Wavelength and polarization multiplexing super-structure lens construction method based on double-layer geometric phase

Abstract

The invention discloses a wavelength and polarization multiplexing super-structure lens construction method based on a double-layer geometric phase, and provides a double-layer geometric phase super-structure surface theoretical model by using a super-structure based on an artificial micro-nano structure, and designs a lens structure of which two working wavelengths and two polarization modes can be regulated and controlled at will by using the model. The working principle of the double-layer geometric phase super-structure lens is elaborated; secondly, optimizing and screening unit structures of the single-layer super-structure lens, establishing a unit structure database, and designing a double-layer super-unit structure on the basis of the unit structures; and finally, a double-layer super-structure lens is constructed by using a super-unit structure, so that the double-layer super-structure lens works at two wavelengths and two polarization states, and the adjustable multifunctional characteristics of dual-wavelength switchability and polarization sensitivity are realized. The method has important application prospects in the fields of dual-wavelength polarization sensitive imaging, optical tomography, sensing, new energy automobile display systems, AR / MR display and the like.

Description

Technical field:

[0001] The present invention relates to the technical field of optical lenses, and in particular to a foldable rotating quad-rotor UAV. Background technology:

[0002] Traditional optical lenses, as an indispensable tool, have been widely used in various scientific fields, such as cameras, telescopes and microscopes. Under traditional conditions, the reshaping of the light wavefront relies on changes in the surface morphology of the optical medium, such as manual cutting, grinding and polishing of the lens surface. Metalenses are constructed by arranging subwavelength metal or dielectric resonant structures according to the phase requirements of lens focusing. They are ultra-thin, lightweight and planar, making them very suitable for the integration and miniaturization of optical systems. Previous research on metalenses has relatively simple and fixed functions, so the realization of multi-functions has become the pursuit of researchers in recent years. Multifunctional metalenses often require complex theoretical and structural design methods to seek more degrees of freedom in light wave control, especially for the design of metalenses using single-layer metasurfaces.

[0003] In the study of single-layer metasurfaces, a common method to expand the spatial freedom of design parameters is to use a spatial multiplexing scheme, that is, one area of ​​the device only controls one wavelength or one polarization state. Spatially divided multiplexing interrupts the smoothness and continuity of the phase required to achieve a certain device function, thereby generating undesirable diffraction orders and performance degradation. Another method is to use the integrated unit structure method, that is, to integrate multiple nanostructures into the same single-layer unit structure, which is essentially a spatial multiplexing method. However, the spatial limitations of the unit structure of the device itself and the inevitable coupling between nanostructures limit the further application of the integrated unit method.

[0004] To this end, Y. Zhou et al. proposed a potential platform. By using closely spaced multilayer dielectric metasurfaces and applying the principle of propagation phase, they developed a novel method for designing multi-wavelength achromatic metalenses, enabling manipulation of multiple wavelengths. The research group further explored dual-layer dielectric metasurfaces to expand the design freedom of devices for light field manipulation. Independently controlling the geometry and function of each metasurface unit structure enables multifunctional development. However, such metasurfaces primarily operate under polarization-insensitive conditions. Other researchers have exploited temperature- and electrical-controlled methods to manipulate the abrupt phase transitions of the unit structures to achieve multifunctional metalenses. For example, L. Chen et al. constructed a dual-layer metalens using low-loss phase-change materials and amorphous silicon. By electrically driving the phase transition of Sb2Se3 by heating an electrically driven ITO layer, the crystalline state of the Sb2Se3 scatterer was altered, achieving electrical actuation of the Sb2Se3 phase transition. This resulted in a dual-focus metalens with arbitrary intensity in the communications C-band. S. Qin et al. combined the electro-optical material barium titanate (BTO) with geometric phase transitions to innovatively propose an electrically modulated dual-layer dual-focus metalens for the visible light band. This research, based on the electro-optic effect, can control the refractive index of BTO nanosheets between 2.4 and 3.07 by applying different voltages (0-60V), thereby achieving the purpose of using voltage to modulate the intensity ratio of the two focal points. However, these studies either operate under polarization-insensitive conditions or only operate under single wavelength conditions. Multifunctional metasurfaces and metalenses that operate simultaneously under multi-wavelength and polarization-sensitive control conditions are still rare. Summary of the invention:

[0005] The technical problem to be solved by the present invention is that in the prior art, the problem of the single function of the meta-lens needs to be solved by adopting the idea of ​​spatial multiplexing, but spatial multiplexing has the problems of redundant diffraction orders and reduced performance.

[0006] To solve the above technical problems, the present invention provides a technical solution: a method for constructing a wavelength and polarization multiplexing meta-lens based on a double-layer geometric phase, characterized by:

[0007] Step 1: Based on the design principle of half-wave plates, two groups of perfect half-wave plates are selected from multiple nanopillar structures using target light waves of two different wavelengths, ensuring that the nanopillar structures in the first group of perfect half-wave plates operate in half-wave plate mode at the first wavelength and in full-wave plate mode at the second wavelength; while the nanopillar structures in the second group of perfect half-wave plates operate in half-wave plate mode at the second wavelength and in full-wave plate mode at the first wavelength;

[0008] Step 2: Arrange the two selected perfect half-wave plates on the upper and lower surfaces of the substrate, respectively, and form a double-layer super-unit structure with two corresponding half-wave plates on the upper and lower surfaces of the substrate. Multiple double-layer super-unit structures form a double-layer meta-lens.

[0009] Step 3: Simulate the double-layer metacell structure using two target light waves of different wavelengths as incident light waves. Focusing the incident light of the target wavelength band at the focal point is the goal. Based on the spatial positions of the lens center and the focal point of the metalens in the metalens surface space, the rotation angles of the nanopillar structures at different positions on the upper and lower surfaces of the substrate are determined.

[0010] Step 4: Complete the construction of the double-layer geometric phase metalens. The constructed double-layer geometric phase metalens operates at two different target wavelengths and LCR / RCP polarization states, achieving dual-wavelength switchability and dual-polarization state controllability.

[0011] Furthermore, in step 1, the nanocolumn structure is rectangular.

[0012] Furthermore, in step 1, the process of obtaining a perfect half-wave plate is as follows:

[0013] 1) Select two visible lights of different wavelengths to enter from the long axis and short axis of the nanorod structure respectively;

[0014] 2) Perform parameter sweep simulation on the length and width of the nanopillar structure to obtain phase data information of the transmitted light along the long axis and short axis;

[0015] 3) Determine the perfect half-wave plate based on the conditions of the perfect nanopillar structure.

[0016] Furthermore, the condition for the perfect nanocolumn structure is that the transmission coefficient of linearly polarized light along the long axis and the short axis needs to satisfy |t o |=|t e |, the difference in phase change between the two linearly polarized lights along the major and minor axes satisfies arg(t o )-arg(t e )=π,and |t o | and |t e |The value is high.

[0017] Furthermore, in step 1, the full-wave plate mode means that when linearly polarized light along the long axis and short axis of the nanorod structure is perpendicularly incident, there is no phase difference between the transmitted light of the same polarization state.

[0018] Furthermore, in step 2, the substrate material is quartz, and the nanorod material is TiO2.

[0019] Furthermore, in step 3, the rotation angles of the nanorod structures at different positions on the upper and lower surfaces of the substrate are obtained by the following formula:

[0020]

[0021] Where 2θ1 is the rotation angle of the nanopillar structure below the substrate, and 2θ2 is the rotation angle of the nanopillar structure above the substrate. is the focal coordinate of the nanopillar structure below the substrate, is the focal coordinate of the nanocolumn structure on the substrate.

[0022] Assume that the center of the lens is at (0,0,0) and the focus is set at (0,0,z f ), the focal coordinates of the nanopillar structure can be obtained by the lens focusing formula:

[0023]

[0024] Where λ is the operating wavelength, f is the focal length, and x and y represent the spatial coordinates of a point on the lens.

[0025] Furthermore, in step four, when the wavelength is the first wavelength, the lower nanocolumns of the substrate operate in half-wave plate mode, and the upper nanocolumns of the substrate operate in full-wave plate mode, then free control of left-handed / right-handed polarization state of light waves with a wavelength of the first wavelength can be achieved; when the wavelength is the second wavelength, the upper nanocolumns of the substrate operate in half-wave plate mode, and the lower nanocolumns of the substrate operate in full-wave plate mode, then free control of left-handed / right-handed polarization state of light waves with a wavelength of the second wavelength can be achieved.

[0026] To solve the above technical problems, the present invention provides another technical solution: a wavelength and polarization multiplexing meta-lens based on double-layer geometric phase, which is constructed using the method according to any one of claims 1 to 8.

[0027] To solve the above technical problems, the present invention provides another technical solution: a method for wavelength and polarization multiplexing control of a meta-lens based on double-layer geometric phase, which uses the method according to any one of claims 1 to 8 to adjust the parameters of the nano-pillars on the substrate in the existing meta-lens to achieve dual-wavelength switchability and dual-polarization state controllability.

[0028] The beneficial effects of the present invention are:

[0029] 1. This application utilizes the proposed double-layer geometric phase metasurface theoretical model to simultaneously operate in two wavelength modes and LCP / RCP circular polarization states without interrupting the phase smoothness and continuity required for lens focusing. Based on this double-layer geometric phase model, a meta-lens with arbitrarily adjustable dual wavelengths and dual polarization states is designed, realizing the multifunctional characteristics of wavelength and polarization multiplexing control, and providing a reference idea for the design of multifunctional metasurfaces with wavelength and polarization multiplexing control.

[0030] 2. This application uses a metasurface based on artificial micro-nanostructures to propose a double-layer geometric phase metasurface theoretical model. Using this model, a lens structure with two arbitrarily controllable working wavelengths (532nm and 632nm) and two polarization modes (LCP and RCP) is designed. First, the working principle of the double-layer geometric phase metalens is explained; then, the unit structure of the single-layer metalens is optimized, and a unit structure database is screened and established. Based on this unit structure, a double-layer super-unit structure is designed; finally, the super-unit structure is used to construct a double-layer metalens, which works at two wavelengths of 632 / 532nm and two polarization states of LCR / RCP, realizing dual-wavelength switchable and polarization-sensitive adjustable multifunctional characteristics. The designed metalens has important application prospects in the fields of dual-wavelength polarization-sensitive imaging, optical tomography, sensing, new energy vehicle display systems, AR / MR display, etc.

[0031] In order to make the above and other objects, features and advantages of the present invention more clearly understood, preferred embodiments are given below with reference to the accompanying drawings for detailed description. Description of the drawings:

[0032] In order to more clearly illustrate the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only six of the drawings of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a flow chart of the metalens construction method of this application.

[0034] Figure 2 This is a schematic diagram of the structure of the meta-lens of this application.

[0035] Figure 3 Schematic diagram of the nanopillar structure optimization simulation.

[0036] Figure 4 Schematic diagram of the simulation of the double-layer super unit structure.

[0037] Figure 5 This is the simulation effect of a double-layer meta-lens with dual wavelength control in the same polarization state.

[0038] Figure 6 This is the simulation effect of the meta-lens with dual polarization states and dual wavelengths simultaneously controlled. Specific implementation method:

[0039] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying 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 described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0040] It should be understood that the various steps described in the method embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method embodiments may include additional steps and / or omit the steps shown. The scope of the present invention is not limited in this respect.

[0041] The names of the messages or information exchanged between multiple devices in the embodiments of the present invention are only used for illustrative purposes and are not used to limit the scope of these messages or information.

[0042] Example

[0043] like Figure 1 As shown, a wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase is characterized by:

[0044] Step S1: Based on the design principle of half-wave plates, two groups of perfect half-wave plates are selected from a plurality of nanorod structures using target light waves of two different wavelengths, ensuring that the nanorod structures in the first group of perfect half-wave plates operate in a half-wave plate mode at a first wavelength and in a full-wave plate mode at a second wavelength; and that the nanorod structures in the second group of perfect half-wave plates operate in a half-wave plate mode at the second wavelength and in a full-wave plate mode at the first wavelength;

[0045] Step S2: Arrange the two selected groups of perfect half-wave plates on the upper and lower surfaces of the substrate, respectively, and form a double-layer super-unit structure with two corresponding half-wave plates on the upper and lower surfaces of the substrate. Multiple double-layer super-unit structures form a double-layer meta-lens.

[0046] Step S3: Simulating the double-layer metacell structure using two target light waves of different wavelengths as incident light waves, with the incident light of the target wavelength band focused at the focal point as the goal. Based on the spatial positions of the lens center and the focal point of the metalens in the metalens surface space, the rotation angles of the nanopillar structures at different positions on the upper and lower surfaces of the substrate are determined;

[0047] Step S4: Complete the construction of the double-layer geometric phase metalens. The constructed double-layer geometric phase metalens operates at two different target wavelengths and two polarization states, LCR / RCP, to achieve dual-wavelength switchability and dual-polarization state controllability.

[0048] like Figure 2 As shown, 2a) is a structural schematic diagram; 2(b) is a super unit structure; 2(c) and 2(d) are top views of the second and first layer sub-unit structures, respectively. Schematic diagram of the structure of wavelength and polarization multiplexing meta-lens based on double-layer geometric phase. The designed meta-lens consists of two layers of rectangular TiO2 nano-column structures, which are arranged on the upper and lower surfaces of the quartz substrate respectively. The first layer of structure (lower layer) effectively controls the wavelength λ1, and the second layer of structure (upper layer) effectively controls the wavelength λ2, and each wavelength can be in two polarization states, LCP or RCP. The upper and lower layers of sub-unit structures form a super-unit structure, as shown Figure 2 (b) To achieve dual-wavelength control, two subunit structures must be able to independently and fully control two different wavelengths. Next, we will theoretically analyze and deduce the working principle of the dual-layer geometric phase metasurface model.

[0049] like Figure 2 (d) shows an anisotropic nanostructure. When linearly polarized light with polarization directions along the long axis e and the short axis o is incident perpendicularly, the complex transmission coefficients of the structure can be expressed as t e and t o When the nanostructure rotates with respect to the x-axis by an angle θ e =θ, the transmission coefficient of the rotating system can be obtained by Jones matrix operation:

[0050]

[0051] Where R(θ) is the rotation matrix. When the incident light is circularly polarized, the linear polarization matrix is and The following circular polarization basis and replace:

[0052]

[0053] Then, the Jones matrix based on circular polarization can be written as follows:

[0054]

[0055] The phases of the two subunit structures of the double-layer transmission phase can be directly added to equal the total phase of the double-layer superunit structure, but the double-layer geometric phase cannot be simply added. If two nanostructures based on geometric phase form a double-layer superposition structure, and it is assumed that the rotation angles of the lower and upper nanostructures are θ1 and θ2 respectively, the complex transmission coefficients of the lower layer are t o , t e , the upper layer complex transmission coefficients are t o ′、t e′, then the Jones matrix of the two-layer structure can be expressed as follows:

[0056]

[0057] Let t o +t e =T1,t o -t e =T2,t o ′+t e ′=T1′,t o ′-t e ′=T2′, simplifying the above formula, we can get:

[0058]

[0059] When right-handed circularly polarized light is incident on the metasurface structure with a double-layer geometric phase, the transmitted light can be expressed as follows:

[0060]

[0061] When T1′=0, that is, the upper nanopillar structure works in half-wave plate mode; and T2=0, that is, the lower nanopillar structure works in full-wave plate mode, formula (7) can be expressed as:

[0062]

[0063] As can be seen from formula (8), rotating the angle θ2 of the upper nanopillar structure can effectively control the geometric phase. The circularly polarized transmitted light orthogonal to the incident light has a geometric phase of -2θ2, and the negative sign indicates that the incident light is RCP light. Therefore, the upper nanopillars can freely control the RCP light with a wavelength of λ2. However, rotating the angle θ1 of the lower nanopillars has no geometric phase control effect. For LCP light, the principle is similar. Here, a full-wave plate means that when linearly polarized light along the long axis e and short axis o of the nanopillar is incident perpendicularly, there is no phase difference between the transmitted light of the same polarization state.

[0064] According to the above theoretical analysis, the appropriate size parameters of the upper and lower nanocolumn structures are selected, and the composition is as follows: Figure 2 (b) shows the double-layer geometric phase supercell structure. When the wavelength is λ1, the lower nanopillars operate in half-wave plate mode and the upper nanopillars operate in full-wave plate mode, enabling free control of left-handed / right-handed polarization states of light waves with a wavelength of λ1. When the wavelength is λ2, the upper nanopillars operate in half-wave plate mode and the lower nanopillars operate in full-wave plate mode, enabling free control of left-handed / right-handed polarization states of light waves with a wavelength of λ2. Therefore, this carefully optimized double-layer supercell structure can achieve arbitrary control of dual wavelengths and dual polarization states.

[0065] In the above step S1, according to the design principle of half-wave plate, in order to obtain a perfect half-wave plate, as shown in FIG. Figure 2 The subunit structure shown in (d) requires that the transmission coefficient of linearly polarized light along the o-axis and e-axis satisfy |t o |=|t e |, phase difference arg(t o )-arg(t e )=π,and |t o | and |t e The value of | is relatively high. The two visible light wavelengths to be controlled are λ1=632nm and λ2=532nm. At wavelengths of 632nm and 532nm, the frequency domain solver of the CST simulation software is used to perform parameter sweep simulation on the length and width of the nanocolumns to obtain the phase data information of the transmitted light along the o-axis and e-axis. The period U of the unit structure is 400nm, the height H of the upper and lower nanocolumns is 600nm, and the width and length vary from 50nm to 350nm. The simulation results of the unit structure are shown in Figure 2. Figure 3 Figures (a) and (b) show the phase shift differences between two linearly polarized light beams at wavelengths of 632nm and 532nm, respectively, along the o-axis and e-axis. From the data obtained, two nanopillar structures were selected: nanopillar 1 with dimensions W1 = 90nm, L1 = 350nm, and nanopillar 2 with dimensions W2 = 190nm, L2 = 95nm. Nanopillar 1 was designed to operate in half-wave plate mode at 632nm and full-wave plate mode at 532nm; nanopillar 2, on the other hand, operates in half-wave plate mode at 532nm and full-wave plate mode at 632nm. The performance of the superunit structure composed of these two selected nanopillars is now investigated.

[0066] Figure 4 The performance simulation of a double-layer super unit structure composed of nanopillars 1 and 2 at operating wavelengths of 632nm and 532nm respectively. Figure 4 As shown in (a), the phase mutation of the orthogonal circularly polarized transmitted light of the super unit structure is at a wavelength of 632nm. The rotation angle θ2 of nanorod 2 remains unchanged, and the angle θ1 of nanorod 1 is rotated. It can be seen that the phase mutation still conforms to the geometric phase relationship, that is, when LCP light is incident, the transmitted RCP light will produce a phase mutation of 2 times the rotation angle, as shown in Figure 4 The black dot solid line in (a); when the RCP light is incident, the transmitted LCP light will produce a phase mutation of -2 times the rotation angle, such as Figure 4 The blue dotted solid line in (a). Although it is a double-layer unit structure, Figure 4(b) It can be seen that when LCP or RCP light is incident, the transmission coefficient of orthogonal circularly polarized light also remains at around 83%. At this time, the circular polarization conversion ratio (PCR) is around 0.72. Here, the decrease in the polarization conversion ratio of the double-layer geometric phase unit structure compared to the single-layer geometric phase unit structure is due to the fact that nanopillar 2 is an approximate full-wave plate. As mentioned earlier, by optimizing and simulating more nanopillar unit structures, a structure closer to a perfect full-wave plate can be found. Figure 4 (c) and (d) are the phase mutation and transmission coefficient of the orthogonal circularly polarized transmitted light of the super unit structure when the incident light is 532nm, the rotation angle θ1 of nanopillar 1 remains unchanged, and the angle θ2 of nanopillar 2 is rotated. The analysis is similar to the above results.

[0067] In the above step S3, through the above analysis, the proposed double-layer geometric phase control principle can be used to achieve arbitrary control of two different wavelengths at the same time without using spatial multiplexing. For example, it can achieve the focusing of lenses with different focal lengths at two wavelengths. Here, it is assumed that the center of the lens is at (0,0,0) and the focus is set at (0,0,z f ), the lens focusing formula can be written as follows:

[0068]

[0069] Where λ is the operating wavelength, f is the focal length, and x and y represent the spatial coordinates of a point on the lens. Initially, the incident light with wavelengths λ1 = 632nm and λ2 = 532nm is LCP light. The lower structure controls the focusing of the 632nm wavelength, while the upper structure controls the focusing of the 532nm wavelength. To focus the two LCP lights of different wavelengths at the designed focal point, the rotation angles of nanopillars 1 and 2 should satisfy the following formulas:

[0070]

[0071] The focal lengths corresponding to the two wavelengths of 532nm and 632nm are set to 8μm and 12μm respectively, and the diameter D of the meta-lens is 10.4μm. Then the numerical apertures of the lens corresponding to the two wavelengths are 0.55 and 0.4 respectively. According to formulas (9), (10) and (11), the rotation angles of the nanopillars at different positions in each layer can be determined, thereby designing a double-layer meta-lens. Figure 4 (a) and (b) show the simulation effects of the designed double-layer meta-lens when the incident light is 532nm and 632nm, respectively. It can be seen that effective focusing of the two wavelengths is achieved.

[0072] The focusing performance of two different wavelengths is verified below.

[0073] like Figure 5 As shown in (c) and (d). Figure 5 (c) shows the electric field energy intensity distribution along the axis under two wavelength conditions, where the focal length of the lens is 7.8μm when the wavelength is incident at 532nm, and the focal length is 11.5μm when the wavelength is incident at 632nm. The errors between the simulated focal length and the theoretical design value are 2.5% and 4.1%, respectively, indicating that the designed double-layer geometric phase control has high accuracy. One reason for this error is the mutual weak coupling between the nanopillars. Another reason is that when the upper nanopillars work in half-wave plate mode at 532nm, it is not a perfect full-wave plate at 632nm; or when the lower nanopillars work in half-wave plate mode at 632nm, it is not a perfect full-wave plate mode at 532nm. More parameter scans can be used to obtain a nanopillar structure that is closer to a perfect full-wave plate to further reduce the error. From Figure 5 (d) As can be seen, the FWHM corresponding to 532nm incident light is 483nm, indicating that the lens has subwavelength focusing performance; the FWHM corresponding to 632nm incident light is 700nm. The lens has better focusing performance for 532nm incident light than for 632nm incident light because its corresponding numerical aperture is larger.

[0074] The following verification is carried out using dual-wavelength focusing under two different circular polarization states of incident light conditions.

[0075] The working wavelengths are set to λ1 = 632nm for LCP light and λ2 = 532nm for RCP light, with corresponding focal lengths of 8μm and 12μm, respectively. The corresponding numerical apertures are 0.55 and 0.4, respectively. According to the design principle of the double-layer geometric phase, when the incident light is RCP light, the rotating half-wave plate nanorods will produce a geometric phase of -2 times the rotation angle; when the incident light is LCP light, the rotating half-wave plate nanorods will produce a geometric phase of 2 times the rotation angle. Figure 5 As shown, the control effect of the designed meta-lens with simultaneous control of dual wavelengths and dual polarization states is achieved.

[0076] The upper nanocolumns control the RCP incident light with a wavelength of 532nm and a focal length of 8μm; the lower nanocolumns control the LCP incident light with a wavelength of 632nm and a focal length of 12μm. The focusing effects are as follows: Figure 6 As shown in (a) and (b). Figure 6 Figures (c) and (d) show the electric field energy intensity distribution along the z-axis and focal plane. When incident with 532nm RCP light and 632nm LCP light, respectively, the simulated focal lengths are 7.5μm and 12.1μm, with errors of 6.3% and 0.8% from the theoretical design values, respectively. The corresponding full widths at half maximum are 460nm and 740nm, respectively. Therefore, despite the change in the polarization state of the 532nm incident light, the lens still maintains subwavelength focusing performance.

[0077] To solve the above technical problems, the present invention provides another technical solution: a wavelength and polarization multiplexing control method for a meta-lens based on double-layer geometric phase. The above method is used to adjust the parameters of the nanocolumns on the substrate in the existing meta-lens to achieve dual-wavelength switchability and dual-polarization state controllability.

[0078] This application verifies the effectiveness of the proposed double-layer geometric phase metalens for dual-wavelength, dual-polarization control. It not only achieves free dual-wavelength control under LCP light conditions, but also achieves dual-wavelength and dual-polarization control, providing a reference for the design of multifunctional metasurfaces for polarization and wavelength multiplexing control. This control mode can be extended to the design of dual-wavelength, dual-polarization beam deflection and vortex metasurfaces, and can easily achieve dual-wavelength achromatic aberration of circular polarization states, with potential applications in optical communications, medical treatment, dual-wavelength imaging, and other fields.

[0079] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will appreciate that the present invention is not limited to the specific embodiments herein, and that various obvious changes, readjustments, and substitutions are possible for those skilled in the art without departing from the scope of protection 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 and may include many other equivalent embodiments without departing from the scope of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for constructing a wavelength and polarization multiplexing meta-lens based on a double-layer geometric phase, characterized by: Step 1: Based on the design principle of half-wave plates, two groups of perfect half-wave plates are selected from multiple nanopillar structures using target light waves of two different wavelengths. The nanopillar structures in the first group of perfect half-wave plates are ensured to operate in half-wave plate mode at the first wavelength and in full-wave plate mode at the second wavelength. The nanorod structure in the second set of perfect half-wave plates operates in half-wave plate mode at the second wavelength and in full-wave plate mode at the first wavelength. Step 2: Arrange the two selected perfect half-wave plates on the upper and lower surfaces of the substrate, respectively, and form a double-layer super-unit structure with two corresponding half-wave plates on the upper and lower surfaces of the substrate. Multiple double-layer super-unit structures form a double-layer meta-lens. Step 3: Simulate the double-layer metacell structure using two target light waves of different wavelengths as incident light waves. Focusing the incident light of the target wavelength band at the focal point is the goal. Based on the spatial positions of the lens center and the focal point of the metalens in the metalens surface space, the rotation angles of the nanopillar structures at different positions on the upper and lower surfaces of the substrate are determined. Step 4: Complete the construction of the double-layer geometric phase metalens. The constructed double-layer geometric phase metalens operates at two different target wavelengths and LCR / RCP polarization states, achieving dual-wavelength switchability and dual-polarization state controllability.

2. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In the step 1, the nanocolumn structure is rectangular.

3. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In step 1, the process of obtaining a perfect half-wave plate is as follows: 1) Select two visible lights of different wavelengths to enter from the long axis and short axis of the nanorod structure respectively; 2) Perform parameter sweep simulation on the length and width of the nanopillar structure to obtain phase data information of the transmitted light along the long axis and short axis; 3) Determine the perfect half-wave plate based on the conditions of the perfect nanopillar structure.

4. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 2 is characterized by: The conditions for the perfect nanocolumn structure are: the transmission coefficients of linearly polarized light along the long axis and the short axis need to satisfy |t o |=|t e |, the difference in phase change between the two linearly polarized lights along the major and minor axes satisfies arg(t o )-arg(t e )=π,and |t o | and |t e |The value is high.

5. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In the step 1, the full-wave plate mode means that when linearly polarized light along the long axis and short axis of the nanorod structure is perpendicularly incident, there is no phase difference between the transmitted light of the same polarization state.

6. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In the step 2, the substrate material is quartz, and the nanorod material is TiO2.

7. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In step 3, the rotation angles of the nanopillar structures at different positions on the upper and lower surfaces of the substrate are obtained by the following formula: Where 2θ1 is the rotation angle of the nanopillar structure below the substrate, and 2θ2 is the rotation angle of the nanopillar structure above the substrate. is the focal coordinate of the nanopillar structure below the substrate, is the focal coordinate of the nanocolumn structure on the substrate. Assume that the center of the lens is at (0,0,0) and the focus is set at (0,0,z f ), the focal coordinates of the nanopillar structure can be obtained by the lens focusing formula: Where λ is the operating wavelength, f is the focal length, and x and y represent the spatial coordinates of a point on the lens.

8. The wavelength and polarization multiplexing meta-lens construction method based on double-layer geometric phase according to claim 1 is characterized by: In the step four, when the wavelength is the first wavelength, the lower nanocolumns of the substrate work in half-wave plate mode, and the upper nanocolumns of the substrate work in full-wave plate mode, then it is possible to freely control the left-handed / right-handed polarization state of light waves with a wavelength of the first wavelength; when the wavelength is the second wavelength, the upper nanocolumns of the substrate work in half-wave plate mode, and the lower nanocolumns of the substrate work in full-wave plate mode, then it is possible to freely control the left-handed / right-handed polarization state of light waves with a wavelength of the second wavelength.

9. A wavelength and polarization multiplexing meta-lens based on double-layer geometric phase, constructed by the method according to any one of claims 1 to 8.

10. A method for wavelength and polarization multiplexing control of a meta-lens based on double-layer geometric phase, which uses the method according to any one of claims 1-8 to adjust the parameters of the nano-pillars on the substrate in the existing meta-lens to achieve dual-wavelength switchability and dual-polarization state controllability.

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