Zero-order asymmetrical metasurface grating proportional beam splitter
By designing a zero-elimination asymmetric metasurface grating proportional beam splitter, using nanostructures and substrates to achieve special beam splitting at asymmetric angles, the problem of difficult suppression of zero-elimination beams in the prior art is solved, and the sub-beams are improved Exit efficiency.
Patent Information
- Application Number
- CN202420244568.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-01
- Publication Date
- 2025-02-07
- Estimated Expiration
- 2034-02-01
AI Technical Summary
It is difficult for existing metasurface grating beam splitters to achieve special beam splitting at asymmetric angles, especially when beam splitting at large angles, zero-order beams are difficult to suppress, affecting the effect of the sub-beam.
A zero-elimination asymmetric metasurface grating proportional beam splitter is designed, using nanostructures and substrates. After the incident light is incident vertically, it is divided into multiple sub-beams on the substrate. Each sub-beam has different beam splitting angles and intensity ratios. , the grating is a two-dimensional grating, and the beam splitting characteristics are related to the polarization state of the incident light.
Special beam splitting at asymmetric angles is realized, which effectively suppresses the intensity of the zero-order beam and increases the output efficiency ratio of the sub-beam, and is suitable for large-angle beam splitting scenarios.
Smart Images
Figure CN222439778U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of super surface application, and in particular relates to a super surface grating proportional beam splitter for eliminating zero-order asymmetry. Background Art
[0002] A grating beam splitter is a planar beam splitter that uses the characteristics of grating multi-order diffraction to split the incident light into multiple independent beams. It is often used in spectral detection, interferometers, lidar and other fields. Common grating beam splitters are uniform beam splitters, such as Dammann gratings, which evenly split the incident light beam into several equal beams, and the beam splitting angles are usually symmetrically distributed along the central axis. With the development of micro-nano technology, optical beam splitters are no longer satisfied with uniform beam splitting at small angles. Metasurface grating beam splitters composed of micro-nano structures have also shown great advantages in high-efficiency and uniform beam splitting at large angles [NanoLetters 2020 20(9),6719-6724].
[0003] However, currently, metasurface grating beam splitters are mostly limited to uniform beam splitting, and do not involve the situation of abnormal beam splitting with different intensity ratios of sub-beams. In abnormal beam splitting, the zero-order beam is usually difficult to suppress, which affects the effects of other sub-beams. In particular, when the splitting angles of each sub-beam are not symmetrically distributed, how to suppress the intensity of the zero-order light is a critical issue. In addition, when the splitting angle is relatively large, the influence of the substrate on the deflection angle and efficiency of the sub-beam will be very obvious. If the influence of the substrate deflection is not considered, the angle and efficiency of the emitted sub-beam will be far from the expected requirements. Utility Model Content
[0004] The purpose of the utility model is to provide a zero-order asymmetric metasurface grating proportional beam splitter, which solves the problem of abnormal beam splitting of the metasurface grating beam splitter.
[0005] The purpose of the utility model is achieved through the following technical solutions:
[0006] A zero-order asymmetric metasurface grating proportional beam splitter comprises a nanostructure and a substrate. When incident light is incident vertically onto one side of the nanostructure of the beam splitter, the incident light is split into two or more sub-beams on the substrate and then emitted through the substrate.
[0007] The metasurface grating proportional beam splitter has different beam splitting angles and is asymmetrically distributed along the central axis at an angle of 0°; each sub-beam has a different intensity ratio;
[0008] The metasurface grating proportional beam splitter has a two-dimensional grating having a long period Tx and a short period Ty in orthogonal directions, and the sub-beam is emitted only in the x direction of the long period;
[0009] The metasurface grating proportional beam splitter has a beam splitting characteristic related to the polarization state of the incident light, and includes one of an s-polarization-only beam splitter, a p-polarization-only beam splitter, and a polarization-insensitive beam splitter.
[0010] Furthermore, the material of the nanostructure is one of silicon, silicon nitride, silicon-rich silicon nitride, silicon oxynitride, titanium dioxide, diamond, gallium nitride, quartz, glass, and polymer;
[0011] The nanostructure is a columnar structure, and its top view shape is one of a circle, a square, an ellipse, a rectangle, a ring, a cross, an I-shape, and a polygon;
[0012] The substrate is made of one of silicon, silicon nitride, titanium dioxide, diamond, gallium nitride, quartz and glass.
[0013] Furthermore, the metasurface grating proportional beam splitter has a metasurface grating with 2M+1 diffraction orders, wherein M is the diffraction order of the edgemost sub-beam.
[0014] Furthermore, the ratio of the intensity or efficiency of the output sub-beams of each level of the metasurface grating proportional beam splitter is τ -M :…:τ0:…:τ M , where M is the diffraction order of the most edge sub-beam, τ0 = 0, that is, the outgoing sub-beam has no vertically emitted zero-order light or the intensity of the zero-order light is negligible relative to the intensity of other orders of light.
[0015] Furthermore, in the metasurface grating proportional beam splitter, the number of nanostructures in a single periodic cell of the device is N≥ceil(Tx / Ty), wherein the function ceil(x) represents rounding x upwards.
[0016] Furthermore, in the metasurface grating proportional beam splitter, the center positions of the nanostructures within a single periodic unit cell of the device are evenly distributed.
[0017] Further, the metasurface grating proportional beam splitter has a short period Ty < λ, where λ is the wavelength of the incident light;
[0018] The long cycle Tx satisfies the following formula:
[0019]
[0020] Where λ is the wavelength of incident light, θ′ max is the emission angle of the edgemost sub-beam, and M is the diffraction order of the edgemost sub-beam, which is an integer.
[0021] Furthermore, the metasurface grating proportional beam splitter has an angle θ′ of each outgoing sub-beam m All conform to the following formula:
[0022]
[0023] Wherein, m is the diffraction order to which the sub-beam belongs.
[0024] Furthermore, the refractive loss of each diffraction order sub-beam after passing through the substrate is taken into account when designing the nanostructure, so that the ratio of the output efficiency of each sub-beam is as close as possible to the given τ -M :…:τ0:…:τ M , and the sum of the diffraction efficiencies of the diffraction orders with a given ratio not equal to 0 in the grating is as high as possible, while the sum of the diffraction efficiencies of the diffraction orders with a given ratio equal to 0 is as low as possible, that is, the efficient ratio emission condition of each sub-beam is minimized, that is, the objective function;
[0025] Since the beam splitter is related to the polarization of the incident light, different polarization beam splitters have different objective functions;
[0026] The objective function of the p-polarization beam splitter is:
[0027]
[0028] The objective function of the s-polarization beam splitter is:
[0029]
[0030] The objective function of the polarization-insensitive beam splitter is:
[0031]
[0032] Among them, γ pm , γ sm are the diffraction efficiencies of the mth diffraction order of the metasurface grating under p-polarization and s-polarization, τ m The ratio of the extraction efficiency set for the mth diffraction order, RMSE p 、RMSE s are the mean square error of the sub-beam ratios under p-polarization and s-polarization, respectively, satisfying the following formula:
[0033]
[0034] Where M is the diffraction order of the edgemost sub-beam, η m,p或s is the emission efficiency of the mth diffraction order sub-beam under p-polarization and s-polarization, η m_target,p或s is the target emission efficiency of the m-th diffraction order sub-beam under p-polarization and s-polarization, which can be expressed as:
[0035]
[0036] where τ m The ratio of the extraction efficiency set for the mth diffraction order, C p , Cs are the constants under p-polarization and s-polarization respectively, which satisfy:
[0037]
[0038] Among them, T m,p或s It is the energy flux transmittance of the m-th order sub-beam under p-polarization or s-polarization after passing through the substrate at different incident angles, which satisfies the Fresnel refraction formula.
[0039] The beneficial effects of the utility model are as follows: after the incident light is vertically incident, it can be split and emitted in one-dimensional direction according to given different splitting angles and given efficiency ratios on one side of the beam splitter substrate. The beam splitter breaks the design concept of the traditional uniform beam splitter, realizes special beam splitting at asymmetric angles, and fully considers the influence of zero-order elimination and substrate deflection loss during the design of the beam splitter, which is of great significance for expanding the design and application of beam splitters. The more flexible design of the beam splitter will provide more free components for applications in the fields of spectral detection, interferometers, laser radars, etc.
[0040] The aforementioned main scheme of the utility model and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection by the utility model; and in the utility model, (non-conflicting options) options and other options can also be freely combined. After understanding the scheme of the utility model, those skilled in the art can understand that there are many combinations based on the existing technology and common knowledge, all of which are technical schemes to be protected by the utility model, and they are not exhaustively listed here. BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Figure 1 This is a schematic diagram of a metasurface grating proportional beam splitter with zero-order asymmetry eliminated in an implementation example of the utility model.
[0042] Figure 2 This is a schematic diagram of the propagation of sub-beams at each level of the metasurface grating proportional beam splitter in an implementation example of the utility model.
[0043] Figure 3 This is a top view of the metasurface grating proportional beam splitter structure (cylindrical) of an implementation example of the utility model.
[0044] Figure 4 3D schematic diagram of the metasurface grating proportional beam splitter structure (cylindrical) of an implementation example of the utility model.
[0045] Figure 5 This is a top view of the metasurface grating proportional beam splitter structure (elliptical cylinder type) of an implementation example of the utility model.
[0046] Figure 6 3D schematic diagram of the metasurface grating proportional beam splitter structure (elliptical cylinder type) of an implementation example of the utility model.
[0047] Figure 7 This is a flow chart for designing a metasurface grating proportional beam splitter for an implementation example of the utility model. DETAILED DESCRIPTION
[0048] The following non-limiting examples are used to illustrate the present invention.
[0049] Example 1
[0050] A zero-order asymmetric super-surface grating proportional beam splitter comprises a nanostructure and a substrate.
[0051] For the metasurface grating proportional beam splitter, when the incident light is incident vertically onto one side of the beam splitter nanostructure, it will be split into two or more sub-beams at the substrate and then emitted through the substrate.
[0052] The metasurface grating proportional beam splitter has sub-beams with different splitting angles and presents an asymmetric distribution along the 0° angle of the central axis; and each sub-beam has a different intensity ratio.
[0053] The metasurface grating proportional beam splitter has a two-dimensional grating having a long period Tx and a short period Ty in orthogonal directions, and the sub-beam is emitted only in the long-period x direction.
[0054] The metasurface grating proportional beam splitter has a beam splitting characteristic related to the polarization state of the incident light, and includes one of an s-polarization-only beam splitter, a p-polarization-only beam splitter, and a polarization-insensitive beam splitter.
[0055] The nanostructure is made of one of silicon, silicon nitride, silicon-rich silicon nitride, silicon oxynitride, titanium dioxide, diamond, gallium nitride, quartz, glass, and polymer. The nanostructure is a columnar structure, and its top view shape is one of a circle, a square, an ellipse, a rectangle, a ring, a cross, an I-shape, and a polygon.
[0056] The substrate is made of one of silicon, silicon nitride, titanium dioxide, diamond, gallium nitride, quartz and glass.
[0057] The metasurface grating proportional beam splitter has a metasurface grating with 2M+1 diffraction orders, wherein M is the diffraction order of the edgemost sub-beam.
[0058] The ratio of the intensity or efficiency of the sub-beams emitted at each level of the metasurface grating proportional beam splitter is τ -M :…:τ0:…:τ M , where M is the diffraction order of the most edge sub-beam, τ0 = 0, that is, the outgoing sub-beam has no vertically emitted zero-order light or the intensity of the zero-order light is negligible relative to the intensity of other orders of light.
[0059] In the metasurface grating proportional beam splitter, the number of nanostructures in a single periodic cell of the device is N≥ceil(Tx / Ty), wherein the function ceil(x) represents rounding x upwards.
[0060] In this metasurface grating proportional beam splitter, the center positions of each nanostructure in a single periodic unit cell of the device are evenly distributed.
[0061] The metasurface grating proportional beam splitter has a short period Ty<λ, where λ is the wavelength of the incident light; and a long period Tx satisfies the following formula:
[0062]
[0063] Where λ is the wavelength of incident light, θ′ max is the emission angle of the edgemost sub-beam, and M is the diffraction order of the edgemost sub-beam, which is an integer.
[0064] The metasurface grating proportional beam splitter has an angle θ′ of each outgoing sub-beam m All conform to the following formula:
[0065]
[0066] Wherein, m is the diffraction order to which the sub-beam belongs.
[0067] The refractive loss of each diffraction order sub-beam after passing through the substrate is taken into account when designing the nanostructure, so that the ratio of the output efficiency of each sub-beam is as close as possible to the given τ -M :…:τ0:…:τ M , and the sum of the diffraction efficiencies of the diffraction orders with a given ratio not equal to 0 in the grating is as high as possible, while the sum of the diffraction order efficiencies with a given ratio equal to 0 is as low as possible, that is, minimizing the efficient ratio exit condition of each sub-beam, that is, the objective function.
[0068] Since the beam splitter is related to the polarization of the incident light, different polarization beam splitters have different objective functions.
[0069] The objective function of the p-polarization beam splitter is:
[0070]
[0071] The objective function of the s-polarization beam splitter is:
[0072]
[0073] The objective function of the polarization-insensitive beam splitter is:
[0074]
[0075] Among them, γ pm , γ smare the diffraction efficiencies of the mth diffraction order of the metasurface grating under p-polarization and s-polarization, τ m The ratio of the extraction efficiency set for the mth diffraction order, RMSE p 、RMSE s are the mean square error of the sub-beam ratios under p-polarization and s-polarization, respectively, satisfying the following formula:
[0076]
[0077] Where M is the diffraction order of the edgemost sub-beam, η m,p或s is the emission efficiency of the mth diffraction order sub-beam under p-polarization and s-polarization, η m_rarget,p或s is the target emission efficiency of the m-th diffraction order sub-beam under p-polarization and s-polarization, which can be expressed as:
[0078]
[0079] where τ m The ratio of the extraction efficiency set for the mth diffraction order, C p , C s are the constants under p-polarization and s-polarization respectively, which satisfy:
[0080]
[0081] Among them, T m,p或s It is the energy flux transmittance of the m-th order sub-beam under p-polarization or s-polarization after passing through the substrate at different incident angles, which satisfies the Fresnel refraction formula.
[0082] Example 2
[0083] A design method of a zero-order asymmetric metasurface grating proportional beam splitter is provided, which is directed to the zero-order asymmetric metasurface grating proportional beam splitter of embodiment 1, and comprises the following steps:
[0084] S1. Determine the incident light band and polarization state;
[0085] S2. Select nanostructure materials and substrate materials;
[0086] S3. Determine the number of sub-beams and the angle of the sub-beams of the beam splitter;
[0087] S4. Determine the efficiency ratio of each sub-beam of the beam splitter;
[0088] S5. Determine the long period Tx and short period Ty of the metasurface grating;
[0089] S6. Determine the number of nanostructures in each periodic unit cell and the center position of each nanostructure;
[0090] S7. Determine the variable parameters in each cycle, namely, the structure thickness and the structure geometric parameters, and initialize their values;
[0091] S8. Calculate the emission efficiency, proportional mean square error and objective function of each sub-beam of the metasurface grating beam splitter according to numerical simulation, where the objective function is the efficient proportional emission condition of each sub-beam;
[0092] S9. Determine whether the objective function meets the threshold requirement. If the objective function does not meet the threshold requirement, calculate the gradient of the objective function with respect to each variable, update the variable value according to the calculated gradient value, and then return to step S8, and iterate until the objective function meets the threshold requirement;
[0093] If the requirements are met, the variable parameter values, namely the structural thickness and structural geometric parameters, are output, thereby obtaining all the design parameters of the required metasurface grating beam splitter.
[0094] Implementation Case 1
[0095] like Figure 1 As shown, this embodiment provides a zero-order asymmetric super-surface grating proportional beam splitter under s-polarization, including a nanostructure and a substrate.
[0096] The metasurface grating proportional beam splitter in this example is designed for s-polarized parallel light incident on one side of the nanostructure, emitted from the other side of the substrate and split, and the wavelength λ of the incident light is selected to be 1550nm.
[0097] The nanostructure material of the metasurface grating proportional beam splitter in this example is silicon material, and the substrate is quartz material.
[0098] like Figure 1 As shown, the metasurface grating proportional beam splitter of this example emits two target sub-beams, and the emission angles of the two target sub-beams are asymmetric. The emission angle of the smaller-angle target sub-beam is θ=-29.50°, and the emission angle of the larger-angle target sub-beam is θ=+80°. The emission efficiency ratio of the two is set to 1:2.
[0099] In this example, the short period Ty of the metasurface grating proportional beam splitter is set to 650nm, and the larger angle target sub-beam is set to the +2nd order sub-beam, so that according to formula (1), the long period Tx can be calculated to be approximately 3148nm.
[0100] Therefore, according to formula (2), the metasurface grating has a total of 5 diffraction orders, that is, 5 sub-beams, such as Figure 2 As shown, the target sub-beam with a smaller angle corresponds to the -1 order, and the target sub-beam with a larger angle corresponds to the +2 order. It is necessary to eliminate other sub-beams as much as possible ( Figure 2 The dotted line indicates that the emission efficiency ratio of the five sub-beams is τ -2 :τ -1:τ0:τ +1 :τ +2 =0:1:0:0:2.
[0101] The nanostructure of the metasurface grating proportional beam splitter in this example is selected as a cylindrical structure, with the structure thickness and the column diameter as variables. According to the formula (N≥ceil(Tx / Ty)), the number of nanostructures in each period can be set to 5. Figure 3 The top view of the beam splitter structure is shown, in which the cylindrical structures of five square frames form a grating period. Each cylinder is different, so the diameter parameters of the nanostructure are only five, namely d1, d2, d3, d4, and d5. Figure 4 A 3D schematic diagram of the beam splitter structure is shown.
[0102] According to formula (7), the ideal output efficiency η required for each sub-beam under s polarization can be calculated: s-2_target , η s-1_target , η s0_target , η s+1_target , η s+2_target They are 0, 0.1933, 0, 0, and 0.3866 respectively.
[0103] The variables of the metasurface grating proportional beam splitter (structure thickness, nanocolumn diameter) are first randomly initialized and then Figure 7 The design method shown in the flowchart was iteratively optimized, and finally the structure thickness of this example was about 1226nm, and the cylinder diameters were 326nm, 177nm, 288nm, 354nm, and 261nm respectively.
[0104] The diffraction efficiency γ of each sub-beam under s-polarization can be calculated by using the finite element full-wave simulation method or the Fourier modal method. s-2 , γ s-1 , γ s0 , γ s+1 , γ s+2 They are 1.45%, 18.80%, 0.16%, 0.86% and 74.31% respectively. It can be obtained that the diffraction efficiency of the two target sub-beams under s-polarization reaches 93.11%, which has a very high diffraction efficiency.
[0105] Taking into account the refraction loss effect of each sub-beam through the substrate, the Fresnel formula can be used to further calculate the emission efficiency η of each sub-beam under s-polarization. s-2 , η s-1 , η s0 , η s+1 , η s+2 They are 0.71%, 17.9%, 0.15%, 0.82% and 36.05% respectively. It can be seen that the emission efficiency of the two target sub-beams is η s-1 :ηs+2 It is about 1:2, which is consistent with the set ratio, and the emission efficiencies of the other three sub-beams are all less than 1%, especially the zero-order light is only 0.15%, which is well suppressed.
[0106] Implementation Case 2
[0107] This embodiment provides a zero-order-eliminating asymmetric metasurface grating proportional beam splitter under p-polarization.
[0108] The incident light wavelength, the number of target sub-beams and the target sub-beam angle, the structure and substrate material, and the grating length and short period of this embodiment are the same as those of Implementation Example 1.
[0109] This embodiment is different from the implementation example 1 in that the polarization state of the incident light is p-polarized, and the nanostructure is selected as an elliptical cylindrical structure, with the structure thickness and the major axis and minor axis of the ellipse as variables, such as Figure 5 The number of nanostructures in each period is also set to 5, where 5 square elliptical cylinder structures form a grating period, and each ellipse is different, so the major axis and minor axis parameters of the nanostructure are 5, namely a1, a2, a3, a4, a5 and b1, b2, b3, b4, b5. Figure 6 A 3D schematic diagram of the beam splitter structure is shown.
[0110] According to formula (7), the ideal output efficiency η required for each sub-beam under p polarization can be calculated: p-2_target , η p-1_target , η p0_target , η p+1_target , η p+2_target They are 0, 0.2739, 0, 0, and 0.5478 respectively.
[0111] The variables of the metasurface grating proportional beam splitter (structure thickness, long and short axes of nanocolumns) are randomly initialized and Figure 7 The design method shown in the flowchart was iteratively optimized, and finally the structure thickness of this example was about 1438nm, the major axes of the elliptical cylinder were 336nm, 150nm, 251nm, 499nm, and 411nm, and the minor axes of the elliptical cylinder were 277nm, 296nm, 446nm, 171nm, and 100nm.
[0112] The diffraction efficiency γ of each sub-beam under p polarization can be calculated by using the finite element full-wave simulation method or the Fourier modal method. p-2 , γ p-1 , γ p0 , γ p+1 , γ p+2They are 0.09%, 26.7%, 0.22%, 0.01% and 68.26% respectively. The diffraction efficiency of the two target sub-beams under p-polarization can reach 94.96%, which has a very high diffraction efficiency.
[0113] Taking into account the refraction loss effect of each sub-beam through the substrate, the Fresnel formula can be used to further calculate the emission efficiency η of each sub-beam under p polarization. p-2 , η p-1 , η p0 , η p+1 , η p+2 They are 0.07%, 26.15%, 0.22%, 0.01% and 51.91% respectively. It can be seen that the emission efficiency of the two target sub-beams is η p-1 :η p+2 It is about 1:2, which is consistent with the set ratio, and the emission efficiencies of the other three sub-beams are all less than 0.25%, which are very well suppressed.
[0114] The above basic examples and further optional examples of the utility model can be freely combined to form multiple embodiments, which are all embodiments that can be adopted and claimed for protection by the utility model. In the scheme of the utility model, each optional example can be arbitrarily combined with any other basic examples and optional examples.
[0115] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A zero-order asymmetric metasurface grating proportional beam splitter, comprising a nanostructure and a substrate, characterized in that: The metasurface grating proportional beam splitter, when incident light is vertically incident on one side of the beam splitter nanostructure, is split into two or more sub-beams on the substrate and then emitted through the substrate; The metasurface grating proportional beam splitter has different beam splitting angles and is asymmetrically distributed along the central axis at an angle of 0°; each sub-beam has a different intensity ratio; The metasurface grating proportional beam splitter has a two-dimensional grating having a long period Tx and a short period Ty in orthogonal directions, and the sub-beam is emitted only in the x direction of the long period; The metasurface grating proportional beam splitter has a beam splitting characteristic related to the polarization state of the incident light, and includes one of an s-polarization-only beam splitter, a p-polarization-only beam splitter, and a polarization-insensitive beam splitter.
2. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1, characterized in that: The nanostructure is made of one of silicon, silicon nitride, silicon-rich silicon nitride, silicon oxynitride, titanium dioxide, diamond, gallium nitride, quartz, glass, and polymer; The nanostructure is a columnar structure, and its top view shape is one of a circle, an ellipse, a ring, a cross, an I-shape, and a polygon; The substrate is made of one of silicon, silicon nitride, titanium dioxide, diamond, gallium nitride, quartz and glass.
3. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1, characterized in that: The metasurface grating proportional beam splitter has a metasurface grating with 2M+1 diffraction orders, wherein M is the diffraction order of the edgemost sub-beam.
4. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1 or 3, characterized in that: The ratio of the intensity or efficiency of the sub-beams emitted at each level of the metasurface grating proportional beam splitter is , where M is the diffraction order of the edgemost beam, , that is, the emitted sub-beam does not have vertically emitted zero-order light or the intensity of the zero-order light is negligible relative to the intensity of other orders of light.
5. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1, characterized in that: In the metasurface grating proportional beam splitter, the number of nanostructures in a single periodic cell of the device is N≥ceil(Tx / Ty), wherein the function ceil(x) represents rounding x upwards.
6. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1 or 5, characterized in that: In this metasurface grating proportional beam splitter, the center positions of each nanostructure in a single periodic unit cell of the device are evenly distributed.
7. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1, characterized in that: The metasurface grating proportional beam splitter has a short period Ty < λ, where λ is the wavelength of the incident light; The long cycle Tx satisfies the following formula: （1）； Where λ is the wavelength of incident light, is the emission angle of the edgemost sub-beam, and M is the diffraction order of the edgemost sub-beam, which is an integer.
8. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1, characterized in that: The metasurface grating proportional beam splitter has an angle of each outgoing sub-beam. All conform to the following formula: （2）； Wherein, m is the diffraction order to which the sub-beam belongs.
9. The zero-order asymmetric metasurface grating proportional beam splitter according to claim 1 or 8, characterized in that: The refractive loss of each diffraction order sub-beam after passing through the substrate is taken into account when designing the nanostructure, so that the output efficiency ratio of each sub-beam is as close as possible to the given , and the sum of the diffraction efficiencies of the diffraction orders with a given ratio not equal to 0 in the grating is as high as possible, while the sum of the diffraction efficiencies of the diffraction orders with a given ratio equal to 0 is as low as possible, that is, the efficient ratio emission condition of each sub-beam is minimized, that is, the objective function; Since the beam splitter is related to the polarization of the incident light, different polarization beam splitters have different objective functions; The objective function of the p-polarization beam splitter is: （3）； The objective function of the s-polarization beam splitter is: （4）； The objective function of the polarization-insensitive beam splitter is: （5）； in, , are the diffraction efficiencies of the mth diffraction order of the metasurface grating under p-polarization and s-polarization, The ratio of the extraction efficiency set for the mth diffraction order, RMSE p 、RMSE s are the mean square error of the sub-beam ratios under p-polarization and s-polarization, respectively, satisfying the following formula: （6）； Where M is the diffraction order of the edgemost sub-beam, is the sub-beam emission efficiency of the mth diffraction order under p-polarization and s-polarization, is the target emission efficiency of the m-th diffraction order sub-beam under p-polarization and s-polarization, which can be expressed as: （7）； in is the extraction efficiency ratio set for the mth diffraction order, , are the constants under p-polarization and s-polarization respectively, which satisfy: （8）； in, It is the energy flux transmittance of the m-th order sub-beam under p-polarization or s-polarization after passing through the substrate at different incident angles, which satisfies the Fresnel refraction formula.