Wavelength-controlled circular dichroism achiral meta-structure surface and design method thereof

Abstract

The invention discloses a wavelength-controlled circular dichroism achiral metasurface and a design method thereof, and belongs to the technical field of electromagnetic wave phase and amplitude regulation and control. The wavelength-controlled circular dichroism achiral metasurface comprises a bottom-layer metal reflecting layer, a substrate dielectric layer, a middle structural layer, a top-layer dielectric layer and a top-layer structural layer which are sequentially stacked from bottom to top, each of the middle structure layer and the top structure layer is composed of a plurality of metastructure units which are periodically arranged, the period length of each metastructure unit is sub-wavelength, and each metastructure unit is of a triple rotational symmetry structure; an achiral structure is adopted by the super-structure surface, the structure is symmetrical, geometric parameters needing to be optimized are fewer, the regulation and control mechanism is more visual, the machining tolerance is high, and the working bandwidth is wider; a triple rotational symmetry structure is adopted as a super-structure unit, and the same surface unit structure of a super-structure plane comprises two triple rotational symmetry structures, so that the circular dichroism can be regulated and controlled by switching the wavelength of incident light.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave phase and amplitude modulation technology, specifically to a wavelength-controlled circular dichroic nonchiral metasurface and its design method. Background Technology

[0002] Circular dichroism refers to the phenomenon that a structure has different absorption rates for left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light. Natural materials typically exhibit weak circular dichroism responses, which are often enhanced through induced microstructures and molecular alignment. However, due to the inherent properties of materials, circular dichroism remains relatively low. Metasurfaces, through the artificial design of subwavelength structures, flexibly control the amplitude, phase, polarization, and frequency of electromagnetic waves, providing a new approach to improving circular dichroism.

[0003] Currently, although various broadband and narrowband circular dichroic metasurfaces have been proposed, most of these metasurfaces have relatively fixed functions, can only absorb a specific circularly polarized optics, and have low tuning flexibility, which limits their further applications.

[0004] To address the aforementioned issues, the reciprocity of chiral structures has been utilized to achieve different dichroisms at different wavelengths, as exemplified by the chiral metasurface and its dynamic control method for circular dichroism, as disclosed in patent publication CN120652694A. However, because the chiral structure breaks the original symmetry of the structure, the design becomes complex, the processing tolerance is low, and the operating bandwidth is narrow.

[0005] Based on this, the present invention designs a wavelength-controlled circular dichroic achiral metasurface and its design method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a wavelength-controlled circular dichroic achiral metasurface and its design method to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A wavelength-controlled circular dichroic nonchiral metasurface includes a bottom metal reflective layer, a substrate dielectric layer, an intermediate structural layer, a top dielectric layer, and a top structural layer stacked sequentially from bottom to top.

[0009] Both the intermediate and top structural layers are composed of multiple periodically arranged metaunits with a period length of subwavelength. The metaunits are triple rotationally symmetric (C3) structures.

[0010] The metasurface is divided into multiple surface unit structures. Two metaunit structures in the same surface unit structure are identical, and the position of one metaunit is rotated relative to the other metaunit by a certain angle, which is set as θ.

[0011] The triple rotational symmetry (C3) structure consists of three cuboids of the same size, evenly arranged along the circumference. That is, one cuboid is rotated counterclockwise by 120° and 240° around the center O and then copied and superimposed to form one of the C3 structures in the surface unit structure. Then, this structure is translated a distance t2 along the z-axis and rotated by 26° or 38° (θ=26° / 38°) to obtain the position of the second C3 structure.

[0012] Preferably, the thickness of the bottom metal reflective layer is t=0.3μm, the thickness of the base dielectric layer is t1=0.26μm, the thickness of the intermediate structural layer is H1=0.3μm, the thickness of the top dielectric layer is t2=0.26μm, and the thickness of the top structural layer is H2=0.3μm.

[0013] Preferably, the bottom metal reflective layer, the middle structural layer and the top structural layer are all made of gold (Au), but the materials can also be replaced with metals such as silver, chromium, and copper.

[0014] Preferably, both the base dielectric layer and the top dielectric layer are made of silicon (Si).

[0015] Preferably, the period length of the superunit arrangement is P=8μm.

[0016] Preferably, in the triple rotational symmetry (C3) structure, the length of the cuboid is L=3.9μm and the width is W=1μm.

[0017] A method for designing a wavelength-controlled circular dichroic achiral metasurface includes the following steps:

[0018] S1. Determine the center point of the distribution of the meta-units, establish a coordinate system with this center point, take one of the directions of the hyper-unit plane arrangement as the x-axis, the other perpendicular direction as the y-axis, and the direction perpendicular to the hyper-plane as the z-axis.

[0019] S2. Determine the structural shape of the superunit, which consists of three cuboids with the same structure and size. The center of one end of the three cuboids coincides at a point, and they are evenly distributed along the circumference with that point as the center, forming a triple rotational symmetry (C3) structure.

[0020] S3. Determine the position of the superstructure unit in the intermediate structural layer. The center point of the superstructure unit in this layer is located at the origin of the coordinate system, and the length direction of one of the cuboids coincides with the y-axis.

[0021] S4. Determine the position of the super unit in the top structural layer. The position of the super unit in the top structural layer is translated by a distance t2 along the z-axis and rotated by θ relative to the super unit in the middle structural layer.

[0022] S5. By changing the incident light wavelength and the rotation angle θ of the meta-units in the top layer, the circular dichroism of the meta-surface can be controlled.

[0023] Preferably, the expression for the electromagnetic wave transmission circular dichroism (CDTL / CDTR) is defined as follows:

[0024]

[0025]

[0026] Among them, T RCP / RCP and T LCP / LCP Let T represent the common polarization transmission amplitudes of incident light RCP and LCP, respectively. RCP / LCP and T LCP / RCP These represent the cross-polarized transmission amplitudes of incident light as RCP and LCP, respectively.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] The metasurface of this invention adopts a non-chiral structure with symmetrical structure, requires fewer geometric parameters to be optimized, has a more intuitive control mechanism, and has a higher processing tolerance and a wider working bandwidth.

[0029] This invention employs a triple rotational symmetry structure as a metaunit, and includes two triple rotational symmetry structures in the same surface unit structure of the metaplane, which can control the circular dichroism by switching the incident light wavelength;

[0030] This invention employs a non-chiral metasurface that is insensitive to polarized light, thus avoiding the influence of polarized light. It can be used in fields such as filters, polarization imaging, and molecular chirality detection. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the present invention;

[0033] Figure 2 This is a planar schematic diagram of the present invention;

[0034] Figure 3This is a graph showing the amplitude distribution of the structure of the present invention at θ=38°;

[0035] Figure 4 This is the CDT curve of the structure of this invention at θ=38°;

[0036] Figure 5 This is a graph showing the amplitude distribution of the structure of this invention at θ=26°;

[0037] Figure 6 This is the CDT curve of the structure of this invention at θ=26°. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please refer to the accompanying drawings. This invention provides a technical solution:

[0040] A wavelength-controlled circular dichroic achiral metasurface, such as Figure 1 As shown, the structure includes, from bottom to top, a bottom metal reflective layer, a substrate dielectric layer, an intermediate structural layer, a top dielectric layer, and a top structural layer. The thickness of the bottom metal reflective layer is t=0.3μm, the thickness of the substrate dielectric layer is t1=0.26μm, the thickness of the intermediate structural layer is H1=0.3μm, the thickness of the top dielectric layer is t2=0.26μm, and the thickness of the top structural layer is H2=0.3μm.

[0041] The bottom metal reflective layer, the middle structural layer, and the top structural layer are all made of gold (Au), but the materials can also be replaced with metals such as silver, chromium, and copper; the base dielectric layer and the top dielectric layer are both made of silicon (Si).

[0042] Both the intermediate and top structural layers are composed of multiple periodically arranged metaunits with a period length of subwavelength. The metaunits are triple rotationally symmetric (C3) structures, where the period length of the metaunit arrangement is P = 8 μm.

[0043] The metasurface is divided into multiple surface unit structures. Two metaunit structures in the same surface unit structure are identical, and the position of one metaunit is rotated relative to the other metaunit by a certain angle, which is set as θ.

[0044] like Figure 1 , Figure 2As shown, the triple rotational symmetry (C3) structure consists of three cuboids of the same size that are uniformly arranged along the circumference. That is, one cuboid is rotated counterclockwise by 120° and 240° around the center O and then copied and superimposed to form one of the C3 structures in the surface unit structure. Then, this structure is translated a distance t2 along the z-axis and rotated by 26° or 38° (θ=26° / 38°) to obtain the position of the second C3 structure.

[0045] In the triple rotational symmetry (C3) structure, the length of the cuboid is L = 3.9 μm and the width is W = 1 μm.

[0046] Furthermore, the cuboid can be rotated multiple times to form multiple rotational symmetry (Cn) structures such as C5 and C7; the cuboid structure can also be replaced with arc, catenary or other shapes to form a structure.

[0047] The metasurface of this invention adopts a non-chiral structure with symmetrical structure, requires fewer geometric parameters to be optimized, has a more intuitive control mechanism, higher processing tolerance, and a wider working bandwidth.

[0048] This invention employs a triple rotational symmetry structure as a metaunit, and includes two triple rotational symmetry structures in the same surface unit structure of the metaplane, and can control the circular dichroism by switching the incident light wavelength.

[0049] The above-mentioned design method for metasurfaces includes the following steps:

[0050] S1. Determine the center point of the hyperstructure distribution. Establish a coordinate system using this center point, with one direction of the hyperstructure plane arrangement as the x-axis, the other perpendicular direction as the y-axis, and the direction perpendicular to the hyperstructure plane as the z-axis. Figure 1 As shown;

[0051] S2. Determine the structural shape of the superunit, which consists of three cuboids with the same structure and size. The center of one end of the three cuboids coincides at a point, and they are evenly distributed along the circumference with that point as the center, forming a triple rotational symmetry (C3) structure.

[0052] S3. Determine the position of the superstructure unit in the intermediate structural layer. The center point of the superstructure unit in this layer is located at the origin of the coordinate system, and the length direction of one of the cuboids coincides with the y-axis.

[0053] S4. Determine the position of the superunit in the top structural layer. Its position is relative to the superunits in the intermediate structural layers, translated a distance t2 along the z-axis and rotated θ. Figure 2 As shown;

[0054] S5. By changing the incident light wavelength and the rotation angle θ of the meta-units in the top layer, the circular dichroism of the meta-surface can be controlled.

[0055] The expression for the electromagnetic wave transmission circular dichroism (CDTL / CDTR) is defined as follows:

[0056]

[0057]

[0058] Among them, T RCP / RCP and T LCP / LCP Let T represent the common polarization transmission amplitudes of incident light RCP and LCP, respectively. RCP / LCP and T LCP / RCP These represent the cross-polarized transmission amplitudes of incident light as RCP and LCP, respectively.

[0059] Depend on Figure 3 , Figure 4 It can be seen that when θ=38°, the results are similar to those of most circular dichroic metasurfaces, exhibiting strong circular dichroism in the broadband range of 10.2-10.9μm. When LCP is incident, it is converted to RCP, with a small average amplitude of 0.05.

[0060] Within this broadband range, RCP is converted to LCP upon incident, with an average amplitude of 0.36, such as Figure 3 As shown; Figure 4 The CDT distribution curves over a wide bandwidth are shown. When LCP and RCP are incident, the CDT values ​​are -0.35 and 0.35 in the range of 10.2-10.9 μm, respectively, indicating that the incident LCP light is mainly absorbed, while the RCP light is transmitted.

[0061] Depend on Figure 5 , Figure 6 It can be seen that when θ=26°, at wavelength λ1=10.2μm, LCP is converted to RCP upon incident incidence with an amplitude of 0.37, while RCP is converted to LCP upon incident incidence with a smaller amplitude of 0.04. At wavelength λ2=10.9μm, LCP is converted to RCP upon incident incidence with an amplitude of 0.18, while RCP is converted to LCP upon incident incidence with a smaller amplitude of 0.49. Figure 3 As shown.

[0062] also, Figure 4 The CDT distribution curves in the 9.5-12 μm range are shown. At λ1, the CDT values ​​for LCP and RCP incident light are 0.29 and -0.29, respectively, indicating that the incident RCP light is mainly absorbed, while the LCP light is transmitted. At λ2, the CDT values ​​for LCP and RCP incident light are -0.27 and 0.27, respectively, indicating that the incident LCP light is mainly absorbed, while the RCP light is transmitted.

[0063] Therefore, the circular dichroism can be controlled by changing the incident light wavelength and the rotation angle of the top layer structure.

[0064] In summary, when LCP light is incident, it is converted into RCP light, with a larger amplitude at wavelength λ1 and a smaller amplitude at wavelength λ2, indicating stronger absorption of RCP light than LCP light. Conversely, when RCP light is incident, it is converted into RCP light, with the opposite result: a smaller amplitude at wavelength λ1 and a larger amplitude at wavelength λ2, indicating stronger absorption of LCP light than RCP light. This allows for wavelength-controlled circular dichroism switching.

[0065] The achiral metasurface of this invention, through its symmetrical design, can work equally well for any polarized light and is expected to be used in fields such as filters, polarization imaging, and molecular chirality detection.

[0066] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0067] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A wavelength-controlled circular dichroic achiral metasurface, characterized in that, It includes, from bottom to top, a bottom metal reflective layer, a base dielectric layer, an intermediate structural layer, a top dielectric layer, and a top structural layer; Both the intermediate and top structural layers are composed of multiple periodically arranged metaunits with a period length of subwavelength, and the metaunits are triple rotationally symmetric structures. The metasurface is divided into multiple surface unit structures. Two metasurface unit structures in the same surface unit structure are identical, and the position of one metasurface unit is rotated relative to the other metasurface unit, with the rotation angle set as θ. The triple rotational symmetry structure consists of three cuboids of the same size, evenly arranged along the circumference.

2. The wavelength-controlled circular dichroic achiral metasurface according to claim 1, characterized in that, The thickness of the bottom metal reflective layer is t=0.3μm, the thickness of the base dielectric layer is t1=0.26μm, the thickness of the intermediate structural layer is H1=0.3μm, the thickness of the top dielectric layer is t2=0.26μm, and the thickness of the top structural layer is H2=0.3μm.

3. The wavelength-controlled circular dichroic achiral metasurface according to claim 1, characterized in that, The bottom metal reflective layer, the middle structural layer, and the top structural layer are all made of gold.

4. The wavelength-controlled circular dichroic achiral metasurface according to claim 1, characterized in that: Both the base dielectric layer and the top dielectric layer are made of silicon.

5. The wavelength-controlled circular dichroic achiral metasurface according to claim 1, characterized in that: The arrangement period length of the metaunit is P=8μm.

6. The wavelength-controlled circular dichroic achiral metasurface according to claim 1, characterized in that: In the triple rotational symmetry structure, the length of the cuboid is L=3.9μm and the width is W=1μm.

7. A method for designing a wavelength-controlled circular dichroic chiral metasurface as described in claim 1, characterized in that, Includes the following steps: S1. Determine the center point of the distribution of the meta-units, establish a coordinate system with this center point, take one of the directions of the hyper-unit plane arrangement as the x-axis, the other perpendicular direction as the y-axis, and the direction perpendicular to the hyper-plane as the z-axis. S2. Determine the structural shape of the superunit. Its structural shape consists of three cuboids with the same structure and size. The center of one end of the three cuboids coincides at a point, and they are evenly distributed along the circumference with that point as the center, forming a triple rotational symmetry structure. S3. Determine the position of the superstructure unit in the intermediate structural layer. The center point of the superstructure unit in this layer is located at the origin of the coordinate system, and the length direction of one of the cuboids coincides with the y-axis. S4. Determine the position of the superunit in the top structural layer, which is translated by a distance t2 along the z-axis relative to the superunit in the middle structural layer, and rotated by θ. S5. By changing the incident light wavelength and the rotation angle θ of the meta-units in the top layer, the circular dichroism of the metasurface is controlled, and the value of θ is determined.

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