Large-range polarization-maintaining characteristic detection system and method based on calculation of matched reflection loop

Abstract

The invention provides a large-range polarization-maintaining characteristic detection system and method based on calculation of a matched reflection loop. The system comprises an imaging ellipsometer, a non-polarization beam splitter, a light spot amplification reflector group and a corner reflector, and the imaging ellipsometer adopts an imaging Mueller matrix spectroscopic ellipsometer, a built-in polarization state generator and a CMOS polarization detector; the type and magnification of the light spot amplification reflector group are matched with the type and diameter parameter calculation of the to-be-measured curved-surface optical element, and the light spot amplification reflector group is used for amplifying the linearly polarized light spot output by the imaging ellipsometer to the size completely covering the to-be-measured curved-surface optical element; according to the invention, the magnification of the auxiliary reflector is calculated and determined according to the diameter of the to-be-measured curved surface by calculating the magnification accurate matching design of the matched reflection loop, and the original light spot of the imaging ellipsometer is amplified to the size matched with the to-be-measured curved surface, so that the full-area coverage of the light spot on the large-aperture curved surface optical element is realized; the defects of large point-by-point splicing error and easy missing of edge polarization distortion due to small light spot local detection in the traditional technology are overcome.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a wide-range polarization-maintaining characteristic detection system and method based on computationally matched reflection circuits. Background Technology

[0002] Off-axis parabolic mirrors, hyperboloid mirrors, and freeform mirrors, among other curved optical elements, are widely used in high-end optical systems such as laser communication, astronomical observation, precision spectral analysis, and advanced photolithography due to their superior performance in beam collimation, focusing, angle transformation, and aberration suppression. In these applications, especially polarization-sensitive optical systems, the polarization-preserving characteristics of curved optical elements directly determine the polarization fidelity and overall performance of the system—if uncontrollable polarization distortion occurs during beam reflection, it can lead to signal attenuation, phase shift, or even information loss.

[0003] From the perspective of current academic research and technological applications, existing surface polarization characteristic detection technologies are mainly based on traditional ellipsometers (UE) or early return path ellipsometers (RPE). When measuring curved surfaces with a traditional UE, if the surface normal is significantly tilted, the reflected light often cannot reach the detector, requiring frequent adjustments to the detector position. Furthermore, the tilted surface normal causes a mismatch between the reference frame of the polarization state generator (PSG) and the p / s polarization direction, introducing additional measurement errors. Although early return path ellipsometers (RPE) have improved stability through loop reflection design, they are mostly constructed based on spherical or plane mirrors. For example, spherical mirror-based RPEs can only measure in the center or near-center region of a rotating wafer, making them unsuitable for imaging ellipsometers (IE) with large beam diameters. Plane mirror-based RPEs have not solved the problem of large-area coverage, only enabling small-area local detection. Neither can meet the requirement of full-area polarization-preserving detection of large-aperture curved surfaces.

[0004] Existing technologies for detecting the polarization characteristics of curved optical elements have significant limitations. Based on academic research and engineering applications, these limitations can be summarized into three core issues: First, the detection range and beam adaptability are limited. Traditional optical element detectors (UEs) rely on small incident light spots, enabling only localized detection, and point-by-point stitching easily introduces errors. Early reverse polarization propagation (RPEs), even with loop designs, are limited by reflector structures and cannot meet the imaging and detection requirements of large beam diameters, covering only small areas (typically no more than 50mm × 50mm), making it difficult to cover the edge areas of large-aperture curved surfaces and easily overlooking edge polarization distortion issues. Second, polarization interference and reference frame matching are prominent problems. Traditional UEs lack closed-loop optical path design, and component interface reflections, air scattering, and optical path offsets all introduce additional polarization changes during optical path transmission. Furthermore, reference frame mismatch exacerbates errors when the surface is tilted. While early RPEs reduced optical path offset interference, they did not solve the problem of systematic distortion compensation during polarization state transmission, making it difficult to accurately distinguish from the polarization distortion of the curved surface itself. Third, the surface adaptability is insufficient. Existing technologies are mostly designed for specific types of curved surfaces (such as rotating wafers) and have not formed a general solution that can adapt to a variety of complex curved surfaces such as off-axis parabolic mirrors (OAP), hyperboloids, and freeform surfaces. For example, RPE based on spherical mirrors is only suitable for small-sized curved surfaces with rotational symmetry and cannot adapt to asymmetric freeform surfaces.

[0005] Therefore, there is an urgent need for a surface-based bias-preserving detection method that combines wide coverage, low interference, high precision, and strong adaptability. Summary of the Invention

[0006] To address the shortcomings of existing technologies in detecting the polarization-maintaining characteristics of curved optical elements, such as small detection range, numerous polarization interferences, low detection accuracy, and insufficient adaptability, this invention provides a large-range polarization-maintaining characteristic detection system and method based on computationally matched reflection circuits. This invention constructs a reflection circuit and an adaptable spot magnification mirror group by calculating and matching the parameters of the surface under test, solving the problems of large-range coverage and multi-surface adaptation. Combined with the circuit reflection optical path, it ensures detection stability and reduces polarization interference, ultimately achieving accurate detection of the polarization-maintaining characteristics of large-range curved optical elements across the entire area.

[0007] In a first aspect, the present invention provides a wide-range polarization-maintaining characteristic detection system based on a computationally matched reflection loop, comprising:

[0008] The imaging ellipsometer employs an imaging Mueller matrix spectroscopic ellipsometer, with a built-in polarization state generator (PSG) and a CMOS polarization detector, used to output stable linearly polarized light and complete the accurate detection and analysis of polarization states.

[0009] The non-polarized beam splitter (NPBS) is used to separate and combine the incident and reflected light paths, propagating the incident light along a preset direction while guiding the returned reflected light to the CMOS polarization detector.

[0010] The spot magnification reflector group is a single auxiliary reflector. The type and magnification of the auxiliary reflector are calculated and matched with the type and diameter parameters of the optical element of the surface under test. It is used to magnify the linearly polarized spot output by the imaging ellipsometer to fully cover the size of the optical element of the surface under test.

[0011] A corner reflector is a multi-faceted right-angle reflecting structure used to return the incident beam along its original incident direction.

[0012] The light-emitting end of the imaging ellipsometer is connected to the light-incident end of the non-polarizing beam splitter. The transmission end of the non-polarizing beam splitter is connected to the spot magnifying mirror assembly. The light-emitting end of the spot magnifying mirror assembly faces the detection surface of the optical element under test. The reflected light from the optical element under test is emitted towards the corner reflector. The reflected light from the corner reflector is transmitted to the non-polarizing beam splitter after passing through the optical element under test and the spot magnifying mirror assembly. The reflection end of the non-polarizing beam splitter is connected to the light-incident end of the CMOS polarization detector.

[0013] Furthermore, the system also includes a collimating lens, which is an aberration-correcting plano-convex lens; the collimating lens is positioned between the imaging ellipsometer and the non-polarizing beam splitter NPBS, and is used to collimate the beam emitted from the laser source into parallel light.

[0014] Furthermore, the system also includes an imaging lens, which is a cemented doublet achromatic lens, positioned between the non-polarizing beam splitter (NPBS) and the CMOS polarization detector, for accurately imaging the polarized light reflected by the NPBS onto the focal plane of the CMOS detector.

[0015] Furthermore, the system also includes a polarization state analyzer (PSA), positioned between the non-polarization beam splitter (NPBS) and the CMOS polarization detector, for performing polarization state analysis on the returned reflected light to extract the polarization state of the reflected light. , Phase difference of polarization components and amplitude ratio The optical polarization signal is converted into an electrical signal and transmitted to the CMOS polarization detector.

[0016] Furthermore, the type of the auxiliary reflector corresponds one-to-one with the type of the optical element to be tested. When the optical element to be tested is an off-axis parabolic mirror (OAP), the auxiliary reflector is an auxiliary off-axis parabolic mirror.

[0017] When the optical element to be tested is a hyperboloid mirror, the auxiliary reflector is an auxiliary hyperboloid mirror;

[0018] When the optical element to be tested is a freeform surface mirror, the auxiliary reflector is an auxiliary freeform surface mirror.

[0019] Furthermore, the magnification of the auxiliary reflector for:

[0020]

[0021] In the formula, The diameter of the surface of the optical element to be tested is denoted as . This represents the maximum spot size of the imaging ellipsometer.

[0022] Furthermore, the corner reflector is a planar reflector.

[0023] Secondly, the present invention provides a method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit, comprising the following steps:

[0024] S1) Based on the type and diameter parameters of the optical element to be tested, calculate and match the corresponding type and magnification of the auxiliary mirror to construct a large-range polarization-maintaining characteristic detection system;

[0025] S2) Start the imaging ellipsometer and set its detection wavelength. Output linearly polarized light and adjust the spot size to the maximum. The incident light is transmitted through the non-polarizing beam splitter (NPBS) to the auxiliary mirror. After being magnified by the auxiliary mirror, it is incident on the central region of the optical element under test. Then, it is reflected by the optical element under test to the corner reflector. The corner reflector returns the beam along the original incident direction to the optical element under test. After being reflected again by the optical element under test, it is transmitted to the auxiliary mirror. The auxiliary mirror restores the spot and guides it to the non-polarizing beam splitter (NPBS).

[0026] S3) The non-polarized beam splitter (NPBS) reflects the returned reflected light to the CMOS polarization detector, which then collects the parameters of the reflected light.

[0027] S4) Using the data analysis module of the imaging ellipsometer, the phase distortion introduced by the optical components is first compensated, and then the phase difference of the reflected light collected from each region of the optical element on the surface under test is calculated. By comparing the incident light reference phase difference with that in step S1), the phase difference offset of each region is calculated, and a phase difference distribution map of the polarization-preserving characteristics of the optical element under test is generated.

[0028] S5) Set the polarization maintenance judgment threshold. If the phase difference offset of the entire area of ​​the optical element under test is less than or equal to the polarization maintenance judgment threshold, its polarization maintenance characteristic is deemed to be qualified.

[0029] If the phase difference offset in a local area is greater than the polarization preservation threshold, mark the position and parameters of the distorted area, and after geometric distortion correction, adjust the parameters and positions of the collimating lens and the imaging lens for a second measurement.

[0030] Preferably, in step S1), a standard polarizer is used to calibrate the wide-range polarization-maintaining characteristic detection system at the detection wavelength, and the reference phase difference is recorded. ;

[0031] The polarization degree of the standard polarizer is ≥99.9%. The core of the calibration of the large-range polarization-maintaining characteristic detection system is to ensure that the linearly polarized light output from the imaging ellipsometer is transmitted through a closed-loop optical path without a test surface, and the phase difference is collected by the CMOS polarization detector. It is 0°.

[0032] Preferably, in step S1), the type of the auxiliary reflector corresponds one-to-one with the type of the optical element to be tested. When the optical element to be tested is an off-axis parabolic mirror (OAP), the auxiliary reflector is an auxiliary off-axis parabolic mirror.

[0033] When the optical element to be tested is a hyperboloid mirror, the auxiliary reflector is an auxiliary hyperboloid mirror;

[0034] When the optical element to be tested is a freeform surface mirror, the auxiliary reflector is an auxiliary freeform surface mirror.

[0035] Preferably, in step S3), the parameters include , Phase difference of polarization components and amplitude ratio , The light is polarized with electric field vibrations perpendicular to the plane of incidence. It is polarized light whose electric field vibrations are parallel to the plane of incidence.

[0036] Preferably, in step S4), the phase distortion introduced by the optical components is first compensated, as follows:

[0037] Large scale leads to uneven spatial response of optical components. Without correction, the spectral consistency between the edge and center of the field of view is poor, affecting the reliability of large spot measurements. Equipment-induced errors are eliminated through system factor stripping, as shown in the following formula:

[0038] ;

[0039] in, PSA transmittance factor PSG transmittance factor The sample represents the true signal; This represents the measured light intensity value under the combined polarization conditions of PSG and PSA; This represents the system's light intensity constant.

[0040] Preferably, in step S5), the geometric distortion correction targets the field curvature and distortion error of the detection system. The field curvature error correction is achieved by obtaining a flat-field mapping model through focal plane fitting, which projects the pixel data of the curved focal plane onto a standard flat field.

[0041] The distortion error is corrected by obtaining a pixel scaling model through distortion coefficient calibration, and the pixels in the edge region are scaled proportionally to match the magnification of the central region.

[0042] Preferably, in step S5), each pixel acquired by the CMOS detector... original coordinates Perform field curvature correction to convert the focal plane coordinates of the curved surface into standard flat field coordinates. ,Right now:

[0043] ;

[0044] ;

[0045] In the formula, This represents the deviation between the actual focal plane and the standard flat focal plane. This is the field curvature correction factor; The radial distance from the pixel to the center of the surface;

[0046] For the corrected standard flat field coordinates Perform distortion correction to obtain the distorted coordinates. ,Right now:

[0047] ;

[0048] ;

[0049] In the formula, This is the distortion correction factor; The effective detection radius of the curved surface optical element under test; The relative radial position of the pixel;

[0050] Then the distortion-corrected coordinates The phase difference data matrix after geometric distortion correction is obtained by remapping it with the actual physical coordinates of the optical element on the surface under test.

[0051] Based on the corrected phase difference data matrix, distortion regions with phase difference offsets greater than the polarization preservation threshold are marked, and their corrected physical center coordinates are recorded. and region radius .

[0052] Preferably, in step S5), the parameters of the collimating lens include the focal length of the collimating lens. Axial position of collimating lens radial position of collimating lens The parameters of the imaging lens include the focal length of the imaging lens. Axial position of imaging lens and the radial position of the imaging lens .

[0053] Preferably, in step S5), if the abnormal area is the edge region of the curved surface optical element under test, the radial position of the collimating lens is finely adjusted. This shifts the optical axis of the incident parallel light towards the anomalous region, ensuring the light spot fully covers the anomalous area; simultaneously, it fine-tunes the radial position of the imaging lens. Matching the optical axis offset of the reflected light, so that the imaging spot in the abnormal area is located at the center of the pixel matrix of the CMOS detector;

[0054] If the phase difference data in the abnormal region is blurry or noisy, fine-tune the axial position of the imaging lens. Adjust the position of the imaging focal plane to ensure that the reflected light is accurately imaged onto the photosensitive surface of the CMOS detector; or fine-tune the axial position of the collimating lens. To optimize the collimation of incident light;

[0055] If the size of the light spot in the abnormal area does not match the actual physical area, fine-tune the focal length of the collimating lens and the focal length of the imaging lens.

[0056] Preferably, in step S5), after the parameters and positions of the collimating lens and imaging lens are adjusted, a standard polarizer with a polarization degree ≥99.9% is used to perform local calibration on the abnormal area, and the local reference phase difference of the secondary measurement is recorded. ;

[0057] Then, the imaging ellipsometer is activated, and local polarization light detection is performed only on the marked abnormal area. The CMOS detector acquires high-resolution phase difference data of this area. The phase difference offset of the second measurement is compared with the result of the first measurement. If the deviation between the two is ≤ the polarization preservation judgment threshold, it is determined to be the true polarization distortion of the surface under test. If the deviation between the two is > the polarization preservation judgment threshold, it is determined to be the false distortion caused by the system optical path error. The abnormal markings in this area are removed, and the second measurement data is used as the standard.

[0058] The beneficial effects of this invention are as follows:

[0059] 1. This invention achieves precise matching design by calculating the magnification of the matching reflection circuit and determining the magnification of the auxiliary reflector according to the diameter of the surface to be measured. The original light spot of the imaging ellipsometer is magnified to match the size of the surface to be measured, realizing full coverage of the large-aperture curved surface optical element by the light spot. This solves the defects of traditional technology, such as local detection of small light spots, large errors in point-by-point splicing, and easy omission of edge polarization distortion.

[0060] 2. The phase offset of the present invention is ≤0.5° and the spatial resolution is about 0.1mm×0.1mm. At this resolution, the curved area corresponding to the pixel is much smaller than its radius of curvature and can be approximated as a plane, ensuring that the detection angle of the incident light spot is consistent and avoiding the additional phase difference caused by non-planarity. At the same time, the polarization state acquisition accuracy of the CMOS detector of the imaging ellipsometer can reach the sub-pixel level, providing a reliable guarantee for the quantitative analysis of polarization preservation characteristics.

[0061] 3. The invention is based on the closed-loop optical path design of the corner reflector, which enables the light beam to return along the original incident direction, avoiding polarization interference such as optical path offset, air scattering and component interface reflection in traditional ellipsometers. Combined with the mature polarization state generation and detection technology of imaging ellipsometer, it ensures the stable transmission of the polarization state of the incident light and greatly reduces the interference error in the polarization transmission process.

[0062] 4. This invention enables adaptation to multiple types of curved surfaces. When replacing optical elements of different types and diameters of the surface to be tested, there is no need to modify the core components of the detection system. Only the auxiliary reflector that is calculated to match the surface to be tested needs to be replaced. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the optical path principle of the detection system in an embodiment of the present invention;

[0064] Figure 2 This is a schematic diagram of the optical path principle of a single pixel in the detection system of this invention.

[0065] Figure 3 This is a flowchart illustrating the detection method in an embodiment of the present invention. Detailed Implementation

[0066] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0067] Example 1

[0068] like Figure 1 and 2 As shown, this embodiment provides a wide-range polarization-maintaining characteristic detection system based on a computationally matched reflection loop, including:

[0069] The imaging ellipsometer employs an imaging Mueller matrix spectroscopic ellipsometer, with a built-in polarization state generator (PSG) and a CMOS polarization detector, used to output stable linearly polarized light and complete the accurate detection and analysis of polarization states.

[0070] The imaging ellipsometer described above can be used for 1064nm wavelength detection, and the spot value of the linearly polarized light is 20 mm × 20 mm.

[0071] The non-polarized beam splitter (NPBS) is used to separate and combine the incident and reflected light paths, propagating the incident light along a preset direction while guiding the returned reflected light to the CMOS polarization detector.

[0072] The spot magnification reflector group is a single auxiliary reflector. The type and magnification of the auxiliary reflector are calculated and matched with the type and diameter parameters of the optical element of the surface under test. It is used to magnify the linearly polarized spot output by the imaging ellipsometer to fully cover the size of the optical element of the surface under test.

[0073] In this embodiment, the type of the auxiliary reflector corresponds one-to-one with the type of the optical element under test. When the optical element under test is an off-axis parabolic mirror (OAP), the auxiliary reflector is an auxiliary off-axis parabolic mirror.

[0074] When the optical element to be tested is a hyperboloid mirror, the auxiliary reflector is an auxiliary hyperboloid mirror;

[0075] When the optical element to be tested is a freeform surface mirror, the auxiliary reflector is an auxiliary freeform surface mirror.

[0076] The magnification of the auxiliary reflector for:

[0077]

[0078] In the formula, The diameter of the surface of the optical element to be tested is denoted as . This represents the maximum spot size of the imaging ellipsometer.

[0079] A corner reflector is a multi-faceted right-angle reflecting structure used to return the incident beam along its original incident direction.

[0080] The light-emitting end of the imaging ellipsometer is connected to the light-incident end of the non-polarizing beam splitter. The transmission end of the non-polarizing beam splitter is connected to the spot magnifying mirror assembly. The light-emitting end of the spot magnifying mirror assembly faces the detection surface of the optical element under test. The reflected light from the optical element under test is emitted towards the corner reflector. The reflected light from the corner reflector is transmitted to the non-polarizing beam splitter after passing through the optical element under test and the spot magnifying mirror assembly. The reflection end of the non-polarizing beam splitter is connected to the light-incident end of the CMOS polarization detector.

[0081] In some embodiments, the corner reflector is a planar reflector.

[0082] In this embodiment, the system further includes a collimating lens, which is an aberration-correcting plano-convex lens; the collimating lens is disposed between the imaging ellipsometer and the non-polarizing beam splitter NPBS, and is used to collimate the beam emitted from the laser source into parallel light.

[0083] In some embodiments, the system further includes an imaging lens, which is a cemented doublet achromatic lens, disposed between the non-polarizing beam splitter (NPBS) and the CMOS polarization detector, for accurately imaging polarized light reflected by the NPBS onto the focal plane of the CMOS detector.

[0084] In some embodiments, the system further includes a polarization state analyzer (PSA) disposed between the non-polarized beam splitter (NPBS) and the CMOS polarization detector, for performing polarization state analysis on the returned reflected light to extract the polarization state of the reflected light. , Phase difference of polarization components and amplitude ratio The optical polarization signal is converted into an electrical signal and transmitted to the CMOS polarization detector.

[0085] Example 2

[0086] like Figure 3 As shown, this embodiment provides a method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit, including the following steps:

[0087] S1) Based on the type and diameter parameters of the optical element to be tested, calculate and match the corresponding type and magnification of the auxiliary mirror to construct a wide-range polarization-maintaining characteristic detection system as described in Example 1.

[0088] In this embodiment, the type of the auxiliary reflector corresponds one-to-one with the type of the optical element under test. When the optical element under test is an off-axis parabolic mirror (OAP), the auxiliary reflector is an auxiliary off-axis parabolic mirror, such as... Figure 1 As shown;

[0089] When the optical element to be tested is a hyperboloid mirror, the auxiliary reflector is an auxiliary hyperboloid mirror;

[0090] When the optical element to be tested is a freeform surface mirror, the auxiliary reflector is an auxiliary freeform surface mirror.

[0091] In this embodiment, a standard polarizer is used to calibrate the wide-range polarization-maintaining detection system at the detection wavelength, and the reference phase difference is recorded. ;

[0092] The polarization degree of the standard polarizer is ≥99.9%. The core of the calibration of the large-range polarization-maintaining characteristic detection system is to ensure that the linearly polarized light output from the imaging ellipsometer is transmitted through a closed-loop optical path without a test surface, and the phase difference is collected by the CMOS polarization detector. It is 0°.

[0093] S2) Start the imaging ellipsometer and set its detection wavelength. Output linearly polarized light and adjust the spot size to the maximum. The incident light is transmitted through the non-polarizing beam splitter (NPBS) to the auxiliary mirror. After being magnified by the auxiliary mirror, it is incident on the central region of the optical element under test. Then, it is reflected by the optical element under test to the corner reflector. The corner reflector returns the beam along the original incident direction to the optical element under test. After being reflected again by the optical element under test, it is transmitted to the auxiliary mirror. The auxiliary mirror restores the spot and guides it to the non-polarizing beam splitter (NPBS).

[0094] S3) The non-polarized beam splitter (NPBS) reflects the returned reflected light to the CMOS polarization detector, which then collects the parameters of the reflected light.

[0095] In this embodiment, the parameters include the reflected light. , Phase difference of polarization components and amplitude ratio .

[0096] S4) Using the data analysis module of the imaging ellipsometer, the phase distortion introduced by the optical components is first compensated, and then the phase difference of the reflected light collected from each region of the optical element on the surface under test is calculated. By comparing the incident light reference phase difference with that in step S1), the phase difference offset of each region is calculated, and a phase difference distribution map of the polarization-preserving characteristics of the optical element under test is generated.

[0097] S5) Set the polarization maintenance judgment threshold to 0.5°. If the phase difference offset of the entire area of ​​the optical element under test is less than or equal to the polarization maintenance judgment threshold, its polarization maintenance characteristic is deemed to be qualified.

[0098] If the phase difference offset in a local area is greater than the polarization preservation threshold, mark the position and parameters of the distorted area, and after geometric distortion correction, adjust the parameters and positions of the collimating lens and the imaging lens for a second measurement.

[0099] In this embodiment, the geometric distortion correction targets the field curvature and distortion error of the detection system. The field curvature error correction is achieved by obtaining a flat-field mapping model through focal plane fitting, which projects the pixel data of the curved focal plane onto a standard flat field.

[0100] The distortion error is corrected by obtaining a pixel scaling model through distortion coefficient calibration, and the pixels in the edge region are scaled proportionally to match the magnification of the central region.

[0101] In this embodiment, each pixel captured by the CMOS detector original coordinates Perform field curvature correction to convert the focal plane coordinates of the curved surface into standard flat field coordinates. ,Right now:

[0102] ;

[0103] ;

[0104] In the formula, This represents the deviation between the actual focal plane and the standard flat focal plane. This is the field curvature correction factor; The radial distance from the pixel to the center of the surface;

[0105] For the corrected standard flat field coordinates Perform distortion correction to obtain the distorted coordinates. ,Right now:

[0106] ;

[0107] ;

[0108] In the formula, This is the distortion correction factor; The effective detection radius of the curved surface optical element under test; The relative radial position of the pixel;

[0109] Then the distortion-corrected coordinates The phase difference data matrix after geometric distortion correction is obtained by remapping it with the actual physical coordinates of the optical element on the surface under test.

[0110] Based on the corrected phase difference data matrix, distortion regions with phase difference offsets greater than the polarization preservation threshold are marked, and their corrected physical center coordinates are recorded. and region radius .

[0111] In this embodiment, the parameters of the collimating lens include the focal length of the collimating lens. Axial position of collimating lens radial position of collimating lens The parameters of the imaging lens include the focal length of the imaging lens. Axial position of imaging lens and the radial position of the imaging lens .

[0112] In this embodiment, if the abnormal region is the edge region of the curved surface optical element under test, the radial position of the collimating lens is finely adjusted. This shifts the optical axis of the incident parallel light towards the anomalous region, ensuring the light spot fully covers the anomalous area; simultaneously, it fine-tunes the radial position of the imaging lens. Matching the optical axis offset of the reflected light, so that the imaging spot in the abnormal area is located at the center of the pixel matrix of the CMOS detector;

[0113] If the phase difference data in the abnormal region is blurry or noisy, fine-tune the axial position of the imaging lens. Adjust the position of the imaging focal plane to ensure that the reflected light is accurately imaged onto the photosensitive surface of the CMOS detector; or fine-tune the axial position of the collimating lens. To optimize the collimation of incident light;

[0114] If the size of the light spot in the abnormal area does not match the actual physical area, fine-tune the focal length of the collimating lens and the focal length of the imaging lens.

[0115] In this embodiment, after the parameters and positions of the collimating lens and imaging lens are adjusted, a standard polarizer with a polarization degree ≥99.9% is used to perform local calibration on the abnormal area, and the local reference phase difference of the secondary measurement is recorded. ;

[0116] Then, the imaging ellipsometer is activated, and local polarization light detection is performed only on the marked abnormal area. The CMOS detector acquires high-resolution phase difference data of this area. The phase difference offset of the second measurement is compared with the result of the first measurement. If the deviation between the two is ≤ the polarization preservation judgment threshold, it is determined to be the true polarization distortion of the surface under test. If the deviation between the two is > the polarization preservation judgment threshold, it is determined to be the false distortion caused by the system optical path error. The abnormal markings in this area are removed, and the second measurement data is used as the standard.

[0117] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A wide-range polarization-maintaining characteristic detection system based on computationally matched reflection loops, characterized in that, include: The imaging ellipsometer employs an imaging Mueller matrix spectroscopic ellipsometer, with a built-in polarization state generator (PSG) and a CMOS polarization detector, used to output stable linearly polarized light and complete the accurate detection and analysis of polarization states. The non-polarized beam splitter (NPBS) is used to separate and combine the incident and reflected light paths, propagating the incident light along a preset direction while guiding the returned reflected light to the CMOS polarization detector. The spot magnification reflector group is a single set of auxiliary reflectors. The type and magnification of the auxiliary reflectors are calculated and matched with the type and diameter parameters of the optical element of the surface under test. It is used to magnify the linearly polarized spot output by the imaging ellipsometer to fully cover the size of the optical element of the surface under test. A corner reflector is a multi-faceted right-angle reflecting structure used to return the incident beam along its original incident direction. The light-emitting end of the imaging ellipsometer is connected to the light-incident end of the non-polarizing beam splitter. The transmission end of the non-polarizing beam splitter is connected to the spot magnifying mirror assembly. The light-emitting end of the spot magnifying mirror assembly faces the detection surface of the optical element under test. The reflected light from the optical element under test is emitted towards the corner reflector. The reflected light from the corner reflector is transmitted to the non-polarizing beam splitter after passing through the optical element under test and the spot magnifying mirror assembly. The reflection end of the non-polarizing beam splitter is connected to the light-incident end of the CMOS polarization detector.

2. The wide-range polarization-maintaining characteristic detection system based on computationally matched reflection loops according to claim 1, characterized in that: The type of auxiliary reflector corresponds one-to-one with the type of the optical element to be tested. When the optical element to be tested is an off-axis parabolic mirror (OAP), the auxiliary reflector is an auxiliary off-axis parabolic mirror. When the optical element to be tested is a hyperboloid mirror, the auxiliary reflector is an auxiliary hyperboloid mirror; When the optical element to be tested is a freeform surface mirror, the auxiliary reflector is an auxiliary freeform surface mirror.

3. The wide-range polarization-maintaining characteristic detection system based on computationally matched reflection loops according to claim 2, characterized in that: The magnification of the auxiliary reflector for: In the formula, The diameter of the surface of the optical element to be tested is denoted as . This represents the maximum spot size of the imaging ellipsometer.

4. The wide-range polarization-maintaining characteristic detection system based on computationally matched reflection loops according to claim 1, characterized in that: The system also includes a collimating lens and an imaging lens. The collimating lens is an aberration-correcting plano-convex lens. The collimating lens is positioned between the imaging ellipsometer and the non-polarizing beam splitter (NPBS) to collimate the laser beam emitted from the laser source into parallel light. The imaging lens is a cemented doublet achromatic lens, positioned between the non-polarizing beam splitter (NPBS) and the CMOS polarization detector, used to accurately image the polarized light reflected by the NPBS onto the focal plane of the CMOS detector.

5. The wide-range polarization-maintaining characteristic detection system based on computationally matched reflection circuits according to claim 4, characterized in that: The system also includes a polarization state analyzer (PSA), positioned between the non-polarization beam splitter (NPBS) and the CMOS polarization detector, for performing polarization state analysis on the returned reflected light to extract the polarization state of the reflected light. , Phase difference of polarization components and amplitude ratio The optical polarization signal is converted into an electrical signal and transmitted to the CMOS polarization detector.

6. A method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit, characterized in that, Includes the following steps: S1) Based on the type and diameter parameters of the optical element to be tested, calculate and match the corresponding type and magnification of the auxiliary mirror to construct a large-range polarization-maintaining characteristic detection system; S2) Start the imaging ellipsometer and set the detection wavelength of the imaging ellipsometer. Output linearly polarized light and adjust the spot size to the maximum. The incident light is transmitted to the auxiliary mirror through the non-polarized beam splitter NPBS. After being magnified by the auxiliary mirror, it is incident on the central region of the optical element of the surface under test. Then it is reflected by the optical element of the surface under test to the corner reflector. The corner reflector returns the beam along the original incident direction to the optical element of the surface under test. After being reflected again by the optical element of the surface under test, it is transmitted to the auxiliary reflector. The auxiliary reflector restores the beam spot and guides it to the non-polarizing beam splitter NPBS. S3) The non-polarized beam splitter (NPBS) reflects the returned reflected light to the CMOS polarization detector, which then collects the parameters of the reflected light. S4) Using the data analysis module of the imaging ellipsometer, the phase distortion introduced by the optical components is first compensated, and then the phase difference of the reflected light collected from each region of the optical element on the surface under test is calculated. By comparing the incident light reference phase difference with that in step S1), the phase difference offset of each region is calculated, and a phase difference distribution map of the polarization-preserving characteristics of the optical element under test is generated. S5) If the phase difference offset of the entire area of ​​the optical element under test is less than or equal to the polarization preservation judgment threshold, its polarization preservation characteristic is deemed to be qualified. If the phase difference offset in a local area is greater than the polarization preservation threshold, mark the position and parameters of the distorted area, and after geometric distortion correction, adjust the parameters and positions of the collimating lens and the imaging lens for a second measurement.

7. The method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit according to claim 6, characterized in that, In step S1), a standard polarizer is used to calibrate the wide-range polarization-maintaining detection system at the detection wavelength, and the reference phase difference is recorded. ; The polarization degree of the standard polarizer is ≥99.9%. The core of the calibration of the large-range polarization-maintaining characteristic detection system is to ensure that the linearly polarized light output from the imaging ellipsometer is transmitted through a closed-loop optical path without a test surface, and the phase difference is collected by the CMOS polarization detector. It is 0°.

8. The method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit according to claim 6, characterized in that, In step S4), the device-induced error is eliminated by system factor stripping, and the phase distortion introduced by the optical components is compensated, as shown in the following formula: ； in, PSA transmittance factor PSG transmittance factor The sample represents the true signal; This represents the measured light intensity value under the combined polarization conditions of PSG and PSA; This represents the system's light intensity constant.

9. The method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit according to claim 6, characterized in that, In step S5), the geometric distortion correction targets the field curvature and distortion error of the detection system. The field curvature error correction is achieved by obtaining a flat-field mapping model through focal plane fitting, which projects the pixel data of the curved focal plane onto a standard flat field. The distortion error is corrected by obtaining a pixel scaling model through distortion coefficient calibration, and the pixels in the edge region are scaled proportionally to match the magnification of the central region. Each pixel captured by the CMOS detector original coordinates Perform field curvature correction to convert the focal plane coordinates of the curved surface into standard flat field coordinates. ,Right now: ； ； In the formula, This represents the deviation between the actual focal plane and the standard flat focal plane. This is the field curvature correction factor; This represents the radial distance from the pixel to the center of the surface. For the corrected standard flat coordinates Perform distortion correction to obtain the distorted coordinates. ,Right now: ； ； In the formula, This is the distortion correction factor; The effective detection radius of the curved surface optical element under test; The relative radial position of the pixel; Then the distortion-corrected coordinates The phase difference data matrix after geometric distortion correction is obtained by remapping it with the actual physical coordinates of the optical element on the surface under test. Based on the corrected phase difference data matrix, distortion regions with phase difference offsets greater than the polarization preservation threshold are marked, and their corrected physical center coordinates are recorded. and region radius .

10. The method for detecting the wide-range polarization-maintaining characteristics based on a computationally matched reflection circuit according to claim 9, characterized in that, In step S5), the parameters of the collimating lens include the focal length of the collimating lens. Axial position of collimating lens radial position of collimating lens The parameters of the imaging lens include the focal length of the imaging lens. Axial position of imaging lens and the radial position of the imaging lens ; If the abnormal region is the edge region of the curved surface optical element under test, fine-tune the radial position of the collimating lens. This shifts the optical axis of the incident parallel light towards the anomalous region, ensuring the light spot fully covers the anomalous area; simultaneously, it fine-tunes the radial position of the imaging lens. Matching the optical axis offset of the reflected light, so that the imaging spot in the abnormal area is located at the center of the pixel matrix of the CMOS detector; If the phase difference data in the abnormal region is blurry or noisy, fine-tune the axial position of the imaging lens. Adjust the position of the imaging focal plane to ensure that the reflected light is accurately imaged onto the photosensitive surface of the CMOS detector; or fine-tune the axial position of the collimating lens. To optimize the collimation of incident light; If the size of the light spot in the abnormal area does not match the actual physical area, fine-tune the focal length of the collimating lens and the focal length of the imaging lens.

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