A polarization modulation unit and a terahertz vortex wave generating device

Abstract

The present invention relates to a polarization modulation unit and a terahertz vortex wave generating device, comprising a substrate and a metal sheet array disposed on the substrate surface. The metal sheet array comprises square metal sheets arranged in a square array with their centers, and configured to deflect the square metal sheets to form a metal sheet array, thereby enabling the square metal sheets to achieve local phase modulation of terahertz spherical waves. The present invention generates a mode number independent of the center-to-center spacing between adjacent square metal sheets, thus avoiding the limitation of the mode number on the size of the square array.

Description

Technical Field

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

[0002] Terahertz beams, with their advantages of wide communication bandwidth, strong anti-interference capabilities, high resolution, and low photon energy, show broad application prospects in spectral detection, bioimaging, holographic projection, high-speed communications, and other fields. In particular, terahertz waves combine the penetrability of millimeter waves with the controllability of light waves, making numerous technological breakthroughs possible.

[0003] Electromagnetic waves possess both linear momentum and angular momentum. Angular momentum comprises spin angular momentum (SAM) and orbital angular momentum (OAM). Electromagnetic beams carrying OAM are called vortex beams. Terahertz vortex waves, because they can achieve super-resolution focused beams, have important applications in nanoparticle capture and rotation, super-resolution imaging, and high-density data storage.

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

[0005] The ring array antenna is based on symmetry constraints and needs to strictly match the phase distribution of the spherical wave. The circumference of the array must meet (R is the array radius, is the mode number, λ is the wavelength). In order to cover a larger number of typical modes (such as ), the value of R needs to be larger. At the same time, the ring array also needs to meet the far-field radiation requirements ( ) to reduce electromagnetic coupling between array elements, suppress cross-polarization and increase in spurious modes. Due to the above two reasons, the size of the ring array antenna is relatively large.

[0006] Spiral phase plates and holographic diffraction gratings are also large in size due to the physical requirements of phase accumulation (such as thickness gradient, periodic structure), wavelength sensitivity and processing accuracy limitations.

[0007] For the above reasons, existing terahertz vortex wave generation equipment is bulky and expensive, making it difficult to meet the requirements of integration and miniaturization. Summary of the Invention

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

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

[0010] A resonant hole is provided in the middle of the square metal sheet, and the shape of the resonant hole is a centrosymmetrical figure, and the center of the resonant hole coincides with the center of the square metal sheet;

[0011] Among them, The square metal pieces satisfy: , as well as , , For the The square metal pieces The co-polarization reflection coefficient under vertical incidence of polarized wave, For the The square metal pieces Co-polarized reflection coefficient under vertical incidence of polarized waves.

[0012] In one embodiment, the The polarization conversion efficiency of the square metal sheet is satisfy: ,in, , For the The co-polarization reflection coefficient of the square metal sheet under vertical incidence of left circularly polarized wave is: For the The co-polarization reflection coefficient of the square metal sheet under vertical incidence of right circularly polarized wave is: and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

[0013] In one embodiment, the The square metal pieces satisfy:

[0014] ;

[0015] ;

[0016] ;

[0017] ;

[0018] in, is the imaginary unit, For the The deflection angle of each square metal piece in the corresponding square space, and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

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

[0020] A design method for a polar modulation unit includes:

[0021] Get the The vortex phase of the square metal sheet ;

[0022] Get the The focusing phase of the square metal piece at the focus of the metal piece array ;

[0023] Get the The compensation spatial phase of the square metal piece ;

[0024] At least based on the vortex phase , focus phase and compensate spatial phase Determine the The deflection angle of the square metal piece ;

[0025] Based on the deflection angle Determine the The same polarization reflection coefficient of the square metal piece , co-polarization reflection coefficient , No. The geometric parameters of the square metal sheet and the The geometric parameters of the resonant hole in the middle of the square metal sheet.

[0026] In one embodiment, it further includes:

[0027] Based on the deflection angle Determine the The same polarization reflection coefficient of the square metal piece and the cross-polarization reflection coefficient ;

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

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

[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] Get the The sequence coordinates of the square metal pieces are ,in For the The number of rows of the square metal sheets in the metal sheet array, For the The number of columns of the square metal sheets in the metal sheet array;

[0033] At least the number of orbital angular momentum modes based on phase singularities and The square metal piece sequence coordinates Determine vortex phase ;

[0034] At least based on the focal length of the metal sheet array , No. The square metal piece sequence coordinates and the emission wavelength of the signal source Determine the focus phase ;

[0035] At least based on the emission wavelength of the signal source , No. The square metal piece sequence coordinates , the number of rows of the metal sheet array , the side length of the square space and the spacing between the metal sheet array and the signal source Determine the compensation spatial phase .

[0036] In one embodiment, the The square metal pieces satisfy:

[0037] vortex phase ;

[0038] Focus Phase ;

[0039] Compensation for spatial phase ;

[0040] Deflection angle ;

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

[0042] A terahertz vortex wave generating device includes a signal source and the polarization modulation unit. The signal source is used to generate a terahertz spherical wave. The signal source is arranged toward the metal sheet array. 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 arranged relative to the geometric center of the metal sheet array.

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

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

[0046] 2. Mode number of the present invention The generation of the square metal pieces has nothing to do with the center distance between adjacent square metal pieces, thus avoiding the large number of modes. Restriction on square array dimensions.

[0047] 3. Through the metasurface design of the square metal sheets (such as the size of the square metal sheets, the size of the resonant holes, and the deflection angles of each square metal sheet), the present invention can limit the adverse effects of near-field control, allowing the square array to perform near-field control of spherical waves, significantly reducing the area of ​​the square array, while also achieving a control effect similar to that of a ring array.

[0048] In summary, the size of the metal sheet array of the present invention is significantly reduced compared to the annular array antenna, spiral phase plate or holographic diffraction grating, while also meeting 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 Schematic diagram of the structure of a terahertz vortex wave generating device according to an embodiment of the present invention;

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

[0051] Figure 3 Schematic diagram of the top view of the square metal sheet in an embodiment of the present invention;

[0052] Figure 4 Schematic diagram of the geometric parameters of the square metal sheet in the embodiment of the present invention Figure 1 ;

[0053] Figure 5 Schematic diagram of the geometric parameters of the square metal sheet in the embodiment of the present invention Figure 2 ;

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

[0055] Figure 7 are the co-polarization reflection coefficient, cross-polarization reflection coefficient, and conversion efficiency of the square metal sheet (sequence coordinates are (1, 1)) under vertical incidence of left circularly polarized waves with no rotation angle in an embodiment of the present invention;

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

[0057] Figure 9 Schematic diagram of the planar structure of the metal sheet array according to an embodiment of the present invention;

[0058] Figure 10 The left-handed and right-handed OAM spectra of the metal sheet array at 4 THz in the embodiment of the present invention are shown in the illustration in the upper right corner. = Vortex wave near-field simulation results in -2 mode;

[0059] Figure 11 3D far-field radiation pattern of vortex waves in the metal sheet array according to an embodiment of the present invention;

[0060] Figure 12 This is a flow chart for preparing a 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 plate; 3. Signal source; 4. Energy absorption area; 5. Electrode contact area; 6. Electrode layer; 7. Passivation layer; 8. Metal patch. DETAILED DESCRIPTION

[0063] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0064] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying 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 therefore should not be understood as limiting the present invention.

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

[0066] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0067] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than 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 may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0069] See also Figure 1 This embodiment provides a terahertz vortex wave generation device, including 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 substrate 1. Signal source 3 is positioned toward the metal sheet array. Signal source 3 generates terahertz spherical waves, and the metal sheet array modulates 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 arranged relative to the geometric center of the metal sheet array.

[0071] The metal sheet array includes A square metal piece 2. Figure 2 and Figure 3 As shown, the shape of the square metal sheet 2 is specifically a square or a rectangle (different square metal sheets 2 are not required to have the same shape), so each square metal sheet 2 must have a geometric center, and the centers of all square metal sheets 2 are on the surface of the substrate 1. Thus, each square metal sheet 2 will occupy an area on the upper surface of the substrate 1. The center of the square metal piece 2 coincides with the center of its corresponding square space. In other words, Not only the side length of the square space, but also the center distance between two adjacent square metal sheets 2. Figure 4 , No. The angle between the symmetry axis of a square metal sheet 2 and the side of the square space occupied by the square metal sheet 2 is ,in It is not a fixed value, It is not necessarily equal to 0° or 90°. When 90°> >0°, indicating The square metal pieces 2 are arranged in a deflected manner in the square space they occupy. That is The deflection angle of each square metal piece 2 in the corresponding square space. In this embodiment, at least part of the square metal pieces 2 are deflected in the square space they occupy to meet the modulation requirements of the terahertz spherical wave.

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

[0073] Each square metal piece 2 can be used to perform phase modulation on the terahertz spherical wave, and all the square metal pieces 2 work together to convert the terahertz spherical wave into a terahertz vortex wave.

[0074] like Figure 2 and Figure 3 As shown, to further enhance the modulation effect of the square metal sheet 2 on the terahertz spherical wave, a resonant hole 21 is also required in the center of the square metal sheet 2. The shape of the resonant hole 21 should be a centrosymmetrical shape, such as a circle, rectangle, or square. The center of the resonant hole 21 coincides with the center of the square metal sheet 2, so the creation of the resonant hole 21 does not change the geometric center of the square metal sheet 2.

[0075] After the tuning capability of each square metal piece 2 is improved by the resonant hole 21, the following relationship can be satisfied:

[0076] , as well as , .in, For the Square metal pieces 2 The co-polarization reflection coefficient under vertical incidence of polarized wave, For the Square metal pieces 2 Co-polarized reflection coefficient under vertical incidence of polarized waves.

[0077] Preferably, .

[0078] Furthermore, in order to give priority to , as well as Based on the three relationships, each square metal piece 2 can further satisfy , For the Polarization conversion efficiency of a square metal sheet 2.

[0079] in, , For the The co-polarization reflection coefficient of a square metal plate 2 under vertical incidence of left circularly polarized wave is: For the The co-polarization reflection coefficient of a square metal plate 2 under vertical incidence of right circularly polarized wave is: and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

[0080] In addition, in this embodiment The square metal piece 2 also satisfies:

[0081] ;

[0082] ;

[0083] ;

[0084] ;

[0085] in, is the imaginary unit, and is the co-polarization reflection coefficient and The corresponding cross-polarization reflection coefficient.

[0086] Among them, the co-polarization reflection coefficient 、 、 、 and the cross-polarization reflection coefficient 、 、 、 It is by The deflection angle of the square metal piece 2, The size parameters of the square metal sheet 2 and the The shape of the resonance hole 21 in the middle of the square metal piece 2 is determined.

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

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

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

[0090] For example, in this embodiment , , , , =1000 μm, =75μm, the thickness of substrate 1 is 9μm. By limiting the number of rows of the metal sheet array and the side length of the square space , which can effectively limit the size of the entire metal sheet array.

[0091] Step 102: Get the The sequence coordinates of the square metal piece 2 are ,in For the The row sequence number of square metal pieces 2 in the metal piece array, For the The number of columns of square metal pieces 2 in the metal piece array.

[0092] Step 103: Get the The vortex phase of the square metal sheet 2 .

[0093] Specifically, at least the orbital angular momentum mode number based on the phase singularity and Square metal piece 2 sequence coordinates Determine vortex phase .

[0094] More specifically, Square metal pieces 2 satisfy: vortex phase . It can be seen from this that the orbital angular momentum mode number and the side length of the square space Irrelevant, orbital angular momentum mode number It will not affect the size of the entire metal sheet array.

[0095] Step 103: Get the The focusing phase of square metal piece 2 at the focus of the metal piece array .

[0096] Specifically, at least based on the focal length of the metal sheet array , No. Sequence coordinates of square metal pieces 2 and the emission wavelength of signal source 3 Determine the focus phase .

[0097] More specifically, Square metal pieces 2 satisfy: focusing phase .in, is the free space wave number, 0.

[0098] Step 104: Get the The compensation spatial phase of the square metal piece 2 .

[0099] Specifically, based at least on the emission wavelength of the signal source 3 , No. Sequence coordinates of square metal pieces 2 , the number of rows of metal sheet array 、Square space side length and the distance between the metal sheet array and the signal source 3 Determine the compensation spatial phase .

[0100] More specifically, Square metal pieces 2 satisfy: compensation of spatial phase .

[0101] Step 105: Based on at least the vortex phase , focus phase and compensate spatial phase Determine the The deflection angle of the square metal piece 2 on the substrate 1 .

[0102] Specifically, the deflection angle .

[0103] Step 106: Based on the deflection angle Determine the The homopolarized reflection coefficient of a square metal piece 2 , co-polarization reflection coefficient , No. The geometric parameters of the square metal sheet 2 and the The geometric parameters of the resonance hole 21 in the middle of the square metal plate 2.

[0104] More specifically, after obtaining all deflection angles Then, compare it with the number of rows of the metal sheet array 、Square space side length , the focal length of the metal sheet array , the distance between the metal sheet array and the signal source 3 , the emission wavelength of signal source 3 and the orbital angular momentum mode number of the phase singularity Input them into CTS simulation software for simulation. 、 、 、 Scan to obtain 、 、 、 Corresponding co-polarization reflection coefficient under different value combinations 、 、 、 and the cross-polarization reflection coefficient 、 、 and The numerical changes of , as well as The three conditions correspond to 、 、 、 Take the value and then determine the The geometric parameters of the square metal plate 2 and the resonance hole 21 in the middle.

[0105] More preferably, when , as well as Three conditions, filter to get multiple 、 、 、 When the value combination of and the cross-polarization reflection coefficient Determine the The polarization conversion efficiency corresponding to the square metal piece 2 , in satisfying Under this condition, further 、 、 、 The value combination is screened based on the polarization conversion efficiency Determine the The geometric parameters of the square metal sheet 2 and the The geometric parameters of the resonance hole 21 in the middle of the square metal plate 2.

[0106] It is worth noting that CTS simulation software 、 、 、 During the value scanning process, it is assumed that all square metal sheets 2 have the same geometric parameters, and all resonant holes 21 have the same geometric parameters. In other words, the simulation process of the CTS simulation software is assumed to be , , , Under this condition.

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

[0108] In the above design process, the phase distribution of the metal sheet array target design is as follows Figure 6 As shown in , its total compensation phase covers 0°-360° and is distributed in a spiral shape. When the deflection angle of the square metal piece is 0° and the terahertz frequency bandwidth of the periodic unit is 2.5THz-5.5THz, as shown in Figure 7 As shown, the homopolarization reflection coefficient of the square metal piece is Greater than 0.858, cross-polarization reflection coefficient Less than 0.413, thus making the polarization conversion efficiency Higher than 0.878. Figure 8As shown in the figure, when the square metal sheet 2 produces a deflection angle, the reflection spectrum phase curves corresponding to different deflection angles remain parallel within the bandwidth frequency range, indicating that in the range of 2.5THz-5.5THz, the phase response of the square metal sheet 2 has the same trend as the frequency change, proving that the main mode of the vortex wave (such as =-2) Stable generation within the frequency band and wide-band stability of square metal plate phase modulation; In addition, the co-polarization reflection coefficient of the square metal plate Higher than 0.828, indicating the homopolarization reflection coefficient of the square metal sheet and is also high, indicating 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 direction ( <0.413), confirming the high polarization retention ability and high energy efficiency of the square metal sheet.

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

[0110] In addition, numerical simulations were performed at a center frequency of 4 THz, and the vortex focusing characteristics of the metal sheet array were verified through near-field and far-field electromagnetic performance. Figure 10 As shown in Figure 2, under the excitation of left-handed circularly polarized waves, the metal sheet array generates OAM mode numbers. = -2. The focusing properties of the vortex waves were verified by decoupling and analyzing the left-handed and right-handed components of the reflected field. The left-handed component of the sampled field shows that the electric field amplitude exhibits a hollow ring shape, and the phase distribution forms a symmetrical double helix around the singularity, with a phase variation range of 0°-360°. This characteristic is consistent with the theoretical characteristics of the OAM mode, demonstrating that the designed metal sheet array can cause the reflected electromagnetic wave to carry OAM.

[0111] When the metal sheet array is excited by a left-handed circularly polarized wave, the three-dimensional far-field radiation pattern of the vortex wave is as follows: Figure 11 As shown in Figure 2, the maximum radiation gain of the left-handed component of the reflected field reaches 14.4 dB, which effectively matches the Figure 7 and Figure 8 The simulation results are shown.

[0112] Furthermore, this embodiment also provides a method for preparing a polarization modulation unit, such as Figure 1 and Figure 12 As shown, the following steps are included:

[0113] Step 201: Select a doping concentration of 5×10 18 cm -3 A high-purity germanium wafer with a thickness of 9 μm is used as the substrate 1. Impurities are removed by ultrasonic cleaning and chemical cleaning, and a microscope inspection is performed to ensure that the surface of the substrate 1 is free of cracks and contamination.

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

[0115] Step 203: uniformly coating a photoresist 202 with a thickness of 0.5 μm on the surface of the conductive material 201 , and pre-calculating the relief depth to be 0.6 μm.

[0116] Step 204: The shape of each square metal piece 2 is designed using computer-aided design (CAD) software. Laser direct write maskless photolithography is used to directly scan and expose the photoresist 202. Development and chemical etching complete the pattern production. The photoresist 202 is then removed, and the remaining conductive material 201 forms each square metal piece 2.

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

[0118] Step 206: Using ultraviolet photolithography technology, a pattern of energy absorption region 4 is formed in the middle of the bonding plate 203 surface corresponding to the position of the square metal sheet 2. The pattern width is 75 μm. A photoresist with a thickness of 0.5 μm is used as a mask for ion implantation. Boron impurities are implanted into the pattern position through multiple ion implantations, so that the ion implanted portion forms the energy absorption region 4. The ion implantation depth is 3 μm, and the doping concentration is 5×10 16 cm -3 .

[0119] Step 207: UV lithography is used again to create a pattern of electrode contact area 5 on the edge of the bonding plate 203. The pattern is 200 μm thick. Boron impurities are implanted into the pattern through multiple ion implantations, so that the ion implanted portion forms the electrode contact area 5. The implantation depth is 3 μm and the doping concentration is 5×10 18 cm -3 .

[0120] Step 208: Using PECVD technology, a 200 nm thick silicon nitride material is deposited on the surface of the bonding plate 203 as a passivation layer 7, and then the portion of the passivation layer 7 above the electrode contact area 5 is removed. The electrode layer 6 is patterned on the surface of the electrode contact area 5 using UV photolithography technology, and an electrode window is opened using RIE etching technology. Using electron beam deposition technology, a 200 nm thick gold layer is deposited at the electrode window as the electrode layer 6.

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

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

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

[0124] 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 patent. 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 patent for this invention shall be determined by the appended claims.

Claims

1. A design method for a polar modulation unit, characterized in that: The polarization modulation unit comprises a substrate (1) and a metal sheet array arranged on the surface of the substrate (1), wherein the metal sheet array comprises N 2 square metal sheets (2), the centers of all the square metal sheets (2) being arranged in an N×N square array on the surface of the substrate (1), so that each of the square metal sheets (2) occupies a p×p square space on the surface of the substrate (1), p being not less than the diagonal length of all the square metal sheets (2), and at least some of the square metal sheets (2) being 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 centrosymmetrical figure, and the center of the resonance hole (21) coincides with the center of the square metal sheet (2); Wherein, the i-th square metal piece (2) satisfies: 0.95≤|r xx (i)|≤1,0.95≤|r yy (i)|≤1 and|arg(r xx (i))-arg(r yy (i))|≥180°, i=1,2,...,N 2 , r xx (i) is the co-polarization reflection coefficient of the i-th square metal piece (2) under the vertical incidence of x-polarized wave, r yy (i) is the co-polarization reflection coefficient of the i-th square metal piece (2) under vertical incidence of y-polarized wave; The design method includes: Obtain the vortex phase α of the i-th square metal piece (2) i ; Obtain the focusing phase β of the i-th square metal piece (2) at the focus of the metal piece array i ; Setting the number of rows N of the metal sheet array, the side length p of the square space, the spacing d between the metal sheet array and the signal source (3), and the emission wavelength λ0 of the signal source (3); Get the sequence coordinates (x i ,y i ), where x i is the row sequence number of the i-th square metal piece (2) in the metal piece array, y i is the column sequence number of the i-th square metal piece (2) in the metal piece array; At least based on the emission wavelength λ0 of the signal source (3), the sequence coordinates (x i ,y i ), the number of rows N of the metal sheet array, the side length p of the square space, and the spacing d between the metal sheet array and the signal source (3) determine the compensation spatial phase γ of the i-th square metal sheet (2) i ; Among them, the compensation spatial phase γ i =k0[(x i -N×p / 2) 2 +(y i -N×p / 2) 2 +d 2 ] 0.5 , k0 is the free space wave number, k0=2π / λ0; At least based on the vortex phase α i , focusing phase β i and compensate for spatial phase γ i Determine the deflection angle φ of the i-th square metal piece (2) i ; Based on the deflection angle φ i Determine the co-polarization reflection coefficient r of the i-th square metal piece (2) xx (i) Co-polarization reflection coefficient r yy (i), geometric parameters of the i-th square metal sheet (2) and geometric parameters of the resonance hole (21) in the middle of the i-th square metal sheet (2).

2. The design method of the polar modulation unit according to claim 1, characterized in that: Also includes: Based on the deflection angle φ i Determine the co-polarization reflection coefficient r of the i-th square metal piece (2) ll (i) and the cross-polarization reflection coefficient r lr (i); Based on the co-polarization reflection coefficient r ll (i) and the cross-polarization reflection coefficient r lr (i) Determine the polarization conversion efficiency E corresponding to the i-th square metal piece (2) eff (i); Based on the polarization conversion efficiency E eff (i) Determining the geometric parameters of the i-th square metal sheet (2) and the geometric parameters of the resonance hole (21) in the middle of the i-th square metal sheet (2).

3. The design method of the polar modulation unit according to claim 1, characterized in that: Also includes: Setting the focal length F of the metal sheet array and the orbital angular momentum mode number L of the phase singularity; At least based on the orbital angular momentum mode number L of the phase singularity and the sequence coordinates (x i ,y i ) Determine the vortex phase α i ; At least based on the focal length F of the metal sheet array, the sequence coordinates (x i ,y i ) and the emission wavelength λ0 of the signal source (3) determine the focusing phase β i .

4. The design method of the polar modulation unit according to claim 3, characterized in that: The i-th square metal piece (2) satisfies: Vortex phase α i =L×arctan(y i / x i ); Focus phase β i =k0[(F 2 +x i 2 +y i 2 ) 0.5 -F]; Deflection angle φ i =(α i +β i +γ i ) / 2.

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