Terahertz broadband metasurface phase regulation and control design method and regulation and control structure

Abstract

The invention discloses a terahertz broadband metasurface phase regulation and control design method and a regulation and control structure, and belongs to the technical field of terahertz. The phase regulation and control structure comprises a metasurface body, the metasurface body is provided with n groups of phase modulation units which are arranged according to a two-dimensional array, and each group of phase modulation units has differentiated phase-frequency change slopes within f1-f2 frequency bands; the invention provides a non-parallel phase design method and a design thought that the slope of the phase changing along with the frequency change is consistent when the metasurface unit is designed, phase difference changes caused by different frequency changes are considered, dynamic matching of the phase difference and the frequency in a broadband is achieved, and the working bandwidth of the metasurface is improved.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz technology, and specifically relates to a terahertz broadband metasurface phase control design method and control structure. Background Art

[0002] Dispersion control designs based on resonant units design the electromagnetic response of resonant units (such as open rings and H-shaped structures) and utilize their dispersion characteristics to achieve a phase gradient within a specific frequency band. During the metasurface design process, the center frequency point is used as a reference, and the unit's geometric parameters are optimized to ensure that the phase response curves of each frequency point within the full frequency band are parallel, that is, the slope of the phase change with frequency is consistent. Although this type of design can reduce the difficulty of metasurface design and expand the bandwidth to a certain extent, it ignores the phase difference requirements and frequency-related issues at different frequencies, resulting in significant defects in practical applications.

[0003] Metasurface, a two-dimensional planar device composed of sub-wavelength artificial units, provides a new way for the efficient manipulation of electromagnetic waves by locally controlling the phase, amplitude and polarization of electromagnetic waves.

[0004] In broadband metasurface design, existing technologies mainly achieve phase control through the following two methods:

[0005] 1. Broadband design based on geometric phase: This approach leverages the geometric phase (Pancharatnam-Berry phase) of rotationally symmetric elements (such as V-shaped antennas and elliptical aperture arrays) to achieve frequency-independent phase control. While this approach offers broadband characteristics, it is only applicable to circularly polarized waves, and the phase control range is fixed (0-2π), making it difficult to adapt to linear polarization or complex wavefront requirements.

[0006] 2. Dispersion control design based on resonant units: By designing the electromagnetic response of the resonant unit (such as an open ring or H-shaped structure), its dispersion characteristics are used to achieve a phase gradient within a specific frequency band. The metasurface design takes the center frequency as the reference, and by optimizing the unit's geometric parameters, the phase response curves of each frequency point in the full frequency band are parallel, that is, the slope of the phase change with frequency is consistent. Although this type of design can expand the bandwidth, its core assumption is that "the phase difference requirement at different frequencies is independent of frequency", which leads to significant defects in practical applications.

[0007] The principle of metasurface lens phase control is to flexibly adjust the phase of the incident electromagnetic wave by designing different metasurface units to achieve the conversion of spherical waves into plane waves:

[0008] To achieve the control of spherical waves to plane waves, the phases of metasurface units at different positions that need to be adjusted can be expressed as:

[0009]

[0010] Metasurface (x i ,y i ) position to be adjusted;

[0011] f: electromagnetic wave frequency;

[0012] c0: speed of light in vacuum;

[0013] (x i ,y i ): represents the position point on the hypersurface;

[0014] F: The distance between the feed source and the metasurface, i.e. the focal length.

[0015] The above formula is the phase compensation principle formula of the metasurface. It can be found that the phase of the unit of the metalens that needs to be compensated is the focal length F of the metasurface, the wavelength λ of the incident wave, and the position of each unit in the metalens (x i ,y i )related.

[0016] When designing a large-bandwidth metasurface, the center frequency is used as the design frequency for metasurface simulation optimization. In order to ensure the consistency of phase control within a large bandwidth, the phase response within the working bandwidth of the metasurface is designed according to the parallel phase response.

[0017] However, according to the phase compensation principle formula, when the center of the metasurface is used as the reference phase point, the phase that needs to be adjusted at the specified position is a phase relative to the current position (x i ,y i ) is a binary function of the frequency f, which will lead to the deterioration of the phase control ability of the metasurface when the frequency changes.

[0018] Current metasurface design processes use the center frequency as a benchmark and optimize the unit's geometric parameters to ensure that the phase response curves at all frequencies within the full frequency band are parallel, meaning that the slope of the phase change with frequency is consistent. While this approach can reduce the difficulty of metasurface design and expand bandwidth to a certain extent, it ignores the phase difference requirements and frequency-dependent issues at different frequencies, resulting in a significant deterioration in the metasurface's phase control accuracy as the frequency changes. Summary of the Invention

[0019] In response to the above-mentioned technical problems existing in the prior art, the present invention proposes a terahertz broadband metasurface phase control design method and control structure, which has a reasonable design, overcomes the shortcomings of the prior art, and has good effects.

[0020] In order to achieve the above object, the present invention adopts the following technical solutions:

[0021] A terahertz broadband metasurface phase control design method specifically includes the following steps:

[0022] Step 1: Determine the metasurface operating frequencies f1-f2, metasurface dimensions a×b, and focal length F;

[0023] Step 2: Based on the parameters determined in step 1, Determining the metasurface phase span As shown in formula (1):

[0024]

[0025] Where c0 is the speed of light in vacuum;

[0026] Step 3: Determine the phase gradient of the metasurface phase modulation unit

[0027] Step 4: According to formula (2), determine the number n of phase modulation units to be designed;

[0028]

[0029] Step 5: Determine the frequency response curve of each phase modulation unit based on the phase gradient and phase compensation at the center frequency f0. The frequency response curve is a non-parallel phase response. The phase compensation is shown in formula (3):

[0030]

[0031] in, is the phase value that needs to be adjusted by the Nth phase modulation unit, is the phase that needs to be adjusted by the first phase modulation unit at f0, and the first unit serves as the reference phase of the phase modulation unit;

[0032] Step 6: Design a metasurface phase modulation unit based on the principle of geometric phase or dispersion control;

[0033] Design n groups of metasurface phase modulation units so that each group of phase modulation units satisfies the position-dependent non-parallel phase response in the f1-f2 frequency band: The non-parallel phase response curve of the jth group of units As shown in formula (4):

[0034]

[0035] Among them, (x j ,y j ) are the characteristic coordinates corresponding to the group of phase modulation units;

[0036] Step 7: According to the principle of proximity, complete the design of the metasurface phase modulation unit arrangement, position (x i ,y i ) where the jth group of units satisfies the relationship, as shown in formula (5):

[0037]

[0038] Preferably, the phase modulation unit in step 4 is implemented based on the geometric phase principle and adopts a rotationally symmetric structure.

[0039] Preferably, the phase modulation unit in step 4 is implemented based on the dispersion control principle and adopts an open ring or H-shaped resonant structure.

[0040] Preferably, the non-parallel phase response in step 5 refers to that the slope of the phase of the metasurface phase modulation unit changes with frequency is inconsistent.

[0041] In addition, the present invention also mentions a terahertz broadband metasurface phase control structure, including a metasurface body, on which are provided n groups of phase modulation units arranged in a two-dimensional array, each group of phase modulation units having a differentiated phase-frequency variation slope within the f1-f2 frequency band, and the arrangement of the phase modulation units satisfies the position mapping relationship:

[0042]

[0043] Among them, j represents the unit group number, (x i ,y i ) represents the position point on the metasurface, i.e., the center coordinate of the phase modulation unit.

[0044] Preferably, the phases that need to be adjusted at different positions of the metasurface need to satisfy the following formula:

[0045]

[0046] in, Indicates that the metasurface is at (x i ,y i ) position; f represents the frequency; c0 represents the speed of light in a vacuum; and F represents the focal length.

[0047] The beneficial technical effects brought about by the present invention are:

[0048] The present invention provides a design method based on non-parallel phase design, which changes the slope of phase change with frequency when designing metasurface units. The phase difference changes caused by different frequency changes are taken into account, and dynamic matching of phase difference and frequency in a wide band is achieved, thereby improving the working bandwidth of the metasurface. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of phase control;

[0050] Figure 1 (a) is the optical path of a spherical wave passing through a uniform medium; (b) is the optical path of a spherical wave passing through a metasurface.

[0051] Figure 2 is a schematic diagram of parallel phase response;

[0052] Figure 3 This is the non-parallel phase response diagram. DETAILED DESCRIPTION

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0054] The present invention provides a method for optimizing the deterioration of metasurface phase control accuracy caused by frequency variation by designing non-parallel phase responses for different phase modulation units.

[0055] When designing a metasurface, the phases that need to be adjusted at different locations on the metasurface need to satisfy the following formula:

[0056]

[0057] Metasurface (x i ,y i ) position to be adjusted;

[0058] F: electromagnetic wave frequency;

[0059] c0: speed of light in vacuum;

[0060] (x i ,y i ): represents the position point on the hypersurface;

[0061] F: The distance between the feed source and the metasurface, i.e. the focal length.

[0062] However, when the metasurface operates at high frequencies and is large in size, designing units for each position requires too many units to be designed, making it impractical for engineering. However, relying solely on the parallel phase design concept to design multiple phase-modulation units within the metasurface's operating bandwidth cannot achieve a large-bandwidth metasurface design. The present invention provides an optimized design solution that effectively corrects phase-modulation errors caused by frequency variations while designing a limited number of phase-modulation units. The solution specifically includes the following steps:

[0063] Step 1: Determine the target metasurface operating frequency f1~f2, metasurface size a×b and focal length F;

[0064] Step 2: Based on the parameters determined in step 1, determining the metasurface phase span;

[0065]

[0066] Step 3: Determine the phase gradient of the metasurface phase modulation unit

[0067] Step 4: If Figure 3 As shown, the number n of units that need to be designed is determined according to the center frequency span and formula (2);

[0068]

[0069] Step 5: Determine the frequency response curve of each unit based on the phase gradient and phase compensation formula at the center frequency f0;

[0070] The frequency response curve of each unit is as follows Figure 3 shown.

[0071] Step 6: Design metasurface units based on the principles of geometric phase or dispersion control;

[0072] Step 7: Complete the design of the metasurface unit arrangement according to the principle of proximity. The unit N at each position j , j satisfies the following relationship:

[0073]

[0074] Figure 1 Schematic diagram of phase control; Figure 1 (a) is the optical path of a spherical wave passing through a uniform medium; (b) is the optical path of a spherical wave passing through a metasurface. Figure 2 Schematic diagram of parallel phase response.

[0075] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A terahertz broadband metasurface phase control design method, characterized in that: The specific steps include: Step 1: Determine the metasurface operating frequencies f1-f2, metasurface dimensions a×b, and focal length F; Step 2: Based on the parameters determined in step 1, Determining the metasurface phase span As shown in formula (1): Where c0 is the speed of light in vacuum; Step 3: Determine the phase gradient of the metasurface phase modulation unit Step 4: According to formula (2), determine the number n of phase modulation units to be designed; Step 5: Determine the frequency response curve of each phase modulation unit based on the phase gradient and phase compensation at the center frequency f0. The frequency response curve is a non-parallel phase response. The phase compensation is shown in formula (3): in, is the phase value that needs to be adjusted by the Nth phase modulation unit, is the phase that needs to be adjusted by the first phase modulation unit at f0, and the first unit serves as the reference phase of the phase modulation unit; Step 6: Design a metasurface phase modulation unit based on the principle of geometric phase or dispersion control; Design n groups of metasurface phase modulation units so that each group of phase modulation units satisfies the position-dependent non-parallel phase response in the f1-f2 frequency band: The non-parallel phase response curve of the jth group of units As shown in formula (4): Among them, (x j ,y j ) are the characteristic coordinates corresponding to the group of phase modulation units; Step 7: According to the principle of proximity, complete the design of the metasurface phase modulation unit arrangement, position (x i ,y i ) where the jth group of units satisfies the relationship, as shown in formula (5):

2. The terahertz broadband metasurface phase control design method according to claim 1, characterized in that: The phase modulation unit in step 4 is implemented based on the geometric phase principle and adopts a rotationally symmetric structure.

3. The terahertz broadband metasurface phase control design method according to claim 1, characterized in that: The phase modulation unit in step 4 is implemented based on the dispersion control principle and adopts an open ring or H-shaped resonant structure.

4. The terahertz broadband metasurface phase control design method according to claim 1, characterized in that: The non-parallel phase response in step 5 refers to the inconsistency of the slope of the phase of the metasurface phase modulation unit as it changes with frequency.

5. A terahertz broadband metasurface phase control structure designed using any of the methods of claims 1-4, characterized in that: The metasurface comprises a metasurface body, on which are arranged n groups of phase modulation units in a two-dimensional array. Each group of phase modulation units has a differentiated phase-frequency variation slope within the frequency band f1 to f2, and the arrangement of the phase modulation units satisfies the position mapping relationship: Among them, j represents the unit group number, (x i ,y i ) represents the position point on the metasurface, i.e., the center coordinate of the phase modulation unit.

6. The terahertz broadband metasurface phase control structure according to claim 5, characterized in that: The phase that needs to be adjusted at different positions on the metasurface needs to satisfy the following formula: in, Indicates that the metasurface is at (x i ,y i ) position; f represents the frequency; c0 represents the speed of light in a vacuum; and F represents the focal length.

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