Transmission grating and preparation method therefor

Abstract

The present invention relates to a transmission grating and a preparation method therefor. The transmission grating comprises: a substrate, which has a first surface; a grating layer, which comprises trapezoidal grating teeth arranged in an array on the first surface, wherein the grating teeth extend in the direction of thickness of the substrate, and a gap is provided between two adjacent grating teeth; and a dielectric layer, which is arranged on a surface of the grating layer and fills the gaps, wherein the dielectric layer has a second surface on the side thereof away from the substrate; there is a difference between the height of the grating teeth and the distance between the second surface and the first surface, the difference being m; and incident light passes through the interior of the grating layer and is incident towards the second surface. By means of the design of a film layer structure and film layer dimensions of the transmission grating, the present invention can acquire transmission gratings having different diffraction efficiencies and polarization degrees, and can accurately control the dimensions of the film layer structure of the transmission grating during machining, thereby facilitating machining.

Description

Transmission grating and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of grating, in particular to a transmission grating and a preparation method thereof. BACKGROUND

[0002] The hyperspectral imager based on grating is a kind of device with wide application, and the design and manufacture of the hyperspectral imager need comprehensive technology of multiple disciplines such as optics, spectroscopy, computer science, remote sensing technology and data processing. With the development of technology, the light splitting element combined with grating and prism appears in the imaging spectrometer system. Different from the traditional grating, the groove shape of the transmission prism grating is immersed in the high refractive index medium, such as SiO2, Si, etc. at the bottom of the grating. Because the groove shape of the prism grating is embedded in the high refractive index medium, the chromatic aberration and resolution of the grating are improved 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 under the same spectral resolution, and achieve more compact design. It is particularly suitable for high-resolution spectrometer for atmospheric greenhouse gas detection. In the published Chinese patent CN111708113A, a low-polarization high-diffraction-efficiency metal reflection immersion grating and an optical system are provided, and a reflection grating structure with a rectangular groove shape is specifically disclosed.

[0003] However, in the actual processing process, the groove shape of the grating is mostly trapezoidal, and compared with the rectangular groove shape, the processing difficulty of the trapezoidal groove shape is increased. How to accurately fill the gap of the trapezoidal groove shape while ensuring that the transmission diffraction efficiency can reach a high level in the entire waveband and has a low polarization rate becomes a problem to be solved. Therefore, it is urgent to provide an easy-to-process transmission grating. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the deficiencies in the prior art, and to provide a transmission grating and a preparation method thereof. The present application can obtain transmission gratings with different diffraction efficiencies and polarization degrees by designing the film layer structure and film layer size of the transmission grating, and can accurately control the size of the film layer structure of the transmission grating during processing, thereby facilitating processing.

[0005] To solve the above technical problems, the present application 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 being arranged along the thickness direction of the substrate, and having a gap between adjacent grating teeth;

[0008] A medium layer is arranged on the surface of the grating layer and fills the gaps, the medium layer has a second surface away from the side of the substrate, the second surface has a difference between the interval from the first surface and the height of the grating teeth, and the difference is m;

[0009] The incident light is incident towards the second surface direction inside the grating layer, and the diffraction effect occurs on the grating layer, the medium layer and the second surface to generate transmitted diffraction light, which is emitted through the second surface of the medium layer.

[0010] In an embodiment of the present application, the medium layer includes a first film layer and a second film layer, the first film layer covers the grating layer and part of the substrate, and 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, and m = m1 + m2.

[0011] In an embodiment of the present application, the cross-sectional shape of the grating teeth along the height direction is isosceles trapezoidal, and the angle θ of the inclined side of the grating teeth is 83 degrees to 88 degrees.

[0012] In an embodiment of the present application, the period Λ of the grating teeth is 700 nm to 2000 nm, 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 = (b / Λ) is 0.39 to 0.48, and the aspect ratio (H / Λ) is 1.65 to 1.76. 中

[0013] In an embodiment of the present application, the angle θ of the inclined side of the grating teeth is 83 degrees to 88 degrees, wherein, In an embodiment of the present application, the medium layer includes titanium dioxide (TiO2), aluminum oxide (Al2O3) and tantalum pentoxide (Ta2O5).

[0014] In an embodiment of the present application, the substrate is prepared from fused quartz optical glass.

[0015] The present application also provides a preparation method of a transmission grating for preparing the transmission grating as described above, and the preparation method includes:

[0016] Step S1, selecting a substrate, coating photoresist on the substrate, exposing the substrate coated with photoresist film, and developing the exposed substrate in a developing solution to obtain a photoresist grating mask;

[0017] Step S2, mask transfer is realized by ion beam etching, the grating mask pattern is transferred to the surface of the substrate to form a grating layer;

[0018] ​Step S3, removing the remaining photoresist, 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.

[0019] In one embodiment of the present application, in the ion beam etching step in the 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.

[0020] In one embodiment of the present application, in the step S1, the substrate coated with the photoresist film is placed in a holographic interference optical system for exposure.

[0021] The above technical solution of the present application has the following advantages compared with the prior art:

[0022] The transmission grating provided by the present application 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 trapezoidal grating teeth arranged in an array on the substrate, and the dielectric layer is arranged on the surface of the grating layer and can fill the gaps between adjacent grating teeth; specifically, the side of the dielectric layer away from the substrate has a second surface, and the difference between the distance between the second surface and the first surface of the substrate and the height of the grating teeth is defined as m, and the difference m can also be regarded as the thickness of the dielectric layer.

[0023] Compared with the prior art, the present application can precisely fill the gaps between the grating teeth while ensuring that the transmission diffraction efficiency is higher than 85% in the entire working waveband and the polarization degree is low; in addition, the grating groove of the transmission grating of the present application is trapezoidal, which can reduce the process manufacturing difficulty of the transmission grating compared with the rectangular groove shape, so that the duty cycle f of the transmission grating is greater than 0.39, and the aspect ratio is reduced to 1.65-1.76.

[0024] The present application can obtain transmission gratings with different diffraction efficiencies and polarization degrees by designing the film layer structure and film layer size of the transmission grating, and the size of the film layer structure of the transmission grating can be accurately controlled during processing, so that the processing is easy. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, in which:

[0026] Fig. 1 is a structural schematic diagram of a preferred embodiment of the present application.

[0027] Fig. 2 is a technical flowchart of the preparation method of the preferred embodiment of the present application.

[0028] Figure 3 is a diagram showing the distribution of the central duty cycle and the grating tooth height when θ = 84° in the specific embodiment 1 of the present application.

[0029] Figure 4 is a diagram showing the distribution of the diffraction efficiency and the wavelength when H = 1895 nm and the central duty cycle is 0.45 in the specific embodiment 1 of the present application.

[0030] Figure 5 is a diagram showing the range distribution of the grating tooth height and the duty cycle when the grating tooth is rectangular and the dielectric layer fully wraps the rectangular groove in the specific embodiment 1 of the present application.

[0031] Figure 6 is a diagram showing the distribution of the diffraction efficiency and the wavelength when H = 1980 nm and the duty cycle is 0.39 in the specific embodiment 1 of the present application.

[0032] Figure 7 is a diagram showing the distribution of the central duty cycle and the grating tooth height when θ = 86° in the specific embodiment 2 of the present application.

[0033] Figure 8 is a diagram showing the distribution of the diffraction efficiency and the wavelength when H = 2060 nm and the central duty cycle is 0.44 in the specific embodiment 2 of the present application.

[0034] Figure 9 is a diagram showing the range distribution of the grating tooth height and the duty cycle when the grating tooth is rectangular and the dielectric layer fully wraps the rectangular groove in the specific embodiment 2 of the present application.

[0035] Figure 10 is a diagram showing the distribution of the diffraction efficiency and the wavelength when H = 2170 nm and the duty cycle is 0.42 in the specific embodiment 2 of the present application.

[0036] The description of the figures of the accompanying drawings is as follows: 1, substrate; 10, first surface; 2, grating layer; 20, grating tooth; 3, dielectric layer; 30, second surface; 31, first film layer; 32, second film layer. Specific Embodiment

[0037] The present application will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it. The embodiments are not intended to limit the present application.

[0038] Example 1

[0039] Referring to Figure 1, the present application discloses a transmission grating, which comprises a substrate 1, wherein the substrate 1 has a first surface 10;

[0040] The transmission grating further comprises a grating layer 2, the grating layer 2 comprises a plurality of trapezoidal grating teeth 20 arranged in an array on the first surface 10, the plurality of grating teeth 20 are arranged along the thickness direction of the substrate 1, and a gap is formed between two adjacent grating teeth 20, so that the grating layer 2 forms a plurality of gaps;

[0041] The transmission grating further comprises a medium layer 3, the medium layer 3 is arranged on the surface of the grating layer 2 and fills the plurality of gaps. Specifically, the medium layer 3 can cover the grating layer 2 and fill the plurality of gaps.

[0042] In detail, the medium layer 3 has a second surface 30 away from the substrate 1, and the difference between the distance of the second surface 30 from the first surface 10 and the height of the grating tooth 20 is m.

[0043] It should be noted that the difference m can also be considered as the thickness of the medium layer 3.

[0044] The grating layer 2 and the medium layer 3 form a first interface, the incident light is incident towards the first interface through the inside of the grating layer 2, and the diffraction effect occurs at the first interface, the medium 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 medium layer 3.

[0045] Therefore, the transmission grating to be protected by the present application comprises a substrate, a grating layer and a medium 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 medium layer is arranged on the surface of the grating layer and can fill the gap between adjacent grating teeth. Specifically, the medium layer has a second surface away from the substrate, and the difference between the distance of the second surface from the first surface of the substrate and the height of the grating tooth is m, which is defined as m. The difference m can also be considered as the thickness of the medium layer. Compared with the prior art, the present application can precisely fill the gap between the grating teeth while ensuring that the transmission and diffraction efficiency is higher than 85% in the entire working waveband and has a lower polarization degree. In addition, the grating groove of the transmission grating of the present application is trapezoidal, which can reduce the process difficulty of the transmission grating, so that the duty cycle f of the transmission grating is greater than 0.39, and the aspect ratio is reduced to 1.65-1.76.

[0046] In detail, 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 part 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 taking the geometric center line of the grating tooth 20 as the reference, the thickness of the first film layer 31 is m1, the thickness of the second film layer 32 is m2, and m = m1 + m2.

[0047] As a preferred embodiment, the first film layer 31 is an equal-thickness film layer.

[0048] As a preferred embodiment, a plurality of grating teeth 20 are arranged at equal intervals on the first surface 10 to form the grating layer 2.

[0049] Specifically, the cross-sectional shape of the grating tooth 20 along its height direction is isosceles trapezoidal.

[0050] Further, the parameters are defined as follows:

[0051] The period Λ of the grating tooth 20 is 700 nm to 2000 nm,

[0052] The bottom width of the grating tooth 20 is a,

[0053] The middle width of the grating tooth 20 is b,

[0054] The height of the grating tooth 20 is H,

[0055] The middle duty cycle f 中 = (b / Λ) is 0.39 to 0.48, and the aspect ratio (H / Λ) is 1.65 to 1.76.

[0056] Further, the bevel angle θ of the grating tooth 20 is 83 degrees to 88 degrees.

[0057] Therefore, the difference m, i.e. the thickness of the dielectric layer 3, is defined as:

[0058] Wherein,

[0059] As a preferred embodiment, the dielectric layer 3 is prepared by using high refractive index materials.

[0060] The material of the dielectric layer 3 includes but is not limited to titanium dioxide (TiO2), aluminum oxide (Al2O3), and tantalum pentoxide (Ta2O5).

[0061] In detail, the substrate 1 is made of fused silica optical glass.

[0062] Therefore, the film layer structure and the film layer size of the transmission grating can be designed to obtain transmission gratings with different diffraction efficiencies and polarization degrees.

[0063] The following is described through two specific embodiments:

[0064] Specific embodiment 1

[0065] Methane is a greenhouse gas that has a significant impact on the climate change of the earth. By monitoring the concentration of methane, the trend of the climate change of the earth can be more accurately evaluated. The atmospheric detection windows of methane mainly include 1.6 microns and 2.3 microns. Here, a transmission grating is given for the 1.6-micron band, which mainly includes a fused silica substrate and a grating layer and a dielectric film layer arranged thereon.

[0066] The grating layer includes etched grating grooves, and the grating grooves are trapezoidal with a period of 1100 nm. The dielectric film layer is made of TiO2. Referring to FIG. 1, the incident angle α of the incident light in the fused silica substrate 1 is set to 31 degrees.

[0067] By optimizing the structure of the grating grooves, the optimal parameters are obtained. When the grating is filled with TiO2 by atomic layer deposition, the range of the tooth height and the duty cycle is obtained. As shown in FIG. 3 (θ = 84° or symmetric 84°), it can be found that when the diffraction efficiency of the central band is greater than 85%, the minimum tooth height required is 1810 nm. Therefore, under the condition that the tooth height is 1895 nm, the aspect ratio (H / Λ) is 1.72, and the middle duty cycle is 0.45, the first-order diffraction efficiency in the 1.59-1.67-micron bandwidth range is calculated. As shown in FIG. 4, it can be seen that the first-order diffraction efficiency in the 1.59-1.67-micron bandwidth range is greater than 85%.

[0068] As shown in FIG. 5, compared with the traditional full-wrapped rectangular groove shape, when the grating is filled with TiO2 by atomic layer deposition, the range of the tooth height and the duty cycle is obtained. It can be found that when the diffraction efficiency of the central band is greater than 85%, the minimum tooth height required is 1910 nm. Therefore, under the condition that the tooth height is 1980 nm, the aspect ratio (H / Λ) is 1.8, and the duty cycle is 0.39, the first-order diffraction efficiency in the 1.59-1.67-micron bandwidth range is calculated. As shown in FIG. 6, it can be seen that the first-order diffraction efficiency in the 1.59-1.67-micron bandwidth range is greater than 80%.

[0069] Therefore, it can be obviously seen that by the new trapezoidal grating groove design, the aspect ratio is effectively reduced, the duty cycle is increased, the polarization degree is effectively reduced, and the first-order diffraction efficiency in the 1.59-1.67 micron bandwidth range is increased from 80% to 85%.

[0070] In detail, in the preparation process, first, photoresist is coated on a fused quartz substrate, and then a photoresist grating mask is made on the photoresist by a holographic lithography method, the duty cycle f = 0.45, and the grating tooth height is 800 nm.

[0071] Secondly, mask transfer is realized by reactive ion beam etching, and trapezoidal (inclination angle θ = 84°) grooves are formed on the fused quartz substrate, and it should be noted that the trapezoidal grooves are trapezoidal grating teeth, and the trapezoidal grating tooth height is 1895 nm. Specifically, the reactive gas is trifluoromethane (CHF3), the ion energy is 550 ev, the ion beam current is 140 mA, the acceleration voltage is 240 v, and the working pressure is 2.5 × 10 -2 Pa;

[0072] After removing the remaining photoresist, a layer of high refractive index material TiO2 is formed by atomic layer deposition method, and the thickness of the TiO2 film layer is calculated according to the formula Wherein The thickness of the TiO2 film layer is calculated to be 446 nm.

[0073] Specific implementation 2

[0074] Carbon dioxide is a typical greenhouse gas, which has the characteristics of absorbing infrared radiation. It can smoothly pass the energy of shorter wavelength from the sun, but it can strongly absorb the longer wavelength infrared energy released from the ground and the near-surface atmosphere, thereby increasing the temperature of the ground and forming a greenhouse effect, which has an important influence on the climate change of the earth. By monitoring the concentration of carbon dioxide, the trend of climate change of the earth can be more accurately evaluated. The main atmospheric detection windows of carbon dioxide are 1.61 microns and 2.06 microns. Here, a transmission grating is given for the 2.06 micron band, which mainly consists of a fused quartz substrate and a grating layer and a dielectric film layer arranged thereon.

[0075] Specifically, the grating layer includes etched grating grooves, the grating grooves are trapezoidal, the period is 1250 nm, and the single-layer high-refractive-index dielectric film layer is TiO2. The incident angle α of the incident light in the fused quartz substrate 1 is set to 38°.

[0076] The best parameters are obtained by optimizing the grating groove structure. When the TiO2 of the grating is just filled, the range of the grating tooth height and the duty cycle is obtained. As shown in Fig. 7 (θ = 86°), it can be found that when the diffraction efficiency is greater than 85%, the minimum grating tooth height required is 2010 nm, and therefore the first-order diffraction efficiency in the 2.042-2.086 μm bandwidth range is calculated with the grating tooth height (H / Λ) = 1.65, the middle duty cycle 0.44, as shown in Fig. 8.

[0077] As compared with the conventional full-wrapped rectangular groove, as shown in Fig. 9, when the TiO2 of the grating is just filled, the range of the grating tooth height and the duty cycle is obtained, and it can be found that when the diffraction efficiency is greater than 85%, the minimum grating tooth height required is 2115 nm, and therefore the first-order diffraction efficiency in the 2.042-2.086 μm bandwidth range is calculated with the grating tooth height (H / Λ) = 1.74, the duty cycle 0.42, as shown in Fig. 10.

[0078] Therefore, it can be obviously seen that by the new grating groove design, the aspect ratio of the grating is effectively reduced, the duty cycle is increased, and the polarization degree is effectively reduced.

[0079] In the preparation process, first, the photoresist is coated on the fused quartz substrate, and then the photoresist grating mask is made on the photoresist by the holographic lithography method, the duty cycle f = 0.44, and the grating tooth height is 960 nm.

[0080] Secondly, the mask transfer is realized by the reactive ion beam etching to form the trapezoidal (inclined angle θ = 86°) groove on the fused quartz substrate. It needs to be noted that the trapezoidal groove is the trapezoidal grating tooth, and the trapezoidal grating tooth height is 2060 nm. Specifically, the reactive gas is trifluoromethane (CHF3), the ion energy is 450 ev, the ion beam current is 140 mA, the acceleration voltage is 240 v, the working pressure is 2.5 × 10 -2 Pa;

[0081] After the remaining photoresist is removed, a layer of high refractive index material TiO2 is formed by atomic layer deposition, and the thickness of the TiO2 film layer is calculated according to the formula Wherein The thickness of the TiO2 film layer is 453 nm.

[0082] Example Two

[0083] The application further discloses a preparation method of the transmission grating, which is used for preparing the transmission grating as described in Example One, and in combination with Fig. 2, the preparation method comprises the following steps.

[0084] Step S1: Select substrate 1, coat the substrate 1 with photoresist, expose the substrate coated with photoresist film, and immerse the exposed substrate in a developing solution to obtain a photoresist grating mask.

[0085] Step S2: Mask transfer is achieved by ion beam etching, transferring the grating mask pattern to the substrate surface to form grating layer 2;

[0086] Step S3: Remove the remaining photoresist and form a dielectric layer 3 on the surface of the grating layer 2 by atomic layer deposition.

[0087] The thickness m of the dielectric layer is calculated using the formula in Example 1. in,

[0088] In a preferred embodiment, in the ion beam etching step of step S2, the working gas is trifluoromethane (CHF3), the ion energy is 200–600 eV, the ion beam current is 50–160 mA, the accelerating voltage is 200–260 V, and the working pressure is 2.4 × 10⁻⁶. -2 Pa.

[0089] In a preferred embodiment, in step S1, the substrate coated with photoresist film is placed in a holographic interference optical system for exposure.

[0090] Example 3

[0091] The present invention also discloses an optical system comprising a transmission grating as described in Embodiment 1, wherein the angle of the incident light is in the range of 30°-50°. The bandwidth of the incident light is in the range of 1.5-2.1 micrometers.

[0092] This invention, through the design and adjustment of the film structure and dimensions of the transmission grating, enables the acquisition of transmission gratings with different diffraction efficiencies and polarization degrees. It achieves precise filling of the grating tooth gaps while ensuring a transmission diffraction efficiency exceeding 85% across the entire operating wavelength range and maintaining a low polarization degree.

[0093] In addition, the grating groove of the transmission grating of the present invention is trapezoidal, which reduces the manufacturing difficulty of the transmission grating compared with the rectangular groove, and makes the duty cycle f of the transmission grating greater than 0.39; and reduces the aspect ratio to 1.65 to 1.76.

[0094] This invention enables the design of the film structure and dimensions of the transmission grating, thereby obtaining transmission gratings with different diffraction efficiencies and polarization degrees. It also facilitates precise control of the dimensions of the transmission grating film structure during processing, making it easier to manufacture.

[0095] In the description of the embodiments of the present application, it also needs to be explained that, unless explicitly specified and limited, if the terms "set", "connected" appear, they should be understood in a broad sense, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be mechanically connected, can be electrically connected; can be directly connected, can be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0096] In the description of the present application, it should be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified and limited.

[0097] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, can be detachably connected, or integrated; can be mechanically connected, can be electrically connected; can be directly connected, can be indirectly connected through an intermediate medium; can be the communication inside two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0098] Obviously, the above embodiments are only examples for the purpose of clarity, and are not limited to the implementation. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A transmission grating, characterized by: Comprising, a substrate having a first surface; a grating layer comprising a trapezoidal grating tooth array arranged on the first surface, the grating tooth extending along the thickness direction of the substrate, and having a gap between two adjacent grating teeth; a dielectric layer arranged on the surface of the grating layer and filling the gap, the dielectric layer having a second surface away from the substrate, the second surface having a difference between the distance from the first surface and the height of the grating tooth, the difference being m; incident light is incident on the second surface through the interior of the grating layer, and the diffraction effect occurs on the grating layer, dielectric layer and second surface to generate transmitted diffraction light, which is emitted through the second surface of the dielectric layer.

2. A transmission grating according to claim 1, wherein: The dielectric layer comprises a first film layer and a second film layer, the first film layer covers the grating layer and part of the substrate, and 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, and m=m1+m2.

3. A transmission grating according to claim 2, wherein: The cross-sectional shape of the grating tooth along its height direction is isosceles trapezoidal, and the angle θ of the inclined side of the grating tooth is 83-88 degrees.

4. A transmission grating according to claim 3, wherein: The period of the grating tooth is 700-2000 nm, 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.

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

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

8. A method of making a transmission grating, characterized by: A method for preparing a transmission grating as claimed in any one of claims 1-7, the preparation method comprising: Step S1, selecting a substrate, coating photoresist on the substrate, exposing the substrate coated with photoresist film, developing the exposed substrate in a developing solution to obtain a photoresist grating mask; Step S2, mask transfer is realized by ion beam etching, the grating mask pattern is transferred to the surface of the substrate to form a grating layer; Step S3, remove the remaining photoresist, form 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 formula in claim 5.

9. The method of claim 8, wherein: In the ion beam etching step in the 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 2.4x10 -2 Pa.

10. The method of claim 8, wherein: In the step S1, the substrate coated with photoresist film is placed in a holographic interference optical system for exposure.

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