Preparation method of grating

Abstract

The invention provides a preparation method of a grating, and the preparation method comprises the steps: alternately placing grating sheets and isolation assemblies in a grating preparation chamber, so as to form a stacked structure in the grating preparation chamber; wherein the isolation assembly is suitable for ensuring that two adjacent grating sheets are spaced at the same distance; the grating sheet and the isolation assembly are kept fixed in the grating preparation chamber; negative pressure is formed in the grating preparation chamber; under the action of negative pressure, the colloid enters the grating preparation chamber and fills a gap between the two adjacent grating sheets so as to bond the two adjacent grating sheets; and curing the colloid, wherein the cured colloid allows the light beam to pass through. The embodiment of the invention provides the preparation method of the grating, which is low in process cost, simple in process flow, short in production period and capable of realizing large-scale production.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to a method for preparing a grating, and in particular, to a method for preparing a grating used in an X-ray imaging device. Background Art

[0002] At present, the preparation of gratings used in X-ray imaging equipment mainly relies on the LIGA (Lithographie, Galvanoformung, Abformung) process. The LIGA process is a microfabrication technology that combines lithography, electroforming and injection molding, and is suitable for manufacturing micron-scale devices with three-dimensional structures. In the preparation of the grating, the LIGA process forms the required pattern on the substrate through a lithography process, and then deposits metal (such as gold) on the pattern through electroforming technology to form a grating structure with a high aspect ratio. Finally, the metal grating structure is transferred to other materials through injection molding or other molding techniques to manufacture X-ray imaging gratings. However, the LIGA process has some significant disadvantages in the preparation of gratings: First, the LIGA process requires high material costs: The LIGA process requires the use of precious metals (such as gold) for electroforming, which leads to a significant increase in manufacturing costs. Especially for gratings that need to be prepared over a large area, material costs have become an issue that cannot be ignored. Second, the LIGA process requires a complex process flow. The LIGA process includes multiple steps such as lithography, electroforming and injection molding, which increases the complexity of the process and the production cycle. LIGA process, because LIGA process requires the use of lithography machines and electroforming equipment. The cost of these equipment is relatively high. Fourth, LIGA process is mainly suitable for the preparation of small batches and devices. For gratings that need to be mass-produced or applied in different fields, LIGA process may not meet the needs. Fifth, some chemical materials used in LIGA process may cause environmental pollution. At the same time, the treatment and recycling of metal waste is also a problem that needs to be solved.

[0003] In summary, the existing LIGA process has many deficiencies in the preparation of gratings, so it is necessary to develop a new grating preparation method. Summary of the invention

[0004] In view of this, at least one embodiment of the present invention provides a method for preparing a grating capable of improving the structural accuracy of the prepared grating and ensuring the stability and reliability of the grating performance.

[0005] As a first aspect of the present invention, the method for preparing the grating comprises:

[0006] Placing grating sheets and isolation components alternately in a grating preparation chamber to form a stacked structure in the grating preparation chamber; wherein the isolation components are adapted to ensure that two adjacent grating sheets are spaced at the same distance;

[0007] Keeping the grating sheet and the isolation assembly fixed in the grating preparation chamber;

[0008] forming a negative pressure in the grating preparation chamber;

[0009] Under the action of the negative pressure, the colloid enters the grating preparation chamber and fills into the gap between two adjacent grating sheets to bond the two adjacent grating sheets; and

[0010] The colloid is cured, and the cured colloid allows the light beam to pass through.

[0011] According to an embodiment of the present invention, the grating preparation chamber comprises a body and a cover;

[0012] The body portion forms a cavity with an opening, and the cover body is sealingly disposed on the opening;

[0013] The cover is configured to be movable along a direction perpendicular to the grating sheet;

[0014] Keeping the grating sheet and the isolation assembly fixed in the grating preparation chamber comprises:

[0015] The cover is driven to apply pressure to the nearest grating sheet, so that the stacking structure is pressed between the cover and the bottom surface of the main body.

[0016] According to an embodiment of the present invention, a colloid inlet is provided on the main body, and the colloid inlet faces the gap of the stacking structure.

[0017] According to an embodiment of the present invention, before alternately stacking the grating sheets and the isolation components and placing them in the grating preparation chamber, the method further comprises:

[0018] Determining the distance between two adjacent grating plates of the grating according to a preset diffraction order; and

[0019] The thickness of the isolation component is determined according to the distance between the two adjacent grating sheets.

[0020] According to an embodiment of the present invention, the grating is suitable for an imaging device for imaging X-rays, and the colloid is configured to allow the X-rays to pass through.

[0021] According to an embodiment of the present invention, after the preparation of the grating is completed, the preparation method further includes:

[0022] The grating is cut according to a preset aspect ratio.

[0023] According to an embodiment of the present invention, an observation window is provided on the grating preparation chamber to facilitate real-time monitoring of the filling state of the colloid.

[0024] According to an embodiment of the present invention, an anti-stick coating is coated on the inner wall of the grating preparation chamber, so that the grating can be separated from the grating preparation chamber after the grating preparation is completed.

[0025] According to an embodiment of the present invention, solidifying the colloid comprises:

[0026] The grating preparation chamber filled with the colloid is kept below the curing temperature of the colloid to cure the colloid.

[0027] According to an embodiment of the present invention, after a negative pressure is formed in the grating preparation chamber, the vacuum degree in the grating preparation chamber is less than 10Pa.

[0028] According to the preparation method provided by the embodiment of the present invention, the negative pressure glue injection process is adopted, that is, the colloid is injected between the grating sheets stacked at equal intervals under negative pressure conditions, which can achieve uniform filling of the colloid, and the grating structure formed after curing has high precision. The colloid used in the negative pressure glue injection process usually has excellent physical and chemical properties, such as high stability, high light transmittance, weather resistance, etc. These characteristics enable the glue to form a strong and stable structure after curing, protecting the grating from erosion by the external environment. Therefore, the grating structure prepared by the method provided by the embodiment of the present invention is stable, not easily affected by the external environment (such as temperature and humidity), and can ensure the stability and reliability of the grating performance.

[0029] According to the negative pressure glue injection process adopted in the embodiment of the present invention, a vacuum pump is used to evacuate the grating preparation chamber to a vacuum state, and then the colloid is used to evenly fill the gaps between the grating sheets using the pressure difference. This process is relatively fast and helps to improve the preparation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0031] Figure 1 A schematic diagram of a grating preparation device provided according to an embodiment of the present invention is shown.

[0032] Figure 2 A flow chart of a method for preparing a grating according to an embodiment of the present invention is shown.

[0033] Figure 3 A schematic diagram of a stacking structure provided according to an embodiment of the present invention is shown.

[0034] Figure 4A top view of a stacking structure provided according to an embodiment of the present invention is shown.

[0035] Figure 5 A cross-sectional view of a grating preparation chamber provided according to an embodiment of the present invention is shown.

[0036] Description of Reference Numerals

[0037] 1 Grating

[0038] 2 Isolation Components

[0039] 3. Grating preparation room

[0040] 31 body part

[0041] 32 Cover

[0042] 4 Vacuum pump

[0043] 5First Valve

[0044] 6 plastic barrels

[0045] 7. Second valve

[0046] 8 Driving mechanism

[0047] 81 Power Unit

[0048] 82 driving rod DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0050] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0051] All terms used herein, including technical and scientific terms, have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0052] Figure 1 A schematic diagram of a grating preparation device provided according to an embodiment of the present invention is shown.

[0053] Figure 2 A flow chart of a method for preparing a grating according to an embodiment of the present invention is shown.

[0054] Figure 3A front view of a stacking structure provided according to an embodiment of the present invention is shown.

[0055] Figure 4 A top view of a stacking structure provided according to an embodiment of the present invention is shown.

[0056] According to an embodiment of the present invention, Figure 1-Figure 4 As shown, a method for preparing a grating applied to an X-ray imaging device is provided, including operations S1 to S5.

[0057] In operation S1, the grating sheets 1 and the isolation components 2 are alternately placed in the grating preparation chamber 3 to form a stacked structure (such as Figure 3 and Figure 4 As shown), the isolation component 2 is suitable for ensuring that the distance between two adjacent grating sheets 1 is the same.

[0058] According to an embodiment of the present invention, the grating sheets 1 and the isolation components 2 are placed alternately in the grating preparation chamber 3 to form a stacked structure, wherein the grating sheets 1 and the isolation components 2 are arranged alternately with each other and together form the basis of the grating. Figure 3 As shown, the grating plates 1 are located at the top and the bottom. The isolation component 2 is placed between two adjacent grating plates 1, and its main function is to ensure that the two grating plates 1 maintain the same distance. The distance between the two grating plates 1 is equal to the thickness of the isolation component 2. This distance is crucial to the overall performance and function of the grating, and it can affect optical phenomena such as light propagation, diffraction and interference. By alternately placing the grating plates 1 and the isolation components 2 and forming a stacking structure in the grating preparation chamber 3, the spacing distance between the grating plates 1 can be precisely controlled to ensure that the grating has the expected optical performance. This stacking structure can also provide additional stability and support, which helps prevent the grating plates 1 from being deformed or damaged during preparation or use. In addition, in order to ensure that the two adjacent grating plates 1 are spaced at the same distance, it is necessary to ensure that each isolation component 2 has the same thickness and each isolation component 2 has a flat surface.

[0059] In operation S2, the grating plate 1 and the isolation assembly 2 are kept fixed in the grating preparation chamber 3. The precise position of the grating plate 1 and the isolation assembly 2 is critical to the overall performance and function of the grating. If the grating plate 1 and the isolation assembly 2 move or misalign during the preparation process, the optical performance of the grating may be degraded and fail to meet specific application requirements.

[0060] In operation S3, negative pressure is formed in the grating preparation chamber 3. This operation can be achieved by using a vacuum pump 4. The grating preparation chamber 3 is connected to the vacuum pump 4 through a first pipe, and a first valve 5 is provided on the first pipe to control the gas flow between the vacuum pump 4 and the grating preparation chamber 3. When vacuuming is required, the first valve 5 is opened to start the vacuum pump 4; when vacuuming is not required or the vacuum state needs to be maintained, the first valve 5 is closed to isolate the vacuum pump 4 from the grating preparation chamber 1.

[0061] In operation S4 , under the action of negative pressure, the colloid enters the grating preparation chamber 1 and fills into the gap between two adjacent grating sheets 1 to bond the two adjacent grating sheets 1 .

[0062] According to an embodiment of the present invention, the grating preparation chamber 3 is connected to the glue barrel 6 through a second pipe, and a second valve 7 is provided on the second pipe. After the second valve 7 is opened, the colloid in the glue barrel 6 is filled into the gaps between the grating sheets 1 under the action of negative pressure.

[0063] According to the embodiment of the present invention, by using the negative pressure, the colloid can be more easily sucked into the grating preparation chamber 3, and flow along the pressure gradient to fill the gaps between the grating sheets 1. Using the negative pressure to allow the colloid to fill the gaps between the grating sheets 1 helps to maintain the cleanliness and stability of the grating preparation chamber 3, thereby improving the preparation quality of the grating.

[0064] In operation S5 , the colloid is cured, and the cured colloid allows the light beam to pass through.

[0065] According to the preparation method provided by the embodiment of the present invention, a negative pressure glue injection process is adopted, that is, a colloid is injected between the grating sheets 1 stacked at equal intervals under negative pressure conditions, so that uniform filling of the colloid can be achieved, and the grating structure formed after curing has high precision. The colloid used in the negative pressure glue injection process usually has excellent physical and chemical properties, such as high stability, high light transmittance, weather resistance, etc. These characteristics enable the glue to form a strong and stable structure after curing, protecting the grating from erosion by the external environment. Therefore, the grating structure prepared by the method provided by the embodiment of the present invention is stable and not easily affected by the external environment (such as temperature and humidity), thereby ensuring the stability and reliability of the grating performance.

[0066] Compared with the electroplating process in the LIGA process, the negative pressure injection process avoids problems such as uneven thickness and edge effects that may occur during the electroplating process, thereby improving the accuracy and quality of the grating.

[0067] According to the grating preparation method of the embodiment of the present invention, the negative pressure glue injection process has low cost, simple process flow, short production cycle, can be mass-produced and causes little pollution to the environment.

[0068] Figure 5 A cross-sectional view of a grating preparation chamber provided according to an embodiment of the present invention is shown.

[0069] According to an embodiment of the present invention, Figure 5 As shown, the grating preparation chamber 3 includes a body 31 and a cover 32. The body 31 forms a cavity with an opening, and the stacked structure formed by the grating sheet 1 and the isolation assembly 2 is placed in the cavity, and the cover 32 is sealed on the opening. The cover 32 is configured to be movable in a direction perpendicular to the grating sheet 1.

[0070] Keeping the grating sheet 1 and the isolation assembly 2 fixed in the grating preparation chamber 3 includes: driving the cover 32 to apply pressure to the nearest grating sheet 1 so that the stacking structure is pressed between the cover 32 and the bottom surface of the main body 31 .

[0071] According to an embodiment of the present invention, after the stacked structure is placed in the grating preparation chamber 3 , the driving mechanism 8 can drive the cover 32 to apply pressure to the nearest grating sheet 1 .

[0072] According to an embodiment of the present invention, the driving mechanism 8 includes a driving rod 82 and a power unit 81. The power unit 81 can be electrically, pneumatically or hydraulically driven. The first end of the driving rod 82 is mounted on the power unit 81, and the second end is connected to the cover 32. The power unit 81 drives the driving rod 82 to move in a direction perpendicular to the grating sheet 1.

[0073] According to an embodiment of the present invention, the power unit 81 may be a linear motor. A linear motor, also known as a linear motor, is a transmission device that directly converts electrical energy into linear motion mechanical energy without requiring any intermediate conversion mechanism. The first end of the driving rod 82 is mounted on the linear motor, and the linear motor drives the driving rod 82 to move in a direction perpendicular to the grating sheet.

[0074] According to the embodiment of the present invention, a vent is provided on the cover 32 or the main body 31. After the stacking structure is formed, the driving mechanism 8 is required to drive the cover 32 to move. At this time, the vent is opened so that the cover 32 can move smoothly. After the cover 32 moves to a predetermined position, the vent is closed, and the grating preparation chamber 3 is evacuated by the vacuum pump 4. After the colloid is cured, the vent is opened and the cover 32 is moved to realize the removal of the grating in the grating preparation chamber.

[0075] According to an embodiment of the present invention, an anti-stick coating is coated on the inner wall of the grating preparation chamber to enable the grating to be separated from the grating preparation chamber after the grating preparation is completed.

[0076] According to an embodiment of the present invention, a colloid inlet is provided on the main body 31, and the colloid inlet faces the gap of the stacked structure. Since the colloid inlet is directly aligned with the gap, the colloid does not need to pass through an additional path or space when flowing, and can directly and unhinderedly enter the gap. This improves the filling efficiency of the colloid, reduces the obstruction and loss of the colloid during the flow process, shortens the preparation time, and helps to maintain the stability of the preparation process.

[0077] According to an embodiment of the present invention, an observation window is provided on the grating preparation chamber to monitor the filling state of the colloid in real time, thereby improving the controllability and accuracy of the injection process. The observation window can be provided on the cover 32 or the main body 31, for example.

[0078] According to an embodiment of the present invention, it is also possible to determine whether the colloid filling is complete by observing the overflow of the colloid. When the colloid overflows from the colloid inlet, it indicates that the colloid injection is complete.

[0079] According to an embodiment of the present invention, before the grating sheets 1 and the isolation components 2 are alternately stacked and placed in a grating preparation chamber, the preparation method further includes: determining the distance between two adjacent grating sheets of the grating according to a preset diffraction order, and determining the thickness of the isolation component 2 according to the distance between the two adjacent grating sheets.

[0080] According to an embodiment of the present invention, the grating diffraction order and the grating period can be determined according to the grating diffraction formula. The grating diffraction formula is expressed as formula (1).

[0081] dsinθ = kλ(1).

[0082] In formula (1), d represents the grating period (grating constant), θ is the angle between the incident light and the normal to the grating plane, λ is the wavelength of the incident light, and k is the grating diffraction order. The grating period is also called the grating constant or the spacing between grating pieces. Therefore, in order to enable the prepared grating to reach the preset diffraction order, it is necessary to determine the spacing between adjacent grating pieces 1. The spacing between adjacent grating pieces 1 is equal to the thickness of the isolation component 2. Therefore, in order to ensure that the prepared grating has the preset diffraction order, it is necessary to further determine the thickness of the isolation component 2.

[0083] According to an embodiment of the present invention, the grating is suitable for an imaging device for imaging X-rays, and the colloid is configured to allow X-rays to pass through and also to have a high X-ray transmittance.

[0084] According to an embodiment of the present invention, the use of a grating to image X-rays requires the use of the diffraction effect of the grating. The diffraction effect of the grating and the characteristics of the X-ray are used to achieve fine imaging of the object. When the X-ray carrying the information of the object passes through the grating, diffraction occurs. The diffraction waves are superimposed on each other in the space behind the grating to form diffraction patterns of light and dark. These patterns contain the structural information of the object. By analyzing this information, the internal structure image of the object can be obtained.

[0085] According to an embodiment of the present invention, in imaging applications, the grating formed by the combination of the grating sheet 1 and the colloid needs to ensure the clarity and contrast of the imaging. The light transmittance and uniformity of the colloid are crucial to reducing blur and noise in the image. If the colloid has inhomogeneity or defects, it may cause light to scatter or reflect when passing through, thereby reducing the imaging quality. Ensuring that the colloid has a high transmittance for the required light beam can reduce the attenuation of the light beam when passing through the colloid, affecting the diffraction efficiency of the grating.

[0086] According to the embodiment of the present invention, the grating sheet 1 and the colloid may need to withstand harsh environments such as high temperature or chemical corrosion, so it is necessary to select a colloid material with high thermal stability and chemical stability.

[0087] According to an embodiment of the present invention, after the preparation of the grating is completed, the preparation method further includes: cutting the grating according to a preset aspect ratio. According to an embodiment of the present invention, the aspect ratio of the grating is one of the key factors affecting its diffraction efficiency, resolution, imaging quality and other performance. Different application scenarios have different requirements for the aspect ratio of the grating. For example, in some optical elements or sensors, the grating is required to have a specific aspect ratio to achieve a specific optical effect or sensing performance. By cutting the grating according to the preset aspect ratio, it can be ensured that the grating meets these specific application requirements. During the preparation of the grating, due to the influence of various factors (such as material properties, processing technology, etc.), the actual aspect ratio of the grating may have a certain deviation from the preset aspect ratio. By cutting the grating according to the preset aspect ratio, the aspect ratio of the grating can be accurately adjusted to keep it consistent with the preset aspect ratio.

[0088] According to an embodiment of the present invention, curing the colloid includes: making the grating preparation chamber 3 filled with the colloid below the curing temperature of the colloid to cure the colloid. The temperature is, for example, about 25° C. and the curing time is about 24 hours. At the same time, when the temperature rises, the curing time will be correspondingly shortened.

[0089] According to the embodiment of the present invention, after negative pressure is formed in the grating preparation chamber, the vacuum degree in the grating preparation chamber is less than 10 Pa. According to the embodiment of the present invention, the vacuum degree in the grating preparation chamber 3 can be monitored by a vacuum gauge that can be connected to the inside of the grating preparation chamber 3 .

[0090] According to an embodiment of the present invention, for precision processes such as grating preparation, the selection of a vacuum degree below 10Pa is mainly based on the following considerations: In an environment where the vacuum degree is lower than 10Pa, the number of gas molecules is greatly reduced, thereby reducing the influence of gas molecules on the grating preparation process. For processes such as grating preparation that require high precision and stability, it is crucial to reduce the interference of gas molecules. This can ensure that there will be no errors or contamination caused by gas molecules during the preparation process, thereby improving the quality and reliability of the product. In the colloid filling process, the selection of vacuum degree has an important influence on the filling accuracy. When the vacuum degree reaches below 10Pa, the bubbles and voids in the colloid can be effectively reduced, thereby improving the uniformity and density of the colloid filling. This is crucial for products such as gratings that require precise control of the distribution and thickness of the colloid. In a vacuum environment, the content of oxygen and other harmful gases is greatly reduced, thereby reducing the possibility of material oxidation. For sensitive materials such as gratings, oxidation will lead to performance degradation and shortened life. In addition, the vacuum environment can also effectively prevent the intrusion of dust and other pollutants, keeping the preparation environment clean and stable.

[0091] According to the negative pressure glue injection process adopted in the embodiment of the present invention, the grating preparation chamber 4 is evacuated to a vacuum state by a vacuum pump 4, and then the colloid is uniformly filled into the gaps between the grating sheets 1 by the pressure difference. This process is relatively fast and helps to improve the preparation efficiency.

[0092] According to an embodiment of the present invention, the negative pressure injection process provides a feasible alternative for preparing gratings with a period of micrometer level and a large aspect ratio, which can meet specific application requirements. The process allows the prepared grating to be cut into corresponding sizes according to actual needs, providing greater flexibility.

[0093] The negative pressure injection process used in the embodiment of the present invention adopts relatively simple preparation steps and materials, which significantly reduces the material and manufacturing costs compared to the expensive materials and complex manufacturing processes used in the LIGA process.

[0094] According to the embodiment of the present invention, due to the reduction in cost and the improvement in preparation efficiency, the negative pressure glue injection process is more conducive to the application of X-ray gratings in imaging technology.

[0095] The embodiments of the present invention are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment is described above, it does not mean that the measures in each embodiment cannot be used in combination. The scope of the present invention is defined by the attached claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A method for preparing a grating, comprising: Placing grating sheets and isolation components alternately in a grating preparation chamber to form a stacked structure in the grating preparation chamber; wherein the isolation components are adapted to ensure that two adjacent grating sheets are spaced at the same distance; Keeping the grating sheet and the isolation assembly fixed in the grating preparation chamber; forming a negative pressure in the grating preparation chamber; Under the action of the negative pressure, the colloid enters the grating preparation chamber and fills into the gap between two adjacent grating sheets to bond the two adjacent grating sheets; and The colloid is cured, and the cured colloid allows the light beam to pass through.

2. The preparation method according to claim 1, wherein The grating preparation chamber comprises a main body and a cover; The body portion forms a cavity with an opening, the cavity is used to accommodate the stacking structure, and the cover body is sealingly arranged on the opening; The cover is configured to be movable along a direction perpendicular to the grating sheet; Keeping the grating sheet and the isolation assembly fixed in the grating preparation chamber comprises: The cover is driven to apply pressure to the nearest grating sheet, so that the stacking structure is pressed between the cover and the bottom surface of the main body.

3. The preparation method according to claim 2, wherein The main body is provided with a colloid inlet, and the colloid inlet faces the gap of the stacking structure.

4. The preparation method according to any one of claims 1 to 3, wherein: Before placing the grating sheets and the spacer components in an alternating stack into a grating preparation chamber, the method further comprises: Determining the distance between two adjacent grating plates of the grating according to a preset diffraction order; and The thickness of the isolation component is determined according to the distance between the two adjacent grating sheets.

5. The preparation method according to any one of claims 1 to 3, wherein: The grating is suitable for an imaging device for imaging X-rays, and the colloid is configured to allow the X-rays to pass through.

6. The preparation method according to any one of claims 1 to 3, wherein: After the preparation of the grating is completed, the preparation method further comprises: The grating is cut according to a preset aspect ratio.

7. The preparation method according to claim 1 or 2, wherein: The grating preparation chamber is provided with an observation window to facilitate real-time monitoring of the filling state of the colloid.

8. The preparation method according to claim 1, wherein The inner wall of the grating preparation chamber is coated with an anti-stick coating so that the grating can be separated from the grating preparation chamber after the grating preparation is completed.

9. The preparation method according to claim 1, wherein Solidifying the colloid comprises: The grating preparation chamber filled with the colloid is kept below the curing temperature of the colloid to cure the colloid. 10 . The preparation method according to claim 1 , wherein after a negative pressure is formed in the grating preparation chamber, the vacuum degree in the grating preparation chamber is less than 10 Pa.

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