A terahertz polarization conversion unit and a terahertz polarization converter

Abstract

The present invention provides a terahertz polarization conversion unit and a terahertz polarization converter. The terahertz polarization conversion unit includes a metal film bottom layer, a first dielectric layer, a phase change material layer, a second dielectric layer, and a resonant strip layer. The resonant strip layer includes phase change material strips and composite material strips that are parallel or perpendicular to each other. The composite material strip includes a metal strip and a phase change material end point. The length of the metal strip is greater than the length of the phase change material strip, and the orthographic projection of the composite material strip on the second dielectric layer penetrates the second dielectric layer. Through the terahertz polarization conversion unit and the terahertz polarization converter provided by the embodiments of the present invention, by causing phase changes in the phase change material layer, the phase change material strips, and the phase change material end points, the thickness of the resonant cavity and the length of the strip generating resonance are changed. Using different resonant cavities in different states, the incident light is modulated in the high-frequency band or the low-frequency band, and the modulation effect of converting broadband terahertz linearly polarized light into circularly polarized light is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz, and in particular, to a terahertz polarization conversion unit and a terahertz polarization converter. Background Art

[0002] Terahertz wave is a new frequency band with great research and development value. Terahertz wave generally refers to electromagnetic radiation with a frequency of 100 GHz - 10 THz, and its frequency band is very wide; therefore, how to better modulate the ultra-wideband terahertz wave (for example, how to cover and process a wider frequency band of terahertz wave to a greater extent) is an important research direction at present.

[0003] The existing terahertz polarization converter can use a metal strip structure and a metal film to form a resonant cavity to realize the function of converting linearly polarized light into circularly polarized light. However, when the terahertz wave is normally incident, compared with the bandwidth of 0.2 THz - 2 THz commonly used in terahertz spectrum testing, the bandwidth that the terahertz polarization converter can modulate is in the range of 0.73 THz - 1.39 THz, and the bandwidth coverage range of the terahertz polarization converter for terahertz wave is relatively small. Summary of the Invention

[0004] To solve the above problems, the purpose of the embodiments of the present invention is to provide a terahertz polarization conversion unit and a terahertz polarization converter.

[0005] In a first aspect, an embodiment of the present invention provides a terahertz polarization conversion unit, including: a metal film bottom layer, a first dielectric layer, a phase change material layer, a second dielectric layer, and a resonant strip layer arranged in a stacked manner in sequence; the first dielectric layer and the second dielectric layer are transparent in the working band; the resonant strip layer includes a phase change material strip and a composite material strip that are located in the same plane and are arranged parallel or perpendicular to each other; the composite material strip includes: a metal strip and a phase change material end point connected to the end of the metal strip; the length of the metal strip is greater than the length of the phase change material strip, and the orthographic projection of the composite material strip on the second dielectric layer penetrates the second dielectric layer; the phase change material layer, the phase change material strip, and the phase change material end point present a conductor state or a semiconductor state at different temperatures.

[0006] Optionally, the number of the phase change material strips is multiple.

[0007] Optionally, the composite material strip coincides with the diagonal of the second dielectric layer.

[0008] Optionally, the number of the phase change material strips is a non-zero even number, and the phase change material strips are symmetrically arranged on both sides of the composite material strip.

[0009] Optionally, the material of the phase change material layer includes: vanadium dioxide or germanium antimony telluride; the material of the phase change material strip includes: vanadium dioxide or germanium antimony telluride; the material of the phase change material end point includes: vanadium dioxide or germanium antimony telluride.

[0010] Optionally, the material of the bottom metal film layer includes: gold, silver, copper, aluminum, platinum or chromium; the material of the metal strip includes: gold, silver, copper, aluminum, platinum or chromium.

[0011] Optionally, the thickness of the bottom metal film layer is greater than or equal to 0.1 μm.

[0012] Optionally, the thickness of the phase change material layer is 0.1 μm to 5 μm; the thickness of the resonant strip layer is 0.1 μm to 5 μm.

[0013] Optionally, the thickness of the first dielectric layer is 25 μm to 45 μm; the thickness of the second dielectric layer is 20 μm to 30 μm.

[0014] Optionally, the length of the metal strip is 230 μm to 270 μm; the width of the metal strip is 2 μm to 30 μm.

[0015] Optionally, the length of the phase change material strip is 100 μm to 140 μm; the width of the phase change material strip is 5 μm to 35 μm.

[0016] Optionally, the distance between the phase change material strip and the composite material strip is 50 μm to 90 μm.

[0017] Optionally, the period of the terahertz polarization conversion unit in the x direction is 180 μm to 220 μm; the period of the terahertz polarization conversion unit in the y direction is 180 μm to 220 μm; and the x direction and the y direction are two mutually perpendicular directions.

[0018] In a second aspect, an embodiment of the present invention provides a terahertz polarization converter, including: a plurality of terahertz polarization conversion units as described in any one of the above, and the plurality of terahertz polarization conversion units are arranged in an array.

[0019] In the solution provided in the first aspect of the embodiments of the present invention, the terahertz polarization conversion unit provided by the embodiments of the present invention can change the structure of the resonant unit (the unit that resonates with the incident light in the terahertz band) by causing phase transitions in the phase change material layer, phase change material strips, and phase change material endpoints, enabling them to switch between the conductor state and the non-conductor state, and changing the thickness of the resonant cavity in the terahertz polarization conversion unit and the length of the strip that generates resonance in the resonant strip layer (if the strip that generates resonance changes, the length of the strip that generates resonance also changes). Thus, different resonant cavities in different states are used to modulate the incident light in the high-frequency band or the low-frequency band, thereby achieving the modulation effect of being able to convert terahertz linearly polarized light in a wider band into circularly polarized light. This terahertz polarization conversion unit has a large bandwidth coverage range for terahertz waves and can cover both the high-frequency band and the low-frequency band of the terahertz band.

[0020] In the solution provided in the second aspect of the embodiments of the present invention, this terahertz polarization converter can expand the reception area of the terahertz polarization conversion unit for incident light in the terahertz band, improve the modulation efficiency of the terahertz polarization converter, and this terahertz polarization converter has a large bandwidth coverage range for the terahertz band.

[0021] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 Shows a three-dimensional view of a terahertz polarization conversion unit provided by an embodiment of the present invention;

[0024] Figure 2 Shows a three-dimensional view of the terahertz polarization conversion unit provided by an embodiment of the present invention, in which the phase change material strip and the composite material strip are perpendicular to each other;

[0025] Figure 3 Shows a top view of the first terahertz polarization conversion unit provided by an embodiment of the present invention;

[0026] Figure 4 Shows a top view of the second terahertz polarization conversion unit provided by an embodiment of the present invention;

[0027] Figure 5Shows a top view of the third terahertz polarization conversion unit provided by an embodiment of the present invention;

[0028] Figure 6 Shows a schematic structural diagram of a terahertz polarization converter provided by an embodiment of the present invention;

[0029] Figure 7 Shows a top view of Embodiment 1;

[0030] Figure 8 Shows a side view of Embodiment 1;

[0031] Figure 9 Shows a schematic diagram of a simulation result of Embodiment 1;

[0032] Figure 10 Shows another schematic diagram of a simulation result of Embodiment 1;

[0033] Figure 11 Shows a schematic diagram of the ellipticity corresponding to the incident light in the terahertz band reflected by Embodiment 1.

[0034] Icon:

[0035] 1 - bottom metal film layer, 2 - first dielectric layer, 3 - phase change material layer, 4 - second dielectric layer, 5 - resonant strip layer, 51 - phase change material strip, 52 - composite material strip, 521 - metal strip, 522 - phase change material end point, 100 - terahertz polarization conversion unit. Detailed implementation manners

[0036] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0037] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0038] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] An embodiment of the present invention provides a terahertz polarization conversion unit. Referring to Figure 1 as shown, the terahertz polarization conversion unit includes: a metal film bottom layer 1, a first dielectric layer 2, a phase change material layer 3, a second dielectric layer 4, and a resonant strip layer 5 that are stacked in sequence; the first dielectric layer 2 and the second dielectric layer 4 are transparent in the working band; Figure 1 The perspective view of the terahertz polarization conversion unit is shown.

[0040] As Figure 1 shown, the resonant strip layer 5 includes a phase change material strip 51 and a composite material strip 52 that are located in the same plane and are arranged parallel or perpendicular to each other; the composite material strip 52 includes: a metal strip 521 and a phase change material end point 522 connected to the end of the metal strip 521; the length of the metal strip 521 is greater than the length of the phase change material strip 51, and the orthographic projection of the composite material strip 52 on the second dielectric layer 4 penetrates the second dielectric layer 4; the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 exhibit a conductor state or a semiconductor state at different temperatures.

[0041] In the terahertz polarization conversion unit provided by the embodiment of the present invention, the above five structural layers (such as Figure 1 the metal film bottom layer 1, the first dielectric layer 2, the phase change material layer 3, the second dielectric layer 4, and the resonant strip layer 5 that are stacked in sequence from bottom to top as shown in Figure 1 form an integral structure; among them, the resonant strip layer 5 located at Figure 1 the topmost layer includes a phase change material strip 51 and a composite material strip 52. Among them, the number of the phase change material strips 51 may be 1. For the convenience of subsequent description in the embodiment of the present invention, the schematic diagram of this case is not shown.

[0042] Taking the case of including two phase change material strips 51 as an example for illustration; alternatively, the number of the phase change material strips 51 is multiple; among them, when the number of the phase change material strips 51 is greater than 1, the terahertz polarization conversion unit with this structure has a higher transmittance for incident light. Figure 1Figure 0 shows a schematic diagram in which the phase change material strip 51 and the composite material strip 52 are arranged parallel to each other; alternatively, reference can be made to Figure 2 as shown in Figure 2 Figure 4 shows a schematic diagram in which the phase change material strip 51 and the composite material strip 52 are arranged perpendicular to each other. The embodiments of the present invention do not limit the arrangement manner of the phase change material strip 51 and the composite material strip 52.

[0043] The terahertz polarization conversion unit provided by the embodiments of the present invention is used to receive incident light that is incident on its surface from the outside (such as vertically incident), and generate resonance for the incident light, and achieve high reflection and phase modulation of the incident light through multiple interference effects. Among them, the incident light is linearly polarized light, and the incident light can enter the resonant strip layer 5 in a polarization direction at an angle of 45 degrees with the composite material strip 52 (or the phase change material strip 51); the incident light is usually light in the terahertz band, that is to say, the working band of the terahertz polarization conversion unit is usually the terahertz band; the first dielectric layer 2 and the second dielectric layer 4 are transparent in the terahertz band, that is, both the first dielectric layer 2 and the second dielectric layer 4 have high transmittance for the light in the terahertz band. Usually, the first dielectric layer 2 and the second dielectric layer 4 can be selected from the same or different terahertz low-loss materials, including quartz, high-resistance silicon, polyimide, PDMS (poly-N,N-dimethylacrylamide material), SU8 (an epoxy-based photoresist material), PMMA (Polymethyl methacrylate, plexiglass), PET (Polyethyleneterephthalate, polyethylene terephthalate plastic), BCB (benzocyclobutene), Al2O3 (aluminum oxide) or MgO (magnesium oxide), etc. In addition, the surface of the terahertz polarization conversion unit that receives the incident light is the side surface of the terahertz polarization conversion unit away from the metal film bottom layer 1, such as Figure 1 the side surface with the resonant strip layer 5 in Figure 9. It should be noted that: since the actual area of the resonant strip layer 5 only corresponds to the areas of the phase change material strip 51 and the composite material strip 52 it contains, when the incident light enters this side surface, part of the light will irradiate on the part of the second dielectric layer 4 that cannot be covered by the resonant strip layer 5.

[0044] such as Figure 1As shown, the composite material strip 52 includes two different materials. One is a metal material, and the metal strip 521 in the composite material strip 52 is formed by this metal material; the other is a phase change material, and the phase change material end points 522 in the composite material strip 52 are formed by this phase change material. Among them, the number of the phase change material end points 522 can be two, which are respectively located at both ends of the metal strip 521 and are connected to the metal strip 521 to form an integral structure (composite material strip 52), and the two phase change material end points 522 can serve as the two end points of the composite material strip 52. In the embodiment of the present invention, the length of the metal strip 521 is greater than the length of the phase change material strip 51. Correspondingly, the length of the composite material strip 52 is also greater than the length of the phase change material strip 51; and, both ends of the composite material strip 52 (such as the two phase change material end points 522) are respectively in contact with the edge or vertex angle of the second dielectric layer 4, that is, the orthographic projection of the composite material strip 52 on the second dielectric layer 4 can penetrate the second dielectric layer 4.

[0045] For example, referring to Figure 3 as shown in Figure 3 (which is a top view of the first terahertz polarization conversion unit), a plane coordinate system is constructed on the side surface of the second dielectric layer 4 away from the metal film bottom layer 1 Figure 3 (not shown in the figure). In the figure, the horizontal direction is the x direction, and the vertical direction perpendicular to the x direction is the y direction. The composite material strip 52 is vertically arranged on the side surface of the second dielectric layer 4 away from the metal film bottom layer 1, and the length of the composite material strip 52 is consistent with the length of the second dielectric layer 4 in the y direction. For example, the phase change material end points 522 at both ends of the composite material strip 52 are respectively in contact with (or flush with) the upper edge and the lower edge of the second dielectric layer 4, and the orthographic projection of the composite material strip 52 on the second dielectric layer 4 can penetrate the second dielectric layer 4; or, as Figure 3 shown in Figure 4 (which is a top view of the second terahertz polarization conversion unit), the composite material strip 52 is horizontally arranged on the side surface of the second dielectric layer 4 away from the metal film bottom layer 1 Figure 4 (not shown in the figure), and the length of the composite material strip 52 is consistent with the length of the second dielectric layer 4 in the x direction. For example, the phase change material end points 522 at both ends of the composite material strip 52 are respectively in contact with (or flush with) the left edge and the right edge of the second dielectric layer 4; or, as Figure 4 shown in Figure 5 (which is a top view of the third terahertz polarization conversion unit and is consistent with the structure shown in Figure 5 ), the composite material strip 52 is arranged on the side surface of the second dielectric layer 4 away from the metal film bottom layer 1 Figure 1 (not shown in the figure). Figure 5One side surface (not shown in the figure) of the composite material strip 52 is arranged diagonally, and the length of the composite material strip 52 is consistent with the diagonal length of the second dielectric layer 4. For example, the phase change material endpoints 522 at both ends of the composite material strip 52 are respectively in contact with (or flush with) the two diagonals of the second dielectric layer 4.

[0046] In the embodiment of the present invention, the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 included in the terahertz polarization conversion unit are all structural layers that can change their own states according to the applied excitation (such as photothermal excitation or electrothermal excitation, etc.), thereby changing their functions. For example, under the action of a certain external excitation, the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 can change from the semiconductor state to the conductor state, and then their functions can change from originally transmitting incident light to reflecting incident light; or, under the action of another external excitation, the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 can also change from the conductor state to the semiconductor state, and then their functions can change from originally reflecting incident light to transmitting incident light.

[0047] Specifically, for the terahertz polarization conversion unit provided by the embodiment of the present invention, when the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 remain in the semiconductor state, the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 are transparent to incident light. For example, the phase change material layer 3, the phase change material strip 51, and the phase change material endpoint 522 have no resonant response to incident light; as Figure 5 shown, the incident light (icon c) is linearly polarized light, and its polarization direction is represented by a double-arrow dashed line. The incident light is incident perpendicularly to the second dielectric layer 4, and the polarization direction of the incident light forms an angle θ of 45 degrees with the composite material strip 52; in this state, the metal strip 521 and the metal film bottom layer 1 form a resonant cavity, and the cavity thickness is the total thickness of the first dielectric layer 2, the phase change material layer 3, and the second dielectric layer 4 (as Figure 1 shown); the incident light resonates in this resonant cavity (the cavity between the metal strip 521 and the metal film bottom layer 1).

[0048] As Figure 5 shown, the electric field of the incident light can be decomposed into orthogonal components parallel to and perpendicular to the metal strip 521 and the incident electric field of the incident light Among them, r1 and r2 are the reflectivities of the incident light in the terahertz band in the direction parallel to the metal strip 521 and the direction perpendicular to the metal strip 521, respectively; θ = 45°; in the embodiment of the present invention, when the incident light in the terahertz band is modulated by the terahertz polarization conversion unit, a terahertz wave will be reflected. By calculating the Stokes parameters of the reflected terahertz wave, the polarization conversion performance of the terahertz wave can be effectively characterized. Further, the calculation formula of the Stokes parameters can be expressed as:

[0049]

[0050]

[0051]

[0052]

[0053] Among them, S0, S1, S2, and S3 represent the Stokes parameters, represents the phase difference between the reflected terahertz wave in the vertical direction and the parallel direction; based on the above Stokes parameters, the ellipticity χ (a standard parameter for determining the polarization state) corresponding to the reflected terahertz wave can be calculated, where χ = S3 / S0; if the calculated ellipticity χ is close to 1, it is determined that the polarization state of the terahertz wave reflected by the terahertz polarization conversion unit is left-handed circularly polarized light; if the calculated ellipticity χ is close to -1, it is determined that the polarization state of the terahertz wave reflected by the terahertz polarization conversion unit is right-handed circularly polarized light.

[0054] In the embodiment of the present invention, due to the relatively long length of the metal strip 521, the wavelength of the incident light corresponding to the resonance of the metal strip 521 is also relatively long, and because the wavelength of the incident light is inversely proportional to the frequency, in this state (the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 remain in the semiconductor state), the resonance cavity formed by the metal strip 521 and the metal film bottom layer 1 can process the incident light in the low-frequency band. When the incident light (broadband terahertz band light) passes through the terahertz polarization conversion unit, it can be resonated and modulated in the lower frequency band, and in this state, according to the above formula, the calculated ellipticity χ is close to -1, which proves that the terahertz polarization conversion unit in this state can convert the incident light in the terahertz band from linearly polarized light to right-handed circularly polarized light, and the terahertz polarization conversion unit exhibits the same modulation effect as a quarter-wave plate.

[0055] Moreover, in the terahertz polarization conversion unit provided by the embodiments of the present invention, when the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 are in the conductor state, the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 reflect the incident light (such as total reflection); the phase change material end point 522 and the metal strip 521 (the combined material strip 52) form a grating structure. The period of this grating structure (the combined material strip 52) is relatively large and the structural bandwidth is relatively small, and the modulation effect on the incident light in the terahertz band is relatively small. Therefore, its modulation effect on the incident light in the terahertz band can be ignored. That is, when the phase change material end point 522 is in the conductor state, the combined material strip 52 has no resonance response to the incident light. Moreover, since the states of both the phase change material strip 51 and the phase change material layer 3 are in the conductor state, in this state, the phase change material strip 51 and the phase change material layer 3 form a resonant cavity, and the cavity thickness becomes smaller. For example, the cavity thickness becomes the thickness of the second dielectric layer 4; the incident light resonates in this resonant cavity (the cavity between the phase change material strip 51 and the phase change material layer 3). Since the length of the phase change material strip 51 is relatively short, the wavelength of the incident light corresponding to the resonance of the phase change material strip 51 will also be relatively short. And because the wavelength of the incident light is inversely proportional to the frequency, in this state (the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 are in the conductor state), the phase change material strip 51 and the phase change material layer 3 forming a resonant cavity can process the incident light in the high-frequency band. When the incident light (the broadband terahertz band light) passes through this terahertz polarization conversion unit, it can be resonated and modulated in a higher frequency band. And in this state, according to the above formula, the ellipticity χ can be calculated to be close to -1, proving that the terahertz polarization conversion unit in this state can convert the incident light in the terahertz band from linearly polarized light to right-handed circularly polarized light.

[0056] In the terahertz polarization conversion unit provided by the embodiments of the present invention, by causing the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 to undergo a phase change and switch between the conductor state and the non-conductor state, the structure of the resonant unit (the unit that resonates with the incident terahertz band incident light) can be changed, and the thickness of the resonant cavity in this terahertz polarization conversion unit and the length of the strip that generates resonance in the resonant strip layer 5 can be changed (such as when the strip that generates resonance changes, the length of the strip that generates resonance also changes). Thus, different resonant cavities in different states are used to modulate the incident light in the high-frequency band or the low-frequency band, so as to achieve the modulation effect of being able to convert the terahertz linearly polarized light in a wider band into circularly polarized light. This terahertz polarization conversion unit has a large bandwidth coverage range for terahertz waves and can cover the high-frequency band and the low-frequency band of the terahertz band.

[0057] Optionally, as shown in Figure 1 and Figure 5 shown, the combined material strip 52 is arranged to coincide with the diagonal of the second dielectric layer 4.

[0058] In the embodiment of the present invention, since the combined material strip 52 is overlapped and arranged on the diagonal line of the second dielectric layer 4, the length of the combined material strip 52 is longer than that when it is arranged at other positions, so that the length of the metal strip 521 is longer, and the frequency band of the incident light (light in the broadband terahertz band) that can be modulated by it is lower, which can cover the low frequency band that cannot be modulated by traditional terahertz polarization converters.

[0059] Optionally, as Figures 1 to 5 shown, the number of phase change material strips 51 is a non-zero even number, and the phase change material strips 51 are symmetrically arranged on both sides of the combined material strip 52.

[0060] Among them, the number of phase change material strips 51 can be set to 2, 4, etc. In this case, the same number of phase change material strips 51 can be symmetrically arranged on both sides of the combined material strip 52. For example, as Figures 1 to 5 shown, the number of phase change material strips 51 is 2, and 1 phase change material strip 51 can be arranged on both sides of the combined material strip 52 (such as Figure 1 , Figure 2 or Figure 5 shown, the upper left and lower right of the combined material strip 52; or, as Figure 3 shown, the left and right sides of the combined material strip 52; or, as Figure 4 shown, the upper and lower sides of the combined material strip 52) to form a symmetric structure on both sides of the combined material strip 52. By such a setting method, the space utilization rate of the terahertz polarization conversion unit can be improved, and it has an improvement effect on the bandwidth and modulation effect of the incident light that the terahertz polarization conversion unit can modulate.

[0061] Optionally, the material of the phase change material layer 3 includes: vanadium dioxide or germanium antimony tellurium; the material of the phase change material strip 51 includes: vanadium dioxide or germanium antimony tellurium; the material of the phase change material end point 522 includes: vanadium dioxide or germanium antimony tellurium.

[0062] In the embodiments of the present invention, vanadium dioxide is a metal oxide with phase change properties, and its phase change temperature is 68 °C. Specifically, vanadium dioxide can be converted between the metallic state (conductor state) and the insulating state (non-conductor state), so as to realize the functions required by the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 in the embodiments of the present invention; alternatively, in the embodiments of the present invention, germanium antimony telluride (GST) material can also be selected as the material of the phase change material layer 3, the phase change material strip 51, or the phase change material end point 522. Under the irradiation of incident light in the terahertz band, the germanium antimony telluride material changes between the crystalline state and the amorphous state, and can also realize the reflection of the incident light. In the embodiments of the present invention, other materials with the above functions (such as doped materials of the same system) can also be selected as the materials of the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522. Moreover, the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 can be made of the same material at the same time. For example, vanadium dioxide material can be selected at the same time, and the embodiments of the present invention do not make specific limitations on this.

[0063] Optionally, the material of the metal film bottom layer 1 includes: gold, silver, copper, aluminum, platinum, or chromium; the material of the metal strip 521 includes: gold, silver, copper, aluminum, platinum, or chromium.

[0064] In the embodiments of the present invention, a metal material with high electrical conductivity can be selected as the material of the metal film bottom layer 1 or the metal strip 521. For example, among the several metal materials listed above, gold has better use effects, and gold can be used as the material of both the metal film bottom layer 1 and the metal strip 521 at the same time.

[0065] Optionally, the thickness of the metal film bottom layer 1 is greater than or equal to 0.1 μm. For example, its thickness can be 0.2 μm. It should be noted that the specific thickness of the metal film bottom layer 1 can be determined according to specific circumstances, and the embodiments of the present invention do not make limitations on this.

[0066] Optionally, the thickness of the phase change material layer 3 is 0.1 μm to 5 μm; the thickness of the resonant strip layer 5 is 0.1 μm to 5 μm. For example, the thickness of the phase change material layer 3 can be 1 μm; the thickness of the resonant strip layer 5 can also be 1 μm.

[0067] Optionally, the thickness of the first dielectric layer 2 is 25 μm to 45 μm; the thickness of the second dielectric layer 4 is 20 μm to 30 μm. For example, the thickness of the first dielectric layer 2 can be 35 μm, and the thickness of the second dielectric layer 4 can be 25 μm.

[0068] Optionally, the length of the metal strip 521 is 230 μm to 270 μm; the width of the metal strip 521 is 2 μm to 30 μm. For example, the length of the metal strip 521 can be 250 μm, and the width of the metal strip 521 can be 5 μm.

[0069] Optionally, the length of the phase change material strip 51 is 100 μm to 140 μm; the width of the phase change material strip 51 is 5 μm to 35 μm. For example, the length of the phase change material strip 51 can be 120 μm; the width of the phase change material strip 51 can be 20 μm.

[0070] Optionally, the spacing between the phase change material strip 51 and the composite material strip 52 is 50 μm to 90 μm. For example, the spacing between the phase change material strip 51 and the composite material strip 52 can be 70 μm.

[0071] Optionally, the period of the terahertz polarization conversion unit in the x direction is 180 μm to 220 μm; the period of the terahertz polarization conversion unit in the y direction is 180 μm to 220 μm.

[0072] As Figure 5 shown, Figure 5 in the horizontal direction is the x direction, the vertical direction perpendicular to the x direction is the y direction, and the period in the x direction or the period in the y direction corresponds to the length of the terahertz polarization conversion unit in the x direction or the length in the y direction. For example, the period of the terahertz polarization conversion unit in the x direction can be the same as its period in the y direction, both being 200 μm.

[0073] The embodiment of the present invention also provides a terahertz polarization converter. Refer to Figure 6 shown, the terahertz polarization converter includes: a plurality of any one of the above-mentioned terahertz polarization conversion units 100, and the plurality of terahertz polarization conversion units 100 are arranged in an array. Among them, the plurality of terahertz polarization conversion units 100 can be arranged in an array ( Figure 6 shown is a schematic diagram of 6 terahertz polarization conversion units 100 arranged in an array), and the composite material strips 52 in the plurality of terahertz polarization conversion units 100 are connected to form a grating when the phase change material endpoints 522 included in each of them are in a conductive state. In this state, resonance cannot be achieved for the incident light. The terahertz polarization converter constituted by the embodiment of the present invention can expand the receiving area of the terahertz polarization conversion unit 100 for the incident light in the terahertz band, improve the modulation efficiency of the terahertz polarization converter, and the terahertz polarization converter has a large bandwidth coverage range for the terahertz band.

[0074] Example 1:

[0075] The specific structure of the terahertz polarization conversion unit is as Figure 1As shown, its specific structural parameters are: Px = Py = 200 μm; l1 = 250 μm; l2 = 120 μm; w1 = 5 μm; w2 = 20 μm; g = 70 μm; t1 = 1 μm; t2 = 1 μm; t3 = 0.2 μm; d1 = 35 μm; d2 = 25 μm; where, Px (the period of the terahertz polarization conversion unit along the x direction), Py (the period of the terahertz polarization conversion unit along the y direction), l1 (the length of the metal strip 521), l2 (the length of the phase change material strip 51), w1 (the width of the metal strip 521), w2 (the width of the phase change material strip 51), and g (the spacing between the phase change material strip 51 and the composite material strip 52) can all be referred to Figure 7 as shown; t1 (the thickness of the resonant strip layer 5), t2 (the thickness of the phase change material layer 3), t3 (the thickness of the metal film bottom layer 1), d1 (the thickness of the first dielectric layer 2), and d2 (the thickness of the second dielectric layer 4) can all be referred to Figure 8 as shown.

[0076] The above specific structural parameters can be input into simulation software for numerical simulation calculations to obtain Figure 9 and Figure 10 two schematic diagrams of simulation results, as well as Figure 11 the schematic diagram of the ellipticity of the incident light in the terahertz band reflected by this Example 1 as shown.

[0077] Among them, when the incident light in the terahertz band is incident on the metal strip 521 at a 45-degree polarization direction in the case where the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 are in the semiconductor state, referring to Figure 9 as shown, from 0.4 THz to 0.85 THz, the reflectivity of the incident light in the terahertz band is close to 100%; and, the component perpendicular to the metal strip 521 and the component parallel to the metal strip 521 decomposed from the incident light at a 45-degree polarization direction, the phase delays of these two directions ( Figure 9 the curve corresponding to the "phase difference" in it) are close to 270 degrees (equivalent to a negative 90-degree phase difference), indicating that in this band (such as from 0.4 THz to 0.85 THz), the linearly polarized incident light in the terahertz band can be effectively converted into circularly polarized light in the terahertz band.

[0078] When the incident light in the terahertz band is incident on the metal strip 521 at a 45-degree polarization direction in the case where the phase change material layer 3, the phase change material strip 51, and the phase change material end point 522 are in the conductor state, referring to Figure 10As shown, from 0.8 THz to 1.5 THz, the reflectivity of the incident light in the terahertz band is close to 100%; and, for the component perpendicular to the metal strip 521 and the component parallel to the metal strip 521 obtained by decomposing the incident light with a polarization direction of 45 degrees, the phase delays in these two directions are close to 270 degrees (equivalent to a phase difference of -90 degrees), indicating that in this band (such as from 0.8 THz to 1.5 THz), the incident linearly polarized terahertz light can be effectively converted into circularly polarized terahertz light. Therefore, Embodiment 1 of the present invention can convert light in the 0.4 THz to 1.5 THz band.

[0079] As described above, the above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of technical solutions of changes or substitutions, and all of them should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A terahertz polarization conversion unit, characterized in that Including: A metal film bottom layer (1), a first dielectric layer (2), a phase change material layer (3), a second dielectric layer (4), and a resonant strip layer (5) arranged in layers in sequence; the first dielectric layer (2) and the second dielectric layer (4) are transparent in the working wavelength band; The resonant strip layer (5) includes phase change material strips (51) and composite material strips (52) that are located in the same plane and are arranged parallel or perpendicular to each other; the composite material strips (52) include: metal strips (521) and phase change material endpoints (522) connected to the ends of the metal strips (521); The length of the metal strip (521) is greater than the length of the phase change material strip (51), and the orthographic projection of the composite material strip (52) on the second dielectric layer (4) penetrates the second dielectric layer (4); the phase change material layer (3), the phase change material strip (51), and the phase change material endpoints (522) exhibit a conductor state or a semiconductor state at different temperatures; Wherein, when the phase change material layer (3), the phase change material strip (51), and the phase change material endpoints (522) maintain the semiconductor state, the metal strip (521) and the metal film bottom layer (1) form a resonant cavity; the resonant cavity formed in the semiconductor state processes incident light in the low frequency band; When the phase change material layer (3), the phase change material strip (51), and the phase change material endpoints (522) maintain the conductor state, the phase change material strip (51) and the phase change material layer (3) form a resonant cavity; the resonant cavity formed in the conductor state processes incident light in the high frequency band.

2. The terahertz polarization conversion unit according to claim 1, wherein The number of the phase change material strips (51) is multiple.

3. The terahertz polarization conversion unit according to claim 1, wherein The composite material strip (52) is arranged to coincide with the diagonal of the second dielectric layer (4).

4. The terahertz polarization conversion unit according to claim 3, wherein The number of the phase change material strips (51) is a non-zero even number, and the phase change material strips (51) are symmetrically arranged on both sides of the composite material strip (52).

5. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that The material of the phase change material layer (3) includes: vanadium dioxide or germanium antimony telluride; the material of the phase change material strip (51) includes: vanadium dioxide or germanium antimony telluride; the material of the phase change material endpoints (522) includes: vanadium dioxide or germanium antimony telluride.

6. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that The material of the metal film bottom layer (1) includes: gold, silver, copper, aluminum, platinum or chromium; the material of the metal strip (521) includes: gold, silver, copper, aluminum, platinum or chromium.

7. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that The thickness of the metal film bottom layer (1) is greater than or equal to 0.1 μm.

8. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that, The thickness of the phase change material layer (3) is 0.1 μm to 5 μm; the thickness of the resonant strip layer (5) is 0.1 μm to 5 μm.

9. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that The thickness of the first dielectric layer (2) is 25 μm to 45 μm; the thickness of the second dielectric layer (4) is 20 μm to 30 μm.

10. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that, The length of the metal strip (521) is 230 μm to 270 μm; the width of the metal strip (521) is 2 μm to 30 μm.

11. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that, The length of the phase change material strip (51) is 100 μm to 140 μm; the width of the phase change material strip (51) is 5 μm to 35 μm.

12. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that, The spacing between the phase change material strip (51) and the composite material strip (52) is 50 μm to 90 μm.

13. The terahertz polarization conversion unit according to any one of claims 1-4, characterized in that, The period of the terahertz polarization conversion unit in the x direction is 180 μm to 220 μm; the period of the terahertz polarization conversion unit in the y direction is 180 μm to 220 μm; and the x direction and the y direction are two mutually perpendicular directions.

14. A terahertz polarization converter, characterized in that, Comprising: A plurality of terahertz polarization conversion units (100) as described in any one of the above claims 1-13, and the plurality of terahertz polarization conversion units (100) are arranged in an array.

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