A terahertz-band space-time vortex-generated metasurface device and its application method

Abstract

This invention provides a terahertz-band space-time vortex generation metasurface device and its application method, belonging to the field of terahertz application technology. It includes a dielectric substrate and an array of dielectric pillar microstructures at the top and bottom of the substrate. Utilizing the inherent topological singularity caused by the breaking of z-axis mirror symmetry, a space-time optical vortex is generated by performing a spiral phase Fourier transform in the domain to the space-time domain. The application method includes: when the incident electric field is parallel to the lateral distance between the upper and lower silicon pillars in the unit cell structure of the metasurface device, the light transmitted through the metasurface device is space-time vortex light. This invention uses a metasurface composed of a quartz substrate and an array of upper and lower high-resistivity silicon pillars, utilizing the topological singularity of the broken z-axis mirror symmetry to generate space-time optical vortices. x The linearly polarized light is converted into spacetime vortex light with transverse orbital angular momentum, achieving efficient generation of spacetime vortices in the terahertz band. The device has a simple structure and reliable fabrication, making it suitable for terahertz imaging, communication and other fields.

Description

Technical Field

[0001] This invention relates to the field of terahertz application technology, and in particular to a terahertz frequency band space-time vortex generation metasurface device and its application method. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies between 0.1 THz and 10 THz, falling between millimeter waves and infrared light. They exhibit immense application potential in high-speed communication, non-destructive imaging, biosensing, and spectral analysis. Vortex beams are special beams with a spiral wavefront phase distribution and phase singularities. Their orbital angular momentum (OAM) provides a completely new physical dimension for the manipulation and multiplexing of terahertz waves. Theoretically, vortex beams support an infinite number of orthogonal OAM modes, providing a physical basis for technological innovations such as ultra-high-capacity communication, rotating Doppler detection, and particle manipulation.

[0003] Traditional methods for generating vortex light mainly include helical phase plates, computational holograms, and antenna arrays. However, these methods face significant challenges in the terahertz band: helical phase plates are typically bulk material structures, which present problems such as design and fabrication difficulties, narrow operating bandwidth, high insertion loss, and incompatibility with semiconductor processes; computational holograms, while highly flexible, generally have low diffraction efficiency; and antenna array solutions based on active devices are constrained by system complexity, high power consumption, and high cost.

[0004] Furthermore, most existing terahertz vortex beam generation technologies focus on the manipulation of spatial phase distribution. The resulting vortex waves exhibit a spiral phase change in space, but are static or quasi-static in time. With the explosive growth in the demand for information capacity and processing speed from next-generation wireless communication and sensing systems, static spatial vortex waves are gradually showing limitations in terms of dynamic modulation, signal encoding, and processing speed.

[0005] The wavefront of a spacetime vortex wave not only possesses a helical phase distribution in space, but this phase distribution also scans in time at an ultrafast speed. This beam simultaneously carries angular momentum in both spatial and frequency dimensions, generating transverse orbital angular momentum components. This opens up a completely new dimension for the manipulation of the angular momentum of light / electromagnetic waves, with potential applications in ultrafast optical switching, etc. It has profound application prospects in multiplexing communication, time-varying particle manipulation and other fields. However, at present, the generation of spacetime vortex waves usually relies on complex bulk optical systems (such as the combination of femtosecond laser pulses and spatial light modulators) or complex electronically controlled phased arrays. These systems are difficult to integrate and generate efficiently and at low cost on a compact platform. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a terahertz-band space-time vortex-generated metasurface device and its application method. This device utilizes a metasurface composed of a substrate with low refractive index contrast and an array of upper and lower dielectric silicon pillar microstructures with high refractive index contrast, taking advantage of the topological singularity arising from broken z-axis mirror symmetry. x By converting linearly polarized light into spacetime vortex light with transverse orbital angular momentum, the device achieves efficient generation of spacetime optical vortices in the terahertz band. Furthermore, the device has a simple structure, reliable fabrication, and is suitable for applications such as terahertz imaging and communication.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] One objective of this invention is to provide a terahertz-band space-time vortex-generated metasurface device, comprising a dielectric substrate with low refractive index contrast and an array of dielectric pillar microstructures with high refractive index contrast disposed on the top and bottom of the dielectric substrate. Utilizing the inherent topological singularity caused by the breaking of z-axis mirror symmetry, by... The spiral phase Fourier transform in the domain is transferred to the spatiotemporal domain to generate a spatiotemporal optical vortex.

[0009] Preferably, the dielectric substrate is made of quartz, and the dielectric pillar microstructure array is made of high-resistivity silicon.

[0010] Preferably, the adjacent upper and lower high-resistivity silicon pillars in the dielectric pillar microstructure array and the quartz substrate form a unit structure of the metasurface device, and the structural period of the metasurface device generated by the space-time vortex is 380-400μm.

[0011] Preferably, the unit structure is a subwavelength structure, and its period is smaller than the wavelength of the incident electromagnetic wave.

[0012] Preferably, the lateral distance between the upper and lower high-resistivity silicon pillars in the unit structure of the metasurface device is 80-120 μm, and the diameter of the upper and lower high-resistivity silicon pillars in the unit structure of the metasurface device is 75-85 μm.

[0013] Preferably, the dielectric pillar microstructure array is an isotropic structure, which includes one or more of square pillars and circular pillars; the height of the high-resistivity silicon pillars in the dielectric pillar microstructure array is 140-160 μm.

[0014] Preferably, the thickness of the dielectric substrate is 240-260 μm.

[0015] The second objective of this invention is to provide a method for using the above-mentioned terahertz frequency band space-time vortex-generated metasurface device, comprising: when the incident electric field is parallel to the lateral distance direction of the upper and lower high-resistivity silicon pillars in the unit structure of the metasurface device, the light transmitted through the metasurface device is space-time vortex light.

[0016] The third objective of this invention is to provide an application of the above-mentioned terahertz frequency band space-time vortex-generated metasurface device, specifically in terahertz imaging, terahertz communication, or terahertz security detection.

[0017] The fourth objective of this invention is to provide an application of the above-mentioned terahertz space-time vortex-generated metasurface device, specifically in the fabrication of a terahertz space-time vortex optical communication device with transverse orbital angular momentum.

[0018] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0019] The terahertz-band space-time vortex generation metasurface device provided by this invention, through a unique structure composed of a quartz substrate and upper and lower high-resistivity silicon pillars, utilizes the inherent topological singularity of broken z-axis mirror symmetry to generate incident... x The device efficiently converts linearly polarized light into spacetime vortex light with transverse orbital angular momentum, achieving stable generation of spacetime optical vortices in the terahertz band and meeting the requirements for functional beam generation. At the same time, the device adopts a subwavelength structure design with small unit structure period and well-defined parameters. The overall structure is simple and novel, and the fabrication process is reliable, making it suitable for various application scenarios such as terahertz imaging, communication, and security detection. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 In Embodiment 1 of the present invention x A schematic diagram of a device that generates spacetime vortex light when polarized light is incident on a metasurface;

[0022] Figure 2 This is a schematic diagram of the metasurface unit structure in Embodiment 1 of the present invention; wherein, Figure 2 (a) in the figure is a front view of the metasurface unit structure. Figure 2 (b) is a top view of the metasurface unit structure;

[0023] Figure 3 This is the amplitude image of the wavenumber-frequency domain of the metasurface in Embodiment 1 of the present invention;

[0024] Figure 4 This is a wavenumber-frequency domain phase image of the metasurface in Embodiment 1 of the present invention;

[0025] Figure 5 This is the spatial-temporal amplitude image of the metasurface in Embodiment 1 of the present invention;

[0026] Figure 6 This is a phase image of the metasurface in the spatial-temporal domain in Embodiment 1 of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Dielectric substrate; 2. High-resistivity silicon pillar; 3. x 4. Polarized incident light; 5. Transmitted spacetime vortex light. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] This embodiment provides a terahertz-band space-time vortex-generated metasurface device and its usage method. The metasurface device includes a dielectric substrate with low refractive index contrast and an array of dielectric pillar microstructures with high refractive index contrast disposed on the top and bottom of the dielectric substrate. The low refractive index contrast is 1.9-2, and the high refractive index contrast is 3.4-3.5. Utilizing the inherent topological singularity caused by the breaking of z-axis mirror symmetry, by... The spiral phase Fourier transform in the domain is transferred to the spatiotemporal domain to generate a spatiotemporal optical vortex.

[0033] In this embodiment, the device consists of a dielectric substrate 1 and a high-resistivity silicon pillar 2. The dielectric substrate 1 is made of quartz material. Figure 2 As shown in (a), its thickness is set to 250 μm, serving as the basic support structure for the device and providing stable support for the upper and lower high-resistivity silicon pillars. The high-resistivity silicon pillars 2 are respectively positioned at the top and bottom of the dielectric substrate 1, combined with... Figure 2In (a) and (b), the height of the high-resistivity silicon pillar 2 is 150 μm. The top high-resistivity silicon pillar 2 has a specific offset in the horizontal direction relative to the edge of the dielectric substrate 1. By utilizing the layout of the high-resistivity silicon pillar 2 and the dielectric substrate 1, a z-axis mirror symmetry broken structure is constructed, introducing inherent topological singularities. In addition, the lateral distance between the vertically arranged high-resistivity silicon pillars 2 in the unit structure of the metasurface device is 100 μm, and the diameter of the vertically arranged high-resistivity silicon pillars 2 in the unit structure of the metasurface device is 80 μm.

[0034] Based on the unit structure of metasurface devices, from Figure 2 As can be seen in (b), in axis, y The axial period is 400μm, and because the period is smaller than the wavelength of the incident electromagnetic wave, it belongs to the subwavelength structure, which can control the phase and propagation characteristics of the electromagnetic wave.

[0035] Additionally, the position of the top high-resistivity silicon pillar 2 on the dielectric substrate 1, from... Figure 2 (b) in the diagram clearly defines parameters such as the horizontal distance between the substrate 1 and the edge of the dielectric substrate 1, which, in conjunction with... Figure 2 The dimensions of each part shown in (a) together constitute a stable metasurface unit structure with specific topological properties.

[0036] Based on the above, the method for using the terahertz-band space-time vortex-generated metasurface device provided in this embodiment is as follows: when the incident electric field is parallel to the lateral distance between the upper and lower silicon pillars in the unit structure of the metasurface device, the light transmitted through the metasurface device is space-time vortex light. Specifically, as follows... Figure 1 As shown, when x When linearly polarized incident light 3 is incident on the metasurface device along the direction shown in the figure, the phase of the incident light is modulated at the subwavelength scale due to the topological singularity structure formed by the dielectric substrate 1 and the high-resistivity silicon pillars 2 arranged on the top and bottom. By... The spiral phase in the wavenumber-frequency domain is transformed to the spacetime domain via Fourier transform, with reference to... Figure 3 The image shows a specific distribution of transmission amplitude, reflecting the modulation effect of the helical phase in this domain, by means of... Figure 3 This can help verify the effectiveness and regularity of phase modulation. (Refer to...) Figure 4 It intuitively presents the distribution of phase in the domain. The phase difference in different regions corresponds to the specific form of spiral phase modulation. It can clearly show the evolution of phase in the process of conversion from incident light to space-time vortex light, and help to understand the mechanism of topological singularity on phase modulation.

[0037] After completing the Fourier transform, as follows Figure 5The spatial-temporal amplitude image of the metasurface shown clearly reflects the energy accumulation and distribution characteristics of the spacetime vortex light in the spatial-temporal domain. The special shape at the center corresponds to the hollow ring structure of the spacetime vortex light, verifying that the transverse orbital angular momentum of the transmitted spacetime vortex light was successfully generated after metasurface modulation. Figure 6 As shown, the distribution law of the phase of the spacetime vortex light in the spatiotemporal domain is further demonstrated. The phase changes in different regions correspond to the unique wavefront structure of the spacetime vortex light. From the phase dimension, the integrity and correctness of the generation of the spacetime vortex light are confirmed. The final result of the transformation from incident light to the generation of spacetime vortex light is intuitively shown. The device's ability to effectively generate spacetime vortex light is confirmed. The spatiotemporal distribution of the phase is reconstructed through transformation. Finally, the light transmitted through the device is transformed into spacetime vortex light with transverse orbital angular momentum, completing the transformation of the terahertz band functional beam from incident light to the generation of spacetime vortex light.

[0038] Based on the above, the device has a simple structure, and the quartz substrate and silicon pillar materials used are common and readily available. The fabrication process is mature and reliable, and the design parameters can be stably reproduced. The generated spacetime vortex light can be applied to the field of terahertz functional beam generation, and also has practical value in terahertz imaging, communication, and security detection scenarios. It can also be used to fabricate terahertz spacetime vortex optical communication devices with transverse orbital angular momentum, providing an effective solution for the practical application of terahertz technology.

[0039] Therefore, by employing the aforementioned terahertz-band space-time vortex-generated metasurface device and its application method, a metasurface composed of a quartz substrate and upper and lower high-resistivity silicon pillars is created. Utilizing the topological singularity of broken z-axis mirror symmetry, the topology of the metasurface is utilized. x By converting linearly polarized light into spacetime vortex light with transverse orbital angular momentum, the device achieves efficient generation of spacetime optical vortices in the terahertz band. Furthermore, the device has a simple structure, reliable fabrication, and is suitable for applications such as terahertz imaging and communication.

[0040] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A terahertz frequency range space-time vortex generating metasurface device, characterized in that, Including a dielectric substrate with low refractive index contrast and an array of dielectric pillar microstructures with high refractive index contrast disposed on the top and bottom of the dielectric substrate, utilizing the inherent topological singularity caused by the breaking of z-axis mirror symmetry, by... k-f The spiral phase Fourier transform in the domain is transferred to the spatiotemporal domain to generate a spatiotemporal optical vortex; the dielectric pillar microstructure array is an isotropic structure, which includes one or more of square pillars and circular pillars; the height of the high-resistivity silicon pillars in the dielectric pillar microstructure array is 140-160 μm. The method for using the space-time vortex generating metasurface device in the terahertz band comprises: when the incident electric field is parallel to the transverse distance direction of the upper and lower high-resistance silicon columns in the unit structure of the metasurface device, the light transmitted through the metasurface device is space-time vortex light.

2. The THz-space-time vortex generating metasurface device according to claim 1, wherein, The material of the dielectric substrate is quartz, and the material of the dielectric column microstructure array is high-resistance silicon.

3. The THz-space-time vortex generating metasurface device of claim 2, wherein, The upper and lower high-resistance silicon columns in the dielectric column microstructure array and the quartz substrate constitute a unit structure of the metasurface device, and the structural period of the space-time vortex generating metasurface device is 380-400 μm.

4. The THz-space-time vortex generating metasurface device of claim 3, wherein, The unit structure is a subwavelength structure, and the period is less than the wavelength of the incident electromagnetic wave.

5. The THz-space-time vortex generating metasurface device of claim 4, wherein, The transverse distance of the upper and lower high-resistance silicon columns in the unit structure of the metasurface device is 80-120 μm, and the diameter of the upper and lower high-resistance silicon columns in the unit structure of the metasurface device is 75-85 μm.

6. The THz-space-time vortex generating metasurface device of claim 2, wherein, The thickness of the dielectric substrate is 240-260 μm.

7. Use of a THz frequency range space-time vortex generating metasurface device according to any one of claims 1 to 6, characterized in that, The application in terahertz imaging, terahertz communication or terahertz safety detection.

8. Use of a THz frequency range space-time vortex generating metasurface device according to any one of claims 1 to 6, characterized in that, The application in preparing a terahertz space-time vortex light communication device with transverse orbital angular momentum.

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