Method for Inducing Deterministic Polishing Process Parameters by Optical System Indexes

Abstract

The present invention relates to the field of optical processing technologies, and particularly to a method for inducing deterministic polishing process parameters for optical system indicators. The method includes: determining the structure of the optical system and identifying the ideal optical element in the optical system for which the mid-frequency error needs to be controlled; calculating the tool mark feature maps generated by the ideal optical element under different process parameters; generating the elevation maps of the optical element corresponding to different process parameters based on the tool mark feature maps; replacing the ideal optical element with different elevation maps of the optical element to obtain the system evaluation indicators of the optical system corresponding to different elevation maps of the optical element; and selecting the optimal system evaluation indicator, and the process parameters corresponding thereto are the optimal process parameters. The present invention corresponds the process parameters of the optical element for which the mid-frequency error needs to be controlled to the system evaluation indicators one by one, determines the optimal system evaluation indicator, and the process parameters corresponding thereto are the optimal process parameters, thereby realizing the optimal manufacturing process parameters determined by the imaging quality of the optical system.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical processing, and particularly relates to a method for inducing deterministic polishing process parameters of optical system indexes. Background Art

[0002] For deterministic processing methods, the characteristic mid-spatial frequency error remaining on the processed surface, i.e., the tool mark error, can be simulated according to their process parameters. An optical element with such an error installed in a system affects the imaging quality of the optical system. The paper "Analysis and Prediction of Image Quality Degradation Caused by Diffraction of Infrared Optical System Turning Marks" published in the journal 《Photonics》 elaborates on the influence of tool marks generated by single-point diamond turning on diffraction. The period of the tool mark error generated by this deterministic process is on the order of micrometers, and it can produce an obvious diffraction effect on visible light.

[0003] The paper "Surface variation analysis of freeform optical systems over surface frequency bands for prescribed wavefront errors" published in the journal 《Optics&Laser Technology》 elaborates on the influence of tool mark errors on optical elements with annular-like errors.

[0004] The period of the tool mark error generated by the magnetorheological process is on the order of millimeters, and the period of the tool mark error generated by the small grinding head process is on the order of centimeters. Moreover, most of the tool mark errors generated by this process are grating-like errors, and their period scale is much larger than the wavelength. Since obvious diffraction effects cannot be generated by the analytical method, it is more appropriate to indirectly analyze its influence on the imaging quality of the optical system using ray optical indexes.

[0005] The paper "Workflow for modeling of generalized mid-spatial frequency errors in optical systems" published in the journal 《OpticsExpress》 gives a flowchart for simulating the influence of mid-spatial frequency errors on the image quality of an optical system.

[0006] If the optimal processing parameters can be determined by simulation before processing, the problem of a long manufacturing cycle can be avoided. Summary of the Invention

[0007] In view of this, the present invention aims to provide a method for inducing deterministic polishing process parameters for optical system indicators, which corresponds the process parameters of the optical element that needs to control the mid-frequency error with the system evaluation indicators one by one, determines the optimal system evaluation indicator, and the corresponding process parameters are the optimal process parameters, thereby realizing the simulation of the deterministic manufacturing error caused by any manufacturing process parameters.

[0008] To achieve the above object, the technical solution of the present invention is realized as follows:

[0009] A method for inducing deterministic polishing process parameters for optical system indicators, including:

[0010] S1: Determine the structure of the optical system and determine the ideal optical element that needs to control the mid-frequency error in the optical system;

[0011] S2: Calculate the tool mark characteristic map generated by the ideal optical element determined in step S1 under different process parameters;

[0012] S3: Generate the optical element sagittal height map corresponding to different process parameters according to the tool mark characteristic map obtained in step S2;

[0013] S4: Replace the ideal optical element of the optical system in step S1 with different optical element sagittal height maps, and obtain the system evaluation indicators of the optical system corresponding to different optical element sagittal height maps;

[0014] S5: Select the optimal system evaluation indicator obtained in step S4, and the corresponding process parameters are the optimal process parameters.

[0015] Furthermore, the tool mark characteristic map is calculated by the following formula:

[0016] ;

[0017] Wherein, represents the error characteristic map algorithm, represents the i-th process parameter cell array, represents the tool mark characteristic map generated by the ideal optical element under the processing of the i-th process parameter cell array.

[0018] Furthermore, in step S3, the tool mark characteristic map and the surface equation of the ideal optical element are added to obtain the optical element sagittal height map.

[0019] Furthermore, in step S4:

[0020] Optical imaging is performed on the optical system corresponding to different optical element sagittal height maps to obtain the corresponding extended diffraction image;

[0021] Based on different extended diffraction images, the system evaluation indicators of the corresponding optical system are calculated.

[0022] Furthermore, the system evaluation index includes the clarity index of the extended diffraction image.

[0023] Furthermore, the clarity index includes the Brenner index.

[0024] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0025] In the method for inducing deterministic polishing process parameters by the optical system index of the present invention, based on the characteristic that different intermediate frequency errors have different influences on the imaging of the optical system, the present invention establishes the optimal polishing process parameters of the optical element determined by the imaging quality of the optical system, can simulate the deterministic manufacturing errors brought by any manufacturing process parameters, and can analyze the influence of manufacturing errors at the millimeter scale or even centimeter scale on the image quality of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0027] Figure 1 is a schematic flow chart of the method for inducing deterministic polishing process parameters by the optical system index according to the embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of a single-element system according to the embodiment of the present invention;

[0029] Figure 3 is a schematic diagram of the removal function according to the embodiment of the present invention;

[0030] Figure 4 are three knife mark feature diagrams according to the embodiment of the present invention;

[0031] Figure 5 are the extended diffraction images corresponding to the ideal optical element according to the embodiment of the present invention, and the extended diffraction images corresponding to three different knife mark feature diagrams.

[0032] Reference numerals:

[0033] 1, image plane; 2, calculation starting plane; 3, parabolic reflecting surface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0035] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0036] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0037] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0038] The present invention will be described in detail below with reference to the drawings and in combination with embodiments.

[0039] As Figure 1 shown, the method for inducing deterministic polishing process parameters of the optical system index described in the embodiment of the present invention includes:

[0040] S1: Determine the structure of the optical system and determine the ideal optical elements in the optical system that need to control the mid-frequency error.

[0041] The optical system can be adaptively selected according to the actual situation, and can be an off-axis three-mirror system, a Gauss objective lens, a coaxial two-mirror system, etc. After determining the optical system, the ideal optical element that needs to control the mid-frequency error is determined according to the actual situation or research experience. For example, in an off-axis three-mirror optical system, the error of the primary mirror is mainly considered. It should be noted that the ideal optical element in the structure of the optical system is in a state without any error. When the surface of the ideal optical element is combined with the knife mark feature maps generated under different process parameters, an optical element with mid-frequency error can be obtained. After replacing the ideal optical element in the optical system with the optical element with mid-frequency error, it is the actual optical system.

[0042] S2: Calculate the knife mark feature maps generated by the ideal optical element determined in step S1 under different process parameters.

[0043] In some embodiments, the knife mark feature maps are calculated in step S2 by the following formula:

[0044] ;

[0045] Among them, represents the error feature map algorithm, represents the i-th process parameter cell array, represents the knife mark feature map generated by the element under the processing of the i-th process parameter cell array. The process parameter cell array is related to the removal function when processing the optical element, that is, the process parameter cell array exists in the process parameter space corresponding to the removal function and can be expressed as . It can be understood that the maximum number of groups of the process parameter cell array is the number of elements in the process parameter space and can be expressed as , represents the function for calculating the number of elements in the set. The processing technology for processing the optical element includes magnetorheological finishing, small grinding head polishing, ion beam polishing, etc. The process parameter cell array includes at least one processing parameter, such as the removal function RF, the processing dwell time dt, the processing angle θ between the flow direction of the magnetorheological fluid and the grating track direction, and the grating polishing track pitch h.

[0046] S3: Generate the optical element sagittal height maps corresponding to different process parameters according to the knife mark feature maps obtained in step S2.

[0047] In some embodiments, the knife mark feature maps are added to the surface equation of the ideal optical element to obtain the optical element sagittal height maps. It can be understood that the surface equation of the ideal optical element is respectively added to the knife mark feature maps corresponding to different process parameters to obtain the optical element sagittal height maps corresponding to different knife mark feature maps.

[0048] S4: Replace the ideal optical elements of the optical system in step S1 with the sagittal diagrams of different optical elements, and obtain the system evaluation indexes of the optical systems corresponding to the sagittal diagrams of different optical elements.

[0049] In some embodiments, perform optical imaging on the optical systems corresponding to the sagittal diagrams of different optical elements to obtain corresponding extended diffraction images.

[0050] Calculate the optical imaging system evaluation indexes of the corresponding optical systems based on different extended diffraction images.

[0051] The system evaluation indexes include but are not limited to the existing root mean square of the spot diagram, the amplitude modulation function, the clarity index of the extended diffraction image, and the composite evaluation indexes formed by the combination of various existing optical system imaging quality evaluation indexes. In a certain embodiment, the system evaluation index includes the clarity index of the extended diffraction image, and preferably the Brenner index is adopted.

[0052] It can be understood that in step S4, replace the ideal optical elements in the optical system with the sagittal diagrams of different optical elements, perform optical imaging on the optical systems corresponding to the sagittal diagrams of different optical elements to obtain corresponding extended diffraction images, and then calculate the Brenner indexes of different extended diffraction images. The higher the Brenner index, the better the clarity index of the extended diffraction image, that is, the smaller the influence of the error on the imaging quality, that is, the better the system evaluation index.

[0053] S5: Select the optimal system evaluation index obtained in step S4, and the corresponding process parameters are the optimal process parameters.

[0054] It can be understood that select the optimal Brenner index obtained in step S4, and the corresponding process parameters are the optimal process parameters.

[0055] To clearly illustrate the method for inducing deterministic polishing process parameters for the optical system indexes described in the embodiments of the present invention, an embodiment is provided.

[0056] Embodiment:

[0057] In this embodiment, the method for inducing deterministic polishing process parameters for the optical system indexes is based on the Zemax software, and specifically includes:

[0058] S1: Determine the structure of the optical system, and determine the ideal optical elements that need to control the mid-frequency error in the optical system.

[0059] In this embodiment, it is determined that the optical system to be analyzed is a single-element system, and this optical system is specifically a reflector, such as Figure 2As shown in the figure, the propagation process of light in this optical system includes: parallel light propagates from the calculation starting surface 2 and reaches the parabolic reflecting surface 3, and after reflection, it converges on the image surface 1 at the focus of the parabolic reflecting surface 3. The system evaluation index is obtained according to the imaging result at the image surface 1. It can be understood that the reflecting mirror is an ideal optical element that needs to control the mid-frequency error, and its surface equation S ( x, y ) is:

[0060] S(x,y)=-(x 2 +y 2 ) / 4f;

[0061] where f represents the focal length of the reflecting mirror. In this embodiment, f = 118.86 mm.

[0062] S2: Calculate the tool mark feature map generated by the ideal optical element determined in step S1 under different process parameters.

[0063] In this embodiment, step S2 calculates the tool mark feature map of the optical element through the following formula:

[0064] ;

[0065] where the error feature map algorithm adopts the error feature map algorithm in the paper "Tool mark prediction on the surface of large-aperture mirrors via magnetorheological finishing" published in the journal Optics Express. The process parameter cell array in the process parameter space includes the included angle process parameter space Θ where the machining angle θ is located, and the spacing process parameter space H where the grating polishing track spacing h is located. That is, the process parameter space can be expressed as:

[0066] ;

[0067] where represents the Cartesian product.

[0068] Correspondingly, each process parameter cell array P RF in the process parameter space K i includes the machining angle θ j and the grating polishing track spacing h q, j represents the number of machining angles, the total number of machining angles is J, q represents the number of grating polishing track spacings, and Q represents the total number of grating polishing track spacings. It can be understood that the process parameter cell array P i can be expressed as P i ={θ j , h r}, and there are J×Q process parameter cell arrays P RF in the process parameter space K i , that is, size(K RF ) = J×Q.

[0069] For the mirror in this embodiment, the included angle process parameter space Θ includes 1 machining angle θ j , which is 0°, that is, J = 1 and Θ = {0°}; the spacing process parameter space H includes 3 grating polishing track spacings h q , which are 0.5mm, 1.5mm, 2mm, 3mm respectively, that is, Q = 4 and H = {0.5mm, 1.5mm, 2mm, 3mm}, and at this time the process parameter space K RF contains 4 process parameter cell arrays P i , size(K RF ) = J×Q = 4, and 4 knife mark feature maps can be obtained correspondingly. The removal function for machining the mirror with the above process parameters is as Figure 3 shown, Figure 4 shows 4 knife mark feature maps, Figure 4 in which (a) shows the knife mark feature map corresponding to h1 = 0.5mm, Figure 4 in which (b) shows the knife mark feature map corresponding to h2 = 1.5mm, and Figure 4 in which (c) shows the knife mark feature map corresponding to h3 = 2mm, and Figure 4 in which (d) shows the knife mark feature map corresponding to h4 = 3mm.

[0070] S3: Generate the optical element sagittal height maps corresponding to different process parameters according to the knife mark feature maps obtained in step S2.

[0071] In this embodiment, the knife mark feature map and the surface equation of the ideal optical element are both written as grid files in the way of Grid Sag, and the surface equation in the form of a grid file is added to the knife mark feature map in the form of a grid file corresponding to different process parameters respectively, and the corresponding grid file is the optical element sagittal height map corresponding to different process parameters. Among them, forming a grid file using Grid Sag is a prior art, and this embodiment will not elaborate.

[0072] S4: Replace the ideal optical elements of the optical system in step S1 with the sagittal diagrams of different optical elements, and obtain the system evaluation indexes of the optical systems corresponding to the sagittal diagrams of different optical elements.

[0073] In this embodiment, replace the ideal optical elements in the optical system with the sagittal diagrams of different optical elements, perform optical imaging on the optical systems corresponding to the sagittal diagrams of different optical elements, use the functions built in the Zemax software to obtain the corresponding extended diffraction images, and then calculate the Brenner indexes of different extended diffraction images.

[0074] In this embodiment, compare the extended diffraction images corresponding to different knife mark feature diagrams. Specifically, in this embodiment, at a processing angle of 0°, compare the extended diffraction images obtained under the process parameters of different grating polishing track spacings, as Figure 5 shown, where Figure 5 (a) in shows the extended diffraction image corresponding to a grating polishing track spacing h1 = 0.5 mm, and its corresponding Brenner index is 16.0871; Figure 5 (b) in shows the extended diffraction image corresponding to a grating polishing track spacing h2 = 1.5 mm, and its corresponding Brenner index is 16.0874; Figure 5 (c) in shows the extended diffraction image corresponding to a grating polishing track spacing h3 = 2 mm, and its corresponding Brenner index is 14.6302; Figure 5 (d) in shows the extended diffraction image corresponding to a grating polishing track spacing h4 = 3 mm, and its Brenner index is 15.9013.

[0075] S5: Select the optimal system evaluation index obtained in step S4, and its corresponding process parameters are the optimal process parameters.

[0076] Combined with Figure 5 and the Brenner index, it can be obtained that for the parabolic surface of the mirror, at a processing angle of 0°, the extended diffraction images corresponding to a polishing track spacing of 0.5 mm and 1.5 mm are clearer and are the optional optimal parameters. Considering the processing angle, a smaller track spacing means more processing data, which will increase the data processing time. When the influence on the imaging quality is almost the same, the process parameters with a larger track spacing should be selected, that is, a grating polishing track spacing of 1.5 m is the optimal parameter.

[0077] It should be understood that various forms of the flow shown above can be used, steps can be reordered, added or deleted. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially or in a different order, as long as the desired results of the technical solutions disclosed in the present invention can be achieved, and no limitations are imposed herein.

[0078] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for inducing deterministic polishing process parameters for optical system indicators, characterized in that, Including: S1: Determine the structure of the optical system and identify the ideal optical elements in the optical system that require control of the intermediate frequency error; S2: Calculate the tool mark characteristic diagrams generated by the ideal optical elements determined in step S1 under different process parameters; S3: Generate the optical element sagittal height diagrams corresponding to different process parameters based on the tool mark characteristic diagrams obtained in step S2; S4: Replace the ideal optical elements of the optical system in step S1 with different optical element sagittal height diagrams and obtain the system evaluation indexes of the optical systems corresponding to different optical element sagittal height diagrams; S5: Select the optimal system evaluation index obtained in step S4, and the corresponding process parameter is the optimal process parameter.

2. The method for inducing deterministic polishing process parameters according to the optical system index described in claim 1, wherein In step S2, calculate the tool mark characteristic diagram by the following formula: ； Among them, represents the error feature map algorithm, represents the i-th process parameter cell array, represents the tool mark feature map generated by the ideal optical element under the processing of the i-th process parameter cell array.

3. The method for inducing deterministic polishing process parameters according to the optical system index described in claim 1, wherein In step S3, add the tool mark characteristic diagram and the surface equation of the ideal optical element to obtain the optical element sagittal height diagram.

4. The method for inducing deterministic polishing process parameters according to the optical system index described in claim 1, characterized in that, In step S4: Perform optical imaging on the optical systems corresponding to different optical element sagittal height diagrams to obtain the corresponding extended diffraction images; Calculate the system evaluation indexes of the corresponding optical systems based on different extended diffraction images.

5. The method for inducing deterministic polishing process parameters according to the optical system index described in claim 4, characterized in that, The system evaluation index includes the clarity index of the extended diffraction image.

6. The method for inducing deterministic polishing process parameters according to the optical system index described in claim 5, characterized in that, The clarity index includes the Brenner index.

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