阅读说明：本技术 一种平面光学元件及其加工方法 (Planar optical element and processing method thereof ) 是由 朱衡 吴迪龙 鲍振军 周衡 李智钢 蔡红梅 鄢定尧 于 2019-11-06 设计创作，主要内容包括：本申请公开了一种平面光学元件及其加工方法,包括研磨待加工平面光学元件的第一表面,使研磨后第一表面的反射面形误差数据小于第一面形误差阈值,得到第一平面光学元件；抛光研磨后第一表面,使抛光后第一表面的反射面形误差数据小于第二面形误差阈值,得到第二平面光学元件；研磨第二平面光学元件的第二表面,使研磨后第二平面光学元件的等厚误差值小于厚度误差阈值,得到第三平面光学元件,其中,第二表面与第一表面相对；抛光第三平面光学元件的第一表面和第二表面,使抛光后第三平面光学元件的第一等厚干涉条纹平均间距大于间距阈值,得到平面光学元件。该加工方法使平面光学元件平行度加工精度得到提高。(The application discloses a planar optical element and a processing method thereof, comprising the steps of grinding a first surface of the planar optical element to be processed, and enabling reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value to obtain a first planar optical element; polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element; grinding a second surface of the second planar optical element to enable the equal-thickness error value of the ground second planar optical element to be smaller than the thickness error threshold value, and obtaining a third planar optical element, wherein the second surface is opposite to the first surface; and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, and obtaining the planar optical element. The processing method improves the processing precision of the parallelism of the plane optical element.)

1. A method of processing a planar optical element, comprising:

grinding the first surface of the planar optical element to be processed to enable the reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value, and obtaining a first planar optical element;

polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element;

grinding a second surface of the second planar optical element to enable the equal thickness error value of the ground second planar optical element to be smaller than a thickness error threshold value, and obtaining a third planar optical element, wherein the second surface is opposite to the first surface;

and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, so as to obtain the planar optical element.

2. A method for processing a planar optical element according to claim 1, further comprising, after obtaining the planar optical element:

polishing the first surface or the second surface of the planar optical element, and measuring the transmission wavefront error and the average distance of the second equal-thickness interference fringes of the polished planar optical element;

judging whether the transmitted wavefront error is less than or equal to a transmitted wavefront threshold value and whether the average distance of the second equal-thickness interference fringes is greater than the distance threshold value;

if not, polishing and correcting by using a sub-aperture polishing and removing function according to a preset processing path until the transmission wavefront error is less than or equal to the transmission wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold, and obtaining the reprocessed planar optical element.

3. A method for processing a planar optical element as set forth in claim 2, wherein said predetermined processing path is any one of a raster type processing path, a spiral type processing path and a random type processing path.

4. A method of processing a planar optical element according to any one of claims 1 to 3, wherein said polishing said ground first surface comprises:

and polishing the ground first surface by adopting a special polishing pad polishing technology.

5. The planar optical element processing method as set forth in claim 4, wherein said polishing the first surface and the second surface of the third planar optical element comprises:

and polishing the first surface and the second surface of the third planar optical element by using a special polishing pad polishing technology.

6. The method for processing a planar optical element according to claim 5, wherein a measuring wavelength of the planar interferometer is 632.8nm when measuring the average pitch of the first equal thickness interference fringes.

7. A method of processing a planar optical element as set forth in claim 6, wherein said grinding the first surface of the planar optical element to be processed comprises:

and grinding the first surface of the planar optical element to be processed in a graded grinding mode.

8. A method of processing a planar optical element as set forth in claim 7, wherein said grinding the first surface of the planar optical element to be processed comprises:

the first surface of the planar optical element to be machined is ground with a boron carbide abrasive.

9. A planar optical element, characterized in that the planar optical element is obtained by the method for processing a planar optical element according to any one of claims 1 to 8.

Technical Field

The present disclosure relates to the field of optical element processing technologies, and in particular, to a planar optical element and a processing method thereof.

Background

Sapphire is a common planar optical element, and sapphire is used as an infrared window material due to excellent optical, mechanical, chemical and electrical properties, particularly high infrared transmittance and the like. The sapphire planar window element mainly plays a role of an optical observation window in an application device and has the characteristics of large overall dimension, high parallelism index requirement, high material hardness and the like.

At present, a high-speed double-side polishing method is mainly adopted in a processing method of a plane optical element, the surface roughness index of the processed element is high, and for high-precision processing of a large-caliber plane window element, the high-speed double-side polishing method causes the parallelism processing precision to be insufficient, and can not meet the comprehensive technical index requirements of modern military equipment on the plane optical element.

Therefore, how to provide a method for improving the parallelism processing precision is a technical problem to be solved urgently by those skilled in the art.

Disclosure of Invention

The invention aims to provide a planar optical element and a processing method thereof, which are used for improving the parallelism processing precision of the planar optical element.

In order to solve the above technical problem, the present application provides a method for processing a planar optical element, including:

grinding the first surface of the planar optical element to be processed to enable the reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value, and obtaining a first planar optical element;

polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element;

grinding a second surface of the second planar optical element to enable the equal thickness error value of the ground second planar optical element to be smaller than a thickness error threshold value, and obtaining a third planar optical element, wherein the second surface is opposite to the first surface;

and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, so as to obtain the planar optical element.

Optionally, after obtaining the planar optical element, the method further includes:

polishing the first surface or the second surface of the planar optical element, and measuring the transmission wavefront error and the average distance of the second equal-thickness interference fringes of the polished planar optical element;

judging whether the transmitted wavefront error is less than or equal to a transmitted wavefront threshold value and whether the average distance of the second equal-thickness interference fringes is greater than the distance threshold value;

if not, polishing and correcting by using a sub-aperture polishing and removing function according to a preset processing path until the transmission wavefront error is less than or equal to the transmission wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold, and obtaining the reprocessed planar optical element.

Optionally, the preset machining path is any one of a grating machining path, a spiral machining path and a random machining path.

Optionally, the polishing the ground first surface comprises:

and polishing the ground first surface by adopting a special polishing pad polishing technology.

Optionally, the polishing the first and second surfaces of the third planar optical element comprises:

and polishing the first surface and the second surface of the third planar optical element by using a special polishing pad polishing technology.

Optionally, when measuring the average distance between the first equal-thickness interference fringes, the measurement wavelength of the planar interferometer is 632.8 nm.

Optionally, the grinding the first surface of the optical element to be processed includes:

and grinding the first surface of the planar optical element to be processed in a graded grinding mode.

Optionally, the grinding the first surface of the optical element to be processed includes:

the first surface of the planar optical element to be machined is ground with a boron carbide abrasive.

The application also provides a planar optical element obtained by any one of the planar optical element processing methods.

The application provides a planar optical element processing method, which comprises the following steps: grinding the first surface of the planar optical element to be processed to enable the reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value, and obtaining a first planar optical element; polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element; grinding a second surface of the second planar optical element to enable the equal thickness error value of the ground second planar optical element to be smaller than a thickness error threshold value, and obtaining a third planar optical element, wherein the second surface is opposite to the first surface; and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, so as to obtain the planar optical element.

Therefore, in the plane optical element processing method, the first surface of the plane optical element to be processed is ground until the reflection surface shape error data of the first surface is smaller than the first surface shape error threshold, then the first surface is polished until the reflection wave front value is smaller than the second surface shape error threshold, the second surface of the plane optical element is ground, so that the equal thickness error value of the first surface and the second surface of the plane optical element is smaller than the thickness error threshold, the first surface and the second surface are further polished, the average distance between the first equal thickness interference fringes of the plane optical element is larger than the distance threshold, and the parallelism processing precision of the plane optical element is improved. The present application further provides a planar optical element having the above-mentioned advantages.

Drawings

For a clearer explanation of the embodiments or technical solutions of the prior art of the present application, the drawings needed for the description of the embodiments or prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a flow chart of a method for processing a planar optical element according to the present disclosure;

fig. 2 is a flow chart of another method for processing a planar optical element according to the present application.

Detailed Description

In order that those skilled in the art will better understand the disclosure, the following detailed description will be given with reference to the accompanying drawings. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

As described in the background section, currently, the processing method of the planar optical element mainly adopts a high-speed double-side polishing method, the surface roughness index of the processed element is high, and for the high-precision processing of the large-aperture planar window element, the high-speed double-side polishing method makes the parallelism processing precision insufficient, and cannot meet the comprehensive technical index requirements of modern military equipment on the element.

In view of the above, the present application provides a method for processing a planar optical element, please refer to fig. 1, in which fig. 1 is a flowchart of the method for processing a planar optical element provided in the present application, the method includes:

step S101: and grinding the first surface of the planar optical element to be processed to enable the reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value, so as to obtain the first planar optical element.

Specifically, a first surface of the planar optical element to be processed is ground, reflection surface shape error data of the ground first surface is measured by a three-coordinate measuring machine, whether the reflection surface shape error data is smaller than a first surface shape error threshold value or not is judged, and if not, the grinding is continued until the reflection surface shape error data is smaller than the first surface shape error threshold value. Wherein, the first profile error threshold can be set to 5 μm, which is adjusted according to actual conditions.

In the grinding process, the surface-shaped edge ruler is used for testing the first surface, and grinding processing parameters such as the planeness of the grinding disc, the rotating speed of the swing frame and the like are optimized according to the test result, and the specific parameter optimization process is well known by the technical personnel in the field and is not described in detail herein.

It should be noted that the first surface is an upper surface or a lower surface of the planar optical element to be processed, and is not particularly limited in this embodiment. Generally, the upper surface and the lower surface of the planar optical element to be processed are circular, but the present embodiment is not limited to this specifically, and may be rectangular, square, or the like.

Step S102: and polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element.

Specifically, the ground first surface is polished by a high-precision uniaxial plane machine tool, reflection surface shape error data of the polished first surface is detected by a plane interferometer, whether the reflection surface shape error data is smaller than a second surface shape error threshold value or not is judged, if not, polishing is continued until the reflection surface shape error data of the polished first surface is smaller than the second surface shape error threshold value. The second surface shape error threshold may be set to 2 λ, which is adjusted according to actual conditions, where λ is the detection wavelength of the planar interferometer.

Step S103: and grinding a second surface of the second planar optical element to enable the equal thickness error value of the ground second planar optical element to be smaller than a thickness error threshold value, so as to obtain a third planar optical element, wherein the second surface is opposite to the first surface.

Specifically, a single-axis grinding and polishing machine tool is used for grinding the second surface of the second planar optical element, the first surface is used as a standard surface, an equal thickness measuring device is used for carrying out equal thickness measurement, whether the equal thickness error value of the ground second planar optical element is smaller than a thickness error threshold value or not is judged, if not, the second surface is continuously ground until the equal thickness error value of the ground second planar optical element is smaller than the thickness error threshold value. Wherein the thickness error threshold may be set to 0.006 mm.

Furthermore, when the uniform thickness measurement is performed, eight positions of the edge of the second planar optical element after grinding can be selected for measurement.

Step S104: and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, so as to obtain the planar optical element.

Specifically, a single-axis precision polishing machine is used for polishing the first surface and the second surface of the third planar optical element, a planar interferometer is used for measuring the parallelism of the polished third planar optical element, whether the average distance between the first equal-thickness interference fringes representing the parallelism is larger than a distance threshold value or not is judged, and if not, the first surface and the second surface are continuously polished until the average distance between the first equal-thickness interference fringes is larger than the distance threshold value. The distance threshold may be set to 12.3 mm, which may be adjusted according to actual situations.

In the polishing process, the average distance of the first equal-thickness interference fringes is larger than a distance threshold value by optimizing various parameters such as a balance weight parameter, the rotating speed of a single-shaft machine, the swinging speed of a swing frame, the rotating speed of a third plane optical element and the like.

It should be noted that, in this embodiment, the aperture of the planar interferometer is not specifically limited, as long as the aperture is larger than the clear aperture of the measured planar optical element.

In the planar optical element processing method in this embodiment, the first surface of the planar optical element to be processed is ground until the reflection surface shape error data of the first surface is smaller than the first surface shape error threshold, the first surface is then polished until the pre-reflection wave value is smaller than the second surface shape error threshold, the second surface of the planar optical element is ground, so that the equal thickness error value between the first surface and the second surface of the planar optical element is smaller than the thickness error threshold, the first surface and the second surface are further polished, so that the average distance between the first equal thickness interference fringes of the planar optical element is larger than the distance threshold, so that the parallelism processing accuracy of the planar optical element is improved, and the parallelism is not greater than 3 ".

Referring to fig. 2, fig. 2 is a flowchart illustrating another method for processing a planar optical element according to an embodiment of the present disclosure, the method including:

step S201: and grinding the first surface of the planar optical element to be processed to enable the reflection surface shape error data of the ground first surface to be smaller than a first surface shape error threshold value, so as to obtain the first planar optical element.

Step S202: and polishing the ground first surface to enable the reflection surface shape error data of the polished first surface to be smaller than a second surface shape error threshold value, and obtaining a second plane optical element.

Step S203: and grinding a second surface of the second planar optical element to enable the equal thickness error value of the ground second planar optical element to be smaller than a thickness error threshold value, so as to obtain a third planar optical element, wherein the second surface is opposite to the first surface.

Step S204: and polishing the first surface and the second surface of the third planar optical element to enable the average distance of the first equal-thickness interference fringes of the polished third planar optical element to be larger than a distance threshold value, so as to obtain the planar optical element.

Step S205: polishing the first surface or the second surface of the planar optical element, and measuring the transmitted wavefront error and the average distance of the second equal-thickness interference fringes of the polished planar optical element.

Specifically, a low-defect polishing process is adopted, a numerical control grinding and polishing machine is used for polishing the first surface or the second surface of the planar optical element, and the transmission wavefront error and the second equal-thickness interference fringe average distance of the polished planar optical element are measured.

Step S206: and judging whether the transmitted wavefront error is smaller than a transmitted wavefront threshold value or not and whether the average distance of the second equal-thickness interference fringes is larger than the distance threshold value or not.

Step S207: if not, polishing and correcting by using a sub-aperture polishing and removing function according to a preset processing path until the transmission wavefront error is less than or equal to the transmission wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold, and obtaining the reprocessed planar optical element.

Specifically, when the transmitted wavefront error is not equal to or less than the transmitted wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold, the sub-aperture polishing removal function is used for polishing and correcting the transmitted wavefront, the single residence time is T, whether the transmitted wavefront error is equal to or less than the transmitted wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold is judged, if not, the polishing is continued until the transmitted wavefront error is equal to or less than the transmitted wavefront threshold and the average distance of the second equal-thickness interference fringes is greater than the distance threshold. Wherein the transmitted wavefront threshold may be set to λ/2; the single residence time is obtained by deconvolution calculation through surface shape error data and a sub-aperture polishing processing removal function.

Preferably, the sub-aperture polishing removal function is obtained by an experimental method, and the processing removal function obtained by the experimental method is closest to the actual processing situation, so that the convergence efficiency of the transmission wavefront and the surface shape error data can be improved. The specific experimental procedures are well known to those skilled in the art and will not be described in detail herein.

It can be understood that if the transmitted wavefront error is less than or equal to the transmitted wavefront threshold and the average spacing of the second equal-thickness interference fringes is greater than the spacing threshold, the polishing is stopped and the processing process is ended.

It should be noted that, in the present embodiment, the preset processing path is not specifically limited, and may be determined as the case may be. For example, the preset machining path may be any one of a raster type machining path, a spiral machining path, and a random machining path.

In this embodiment, the first surface or the second surface of the planar optical element is polished to make the transmission wavefront error of the obtained reworked planar optical element less than or equal to the transmission wavefront threshold and the average distance between the second equal-thickness interference fringes greater than the distance threshold, so that not only the parallelism accuracy of the reworked planar optical element is improved, but also the accuracy of the transmission wavefront is improved

Preferably, in one embodiment of the present application, the polishing the ground first surface includes:

and polishing the ground first surface by adopting a special polishing pad polishing technology, so that the polished first surface has high finish, small roughness and good surface shape retention.

On the basis of the above-described embodiments, in an embodiment of the present application, the polishing the first surface and the second surface of the third planar optical element includes:

and polishing the first surface and the second surface of the third planar optical element by using a special polishing pad polishing technology.

In the processing method in this embodiment, the polishing technologies of the first surface and the second surface of the third planar optical element after polishing and grinding are both polished by using a special polishing pad polishing technology, so that the surface of the obtained planar optical element has high smoothness and small roughness, the index Ra of the surface roughness is less than or equal to 0.8 nm, the root mean square value RMS is less than or equal to lambda/10, and the quality of surface defects meets the national standard iv-level requirement.

On the basis of the above embodiments, in one embodiment of the present application, when the average pitch of the first equal-thickness interference fringes is measured, the measurement wavelength of the planar interferometer is 632.8nm, but the present application does not specifically limit this, and in other embodiments of the present application, the measurement wavelength of the planar interferometer is 1053 nm.

Preferably, in an embodiment of the present application, the grinding the first surface of the planar optical element to be processed includes:

the first surface of the optical element with the plane to be processed is ground in a grading grinding mode, so that the grinding efficiency can be accelerated.

Optionally, the first surface of the planar optical element to be processed is ground by using a boron carbide abrasive, and the hardness of the boron carbide abrasive is super-hard and has better processing randomness with the hardness of the planar optical element to be processed.

The processing method in the present application is further explained by taking the example that the optical element of the plane to be processed is a sapphire window element to be processed with the external dimension of phi 200mm × 10mm, and the initial state of the sapphire window element to be processed is a blank.

Step one, carrying out graded grinding on the upper surface of a sapphire window element to be processed by adopting boron carbide grinding materials with specifications of W28, W14 and W7, wherein the removal amount of each grinding material of W28, W14 and W7 is not less than 0.05mm, 0.03mm and 0.02mm respectively, optimizing grinding processing parameters according to test data of a surface-shaped knife edge ruler by utilizing a boron carbide grinding material grinding process with specifications of W28 and W14, carrying out single-side reflection fine grinding surface shape measurement on the upper surface of the sapphire window to be processed by utilizing a three-coordinate measuring machine at the last stage of grinding by utilizing the W7 boron carbide grinding material with specification, and carrying out fine grinding reflection surface shape error correction according to a measurement result until the reflection surface shape error data of the upper surface is less than 5 mu m;

polishing the upper surface of the sapphire element to be processed by using a special polishing pad polishing technology and a high-precision uniaxial plane machine tool, quickly polishing surface blowholes and correcting reflection surface shape errors, and detecting reflection surface shape error data H (x, y) of the polished upper surface by using a 600 mm-caliber plane interferometer and a wavelength lambda of 632.8 nanometers in the detection process until the reflection surface shape error data H (x, y) are smaller than 2 lambda;

grinding the lower surface of the sapphire element to be processed by using a single-shaft grinding and polishing machine tool, primarily correcting the parallelism index, measuring the equal thickness index of the grinding process by using a planar optical element equal thickness measuring device in the processing process, taking eight thickness measurement values at the edge as a standard surface to perform equal thickness measurement, optimally designing the balance weight parameters according to equal thickness distribution in the processing process according to the technical index requirement that the parallelism of the sapphire element to be processed is less than 3', and continuously approaching the thickness error threshold until the equal thickness error value is processed to be less than 0.006 mm;

polishing the upper surface and the lower surface of the sapphire element to be processed by using a special polishing pad polishing technology and a single-shaft precision polishing machine, detecting the parallelism difference of the polished two surfaces by using a 600 mm-caliber plane interferometer, analyzing the parallelism according to the shape distribution of the equal-thickness fringes, and adjusting the balance weight parameters and other processing key parameters in the polishing process to polish and correct the surface parallelism until the number of the equal-thickness fringes is 16 and the distance between the fringes is not less than 12 mm;

step five, adopting a polishing process of a low-defect superhard sapphire material, utilizing a three-axis numerical control grinding and polishing machine to process the upper surface of the sapphire element to be processed for precise control of transmitted wavefront, and adopting a 600 mm-caliber plane interferometer to detect the transmitted wavefront error H after polishing_t(x, y) and surface parallelism difference, selecting a proper sub-aperture polishing and removing function R (x, y) to perform polishing correction of the transmission wavefront according to the fringe distribution condition of the transmission wavefront and the surface parallelism difference, wherein the single dwell time is T (x, y), the processing path adopts a grating type processing path, the parallelism index is not damaged in the processing process, and the processing of the sapphire element to be processed is completed through eight times of controlled polishing, so that the sapphire element is obtained. The sapphire element had a parallelism of 2.4", the number of interference fringes of equal thickness within 190mm of the clear aperture was 13, and the transmitted wavefront PV was 0.35 λ (λ 632.8 nm).

The application also provides a planar optical element obtained by the processing method of the planar optical element in any one of the embodiments disclosed above.

In the planar optical element in this embodiment, the first surface of the planar optical element to be processed is ground until the reflection surface shape error data of the first surface is smaller than the first surface shape error threshold, the first surface is polished until the pre-reflection wave value is smaller than the second surface shape error threshold, the second surface of the planar optical element is ground, so that the equal thickness error value of the first surface and the second surface of the planar optical element is smaller than the thickness error threshold, the first surface and the second surface are further polished, the average distance between the first equal thickness interference fringes of the planar optical element is larger than the distance threshold, and the accuracy of the parallelism of the planar optical element is improved.

The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same or similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The planar optical element and the processing method thereof provided by the present application are described in detail above. The principles and embodiments of the present application are explained herein using specific examples, which are provided only to help understand the method and the core idea of the present application. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications also fall within the scope of the claims of the present application.