Transmission grating and method of manufacturing the same

Abstract

The present application relates to a kind of transmission grating and its manufacturing method, including substrate, with first surface in thickness direction;Grating layer, including array arrangement grating tooth in first surface, with gap between adjacent grating tooth;Grating tooth is two-section type tower shape structure, grating tooth includes upper grating block and lower grating block, and lower grating block is connected with the first surface;First dielectric layer, set in grating layer surface, and fill gap, form continuous layer structure;First dielectric layer has second surface away from substrate side;First dielectric layer and gap opposite place form groove;Second dielectric layer, set in groove, second dielectric layer has third surface, and the edge of third surface is connected with second surface.The present application designs tower shape structure grating tooth layer and dielectric film layer structure, to obtain high diffraction efficiency and low polarization sensitivity transmission grating, so that grating appearance can be more stable, and it is convenient to carry out accurate processing.

Description

Technical Field

[0001] This invention relates to the field of grating technology, and in particular to a transmission grating and its manufacturing method. Background Technology

[0002] Hyperspectral imagers based on gratings are widely used in high-precision atmospheric remote sensing monitoring. They are a comprehensive technology integrating optics, spectroscopy, computer science, remote sensing technology, and data processing. With technological advancements, spectral elements combining gratings and prisms have emerged in hyperspectral imager systems. Unlike traditional gratings, transmission prism gratings consist of a grating and a prism, with the grating immersed in a high-refractive-index medium, such as SiO2 or Si. Because the prism grating's grooves are embedded in the high-refractive-index medium, the optical path difference and angular dispersion increase proportionally. Applying prism gratings to spectrometers not only achieves high spectral resolution but also reduces the focal length of the collimation system, significantly reducing the spectrometer's size and achieving a more compact design. This is particularly suitable for high-precision atmospheric remote sensing monitoring.

[0003] However, the shortcomings of the existing technology are that in actual processing, if the grating duty cycle is too small (less than 0.2), the grating grooves will easily collapse, resulting in the inability to preserve the grating morphology. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a transmission grating and its manufacturing method. By designing the grating tooth layer and dielectric film layer structure with the shape of an iron tower, a transmission grating with high diffraction efficiency and low polarization sensitivity can be obtained, so that the grating morphology can be more stable and the size of the transmission grating film layer structure can be accurately controlled during processing, thus making it easy to process.

[0005] To solve the above-mentioned technical problems, the present invention provides a transmission grating, comprising,

[0006] A substrate having a first surface along its thickness direction;

[0007] A grating layer includes grating teeth arranged in an array on a first surface, with gaps between adjacent grating teeth; each grating tooth has a top surface and a bottom surface, and includes an upper grating block and a lower grating block, the lower grating block being connected to the first surface, and the upper and lower grating blocks cooperating to form a two-section tower-shaped structure; the lower grating block has a trapezoidal cross-sectional shape, the upper grating block has a rectangular cross-section, the width of the bottom surface is the same as the width of the bottom surface of the lower grating block, and the width of the top surface is the same as the width of the upper grating block;

[0008] A first dielectric layer is disposed on the surface of the grating layer and fills the gap to form a continuous layer structure; the first dielectric layer has a second surface on the side away from the substrate; a groove is formed in the first dielectric layer opposite to the gap;

[0009] A second dielectric layer is disposed in the trench, the second dielectric layer having a third surface, the edge of the third surface being connected to the second surface;

[0010] Incident light passes through the interior of the grating layer and is incident toward the second and third surfaces. Diffraction occurs in the grating layer, the first dielectric layer, the second dielectric layer, and the second and third surfaces to generate transmitted diffracted light. The transmitted diffracted light exits through the second surface of the first dielectric layer and the third surface of the second dielectric layer.

[0011] In one embodiment of the present invention, the grating teeth include an upper grating block and a lower grating block arranged sequentially along the height direction, the lower grating block being connected to the first surface; along the height direction of the grating teeth, the cross-sectional shape of the lower grating block is an isosceles trapezoid, and the cross-sectional shape of the upper grating block is a rectangle; the width of the rectangle is equal to the upper base of the isosceles trapezoid.

[0012] In one embodiment of the present invention, along the height direction of the grating teeth, the distance between the second surface and the first surface has a difference with the height of the grating teeth, and the difference is m, where m is calculated using the formula: , ,

[0013] ,

[0014] Wherein, the refractive index of the first dielectric layer is n1, the refractive index of air is n0, the wavelength of the incident light is λ, the period of the grating teeth is Λ, where Λ is 300nm~2000nm; the bottom width of the grating teeth is a, the top width of the grating teeth is b, the height of the upper grating block is H1, the height of the lower grating block is H2, the height of the grating teeth is H, where H=H1+H2, and the aspect ratio H / Λ is 1.92~2.17; the height ratio of the upper grating block to the lower grating block is k, where k=H1 / H2, and k is 0.5~1; the angle of the isosceles trapezoid is θ, where θ is 84.5°~87.5°, and the top occupancy ratio is f. 顶 =b / Λ is 0.1~0.12, and the bottom width ratio is 0.1~0.12. It ranges from 0.2 to 0.4.

[0015] In one embodiment of the present invention, the material of the first dielectric layer includes titanium dioxide, aluminum oxide, or tantalum pentoxide.

[0016] In one embodiment of the present invention, the material of the second dielectric layer includes titanium dioxide, aluminum oxide, or tantalum pentoxide.

[0017] In one embodiment of the present invention, the thickness of the second dielectric layer is h, where h < H2; the thickness h of the second dielectric layer is 50-160 nm.

[0018] The present invention also provides a method for manufacturing a transmission grating, for manufacturing the transmission grating as described above, the method comprising,

[0019] Step S1: Obtain a prism substrate, coat the prism substrate with photoresist, and pre-bake; expose the baked prism substrate with photoresist film, and then develop the exposed prism substrate to obtain a photoresist mask.

[0020] Step S2 involves transferring the mask pattern to the surface of the prism substrate material through ion beam etching, and forming a tower-shaped grating layer by adjusting the etching parameters; the grating layer includes an array of grating teeth.

[0021] Step S3: Remove the remaining photoresist. A first dielectric layer is formed on the grating layer by atomic layer deposition. The distance between the first dielectric layer and the grating teeth along the thickness direction of the grating layer is m, which is calculated by the above formula. Then, a second dielectric layer is formed on the first dielectric layer by vacuum evaporation deposition. The second dielectric layer is formed in the trench of the first dielectric layer. The vacuum evaporation deposition material on the top of the grating teeth is removed by polishing.

[0022] In one embodiment of the present invention, the period Λ of the grating layer formed by the steps S1 to S3 is 300nm to 2000nm; the bottom aspect ratio is 0.2 to 0.4; and the depth-to-width ratio H / Λ is 1.92 to 2.17.

[0023] In one embodiment of the present invention, in step S2, during the ion beam etching process, the reaction gas is trifluoromethane, 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 2.0 × 10⁻⁶. -2 Pa.

[0024] In one embodiment of the present invention, in step S1, a prism substrate with a photoresist film after pre-baking is placed into an interference optical system for exposure using a holographic lithography method.

[0025] The technical solution of the present invention has the following advantages compared with the prior art:

[0026] The present invention discloses a transmission grating comprising a substrate, a grating layer, a first dielectric layer, and a second dielectric layer. During manufacturing, a combination of vacuum evaporation deposition and inclined etching and polishing processes is used to add a high-refractive-index material to the surface of the grating layer, further improving the refractive efficiency. The thickness of the atomic-layer deposited titanium oxide coating can be calculated using a film thickness formula, thus facilitating precise control of the coating thickness. In actual processing, a grating duty cycle that is too small (less than 0.2) will cause the grating grooves to easily collapse, resulting in the inability to retain the grating morphology. By using a tower-shaped grating tooth structure design, the grating duty cycle is increased from the original 0.14-0.16 to 0.2-0.4, while simultaneously improving the transmission diffraction efficiency across the entire wavelength range and further reducing the polarization sensitivity. The diffraction efficiency can be increased from 75% to 86.5%, and the polarization sensitivity reduced from 10% to 2.5%. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] Figure 1 This is a cross-sectional structural diagram of a transmission grating according to a preferred embodiment of the present invention.

[0029] Figure 2 This is a three-dimensional structural schematic diagram of a transmission grating according to a preferred embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the manufacturing process of a transmission grating according to a preferred embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram showing the distribution of rectangular slot shape, duty cycle, and tooth height in the first specific embodiment of the present invention.

[0032] Figure 5 This is a diagram showing the relationship between a rectangular groove shape, wavelength, diffraction efficiency, and polarization sensitivity in the first specific embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram showing the distribution of the tower-shaped groove, groove depth, and grating tooth angle in the first specific embodiment of the present invention.

[0034] Figure 7 This is a diagram showing the relationship between wavelength, diffraction efficiency, and polarization sensitivity in the first specific embodiment of the present invention, with the shape of the iron tower-shaped groove.

[0035] Figure 8 This is a schematic diagram showing the distribution of rectangular slot shape, duty cycle, and tooth height in a second specific embodiment of the present invention.

[0036] Figure 9This is a second specific embodiment of the present invention, showing the relationship between the rectangular groove shape, wavelength, diffraction efficiency, and polarization sensitivity.

[0037] Figure 10 This is a schematic diagram showing the distribution of the tower-shaped groove, groove depth, and grating tooth angle in the second specific embodiment of the present invention.

[0038] Figure 11 This is a second specific embodiment of the present invention, showing the relationship between the tower-shaped groove, wavelength, diffraction efficiency, and polarization sensitivity.

[0039] Explanation of reference numerals in the instruction manual:

[0040] 1. Substrate; 11. First surface;

[0041] 2. Grating teeth; 21. Upper grating block; 22. Lower grating block;

[0042] 3. First dielectric layer; 31. Second surface;

[0043] 4. Second dielectric layer; 41. Third surface. Detailed Implementation

[0044] 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 and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0045] Example 1

[0046] Reference Figures 1 to 11 As shown, the present invention discloses a transmission grating, including a substrate 1, wherein the substrate 1 has a first surface 11 along the thickness direction;

[0047] The transmission grating further includes a grating layer, which includes grating teeth 2 arranged in an array on the first surface 11, with gaps formed between adjacent grating teeth 2;

[0048] It should be noted that, along the height direction of the grating teeth 2, the grating teeth 2 have a top surface and a bottom surface, and the width of the bottom surface is greater than the width of the top surface. Thus, the grating teeth 2 can form a tower-shaped structure. At the same time, since the bottom surface width of the grating teeth 2 is greater than the top surface width, it can help enhance the localization effect of light in the grating region, thereby improving the diffraction efficiency.

[0049] In detail, the grating teeth 2 include an upper grating block 21 and a lower grating block 22 arranged sequentially along the height direction. The lower grating block 22 is connected to the first surface 11. Along the height direction of the grating teeth 2, the cross-sectional shape of the lower grating block 22 is trapezoidal, and the cross-sectional shape of the upper grating block 21 is rectangular. The width of the bottom surface is the same as the width of the bottom surface of the lower grating block 22. The width of the top surface is the same as the width of the upper grating block 21.

[0050] The transmission grating further includes a first dielectric layer 3, which is a high refractive index layer. The first dielectric layer 3 is disposed on the upper surface of the grating layer. At the same time, the first dielectric layer 3 can fill the gap, thereby forming a continuous layer structure on the upper surface of the grating layer. The side of the first dielectric layer 3 away from the substrate 1 has a second surface 31.

[0051] Furthermore, a groove is formed at the location where the first dielectric layer 3 is opposite to the gap;

[0052] The transmission grating further includes a second dielectric layer 4, which is filled in the trench and has a third surface 41; the edge of the third surface 41 is connected to (in contact with) the second surface 31.

[0053] Incident light enters the substrate 1 and is incident on the grating layer. It passes through the grating layer and is incident on the second surface 31 and the third surface 41. Diffraction effect occurs in the grating layer, the first dielectric layer 3, the second dielectric layer 4, and the second surface 31 and the third surface 41 to generate transmitted diffracted light. The transmitted diffracted light exits through the second surface 31 of the first dielectric layer 3 and the third surface 41 of the second dielectric layer 4.

[0054] The first dielectric layer 3 fills the gaps and forms a continuous layer, which facilitates the subsequent deposition of the second dielectric layer 4 or device integration, and effectively reduces scattering loss. Simultaneously, it works with the second dielectric layer 4 to form two different transmission and diffraction optical paths, allowing the incident light energy to be more effectively split and utilized. Furthermore, the trench structure formed by the first dielectric layer 3 can naturally position the second dielectric layer 4, reducing alignment difficulties and improving manufacturing tolerances during production.

[0055] By selecting parameters such as the refractive index, thickness, grating period, and duty cycle of the first dielectric layer 3 and the second dielectric layer 4, the phase, intensity, and angular distribution of the two transmitted diffracted beams can be independently controlled, thus expanding the design freedom.

[0056] Therefore, it can be understood that the transmission grating protected by this invention comprises a substrate, a grating layer, a first dielectric layer, and a second dielectric layer. During the manufacturing process, a combination of vacuum evaporation coating and inclined etching and polishing processes is used to add a high refractive index material to the surface of the grating layer, thereby further improving the refractive efficiency. The coating thickness of atomic layer deposited titanium oxide can be calculated using the film thickness formula, which is beneficial for precise control of the coating thickness. In actual processing, if the grating duty cycle is too small (less than 0.2), the grating grooves will easily collapse, and the grating morphology cannot be preserved. Through the design of the tower-shaped grating tooth structure, the grating duty cycle is increased from the original 0.14-0.16 to 0.2-0.4, while the transmission diffraction efficiency is further improved in the entire wavelength band, and the polarization sensitivity is further reduced. The diffraction efficiency can be increased from 75% to 86.5%, and the polarization sensitivity is reduced from 10% to 2.5%.

[0057] In a preferred embodiment, along the height direction of the grating teeth 2, the lower grating block 22 has an isosceles trapezoidal cross-sectional shape, and the upper grating block 21 has a rectangular cross-sectional shape; the width of the rectangle is equal to the upper base of the isosceles trapezoid; with this arrangement, the upper grating block 21 and the lower grating block 22 can cooperate to form a grating tooth structure similar to an iron tower, thereby forming a transmission grating with high diffraction efficiency and low polarization sensitivity, and facilitating precise control of the dimensions of the transmission grating film structure during processing, making it easy to process.

[0058] Along the height direction of the grating teeth 2, there is a difference between the distance between the second surface 31 and the first surface 11 and the height of the grating teeth 2, and this difference is defined as m.

[0059] The formula for calculating m is: , ,

[0060] ,

[0061] Wherein, the refractive index of the first dielectric layer is n1, the refractive index of air is n0, and the wavelength of the incident light is λ.

[0062] The period of the grating teeth 2 is Λ, where Λ is 300nm to 2000nm;

[0063] The bottom width of the grating teeth 2 is a.

[0064] The top width of the grating tooth 2 is b.

[0065] The height of the upper grating block 21 is H1, and the height of the lower grating block 22 is H2.

[0066] The height of the grating teeth 2 is H, where H = H1 + H2;

[0067] The aspect ratio H / Λ is 1.92 to 2.17;

[0068] The height ratio of the upper grating block to the lower grating block is k, k = H1 / H2, and k is 0.5 to 1.

[0069] The angle of the isosceles trapezoid is θ, where θ is between 84.5° and 87.5°.

[0070] Top aspect ratio f 顶 =b / Λ is 0.1 to 0.12,

[0071] Bottom aspect ratio f 底 for It ranges from 0.2 to 0.4.

[0072] It should be noted that the first dielectric layer 3 and the second dielectric layer 4 are configured as oxide dielectric films;

[0073] In a preferred embodiment, the material of the first dielectric layer 3 includes titanium dioxide (TiO2), aluminum oxide (Al2O3), or tantalum pentoxide (Ta2O5).

[0074] In a preferred embodiment, the material of the second dielectric layer 4 includes titanium dioxide (TiO2), aluminum oxide (Al2O3), or tantalum pentoxide (Ta2O5).

[0075] The thickness of the second dielectric layer 4 is defined as h, where h < H2; preferably, the thickness h of the second dielectric layer is 50-160 nm.

[0076] Example 2

[0077] The present invention also discloses a method for manufacturing a transmission grating, used to manufacture the transmission grating as described in Example 1, referenced... Figures 1 to 11 As shown, the manufacturing method includes,

[0078] Step S1: Obtain a prism substrate, coat the prism substrate with photoresist, and pre-bake; then, expose the baked prism substrate with photoresist film, and then immerse the exposed prism substrate in a developing solution to obtain a photoresist mask.

[0079] Step S2: After the photoresist mask that meets the requirements is fabricated, the mask is transferred by ion beam etching to transfer the mask pattern to the surface of the prism substrate material to form a grating layer; the grating layer includes a plurality of grating teeth 2; there are gaps between adjacent grating teeth 2; each grating tooth 2 is a tower-shaped structure;

[0080] Step S3: Remove the remaining photoresist and form a first dielectric layer 3 with a high refractive index on the grating layer by atomic layer deposition; trenches are formed on the first dielectric layer 3; along the height direction of the transmission grating, the trenches are opposite to the gaps;

[0081] Then, a second dielectric layer 4 with a high refractive index is formed on the first dielectric layer 3 by vacuum evaporation coating. The second dielectric layer 4 is located at the position of the trench of the first dielectric layer 3. Then, the vacuum evaporation coating material on the top of the grating teeth 2 is removed by polishing process to complete the fabrication.

[0082] Along the thickness direction of the grating teeth 2, the distance between the first dielectric layer 3 and the grating teeth 2 is m, and the distance m can be calculated by the formula in Embodiment 1.

[0083] It should be noted that since atomic layer deposition of titanium dioxide forms a film of uniform thickness, when forming the second dielectric layer 4, the second dielectric layer 4 fills the trenches of the first dielectric layer 3 and has a thickness h, which needs to be achieved through vacuum evaporation coating and tilted etching and polishing processes.

[0084] Specifically, the grating layer formed by steps S1 to S3 has a period Λ of 300nm to 2000nm; a bottom aspect ratio of 0.2 to 0.4; and a depth-to-width ratio H / Λ of 1.92 to 2.17.

[0085] In a preferred embodiment, during step S2, the reaction gas used in the ion beam etching process is trifluoromethane, the ion energy is 200–600 eV, the ion beam current is 50–160 mA, the accelerating voltage is 200–260 V, and the operating pressure is 2.0 × 10⁻⁶. -2 Pa.

[0086] Preferably, in step S1, a prism substrate with a photoresist film after pre-baking is placed into an interference optical system for exposure using a holographic lithography method.

[0087] The technical effects of the present invention will be described below with reference to two specific embodiments:

[0088] (1) First specific implementation method

[0089] The primary cause of global warming is the increasing emission of greenhouse gases into the atmosphere, with carbon dioxide accounting for 80% of these emissions and considered a major contributor. Therefore, monitoring atmospheric carbon dioxide concentration has become a key focus of energy conservation, emission reduction, and environmental protection research in various countries. The characteristic spectral absorption bands of carbon dioxide mainly include the 1.61µm, 2.06µm, 2.7µm, 4.3µm, and 15µm bands. The 1.61µm band, formed by the vibrational-rotational changes of carbon dioxide molecules, is less affected by other gases and is a weak absorption band, making it less prone to saturation. Therefore, the 1.61µm band exhibits a significant advantage in detecting atmospheric carbon dioxide concentration.

[0090] In this embodiment, for the 1.61-micron band, combined with Figures 4 to 7 As shown, a transmission grating is presented, which is mainly composed of a quartz prism substrate and a grating layer and a dielectric film layer disposed thereon.

[0091] The grating layer includes etched grating grooves with a period of 1100 nm; the dielectric film is TiO2; the incident angle of the incident light in the prism substrate 1 is 30.9 degrees.

[0092] By optimizing the structure of the grating layer grooves, the optimal parameters are obtained. When the grating is deposited with TiO2 at an atomic layer to an optical thickness of λ / 4n, the reflected light can undergo the most effective destructive interference, which can effectively suppress interface reflection, thereby maximizing the retention of transmitted light energy and improving diffraction efficiency.

[0093] After the atomic layer deposition of TiO2 reaches a thickness of λ / 4n, continuing to vacuum evaporate TiO2 at the bottom will further improve diffraction efficiency and reduce polarization sensitivity, where h is the thickness of the vacuum evaporated TiO2 coating.

[0094] Traditional rectangular slot gratings, when deposited at an atomic layer of TiO2 to an optical thickness of λ / 4n, achieve a range of grating tooth height and duty cycle. For example... Figure 4 As shown, it can be observed that when the diffraction efficiency in the center band is greater than 80%, the minimum required grating height is 2280 nm. Therefore, with a grating height of 2320 nm (H / Λ) = 2.11 and a duty cycle of 0.16, the first-order diffraction efficiency in the bandwidth range of 1.59-1.63 micrometers was calculated. Figure 5 As shown, the first-order diffraction efficiency is greater than 75% and the polarization sensitivity is less than 10% in the bandwidth range of 1.59-1.63 micrometers.

[0095] By optimizing the structure of the grating groove, a tower-shaped grating tooth structure with a rectangular-trapezoidal cross section is obtained.

[0096] When the top duty cycle is 0.1,

[0097] Through formula Calculate the thickness m of the atomic layer deposition titanium dioxide film. In this wavelength range, the refractive index of titanium dioxide n1=2.3. When λ is taken as the center wavelength of 1.61μm, m=238nm. Then, continue to vacuum evaporate and deposit a TiO2 film with a thickness h at the bottom.

[0098] When the ratio of the upper and lower gate tooth heights (k=H1 / H2) is 0.6, and the thickness h of the vacuum evaporation coating is 100nm, the ranges of gate tooth height and gate tooth bottom angle are obtained, such as... Figure 6 As shown, it can be found that when the diffraction efficiency in the center band is greater than 85%, the required minimum grating height is 2260 nm. Therefore, with a grating height of 2320 nm (H / Λ) = 2.11 and a grating base angle of 86°, the first-order diffraction efficiency in the bandwidth range of 1.59-1.63 μm was calculated. Figure 7 As shown, the first-order diffraction efficiency is greater than 86.5% and the polarization sensitivity is less than 2.5% in the bandwidth range of 1.59-1.63 micrometers.

[0099] It is evident that the duty cycle is increased through the novel grating slot design. The polarization sensitivity is effectively reduced from 10% to below 2.5%, and the first-order diffraction efficiency in the 1.59-1.63 micrometer bandwidth range is improved from 75% to 86.5%.

[0100] In the manufacturing process, firstly, photoresist is coated onto the prism substrate. Then, a photoresist grating mask is fabricated on the photoresist using holographic lithography, with its top portion having an aspect ratio f. 顶 =0.1, and the gate height is 800nm;

[0101] Secondly, mask transfer is achieved through reactive ion beam etching, forming trenches on the quartz prism substrate with a depth of 2320 nm. Specifically, the reactive gas used is trifluoromethane (CHF3), the ion energy is 550 eV, the ion beam current is 140 mA, the accelerating voltage is 240 V, and the operating pressure is 2.0 × 10⁻⁶. -2 Pa;

[0102] After removing the remaining photoresist, an atomic layer of high-refractive-index TiO2 is deposited, according to... ,

[0103] Wherein, the top width ratio f is taken. 顶 =0.1, the calculated thickness of the TiO2 film is 238 nm;

[0104] A 100nm TiO2 layer is then deposited by evaporation. 2， Next, a polishing process is used to remove the evaporated TiO2 coating on top to complete the fabrication of the grating.

[0105] (2) Second specific implementation method

[0106] For the 2.06 micrometer band, combined with Figures 8 to 11 As shown, a transmission grating is presented, which is mainly composed of a quartz prism substrate and a grating layer and a dielectric film layer disposed thereon.

[0107] The grating layer includes etched grating grooves with a period of 1250 nm; the dielectric film layer is TiO2. 2， The incident angle of the incident light in the prism substrate 1 is 39 degrees.

[0108] By optimizing the grating groove structure, optimal parameters were obtained. When the grating is deposited with TiO2 at an atomic layer to an optical thickness of λ / 4n, the most effective destructive interference of reflected light is ensured, which can effectively suppress interface reflection, thereby maximizing the retention of transmitted light energy and improving diffraction efficiency.

[0109] After the atomic layer deposition of TiO2 reaches a thickness of λ / 4n, continuing to vacuum evaporate TiO2 at the bottom will further improve diffraction efficiency and reduce polarization sensitivity, where h is the thickness of the vacuum evaporated TiO2 coating.

[0110] Traditional rectangular slot gratings, when deposited at an atomic layer of TiO2 to an optical thickness of λ / 4n, achieve a range of grating tooth height and duty cycle, such as... Figure 8 As shown, it can be found that when the diffraction efficiency in the center band is greater than 85%, the minimum required grating height is 2420 nm. Therefore, with a grating height of 2450 nm (H / Λ) = 1.96 and a duty cycle of 0.12, the first-order diffraction efficiency in the bandwidth range of 2.04-2.084 μm was calculated. Figure 9 As shown, it can be seen that the first-order diffraction efficiency is greater than 80% and the polarization sensitivity is less than 10% in the bandwidth range of 2.04-2.084 micrometers.

[0111] By optimizing the grating slot structure, a tower-shaped grating tooth structure with a rectangular-trapezoidal cross-section is obtained. When the top duty cycle is 0.1, the film thickness formula is used... ,

[0112] The thickness of the atomic layer deposition (ALD) titanium dioxide film was calculated. At this wavelength, the refractive index of titanium dioxide, n1, is 2.28. Taking λ as the center wavelength of 2.062 μm, m = 297 nm. A TiO2 layer of thickness h was then deposited at the bottom via vacuum evaporation. When the ratio of the upper and lower gate heights (k = H1 / H2) is 1, and the thickness h of the vacuum evaporation layer is 120 nm, the ranges of the gate height and gate bottom angle were obtained, as shown below. Figure 10As shown, it can be found that when the diffraction efficiency in the center band is greater than 85%, the required minimum grating height is 2390 nm. Therefore, with a grating height of 2500 nm (H / Λ) = 2 and a grating base angle of 85°, the first-order diffraction efficiency in the bandwidth range of 2.04-2.084 μm was calculated. Figure 11 As shown, the first-order diffraction efficiency is greater than 86.5% in the bandwidth range of 2.04-2.084 micrometers, while the polarization sensitivity is less than 2.5%.

[0113] It is evident that the novel grating slot design significantly increases the duty cycle. Polarization sensitivity is effectively reduced from 10% to below 2.5%, and the first-order diffraction efficiency in the 2.04-2.084 micrometer bandwidth range is increased from 80% to 86.5%.

[0114] In the manufacturing process, firstly, photoresist is coated onto the prism substrate. Then, a photoresist grating mask is fabricated on the photoresist using holographic lithography, with its top portion having an aspect ratio f. 顶 =0.1, and the gate tooth height is 1000nm;

[0115] Secondly, mask transfer is achieved through reactive ion beam etching, forming trenches on the quartz prism substrate with a depth of 2500 nm. Specifically, the reactive gas used is trifluoromethane (CHF3), the ion energy is 550 eV, the ion beam current is 140 mA, the accelerating voltage is 240 V, and the operating pressure is 2.0 × 10⁻⁶. -2 Pa;

[0116] After removing the remaining photoresist, an atomic layer of high-refractive-index TiO2 is deposited, according to... ,

[0117] Wherein, the top width ratio f is taken. 顶 =0.1, the calculated thickness of the TiO2 film is 297 nm;

[0118] A 120nm TiO2 layer is then evaporated and deposited, followed by a polishing process to remove the evaporated TiO2 layer on top to complete the fabrication of the grating.

[0119] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0120] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0121] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A transmission grating, characterized in that: include, A substrate having a first surface along its thickness direction; A grating layer includes grating teeth arranged in an array on a first surface, with gaps between adjacent grating teeth; each grating tooth has a top surface and a bottom surface, and includes an upper grating block and a lower grating block, the lower grating block being connected to the first surface, and the upper and lower grating blocks cooperating to form a two-section tower-shaped structure; the lower grating block has an isosceles trapezoidal cross-section, the upper grating block has a rectangular cross-section, the width of the bottom surface is the same as the width of the bottom surface of the lower grating block, and the width of the top surface is the same as the width of the upper grating block; A first dielectric layer is disposed on the surface of the grating layer and fills the gaps to form a continuous layer structure; The first dielectric layer has a second surface on the side away from the substrate; A groove is formed at the location where the first dielectric layer is opposite to the gap; A second dielectric layer is disposed in the trench, the second dielectric layer having a third surface, the edge of the third surface being connected to the second surface; Incident light passes through the interior of the grating layer and is incident toward the second and third surfaces, and undergoes diffraction effects in the grating layer, the first dielectric layer, the second dielectric layer, and the second and third surfaces to generate transmitted diffracted light, which exits through the second surface of the first dielectric layer and the third surface of the second dielectric layer. Along the height direction of the grating teeth, the distance between the second surface and the first surface differs from the height of the grating teeth by a value m, where m is calculated using the formula: , , Right now , Wherein, the refractive index of the first dielectric layer is n1, the refractive index of air is n0, the wavelength of the incident light is λ, the period of the grating teeth is Λ, where Λ is 300nm~2000nm; the bottom width of the grating teeth is a, the top width of the grating teeth is b, the height of the upper grating block is H1, the height of the lower grating block is H2, the height of the grating teeth is H, where H=H1+H2, and the aspect ratio H / Λ is 1.92~2.17; the height ratio of the upper grating block to the lower grating block is k, where k=H1 / H2, and k is 0.5~1; the angle of the isosceles trapezoid is θ, where θ is 84.5°~87.5°, and the top occupancy ratio is f. 顶 =b / Λ is 0.1~0.12, and the bottom width ratio is 0.1~0.

12. It ranges from 0.2 to 0.

4.

2. The transmission grating according to claim 1, characterized in that: Along the height direction of the grating teeth, the cross-sectional shape of the lower grating block is an isosceles trapezoid, and the cross-sectional shape of the upper grating block is a rectangle; the width of the rectangle is equal to the upper base of the isosceles trapezoid.

3. A transmission grating according to claim 1, characterized in that: The material of the first dielectric layer includes titanium dioxide, aluminum oxide, or tantalum pentoxide.

4. A transmission grating according to claim 1, characterized in that: The material of the second dielectric layer includes titanium dioxide, aluminum oxide, or tantalum pentoxide.

5. A transmission grating according to claim 1, characterized in that: The thickness of the second dielectric layer is h, where h < H2; the thickness h of the second dielectric layer is 50-160 nm.

6. A method for manufacturing a transmission grating, characterized in that: The method for manufacturing a transmission grating as described in any one of claims 1-5 includes: Step S1: Obtain a prism substrate, coat the prism substrate with photoresist, and perform pre-baking; The baked prism substrate with photoresist film is exposed, and then the exposed prism substrate is developed to obtain a photoresist mask. Step S2 involves transferring the mask pattern to the surface of the prism substrate material through ion beam etching, and forming a tower-shaped grating layer by adjusting the etching parameters; the grating layer includes an array of grating teeth. Step S3: Remove the remaining photoresist. A first dielectric layer is formed on the grating layer by atomic layer deposition. The distance between the first dielectric layer and the grating teeth is m along the thickness direction of the grating layer. Then, a second dielectric layer is formed on the first dielectric layer by vacuum evaporation deposition. The second dielectric layer is formed in the trench of the first dielectric layer. The vacuum evaporation deposition material on the top of the grating teeth is removed by polishing.

7. A method for manufacturing a transmission grating according to claim 6, characterized in that: The grating layer formed by steps S1 to S3 has a period Λ of 300nm to 2000nm, a bottom aspect ratio of 0.2 to 0.4, and a depth-to-width ratio H / Λ of 1.92 to 2.

17.

8. A method for manufacturing a transmission grating according to claim 6, characterized in that: In step S2, during the ion beam etching process, trifluoromethane is used as the reactive gas, the ion energy is 200–600 eV, the ion beam current is 50–160 mA, the accelerating voltage is 200–260 V, and the operating pressure is 2.0 × 10⁻⁶. -2 Pa.

9. A method for manufacturing a transmission grating according to claim 6, characterized in that: In step S1, a prism substrate with a photoresist film after pre-baking is placed into an interference optical system for exposure using holographic lithography.

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