A circularly polarization-selective wavefront shaping device in the terahertz band and its application method

Abstract

This invention discloses a circularly polarized selective wavefront shaping device and its application method in the terahertz band, relating to the field of terahertz application technology. The device comprises a dielectric substrate layer and a dielectric pillar microstructure layer, with the microstructure layer disposed on top of the substrate layer. The microstructure layer consists of an array of supramolecular dielectric pillars, each pillar composed of two dielectric pillars of different sizes: a first dielectric pillar and a second dielectric pillar. The first and second dielectric pillars are subwavelength structures, with the spacing between adjacent rows and columns of the superatoms smaller than the wavelength of the incident terahertz wave. The first and second dielectric pillars, together with their corresponding substrates, form geometric phase units, and the rotation angles of the dielectric pillars vary with coordinates. This device enables the selection and wavefront shaping of right-handed or left-handed circularly polarized terahertz waves and can be widely applied in terahertz polarization spectroscopy measurement and imaging.

Description

Technical Field

[0001] This invention relates to the field of terahertz application technology, and in particular to a circularly polarized selective wavefront shaping device and its usage method in the terahertz band. Background Technology

[0002] Terahertz waves, with frequencies ranging from 0.1 to 10 THz, occupy a unique position in the electromagnetic spectrum, falling within the transition band between microwaves and infrared light. Terahertz waves possess unique physical properties: firstly, the photon energy is only on the order of millielectron volts, avoiding damage to the object being detected in biomedical testing and security screening, thus achieving truly non-destructive detection; secondly, most biological macromolecules and chemical substances possess unique fingerprint spectra in the terahertz band, enabling precise identification of substances through spectral analysis; and thirdly, terahertz waves have a certain degree of penetrability, capable of penetrating non-metallic materials such as paper, plastics, and ceramics, demonstrating significant advantages in non-destructive imaging and concealed target detection. Based on these characteristics, terahertz technology has become a core development direction in fields such as non-destructive imaging, sixth-generation (6G) wireless communication, high-precision chemical sensing, biomedical testing, and public safety screening, with extremely broad market application prospects.

[0003] Currently, the functional limitations of commercially available terahertz polarization control devices further exacerbate the difficulties in technology application. Existing products mainly focus on the generation and selection of linearly polarized light, including metal wire-grid polarizers and total internal reflection prisms based on the Brewster angle effect. While these two types of products are technologically mature, their functionality is limited to linear polarization operations. To generate or detect circularly polarized terahertz waves, a cascaded scheme of a linear polarizer and a quarter-wave plate (λ / 4 waveplate) must be used. First, linearly polarized light is generated through a wire grid or prism, and then the λ / 4 waveplate is used to convert the linearly polarized light into circularly polarized light or vice versa for the detection of circularly polarized light. However, this cascaded scheme has the following drawbacks:

[0004] High system complexity: The combination of multiple discrete optical components requires precise optical path alignment, which not only increases the difficulty of equipment debugging, but also makes the optical path prone to deviation due to environmental factors such as vibration and temperature changes, thus reducing system stability;

[0005] Uncontrolled size and weight: The cascading of discrete components inevitably leads to a large size and increased weight of the optical system, which is seriously contrary to the development trend of miniaturization, lightweighting and integration of modern electronic devices, and limits the application of terahertz technology in portable detection equipment, integrated optoelectronic chips and other scenarios.

[0006] Poor functional scalability: If further control of the terahertz wavefront is required, additional bulk optical components such as lenses, prisms or spatial light modulators must be introduced, which will further increase the bulkiness of the system and cause a significant decrease in overall efficiency due to multi-interface reflection and transmission loss.

[0007] Most importantly, no single-function device capable of directly generating or selecting circularly polarized light has yet emerged in the terahertz band, and there are no reports in the industry of devices integrating circular polarization selection and wavefront shaping functions. This technological gap has prevented terahertz systems from escaping the predicament of multi-component stacking, severely hindering the industrialization process of terahertz technology.

[0008] Therefore, there is an urgent need in this field for a breakthrough terahertz functional device that can integrate the generation or selection of circular polarization with flexible wavefront modulation on an ultra-thin, compact platform, fundamentally solving the problems of system complexity, low efficiency, and difficulty in integration of traditional solutions. Summary of the Invention

[0009] The purpose of this invention is to propose a circular polarization selective wavefront shaping device and its usage method in the terahertz band, so as to solve the problems of complex systems, low efficiency and difficulty in integration of traditional circular polarization control schemes, and to meet the development needs of miniaturization and lightweighting of modern optical systems.

[0010] To achieve the above objectives, this invention proposes a circularly polarization-selective wavefront shaping device in the terahertz band, comprising a dielectric substrate layer and a dielectric pillar microstructure layer, wherein the dielectric pillar microstructure layer is disposed on top of the dielectric substrate layer; the dielectric pillar microstructure layer is composed of arrayed supramolecular dielectric pillars, each supramolecular dielectric pillar consisting of dielectric pillar superatoms I and II of different sizes; the dielectric pillar superatoms I and II are subwavelength structures, the spacing between dielectric pillar superatoms in adjacent rows and columns is smaller than the wavelength of the incident terahertz wave, the relative rotation angle between dielectric pillar superatoms I and II is 45°, and the relative delay of the fast axis of dielectric pillar superatoms I and II with respect to the terahertz wave is 90°; the dielectric pillar superatoms I and II, together with their corresponding substrates, constitute geometric phase units, and the rotation angle of the dielectric pillars of dielectric pillar superatoms I and II varies with coordinates.

[0011] Preferably, the materials of the dielectric pillar microstructure layer and the dielectric substrate layer are low-loss dielectric materials or intrinsic semiconductor materials.

[0012] Preferably, the thickness of the dielectric substrate layer is 500-2000 μm, and the height of the dielectric pillar microstructure layer is 150 μm-250 μm.

[0013] Preferably, the dielectric pillar structures of both the first and second dielectric pillars are optically anisotropic pillar structures.

[0014] Preferably, the period of the first and second dielectric columns is 130μm-170μm, and the height is 150μm-250μm.

[0015] Preferably, the relative delay of the first dielectric pillar superatom is set to be 90° greater than the relative delay of the second dielectric pillar superatom. When the terahertz light wave is incident on the dielectric pillar microstructure layer from the substrate side, the device is a right-hand circularly polarized selective wavefront shaping device when the rotation angle of the second dielectric pillar superatom is 45° greater than that of the first dielectric pillar superatom; when the rotation angle of the second dielectric pillar superatom is 45° less than that of the first dielectric pillar superatom, the device is a left-hand circularly polarized selective wavefront shaping device.

[0016] This invention also provides a method for using a circularly polarized selective wavefront shaping device in the terahertz band, the specific steps of which are as follows:

[0017] Step S1: Place the circularly polarized selective wavefront shaping device in the terahertz wave incident optical path so that the terahertz wave is incident perpendicularly from the dielectric substrate side to the dielectric pillar microstructure layer.

[0018] Step S2: At the center operating frequency of 1.0THz, the device selectively transmits specific circularly polarized light and performs wavefront shaping on the transmitted circularly polarized light, while blocking orthogonal circularly polarized light.

[0019] Step S3: If it is necessary to switch the selected circularly polarized light type, the circularly polarized selective wavefront shaper is flipped 180° in the horizontal or vertical direction. After flipping, the circularly polarized selective wavefront shaper selectively transmits and shapes the original orthogonal circularly polarized light, but does not transmit the original specific circularly polarized light.

[0020] Therefore, this invention proposes a circularly polarization-selective wavefront shaping device and its usage method in the terahertz band, with the following beneficial effects:

[0021] (1) This invention integrates the two core functions of circular polarization selection and wavefront shaping into a single device for the first time in the terahertz band. It eliminates the need for cascading multiple discrete optical components in traditional solutions, and completely solves the problems of long optical paths, complex structures, and difficulty in integration in traditional systems. It meets the development needs of miniaturization and lightweighting of modern optical systems.

[0022] (2) By adjusting the parameters and array arrangement of the medium superatoms in the medium supramolecular, the present invention can meet different wavefront shaping requirements; at the same time, it is only necessary to flip the device 180° laterally or longitudinally to switch the type of circularly polarized light that can be transmitted, which greatly expands the application flexibility of the device in different scenarios.

[0023] (3) The present invention uses low-loss dielectric or intrinsic semiconductor materials, which can ensure the stable working performance of the device in the terahertz band. Moreover, high-precision manufacturing can be achieved by relying on mature micro-machining technology. The processing difficulty is low and the cost is controllable, which lays the foundation for its wide application in the field of terahertz polarization spectroscopy measurement and imaging.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a three-dimensional structural schematic diagram of a circularly polarized selective wavefront shaping device in the terahertz band according to an embodiment of the present invention.

[0026] Figure 2 These are two-dimensional and three-dimensional structural diagrams of the geometric phase unit in the embodiments of the present invention;

[0027] Figure 3 This is a transmission amplitude curve of the geometric phase unit in an embodiment of the present invention;

[0028] Figure 4 This is a transmission amplitude curve of the geometric phase unit after the circular polarization selective wavefront shaping device is flipped laterally by 180° in an embodiment of the present invention.

[0029] Figure 5 The diagram shows the phase modulation curve of the geometric phase unit as a function of relative angle and the corresponding transmission amplitude curve in the embodiment of the present invention.

[0030] Figure 6 This is a schematic diagram of the simulation results of the real part of the electric field of the propagation field section (y=0) of the circularly polarized selective wavefront shaping device at 1.0THz in an embodiment of the present invention;

[0031] Figure 7 This is a schematic diagram of the far-field diffraction intensity of the circularly polarized selective wavefront shaping device at 1.0 THz in an embodiment of the present invention.

[0032] Figure 8 This is a schematic diagram of the simulation results of the real part of the electric field of the propagation field section (y=0) at 1.0THz after the circular polarization selective wavefront shaping device is flipped laterally by 180° in an embodiment of the present invention.

[0033] Figure 9 This is a schematic diagram of the far-field diffraction intensity after the circular polarization selective wavefront shaper is flipped 180° laterally at 1.0 THz in an embodiment of the present invention.

[0034] Figure Labels

[0035] 1. Dielectric substrate layer; 2. Dielectric pillar microstructure layer; 3. Right-hand circularly polarized wave; 4. Left-hand circularly polarized wave; 5. Dielectric pillar superatom one; 6. Dielectric pillar superatom two. Detailed Implementation

[0036] To make the technical solutions, advantages, and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0037] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0038] Example 1

[0039] like Figure 1 As shown, this invention provides a circularly polarization-selective wavefront shaping device in the terahertz band, comprising a dielectric substrate layer 1 and a dielectric pillar microstructure layer 2, with the dielectric pillar microstructure layer 2 disposed on top of the dielectric substrate layer 1. Both the dielectric pillar microstructure layer 2 and the dielectric substrate layer 1 are made of low-loss dielectric materials or intrinsic semiconductor materials, and the thickness of the dielectric substrate layer 1 is 500-2000 μm. The dielectric pillar microstructure layer 2 is composed of an array of supramolecular dielectric pillars, each consisting of a first dielectric pillar (5) and a second dielectric pillar (6). The period of the first dielectric pillar (5) and the second dielectric pillar (6) is 130 μm-170 μm, and their height is 150 μm-250 μm. Both the first and second dielectric pillars are subwavelength structures, with the spacing between adjacent rows and columns smaller than the wavelength of the terahertz wave at the target design frequency, and the dielectric pillar structures are optically anisotropic.

[0040] The use of dielectric pillar superatoms 1-5 and 2-6 as subwavelength structures has the following technical contributions: (1) it avoids diffraction effects, enabling the circular polarization selection device to be designed and analyzed using effective medium theory; (2) it enhances the ability of the circular polarization selection device to control electromagnetic waves, enabling precise polarization selection control at the subwavelength scale; (3) it reduces scattering loss and improves the efficiency of the circular polarization selection device; (4) it enables the circular polarization selection device to maintain good performance over a wider range of incident angles, enhancing the robustness of the circular polarization selection device.

[0041] In this embodiment, both the dielectric substrate layer 1 and the dielectric pillar microstructure layer 2 are made of high-resistivity silicon. The selection of silicon as the dielectric substrate layer 1 has several technical advantages: (1) Silicon has low loss in the terahertz band, which is beneficial to improving the overall efficiency of the beam deflection device; (2) Silicon has mature processing technology, which can realize high-precision microstructure manufacturing, which helps to improve the performance consistency of the beam deflection device; (3) Silicon has good thermal stability and mechanical strength, which is beneficial to the stable operation of the circular polarization selection device in various environments.

[0042] The use of silicon material to fabricate the dielectric pillar microstructure layer 2 has the following technical contributions: (1) It ensures the material consistency of the entire circular polarization selection device, reduces the loss and reflection that may be caused by the interface of different materials, reduces the interface effect, and improves the stability and reliability of the circular polarization selection device; (2) Silicon material has a suitable dielectric constant in the terahertz band, which is conducive to achieving the required polarization selection; (3) Silicon material can achieve a high aspect ratio microstructure through precision processing technology (such as deep reactive ion etching), which helps to improve the performance of the circular polarization selection device; (4) The thermal expansion coefficient of silicon material is the same as that of the dielectric substrate layer 1, which can improve the stability of the circular polarization selection device when the temperature changes.

[0043] In this embodiment, the dielectric substrate layer 1 has a thickness of 500 μm, and the dielectric pillar microstructure layer 2 has a height of 200 μm, which helps to achieve the goal of a compact design. The thickness of 700 μm (composed of the 500 μm thick dielectric substrate layer 1 and the 200 μm high dielectric pillar microstructure layer 2) ensures the performance of the circular polarization selection device while also making the circular polarization selection device thin enough for easy integration and application. This thickness is a precise combination of the height of the dielectric substrate layer 1 and the dielectric pillar microstructure layer 2, ensuring sufficient mechanical strength without excessively increasing the device size and weight.

[0044] Figure 2 The basic building block of a circularly polarized selective wavefront shaping device is called the geometric phase unit. Assuming the terahertz wave propagates along the +z direction, the relative delay of dielectric pillar superatom-5 is 90° greater than that of dielectric pillar superatom-6. When the rotation angle of dielectric pillar superatom-6 is 45° greater than that of dielectric pillar superatom-5, the device is a right-hand circularly polarized selective wavefront shaping device; when the rotation angle of dielectric pillar superatom-6 is 45° less than that of dielectric pillar superatom-5, the device is a left-hand circularly polarized selective wavefront shaping device.

[0045] In this embodiment, the period of the medium column superatom 5 and the medium column superatom 6 is 150 μm, the height is 200 μm, the aspect ratio of the supramolecular medium column is 1.33:1, and the cross section accounts for 21.8% of the supramolecular unit.

[0046] To verify that the circularly polarized selective wavefront shaping device of the present invention has the effect of circular polarization selection, left-handed circularly polarized wave 4 and right-handed circularly polarized wave 3 were respectively incident from the dielectric substrate side onto the wavefront shaping device. Figure 2 A uniform metasurface composed of geometric phase units was subjected to spectral simulation analysis, and the results are as follows: Figure 3 As shown in the figure. Simulation results show that at the center operating frequency of 1.0 THz, the right-hand circularly polarized wave 3 can pass through the shaping device and be converted into left-hand circularly polarized light, while the left-hand circularly polarized wave 4 cannot pass through the shaping device, thus achieving the effect of right-hand circular polarization selection.

[0047] Meanwhile, to further verify the circular polarization selection effect of the shaping device, the device was horizontally flipped 180° along the transverse direction (x-axis) while the terahertz wave propagation direction remained unchanged. Spectral simulation analysis was then performed, and the results are as follows: Figure 4 As shown in the figure. Simulation results show that at the center operating frequency of 1.0 THz, the left-hand circularly polarized wave 4 can pass through the device and be converted into right-hand circularly polarized light, while the right-hand circularly polarized wave 3 cannot pass through, thus achieving the effect of left-hand circular polarization selection.

[0048] Example 2

[0049] Will Figure 2 In the geometric phase unit, the two dielectric pillar superatoms rotate synchronously around the center of each superatomic structure by an angle θ. r =[0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°], then the relative phase change from right-handed optical input to left-handed optical output at a frequency of 1.0 THz and the transmission amplitude under the circularly polarized orthogonal basis are as follows: Figure 5 As shown. The results indicate that the relationship between the relative phase change and the relative rotation angle of the geometric phase unit satisfies: relative phase change = 2θ r .

[0050] The phase distribution of the circularly polarized selective wavefront shaping device is set to a linear phase gradient with the gradient direction along the x-axis, and the corresponding geometric phase units are arranged sequentially according to the x-coordinate.

[0051] Figure 6 This is a schematic diagram of the simulation results of the real part of the electric field at 1.0 THz for the propagation field cross section (y=0) of a circularly polarized selective wavefront shaper. The results show that when right-handed optical input is used, the output terahertz wave is effectively converted into left-handed optical with a significant wavefront deflection effect. The right-handed optical output is very weak when right-handed optical input is used, while there is almost no output when left-handed optical input is used. Figure 7This is a schematic diagram of the far-field diffraction intensity of a circularly polarized selective wavefront shaper at 1.0 THz. The +1st order diffraction intensity is strongest when the input is right-handed and the output is left-handed, while the diffraction intensity of other components is very small, thus achieving polarization selection and wavefront shaping effects of right-handed circular polarization.

[0052] Figure 8 This is a schematic diagram of the simulation results of the real part of the electric field at 1.0 THz for the propagation field cross section (y=0) after the above-mentioned circularly polarized selective wavefront shaper is horizontally flipped 180° along the transverse (x-axis). The results show that when left-handed light is input, the output terahertz wave is effectively converted into right-handed light and has a significant wavefront deflection effect. Figure 9 This is a schematic diagram of the far-field diffraction intensity of a circularly polarized selective wavefront shaper at 1.0 THz. The -1st order diffraction intensity is strongest when the light input is left-handed and the light output is right-handed, while the diffraction intensity of other components is very small, thus achieving polarization selection and wavefront shaping effects of left-handed circular polarization.

[0053] This invention also provides a method for using a circularly polarized selective wavefront shaping device in the terahertz band, the specific steps of which are as follows:

[0054] Step S1: Place the circularly polarized selective wavefront shaping device in the terahertz wave optical path, set the terahertz wave to propagate along the +z direction, and incident the circularly polarized selective wavefront shaping device from the dielectric substrate side.

[0055] Step S2: At the center operating frequency of 1.0THz, the device selectively transmits specific circularly polarized light and performs wavefront shaping on the transmitted circularly polarized light, while preventing transmission of orthogonal circularly polarized light.

[0056] Step S3: If it is necessary to switch the selected circularly polarized light type, rotate the circularly polarized selective wavefront shaper 180° in the horizontal or vertical direction. After rotation, the circularly polarized selective wavefront shaper selectively transmits and shapes the original orthogonal circularly polarized light, but does not transmit the original specific circularly polarized light.

[0057] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art.

[0058] Therefore, this invention provides a circularly polarized selective wavefront shaping device and its usage method in the terahertz band, which integrates the dual functions of circular polarization selection and wavefront shaping. It is simple in design and easy to manufacture, and the type of circularly polarized light transmitted can be switched by lateral flipping. It can effectively solve the problems of complex systems, low efficiency and difficulty in integration of traditional solutions, and can be widely used in the field of terahertz polarization spectroscopy measurement and imaging.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A circular polarization selective wavefront shaping device in the terahertz band, characterized by, The device comprises a medium substrate layer and a medium column microstructure layer arranged on top of the medium substrate layer; the medium column microstructure layer is composed of an array of supramolecular medium columns, each of which is composed of a medium column superatom I and a medium column superatom II; the medium column superatom I and the medium column superatom II are subwavelength structures, the medium column superatom spacing between adjacent rows and adjacent columns is less than the wavelength of the incident terahertz wave, the relative rotation angle of the medium column superatom I and the medium column superatom II is 45°, and the relative delay of the fast axis of the medium column superatom I and the medium column superatom II to the terahertz wave is 90°; the medium column superatom I and the medium column superatom II and the corresponding substrate respectively form a geometric phase unit, and the medium column sub-rotation angle of the medium column superatom I and the medium column superatom II changes with the coordinates; The relative delay of the medium column superatom I is 90° larger than that of the medium column superatom II, and the terahertz light wave is vertically incident on the medium column microstructure layer from the substrate side; when the rotation angle of the medium column superatom II is 45° larger than that of the medium column superatom I, the device is a right-handed circularly polarized selective wavefront shaping device; when the rotation angle of the medium column superatom II is 45° smaller than that of the medium column superatom I, the device is a left-handed circularly polarized selective wavefront shaping device.

2. The terahertz waveband circular polarization selective wavefront shaping device according to claim 1, characterized in that, The materials of the medium column microstructure layer and the medium substrate layer are low-loss dielectric materials or intrinsic semiconductor materials.

3. The terahertz waveband circular polarization selective wavefront shaping device according to claim 1, characterized in that, The thickness of the medium substrate layer is 500-2000 μm, and the height of the medium column microstructure layer is 150 μm-250 μm.

4. The terahertz waveband circular polarization selective wavefront shaping device according to claim 1, characterized in that, The medium column sub-structures of the medium column superatom I and the medium column superatom II are optically anisotropic column structures.

5. The terahertz waveband circular polarization selective wavefront shaping device according to claim 1, characterized in that, The period of the medium column superatom I and the medium column superatom II is 130-170 μm, and the height is 150 μm-250 μm.

6. A method of using a circular polarization selective wavefront shaping device in the terahertz regime according to any one of claims 1 to 5, characterized in that, The specific steps are as follows: Step S1, place the circular polarization selective wavefront shaping device in the terahertz wave optical path, so that the terahertz wave is vertically incident on the medium column microstructure layer from the medium substrate side; Step S2, at the center working frequency 1.0 THz, the device realizes selective transmission of a specific circularly polarized light and wavefront shaping of the transmitted circularly polarized light, and does not transmit the orthogonal circularly polarized light; Step S3, if it is necessary to switch the type of selected circularly polarized light, the circular polarization selective wavefront shaping device is flipped by 180° in the transverse or longitudinal direction, the flipped circular polarization selective wavefront shaping device realizes selective transmission of the original orthogonal circularly polarized light and wavefront shaping, and does not transmit the original specific circularly polarized light.

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