Orbital angular momentum circularly polarized antenna based on magneto-optical photonic crystal chiral corridor mode

Abstract

This invention proposes an orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal. The antenna comprises a magneto-optical photonic crystal cluster and two metal plates. The cluster is composed of a periodically arranged array of magneto-optical photonic crystal cells, each with an applied bias magnetic field. The two metal plates are clamped to the upper and lower sides of the cluster, forming upper and lower electric walls to constrain the electric field direction. A perimeter fence surrounds the cluster, connecting to the two metal plates to form a corridor cavity supporting the chiral corridor mode. Multiple radiating slots are evenly spaced along the circumference on the top or sidewalls of the corridor cavity. These slots couple the confined electromagnetic modes within the cavity into directional radiation in free space. This invention utilizes the tensor permeability of the magneto-optical photonic crystal to construct the chiral corridor cavity. Through lateral slotted coupling radiation, it achieves pure excitation of high-order orbital angular momentum beams while simplifying the antenna structure and reducing feeding complexity.

Description

Technical Field

[0001] This invention relates to the field of orbital angular momentum communication antenna technology, and in particular to an orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal. Background Technology

[0002] Orbital Angular Momentum (OAM) antennas are an antenna technology that utilizes the orbital angular momentum characteristics of electromagnetic waves for signal transmission. OAM beams possess a helical phase wavefront, enabling them to carry multiple independent signal modes, thereby improving the capacity and efficiency of communication systems with limited spectrum resources. Existing mainstream OAM antenna solutions all have limitations: 1. Metasurfaces and discrete feed arrays rely on complex phase control, resulting in large system size, complex feed networks, and high costs. 2. While the ring corridor cavity scheme has a compact structure, it is hampered by mode degeneracy, making it difficult to output pure high-order OAM modes. 3. Helical phase plates suffer from high losses, fixed modes, and difficulties in integration.

[0003] Photonic crystals are artificial electromagnetic materials composed of periodically arranged dielectric or magnetic materials. They possess unique photonic bandgap characteristics, allowing for precise control of the propagation, confinement, and radiation of electromagnetic waves at specific wavelengths, providing a novel technological path for precise control of electromagnetic modes. Magneto-optical photonic crystals, as novel composite materials integrating magneto-optical materials and photonic crystal structures, exhibit tensor properties in their permeability under an applied bias magnetic field. This allows them to break the reciprocity of electromagnetic transmission, achieving unique electromagnetic effects such as unidirectional waveguides, topological boundary state propagation, and dynamically tunable photonic bandgap. They are key materials for constructing topological photonic devices, optical isolators, and tunable resonant devices. However, how to utilize the non-reciprocal tunability of magneto-optical photonic crystals to excite chiral corridor resonant modes, thereby achieving pure radiation of higher-order OAM waves, remains a gap in the current technological field. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention aims to provide an orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal. The chiral corridor cavity is constructed using the tensor permeability characteristics of the magneto-optical photonic crystal, and pure excitation of high-order orbital angular momentum beams is achieved through lateral slotted coupling radiation. At the same time, the antenna structure is simplified and the feeding complexity is reduced.

[0005] To achieve the above objectives, this invention proposes an orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal, comprising a magneto-optical photonic crystal cluster and two metal plates. The magneto-optical photonic crystal cluster is composed of a number of periodically arranged magneto-optical photonic crystal cells. A bias magnetic field is applied to the magneto-optical photonic crystal cells, and the permeability exhibits tensor characteristics under the action of the bias magnetic field. The two metal plates are arranged in parallel and are respectively clamped on the upper and lower sides of the magneto-optical photonic crystal cluster to form upper and lower electric walls to constrain the direction of the electric field. A fence is provided around the magneto-optical photonic crystal cluster, and the fence is connected to the two metal plates to form a corridor cavity that supports the chiral corridor mode. Multiple radiation slots are equally spaced along the circumference on the top surface or side wall of the corridor cavity. The radiation slots can couple the electromagnetic mode confined in the cavity into directional radiation in free space.

[0006] In the above scheme: the magneto-optical photonic crystal cell is composed of multiple dielectric pillars with magneto-optical effects, and the dielectric pillars are arranged in a periodic lattice. Utilizing the tensor permeability characteristics of magneto-optical materials under a bias magnetic field, their off-diagonal non-zero components cause the energy bands of the crystal to have a topologically nontrivial band gap in momentum space, and the overall structure exhibits time-reversal symmetry breaking.

[0007] In the above scheme: the material of the dielectric pillar is yttrium iron garnet or barium ferrite or a rare-earth iron garnet or gadolinium gallium garnet-based magneto-optical thin film with bismuth as a substitute; the shape of the dielectric pillar is cylindrical, square, annular, or cross-shaped. In the microwave band, the dielectric pillar material is yttrium iron garnet or barium ferrite; in the optical wave and terahertz band, the dielectric pillar material is a rare-earth iron garnet or gadolinium gallium garnet-based magneto-optical thin film with bismuth as a substitute.

[0008] In the above scheme: the dielectric pillars are yttrium iron garnet cylinders with a diameter of 5 mm and a height of less than 10 mm. Six dielectric pillars are arranged symmetrically in a hexagonal lattice within a single magneto-optical photonic crystal cell, with a lattice constant of 16 mm. By precisely adjusting the ratio of the yttrium iron garnet cylinder diameter to the lattice constant, the required photonic bandgap can be opened in the target frequency band.

[0009] In the above scheme: the magneto-optical photonic crystal cluster is formed by arranging magneto-optical photonic crystal cells in a hexagonal lattice, square lattice, triangular lattice, or quasi-periodic Penrose lattice. The shape of the corridor cavity is not limited to a regular hexagon; circular, square, racetrack-shaped, or other closed annular cavities are also possible, as long as they support stable angular traveling wave modes.

[0010] In the above scheme: the magneto-optical photonic crystal cluster is a regular hexagonal cluster structure composed of 19 magneto-optical photonic crystal cells, and the number of radiation slots is at least 12. According to the principle of electromagnetic duality, these radiation slots can be equivalent to a series of magnetic current sources with a specific phase distribution, the phase distribution of which is determined by the angular variation of the chiral wave in the cavity.

[0011] In the above scheme: the fence is set at a distance of 0.6 to 1 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster to ensure that a corridor cavity supporting the chiral corridor mode can be formed.

[0012] In the above scheme: the fence is set at a position 0.85 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster.

[0013] In the above scheme, the external bias magnetic field adopts a discrete bias design, with each dielectric pillar independently equipped with a permanent magnet. This "one pillar, one magnet" discrete bias scheme ensures that each dielectric pillar experiences a basically consistent bias magnetic field along its axis, achieving uniform magnetization. This effectively avoids the problem of uneven magnetization caused by magnetic field attenuation in the edge region when using a single large magnet, ensuring the uniform breaking of the time reversal symmetry throughout the entire photonic crystal region.

[0014] In the above scheme: the fence is made of metal material or topological insulator material with a band gap within the antenna operating frequency band.

[0015] The beneficial effects of this invention are:

[0016] 1. Integrating mode generation (cavity), non-reciprocal stabilization (magneto-optical effect), and directional radiation (slotting) functions into one system, it can directly and efficiently excite and radiate high-order, high-purity OAM beams without the need for complex feeding networks or phase plates, solving the inherent problems of traditional solutions in terms of size, cost, and mode purity. 2. Utilizing the tensor permeability characteristics of magneto-optical photonic crystals under an applied magnetic field, the degeneracy of the electromagnetic modes within the cavity is broken. Combined with the directional constraint effect of the chiral corridor structure, a single high-order angular mode can be accurately separated and excited. The radiating slot couples the cavity mode to free space. The orbital angular momentum topological charge L and spin angular momentum s of the radiated field are directly determined by the angular mode n (n=L+s). Without spurious mode interference, it effectively ensures the signal quality of multi-mode multiplexed communication, significantly reduces channel crosstalk, and improves system transmission stability. 3. By changing the strength of the applied bias magnetic field to the magneto-optical material, the antenna's operating frequency and bandwidth can be continuously and dynamically adjusted. Furthermore, by changing the direction of the applied bias magnetic field, the antenna's polarization can be adjusted (switching from left-hand circular polarization to right-hand circular polarization). 4. The electric wall structure formed by the upper and lower metal plates, in conjunction with the outer perimeter fence, achieves omnidirectional and efficient confinement of electromagnetic waves within the corridor cavity, minimizing lateral and vertical leakage. 5. The inherent non-reciprocal transmission characteristics of the magneto-optical photonic crystal effectively suppress the reverse intrusion of external clutter signals, preventing external electromagnetic interference to the cavity's electromagnetic modes, ensuring stable output of the high-order OAM beam, and reducing the antenna's own signal reflection loss, thereby improving the overall anti-interference performance and operational reliability of the communication system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a magneto-optical photonic crystal unit cell.

[0018] Figure 2 This is a schematic diagram of a chiral corridor cavity orbital angular momentum antenna.

[0019] Figure 3 This is a schematic diagram of the experimental testing equipment of the present invention.

[0020] Figure 4 The diagram shows the electric field distribution characteristics within the chiral corridor cavity structure. The left figure shows the electric field distribution within the chiral corridor cavity, and the right figure shows the electric field phase diagram within the chiral corridor cavity.

[0021] Figure 5 The figure shows the normalized electric field and phase distribution of the electromagnetic wave radiated by the chiral corridor cavity antenna after feeding in the far field. The left figure shows the electric field amplitude, and the right figure shows the electric field phase. Detailed Implementation

[0022] like Figure 1 As shown in Figure 2, an orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal operates in the microwave band (e.g., 7.5 GHz) and is mainly composed of a magneto-optical photonic crystal cluster 1, a fence 4, and two metal plates 2.

[0023] The magneto-optical photonic crystal cluster 1 is composed of several magneto-optical photonic crystal cells 3 arranged periodically. A bias magnetic field is applied to each magneto-optical photonic crystal cell 3. Under the influence of the bias magnetic field, the permeability exhibits tensor characteristics. Its off-diagonal, non-zero components cause a topologically nontrivial band gap in momentum space, resulting in a broken time-reversal symmetry in the overall structure. Two metal plates 2 (which can be aluminum plates with a thickness less than...) are also present. / 20, The antennas (corresponding to the operating frequency band of the antenna) are arranged in parallel and clamped on the upper and lower sides of the magneto-optical photonic crystal cluster 1, forming upper and lower electric walls to constrain the direction of the electric field. A perimeter fence 4 (thickness less than...) is provided around the magneto-optical photonic crystal cluster 1. / 20), the fence 4 is connected to the two metal plates 2, thus forming a corridor cavity that supports the chiral corridor pattern.

[0024] On the top surface or side wall of the corridor cavity, multiple radial slots 5 are equally spaced along the circumference (the slot width is...). / 10~ / 20, the groove length is / 8~ / 4, the radiation slot 5 can couple the confined electromagnetic mode in the cavity into directional radiation in free space. The number of wavelengths that orbit around the cavity (i.e., the angular modulus n) and the clockwise direction of the electromagnetic wave energy flow in the cavity directly determine the topological charge L and spin angular momentum s (n=L+s) of the orbital angular momentum (OAM) carried by the radiation wave.

[0025] The unit cell 3 of the magneto-optical photonic crystal is composed of multiple dielectric pillars 6 with magneto-optical effects, which are arranged in a periodic lattice. Utilizing the tensor permeability characteristics of magneto-optical materials under a magnetic field, the off-diagonal non-zero components cause the energy bands of the crystal to have topologically nontrivial band gaps in momentum space, and the overall structure exhibits time-reversal symmetry breaking.

[0026] Specifically, the dielectric pillar 6 is a yttrium iron garnet cylinder with a diameter of 5 mm and a height of less than 10 mm. Six dielectric pillars 6 are arranged symmetrically in a hexagonal lattice within a single magneto-optical photonic crystal cell 3, with a lattice constant of 16 mm. By precisely adjusting the ratio of the yttrium iron garnet cylinder diameter to the lattice constant, the desired photonic bandgap can be opened in the target frequency band. The shape of the dielectric pillar 6 is not limited to a cylinder; it can be a square pillar, ring, cross, or other complex-shaped magneto-optical dielectric pillar. An air-hole type photonic crystal can also be used, i.e., periodically perforated within the magneto-optical dielectric plate. The material of the dielectric pillar 6 is not limited to yttrium iron garnet (YIG). In the microwave band, other ferrite materials (such as barium ferrite) can be used alternatively. In the optical and terahertz bands, materials with significant magneto-optical effects, such as bismuth-substituted rare-earth iron garnet (e.g., Bi:YIG, which has a stronger magneto-optical effect) and gadolinium gallium garnet-based magneto-optical thin films, can be used.

[0027] Specifically, the magneto-optical photonic crystal cluster 1 is a hexagonal cluster structure composed of 19 magneto-optical photonic crystal cells 3, with 16 radiating slots 5. The lattice type is not limited to hexagonal lattices. Square lattices, triangular lattices, or quasi-periodic arrangements (such as Penrose lattices) can also form the required photonic bandgap to construct the corridor cavity. The number, size, and position of the radiating slots 5 are optimized and fed from the bottom of the cavity via a coaxial probe, exciting the eigenmode of the corridor cavity. This eigenmode has a defined angular modulus n (i.e., the electric field phase varies by 2πn along the cavity circumference).

[0028] Figure 3 This is a schematic diagram of the experimental testing equipment for this invention. The central area in the diagram is a metal corridor cavity, inside which YIG (yttrium iron garnet) is assembled, and a magnet is added to the bottom of the cavity to provide a bias magnetic field for the YIG. By adding a coaxial probe along the path of the corridor cavity for antenna feeding, higher-order orbital angular momentum circularly polarized wavefronts can be observed in the far field.

[0029] like Figure 4 As shown in the figure, in this embodiment, it can be clearly seen that the electric field phase changes by 2π*5 in the chiral resonant cavity, which directly indicates that the angular modulus of this eigenmode is 5. Therefore, according to the above principle, this mode will radiate a high-order orbital angular momentum electromagnetic wave with L=4 and right-hand circular polarization characteristics (SAM=+1) after loading the radiation slot.

[0030] Figure 5This diagram illustrates the normalized electric field and phase distribution in the far field of the electromagnetic wave radiated by a chiral corridor cavity antenna after feeding. The left figure shows the electric field amplitude, and the right figure shows the electric field phase. Figure 5 It is evident that in the far-field region, the antenna's radiation mode exhibits a higher-order orbital angular momentum mode with L=4.

[0031] The operating frequency of an orbital angular momentum antenna can be coarsely tuned by changing the geometric parameters (diameter, lattice constant) of the orbital dielectric pillar. Furthermore, by altering the strength of the applied bias magnetic field to the orbital angular momentum, its tensor permeability can be continuously adjusted, thereby achieving fine, dynamic tuning of the antenna's operating frequency and bandwidth.

[0032] Enclosure 4 is positioned 0.6 to 1 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster 1 to ensure the formation of a corridor cavity that supports the chiral corridor mode. Specifically, enclosure 4 is positioned 0.85 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster 1.

[0033] The applied bias magnetic field adopts a discrete bias design, with each dielectric pillar 6 independently equipped with a permanent magnet. The discrete bias scheme of "one pillar, one magnet" ensures that each dielectric pillar 6 is subjected to a basically consistent bias magnetic field along its axis, thereby achieving uniform magnetization. This effectively avoids the problem of uneven magnetization caused by the attenuation of the magnetic field in the edge region when using a single large magnet, and ensures the uniform breaking of the time reversal symmetry of the entire photonic crystal region.

[0034] Fence 4 is made of metal or a topological insulator material with a bandgap within the antenna's operating frequency band.

[0035] The frequency and bandwidth tuning characteristics of the antenna were verified and realized through the following methods: In electromagnetic simulation, the main resonant frequency of the antenna can be effectively adjusted by systematically parametrically scanning key geometric parameters such as lattice constant and diameter of the yttrium iron garnet cylinder. Simultaneously, by changing the strength of the external bias magnetic field applied to the yttrium iron garnet material, its operating bandwidth can be dynamically controlled. Furthermore, by changing the direction of the external bias magnetic field applied to the magneto-optical material, the polarization of the antenna can be adjusted (it can switch from left-hand circular polarization to right-hand circular polarization). In experimental verification, a measurement platform was constructed using a high-performance microwave vector network analyzer (VNA) and a free-space dual-port waveguide probe scanning system. The antenna was directly fed through a coaxial probe, thereby accurately characterizing its radiation and tuning performance.

Claims

1. An orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal, characterized in that: The device includes a magneto-optical photonic crystal cluster (1) and two metal plates (2). The magneto-optical photonic crystal cluster (1) is composed of a number of magneto-optical photonic crystal cells (3) arranged periodically. The magneto-optical photonic crystal cells (3) are subjected to a bias magnetic field, and the magnetic permeability exhibits tensor characteristics under the action of the bias magnetic field. The two metal plates (2) are arranged in parallel and are respectively clamped on the upper and lower sides of the magneto-optical photonic crystal cluster (1) to form upper and lower electric walls to constrain the direction of the electric field. A fence (4) is provided around the magneto-optical photonic crystal cluster (1). The fence (4) is connected to the two metal plates (2) to form a corridor cavity that supports the chiral corridor mode. On the top surface or side wall of the corridor cavity, multiple radiation slots (5) are opened at equal intervals along the circumference. The radiation slots (5) can couple the electromagnetic mode bound in the cavity into directional radiation in free space.

2. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 1, characterized in that: The magneto-optical photonic crystal cell (3) is composed of multiple dielectric pillars (6) with magneto-optical effect, and the dielectric pillars (6) are arranged in a periodic lattice.

3. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 2, characterized in that: The material of the dielectric pillar (6) is yttrium iron garnet or barium ferrite or rare earth iron garnet or gadolinium gallium garnet-based magneto-optical thin film, and the shape of the dielectric pillar (6) is cylindrical or square or ring-shaped or cross-shaped.

4. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 3, characterized in that: The dielectric pillar (6) is a yttrium iron garnet cylinder with a diameter of 5 mm and a height of less than 10 mm. Six dielectric pillars (6) are arranged symmetrically in a hexagonal lattice within a single magneto-optical photonic crystal cell (3), and the lattice constant is 16 mm.

5. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 1, characterized in that: The magneto-optical photonic crystal cluster (1) is formed by arranging magneto-optical photonic crystal cells (3) in a hexagonal lattice, a square lattice, a triangular lattice, or a quasi-periodic Penrose lattice.

6. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 5, characterized in that: The magneto-optical photonic crystal cluster (1) is a regular hexagonal cluster structure composed of 19 magneto-optical photonic crystal cells (3) spliced ​​together, and the number of radiation slots (5) is at least 12.

7. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 1, characterized in that: The fence (4) is placed 0.6 to 1 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster (1).

8. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 7, characterized in that: The fence (4) is placed 0.85 times the lattice constant outside the boundary of the magneto-optical photonic crystal cluster (1).

9. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 2, characterized in that: The bias magnetic field adopts a discrete bias design, and each dielectric column (6) is independently configured with a permanent magnet.

10. The orbital angular momentum circularly polarized antenna based on the chiral corridor mode of a magneto-optical photonic crystal according to claim 1, characterized in that: The fence (4) is made of metal or a topological insulator material with a band gap within the antenna operating frequency band.

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