Complex amplitude vector light field system based on terahertz on-chip metasurface

Abstract

The present invention discloses a complex amplitude vector light field system based on a terahertz on-chip metasurface, comprising a metasurface region and an intrinsic region spliced ​​together in the horizontal direction, a plurality of compound metaperiodic units arranged along the horizontal and vertical planes, and an intrinsic primitive cell. The plurality of compound metaperiodic units arranged along the horizontal and vertical planes are arranged in the metasurface region, each compound metaperiodic unit comprises a 2*2 array of metasurface primitive cells, each metasurface primitive cell comprises a metal microstructure layer, a first dielectric film layer, and a first metal thin layer arranged in sequence along the vertical direction, and the metal microstructure layers of the plurality of metasurface primitive cells are rotated and arranged according to a required phase distribution; the odd-numbered columns in the compound metaperiodic units radiate left-handed circularly polarized complex amplitude light fields, and the even-numbered columns radiate right-handed circularly polarized complex amplitude light fields, and a vector light field with a preset polarization state is synthesized through interference of left-handed circular polarization and right-handed circular polarization in free space.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a complex amplitude vector light field system based on a terahertz on-chip metasurface. Background Art

[0002] With the advancement of wireless communication technology, electromagnetic shielding has become increasingly important, especially in high-tech fields such as modern communications, smart devices, and medical equipment. Electromagnetic shielding has become an indispensable technology. Traditional electromagnetic shielding technology primarily relies on metal materials such as aluminum and copper, which typically absorb or reflect electromagnetic waves through their conductivity and magnetism. However, these traditional materials have several drawbacks, such as heavy weight, high thickness requirements, and difficulty in achieving precise control of specific frequencies. With the increasing demand for more efficient and precise electromagnetic control, metasurface technology has emerged.

[0003] Precise manipulation of on-chip electromagnetic radiation has always been a core technological challenge in the field of integrated photonics. Surface plasmons, localized electromagnetic eigenmodes generated by excitation at metal-dielectric interfaces, offer a revolutionary technological path to this goal, thanks to their diffraction-limited subwavelength localization and significantly enhanced local electric field. On-chip surface plasmons exhibit unprecedented potential, particularly in multidisciplinary applications such as subwavelength optical devices, super-resolution imaging systems, nanophotonic integrated circuits, and plasmonic nanolasers. However, the realization of these functions relies heavily on a versatile coupling / decoupling platform that efficiently connects free-space light with near-field surface wave modes. Traditional refractive optical elements, such as diffraction gratings, are widely used for the excitation and radiation control of surface waves, but their bulkiness and inherent mode conversion losses severely limit the device's integration density and performance ceiling.

[0004] As a kind of artificially designed two-dimensional planar optical device, metasurface has opened up a new paradigm for deep manipulation of light fields by virtue of the precise electromagnetic response control of artificial atoms at the subwavelength scale. Its typical applications include anomalous refraction and reflection at the subwavelength scale, structured light field generation, and holographic wavefront control. The core physical mechanism stems from the synergy between the local resonant response of the subwavelength unit structure and the phase gradient control. Based on the phase gradient compensation principle in the generalized Snell's law, metasurface provides a breakthrough path for efficient mode conversion between free-space light and surface waves. By introducing two-dimensional phase modulation technology, researchers have developed a metacoupler with predefined wavefront control capabilities, achieving key technological breakthroughs in multi-dimensional phase gradient design and near-field wavevector matching. This type of device has been widely used in cutting-edge directions such as efficient light field coupling and enhanced light-matter interaction in on-chip integrated photonic devices, and has laid a solid physical foundation for the development of new quantum optical integrated chips.

[0005] Faced with the urgent need for applications such as augmented reality and holographic displays, achieving efficient decoupling of surface waves into free-space light has become a key challenge in the field of nanophotonics. Traditional approaches rely on phase manipulation of metasurfaces to achieve unidirectional surface wave radiation or the generation of vortex light fields. While some progress has been made in certain areas, these approaches suffer from limited control freedom, a lack of research in the terahertz band, and modal crosstalk. Of particular concern is that existing research primarily focuses on controlling the surface wave's radiated wavefront through phase modulation, while lacking systematic control methods for other key characteristics such as amplitude and polarization.

[0006] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0007] The main purpose of the present invention is to provide a complex amplitude vector light field system based on a terahertz on-chip metasurface, aiming to solve the above-mentioned technical problems in the prior art.

[0008] To achieve the above objectives, the present invention provides a complex amplitude vector light field system based on a terahertz on-chip metasurface, the complex amplitude vector light field system based on a terahertz on-chip metasurface comprising:

[0009] a metasurface region and an intrinsic region stitched together in a transverse direction;

[0010] A plurality of compound super-structure periodic units arranged along the horizontal and vertical planes are provided in the metasurface region, each compound super-structure periodic unit includes a 2*2 arranged metasurface primitive cell, each metasurface primitive cell includes a metal microstructure layer, a first dielectric film layer, and a first metal thin layer arranged in sequence along the vertical direction, and the metal microstructure layers of the plurality of metasurface primitive cells are rotated and arranged according to the required phase distribution; the odd-numbered columns in the compound super-structure periodic unit radiate a left-handed circularly polarized complex amplitude light field, and the even-numbered columns radiate a right-handed circularly polarized complex amplitude light field, through the left-handed circular polarization and The interference of right-handed circular polarization in free space synthesizes a vector light field with a preset polarization state; the metal microstructure layer has a two-fold symmetric structure and includes an upper beam and a lower beam extending in the transverse direction and spaced apart in the longitudinal direction, and a longitudinal beam connecting the upper beam and the lower beam; the reflection polarization conversion rate of the metal microstructure layer is 0.05-0.15, wherein the metal microstructure layer of the metasurface unit cells in odd columns rotates at angles of θ1 and θ2, respectively, and the metal microstructure layer of the metasurface unit cells in even columns rotates at angles of θ3 and θ4, respectively;

[0011] An intrinsic primitive cell is located in the intrinsic region, and the intrinsic primitive cell includes a second dielectric thin film layer and a second metal thin layer arranged in sequence along the vertical direction;

[0012] The metasurface unit cell and the intrinsic unit cell have the same size and are both square; the surface wave propagates in the transverse direction and is incident from the intrinsic region to the metasurface region;

[0013] The calculation formulas for θ1, θ2, θ3, and θ4 are as follows:

[0014] ; (1)

[0015] ; (2)

[0016] in, 、 are the complex amplitude distributions of left-hand circular polarization and right-hand circular polarization at coordinates (x, y), respectively;

[0017] 、 are the amplitude distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y);

[0018] 、 are the phase distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y);

[0019] 、 are the phase delays of the surface waves, respectively, where ;in, ;

[0020] i is the imaginary unit;

[0021] k0 is the vacuum wave vector;

[0022] θ r is the emission direction of the radiation wave;

[0023] ξ is the phase gradient provided by the metasurface region;

[0024] e is a mathematical constant, the base of natural logarithms.

[0025] Preferably, in the complex amplitude vector light field system based on the terahertz chip metasurface, the length and width of the upper beam and the lower beam are the same, and both are arc-shaped structures. The radius of the outer circle of the arc-shaped structure is 35 μm, and the radius of the inner circle is 30 μm. The line width of the longitudinal beam, the upper beam, and the lower beam are all the same and are 5 μm. The angle of the vacant central structure is θ, and θ=145°.

[0026] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the first dielectric film layer is an isotropic uniform medium with a relative dielectric constant of 3.9, a relative magnetic permeability of 1, a relative electrical conductivity of 0, a thickness d of 55 μm, and a size of 80 μm.

[0027] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the first dielectric film layer and the second dielectric film layer are made of isotropic glass, and the first metal thin layer and the second metal thin layer are complete gold layers.

[0028] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the thickness of the first metal thin layer is 100 nm.

[0029] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the operating frequency of the surface wave is 0.3 to 0.5 THz.

[0030] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the operating frequency of the surface wave is 0.4 THz.

[0031] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the metasurface unit cell in the metasurface area has 80*80 units and a size of 6.4mm*6.4mm.

[0032] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the size of the metasurface area is N*N, where N is the number of metasurface cells, and N is 80.

[0033] Preferably, in the complex amplitude vector light field system based on the terahertz on-chip metasurface, the complex amplitudes of LCP and RCP on the holographic surface and the metasurface are designed respectively through a double-loop complex amplitude GS holographic algorithm, and the geometric rotation angles θ1, θ2, θ3 and θ4 required for each atom in the metasurface are obtained according to formulas (1) and (2), and a complex amplitude vector holographic light field is generated.

[0034] The present invention has at least the following beneficial effects:

[0035] The present invention provides a complex amplitude vector light field system based on a terahertz chip metasurface, which includes a metasurface area and an intrinsic area spliced ​​together in the horizontal direction, a plurality of complex metaperiodic units arranged along the horizontal and vertical planes, and an intrinsic primitive cell; a plurality of complex metaperiodic units arranged along the horizontal and vertical planes are provided in the metasurface area, each complex metaperiodic unit includes a 2*2 arranged metasurface primitive cell, each metasurface primitive cell includes a metal microstructure layer, a first dielectric film layer, and a first metal thin layer arranged in sequence along the vertical direction, and the metal microstructure layers of the plurality of metasurface primitive cells are rotated and arranged according to the required phase distribution; the odd-numbered columns in the complex metaperiodic unit radiate left-handed circularly polarized complex amplitude light fields, and the even-numbered columns radiate right-handed circularly polarized complex amplitude light fields, and a vector light field of a preset polarization state is synthesized through interference of left-handed circular polarization and right-handed circular polarization in free space; the metal microstructure layer is two The invention discloses a symmetrical structure comprising an upper beam and a lower beam extending in the transverse direction and spaced apart in the longitudinal direction, and a longitudinal beam connecting the upper beam and the lower beam, wherein the reflection polarization conversion rate of the metal microstructure layer is 0.05-0.15, wherein the rotation angles of the metal microstructure layer of the odd-numbered metasurface primitive cells are θ1 and θ2, respectively, and the rotation angles of the metal microstructure layer of the even-numbered metasurface primitive cells are θ3 and θ4, respectively; the intrinsic primitive cells are located in the intrinsic region, and the intrinsic primitive cells comprise a second dielectric film layer and a second metal thin layer arranged in sequence in the vertical direction; wherein the metasurface primitive cells and the intrinsic primitive cells have the same size and are both square; the surface wave propagates in the transverse direction from the intrinsic region to the metasurface region, so that the phase, amplitude and polarization state distribution of the surface wave in the process of radiation into free space can be precisely controlled by the geometric phase gradient distribution, breaking through the technical bottleneck of traditional diffraction optical elements in terms of mode crosstalk and energy efficiency.

[0036] Furthermore, compared to traditional near-field couplers, this system effectively addresses key issues such as multimode interference, energy loss, and poor process compatibility, offering broad application prospects in terahertz communications, integrated imaging, and quantum optics. Its planar architecture and high process compatibility provide an innovative technological path for the development of next-generation on-chip photonic integrated circuits.

[0037] Furthermore, the present invention realizes the efficient conversion of surface waves into arbitrary vector light fields in free space by constructing a complex sub-wavelength artificial atomic structure, overcoming the problems of multi-mode interference, low efficiency and limited control freedom of traditional couplers in far-field radiation control, and filling the technical gap in multi-dimensional control devices in the terahertz band.

[0038] Furthermore, by constructing a complex geometric phase metasurface, multi-parameter coordinated control of wavefront, amplitude and polarization state in the near-field-far-field radiation process is achieved. Based on the precise design of the phase distribution of the electromagnetic metasurface in the terahertz band, the system can theoretically realize the simultaneous control of arbitrarily complex wavefronts and arbitrary polarization states, thereby generating a spatial light field with specific vector characteristics. The present invention adopts the physical mechanism of phase gradient control of electromagnetic wave wavefronts, combined with the geometric design of a complex artificial metastructure unit, to construct a complex geometric phase metasurface that can simultaneously control phase, amplitude and polarization state. This metasurface is suitable for a variety of surface wave modes, including surface plasmons, artificial surface plasmons, and waveguide-type surface waves, and can achieve high-precision control of surface waves radiating in any direction and position in free space with arbitrary wavefront, amplitude and polarization distribution.

[0039] Furthermore, the present invention can achieve full electromagnetic parameter control of TM mode surface wave far-field radiation, and can realize the design of arbitrary radiation light field according to actual needs.

[0040] Furthermore, by designing independent amplitude and phase distributions for the complex structures on the metasurface, the present invention enables surface wave far-field radiation of complex wavefronts, such as holographic imaging. By adjusting the phase difference between the LCP and RCP light fields at different locations on the imaging surface, the distribution of polarization states within the far-field radiation region can be flexibly controlled, thereby achieving continuous complex amplitude vector holography. This method is also widely applicable to other types of vector holographic distributions, such as discretized vector holography and vector holography with axial rotation of the polarization state.

[0041] Furthermore, the design of the artificial meta-structure unit of the present invention is generalized, and the structure only needs to satisfy double rotational symmetry, which effectively reduces the difficulty of processing and preparing experimental samples.

[0042] Furthermore, the design proposed in the present invention is generalized, and the near-field surface wave far-field radiation space vector evolved beam coupler can be extended to other working frequency bands, such as the near-infrared band, the optical band, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic diagram of a duplex superstructure periodic unit provided by the present invention;

[0044] Figure 2 for Figure 1 Schematic diagram of the super-surface unit cell;

[0045] Figure 3 A schematic diagram of multiple metasurface primitive cells provided by the present invention;

[0046] Figure 4 A schematic diagram of the intrinsic primitive cell provided by the present invention;

[0047] Figure 5Schematic diagram of the complex amplitude vector light field system based on the terahertz on-chip metasurface provided by the present invention;

[0048] Figure 6 The reflection phase curve of the metasurface unit cell provided by the present invention;

[0049] Figure 7 The metasurface atomic reflection amplitude curve provided by the present invention;

[0050] Figure 8 This is the polarization conversion rate curve of the metasurface atoms provided by the present invention;

[0051] Figure 9 A surface wave dispersion relation curve of the intrinsic region structure provided by the present invention;

[0052] Figure 10 Schematic diagram of multi-beam emission of near-field surface wave far-field radiation;

[0053] Figure 11 Schematic diagram of the multi-beam emission structure and amplitude and phase distribution of near-field surface wave far-field radiation, including (a) a partial photo of the dual-beam emission sample, (b) the corresponding amplitude distribution, and (c) the corresponding phase distribution;

[0054] Figure 12 The simulation and experimental results of multi-beam emission of near-field surface wave far-field radiation, including X-polarization, LCP and RCP effects, (a) simulation results and (b) experimental results;

[0055] Figure 13 Amplitude and phase distribution of the complex amplitude vector light field metasurface under dual channels, where (a) and (b) are the amplitude and phase distribution of the LCP complex amplitude light field, respectively; (c) and (d) are the amplitude and phase distribution of the RCP complex amplitude light field, respectively;

[0056] Figure 14 Metasurface phase distribution for generating vector light field;

[0057] Figure 15 A photo of a partial sample of the metasurface used to generate a vector light field;

[0058] Figure 16 The simulation results and experimental results of the Xoy surface field distribution of the complex amplitude vector holographic light field under different polarizers are shown, where (a) is the simulation result and (b) is the experimental result.

[0059] 1-metasurface region, 2-intrinsic region, 3-metasurface unit cell, 31-metal microstructure layer, 311-upper beam, 312-lower beam, 313-longitudinal beam, 32-first dielectric film layer, 33-first metal thin layer, 4-intrinsic unit cell, 41-second dielectric film layer, 42-second metal thin layer.

[0060] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0061] The technical solutions of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments of the present invention and the features therein may be combined with each other unless there is a conflict.

[0062] In embodiments of the present invention, the term "and / or" describes the association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0063] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0064] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0065] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity direction; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above directional words are not used to limit the present invention.

[0066] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in the embodiments of the present invention, many technical details are provided to enable the reader to better understand the present invention. However, even without these technical details and the various changes and modifications based on the following embodiments, the technical solutions claimed in the present invention can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction.

[0067] Vector light field control, as the development direction of the next generation of integrated photonic technology, breaks through the limitations of traditional scalar light fields in the dimension of light intensity distribution. Its core value lies in achieving multi-dimensional coordinated control of light field amplitude, phase, and polarization state. In on-chip optical systems, efficient generation of vector light fields and precise control of their various parameters are of great significance for promoting the functional integration and performance improvement of integrated photonic devices. Compared with traditional scalar light fields that only focus on light intensity distribution, vector light fields, with the expansion of degrees of freedom brought about by their non-uniform polarization distribution, have shown significant application potential in cutting-edge technology fields such as super-resolution imaging, optical micromanipulation, and high-sensitivity sensing, providing an innovative solution path for light field control technology.

[0068] The present invention provides a complex amplitude vector light field system based on a terahertz on-chip metasurface. Figures 1 to 5 The complex amplitude vector light field system based on the terahertz on-chip metasurface includes a metasurface region and an intrinsic region spliced ​​together in the horizontal direction, a plurality of compound metaperiodic units arranged along the horizontal and vertical planes, and an intrinsic primitive cell; a plurality of compound metaperiodic units arranged along the horizontal and vertical planes are provided in the metasurface region, each compound metaperiodic unit includes a 2*2 arranged metasurface primitive cell, each metasurface primitive cell includes a metal microstructure layer, a first dielectric film layer, and a first metal thin layer arranged in sequence along the vertical direction, and the metal microstructure layers of the plurality of metasurface primitive cells are rotated and arranged according to the required phase distribution; the odd-numbered columns in the compound metaperiodic unit radiate left-handed circularly polarized complex amplitude light fields, and the even-numbered columns radiate right-handed circularly polarized complex amplitude light fields, and through the interference of left-handed circular polarization and right-handed circular polarization in free space, the complex amplitude light field is combined. The invention discloses a vector light field with a preset polarization state; the metal microstructure layer is a doubly symmetrical structure and includes an upper beam and a lower beam extending in the transverse direction and arranged at intervals in the longitudinal direction, and a longitudinal beam connecting the upper beam and the lower beam. The reflection polarization conversion rate of the metal microstructure layer is 0.05-0.15, wherein the rotation angles of the metal microstructure layer of the metasurface primitive cells in odd columns are θ1 and θ2 respectively, and the rotation angles of the metal microstructure layer of the metasurface primitive cells in even columns are θ3 and θ4 respectively; the intrinsic primitive cell is located in the intrinsic region, and the intrinsic primitive cell includes a second dielectric thin film layer and a second metal thin layer arranged in sequence in the vertical direction; wherein the metasurface primitive cell and the intrinsic primitive cell have the same size and are both square; the surface wave propagates in the transverse direction and is incident from the intrinsic region to the metasurface region.

[0069] The calculation formulas for θ1, θ2, θ3, and θ4 are as follows:

[0070] ; (1)

[0071] ; (2)

[0072] in, 、 are the complex amplitude distributions of left-hand circular polarization and right-hand circular polarization at coordinates (x, y), respectively;

[0073] 、 are the amplitude distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y);

[0074] 、 are the phase distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y);

[0075] 、 are the phase delays of the surface waves, respectively, where ;in, ;

[0076] i is the imaginary unit;

[0077] k0 is the vacuum wave vector;

[0078] θ r is the emission direction of the radiation wave;

[0079] ξ is the phase gradient provided by the metasurface region.

[0080] The complex amplitude vector light field system is composed of a metasurface region and an intrinsic region spliced ​​together. The intrinsic region is used to support surface wave transmission. The metasurface region is provided with a plurality of compound hyperstructure periodic units arranged along the horizontal and vertical planes, and the metasurface primitive cells of each compound hyperstructure periodic unit are rotated and arranged according to the phase distribution required for calculation. Compared with the metasurface primitive cells, the intrinsic primitive cells have removed the top metal microstructure layer. The intrinsic primitive cells and the metasurface primitive cells have the same size and are both square. In some embodiments, the metal microstructure layer is gold (Au), the first dielectric film layer and the second dielectric film layer are isotropic glass materials, and the first metal thin layer and the second metal thin layer are complete gold layers (Au).

[0081] It should be noted that the doubly symmetric structure mentioned in the present invention is the same as the original shape after being rotated 180 degrees. The metasurface unit cell is also a doubly symmetric structure. The phase distribution of the metasurface unit cell is rotated, and its rotation angle refers to the angle between the left and right symmetry axes of the metal microstructure with a doubly rotationally symmetric geometric shape and the Y direction. The surface wave propagates along the x-axis and is incident on the metasurface area from the intrinsic area. In some embodiments, the size of the metasurface area is N*N, where N is the number of metasurface units. In this embodiment, N is 80.

[0082] Surface waves may include, but are not limited to, surface plasmons, artificial surface plasmons, and waveguide surface waves.

[0083] In some embodiments, the metal microstructure layer is a curved, arc-shaped "I" structure. The length of the upper beam is the same as the length of the lower beam, the width of the upper beam is the same as the width of the lower beam, the line width of the upper beam, the lower beam, and the longitudinal beam are the same, and the longitudinal beam serves as the axis of symmetry. In some embodiments, the metal microstructure is Au with a thickness of 100 nm. The upper and lower beams are both arc-shaped structures, the outer radius r1 of the arc structure is 35 μm, and the inner radius r2 is 30 μm. The line width w of the longitudinal beam, the upper beam, and the lower beam is the same and is 5 μm. The angle of the central structure vacancy is θ, θ = 145°. The first dielectric thin film layer is an isotropic, uniform medium with a relative dielectric constant of 3.9, a relative magnetic permeability of 1, a relative electrical conductivity of 0, a thickness d of 55 μm, and a size of 80 μm. The first metal thin layer is Au with a thickness of 100 nm.

[0084] The upper layer of the intrinsic unit cell has no metal structure and is composed only of a second dielectric thin film layer and a second metal thin layer. The dispersion curve of the surface wave is obtained through finite time-domain difference (FDTD) simulation. According to electromagnetic wave theory, the dispersion relationship of the surface wave is only related to the dielectric constant and dielectric thickness of the intrinsic unit cell, and is independent of the period of the intrinsic unit cell.

[0085] Among them, the operating frequency of the surface wave is 0.3~0.5THz, and the metasurface unit cell in the metasurface area has 80*80 units and a size of 6.4mm*6.4mm.

[0086] To achieve multidimensional light field manipulation with arbitrary wavefront, amplitude, and polarization states, this paper employs a dual-channel light field decomposition strategy. This decomposes the target vector light field into two orthogonal polarization components: left-hand circular polarization (LCP) and right-hand circular polarization (RCP). The desired complex amplitude distribution is then inverted for each component. Based on the principle of geometric phase manipulation, the rotation angle distribution of each structural unit within the complex hyperstructure periodic unit is further derived, enabling precise control of the radiated light field.

[0087] Among them, in the complex unit array formed by the 2*2 arranged metasurface cells, the odd-numbered columns radiate the complex amplitude light field of left-handed circular polarization through geometric phase design, and the even-numbered columns radiate the complex amplitude light field of right-handed circular polarization through control. The coherent superposition of these two orthogonal circular polarization states can synthesize a light field with arbitrary polarization distribution, and then the amplitude and phase distribution under the target polarization state are calculated through the algorithm.

[0088] Surface wave far-field radiation is essentially the reverse process of space wave excitation of surface waves. Based on Fermat's principle, the conditions for surface wave far-field radiation can be derived: the surface wave propagates along the x-axis, incident from the intrinsic region to the metasurface region. Geometric phase metasurfaces can provide a certain phase gradient ξ to the surface wave according to a certain rotational order. Based on the reverse process of surface wave excitation, the reverse process defined by generalized Snell is obtained:

[0089] .

[0090] According to the above equations, the phase gradient of the geometric phase metasurface can be manipulated to allow surface wave far-field radiation to reach any location in free space. The polarization state of an electromagnetic wave describes the direction of vibration of the electric field component of a spatial electromagnetic wave and is the most obvious characteristic distinguishing transverse and longitudinal waves. It is worth noting that the polarization state of surface wave far-field radiation is determined by the rotation order of the geometric phase metasurface atoms. Clockwise or counterclockwise rotations yield polarization states of left-handed circular polarization (LCP) and right-handed circular polarization (RCP). Therefore, taking a 2x2 compound structure as a period, the odd-numbered rows of artificial atoms within this compound period generate LCP complex amplitude fields, while the even-numbered rows of artificial atoms within this compound period generate RCP complex amplitude fields. By ensuring the consistency of the phase gradients ξ provided by the two and adjusting the phase difference between them, the LCP and RCP can interfere in space to synthesize a far-field radiation field with arbitrary vector polarization state distribution on the same wavefront. This means that the polarization state distribution exists at any point on the Poincare sphere within the same wavefront. The specific expressions of the complex amplitude light field corresponding to the 2*2 composite artificial atom are shown in Formula (1) and Formula (2). In this way, θ1, θ2, θ3, and θ4, that is, the four different artificial atom rotation angles within the compound superstructure periodic unit, can be calculated. By controlling the four rotation angles, the complex amplitude distribution corresponding to the LCP and RCP light fields can be controlled, realizing the emission of two plane waves with cross-polarization states and different intensities and exit angles.

[0091] In some embodiments, a double-loop complex amplitude GS holographic algorithm can be used to design the complex amplitudes of LCP and RCP on the holographic surface and the metasurface, respectively, and the geometric rotation angles θ1, θ2, θ3, and θ4 required for each atom in the metasurface can be obtained according to formulas (1) and (2), thereby generating a complex amplitude vector holographic light field.

[0092] By controlling the amplitude and phase distribution of the LCP and RCP components respectively on the holographic imaging plane, the polarization state of the synthetic light field can be gradually changed in a specified direction, thereby constructing a spatial light field distribution with vector characteristics.

[0093] The complex amplitude vector light field system based on a terahertz on-chip metasurface, proposed in this paper, achieves multi-parameter coordinated control of wavefront, amplitude, and polarization state during near-field-to-far-field radiation by constructing a complex geometric phase metasurface. Based on the precise design of the phase distribution of the electromagnetic metasurface in the terahertz band, the system can theoretically achieve simultaneous control of arbitrarily complex wavefronts and arbitrary polarization states, thereby generating a spatial light field with specific vector characteristics.

[0094] Furthermore, the present invention utilizes the physical mechanism of phase gradient control of electromagnetic wavefronts, combined with the geometric design of a complex artificial metastructure unit, to construct a complex geometric phase metasurface that can simultaneously control phase, amplitude, and polarization state. This metasurface is applicable to a variety of surface wave modes, including surface plasmons, artificial surface plasmons, and waveguide-type surface waves. It can achieve high-precision control of surface wave radiation in any direction and position in free space with arbitrary wavefront, amplitude, and polarization distribution.

[0095] In order to further verify the effect of the present invention, Figure 3 By conducting experimental tests on multiple metasurface primitive cells (real structures of artificial units on metasurfaces), we can obtain the reflection phase, amplitude, and polarization conversion efficiency (PCR) of artificial atoms, such as Figures 6 to 8 shown. Figure 4 The schematic diagram of the intrinsic primitive cell provided by the present invention is shown, and the dispersion curve of the surface wave is obtained by finite time-domain difference method (FDTD) simulation, as shown in FIG. Figure 8 According to electromagnetic wave theory, the dispersion relation of surface waves is only related to the dielectric constant and dielectric thickness of the intrinsic unit cell, and has nothing to do with the period of the intrinsic unit cell.

[0096] Based on two rows of artificial atoms with periodic boundary conditions, a near-field surface wave far-field radiation model with dual beam emission under cross-polarization state is realized. By controlling the odd number of rows in the two rows of structures, the complex amplitude plane wave emission of LCP is realized, and by controlling the even number of rows, the complex amplitude plane wave emission of RCP is realized, as shown in Figure 2. Figure 10 The corresponding amplitude and phase as well as the processed sample structure are shown in Figure 11 As shown. We used simulation and near-field testing to confirm the mechanism of near-field surface wave far-field complex amplitude light field radiation control. Then, according to the optimized double-cycle GS complex amplitude holographic algorithm, we constructed a metasurface that generates vector holographic light field based on artificial metaunits and intrinsic cells. The metasurface has 80*80 units with a size of 6.4mm*6.4mm. The operating frequency is 0.4THz. According to this algorithm, the complex amplitude light field distribution on the imaging plane under two cross-polarization states can be effectively controlled, and the amplitude and phase distribution on the metasurface can be obtained by Fresnel reverse diffraction, as shown Figure 13Finally, according to the phase design derivation, we calculated the phase distribution of the metasurface, and the results are shown as follows: Figure 14 As shown. FDTD was used to simulate the electromagnetic field radiation behavior at f=0.4THz. The experimental sample metasurface was manufactured by photolithography technology, as shown Figure 15 As shown; the experimental results are compared with the simulation results. Figure 16 shown.

[0097] 1. Artificial superstructure unit reflection coefficient measurement

[0098] Artificial superstructure unit design Figure 2 As shown, the experimental samples are Figure 3 When measuring the reflection coefficient of the artificial metastructure unit, a linearly polarized antenna is used to transmit the signal and a linearly polarized antenna is used to receive the signal, and the two antennas maintain the same polarization state. The experimental results of the unit reflection phase, amplitude and polarization conversion efficiency are shown in Figures 6 to 8 As shown, it is consistent with the corresponding simulation results.

[0099] 2. Radiation field near field test

[0100] The near-field test framework of the terahertz time-domain detection system is as follows: Figure 9 As shown. When the surface wave is incident on the metasurface area, it generates radiation. The corresponding field information can be obtained by scanning the radiation area with a probe. To measure the electric field with different polarizations, it is necessary to change the direction of the probe so that the probe and the electric field polarization remain parallel. The radiated electric field E of the dual beam output x , and the comparison of simulation and experimental results of LCP and RCP light fields. Figure 12 shown.

[0101] To obtain the electric field distribution of the circular polarization state, it is necessary to measure E x and E y The electric field distribution is finally The comparison between the experimental results and simulation results of the electric field distribution of the vector holographic light field is shown in Figure 2. Figure 16 As shown, it confirms the vector holographic light field effect it produces.

[0102] Obviously, the embodiments described above are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, those skilled in the art may make other different forms of changes or modifications without making any creative work, and all of these should fall within the scope of protection of the present invention.

Claims

1. A complex amplitude vector light field system based on a terahertz on-chip metasurface, characterized in that: include: a metasurface region and an intrinsic region stitched together in a transverse direction; A plurality of compound super-structure periodic units arranged along the horizontal and vertical planes are provided in the metasurface region, each compound super-structure periodic unit includes a 2*2 arranged metasurface primitive cell, each metasurface primitive cell includes a metal microstructure layer, a first dielectric film layer, and a first metal thin layer arranged in sequence along the vertical direction, and the metal microstructure layers of the plurality of metasurface primitive cells are rotated and arranged according to the required phase distribution; the odd-numbered columns in the compound super-structure periodic unit radiate a left-handed circularly polarized complex amplitude light field, and the even-numbered columns radiate a right-handed circularly polarized complex amplitude light field, through the left-handed circular polarization and The interference of right-handed circular polarization in free space synthesizes a vector light field with a preset polarization state; the metal microstructure layer has a two-fold symmetric structure and includes an upper beam and a lower beam extending in the transverse direction and spaced apart in the longitudinal direction, and a longitudinal beam connecting the upper beam and the lower beam; the reflection polarization conversion rate of the metal microstructure layer is 0.05-0.15, wherein the metal microstructure layer of the metasurface unit cells in odd columns rotates at angles of θ1 and θ2, respectively, and the metal microstructure layer of the metasurface unit cells in even columns rotates at angles of θ3 and θ4, respectively; An intrinsic primitive cell is located in the intrinsic region, and the intrinsic primitive cell includes a second dielectric thin film layer and a second metal thin layer arranged in sequence along the vertical direction; The metasurface unit cell and the intrinsic unit cell have the same size and are both square; the surface wave propagates in the transverse direction and is incident from the intrinsic region to the metasurface region; The calculation formulas for θ1, θ2, θ3, and θ4 are as follows: ；（1） ；（2） in, 、 are the complex amplitude distributions of left-hand circular polarization and right-hand circular polarization at coordinates (x, y), respectively; 、 are the amplitude distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y); 、 are the phase distributions of the left-handed circularly polarized light field and the right-handed circularly polarized light field at coordinates (x, y); 、 are the phase delays of the surface waves, respectively, where ;in, ; i is the imaginary unit; k0 is the vacuum wave vector; θ r is the emission direction of the radiation wave; ξ is the phase gradient provided by the metasurface region; e is a mathematical constant, the base of natural logarithms.

2. The complex amplitude vector light field system based on the terahertz on-chip metasurface according to claim 1, characterized in that: The length and width of the upper crossbeam and the lower crossbeam are the same, and both are arc-shaped structures. The radius of the outer circle of the arc-shaped structure is 35 μm, and the radius of the inner circle is 30 μm. The line width of the longitudinal beam, the upper crossbeam, and the lower crossbeam are all the same and are 5 μm. The angle of the vacant center structure is θ, and θ=145°.

3. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1 or 2, characterized in that: The first dielectric film layer is an isotropic uniform medium with a relative dielectric constant of 3.9, a relative magnetic permeability of 1, a relative electrical conductivity of 0, a thickness d of 55 μm, and a size of 80 μm.

4. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1, wherein: The first dielectric film layer and the second dielectric film layer are made of isotropic glass, and the first metal thin layer and the second metal thin layer are complete gold layers.

5. The complex amplitude vector light field system based on the terahertz on-chip metasurface according to claim 4, characterized in that: The thickness of the first metal thin layer is 100 nm.

6. The complex amplitude vector light field system based on the terahertz on-chip metasurface according to claim 1, characterized in that: The operating frequency of the surface wave is 0.3-0.5 THz.

7. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1, characterized in that: The operating frequency of the surface wave is 0.4THz.

8. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1, wherein: The metasurface unit cell in the metasurface area has 80*80 units and a size of 6.4mm*6.4mm.

9. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1, characterized in that: The size of the metasurface area is N*N, where N is the number of metasurface cells and N is 80.

10. The complex amplitude vector light field system based on a terahertz on-chip metasurface according to claim 1, characterized in that: Through the double-loop complex amplitude GS holographic algorithm, the complex amplitudes of LCP and RCP on the holographic surface and the metasurface are designed respectively, and the geometric rotation angles θ1, θ2, θ3 and θ4 required for each atom in the metasurface are obtained according to formulas (1) and (2), and a complex amplitude vector holographic light field is generated.

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