Broadband waveplate and polarization grating based on subwavelength structures

Abstract

The application provides a broadband wave plate and a polarization grating based on a sub-wavelength structure, and relates to the technical field of optical elements. The broadband wave plate comprises a substrate, an antireflection layer on one side of the substrate, and a periodically arranged columnar sub-wavelength structure on the other side of the substrate, wherein the columnar sub-wavelength structure comprises a plurality of sub-wavelength structure layers of different refractive index media. The broadband wave plate and the polarization grating provided by the application can effectively reduce the reflection of light, improve the transmittance and polarization conversion efficiency, because the columnar sub-wavelength structure comprises a plurality of sub-wavelength structure layers of different refractive index media, and the refractive index of the columnar sub-wavelength structure can be matched with the impedance of air.

Description

Technical Field

[0001] This application relates to the field of optical element technology, and more specifically, to a broadband waveplate and polarization grating based on a subwavelength structure. Background Technology

[0002] A broadband waveplate is an optical element used to adjust the phase of light. It maintains stable phase delay over a wide wavelength range, thus playing a crucial role in optical systems. By controlling the phase delay of light at different wavelengths, broadband waveplates can achieve effective modulation and control of light. Broadband waveplates can effectively reduce the wavelength dependence of phase delay, making them valuable in various fields such as spectral shaping, polarization imaging, and broadband laser source research. However, existing broadband waveplates are mainly concentrated in the visible and near-infrared bands.

[0003] In the long-wave infrared band (8-14 micrometers), dielectric silicon is widely used in the design of subwavelength structures due to its compatibility with semiconductor processing technologies. However, existing silicon subwavelength structures suffer from strong reflection losses, which can affect the absolute polarization conversion efficiency of the subwavelength waveplate. Summary of the Invention

[0004] In order to overcome at least the above-mentioned shortcomings in the prior art, the purpose of this application is to provide a broadband waveplate and polarization grating based on a subwavelength structure to solve the technical problem that the existing subwavelength structure of silicon material (especially in the long-wave infrared band) has strong reflection loss, resulting in low polarization conversion efficiency of the corresponding broadband waveplate.

[0005] In a first aspect, embodiments of this application provide a broadband waveplate based on a subwavelength structure, the broadband waveplate comprising:

[0006] Substrate;

[0007] An antireflection layer located on one side of the substrate;

[0008] A periodically arranged columnar subwavelength structure located on the other side of the substrate;

[0009] The columnar subwavelength structure comprises multiple layers of dielectric subwavelength structures with different refractive indices.

[0010] In the above implementation, since the columnar subwavelength structure comprises multiple layers of dielectric subwavelength structures with different refractive indices, the refractive index of the columnar subwavelength structure can be adjusted to achieve impedance matching with air, thereby effectively reducing light reflection and improving transmittance and polarization conversion efficiency. This solves the technical problem of strong reflection loss in existing silicon dielectric subwavelength structures (especially in the long-wave infrared band), which leads to low polarization conversion efficiency of the corresponding broadband waveplates.

[0011] In one possible implementation, the refractive index of the dielectric subwavelength structure layer is greater closer to the substrate. In this implementation, by setting the refractive index of the dielectric subwavelength structure layer closer to the substrate to be greater, impedance matching between the columnar subwavelength structure and air can be achieved, effectively reducing light reflection and improving transmittance and polarization conversion efficiency.

[0012] In one possible implementation, the columnar subwavelength structure includes: a first dielectric subwavelength structure layer made of silicon and a second dielectric subwavelength structure layer made of zinc sulfide.

[0013] In the above implementation, since zinc sulfide has a low refractive index in the long-wave infrared band and is between that of silicon and air, silicon, zinc sulfide, and air can form impedance matching, thereby effectively reducing interface reflection of the subwavelength structure and improving the absolute polarization conversion efficiency of broadband waveplates and polarization gratings.

[0014] In one possible implementation, the antireflection layer includes: a first sublayer and a second sublayer; the first sublayer is located on the side of the second sublayer away from the substrate, the refractive index of the first sublayer is less than the refractive index of the second sublayer, and the refractive index of the second sublayer is less than the refractive index of the substrate.

[0015] In the above implementation method, the transmittance on the substrate side can be further improved by setting multiple anti-reflection layers.

[0016] In one possible implementation, a plurality of the columnar subwavelength structures are arranged along a second direction, each of the columnar subwavelength structures extends along a first direction, and there is a gap between adjacent columnar subwavelength structures; wherein the first direction and the second direction are perpendicular to each other.

[0017] In one possible implementation, the period of the broadband waveplate includes 1 micrometer to 3 micrometers; in the direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers, and the width of the columnar subwavelength structure in the second direction is less than the period of the broadband waveplate; in the direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 2 micrometers to 5 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers.

[0018] In the above implementation, a quarter-wave plate can be realized by setting "the period of the broadband waveplate includes 1 micrometer to 3 micrometers; in the direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers; in the direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 2 micrometers to 5 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers".

[0019] In one possible implementation, the period of the broadband waveplate includes 1 micrometer to 3 micrometers; in the direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers, and the width of the columnar subwavelength structure in the second direction is less than the period of the broadband waveplate; in the direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 4 micrometers to 7 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers.

[0020] In the above implementation, a half-wave plate can be realized by setting "the period of the broadband waveplate includes 1 micrometer to 3 micrometers; in the direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers; in the direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 4 micrometers to 7 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers".

[0021] In one possible implementation, the broadband waveplate has an absolute polarization conversion efficiency of 92.4% and an average relative polarization conversion efficiency of 99.8% in the 8-14 micrometer wavelength range.

[0022] Secondly, embodiments of this application also provide a polarization grating, the polarization grating comprising a plurality of broadband waveplates as described in any one of the first aspects above.

[0023] In one possible implementation, the arrangement of the plurality of columnar subwavelength structures in each broadband waveplate is consistent, while the arrangement of the columnar subwavelength structures in two adjacent broadband waveplates is different.

[0024] In one possible implementation, the angular spacing between the columnar subwavelength structures in any two adjacent broadband waveplates is consistent.

[0025] In one possible implementation, the period of the polarization grating comprises 500 micrometers.

[0026] Based on any of the above aspects, the broadband waveplate and polarization grating based on subwavelength structures provided in this application, because the columnar subwavelength structure includes multiple layers of dielectric subwavelength structures with different refractive indices, can achieve impedance matching with air, thereby effectively reducing light reflection and improving transmittance and polarization conversion efficiency. This solves the technical problem of strong reflection loss in existing silicon dielectric subwavelength structures (especially in the long-wave infrared band), leading to low polarization conversion efficiency of the corresponding broadband waveplate.

[0027] Furthermore, the broadband waveplate and polarization grating based on subwavelength structure provided in this application can also achieve the functions of quarter-waveplate and half-waveplate in the infrared broadband band (8 micrometers-14 micrometers) by changing the geometric dimensions of the columnar subwavelength structure. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings required in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is one of the structural schematic diagrams of the broadband waveplate provided in this embodiment;

[0030] Figure 2 This is the second schematic diagram of the structure of the broadband waveplate provided in this embodiment;

[0031] Figure 3 This is the third schematic diagram of the structure of the broadband waveplate provided in this embodiment;

[0032] Figure 4 This is a schematic diagram comparing the polarization conversion efficiency of the quarter-wave plate provided in this embodiment;

[0033] Figure 5 This is a schematic diagram comparing the polarization conversion efficiency of the half-wave plate provided in this embodiment;

[0034] Figure 6 This is a schematic diagram of the polarization grating provided in this embodiment;

[0035] Figure 7 This is a simulation diagram of the diffraction efficiency of the polarization grating provided in this embodiment.

[0036] Icons: 100-Broadband waveplate; 110-Substrate; 120-Antireflective layer; 121-First sublayer; 122-Second sublayer; 130-Columnar subwavelength structure; 131-First dielectric subwavelength structure layer; 132-Second dielectric subwavelength structure layer. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0039] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0040] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0041] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0042] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0043] It should be noted that, where there is no conflict, different features in the embodiments of this application can be combined with each other.

[0044] In subwavelength structures, due to their three-dimensional morphology, the optical performance is determined by the width and depth of the structural grooves. Traditional antireflective coatings consist of multiple layers of different dielectric materials. Directly depositing an antireflective coating on a dielectric subwavelength structure alters the width and depth of the structural grooves, and the change in bandwidth is uneven and difficult to control, thus affecting optical performance. Therefore, traditional antireflective coatings cannot be used to reduce the reflection loss of existing subwavelength structures.

[0045] After discovering this problem, this application designed a columnar subwavelength structure including multiple subwavelength structures of media with different refractive indices, and realized a broadband waveplate and polarization grating with high polarization conversion efficiency.

[0046] This embodiment provides a solution to the above problems. The specific implementation of this application will be described in detail below with reference to the accompanying drawings.

[0047] Please refer to Figure 1 , Figure 1 This is one of the structural schematic diagrams of the broadband waveplate 100 provided in this embodiment. For example... Figure 1 As shown, the broadband waveplate 100 may include:

[0048] Substrate 110;

[0049] Antireflection layer 120 located on one side of substrate 110;

[0050] Periodically arranged columnar subwavelength structures 130 located on the other side of substrate 110;

[0051] The columnar subwavelength structure 130 includes multiple layers of medium subwavelength structure with different refractive indices.

[0052] The broadband waveplate 100 can be an infrared broadband waveplate. The antireflection layer 120 can completely cover one side of the substrate 110 surface. The antireflection layer 120 can include a multilayer film structure to improve the transmittance of one side of the substrate 110. The antireflection layer 120 can be deposited using various thin film deposition techniques (such as physical vapor deposition, chemical vapor deposition, etc.), thus allowing for flexible adjustment of the thickness of the antireflection layer 120 to optimize its optical performance. The columnar subwavelength structure 130 can be located on the side of the substrate 110 away from the antireflection layer 120. The columnar subwavelength structure 130, as a unit structure, can be periodically extended, and its shape is columnar. The number of dielectric subwavelength structure layers included in the columnar subwavelength structure 130 can be 2, 3, 5, or other reasonable values. The specific number of dielectric subwavelength structure layers can be adjusted according to the actual application scenario. In practical applications, polarized light can be incident from the side of the antireflection layer 120 away from the substrate 110, or from the side of the columnar subwavelength structure 130 away from the substrate 110.

[0053] For example, such as Figure 1 As shown, the columnar subwavelength structure 130 can extend along the first direction D1, and multiple columnar subwavelength structures 130 can be arranged along the second direction D2. There is a gap between any two adjacent columnar subwavelength structures 130, and the gaps between adjacent columnar subwavelength structures 130 are generally equal. The first direction D1 is perpendicular to the second direction D2. The orthographic projection of the multiple columnar subwavelength structures 130 onto the substrate 110 can lie within the orthographic projection of the antireflection layer 120 onto the substrate 110. It should be noted that... Figure 1 The illustration only shows three columnar subwavelength structures 130 as an example. In other examples, the number of columnar subwavelength structures 130 is not limited to three; it can be two or more, and no specific limitation is made here. Furthermore, the widths of the multiple columnar subwavelength structures 130 in the second direction D2 can be consistent. Since the lateral dimensions of the columnar subwavelength structures 130 are consistent, they can be directly processed using an etching process.

[0054] In some alternative embodiments, the refractive index of the dielectric subwavelength structure layer is greater closer to the substrate 110.

[0055] By setting the refractive index of the dielectric subwavelength structure layer closer to the substrate 110 to be larger, the columnar subwavelength structure 130 can achieve impedance matching with air, thereby effectively reducing light reflection and improving transmittance and polarization conversion efficiency.

[0056] Please refer to Figure 2 , Figure 2 This is the second schematic diagram of the structure of the broadband waveplate provided in this embodiment.

[0057] like Figure 2 As shown, in some optional embodiments, the columnar subwavelength structure 130 may include: a first dielectric subwavelength structure layer 131 made of silicon material, and a second dielectric subwavelength structure layer 132 made of zinc sulfide material.

[0058] The columnar subwavelength structure 130 can be formed by first uniformly depositing a second dielectric subwavelength structure layer 132 onto the surface of a first dielectric subwavelength structure layer 131, then coating the surface of the second dielectric subwavelength structure layer 132 with photoresist, followed by patterning the photoresist using laser direct writing technology, and finally forming it through an etching process. Since zinc sulfide has a low refractive index in the long-wave infrared band and is between that of silicon and air, silicon, zinc sulfide, and air can form impedance matching, thereby effectively reducing interface reflection of the subwavelength structure and improving the absolute polarization conversion efficiency of the broadband waveplate and polarization grating. It should be noted that the material used to manufacture the first dielectric subwavelength structure layer 131 can also include germanium, and the material used to manufacture the second dielectric subwavelength structure layer 132 can also include ytterbium fluoride; this application does not specifically limit this.

[0059] In this embodiment, since there is a large refractive index difference between the first dielectric subwavelength structure layer 131, which is made of silicon, and air, it is easy to cause strong reflection loss. Therefore, a second dielectric subwavelength structure layer 132, which is made of zinc sulfide, can be added between the first dielectric subwavelength structure layer 131 and air to form impedance matching, thereby reducing reflection, increasing transmittance, and effectively controlling the phase delay of light.

[0060] The second dielectric subwavelength structure layer 132 can be located on the side of the columnar subwavelength structure 130 away from the substrate 110. The orthographic projection of the second dielectric subwavelength structure layer 132 on the substrate 110 can completely coincide with the orthographic projection of the first dielectric subwavelength structure layer 131 on the substrate 110.

[0061] The refractive index of the substrate 110 can be the same as that of the first dielectric subwavelength structure layer 131, and the material used to manufacture the substrate 110 can also be the same as that used to manufacture the first dielectric subwavelength structure layer 131. Both the substrate 110 and the first dielectric subwavelength structure layer 131 can be made of transparent materials, such as silicon or germanium (germanium's transparency is mainly concentrated in the infrared spectrum, exhibiting high transmittance to infrared light). Silicon has a high refractive index in the long-wave infrared band (8-14 micrometers) and is compatible with semiconductor processing technologies. The material used to manufacture the second dielectric subwavelength structure layer 132 is not limited to zinc sulfide; other materials can also be included, without specific limitations, as long as the refractive index of the second dielectric subwavelength structure layer 132 is between that of the first dielectric subwavelength structure layer 131 and air.

[0062] Furthermore, the materials of the substrate 110 and the first dielectric subwavelength structure layer 131 are not limited to silicon, but may include other materials. No specific limitation is made here, as long as the substrate 110 is greater than the refractive index of each film layer in the antireflection layer 120, and the refractive index of the first dielectric subwavelength structure layer 131 is greater than the refractive index of the second dielectric subwavelength structure layer 132.

[0063] In another possible implementation, the second dielectric subwavelength structure layer 132 can be further divided into multiple subwavelength structure layers, and the refractive indices of the multiple subwavelength structure layers are different, with the refractive index of each subwavelength structure layer being between that of the first dielectric subwavelength structure layer 131 and air.

[0064] In some optional embodiments, the antireflection layer 120 includes a first sublayer 121 and a second sublayer 122; the first sublayer 121 may be located on the side of the second sublayer 122 away from the substrate 110, and constitute a multilayer film structure. The refractive index of the first sublayer 121 is less than the refractive index of the second sublayer 122, and the refractive index of the second sublayer 122 is less than the refractive index of the substrate 110.

[0065] It should be noted that the antireflection layer 120 includes film layers that are not limited to the first sublayer 121 and the second sublayer 122. The antireflection layer 120 may also include a third sublayer, a fourth sublayer, etc. There are no specific limitations here, as long as the multiple film layers included in the antireflection layer 120 can achieve the effect of increasing transmittance.

[0066] In some optional embodiments, a plurality of columnar subwavelength structures 130 are arranged along a second direction D2, each columnar subwavelength structure 130 extends along a first direction D1, and there is a gap between adjacent columnar subwavelength structures 130; wherein the first direction D1 and the second direction D2 are perpendicular to each other.

[0067] In the above structure, changing the geometric dimensions of the columnar subwavelength structure 130 can realize the functions of quarter-wave plate, half-wave plate, etc. in the infrared broadband band (8 micrometers-14 micrometers). Furthermore, since the refractive index of the columnar subwavelength structure 130 can achieve impedance matching with air, it can effectively reduce light reflection and improve transmittance and polarization conversion efficiency.

[0068] Please refer to Figure 3 , Figure 3 This is the third schematic diagram of the structure of the broadband waveplate provided in this embodiment.

[0069] In one possible implementation, such as Figure 3As shown, when the broadband waveplate 100 is used to realize the function of a quarter-wave plate in the infrared broadband band (8 μm-14 μm), the period T of the broadband waveplate 100 can include 1 μm-3 μm. In the direction parallel to the substrate 110, the width L of each columnar subwavelength structure 130 in the second direction D2 can include 0.5 μm-2.5 μm. In the direction perpendicular to the substrate 110, the height H1 of each first dielectric subwavelength structure layer 131 can include 2 μm-5 μm, and the height H2 of the second dielectric subwavelength structure layer 132 can include 0.5 μm-2 μm. The quarter-wave plate can generate a phase delay of π / 2 between the fast axis and the slow axis. One of its main functions is to realize the conversion between different types of polarized light, including the conversion from linearly polarized light to circularly polarized light.

[0070] Specifically, when the broadband waveplate 100 is used to realize the function of a quarter-waveplate in the infrared broadband band (8 μm-14 μm), the period T of the broadband waveplate 100 can be 1 μm, 2 μm, or 3 μm. The width L of each columnar subwavelength structure 130 in the second direction D2 can be 0.5 μm, 1.6 μm, or 2.5 μm. In the direction perpendicular to the substrate 110, the height H1 of each first dielectric subwavelength structure layer 131 can be 2 μm, 3.2 μm, or 5 μm. In the direction perpendicular to the substrate 110, the height H2 of each second dielectric subwavelength structure layer 132 can be 0.5 μm, 1 μm, or 2 μm. For example, when the broadband waveplate 100 is used to realize the function of a quarter-wave plate in the infrared broadband band (8 micrometers-14 micrometers), when the period T of the broadband waveplate 100 is 2 micrometers: in the direction parallel to the substrate 110, the width L of each columnar subwavelength structure 130 in the second direction D2 can specifically be 1.6 micrometers; in the direction perpendicular to the substrate 110, the height H1 of each first dielectric subwavelength structure layer 131 can specifically be 3.2 micrometers, and the height H2 of the second dielectric subwavelength structure layer 132 can specifically be 1 micrometer.

[0071] Please refer to Figure 4 , Figure 4 This is a schematic diagram comparing the polarization conversion efficiency of the quarter-wave plate provided in this embodiment. Figure 4A specific example illustrates the comparison of absolute and relative polarization conversion efficiencies between a silicon-zinc sulfide combined subwavelength quarter-wave plate and an all-silicon subwavelength quarter-wave plate. The silicon-zinc sulfide combined subwavelength structure corresponds to the case where "the columnar subwavelength structure 130 includes: a first dielectric subwavelength structure layer 131 made of silicon material and a second dielectric subwavelength structure layer 132 made of zinc sulfide material." In the 8-14 micrometer wavelength range, the silicon-zinc sulfide combined quarter-wave plate has an average absolute polarization conversion efficiency of 92.4%, an average relative polarization conversion efficiency of 99.8%, and an average transmittance of 92.6%. In the 8-14 micrometer wavelength range, the all-silicon quarter-wave plate has an average absolute polarization conversion efficiency of 80%, an average relative polarization conversion efficiency of 98.7%, and an average transmittance of 81%. The relative / absolute polarization conversion efficiency is defined as the ratio of the energy of the emitted target polarized light to the energy of the transmitted / incident light. It can be seen that the average absolute polarization conversion efficiency of the silicon-zinc sulfide combination subwavelength structure can be improved by more than 12% compared with the traditional subwavelength structure in the 8-14 micrometer wavelength range.

[0072] In one possible implementation, please refer again. Figure 3 When the broadband waveplate 100 is used to realize the function of a half-wave plate in the infrared broadband band (8 μm-14 μm), the period T of the broadband waveplate 100 can include 1 μm-3 μm. In the direction parallel to the substrate 110, the width L of the columnar subwavelength structure 130 in the second direction D2 can include 0.5 μm-2.5 μm. In the direction perpendicular to the substrate 110, the height H1 of the first dielectric subwavelength structure layer 131 can include 4 μm-7 μm, and the height H2 of the second dielectric subwavelength structure layer 132 can include 0.5 μm-2 μm. The half-wave plate can generate a phase delay of π between the fast axis and the slow axis. One of its main functions is to realize the conversion between different types of polarized light, including the conversion from circular polarization to cross-circular polarization.

[0073] Specifically, when the broadband waveplate 100 is used to function as a half-waveplate in the infrared broadband band (8 μm-14 μm), the period T of the broadband waveplate 100 can be 1 μm, 2.4 μm, or 3 μm. The width L of each columnar subwavelength structure 130 in the second direction D2 can be 0.5 μm, 1.57 μm, or 2.5 μm. In the direction perpendicular to the substrate 110, the height H1 of each first dielectric subwavelength structure layer 131 can be 4 μm, 5.7 μm, or 7 μm. In the direction perpendicular to the substrate 110, the height H2 of each second dielectric subwavelength structure layer 132 can be 0.5 μm, 1 μm, or 2 μm. For example, when the broadband waveplate 100 is used to realize the function of a half-wave plate in the infrared broadband band (8 micrometers-14 micrometers), when the period T of the broadband waveplate 100 is 2.4 micrometers: in the direction parallel to the substrate 110, the width L of each columnar subwavelength structure 130 in the second direction D2 can specifically be 1.57 micrometers; in the direction perpendicular to the substrate 110, the height H1 of each first dielectric subwavelength structure layer 131 can specifically be 5.7 micrometers, and the height H2 of the second dielectric subwavelength structure layer 132 can specifically be 1 micrometer.

[0074] Please refer to Figure 5 , Figure 5 This is a schematic diagram comparing the polarization conversion efficiency of the half-wave plate provided in this embodiment. Figure 5 A schematic diagram comparing the absolute and relative polarization conversion efficiencies of a silicon-zinc sulfide combined subwavelength half-wave plate and an all-silicon subwavelength half-wave plate is shown. In the 8-14 micrometer wavelength range, the silicon-zinc sulfide combined half-wave plate exhibits an average absolute polarization conversion efficiency of 91.3%, an average relative polarization conversion efficiency of 99.3%, and an average transmittance of 91.9%. In the same wavelength range, the all-silicon half-wave plate demonstrates an average absolute polarization conversion efficiency of 82.5%, an average relative polarization conversion efficiency of 98.7%, and an average transmittance of 83.6%. It can be seen that the silicon-zinc sulfide combined subwavelength structure can improve the average absolute polarization conversion efficiency by more than 10% compared to the traditional subwavelength structure in the 8-14 micrometer wavelength range.

[0075] It should be noted that the dimensions of the broadband waveplate 100 can be adjusted according to actual needs, and no specific limitation is made here. For example, the geometric dimensions of the columnar subwavelength structure 130 can be adjusted according to the actual manufacturing materials and the optimization of the designed waveband.

[0076] like Figure 4 , Figure 5As shown, the average absolute polarization conversion efficiency of existing broadband waveplates in the 8-14 micrometer wavelength range is about 82%. Compared with the prior art, the average absolute polarization conversion efficiency and average relative polarization conversion efficiency of the broadband waveplate 100 provided in this application are both greater than those of the broadband waveplates in the prior art. The average absolute polarization conversion efficiency of the broadband waveplate 100 provided in this application can reach 92.4% and the average relative polarization conversion efficiency can reach 99.8% in the 8-14 micrometer wavelength range.

[0077] Please refer to Figure 6 , Figure 6 This is a schematic diagram of the polarization grating provided in this embodiment.

[0078] This application also provides a polarization grating, which may include a plurality of broadband waveplates 100 as described in any one of the first aspects above.

[0079] Specifically, the polarization grating can be constructed from the half-wave plate provided in this embodiment.

[0080] In one possible implementation, the polarization grating may include a plurality of broadband waveplates 100, wherein the arrangement direction of the plurality of columnar subwavelength structures on each broadband waveplate 100 is consistent, and the arrangement direction of the columnar subwavelength structures on two adjacent broadband waveplates 100 is different.

[0081] like Figure 6 As shown, multiple broadband waveplates 100 can be arranged along the first direction D1, and the columnar subwavelength structures on adjacent broadband waveplates 100 have different arrangement directions.

[0082] In one possible implementation, the angular spacing between the columnar subwavelength structures in any two adjacent broadband waveplates 100 is consistent.

[0083] In one possible implementation, the polarization grating can be formed by rotating and arranging the half-wave plates. The length of the polarization grating in the first direction D1 can be 500 micrometers, and the length of the polarization grating in the second direction D2 can be 100 micrometers.

[0084] In one possible implementation, when the coverage phase of the polarization grating is 0-2π and the number of broadband waveplates 100 is 10, the angular interval between the columnar subwavelength structures in any two adjacent broadband waveplates 100 can be 18°. It should be noted that the number of broadband waveplates 100 is not limited to 10, but may also include 16, 8, etc., without specific limitation here.

[0085] In one possible implementation, the period of the polarization grating may include 500 micrometers.

[0086] To verify the validity of this application, experimental verification was conducted.

[0087] Please refer to Figure 7 , Figure 7 This is a simulation diagram of the diffraction efficiency of the polarization grating provided in this embodiment. After modulation by the polarization grating, the incident left-handed circularly polarized light (LCP) is converted into right-handed circularly polarized light (RCP) and diffracted to the -1st order. The absolute diffraction efficiency of the polarization grating in the wavelength range of 8-14 micrometers is 95%. The absolute diffraction efficiency is defined as the ratio of the energy of the -1st order diffraction order to the energy of the incident circularly polarized light.

[0088] In summary, this embodiment provides a broadband waveplate and polarization grating based on a subwavelength structure. An antireflection layer 120 is disposed on one side of the substrate 110, and a columnar subwavelength structure 130 is disposed on the other side of the substrate 110. Since the columnar subwavelength structure comprises multiple layers of dielectric subwavelength structures with different refractive indices, the refractive index of the columnar subwavelength structure can achieve impedance matching with air, effectively reducing light reflection and improving transmittance and polarization conversion efficiency. It can also realize the functions of quarter-wave plates and half-wave plates in the infrared broadband band (8 micrometers-14 micrometers), and a polarization grating can be fabricated using a half-wave plate.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0090] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A broadband waveplate, characterized in that, The broadband waveplate includes: Substrate; An antireflection layer located on one side of the substrate; A periodically arranged columnar subwavelength structure located on the other side of the substrate; The columnar subwavelength structure includes multiple layers of medium subwavelength structure with different refractive indices. The columnar subwavelength structure includes: a first dielectric subwavelength structure layer made of silicon material and a second dielectric subwavelength structure layer made of zinc sulfide material. The plurality of columnar subwavelength structures are arranged along a second direction, each columnar subwavelength structure extends along a first direction, and there is a gap between adjacent columnar subwavelength structures. Wherein, the first direction and the second direction are perpendicular to each other; The period of the broadband waveplate ranges from 1 micrometer to 3 micrometers. In a direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers, and the width of the columnar subwavelength structure in the second direction is less than the period of the broadband waveplate; In a direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 2 micrometers to 5 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers.

2. The broadband waveplate according to claim 1, characterized in that, in, The refractive index of the dielectric subwavelength structure layer is greater the closer it is to the substrate.

3. The broadband waveplate according to claim 1, characterized in that, The antireflective layer comprises: a first sublayer and a second sublayer; The first sublayer is located on the side of the second sublayer away from the substrate, and the refractive index of the first sublayer is less than the refractive index of the second sublayer, which in turn is less than the refractive index of the substrate.

4. The broadband waveplate according to claim 1, characterized in that, The period of the broadband waveplate ranges from 1 micrometer to 3 micrometers; In a direction parallel to the substrate, the width of the columnar subwavelength structure in the second direction includes 0.5 micrometers to 2.5 micrometers, and the width of the columnar subwavelength structure in the second direction is less than the period of the broadband waveplate; In a direction perpendicular to the substrate, the height of the first dielectric subwavelength structure layer includes 4 micrometers to 7 micrometers, and the height of the second dielectric subwavelength structure layer includes 0.5 micrometers to 2 micrometers.

5. A polarization grating, characterized in that, The polarization grating includes: a plurality of broadband waveplates as described in any one of claims 1-4 above.

6. The polarization grating according to claim 5, characterized in that, in, The arrangement direction of the multiple columnar subwavelength structures in each broadband waveplate is consistent, while the arrangement direction of the columnar subwavelength structures in two adjacent broadband waveplates is different.

7. The polarization grating according to claim 6, characterized in that, in, The angular spacing between the columnar subwavelength structures in any two adjacent broadband waveplates is consistent.

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