Transmission-type broadband vortex light excitation device with circular polarization preservation

Abstract

The present invention discloses a transmission-type broadband vortex light excitation device preserving circular polarization, comprising an incident module, an excitation module and a receiving module. The incident module uses a loudspeaker to excite circularly polarized polarized plane light to be vertically incident on the excitation module. The receiving module is used to receive vortex light. The excitation module adopts a Huygens metasurface, which comprises a first conductive metal layer, a second conductive metal layer and a third conductive metal layer arranged overlappingly from top to bottom. The thickness of each conductive metal layer is greater than the skin depth. Two adjacent conductive metal layers are connected by a dielectric layer. Each conductive metal layer is provided with a hollow pattern. Phase coverage is achieved by regulating the torsion angle of the hollow pattern on the first conductive metal layer, so that the three-layer hollow pattern can achieve phase regulation of the same polarization transmission component, thereby generating vortex light. The present invention realizes the generation of vortex light of the same polarization transmission, and realizes phase coverage by regulating the torsion angle, without the need to design a large number of complex structures.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic control technology, and in particular to a transmission-type broadband vortex light excitation device preserving circular polarization. Background Art

[0002] The concept of electromagnetic metamaterials proposes a new approach to expand the ability to control electromagnetic waves. By designing artificial atoms with structural resonances and arranging them into two-dimensional or three-dimensional arrays, metamaterials and metasurfaces that extend the functions of natural materials can be realized. Electromagnetic metamaterials significantly expand the degrees of freedom for controlling electromagnetic waves and have broad application prospects. Among them, the manipulation of orbital angular momentum (OAM) is a research topic of great significance in the control of electromagnetic waves. At present, OAM manipulation based on metasurfaces has made significant progress, but it still faces some challenges, such as the complexity of resonant phase design, severe bandwidth limitation, and polarization conversion problems related to geometric phase. To address these challenges, this study aims to develop and verify metasurfaces with circular polarization, especially in generating and controlling orbital angular momentum light fields with high transmittance. Orbital angular momentum is a special degree of freedom of light fields. Since there is a quantum number l in its characteristics that can be any integer, different orthogonal modes can be achieved by adjusting l. Orbital angular momentum is widely considered to be the key to ultra-high capacity and speed of future information processing (including transmission, computing, storage, etc.).

[0003] The existing technical solutions and their limitations mainly include: 1. Geometric phase method: Traditionally, it relies on spin-orbit coupling to generate vortex light, which will result in the generation of vortex light of different polarizations. For applications that need to maintain polarization, additional polarization conversion devices are often required, which will not only reduce efficiency, but also hinder further integration of the system and limit the flexibility of application. 2. Complex structure design: Existing broadband vortex light generation devices usually require the design of complex structures, which increases the difficulty of processing and the complexity of the experiment, and is not conducive to simplifying the experimental process. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention aims to provide a transmission-type broadband vortex light excitation device with circular polarization preservation, which can realize the generation of vortex light with co-polarization transmission without the need to design a large number of complex structures.

[0005] In order to achieve the above-mentioned purpose, the present invention proposes a circularly polarized transmission-type broadband vortex light excitation device, comprising an incident module, an excitation module and a receiving module. The incident module uses a horn to excite circularly polarized polarized plane light to be vertically incident on the excitation module. The receiving module is used to receive vortex light. The excitation module adopts a Huygens metasurface, which comprises a first conductive metal layer, a second conductive metal layer and a third conductive metal layer which are overlapped and arranged from top to bottom. The thickness of each conductive metal layer is greater than the skin depth. Two adjacent conductive metal layers are connected by a dielectric layer. Each conductive metal layer is provided with a hollow pattern. Phase coverage is achieved by regulating the torsion angle θ of the hollow pattern on the first conductive metal layer, so that the three-layer hollow pattern can achieve phase regulation of the same polarization transmission component, thereby generating vortex light.

[0006] The hollow patterns of the first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all composed of a number of regular hexagonal hollow units, starting from the regular hexagonal hollow unit at the center of the metasurface, and the regular hexagonal hollow units are distributed in circles from the inside to the outside according to a regular hexagonal array; and the regular hexagonal hollow units of the three conductive metal layers are equal in size and corresponding in position;

[0007] The regular hexagonal hollow unit on the first conductive metal layer is composed of a circular groove and six fan-shaped grooves, the circular groove is located at the center of the regular hexagonal unit, the six fan-shaped grooves are arranged alternately, one long and one short, and the six fan-shaped grooves are evenly distributed outside the circular groove and connected to the circular groove; the regular hexagonal hollow unit on the second conductive metal layer is composed of six fan-shaped holes evenly distributed on the edge of the regular hexagonal unit, and each fan-shaped hole takes the hexagon of the regular hexagonal unit as the center of the circle; the third conductive metal layer is the same as the regular hexagonal hollow unit on the first conductive metal layer. The hollow pattern on the second conductive metal layer can be used to couple the structural electromagnetic response of the other two layers. The three-layer hollow pattern can achieve phase control of the co-polarized transmission component, which can be used to generate vortex light.

[0008] In the above scheme: On each circle of the first conductive metal layer, a single regular hexagonal hollow unit rotates around itself to generate a torsion angle θ, the rightmost regular hexagonal hollow unit has the same torsion angle θ as the regular hexagonal hollow unit in the center, both of which are 0, and the torsion angle θ of each regular hexagonal hollow unit on the same circle is uniformly increased in a counterclockwise order, as the torsion angle θ of the hollow pattern on the first conductive metal layer to achieve phase coverage. That is, the parameter θ can be changed, which is the torsion angle of each regular hexagonal hollow unit on the first conductive metal layer rotating around its own center. Since the structure has three-dimensional rotational symmetry, when the torsion angle θ rotates from 0° to 120°, the structure returns to the initial state, and in this process, the phase modulation of the same circular polarization transmission can cover 2π. In the setting of generating vortex light, the torsion angle parameter of the specific structure is associated with the azimuth angle α (with the center as the origin), where the torsion angle θ of each unit is l*α / 3.

[0009] In the above scheme: the hexagonal lattice constant of each regular hexagonal hollow unit is a, the radius of the circular groove is R0, the radius of the long fan-shaped groove is R1, the radius of the short fan-shaped groove is R2, and the radius of the fan-shaped hole is R c , where a=6.0mm; R0=0.5±0.1mm; R c =1.5±0.1mm; R1-R2≥0.15mm; the thickness of the single dielectric layer is 0.1mm~6mm.

[0010] In the above solution: R1 = 2.9 mm; R2 = 2.5 mm.

[0011] In the above scheme: the dielectric layer is a F4BTMS300 board with a thickness of 1mm and a dielectric constant of 3, and the first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all copper plates with a thickness of 18um. Conventional purchased parts usually have a structure of two conductive metal layers, with a dielectric layer sandwiched between the two conductive metal layers, while this design has a three-layer conductive metal layer structure. Therefore, after the purchased parts are purchased, a conductive metal layer needs to be added to the purchased parts, and a dielectric layer also needs to be set between the newly added conductive metal layer and the purchased parts for connection, and the dielectric layer needs to be connected to the purchased parts with the help of a 0.2mm 4450pp board with a dielectric constant of 3.52.

[0012] The beneficial effects of the present invention are:

[0013] 1. The broadband co-polarized transmission vortex light generation is realized. Before this, the broadband vortex light mainly uses geometric phase, and the geometric phase mainly relies on spin-orbit coupling to generate vortex light of different polarization states. The transmission-type broadband vortex light excitation device of the present invention can simplify the experimental process of vortex light generation. 2. The structure is relatively simple, easy to make, convenient to adjust, and smaller in volume than traditional materials. Phase coverage can be achieved by adjusting the torsion angle θ, and there is no need to design a large number of complex structures. 3. Compared with traditional vortex light generation devices, it has the characteristics of polarization preservation and high transmission efficiency, meets the standard of four-port system transmission greater than 25% under normal circumstances, and the average transmission meets the requirement of greater than 60%. At the same time, it has the advantage of thin thickness and easy integration. 4. A new metasurface design method is proposed, and functional devices of other bands can be designed based on this theory. 5. The generation of vortex light of various orders can be realized within the working frequency range. By optimizing structural parameters and selecting low-loss media, higher-order vortex light generation effects can be efficiently achieved.

[0014] In summary, the present invention breaks through the locking relationship between spin angular momentum and orbital angular momentum in the traditional geometric phase, designs a new phase control principle, realizes phase control of the transmitted co-polarization while keeping the incident spin polarization unchanged, and adjusts the microelement distribution according to the phase of the required output light, thereby generating vortex light with a l-order spiral phase structure; the operating frequency of the present invention is 16GHz to 18GHz, not limited to the microwave range; if vortex light of other frequencies is needed, it can be proportionally scaled or the geometric parameters of the unit structure can be redesigned according to the electromagnetic wave scaling law, and extended to any frequency range; it can be used for vortex light excitation devices in the fields of microwave, terahertz and light waves, and provides a solution for experimental workers to efficiently generate multi-order vortex light without changing the polarization chirality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the present invention.

[0016] Figure 2 It is a plan schematic diagram of the regular hexagonal hollow units on each conductive metal layer.

[0017] Figure 3 It is a three-dimensional schematic diagram of regular hexagonal hollow units on each conductive metal layer.

[0018] Figure 4 Schematic diagram of the central part of the hollow pattern on the first conductive metal layer (when l=3).

[0019] Figure 5 It is a schematic diagram of the structure of each layer of the present invention.

[0020] Figure 6 This is a schematic diagram of vortex light generation.

[0021] Figure 7 It is the frequency domain transmission amplitude spectrum line and the corresponding complex frequency domain transmission phase of the present invention.

[0022] Figure 8 It is the parameter space transmission spectrum of the present invention.

[0023] Fig. 9 is a plan view schematically showing the first conductive metal layer.

[0024] Fig.10 4 is a schematic plan view of the second conductive metal layer.

[0025] Fig.11 4 is a plan view of the third conductive metal layer. DETAILED DESCRIPTION

[0026] like Figure 1 As shown in FIG. 11 , a circularly polarized transmission-type broadband vortex light excitation device is mainly composed of an incident module, an excitation module and a receiving module. The incident module uses a horn to excite circularly polarized plane light vertically incident on the excitation module, and the receiving module is used to receive the vortex light.

[0027] The excitation module adopts a Huygens metasurface, which includes a first conductive metal layer, a second conductive metal layer and a third conductive metal layer arranged in an overlapping manner from top to bottom, the thickness of each conductive metal layer is greater than the skin depth, and two adjacent conductive metal layers are connected by a dielectric layer. A hollow pattern is provided on each conductive metal layer, and phase coverage is achieved by adjusting the torsion angle θ of the hollow pattern on the first conductive metal layer, so that the three-layer hollow pattern can achieve phase control of the same polarization transmission component, thereby generating vortex light.

[0028] The hollow patterns of the first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all composed of a number of regular hexagonal hollow units. The regular hexagonal hollow units at the center of the metasurface are used as the starting point, and the regular hexagonal hollow units are distributed in circles from the inside to the outside according to a regular hexagonal array; and the regular hexagonal hollow units of the three conductive metal layers are equal in size and corresponding in position.

[0029] The regular hexagonal hollow unit on the first conductive metal layer is composed of a circular groove and six fan-shaped grooves, the circular groove is located at the center of the regular hexagonal unit, the six fan-shaped grooves are arranged alternately, one long and one short, and the six fan-shaped grooves are evenly distributed outside the circular groove and connected to the circular groove. The regular hexagonal hollow unit on the second conductive metal layer is composed of six fan-shaped holes evenly distributed on the edge of the regular hexagonal unit, and each fan-shaped hole takes the hexagon of the regular hexagonal unit as the center. The third conductive metal layer is the same as the regular hexagonal hollow unit on the first conductive metal layer.

[0030] The hollow pattern on the second conductive metal layer can be used to couple the structural electromagnetic responses of the other two layers. The three-layer hollow pattern can achieve phase control of the co-polarized transmission component and can be used to generate vortex light.

[0031] On each circle of the first conductive metal layer, a single regular hexagonal hollow unit rotates around itself to produce a torsion angle θ, the rightmost regular hexagonal hollow unit has the same torsion angle θ as the regular hexagonal hollow unit in the center, both of which are 0, and the torsion angle θ of each regular hexagonal hollow unit on the same circle is uniformly increased in a counterclockwise order, as the torsion angle θ of the hollow pattern on the first conductive metal layer to achieve phase coverage. That is, the parameter θ can be changed, which is the torsion angle of each regular hexagonal hollow unit on the first conductive metal layer rotating around its own center. Since the structure has three-dimensional rotational symmetry, when the torsion angle θ rotates from 0° to 120°, the structure returns to the initial state, and in this process, the phase modulation of the same circular polarization transmission can cover 2π. In the setting of generating vortex light, the torsion angle parameter of the specific structure is associated with the azimuth angle α (with the center as the origin), where the torsion angle θ of each unit is l*α / 3.

[0032] The hexagonal lattice constant of each regular hexagonal hollow unit is a, the radius of the circular groove is R0, the radius of the long fan-shaped groove is R1, the radius of the short fan-shaped groove is R2, and the radius of the fan-shaped hole is R c , where a=6.0mm; R0=0.5±0.1mm; R c =1.5±0.1mm; R1-R2≥0.15mm; the thickness of a single dielectric layer is 0.1mm-6mm. Specifically: R1=2.9mm; R2=2.5mm.

[0033] The dielectric layer is a F4BTMS300 board with a thickness of 1mm and a dielectric constant of 3, and the first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all copper plates with a thickness of 18um. Conventional purchased parts usually have a structure of two conductive metal layers, with a dielectric layer sandwiched between the two conductive metal layers, while this design has a three-layer conductive metal layer structure. Therefore, after the purchased parts are purchased, a conductive metal layer needs to be added to the purchased parts, and a dielectric layer also needs to be set between the newly added conductive metal layer and the purchased parts for connection, and the dielectric layer needs to be connected to the purchased parts with the help of a 0.2mm 4450pp board with a dielectric constant of 3.52.

[0034] The present invention overcomes these limitations by designing a simplified polarization-preserving transmission-type broadband vortex light device, realizes the generation of vortex light with co-polarization transmission, and achieves phase coverage by adjusting the torsion angle θ, without the need to design a large number of complex structures. Figure 6As shown in the figure, the vortex light generation with orbital angular momentum l of 1 and 3 is successfully achieved within the designed working frequency (the verification of orbital angular momentum l of 1 and 3 is completed), in which the special phase pattern and the different singular points corresponding to the two different orbital angular momentum can be seen in both the real part and the phase diagram. The present invention mainly realizes broadband co-polarization transmission phase modulation based on the zero point position of the matching structure, and vortex light can be obtained through phase modulation. Figure 7 As shown in the transmission spectrum, when the torsion angle θ of the structure is 60°, there are two zero points in the co-polarization transmission spectrum of the structure. When we shift the parameter by 60°, that is, when the torsion angle is set to 50° and 70°, we can see the reverse movement of the zero points in the transmission phase spectrum in the complex frequency domain. By summarizing different torsion angle parameters, we can further obtain the transmission spectrum in the parameter space, such as Figure 8 As shown. In the transmission spectrum of the parameter space, we can see that there is a curve connecting the two zero points of 60° (180°). This curve connecting two different zero points is called a dividing line. When our frequency is in the middle of the range of the two zero points, we can get the effect that the transmission phase satisfies the coverage of 2π. That is, by adjusting the geometric parameters, it will eventually affect the zero point position of the transmission spectrum in the frequency domain, and then affect the longitudinal frequency range of the dividing line of the parameter space, so that the operating frequency can be widely adjusted to meet different requirements.

Claims

1. A transmission-type broadband vortex light excitation device that preserves circular polarization, comprising an incident module, an excitation module and a receiving module, wherein the incident module uses a horn to excite circularly polarized plane light to be vertically incident on the excitation module, and the receiving module is used to receive vortex light. The excitation module adopts a Huygens metasurface, and is characterized in that: The Huygens metasurface includes a first conductive metal layer, a second conductive metal layer and a third conductive metal layer which are overlapped and arranged from top to bottom. The thickness of each conductive metal layer is greater than the skin depth. Two adjacent conductive metal layers are connected by a dielectric layer. Each conductive metal layer is provided with a hollow pattern. Phase coverage is achieved by adjusting the torsion angle θ of the hollow pattern on the first conductive metal layer, so that the three-layer hollow pattern can achieve phase control of the same polarization transmission component, thereby generating vortex light. The hollow patterns of the first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all composed of a plurality of regular hexagonal hollow units, starting from the regular hexagonal hollow unit at the center of the metasurface, and the regular hexagonal hollow units are distributed in circles from the inside to the outside according to a regular hexagonal array; and the regular hexagonal hollow units of the three conductive metal layers are equal in size and corresponding in position; The regular hexagonal hollow unit on the first conductive metal layer is composed of a circular groove and six fan-shaped grooves, the circular groove is located at the center of the regular hexagonal unit, the six fan-shaped grooves are arranged alternately, one long and one short, and the six fan-shaped grooves are evenly distributed outside the circular groove and connected to the circular groove; the regular hexagonal hollow unit on the second conductive metal layer is composed of six fan-shaped holes evenly distributed on the edge of the regular hexagonal unit, and each fan-shaped hole takes the hexagon of the regular hexagonal unit as the center of the circle; the third conductive metal layer is the same as the regular hexagonal hollow unit on the first conductive metal layer.

2. The circular polarization-preserving transmission-type broadband vortex light excitation device according to claim 1, characterized in that: On each circle of the first conductive metal layer, a single regular hexagonal hollow unit rotating around itself will produce a torsion angle θ, the torsion angle θ of the regular hexagonal hollow unit on the far right is the same as the torsion angle θ of the regular hexagonal hollow unit in the center, and both are 0. The torsion angle θ of each regular hexagonal hollow unit on the same circle starts from the torsion angle θ of the regular hexagonal hollow unit on the far right, and increases uniformly in a counterclockwise order, so as to adjust the torsion angle θ of the hollow pattern on the first conductive metal layer to achieve phase coverage.

3. The circular polarization-preserving transmission-type broadband vortex light excitation device according to claim 1 or 2, characterized in that: The radius of the circular groove is R0, the radius of the long fan-shaped groove is R1, the radius of the short fan-shaped groove is R2, and the radius of the fan-shaped hole is R c , where R0 = 0.5 ± 0.1 mm; R c =1.5±0.1mm; R1-R2≥0.15mm; the thickness of the single dielectric layer is 0.1mm~6mm.

4. The circular polarization-preserving transmission-type broadband vortex light excitation device according to claim 3, characterized in that: R1=2.9mm; R2=2.5mm.

5. The circular polarization-preserving transmission-type broadband vortex light excitation device according to claim 4, characterized in that: The dielectric layer is a F4BTMS300 board with a thickness of 1 mm and a dielectric constant of 3. The first conductive metal layer, the second conductive metal layer and the third conductive metal layer are all copper plates with a thickness of 18 um.

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