A design method for compact element of metasurface that produces circular dichroism spectrum

Abstract

The present invention discloses a method for designing a compact element for generating circular dichroism metasurface, which relates to the field of electromagnetic metasurface design, including: firstly, designing and determining the meta-atom unit structure according to the electromagnetic response characteristics of two kinds of handedness circularly polarized waves after passing through the unit structure, and the meta-atom phase compensation requirements; then ensuring the narrow distribution of the spectrum line in space, thereby determining the phase compensation distribution requirements of the left-handed circularly polarized wave and the right-handed circularly polarized wave; finally determining the combined distribution of the meta-atom unit, thereby designing a compact element for generating circular dichroism metasurface. The present invention can realize polarization testing and spectrum testing at the same time, and utilizes the arrangement of the meta-atoms to realize the narrow distribution of the spectrum line in space.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic supersurface design, and in particular to a method for designing a compact element of a supersurface that generates circular dichroism spectra. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Spectrum analyzer is an important instrument based on spectrum modulation, and dispersion spectrum analyzer is an important branch of spectrum analyzer. Dispersion spectrum analyzer usually consists of the following four parts: wave source, collimation system, dispersion element and detector.

[0004] In recent years, miniature spectrometer systems have been fully developed and can be used in a variety of handheld, portable and integrated applications, including soil and crop analysis, food industry production line monitoring, and marine / underwater scientific research, where the goal is usually to obtain indicative, immediate results on site rather than transporting samples to a laboratory for ultra-high resolution analysis. To further miniaturize spectrometers, sub-wavelength gratings and sub-millimeter metasurfaces offer the possibility of development.

[0005] Metasurfaces are two-dimensional metamaterials whose electromagnetic response can be characterized by conductivity and magnetic polarizability. In some literature, they are also called ultrathin films. Metasurfaces and metamaterials have the same electromagnetic interaction. When electromagnetic waves are incident on metasurfaces, electric dipole moments and magnetic dipole moments are generated due to the polarization effect of the material itself, forming an electromagnetic response. Based on the above conditions, metasurfaces can achieve the electromagnetic response of huge structures on single-layer films.

[0006] Currently, traditional spectrometers can only arrange the spatial positions of electromagnetic waves in order of frequency or wavelength, but cannot arrange them according to polarization states. To solve this problem, the present invention combines spectral dispersion detection with polarization testing, and proposes a design method for a metasurface element that can achieve both purposes simultaneously, thereby deriving a design method for a circular dichroism dispersion element. Summary of the invention

[0007] The purpose of the present invention is to: in view of the problems existing in the current technology, on the one hand, provide a meta-atom that can simultaneously realize different phase compensation for left-hand circularly polarized waves and right-hand circularly polarized waves, and on the other hand, by determining the phase compensation distribution of left-hand circularly polarized waves and right-hand circularly polarized waves, determine the arrangement of certain geometric structure parameters in the meta-atom, thereby deriving an element that can produce different phase compensation distributions for circularly polarized waves of two different rotation directions, thereby solving the above problems.

[0008] The technical solution of the present invention is as follows:

[0009] A method for designing a compact element on a metasurface that generates circular dichroism spectra, comprising:

[0010] Step S1: designing and determining the meta-atom unit structure according to the electromagnetic response characteristics of two kinds of circularly polarized waves after passing through the unit structure and the meta-atom phase compensation requirements;

[0011] Step S2: ensuring the narrow distribution of the spectrum lines in space, thereby determining the phase compensation distribution requirements of the left-hand circularly polarized wave and the right-hand circularly polarized wave;

[0012] Step S3: Combine step S1 and step S2 to determine the binding distribution of the meta-atomic units, so as to design a compact element capable of producing a circular dichroism metasurface.

[0013] Furthermore, the meta-atom unit structure comprises:

[0014] A dipole is formed by two nanorods with different rotation directions, and the two rotation angles are controlled to control the phase compensation of left-handed circularly polarized waves and right-handed circularly polarized waves.

[0015] Furthermore, the compensation method of phase compensation by nanorods is as follows:

[0016]

[0017] Among them, E LCP represents the electric field of left-hand circularly polarized wave, E RCP represents the electric field of the right-hand circularly polarized wave, θ represents the handedness angle of the nanorod, j represents a natural imaginary number, and e represents a natural logarithm;

[0018] Output electric field E out The phase compensation change is shown as follows:

[0019] E out =e 2jθ E LC e LC +e -2jθ E RC e RC

[0020] Among them, e LC and e RC They represent the basis of left-hand circularly polarized waves and right-hand circularly polarized waves respectively.

[0021] Furthermore, the step S2 comprises:

[0022] According to the distribution of narrow positions of spatial spectral lines and the phase compensation requirements of meta-atoms, the required phase compensation distribution requirements for electromagnetic waves of different rotation directions after passing through the components are determined.

[0023] Furthermore, in order to meet the compact requirement of spectral line distribution in space, a phase compensation distribution function of off-axis focusing is proposed. The specific formula is expressed as follows:

[0024]

[0025] in, represents the phase compensation distribution, r represents the distance from the element atom to the center of the element, and f 0 represents the center frequency of the spectrum line distribution, (x, y, z) represents the position of any point in the space of the right-hand rectangular coordinate system, c represents the speed of electromagnetic wave propagation in a vacuum, and π is the pi constant;

[0026] Spectral line distribution position coordinates (x F ,y F , z F ) and the focal length F satisfy the following relationship:

[0027]

[0028] In order to make the left-hand circularly polarized wave and the right-hand circularly polarized wave distributed on both sides of the space, the phase distribution function is:

[0029]

[0030] in, and They represent left-hand circularly polarized waves in space. and right-hand circularly polarized waves Phase compensation distribution after the component, Indicates the central wavelength of the distribution spectrum.

[0031] Furthermore, the step S3 comprises:

[0032] Combining the requirements of meta-atom phase compensation and phase compensation distribution, the periodic arrangement of certain geometric parameters of meta-atoms is determined, and based on this, a compact element of the metasurface that can produce circular dichroism spectra is designed.

[0033] Furthermore, the handedness angle distribution of the two nanopillars of the meta-atom is:

[0034]

[0035] Among them, θ 1 and θ 2 Represent the handedness angles of the two nanorods respectively.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention realizes spectral dispersion by designing a periodic arrangement structure of micro-thin film units and utilizing the characteristic that phase compensation is independent of the wavelength of electromagnetic waves; at the same time, polarization detection is realized by utilizing the different phase compensations of left-handed circularly polarized waves and right-handed circularly polarized waves passing through the unit structure designed by the present invention; the present invention combines the characteristics of both designs to realize circular dichroism for the first time.

[0038] 2. The present invention can simultaneously realize polarization testing and spectrum testing, and utilize the arrangement of meta-atoms to achieve a narrow distribution of spectral lines in space. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flow chart of a method for designing a compact element of a metasurface that produces circular dichroism spectra;

[0040] Figure 2 This is the isometric view of the designed meta-atom;

[0041] Figure 3 The top view of the designed dispersion element;

[0042] Figure 4 is an isometric view of a dispersive element of an example;

[0043] Figure 5 Axonometric view of the dispersion element of the example. DETAILED DESCRIPTION

[0044] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0045] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0046] Embodiment 1

[0047] See also Figure 1 A method for designing a compact element of a metasurface that generates circular dichroism spectra comprises the following steps:

[0048] Step S1: designing and determining the meta-atom unit structure according to the electromagnetic response characteristics of two kinds of circularly polarized waves after passing through the unit structure and the meta-atom phase compensation requirements;

[0049] Step S2: ensuring the narrow distribution of the spectrum lines in space, thereby determining the phase compensation distribution requirements of the left-hand circularly polarized wave and the right-hand circularly polarized wave;

[0050] Step S3: Combine step S1 and step S2 to determine the binding distribution of the meta-atomic units, so as to design a compact element capable of producing a circular dichroism metasurface.

[0051] In this embodiment, it should be noted that the meta-atom refers to a unit structure that constitutes the entire metasurface.

[0052] In this embodiment, specifically, the meta-atom unit structure includes:

[0053] A dipole is composed of two rectangular nanorods with different rotation directions, and the two rotation angles are controlled to control the phase compensation of left-handed circularly polarized waves and right-handed circularly polarized waves.

[0054] In this embodiment, specifically, in order to achieve phase compensation of circularly polarized waves of two different handednesses, the compensation method of phase compensation by nanorods is as follows:

[0055]

[0056] Among them, E LCP represents the electric field of left-hand circularly polarized wave, E RCP represents the electric field of the right-hand circularly polarized wave, θ represents the handedness angle of the nanorod, j represents a natural imaginary number, and e represents a natural logarithm;

[0057] Output electric field E out The phase compensation change is shown as follows:

[0058] E out =e 2jθ E LC e LC +e -2jθ E RC e RC

[0059] Among them, e LC and e RC They represent the basis of left-hand circularly polarized waves and right-hand circularly polarized waves respectively.

[0060] It should be noted that the meta-atom designed in the present invention includes two kinds of rotation angles (θ 1 ,θ 2 ) of a rectangular nanorod, the phase compensation method is:

[0061] The compensation methods for left-hand circularly polarized waves and right-hand circularly polarized waves are:

[0062]

[0063] Therefore, if Figure 2 As shown, the phase compensation of the meta-atom (i.e., the dipole) for left-hand rotation and right-hand rotation is shown in the above formula.

[0064] In this embodiment, specifically, step S2 includes:

[0065] According to the distribution of narrow positions of spatial spectral lines and the phase compensation requirements of meta-atoms, the required phase compensation distribution requirements for electromagnetic waves of different rotation directions after passing through the components are determined.

[0066] In this embodiment, specifically, in order to meet the compact requirement of spectral line distribution in space, a phase compensation distribution function of off-axis focusing is proposed, and the specific formula is expressed as follows:

[0067]

[0068] in, represents the phase compensation distribution, r represents the distance from the element atom to the center of the element, and f 0 represents the center frequency of the spectrum line distribution, (x, y, z) represents the position of any point in the space of the right-hand rectangular coordinate system, c represents the speed of electromagnetic wave propagation in a vacuum, and π is the pi constant;

[0069] In the above formula, the coordinates of the spectral line distribution position (x F ,y F , z F ) and the focal length F satisfy the following relationship:

[0070]

[0071] In order to make the left-hand circularly polarized wave and the right-hand circularly polarized wave distributed on both sides of the space, the phase distribution function is:

[0072]

[0073] in, and They represent two circularly polarized waves with different rotation directions in space (left-hand circularly polarized waves and right-hand circularly polarized waves Phase compensation distribution after the component, Indicates the central wavelength of the distribution spectrum.

[0074] In this embodiment, specifically, step S3 includes:

[0075] Combining the requirements of meta-atom phase compensation and phase compensation distribution, the periodic arrangement of certain geometric parameters of meta-atoms is determined, and based on this, a compact element of the metasurface that can produce circular dichroism spectra is designed.

[0076] In this embodiment, specifically, the handedness angle distribution of the two nanopillars of the meta-atom is:

[0077]

[0078] Among them, θ 1 and θ 2 Represent the handedness angles of the two nanorods respectively.

[0079] Embodiment 2

[0080] See also Figure 1-Figure 5 , in order to solve the problem that the geometric phase element surface can only focus electromagnetic waves of one polarization state, such as Figure 1 As shown, the nanoantenna is composed of Si material, and the dipole carrier is composed of two identical nanocolumns, where px=700um, py=350um, h1=800um, and h2=280um.

[0081] The focal positions of the left-hand circularly polarized wave and the right-hand circularly polarized wave are (x_F, y_F, z_F) and (-x_F, y_F, z_F), respectively, where y_F = 1mm, x_F = 0um, z_F = 10mm, which are the focal points of the LCP wave and the RCP wave on both sides. F represents the focal length of the off-axis focus and represents the design wavelength.

[0082] According to the phase compensation characteristics of the geometric phase plane, the rotation angle distribution of the two pairs of dipoles and the z-axis can be obtained.

[0083] Therefore, the observation planes of the spectral lines are located at y F = ±1um, the spectral lines are analyzed on the off-axis planes on both sides to obtain the circular dichroism spectrum.

[0084] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0085] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A method for designing a compact element for a metasurface that generates circular dichroism spectra, characterized in that: include: Step S1: designing and determining the meta-atom unit structure according to the electromagnetic response characteristics of two kinds of circularly polarized waves after passing through the unit structure and the meta-atom phase compensation requirements; Step S2: ensuring the narrow distribution of the spectrum lines in space, thereby determining the phase compensation distribution requirements of the left-hand circularly polarized wave and the right-hand circularly polarized wave; Step S3: Combine step S1 and step S2 to determine the binding distribution of the meta-atomic units, so as to design a compact element capable of producing a circular dichroism metasurface.

2. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 1, characterized in that: The meta-atom unit structure comprises: A dipole is formed by two nanorods with different rotation directions, and the two rotation angles are controlled to control the phase compensation of left-handed circularly polarized waves and right-handed circularly polarized waves.

3. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 2, characterized in that: The compensation method for phase compensation by nanorods is as follows: Among them, E LCP represents the electric field of left-hand circularly polarized wave, E RCP represents the electric field of the right-hand circularly polarized wave, θ represents the handedness angle of the nanorod, j represents a natural imaginary number, and e represents a natural logarithm; Output electric field E out The phase compensation change is shown as follows: AND out =and 2jθ AND LC And LC +e -2jθ AND RC And RC Among them, e LC and e RC They represent the basis of left-hand circularly polarized waves and right-hand circularly polarized waves respectively.

4. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 2, characterized in that: The step S2 comprises: According to the distribution of narrow positions of spatial spectral lines and the phase compensation requirements of meta-atoms, the required phase compensation distribution requirements for electromagnetic waves of different rotation directions after passing through the components are determined.

5. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 4, characterized in that: In order to meet the compact requirements of spectral line distribution in space, the phase compensation distribution function of off-axis focusing is proposed. The specific formula is expressed as follows: in, represents the phase compensation distribution, r represents the distance from the element atom to the center of the element, f0 represents the center frequency of the spectrum line distribution, (x, y, z) represents the position of any point in the space of the right-hand rectangular coordinate system, c represents the speed of electromagnetic wave propagation in vacuum, and π is the pi constant; Spectral line distribution position coordinates (x F ,y F , z F ) and the focal length F satisfy the following relationship: In order to make the left-hand circularly polarized wave and the right-hand circularly polarized wave distributed on both sides of the space, the phase distribution function is: in, and They represent left-hand circularly polarized waves in space. and right-hand circularly polarized waves Phase compensation distribution after the component, Indicates the central wavelength of the distribution spectrum.

6. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 5, characterized in that: The step S3 comprises: Combining the requirements of meta-atom phase compensation and phase compensation distribution, the periodic arrangement of certain geometric parameters of meta-atoms is determined, and based on this, a compact element of the metasurface that can produce circular dichroism spectra is designed.

7. The method for designing a compact element for generating a circular dichroism spectrum metasurface according to claim 6, characterized in that: The handedness angle distribution of the two nanopillars of the meta-atom is: Where θ1 and θ2 represent the handedness angles of the two nanorods, respectively.

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