Thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide

Abstract

The application provides a hot tunable broadband achromatic terahertz metasurface lens based on indium antimonide, relates to the field of electromagnetic metasurfaces, and utilizes the dielectric properties of indium antimonide material sensitive to temperature to realize dynamic switching of functions by regulating the working temperature. The metasurface lens is composed of a high-resistivity silicon column layer and an indium antimonide dielectric layer, and the dielectric parameters of indium antimonide continuously change with the continuous change of temperature. Under the incidence of a conventional Gaussian beam, the device exhibits broadband achromatic focusing performance; under the incidence of a vortex beam, the device maintains a stable focal length position and high mode purity. The application integrates the functions of a broadband achromatic superlens and a tunable vortex generator in a single metasurface structure, breaks through the limitation of single function of a traditional metasurface, and significantly improves the flexibility, adaptability and integration of the device in the application in the terahertz wave band.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic metasurfaces, and in particular to thermally tunable broadband achromatic terahertz metasurface lenses based on indium antimonide. Background Technology

[0002] Terahertz metasurface lenses are one of the most attractive research topics in the terahertz field, attracting increasing attention due to their promising applications in focusing, imaging, and modulation. The introduction of the metasurface concept has spurred the development of terahertz metasurface lenses.

[0003] However, existing terahertz metasurface lenses still face two major bottlenecks. First, most devices can only perform a single task, such as supporting only Gaussian beam focusing or generating only vortex beams of a specific order, making it difficult to achieve both broadband achromatic performance and orbital angular momentum control in the same structure. Second, they lack dynamic reconfigurability. Some designs introduce liquid crystals, graphene, or phase change materials to achieve tuning, but these are often limited by defects such as slow response speed, complex driving, high insertion loss, or discrete control, making it impossible to achieve continuous and low-loss adjustment of focus intensity while maintaining focal length stability.

[0004] When integrating achromatic focusing and vortex beam generation into the same metasurface, traditional designs often sacrifice bandwidth or mode purity due to conflicting phase compensation strategies. Furthermore, relying on external excitation for function switching can easily lead to focus drift or a sharp drop in efficiency. How to simultaneously achieve broadband achromatic focusing and high-purity vortex beam generation within a single, compact metasurface structure, while possessing a certain degree of dynamic tunability, has become a core problem urgently needing breakthroughs in the current process of multifunctionalizing and practicalizing terahertz metasurfaces.

[0005] Therefore, there is a need to provide a thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide, which integrates the dual functions of a broadband achromatic metalens and a tunable vortex generator into a single metasurface structure, breaking through the limitation of the single function of traditional metasurfaces and significantly improving the flexibility, adaptability and integration of the device in terahertz band applications.

[0007] To achieve the above objectives, the present invention provides a thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide, which is composed of periodically arranged metaatomic units, including high resistivity silicon rectangular pillars and indium antimonide pillars placed on top of the silicon rectangular pillars. The metasurface lens operates in the 1.7-2.1 THz frequency range and employs a dual-phase compensation strategy to modulate the incident circularly polarized terahertz wave. The phase distribution in the xy plane satisfies the following condition: ; In the formula, As the basic phase term, it simultaneously achieves beam focusing and orbital angular momentum vortex phase generation; To compensate for the phase term, used to suppress chromatic aberration; This is the phase term induced by focal length variation, used to unify the focusing point at different frequencies; The dielectric properties of indium antimonide as a function of temperature are described using the Drude model: ; Among them, the high-frequency dielectric constant Damping coefficient Plasma resonant frequency The square of the intrinsic carrier concentration in relation to temperature dependence Proportional It changes continuously with temperature.

[0008] Preferred, ; In the formula, For topological load number, Focal length; ; In the formula, The maximum wavelength within the operating wavelength range. and These represent the horizontal and vertical coordinates in the spatial coordinate system, respectively, and a rectangular coordinate system is established with the optical axis of the optical system as the reference.

[0009] By continuously adjusting the operating temperature of the device within the range of 180K to 270K, and thereby continuously controlling the dielectric parameters of indium antimonide, the focusing intensity of the superlens can be dynamically adjusted, while keeping the drift of the focal length position within 5%.

[0010] Preferably, the refractive index of the high resistivity silicon rectangular pillar is 3.45.

[0011] Preferably, the lattice constant of the superatomic unit = The total height of the high-resistivity silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar. = The lengths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 16 to 48 µm, and the widths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 5 to 30 µm. The overall diameter D of the lens is... .

[0012] Preferably, the metasurface lens supports two working modes: Gaussian beam focusing and vortex beam focusing. The Gaussian beam focusing mode is used to generate a conventional focused spot; the vortex beam focusing mode is used to generate an annular focused spot carrying orbital angular momentum.

[0013] Preferably, when the metasurface lens is configured in the vortex beam focusing mode, the interaction between the spiral phase wavefront generated by the metasurface lens and the object under test is utilized to achieve optical edge enhancement detection over a wide bandwidth.

[0014] Preferably, within the full operating bandwidth of 1.7-2.1 THz, the polarization conversion efficiency of the composite metaatomic unit is higher than 60%, and the unit phase response changes approximately linearly with frequency, fully covering the phase range required for dual-phase compensation.

[0015] Therefore, the present invention employs the above-mentioned thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide, and the technical effects are as follows: (1) The dual-phase compensation strategy proposed in this invention effectively suppresses dispersion, enabling the superlens to achieve achromatic focusing for both Gaussian and vortex beam modes in a broadband range of 1.7-2.1THz, with the maximum focal length deviation controlled within 4.2% and focusing efficiency exceeding 40%.

[0016] (2) This invention utilizes the temperature-sensitive properties of indium antimonide material to achieve continuous and gradual adjustment of the focus intensity through continuous thermal control in the range of 180K to 270K. It does not require complex external circuits, and the focal length position hardly shifts during the entire tuning process, maintaining excellent broadband achromatic performance.

[0017] (3) The superlens structure of this invention is compact, integrating multimode focusing and thermally tunable functions, providing a highly efficient and multifunctional platform for terahertz structured light applications. At a topological charge number of... l The vortex focusing mode with a value of 2 enables broadband spiral contrast edge detection, verifying its practical value in real-time optical image processing. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the phase requirements of the thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to the present invention. Figure 2 This is a schematic diagram of the meta-unit structure and a schematic diagram of the overall working principle of the lens in the embodiments of the present invention; Figure 3 The graph shows the polarization conversion efficiency and phase response of metaunits with different geometric parameters in the embodiments of the present invention as a function of frequency. Figure 4 In the embodiments of the present invention, the topological load number lIn the =0 mode, the normalized intensity distribution, focal length, focal spot profile, and intensity distribution along the x-direction at different operating frequencies are shown; where (a) is the normalized intensity distribution at different operating frequencies; (b) is the focal length distribution at different operating frequencies; (c) is the focal spot profile distribution at different operating frequencies; and (d) is the intensity distribution along the x-direction at different operating frequencies. Figure 5 In the embodiments of the present invention, the topological load number l In the =2 mode, the normalized intensity distribution, focal length, focal spot profile, intensity distribution along the x-direction, focal length, full width at half maximum (FWHM), and focusing efficiency are plotted at different operating frequencies; where (a) is the normalized intensity distribution at different operating frequencies; (b) is the focal length distribution at different operating frequencies; (c) is the focal spot profile distribution at different operating frequencies; and (d) is the intensity distribution along the x-direction at different operating frequencies. Figure 6 In the embodiments of the present invention, the topological load number l The result of broadband edge detection of the U-shaped character using the lens in =2 mode; Figure 7 This illustrates how focusing performance changes with temperature in an embodiment of the present invention. Figure 8 This is a focal plane intensity distribution diagram at the center frequency when extended to a higher topological charge number in an embodiment of the present invention, where (a) represents the topological charge number. l (a) Focal plane intensity distribution in the =2 mode, and (b) Topological charge number. l Focal plane intensity distribution in the =3 mode, (c) represents the topological charge number. l Focal plane intensity distribution map in =5 mode. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] Example 1 Thermally tunable broadband achromatic terahertz metasurface lenses based on indium antimonide are composed of periodically arranged metaatomic units, such as... Figure 2As shown, the meta-atomic unit comprises a high-resistivity silicon rectangular pillar and an indium antimonide pillar placed on top of the silicon rectangular pillar; the silicon rectangular pillar serves as the primary electromagnetic resonator, and the high-resistivity silicon rectangular pillar has a refractive index of 3.45. The indium antimonide pillar utilizes its temperature-sensitive dielectric properties to provide thermally tunable functionality for the device. The entire metasurface lens is composed of a large number of such meta-atomic units arranged in a specific phase distribution. When a right-hand circularly polarized terahertz wave is incident perpendicularly from the substrate side, the lens can simultaneously apply a helical phase and a hyperbolic phase through geometric phase modulation, thereby achieving multimode achromatic focusing. The helical phase is applied to generate a vortex beam; the hyperbolic phase is applied for focusing.

[0022] like Figure 3 As shown, the lattice constant of the superatomic unit = The total height of the high-resistivity silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar. = The lengths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 16 to 48 µm, and the widths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 5 to 30 µm. The overall diameter D of the lens is... Full-wave finite-difference time-domain simulations were used to calculate the polarization conversion efficiency and phase response of each metaunit at different frequencies. Parameter sweep results for two metaunits with different geometric parameters are presented. Their phase responses are approximately linear within the target frequency band, and their polarization conversion efficiencies are both higher than 60%, demonstrating that the design can effectively achieve broadband phase coverage and efficient polarization conversion. Figure 1 The target phase distribution is shown, and suitable units are selected from this meta-atom library for spatial arrangement.

[0023] The metasurface lens operates in the 1.7-2.1 THz frequency range. The polarization conversion efficiency of the composite metaatomic units is higher than 60%, and the unit phase response changes approximately linearly with frequency, fully covering the phase range required for dual-phase compensation. For example... Figure 1 As shown, this embodiment employs a dual-phase compensation strategy to modulate the incident circularly polarized terahertz wave. The phase distribution in the xy plane satisfies the following condition: ; In the formula, As the basic phase term, it simultaneously achieves beam focusing and orbital angular momentum vortex phase generation; To compensate for the phase term, used to suppress chromatic aberration; This is the phase term induced by focal length variation, used to unify the focusing point at different frequencies; The dielectric properties of indium antimonide as a function of temperature are described using the Drude model: ; Among them, the high-frequency dielectric constant Damping coefficient rad / s, plasma resonant frequency The square of the intrinsic carrier concentration in relation to temperature dependence Proportional It changes continuously with temperature.

[0024] ; In the formula, For topological load number, Focal length; ; In the formula, The maximum wavelength within the operating wavelength range. and These represent the horizontal and vertical coordinates in the spatial coordinate system, respectively, and a rectangular coordinate system is established with the optical axis of the optical system as the reference.

[0025] By continuously adjusting the operating temperature of the device within the range of 180K to 270K, and thereby continuously controlling the dielectric parameters of indium antimonide, the focusing intensity of the superlens can be dynamically adjusted, while keeping the drift of the focal length position within 5%.

[0026] The metasurface lens supports two working modes: Gaussian beam focusing mode, used to generate a conventional focused spot; and vortex beam focusing mode, used to generate an annular focused spot carrying orbital angular momentum.

[0027] When the metasurface lens is configured in the vortex beam focusing mode, the helical phase wavefront generated by the metasurface lens interacts with the object under test, achieving optical edge enhancement detection over a wide bandwidth.

[0028] When topological load number At that time, achromatic focusing of the Gaussian beam is achieved; such as Figure 4 As shown in (a), (b), (c), and (d), the present invention maintains the focusing of the Gaussian beam at essentially the same position over a wide frequency range, with an axial drift of less than 50µm. The focal length variation with frequency is quantitatively presented, with a stable value around 4.6mm and a maximum deviation of only 4.11%. Furthermore, the spot profile on the focal plane and the normalized intensity distribution along the x-axis show a perfect Gaussian shape, with a full width at half maximum (FWHM) approaching the diffraction limit, confirming its excellent focusing quality.

[0029] like Figure 5 As shown in (a), (b), (c), and (d), when the topological load number At this time, achromatic focusing of the vortex beam is achieved. For the topological charge number... lThe vortex beam with a focal length of 2 exhibits a clear bimodal ring structure at the focal plane. The intensity distribution at the focal plane displays a typical structure of a central dark core and ring-shaped energy convergence. The normalized intensity profile at the focal plane at all frequencies shows a nearly symmetrical bimodal distribution, indicating that the vortex mode characteristics are maintained within the operating frequency band without significant ring structure collapse or mode distortion. Quantitative results show that its focal length remains stable at 4.5 mm, with a relative deviation of only 1.78%, and the focusing efficiency is above 40% throughout the entire operating bandwidth.

[0030] like Figure 6 As shown, this embodiment uses topological charges. l The =2 mode can be used for broadband spiral phase contrast edge detection. When the device in this scheme is used to perform edge recognition on a U-shaped object, the edge information of the object can be clearly extracted throughout the entire operating frequency band, verifying its practical value in optical image processing.

[0031] like Figure 7 As shown, in this embodiment, when the ambient temperature increases from 180K to 270K, the focal plane position remains almost unchanged, but the peak intensity gradually decreases. The maximum drift of the focal length with temperature at different frequencies is less than 5%, the average focal length fluctuation is less than 1.5%, and the peak intensity exhibits a controllable linear decreasing trend. This characteristic allows this device to achieve focus-shift-free intensity modulation without complex circuitry.

[0032] like Figure 8 As shown in (a), (b), and (c), this scheme is not limited to and The pattern, at a center frequency of 1.9 THz, can be extended to higher-order topological charge cases, generating more complex focal spot patterns. This demonstrates the invention's potential to generate arbitrary vortex patterns, laying the foundation for more complex optical field manipulation and information encoding.

[0033] Therefore, the present invention adopts the above-mentioned thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide, which integrates the dual functions of broadband achromatic metalens and tunable vortex generator into a single metasurface structure, breaking through the limitation of the single function of traditional metasurfaces, and significantly improving the flexibility, adaptability and integration of the device in terahertz band applications.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide, composed of periodically arranged metaatomic units, characterized in that... The metaatomic unit comprises a high-resistivity silicon rectangular pillar and an indium antimonide pillar placed on top of the silicon rectangular pillar; The metasurface lens operates in the 1.7-2.1 THz frequency range and employs a dual-phase compensation strategy to modulate the incident circularly polarized terahertz wave. The phase distribution in the xy plane satisfies the following condition: ； In the formula, As the basic phase term, it simultaneously achieves beam focusing and orbital angular momentum vortex phase generation; To compensate for the phase term, used to suppress chromatic aberration; This is the phase term induced by focal length variation, used to unify the focusing point at different frequencies; The dielectric properties of indium antimonide as a function of temperature are described using the Drude model: ； Among them, the high-frequency dielectric constant Damping coefficient Plasma resonant frequency The square of the intrinsic carrier concentration in relation to temperature dependence Proportional It changes continuously with temperature.

2. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 1, characterized in that, ； In the formula, For topological load number, Focal length; ； In the formula, The maximum wavelength within the operating wavelength range. and These represent the horizontal and vertical coordinates in the spatial coordinate system, respectively, and a rectangular coordinate system is established with the optical axis of the optical system as the reference. By continuously adjusting the operating temperature of the device within the range of 180K to 270K, and thereby continuously controlling the dielectric parameters of indium antimonide, the focusing intensity of the superlens can be dynamically adjusted, while keeping the drift of the focal length position within 5%.

3. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 1, characterized in that, The refractive index of the high resistivity silicon rectangular pillar is 3.

45.

4. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 1, characterized in that, Lattice constant of superatomic unit = The total height of the high-resistivity silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar. = The lengths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 16 to 48 µm, and the widths of the silicon rectangular pillar and the indium antimonide pillar placed on top of the silicon rectangular pillar range from 5 to 30 µm. The overall diameter D of the lens is... .

5. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 1, characterized in that, The metasurface lens supports two working modes: Gaussian beam focusing and vortex beam focusing. In the Gaussian beam focusing mode, a conventional focused spot is generated; in the vortex beam focusing mode, an annular focused spot carrying orbital angular momentum is generated.

6. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 5, characterized in that, When the metasurface lens is configured in vortex beam focusing mode, it utilizes the interaction between the spiral phase wavefront generated by the metasurface lens and the object under test to achieve optical edge enhancement detection over a wide bandwidth.

7. The thermally tunable broadband achromatic terahertz metasurface lens based on indium antimonide according to claim 1, characterized in that, Within the full operating bandwidth of 1.7–2.1 THz, the polarization conversion efficiency of the composite metaatomic unit is higher than 60%, and the unit phase response changes approximately linearly with frequency, fully covering the phase range required for dual-phase compensation.

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