CGH-based optical manufacturing assembly and adjustment auxiliary zero-point calibration measurement system and method

Abstract

This invention relates to the field of measurement technology and provides a zero-position calibration measurement system and method for optical manufacturing and assembly based on a computer-generated hologram (CGH). The system includes an interferometric measurement module, an improved PSF measurement module, a semi-transparent mirror, and a CGH. The CGH is used for phase modulation of the interferometric measurement module and the improved PSF measurement module. The CGH includes an improved PSF measurement phase portion, a tilt angle measurement phase portion, and a positioning holographic phase portion. This invention utilizes the partitionable characteristics of computer-generated holograms (CGH) to achieve precise calibration of the relative positions of the system's optomechanical components, effectively reducing inherent errors generated during the assembly of the processing or measurement system. This invention exhibits advantages such as modular structure, real-time response, and high-precision measurement, and is particularly suitable for high-precision measurement of the attitude of optical components, thereby significantly improving the accuracy and stability of high-end equipment processing platforms and optical manufacturing and assembly processes.

Description

Technical Field

[0001] This invention belongs to the field of measurement technology, and in particular relates to a zero-position calibration measurement system and method for optical manufacturing assembly and adjustment based on CGH. Background Technology

[0002] With the continuous improvement of photoelectric detection accuracy, the demand for three-dimensional real-time high-precision measurement methods for high-end equipment processing platforms is becoming increasingly urgent, aiming to ensure the accuracy and validity of real-time measurement results from photoelectric detection systems. Therefore, it is necessary to design a multi-dimensional (yaw angle, pitch angle, and axial / lateral displacement) measurement system capable of simultaneously achieving high-precision tilt angle measurement and displacement measurement, and recording status data in real time to provide a foundation for subsequent analysis.

[0003] Optomechanical systems typically consist of multiple optomechanical components. Tilting and jittering of high-end equipment processing platforms can cause minute changes in the relative positions of these components, leading to a decrease in measurement and processing accuracy. Therefore, precise position measurement and calibration of optomechanical components is a crucial technology in the manufacturing and assembly processes of optomechanical equipment. Even minute deviations in the position and orientation of optomechanical components can significantly degrade system performance, or even prevent the achievement of the expected optical effects. Existing measurement methods suffer from low accuracy, poor real-time performance, and complex error correction, especially in high-precision manufacturing and assembly processes, where accurate measurement and real-time error compensation become major challenges. Interferometric measurement methods offer high precision, non-contact, and non-destructive characteristics. Furthermore, computer-generated holography (CGH) technology has rapidly developed in recent years and is increasingly being applied to high-precision optical wavefront modulation. To address these issues, this invention proposes a CGH-based optical manufacturing and assembly-assisted zero-position calibration measurement system and method. Summary of the Invention

[0004] The purpose of this invention is to provide a zero-point calibration measurement system and method for optical manufacturing and assembly based on CGH, which aims to solve the problems mentioned in the background art.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The CGH-based optical manufacturing assembly and adjustment auxiliary zero-point calibration measurement system includes:

[0007] The interferometric measurement module is used for coarse measurements of pitch angle, yaw angle, and axial displacement, and has one interferometric optical path; the interferometric measurement module includes a standard spherical interferometer and a reference mirror;

[0008] An improved PSF measurement module is used for high-precision measurement of axial displacement and measurement of large lateral eccentric displacement. It is an optical 4f system. The improved PSF measurement module includes a laser reference point, a sensor and two objectives. The laser reference point is installed in the central area of ​​the reference mirror support structure, and the two objectives are objective lens one and objective lens two.

[0009] A semi-transparent and semi-reflective mirror is used to separate the measurement light of the improved PSF measurement module and the interferometric measurement module. Part of the measurement light in the interferometric measurement module enters the standard spherical interferometer, and the other part enters the sensor plane.

[0010] The CGH, mounted in the Fourier plane of the 4f system, is used for phase modulation of the interferometric measurement module and the improved PSF measurement module, including:

[0011] Improve the phase measurement portion of the PSF, including the central region, for phase modulation, and achieve axial / lateral displacement measurement by changing the PSF morphology on the sensor;

[0012] The tilt measurement phase section includes an annular region used to modulate the phase of the standard spherical wavefront, making it consistent with the reference mirror shape, thereby realizing biaxial tilt measurement;

[0013] The holographic phase portion is located, including a wavefront-modulated annular reflection region for locating the CGH and a wavefront-modulated dotted transmission region for locating the reference mirror.

[0014] Furthermore, the central region modulates the standard PSF, which diffuses with increasing defocus, into two continuously rotating main lobes that change with the system's defocus amount by modulating the phase.

[0015] Furthermore, the phase of the central region is obtained through the Fresnel zone method. The phase is related to the total number of Fresnel zones L and the phase plate radius R1. The distance between the two main lobes and the axial range corresponding to a 180° rotation are changed only by modifying the total number of Fresnel zones L. The optical path transmission of the 4f system is derived based on the Fresnel diffraction principle to obtain the sensitivity of the PSF rotation angle θ to the axial displacement Δz of the object.

[0016] When L remains constant, meaning the phase of the central region remains constant, the size of the measurement range is adjusted by adjusting the numerical aperture NA of the 4f system, enabling high-precision measurement within a small axial displacement range; NA = R1 / f1, where f1 is the focal length of objective lens one of the 4f system, and NA is adjusted by adjusting f1.

[0017] Furthermore, after the laser emitted from the laser reference point is collimated by the second objective lens, it is phase-modulated by the central region in the Fourier plane of the 4f system. The light from the first objective lens of the 4f system converges to the sensor. The PSF no longer diffuses with the increase of defocus. The two main lobes rotate continuously as the position of the laser reference point changes, and the rotation angle changes with the axial displacement of the laser reference point. The imaging position of the PSF on the sensor plane changes with the lateral displacement of the laser reference point.

[0018] Furthermore, the standard spherical interferometer uses an optical wavelength of 632.8 nm.

[0019] Furthermore, the wavelength of the laser reference point is 520nm.

[0020] A CGH-based optical manufacturing assembly-aided zero-point calibration measurement method, applied to the system described above, includes the following steps:

[0021] The calibration phase specifically includes:

[0022] Step S11: Calculate the relative position of CGH using the reflection area. When the contrast of the interferogram of the standard spherical interferometer is zero, the position of CGH can be accurately located and calculated.

[0023] Step S12: Using the transmission region to position the reference mirror, after the incident light is modulated, its third-order diffracted light projects two vertical line segments at a designated position on the edge of the reference mirror, forming a crosshair as a positioning reference. One crosshair is projected in each of the positive and negative X and Y directions, forming a total of eight crosshairs. At the same time, the measuring mirror is finely adjusted so that the first to sixth terms of the Zernike coefficient are less than 0.01, thus accurately positioning the reference mirror.

[0024] Step S13: Accurately locate the CGH position according to step S11, that is, locate the position of the Fourier transform surface of the 4f system; accurately locate the reference mirror position according to step S12, that is, locate the laser point reference position; further locate the positions of the objective lens and the sensor. When the rotation angle of the two main lobe spots displayed on the sensor plane is 0°, the displacement measurement calibration is completed.

[0025] The measurement phase specifically includes:

[0026] Step S21: Use the interferometric measurement module to measure the pitch angle, yaw angle, and coarsely measure the axial displacement;

[0027] Step S22: Based on the coarse axial displacement measurement, adjust the focal length of the objective lens in the PSF measurement module to narrow the measurement range to near the displacement value, and further measure the axial displacement with high precision; based on the pitch angle and yaw angle, further measure the lateral displacement with high precision; finally, achieve multi-dimensional measurement.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention utilizes the partitionable nature of computer-generated holograms (CGHs) to achieve precise calibration of the relative positions of system optomechanical components, effectively reducing inherent errors generated during the assembly of processing or measurement systems. This invention exhibits advantages such as modular structure, real-time response, and high-precision measurement, and is particularly suitable for high-precision measurement of the attitude (including yaw angle, pitch angle, and axial displacement) of optical components, thereby significantly improving the accuracy and stability of high-end equipment processing platforms and optical manufacturing and assembly processes. Attached Figure Description

[0030] Figure 1 This is a structural diagram of the system in this invention.

[0031] Figure 2 This is a schematic diagram of the structure of CGH in the system of the present invention.

[0032] Figure 3 This is a schematic diagram of the present invention.

[0033] In the diagram: 1-Standard spherical interferometer; 2-Semi-transparent mirror; 3-Objective lens one; 4-CGH; 5-Objective lens two; 6-Reference mirror; 7-Sensor; 8-Central region; 9-Annular region; 10-Reflection region; 11-Transmission region. Detailed Implementation

[0034] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0035] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0036] One embodiment of the present invention provides an optical manufacturing assembly and adjustment auxiliary zero-position calibration measurement system based on CGH. The system integrates an interferometric measurement module, an improved point spread function (PSF) measurement module, a semi-transparent mirror 2, and a CGH 4. In conjunction with the semi-transparent mirror 2 and CGH 4, the interferometric measurement module is used to perform coarse measurements of pitch angle, yaw angle, and axial displacement, while the improved PSF measurement module is used to perform high-precision measurements of axial displacement and large lateral eccentric displacement, thereby realizing three-dimensional measurement.

[0037] The interferometric measurement module has only one interferometric optical path, including a standard spherical interferometer 1 (wavelength 632.8nm) and a reference mirror 6.

[0038] The improved PSF (point spread function) measurement module is an optical 4f system, including a laser reference point, a sensor 7, and two objectives. The laser reference point is installed in the central region of the support structure of the reference mirror 6, and the laser wavelength is 520nm. The two objectives are objective 3 and objective 5.

[0039] The semi-transparent mirror 2 is used to separate the measurement light from the improved PSF measurement module and the interferometric measurement module. The 632.8nm measurement light in the interferometric measurement module enters the standard spherical interferometer 1 behind the semi-transparent mirror 2, while the other part of the measurement light is reflected by the metal film and enters the sensor 7 plane in the improved PSF measurement module.

[0040] CGH 4, mounted in the Fourier plane of the 4f system, is used for phase modulation of the interferometric measurement module and the improved PSF measurement module, including:

[0041] The phase measurement section of the PSF is improved, including a central region 8, used for phase modulation to change the PSF morphology on sensor 7, enabling axial / lateral displacement measurement. By modulating the phase, the standard PSF, which diffuses with increasing defocus, is modulated into two continuously rotating main lobes that change with the system's defocus, maintaining a relatively concentrated light intensity. The rotation angles of the two main lobes are directly related to depth information. The laser emitted from the laser reference point, after being collimated by objective lens 5, is phase-modulated by the central region 8 in the Fourier plane of the 4f system. It then converges through objective lens 3 in the 4f optical path to sensor 7. The PSF no longer diffuses with increasing defocus; the two main lobes rotate continuously with the position of the laser reference point, their rotation angles changing with the axial displacement of the laser reference point. The imaging position of the PSF on the sensor 7 plane changes with the lateral displacement of the laser reference point. The phase of the central region 8 is obtained using the Fresnel zone method. The phase is related to the total number of Fresnel zones L and the phase plate radius R1, and the spacing between the two main lobes and the axial range corresponding to a 180° rotation are changed only by modifying the total number of Fresnel zones L. The optical path propagation of the 4f system is derived based on the Fresnel diffraction principle, yielding the sensitivity of the point spread function (PSF) rotation angle θ to the axial displacement Δz of the object:

[0042]

[0043] Where NA is the numerical aperture of the 4f system; L is the total number of Fresnel bands; and λ is the system measurement wavelength.

[0044] When L remains constant, meaning the phase of the central region 8 remains constant, the measurement range is adjusted by changing the numerical aperture NA of the 4f system, allowing for more precise measurements within a small axial displacement range. The numerical aperture NA of the 4f system is R1 / f1, where f1 is the focal length of objective lens 3 of the 4f system. NA is adjusted by changing f1.

[0045] The tilt measurement phase section includes an annular region 9, which is used to modulate the phase of the standard spherical wavefront to make it consistent with the surface shape of the reference mirror 6, thereby realizing biaxial tilt measurement.

[0046] The positioning holographic phase portion includes a wavefront-modulated annular reflection region 10 for positioning CGH4 and a wavefront-modulated dot-shaped transmission region 11 for positioning the reference mirror 6.

[0047] One embodiment of the present invention provides a zero-position calibration measurement method for optical manufacturing assembly and adjustment based on CGH, which is applied to the system described above. The measurement process of this method is divided into a calibration stage and a measurement stage, and the specific steps are as follows:

[0048] The calibration phase includes:

[0049] Step S11: Calculate the relative position of CGH 4 using the reflection area 10. When the contrast of the interferogram of the standard spherical interferometer 1 is zero, the position of CGH 4 can be accurately located and calculated.

[0050] Step S12: Position the reference mirror 6 using the transmission region 11. After modulation, the incident light's third-order diffracted light projects two vertical line segments at a designated position on the edge of the reference mirror 6, forming a crosshair as a positioning reference. One crosshair is projected in each of the positive and negative X and Y directions, forming a total of eight crosshairs. Simultaneously, the measuring mirror is finely adjusted so that the first to sixth terms of the Zernike coefficient are less than 0.01 (based on calculations, it is assumed that the system is zeroed at this point, and the inherent error is very small and can be ignored in terms of its impact on measurement accuracy), thereby accurately positioning the reference mirror 6.

[0051] Step S13: Accurately locate the position of CGH 4 according to step S11, that is, locate the position of the Fourier transform surface of the 4f system; accurately locate the position of the reference mirror 6 according to step S12, that is, locate the laser point reference position; further locate the positions of the objective lens and sensor 7. When the rotation angle of the two main lobe spots displayed on the plane of sensor 7 is 0°, the displacement measurement calibration is completed, the entire measurement system is in the "zeroing" state, and measurement can begin.

[0052] The measurement phase includes:

[0053] Step S21: Use the interferometric measurement module to measure the pitch angle, yaw angle, and coarsely measure the axial displacement;

[0054] Step S22: Based on the coarse axial displacement measurement, adjust the focal length of the objective lens in the PSF measurement module to narrow the measurement range to near the displacement value, and further measure the axial displacement with high precision; based on the pitch angle and yaw angle, further measure the lateral displacement with high precision; finally, achieve multi-dimensional measurement.

[0055] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A null calibration measurement system for optical manufacturing alignment assistance based on CGH, characterized in that, Comprise: Interferometric module for measuring the pitch angle, yaw angle and axial displacement, with an interferometric optical path; the interferometric module comprises a standard spherical interferometer and a reference mirror; Improved PSF measurement module for high-precision measurement of axial displacement and measurement of large lateral eccentric displacement, which is an optical 4f system; the improved PSF measurement module comprises a laser reference point, a sensor and two objectives, the laser reference point is installed in the center area of the reference mirror support structure, and the two objectives comprise objective one and objective two; Semi-transparent mirror for separating the measurement light of the improved PSF measurement module and the interferometric module, part of the measurement light in the interferometric module enters the standard spherical interferometer, and the other part enters the sensor plane; CGH installed in the Fourier plane of the 4f system for phase modulation of the interferometric module and the improved PSF measurement module, comprising: Improved PSF measurement phase part, including a central area for phase modulation, which realizes axial / lateral displacement measurement by changing the PSF shape on the sensor; Inclination measurement phase part, including an annular area for modulating the phase of the standard spherical wavefront to make it consistent with the reference mirror surface, realizing two-axis inclination measurement; the standard spherical wavefront is emitted by the standard spherical interferometer and enters the annular area of the CGH through the semi-transparent mirror; Positioning holographic phase part, including a wavefront modulation annular reflection area for positioning the CGH and a wavefront modulation point-shaped transmission area for positioning the reference mirror.

2. The CGH-based optical manufacturing alignment aid null calibration metrology system of claim 1, wherein, The central area modulates the standard PSF that disperses with the increase of the defocusing amount into two continuously rotating main lobes that change with the system defocusing amount.

3. The CGH-based optical manufacturing alignment aid null calibration metrology system of claim 2, wherein, The phase of the central area is obtained by the Fresnel zone method, and the phase is related to the total number of Fresnel zones L and the phase sheet radius R1, and only by modifying the total number of Fresnel zones L to change the distance between the two main lobes and the axial range corresponding to a rotation of 180°; the optical path transfer of the 4f system is derived according to the Fresnel diffraction principle, and the sensitivity of the PSF rotation angle θ to the object axial displacement Δz is obtained; When L is constant, i.e. the phase of the central area is constant, the size of the measurement range is adjusted by adjusting the numerical aperture NA of the 4f system, and high-precision measurement is performed in a small axial displacement range; NA=R1 / f1, f1 is the focal length of objective one of the 4f system, and NA is adjusted by adjusting f1.

4. The CGH-based optical manufacturing alignment aid null calibration metrology system of claim 3, wherein, The laser emitted by the laser reference point is collimated by objective two, modulated by the phase of the central area in the Fourier plane of the 4f system, and converged by objective one of the 4f system to reach the sensor, and the PSF no longer disperses with the increase of the defocusing amount, the two main lobes continuously rotate with the change of the laser reference point position, the rotation angle changes with the axial displacement of the laser reference point, and the imaging position of the PSF on the sensor plane changes with the lateral displacement of the laser reference point.

5. The CGH-based optical manufacturing alignment aid null calibration metrology system of claim 1, wherein, The wavelength of the light wave used by the standard spherical interferometer is 632.8nm.

6. The CGH-based optical manufacturing alignment aid null calibration metrology system of claim 1, wherein, The wavelength of the laser reference point is 520nm.

7. A null calibration measurement method for optical manufacturing alignment assistance based on CGH, applied in the system as claimed in any one of claims 1-6, characterized in that, The measurement method comprises the following steps: The calibration stage, specifically comprising: Step S11: locating the relative position of CGH by using reflection area, the position of CGH can be located accurately when the contrast of interference figure of standard spherical interferometer is zero; Step S12: locating the reference mirror by using transmission area, the incident light is modulated, and the third order diffraction light is projected on the edge of the reference mirror to form two vertical line segments, which form a cross as a positioning reference, X and Y positive and negative directions each project a cross, a total of eight crosses; at the same time, the measuring mirror is fine-tuned, and the first to sixth terms of Zernike coefficient are less than 0.01, so that the position of the reference mirror can be located accurately; Step S13: according to the accurate positioning of CGH position in step S11, the position of 4f system Fourier plane is located; according to the accurate positioning of the reference mirror position in step S12, the position of the laser point reference is located; further, the positions of the objective lens and the sensor are located, and when the rotation angle of the two main lobe spot spots on the sensor plane is 0°, the displacement measurement calibration is completed; The measurement stage specifically includes: Step S21: using the interference measurement module to measure the pitch angle, yaw angle and the coarse measurement of axial displacement; Step S22: according to the coarse measurement of axial displacement, adjusting the focal length of the objective lens in the PSF measurement module, the measurement range is reduced to the vicinity of the displacement value, and the axial displacement is further measured with high precision; according to the pitch angle and the yaw angle, the lateral displacement is further measured with high precision; finally, multi-dimensional measurement is realized.

Images