CN109029288B - Reflective large-gradient aspheric surface and free-form surface detection device and method based on DMD wave-front sensing technology - Google Patents

Abstract

The invention relates to a device and a method for detecting a reflective large-gradient aspheric surface and a free-form surface based on a DMD wave-front sensing technology, and belongs to the field of optical detection. The method introduces a digital micromirror array (DMD) to measure the aberration of the distorted wavefront, and combines light ray tracing software to realize the non-zero detection of the aspheric surface and the free-form surface. Specifically, the working state of each micro-mirror unit is programmed and controlled by the DMD, and then the sequential scanning of the whole wave front is completed. The sequential scanning imaging mode not only enlarges the dynamic range of the traditional wavefront sensing such as Hartmann measurement, but also greatly improves the transverse resolution of the traditional wavefront sensing. The method designs a universal non-zero detection method aiming at the reflective aspheric surface and the free curved surface, and has compact structure and strong expandability.

Description

A Reflective Large Steep Aspheric Surface and Free Curve Based on DMD Wavefront Sensing Technology Surface detection device and method

technical field

The invention belongs to the field of advanced optical manufacturing and detection, and in particular relates to a reflection type large-steepness aspheric surface and free-form surface detection device and method based on DMD wavefront sensing technology.

Background technique

Modern optical systems are developing towards miniaturization and high performance. The application of aspheric surfaces and even free-form surfaces in optical systems can not only simplify the system structure, but also improve system performance. Since the 1980s, aspheric surfaces have been widely used in aerospace cameras, astronomical telescopic systems, and infrared remote sensing systems. The optical free-form surface has a greater degree of freedom in design, a large number of variables, a large change in the surface degree of freedom, and a flexible structure, which can break through the limitations of traditional optical components, and simplify the system structure while correcting almost all aberrations. It has a good application. prospect. However, the special geometry of aspheric and free-form surfaces makes its fabrication very difficult. As the premise of processing, the detection of large-steep aspheric surfaces and free-form surfaces also faces huge difficulties.

At present, corresponding detection technologies have been developed for aspheric surfaces and free-form surfaces at different stages in the processing process. Such as the surface profile method in the rough grinding stage, the geometric light detection method in the fine grinding and rough polishing stages, and the interferometry method in the later stage of polishing. For the measurement of large-steep aspheric surfaces and free-form surfaces, the accuracy of profile measurement such as three-coordinates is low, generally only reaching the sub-micron level, and coordinate measurement is extremely time-consuming for large-diameter aspheric surface measurement; while the interferometry method has high precision , non-contact, full field of view advantages. However, a corresponding compensator or computational holography (CGH) must be designed for each DUT, which requires a large number of additional auxiliary optical components, resulting in complex structure, strict tolerance requirements, and installation and adjustment errors will also affect the detection accuracy. In addition, for devices with large asphericity, the fringes to be drawn on the calculation holographic plate are very dense, which makes the fabrication more complicated and expensive; geometric light methods, such as Hartmann wavefront measurement, are dynamic relative to interferometry. The range is large and the relative coordinate measurement accuracy is high, so it is often used as a detection problem for connecting aspheric optics in the fine grinding and initial polishing stages. However, for steep aspheric and free-form surfaces, traditional Hartmann sensors are limited in dynamic range and lateral resolution. Therefore, it is urgent to develop an optical detection method for large-diameter, high-order aspheric surfaces and free-form surfaces.

The invention utilizes the wavefront detection technology, and belongs to the geometric ray method in principle. Compared with the traditional Hartmann wavefront sensor, the sequential scanning wavefront technology is used to image the subregions of the wavefront to be measured, which greatly improves the dynamic range of wavefront detection. In addition, since the micro-reflection array DMD is used to divide and scan the wavefront in the present invention, its lateral resolution will also be greatly improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a reflective type large-steep aspheric surface and free-form surface detection device and method based on DMD wavefront sensing technology. on the detector. The slope of the wavefront is calculated by detecting the position of the imaging point, and the wavefront phase is obtained through the later slope integration algorithm. The final surface shape result is calculated by comparing it with the theoretical wave aberration of the theoretical aspheric surface in the ray tracing software.

The technical scheme of the present invention is: a reflection type large-steep aspheric surface and free-form surface detection device based on DMD wavefront sensing technology, the device includes:

One-dimensional electronic control platform is used to drive the laser light source to precisely move to different off-axis positions or optical axis positions;

Lasers for generating high-power, frequency-stabilized laser beams;

The collimating lens is used to collimate the conical beam emitted by the laser into parallel light;

The beam splitter prism is used to reflect a part of the parallel light to the focusing lens; the beam splitter prism is also used to project the measured wavefront reflected from the measured aspheric surface or free-form surface to the telescopic beam expander system;

The focusing lens is used to focus the parallel beam reflected by the beam splitter and then irradiate it on the measured aspheric or free-form surface. The focusing lens is also used to collimate the beam reflected by the aspheric or free-form surface and compensate for the spherical aberration term. Form the actual measured wavefront;

Telescopic beam expander system, which is used to scale the beam size of the system to the same size as the DMD to maximize the utilization of the DMD array;

The micro-mirror array DMD uses the sub-mirror array in the "on" state to divide the measured wavefront, and sequentially reflects the divided measured sub-wavefront to the imaging lens; other parts of the measured wavefront are in the "on" state through DMD. The sub-mirror reflection in the "off" state is absorbed by the cassette;

an imaging lens for imaging the wavefront reflected by the DMD onto the detector;

a detector for imaging the wavefront and recording the position of the imaging point;

A cassette for receiving another part of the wavefront reflected by the sub-mirror array in the "off" state of the DMD.

Wherein, the F-number of the focusing lens is greater than the F-number of the measured aspheric surface and free-form surface.

其中D为系统光瞳大小，这里由准直透镜决定，d为DMD尺寸的短边长度。Among them, the amplification ratio of the telephoto beam expander system is:

Where D is the pupil size of the system, which is determined by the collimating lens here, and d is the length of the short side of the DMD size.

Wherein, the detector may be a CCD camera or a position detector (Position Sensitive Device, PSD)

A reflective large-steepness aspheric surface and free-form surface detection method based on DMD wavefront sensing technology, the detection method is based on the reflective large-steepness aspheric surface and free-form surface based on DMD wavefront sensing technology A curved surface detection device, the method includes:

S1. First, calibrate the entire device to obtain a calibration file;

S2. Modeling in Zemax ray tracing software to obtain the theoretical wave aberration of the aspheric surface and free-form surface to be measured;

S3. Use the calibration file to perform experimental measurement. The obtained experimental result minus the theoretical wave aberration obtained in Zemax is the surface error of the aspheric surface and the free-form surface to be measured.

Wherein, the device calibration method in the step S1 is as follows:

A plane mirror is placed at the rear focus position of the focusing lens, and the laser is controlled at different off-axis values through the horizontal electronic control platform, and then plane wavefronts with different inclinations can be introduced through the plane mirror to record and form calibration files.

The principle of the invention is: a reflective type large-steep aspheric surface and free-form surface detection device based on DMD wavefront sensing technology, comprising a one-dimensional electronic control platform, a laser, a collimating lens, a beam splitting prism, a focusing lens, a telephoto Beam expander system, micro-mirror array DMD, imaging lens, CCD camera, cassette. The detection device is aimed at a reflective large-steep aspherical optical element.

The specific steps for detecting a reflective large-steep aspheric surface are as follows:

1) According to the light source, set the size of the DMD sub-mirror array and write the scanning mode of the DMD sub-mirror array.

2) A plane mirror is placed at the back focus position of the focusing lens, and the laser is precisely controlled at different off-axis positions through the horizontal electronic control platform, and then plane wavefronts with different tilt amounts (tilt angles) can be introduced through the plane mirror, and the measurement results can be recorded and formed. document.

3) Modeling in ray tracing software such as Zemax to obtain the theoretical wave aberration of the aspheric surface and free-form surface to be measured on the imaging surface.

4) Use the calibration file to perform the experimental measurement, and the obtained experimental result minus the theoretical wave aberration obtained in Zemax is the surface error of the aspheric surface and free-form surface to be measured.

As shown in Figure 2, there are several schemes for setting the size of the DMD sub-mirror array and writing the scanning method of the DMD sub-mirror array: Take the DMD size of 1024*768 as an example: AperturePosX and AperturePosY respectively represent the center position of the scanning range Coordinates; SuperPixelAmountX and SuperPixelAmountY represent the number of sub-mirror arrays in the X and Y directions respectively; SuperPixelPitch represents the distance between the center points of two adjacent sub-mirror arrays during scanning; SuperPixelLength represents the length of the sub-mirror array. The upper left scanning mode indicates the case where the size of the DMD sub-mirror unit is equal to the scanning motion distance; the upper right scanning mode indicates the case that the size of the DMD sub-mirror unit is smaller than the scanning motion distance; the lower left scanning mode indicates the case that the size of the DMD sub-mirror unit is greater than the scanning motion distance; right The downward scanning mode indicates that the DMD scanning range is not in the center position.

The laser is precisely controlled at different off-axis positions through the lateral electric control platform, and the plane wavefronts with different inclinations (inclination angles) are introduced through the rear focus position plane mirror of the focusing lens. The reference optical path is shown in Figure 3. The maximum off-axis magnitude represents the maximum gradient the system can detect for an aspheric or free-form surface.

The model is modeled in ray tracing software such as Zemax, and the theoretical wave aberration of the aspheric surface and free-form surface to be measured on the imaging surface is obtained. By inputting the theoretical expression of the measured aspheric or free-form surface into ray tracing software such as Zemax, the system ray tracing model can be obtained as shown in Figure 5.

The advantages of the present invention compared with the prior art are:

(1) Compared with the coordinate measurement of the contour surface, the method of the present invention has the advantages of full aperture, non-contact, high precision and high detection efficiency;

(2) Compared with the geometric ray method, it has the advantages of large dynamic range and high lateral resolution;

(3) Compared with interferometry based on compensator and CGH, it has the advantages of simple structure, low cost and strong versatility.

(4) The present invention better balances the performance of the detection system, the detection cost and the detection efficiency.

(5) The present invention is a general detection scheme for the large-steep aspheric surface and the free-form surface shape from the fine grinding to the initial polishing stage, which is not available in the existing methods.

Description of drawings

FIG. 1 is a schematic structural diagram of a detection device according to an embodiment of the present invention;

2 is a schematic diagram of a DMD scanning method according to an embodiment of the present invention;

3 is a schematic diagram of a system calibration optical path according to an embodiment of the present invention;

4 is a schematic diagram of a system calibration method according to an embodiment of the present invention;

5 is a schematic diagram of a system Zemax model according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a theoretical aspherical aberration to be measured according to an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , a reflective type large-steep aspheric and free-form surface detection device based on DMD wavefront sensing technology in this embodiment, a one-dimensional electronic control platform 11, is used to drive the laser light source to accurately move to different from the (optical) axis position;

Laser 1, used to generate a high-power, frequency-stable laser beam;

The collimating lens 2 is used for collimating the conical beam emitted by the laser 1 into parallel light;

The beam splitting prism 3 is used to reflect a part of the parallel light to the focusing lens 4; the beam splitting prism 3 is also used to project the measured wavefront reflected back from the measured aspheric surface or free curved surface 5 to the telephoto beam expander system 6;

The focusing lens 4 is used to focus the parallel beam reflected back by the beam splitting prism 3 and then irradiate it onto the measured aspheric or free-form surface 5, and the focusing lens 4 is also used to collimate the beam reflected back by the aspheric or free-form surface 5 ( After compensating the spherical aberration term), the actual measured wavefront is formed;

Telescopic beam expander system 6, which is used to scale the beam size of the system to the same size as the DMD, so as to maximize the utilization of the DMD array;

The micro-mirror array DMD 7 divides the measured wavefront with the sub-mirror array in the "on" state, and sequentially reflects the divided measured sub-wavefronts to the imaging lens 8 in different regions; other parts of the measured wavefront pass through the DMD 7 The sub-mirror reflection in the "off" state is absorbed by the cassette 10.

The imaging lens 8 is used to image the subwavefront reflected by the DMD 7 onto the detector 9;

a detector 9 for imaging the wavefront and recording the position of the imaging point;

The cassette 10 is used to receive another part of the wavefront reflected by the sub-mirror array in the "off" state of the DMD 7.

The measurement process and detection steps of the device of the present invention are as follows:

Step 1: According to the light source, set the size of the DMD sub-mirror array and write the scanning method of the DMD sub-mirror array. For example, the first scanning method in Figure 2.

Step 2: Place a plane mirror at the back focus position of the focusing lens 4, and control the laser to be at different off-axis values through the one-dimensional electronic control platform 11 (horizontal electronic control platform), such as 0, 2mm, 2mm, 3mm, 4mm, 5mm , 6mm, 7mm and then can introduce plane wavefronts with different inclinations (inclination angles) through the plane mirror, as shown in Figure 3, record the measurement results and form a calibration file.

Step 3: Modeling in ray tracing software such as Zemax, assuming that the model optical path of the aspheric surface to be measured is shown in Figure 5. The theoretical wave aberration of the aspheric surface and free-form surface to be measured on the imaging surface can be obtained by ray tracing, as shown in Figure 6.

Step 4: Use the calibration file to perform experimental measurement. The calibrated experimental results obtained by the calibration method shown in Figure 4, minus the theoretical wave aberration obtained in Zemax is the surface error of the aspheric surface and free-form surface to be measured.

The method has the advantages of simple structure, easy construction, low cost and short detection period, and provides an effective inspection method for the polishing stage of the large-diameter aspherical primary mirror and the measurement of the final mirror surface parameters.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this, and any partial modification or replacement within the technical scope disclosed by the present invention by anyone familiar with the technology shall cover within the scope of the present invention.

Claims (1)

1. A reflection type large-steepness aspheric surface and free-form surface detection method based on DMD wavefront sensing technology, the detection method utilizes a reflection-type large-steepness aspheric surface and free-form surface detection device based on DMD wavefront sensing technology , the device includes: The one-dimensional electronic control platform (11) is used to drive the laser light source to precisely move to different off-axis positions or optical axis positions; A laser (1) for generating a high-power, frequency-stabilized laser beam; a collimating lens (2) for collimating the conical light beam emitted by the laser (1) into parallel light; The beam splitter prism (3) is used to reflect a part of the parallel light to the focusing lens (4); the beam splitter prism (3) is also used to project the measured wavefront reflected back from the measured aspheric surface or free-form surface (5) to the focusing lens (4). Telescopic beam expander system (6); The focusing lens (4) is used for focusing the parallel beam reflected back by the beam splitting prism (3) and then irradiating it onto the measured aspherical surface or free-form surface (5). (5) The reflected beam is collimated and compensated for spherical aberration to form the actual measured wavefront; A telephoto beam expander system (6), which is used to scale the beam size of the system to the same size as the DMD, so as to maximize the utilization of the DMD array; The micro-mirror array DMD (7) divides the measured wavefront with the sub-mirror array in the “on” state, and sequentially reflects the divided measured sub-wavefront to the imaging lens (8) in different regions; Other parts are absorbed by the cassette (10) through the reflection of the sub-mirror in the "off" state of the DMD (7); an imaging lens (8) for imaging the subwavefront reflected by the DMD (7) onto the detector (9); a detector (9) for imaging the wavefront and recording the position of the imaging point; A cassette (10) for receiving another part of the wavelet front reflected by the sub-mirror array in the "off" state of the DMD (7), characterized in that the method comprises: S1. First, calibrate the entire device to obtain a calibration file; S2. Modeling in Zemax ray tracing software to obtain the theoretical wave aberration of the aspheric surface and free-form surface to be measured; S3. Use the calibration file to perform experimental measurement, and the obtained experimental result minus the theoretical wave aberration obtained in Zemax is the surface error of the aspheric surface and free-form surface to be measured; The device calibration method in the step S1 is as follows: A plane mirror is placed at the rear focus position of the focusing lens (4), and the laser is controlled at different off-axis amounts through a one-dimensional electronic control platform (11), and then plane wavefronts with different inclination amounts can be introduced through the plane mirror to record and form a calibration file.

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