Design of dynamic linear polarization device based on phase change diatomic metasurface

Abstract

The invention discloses a dynamic linear polarization device design based on a phase-change diatomic metasurface, and relates to the technical field of phase-change metasurfaces, and the linear polarization device is a single-layer metasurface formed by a super unit composed of a dielectric material nano column 1 and a phase-change material nano column 2. Wherein the nanorod 1 is represented as a half-wave plate and is responsible for realizing the conversion of a polarization state, and the nanorod 2 can realize the change of a phase from 0 to pi by changing the state of a phase change material, so that the effect of maintaining the polarization is achieved. When light rays act on the two kinds of nano-columns at the same time, the nano-columns 2 allow transmission light to keep the original polarization state of incident light, and the nano-columns 1 change the polarization state of the transmission light. And the two kinds of transmission light are superposed subsequently, so that the transmission light output by the whole super-unit shows the linear polarization characteristic, and the polarization angle of the transmission light and the rotation angle of the nano-column are kept consistent or form an orthogonal relationship. According to the invention, a phase-change diatomic structure is adopted, so that the metasurface can realize a linear polarizer with an adjustable polarization angle under the incidence of any polarization angle.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change metasurfaces, and more particularly to the design of a dynamic linear polarization device based on a phase change diatomic metasurface Background Art

[0002] Traditional optical polarization devices, such as linear polarizers, polarization beam splitters, and wave plates, play a key role in fields such as optical communication, image processing, optical detection, and optical information processing by improving the working efficiency of complex optical systems. However, traditional optical polarization devices have the limitation of large volume, which restricts their application in compact devices. In view of this, metasurfaces, as an emerging technology, exhibit extremely powerful light polarization modulation capabilities at the subwavelength scale, providing great potential for constructing ultra-compact planar optical components to replace traditional devices. Compared with traditional polarization devices, polarization devices based on metasurfaces have significant advantages in terms of size, integration, and light field modulation. However, once such polarization devices are fabricated, their functions are fixed, and a single function is difficult to meet diverse optical requirements, limiting their flexibility. With the introduction of phase change materials, the ability to rapidly undergo reversible phase changes at different temperatures (similar to the function of an optical switch) provides the possibility for the dynamic tunability of polarization devices. It is worth noting that most current polarization devices based on phase change metasurfaces can achieve the switching of functions between wave plates under incident light of a specific polarization state. To date, the related research on dynamic tunable linear polarization devices based on phase change metasurfaces is still limited

[0003] That is to say, the following technical problems exist in current polarization devices based on metasurfaces

[0004] (1) For the linear polarization device designed based on the traditional metasurface, once it is processed, its function is relatively fixed, and a single function is difficult to meet diverse optical requirements, which significantly narrows the application scenarios and flexibility of this type of polarization device in complex optical systems

[0005] (2) The exploration of linear polarizers is still insufficient: The polarization elements designed for phase change metasurfaces mainly focus on the realization of wave plate functions, while the research on linear polarizers based on phase change metasurfaces is relatively scarce, which greatly restricts the extensive application and exploration of this type of polarization device in the field of optical encryption technology Summary of the Invention

[0006] Aiming at the defects existing in the prior art, the technical solution adopted by the present invention to achieve the above object is

[0007] In this paper, a nanorod 1 with polarization conversion function and a nanorod 2 with dynamically adjustable phase are innovatively and skillfully integrated to construct a phase change diatomic metasurface, realizing a linear polarizer with dynamically adjustable polarization angle

[0008] The dynamic linear polarizer is a single-layer metasurface composed of supercells formed by dielectric material nanorods 1 and phase change material nanorods 2. This periodically arranged supercell structure array has the ability to regulate the polarization angle by changing the temperature.

[0009] When nanorod 2 is in the crystalline state, the transmitted light is linearly polarized light with a polarization angle the same as the rotation angle of nanorod 1; when nanorod 2 is in the amorphous state, the transmitted light is linearly polarized light with a polarization angle orthogonal to the rotation angle of nanorod 1.

[0010] In a further technical solution, the supercell is jointly constructed by the dual-atom structure of nanorod 1 and nanorod 2. Among them, the constituent material of nanorod 2 is a phase change material, and the phase difference before and after the phase change is π. Nanorod 1 is composed of a highly transparent dielectric material and acts as a half-wave plate.

[0011] The phase change dual-atom metasurface is located on a silica substrate, and its working mode is transmissive.

[0012] In a further technical solution, the incident light can convert incident light with any polarization state into linearly polarized light with any polarization angle after passing through the supercell. The principle is as follows:

[0013] When light acts on both types of nanorods simultaneously, nanorod 2 allows the transmitted light to maintain the original polarization state of the incident light, while nanorod 1 changes the polarization state of the incident light. These two transmitted lights are then superimposed. After the superposition, the polarization angle of the transmitted light of the supercell is only related to the rotation angle of nanorod 1, making the transmitted light output by the entire supercell exhibit linear polarization characteristics. When a phase change occurs in nanorod 2, the polarization angle of the transmitted light will change by an angle of ±90°.

[0014] In a further technical solution, for the dynamic linear polarizer device based on the phase change dual-atom metasurface, it is characterized in that at the incident wavelength, nanorod 2 is designed such that the phase difference before and after the phase change is π, that is, the nanorod 2 composed of the phase change material in the periodically arranged supercell dual atoms satisfies high transmittance and a phase difference of π both before and after the phase change under the same polarized incidence; the size of nanorod 2 meets this requirement.

[0015] Nanorod 1 is designed as a half-wave plate, that is, nanorod 1 in the periodically arranged supercell dual atoms satisfies high transmittance and a phase difference of π when x- and y-linearly polarized light is incident; the size design of nanorod 1 meets the requirements of a half-wave plate.

[0016] Further technical solution: when the rotation angle of the nanorod 1 varies from 0° to 180° and any polarization state is incident, when the nanorod 2 is in the amorphous state, the transmitted light is linearly polarized light with a polarization angle orthogonal to the rotation angle of the nanorod 1; when the temperature rises to 200 °C and the nanorod 2 is in the crystalline state, the transmitted light is linearly polarized light with a polarization angle the same as the rotation angle of the nanorod 1.

[0017] Based on the above technical solution, compared with the prior art, the advantages of the present invention are as follows:

[0018] 1. Compared with the static metasurface polarization device with fixed functions, the present invention constructs a phase-tunable meta-atom by introducing a phase change material, realizing a linear polarizer that can freely switch the polarization angle between the crystalline state and the amorphous state, increasing its flexibility and expanding the application scenarios of existing linear polarization devices in the fields of optical encryption technology, polarization imaging, etc.

[0019] 2. Compared with the phase change metasurface relying on a single phase change meta-atom, which only focuses on realizing the function switching or switching of a wave plate, the present invention combines phase change meta-atoms and non-phase change meta-atoms with different morphologies to construct a dual-atom super unit, and a linear polarizer with an arbitrary polarization angle can be realized by simply adjusting the rotation angle of the nanorod. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a functional schematic diagram of the phase change dual-atom metasurface in different states and a schematic diagram of its metasurface unit structure proposed by the present invention.

[0022] Figure 2 It is a scan diagram of the transmittance of the transmitted light and the phase difference between the fast and slow axes when x-polarized light is incident on rectangular nanorods with different lengths (L) and widths (W) in the present invention.

[0023] Figure 3 It is a relationship curve diagram of the transmittance of the transmitted light, the degree of linear polarization (DOLP), and the principal axis angle of different radii before and after the phase change of the cylindrical nanorod in the present invention.

[0024] Figure 4 It is a curve diagram of the transmittance of the transmitted light, the degree of linear polarization (DOLP), and the principal axis angle when x-polarized light with different polarization angles is incident on the selected structure in different states in the present invention.

[0025] Figure 5It is the scan chart of the transmittance, degree of linear polarization (DOLP), and principal axis angle of the transmitted light when the selected structure of the present invention is in the crystalline state, the rotation angle of the selected supercell is changed, and linearly polarized light at an arbitrary angle is incident.

[0026] Figure 6 It is the scan chart of the transmittance, degree of linear polarization (DOLP), and principal axis angle of the transmitted light when the selected structure of the present invention is in the amorphous state, the rotation angle of the selected supercell is changed, and linearly polarized light at an arbitrary angle is incident. Detailed implementation manners

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0028] The following further elaborates on the embodiments of the present invention with reference to the accompanying drawings.

[0029] This case innovatively proposes an advanced phase-change dual-atom metasurface design that integrates dielectric material nanocolumns and phase-change material nanocolumns. This design not only endows the metasurface with excellent flexibility in polarization direction regulation but also enables its function to change dynamically with the switching of the phase-change material state.

[0030] Specifically, in the basic unit of this metasurface, nanocolumn 1 is designed as a rectangular nanocolumn composed of hydrogenated amorphous silicon, and nanocolumn 2 is designed as a cylindrical nanocolumn composed of the phase-change material antimony selenide. The cylindrical nanocolumn plays the role of dynamic phase regulation, while the rectangular nanocolumn is equivalent to a half-wave plate responsible for realizing polarization state conversion. When light acts on both types of nanocolumns simultaneously, the cylindrical nanocolumn allows the transmitted light to maintain the original polarization state of the incident light, while the rectangular nanocolumn changes the polarization state of the incident light. These two transmitted lights are then superimposed. After superimposition, the polarization angle of the transmitted light of the supercell is only related to the rotation angle of the rectangular nanocolumn, making the transmitted light output by the entire supercell exhibit linearly polarized characteristics, and its polarization angle is consistent or orthogonal to the rotation angle of the nanocolumn. Therefore, this phase-change dual-atom metasurface realizes a linear polarizer at an arbitrary angle. When a phase change occurs, the polarization angle of the linear polarizer changes from being the same as the rotation angle of the rectangular nanocolumn to being orthogonal to the rotation angle of the rectangular nanocolumn.

[0031] Figure 1 The functional schematic diagram of the phase-change dual-atom metasurface of the present invention in different states and the schematic diagram of the metasurface unit structure are given. As Figure 1As shown in the functional schematic diagram, when the rotation angle of the rectangular nanorods is α, at the incident wavelength, when the cylindrical nanorods are in the amorphous state, the metasurface behaves as a linear polarizer with a polarization angle of α±90°, that is, the polarization angle of the transmitted light always remains ±90° with respect to the rotation angle of the rectangular nanorods. When the temperature rises to 200 °C, the cylindrical nanorods are converted from the amorphous state to the crystalline state, and the metasurface still behaves as a linear polarizer, but the polarization angle of its transmitted light is converted to α, which is consistent with the rotation angle of the rectangular nanorods. By simply changing the rotation angle of the rectangular nanorods, the polarization angle of the transmitted light of the metasurface also changes. As Figure 1 shown, the metasurface is composed of a series of antimony selenide cylindrical nanorods and hydrogenated amorphous silicon rectangular nanorods arranged on a silica substrate. The supercell structure is square, with a period of P = 636 nm, and the height of all nanorods is H = 700 nm.

[0032] For anisotropic rectangular nanorods, its Jones matrix can be expressed as:

[0033]

[0034] where |t xx1 | (|t yy1 |), are the amplitude and phase of the transmitted light when light is incident along the x (y) axis. By applying a rotation angle α relative to the x-axis to the structure, the Jones matrix can be expressed as:

[0035]

[0036] When |t xx1 | = |t yy1 |, that is , the Jones matrix of the rectangular nanorods can be expressed as:

[0037]

[0038] For isotropic cylindrical nanorods, its Jones matrix can be expressed as:

[0039]

[0040] When |t xx1 | = |t xx2 |, , the Jones matrix of the supercell can be expressed as:

[0041]

[0042] When any polarized light is incident, the Jones vector of the transmitted light can be expressed as:

[0043]

[0044] It can be seen from the Jones vector of the transmitted light that appropriate cylindrical nanocolumns and rectangular nanocolumns can be equivalent to a linear polarizer, and its polarization angle is consistent with the rotation angle of the rectangular nanocolumn.

[0045] To verify the above theory, the finite-difference time-domain method is used for numerical simulation to determine the geometric dimensions of the two nanocolumns. First, for the rectangular nanocolumn half-wave plate, its dimensions are scanned, and the transmittance (x-linearly polarized light with an incident wavelength of λ = 1215 nm) and the phase difference between the fast and slow axes of the nanocolumn are observed under different length and width settings (100 nm - 315 nm), as Figure 2 shown. According to the scanning results, a structure that simultaneously satisfies high transmittance and a phase difference of π is selected. Here, we select a rectangular nanocolumn with a length of L = 300 nm and a width of W = 160 nm as an example, whose transmittance exceeds 90%, and the phase difference is π.

[0046] For the dimensions of the cylindrical nanocolumn, a two-atom model is constructed, where the rotation angle of the rectangular nanocolumn is set to 45° (x-linearly polarized light with an incident wavelength of λ = 1215 nm). By changing the diameter of the cylindrical nanocolumn (180 nm - 300 nm), the degree of linear polarization (DOLP), the principal axis angle, and the transmittance of the transmitted light are observed in different states. As Figure 3 shown, the DOLP of the transmitted light should not be lower than 0.9. In the amorphous state, its principal axis angle should be around -45°, and in the crystalline state, its principal axis angle should be around 45°. According to Malus' law, the ideal transmittance value of the transmitted light at this time is 50%. After the above screening conditions, the diameter (D) of the cylindrical nanocolumn is finally selected as 252 nm.

[0047] To verify our hypothesis, when the cylindrical nanocolumn is in the crystalline state, the metasurface behaves as a 45° linear polarizer, and when the cylindrical nanocolumn is in the amorphous state, the metasurface behaves as a -45° linear polarizer. The present invention changes the polarization angle of the incident light, and the polarization angle changes in the range of (0° - 180°), and the DOLP, the principal axis angle, and the transmittance of the transmitted light are observed. According to Malus' law, when the rotation angle of the rectangular nanocolumn is 45°, the ideal transmittance value of the transmitted light at this time should be 50%. As Figure 4 shown, we obtain that in the crystalline state, except for the gray part (the incident light polarization angle range is 20° - 70°), for the rest, the DOLP, the principal axis angle, and the transmittance of the transmitted light all meet the conditions. In the amorphous state, except for the gray part (the incident light polarization angle range is 110° - 160°), for the rest, the DOLP, the principal axis angle, and the transmittance of the transmitted light all meet the conditions. Since the transmittance of the transmitted light in the gray part is lower than 20%, it is not meaningful to discuss the DOLP and the principal axis angle of the transmitted light here, so the anomalies of the DOLP and the principal axis angle here can be ignored.

[0048] To further verify that the designed metasurface can realize a linear polarizer at any angle, the present invention changes the polarization angle of the incident light and the rotation angle of the rectangular nanocolumn in the crystalline and amorphous states, respectively, with the range of (0°-180°). Figure 5 As shown, in the crystalline state, we scanned DOLP, principal axis angle, and transmittance for different incident light polarization angles and rectangular nanorod rotation angles (0°-180°). At this time, the DOLP of the linear polarizer should not be less than 0.9, the polarization angle should be consistent with the rotation angle α of the rectangular nanorod, and the ideal value of its transmittance follows Malus's law.

[0049] It can be seen from the figure that the DOLP and the principal axis angle meet the requirements and the transmittance follows Malus's law. It is worth noting that in the circled area of ​​the DOLP and principal axis angle diagram (part of the gray area mentioned above), anomalies can be seen, which are explained as follows: for incident light with a polarization angle of θ, the transmitted light of the cylindrical nanorod maintains the same polarization angle θ, and when the rectangular nanorod is set along the α direction, it will change the polarization angle of the transmitted light to 2α-θ. As long as the two beams of transmitted light can be decomposed and have a field component in the α direction, it is possible to obtain a polarization component in the α direction during transmission. However, near the area where the incident light polarization angle is orthogonal to the fast axis of the rectangular nanorod, that is, θ = α ± 90°, the polarization angles of the transmitted light of the two nanorods are both α ± 90°, and the field component along the α direction cannot be decomposed. Therefore, a slight change in the amplitude and phase of the metasurface transmitted light may lead to elliptical polarization rather than linear polarization. The faults in the area indicated by the arrows in the principal axis angle diagram are due to the fact that when the super-element is numerically simulated using the finite difference method, FDTD will perform modular operations in the range of -90°-90°. For example, when the principal axis angle of the transmitted light is 90.5°, FDTD will regard the principal axis angle as -89.5°, resulting in faults in the diagram.

[0050] like Figure 6 As shown, in the amorphous state, we also scanned DOLP, principal axis angle, and transmittance for different incident light polarization angles and rectangular nanocolumn rotation angles (0°-180°). At this time, DOLP is not less than 0.9, and the linear polarizer polarization angle is in a ±90° relationship with the rectangular nanocolumn rotation angle α. Its ideal transmittance follows Malus's law. It can be seen from the figure that DOLP and principal axis angle meet the requirements and the transmittance follows Malus's law. It is worth noting that there are also abnormal points near the area where the incident light polarization angle is parallel to the fast axis of the rectangular nanocolumn (part of the gray area mentioned above). Here, because the transmitted light of the two nanocolumns cannot decompose the field component along the α direction, slight changes in the amplitude and phase of the metasurface transmitted light may lead to elliptical polarization rather than linear polarization. In the area indicated by the arrow in the principal axis angle diagram, a fault occurs, which is also due to the modular operation of the numerical simulation results.

[0051] The dynamic linear polarization device based on the phase-change diatomic metasurface proposed in the embodiment of the present invention can achieve the conversion of two linear polarizers with different polarization angles only by changing the temperature, has high sensitivity and flexibility, and can effectively expand the application scenarios of this type of device in the fields of optical encryption technology, polarization imaging, etc.

[0052] It should be noted that in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0053] The above are only specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. Design of a dynamic linear polarization device based on a phase-change dual-atom metasurface, characterized in that, The linear polarization device is a single-layer metasurface composed of supercells formed by dielectric material nanocolumns 1 and phase change material nanocolumns 2; When the phase change material is in the crystalline state, the transmitted light is linearly polarized light with a polarization angle equal to the rotation angle of nanocolumn 1; when the phase change material is in the amorphous state, the transmitted light is linearly polarized light with a polarization angle orthogonal to the rotation angle of nanocolumn 1.

2. The dynamic linear polarization device based on a phase change diatomic metasurface according to claim 1, wherein The phase change double-atom metasurface is composed of an array of periodically arranged supercell structures and has the ability to adjust the polarization angle by changing the temperature.

3. The dynamic linear polarization device based on the phase change diatomic metasurface according to claim 1, characterized in that, The supercell is jointly constructed by the double-atom structure of nanocolumn 1 and nanocolumn 2. Among them, the constituent material of nanocolumn 2 is a phase change material, while nanocolumn 1 is composed of a highly transparent dielectric material; The phase change double-atom metasurface is located on a silica substrate and its working mode is transmissive.

4. The dynamic linear polarization device based on the phase-change diatomic metasurface according to claim 1, wherein Among them, nanocolumn 2 is used for dynamic phase regulation, and the phase difference between its amorphous state and crystalline state is designed to be π. Nanocolumn 1 is designed as a half-wave plate, which is responsible for realizing the conversion of polarization states; When light acts on these two types of nanocolumns simultaneously, nanocolumn 2 allows the transmitted light to maintain the original polarization state of the incident light, while nanocolumn 1 changes the polarization state of the incident light. These two transmitted lights are then superimposed. After superimposition, the polarization angle of the transmitted light of the supercell is only related to the rotation angle of nanocolumn 1, making the transmitted light output by the entire supercell exhibit linear polarization characteristics. When a phase change occurs in nanocolumn 2, a phase difference of π is generated before and after the phase change, causing the polarization angle of the transmitted light to change by ±90°.

5. The dynamic linear polarization device based on a phase change diatomic metasurface according to claim 1, characterized in that, At the incident wavelength, the nanocolumn 2 composed of a phase change material in the periodically arranged supercell double-atom is designed to have a phase difference of π before and after the phase change, that is, nanocolumn 2 needs to satisfy that when the same linearly polarized light is incident, it shows high transmittance and a phase difference of π before and after the phase change; the size of nanocolumn 2 meets this requirement; Nanocolumn 1 is designed as a half-wave plate, that is, it is composed of a dielectric material in the periodically arranged supercell double-atom, and satisfies that the transmittance is equal and the phase difference is π when x and y linearly polarized lights are incident; the size design of nanocolumn 1 meets the requirements of a half-wave plate.

6. The dynamic linear polarizer based on the phase-change diatomic metasurface according to claim 1, wherein, When the rotation angle of nanocolumn 1 is α and nanocolumn 2 is in the crystalline state, the transmitted light of the supercell is linearly polarized light with a polarization angle of α. When nanocolumn 2 is in the amorphous state, the transmitted light of the supercell is linearly polarized light with a polarization angle of α±90°.

7. A dynamic linear polarization device based on a phase change diatomic metasurface according to claim 1, characterized in that, When the rotation angle of nanocolumn 1 changes from 0° to 180° and nanocolumn 2 is in the amorphous state, the transmitted light is linearly polarized light with a polarization angle orthogonal to the rotation angle of nanocolumn 1; When the temperature rises to 200 °C and nanocolumn 2 is in the crystalline state, the transmitted light is linearly polarized light with a polarization angle equal to the rotation angle of nanocolumn 1.

8. A dynamic linear polarization device based on a phase-change diatomic metasurface, characterized in that, Using the dynamic linear polarization device based on the phase change double-atom metasurface as described in any one of claims 1-7 to polarize the incident light, including: Under normal temperature conditions, nanocolumn 2 is in the amorphous state. The incident light is incident into the designed dynamic linear polarization device, and its transmitted light is converted into linearly polarized light with a polarization angle orthogonal to the rotation angle of nanocolumn 1. Further, by changing the rotation angle of nanocolumn 1, the polarization angle of the transmitted light can be changed; When the temperature rises to 200 °C, the nanocolumn 2 is in a crystalline state. When incident light is injected into the designed dynamic linear polarization device, its transmitted light can be converted into linearly polarized light with a polarization angle the same as the rotation angle of the nanocolumn 1.

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