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Shared-aperture terahertz metasurface with switchable channels

Shu-ping Zhang, Jiu-Sheng Li, Feng-lei Guo, and Yi Chen

Open Access Open Access

Abstract

Multifunctional and multiplexed terahertz metasurfaces have attracted considerable attention due to their freedom of manipulating terahertz waves in the space domain. In this paper, we proposed a shared-aperture channel switchable terahertz metasurface, which consists of a top elliptical pattern (i.e., vanadium dioxide (VO2) and gold configuration), an intermediate SiO2 layer and a bottom metal plate. Several coding-pattern arrays are designed to achieve multi-function such as beam splitting, beam focusing, beam deflection, vortex beam, and vortex focusing beams based on Pancharatnam-Berry (PB) mechanism combined with shared-aperture. Furthermore, the single and dual channels can be switched when VO2 undergoes a reversible dielectric-metal phase transition around 68°C by controlling the ambient temperature. The full-wave simulation results are in good agreement with the computational predictions. This study greatly enriches the design of terahertz metasurface devices and is highly expected for promising practical applications in future terahertz multiplexing systems.

© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

1. Introduction

In recent years, coding metasurfaces have gained great attention due to unprecedented advantages in terahertz wave manipulation in subwavelength scale arrays [1,2]. By changing the size of coding elements and arrays arrangement, various functions terahertz devices based on metasurfaces have been proposed, such as imaging [3,4], focusing [5,6], anomalous refraction [7,8], and vortex beam [9,10]. For example, in 2020, Fang et al. [11] proposed the terahertz wave beam splitting and deflection functions based on dielectric elliptical cylindrical cells. Tian et al. [12] designed a notched square ring metallic cell structure to realize scattering angle control of transmission terahertz wave. In 2021, Wang et al. [13] realized the generation of vortex beams by arranging the square metal sheet structure. Wei et al. [14] combined the outer “C” ring and the inner “╪” structure to produce beam splitting, deflection, and RCS (Radar Cross Section) noise reduction. More recently, VO2-integrated coding metasurfaces are used to realize tunable beam manipulation [15–18]. Furthermore, different coding metasurfaces have been reported [19–25] to regulate wavefront by creating 1-bit or multi-bit coding subarrays. However, most of previous literature metasurfaces just work in single channel, which hinders their application in multiplexed communication fields.

Here, we exploit an elliptical oval coding elements based on VO2 and gold medium with shared-aperture method distribution on the same substrate surface. The unit cell consists of a top elliptical oval VO2 pattern or gold pattern, a middle layer of SiO2 and a bottom metal plate. Such a metasurface supports dual-channel split-beam with different deflection directions, dual-channel focusing, dual-channel vortex beam generation with l=±1 and l=±2, and dual-channel vortex focusing beam with l=±1 under right circularly polarized (RCP) waves incidence. Meanwhile, the metasurface exhibits adjustable channel numbers at different the ambient temperature. By exploiting multiple degrees of freedom, the designed metasurface manifests particularly different functionalities. It provides a new idea for the design of switchable channel terahertz devices.

2. Structure design

Figure 1 presents the schematic diagram of the presented shared-aperture dual-channel switchable terahertz metasurface, which consists of elliptical oval coding elements (constituting VO2 and gold can be seen in Fig. 1(a) and 1(b)), intermediate silicon dioxide dielectric substrate and gold plate bottom layer, whose conductivity is 4.6 × 107S/m. The dielectric layer with a thickness of 40 µm is made of silicon dioxide with relative permittivity of 3.75 and a loss tangent of 0.0004. The thicknesses of both gold- and VO2- elliptical oval coding structures are 1µm. The diameter of the long axis and short axis of the oval coding element are a = 96µm and b = 10µm, respectively. The period of the coding elements is P = 100µm. We employed the commercial CST Microwave Studio to optimize the coding element under circularly polarized waves incidence. Both x- axis and y- axis are set as periodic boundary conditions and z-axis is set as open space.

 figure: Fig. 1.

Fig. 1. Schematic structure of the proposed shared-aperture dual-channel switchable metasurface, (a) top view of the elliptical metasurface element (VO2), (b) top view of the elliptical metasurface element (gold), (c) 3D-view of the metasurface.

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The electrical conductivity ε(ω) of VO2 can be expressed by

$$\varepsilon (\omega )\textrm{ = }{\varepsilon _\infty }\textrm{ - }\omega _{p}^2\frac{\sigma }{{{\sigma _0}}}/({{\omega^2} + i{\omega_d}\omega } )$$
where ε∞=12, ωp = 1.4 × 1015S-1, ωd = 5.6 × 1013S-1, σ0 = 3.0 × 105S/m. The phase transition of VO2 can be changed from insulator state to metallic state by dynamic control of external ambient temperature. The conductivities of VO2 are 20 S/m and 2.0 × 105S/m for the insulator state and metallic state, respectively [26].

In order to meet the required gradient phase for the shared-aperture metasurface, eight kinds of coding elements are designed based on the PB phase principle. The reflection coefficients and phases of the eight kinds of coding elements are shown in Fig. 2. From Figs. 2(a)∼2(e), one can see that the reflection coefficients of the eight kinds of elliptical oval coding elements based on VO2 at 68°C are larger than 0.88 at 1THz and the reflection phase difference of between adjacent coding elements is approximately 45°. Furthermore, at 25°C, the reflection coefficients of the eight kinds of oval coding elements based on VO2 are lower than 0.006 at 1THz. Although the reflection phase difference between adjacent coding elements keeps approximately 45°. For the eight kinds of oval coding elements based on gold, the reflection coefficients are larger than 0.91 at 1 THz and the reflection phase difference between adjacent coding elements is approximately 45°, as shown in Figs. 2(f) ∼2(h). The proposed metasurface contains multiple interleaved subarrays, which share the same aperture of the metasurface. Each subarray carries a geometric phase profile, which can excite different spatial channels. To obtain anticipatory performance, it is desirable to arrange these subarrays regularly or randomly in an interleaved fashion. Usually, different sub-arrays contain the same number of meta-atoms to maintain equal energy in each channel. Here, we implement the generation of multi-channel split beam beams, vortex beams, and vortex focusing beams based on the shared-aperture principle. To achieve these functions, the phase φ need to satisfy the following distribution [26]

$${\varphi _{A}}(x )= 2\pi {x}/\Gamma $$
$${\varphi _{B}}({x,y} )= l{\tan ^{ - 1}}({y/x} )$$
$${\varphi _{C}}({x,y} )= 2\mathrm{\pi }\left( {\sqrt {{{F}^2} + {x^2} + {y^2}} \textrm{ - }{{F}^2}} \right)/\lambda$$
$$\varphi ({x,y} )= {\varphi _{A}}({x,y} )\textrm{ + }{\varphi _{B}}({x,y} )\textrm{ + }{\varphi _{C}}({x,y} )$$
where x and y represent the transverse and ordinate coordinates of the element center (taking the array center as the origin), Γ represents the gradient period length of the deflection coding metasurface, λ represents the wavelength, F represents the focal length, φA(x) represents the phase distribution of beam deflection, φB(x, y) and φC(x, y) are used to generate vortex and focusing beams, respectively. The units of the two subarrays are interleaved according to the following relation
$$\left\{ {\begin{array}{{c}} {\varphi (i,j) = {\varphi_1}(i,j)\textrm{ Mod(}|{i - j} |,N) = 0\textrm{ }}\\ {\varphi (i,j) = {\varphi_2}(i,j)\textrm{ Mod(}|{i - j} |,N) = 1\textrm{ }}\\ {\mathrm{\cdot{\cdot}\cdot}}\\ {\varphi (i,j) = {\varphi_N}(i,j)\textrm{ Mod(}|{i - j} |,N) = N - 1} \end{array}} \right.$$
where N represents the number of subarrays used to compose the main array, φ1∼φN represents the phase distribution of the 1st ∼Nth subarray, and i and j represent the position of the corresponding element of this phase in the array along the z-axis and y-axis, respectively.

 figure: Fig. 2.

Fig. 2. Simulation reflection responses and phase diagram of unit cells under two kinds of operating temperature. (a) Top view of VO2 unit cell, (b) Reflection coefficient at ambient temperature of 68°C, (c) Reflection phase at ambient temperature of 68 °C, (d) Reflection coefficient at ambient temperature of 25°C, (e) Reflection phase at ambient temperature of 25 °C, (f) Top view of gold unit cell, (g) Reflection coefficient, (h) Reflection phase.

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Figure 3 illustrates the shared-aperture channel switchable terahertz metasurface, which can perform different functions including splitting beams with different deflection angles, vortex and vortex-focusing beams with different topological charges. When RCP wave irradiates the metasurface, which can perform longitudinal two splitting beams, single-channel right directional deflection focusing, single-channel right directional deflection vortex beam (l = 1), downward deflection vortex beam (l = 2) and right directional deflection vortex focusing beam (l = 1) at ambient temperature of 25°C. For the ambient temperature of 68°C, the proposed metasurface can realize four splitting beams, dual-channel transverse focusing beams, dual-channel transverse vortex beams with topological charge of l=± 1, and dual-channel longitudinal vortex beams with topological charge of l=± 2.

 figure: Fig. 3.

Fig. 3. Function illustration of the designed shared-aperture dual-channel switchable metasurface.

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3. Simulation results and analysis

Figures 4(a) and 4(b) show the phase distributions of transverse and longitudinal beam splitting metasurfaces, respectively. Figure 4(c) displays the schematic diagram of the dual-channel shared-aperture principle. Figure 4(d) illustrates the phase distribution of dual-channel dual-channel beam splitting metasurface. The gradient periods of the transverse and longitudinal metasurface are set as Γa = 400µm and Γb = 800µm, respectively. The deflection angle θ of the split-beam wave can be described by

$$\theta \textrm{ = }\arcsin ({\lambda /\Gamma } )$$

 figure: Fig. 4.

Fig. 4. The phase distribution of the proposed dual-channel beam splitting metasurface. (a) Phase distribution of the transverse beam splitting metasurface, (b) Phase distribution of the longitudinal beam splitting metasurface, (c) Schematic diagram of the dual-channel shared-aperture metasurface, (d) Phase distribution of the dual-channel beam splitting metasurface.

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From this equation, the theoretical deflection angles of the transverse and longitudinal dichotomous beam waves are 48.6° and 22.0°, respectively. Figures 5(a) and 5(b) reveal the far-field intensity and the normalized reflected energy amplitude curves of the longitudinal dichotomous beam wave when the ambient temperature is 25°C (VO2 is in insulating state), respectively. One can see that the azimuth angles of the two reflected wave peaks is 90° and 270°, respectively, and the deflection angle is 22.0°, which is consistent with the theoretical predictions. Figures 6(a)∼6(c) illustrates the far-field intensity of the transverse and longitudinal dichotomous beam waves of the dual-channel and the normalized reflection amplitude curves for different channels when the ambient temperature is 68°C (VO2 is in metallic state), respectively. As can be seen from the figures, the azimuthal angles of the two reflected wave peaks of the longitudinal dichotomous beam are 90° and 270°, respectively, with a deflection angle of 22.0°. In addition, the azimuthal angles of the two reflected wave peaks of the transverse dichotomous beam are 0° and 180°, respectively, with a deflection angle of 48.6°. They are also consistent with the theoretical calculation.

 figure: Fig. 5.

Fig. 5. The far-field intensity diagram and the normalized reflection curve of the dual-channel beam splitting metasurface at 1.0THz. (a) Far field intensity diagram and (b) normalized reflection curve of longitudinal dual-channel beam splitting.

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 figure: Fig. 6.

Fig. 6. The far-field intensity diagram and the normalized reflection curve of the dual-channel beam splitting metasurface at 1.0THz. (a) Far field intensity diagram of the multi-channel beam splitting, (b) normalized reflection curve of the longitudinal beam splitting, (c) normalized reflection curve of the transverse beam splitting.

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Figures 7(a) and 7(b) give the phase distribution of the focusing metasurface based on VO2 and gold oval coding elements, respectively. Figure 7(c) plots the schematic diagram of the dual-channel shared-aperture principle. The phase distribution of the dual-channel focusing beam metasurface is shown in Fig. 7(d). Figures 8(a) and 8(b) show the electric field distribution of the focusing beam in xoy and xoz planes at 25°C, respectively. The focal length is F = 800µm. The theoretical deflection angle and the azimuth angle of the focusing beam are 22.0° and 0°, respectively. The focusing beam deflection angle θ’ can be calculated by

$$\theta ^{\prime}\textrm{ = }\arctan ({X/F} )$$
where X represents the absolute value of the difference between the peak coordinate of the deflection beam and the center of the array. The electric field intensity of the deflected focusing beam is 3.40 V/m, as illustrated in Fig. 8(c).

 figure: Fig. 7.

Fig. 7. The phase distribution of the proposed transverse dual-channel focusing beam metasurface. (a) Phase distribution of the left skewed focusing beam metasurface, (b) Phase distribution of the right skewed focusing beam metasurface, (c) Schematic diagram of the dual-channel shared-aperture metasurface, (d) Phase distribution of the dual-channel focusing beam metasurface.

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 figure: Fig. 8.

Fig. 8. The electric field distribution of the transverse dual-channel focusing beam metasurface at 1.0THz. (a) Eelectric field intensity in xoy plane, (b) Electric field intensity in xoz plane, (c) Three-dimensional diagram of the electric field intensity in xoy plane.

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Figures 9(a) and 9(b) show the electric field distribution of the focusing beam in xoy and xoz planes at 68°C, respectively. Obviously, the focal length of the dual-channel focus is 800µm. According to equation, the theoretical deflection angle of the dual-channel focusing beam is 22.0°, and the azimuth angles are 180° and 0°, respectively. As shown in Fig. 9(c), the electric field intensity of the focusing beam along left and right channels are 1.85 V/m and 2.88 V/m, respectively.

 figure: Fig. 9.

Fig. 9. The electric field performance of the transverse dual-channel focusing beam metasurface at 1.0THz. (a) Electric field intensity in xoy plane, (b) Electric field intensity in xoz plane, (c) Three-dimensional diagram of the electric field intensity in xoy plane

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Figures 10(a) and 10(b) display the metasurface phase distribution of the left deflection vortex beam based on VO2 coding element and right deflection vortex beam based on gold coding element, respectively. Figure 10(c) shows the schematic diagram of dual-channel shared-aperture metasurface. Figure 10(d) presents the metasurface arrangement of dual-channel adjustable vortex beam with topological charge of l=±1. When the ambient temperature is 25°C (i.e. VO2 is in insulating state), the proposed metasurface generates a single-channel function. Figures 11(a) and 11(b) show the far-field intensity and far-field phase of the transverse single-channel vortex beam with topological charge of l = -1. It is worth noting that the simulated vortex beam purity of l = -1 is closed to 60.0%, as illustrated in Fig. 11(c). Figures 12(a) ∼12(c) display the far-field intensity and phase diagram of the transverse dual-channel vortex beam with topological charge of l=±1 at the ambient temperature of 68°C (i.e. VO2 is in metallic state). The theoretical deflection angle of the dual-channel vortex beam is 48.6°, and the azimuth of the transverse l=±1 vortex beam are 0° (l = -1) and 180° (l = 1), respectively.

 figure: Fig. 10.

Fig. 10. Phase distribution of the transverse channel switchable vortex beam metasurface, (a) phase distribution of the left skewed vortex beam metasurface, (b) phase distribution of the right skewed vortex beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the transverse dual-channel vortex beam metasurface.

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 figure: Fig. 11.

Fig. 11. Far-field intensity and far-field phase of the transverse single-channel vortex beam (l = -1) at 1.0THz. (a) Far-field intensity of the single-channel right deflected vortex beam, (b) Far-field phase of the single-channel right deflected vortex beam, (c) Mode purity of the simulated vortex beam.

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 figure: Fig. 12.

Fig. 12. Far-field intensity and far-field phase of the transverse dual-channel vortex beam (l=±1) at 1.0THz. (a) Far-field intensity of the transverse dual-channel vortex beam, (b) Far-field phase of left-channel vortex beam (l = 1), (c) Far-field phase of the right-channel vortex beam (l = -1).

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Figures 13(a) and 13(b) present the metasurface phase distribution of the upward-deflected vortex beam by using VO2 coding element and down deflection vortex beam by using gold coding element, respectively. Figure 13(c) illustrates the schematic diagram of dual-channel shared-aperture metasurface. Figure 13(d) shows the metasurface arrangement of dual-channel switchable vortex beam with the topological charge of l=±2. At 25°C, the proposed metasurface produces downward deflection vortex beam with topological charge of l = -2, as shown in Figs. 14(a) and 14(b). It can be observed that the simulated vortex beam purity of l = -2 is closed to 83.0%, as revealed in Fig. 14(c). At the ambient temperature of 68°C, the proposed metasurface generates the far-field intensity and far-field phase of the longitudinal dual-channel vortex beam (l=±2), as shown in Fig. 15. The theoretical deflection angle of the dual-channel vortex beam is 48.6°, and the azimuth of the transverse vortex beam are 90° (l = 2) and 270° (l = -2), respectively.

 figure: Fig. 13.

Fig. 13. Phase distribution of the longitudinal channel switchable vortex beam metasurface, (a) phase distribution of the lower skewed vortex beam metasurface, (b) phase distribution of the upper skewed vortex beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the longitudinal dual-channel vortex beam metasurface.

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 figure: Fig. 14.

Fig. 14. Far-field intensity and far-field phase of the longitudinal single-channel vortex beam (l = -2) at 1.0THz. (a) Far-field intensity of the single-channel lower deflected vortex beam, (b) Far-field phase of the single-channel lower deflected vortex beam, (c) Mode purity of the simulated vortex beam.

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 figure: Fig. 15.

Fig. 15. Far-field intensity and far-field phase of the longitudinal dual-channel vortex beam (l=±2) at 1.0THz. (a) Far-field intensity of the longitudinal dual-channel vortex beam, (b) Far-field phase of upper-channel vortex beam (l = 2), (c) Far-field phase of the lower-channel vortex beam (l = -2).

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Further, we proposed a single- and dual-channel switchable vortex-focusing shared-aperture coding metasurface with gradient cycle length Γb = 800µm. Figures 16(a) and 16(b) show the phase distributions of the left-skewed l = 1 and right-skewed l = -1 vortex-focusing beam metasurfaces, respectively. Figure 16(c) indicates the schematic diagram of the dual-channel shared-aperture metasurface principle. The phase distribution of the adjustable channel numbers vortex-focusing beam metasurface is displayed in Fig. 16(d). For the ambient temperature of 25°C (VO2 is in insulated state), the metasurface presents as a single-channel vortex-focusing beam in xoy and xoz planes, as shown in Figs. 17(a) and 17(b). Figure 17(c) gives the phase of the vortex focusing beam. One can obviously find that the vortex focusing beam phase distributes along clockwise with its topological charge of l = -1. Figure 17(d) displays that the electric field intensity of the vortex focusing beam is about 3.04 V/m. Similarly, for the ambient temperature of 68°C (VO2 is in metallic state), the metasurface generates the dual-channel vortex-focusing beam in the xoy and xoz planes, as shown in Figs. 18(a) and 18(b). Figures 18(c) and 18(d) show the phases of the left and right channel vortex focusing beams, respectively. It is obvious that the phase of the left channel vortex focusing beam distributes along counterclockwise with topological charge l = 1, and the phase of the right channel vortex focusing beam distributes along clockwise with topological charge l = -1. The electric field intensities of the left- and right- channels vortex focusing beam are 0.94 V/m and 1.95 V/m, respectively. Obviously, the designed metasurface achieves switching of channel numbers and adjustable of electric field intensity. Compared with previous designs, the performance comparison results are displayed in Table 1. One can see that the proposed shared-aperture terahertz metasurface structure allows for flexible channels regulation. Based on the above analysis, we can find that by changing the temperature, the dielectric-metal phase states of phase change materials VO2 can be changed. Then, the same shared-aperture metasurface can achieve functional control of terahertz waves with different channel numbers.

 figure: Fig. 16.

Fig. 16. Phase distribution of the dual-channel vortex focusing beam metasurface, (a) phase distribution of the left vortex focusing beam metasurface, (b) phase distribution of the right vortex focusing beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the dual-channel vortex focusing beam metasurface.

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 figure: Fig. 17.

Fig. 17. Electric field performance of the single-channel vortex focusing beam (l = -1) at 1.0THz. (a) electric field intensity in xoy plane, (b) electric field intensity in xoz plane, (c) vortex phase in xoy plane, (d) three-dimensional electric field intensity diagram in xoy plane.

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 figure: Fig. 18.

Fig. 18. Electric field performance of the dual-channel vortex focusing beam (l=±1) at 1.0THz. (a) Electric field intensity in xoy plane, (b)Electric field intensity in xoz plane, (c) phase distribution of the left-channel vortex focusing beam (l = 1), (d) phase distribution of the right-channel vortex focusing beam (l = -1), (e) three-dimensional electric field intensity diagram in xoy plane.

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Tables Icon

Table 1. Performance comparison between the proposed structure with reported structures

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4. Conclusion

To sum up, we designed a shared-aperture channel switchable terahertz metasurface. The full-wave simulation and theoretical calculation results show that the proposed metasurface can realize beams splitting with different deflection directions, vortex beams with different topological charges, focusing beams, and vortex focusing beams with different topological charges when the RCP wave is incident. Furthermore, the metasurface exhibits single-channel and double-channel switchable function, which can be switched freely by adjusting ambient temperature. This study is expected to have promising applications in future terahertz multichannel multiplexing device.

Funding

Natural Science Foundation of Xinjiang Uygur Autonomous Region (2021D01A73).

Acknowledgments

This work was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (2021D01A73).

Disclosures

The authors declare that there are no conflicts of interest related to this article

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (18)
Fig. 1.
Fig. 1. Schematic structure of the proposed shared-aperture dual-channel switchable metasurface, (a) top view of the elliptical metasurface element (VO2), (b) top view of the elliptical metasurface element (gold), (c) 3D-view of the metasurface.

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Fig. 2.
Fig. 2. Simulation reflection responses and phase diagram of unit cells under two kinds of operating temperature. (a) Top view of VO2 unit cell, (b) Reflection coefficient at ambient temperature of 68°C, (c) Reflection phase at ambient temperature of 68 °C, (d) Reflection coefficient at ambient temperature of 25°C, (e) Reflection phase at ambient temperature of 25 °C, (f) Top view of gold unit cell, (g) Reflection coefficient, (h) Reflection phase.

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Fig. 3.
Fig. 3. Function illustration of the designed shared-aperture dual-channel switchable metasurface.

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Fig. 4.
Fig. 4. The phase distribution of the proposed dual-channel beam splitting metasurface. (a) Phase distribution of the transverse beam splitting metasurface, (b) Phase distribution of the longitudinal beam splitting metasurface, (c) Schematic diagram of the dual-channel shared-aperture metasurface, (d) Phase distribution of the dual-channel beam splitting metasurface.

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Fig. 5.
Fig. 5. The far-field intensity diagram and the normalized reflection curve of the dual-channel beam splitting metasurface at 1.0THz. (a) Far field intensity diagram and (b) normalized reflection curve of longitudinal dual-channel beam splitting.

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Fig. 6.
Fig. 6. The far-field intensity diagram and the normalized reflection curve of the dual-channel beam splitting metasurface at 1.0THz. (a) Far field intensity diagram of the multi-channel beam splitting, (b) normalized reflection curve of the longitudinal beam splitting, (c) normalized reflection curve of the transverse beam splitting.

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Fig. 7.
Fig. 7. The phase distribution of the proposed transverse dual-channel focusing beam metasurface. (a) Phase distribution of the left skewed focusing beam metasurface, (b) Phase distribution of the right skewed focusing beam metasurface, (c) Schematic diagram of the dual-channel shared-aperture metasurface, (d) Phase distribution of the dual-channel focusing beam metasurface.

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Fig. 8.
Fig. 8. The electric field distribution of the transverse dual-channel focusing beam metasurface at 1.0THz. (a) Eelectric field intensity in xoy plane, (b) Electric field intensity in xoz plane, (c) Three-dimensional diagram of the electric field intensity in xoy plane.

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Fig. 9.
Fig. 9. The electric field performance of the transverse dual-channel focusing beam metasurface at 1.0THz. (a) Electric field intensity in xoy plane, (b) Electric field intensity in xoz plane, (c) Three-dimensional diagram of the electric field intensity in xoy plane

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Fig. 10.
Fig. 10. Phase distribution of the transverse channel switchable vortex beam metasurface, (a) phase distribution of the left skewed vortex beam metasurface, (b) phase distribution of the right skewed vortex beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the transverse dual-channel vortex beam metasurface.

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Fig. 11.
Fig. 11. Far-field intensity and far-field phase of the transverse single-channel vortex beam (l = -1) at 1.0THz. (a) Far-field intensity of the single-channel right deflected vortex beam, (b) Far-field phase of the single-channel right deflected vortex beam, (c) Mode purity of the simulated vortex beam.

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Fig. 12.
Fig. 12. Far-field intensity and far-field phase of the transverse dual-channel vortex beam (l=±1) at 1.0THz. (a) Far-field intensity of the transverse dual-channel vortex beam, (b) Far-field phase of left-channel vortex beam (l = 1), (c) Far-field phase of the right-channel vortex beam (l = -1).

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Fig. 13.
Fig. 13. Phase distribution of the longitudinal channel switchable vortex beam metasurface, (a) phase distribution of the lower skewed vortex beam metasurface, (b) phase distribution of the upper skewed vortex beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the longitudinal dual-channel vortex beam metasurface.

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Fig. 14.
Fig. 14. Far-field intensity and far-field phase of the longitudinal single-channel vortex beam (l = -2) at 1.0THz. (a) Far-field intensity of the single-channel lower deflected vortex beam, (b) Far-field phase of the single-channel lower deflected vortex beam, (c) Mode purity of the simulated vortex beam.

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Fig. 15.
Fig. 15. Far-field intensity and far-field phase of the longitudinal dual-channel vortex beam (l=±2) at 1.0THz. (a) Far-field intensity of the longitudinal dual-channel vortex beam, (b) Far-field phase of upper-channel vortex beam (l = 2), (c) Far-field phase of the lower-channel vortex beam (l = -2).

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Fig. 16.
Fig. 16. Phase distribution of the dual-channel vortex focusing beam metasurface, (a) phase distribution of the left vortex focusing beam metasurface, (b) phase distribution of the right vortex focusing beam metasurface, (c) schematic diagram of the dual-channel shared aperture principle, (d) phase distribution of the dual-channel vortex focusing beam metasurface.

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Fig. 17.
Fig. 17. Electric field performance of the single-channel vortex focusing beam (l = -1) at 1.0THz. (a) electric field intensity in xoy plane, (b) electric field intensity in xoz plane, (c) vortex phase in xoy plane, (d) three-dimensional electric field intensity diagram in xoy plane.

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Fig. 18.
Fig. 18. Electric field performance of the dual-channel vortex focusing beam (l=±1) at 1.0THz. (a) Electric field intensity in xoy plane, (b)Electric field intensity in xoz plane, (c) phase distribution of the left-channel vortex focusing beam (l = 1), (d) phase distribution of the right-channel vortex focusing beam (l = -1), (e) three-dimensional electric field intensity diagram in xoy plane.

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Tables (1)

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Table 1. Performance comparison between the proposed structure with reported structures

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Equations (8)

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ε ( ω )  =  ε ∞  -  ω p 2 σ σ 0 / ( ω 2 + i ω d ω )
φ A ( x ) = 2 π x / Γ
φ B ( x , y ) = l tan − 1 ( y / x )
φ C ( x , y ) = 2 π ( F 2 + x 2 + y 2  -  F 2 ) / λ
φ ( x , y ) = φ A ( x , y )  +  φ B ( x , y )  +  φ C ( x , y )
{ φ ( i , j ) = φ 1 ( i , j )  Mod( | i − j | , N ) = 0   φ ( i , j ) = φ 2 ( i , j )  Mod( | i − j | , N ) = 1   ⋅ ⋅ ⋅ φ ( i , j ) = φ N ( i , j )  Mod( | i − j | , N ) = N − 1
θ  =  arcsin ⁡ ( λ / Γ )
θ ′  =  arctan ⁡ ( X / F )
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