GST-based terahertz surface plasmon dynamic wavefront regulation and control device

Abstract

The invention relates to a terahertz dynamic surface plasmon wavefront regulation and control device, and provides a new device for realizing terahertz surface plasmon wavefront dynamic regulation and control on a GST metasurface. According to the terahertz surface plasmon dynamic wavefront regulation and control device based on the GST, a silicon substrate is arranged at the bottom, and a lossy metal aluminum film with a sub-wavelength rectangular slit resonator array is arranged on the silicon substrate; two columns of slit resonator arrays which are perpendicular to each other and distributed along the y axis form an active group or a passive group, the difference between the active group and the passive group is that a germanium antimony tellurium GST thin film strip is deposited on the surface of a metal aluminum film of the active group, the surface of the passive group is not deposited, and the active group and the passive group are arranged adjacently; switching of different functions of the surface plasmon is realized by using the rotation angle of the sub-wavelength slit resonators, the relative distance between the sub-wavelength slit resonators and the GST phase change characteristic. The surface plasmon wavefront regulation and control device is mainly applied to design and manufacturing occasions of the surface plasmon wavefront regulation and control device.

Description

Technical Field

[0001] This invention relates to terahertz dynamic surface plasmon wavefront modulation devices, and more particularly to dynamic wavefront modulation of terahertz surface plasmons by integrating a phase change material Ge2Sb2Te5 (GST) onto the device surface and utilizing the metal-dielectric properties of GST before and after the phase transition. Specifically, it relates to a GST-based terahertz surface plasmon dynamic wavefront modulation device. Background Technology

[0002] Surface plasmons (SPs) formed by free-space light coupling to a metal-dielectric surface are a special form of electromagnetic wave [1]. Given their two-dimensional propagation characteristics, they have broad application prospects in many fields such as biosensing [2], nonlinear applications [3], waveguides [4] and communications [5], and therefore have attracted much attention in the development of next-generation compact and integrated on-chip plasmon devices. However, previous research on most surface plasmons has certain limitations. They are either carried out in a passive manner, that is, lacking active control methods, and can only be generated and propagated passively by relying on specific external conditions; or they are only dynamically controllable during propagation, and such controllability is often limited and difficult to meet the growing application needs. Therefore, it is urgent to find new and effective methods to excite and dynamically control surface plasmons on the wavefront in order to expand their application potential in the terahertz field.

[0003] In recent years, metasurfaces composed of subwavelength artificial microstructures have attracted widespread attention. Their dielectric constant and permeability can be adjusted at will through careful design of microstructures, and they have shown excellent ability to control the amplitude, phase and polarization of electromagnetic waves. As a result, many ultra-thin functional devices have been realized, such as beam control[6], holography[7] and metalenses[8], and a robust method for coupling and controlling surface plasmons[9]. Although metasurfaces are crucial to the development of optical devices, their functions are usually fixed after design and manufacturing, which hinders the application of advanced photonics. At present, the surface plasmons controlled by metasurfaces are mostly passive and untunable. After the structure is fixed, the dynamic control of the wavefront is difficult and costly, which greatly hinders the application of surface plasmon devices on the chip system. With the development of society, modern electromagnetic and photonic systems have an urgent need for active and tunable devices, and the importance of using metasurfaces to dynamically control surface plasmons is increasing.

[0004] In recent years, by integrating functional materials into metasurface structures, the response of metasurfaces can be further modulated by external stimuli (such as heat, electricity, or light). To date, a variety of functional materials, including semiconductors [10-12], liquid crystals [13-16], MEMS [17-21], graphene [22-25], perovskites

[26] , VO2 [27-30], and transistors [31,32], have been used to dynamically manipulate THz waves. However, these functional materials are volatile and require continuous external excitation to maintain the phase transition. Once the excitation disappears, the phase transition stops, increasing the complexity and energy consumption of the system. Therefore, it is urgent to develop an energy-efficient active metasurface in the terahertz field. Among them, germanium-antimony-tellurium Ge2Sb2Te5 (GST) is a high-performance chalcogenide phase transition material that exhibits significant differences between its amorphous and crystalline states. Amorphous GST can be locally heated to its crystallization temperature by applying light or electrical pulses, or crystallized by heating the entire sample [33-35]. In contrast, the amorphization of GST can be achieved by applying high-intensity short pulses to heat crystalline GST to a temperature above its melting point, followed by rapid cooling to prevent recrystallization

[36] . Once in a crystalline or amorphous state, GST is very stable, typically remaining stable at zero power for several years at room temperature [37,38]. For this reason, GST has received widespread attention from researchers over the past few decades. By combining GST with metasurfaces, its enormous potential in tunable photonics has been gradually explored. Compared to other materials commonly used in terahertz wave tunable devices, it eliminates the need for frequent excitation to maintain performance, greatly improving the reliability and stability of the system. However, the use of GST metasurfaces to control surface plasmon resonances is still in its early stages, but it has broad application prospects. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention aims to propose a new method for dynamic control of terahertz surface plasmon wavefronts using GST metasurfaces. Therefore, the technical solution adopted in this invention is a terahertz surface plasmon dynamic wavefront modulation device based on GST. The bottom is a silicon substrate, and on the silicon substrate is a lossy aluminum film with a subwavelength rectangular slit resonator array. Two columns of slit resonator arrays distributed perpendicularly along the y-axis constitute an active group or a passive group. The difference between the active group and the passive group is that the surface of the aluminum film of the active group is deposited with a germanium-antimony-tellurium GST thin film strip, while the surface of the passive group is not deposited. The active group and the passive group are arranged adjacent to each other. The slit resonators in each column are arranged according to the phase distribution and deflected by angles along the x-direction. The overall surface plasmon excitation process is as follows: the incident terahertz wave first enters perpendicularly to the substrate. After passing through the substrate, most of the light is reflected by the aluminum film. A small portion of the light generates a local field with the subwavelength rectangular slit resonator and couples with the active free electrons on the metal surface to form surface plasmons. By utilizing the rotation angle of the subwavelength slit resonator, the relative distance between the subwavelength slit resonators, and the phase transition characteristics of GST, the switching of different functions of the surface plasmons is realized.

[0006] The device comprises two active groups and a passive group positioned between the active groups. When the GST is in the pre-phase transition state, the GST acts as a dielectric, and the two active groups U1 and U2 and the passive group U3 operate simultaneously. However, due to the π phase shift of the surface plasmons excited by U2 and U3, destructive interference occurs, so the device's function is provided solely by U1. When the GST is in the post-phase transition state, the GST acts like a metal, thereby shutting off the terahertz wave response of the subwavelength slit resonator, causing the active groups U1 and U2 to cease operation, and the device's function is provided solely by U3. By utilizing the rotation angle of the subwavelength slit resonator and the relative distance between the subwavelength slit resonators to form the wavefronts of U1 and U3, the device can exhibit different functions before and after the GST phase transition.

[0007] Along the x-axis, the passive group U3 satisfies the following condition: θ2-θ1=3π / 2, s is the distance between the two resonators and s=λ SP / 2,λ SP The operating wavelength of the surface plasmon polariton is θ1, and θ2 are the electric field values, respectively. The angle with the x-axis, These are the field components that can excite the left and right column slit resonators in the incident terahertz wave, respectively, when the incident light is circularly polarized. in The incident electric field vector, (1,σi) are the components of the Jones vector, and i is the imaginary unit. 2=-1, σ∈{+1,-1} represent left-handed circularly polarized terahertz wave LCP and right-handed circularly polarized terahertz wave RCP, respectively. The field representation of the excited surface plasmons is:

[0008]

[0009] Where A is the amplitude of the surface plasmon resonance, and i is the imaginary unit. 2 =-1, θ1 and θ2 are the electric fields The angle with the x-axis, l is the distance between the center point of the two resonators and point N, N is a point on the aluminum film outside the active and passive groups, s is the distance between the two rows of resonators, and the wavenumber of the surface plasmon resonance is ksp = 2π / λ. SP , λ SP It is the operating wavelength of the surface plasmon polariton, determined by the surface plasmon field E. U3 The formula shows that the field amplitude of the surface plasmon excited by the passive group U3 at point N is fixed, while the phase is freely controllable. Its sign is determined by the direction of circular polarization and varies with the rotation angle of the subwavelength slit resonator. Since the subwavelength slit resonator can rotate 180°, the phase change can cover the entire 2π range. Therefore, arbitrary phase distributions can be achieved using slit resonators. For subwavelength slit resonators, when the distance s between the corresponding subwavelength slit resonators becomes mλ... SP Where m is an integer, and considering the low loss of surface plasmon resonances, the phase response of the subwavelength slit resonator is nearly constant. The active and passive groups have the same dimensions but different geometric phases and propagation phases. The geometric phase refers to the rotation angle of the subwavelength slit resonator, and the propagation phase refers to the horizontal distance between the subwavelength slit resonators. At point N, the field E... N It is a superposition of surface plasmons excited by the active / passive groups U1, U2, and U3: E N =E U1N +E U2N +E U3N , E U1N E U2N E U3N The surface plasmons excited by the active / passive groups U1, U2, and U3 are respectively. The active groups U1 and U2 have the same geometric phase, but their propagation phases are different: s U1 =s+λ SP s U1 and s represent the horizontal distances between different groups of subwavelength slit resonators, i.e., E U1N =e iπ E U2N This means that the surface plasmons E excited by the U1 structure U1N With surface plasmons E excited by the U2 structure U2NCompared to having a π phase shift, i.e., E U1N =-E U2N Therefore, when active groups U1 and U2 are working, destructive interference will occur, meaning E N =E U1N The device's functionality is provided solely by the active group U1; furthermore, if the active groups U1 and U2 are turned off by the crystalline GST, the device's functionality will be provided solely by the passive group U3.

[0010] The device comprises two active groups and a passive group sandwiched between the active groups, and achieves surface plasmon coupling by designing different phases of two metal slits: this coupling effect is expressed as when the phase of the subwavelength slit resonator is tuned such that... When this coupling is applied, it can act as a secondary emission source, and the excited surface plasmons collectively generate an in-phase wavefront. This allows the subwavelength slit resonators to be arranged in a linear phase distribution along the y-direction, and the phase gradient can be controlled. To control the anomalous refraction angle of surface plasmons Where σ∈{+1,-1} represent the incident left-hand circularly polarized terahertz wave (LCP) and right-hand circularly polarized terahertz wave (RCP), respectively:

[0011]

[0012] Both the active and passive groups are obtained by arranging subwavelength metal slits with different rotation directions along the y-axis, and the rotation angle is calculated by formula (1):

[0013]

[0014] Where y is the coordinate position of the slit resonator on the y-axis. When the chirality of the circularly polarized CP changes, the direction of the excited surface plasmons will also change. When the circularly polarized terahertz wave is incident perpendicularly, the corresponding phases of the three structures are shown in formula (2).

[0015] It comprises two active groups U1 and U2, and a passive group U3 positioned between the active groups. This transforms the linear phase distribution of the subwavelength slit resonator into a lens phase distribution, thus achieving the function of a superlens. Specifically, both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with rotation angle distributions... The relationship with position y is calculated using formula (3):

[0016]

[0017] Where f is the focal length of the superlens, and according to the formula, the subwavelength slit resonator rotation angle at the corresponding y position is... From formula (3), the signs of the corresponding superlens phase distributions of U1 and U3 differ by a negative sign, so the polarities of the superlenses formed by the two groups of U1 and U3 are opposite; U2 and U3 have the same polarity and realize the function of convex lens / concave lens when right-hand circularly polarized light / left-hand circularly polarized light terahertz wave is incident, but the phases of the two groups of U2 and U3 have a π phase shift, and coherent cancellation will occur when the two groups work at the same time, and the opening and closing of U1 and U2 can be controlled by GST; through such structural distribution, the device can exhibit the functions of U1 and U3 before and after the GST phase transition, respectively, to realize the function switching: after being excited by right-hand circularly polarized light terahertz wave at room temperature, it exhibits a diverging wavefront, and the polarity of the superlens is a concave lens. As the annealing temperature increases, after GST is induced to crystallize, the polarity of the superlens is reversed and becomes a convex lens.

[0018] The device comprises two active groups and a passive group sandwiched between the two active groups. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis. The rotation angle is calculated by formula (4). Both the active and passive groups are lens phase distributions. The polarity of structure U1 is the same as that of U2 and U3, but the focal length of U1 is designed to be f1 = 6 mm, while the focal lengths of U2 and U3 are both f2 = 4 mm. The relationship with position y is:

[0019]

[0020] When right-hand circularly polarized light is incident, as the annealing temperature increases, the superlens becomes a convex lens, and the focal length changes from 6mm to 4mm, thus realizing the zoom function of the superlens. Due to spin correlation, when left-hand circularly polarized light is incident, the superlens remains a concave lens. Under nanosecond laser irradiation, the function of the device is reconstructed back to its initial state.

[0021] The characteristics and beneficial effects of the present invention are:

[0022] 1. A surface plasmon excitation phase control technology based on a dual-hole structure is proposed, which breaks through the strong correlation between the traditional excitation region shape and the wave surface shape, realizes the local control of arbitrary phase distribution in any excitation region, and allows for free design of surface plasmon wave surface shape;

[0023] 2. By deeply integrating GST with metasurfaces, the phase change characteristics of phase change materials can overcome the limitations of traditional metasurface functional solidification, providing high-performance solutions for fields such as reconfigurable photonic devices, dynamic holographic displays, and intelligent sensing;

[0024] 3. By combining the dynamically tunable characteristics of active metasurfaces with the control principles of the propagation phase and geometric phase of surface plasmons, a general method for actively controlling surface plasmons is proposed. Attached Figure Description

[0025] Figure 1 This illustrates the working principle of an active metasurface. (a) and (b) are schematic diagrams of a surface plasmon coupler with variable refractive angles, consisting of three sets of structures U1, U2, and U3. Any two functions can be reversibly switched through GST crystallization and amorphization; (c) and (d) are schematic diagrams of a polarity-variable surface plasmon superlens; (e) and (f) are schematic diagrams of a variable surface plasmon superlens; (g) is a schematic diagram used to derive the phase of surface plasmons excited by the metasurface, showing the active group U1 and U2, and the passive group U3. The dark and light stripes in the diagram represent the excited surface plasmons.

[0026] Figure 2 The performance characterization results of GST, a schematic diagram of the NSTM system, and partial microscopic images of three metasurface devices are presented. (a) The real parts of the transmittance and conductivity of GST at different annealing temperatures and after nanosecond laser irradiation are shown at an operating frequency of 0.75 THz. (b) A schematic diagram of the NSTM system is depicted; the upper right inset shows a microscopic image of the angle-variable surface plasmon coupler during the experimental characterization process, the structure of which corresponds to the part within the white dashed box in (c). (c) A partial microscopic image of the angle-variable surface plasmon coupler of sample 1. (d) A partial microscopic image of the polarity-variable surface plasmon metal lens of sample 2. (e) A partial microscopic image of the focal length-variable surface plasmon metal lens of sample 3.

[0027] Figure 3 Experimental and simulation characterization of the angle-variable surface plasmon coupler are presented. (a) and (c) show the real parts of Ez obtained experimentally under right-handed and left-handed circularly polarized terahertz wave incidence, respectively. (b) and (d) show the real parts of Ez simulated under RCP and LCP incidence, corresponding to (a) and (c). The labels in the lower right corner indicate the GST state, listing the initial unheated state, the state after annealing in the temperature range of 150°C to 260°C, and the state exposed to 120 mJ / cm². 2 The state after reconstruction by nanosecond laser.

[0028] Figure 4 Experimental and simulation characterization of the polarimetric surface plasmon superlens are presented. (a) and (c) show the real parts of Ez obtained experimentally under right-handed and left-handed circularly polarized terahertz wave incidence, respectively. (b) and (d) show the real parts of Ez simulated under RCP and LCP incidence, corresponding to (a) and (c). The labels in the lower right corner indicate the state of the GST, listing the initial unheated state, the state after annealing in the temperature range of 150°C to 260°C, and the state exposed to 120 mJ / cm². 2 The state after reconstruction by nanosecond laser.

[0029] Figure 5 Experimental and simulation characterization of the angle-variable surface plasmon coupler are presented. (a) and (c) show the real parts of Ez obtained experimentally under right-handed and left-handed circularly polarized terahertz wave incidence, respectively. (b) and (d) show the real parts of Ez simulated under RCP and LCP incidence, corresponding to (a) and (c). The labels in the lower right corner indicate the GST state, listing the initial unheated state, the state after annealing in the temperature range of 150°C to 260°C, and the state exposed to 120 mJ / cm². 2 The state after reconstruction by nanosecond laser. Detailed Implementation

[0030] In the field of terahertz surface plasmon dynamic wavefront modulation technology, this invention specifically relates to a general method for actively modulating surface plasmons by combining the dynamically tunable characteristics of GST with the control principles of the propagation phase and geometric phase of surface plasmons. Three active devices were fabricated for verification.

[0031] The technical solution adopted in this invention is a terahertz surface plasmon dynamic wavefront modulation device based on GST. The bottom is a silicon substrate, and on the silicon substrate is a lossy aluminum film with a subwavelength rectangular slit resonator array. Two columns of slit resonator arrays distributed perpendicularly along the y-axis form an active group or a passive group. The difference between the active group and the passive group is that the surface of the aluminum film of the active group is deposited with a germanium-antimony-tellurium GST thin film strip, while the surface of the passive group is not deposited. The active group and the passive group are arranged adjacent to each other. The slit resonators in each column are arranged according to the phase distribution and deflected by angles along the x-direction. The overall surface plasmon excitation process is as follows: the incident terahertz wave first enters perpendicularly to the substrate. After passing through the substrate, most of the light is reflected by the aluminum film. A small portion of the light generates a local field with the subwavelength rectangular slit resonator and couples with the active free electrons on the metal surface to form surface plasmons. By utilizing the rotation angle of the subwavelength slit resonator, the relative distance between the subwavelength slit resonators, and the phase transition characteristics of GST, the switching of different functions of the surface plasmons is realized.

[0032] The device comprises two active groups and a passive group positioned between the active groups. When the GST is in the pre-phase transition state, the GST acts as a dielectric, and the two active groups U1 and U2 and the passive group U3 operate simultaneously. However, due to the π phase shift of the surface plasmons excited by U2 and U3, destructive interference occurs, so the device's function is provided solely by U1. When the GST is in the post-phase transition state, the GST acts like a metal, thereby shutting off the terahertz wave response of the subwavelength slit resonator, causing the active groups U1 and U2 to cease operation, and the device's function is provided solely by U3. By utilizing the rotation angle of the subwavelength slit resonator and the relative distance between the subwavelength slit resonators to form the wavefronts of U1 and U3, the device can exhibit different functions before and after the GST phase transition.

[0033] Along the x-axis, the passive group U3 satisfies the following condition: θ2-θ1=3π / 2, s is the distance between the two resonators and s=λ SP / 2,λ SP The operating wavelength of the surface plasmon polariton is θ1, and θ2 are the electric field values, respectively. The angle with the x-axis, These are the field components that can excite the left and right column slit resonators in the incident terahertz wave, respectively, when the incident light is circularly polarized. in The incident electric field vector, (1,σi) are the components of the Jones vector, and i is the imaginary unit. 2 =-1, σ∈{+1,-1} represent left-handed circularly polarized terahertz wave LCP and right-handed circularly polarized terahertz wave RCP, respectively. The field representation of the excited surface plasmons is:

[0034]

[0035] Where A is the amplitude of the surface plasmon resonance, i is the imaginary unit, i2 = -1, and θ1 and θ2 are the electric field values, respectively. The angle with the x-axis, l is the distance between the center point of the two resonators and point N, N is a point on the aluminum film outside the active and passive groups, s is the distance between the two rows of resonators, and the wavenumber of the surface plasmon resonance is ksp = 2π / λ. SP , λ SP The operating wavelength of the surface plasmon resonance (SPR) is given by the formula. The field amplitude of the SPR excited by the passive group U3 at point N is fixed, while the phase is freely controllable. Its sign is determined by the direction of circular polarization and varies with the rotation angle of the subwavelength slit resonator. Since the subwavelength slit resonator can rotate 180°, the phase change can cover the entire 2π range. Therefore, arbitrary phase distributions can be achieved using slit resonators. For subwavelength slit resonators, when the distance s between the corresponding subwavelength slit resonators becomes mλ... SP Where m is an integer, and considering the low loss of surface plasmon resonances, the phase response of the subwavelength slit resonator is nearly constant. The active groups have the same dimensions but different geometric phases and propagation phases. The geometric phase refers to the rotation angle of the subwavelength slit resonator, and the propagation phase refers to the horizontal distance between the subwavelength slit resonators. At point N, the field E... N It is a superposition of surface plasmons excited by the active / passive groups U1, U2, and U3: E N =E U1N +E U2N +E U3N , E U1N E U2N E U3NThe surface plasmons excited by the active / passive groups U1, U2, and U3 are respectively. The active groups U1 and U2 have the same geometric phase, but their propagation phases are different: s U1 =s+λ SP s U1 and s represent the horizontal distances between different groups of subwavelength slit resonators, i.e., E U1N =e iπ E U2N This means that the surface plasmons E excited by the U1 structure U1N With surface plasmons E excited by the U2 structure U2N Compared to having a π phase shift, i.e., E U1N =-E U2N Therefore, when active groups U1 and U2 are working, destructive interference will occur, meaning E N =E U1N The device's functionality is provided solely by the active group U1; furthermore, if the active groups U1 and U2 are turned off by the crystalline GST, the device's functionality will be provided solely by the passive group U3.

[0036] The device comprises two active groups and a passive group sandwiched between the active groups, and achieves surface plasmon coupling by designing different phases of two metal slits: this coupling effect is expressed as when the phase of the subwavelength slit resonator is tuned such that... When this coupling is applied, it can act as a secondary emission source, and the excited surface plasmons collectively generate an in-phase wavefront. This allows the subwavelength slit resonators to be arranged in a linear phase distribution along the y-direction, and the phase gradient can be controlled. To control the anomalous refraction angle of surface plasmons Where σ∈{+1,-1} represent the incident left-hand circularly polarized terahertz wave (LCP) and right-hand circularly polarized terahertz wave (RCP), respectively:

[0037]

[0038] Both the active and passive groups are obtained by arranging subwavelength metal slits with different rotation directions along the y-axis, and the rotation angle is calculated by formula (2):

[0039]

[0040] Where y is the coordinate position of the slit resonator on the y-axis. When the chirality of the circularly polarized CP changes, the direction of the excited surface plasmons will also change. When the circularly polarized terahertz wave is incident perpendicularly, the corresponding phases of the three structures are shown in formula (2).

[0041] It comprises two active groups U1 and U2, and a passive group U3 positioned between the active groups. This transforms the linear phase distribution of the subwavelength slit resonator into a lens phase distribution, thus achieving the function of a superlens. Specifically, both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with rotation angle distributions... The relationship with position y is calculated using formula (3):

[0042]

[0043] Where f is the focal length of the superlens, and according to the formula, the subwavelength slit resonator rotation angle at the corresponding y position is... From formula (3), the signs of the corresponding superlens phase distributions of U1 and U3 differ by a negative sign, so the polarities of the superlenses formed by the two groups of U1 and U3 are opposite; U2 and U3 have the same polarity and realize the function of convex lens / concave lens when right-hand circularly polarized light / left-hand circularly polarized light terahertz wave is incident, but the phases of the two groups of U2 and U3 have a π phase shift, and coherent cancellation will occur when the two groups work at the same time, and the opening and closing of U1 and U2 can be controlled by GST; through such structural distribution, the device can exhibit the functions of U1 and U3 before and after the GST phase transition, respectively, to realize the function switching: after being excited by right-hand circularly polarized light terahertz wave at room temperature, it exhibits a diverging wavefront, and the polarity of the superlens is a concave lens. As the annealing temperature increases, after GST is induced to crystallize, the polarity of the superlens is reversed and becomes a convex lens.

[0044] The device comprises two active groups and a passive group sandwiched between the two active groups. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis. The rotation angle is calculated by formula (4). Both the active and passive groups are lens phase distributions. The polarity of structure U1 is the same as that of U2 and U3, but the focal length of U1 is designed to be f1 = 6 mm, while the focal lengths of U2 and U3 are both f2 = 4 mm. The relationship with position y is:

[0045]

[0046] When right-hand circularly polarized light is incident, as the annealing temperature increases, the superlens becomes a convex lens, and the focal length changes from 6mm to 4mm, thus realizing the zoom function of the superlens. Due to spin correlation, when left-hand circularly polarized light is incident, the superlens remains a concave lens. Under nanosecond laser irradiation, the function of the device is reconstructed back to its initial state.

[0047] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples.

[0048] The technical solution adopted in this invention is a terahertz surface plasmon dynamic wavefront modulation device based on GST. In the terahertz band, the concept of phase discontinuity in free space is introduced into a metasurface composed of subwavelength slit resonators. Simultaneously, GST is integrated onto the metasurface. By controlling the phase transition state of the GST, the excitation and dynamic wavefront modulation of terahertz surface plasmons are realized. Furthermore, by appropriately designing the spatial distribution of the subwavelength slit resonators, almost arbitrary phase distributions can be achieved, thus realizing different functions. This method consists of three sets of structures: two active sets (U1, U2) integrating GST subwavelength slit resonators, and one passive set (U3) composed of subwavelength slit resonators. The effective working structure of the device is switched by changing different phase states of the GST. When the GST is in an amorphous state, the function of the surface plasmon device is determined by the combined action of the three sets of structures. When the GST is in a crystalline state, the function of the device is determined solely by the passive set (U3). Dynamic wavefront modulation of the device can be achieved by rationally designing the phase distribution of the three sets of structures.

[0049] Specifically, different wavefront modulations are achieved through the interaction of three sets of subwavelength slit resonators. Two active groups, U1 and U2, have GST phase-change material integrated on their surfaces. The remaining passive group, U3, has a propagation phase difference of π between the surface plasmons excited by the active group U2 and the surface plasmons excited by the active group. When the GST is in the pre-phase-change state, it acts as a medium, and both the active and passive groups work simultaneously. However, due to the π phase shift of the surface plasmons excited by U2 and U3, destructive interference occurs, so the device function is provided only by U1. When the GST is in the post-phase-change state, it acts like a metal, and its high conductivity can shut down the terahertz wave response of the subwavelength slit resonator. Therefore, the active groups U1 and U2 do not work, and the device function is provided only by U3. At this time, by reasonably designing the wavefronts of U1 and U3, the device function can exhibit different functions before and after the GST phase change.

[0050] Subwavelength slit resonators with surface-integrated phase change material GST are active groups U1 and U2, while those without integrated GST are passive group U3. The positive phase transition from amorphous to crystalline GST is achieved by heating GST at an annealing temperature on a heating stage, and the reverse phase transition from crystalline to amorphous GST is achieved by irradiating GST with a nanosecond laser generated by a laser. Before the phase transition, GST in a dielectric state has a transmission coefficient close to 1 relative to the silicon substrate in the terahertz band, so it will not short-circuit active groups U1 and U2. All three metasurface structures work normally at the same time. When U2 and U3 are in the working state at the same time, the excited surface plasmons have a π phase shift and will cause destructive interference, so the device exhibits the function of structure U1. After the GST phase transition, the greatly enhanced metallicity of the GST will short-circuit structures U1 and U2, turning off U1 and U2. The device then exhibits the function of structure U3. By rationally designing and arranging the three sets of structures, any two functions can be achieved before and after the GST phase transition, and the achieved functions can be reconfigured, providing a theoretical basis for realizing tunable surface plasmon resonance devices.

[0051] The overall structure is designed with three layers, enabling simultaneous wavefront shaping and surface plasmon excitation. The bottom layer is a 650 μm thick silicon substrate (ε = 11.9), upon which sits a 200 nm thick lossy aluminum film (σ = 3.56 × 10⁻⁶) with a subwavelength rectangular slit resonator array. 7 The device consists of two active groups and one passive group, composed of subwavelength aluminum slit resonators at different angles. A 100 nm thick and 300 μm wide GST thin film strip is deposited on the surface of the two active groups on the aluminum film, while no GST film is deposited on the surface of the passive group. The selected subwavelength slit resonator has a length of a = 66 μm and a width of b = 12 μm. Within these dimensions, the device operates at a frequency of 0.75 THz (λ). SP =400μm). The designed tunable metasurface utilizes circularly polarized-dependent geometric phase (rotation angle of the subwavelength slit resonator), circularly polarized-independent propagation phase (relative distance between the subwavelength slit resonators), and GST phase transition characteristics to achieve switching between different functions of the surface plasmon resonance device. The slit resonators are distributed perpendicularly along two columns along the y-axis, and the different angles are calculated and arranged according to different phase distributions. The overall surface plasmon resonance excitation process is as follows: the incident terahertz wave is first incident perpendicularly from the substrate. After passing through the substrate, most of the light is reflected by the aluminum mode, and a small portion of the light generates a strong local field with the subwavelength rectangular slit resonator, which couples with the active free electrons on the metal surface to form surface plasmons.

[0052] Taking a passive group U3 as an example, along the x-axis, U3 satisfies the following conditions: θ2-θ1=3π / 2, s=λ SP / 2, when the incident light is circularly polarized, i.e. in The incident electric field vector, (1,σi) are the components of the Jones vector. i is the imaginary unit (i... 2 =-1). σ∈{+1,-1} represent left-handed circularly polarized terahertz waves (LCP) and right-handed circularly polarized terahertz waves (RCP), respectively. The field of the excited surface plasmons can be expressed as:

[0053]

[0054] Where A is the amplitude of the surface plasmon resonance, and i is the imaginary unit (ii). 2 =-1), θ 1,2 They are electric fields The angle with the x-axis, l is the distance between the center point of the two resonators and point N, s is the distance between the two resonators, and the wavenumber of the surface plasmon resonance is ksp = 2π / λ. SP , λ SP This is the operating wavelength of the surface plasmon resonance (SPR). From Equation 1, it can be deduced that the field amplitude of the SPR excited by structure U3 at N is fixed, while the phase is freely controllable. Its sign is determined by the direction of circular polarization and varies with the rotation angle of the subwavelength slit resonator. Since the subwavelength slit resonator can rotate 180°, the phase change can cover the entire 2π range, so almost arbitrary phase distributions can be achieved using slit resonators. Fortunately, for subwavelength slit resonators, when the distance s between the corresponding subwavelength slit resonators becomes mλ... SP (Where m is an integer) and considering the low loss of surface plasmon resonances, the phase response of the subwavelength slit resonator can be considered nearly constant. This allows the subwavelength slit resonators to be further separated, permitting concentric arrangement of subwavelength slit resonators with different spacings while sharing the same phase center. Therefore, the metasurface uses three sets of SR structures, all with the same dimensions but different geometric phases (rotation angle θ) and propagation phases (distance s between SRs). At point N, the field E N It is a superposition of surface plasmons excited by structures U1, U2, and U3: E N =E U1N +E U2N +E U3N Structures U2 and U3 have the same geometric phase, but their propagation phases are different (s U2 =s+λ SP That is, E. U2N =e iπ E U3N This means that surface plasmons excited by the U2 structure have a π phase shift compared to surface plasmons excited by the U3 structure, i.e., E U2N =-E U3NTherefore, when GST is in the amorphous state, U2 and U3 will exhibit destructive interference, meaning that E N =E U1N The device's function is provided solely by the active group U1. Furthermore, if the active groups U1 and U2 are turned off by the crystalline GST, the device's function will be provided solely by the passive group U3. A method for dynamic control before and after the GST phase transition was found, and three active devices were designed and characterized based on this scheme.

[0055] The following are three specific examples of the present invention.

[0056] The first device is an angle-variable surface plasmon coupler, consisting of two active groups and one passive group. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with the rotation angle calculated using Equation 2. According to the generalized Snell's law, surface plasmon coupling can be achieved by designing different phases of the two metal slits. This coupling effect is expressed as follows: when the phase of the subwavelength slit resonator is adjusted such that… When this coupling is applied, it can act as a secondary emission source, and the excited surface plasmons collectively generate a wavefront in phase. By arranging the subwavelength slit resonators in a linear phase distribution along the y-direction, the phase gradient can be controlled. To control the anomalous refraction angle of surface plasmons Where σ∈{+1,-1} represents the incident left-handed circularly polarized terahertz wave LCP and right-handed circularly polarized terahertz wave RCP, respectively.

[0057]

[0058] It can be observed that the orientation of the excited surface plasmons also changes when the circular polarization (CP) chirality changes. A schematic diagram of the device is shown below. Figure 1 As shown in (a) and (b), the subwavelength slit resonators are arranged equidistantly along the y-axis. The rotation angle θ1 between any two adjacent pairs of SRs along the y-direction is 30°. The spacing d = 160 μm. Therefore, the length of one phase period is 960 μm. The final designed device contains four phase periods. When a circularly polarized terahertz wave is incident perpendicularly, the corresponding phase distributions of the three structures are as follows:

[0059]

[0060] Where y is the coordinate position of the slit resonator on the y-axis. In order to measure the excitation response of surface plasmons, the probe of the near-field scanning optical microscope (NSTM) system is placed about 50 μm above the sample to detect the electric field component Ez of the excited surface plasmons. Figure 3(a) and (c) show the real part of Ez of surface plasmons excited by a surface plasmon coupler with a variable anomalous refraction angle in the xy plane under right-handed and left-handed circularly polarized light incident light, respectively. The experimental results show that when right-handed (left-handed) circularly polarized light is incident, the surface plasmons propagate downwards (upwards) without heating. This is because the GST is in an amorphous state after sample processing, acting as a medium. In this active device, U2 and U3 have the same geometric phase, but their propagation phases have a π phase shift. When both structures operate simultaneously, the excited surface plasmons undergo coherent destructive propagation. The geometric phase of U1 determines the device's function. When right-handed circularly polarized light is incident, the surface plasmons propagate downwards with an anomalous refraction angle of approximately -24.6°. Due to the spin-dependent characteristics of the geometric phase, when left-handed circularly polarized light is incident, the surface plasmons propagate upwards with an anomalous refraction angle of approximately 24.6°. As the temperature rises to 260℃, when the GST is in a crystalline state, the surface plasmon resonance response of the subwavelength slit resonator under the GST cover is shut down, and only the passive group U3 provides the device's function. When right-handed circularly polarized light is incident, the surface plasmons propagate upwards at an anomalous refraction angle of approximately 24.6°; when left-handed circularly polarized light is incident, the surface plasmons propagate downwards at an anomalous refraction angle of approximately -24.6°. Furthermore, after irradiation with a laser pulse of 1064nm wavelength, 7ns pulse width, 1cm spot diameter, and 120mJ / cm² energy density, the device's function returns to its initial, unheated state, verifying the device's reconstruction characteristics. Therefore, the two functions of the device are determined by U1 and U3 respectively. In this device design, the phase gradients of U1 and U3 differ by a negative sign, causing the propagation directions of the device to be opposite before and after the GST phase transition. Meanwhile, the chiral phases of different circular polarizations differ by a negative sign. Therefore, the switching of device function by changing the GST phase transition state is consistent with the switching of device function by the circular polarization chiral transition, which can also be well verified by experimental results. Furthermore, numerical simulations of the sample were performed using CST software. The y-direction was set as a periodic boundary condition, and the x and z directions were set as open. The incident light was a plane wave, illuminating the sample perpendicularly from the substrate. The surface plasmon field distribution information was obtained using a field monitor at a frequency of 0.75 THz. The simulation results are as follows: Figure 3 As shown in (b, d), the anomalous refraction angles are in excellent agreement with the experimental results.

[0061] The second device is a polarimetric surface plasmon superlens, consisting of two active groups and one passive group. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with the rotation angle calculated using Equation 3. By transforming the linear phase distribution of the subwavelength slit resonator into the lens phase distribution, the superlens function can be achieved. Based on this, a polarimetric surface plasmon superlens was designed at 0.75 THz. Without changing the incident circular polarization state, the polarity of the superlens can be switched simply by changing the amorphous and crystalline states of the GST, such as... Figure 1 As shown in (c) and (d), it consists of three sets of structures, where U1 and U3 are designed with specific phase distributions to achieve a polarity reversal of the lens, and U2 has a phase delay of π compared to U3, which leads to destructive interference. Phase distribution The relationship with position y is:

[0062]

[0063] Where f is the focal length of the superlens, the focal length of which is designed to be f = 6mm. To make the focusing and diverging effects of the superlens more pronounced, a total of 61 structures are arranged in the y-direction, with a span of 9.76mm. According to the formula, the rotation angle of the subwavelength slit resonator at the corresponding y position can be determined. Formula 3 also shows that the signs of the phase distributions of the corresponding superlenses U1 and U3 differ by a negative sign, indicating that the polarities of the two superlenses are opposite. U2 and U3 have the same polarity, functioning as convex (concave) lenses when right-handed (left-handed) circularly polarized (or left-handed) terahertz waves are incident. However, there is a π phase shift between the phases of U2 and U3, leading to coherent destructive phase transitions when both groups operate simultaneously. This can be considered as the two structures being "closed." Furthermore, the opening and closing of U1 and U2 can be controlled by the GST. This structural distribution allows the device to exhibit the functions of U1 and U3 before and after the GST phase transition, respectively, achieving functional switching. Experimental characterization using the NSTM system yields the following results: Figure 4 As shown in (a) and (c), the superlens exhibits a diverging wavefront after being excited by right-handed circularly polarized terahertz waves at room temperature. The superlens is initially concave. With increasing annealing temperature, after GST is induced to crystallize, the polarity of the superlens reverses, transforming it into a convex lens with a focal length of 6 mm. Under nanosecond laser irradiation, the polarity of the superlens returns to its pre-annealing state. Due to spin dependence, the polarity of the superlens is reversed under left-handed circularly polarized terahertz wave excitation compared to when right-handed circularly polarized light is incident. Therefore, the designed superlens can change its polarity by adjusting the chirality of the incident terahertz circularly polarized wave or increasing the annealing temperature of GST, possessing two degrees of freedom for more flexible switching of lens polarity.

[0064] Simulation verification was performed, with similar settings to previous simulations. Open boundary conditions were used in the x, y, and z directions, and surface plasmon field distribution information was obtained using a field monitor at a frequency of 0.75 THz. Figure 4 As shown in (b) and (d), it can be seen that under the incident light of right-handed circularly polarized light (left-handed circularly polarized light), as the annealing temperature gradually increases, the polarity of the superlens changes from a concave (convex) lens to a convex (concave) lens. The simulation results are consistent with the experimental results.

[0065] The third device is a focal length variable surface plasmonic superlens, consisting of two active groups and one passive group. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with the rotation angle calculated using formula 4. Similar to the design principle of the polarity variable surface plasmonic superlens, it also consists of a structure with three lens phase distributions. However, unlike the polarity variable surface plasmonic superlens, the polarity of structure U1 is the same as that of U2 and U3, but the focal length of U1 is designed to be f1 = 6mm, while the focal lengths of U2 and U3 are f2 = 4mm. (Phase distribution) The relationship with position y is:

[0066]

[0067] A total of 61 structures were arranged in the y-direction, with a span of 9.76 mm. The test results using the NSTM system are as follows... Figure 5 As shown in (a) and (c), the experimental results show that when right-handed circularly polarized light is incident, the superlens becomes a convex lens with increasing annealing temperature, and the focal length changes from 6 mm to 4 mm, thus realizing the zoom function of the superlens. Due to spin dependence, the superlens remains a concave lens when left-handed circularly polarized light is incident. Under nanosecond laser irradiation, the device's function is reconstructed back to its initial state, which is highly consistent with the design results. Simulation of the zoom superlens, with the same simulation settings as sample 2, yields the following results: Figure 5 As shown in (b) and (d), the results are in high agreement with the experimental results.

[0068] Among the three devices mentioned above, the subwavelength slit resonator is a small hole etched on a metal aluminum mold, and the metal aluminum film after etching the small hole is the metasurface. Since three devices were designed, each device consists of one passive group and two active groups. The overall structure can be regarded as a concentric arrangement of passive groups (without GST covering the surface) with increased spacing. Each passive group and active group consists of two rows of slits, and the two rows of slits are perpendicular. Figure 1 This is a schematic diagram; the exact structural location can be found in [the diagram]. Figure 2 Microscopic image. The main difference lies in the rotation angle of the aperture, which determines its function. These different rotation angles are calculated using the phase formula, derived from formulas (2), (3), and (4). GST is deposited directly on the surface, corresponding to Figure 2 In the micrograph, the black area represents the GST, which acts as a switch. Before the GST phase transition, terahertz waves incident from the bottom can pass through the small hole normally, and all three structures normally excite surface plasmons. Since the device functions through destructive interference, only U1 provides the functionality. After the GST phase transition, the terahertz waves can no longer pass through the small hole covered by the GST, effectively closing the hole. The device's functionality is then provided solely by the passive group U3, whose surface is not covered by the GST film.

[0069] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A terahertz surface plasmon dynamic wavefront modulation device based on GST, characterized in that, The bottom is a silicon substrate, on which is a lossy aluminum film with a subwavelength rectangular slit resonator array. Two columns of slit resonators, perpendicularly distributed along the y-axis, form either an active or passive group. The difference between the active and passive groups is that the aluminum film in the active group has a germanium-antimony-tellurium (GST) thin film strip deposited on its surface, while the passive group does not. The active and passive groups are arranged adjacent to each other. The slit resonators in each column are arranged according to their phase distribution, rotating sequentially along the y-direction. The overall surface plasmon excitation process is as follows: the incident terahertz wave is first incident perpendicularly from the substrate. After passing through the substrate, most of the light is reflected by the aluminum film, while a small portion of the light generates a local field with the subwavelength rectangular slit resonators. This field couples with the active free electrons on the metal surface to form surface plasmons. By utilizing the rotation angle of the subwavelength slit resonators, the relative distance between the subwavelength slit resonators, and the GST phase transition characteristics, the different functions of the surface plasmons are switched.

2. The terahertz surface plasmon dynamic wavefront modulation device based on GST as described in claim 1, characterized in that, The device comprises two active groups and a passive group positioned between the active groups. When the GST is in the pre-phase transition state, the GST acts as a dielectric, and the two active groups U1 and U2 and the passive group U3 operate simultaneously. However, due to the π phase shift of the surface plasmons excited by U2 and U3, destructive interference occurs, so the device's function is provided solely by U1. When the GST is in the post-phase transition state, the GST acts like a metal, thereby shutting off the terahertz wave response of the subwavelength slit resonator, causing the active groups U1 and U2 to cease operation, and the device's function is provided solely by U3. By utilizing the rotation angle of the subwavelength slit resonator and the relative distance between the subwavelength slit resonators to form the wavefronts of U1 and U3, the device can exhibit different functions before and after the GST phase transition.

3. The terahertz surface plasmon dynamic wavefront modulation device based on GST as described in claim 2, characterized in that, Along the x-axis, the passive group U3 satisfies the following condition: θ2-θ1=3π / 2, s is the distance between the two resonators and s=λ SP / 2,λ SP The operating wavelength of the surface plasmon polariton is θ1, and θ2 are the electric field values, respectively. The angle with the x-axis, These are the field components that can excite the left and right column slit resonators in the incident terahertz wave, respectively, when the incident light is circularly polarized. in The incident electric field vector, (1,σi) are the components of the Jones vector, and i is the imaginary unit. 2 =-1, σ∈{+1,-1} represent left-handed circularly polarized terahertz wave LCP and right-handed circularly polarized terahertz wave RCP, respectively. The field representation of the excited surface plasmons is: Where A is the amplitude of the surface plasmon resonance, and i is the imaginary unit. 2 =-1, θ1 and θ2 are the electric fields The angle with the x-axis, l is the distance between the center point of the two resonators and point N, N is a point on the aluminum film outside the active and passive groups, s is the distance between the two rows of resonators, and the wavenumber of the surface plasmon resonance is ksp = 2π / λ. SP , λ SP It is the operating wavelength of the surface plasmon polariton, determined by the surface plasmon field E. U3 The formula shows that the field amplitude of the surface plasmon excited by the passive group U3 at point N is fixed, while the phase is freely controllable. Its sign is determined by the direction of circular polarization and varies with the rotation angle of the subwavelength slit resonator. Since the subwavelength slit resonator can rotate 180°, the phase change can cover the entire 2π range. Therefore, arbitrary phase distributions can be achieved using slit resonators. For subwavelength slit resonators, when the distance s between the corresponding subwavelength slit resonators becomes mλ... SP Where m is an integer, and considering the low loss of surface plasmon resonances, the phase response of the subwavelength slit resonator is nearly constant. The active and passive groups have the same dimensions but different geometric phases and propagation phases. The geometric phase refers to the rotation angle of the subwavelength slit resonator, and the propagation phase refers to the horizontal distance between the subwavelength slit resonators. At point N, the field E... N It is a superposition of surface plasmons excited by the active / passive groups U1, U2, and U3: E N =E U1N +E U2N +E U3N E U1N 、E U2N 、E U3N The surface plasmons excited by the active / passive groups U1, U2, and U3 are respectively. The active groups U1 and U2 have the same geometric phase, but their propagation phases are different: s U1 =s+λ SP s U1 and s are the horizontal distances between the subwavelength slit resonators, i.e., E U1N =e iπ E U2N This means that the surface plasmons E excited by the U1 structure U1N With surface plasmons E excited by the U2 structure U2N Compared to having a π phase shift, i.e., E U1N =-E U2N Therefore, when active groups U1 and U2 are working, destructive interference will occur, meaning E N =E U1N The device's functionality is provided solely by the active group U1; furthermore, if the active groups U1 and U2 are turned off by the crystalline GST, the device's functionality will be provided solely by the passive group U3.

4. The terahertz surface plasmon dynamic wavefront modulation device based on GST as described in claim 1, characterized in that, The control device comprises two active groups and a passive group sandwiched between the active groups, and achieves surface plasmon coupling by designing different phases of the two metal slits: this coupling effect is expressed as follows: when the phase of the subwavelength slit resonator is adjusted such that... When this coupling is applied, it can act as a secondary emission source, and the excited surface plasmons collectively generate an in-phase wavefront. This allows the subwavelength slit resonators to be arranged in a linear phase distribution along the y-direction, and the phase gradient can be controlled. To control the anomalous refraction angle of surface plasmons Where σ∈{+1,-1} represent the incident left-hand circularly polarized terahertz wave (LCP) and right-hand circularly polarized terahertz wave (RCP), respectively: Both the active and passive groups are obtained by arranging subwavelength metal slits with different rotation directions along the y-axis, and the rotation angle is calculated by formula (2): Where y is the coordinate position of the slit resonator on the y-axis. When the chirality of the circularly polarized CP changes, the direction of the excited surface plasmons will also change. When the circularly polarized terahertz wave is incident perpendicularly, the corresponding phases of the three structures are shown in formula (2).

5. The terahertz surface plasmon dynamic wavefront modulation device based on GST as described in claim 1, characterized in that, The control device comprises two active groups U1 and U2 and a passive group U3 positioned between the active groups, transforming the linear phase distribution of the subwavelength slit resonator into a lens phase distribution to achieve the function of a superlens. Specifically, both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis, with rotation angle distributions... The relationship with position y is calculated using formula (3): Where f is the focal length of the superlens, and according to the formula, the subwavelength slit resonator rotation angle at the corresponding y position is... From formula (3), the signs of the corresponding superlens phase distributions of U1 and U3 differ by a negative sign, so the polarities of the superlenses formed by the two groups of U1 and U3 are opposite; U2 and U3 have the same polarity and realize the function of convex lens / concave lens when right-hand circularly polarized light / left-hand circularly polarized light terahertz wave is incident, but the phases of the two groups of U2 and U3 have a π phase shift, and coherent cancellation will occur when the two groups work at the same time, and the opening and closing of U1 and U2 can be controlled by GST; through such structural distribution, the device can exhibit the functions of U1 and U3 before and after the GST phase transition, respectively, to realize the function switching: after being excited by right-hand circularly polarized light terahertz wave at room temperature, it exhibits a diverging wavefront, and the polarity of the superlens is a concave lens. As the annealing temperature increases, after GST is induced to crystallize, the polarity of the superlens is reversed and becomes a convex lens.

6. The terahertz surface plasmon dynamic wavefront modulation device based on GST as described in claim 1, characterized in that, The control device comprises two active groups and a passive group sandwiched between the two active groups. Both the active and passive groups are formed by arranging subwavelength metal slits with different rotation directions along the y-axis. The rotation angle is calculated by formula (4). Both the active and passive groups are lens phase distributions. The polarity of structure U1 is the same as that of U2 and U3, but the focal length of U1 is designed to be f1 = 6 mm, while the focal lengths of U2 and U3 are both f2 = 4 mm. The relationship with position y is: When right-hand circularly polarized light is incident, as the annealing temperature increases, the superlens becomes a convex lens, and the focal length changes from 6mm to 4mm, thus realizing the zoom function of the superlens. Due to spin correlation, when left-hand circularly polarized light is incident, the superlens remains a concave lens. Under nanosecond laser irradiation, the function of the device is reconstructed back to its initial state.

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