Phase and amplitude cooperative regulation and control method based on double-layer transmission phase super-structure lens

Abstract

The invention discloses a phase and amplitude coordinated regulation and control method based on a double-layer transmission phase metamaterial lens, two layers of metamaterial lenses are stacked up and down to construct the double-layer transmission phase metamaterial lens, and an upper subunit structure and a lower subunit structure in the double-layer transmission phase metamaterial lens correspond up and down to form a super-unit structure; according to the total phase and the total amplitude required by the super-unit structure, the amplitudes and phases of the upper and lower subunit structures and the width of the nano-column are obtained respectively, and according to the relation between the total amplitude and the total phase and the amplitude of the lower subunit structure and the relation between the total phase and the phase of the upper subunit structure, the amplitude and the phase of the super-unit structure are subjected to double-parameter separation regulation and control; on the basis of a single-layer polarization insensitive super-structure lens, an amplitude regulation and control layer is added, a double-layer transmission phase super-structure lens theoretical model is provided, simultaneous coordinated regulation and control of amplitude and phase are achieved, and the dimension of super-structure surface parameter regulation and control is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurface lens regulation, and particularly to a method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens. Background Art

[0002] Lenses are important components widely used in optical systems. Compared with traditional lenses, lenses based on metasurfaces have the characteristics of being ultra-light, ultra-thin, and planar. Starting from the metasurface lens constructed by V-shaped metal nanostructures proposed by researchers in the early stage, to the dielectric metasurface lens based on the geometric phase principle, its types have been continuously enriched, and its functions have also developed towards intelligent and multi-functional directions. Currently, the phase regulation principles of metasurface lenses include transmission phase, resonant phase, and geometric phase principles. The metasurface lens designed based on single-layer geometric phase can focus incident RCP / LCP light, but diverges incident LCP / RCP light. Therefore, the metasurface lens designed using anisotropic nanostructures has specific requirements for the polarization state of incident light, so it can only work under a given circular polarization state, that is, it has the characteristic of polarization sensitivity.

[0003] To address this defect, based on the transmission phase principle and square dielectric nanorod structures, a polarization-insensitive metasurface lens can be designed in the visible light band, that is, the focusing effects of incident LCP and RCP light are the same. For a single-layer polarization-insensitive metasurface lens, each unit structure that makes up the lens is mainly used to regulate the phase required for focusing, and cannot arbitrarily regulate the amplitude at the same time. On the contrary, the amplitude needs to be kept as consistent as possible to achieve a good focusing effect. When the height of the nanorod is determined, the amplitudes of each unit structure should be as large as possible and the amplitude fluctuations should be small. However, it is not easy to achieve a decreasing gradient of amplitude while ensuring 2π phase coverage for single-layer metasurface devices. In this case, it is impossible to accurately regulate the amplitude size under polarization-insensitive conditions. In addition, some research results have achieved the regulation of both the amplitude and phase of metasurface devices, but these regulations all introduce the geometric phase principle. Therefore, when working under polarization-sensitive conditions, it is necessary to work under the condition of given circularly polarized light. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens. Based on a single-layer polarization-insensitive metasurface lens, an amplitude regulation layer is added, and a theoretical model of a double-layer transmission phase metasurface lens is proposed to achieve the collaborative regulation of amplitude and phase.

[0005] To solve the above technical problems, a technical solution provided by the present invention is: a method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens, characterized in that:

[0006] A double - layer transmissive - phase metasurface lens is constructed by stacking two layers of metasurface lenses on top of each other, and the upper and lower sub - unit structures in the double - layer transmissive - phase metasurface lens correspond to each other up and down to form a super - unit structure;

[0007] According to the total phase and total amplitude required by the super - unit structure, the amplitudes and phases of the upper and lower sub - unit structures are obtained respectively, and the double - parameter separation regulation of the amplitude and phase of the super - unit structure is carried out according to Formula (1) and Formula (2). Formula (1) and Formula (2) are as follows:

[0008]

[0009] T=t1t2 (2)

[0010] In the formula: Ф is the total phase of the super - unit structure, is the phase of the lower - layer sub - unit structure, is the phase of the upper - layer sub - unit structure, T is the total amplitude of the super - unit structure, t1 is the amplitude of the lower - layer sub - unit structure, and t2 is the amplitude of the upper - layer sub - unit structure.

[0011] Furthermore, both layers of metasurface lenses are single - layer transmissive - phase polarization - insensitive metasurface lenses.

[0012] Furthermore, the upper and lower sub - unit structures both include square nanocolumns and substrates; the height of the square nanocolumns in the lower - layer metasurface lens is H1, and the width is W1, and the height of the square nanocolumns in the upper - layer metasurface lens is H2, and the width is W2.

[0013] Furthermore, the square nanocolumns are made of TiO2 material, the height H1 of the lower - layer nanocolumns is 400 nm, and the height H2 of the upper - layer nanocolumns is 600 nm.

[0014] Furthermore, the distance between the square nanocolumns in the upper and lower sub - unit structures is d, and the size of d should be appropriate to prevent coupling and divergence effects between the two layers.

[0015] Furthermore, the incident light is LCP light, and the working wavelength of the incident light is 532 nm.

[0016] Furthermore, the process of double - parameter separation regulation of the amplitude and phase of the super - unit structure is as follows: the amplitude t2 of the upper - layer sub - unit structure of the super - unit structure remains unchanged, and the total amplitude T is regulated by the amplitude t1 of the lower - layer sub - unit structure. Among them, the change of the amplitude t1 from 0 to 1 is obtained by changing the width W1 of the square nanocolumns in the lower - layer sub - unit structure; the phase of the lower - layer sub - unit structure of the super - unit structure remains unchanged, and the total phase Ф is regulated by the phase of the upper - layer sub - unit structure. Among them, the phase from 0 to 2π is obtained by changing the width W2 of the square nanocolumns in the upper - layer sub - unit structure The change achieves the dual-parameter separation control of the amplitude and phase of the supercell structure.

[0017] Furthermore, during the process of controlling the phase by the width W2 of the square nanocolumns in the upper subunit structure, the width W2 of the square nanocolumns in the upper subunit structure is not equal to 136 nm.

[0018] Another technical solution provided by the present invention is: a multi-focus intensity tunable metasurface lens array, including a double-layer transmission phase metasurface lens constructed according to the above method, characterized in that: double-layer transmission phase metasurface lenses with different focus intensities are cascaded together to form a multi-focus intensity tunable metasurface lens array.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. Based on the polarization-insensitive metasurface lens with single-layer transmission phase, this application adds an amplitude control layer. According to the fact that the total amplitude of the supercell structure is equal to the product of the amplitudes of the upper and lower subunit structures, and the total phase is equal to the sum of the phases of the upper and lower subunit structures, the dual-parameter collaborative control of the phase and amplitude is realized, and the design difficulty of the double-layer metasurface lens is reduced. At the same time, by optimizing the size of the subunit structure of the amplitude control layer to achieve the adjustment of the transmittance from 0 to 1, a multi-focus lens array with simultaneous collaborative control of the amplitude and phase dual-parameters is designed. Through the simultaneous collaborative control of the double-layer metasurface, the multi-point focusing characteristics with different beam splitting ratios can be realized, and the incident light can be focused at any position in space, and the ratio of the focus intensities is tunable, which has important application potential in the fields of imaging, information detection, optical communication, biomedical and optical system integration.

[0021] 2. The lower metasurface lens in this application is composed of subunit structures with the same nanocolumn structure size, that is, the height is all H1 and the width is all W1. Therefore, the phases and amplitudes corresponding to these nanocolumn structures are also the same. When the width is changed, an amplitude change from 0 to 1 (i.e., adjusting the transmittance) can be obtained; the height H2 of the nanocolumns in the subunit structure of the upper metasurface lens remains unchanged, and when the width W2 changes, a phase control covering 0 to 2π can be obtained, and the amplitude can be kept basically consistent at the same time; when the incident light remains unchanged, if it is desired to design a lens with a tunable focus intensity, the width W1 of the lower nanocolumns can be changed to adjust the amplitude; at the same time, when the width of the lower nanocolumns changes, the phase shift generated can be offset by the upper nanocolumns adjusting their own widths, realizing the dual-parameter collaborative control of the phase and amplitude.

[0022] 3. In the present application, the upper and lower layers of the metasurface lens can be separated from each other, and the individual parameter scans of W1 of the lower layer structure and W2 of the upper layer structure can be performed respectively, which can avoid the huge computational amount generated by the simultaneous parameter scan of the double-layer supercell structures W1 and W2, improve the design efficiency, and the computational amount required by the present application is much smaller, thereby reducing the difficulty of designing the double-layer metasurface.

[0023] In order to make the above and other objects, features and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given, and in conjunction with the accompanying drawings, the detailed description is as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only five of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0025] Figure 1 Structural diagram of a metasurface lens for amplitude and phase co-regulation of double-layer transmission phase;

[0026] Figure 2 Simulation diagram of the unit structure of the amplitude regulation layer;

[0027] Figure 3 Relationship verification diagram between the supercell structure and the subunit structure;

[0028] Figure 4 Comparison diagram of the total phase and total amplitude of the supercell structure with the sum of the phases and the product of the amplitudes of the two-layer subunit structures when W1 is equal to 186 nm and W2 changes;

[0029] Figure 5 Focusing effect and electric field energy intensity distribution diagram of the designed three-focus metasurface lens array with simultaneous amplitude and phase co-regulation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not used to limit the protection scope of the present invention.

[0031] Embodiment

[0032] As Figure 1As shown, a method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens is provided, characterized in that:

[0033] A double-layer transmission phase metasurface lens is constructed by stacking two single-layer metasurface lenses on top of each other, and the upper and lower sub-unit structures of the double-layer transmission phase metasurface lens correspond to each other up and down to form a super-unit structure;

[0034] According to the total phase and total amplitude required by the super-unit structure, the amplitudes and phases of the upper and lower sub-unit structures are respectively obtained, and the double-parameter separation regulation of the amplitude and phase of the super-unit structure is carried out according to formula (1) and formula (2). Formula (1) and formula (2) are as follows:

[0035]

[0036] T = t1t2 (2)

[0037] In the formula: Ф is the total phase of the super-unit structure, is the phase of the lower sub-unit structure, is the phase of the upper sub-unit structure, T is the total amplitude of the super-unit structure, t1 is the amplitude of the lower sub-unit structure, and t2 is the amplitude of the upper sub-unit structure.

[0038] Among them, both of the two single-layer metasurface lenses are polarization-insensitive metasurface lenses with single-layer transmission phase. The up-and-down setting method of the two single-layer transmission phase polarization-insensitive metasurface lenses is as Figure 1 (a) shown; the schematic diagram of the "super-unit structure" composed of two layers of sub-unit structures is as Figure 1 (b) shown. The upper and lower sub-unit structures both include square nanocolumns and substrates. The square nanocolumns are made of TiO2 material; the height of the square nanocolumns in the lower metasurface lens is H1, the width is W1, the height of the square nanocolumns in the upper metasurface lens is H2, and the width is W2.

[0039] Among them, the height H2 of the nanocolumns in the upper sub-unit structure of the super-unit structure is 600 nm. By changing the width of the nanocolumns, a phase coverage range of 0 to 2π can be obtained, and the amplitudes are all above 90%. Therefore, the optimization of the upper sub-unit structure is no longer discussed; the amplitude regulation layer formed by the lower sub-unit structure is designed below.

[0040] The lower sub-unit structure that regulates the total amplitude of the super-unit structure is optimized and simulated to obtain a continuous change in the regulation of the amplitude from 0 to 1 range. As Figure 2 (a) shown, it is a schematic diagram of the lower unit structure of the double-layer metasurface lens. This structure is optimized and simulated to screen out a suitable nanocolumn height to ensure that the amplitude regulation range can be satisfied. The incident light is LCP light, and the working wavelength is 532 nm. As Figure 2(b) and (c) show the amplitude and phase data distributions of the LCP transmitted light with the same polarization state when W1 varies from 60 to 260 nm and H1 varies from 300 to 450 nm respectively. To achieve continuous regulation of the amplitude of the supercell structure, it is necessary to design the amplitude of the lower-layer unit structure to cover the range of 0 to 1. Therefore, as can be seen from the dashed line marked in Figure 2 (d), when H1 is 400 nm, the regulation of the amplitude can cover the range from 0 to 1, that is, the transmittance is also continuously adjustable from 0 to 1.

[0041] Next, analyze the relationship between the supercell structure and the upper and lower sub-unit structures.

[0042] Figure 3 In (a) and (b), they are respectively the sum of the phase mutations generated by the lower-layer and upper-layer sub-unit structures when the widths W1 and W2 change, and the product of the amplitudes t1 and t2. And the sum of the phase mutations generated by the lower-layer and upper-layer sub-unit structures when the widths W1 and W2 change, and the product of the amplitudes t1 and t2. Figure 3 In (c) and (d), taking the overall supercell structure as the object, the total phase Ф and total amplitude T obtained by simulation. Comparing the phase and amplitude results obtained in the two cases, it can be seen that the total phase and total amplitude obtained by the two methods are basically the same. Design the upper and lower sub-unit structures separately, and then according to the total phase and total amplitude required by the double-layer supercell structure, and then use formulas (1) and (2) to combine the upper and lower sub-unit structures, so as to achieve arbitrary simultaneous regulation of the amplitude and phase of the supercell structure.

[0043] Among them, the spacing distance d between the square nanocolumns in the upper and lower sub-unit structures should be appropriate so that no coupling and divergence effects occur between the two layers.

[0044] The process of separating and regulating the amplitude and phase dual parameters of the supercell structure is as follows: the amplitude t2 of the upper sub-unit structure of the supercell structure remains unchanged, and the total amplitude T is regulated by the amplitude t1 of the lower sub-unit structure. Among them, the amplitude t1 change from 0 to 1 is obtained by changing the width W1 of the square nanocolumn in the lower sub-unit structure; the phase of the lower sub-unit structure of the supercell structure remains unchanged, and the total phase Ф is regulated by the phase of the upper sub-unit structure Among them, the phase change from 0 to 2π is obtained by changing the width W2 of the square nanocolumn in the upper sub-unit structure, achieving the separation and regulation of the amplitude and phase dual parameters of the supercell structure. Among them, in the process of regulating the phase by the width W2 of the square nanocolumn in the upper sub-unit structure, the width W2 of the square nanocolumn in the upper sub-unit structure is not equal to 136 nm.

[0045] Among them, in the process of regulating the phase by the width W2 of the square nanocolumn in the upper sub-unit structure, the width W2 of the square nanocolumn in the upper sub-unit structure is not equal to 136 nm. Among them, in the process of regulating the phase by the width W2 of the square nanocolumn in the upper sub-unit structure, the width W2 of the square nanocolumn in the upper sub-unit structure is not equal to 136 nm.

[0046] Figure 4In (a) and (b), when the width W1 and amplitude t1 of the lower-layer nanocolumns are determined to be 186 nm and 0.69, and the width W2 of the upper-layer nanocolumns varies from 50 to 200 nm, the comparison results of the phase and amplitude obtained according to the above two methods are shown respectively. Consistent with the previous theoretical analysis, that is, by designing the upper and lower sub-unit structures respectively, and then combining them using formulas (1) and (2) to obtain the total phase and total amplitude ( Figure 4 (shown by the dashed lines in (a) and (b)), is consistent with the total phase and total amplitude obtained by directly designing the meta-unit structure ( Figure 4 (the solid lines in (a) and (b))), with a tiny error. However, an obvious abnormal point can be seen in the figure, located at W2 equal to 136 nm. The generation of this abnormal point is due to the phase mutation caused by the strong mode resonance of the nanocolumns at this time, which does not conform to the combination principle of the double-layer transmission phase structure. Therefore, the selection of such nanocolumns needs to be avoided.

[0047] Another technical solution provided by the present invention is: a multi-focus intensity tunable metasurface lens array, including a double-layer transmission phase metasurface lens constructed according to the above method, characterized in that: double-layer transmission phase metasurface lenses with different focus intensities are cascaded together to form a multi-focus intensity tunable metasurface lens array.

[0048] Under the condition of the same incident light beam, the three focus intensities of the lens array can be freely adjusted by the lower metasurface. For each lens, its lower metasurface is composed of unit structures of the same size, and the same unit structures have the same amplitude and phase; the amplitudes of the upper-layer unit structures are basically the same, and the phase can be adjusted by changing W2 to achieve the focusing design. If it is necessary to adjust the different focus intensities of the lens array, the total amplitude size (i.e., the transmittance) can be adjusted by changing the width W1 of the lower-layer nanocolumns, while adjusting the width W2 of the upper-layer nanocolumns to meet the lens focusing phase requirements.

[0049] As Figure 5 (a) shows, it is the focusing effect of the designed three-focus metasurface lens array with simultaneous coordinated regulation of amplitude and phase. It can be seen from the figure that a beam of incident light is divided into three beams by three lenses, and then focused at three focal points respectively, and the focus intensities are all different. The widths of the lower-layer nanocolumns of the left, middle and right lenses are designed to be 186, 96 and 178 nm respectively, and the amplitude ratio is 0.71:1:0.57. Figure 5(b) shows the extracted electric field energy intensity distribution along the focal planes of the three foci. The intensity ratios of the left, middle, and right lens foci are 0.46:1:0.36. The obtained focal intensity ratios are also consistent with the trend of the amplitude ratios of the lower-layer unit structures of the left, middle, and right lenses. The FWHM (Full Width at Half Maximum) of the left lens focus is 540 nm, which is close to the incident light wavelength of 532 nm; the FWHMs of the middle and right lens foci are 430 and 520 nm respectively. Thus, a sub-wavelength focusing effect is achieved. The above analysis results show that the proposed and designed three-focus metasurface lens array still has good focusing performance. Through the above research, this paper uses the proposed double-layer transmission phase metasurface design theory to achieve a method of coordinated regulation of amplitude and phase.

[0050] Based on a single-layer polarization-insensitive metasurface lens, this application adds an amplitude regulation layer and proposes a theoretical model of a double-layer transmission phase metasurface lens to achieve simultaneous coordinated regulation of amplitude and phase, expanding the dimension of metasurface parameter regulation. The research results show that the total amplitude of the supercell structure is equal to the product of the amplitudes of the upper and lower sub-cell structures, and the total phase is equal to the sum of the phases of the upper and lower sub-cell structures, demonstrating the effectiveness and universality of the proposed method. The proposed design method can not only achieve simultaneous coordinated regulation of the two parameters of amplitude and phase but also reduce the difficulty of designing a double-layer metasurface lens. In addition, by optimizing the unit structure size of the amplitude regulation layer to achieve the adjustment of the transmittance from 0 to 1, a multi-focus lens array with simultaneous coordinated regulation of amplitude and phase is designed, and the multi-point focusing characteristics with different beam splitting ratios are achieved through simultaneous coordinated regulation of the double-layer metasurface. The multi-focus metasurface lens array mode proposed and designed in this paper can focus the incident light at arbitrary positions in space, and the ratio of the focal intensities is tunable, having important application potential in the fields of imaging, information detection, optical communication, biomedicine, and optical system integration.

[0051] The descriptions of the above embodiments tend to emphasize the differences between the embodiments. Their similarities can be referred to each other. For the sake of brevity, this application will not elaborate further.

[0052] Note that the above are only the preferred embodiments of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments here. Various obvious changes, re-adjustments, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens, characterized in that: A double-layer transmission phase metasurface lens is constructed by stacking two layers of metasurface lenses up and down, and the upper and lower sub-unit structures in the double-layer transmission phase metasurface lens correspond to each other up and down to form a super-unit structure; According to the total phase and total amplitude required by the super-unit structure, the amplitudes, phases and nano-pillar widths of the upper and lower sub-unit structures are respectively obtained, and the double-parameter separation regulation of the amplitude and phase of the super-unit structure is carried out according to formula (1) and formula (2). Formula (1) and formula (2) are as follows: T = t1t2 (2) Where: Ф is the total phase of the super-element structure, is the phase of the lower sub-element structure, is the phase of the upper sub-element structure, T is the total amplitude of the super-element structure, t1 is the amplitude of the lower sub-element structure, and t2 is the amplitude of the upper sub-element structure.

2. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 1, characterized in that: Both layers of metasurface lenses are polarization-insensitive metasurface lenses with single-layer transmission phase.

3. A method for collaborative regulation of phase and amplitude based on a double - layer transmission phase metasurface lens according to claim 1, characterized in that: The upper and lower sub-unit structures both include square nano-pillars and substrates; the height H1 and width W1 of the square nano-pillars in the lower metasurface lens are the same, and the height H2 and width W2 of the square nano-pillars in the upper metasurface lens are the same.

4. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 3, characterized in that: The square nano-pillars are made of TiO2 material, the height H1 of the lower nano-pillars is 400 nm, and the height H2 of the upper nano-pillars is 600 nm.

5. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 4, characterized in that: The spacing distance between the square nano-pillars in the upper and lower sub-unit structures is d, and the size of d should be appropriate to prevent coupling and divergence effects between the two layers.

6. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 4, characterized in that: The incident light is LCP light, and the working wavelength of the incident light is 532 nm.

7. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 1, characterized in that: The process of separating and regulating the amplitude and phase dual parameters of the supercell structure is as follows: the amplitude t2 of the upper subunit structure of the supercell structure remains unchanged, and the total amplitude T is regulated by the amplitude t1 of the lower subunit structure. Among them, the amplitude t1 change from 0 to 1 is obtained by changing the width W1 of the square nanocolumn in the lower subunit structure; the phase of the lower subunit structure of the supercell structure remains unchanged, and the total phase Ф is regulated by the phase of the upper subunit structure Among them, the phase change from 0 to 2π is obtained by changing the width W2 of the square nanocolumn in the upper subunit structure change, achieving the separation and regulation of the amplitude and phase dual parameters of the supercell structure.

8. A method for collaborative regulation of phase and amplitude based on a double-layer transmission phase metasurface lens according to claim 7, characterized in that: During the process of regulating the phase by the width W2 of the square nanocolumns in the upper subunit structure the width W2 of the square nanocolumns in the upper subunit structure is not equal to 136 nm.

9. A multi-focus intensity tunable metasurface lens array, comprising a double-layer transmission phase metasurface lens constructed according to the method described in any one of the above claims 1-8, characterized in that: Double-layer transmission phase metasurface lenses with different focal intensities are cascaded together to form a metasurface lens array with tunable multi-focal intensities.

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