Linear polarization vortex beam generator and beam generation method thereof

Abstract

The invention discloses a linear polarization vortex beam generator, and relates to the technical field of metasurfaces, a generating device is a silicon dioxide substrate, a plurality of rectangular columns and cubic columns are arranged on the substrate and distributed in a matrix mode, and the length and the width of each cubic column are composed of eight groups of different parameters. In addition, the cubic columns have different rotation angles according to different positions where the cubic columns are located. The beam generation method comprises the following steps: expanding a standard W-waveband waveguide port to realize TE01 mode output, and generating linear polarization vortex beam output under vertical incidence. The amplitude and the phase of the transmission electromagnetic field are changed by controlling the geometric dimension and the rotation angle of the rectangular column. The invention further discloses a light beam generation method of the linear polarization vortex light beam generator, the dual-function metasurface is simple in structure, light in weight and small in size, convenience is brought to generation of vortex light beams in practical application, and the dual-function metasurface can be used for generating deflection of quasi-light light beams and outputting of high-power special light beams.

Description

Technical Field

[0001] The present invention relates to the field of super surface technology, in particular to a linear polarization vortex beam generator and a beam generating method thereof. Background Art

[0002] Orbital angular momentum (OAM) vortex beam is a wavefront with a vortex phase, which has great application prospects in large-capacity optical communications, super-resolution imaging, particle detection, etc. Methods for generating OAM vortex beam arrays include spiral phase plates, spatial light modulators, etc. Gyrotrons can generate high-power electromagnetic fields. TE generated by gyrotrons 01 The output of the vortex beam realized by the mode has high power characteristics. High-power vortex beams have good application prospects in microwave anti-stealth radar and interaction with plasma. There are currently two methods to realize high-power vortex beams based on gyrotrons. The first is to realize TE through optical devices. 01 The quasi-light output of the mode is then phase modulated based on the spiral phase plate to achieve the output of the vortex beam. The optical system of this method is relatively complicated and occupies a large area. Chao Zhang et al. redesigned the gyrotron by allowing microwave photons to interact with vortex quanta to directly achieve the output of vortex beams. This new type of gyrotron design is relatively complex and difficult to achieve large-scale application.

[0003] As a two-dimensional array plane composed of periodic artificial microstructures, metasurface can effectively manipulate the phase, amplitude, polarization, etc. of electromagnetic waves based on the generalized Fresnel law. It is widely used in the fields of beam polarization, superlens design, holographic imaging, etc. As for the dual-function metasurface, it can realize the regulation of polarization direction and propagation phase. However, in the applications of these metasurfaces, most of the incident beams are single linear polarization or circular polarization. For the electromagnetic wave mode in the circular waveguide, its polarization direction is often related to its radial direction, and the polarization direction of the electromagnetic field at different positions is different. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a linearly polarized vortex beam generator and a beam generation method thereof, based on a circular waveguide TE 01 A linearly polarized vortex beam generator with mode as feed source and a beam generation method thereof, such a dual-function metasurface can realize circular waveguide TE 01 The simultaneous modulation of the polarization direction and transmission phase of the mode enables the simultaneous realization of quasi-optical output and vortex phase output.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] According to the present invention, a linearly polarized vortex beam generator includes a metasurface and a substrate. The metasurface is arranged on the substrate, and the metasurface includes a plurality of periodically arranged cubic columns. An external waveguide energy transmission window outputs a TE 01 The mode is vertically incident on the metasurface, and a linearly polarized vortex beam is generated by simultaneously modulating the polarization direction and phase of the electric field.

[0007] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the substrate and the metasurface are placed at a preset distance behind the external waveguide energy transmission window; the length a and width b of each cubic column are determined, TE 01 The electric field of the mode Characterized by Where A represents the amplitude, J′0(Tρ) represents the zero-order Bessel function, e represents the natural base, j represents the imaginary unit, β represents the wave number, z represents the Z direction, and the Z direction represents the transmission direction of the electromagnetic field; Indicates TE 01 The electric field polarization direction at each position is axial linear polarization.

[0008] As a further optimization solution of the linear polarization vortex beam generator described in the present invention, the method for determining the length a and width b of each cubic column is as follows:

[0009] Based on the Jones matrix, the geometric parameters of the cubic column are scanned to determine the length and width of the cubic column so that δ xy = ±π, δ xy Represents the phase difference between the x-polarized incident and x-polarized emitted electromagnetic waves and the y-polarized emitted electromagnetic waves; the a and b scanning ranges are 0.3mm-1.3mm, and then the amplitude and phase of each scanned parameter are determined. All parameters form a matrix array for visualization, and the amplitude distribution diagram and phase distribution diagram of the matrix array composed of different parameters are obtained. From the amplitude distribution diagram and the phase distribution diagram, eight (a, b) arrays that can evenly cover the 2π phase and have a transmittance greater than 80% are found.

[0010] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the cubic column is a sub-wavelength cubic column and the substrate is a silicon dioxide substrate.

[0011] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the electric field of the incident metasurface is the TE output by the waveguide energy transmission window of the W-band gyrotron. 01 mode, the radius of the waveguide energy transmission window r0 = 16 mm, the waveguide length d2 = 3 mm; the distance between the waveguide energy transmission window and the substrate of the metasurface d0 = 8 mm.

[0012] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the cubic column is a dielectric column made of aluminum oxide, and its dielectric constant is 9.4.

[0013] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the substrate of the cubic column includes multiple substrate unit structures, the cross-section of the substrate unit structure is square, the thickness of the substrate unit structure is h=0.5mm, and the period P=1.5mm.

[0014] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the rotation angle of each cubic column on the metasurface varies due to different positions. A rectangular coordinate system is established with the center of the metasurface as the origin. The rotation angles of the cubic structures in the first, second, third and fourth quadrants are arctan(x / y) / 2-π / 2, arctan(x / y) / 2+π, arctan(x / y) / 2-π and arctan(x / y) / 2+π / 2; wherein x is the x-coordinate of the coordinate system established with the midpoint of the metasurface as the center; y is the y-coordinate of the coordinate system established with the midpoint of the metasurface as the center.

[0015] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the phase distribution of the metasurface satisfies the classical vortex phase distribution: Φ OAM (x,y)=l*arctan(y / x), l represents the OAM mode number, Φ OAM (x,y) is the phase distribution of the vortex beam.

[0016] Based on the above-mentioned beam generation method of a linearly polarized vortex beam generator, a circular waveguide TE based on a dual-function metasurface 01 The mode is a linearly polarized vortex beam generator with a feed source. The cubic column has different rotation angles depending on its location. 01 The mode is the output mode. Under vertical incidence, a linearly polarized vortex beam output is generated, and the amplitude and phase of the transmitted electric field are changed by controlling the geometric size and rotation angle of the cubic column.

[0017] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0018] The invention discloses a circular waveguide TE based on a dual-functional metasurface 01The linearly polarized vortex beam generator and beam generation method with the mode as the feed source are designed. A dual-function metasurface with both polarization control and transmission phase control is designed. The metasurface is composed of sub-wavelength cubic column unit structures arranged in a periodic manner, and the size is only a few wavelengths. Only the length and width of the cubic column and its rotation angle need to be considered to achieve the output of the linearly polarized vortex beam. The device is simple in design and thinner. It can provide great convenience for generating high-power vortex beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the dual-functional metasurface in the present invention.

[0020] Figure 2 It is a schematic diagram of the rotation angle and phase transformation of the unit structure of the dual-functional metasurface in the present invention; wherein, (a) represents the rotation angle, wherein different gray values ​​represent different rotation angles, and (b) represents the phase transformation, wherein different gray values ​​represent different transmission phases.

[0021] Figure 3 is the 90GHz transmission amplitude T when the incident direction is x polarization in the present invention. xx Schematic diagram of the changes with the changes in the side lengths a and b of the metasurface unit structure.

[0022] Figure 4 is the 90GHz transmission amplitude T when the y polarization direction is incident in the present invention. yy Schematic diagram of the changes with the changes in the side lengths a and b of the metasurface unit structure.

[0023] Figure 5 When the incident light is in the x-polarization direction, the phase of 90 GHz Schematic diagram of the changes with the side lengths a and b of the metasurface unit structure.

[0024] Figure 6 When the incident light is incident in the y-polarization direction, the phase of 90 GHz Schematic diagram of the changes with the side lengths a and b of the metasurface unit structure.

[0025] Figure 7 It is a schematic diagram of the transmittance of eight unit structures designed in the present invention.

[0026] Figure 8 It is a schematic diagram of the phases of the eight unit structures designed in the present invention.

[0027] Fig. 9 It is a schematic diagram of the waveguide structure and metasurface position distribution and specific dimensions designed in the present invention; wherein, (a) is the waveguide structure and metasurface position distribution, and (b) is a schematic diagram of the metasurface structure.

[0028] Fig.10 It is the mode purity when the orbital angular momentum l=±1 and the frequency is 85GHz in the present invention. The illustrations are the intensity and phase distribution in the transmission direction of the electromagnetic wave when the orbital angular momentum l=1 and l=-1 respectively.

[0029] Fig.11 It is the mode purity when the orbital angular momentum l=±1 and the frequency is 90GHz in the present invention. The illustrations are the intensity and phase distribution in the transmission direction of the electromagnetic wave when the orbital angular momentum l=1 and l=-1 respectively.

[0030] Fig.12 It is the mode purity when the orbital angular momentum l=±1 and the frequency is 95GHz in the present invention. The illustrations are the intensity and phase distribution in the transmission direction of the electromagnetic wave when the orbital angular momentum l=1 and l=-1 respectively.

[0031] Fig.13 It is the far-field radiation diagram at three frequencies of 85 GHz, 90 GHz and 95 GHz when the orbital angular momentum l=1 in the present invention; wherein, (a) is the energy distribution in different radiation directions at a frequency of 85 GHz, (b) is the energy distribution in different radiation directions at a frequency of 90 GHz, (c) is the energy distribution in different radiation directions at a frequency of 90 GHz, (d) is the axial ratio distribution in different radiation directions at a frequency of 85 GHz, (e) is the axial ratio distribution in different radiation directions at a frequency of 90 GHz, and (f) is the axial ratio distribution in different radiation directions at a frequency of 95 GHz.

[0032] Fig.14 It is the distribution of the magnitude of the axial ratio in the radiation direction at the three frequency points of 85 GHz, 90 GHz and 95 GHz when the orbital angular momentum l=-1 in the present invention; wherein, (a) is the energy distribution in different radiation directions at a frequency of 85 GHz; (b) is the axial ratio distribution in different radiation directions at a frequency of 90 GHz; (c) is the energy distribution in different radiation directions at a frequency of 90 GHz; (d) is the axial ratio distribution in different radiation directions at a frequency of 85 GHz; (e) is the axial ratio distribution in different radiation directions at a frequency of 90 GHz; (f) is the axial ratio distribution in different radiation directions at a frequency of 95 GHz. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] The invention proposes a linearly polarized vortex beam generator, comprising a metasurface and a substrate, wherein the metasurface is arranged on the substrate, and the metasurface comprises a plurality of periodically arranged cubic columns; after the substrate and the metasurface are placed in a waveguide energy transmission window, the waveguide energy transmission window outputs TE 01 The mode is vertically incident on the metasurface, and a linearly polarized vortex beam is generated by simultaneously modulating the polarization direction and phase of the electric field. The substrate and the metasurface are placed at a certain distance behind the external waveguide energy transmission window. The present invention is that the single-layer structure realizes two functions, namely, modulating the polarization direction and phase of the electric field simultaneously.

[0035] As a further optimization scheme of the linear polarization vortex beam generator described in the present invention, the length a and width b of each cubic column are determined, TE 01 The electric field of the mode Characterized by Where A represents the amplitude, J′0(Tρ) represents the zero-order Bessel function, e is the natural base, j is the imaginary unit, β represents the wave number, z Indicates the Z direction, which indicates the transmission direction of the electromagnetic field; Indicates TE 01 The electric field polarization direction at each position is axial linear polarization.

[0036] As a further optimization solution of the linear polarization vortex beam generator described in the present invention, the method for determining the length a and width b of each cubic column is as follows:

[0037] Based on the Jones matrix, the geometric parameters of the cubic column are scanned to determine the length and width of the cubic column so that δ xy = ±π, δ xy Represents the phase difference between the x-polarized incident and x-polarized emitted electromagnetic waves and the y-polarized emitted electromagnetic waves; the a and b scanning ranges are 0.3mm-1.3mm, and then the amplitude and phase of each scanned parameter are determined. All parameters form a matrix array for visualization, and the amplitude distribution diagram and phase distribution diagram of the matrix array composed of different parameters are obtained. From the amplitude distribution diagram and the phase distribution diagram, eight (a, b) arrays that can evenly cover the 2π phase and have a transmittance greater than 80% are found.

[0038] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the cubic column is a sub-wavelength cubic column and the substrate is a silicon dioxide substrate.

[0039] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the electric field of the incident metasurface is the TE output by the waveguide energy transmission window of the W-band gyrotron. 01 mode, the radius of the waveguide energy transmission window r0 = 16 mm, the waveguide length d2 = 3 mm; the distance between the waveguide energy transmission window and the substrate of the metasurface d0 = 8 mm.

[0040] As a further optimization scheme of the linearly polarized vortex beam generator described in the present invention, the cubic column is a dielectric column made of aluminum oxide, and its dielectric constant is 9.4.

[0041] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the substrate of the cubic column includes multiple substrate unit structures, the cross-section of the substrate unit structure is square, the thickness of the substrate unit structure is h=0.5mm, and the period P=1.5mm.

[0042] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the rotation angle of each cubic column on the metasurface varies due to different positions. A rectangular coordinate system is established with the center of the metasurface as the origin. The rotation angles of the cubic structures in the first, second, third and fourth quadrants are arctan(x / y) / 2-π / 2, arctan(x / y) / 2+π, arctan(x / y) / 2-π and arctan(x / y) / 2+π / 2; wherein x is the x-coordinate of the coordinate system established with the midpoint of the metasurface as the center; y is the y-coordinate of the coordinate system established with the midpoint of the metasurface as the center.

[0043] As a further optimization scheme of a linearly polarized vortex beam generator described in the present invention, the phase distribution of the metasurface satisfies the classical vortex phase distribution: Φ OAM (x,y)=l*arctan(y / x), l represents the OAM mode number, Φ OAM (x,y) is the phase distribution of the vortex beam.

[0044] Based on the above-mentioned beam generation method of a linearly polarized vortex beam generator, a circular waveguide TE based on a dual-function metasurface 01 The mode is a linearly polarized vortex beam generator with a feed source. The cubic column has different rotation angles depending on its location. 01 The mode is the output mode. Under vertical incidence, a linearly polarized vortex beam output is generated, and the amplitude and phase of the transmitted electric field are changed by controlling the geometric size and rotation angle of the cubic column.

[0045] In addition to being able to realize the conversion of the TE01 mode into a linearly polarized vortex beam, the method of the present invention can also realize the conversion of other circular waveguide modes, such as TE11 and TE21 modes into linearly polarized vortex beams. The difference lies in the different designs of the metasurface according to the distribution characteristics of different modes.

[0046] Here is an example:

[0047] Circular waveguide TE based on dual-functional metasurface 01A linear polarization vortex beam generator with a feed mode and a beam generation method thereof, comprising a silicon dioxide substrate, a plurality of cubic columns are arranged on the substrate, the length of the cubic column is a, and the width of the cubic column is b. TE output of the W-band gyrotron energy transmission window 01 The mode is the input electromagnetic field mode, and under vertical incidence, a linearly polarized vortex beam is generated.

[0048] The aforementioned circular waveguide TE based on the dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator of the feed source, and the electric field of the incident metasurface is TE in the W band 01 mode, the input port radius is r0 = 16 mm, the waveguide length is d2 = 3 mm, and the distance between the output port and the metasurface substrate is d0 = 8 mm.

[0049] The aforementioned circular waveguide TE based on the dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator of a feed source, and the cubic column is a dielectric column made of alumina with a dielectric constant of 9.4.

[0050] The aforementioned circular waveguide TE based on the dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator with a feed source, wherein the substrate of the cubic column is composed of a plurality of substrate unit structures, the cross section of the substrate structure is square, the thickness of the substrate unit is h=0.5 mm, and the period is P=1.5 mm.

[0051] The aforementioned circular waveguide TE based on the dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator with feed source. The rotation angle of each cubic column on the metasurface is different due to its different position. A rectangular coordinate system is established with the center of the metasurface as the origin. The rotation angles of the cubic structures in the first, second, third and fourth quadrants are arctan(x / y) / 2-π / 2, arctan(x / y) / 2+π, arctan(x / y) / 2-π and arctan(x / y) / 2+π / 2.

[0052] The aforementioned circular waveguide TE based on the dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator with a feed source, and the phase distribution of the dual-function metasurface satisfies the classical vortex phase distribution: l*arctan(y / x), where x and y represent the positions of the cubic columns, and l represents the OAM mode number.

[0053] like Figure 1 As shown, the metasurface structure consists of 24×24 metasurface unit structures, the substrate material of the metasurface unit structure is silicon dioxide, and a plurality of cubic columns are arranged on the substrate, the length of the cubic column is a, and the width of the cubic column is b. Under vertical incidence, a linearly polarized vortex beam is generated.

[0054] The cubic column is a dielectric column made of alumina with a dielectric constant of 9.4.

[0055] The substrate of the cubic column is composed of a plurality of substrate unit structures. The cross section of the substrate structure is square. The thickness of the substrate unit is h=0.5 mm and the period is P=1.5 mm.

[0056] Any polarized electric field can be decomposed into two mutually perpendicular polarized waves along the x and y directions. The polarization conversion process in the microwave field can be represented by the Jones matrix Where T xx and T yy is the co-polarization transformation. xy and T yx is the cross-polarization transformation. i is the incident electric field, E t represents the final electric field. Where k is the wave number and ω is the electromagnetic field frequency. The required function mentioned in the present invention only needs to perform linear polarization conversion. Therefore, the complex amplitude in the Jones matrix needs to satisfy the following conditions: |T xx |=|T yy |=1,|T xy |=|T yx |=0,δ xy = ±π, where δ xy is the phase difference between the decomposed x-polarized and y-polarized electromagnetic waves.

[0057] TE 01 The electric field of the mode can be characterized as: E ρ =0, E z = 0. Where A is the amplitude of the input wave; J′0 represents the first-order derivative of the zero-order Bessel function; T is the TE in the cylindrical waveguide 01 The eigenvalue of the mode; β represents the wave number of the input wave. It can be seen that TE 10 The polarization direction at any position of the mode is perpendicular to the radial direction of the position.

[0058] like Figure 2 As shown in (a), the different gray values ​​shown in the figure represent the rotation angles of the metasurface unit structure at different positions. 01 The quasi-light output process of the mode can be considered as the inverse process of radial vector field generation. The rotation angle of each cubic column on the metasurface is different due to different positions. When the rotation angle of the metasurface unit cell and the polarization direction of the incident electric field are at an angle of θ, the polarization direction of the electric field will rotate by 2θ. Quasi-light output can be achieved by changing the rotation angle of the metasurface unit cell at different positions. TE 01The electric field polarization direction of each position of the mode is distributed along the axial direction. Therefore, a rectangular coordinate system is established with the center of the metasurface as the origin, and the rotation angles of the cube structure in the first, second, third, and fourth quadrants are arctan(x / y) / 2-π / 2, arctan(x / y) / 2+π, arctan(x / y) / 2-π, and arctan(x / y) / 2+π / 2, respectively.

[0059] like Figure 2 As shown in (b), the different grayscale values ​​shown in the figure represent the phase of the metasurface unit structure at different positions.

[0060] The phase distribution satisfies the classical vortex phase distribution: Φ OAM (x,y) = l*arctan(y / x), where x and y represent the position of the cubic column, and l represents the orbital angular momentum mode number. Figure 2 The orbital angular momentum number l=2 for the phase diagram shown in (b).

[0061] like Figure 3 , 4, 5, and 6 show that by changing the length a and width b values ​​of the metasurface unit structure to scan the parameters, the changes in the transmission phase and transmission amplitude corresponding to different a and b values ​​are obtained, from which eight values ​​are found that can simultaneously achieve uniform phase distribution and a phase span of 2π.

[0062] The eight determined (a, b) value combinations are: 0.54mm, 1.14mm), (0.48mm, 1.05mm), (0.3mm, 1.3mm), (1.26mm, 0.57mm), (1.14mm, 0.54mm), (1.05mm, 0.48mm), (1.3mm, 0.3mm) (0.57mm, 1.26mm), which also correspond to the eight different metasurface unit structures designed. Figure 7 The transmittance of eight structures was characterized: their transmittances were all greater than 80%. Figure 8 The phases of eight structures are characterized: their phases satisfy the phase modulation of 2π.

[0063] like Fig. 9 As shown in the figure, the electric field incident on the metasurface is output by the W waveguide. 01 mode, and its output port is the output port of the commonly used gyrotron. Fig. 9 In (a), the radius of the waveguide energy transmission window r0 = 16 mm; the distance between the waveguide energy transmission window and the metasurface substrate d0 = 8 mm; the simulation example waveguide length d1 = 3 mm; Fig. 9 In (b), the length of the super surface structure is S = 36 mm.

[0064] The electric and magnetic field monitors were placed 50 mm behind the metasurface.

[0065] Fig.10 is the mode purity at a frequency of 85 GHz and orbital angular momentum l = ±1.

[0066] Fig.11 is the mode purity when the frequency is 90 GHz and the orbital angular momentum l = ±1.

[0067] Fig.12 is the mode purity at a frequency of 95 GHz and orbital angular momentum l = ±1.

[0068] Fig.10 , 11 The left illustration in Figure 12 shows the intensity distribution and phase distribution on the monitor plane when l = -1. The right illustration shows the intensity distribution and phase distribution on the monitor plane when l = 1. It can be seen that the intensity distribution is a hollow ring distribution, and the phase distribution is a spiral phase distribution. The distribution is consistent with the distribution characteristics of the vortex beam.

[0069] Fig.13 is the far-field radiation pattern with the orbital angular momentum l = -1. Specifically, Fig.13 (a), (b), and (c) are the far-field radiation diagrams at frequencies of 85 GHz, 90 GHz, and 95 GHz, respectively; Fig.13 (d), (e), and (f) are the axial rates at frequencies of 85 GHz, 90 GHz, and 95 GHz, respectively; Fig.14 is the far-field radiation pattern with the orbital angular momentum l = -1. Specifically, Fig.14 (a), (b), and (c) are the far-field radiation diagrams at frequencies of 85 GHz, 90 GHz, and 95 GHz, respectively; Fig.14 (d), (e), and (f) are the axial ratios at frequencies of 85 GHz, 90 GHz, and 95 GHz, respectively. It can be seen that it has a good polarizability in the radiation direction of the electromagnetic field and can achieve good linear polarization.

[0070] The present invention introduces a circular waveguide TE based on a dual-functional metasurface. 01 A linear polarization vortex beam generator with a mode as a feed source and a beam generation method thereof, wherein the cubic column has different rotation angles according to different positions. The beam generation method comprises: 01 The mode is the output mode. Under vertical incidence, a linearly polarized vortex beam output is generated. The amplitude and phase of the transmitted electric field are changed by controlling the geometric size and rotation angle of the rectangular column. Compared with the traditional two-step method of first achieving quasi-beam output through the optical path and then passing through the spiral phase plate to achieve vortex beam output, the dual-function metasurface has a simple structure, is more lightweight and miniaturized, and brings convenience to the generation of high-power vortex beams and other high-power special beams in practical applications.

[0071] The above description is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the technical field within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A linearly polarized vortex beam generator, characterized in that: It includes a metasurface and a substrate, wherein the metasurface is arranged on the substrate, and the metasurface includes a plurality of periodically arranged cubic columns; an external waveguide energy transmission window outputs TE 01 The mode is vertically incident on the metasurface, and a linearly polarized vortex beam is generated by simultaneously modulating the polarization direction and phase of the electric field.

2. A linearly polarized vortex beam generator according to claim 1, characterized in that: The substrate and metasurface are placed at a preset distance behind the external waveguide energy transmission window; the length a and width b of each cubic column are determined, TE 01 The electric field of the mode Characterized by Where A represents the amplitude, J0(Tρ) represents the zero-order Bessel function, e is the natural base, j is the imaginary unit, β represents the wave number, z Indicates the Z direction, which indicates the transmission direction of the electromagnetic field; Indicates TE 01 The electric field polarization direction at each position is axial linear polarization.

3. A linearly polarized vortex beam generator according to claim 1, characterized in that: The method for determining the length a and width b of each cubic column is as follows: Based on the Jones matrix, the geometric parameters of the cubic column are scanned to determine the length and width of the cubic column so that δ xy = ±π, δ xy Represents the phase difference between the x-polarized incident and x-polarized emitted electromagnetic waves and the y-polarized emitted electromagnetic waves; the a and b scanning ranges are 0.3mm-1.3mm, and then the amplitude and phase of each scanned parameter are determined. All parameters form a matrix array for visualization, and the amplitude distribution diagram and phase distribution diagram of the matrix array composed of different parameters are obtained. From the amplitude distribution diagram and the phase distribution diagram, eight (a, b) arrays that can evenly cover the 2π phase and have a transmittance greater than 80% are found.

4. A linearly polarized vortex beam generator according to claim 1, characterized in that: The cubic column is a sub-wavelength cubic column, and the substrate is a silicon dioxide substrate.

5. A linearly polarized vortex beam generator according to claim 1, characterized in that: The electric field incident on the metasurface is the TE output from the waveguide energy window of the W-band gyrotron. 01 mode, the radius of the waveguide energy transmission window r0 = 16 mm, the waveguide length d2 = 3 mm; the distance between the waveguide energy transmission window and the substrate of the metasurface d0 = 8 mm.

6. The linearly polarized vortex beam generator according to claim 1, characterized in that: The cubic column is a dielectric column made of alumina with a dielectric constant of 9.

4.

7. The linearly polarized vortex beam generator according to claim 1, characterized in that: The substrate of the cubic column includes a plurality of substrate unit structures, the cross section of the substrate unit structure is a square, the thickness of the substrate unit structure is h=0.5 mm, and the period P=1.5 mm.

8. The linearly polarized vortex beam generator according to claim 1, characterized in that: The rotation angle of each cubic column on the hypersurface varies with its position. A rectangular coordinate system is established with the center of the hypersurface as the origin. The rotation angles of the cubic structures in the first, second, third, and fourth quadrants are arctan(x / y) / 2-π / 2, arctan(x / y) / 2+π, arctan(x / y) / 2-π, and arctan(x / y) / 2+π / 2; where x is the x-coordinate of the coordinate system established with the midpoint of the hypersurface as the center; y is the y-coordinate of the coordinate system established with the midpoint of the hypersurface as the center.

9. A linearly polarized vortex beam generator according to claim 8, characterized in that: The phase distribution of the metasurface satisfies the classical vortex phase distribution: Φ OAM (x,y)=l*arctan(y / x), l represents the OAM mode number, Φ OAM (x,y) is the phase distribution of the vortex beam.

10. A beam generating method based on a linearly polarized vortex beam generator according to claim 1, characterized in that: Circular waveguide TE based on dual-functional metasurface 01 The mode is a linearly polarized vortex beam generator with a feed source. The cubic column has different rotation angles depending on its location. 01 The mode is the output mode. Under vertical incidence, a linearly polarized vortex beam output is generated, and the amplitude and phase of the transmitted electric field are changed by controlling the geometric size and rotation angle of the cubic column.

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