Terahertz wave band circular polarization selection type wavefront shaping device and use method

Abstract

The invention specifically discloses a circular polarization selection type wavefront shaping device of a terahertz wave band and a use method, and relates to the technical field of terahertz application. The device comprises a dielectric substrate layer and a dielectric cylinder microstructure layer, wherein the dielectric cylinder microstructure layer is arranged at the top of the dielectric substrate layer; the dielectric cylinder microstructure layer is composed of supramolecular dielectric cylinders arranged in an array mode, and each supramolecular dielectric cylinder is composed of a first dielectric cylinder superatom and a second dielectric cylinder superatom which are different in size. The first dielectric cylinder superatoms and the second dielectric cylinder superatoms are of sub-wavelength structures, and the distances between the dielectric cylinder superatoms in the adjacent rows and between the dielectric cylinder superatoms in the adjacent columns are smaller than the wavelength of incident terahertz waves. The first dielectric cylinder super atoms and the second dielectric cylinder super atoms and the corresponding substrates form geometric phase units respectively, and the dielectric cylinder rotation angles of the first dielectric cylinder super atoms and the second dielectric cylinder super atoms change along with coordinates. The device realizes selection and wavefront shaping of right-handed or left-handed circularly polarized terahertz waves, and can be widely applied to the fields of terahertz polarization spectrum measurement and imaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz applications, and particularly relates to a circular polarization selection type wavefront shaping device in a terahertz wave band and a use method. BACKGROUND

[0002] As electromagnetic waves with a frequency of 0.1-10 THz, terahertz waves are in the transition band between microwaves and infrared light, and occupy a special position in the electromagnetic spectrum. Terahertz waves have unique physical characteristics: on the one hand, the photon energy of terahertz waves is only in the order of millielectron volts, which can avoid damage to the detected object in the scenarios of biomedical detection, security screening, etc., and realize truly non-destructive detection; on the other hand, most biological macromolecules and chemical substances have exclusive fingerprint spectra in the terahertz wave band, which can realize accurate identification of substances through spectral analysis; at the same time, terahertz waves also have certain penetration, which can penetrate non-metallic materials such as paper, plastic and ceramic, and show significant advantages in non-destructive imaging, hidden target detection and other fields. With these characteristics, terahertz technology has become the core development direction in the fields of non-destructive imaging, the sixth generation (6G) wireless communication, high-precision chemical sensing, biomedical detection and public security screening, and has extremely broad market application prospects.

[0003] At present, the function of commercial terahertz polarization control devices is limited, which further aggravates the difficulties of technology application. The existing products mainly focus on the generation and selection of linearly polarized light, and the products include metal wire grid polarizers and total reflection prisms based on Brewster angle effect. These two types of products are mature in technology, but their functions are limited to linear polarization operation. If circularly polarized terahertz waves are needed to be generated or detected, a cascade scheme of linear polarizer device + quarter wave plate (λ / 4 wave plate) must be used, that is, linearly polarized light is generated by a linear grating or prism, and then the linearly polarized light is converted into circularly polarized light by a λ / 4 wave plate or the detection of circularly polarized light is completed in the reverse direction. However, this cascade scheme has the following defects:

[0004] High system complexity: the combination of multiple discrete optical elements requires accurate optical path alignment, which not only increases the difficulty of equipment debugging, but also easily causes optical path deviation due to environmental factors such as vibration and temperature change, thereby reducing the system stability; Uncontrolled volume and weight: the cascade of discrete elements inevitably leads to a large optical system volume and weight increase, which is seriously inconsistent with the development trend of modern electronic devices towards miniaturization, light weight and integration, thereby limiting the application of terahertz technology in portable detection devices, integrated optoelectronic chips and other scenarios; Poor function expansion: if further terahertz wavefront regulation is needed, additional introduction of lens, prism or spatial light modulator and other bulk optical elements will further increase the system bulkiness, and the overall efficiency will be greatly reduced due to multi-interface reflection and transmission loss.

[0005] It is particularly important that there is no single functional device that can directly generate or select circularly polarized light in the terahertz band, and there is no report on a device integrating the functions of circular polarization selection and wavefront shaping. This technical gap makes the terahertz system always unable to get rid of the predicament of multi-element stacking, which seriously restricts the industrialization process of terahertz technology.

[0006] Therefore, there is an urgent need in the art for a breakthrough terahertz functional device that can integrate the generation or selection of circular polarization and flexible wavefront shaping functions on a super-thin and compact platform, and fundamentally solve the problems of system complexity, low efficiency and difficulty in integration existing in traditional solutions. SUMMARY

[0007] The purpose of the present application is to provide a circular polarization selection type wavefront shaping device in the terahertz band and a use method, to solve the problems of system complexity, low efficiency and difficulty in integration of traditional circular polarization control schemes, and to meet the development needs of modern optical systems in miniaturization and light weight.

[0008] To achieve the above-mentioned purpose, the present application provides a circular polarization selection type wavefront shaping device in the terahertz band, comprising a dielectric substrate layer and a dielectric column microstructure layer, the dielectric column microstructure layer is arranged on the top of the dielectric substrate layer; the dielectric column microstructure layer is composed of an array of supramolecular dielectric columns, each supramolecular dielectric column is composed of dielectric column superatoms one and dielectric column superatoms two with different sizes; the dielectric column superatoms one and the dielectric column superatoms two are subwavelength structures, the spacing between the dielectric column superatoms in adjacent rows and adjacent columns is less than the wavelength of the incident terahertz wave, the relative rotation angle of the dielectric column superatoms one and the dielectric column superatoms two is 45°, and the relative delay of the fast axis of the dielectric column superatoms one and the dielectric column superatoms two to the terahertz wave is 90°; the dielectric column superatoms one and the dielectric column superatoms two and the corresponding substrates form geometric phase units, respectively, and the dielectric column sub-rotation angle of the dielectric column superatoms one and the dielectric column superatoms two changes with coordinates.

[0009] Preferably, the materials of the dielectric column microstructure layer and the dielectric substrate layer are low-loss dielectric materials or intrinsic semiconductor materials.

[0010] Preferably, the thickness of the dielectric substrate layer is 500-2000 μm, and the height of the dielectric column microstructure layer is 150 μm-250 μm.

[0011] Preferably, the dielectric column sub-structures of the dielectric column superatoms one and the dielectric column superatoms two are optically anisotropic column structures.

[0012] Preferably, the period of the medium column supramolecule one and the medium column supramolecule two is 130-170 um, and the height is 150-250 um.

[0013] Preferably, the relative retardation of the medium column supramolecule one is greater than that of the medium column supramolecule two by 90°, and the terahertz light wave is incident from the substrate side to the medium column microstructure layer, when the rotation angle of the medium column supramolecule two is greater than that of the medium column supramolecule one by 45°, the device is a right-handed circular polarization selective wavefront shaping device; when the rotation angle of the medium column supramolecule two is less than that of the medium column supramolecule one by 45°, the device is a left-handed circular polarization selective wavefront shaping device.

[0014] The application also provides a use method of the circular polarization selective wavefront shaping device in the terahertz wave band, and the specific steps are as follows: Step S1, the circular polarization selective wavefront shaping device is placed in the terahertz wave incident light path, so that the terahertz wave is vertically incident from the medium substrate side to the medium column microstructure layer; Step S2, at the center working frequency 1.0 THz, the device realizes selective transmission for specific circularly polarized light, and performs wavefront shaping on 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 the selected circularly polarized light, the circular polarization selective wavefront shaping device is flipped by 180° in the transverse direction or the longitudinal direction, the flipped circular polarization selective wavefront shaping device realizes selective transmission for the original orthogonal circularly polarized light and performs wavefront shaping, and does not transmit the original specific circularly polarized light.

[0015] Therefore, the application provides a circular polarization selective wavefront shaping device in the terahertz wave band and a use method, which has the following beneficial effects: (1) The application first integrates the two core functions of circular polarization selection and wavefront shaping in a single device in the terahertz wave band, without the cascade of multiple discrete optical elements in the traditional scheme, completely solving the problems of long optical path, complex structure and difficulty in integration in the traditional system, and meeting the development needs of modern optical systems in miniaturization and light weight.

[0016] (2) The application can meet different wavefront shaping requirements by adjusting the parameters and array arrangement of the medium supramolecule, and can switch the type of the transmitted circularly polarized light by only flipping the device by 180° in the transverse direction or the longitudinal direction, greatly expanding the application flexibility of the device in different scenarios.

[0017] (3) The application adopts low-loss dielectric or intrinsic semiconductor material, can guarantee stable working performance of the device in the terahertz wave band, and can realize high-precision manufacturing relying on mature micro-processing technology, has low processing difficulty and controllable cost, and lays a foundation for wide application of the device in the terahertz polarization spectrum measurement and imaging field.

[0018] The technical solutions of the application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 is a three-dimensional structure schematic diagram of a circular polarization selection type wavefront shaping device in a terahertz wave band in an embodiment of the application; Figure 2 FIG. 2 is a two-dimensional and three-dimensional structure diagram of a geometric phase unit in an embodiment of the application; Figure 3 FIG. 3 is a transmittance amplitude curve diagram of the geometric phase unit in an embodiment of the application; Figure 4 FIG. 4 is a transmittance amplitude curve diagram of the geometric phase unit after the circular polarization selection type wavefront shaping device is flipped by 180° in the lateral direction in an embodiment of the application; Figure 5 FIG. 5 is a phase control curve diagram and a corresponding transmittance amplitude curve diagram of the geometric phase unit with a change in the relative angle in an embodiment of the application; Figure 6 FIG. 6 is a simulation result schematic diagram of the real part of the electric field of the propagation field cross section (y=0) of the circular polarization selection type wavefront shaping device at 1.0 THz in an embodiment of the application; Figure 7 FIG. 7 is a far-field diffraction intensity schematic diagram of the circular polarization selection type wavefront shaping device at 1.0 THz in an embodiment of the application; Figure 8 FIG. 8 is a simulation result schematic diagram of the real part of the electric field of the propagation field cross section (y=0) of the circular polarization selection type wavefront shaping device after the device is flipped by 180° in the lateral direction at 1.0 THz in an embodiment of the application; Figure 9 FIG. 9 is a far-field diffraction intensity schematic diagram of the circular polarization selection type wavefront shaping device after the device is flipped by 180° in the lateral direction at 1.0 THz in an embodiment of the application.

[0020] REFERENCE NUMERALS 1, dielectric substrate layer; 2, dielectric column microstructure layer; 3, right-handed circularly polarized wave; 4, left-handed circularly polarized wave; 5, dielectric column superatom one; 6, dielectric column superatom two. DETAILED DESCRIPTION

[0021] 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.

[0022] 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.

[0023] Example 1 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.

[0024] 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.

[0025] 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.

[0026] The following technical contributions are provided by selecting silicon material to manufacture the dielectric column microstructure layer 2: (1) The material consistency of the entire circular polarization selection device is ensured, the loss and reflection caused by the interface of different materials are reduced, the interface effect is reduced, and the stability and reliability of the circular polarization selection device are improved; (2) The silicon material has a suitable dielectric constant in the terahertz frequency band, which is conducive to achieving the required polarization selection; (3) The silicon material can realize high-aspect-ratio microstructures through precision machining techniques (such as deep reactive ion etching), which helps to improve the performance of the circular polarization selection device; (4) The thermal expansion coefficient of the silicon material is the same as that of the dielectric substrate layer 1, which can improve the stability of the circular polarization selection device under temperature changes.

[0027] In this embodiment, the thickness of the dielectric substrate layer 1 is 500 μm, and the height of the dielectric column microstructure layer 2 is 200 μm, which helps to achieve the goal of compact design. The thickness of 700 μm (composed of a 500 μm thick dielectric substrate layer 1 and a 200 μm high dielectric column microstructure layer 2) not only ensures the performance of the circular polarization selection device, but also makes the circular polarization selection device thin enough for integration and application. This thickness is the precise combination of the height of the dielectric substrate layer 1 and the dielectric column microstructure layer 2, which not only ensures sufficient mechanical strength, but also does not excessively increase the size and weight of the device.

[0028] Figure 2 The circular polarization selection type wavefront shaping device is the basic component unit of the circular polarization selection type wavefront shaping device, which is called a geometric phase unit. The terahertz wave propagates along the +z direction, the relative delay of the dielectric column super atom 5 is 90° larger than that of the dielectric column super atom 6, when the rotation angle of the dielectric column super atom 6 is 45° larger than that of the dielectric column super atom 5, the device is a right-handed circular polarization selection type wavefront shaping device; when the rotation angle of the dielectric column super atom 6 is 45° smaller than that of the dielectric column super atom 5, the device is a left-handed circular polarization selection type wavefront shaping device.

[0029] In this embodiment, the period of the dielectric column super atom 5 and the dielectric column super atom 6 is 150 μm, the height is 200 μm, the aspect ratio of the supermolecular dielectric column is 1.33:1, and the cross-sectional area of the supermolecular unit is 21.8%.

[0030] In order to verify that the circular polarization selection type wavefront shaping device of the present application has the effect of circular polarization selection, left-handed circularly polarized wave 4 and right-handed circularly polarized wave 3 are respectively incident from the dielectric substrate side to the uniform super surface composed of geometric phase units in Figure 2 The simulation results are shown in Figure 3 The simulation results show that at the center frequency of 1.0 THz, the right-handed circularly polarized wave 3 can pass through the shaping device and be converted into left-handed circularly polarized light, while the left-handed circularly polarized wave 4 cannot pass through the shaping device, thereby realizing the effect of right-handed circular polarization selection.

[0031] At the same time, in order to further verify the circular polarization selection effect of the shaping device, the device is horizontally flipped by 180° along the transverse direction (x coordinate axis), and the spectrum simulation analysis is carried out on the device with the propagation direction of the terahertz wave unchanged, and the result is shown in Figure 4 The simulation result shows that the left circularly polarized wave 4 can be transmitted through the device and converted into the right circularly polarized light at the center working frequency of 1.0 THz, while the right circularly polarized wave 3 cannot pass through, thereby realizing the effect of left circularly polarized selection.

[0032] Example Two The two medium column superatoms in the geometric phase unit in Figure 2 are synchronously rotated by an angle θ r =[0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°] around the center of each superatom structure, and the relative phase change of the right circularly polarized light input to the left circularly polarized light output and the transmission amplitude in the circularly polarized orthogonal basis at the frequency of 1.0 THz are shown in Figure 5 The result shows that the relationship between the relative phase change of the geometric phase unit and the relative rotation angle satisfies: relative phase change = 2θ r .

[0033] The phase distribution of the circular polarization selection type wavefront shaping device is set to be a linear phase gradient, and the gradient direction is along the x-axis direction. The corresponding geometric phase units are arranged in sequence according to the x coordinate.

[0034] Figure 6 The simulation result of the electric field real part of the propagation field cross section (y=0) of the circular polarization selection type wavefront shaping device at 1.0 THz is shown in the figure. The result shows that when the right circularly polarized light is input, the output terahertz wave is effectively converted into the left circularly polarized light and has obvious wavefront deflection effect. The right circularly polarized light output of the right circularly polarized light input is very weak, and the left circularly polarized light input has almost no output. Figure 7 The far-field diffraction intensity of the circular polarization selection type wavefront shaping device at 1.0 THz is shown in the figure. The +1 order diffraction intensity of the right circularly polarized light input left circularly polarized light output is the strongest, and the diffraction intensity of other components is very small, thereby realizing the polarization selection and wavefront shaping effect of the right circularly polarized light.

[0035] Figure 8 The simulation result of the electric field real part of the propagation field cross section (y=0) of the circular polarization selection type wavefront shaping device after being horizontally flipped by 180° along the transverse direction (x coordinate axis) at 1.0 THz is shown in the figure. The result shows that when the left circularly polarized light is input, the output terahertz wave is effectively converted into the right circularly polarized light and has obvious wavefront deflection effect. Figure 9The schematic diagram of far field diffraction intensity of the circular polarization selection type wavefront shaping device at 1.0 THz, the-1 order diffraction intensity of left circularly polarized light input and right circularly polarized light output is the strongest, and the diffraction intensity of other components is very small, so that the polarization selection and wavefront shaping effect of left circularly polarized light are realized.

[0036] The application also provides a use method of the circular polarization selection type wavefront shaping device in the terahertz wave band, and the specific steps are as follows: Step S1, the circular polarization selection type wavefront shaping device is placed in the terahertz wave light path, the terahertz wave is set to propagate along the +z direction, and is normally incident to the circular polarization selection type wavefront shaping device from the medium substrate side; Step S2, at the center working frequency 1.0 THz, the device realizes selective transmission for specific circularly polarized light, and performs wavefront shaping on the transmitted circularly polarized light, and does not transmit the orthogonal circularly polarized light; Step S3, if it is necessary to switch the selected circularly polarized light type, the circular polarization selection type wavefront shaping device is flipped by 180° along the horizontal or vertical direction, the flipped circular polarization selection type wavefront shaping device realizes selective transmission for the original orthogonal circularly polarized light and performs wavefront shaping, and does not transmit the original specific circularly polarized light.

[0037] It is worth noting that the contents not elaborated in the application are all prior art and are well known to those skilled in the art.

[0038] Therefore, the application provides a circular polarization selection type wavefront shaping device in the terahertz wave band and a use method, which integrates the functions of circular polarization selection and wavefront shaping, is simple in design and easy to process, can switch the selected circularly polarized light type through transverse flipping, can effectively solve the problems of complex system, low efficiency and difficulty in integration of the traditional scheme, and can be widely applied to the fields of terahertz polarized light spectrum measurement and imaging.

[0039] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application but not to limit it, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the application.

Claims

1. A circular polarization selective wavefront shaping device in the terahertz band, characterized in that, 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.

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-structure of the medium column superatom I and the medium column superatom II is an optically anisotropic column structure.

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. The terahertz waveband circular polarization selective wavefront shaping device according to claim 1, characterized in that, 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.

7. A method of using a circular polarization selective wavefront shaping device in the terahertz regime according to any one of claims 1 to 6, 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, and 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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