Metallic hyperlens structure for terahertz wavefront manipulation

Abstract

This invention discloses a metallic metalens structure for wavefront manipulation in the terahertz band, belonging to the field of optical device manufacturing technology. A first and second metallic grating layer constitute a polarization selection structure for polarization screening of incident terahertz waves. Precise phase modulation of the transmitted terahertz wave is achieved through a metallic unit array, realizing efficient wavefront shaping. The synergistic resonance design between multiple metallic metasurfaces ensures structural planarity and compactness while improving the overall control efficiency and stability of the device. By introducing the polarization selection structure, terahertz wave components with undesigned polarizations are effectively suppressed, reducing background noise on the focusing plane and improving the signal-to-noise ratio of the focused spot. Under the synergistic effect of the above three-layer structure, the metallic metalens can effectively focus incident terahertz waves at the target terahertz operating frequency, making the focused spot size smaller than the diffraction limit at the corresponding frequency, thereby achieving super-resolution focusing.

Description

Technical Field

[0001] This invention belongs to the field of optical device manufacturing technology, and more specifically, relates to a metal superlens structure for wavefront modulation in the terahertz band. Background Technology

[0002] Terahertz waves, with their spectral position between microwaves and infrared light, possess both strong penetrating power and high spatial resolution potential, and have broad application prospects in fields such as high-speed wireless communication, non-destructive testing, high-resolution imaging, biomedical diagnostics, and terahertz spectral analysis.

[0003] In existing terahertz systems, wavefront modulation devices are key components for achieving terahertz wave focusing, imaging, and signal enhancement. In recent years, the development of metasurface technology has provided a new solution for terahertz wavefront modulation. Metasurfaces are typically composed of artificial structural units arranged in a two-dimensional plane. Through precise design of the unit geometry parameters, flexible control of the phase, amplitude, and polarization state of electromagnetic waves can be achieved within ultra-thin thicknesses. Terahertz metasurfaces based on metallic structures have been extensively studied in the terahertz band due to their strong local electromagnetic response capabilities and have been used to achieve functions such as anomalous refraction, focusing, imaging, and sensing.

[0004] However, metallic structures inevitably suffer from ohmic losses in the terahertz band. If the structural design is flawed, transmission efficiency can easily decrease, further weakening the focusing effect. Therefore, achieving efficient focusing while maintaining a compact and planar structure remains a critical problem that terahertz superlens technology urgently needs to solve. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a metal superlens structure for wavefront modulation in the terahertz band. Its purpose is to solve the technical problem of how to achieve efficient focusing while ensuring structural compactness and planarity.

[0006] To achieve the above objectives, according to one aspect of the present invention, a metal metalens structure for wavefront modulation in the terahertz band is provided, comprising: a dielectric substrate and a metal metasurface structure disposed on the dielectric substrate; The metal metasurface structure comprises, from top to bottom, a first metal grating layer, a metal pattern layer, and a second metal grating layer; The orientations of the first metal grating layer and the second metal grating layer are orthogonal to each other; the orthogonally arranged first metal grating layer and second metal grating layer are used to polarize the incident terahertz wave of the metal superlens structure; The metal pattern layer is an array of multiple metal units arranged along a planar direction, and at least one geometric parameter of the metal unit changes with its position in the array; The first metal grating layer, the metal pattern layer, and the second metal grating layer constitute an integrated resonant system, which collaboratively controls the operating frequency and wavefront modulation performance of the metal superlens structure.

[0007] Furthermore, the metal strip directions of the first metal grating layer and the second metal grating layer are perpendicular to each other.

[0008] Furthermore, the geometric parameters of the metal unit that vary with position include one or more of the metal unit's size, rotation angle, and shape profile.

[0009] Furthermore, the metal unit is an open annular structure; at least one of the opening direction, opening size, ring width, and major-minor axis ratio of the open annular structure can be adjusted.

[0010] Furthermore, the metal unit is an anisotropic metal structure.

[0011] Furthermore, the metal unit is a subwavelength scale structure.

[0012] Furthermore, the metal units in the metal pattern layer are arranged in a two-dimensional planar periodic arrangement, a two-dimensional planar non-periodic arrangement, or a two-dimensional planar gradually changing periodic arrangement.

[0013] Furthermore, the metal material of the first metal grating layer, the metal pattern layer, and the second metal grating layer is one of gold, silver, or aluminum.

[0014] Furthermore, the dielectric substrate is a low-loss material that is transparent in the terahertz band.

[0015] Furthermore, the metal superlens forms a focused light spot that breaks the diffraction limit at frequencies ranging from 0.1 THz to 10 THz.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: (1) The metal superlens structure provided by the present invention comprises a polarization selection structure consisting of a first metal grating layer and a second metal grating layer, used for polarization screening of incident terahertz waves to improve the signal-to-noise ratio of the focused spot. Precise phase modulation of the transmitted terahertz wave is achieved through a metal unit array, realizing efficient wavefront shaping and forming a tightly focused spot that breaks the diffraction limit at the target terahertz frequency. Through the synergistic resonance design between multiple metal metasurfaces, the overall control efficiency and stability of the device are improved while ensuring structural planarity and compactness. By introducing the polarization selection structure, terahertz wave components with non-designed polarization are effectively suppressed, reducing background noise on the focusing plane and improving the signal-to-noise ratio of the focused spot. Under the synergistic effect of the above three-layer structure, the metal superlens can effectively focus the incident terahertz wave at the target terahertz operating frequency, making the focused spot size smaller than the diffraction limit at the corresponding frequency, thereby achieving a super-resolution focusing effect.

[0017] (2) The metal superlens structure provided by the present invention effectively filters the polarization of the incident terahertz wave by introducing a vertically oriented upper second metal grating layer, significantly suppressing undesigned polarization components and stray waves, thereby reducing the background noise of the focusing plane and improving the signal-to-noise ratio of the focused spot.

[0018] (3) The metal superlens structure provided by the present invention has at least one geometric parameter of the metal unit that changes continuously or discretely with its position in the array, so that the metal metasurface applies a preset phase distribution to the transmitted terahertz wave to achieve the required wavefront modulation function. By precisely modulating the phase of the transmitted terahertz wave through the metal pattern layer and forming a cooperative resonance mechanism with the upper second metal grating layer, the superlens can achieve tight focusing at the subwavelength scale at the target operating frequency, breaking through the diffraction limit limitation of traditional terahertz lenses.

[0019] (4) The metal superlens structure provided by the present invention is designed as an integrated resonant system, avoiding the performance loss caused by the simple superposition of functional units. While ensuring the planarity and compactness of the structure, it improves the wavefront modulation efficiency and device working stability.

[0020] (5) The metal superlens structure provided by the present invention is a planar thin-layer structure that can be fabricated by standard micro-nano fabrication processes. It has good manufacturing consistency and scalability, and is easy to integrate with terahertz imaging, sensing and communication systems. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of a metal superlens structure for wavefront modulation in the terahertz band according to an embodiment of the present invention. Figure 2(a) is a schematic diagram of the structure of the first metal grating layer in one embodiment of the present invention; Figure 2(b) is a schematic diagram of the structure of the metal patterned layer in one embodiment of the present invention; Figure 2(c) is a schematic diagram of the structure of the second metal grating layer in one embodiment of the present invention; Figure 3 This is a schematic diagram of the simulation setup for electromagnetic simulation verification of the metal superlens structure described in an embodiment of the present invention; Figure 4 This is a schematic diagram of the focusing effect of the metal superlens structure described in an embodiment of the present invention in electromagnetic simulation software; Figure 5 This is a cross-sectional view of the energy distribution along the central axis at the focal plane of the metal superlens structure according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] This invention provides a metallic superlens in the terahertz band, such as Figure 1 As shown, it includes: a dielectric substrate and a metal metasurface structure disposed on the dielectric substrate.

[0024] The dielectric substrate is made of a material with high transmittance and low loss for terahertz waves, such as high-resistivity silicon, quartz, or polyimide. Its thickness can be selected according to specific application requirements to balance mechanical stability and transmission efficiency.

[0025] The metallic metasurface structure comprises, from top to bottom, a first metallic grating layer, a metallic pattern layer, and a second metallic grating layer. These three metallic layers are separated by a dielectric layer and integrated onto the same substrate, forming an electromagnetically coordinated integrated resonant system.

[0026] As shown in Figures 2(a) and 2(c), both the first and second metal grating layers are composed of periodically arranged metal strips, and the orientations of the metal strips are orthogonal to each other. This orthogonal grating structure can perform polarization selection on the incident terahertz wave, allowing only the polarization component matching the grating transmission direction to pass through efficiently, thereby suppressing undesigned polarization components and the stray waves they generate, and improving the signal-to-noise ratio of the focused spot.

[0027] As shown in Figure 2(b), the metal pattern layer is formed by arranging subwavelength-scale metal units in an array along a two-dimensional plane. The metal units are anisotropic structures, and in this embodiment, they are preferably open-ring structures, such as open-elliptical ring structures. The geometric parameters of the metal units, including but not limited to at least one of the following: opening direction, opening size, ring width, and major-minor axis ratio, change with their position in the array, thereby enabling the transmitted terahertz waves to obtain a predetermined phase distribution in space.

[0028] By rationally designing the spatial distribution of the geometric parameters of the aforementioned metal unit, the metal superlens can apply secondary phase modulation to the incident wavefront at the target terahertz operating frequency, thereby achieving wavefront convergence.

[0029] It is important to emphasize that the first metal grating layer, the metal pattern layer, and the second metal grating layer are not simply functional superpositions, but rather designed as a whole for synergistic resonance. By adjusting the grating period, linewidth, and geometric parameters of the intermediate metal units, the resonant frequency, transmission characteristics, and wavefront modulation capability of the superlens can be jointly controlled.

[0030] To verify the focusing performance of the metallic superlens structure for terahertz wavefront modulation described in this invention, numerical simulation analysis was performed using electromagnetic simulation software. For example... Figure 3 As shown, in this embodiment, the simulation uses a plane wave as the incident wave source, with the incident direction perpendicular to the superlens plane, and the polarization direction of the incident terahertz wave is consistent with the transmission direction of the first metal grating layer.

[0031] For example, the target operating frequency is set to 2.52 THz. By rationally designing the geometric parameters of each metal unit in the metal pattern layer, the superlens achieves the desired phase distribution at this frequency.

[0032] like Figure 4 As shown, simulation results indicate that after the incident terahertz plane wave is controlled by the metal superlens described in this embodiment, a distinct focused spot is formed at a predetermined position, with highly concentrated energy. Furthermore, the size of the focused spot is smaller than the diffraction limit at the corresponding frequency, verifying that the superlens described in this invention possesses super-resolution focusing capability.

[0033] like Figure 5 As shown, by extracting the energy distribution cutoff line along the central axis at the focal plane, it can be observed that the focused spot exhibits an approximately Gaussian distribution, and the background energy in the region outside the main lobe is significantly reduced. This indicates that the orthogonal polarization grating structure effectively suppresses undesigned polarization stray waves, resulting in a clean background on the final focused plane and a high signal-to-noise ratio for the focused spot.

[0034] Furthermore, the metal unit array can be arranged in a two-dimensional planar periodic pattern, an aperiodic pattern, or a gradually changing periodic pattern to meet different wavefront modulation requirements. The metal materials of the first metal grating layer, the metal pattern layer, and the second metal grating layer can be selected from highly conductive metal materials such as gold, silver, or aluminum.

[0035] Furthermore, the metal superlens structure for wavefront modulation in the terahertz band described in this invention can be fabricated using micro-nano fabrication processes such as photolithography, electron beam etching, or laser direct writing, exhibiting good process compatibility and suitability for large-scale manufacturing and system integration.

[0036] Furthermore, the metal units in the metal pattern layer are arranged in a two-dimensional planar periodic arrangement, a two-dimensional planar non-periodic arrangement, or a two-dimensional planar gradually changing periodic arrangement.

[0037] Furthermore, the metal material of the first metal grating layer, the metal pattern layer, and the second metal grating layer is one of gold, silver, or aluminum.

[0038] Furthermore, the dielectric substrate is a low-loss material that is transparent in the terahertz band.

[0039] Furthermore, the metal superlens forms a focused light spot that breaks the diffraction limit at frequencies ranging from 0.1 THz to 10 THz.

[0040] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that the terms "in one embodiment," "for example," and "again" in this invention are intended to illustrate the invention and are not intended to limit the invention.

[0041] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A metallic superlens structure for wavefront modulation in the terahertz band, characterized in that, include: A dielectric substrate and a metallic metasurface structure disposed on the dielectric substrate; The metal metasurface structure comprises, from top to bottom, a first metal grating layer, a metal pattern layer, and a second metal grating layer; The orientations of the first metal grating layer and the second metal grating layer are orthogonal to each other; the orthogonally arranged first metal grating layer and second metal grating layer are used to polarize the incident terahertz wave of the metal superlens structure; The metal pattern layer is an array of multiple metal units arranged along a planar direction, and at least one geometric parameter of the metal unit changes with its position in the array; The first metal grating layer, the metal pattern layer, and the second metal grating layer constitute an integrated resonant system, which collaboratively controls the operating frequency and wavefront modulation performance of the metal superlens structure.

2. The metallic superlens structure for terahertz wavefront modulation as described in claim 1, characterized in that, The metal strips of the first metal grating layer and the second metal grating layer are perpendicular to each other.

3. The metallic superlens structure for terahertz wavefront modulation as described in claim 1, characterized in that, The geometric parameters of the metal element that vary with position include one or more of the metal element's size, rotation angle, and shape profile.

4. The metallic superlens structure for terahertz wavefront modulation as described in claim 3, characterized in that, The metal unit is an open annular structure; at least one of the opening direction, opening size, ring width, and major-minor axis ratio of the open annular structure can be adjusted.

5. The metallic superlens structure for terahertz wavefront modulation as described in claim 3, characterized in that, The metal unit is an anisotropic metal structure.

6. The metallic superlens structure for terahertz wavefront modulation as described in claim 1, characterized in that, The metal unit is subwavelength scale.

7. The metallic superlens structure for terahertz wavefront modulation as described in claim 1, characterized in that, The metal units in the metal pattern layer are arranged in a two-dimensional planar periodic arrangement, a two-dimensional planar non-periodic arrangement, or a two-dimensional planar gradually changing periodic arrangement.

8. The metallic superlens structure for terahertz wavefront modulation as described in claim 1, characterized in that, The metal material of the first metal grating layer, the metal pattern layer and the second metal grating layer is one of gold, silver or aluminum.

9. The metallic superlens structure for terahertz wavefront modulation according to claim 1 is characterized in that, The dielectric substrate is a transparent, low-loss material in the terahertz band.

10. The metallic superlens structure for terahertz wavefront modulation as described in any one of claims 1-9, characterized in that, The metal superlens forms a focused light spot that breaks the diffraction limit at frequencies ranging from 0.1 THz to 10 THz.

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