A transmission grating and its preparation method

Abstract

The present invention relates to a transmission grating and a method for manufacturing the same. The grating comprises a substrate having a first surface; a grating layer comprising trapezoidal grating teeth arrayed on the first surface, the grating teeth extending along the thickness of the substrate, with gaps between adjacent grating teeth; a dielectric layer disposed on the surface of the grating layer and filling the gaps, the dielectric layer having a second surface on a side facing away from the substrate, the second surface having a distance from the first surface and a height difference between the grating teeth, the difference being m; and incident light passing through the interior of the grating layer and incident toward the second surface. The present invention can design the film structure and dimensions of the transmission grating to obtain transmission gratings with different diffraction efficiencies and polarization degrees. This allows for precise control of the dimensions of the transmission grating film structure during processing, thereby facilitating easy processing.

Description

Technical Field

[0001] The present invention relates to the field of grating technology, and in particular to a transmission grating and a preparation method thereof. Background Art

[0002] Grating-based hyperspectral imagers are a widely used device. Their design and manufacture require a comprehensive approach that integrates multiple disciplines, including optics, spectroscopy, computer science, remote sensing, and data processing. With technological advancements, spectroscopic elements combining gratings and prisms have emerged in imaging spectrometer systems. Unlike traditional gratings, the grooves of a transmission prism grating are immersed in a high-refractive-index medium, such as SiO2 or Si. Because the prism grating grooves are embedded in the high-refractive-index medium, the angular dispersion and resolution of the grating are both increased by a factor of n, where n is the refractive index of the high-refractive-index medium. Therefore, compared to traditional gratings, prism gratings can reduce grating size while maintaining the same spectral resolution, resulting in a more compact design. This is particularly suitable for high-resolution spectrometers used for atmospheric greenhouse gas detection. The previously published Chinese patent CN111708113A provides a low-polarization, high-diffraction-efficiency metal reflective immersion grating and optical system, specifically disclosing a reflective grating structure with rectangular grooves.

[0003] However, in the actual processing process, the groove shape of the grating is mostly trapezoidal. Compared with the rectangular groove shape, the processing technology of the trapezoidal groove is more difficult. How to accurately fill the gaps in the trapezoidal groove while ensuring that the transmission diffraction efficiency can reach a high level in the entire band and has a low polarization rate has become an urgent problem to be solved. Therefore, there is an urgent need to provide a transmission grating that is easy to process. Summary of the Invention

[0004] To this end, the technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a transmission grating and a method for preparing the same. The present invention can obtain transmission gratings with different diffraction efficiencies and polarization degrees by designing the film structure and film size of the transmission grating, and can facilitate precise control of the size of the transmission grating film structure during processing, thereby facilitating processing.

[0005] In order to solve the above technical problems, the present invention provides a transmission grating, comprising:

[0006] a substrate having a first surface;

[0007] a grating layer comprising trapezoidal grating teeth arranged in an array on the first surface, the grating teeth extending along the thickness direction of the substrate, with a gap between two adjacent grating teeth;

[0008] a dielectric layer disposed on a surface of the grating layer and filling the gap, wherein the dielectric layer has a second surface on a side away from the substrate, and a difference between the spacing between the second surface and the first surface and the height of the grating teeth is m;

[0009] Incident light passes through the grating layer and enters toward the second surface, and generates a diffraction effect in the grating layer, the dielectric layer and the second surface to generate transmitted diffraction light, which is emitted through the second surface of the dielectric layer.

[0010] In one embodiment of the present invention, the dielectric layer includes a first film layer and a second film layer, the first film layer covers the grating layer and a portion of the substrate, the second film layer covers the first film layer, the thickness of the first film layer is m1, the thickness of the second film layer is m2, m=m1+m2.

[0011] In one embodiment of the present invention, the cross-sectional shape of the grating teeth along the height direction thereof is an isosceles trapezoid, and the hypotenuse angle θ of the grating teeth is 83 degrees to 88 degrees.

[0012] In one embodiment of the present invention, the period Λ of the grating teeth is 700nm to 2000nm, the bottom width of the grating teeth is a, the middle width of the grating teeth is b, the height of the grating teeth is H, and the middle duty cycle f 中 =(b / Λ) is 0.39~0.48, and the aspect ratio (H / Λ) is 1.65~1.76.

[0013] In one embodiment of the present invention, the bevel angle θ of the grating teeth is 83 degrees to 88 degrees. in,

[0014] In one embodiment of the present invention, the dielectric layer includes titanium dioxide (TiO2), aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5).

[0015] In one embodiment of the present invention, the substrate is made of fused silica optical glass.

[0016] The present invention also provides a method for preparing a transmission grating, which is used to prepare the transmission grating described above, and the preparation method comprises:

[0017] Step S1, selecting a substrate, coating the substrate with a photoresist, exposing the substrate coated with the photoresist film, placing the exposed substrate in a developer for development, and obtaining a photoresist grating mask;

[0018] Step S2, performing mask transfer by ion beam etching to transfer the grating mask pattern to the substrate surface to form a grating layer;

[0019] Step S3, removing the remaining photoresist, and forming a dielectric layer on the surface of the grating layer by atomic layer deposition. The thickness m of the dielectric layer is calculated by the above formula.

[0020] In one embodiment of the present invention, in the ion beam etching step in step S2, the working gas is trifluoromethane (CHF3), the ion energy is 200-600 eV, the ion beam current is 50-160 mA, the acceleration voltage is 200-260 V, and the working pressure is 2.4×10 -2 Pa.

[0021] In one embodiment of the present invention, in step S1, the substrate coated with the photoresist film is placed in a holographic interference optical system for exposure.

[0022] The above technical solution of the present invention has the following advantages over the prior art:

[0023] A transmission grating according to the present invention comprises a substrate, a grating layer, and a dielectric layer, which are sequentially arranged along the thickness direction of the transmission grating. The grating layer comprises trapezoidal grating teeth arranged in an array on the substrate. The dielectric layer covers the surface of the grating layer and is capable of filling the gaps between adjacent grating teeth. Specifically, the dielectric layer has a second surface on a side away from the substrate. The spacing between the second surface and the first surface of the substrate and the height of the grating teeth have a difference, defined as m. The difference m can also be considered as the thickness of the dielectric layer.

[0024] Compared with the existing technology, the present invention can accurately fill the grating tooth gaps while ensuring that the transmission diffraction efficiency is higher than 85% in the entire operating band and has a lower polarization degree. In addition, the grating groove shape of the transmission grating of the present invention is trapezoidal, which can reduce the process difficulty of the transmission grating compared to the rectangular groove shape, so that the duty cycle f of the transmission grating is greater than 0.39; and the aspect ratio can be reduced to 1.65-1.76.

[0025] The present invention can obtain transmission gratings with different diffraction efficiencies and polarization degrees by designing the film structure and film size of the transmission grating, and can facilitate precise control of the size of the transmission grating film structure during processing, thereby facilitating processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 It is a structural schematic diagram of a preferred embodiment of the present invention.

[0028] Figure 2 It is a technical flow chart of the preparation method of the preferred embodiment of the present invention.

[0029] Figure 3 1 is a schematic diagram of the distribution of the middle duty cycle and the height of the grating teeth when θ=84° in the specific embodiment 1 of the present invention.

[0030] Figure 4 1 is a schematic diagram of the distribution of diffraction efficiency and wavelength when H=1895nm and the middle duty cycle is 0.45 in specific embodiment 1 of the present invention.

[0031] Figure 5 This is a range distribution diagram of the grating tooth height and duty cycle when the grating teeth are rectangular and the dielectric layer completely covers the rectangular grooves in the specific embodiment 1 of the present invention.

[0032] Figure 6 1 is a schematic diagram showing the distribution of diffraction efficiency and wavelength when H=1980nm and the duty cycle is 0.39 in the specific embodiment 1 of the present invention.

[0033] Figure 7 Schematic diagram of distribution of middle duty cycle and grating tooth height in specific embodiment 2 of the present invention, θ=86°.

[0034] Figure 8 1 is a schematic diagram showing the distribution of diffraction efficiency and wavelength when H=2060nm and the middle duty cycle is 0.44 in specific embodiment 2 of the present invention.

[0035] Figure 9 This is a distribution diagram of the range of grating tooth height and duty cycle when the grating teeth are rectangular and the dielectric layer completely covers the rectangular groove in the specific embodiment 2 of the present invention.

[0036] Figure 10 1 is a schematic diagram showing the distribution of diffraction efficiency and wavelength when H=2170nm and the duty cycle is 0.42 in specific embodiment 2 of the present invention.

[0037] Description of the accompanying drawings in the specification: 1. substrate; 10. first surface; 2. grating layer; 20. grating teeth; 3. dielectric layer; 30. second surface; 31. first film layer; 32. second film layer. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0039] Example 1

[0040] Reference Figure 1As shown, the present invention discloses a transmission grating, comprising a substrate 1, wherein the substrate 1 has a first surface 10;

[0041] The transmission grating further includes a grating layer 2, wherein the grating layer 2 includes a plurality of trapezoidal grating teeth 20 arrayed on the first surface 10, wherein the plurality of grating teeth 20 extend along the thickness direction of the substrate 1, and a gap exists between two adjacent grating teeth 20, thereby forming a plurality of gaps in the grating layer 2;

[0042] The transmission grating further comprises a dielectric layer 3, which is disposed on the surface of the grating layer 2 and fills the plurality of gaps. Specifically, the dielectric layer 3 can cover the grating layer 2 and fill the plurality of gaps.

[0043] In detail, the dielectric layer 3 has a second surface 30 on a side away from the substrate 1 . There is a difference between the distance between the second surface 30 and the first surface 10 and the height of the grating teeth 20 , and the difference is m.

[0044] It should be noted that the difference m can also be considered as the thickness of the dielectric layer 3 .

[0045] A first interface is formed between the grating layer 2 and the dielectric layer 3. Incident light passes through the interior of the grating layer 2 and is incident toward the first interface. A diffraction effect occurs at the first interface, the dielectric layer 3, and the second surface 30 to generate diffracted light and transmitted light. The transmitted light is emitted through the second surface 30 of the dielectric layer 3.

[0046] It can be seen from this that the transmission grating to be protected by the present invention comprises a substrate, a grating layer, and a dielectric layer arranged in sequence along the thickness direction of the transmission grating, wherein the grating layer comprises a plurality of trapezoidal grating teeth arranged in an array on the substrate, and the dielectric layer covers the surface of the grating layer and is capable of filling the gaps between adjacent grating teeth. Specifically, the dielectric layer has a second surface on the side away from the substrate, and the difference between the spacing between the second surface and the first surface of the substrate and the height of the grating teeth is defined as m, which can also be considered as the thickness of the dielectric layer. Compared with the prior art, the present invention can accurately fill the gaps between the grating teeth while ensuring that the transmission diffraction efficiency is greater than 85% across the entire operating band and has a low degree of polarization. In addition, the grating grooves of the transmission grating of the present invention are trapezoidal, which can reduce the difficulty of the transmission grating process compared to rectangular grooves, making the duty cycle f of the transmission grating greater than 0.39 and reducing the aspect ratio to 1.65-1.76.

[0047] Specifically, the second surface 30 of the dielectric layer 3 is parallel to the first surface 10. The dielectric layer 3 comprises a first film layer 31 and a second film layer 32. The first film layer 31 covers the grating layer 2 and a portion of the substrate 1, while the second film layer 32 covers the first film layer 31. Specifically, along the height direction of the transmission grating, and with the geometric centerline of the grating teeth 20 as a reference, the thickness of the first film layer 31 is m1, and the thickness of the second film layer 32 is m2, where m = m1 + m2.

[0048] As a preferred embodiment, the first film layer 31 is a film layer of uniform thickness.

[0049] As a preferred embodiment, a plurality of the grating teeth 20 are arranged at equal intervals on the first surface 10 to form the grating layer 2 .

[0050] Specifically, the cross-section of the grating tooth 20 along its height direction is in the shape of an isosceles trapezoid.

[0051] Furthermore, the parameters are defined as follows:

[0052] The period Λ of the grating teeth 20 is 700nm to 2000nm.

[0053] The bottom width of the grating tooth 20 is a,

[0054] The middle width of the grating tooth 20 is b,

[0055] The height of the grating teeth 20 is H.

[0056] Middle duty cycle f 中 =(b / Λ) is 0.39~0.48; the aspect ratio (H / Λ) is 1.65~1.76.

[0057] Furthermore, the hypotenuse angle θ of the grating teeth 20 is 83 degrees to 88 degrees.

[0058] Therefore, the calculation formula of the difference m, that is, the thickness of the dielectric layer 3, is defined as:

[0059] in,

[0060] As a preferred embodiment, the dielectric layer 3 is made of a high refractive index material.

[0061] The material of the dielectric layer 3 includes but is not limited to titanium dioxide (TiO 2 ), aluminum oxide (Al 2 O 3 ) and tantalum pentoxide (Ta 2 O 5 ).

[0062] In detail, the substrate 1 is made of fused quartz optical glass.

[0063] Therefore, by designing the film structure and film size of the transmission grating, it is possible to obtain transmission gratings with different diffraction efficiencies and polarization degrees.

[0064] The following is explained through two specific embodiments: Specific implementation method 1

[0066] Methane is a greenhouse gas that significantly impacts global climate change. Monitoring methane concentrations allows for more accurate assessment of global climate change trends. The atmospheric detection windows for methane are primarily 1.6 and 2.3 microns. Here, a transmission grating for the 1.6 micron band is presented. It consists of a fused quartz substrate, a grating layer, and a dielectric film layer disposed thereon.

[0067] The grating layer includes etched grating grooves, which are trapezoidal with a period of 1100nm, and the dielectric film layer is made of TiO2. Figure 1 As shown, the incident angle α of the incident light in the fused silica substrate 1 is set to 31 degrees.

[0068] By optimizing the grating groove structure, the optimal parameters were obtained. When the grating is completely filled with TiO2 by atomic layer deposition, the range of grating tooth height and duty cycle is obtained. Figure 3 As shown in the figure (θ = 84° or symmetrical 84°), it can be found that when the diffraction efficiency in the central band is greater than 85%, the minimum required grating tooth height is 1810nm. Therefore, under the conditions of grating tooth height of 1895nm, aspect ratio (H / Λ) of 1.72, and central duty cycle of 0.45, the first-order diffraction efficiency in the bandwidth range of 1.59-1.67 microns is calculated. Figure 4 As shown, it can be seen that the first-order diffraction efficiency in the bandwidth range of 1.59-1.67 μm is greater than 85%.

[0069] like Figure 5 As shown in the figure, compared with the traditional fully wrapped rectangular slot, when the grating is completely filled with atomic layer deposited TiO2, the range of grating tooth height and duty cycle is obtained. It can be found that when the diffraction efficiency in the central band is greater than 85%, the minimum grating tooth height required is 1910nm. Therefore, the first-order diffraction efficiency in the bandwidth range of 1.59-1.67 microns is calculated under the conditions of a grating tooth height of 1980nm, an aspect ratio (H / Λ) of 1.8, and a duty cycle of 0.39. Figure 6 As shown, it can be seen that the first-order diffraction efficiency in the bandwidth range of 1.59-1.67 μm is greater than 80%.

[0070] It is clear that the new trapezoidal grating groove design effectively reduces the aspect ratio, increases the duty cycle, reduces the degree of polarization, and increases the first-order diffraction efficiency from 80% to 85% in the 1.59-1.67 μm bandwidth.

[0071] In detail, during the preparation process, first, a photoresist is coated on a fused quartz substrate, and then a photoresist grating mask is made on the photoresist using a holographic lithography method, with a duty cycle f = 0.45 and a grating tooth height of 800nm;

[0072] Secondly, mask transfer was achieved by reactive ion beam etching, and a trapezoidal groove (bevel angle θ = 84°) was formed on the fused quartz substrate. It should be noted that the trapezoidal groove was a trapezoidal grid tooth with a height of 1895 nm. Specifically, the reaction gas used was trifluoromethane (CHF3), the ion energy was 550 eV, the ion beam current was 140 mA, the acceleration voltage was 240 V, and the working pressure was 2.5×10 -2 Pa;

[0073] After removing the remaining photoresist, a layer of high refractive index material TiO2 is formed by atomic layer deposition method. According to the formula in The calculated thickness of the TiO2 film is 446nm. Specific embodiment 2

[0075] Carbon dioxide is a typical greenhouse gas that absorbs infrared radiation. While allowing shorter-wavelength energy from the sun to pass through, it strongly absorbs longer-wavelength infrared energy emitted from the Earth's surface and near-surface atmosphere. This increases surface temperatures and creates a greenhouse effect, significantly impacting global climate change. Monitoring carbon dioxide concentrations allows for more accurate assessment of global climate change trends. The atmospheric detection windows for carbon dioxide are primarily 1.61 microns and 2.06 microns. Here, a transmission grating is proposed for the 2.06 micron band. It consists primarily of a fused quartz substrate, a grating layer, and a dielectric film layer disposed thereon.

[0076] Specifically, the grating layer includes etched grating grooves, which are trapezoidal with a period of 1250 nm; the single-layer high-refractive-index dielectric film is TiO2, and the incident angle α of the incident light in the fused silica substrate 1 is set to 38°.

[0077] By optimizing the grating groove structure, the optimal parameters were obtained. When the TiO2 of the grating is completely filled, the range of grating tooth height and duty cycle is obtained. Figure 7As shown in Figure 1 (θ = 86°), it can be found that when the diffraction efficiency is greater than 85%, the minimum required grating tooth height is 2010nm. Therefore, with a grating tooth height of 2060nm (H / Λ = 1.65) and a middle duty cycle of 0.44, the first-order diffraction efficiency in the bandwidth range of 2.042-2.086 microns is calculated as follows: Figure 8 shown.

[0078] Compared with the traditional fully wrapped rectangular trough, such as Figure 9 As shown in FIG, when the grating is completely filled with TiO2, the range of grating tooth height and duty cycle is obtained. It can be found that when the diffraction efficiency is greater than 85%, the minimum grating tooth height required is 2115nm. Therefore, with a grating tooth height of 2170nm (H / Λ) = 1.74 and a duty cycle of 0.42, the first-order diffraction efficiency in the bandwidth range of 2.042-2.086 microns is calculated, as shown in FIG. Figure 10 shown.

[0079] From this, it can be clearly seen that the new grating groove design effectively reduces the grating's aspect ratio, increases the duty cycle, and effectively reduces the degree of polarization.

[0080] During the preparation process, a photoresist is first coated on a fused quartz substrate, and then a photoresist grating mask is fabricated on the photoresist using a holographic lithography method, with a duty cycle f = 0.44 and a grating tooth height of 960nm;

[0081] Secondly, mask transfer was achieved by reactive ion beam etching to form trapezoidal grooves (bevel angle θ = 86°) on the fused quartz substrate. It should be noted that the trapezoidal grooves are trapezoidal grating teeth with a height of 2060 nm. Specifically, the reaction gas used was trifluoromethane (CHF3), the ion energy was 450 eV, the ion beam current was 140 mA, the acceleration voltage was 240 V, and the working pressure was 2.5 × 10 -2 Pa;

[0082] After removing the remaining photoresist, a layer of high refractive index material TiO2 is formed by atomic layer deposition. According to the formula in The calculated thickness of the TiO2 film is 453nm.

[0083] Example 2

[0084] The present invention also discloses a method for preparing a transmission grating, which is used to prepare a transmission grating as described in the first embodiment, combined with Figure 2 As shown, the preparation method includes:

[0085] Step S1, selecting a substrate 1, coating the substrate 1 with a photoresist, exposing the substrate coated with the photoresist film, placing the exposed substrate in a developer for development, and obtaining a photoresist grating mask;

[0086] Step S2, transferring the grating mask pattern to the substrate surface by ion beam etching to form a grating layer 2;

[0087] Step S3 , removing the remaining photoresist, and forming a dielectric layer 3 on the surface of the grating layer 2 by atomic layer deposition.

[0088] The thickness m of the dielectric layer is calculated using the formula in Example 1: in,

[0089] As a preferred embodiment, in the ion beam etching step in step S2, the working gas is trifluoromethane (CHF3), the ion energy is 200-600 eV, the ion beam current is 50-160 mA, the acceleration voltage is 200-260 V, and the working pressure is 2.4×10 -2 Pa.

[0090] As a preferred embodiment, in step S1, the substrate coated with the photoresist film is placed in a holographic interference optical system for exposure.

[0091] Example 3

[0092] The present invention further discloses an optical system comprising the transmission grating as described in the first embodiment, wherein the angle range of the incident light is 30°-50° and the bandwidth range of the incident light is 1.5-2.1 microns.

[0093] The present invention achieves transmission gratings with varying diffraction efficiencies and polarization degrees by designing and adjusting the film structure and dimensions of the transmission grating. While accurately filling the grating tooth gaps, it also ensures a transmission diffraction efficiency exceeding 85% across the entire operating band and a low polarization degree.

[0094] In addition, the grating groove of the transmission grating of the present invention is trapezoidal, which can reduce the difficulty of manufacturing the transmission grating compared to rectangular grooves, so that the duty cycle f of the transmission grating is greater than 0.39 and the aspect ratio can be reduced to 1.65-1.76.

[0095] The present invention can obtain transmission gratings with different diffraction efficiencies and polarization degrees by designing the film structure and film size of the transmission grating, and can facilitate precise control of the size of the transmission grating film structure during processing, thereby facilitating processing.

[0096] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "disposed" and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0097] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0098] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0099] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A transmission grating, characterized in that: include, a substrate having a first surface; a grating layer comprising trapezoidal grating teeth arranged in an array on the first surface, the grating teeth extending along the thickness direction of the substrate, with a gap between two adjacent grating teeth; a dielectric layer disposed on a surface of the grating layer and filling the gap, wherein the dielectric layer has a second surface on a side away from the substrate, and a difference between the spacing between the second surface and the first surface and the height of the grating teeth is m; Incident light passes through the interior of the grating layer and is incident toward the second surface, and generates a diffraction effect in the grating layer, the dielectric layer, and the second surface to generate transmitted diffraction light, and the transmitted diffraction light is emitted through the second surface of the dielectric layer; The dielectric layer includes a first film layer and a second film layer, the first film layer covers the grating layer and a portion of the substrate, the second film layer covers the first film layer, the thickness of the first film layer is m1, and the thickness of the second film layer is m2; The calculation formula for m is defined as Formula 1: ;in, ; ; The hypotenuse angle θ of the grating tooth is 83 degrees to 88 degrees; the period Λ of the grating tooth is 700nm to 2000nm, the bottom width of the grating tooth is a, the middle width of the grating tooth is b, the height of the grating tooth is H, and the middle duty cycle f 中 = (b / Λ) is 0.39~0.48, and the aspect ratio (H / Λ) is 1.65~1.

76.

2. The transmission grating according to claim 1, wherein: The cross-sectional shape of the grating teeth along the height direction thereof is an isosceles trapezoid.

3. A transmission grating according to claim 1 or 2, characterized in that: The dielectric layer includes titanium dioxide (TiO2), aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5).

4. The transmission grating according to claim 3, wherein: The substrate is made of fused quartz optical glass.

5. A method for preparing a transmission grating, characterized in that: Used for preparing a transmission grating according to any one of claims 1 to 4, the preparation method comprising: Step S1, selecting a substrate, coating the substrate with a photoresist, exposing the substrate coated with the photoresist film, placing the exposed substrate in a developer for development, and obtaining a photoresist grating mask; Step S2, performing mask transfer by ion beam etching to transfer the grating mask pattern to the substrate surface to form a grating layer; Step S3 , removing the remaining photoresist, and forming a dielectric layer on the surface of the grating layer by atomic layer deposition. The thickness m of the dielectric layer is calculated by formula 1.

6. The method for preparing a transmission grating according to claim 5, wherein: In the ion beam etching step in step S2, the working gas is trifluoromethane (CHF3), the ion energy is 200-600 eV, the ion beam current is 50-160 mA, the acceleration voltage is 200-260 V, and the working pressure is 2.4×10 -2 Pa.

7. The method for preparing a transmission grating according to claim 5, wherein: In the step S1, the substrate coated with the photoresist film is placed in a holographic interference optical system for exposure.

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