Polarization modulation unit and terahertz vortex wave generation device

Abstract

The invention relates to a polarization modulation unit and a terahertz vortex wave generation device, the polarization modulation unit comprises a substrate and a metal sheet array arranged on the surface of the substrate, the metal sheet array comprises square metal sheets, a square array arrangement mode of the center of the square metal sheets is matched with deflection arrangement of the square metal sheets to form the metal sheet array, and the square metal sheets are arranged on the substrate. Therefore, the square metal sheet is allowed to realize local phase modulation on the terahertz spherical wave. The generation of the pattern number is irrelevant to the center distance between the adjacent square metal sheets, so that the limitation of the pattern number on the size of the square array is avoided.

Description

Technical Field

[0001] The present invention relates to the field of terahertz vortex waves, and particularly to a polarization modulation unit and a terahertz vortex wave generating device. Background Art

[0002] Due to its advantages such as large communication bandwidth, strong anti-interference ability, high resolution, and low photon energy, terahertz beams exhibit broad application prospects in fields such as spectral detection, biological imaging, holographic projection, and high-speed communication. In particular, terahertz waves simultaneously possess the penetrability of millimeter waves and the manipulability of light waves, providing possibilities for many technological breakthroughs.

[0003] Electromagnetic waves have linear momentum and angular momentum, and the angular momentum includes spin angular momentum (SAM) and orbital angular momentum (OAM). An electromagnetic wave beam carrying OAM is called a vortex beam. Terahertz vortex waves are very important in the fields of nanoparticle capture and rotation, super-resolution imaging, and high-density data storage because they can achieve super-resolution focused spots.

[0004] Traditional terahertz vortex waves are realized by a terahertz spherical wave signal source in cooperation with an annular array antenna, a spiral phase plate, or a holographic diffraction grating.

[0005] Based on symmetry restrictions, the annular array antenna needs to be strictly matched with the phase distribution of the spherical wave, and the perimeter of the array needs to satisfy (R is the radius of the array, is the mode number, and λ is the wavelength). To cover a larger typical mode (such as ), the value of R needs to be large. At the same time, the annular array also needs to meet the far-field radiation requirement ( ) to reduce the electromagnetic coupling between array elements, suppress cross polarization, and increase spurious modes. Due to the above two reasons, the volume of the annular array antenna is large.

[0006] The spiral phase plate and the holographic diffraction grating also result in large volumes due to reasons such as the physical requirements of phase accumulation (such as thickness gradient, periodic structure), wavelength sensitivity, and processing accuracy limitations.

[0007] Due to the above reasons, the existing terahertz vortex wave generating devices are large in volume and high in cost, and it is difficult to meet the requirements of integration and miniaturization. Summary of the Invention

[0008] Based on this, in view of the problems of large volume and high cost of the existing terahertz vortex wave generating device, it is necessary to provide a polarization modulation unit and a terahertz vortex wave generating device.

[0009] A polarization modulation unit includes a substrate and a metal sheet array disposed on the surface of the substrate. The metal sheet array includes A square metal sheet, the centers of all the square metal sheets are arranged in a square array on the substrate surface, so that each square metal sheet occupies a square space on the substrate surface, not less than the diagonal length of all the square metal sheets, and at least part of the square metal sheets are arranged in a deflected manner in the square space they occupy;

[0010] A resonance hole is arranged in the middle of the square metal sheet, the shape of the resonance hole is a centrosymmetric figure, and the center of the resonance hole coincides with the center of the square metal sheet;

[0011] Among them, the th square metal sheet satisfies: , and , , is the co-polarized reflection coefficient of the th square metal sheet under the perpendicular incidence of the polarized wave, is the co-polarized reflection coefficient of the th square metal sheet under the perpendicular incidence of the polarized wave.

[0012] In one embodiment, the polarization conversion efficiency of the th square metal sheet satisfies: , where , is the co-polarized reflection coefficient of the th square metal sheet under the perpendicular incidence of the left circularly polarized wave, is the co-polarized reflection coefficient of the th square metal sheet under the perpendicular incidence of the right circularly polarized wave, and are the cross-polarized reflection coefficients corresponding to the co-polarized reflection coefficients and .

[0013] In one embodiment, the th square metal sheet satisfies:

[0014] ;

[0015] ;

[0016] ;

[0017] ;

[0018] Wherein, is the imaginary unit, is the deflection angle of the th square metal sheet in the corresponding square space, and are the co-polarization reflection coefficients and corresponding cross-polarization reflection coefficients.

[0019] In one embodiment, the shape of the resonant hole is circular or square.

[0020] A design method of the polarization modulation unit described above includes:

[0021] Obtain the vortex phase of the th square metal sheet ;

[0022] Obtain the focusing phase of the th square metal sheet at the focus of the metal sheet array ;

[0023] Obtain the compensation space phase of the th square metal sheet ;

[0024] Determine the deflection angle of the th square metal sheet based on at least the vortex phase , focusing phase and compensation space phase ;

[0025] Determine the co-polarization reflection coefficient of the th square metal sheet based on the deflection angle , co-polarization reflection coefficient , geometric parameters of the th square metal sheet and geometric parameters of the resonant hole in the middle of the th square metal sheet.

[0026] In one embodiment, it further includes:

[0027] Determine the co-polarization reflection coefficient of the th square metal sheet and the cross-polarization reflection coefficient based on the deflection angle ;

[0028] Based on the co-polarization reflection coefficient and the cross-polarization reflection coefficient Determine the polarization conversion efficiency corresponding to the th square metal sheet;

[0029] Based on the polarization conversion efficiency Determine the geometric parameters of the th square metal sheet and the geometric parameters of the resonant hole in the middle of the

[0030] In one embodiment, it further includes:

[0031] Set the number of rows of the metal sheet array , the side length of the square space , the focal length of the metal sheet array , the distance between the metal sheet array and the signal source , the emission wavelength of the signal source and the orbital angular momentum mode number of the phase singularity ;

[0032] Obtain the sequence coordinates of the th square metal sheet as , where is the row sequence number of the th square metal sheet in the metal sheet array, is the column sequence number of the th square metal sheet in the metal sheet array;

[0033] Determine the vortex phase at least based on the orbital angular momentum mode number of the phase singularity and the sequence coordinates of the th square metal sheet ;

[0034] Determine the focusing phase at least based on the focal length of the metal sheet array , the sequence coordinates of the th square metal sheet and the emission wavelength of the signal source ;

[0035] Determine the focusing phase at least based on the emission wavelength of the signal source , the sequence coordinates of the th square metal sheet, the number of rows of the metal sheet array , the side length of the square space and the distance between the metal sheet array and the signal source Determine the compensation space phase .

[0036] In one embodiment, the th square metal sheet satisfies:

[0037] Vortex phase ;

[0038] Focusing phase ;

[0039] Compensation space phase ;

[0040] Deflection angle ;

[0041] Wherein, is the free space wave number, .

[0042] A terahertz vortex wave generating device includes a signal source and the polarization modulation unit described above. The signal source is used to generate a terahertz spherical wave, the signal source is arranged facing the metal sheet array, and the metal sheet array is used to modulate the terahertz spherical wave into a terahertz vortex wave.

[0043] In one embodiment, the signal source is a circularly polarized antenna feed, and the center of the signal source is oppositely arranged with the geometric center of the metal sheet array.

[0044] The present invention has the following beneficial effects:

[0045] 1. The square array arrangement mode at the center of the square metal sheet, combined with the deflection setting of the square metal sheet, forms a metal sheet array to allow the square metal sheet to perform local phase modulation on the terahertz spherical wave.

[0046] 2. The generation of the mode number of the present invention is independent of the center spacing between adjacent square metal sheets, avoiding the limitation of the mode number on the size of the square array.

[0047] 3. Through the metasurface design of the square metal sheet (such as the size of the square metal sheet, the size of the resonant hole, and the deflection angle of each square metal sheet), the present invention can limit the adverse effects of near-field regulation, allow the square array to perform near-field regulation on the spherical wave, greatly compress the area of the square array, and at the same time achieve a regulation effect similar to that of the annular array.

[0048] In summary, the size of the metal sheet array of the present invention is significantly reduced compared with that of the circular array antenna, the spiral phase plate or the holographic diffraction grating, and at the same time, it can meet the modulation requirements of the vortex wave, which helps to miniaturize the terahertz vortex wave generating device and reduce its cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic structural diagram of the terahertz vortex wave generating device in an embodiment of the present invention;

[0050] Figure 2 is a three-dimensional structural schematic diagram of the square metal sheet in an embodiment of the present invention;

[0051] Figure 3 is a top view structural schematic diagram of the square metal sheet in an embodiment of the present invention;

[0052] Figure 4 is a schematic diagram of the geometric parameters of the square metal sheet in an embodiment of the present invention Figure 1 ;

[0053] Figure 5 is a schematic diagram of the geometric parameters of the square metal sheet in an embodiment of the present invention Figure 2 ;

[0054] Figure 6 is the target phase diagram of the metal sheet array in an embodiment of the present invention;

[0055] Figure 7 is the co-polarization reflection coefficient, cross-polarization reflection coefficient and conversion efficiency of the square metal sheet (sequence coordinates are (1, 1)) in an embodiment of the present invention when the left circularly polarized wave is vertically incident without rotation angle;

[0056] Figure 8 is the co-polarization reflection coefficient and reflection phase corresponding to different rotation angles of the square metal sheet (sequence coordinates are (1, 1)) under the excitation of the left circularly polarized wave in an embodiment of the present invention;

[0057] Figure 9 is a schematic plane structure diagram of the metal sheet array in an embodiment of the present invention;

[0058] Figure 10 is the left-handed and right-handed OAM spectra corresponding to the metal sheet array at 4THz frequency in an embodiment of the present invention, and the upper right inset is the near-field simulation result diagram of the vortex wave in the = -2 mode;

[0059] Figure 11 is the three-dimensional far-field radiation pattern of the vortex wave of the metal sheet array in an embodiment of the present invention;

[0060] Figure 12 is the preparation flow chart of the terahertz vortex wave generating device in an embodiment of the present invention.

[0061] Reference numerals:

[0062] 1. Substrate; 2. Square metal sheet; 21. Resonant hole; 201. Conductive material; 202. Photoresist; 203. Bonding pad; 3. Signal source; 4. Energy absorption region; 5. Electrode contact region; 6. Electrode layer; 7. Passivation layer; 8. Metal patch. Detailed implementation manners

[0063] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0064] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are 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 of the present invention.

[0065] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0066] In the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly limited. 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.

[0067] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or merely indicates that the horizontal height of the first feature is less than that of the second feature.

[0068] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only implementation.

[0069] See Figure 1 , this embodiment provides a terahertz vortex wave generating device, which includes a signal source 3 and a polarization modulation unit. The polarization modulation unit specifically includes a substrate 1 and a metal sheet array disposed on the surface of the substrate 1, and the signal source 3 is arranged facing the metal sheet array. The signal source 3 can generate terahertz spherical waves, and the metal sheet array can modulate the terahertz spherical waves into terahertz vortex waves.

[0070] Preferably, the signal source 3 is a circularly polarized antenna feed, and the center of the signal source 3 is disposed opposite to the geometric center of the metal sheet array.

[0071] The metal sheet array includes square metal sheets 2. As Figure 2 and Figure 3 shown, the shape of the square metal sheet 2 is specifically a square or a rectangle (the shapes of different square metal sheets 2 are not required to be the same), so each square metal sheet 2 necessarily has a geometric center, and the centers of all square metal sheets 2 are arranged in a square array on the upper surface of the substrate 1. Thus, each square metal sheet 2 will occupy a square space on the upper surface of the substrate 1, and the center of the square metal sheet 2 coincides with the center of its corresponding square space. In other words, is not only the side length of the square space but also the center distance between adjacent two square metal sheets 2. Further, see Figure 4 , the included angle between the axis of symmetry of the th square metal sheet 2 and the side of the square space occupied by the square metal sheet 2 is , where is not a fixed value, and at the same time is not necessarily equal to 0° or 90°. When 90° > > 0°, it indicates that the th square metal sheet 2 is deflected in the square space it occupies. That is, the th square metal sheet 2 has a deflection angle in the corresponding square space. In this embodiment, at least some of the square metal sheets 2 are deflected in the square space they occupy to meet the modulation requirements for terahertz spherical waves.

[0072] To prevent adjacent square metal sheets 2 from contacting each other, should not be less than the diagonal length of all square metal sheets 2.

[0073] Each square metal sheet 2 can be used to perform phase modulation on terahertz spherical waves, and all square metal sheets 2 cooperate together to convert terahertz spherical waves into terahertz vortex waves.

[0074] As Figure 2 and Figure 3 shown, in order to further improve the modulation effect of the square metal sheet 2 on terahertz spherical waves, a resonant hole 21 needs to be provided in the middle of the square metal sheet 2. The shape of the resonant hole 21 should be a centrosymmetric figure, commonly, such as a circle, a rectangle or a square. The center of the resonant hole 21 coincides with the center of the square metal sheet 2, so the opening of the resonant hole 21 will not cause the geometric center of the square metal sheet 2 to change.

[0075] After the tuning ability of each square metal sheet 2 is improved through the resonant hole 21, the following relational expressions can be satisfied:

[0076] , and , . Among them, is the co-polarized reflection coefficient of the th square metal sheet 2 under the perpendicular incidence of the polarized wave, is the co-polarized reflection coefficient of the th square metal sheet 2 under the perpendicular incidence of the polarized wave.

[0077] Preferably, .

[0078] Furthermore, on the basis of preferentially satisfying , and these three relational expressions, each square metal sheet 2 can further satisfy , is the polarization conversion efficiency of the th square metal sheet 2.

[0079] Among them, , is the co-polarization reflection coefficient of the th square metal sheet 2 under the vertical incidence of the left circularly polarized wave, is the co-polarization reflection coefficient of the th square metal sheet 2 under the vertical incidence of the right circularly polarized wave, and are the co-polarization reflection coefficients and corresponding cross-polarization reflection coefficients.

[0080] In addition, in this embodiment, the th square metal sheet 2 also satisfies:

[0081] ;

[0082] ;

[0083] ;

[0084] ;

[0085] Among them, is the imaginary unit, and are the co-polarization reflection coefficients and corresponding cross-polarization reflection coefficients.

[0086] Among them, the co-polarization reflection coefficients , , , and the cross-polarization reflection coefficients , , , are determined by the deflection angle of the th square metal sheet 2, the dimensional parameters of the th square metal sheet 2, and the shape of the resonant hole 21 in the th square metal sheet 2.

[0087] Based on this, this embodiment also additionally provides a design method for the polarization modulation unit, which is used to design the deflection angles of all the square metal sheets 2, the geometric parameters of all the square metal sheets 2, and the geometric parameters of all the resonant holes 21. As an example, the shapes of all the resonant holes 21 in this embodiment are all rectangular. AsFigure 4 and Figure 5 As shown, for the th square metal sheet 2, its deflection angle is , the width is , and the length is . The width of the resonance hole 21 in the middle is , and the length is . In other words, the purpose of the described design method is to obtain all , , , , .

[0088] Specifically, the described design method includes the following steps:

[0089] Step 101: Set the number of rows of the metal sheet array, the side length of the square space, the focal length of the metal sheet array, the distance between the metal sheet array and the signal source 3, the emission wavelength of the signal source 3, and the orbital angular momentum mode number of the phase singularity.

[0090] Exemplarily, in this embodiment , , , , = 1000 μm, = 75 μm, and the thickness of the substrate 1 is 9 μm. By defining the number of rows of the metal sheet array and the side length of the square space, the size of the entire metal sheet array can be effectively limited.

[0091] Step 102: Obtain the sequence coordinates of the th square metal sheet 2 as , where is the row sequence number of the th square metal sheet 2 in the metal sheet array, and is the column sequence number of the th square metal sheet 2 in the metal sheet array.

[0092] Step 103: Obtain the vortex phase of the th square metal sheet 2.

[0093] Specifically, at least based on the orbital angular momentum mode number of the phase singularity and the Sequence coordinates of the nth square metal sheet 2 Determine the vortex phase .

[0094] More specifically, the nth square metal sheet 2 satisfies: the vortex phase . It can be seen that the number of orbital angular momentum modes is independent of the side length of the square space, and the number of orbital angular momentum modes will not affect the size of the entire metal sheet array.

[0095] Step 103: Obtain the focusing phase of the nth square metal sheet 2 at the focal point of the metal sheet array .

[0096] Specifically, based at least on the focal length of the metal sheet array , the sequence coordinates of the nth square metal sheet 2 and the emission wavelength of the signal source 3 to determine the focusing phase .

[0097] More specifically, the nth square metal sheet 2 satisfies: the focusing phase . Wherein, is the free space wave number, 0.

[0098] Step 104: Obtain the compensation space phase of the nth square metal sheet 2 .

[0099] Specifically, based at least on the emission wavelength of the signal source 3 , the sequence coordinates of the nth square metal sheet 2 , the number of rows of the metal sheet array , the side length of the square space and the distance between the metal sheet array and the signal source 3 to determine the compensation space phase .

[0100] More specifically, the nth square metal sheet 2 satisfies: the compensation space phase .

[0101] Step 105: Based at least on the vortex phase , the focusing phase and the compensation space phase to determine the nth The deflection angle of the square metal sheet 2 on the substrate 1 .

[0102] Specifically, the deflection angle .

[0103] Step 106: Based on the deflection angle Determine the co-polarization reflection coefficient of the th square metal sheet 2 , the co-polarization reflection coefficient , the th geometric parameters of the square metal sheet 2 and the geometric parameters of the intermediate resonant hole 21 of the th square metal sheet 2

[0104] More specifically, after obtaining all the deflection angles , input them together with the number of rows of the metal sheet array , the side length of the square space , the focal length of the metal sheet array , the distance between the metal sheet array and the signal source 3 , the emission wavelength of the signal source 3 and the orbital angular momentum mode number of the phase singularity into the CTS simulation software for simulation. During the simulation, scan , , , to obtain , , , The corresponding co-polarization reflection coefficient under different numerical combinations , , , and the cross-polarization reflection coefficient , , and value changes, and screen out the corresponding , and when the three conditions are met , , , values, and then determine the geometric parameters of the th square metal sheet 2 and its intermediate resonant hole 21

[0105] Further preferably, when meeting , and the three conditions, screen out multiple , , , When taking the value combinations of and the cross-polarization reflection coefficient , the polarization conversion efficiency corresponding to the second square metal sheet 2 can be further determined. Under the condition of satisfying , the value combinations of , , , , are further screened. Based on the polarization conversion efficiency , the geometric parameters of the second square metal sheet 2 and the geometric parameters of the intermediate resonant hole 21 of the second square metal sheet 2 are determined.

[0106] It should be noted that during the value scanning process of , , , by the CTS simulation software, it is default that all the square metal sheets 2 have the same geometric parameters and all the resonant holes 21 have the same geometric parameters. In other words, the simulation process of the CTS simulation software is carried out under the default condition of , , , .

[0107] The final result screened in this embodiment is = 24 μm, = 8 μm, = 7.2 μm, = 3 μm. The final design result of the entire metal sheet array is shown in Figure 9 .

[0108] During the above design process, the phase distribution of the target design of the metal sheet array is as shown in Figure 6 . Its total compensation phase covers 0° - 360° and is distributed in a spiral shape. Among them, when the deflection angle of the square metal sheet is 0° and the terahertz frequency band bandwidth of the periodic unit is 2.5 THz - 5.5 THz, as shown in Figure 7 , the co-polarization reflection coefficient of the square metal sheet is greater than 0.858, and the cross-polarization reflection coefficient is less than 0.413, thereby making the polarization conversion efficiency higher than 0.878. Further, as shown in Figure 8As shown, when the square metal sheet 2 generates a deflection angle, the reflection spectrum phase curves corresponding to different deflection angles remain parallel within the bandwidth frequency range, indicating that within the range of 2.5 THz - 5.5 THz, the phase response of the square metal sheet 2 has a consistent trend with frequency change, proving the stable generation of the main mode of the vortex wave (such as =-2) within the frequency band and the broadband stability of the phase modulation of the square metal sheet; in addition, the co-polarization reflection coefficient of the square metal sheet is higher than 0.828, indicating that the co-polarization reflection coefficients of the square metal sheet and are also relatively high, proving that most of the incident wave energy is reflected in the original polarization direction, and only a small amount of energy leaks to the cross polarization ( <0.413), confirming the high polarization retention ability and high energy efficiency of the square metal sheet.

[0109] The OAM mode purity is used to describe the proportion of the energy of the vortex waves with various different mode numbers in the reflected field, for quantitatively analyzing the quality of the vortex waves. Taking the phase singularity of the vortex beam as the center, an annular electric field data is selected along the beam, and its Fourier transform is performed. The Fourier transform can decompose each OAM mode in the reflected field. As Figure 10 shown, the main mode =-2 occupies the highest energy, proving that the main mode of the vortex wave finally generated by the metal sheet array is consistent with the designed mode.

[0110] In addition, numerical simulations are carried out at the central frequency of 4 THz, and the vortex focusing characteristics of the metal sheet array are verified through the electromagnetic properties of the near field and the far field. Specifically, as Figure 10 shown, under the excitation of a left-handed circularly polarized wave, the metal sheet array generates a terahertz vortex wave with an OAM mode number =-2. Through the decoupling and analysis of the left-handed and right-handed components in the reflected field, the focusing characteristics of the vortex wave are verified. It can be observed from the left-handed component of the sampling field that the electric field amplitude presents a hollow ring shape, and the phase distribution is symmetrically double-helical around the singularity, with the phase change range of 0° - 360°. This characteristic is consistent with the theoretical characteristics of the OAM mode, proving that the designed metal sheet array can enable the reflected electromagnetic wave to carry OAM.

[0111] Under the excitation of a left-handed circularly polarized wave, the three-dimensional far-field radiation pattern of the vortex wave of the metal sheet array is as Figure 11 shown, where the maximum radiation gain of the left-handed component of the reflected field reaches 14.4 dB, and this gain effect effectively matches the Figure 7 and Figure 8 simulation results shown.

[0112] Furthermore, this embodiment also provides a preparation method for the polarization modulation unit, as Figure 1 andFigure 12 As shown, it includes the following steps:

[0113] Step 201: Select a high-purity germanium wafer with a doping concentration of 5×10 18 cm -3 and a thickness of 9 μm as Substrate 1. Remove impurities through ultrasonic cleaning and chemical cleaning, and use a microscope to check to ensure that the surface of Substrate 1 has no cracks or contamination.

[0114] Step 202: Use electron beam deposition technology to deposit a 100-nm-thick conductive material 201 on Substrate 1. The conductive material 201 will serve as the precursor of the square metal sheet 2. Optionally, the material of the conductive material 201 can be gold or copper.

[0115] Step 203: Uniformly coat a 0.5-μm-thick photoresist 202 on the surface of the conductive material 201, and pre-calculate the relief depth to be 0.6 μm.

[0116] Step 204: Use computer-aided design (CAD) software to design the shape of each square metal sheet 2. Adopt laser direct writing maskless lithography technology to directly scan and expose on the photoresist 202, and complete the pattern making through development and chemical etching. Subsequently, remove the photoresist 202, and the remaining conductive material 201 forms each square metal sheet 2.

[0117] Step 205: Use another 3-μm-thick high-purity germanium wafer as the bonding plate 203, and bond it to Substrate 1 through wafer bonding technology.

[0118] Step 206: Adopt ultraviolet lithography technology to make a pattern of the energy absorption region 4 at the middle position corresponding to the square metal sheet 2 on the surface of the bonding plate 203. The width of the pattern is 75 μm. Use a 0.5-μm-thick photoresist as the mask for ion implantation. Through multiple ion implantations, boron impurities are implanted into the pattern position, so that the ion-implanted part forms the energy absorption region 4. Among them, the ion implantation depth is 3 μm, and the doping concentration is 5×10 16 cm -3 .

[0119] Step 207: Again adopt ultraviolet lithography technology to make a pattern of the electrode contact region 5 at the edge of the surface of the bonding plate 203. The pattern is 200 μm. Through multiple ion implantations, boron impurities are implanted into this pattern, so that the ion-implanted part forms the electrode contact region 5. The implantation depth is 3 μm, and the doping concentration is 5×10 18 cm -3 .

[0120] Step 208: Using PECVD technology, deposit a 200-nm-thick silicon nitride material on the surface of the bonding plate 203 as the passivation layer 7, then remove the part of the passivation layer 7 above the electrode contact area 5, fabricate the pattern of the electrode layer 6 on the surface of the electrode contact area 5 through ultraviolet lithography technology, use RIE etching technology to open the electrode window, and use electron beam deposition technology to deposit a 200-nm-thick gold layer at the electrode window as the electrode layer 6.

[0121] Step 209: Perform rapid annealing on the detection unit device, set the temperature to 300 °C and the annealing time to 300 seconds to optimize the device performance, and finally set the metal patch 8 on the lower surface of the substrate.

[0122] Among them, after the terahertz spherical wave is modulated into a terahertz vortex wave by the square metal sheet 2, it is absorbed by the energy absorption area 4 to generate a photocurrent, and the photocurrent is transmitted to the external circuit through the electrode layer 6 and the metal patch 8 and detected.

[0123] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0124] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A polar modulation unit, characterized in that: It comprises a substrate (1) and a metal sheet array arranged on the surface of the substrate (1), wherein the metal sheet array comprises square metal sheets (2), the centers of all the square metal sheets (2) being on the surface of the substrate (1) The square array is arranged so that each of the square metal sheets (2) occupies a surface area of ​​the substrate (1). square space, The length of the diagonal line of the square metal sheets (2) is not less than that of the diagonal line of the square metal sheets (2), and at least part of the square metal sheets (2) are arranged in a deflected manner in the square space they occupy; A resonance hole (21) is provided in the middle of the square metal sheet (2), the shape of the resonance hole (21) is a centrally symmetrical figure, and the center of the resonance hole (21) coincides with the center of the square metal sheet (2); Among them, The square metal sheet (2) satisfies: , as well as , , For the The square metal sheet (2) is The co-polarized reflection coefficient under vertical incidence of polarized waves, For the The square metal sheet (2) is Co-polarized reflection coefficient for vertically incident polarized waves.

2. The polarization modulation unit according to claim 1, characterized in that: No. The polarization conversion efficiency of the square metal sheet (2) is satisfy: ,in, , For the The co-polarization reflection coefficient of the square metal sheet (2) under vertical incidence of left circularly polarized wave, For the The co-polarization reflection coefficient of the square metal sheet (2) under the vertical incidence of right circularly polarized wave, and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

3. The polar modulation unit according to claim 1, characterized in that: No. The square metal sheet (2) satisfies: ； ； ； ； in, is an imaginary unit, For the The deflection angle of the square metal sheet (2) in the corresponding square space, and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

4. The polar modulation unit according to claim 1, characterized in that: The resonance hole (21) is in a circular or square shape.

5. A method for designing a polar modulation unit according to any one of claims 1 to 4, characterized in that: include: Get the The vortex phase of the square metal sheet (2) ; Get the The focusing phase of the square metal pieces (2) at the focus of the metal piece array ; Get the The compensation spatial phase of the square metal sheet (2) ; At least based on the vortex phase , Focus Phase And compensate spatial phase Determine The deflection angle of the square metal sheet (2) ; Based on the deflection angle Determine The same polarization reflection coefficient of the square metal sheet (2) is , co-polarization reflection coefficient , No. The geometric parameters of the square metal sheet (2) and The geometric parameters of the resonance hole (21) in the middle of the square metal sheet (2).

6. The design method of the polar modulation unit according to claim 5, characterized in that: Also includes: Based on the deflection angle Determine The same polarization reflection coefficient of the square metal sheet (2) is and the cross-polarization reflection coefficient ; Based on the co-polarization reflection coefficient and the cross-polarization reflection coefficient Determine The polarization conversion efficiency corresponding to the square metal sheet (2) is ; Based on polarization conversion efficiency Determine The geometric parameters of the square metal sheet (2) and The geometric parameters of the resonance hole (21) in the middle of the square metal sheet (2).

7. The design method of the polar modulation unit according to claim 5, characterized in that: Also includes: Set the number of rows of the metal sheet array , the side length of the square space , the focal length of the metal sheet array , the distance between the metal sheet array and the signal source (3) , the emission wavelength of the signal source (3) and the orbital angular momentum mode number of the phase singularity ; Get the The sequence coordinates of the square metal pieces (2) are ,in For the The number of rows of the square metal sheets (2) in the metal sheet array, For the The number of columns and sequences of the square metal sheets (2) in the metal sheet array; At least the number of orbital angular momentum modes based on phase singularities and The sequence coordinates of the square metal pieces (2) Determining the vortex phase ; At least based on the focal length of the metal sheet array , No. The sequence coordinates of the square metal pieces (2) and the emission wavelength of the signal source (3) Determine the focus phase ; At least based on the emission wavelength of the signal source (3) , No. The sequence coordinates of the square metal pieces (2) , the number of rows of the metal sheet array , the side length of the square space and the distance between the metal sheet array and the signal source (3) Determine the compensation spatial phase .

8. The design method of the polar modulation unit according to claim 7, characterized in that: No. The square metal sheet (2) satisfies: Vortex Phase ; Focus Phase ; Compensation for spatial phase ; Deflection Angle ; in, is the free space wave number, .

9. A terahertz vortex wave generating device, characterized in that: It comprises a signal source (3) and a polarization modulation unit as claimed in any one of claims 1 to 4, wherein the signal source (3) is used to generate a terahertz spherical wave, the signal source (3) is arranged toward the metal sheet array, and the metal sheet array is used to modulate the terahertz spherical wave into a terahertz vortex wave.

10. The terahertz vortex wave generating device according to claim 9, characterized in that: The signal source (3) is a circularly polarized antenna feed source, and the center of the signal source (3) is arranged relative to the geometric center of the metal sheet array.

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