Multi-channel holographic method based on total-space dynamic switching metasurface

Abstract

The invention discloses a multi-channel holographic method based on a total-space dynamic switching metasurface. The method comprises the following steps: 1) constructing a nano-structure unit; 2) optimizing the structure parameters of the nano structure unit according to the incident light wavelength lambda; and 3) constructing a nano-structure array, wherein the nano-structure array comprises a plurality of nano-structure units. According to the invention, left-handed / right-handed circularly polarized light is set to be incident to the nano-structure array, and dynamic switching of four holographic channels is carried out by rotating a mask plate in a reflection space; in a transmission space, the relative positions of the two layers of nano-arrays are changed by translating the second layer of nano-structure array to obtain dynamic switching of the three holographic channels, and the seven holographic channels can be subjected to mutually independent and continuous phase regulation and control through the nano-bricks. According to the invention, full-space information utilization can be realized, multi-channel dynamic switching is realized, the information capacity of the device is increased, the functionality of the device is improved, and the device can be applied to the fields of large-capacity optical information storage and coding and the like.

Description

Technical Field

[0001] The present invention belongs to the technical fields of micro-nano optics and polarization optics, and in particular relates to a multi-channel holographic method based on full-space dynamic switching metasurface. Background Art

[0002] Metasurface materials are new nanomaterials composed of subwavelength structure arrays that have ultra-strong control over the polarization, phase, and amplitude of light waves. Its emergence provides a new method for achieving miniaturization, integration, and high performance of optoelectronic devices. With the continuous development of information technology, how to achieve the storage and encoding of large-capacity information is a problem of widespread concern in the current optoelectronics field.

[0003] In order to increase the information capacity of devices and improve the functionality of devices, many multi-channel information encoding methods based on metasurface materials have been proposed one after another. According to the type of nanostructure, they can be roughly divided into two categories: 1) dynamic switching method of reconfigurable metasurface based on phase change materials; 2) mechanical dynamic switching method of reconfigurable metasurface based on cascaded metasurfaces;

[0004] At present, the dynamic switching multi-channel information encoding based on reconfigurable metasurfaces only occurs in the transmission space or reflection space, which leads to the sacrifice of half of the spatial information. In essence, the information capacity has not been significantly improved. Based on the full-space metasurface structure, this paper proposes a multi-channel holographic method based on the full-space dynamic switching metasurface. Summary of the invention

[0005] The present invention aims to overcome the above problems existing in the prior art and provide a multi-channel holographic method based on full-space dynamic switching metasurface. The present invention can realize the conversion between seven channels of information by cleverly designing the size angle and cascade state of the nanostructure, and has a good development prospect in the fields of high-end anti-counterfeiting, polarization display, image hiding, etc.

[0006] The technical scheme of the present invention is as follows:

[0007] A multi-channel holographic method based on a full-space dynamic switching metasurface. When the relative position between the two metasurfaces changes, the hologram in the transmission space will be dynamically switched; when the mask is rotated, the hologram in the reflection space can be dynamically switched. There is no need to change the incident light conditions, and the dynamic switching of multi-channel holography can be achieved by mechanically moving the metasurface.

[0008] Furthermore, the method specifically includes the following steps:

[0009] 1) constructing a nanostructure unit; the nanostructure unit comprises a fused quartz substrate, a silicon nanobrick I deposited on a working surface of the substrate, and a silicon nanobrick II embedded in the substrate, and an xoy coordinate system is established with the right-angled sides of the structure unit as the x-axis and the y-axis, the long side of the nanobrick is the major axis, the short side is the minor axis, and the angle between the long axis of the nanobrick and the x-axis is the steering angle θ of the nanobrick;

[0010] 2) Optimizing the structural parameters of the nanostructure unit according to the wavelength λ of the incident light, the structural parameters including: the side length C of the substrate working surface, the major axis L1, the minor axis W1, the height H1 of the nanobrick I, and the major axis L2, the minor axis W2, the height H2 of the nanobrick II;

[0011] 3) constructing a nanostructure array, wherein the nanostructure array comprises a plurality of nanostructure units;

[0012] 4) Setting left-handed / right-handed circularly polarized light to be incident on the nanostructure array, placing a mask in front of the nanostructure unit, and rotating the mask, four-channel different holographic images can be obtained in the reflection space; removing the mask, moving the second layer of nanostructure units, changing the cascade state of the first layer of nanostructure units and the second layer of nanostructure units, and three-channel different holographic images can be obtained in the transmission space.

[0013] Furthermore, the transparent substrate in step 1) is a fused quartz glass material, and the nanobricks are a silicon material.

[0014] Furthermore, the structural parameters of the nanostructure unit in step 2) are obtained by electromagnetic simulation optimization according to the selected incident light wavelength λ.

[0015] Furthermore, in the nanostructure array in step 3), the first layer of nanostructure units is equivalent to a semi-transmissive and semi-reflective half-wave plate, and the second layer of nanostructure units is equivalent to a high-transmittance half-wave plate.

[0016] a. When circularly polarized light passes through the first layer of nanostructure units, half of the light beam is reflected. The Jones matrix of the reflected light can be expressed based on circular polarization as follows:

[0017]

[0018] Where: θ1 is the turning angle of the first layer of nanobricks, is the common polarization component of the reflected light generated on the first layer of nanobricks, is the cross-polarization component in the reflected light;

[0019] b. When circularly polarized light passes through the first layer of nanostructure units, half of the light beam is transmitted, and then passes through the second layer of nanobricks. The Jones matrix of the transmitted light can be expressed based on circular polarization as follows:

[0020]

[0021] Where: θ2 is the turning angle of the second layer of nanobricks, are the co-polarized and cross-polarized components of the transmitted light generated on the first layer of nanobricks, are the co-polarized and cross-polarized components of the transmitted light generated on the second layer of nanobricks.

[0022] Furthermore, the phase change relationship between the reflected light phase restoration and the transmitted light phase restoration in the range [0,2π] of the steering angles θ1 and θ2 of the nanobrick is:

[0023] a. When the steering angle θ1 of the nanobrick changes in the range of [0,2π], its corresponding phase changes, which can achieve the intensity modulation of the reflected light;

[0024] b. The phase distribution of the first layer of nanobricks can be obtained by performing phase restoration of four holograms according to the GS algorithm;

[0025] c. When the steering angles θ1 and θ2 of the nanobricks vary within the range of [0,2π], the corresponding phase changes can achieve intensity modulation of the transmitted light;

[0026] d. The phase distribution of the second layer of nanobricks can be obtained by performing phase restoration of the three holograms in three cascade states according to the simulated annealing algorithm;

[0027] By properly arranging the steering angles of the nanobricks, it is possible to encode seven images simultaneously on a metasurface.

[0028] Furthermore, the two-layer nanostructure arrays are nanobricks of the same size but with different rotation angles, wherein the nanobricks are micro-nano half-wave plates capable of modulating a circularly polarized light beam having an orthogonal polarization to the incident circularly polarized light being reflected or transmitted.

[0029] Furthermore, the seven channels appear as decoupled independent holographic images.

[0030] The present invention sets left-handed / right-handed circularly polarized light incident on the nanostructure array, and in the reflection space, four holographic channels are dynamically switched by rotating the mask; in the transmission space, the second layer of nanostructure array is translated to change the relative position of the two layers of nanoarrays to obtain dynamic switching of three holographic channels. The seven holographic channels in the present invention can be independently and continuously phase-controlled by nanobricks. The present invention can realize the information utilization of the whole space, realize the dynamic switching of multiple channels, increase the information capacity of the device and improve the functionality of the device, and can be applied to the fields of large-capacity optical information storage and encoding.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1) By adopting the technical solution of the present invention, the seven images formed by the variable angle nanostructure array in different cascade states can be designed separately without any correlation, and cannot be inferred from each other. They can be designed arbitrarily, so they can be applied to polarization display, encryption, high-end anti-counterfeiting and other fields, providing a new method and approach for future security technology;

[0033] 2) The design method of the present invention proposes a new degree of freedom for light wave manipulation. The design method is ingenious and the structure used is simple. Only a double-layer nanobrick structure unit is needed to realize full-space dynamic control. Therefore, the metasurface designed by the present invention is small in size, light in weight, and can be highly integrated, which is suitable for the development of miniaturization and micro-miniaturization in the future.

[0034] 3) The seven holographic phases produced by the present invention are continuously and precisely controlled, patterns can be generated arbitrarily, and crosstalk between images is small, so it is suitable for high-quality holographic imaging;

[0035] 4) The present invention can realize the information utilization of the whole space, realize the dynamic switching of multiple channels, increase the information capacity of the device and improve the functionality of the device, and realize the storage and encoding of large-capacity information. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic diagram of a nanobrick structural unit of the present invention;

[0037] Figure 2 is a scanning diagram of the transmittance and reflectance of the first layer of the nanostructure unit of the present invention;

[0038] Figure 3 is a scanning diagram of the transmittance and reflectance of the second layer of the nanostructure unit of the present invention;

[0039] Figure 4 is a schematic diagram of the relationship between the reflection phase modulation function and the nanobrick steering angle of the present invention;

[0040] Figure 5 is a schematic diagram of the relationship between the transmission phase modulation function and the nanobrick steering angle of the present invention;

[0041] Figure 6 These are four switching states of the reflective area of ​​the present invention and the restored image;

[0042] Figure 7 The three switching states of the transmission area of ​​the present invention and the restored image;

[0043] Figure 8 It is a flow chart of the phase iterative optimization of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with embodiments, but the scope of protection of the present invention is not limited to the described scope.

[0045] This embodiment relates to a multi-channel holographic method based on full-space dynamic switching metasurface, and the specific steps are as follows:

[0046] First, construct nanostructured units, such as Figure 1 As shown, the nano unit structure is composed of silicon nanobricks and a silicon dioxide base layer. Secondly, the design wavelength is selected as λ=633nm. For this wavelength, the nano-rotation structure unit is optimized and simulated by the electromagnetic simulation software CST, and the size parameters of the optimized silicon nanobricks are: the length of the first layer of silicon nanobricks is L1=153nm, the width is W1=103nm, and the height is H1=258nm; the length of the first layer of silicon nanobricks is L2=240nm, the width is W2=80nm, and the height is H2=350nm; the side length of the unit structure base is CS=300nm.

[0047] Under this structural parameter, the polarization conversion efficiency of nanobricks in the transmission and reflection space of circularly polarized light is as follows: Figure 2 , 3 As shown, R-Co and R-Cross represent the co-polarization conversion efficiency and cross-polarization conversion rate of the reflected light, respectively, and T-Co and T-Cross represent the co-polarization conversion efficiency and cross-polarization conversion rate of the transmitted light, respectively.

[0048] Depend on Figure 2 It can be seen that at the working wavelength of 633nm, R1-Cross is as high as 47.2%, T1-Cross is as high as 49.1%, and R1-Co and T1-Co are suppressed to less than 2%, indicating that about half of the incident light of the first layer of nanobricks is reflected as cross-polarization and the other half is transmitted as cross-polarization. Therefore, the optimized nanobrick unit structure can realize the function of a semi-transmissive and semi-reflective half-wave plate, that is, the reflected light is regulated by the rotation angle θ1. Figure 3 It can be seen that at the working wavelength of 633nm, T2-Cross is as high as 92.5%, and R2-Co, R2-Cross and T2-Co are suppressed to less than 5%, indicating that the incident light of the second layer of nanobricks is almost transmitted as cross-polarization. Therefore, the optimized nanobrick unit structure can realize the function of a high-transmittance half-wave plate, that is, the transmission light is regulated by the rotation angles θ1 and θ2.

[0049] Finally, a nanostructure array is constructed, which includes multiple nanostructure units. When the incident light is incident on the first layer of nanobricks, half of the energy is reflected by cross-polarization conversion, and the first layer of nanobricks is modulated according to the phase restored by the GS algorithm. The relationship between the reflection phase modulation function and the nanobrick steering angle is as follows: Figure 4 As shown, the continuous phase control of the reflected light can be realized, and the dynamic switching of the four holograms can be obtained by combining the rotation of the mask, as shown in Figure 6As shown. The other half of the energy continues to be transmitted through the second layer of nanobricks for cross-polarization conversion, and is modulated by the second layer of nanobricks and the first layer of nanobricks according to the phase restored by the simulated annealing algorithm. The phase distribution is obtained by independent holographic reconstruction under three cascade states. The relationship between the transmission phase modulation function and the nanobrick steering angle is shown in Figure 5 As shown, the continuous phase control of the transmitted light can be realized, and the relative positions of the two layers of nanoarrays can be changed by combining the mechanical movement of the second layer of nanobricks to obtain the dynamic switching of the three holograms, as shown in Figure 7 The phase optimization algorithm flow in the above method is as follows Figure 8 shown.

[0050] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A multi-channel holographic method based on full-space dynamic switching metasurface, characterized in that: The left-handed / right-handed circularly polarized light is set to be incident on the nanostructure array, and the four holographic channels are dynamically switched by rotating the mask in the reflection space; In the transmission space, the dynamic switching of three holographic channels is achieved by translating the second-layer nanostructure array to change the relative position of the double-layer nanostructure, and all seven holographic channels are independently and continuously phase-controlled by the nanobricks.

2. According to claim 1, a multi-channel holographic method based on full-space dynamic switching metasurface is characterized in that: The specific steps include: 1) constructing a nanostructure unit; the nanostructure unit comprises a fused quartz substrate, a silicon nanobrick I deposited on a working surface of the substrate, and a silicon nanobrick II embedded in the substrate, and an xoy coordinate system is established with the right-angled sides of the structure unit as the x-axis and the y-axis, the long side of the nanobrick is the major axis, the short side is the minor axis, and the angle between the long axis of the nanobrick and the x-axis is the steering angle θ of the nanobrick; 2) Optimizing the structural parameters of the nanostructure unit according to the wavelength λ of the incident light, the structural parameters including: the side length C of the substrate working surface, the major axis L1, the minor axis W1, the height H1 of the nanobrick I, and the major axis L2, the minor axis W2, the height H2 of the nanobrick II; 3) constructing a nanostructure array, wherein the nanostructure array comprises a plurality of nanostructure units; 4) setting left-handed / right-handed circularly polarized light to be incident on the nanostructure array, placing a mask in front of the nanostructure unit, rotating the mask, and obtaining four different images in the reflection space; removing the mask, moving the second-layer nanostructure unit, changing the cascade state of the first-layer nanostructure unit and the second-layer nanostructure unit, and obtaining three new images in the transmission space.

3. The multi-channel holographic method based on full-space dynamic switching metasurface according to claim 2, characterized in that: The structural parameters of the nanostructure unit in step 2) are obtained by electromagnetic simulation optimization according to the selected incident light wavelength λ.

4. The multi-channel holographic method based on full-space dynamic switching metasurface according to claim 2, characterized in that: In the nanostructure array described in step 3), the first layer of nanostructure units is equivalent to a semi-transmissive and semi-reflective half-wave plate, and the second layer of nanostructure units is equivalent to a high-transmittance half-wave plate; a. When circularly polarized light passes through the first layer of nanostructure units, half of the light beam is reflected. The Jones matrix of the reflected light is expressed based on circular polarization as follows: Where: θ1 is the turning angle of the first layer of nanobricks, is the common polarization component of the reflected light generated on the first layer of nanobricks, is the cross-polarization component in the reflected light; b. When circularly polarized light passes through the first layer of nanostructure units, half of the light beam is transmitted, and then passes through the second layer of nanobricks. The Jones matrix of the transmitted light is expressed based on circular polarization as follows: Where: θ2 is the turning angle of the second layer of nanobricks, are the co-polarized and cross-polarized components of the transmitted light generated on the first layer of nanobricks, are the co-polarized and cross-polarized components of the transmitted light generated on the second layer of nanobricks.

5. The multi-channel holographic method based on full-space dynamic switching metasurface according to claim 4, characterized in that: The phase change relationship between reflected light phase restoration and transmitted light phase restoration in the range of [0,2π] of the steering angles θ1 and θ2 of the nanobrick is: a. When the steering angle θ1 of the nanobrick changes in the range of [0,2π], its corresponding phase changes to achieve reflected light intensity modulation; b. According to the phase restoration of the four holograms and the light transmission position of the mask, the phase distribution of the first layer of nanobricks is obtained; c. When the steering angles θ1 and θ2 of the nanobricks vary within the range of [0,2π], the corresponding phase changes to achieve intensity modulation of the transmitted light; d. Performing phase restoration of the second layer of nanobricks of the three transmission holograms in three cascade states according to the simulated annealing algorithm to obtain the phase distribution of the first layer of nanobricks; By arranging the steering angles of the nanobricks, seven images can be encoded simultaneously on a metasurface.

6. The multi-channel holographic method based on full-space dynamic switching metasurface according to claim 1, characterized in that: The double-layer nanostructure is a nanobrick with different rotation angles and the same size. The first layer of nanobricks is a semi-transparent and semi-reflective half-wave plate, which reflects or transmits the incident circularly polarized light; the second layer of nanobricks is a high-transmittance half-wave plate, which only transmits one type of circularly polarized light that can be modulated in phase.

7. The multi-channel holographic method based on full-space dynamic switching metasurface according to claim 1, characterized in that: Realize decoupling and independent modulation of seven channel beams under full-space dynamic switching.

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