Terahertz broadband wave plate based on phase shift addition and subtraction operation
By performing phase shift addition and subtraction operations on a double-layer subwavelength dielectric grating, a simple structural design for a broadband terahertz waveplate was realized, solving the bandwidth limitation problem in the prior art and achieving easy fabrication and low-loss polarization state conversion of the device.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-27
- Publication Date
- 2026-04-07
AI Technical Summary
Existing terahertz polarization devices have limited operating bandwidth, and their multi-layer structure design makes fabrication difficult and limits performance improvement.
A double-layer subwavelength dielectric grating is used to achieve 180° and 90° phase shifts through phase shift addition and subtraction operations, realizing the functions of broadband half-wave and quarter-wave plates respectively. It is fabricated using a high-resistivity silicon wafer, with a grating period and duty cycle of 50μm and 0.4.
A simple structural design for a broadband terahertz waveplate was achieved. The device has low insertion loss, is easy to fabricate, and possesses ultra-wideband characteristics, meeting the requirements for polarization state conversion.
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Figure CN121806174A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of terahertz technology, and in particular to a terahertz broadband waveplate based on phase shift addition and subtraction operations. Background Technology
[0002] Terahertz waves, located in the electromagnetic band between infrared and microwaves, possess unique advantages such as low photon energy, high penetration, and characteristic spectral properties, showing broad application prospects in fields such as human security inspection, biomedicine, imaging, and next-generation wireless communication. Terahertz polarization control devices, such as quarter-wave plates and half-wave plates, play an irreplaceable role in achieving polarization state conversion. Currently, terahertz polarization devices mainly rely on natural crystal materials, but their operating bandwidth is severely limited. To expand the device bandwidth, researchers have introduced artificial metamaterials. For example, existing technologies such as twisted optical metamaterials achieve broadband circular polarization response by stacking multiple rod-like structures to connect multiple independent resonant frequencies; and multilayer metamaterial broadband linear polarization converters using metal wires as periodic units. However, these schemes generally employ multilayer structural designs, which leads to difficulties in fabrication and, to some extent, limits further improvements in device performance.
[0003] To reduce the number of structural layers and explore new mechanisms, dispersion modulation methods have been employed in existing technologies to achieve near-dispersion-free terahertz broadband polarization control. This indicates that research on terahertz polarization modulation, based on the fundamental principles of phase dispersion and polarization modulation, is becoming a hot topic. Therefore, developing a general physical model based on dispersion modulation theory and enriching and expanding the design concepts of terahertz broadband devices are of great significance for promoting the further development and application of terahertz technology. Summary of the Invention
[0004] To address the aforementioned challenges, this application provides a terahertz broadband waveplate based on phase shift addition and subtraction operations, overcoming the bottleneck of narrow operating bandwidth of the device.
[0005] To achieve the above objectives, this application provides a terahertz broadband waveplate based on phase shift addition and subtraction operations, comprising a double-layer subwavelength dielectric grating, wherein the double-layer subwavelength dielectric grating comprises an upper subwavelength dielectric grating and a lower subwavelength dielectric grating. When the upper subwavelength grating and the lower subwavelength grating are oriented parallel to each other, a phase shift and addition operation is realized, generating a 180° phase shift in the broadband range, thus realizing the function of a broadband half-wave plate. When the upper subwavelength grating and the lower subwavelength grating are oriented perpendicularly, a phase shift and subtraction operation is performed, generating a 90° phase shift within the broadband range, thus realizing the function of a broadband quarter-wave plate.
[0006] Preferably, the upper and lower subwavelength gratings of the half-wave plate are oriented along the same coordinate axis.
[0007] Preferably, the upper subwavelength grating and the lower subwavelength grating of the quarter-wave plate are oriented along the first coordinate axis and the lower subwavelength grating is oriented along the second coordinate axis perpendicular to the first coordinate axis.
[0008] Preferably, the polarization state of the incident light on the double-layer subwavelength dielectric grating is linearly polarized, and the vibration direction of the linear polarization forms a 45° angle with the grating orientation.
[0009] Preferably, the double-layer subwavelength dielectric grating is fabricated using a high-resistivity silicon wafer with a dielectric constant of 11.7.
[0010] Preferably, the upper etching depth of the dual-layer subwavelength dielectric grating is 83 μm, and the lower etching depth is 29 μm.
[0011] Preferably, the grating period of the dual-layer subwavelength dielectric grating is 50 μm and the duty cycle is 0.4.
[0012] Therefore, the terahertz broadband waveplate based on phase shift addition and subtraction operations described above has the following beneficial effects: (1) The technical solution disclosed in this application is different from the traditional simple use of birefringence, chiral polarization conversion, resonance-induced polarization conversion and other mechanisms. This application adopts the technical means of phase shift addition and subtraction operation, and generates a 180° phase shift by superimposing a 45° phase shift and a 135° phase shift; generates a 90° phase shift by cancelling a 45° phase shift and a 135° phase shift, and the generated phase shift has a dispersion of less than 5° in the broadband range.
[0013] (2) This application develops two types of terahertz waveplates, which can be switched between quarter-waveplates and half-waveplates simply by changing the orientation of the lower grating; (3) Based on the mechanism of phase shift operation, the period and duty cycle of the double-layer grating are completely consistent. The difference lies in the different grating orientations. The structure is simple and there are no other complex physical effects inside the double-layer grating structure. The insertion loss of the device is small. The technical solution of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the working principle of a terahertz broadband waveplate based on phase shift addition and subtraction operations in this application; wherein, (a), (d) and (g) are schematic diagrams and phase shift spectra of the upper structure 1; (b), (e) and (h) are schematic diagrams and phase shift spectra of the lower structure 2; (c), (f) and (i) are schematic diagrams and phase shift spectra of the double-layer structure; Figure 2The images show the specific structural diagrams, time-domain spectra, and phase-shift spectra of the upper and lower gratings in this application; where (a), (b), and (c) are schematic diagrams, time-domain spectra, and phase-shift spectra of the upper structure 1; and (d), (e), and (f) are schematic diagrams, time-domain spectra, and phase-shift spectra of the lower structure 2. Figure 3 This is a phase shift addition operation implemented by the double-layer structure 1+2 in this application; where (a) is a schematic diagram of the polarization transformation of the double-layer structure 1+2; (b) is the amplitude spectrum of the double-layer structure 1+2 in TE and TM modes; and (c) is the phase shift spectrum of the double-layer structure 1+2. Figure 4 The phase shift addition operation is implemented in the double-layer structure 1-2 of this application; wherein, (a) is a schematic diagram of polarization transformation of the double-layer structure 1-2; (b) is the amplitude spectrum of the double-layer structure 1-2 in TE and TM modes; and (c) is the phase shift spectrum of the double-layer structure 1-2. Detailed Implementation
[0015] The following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.
[0016] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning as understood by a person of ordinary skill in the art to which this application pertains.
[0017] The terms "comprising" or "including," as used in this application, mean that the element preceding the term encompasses the element listed after the term, and do not exclude the possibility of encompassing other elements as well. The terms "inner," "outer," "upper," and "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In this application, unless otherwise expressly specified and limited, the term "attached," etc., should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction relationship between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0018] Example 1: A terahertz broadband waveplate based on phase shift addition and subtraction operations includes a double-layer subwavelength dielectric grating, which includes an upper subwavelength dielectric grating and a lower subwavelength dielectric grating. When the upper subwavelength grating and the lower subwavelength grating are oriented parallel to each other, phase shift addition operation is realized, generating a 180° phase shift in the broadband range, realizing the function of a broadband half-wave plate; the upper and lower subwavelength gratings of the half-wave plate are oriented along the same coordinate axis.
[0019] When the upper subwavelength grating and the lower subwavelength grating are oriented perpendicularly, phase shift and subtraction operations are performed to generate a 90° phase shift within the broadband range, thus realizing the function of a broadband quarter-wave plate.
[0020] The quarter-wave plate has an upper subwavelength grating and a lower subwavelength grating. The upper subwavelength grating is oriented along the first coordinate axis, and the lower subwavelength grating is oriented along the second coordinate axis, which is perpendicular to the first coordinate axis.
[0021] The polarization state of the incident light on the double-layer subwavelength dielectric grating is linearly polarized, and the vibration direction of the linear polarization is at a 45° angle to the grating orientation.
[0022] The double-layer subwavelength dielectric grating is fabricated using a high-resistivity silicon wafer with a dielectric constant of 11.7.
[0023] The upper layer of the double-layer subwavelength dielectric grating has an etching depth of 83 μm, and the lower layer has an etching depth of 29 μm.
[0024] The grating period of the double-layer subwavelength dielectric grating is 50 μm and the duty cycle is 0.4.
[0025] Example 2: To clearly describe the phase-shift dispersion addition and subtraction operation mechanism involved in this application, this embodiment combines... Figure 1The scheme of this application is described in detail. According to classical crystal polarization optics: linearly polarized light incident on the surface of a device can be decomposed into arbitrary orthogonal polarization components, transverse magnetic mode (TM) and transverse electric mode (TE) components, and the amplitude and phase shift of the TM and TE components together determine the polarization state of the final output device. Therefore, when the amplitude is equal and the phase shift is equal, a quarter or half waveplate can be realized. Furthermore, if the amplitude and phase shift conditions are met within a wide bandwidth, it is expected to obtain an ultra-wideband (>1THz bandwidth) terahertz waveplate. However, it is difficult to realize a single-layer electromagnetic microstructure with 90° or 180° zero phase shift dispersion (zero phase shift dispersion means that the phase shift does not change with frequency). Therefore, this application adopts a double-layer structure design, in which the first layer has 135° zero phase shift dispersion; the second layer has 45° zero phase shift dispersion, such as... Figure 1 The phase shift spectra in (d), (g), (e), and (h) are shown. Theoretically, the superposition of phase shifts from two layers will produce 180° zero-phase-shift dispersion (i.e., a half-waveplate), such as... Figure 1 (f) In the second layer, when the second layer is rotated 90°, the phase shifts of the two layers cancel each other out, resulting in 90° zero-phase-shift dispersion (i.e., a quarter-wave plate), as shown in the diagram. Figure 1 (i) in the present application. The implementation of the broadband terahertz polarization device is based on the idea of phase-shift dispersion addition and subtraction.
[0026] This application is based on Figure 1 The concept behind phase-shift dispersion addition and subtraction operations uses a grating structure as the basic structure for phase-shift addition and subtraction. For example... Figure 2 As shown, the phase shift characteristics of each grating layer in the double-layer grating structure are first discussed. Figure 2 (a) shows a schematic diagram of the upper grating structure, with a grating period of 50 μm, a duty cycle of 0.4, and an etching depth of 83 μm. The direction along the grating orientation is defined as the y-axis, i.e., the TE mode; the direction perpendicular to the grating orientation is defined as the x-axis, i.e., the TM mode; the vertically downward z-axis represents the propagation direction of the terahertz wave; the x-axis, y-axis and z-axis satisfy the right-hand rule. Figure 2 Image (b) shows the time-domain spectra of the upper grating in TE and TM modes. A significant time delay can be observed between the two polarization modes, primarily due to the birefringence of the grating. The corresponding frequency-domain information is obtained by performing a Fourier transform on the time-domain spectrum. Figure 2 (c) shows the phase shift spectrum of the upper grating, which is stable at around 135° in a wide bandwidth of 1.4-2.0 THz. Figure 2 (d) shows a schematic diagram of the lower grating structure, whose grating period and duty cycle are consistent with the upper grating, and the etching depth is 29 μm. Figure 2Figure (e) shows the time-domain spectra of the lower-layer grating in TE and TM modes. It can be observed that the time delay is relatively small in both polarization modes. The corresponding frequency-domain information is obtained by Fourier transforming the time-domain spectra. Figure 2 Figure (f) shows the phase shift spectrum of the lower grating, which is stable at around 45° in a wide bandwidth of 1.4–2.0 THz. Therefore, the phase shifts of the individual dielectric gratings are 135° and 45°, respectively.
[0027] Figure 3 The figure shows the case of a double-layer subwavelength grating under phase-shift addition operation. Figure 3 Figure (a) shows a schematic diagram of a double-layer grating structure and terahertz transmission. The upper and lower gratings are aligned, and the incident terahertz linear polarization is along the 45° direction between the x and y axes, meaning the incident linear polarization is at a 45° angle to the grating orientation. After polarization conversion by the double-layer grating, the target causes a 90° polarization conversion of the outgoing terahertz linear polarization, thus achieving the function of a terahertz half-waveplate. Figure 3 (b) in the figure shows the amplitude spectrum of the double-layer grating in TE and TM modes, and it can be found that their amplitudes are close. Figure 3 In the diagram, (c) represents the phase shift spectrum of the double-layer grating under two polarization modes, indicated by solid spherical lines. For reference, the phase shifts of the upper and lower single-layer gratings are represented by gray lines. It can be seen that the phase shift of the double-layer grating is 180°, which is the superposition of the phase shifts of the two single layers. Combining the amplitude and phase shift conditions, according to crystal optics, it satisfies the half-waveplate condition.
[0028] Figure 4 The figure shows the case of a double-layer subwavelength grating under phase shift and subtraction operations. Figure 4 Figure (a) shows a schematic diagram of a double-layer grating structure and terahertz transmission. The upper and lower gratings are oriented perpendicularly, and the incident ray polarization is at 45° to the grating orientation. After polarization conversion by the double-layer grating, the target makes the outgoing terahertz polarization state circularly polarized, thus realizing the function of a terahertz quarter-wave plate. Figure 4 (b) in the figure shows the amplitude spectrum of the double-layer grating in TE and TM modes, and it can be found that their amplitudes are close. Figure 4 In the diagram, (c) represents the phase shift spectrum of the double-layer grating under two polarization modes, indicated by solid spherical lines. For reference, the phase shifts of the upper and lower single-layer gratings are represented by gray lines. It can be seen that the phase shift of the double-layer grating is 90°, which is the difference between the phase shifts of the two single layers. Combining the amplitude and phase shift conditions, according to crystal optics, it satisfies the quarter-wave plate condition.
[0029] Therefore, this application employs a terahertz broadband waveplate based on phase shift addition and subtraction operations. By utilizing the mechanism of phase shift addition and subtraction operations and a simple double-layer subwavelength grating structure, a quarter-waveplate or half-waveplate of terahertz wavelengths is realized. When the double-layer subwavelength gratings are aligned parallel, phase shift addition is achieved, resulting in a broadband 180° phase shift, thus realizing the function of a broadband half-waveplate. When the double-layer subwavelength gratings are aligned perpendicularly, phase shift subtraction is achieved, resulting in a broadband 90° phase shift, thus realizing the function of a quarter-waveplate. The double-layer grating structure of this application has no other complex physical effects, and the device has advantages such as low insertion loss, simple structure, ease of fabrication, and broadband performance.
[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application 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 this application, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of this application.
Claims
1. A terahertz broadband waveplate based on phase shift addition and subtraction operations, characterized in that: It includes a double-layer subwavelength dielectric grating, which comprises an upper subwavelength dielectric grating and a lower subwavelength dielectric grating; When the upper subwavelength grating and the lower subwavelength grating are oriented parallel to each other, a phase shift and addition operation is realized, generating a 180° phase shift in the broadband range, thus realizing the function of a broadband half-wave plate. When the upper subwavelength grating and the lower subwavelength grating are oriented perpendicularly, a phase shift and subtraction operation is performed, generating a 90° phase shift within the broadband range, thus realizing the function of a broadband quarter-wave plate.
2. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 1, characterized in that: The upper and lower subwavelength gratings of the half-wave plate are both oriented along the same coordinate axis.
3. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 2, characterized in that: The quarter-wave plate has an upper subwavelength grating and a lower subwavelength grating. The upper subwavelength grating is oriented along the first coordinate axis, and the lower subwavelength grating is oriented along the second coordinate axis, which is perpendicular to the first coordinate axis.
4. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 3, characterized in that: The polarization state of the incident light on the double-layer subwavelength dielectric grating is linearly polarized, and the vibration direction of the linear polarization is at a 45° angle to the grating orientation.
5. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 4, characterized in that: The dual-layer subwavelength dielectric grating is fabricated using a high-resistivity silicon wafer with a dielectric constant of 11.
7.
6. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 5, characterized in that: The upper layer of the dual-layer subwavelength dielectric grating has an etching depth of 83 μm, and the lower layer has an etching depth of 29 μm.
7. A terahertz broadband waveplate based on phase shift addition and subtraction operations as described in claim 6, characterized in that: The grating period of the dual-layer subwavelength dielectric grating is 50 μm and the duty cycle is 0.4.