Aspheric surface shape detection system and method based on polarized light wavefront modulation

Abstract

The invention relates to an aspheric surface shape detection system and method based on polarized light wavefront modulation. The system comprises a laser interferometer, a first aperture diaphragm, a polarization splitting prism, a 1 / 4 wave plate and a to-be-detected aspheric surface which are coaxially arranged, and a half wave plate, a second aperture diaphragm and a spatial light modulator which are coaxially arranged, before the laser interferometer emits spherical waves, the polarization state is changed into a horizontal line polarization state after passing through the first aperture diaphragm and the polarization splitting prism, the polarization state is changed into a circular polarization state after passing through the 1 / 4 wave plate, the spherical waves are reflected on the aspheric surface to be measured, the reflected light is changed into a vertical line polarization state after passing through the 1 / 4 wave plate, and the reflected light is reflected on a polarization splitting film of the polarization splitting prism. And the light passes through the second aperture diaphragm and is modulated by the spatial light modulator, the modulated light returns along the original light path to form interference fringes, and the interference fringes are analyzed by the laser interferometer to obtain measurement data. Compared with the prior art, the method has the advantages of no need of additional compensation elements, easiness in adjustment and measurement, high universality and the like.

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 performances are superior to traditional spherical optical elements. They can effectively correct image distortion, eliminate coma, and help 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 in the interferometric detection method has high processing cost and difficulty. When there are a large number of aspheric surfaces in the optical system, it is often necessary to process different compensators for each different aspheric surface, which has poor versatility, long detection cycle, and high cost. Therefore, the demand for compensators that can achieve adaptive aberration compensation for different aspheric surfaces in surface shape detection is becoming more and more urgent.

[0003] As a programmable light field control device, the spatial light modulator can change the amplitude, polarization state or phase of the light distribution in space under the control of the applied signal, or convert incoherent light into coherent light, write specific information into the light field, and realize wavefront modulation. Spatial light modulators have been widely developed in the fields of AR / VR holographic display, micro-nano lithography, biomedicine, etc. Due to their high resolution and simple control, they have broad prospects in aspheric surface shape detection. Designing a compensator based on the spatial light modulator can meet the needs of high-precision surface shape detection of aspheric components with different profile parameters.

[0004] The existing aspheric SLM (spatial light modulator) detection method is affected by the resolution and optical path design of the spatial light modulator, which limits its 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 in 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 a non-spherical interferometry measurement method based on a spatial light modulator reference surface, including establishing a non-spherical interferometry measurement system based on a spatial light modulator reference surface, and calculating the wavefront aberration of a test beam by ray tracing; the non-spherical interferometry measurement system includes a laser 4, a collimating objective lens 3, a beam splitter 6, a reference mirror 5, a partial compensator 7, a non-spherical 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 non-spherical 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 the light beam is defined as a reference beam, in which the SLM reference mirror 5 performs phase contrast on the parallel light formed after collimation by the collimating objective lens 3 The phase modulation of the reference beam wavefront by the SLM reference mirror 5 is equal to the wavefront aberration of the test beam; only when the modulation amount of the SLM reference mirror 5 is insufficient, a partial compensator 7 is added to the test optical path to partially compensate for the aberration generated by the aspheric surface 8; another beam passes through the partial compensator 7 to reach the aspheric surface 8 to be tested, and after being reflected by the aspheric surface 8, it carries the surface error information of the aspheric surface 8 to be tested and returns to the beam splitter 6 through the partial compensator 7, which is defined as the test beam; the reference beam and the test beam converge through the beam splitter 6, interfere at the beam splitter 6, form interference fringes, and are collected at the CCD detector 1 through the imaging objective 2; while using the SLM reference mirror 5 to modulate the reference beam, multiple phase modulations are introduced to the reference beam to complete the phase shift, and multiple interference patterns are collected, and the surface error of the aspheric surface 8 to be tested is obtained by solving the phase shift algorithm. The existing patent has the problem of off-axis oblique incidence of the beam and the need for partial compensation.

[0006] How to realize aspheric surface shape detection without compensation elements 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 a non-spherical 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 its polarization state changes to a horizontal linear polarization state. After passing through a quarter wave plate, its polarization state changes to a circular polarization state. It 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. It is reflected on the polarization splitter film of the polarization splitter prism, and its polarization state changes to a horizontal linear polarization state after passing through a half wave plate. After passing through the second aperture diaphragm, it is modulated by a spatial light modulator. The modulated light returns to the laser interferometer along the original optical path to form 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 of the reflected light becomes a horizontal linear polarization state, which 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, wherein the computer 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 a 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 tested as the detection target in optical simulation software, determines the distance and position between each element, 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 convergence 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, part of it will pass through the polarization beam splitter prism, and a light spot will appear on the first aperture diaphragm. The bracket paddle of the 1 / 4 wave plate is rotated until the light spot on the first aperture diaphragm 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, the optical simulation software determines the distance and position between each element using the profile parameters of the aspheric surface to be tested 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, the distance and position between the components in step S1 are used to build a detection optical path. If a light spot appears on the first aperture diaphragm, the support paddle of the 1 / 4 wave plate is rotated until the light spot on the first aperture diaphragm 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 wave plates, polarized light splitting prisms, spatial light modulators and other components to form a coaxial detection optical path. The light beam does not need to be incident off-axis at an angle. Based on the principle of polarization, the splitting and aliasing phenomena can be effectively avoided. Therefore, there is no need to process additional compensation components. The optical path installation and detection are simple, the detection system has a large tolerance range, and is easy to adjust.

[0027] 2) The present invention realizes the free programming of the spatial light modulator by combining the spatial light modulator with computer simulation, 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 need to make the light beam incident obliquely off-axis. It only needs to roughly adjust 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 the computer simulation calculation value, and then fine-tune the pitch, azimuth and relative distance between the aspheric surface to be measured and the spatial light modulator until the interference fringes converge to stability, and the measurement result can be obtained. The adjustment and measurement are simple 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 in the present invention;

[0030] Figure 2 Calculate the optimized aspheric 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 be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] The present embodiment relates to an aspheric surface shape detection system based on polarized light wavefront modulation, which comprises 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 into a horizontal linear polarization state after passing through the first aperture diaphragm 2 and the polarization beam splitter prism 3, changes into a circular polarization state after passing through the 1 / 4 wave plate 4, and is reflected on the aspheric surface 5 to be measured. The reflected light changes into 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, and then changes into 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 modulation The light after the reflection returns along the original optical path, and the returning process is as follows: passing through the second aperture diaphragm 7 and the half-wave plate 6, it becomes a vertical linear polarization state, and is reflected on the beam splitting film of the polarization beam splitter prism 3. After reflection, it passes through the 1 / 4 wave plate 4 and 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 the measurement data.

[0036] The computer 9 has a lateral resolution of 4000 pixels or more and is equipped with optical simulation software for Figure 1 The detection optical path structure sets the parameters of each component, and performs simulation to calculate the phase modulation distribution of the spatial light modulator 8 and converts it 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 into the spatial light modulator 8 via the light field control software as an input signal.

[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 shape 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 the 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 the shape of an aspheric surface 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 the ZEMAX sequence mode on the computer 9, set the parameters of the wave plate, polarization beam splitter prism and the aspheric surface to be tested, set the spatial light modulator 8 to the 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 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 convergence spot of the spherical wave emitted by the laser interferometer 1 after passing through various components in the optical system and passing through the half-wave plate 6 for the first time is the smallest.

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

[0046] 3) According to the position of each component set by ZEMAX, build the detection optical path, install the even-order aspheric surface to be tested and the spatial light modulator 8 on the six-dimensional adjustment frame respectively, if a light spot appears on the first aperture stop 2, rotate the bracket paddle of the 1 / 4 wave plate 4 until the light spot on the first aperture stop 2 gradually darkens and disappears;

[0047] 4) The grayscale image is used as an input signal and input into the spatial light modulator 8 through the light field control software to collect measurement data: After the positions of the optical components are preliminarily adjusted, the input signal calculated corresponding to the even-order aspheric surface to be measured is loaded on 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, and the measurement data is collected to obtain the surface error data of the aspheric surface 5 to be measured.

[0048] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A non-spherical surface shape detection system based on polarized light wavefront modulation, characterized in that: The system comprises 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 a first aperture diaphragm (2) and a polarization beam splitter prism (3) in sequence, and its polarization state changes to a horizontal linear polarization state. After passing through a quarter wave plate (4), its polarization state changes to a circular polarization state. It is reflected on a non-spherical surface (5) to be measured. After passing through a quarter wave plate (4), its polarization state changes to a vertical linear polarization state. It is reflected on a polarization beam splitter film of the polarization beam splitter prism (3). After passing through a half wave plate (6), its polarization state changes to a horizontal linear polarization state. After passing through a second aperture diaphragm (7), it is modulated by a spatial light modulator (8). The modulated light returns to the laser interferometer (1) along the original optical path, forming interference fringes. After being analyzed by the laser interferometer (1), measurement data is obtained.

2. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, characterized in that: 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) to change into a vertical linear polarization state, is reflected on the beam splitting film of the polarization beam splitting prism (3), passes through the quarter wave plate (4) after reflection to change into 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 splitting prism (3) and the first aperture diaphragm (2) for the last time, and the polarization state of the reflected light changes into a horizontal linear polarization state and returns to the laser interferometer (1), forming interference fringes.

3. 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.

4. 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), wherein the computer (9) is connected to the phase modulation signal input port of the spatial light modulator (8).

5. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 1, 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).

6. The aspheric surface shape detection system based on polarized light wavefront modulation according to claim 5, 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 element, simulates and calculates the phase modulation distribution of the spatial light modulator (8), and converts it into a grayscale image.

7. 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 stop (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 the smallest after passing through the half-wave plate (6) for the first time.

8. 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 (5) to be measured for the first time and passes through the quarter wave plate (4), if the optical axis of the quarter 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 support paddle of the quarter wave plate (4) is rotated until the light spot on the first aperture diaphragm (2) gradually darkens and disappears.

9. A method for detecting an aspheric surface shape based on polarized light wavefront modulation according to any one of claims 1 to 8, characterized in that: The method includes: Step S1, the optical simulation software determines the distance and position between each element using the profile parameters of the aspheric surface to be tested 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 support paddle of the 1 / 4 wave plate (4) until the light spot on the first aperture diaphragm (2) gradually darkens and disappears; 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.

10. The method according to claim 9, characterized in that The process of collecting the surface error data of the aspheric surface (5) to be measured in step S4 comprises: finely adjusting the pitch, azimuth and relative distance between the aspheric surface (5) to be measured and the spatial light modulator (8), and observing the change of the interference fringes collected by the laser interferometer (1) until the interference fringes converge to stable ones, collecting the measurement data, and obtaining the surface error data of the aspheric surface (5) to be measured.

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