Transmission grating and preparation method thereof

Abstract

The invention relates to a transmission grating and a preparation method thereof, and the transmission grating comprises a substrate which is provided with a first surface; the grating layer comprises trapezoidal grating teeth arranged on the first surface in an array mode, the grating teeth extend in the thickness direction of the substrate, and a gap is formed between every two adjacent grating teeth; the dielectric layer is arranged on the surface of the grating layer and fills the gap, one side, far away from the substrate, of the dielectric layer is provided with a second surface, a difference value exists between the distance between the second surface and the first surface and the height of the grating teeth, and the difference value is m; incident light enters the second surface through the inside of the grating layer. By designing the film layer structure and the film layer size of the transmission grating, the transmission grating with different diffraction efficiencies and polarization degrees can be obtained, the size of the film layer structure of the transmission grating can be accurately controlled during processing, and processing is easy.

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] The grating-based hyperspectral imager is a widely used device. The design and manufacture of the hyperspectral imager requires a comprehensive technology that integrates multiple disciplines such as optics, spectroscopy, computer science, remote sensing technology, and data processing. With the development of technology, a grating and a prism-combined spectrometer element has appeared in the imaging spectrometer system. Unlike the traditional grating, the groove of the transmission prism grating is immersed in a high refractive index medium at the bottom of the grating, such as SiO2, Si, etc. Since the prism grating groove is embedded in the high refractive index medium, the angular dispersion and resolution of the grating are increased by n times, where n is the refractive index of the high refractive index medium. Therefore, compared with the traditional grating, the prism grating can reduce the size of the grating at the same spectral resolution, achieving a more compact design. This is particularly suitable for high-resolution spectrometers for atmospheric greenhouse gas detection. The already disclosed Chinese patent CN111708113A provides a low-polarization high diffraction efficiency metal reflection immersion grating and an optical system, and specifically discloses a reflection grating structure with a rectangular groove.

[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, it is urgent 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, wherein the grating teeth are extended along the thickness direction of the substrate, and there is a gap between two adjacent grating teeth;

[0008] a dielectric layer, which is disposed on the surface of the grating layer and fills 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] The incident light passes through the grating layer and enters toward the second surface, and a diffraction effect occurs in the grating layer, the dielectric layer and the second surface to generate transmissive diffraction light, and the transmissive diffraction light 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 tooth along its height direction is an isosceles trapezoid, and the hypotenuse angle θ of the grating tooth 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 as 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, transferring the mask 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 compared with the prior art:

[0023] A transmission grating described in 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, wherein the grating layer comprises trapezoidal grating teeth arranged in an array on the substrate, and the dielectric layer covers the surface of the grating layer and can fill the gaps between adjacent grating teeth; specifically, the dielectric layer has a second surface on a side away from the substrate, and there is a difference between the spacing between the second surface and the first surface of the substrate and the height of the grating teeth, the difference is defined as m, and the difference m can also be regarded as the thickness of the dielectric layer.

[0024] Compared with the prior art, the present invention can accurately fill the grating tooth gaps while ensuring that the transmission diffraction efficiency is higher than 85% in the entire working 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 according to 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 It 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 implementation mode 1 of the present invention.

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

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

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

[0033] Figure 7 It is a schematic diagram of the distribution of the middle duty cycle and the height of the grating teeth when θ=86° in the specific implementation mode 2 of the present invention.

[0034] Figure 8 This is a schematic diagram of 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] Fig. 9 This is a range distribution diagram of grating tooth height and duty cycle in specific implementation mode 2 of the present invention, when the grating teeth are rectangular and the dielectric layer completely wraps the rectangular groove.

[0036] Fig.10 This is a schematic diagram of 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] Explanation of the reference numerals 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 is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0039] Embodiment 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 are extended along the thickness direction of the substrate 1, and there is a gap between two adjacent grating teeth 20, so that the grating layer 2 forms a plurality of gaps;

[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 , and 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. The incident light passes through the grating layer 2 toward the first interface, and 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 known 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 can fill the gaps between adjacent grating teeth; specifically, the dielectric layer has a second surface on the side away from the substrate, and there is a difference between the spacing between the second surface and the first surface of the substrate and the height of the grating teeth, and the difference is defined as m, and the difference m can also be considered as the thickness of the dielectric layer. Compared with the prior art, the present invention can accurately fill the grating tooth gap while ensuring that the transmission diffraction efficiency is higher than 85% in the entire working band and has a lower polarization degree; in addition, the grating groove shape of the transmission grating of the present invention is a trapezoidal shape, which can reduce the difficulty of the process of manufacturing the transmission grating compared with the rectangular groove shape, so that the duty cycle f of the transmission grating is greater than 0.39; so that the aspect ratio can be reduced to 1.65-1.76.

[0047] In detail, the second surface 30 of the dielectric layer 3 is parallel to the first surface 10, and the dielectric layer 3 includes a first film layer 31 and a second film layer 32, wherein the first film layer 31 covers the grating layer 2 and a portion of the substrate 1; and the second film layer 32 covers the first film layer 31. Specifically, along the height direction of the transmission grating, and with the geometric center line of the grating tooth 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 implementation, the first film layer 31 is a film layer of uniform thickness.

[0049] As a preferred implementation, 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 tooth 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]

[0060] in,

[0061] As a preferred implementation, the dielectric layer 3 is made of a high refractive index material.

[0062] The material of the dielectric layer 3 includes but is not limited to titanium dioxide (TiO2), aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5).

[0063] In detail, the substrate 1 is made of fused quartz optical glass.

[0064] 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.

[0065] The following is explained through two specific embodiments: Specific implementation method 1

[0067] Methane is a greenhouse gas that has a significant impact on the earth's climate change. By monitoring the concentration of methane, the trend of the earth's climate change can be more accurately assessed. The atmospheric detection windows of methane are mainly 1.6 microns and 2.3 microns. Here, for the 1.6 micron band, a transmission grating is given, which is mainly composed of a fused quartz substrate and a grating layer and a dielectric film layer arranged thereon.

[0068] The grating layer includes an etched grating groove, the grating groove is a trapezoid, and its period is 1100nm, and the dielectric film layer is TiO2. Figure 1 As shown, the incident angle α of the incident light in the fused silica substrate 1 is set to 31 degrees.

[0069] The optimal parameters were obtained by optimizing the structure of the grating groove. When the grating is completely filled with atomic layer deposited TiO2, the range of grating tooth height and duty cycle is obtained. Figure 3 As shown in (θ=84°or symmetrical 84°), it can be found that when the diffraction efficiency of 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 middle 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 microns is greater than 85%.

[0070] like Figure 5 As shown in the figure, compared with the traditional fully wrapped rectangular slot, when the grating is fully 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 of 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 grating tooth height of 1980nm, aspect ratio (H / Λ) of 1.8 and 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 microns is greater than 80%.

[0071] It can be clearly seen that the new trapezoidal grating groove design can effectively reduce the aspect ratio, increase the duty cycle, effectively reduce the degree of polarization, and increase the first-order diffraction efficiency from 80% to 85% in the bandwidth range of 1.59-1.67 microns.

[0072] 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 of f = 0.45 and a grating tooth height of 800nm;

[0073] Secondly, mask transfer is achieved by reactive ion beam etching, and a trapezoidal groove (angle θ=84°) is formed on the fused quartz substrate. It should be noted that the trapezoidal groove is a trapezoidal grid tooth, and the height of the trapezoidal grid tooth is 1895nm. Specifically, the reaction gas used is trifluoromethane (CHF3), the ion energy is 550ev, the ion beam current is 140mA, the acceleration voltage is 240v, and the working pressure is 2.5×10 -2 Pa;

[0074] 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 446nm. Specific implementation method 2

[0076] Carbon dioxide is a typical greenhouse gas with the characteristic of absorbing infrared radiation. It allows shorter wavelength energy from the sun to pass smoothly, but it will strongly absorb longer wavelength infrared energy released from the surface and near-ground atmosphere, thereby increasing the surface temperature and forming a greenhouse effect, which has an important impact on the earth's climate change. By monitoring the concentration of carbon dioxide, the trend of the earth's climate change can be more accurately assessed. The atmospheric detection windows of carbon dioxide are mainly 1.61 microns and 2.06 microns. Here, a transmission grating is given for the 2.06 micron band, which is mainly composed of a fused quartz substrate and a grating layer and a dielectric film layer arranged thereon.

[0077] Specifically, the grating layer includes etched grating grooves, the grating grooves are trapezoidal, and the period is 1250nm; the single-layer high refractive index dielectric film layer is TiO2. The incident angle α of the incident light in the fused silica substrate 1 is set to 38°.

[0078] The optimal parameters were obtained by optimizing the grating groove structure. When the TiO2 of the grating is completely filled, the range of grating tooth height and duty cycle is obtained. Figure 7As shown in FIG. 1 (θ = 86°), it can be found that when the diffraction efficiency is greater than 85%, the minimum required grating tooth height is 2010 nm. Therefore, with a grating tooth height of 2060 nm (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 μm is calculated as follows: Figure 8 shown.

[0079] Compared with the traditional fully wrapped rectangular channel, such as Fig. 9 As shown in FIG. 1 , when the TiO2 of the grating is just fully filled, the range of the grating tooth height and the duty cycle is obtained. It can be found that when the diffraction efficiency is greater than 85%, the minimum grating tooth height required is 2115 nm. Therefore, with a grating tooth height of 2170 nm (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 μm is calculated, as shown in FIG. Fig.10 shown.

[0080] From this, it can be clearly seen that the new grating groove design can effectively reduce the grating's aspect ratio, increase the duty cycle, and effectively reduce the degree of polarization.

[0081] 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 of f=0.44 and a grating tooth height of 960nm;

[0082] Secondly, mask transfer is achieved by reactive ion beam etching to form a trapezoidal groove (angle θ=86°) on the fused quartz substrate. It should be noted that the trapezoidal groove is a trapezoidal grid tooth with a height of 2060 nm. Specifically, the reaction gas used is trifluoromethane (CHF3), the ion energy is 450 eV, the ion beam current is 140 mA, the acceleration voltage is 240 V, and the working pressure is 2.5×10 -2 Pa;

[0083] 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.

[0084] Embodiment 2

[0085] 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 comprises:

[0086] 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;

[0087] Step S2, transferring the mask by ion beam etching to transfer the grating mask pattern to the substrate surface to form a grating layer 2;

[0088] Step S3, removing the remaining photoresist, and forming a dielectric layer 3 on the surface of the grating layer 2 by atomic layer deposition.

[0089] The thickness m of the dielectric layer is calculated by the formula in the first embodiment: in,

[0090] 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.

[0091] As a preferred implementation, in the step S1, the substrate coated with the photoresist film is placed in a holographic interference optical system for exposure.

[0092] Embodiment 3

[0093] The present invention also discloses an optical system, comprising a 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.

[0094] The present invention can obtain a transmission grating with different diffraction efficiencies and polarization degrees by designing and adjusting the film structure and size of the transmission grating. While accurately filling the grating tooth gap, it can also ensure that the transmission diffraction efficiency is higher than 85% in the entire working band and has a low polarization degree;

[0095] 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.

[0096] 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.

[0097] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0098] 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 as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0099] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0100] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still 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, wherein the grating teeth are extended along the thickness direction of the substrate, and there is a gap between two adjacent grating teeth; a dielectric layer, which is disposed on the surface of the grating layer and fills 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; The incident light passes through the grating layer and enters toward the second surface, and a diffraction effect occurs in the grating layer, the dielectric layer and the second surface to generate transmissive diffraction light, and the transmissive diffraction light is emitted through the second surface of the dielectric layer.

2. A transmission grating according to claim 1, characterized in that: 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.

3. A transmission grating according to claim 2, characterized in that: The cross-sectional shape of the grating tooth along its height direction is an isosceles trapezoid, and the hypotenuse angle θ of the grating tooth is 83 degrees to 88 degrees.

4. A transmission grating according to claim 3, characterized in that: The period Λ of the grating teeth is 700nm-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.

5. A transmission grating according to claim 4, characterized in that: in, 6. A transmission grating according to any one of claims 1 to 5, characterized in that: The dielectric layer includes titanium dioxide (TiO2), aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5).

7. A transmission grating according to claim 6, characterized in that: The substrate is made of fused quartz optical glass.

8. A method for preparing a transmission grating, characterized in that: Used to prepare a transmission grating as claimed in any one of claims 1 to 7, 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, transferring the mask 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, wherein the thickness m of the dielectric layer is calculated by the formula in claim 5.

9. The method for preparing a transmission grating according to claim 8, characterized in that: 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.

10. The method for preparing a transmission grating according to claim 8, characterized in that: 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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