A bidirectional expander structure based on biaxial anisotropic medium

Abstract

The application relates to the technical field of electromagnetic wave regulation, metamaterials and non-reciprocal devices, and most of existing beam expanders are based on reciprocal structures such as lens groups or gradient refractive index media, and cannot meet the demand for bidirectional consistent beam expansion in bidirectional communication, radar detection and integrated photonics systems; the application provides a bidirectional beam expander structure based on double anisotropic media, which comprises two double anisotropic media, simultaneously has dielectric response, magnetic response and electromagnetic coupling characteristics, and parameters a are continuous functions of spatial coordinates, the beam expansion effect is controlled by adjusting the absolute value of the parameter a , the limitation of traditional reciprocal beam expanders is broken through, and the use of an external magnetic field is avoided; the application has the advantages of bidirectional beam expansion, adjustable beam expansion strength and bidirectional response consistency, and can be widely applied to the fields of bidirectional free space optical communication systems, radars and laser radars, millimeter wave / terahertz beam shaping systems and integrated photonics devices.

Description

Technical Field

[0001] This invention relates to the fields of electromagnetic wave manipulation, metamaterials, non-reciprocal devices, and beam shaping, and more specifically, to a bidirectional beam expander structure based on a dual anisotropic medium. Background Technology

[0002] With the rapid development of technologies such as free-space optical communication, lidar, millimeter-wave communication, terahertz imaging, and integrated photonics, efficient electromagnetic beam manipulation has become one of the key technologies in modern electromagnetic information systems. Beam expanders, as important beam manipulation devices, can increase the lateral size of the beam, reduce the divergence angle, and improve the quality of long-distance transmission. Therefore, they are widely used in laser communication systems, target detection systems, beamforming systems, and optical information processing systems. Currently, common beam expanders mainly employ structures such as lens groups, prism groups, mirror groups, or gradient refractive index media. These beam expanders are typically based on geometric optics principles, expanding the beam size by changing the electromagnetic wave propagation path or wavefront curvature. Because their material and structural parameters satisfy the Lorentz reciprocity principle, they are typical reciprocal devices.

[0003] For a reciprocal beam expander, it can expand the beam when the electromagnetic wave is incident from the designed direction; however, when the electromagnetic wave is incident from the opposite direction, according to the principle of optical path reversibility, the beam expansion process will turn into a beam contraction process. In other words, a traditional beam expander behaves as a beam expander when propagating in the forward direction, but as a beam concentrater or compressor when propagating in the reverse direction, and its forward and reverse propagation characteristics are not consistent.

[0004] However, in many practical applications, devices often need to be able to expand beams in both propagation directions. For example, in bidirectional free-space optical communication systems, both ends of the communication link require a large beam coverage area; in bistatic radar and lidar systems, both the transmitted beam and the echo signal may require beam broadening processing; and in integrated photonics and on-chip optical interconnect systems, consistent beam control under bidirectional propagation conditions is also desired. Therefore, traditional reciprocal beam expanders are difficult to meet these application requirements.

[0005] In recent years, researchers have proposed various schemes for realizing non-reciprocal electromagnetic devices. For example, non-reciprocal propagation can be achieved using magneto-optical materials under an applied magnetic field, direction-correlated propagation can be achieved using nonlinear materials, and non-reciprocal wave propagation can be achieved using time-varying media, time-controlled metamaterials, and dynamic coupling structures. These studies mainly focus on isolators, circulators, unidirectional transmission devices, and non-reciprocal phase-modulated devices, achieving significant progress in realizing non-reciprocal propagation. However, most existing non-reciprocal devices focus on the selective control of propagation direction, and their design goals are usually to achieve unidirectional transmission, unidirectional reflection, or direction-correlated phase modulation, with less attention paid to the problem of "beam expansion in both forward and reverse propagation." Currently, there is a lack of a simple electromagnetic wave beam expander structure that requires no external magnetic field, can simultaneously achieve bidirectional beam expansion, and has adjustable beam expansion intensity. Therefore, how to construct a novel beam expander structure using a bi-anisotropic medium that requires no external magnetic field, can achieve beam expansion under both forward and reverse propagation conditions, and has adjustable beam expansion intensity has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention proposes a bidirectional beam expander structure based on a bi-anisotropic medium. By constructing a bi-anisotropic medium with a specific electromagnetic coupling parameter distribution, the beam expander function of electromagnetic waves in two propagation directions is achieved. Furthermore, the beam expander can be adjusted by modifying the parameters of the bi-anisotropic medium. a Achieve flexible control over beam expansion intensity, meaning that beam expansion can be achieved regardless of whether the electromagnetic wave is incident in the forward or reverse direction. The beam expansion effect is controlled by parameters | a Adjust the size of the | symbol.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A bidirectional beam expander structure based on bi-anisotropic media includes two bi-anisotropic media with identical shapes and dimensions. The parameters of the two bi-anisotropic media are... a Different, parameters a A bi-anisotropic medium with a value greater than 0 is located above, with parameters... a The bi-anisotropic medium with a value less than 0 is located below, and the contact surfaces of the two bi-anisotropic media are in contact, forming a coupling distribution with opposite signs.

[0008] Furthermore, parameters a It is a continuous function of spatial coordinates, and the parameters are adjusted. a The magnitude of the absolute value controls the beam expansion effect. a=f (x, y ), x Represents the horizontal coordinate ，y Represents the vertical coordinate.

[0009] Furthermore, the relative permittivity of bi-anisotropic media ε Relative permeability µ and electromagnetic coupling coefficient ξζ The calculation formula is as follows: in, , .

[0010] Furthermore, the incident direction of the electromagnetic wave is parallel to the contact surface of the two bi-anisotropic media, and the incident interface of the electromagnetic wave is perpendicular to the contact surface.

[0011] Furthermore, the incident angle of the electromagnetic wave is 0°.

[0012] In summary, the invention has the following beneficial effects: (1) To achieve bidirectional beam expansion function, unlike traditional reciprocal beam expanders such as lens groups, this invention uses a bidirectional anisotropic medium with specific electromagnetic coupling characteristics to construct a bidirectional beam expansion structure, so that electromagnetic waves can obtain obvious beam expansion effect when incident from both sides of this invention, breaking through the reciprocity limitation of traditional beam expanders of "forward beam expansion and reverse beam contraction".

[0013] (2) The beam expansion intensity can be continuously adjusted. This invention adjusts the parameters in the bi-anisotropic medium. a It can flexibly control the degree of propagation and deflection of electromagnetic waves in the medium, and realize the continuous adjustment of beam expansion angle and beam expansion intensity to meet the beam control requirements of different application scenarios.

[0014] (3) The bidirectional beam expanding performance has high consistency, and the parameters are consistent. a Under the same conditions, the beam-expanding effect is the same when electromagnetic waves are incident from two opposite directions, which can ensure that the transmitting link and the receiving link in the two-way system have similar beam coverage capabilities, thereby improving the stability and consistency of the two-way system.

[0015] (4) Non-reciprocal beam control can be achieved without an external magnetic field. Compared with traditional magneto-optical non-reciprocal devices, this invention utilizes the electromagnetic coupling effect inside the dual anisotropic medium to achieve bidirectional beam expansion without the need for an external bias magnetic field, reducing the complexity of the transmission system and facilitating engineering implementation and integration.

[0016] (5) The structure is simple and easy to implement. The two bi-anisotropic media of the present invention do not require complex resonant cavities, gyromagnetic materials or multi-stage lens systems. The structure is compact and the manufacturing process is simple, which is conducive to the miniaturization and integration of the device. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention. Arrows indicate...a The sign of the arrow indicates the direction of the arrow. a A positive value indicates that the arrow points in the -y direction. a It is a negative value.

[0018] Figure 2 for b =2.38 m -1 The electric field mode distribution diagram in the xy plane of the bidirectional beam expander structure of the present invention, which is induced from the left by a Gaussian beam.

[0019] Figure 3 for b =2.38 m -1 The electric field mode distribution diagram in the xy plane of the bidirectional beam expander structure of the present invention, with the Gaussian beam incident from the right side.

[0020] Figure 4 for b =1.33 m -1 The electric field mode distribution diagram in the xy plane of the bidirectional beam expander structure of the present invention, which is induced from the left by a Gaussian beam.

[0021] Figure 5 for b =1.33 m -1 The electric field mode distribution diagram in the xy plane of the bidirectional beam expander structure of the present invention, with the Gaussian beam incident from the right side.

[0022] In the diagram, 1 represents... a >0 for biisotropic media, 2 for a Bi-anisotropic medium with <0. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings.

[0024] It should be noted that, for ease of description, the descriptions of direction in the following text are consistent with the directions in the accompanying drawings, but they do not limit the structure of the present invention.

[0025] like Figures 1-5 As shown, this invention discloses a bidirectional beam expander structure based on bi-anisotropic media, comprising two bi-anisotropic media with identical shapes and dimensions, and parameters of the two bi-anisotropic media. a Different, parameters a A bi-anisotropic medium with a value greater than 0 is located above, with parameters... aA bi-anisotropic medium with a value less than 0 is located below, and the contact surfaces of the two bi-anisotropic media are in contact. The two bi-anisotropic media form a coupling distribution with opposite signs. When an electromagnetic wave is incident from either direction, equivalent direction-dependent wave vector modulation and transverse phase gradient accumulation can occur in this invention, achieving a bidirectional beam expansion effect. Under the same parameter |a|, the beam expansion effect obtained when the electromagnetic wave is incident in the forward and reverse directions is basically the same, realizing bidirectional symmetrical beam control capability; parameters a It is a continuous function of spatial coordinates, and the parameters are adjusted. a The magnitude of the absolute value controls the beam expansion effect. a=f (x, y ), x Represents the horizontal coordinate ，y Represents the vertical coordinates, parameters a It can be selected to vary with coordinates x and / or y. The incident direction of the electromagnetic wave is parallel to the contact surface of the two bi-anisotropic media, the incident interface of the electromagnetic wave is perpendicular to the contact surface, and the incident angle of the electromagnetic wave is 0°. Figure 1 In the embodiment shown, the incident interface of the electromagnetic wave is parallel to the vertical coordinate, i.e., the y-axis.

[0026] Relative permittivity of bi-anisotropic media ε Relative permeability µ and electromagnetic coupling coefficient ξζ The calculation formula is as follows: in, , .

[0027] Electromagnetic coupling coefficient ξζ Represents the electromagnetic coupling tensor and electromagnetic coupling coefficient. ξζ The transposes are equal. Incident electromagnetic waves can be incident from either the forward or reverse direction of this invention, with the forward direction being the incident direction. Figure 1 The x-axis is shown as positive, and the opposite is the negative x-axis.

[0028] Example: To verify the effectiveness of the present invention, an air domain of 125×200cm was set as the simulation area in the numerical simulation of this embodiment. The bidirectional beam expander structure of the present invention was placed in the center of the air domain. The overall size of the bidirectional beam expander structure in this embodiment was set to 25cm×200cm. In this embodiment, it is set that... a = b • y ,in b (Unit is m) -1 The beam expansion intensity is a parameter that directly determines the beam expansion intensity; it can be adjusted by... b The size can adjust the beam expansion intensity.a = b • y The distribution ensures that the upper part of the structure a >0, the lower half a <0. In this embodiment, the incident electromagnetic wave is a Gaussian beam, and the wavelength of the Gaussian beam in free space is set to... λ 0 = 0.05m, waist radius w 0 = 4 λ 0. When b =2.38m -1 When the Gaussian beam is incident from the left side of the structure, the electric field mode distribution is as follows: Figure 2 As shown, a significant beam expansion effect can be observed, and the electric field mode distribution when the Gaussian beam is incident from the right side of the structure is shown in the figure. Figure 3 As shown, the beam expansion effect is almost identical to that of the left-side incident beam, indicating that this bidirectional beam expander structure can achieve bidirectional beam expansion. When b =1.33 m -1 When the Gaussian beam is incident from the left side of the structure, the electric field mode distribution is as follows: Figure 4 As shown, a beam-expanding effect can still be observed, but the beam-expanding intensity is relatively low. b =2.38 m -1 It has become noticeably smaller. Figure 5 When shown b =1.33 m -1 The electric field mode distribution diagram of the Gaussian beam incident from the right side of the medium also shows that the beam expansion effect is significantly smaller than that of the Gaussian beam. Figure 3 The beam-expanding effect demonstrates that the beam-expanding intensity of this bidirectional beam expander can be freely adjusted.

[0029] The bidirectional beam expander structure based on a bi-anisotropic medium of the present invention can achieve propagation characteristics that are unattainable by traditional media by setting the dielectric constant, magnetic permeability and electromagnetic coupling parameters. Especially in the field of non-reciprocal electromagnetic control, the bi-anisotropic medium can introduce additional electromagnetic coupling effects, providing new design freedom for achieving direction-dependent beam control. It can be widely used in bidirectional free-space optical communication systems, radar and lidar systems, millimeter-wave / terahertz beamforming systems and integrated photonic devices.

[0030] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A bidirectional beam expander structure based on a dual anisotropic medium, characterized in that, It includes two bianisotropic media, both of identical shape and size, and the parameters of the two bianisotropic media are... a Different, parameters a A bi-anisotropic medium with a value greater than 0 is located above, with parameters... a The bi-anisotropic medium with a value less than 0 is located below, and the contact surfaces of the two bi-anisotropic media are in contact, forming a coupling distribution with opposite signs.

2. The bidirectional beam expander structure based on a dual anisotropic medium according to claim 1, characterized in that, The parameters a It is a continuous function of spatial coordinates, and the parameters are adjusted. a The magnitude of the absolute value controls the beam expansion effect. a=f (x, y ), x Represents the horizontal coordinate ，y Represents the vertical coordinate.

3. The bidirectional beam expander structure based on a dual anisotropic medium according to claim 2, characterized in that, The relative permittivity of the bi-anisotropic medium ε Relative permeability µ and electromagnetic coupling coefficient ξζ The calculation formula is as follows: in, , .

4. The bidirectional beam expander structure based on a dual anisotropic medium according to claim 1, characterized in that, The incident electromagnetic wave is incident in a direction parallel to the contact surface of the two bi-anisotropic media, and the incident interface of the electromagnetic wave is perpendicular to the contact surface.

5. The bidirectional beam expander structure based on a bi-anisotropic medium according to claim 4, characterized in that, The incident angle of the electromagnetic wave is 0°.

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