Chiral metasurface devices with tunable strong circular dichroism based on GST phase-change materials

Abstract

The application provides a chiral metasurface device with adjustable strong circular dichroism based on a GST phase change material, comprising a plurality of unit structures arranged periodically along an XOY plane, each unit structure comprising, from bottom to top along a Z-axis direction, a silicon dioxide base layer, a GST layer and a germanium resonance layer which are sequentially stacked; the GST layer and the germanium resonance layer are arranged in the middle of the upper surface of the silicon dioxide base layer; the GST layer is made of a GST phase change material; by applying different bias voltages to the GST layer, the dielectric constant of the GST layer is changed, so that the circularly polarized light transmittance of the chiral metasurface device changes, and dynamic regulation of the circularly polarized light transmittance is realized. The application has the characteristics of good circular dichroism effect, double-band adjustment, and reversible circular dichroism adjustment; meanwhile, the application has the advantages of simple structure, wide application range and easy integration, and has strong practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metasurface devices, and in particular to a chiral metasurface device based on GST phase change material with adjustable strong circular dichroism. BACKGROUND

[0002] Chiral structure refers to a structure that cannot coincide with its mirror image. The difference in transmission degree for left circularly polarized light (LCP) and right circularly polarized light (RCP) is called circular dichroism (CD), and the relationship between this transmission degree and wavelength is called circular dichroism spectrum. Devices made using this feature play a crucial role in the fields of biological detection and analytical chemistry.

[0003] Many biochemical molecules known at present have chiral structures, such as DNA double helix, carbon nanotubes and some viruses, but the circular dichroism of naturally occurring chiral structures is relatively weak. In recent years, in order to solve the above problems, researchers have achieved stronger chiral structures by breaking the symmetry of artificially designed metasurface structures, thereby obtaining stronger circular dichroism. However, these chiral metasurface structures lack the ability of dynamic control, making it difficult to apply them to engineering practice.

[0004] In the prior art, in order to achieve dynamic control of circular dichroism, researchers use flexible polydimethylsiloxane (PDMS), electrically controlled graphene, liquid crystals, semiconductors and vanadium dioxide phase change materials to design tunable metasurfaces. Although tunable circular dichroism is obtained, these metasurface structures also have their own limitations. For example, the switching speed of flexible substrate devices is relatively slow; the working waveband of graphene metasurface structure is limited to the mid-infrared and terahertz waveband; liquid crystal devices are greatly limited due to their strong anisotropic behavior and instability; and the state switching of vanadium dioxide metasurface is not reversible due to the irreversibility of the phase change of vanadium dioxide.

[0005] Therefore, the metasurface structures in the prior art still have many defects and need to be further improved and perfected. SUMMARY

[0006] The present application aims to solve the problems in the prior art by providing a chiral metasurface device based on GST phase change material with adjustable strong circular dichroism, which provides a more convenient and flexible control means while ensuring strong circular dichroism.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A chiral metasurface device with adjustable strong circular dichroism based on GST phase-change material comprises a plurality of unit structures periodically arranged along an XOY plane, each unit structure comprising a silicon dioxide base layer, a GST layer, and a germanium resonant layer stacked in sequence from bottom to top along the Z-axis; the GST layer and the germanium resonant layer are disposed in the middle of the upper surface of the silicon dioxide base layer; and the GST layer is made of GST phase-change material.

[0009] The projection shapes of the GST layer and the germanium resonant layer on the XOY plane are identical and overlap with each other; the projection shapes of the GST layer and the germanium resonant layer on the XOY plane are Z-shaped, including a first rectangular strip, a second rectangular strip, and a third rectangular strip connected vertically in sequence; the length directions of the first rectangular strip and the third rectangular strip are parallel to the X-axis, the length direction of the second rectangular strip is parallel to the Y-axis, one end of the second rectangular strip is vertically connected to the end of the first rectangular strip in the positive direction of the X-axis, and the other end of the second rectangular strip is vertically connected to the end of the first rectangular strip in the negative direction of the X-axis;

[0010] By applying different bias voltages to the GST layer and changing the dielectric constant of the GST layer, the circularly polarized light transmittance of the chiral metasurface device changes, thereby achieving dynamic regulation of the circularly polarized light transmittance.

[0011] Furthermore, the length of the first rectangular strip and the third rectangular strip is 460-480 nm, and the width is 140-150 nm; the length of the second rectangular strip is 280-300 nm, and the width is 130-150 nm.

[0012] Furthermore, the thickness of the germanium resonance layer is 890-910 nm; the thickness of the GST layer is 205-225 nm; and the thickness of the silicon dioxide base layer is 2580-2600 nm.

[0013] Furthermore, in a single unit structure, the width of the silicon dioxide base layer in the X-axis direction is 1200-1220 nm, and the width in the Y-axis direction is 1120-1150 nm.

[0014] Furthermore, the dielectric constant of the silicon dioxide base layer is 2.1025.

[0015] Furthermore, the dielectric constant of the germanium resonance layer is 18.0625.

[0016] Compared with the prior art, the present invention has the following technical advantages:

[0017] 1. The chiral metasurface device of the present invention is an all-dielectric metasurface. The electric field enhancement mainly occurs inside the dielectric resonant cavity. Its resonant mode has a large working space and low heat loss, which is more conducive to the production of high-efficiency optical devices.

[0018] 2. The chiral metasurface device of the present invention is made of only three layers, has the characteristics of simple structure, and adopts a two-dimensional periodic structure, which is convenient for large-scale integration.

[0019] 3. The resonator of the chiral metasurface device of the present invention is composed of a Z-shaped germanium resonant layer and a Z-shaped GST layer, which has different local field enhancement effects on left-handed circularly polarized light and right-handed circularly polarized light, so that left-handed circularly polarized light and right-handed circularly polarized light have different transmittances, realizing strong circular dichroism.

[0020] 4. The chiral metasurface device of the present invention uses electrical control to cause the phase change of the GST layer. The dielectric constant of the GST layer is different under different bias voltages, which causes the transmittance of the chiral metasurface device to left-handed circularly polarized light and right-handed circularly polarized light to change, resulting in a huge change in the circular dichroism of the GST layer before and after the phase change, realizing a large-scale switching capability.

[0021] In summary, the present invention provides a chiral metasurface device with adjustable strong circular dichroism based on GST phase change material, which has the characteristics of good circular dichroism effect, dual-band tunability, and reversible circular dichroism adjustment; at the same time, the present invention also has the advantages of simple structure, wide range of applications and easy integration, and has extremely strong practicality.

[0022] The chiral metasurface device of the present invention has strong circular dichroism, and its dielectric constant can be changed by controlling the phase change of the GST layer, thereby realizing the circular dichroism regulation of the chiral metasurface device. It has the advantages of convenient and flexible regulation and fast response speed. It can be widely used in fields such as optical detection and medical detection, has very broad market value and application prospects, and is of great significance for promoting the development and application of active chip devices such as chiral sensing and near-field imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the overall structure of a unit structure in a chiral metasurface device with adjustable strong circular dichroism based on GST phase change material provided by an embodiment of the present invention.

[0024] Figure 2 is a top view of the unit structure in an embodiment of the present invention.

[0025] Figure 3 This is a polarization transmission spectrum diagram of the chiral metasurface device of an embodiment of the present invention when the GST layer is in an amorphous state.

[0026] Figure 4 This is a polarization transmission spectrum diagram of the chiral metasurface device of an embodiment of the present invention when the GST layer is in a crystalline state.

[0027] Figure 53 is a comparison diagram of the circular dichroism difference of the chiral metasurface device before and after the phase change of the GST layer of the embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 As shown, an embodiment of the present invention provides a chiral metasurface device with tunable strong circular dichroism based on GST phase-change material, comprising a plurality of unit structures periodically arranged along the XOY plane. Each unit structure comprises a silicon dioxide base layer 1, a GST layer 2, and a germanium resonant layer 3, stacked in sequence from bottom to top along the Z-axis. The GST layer 2 and the germanium resonant layer 3 are disposed in the middle of the upper surface of the silicon dioxide base layer 1. The GST layer is made of GST phase-change material.

[0030] The projection shapes of the GST layer 2 and the germanium resonance layer 3 on the XOY plane are identical and overlap with each other. Figure 2 As shown, the projection shape of the GST layer 2 and the germanium resonant layer 3 on the XOY plane is Z-shaped, including a first rectangular strip 41, a second rectangular strip 42 and a third rectangular strip 43 vertically connected in sequence; the length directions of the first rectangular strip 41 and the third rectangular strip 42 are parallel to the X-axis, the length direction of the second rectangular strip 42 is parallel to the Y-axis, one end of the second rectangular strip 42 is vertically connected to the end of the first rectangular strip 41 in the positive direction of the X-axis, and the other end of the second rectangular strip 42 is vertically connected to the end of the first rectangular strip 41 in the negative direction of the X-axis.

[0031] When the embodiment of the present invention is working, different bias voltages can be applied to the GST layer to change the dielectric constant of the GST layer, so that the circularly polarized light transmittance of the chiral metasurface device changes, thereby realizing dynamic regulation of the circularly polarized light transmittance.

[0032] Specifically, the GST phase-change material (GST) that makes up the GST layer is composed of three elements: germanium (Ge), antimony (Sb), and tellurium (Te). Solid GST phase-change material exists in two phases: crystalline and amorphous, with significant differences in dielectric constant. Changing the temperature of the GST phase-change material allows it to transition between the crystalline and amorphous states, thereby altering the dielectric constant of the GST phase-change material. The present invention, however, uses an external bias voltage to alter the temperature of the GST phase-change material, thereby changing the dielectric constant of the GST layer and achieving dynamic control of the transmittance of circularly polarized light.

[0033] Furthermore, the length of the first rectangular strip 41 and the third rectangular strip 43 is 460-480 nm, and the width is 140-150 nm; the length of the second rectangular strip 42 is 280-300 nm, and the width is 130-150 nm.

[0034] Preferably, in this embodiment, the first rectangular strip 41, the second rectangular strip 42, and the third rectangular strip 43 constituting the Z-shaped projection shape of the GST layer 2 and the germanium resonance layer 3 are designed with the following dimensions: the length W2 of the first rectangular strip 41 and the third rectangular strip 43 is 470 nm, and the width L2 is 145 nm; the length L1 of the second rectangular strip 42 is 290 nm, and the width W1 is 140 nm.

[0035] Furthermore, in a single unit structure, the width of the silicon dioxide base layer in the X-axis direction is 1200-1220 nm, and the width in the Y-axis direction is 1120-1150 nm.

[0036] As a preference, in this embodiment, the arrangement period of the unit structure is P x =1210nm, P y =1135nm; that is, in a single unit structure, the width of the silicon dioxide base layer in the X-axis direction is P x =1210nm, the width in the Y-axis direction is P y =1135nm.

[0037] Furthermore, the thickness of the germanium resonance layer is 890-910 nm; the thickness of the GST layer is 205-225 nm; and the thickness of the silicon dioxide base layer is 2580-2600 nm.

[0038] Preferably, in this embodiment, the thickness of the germanium resonance layer is 900 nm; the thickness of the GST layer is 215 nm; and the thickness of the silicon dioxide base layer is 2590 nm.

[0039] Furthermore, the dielectric constant of the silicon dioxide base layer is 2.1025; the dielectric constant of the germanium resonance layer is 18.0625.

[0040] When the embodiment of the present invention is working, circularly polarized light is used as the incident light and is incident on the upper surface of the chiral metasurface device at an incident angle of 0°. The incident light passes through the Z-shaped germanium resonance layer and the Z-shaped GST layer in sequence, and is finally emitted from the bottom of the silicon dioxide base layer.

[0041] Among them, circularly polarized light includes left-handed circularly polarized light and right-handed circularly polarized light; when viewed from the direction of the light, any light with an electric vector rotating clockwise is called right-handed circularly polarized light RCP, and any light with an electric vector rotating counterclockwise is called left-handed circularly polarized light LCP.

[0042] During operation, different bias voltages can be applied to the GST layer to transform the GST phase change material from an amorphous state to a crystalline state, thereby changing the dielectric constant of the GST layer and causing the circularly polarized light transmittance of the chiral metasurface device to change, thereby achieving dynamic regulation of the transmittance of left-handed circularly polarized light and right-handed circularly polarized light.

[0043] In this embodiment of the present invention, a Z-shaped germanium resonator layer and a Z-shaped GST layer form a Z-shaped resonator array above the chiral metasurface device. These resonators can break the in-plane mirror symmetry and induce cross-polarization conversion. On the one hand, the Z-shaped structure is chiral, which is conducive to the generation of chiral optical effects, thereby improving the circular dichroism of the chiral metasurface device. On the other hand, the Z-shaped all-dielectric structure can excite Mie resonances under different polarizations, thereby amplifying the control effect of the GST layer.

[0044] More specifically, the Z-shaped resonator array composed of a Z-shaped germanium resonant layer and a Z-shaped GST layer in the embodiment of the present invention has different local field enhancement effects on left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP), resulting in different transmittances for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP), providing feasibility for achieving polarization selectivity. The frequency-domain finite element method simulated using the electromagnetic simulation software CST Studio Suite can be used to numerically calculate the polarization transmission and transmission spectrum of the embodiment of the present invention. During the simulation calculation, unit cell periodic boundary conditions are selected in the X-axis and Y-axis directions, and open boundary conditions are selected in the Z-axis direction.

[0045] like Figure 3 and Figure 4 , which is a simulation result diagram of a chiral metasurface device provided by an embodiment of the present invention. Figure 3 is the polarization transmission spectrum of the chiral metasurface device when the GST layer is in the amorphous state, Figure 4 is the polarization transmission spectrum of the chiral metasurface device when the GST layer is in the crystalline state. L 、T R They are the transmission spectra of LCP incident and RCP incident, a-GST represents the GST layer in an amorphous state, and c-GST represents the GST layer in a crystalline state. Figure 3 and Figure 4 It can be seen that the transmittance of left-handed circularly polarized light LCP and right-handed circularly polarized light RCP changes before and after the phase change of the GST layer.

[0046] Regarding circular dichroism CD, we can use the formula CD=T L -T R Calculated. Figure 5 The change of circular dichroism before and after the phase transition of the GST layer is more intuitively shown. (a-GST)is the circular dichroism value of the GST layer in the amorphous state, CD (c-GST) is the circular dichroism value when the GST layer is in a crystalline state.

[0047] from Figure 5 It can be seen that the CD values ​​of the GST layer undergo significant changes before and after the phase transition: when the GST layer is amorphous, the CD value near 1499nm is approximately -0.92, and near 1520nm is approximately 0.94. When the GST layer is crystalline, the CD value near 1499nm increases to -0.32, and near 1520nm decreases to -0.04.

[0048] In order to quantify the switching properties caused by the change in CD, the difference in CD caused by the phase change of the GST layer is expressed as ΔCD = CD (a-GST) -CD (c-GST) .according to Figure 5 It can be seen that the ΔCD near 1499nm is about 0.6, and the ΔCD near 1520nm is about 0.98; this shows that before and after the phase change of the GST layer, the transmittance of the chiral metasurface device to left-handed circularly polarized light and right-handed circularly polarized light undergoes a huge change.

[0049] The above simulation results show that the chiral metasurface device of the embodiment of the present invention can fully demonstrate the difference in transmittance for left-handed circularly polarized light and right-handed circularly polarized light, and has strong circular dichroism; at the same time, the phase change of the GST layer brings excellent switching capability, realizing dynamic regulation of the transmittance of circularly polarized light.

[0050] Specifically, when the GST layer is in an amorphous state, the circular dichroism reaches -0.92 and 0.94 at 1499nm and 1520nm, respectively, demonstrating differential responses to the transmission of left-handed and right-handed circularly polarized light. After the phase transition, the GST layer transforms into a crystalline state, with the circular dichroism changing to -0.32 and -0.04 at 1499nm and 1520nm, respectively. The differences in circular dichroism before and after the GST layer phase transition are 0.6 and 0.98 at 1499nm and 1520nm, respectively, demonstrating the strong circular dichroism and wide-range switching capability of the chiral metasurface device.

[0051] In summary, the present invention designs a metasurface structure with a Z-shaped resonator to produce different local field enhancements for left-handed circularly polarized light and right-handed circularly polarized light, so that the chiral metasurface device has different transmittances for left-handed circularly polarized light and right-handed circularly polarized light. At the same time, the introduction of GST phase change material makes the chiral metasurface device adjustable, realizing active regulation of the metasurface device. The phase change of the GST layer is used to regulate the transmittance of left-handed circularly polarized light and right-handed circularly polarized light, thereby generating strong circular dichroism and a wide range of switching capabilities.

[0052] This invention leverages the adjustable dielectric constant of GST phase-change materials to achieve adjustable height of the circular dichroism peak. By varying the overall structural dimensions, the circular dichroism peak can also be red-shifted or blue-shifted while maintaining its intensity. The present invention provides a chiral metasurface device with adjustable strong circular dichroism based on GST phase-change materials. The device exhibits strong circular dichroism, and the circular dichroism peak can be flexibly adjusted in height or left or right, tailored to suit a variety of application scenarios.

[0053] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A chiral metasurface device with tunable strong circular dichroism based on GST phase change material, characterized in that: The invention comprises a plurality of unit structures periodically arranged along an XOY plane, each unit structure comprising a silicon dioxide base layer, a GST layer and a germanium resonance layer stacked in sequence from bottom to top along the Z-axis direction; the GST layer and the germanium resonance layer are arranged in the middle of the upper surface of the silicon dioxide base layer; the GST layer is made of a GST phase change material; The projection shapes of the GST layer and the germanium resonant layer on the XOY plane are identical and overlap with each other; the projection shapes of the GST layer and the germanium resonant layer on the XOY plane are Z-shaped, including a first rectangular strip, a second rectangular strip, and a third rectangular strip connected vertically in sequence; the length directions of the first rectangular strip and the third rectangular strip are parallel to the X-axis, the length direction of the second rectangular strip is parallel to the Y-axis, one end of the second rectangular strip is vertically connected to the end of the first rectangular strip in the positive direction of the X-axis, and the other end of the second rectangular strip is vertically connected to the end of the first rectangular strip in the negative direction of the X-axis; By applying different bias voltages to the GST layer and changing the dielectric constant of the GST layer, the circularly polarized light transmittance of the chiral metasurface device changes, thereby achieving dynamic regulation of the circularly polarized light transmittance.

2. The chiral metasurface device with tunable strong circular dichroism based on GST phase change material according to claim 1, characterized in that: The length of the first rectangular strip and the third rectangular strip is 460-480 nm, and the width is 140-150 nm; the length of the second rectangular strip is 280-300 nm, and the width is 130-150 nm.

3. The chiral metasurface device with tunable strong circular dichroism based on GST phase change material according to claim 1, characterized in that: The thickness of the germanium resonance layer is 890-910 nm; the thickness of the GST layer is 205-225 nm; and the thickness of the silicon dioxide base layer is 2580-2600 nm.

4. The chiral metasurface device with tunable strong circular dichroism based on GST phase change material according to claim 1, characterized in that: In a single unit structure, the width of the silicon dioxide base layer in the X-axis direction is 1200-1220 nm, and the width in the Y-axis direction is 1120-1150 nm.

5. The chiral metasurface device with tunable strong circular dichroism based on GST phase change material according to claim 1, characterized in that: The dielectric constant of the silicon dioxide base layer is 2.1025.

6. The chiral metasurface device with tunable strong circular dichroism based on GST phase change material according to claim 1, characterized in that: The dielectric constant of the germanium resonance layer is 18.0625.

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