optical simulation software, determines the distance and position between each component, simulates and calculates the phase modulation amount distribution of the spatial light modulator (8), and converts it into a grayscale image.

6. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, characterized in that: The first aperture stop (2) is placed at the convergence point of the spherical wave emitted by the laser interferometer (1). The second aperture diaphragm (7) is placed between the spatial light modulator (8) and the half-wave plate (6), that is, at the point where the convergence spot of the spherical wave emitted by the laser interferometer (1) is minimum after passing through the half-wave plate (6) for the first time.

7. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, characterized in that: After the spherical wave emitted by the laser interferometer (1) is reflected by the aspheric surface to be measured (5) for the first time and passes through the 1 / 4 wave plate (4), if the optical axis of the 1 / 4 wave plate (4) is not aligned, part of the spherical wave will pass through the polarization beam splitter prism (3) and a light spot will appear on the first aperture diaphragm (2). The bracket of the 1 / 4 wave plate (4) is rotated until the light spot on the first aperture diaphragm (2) gradually darkens and disappears.

8. A method for detecting an aspheric surface shape using the polarized light wavefront modulation-based aspheric surface shape detection system according to any one of claims 1 to 7, characterized in that: The method includes: Step S1, optical simulation software determines the distance and position between each component using the profile parameters of the aspheric surface to be measured as the detection target; Step S2, optical simulation software calculates the phase modulation distribution of the spatial light modulator (8) and converts it into a grayscale image; Step S3, constructing a detection optical path based on the distance and position between the components in step S1, and if a light spot appears on the first aperture diaphragm (2), rotating the bracket paddle of the 1 / 4 wave plate (4) until the light spot on the first aperture diaphragm (2) gradually darkens and disappears; In step S4, after the positions of the optical elements are preliminarily adjusted, the grayscale image of step S2 is input as an input signal to the spatial light modulator (8) to collect the surface error data of the aspheric surface (5) to be measured.

9. The method according to claim 8, characterized in that The process of collecting the surface error data of the aspheric surface (5) to be measured in step S4 includes: fine-tuning the pitch, azimuth and relative distance of the aspheric surface to be measured (5) and the spatial light modulator (8), while observing the changes in the interference fringes collected by the laser interferometer (1) until they converge to stable interference fringes, collecting measurement data, and obtaining the surface error data of the aspheric surface (5) to be measured.

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