Single-order diffraction grating and preparation method therefor

Abstract

A single-order diffraction grating and a preparation method therefor. The single-order diffraction grating comprises a base substrate (1); the base substrate (1) is divided into a plurality of grid regions (2), and each grid region (2) is provided with a metal film (3) according to a corresponding set area duty ratio; the metal films (3) are reflective films or light blocking films; in a first set direction, a set area duty ratio corresponding to the x-th grid region (2) satisfies 0.5*m*cos(2*π*x / d)+0.5, wherein d is a grating period, and m is a set amplitude value; in the grid region (2) where the set area duty ratio is less than 50%, the metal film (3) is arranged to cover the central position of the grid region (2); and in the grid region (2) where the set area duty cycle is not less than 50%, the metal film (3) is an annular film layer arranged to cover the edge position of the grid region (2), so as to form a through hole at the central position of the grid region (2). The single-order diffraction grating can reduce the processing difficulty of single-order diffraction gratings to a certain extent and ensure the single-order diffraction effect of gratings.

Description

A single-stage diffraction grating and its preparation method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 21, 2023, with application number 202311768792.2 and invention name “A single-stage diffraction grating and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of grating processing, and in particular to a single-order diffraction grating and a preparation method thereof. Background Art

[0003] A single-order diffraction grating is a grating that contains only 0th-order and positive and negative first-order diffraction light. Through the design and fabrication of the grating, its higher-order diffraction is suppressed. The key to a single-order diffraction grating is to achieve a gradual change in transmittance or reflectance, so that the transmittance or reflectance gradually changes within the range of [0,1] within each grating period.

[0004] However, when actually processing a single-order diffraction grating, it is often relatively difficult to process a grating structure with a transmittance or reflectivity close to 0 or close to 1, which makes it difficult to ensure the grating processing accuracy, affecting the grating diffraction effect.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a single-stage diffraction grating and a preparation method thereof, which can reduce the difficulty of grating processing to a certain extent and ensure the grating diffraction effect.

[0007] To solve the above technical problems, the present invention provides a single-stage diffraction grating, comprising:

[0008] Base substrate; the base substrate is divided into a plurality of grid areas, each of the grid areas is provided with a metal film according to a corresponding set area duty ratio; the metal film is a reflective film or a light-blocking film;

[0009] Wherein, in the first set direction, the set area duty ratio corresponding to the x-th grid area satisfies the variation rule of 0.5*m*cos(2*π*x / d)+0.5, d is the grating period, m is the set amplitude value, m∈[0,1];

[0010] In the grid area with a set area duty ratio less than 50%, the metal film is arranged to cover the center position of the grid area;

[0011] In the grid area with a set area duty ratio of not less than 50%, the metal film is an annular film layer arranged to cover the edge position of the grid area, so that a through hole is formed at the center position of the grid area.

[0012] In an optional embodiment of the present application, the grid areas are distributed in multiple columns; wherein the grid areas in each column are arranged sequentially along the first set direction;

[0013] The grid areas in the same column include a plurality of grid areas sequentially arranged along the second set direction; and the set area duty ratios corresponding to the shapes and areas of the grid areas in the same column are all the same.

[0014] In an optional embodiment of the present application, each of the grid areas is a square area;

[0015] In the grid area where the area duty ratio is set to be less than 50%, the metal film is a square film;

[0016] In the grid area where the area duty ratio is set to be no less than 50%, the through hole in the center of the metal film is a square hole.

[0017] In an optional embodiment of the present application, in the grid area where the corresponding set area duty ratio is less than 50%, the metal film is a square film with a side length of

[0018] In the grid area with the corresponding set area duty ratio not less than 50%, the through hole in the center of the metal film is a square hole with a side length of

[0019] Wherein, r is the set area duty cycle; D is the side length of the grid area.

[0020] In an optional embodiment of the present application, the grid areas in two adjacent columns are staggered with each other along the second set direction.

[0021] In an optional embodiment of the present application, each of the grid areas is a regular hexagonal area;

[0022] The metal film in the grid area where the corresponding set area duty ratio is less than 50% is a circular reflective film;

[0023] The through hole in the center of the metal film in the corresponding grid area with a set area duty ratio of not less than 50% is a circular hole.

[0024] In an optional embodiment of the present application, the substrate is any one of a silicon substrate, a quartz substrate, or a glass substrate.

[0025] In an optional embodiment of the present application, the metal film is any one of a gold film, a metal aluminum film or a metal platinum film.

[0026] A method for preparing a single-order diffraction grating, for preparing the single-order diffraction grating as described in any one of the above items; the preparation method comprises:

[0027] Spin-coating a photoresist layer on a substrate, and exposing the photoresist layer according to a set pattern;

[0028] Developing the exposed photoresist layer to remove the photoresist layer in the area where the metal thin film is to be formed on the substrate;

[0029] A metal film is formed by deposition, and the metal film in the area where the photoresist layer is retained on the substrate is removed, and the metal film in the area where the photoresist layer is not retained is retained.

[0030] The present invention provides a single-order diffraction grating and a preparation method thereof. The single-order diffraction grating includes a base substrate; the base substrate is divided into multiple grid areas, and a metal film is provided in each grid area according to a corresponding set area duty ratio; the metal film is a reflective film or a light-blocking film; wherein, in a first set direction, the set area duty ratio corresponding to the x-th grid area changes according to a variation rule of 0.5*m*cos(2*π*x / d)+0.5, d is the grating period, m is the set amplitude value, and m∈[0,1]; in grid areas where the set area duty ratio is less than 50%, the metal film is provided to cover the center position of the grid area; in grid areas where the set area duty ratio is not less than 50%, the metal film is an annular film layer provided to cover the edge position of the grid area, so that a through hole is formed at the center position of the grid area.

[0031] The area duty ratio of the metal film in the single-stage diffraction grating of the present application satisfies the variation rule of 0.5*m*cos(2*π*x / d)+0.5, which can greatly suppress the high-order diffraction light to a certain extent, thereby avoiding the grating spectrum aliasing effect to a certain extent, and thus ensuring the diffraction effect of the single-stage diffraction grating; on this basis, the present application further sets the metal film in the grid area with a relatively small area duty ratio in each grid area at the center of the grid area, that is, the metal film with a smaller area is concentrated; and the metal film in the corresponding grid area with a relatively large area duty ratio is set as an annular film layer, and then the central area of ​​the metal film forms a relatively concentrated through-hole, thereby reducing the difficulty of processing the metal film and through-hole with a smaller area to a certain extent, that is, reducing the processing difficulty of the grating and ensuring the processing accuracy. It can be seen that the present application can reduce the processing difficulty of the single-machine diffraction grating to a certain extent while ensuring the single-stage diffraction effect of the grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] FIG1 is a schematic structural diagram of a single-stage diffraction grating provided in an embodiment of the present application;

[0034] FIG2 is a schematic diagram of another structure of a single-stage diffraction grating provided in an embodiment of the present application;

[0035] FIG3 is a schematic flow chart of a method for preparing a stand-alone diffraction grating provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] The core of the present invention is to provide a single-stage diffraction grating and a method for preparing the single-stage diffraction grating, which can reduce the difficulty of grating preparation to a certain extent and ensure the grating diffraction effect.

[0037] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0038] As shown in Figures 1 and 2, Figure 1 is a structural schematic diagram of a single-stage diffraction grating provided in an embodiment of the present application; Figure 2 is another structural schematic diagram of a single-stage diffraction grating provided in an embodiment of the present application.

[0039] In a specific embodiment of the present application, the single-order diffraction grating may include:

[0040] The base substrate 1 is divided into a plurality of grid areas 2, each of which is provided with a metal film 3 according to a corresponding set area duty ratio; the metal film 3 is a reflective film or a light-blocking film;

[0041] Among them, in the first set direction, the set area duty ratio corresponding to the x-th grid area 2 satisfies the variation rule of 0.5*m*cos(2*π*x / d)+0.5, d is the grating period, m is the set amplitude value, m∈[0,1];

[0042] In the grid area 2 where the area duty ratio is set to be less than 50%, the metal film 3 is set to cover the center position of the grid area 2;

[0043] In the grid area 2 with a set area duty ratio of not less than 50%, the metal film 3 is an annular film layer arranged to cover the edge of the grid area 2 , so that a through hole is formed at the center of the grid area 2 .

[0044] It should be noted that single-order diffraction gratings include reflective single-order diffraction gratings and transmissive diffraction gratings. When the single-order diffraction grating is a reflective diffraction grating, the base substrate 1 in this embodiment should be a substrate of a material with relatively low reflectivity. For example, the reflectivity of the base substrate 1 can be no greater than 0.01, and it can be any of a silicon substrate, a quartz substrate, or a glass substrate. In this case, the metal film 3 disposed in each grid area 2 on the base substrate 1 is a reflective film, which can be a metal film layer structure with strong reflectivity, such as a gold film, a metal aluminum film, or a metal platinum film.

[0045] When the single-order diffraction grating is a transmission diffraction grating, the base substrate 1 in this embodiment is a substrate with a relatively high transmittance. Correspondingly, the metal film 3 arranged in each grid area 2 is a film layer that can block light, and its transmittance should be less than 0.01.

[0046] In addition, it can be understood that, for a reflective diffraction grating, the set area duty ratio corresponding to the metal film 3 in each grid area 2 is also the reflectivity of the grid area 2 to light; while for a transmissive diffraction grating, the set area duty ratio corresponding to the metal film 3 in each grid area 2 is inversely proportional to the transmittance corresponding to the grid area 2, and the transmittance corresponding to each grid area 2 should be the difference between 1 and the set area duty ratio.

[0047] Based on the above discussion, regardless of whether the single-stage diffraction grating in this application is a reflective diffraction grating or a transmissive diffraction grating, the set area duty ratio corresponding to each grid region 2 along the first set direction should satisfy 0.5*m*cos(2*π*x / d)+0.5. The first set direction should be the direction in which the grating structure period in the single-stage diffraction grating extends.

[0048] Take a single-stage diffraction grating as a transmission diffraction grating as an example; the transmittance of the single-stage diffraction grating needs to change continuously between [0, 1]. The single-stage diffraction grating generates amplitude modulation on the incident light wave in the form of a cosine wave, and its complex amplitude transmittance function is:

[0049] Where f0 is the grating frequency and L is the size of the grating. The rect function is a matrix box function, which forms a Fourier transform pair with the sin function.

[0050] The grating spectrum is calculated using the convolution theorem:

[0051] The first term in the above formula is:

[0052] The second term in the above formula is:

[0053] The spectrum of the grating is obtained as follows:

[0054] The grating is illuminated perpendicularly with a monochromatic plane wave of amplitude 1. The intensity of the Fraunhofer diffraction image is:

[0055] The above equation includes three diffraction orders: the first term is the zeroth order diffracted light, and the second and third terms are the positive and negative first order diffracted light, respectively. Therefore, the diffracted light from a grating with cosine transmittance does not contain higher-order diffracted light, resulting in a good single-order diffraction effect. Similarly, the same principle applies to reflective single-order diffraction gratings. Therefore, gratings with a grating structure that changes according to the law of 0.5*m*cos(2*π*x / d)+0.5 exhibit good diffraction effects.

[0056] On this basis, in order to further adjust the intensity amplitude of the diffraction output light, this application further sets the change law of the grating structure to satisfy 0.5*m*cos(2*π*x / d)+0.5, thereby changing the diffraction efficiency of the single-order diffraction grating to light to a certain extent.

[0057] As described above, in the present application, the metal film 3 in each grid area 2 has a different area duty ratio of the grid area 2, and the metal film 3 in each grid area 2 is also set in a different manner. When the set area duty ratio of the metal film 3 at the location of the grid area 2 is required to be less than 50%, the metal film 3 is set at the center of the grid area 2, that is, the metal film 3 is concentrated in the center area of ​​the grid area 2. Compared with the current conventional multi-processing strip-shaped metal film 3 structure, it is obvious that the metal film 3 concentrated at the center of the grid area 2 is less difficult to process. For example, the metal film 3 can be set in a circular, square, or other regular polygonal shape, etc., and the metal film 3 should be set in a regular polygonal structure as much as possible. Obviously, compared with the elongated strip-shaped metal film 3 of the same area, the circular or regular polygonal metal film 3 is less difficult to process. Similarly, when the area that the metal film 3 needs to cover in a grid area 2 is relatively large, the area not covered by the metal film 3 is relatively small. For this reason, in this embodiment, the metal film 3 in the grid area 2 where the set area duty ratio of the metal film 3 is not less than 50% is set to be an annular film with a through hole in the middle. Similarly, the through hole can also be a circular through hole or a regular polygonal through hole, thereby reducing the difficulty of forming a through hole with a smaller area.

[0058] Based on the above discussion, in this embodiment, the set area duty ratio corresponding to the metal film 3 in the grid area 2 is relatively small, and the metal film 3 is set to a structure concentrated in the center of the grid area 2 to avoid the problem that the metal film 3 extends too large in a single dimension direction, which in turn causes the metal film 3 to be too small in other directions and thus causes great difficulty in processing; similarly, when the set area duty ratio of the metal film 3 in the grid area 2 is relatively large, a through hole is formed in the middle of the metal film 3, which can also avoid the problem that the through hole with a relatively small area extends too large in a single direction and causes the through hole with a relatively small area to be too small in other directions and thus causes great difficulty in processing. In this application, both the metal film 3 with a smaller area and the through hole with a smaller area can be better concentrated in the central area of ​​the grid area 2, which greatly reduces the difficulty in processing the thin film structure in each grid area 2, and also reduces the difficulty in processing the entire grating structure.

[0059] As shown in FIG1 and FIG2, in the single-stage diffraction grating, the first set direction is the extension direction of the grating period, and x in 0.5*m*cos(2*π*x / d)+0.5 is the number of grid areas 2 along the first set direction.

[0060] In an optional embodiment of the present application, the grid areas 2 are distributed in multiple columns; wherein the grid areas 2 in each column are arranged sequentially along the first set direction;

[0061] The same column of grid areas 2 includes a plurality of grid areas 2 sequentially arranged along the second set direction; and the set area duty ratios corresponding to the shapes and areas of the grid areas 2 in the same column are all the same.

[0062] As shown in Figures 1 and 2, in the embodiments shown in Figures 1 and 2, the set duty cycles corresponding to the grid areas 2 in the same column are the same, and the second set direction in which the grid areas 2 in the same column extend and the first set direction in which the grid areas 2 in each column are arranged in sequence are perpendicular to each other.

[0063] In the embodiments shown in Figures 1 and 2, all grid areas 2 are the same size. In actual applications, the sizes of the grid areas 2 in the same column can also be set to be the same, while the sizes of the grid areas 2 in different columns can be different. This application does not make any specific restrictions on this.

[0064] On this basis, as shown in Figure 1, in another optional embodiment of the present application, each grid area 2 can adopt a square area. On this basis, in the corresponding grid area 2 with a set area duty ratio of less than 50%, the metal film 3 is a square film; in the corresponding grid area 2 with a set area duty ratio of not less than 50%, the through hole in the center of the metal film 3 is a square hole.

[0065] In this application, the base substrate 1 is divided into several square areas. Accordingly, the metal film 3 with a relatively small area duty ratio is also set to a square, while the metal film 3 with a relatively large area duty ratio is formed with a square through hole in the middle area, which can simplify the processing difficulty to a certain extent.

[0066] For a square metal film 3, its side length can be For an annular film with a through hole in the middle, the side length of the through hole in the center is Where r is the set area duty cycle; D is the side length of grid area 2.

[0067] On this basis, in order to further enhance the single-order diffraction effect of the grating structure and thus better eliminate stray light, in another optional embodiment of the present application, two adjacent columns of grid areas 2 may be staggered along a second set direction.

[0068] As shown in Figure 1, in the embodiment shown in Figure 1, the grid areas 2 between two adjacent columns are offset from each other by half the length of the side of the grid area, and the centers of the light-transmitting areas or reflective areas in two adjacent columns of the grid area are also offset from each other by half the length of the side of the grid area 2, thereby making the lattice direction and the grating direction staggered with each other, which is beneficial to eliminating the stray light generated during the diffraction process.

[0069] In another optional embodiment of the present application, each grid area 2 is a regular hexagonal area;

[0070] The metal film 3 in the corresponding grid area 2 with a set area duty ratio of less than 50% is a circular reflective film;

[0071] The through hole at the center of the metal film 3 in the corresponding grid area 2 with a set area duty ratio of not less than 50% is a circular hole.

[0072] In this embodiment, regular hexagonal areas are used as the grid areas 2 , and the centers of the light-transmitting areas or light-reflecting areas in two adjacent columns of the grid areas 2 are also staggered, which is beneficial for eliminating stray light generated during the diffraction process.

[0073] In summary, the area duty ratio of the metal film in the grid area in the single-order diffraction grating of the present application satisfies the variation law of 0.5*m*cos(2*π*x / d)+0.5, which can greatly suppress the high-order diffraction light to a certain extent, thereby avoiding the grating spectrum aliasing effect to a certain extent, and thus ensuring the diffraction effect of the single-order diffraction grating; the metal film in the grid area with a relatively small area duty ratio in each grid area is set at the center of the grid area, that is, the metal film with a smaller area is concentratedly distributed; and the metal film in the corresponding grid area with a relatively large area duty ratio is set as an annular film layer, and then the central area of ​​the metal film forms a relatively concentrated through-hole, thereby reducing the difficulty of processing and forming a metal film with a smaller area and through-holes to a certain extent, that is, reducing the processing difficulty of the grating and ensuring the processing accuracy.

[0074] The present application also provides an embodiment of a method for preparing a single-stage diffraction grating, which is used to prepare the single-stage diffraction grating described in any of the above items. As shown in Figure 3, Figure 3 is a schematic flow chart of the method for preparing a single-stage diffraction grating provided in an embodiment of the present application. The preparation method may include:

[0075] S1: Spin-coat a photoresist layer on a substrate and expose the photoresist layer according to a set pattern.

[0076] In practical applications, a substrate of suitable material and size can be selected first, and the substrate can be cleaned to remove impurities on the surface of the substrate, including organic pollutants and metal ion contamination; then a spin coater can be used to spin coat a layer of photoresist on the entire surface of the substrate.

[0077] Before exposing the photoresist layer, the photoresist layer is pre-baked using an oven or a hot plate, and then the photoresist layer is exposed according to a pre-designed pattern using electron beam exposure or other photolithography techniques.

[0078] It can be understood that the set pattern in this embodiment is the pattern of the area covered by the metal thin film on the base substrate in the single-order diffraction grating in each of the above embodiments.

[0079] S2: Developing the exposed photoresist layer to remove the photoresist layer in the area where the metal thin film is to be formed on the substrate.

[0080] After exposure, the base substrate is placed in a developer to develop the pattern of the area where the metal film needs to be covered. The base substrate is then placed in a fixing solution and then post-baked to expose the area on the base substrate where the metal film needs to be formed.

[0081] S3: depositing a metal thin film, and removing the metal thin film in the area where the photoresist layer remains on the substrate, and retaining the metal thin film in the area without the photoresist layer.

[0082] Using electron beam evaporation or sputtering equipment, a metal film is formed on a substrate. The required thickness of the metal film is determined based on actual needs. The substrate is then placed in an acetone solution and ultrasonicated. A stripping process is used to remove the metal film attached to the photoresist surface, while retaining the metal film directly attached to the substrate surface. After the metal film on the photoresist surface is removed, the remaining photoresist is further removed, leaving only the metal film deposited on the substrate. The substrate is then placed in an ethanol solution and ultrasonicated for cleaning, followed by drying with nitrogen gas. This results in a single-stage diffraction grating.

[0083] After the single-order diffraction grating is completed, the structure of the metal film can be detected on the surface of the substrate using a microscope; the single-order diffraction grating is placed in a scanning electron microscope to detect and obtain parameters such as the structural size of the metal film.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device comprising a series of elements are inherent to the elements. In the absence of further restrictions, the elements limited by the statement "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device comprising the elements. In addition, the above-mentioned technical solutions provided in the embodiments of the present application are not described in detail in accordance with the corresponding technical solutions in the prior art to achieve the same principle, so as to avoid excessive elaboration.

[0085] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A single-order diffraction grating, characterized in that: include: substrate substrate; The base substrate is divided into a plurality of grid areas, and a metal film is disposed in each of the grid areas according to a corresponding set area duty ratio; The metal film is a reflective film or a light-blocking film; Wherein, in the first set direction, the set area duty ratio corresponding to the x-th grid area satisfies the variation rule of 0.5*m*cos(2*π*x / d)+0.5, d is the grating period, m is the set amplitude value, m∈[0,1]; In the grid area where the area duty ratio is set to be less than 50%, the metal film is arranged to cover the center position of the grid area; In the grid area with a set area duty ratio of not less than 50%, the metal film is an annular film layer arranged to cover the edge position of the grid area, so that a through hole is formed at the center position of the grid area.

2. The single-stage diffraction grating according to claim 1, characterized in that: The grid areas are distributed in multiple columns; wherein the grid areas in each column are arranged in sequence along the first set direction; The grid areas in the same column include a plurality of grid areas arranged in sequence along a second set direction; and the set area duty ratios corresponding to the shapes and areas of the grid areas in the same column are the same.

3. The single-order diffraction grating according to claim 2, characterized in that: Each of the grid areas is a square area; In the grid area where the area duty ratio is set to be less than 50%, the metal film is a square film; In the grid area where the area duty ratio is set to be not less than 50%, the through hole in the center of the metal film is a square hole.

4. The single-stage diffraction grating according to claim 3, characterized in that: In the grid area where the corresponding set area duty ratio is less than 50%, the metal film is a square film with a side length of In the grid area with a corresponding set area duty ratio of not less than 50%, the through hole in the center of the metal film is a square hole with a side length of Wherein, r is the set area duty ratio; D is the side length of the grid area.

5. The single-stage diffraction grating according to claim 3, characterized in that: The grid areas in two adjacent columns are staggered with each other along the second set direction.

6. The single-stage diffraction grating according to claim 2, characterized in that: Each of the grid areas is a regular hexagonal area; The metal film in the grid area with a corresponding set area duty ratio less than 50% is a circular reflective film; The through hole at the center of the metal film in the grid area with a corresponding set area duty ratio of not less than 50% is a circular hole.

7. The single-order diffraction grating according to claim 1, characterized in that: The substrate is any one of a silicon substrate, a quartz substrate, or a glass substrate.

8. The single-order diffraction grating according to claim 1, characterized in that: The metal film is any one of a gold film, a metal aluminum film or a metal platinum film.

9. A method for preparing a single-order diffraction grating, characterized in that: Used to prepare the single-order diffraction grating according to any one of claims 1 to 8; the preparation method comprises: Spin coating a photoresist layer on the substrate, and exposing the photoresist layer according to a set pattern; Developing the exposed photoresist layer to remove the photoresist layer in the area where the metal film needs to be formed on the substrate; A metal film is formed by deposition, and the metal film in the area where the photoresist layer is retained on the substrate is removed, and the metal film in the area without the photoresist layer is retained.

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