A terahertz electromagnetic induced transparency modulation device based on liquid crystal material and application

Abstract

This invention discloses a terahertz electromagnetically induced transparent modulation device based on liquid crystal material and its application. The modulation device consists of transparent modulation units arranged in an array. From top to bottom, each transparent modulation unit comprises a dielectric substrate, an electromagnetically induced transparent microstructure, a liquid crystal layer, and a silicon backplane. The electromagnetically induced transparent microstructure includes a truncated line and a gold-plated electric field coupling capacitor-inductor resonant structure. A silicon island is introduced into the electric field coupling capacitor-inductor resonant structure to control the propagation of terahertz waves. The liquid crystal layer serves as an active modulation module. This invention achieves logic modulation based on the electromagnetically induced transparency effect through a silicon-gold composite electromagnetically induced transparent microstructure, and achieves modulation of the device's operating frequency band by filling with liquid crystal material. The designed modulation device meets the requirements of wide modulation frequency range, simple structure, and continuous multi-band modulation of terahertz waves, thus broadening the application scope of liquid crystal materials in the field of terahertz wave modulation.

Description

Technical Field

[0001] This invention belongs to the field of terahertz control devices, and relates to a terahertz electromagnetically induced transparent control device based on liquid crystal material and its application. Background Technology

[0002] Terahertz control devices are instruments that enable precise control and manipulation of electromagnetic waves within the terahertz frequency band. Terahertz waves, located between microwaves and infrared radiation, possess many unique physical properties, such as strong penetrability and high information carrying capacity, thus showing broad application prospects in wireless communication, imaging technology, materials science, and other fields.

[0003] To achieve these applications, terahertz control devices need to possess characteristics such as high sensitivity, fast response, and wide bandwidth control. These devices typically employ advanced materials, precise processes, and innovative structural designs to achieve flexible control over parameters such as amplitude, phase, and polarization of terahertz waves.

[0004] Among numerous control technologies, electromagnetically induced transparency (EMI) has been widely applied in refractive index sensing, optical switching, optical modulation, optical filtering, and slow-light devices due to its advantages of strong dispersion and enhanced transmission window. EMI refers to the phenomenon where, due to destructive interference between two quantum transition paths in a three-level atomic system, an abnormal transmission peak and a large group delay occur across a broad absorption spectrum, accompanied by a significant decrease in group velocity. However, achieving typical EMI requires ultra-low temperatures and high energy. Circuits, plasma structures, microcavities, photonic crystal waveguides, and metamaterials can realize EMI under room-temperature conditions.

[0005] Terahertz electromagnetically induced transparency (EMIT) control devices utilize the EMIT effect to achieve a high transmission peak within a narrow bandwidth at a specific frequency, while generating high dispersion and group delay around the transmission peak. At least two types of resonators are required to achieve EMIT in a single frequency band, while multi-band EMIT requires three or more resonators. In the terahertz band, the use of multiple resonator types complicates the structure of EMIT control devices, increases fabrication difficulty, and consequently raises manufacturing costs.

[0006] Liquid crystal materials, as metamaterials with tunable dielectric properties, have molecular orientation axes that are strongly dependent on surface effects and ambient temperature. Their tuning characteristics are particularly sensitive to changes in external fields (such as electric fields, magnetic fields, and light fields), exhibiting continuous tunability, low loss, and high linearity. In fact, this tunable dielectric constant characteristic of liquid crystal materials can be maintained over a wide frequency range, from DC to the visible light range, including microwave and terahertz bands.

[0007] Achieving electromagnetically induced transparency while broadening the control frequency band using a simple structure is a key challenge for terahertz control devices. To address this challenge, a terahertz electromagnetically induced transparency control device was designed using liquid crystal material as a tunable metamaterial, achieving continuous multi-band control of terahertz frequencies through electromagnetic induction. Summary of the Invention

[0008] The purpose of this invention is to provide a terahertz electromagnetically induced transparent control device based on liquid crystal material, and the technical problems to be solved include:

[0009] (1) Design a transparent control unit and array to realize terahertz wave transmission;

[0010] (2) Design silicon-gold composite electromagnetically induced transparent microstructures to realize logic control based on electromagnetically induced transparency effect;

[0011] (3) Using liquid crystal materials as tunable metamaterials to achieve multi-band modulation and broaden the frequency band modulation range of the device.

[0012] The technical solution of this invention is as follows:

[0013] A terahertz electromagnetically induced transparent control device based on liquid crystal material is disclosed. This device comprises transparent control units arranged in an array. Each transparent control unit consists of four parts from top to bottom: a dielectric substrate, an electromagnetically induced transparent microstructure, a liquid crystal layer, and a silicon backplane. Specifically: the top layer is a 5μm thick polyimide dielectric substrate with a relative permittivity of 3.1 and a loss tangent of 0.05; the second layer is a 0.2μm thick silicon-gold composite electromagnetically induced transparent microstructure, with a gold-plated cross-section and an electric field coupling capacitor-inductor resonant structure. Silicon islands are introduced into the electric field coupling capacitor-inductor resonant structure to control the propagation of terahertz waves. The relative permittivity of silicon is 11.7, and the conductivity of gold is 4.56 × 10⁻⁶. 4 S / m; the third layer is a 5μm thick liquid crystal layer used as an active modulation module, with a relative permittivity of 2.56-3.61; the fourth layer is a 5μm thick silicon backplane with a relative permittivity of 11.7.

[0014] The transparent control unit is a square with a side length of a = 100 μm, a cross-section length of b = 58 μm, a cross-section width of d = 5 μm, a cross-section width of d = 5 μm for its electric field coupling capacitor-inductor structure, a silicon island length of e = 17.5 μm, a distance of f = 21 μm between the cross-section and the electric field coupling capacitor-inductor structure, an outer width of w = 47 μm for the electric field coupling capacitor-inductor structure, and an outer length of l = 76.5 μm for the electric field coupling capacitor-inductor structure.

[0015] The transparent control unit forms a 100×100 transmission array (containing 10,000 silicon-gold composite electromagnetically induced transparent microstructures), and the dielectric substrate, liquid crystal layer, and silicon backplate have a length and width of 10mm×10mm.

[0016] The terahertz electromagnetically induced transparent control device based on liquid crystal material of the present invention can be applied in terahertz wireless communication.

[0017] Specifically, this device, acting as a transmission array, possesses the capability to actively modulate its operating frequency and is placed in communication links where terahertz waves require modulation. Through optical pumping excitation and liquid crystal modulation, it can achieve precise control over the on / off state and signal strength of terahertz waves at specific frequencies. This modulation capability enables the device to modulate and demodulate terahertz signals as needed, thereby encoding and transmitting information and supporting ultra-high-speed terahertz wireless communication.

[0018] The beneficial effects of this invention include:

[0019] This invention achieves terahertz wave transmission through a reasonable unit structure design, realizes logic control based on electromagnetically induced transparency effect through a silicon-gold composite electromagnetically induced transparent microstructure, and realizes the control of the device's operating frequency band by filling with liquid crystal material. The designed control device meets the requirements of terahertz control with a wide control frequency band, simple structure, and continuous control of multiple frequency bands, thus broadening the application scope of liquid crystal materials in the field of terahertz wave control. Attached Figure Description

[0020] Figure 1 : Transparent control unit structure diagram, where: 1-dielectric substrate, 2-electromagnetically induced transparent microstructure, 3-liquid crystal layer, 4-silicon backplate.

[0021] Figure 2 Side view of the transparent control unit.

[0022] Figure 3 Schematic diagram of a silicon-gold composite electromagnetically induced transparent microstructure.

[0023] Figure 4 Schematic diagram of a 100×100 array structure.

[0024] Figure 5 : Transmission spectrum.

[0025] Figure 6 Schematic diagram of a dual oscillator model.

[0026] Figure 7 Schematic diagram of liquid crystal control scheme.

[0027] Figure 8 Schematic diagram of axial deflection of liquid crystal molecules.

[0028] Figure 9 Simulated transmission spectra with different relative permittivity. Detailed Implementation

[0029] Example 1

[0030] The unit structure design of terahertz electromagnetically induced transparent control devices is as follows: Figure 1 and Figure 2 The unit structure consists of four parts: a dielectric substrate 1, an electromagnetically induced transparent microstructure 2, a liquid crystal layer 3, and a silicon backplane 4. The top layer is a 5μm thick polyimide dielectric substrate 1 with a relative permittivity of 3.1 and a loss tangent of 0.05. The second layer is a 0.2μm thick silicon-gold composite electromagnetically induced transparent microstructure 2, with a gold-plated cross-section and an electric field coupling capacitor-inductor resonant structure. Silicon islands are introduced into the electric field coupling capacitor-inductor resonant structure to control the propagation of terahertz waves. The relative permittivity of silicon is 11.7, and the conductivity of gold is 4.56 × 10⁻⁶. 4 S / m. The third layer is a 5μm thick liquid crystal layer 3, used as an active modulation module, with a relative permittivity of 2.56-3.61. The fourth layer is a 5μm thick silicon backplane 4, with a relative permittivity of 11.7.

[0031] Silicon-gold composite electromagnetically induced transparent microstructures such as Figure 3 As shown, the unit is a square with a side length of a = 100 μm, the length of the slit is b = 58 μm, the width of the slit is d = 5 μm, the cross-sectional width of the electric field coupling capacitor-inductor structure is d = 5 μm, the length of the silicon island is e = 17.5 μm, the distance between the slit and the electric field coupling capacitor-inductor structure is f = 21 μm, the outer width of the electric field coupling capacitor-inductor structure is w = 47 μm, and the outer length of the electric field coupling capacitor-inductor structure is l = 76.5 μm.

[0032] The unit structures form a 100×100 transmission array, such as Figure 4 As shown, there are a total of 10,000 silicon-gold composite electromagnetically induced transparent microstructures. The dimensions of the dielectric substrate 1, liquid crystal layer 3, and silicon backplate 4 are 10mm × 10mm (length × width).

[0033] Example 2: Logic Control Design

[0034] The transmission spectrum of electromagnetically induced transparent microstructures (0.5–1.5 THz) was obtained by solving the frequency domain problem using electromagnetic simulation software. The solutions consisted only of truncated structures, electric field-coupled capacitive-inductive resonant structures, and combinations thereof. Figure 5 As shown, the conductivity of the silicon island is 6 × 10⁻⁶. 3The relative permittivity of the liquid crystal is 2.56 (S / m). For the truncated structure alone, a sharp drop in transmittance occurs in the approximately 0.3 THz range at 1.15 THz due to high radiation loss, indicating that the truncated structure is opaque to incident terahertz waves around 1.15 THz. Conversely, the electric field-coupled capacitor-inductor resonant structure alone exhibits good transmission characteristics in the 0.5-1.5 THz range, indicating that the electric field-coupled capacitor-inductor resonant structure is transparent to incident terahertz waves. The combined electromagnetically induced transparent microstructure exhibits a distinct "W"-shaped curve. Compared with the truncated structure, the transparent window with a transmittance of 0.87 opens near 1.18 THz, indicating that the originally opaque terahertz wave frequency band in the truncated structure becomes transparent in the combined electromagnetically induced transparent microstructure, exhibiting typical electromagnetically induced transparency characteristics.

[0035] The electromagnetically induced transparency characteristics described above can be explained using a dual-oscillator model, such as... Figure 6 As shown, the model consists of two particles with masses m1 and m2 and three springs with elastic coefficients k1, K, and k2 respectively. Particle 1 on the left is subjected to a harmonic force to the right. Particle 1, acted upon by force F(t), is considered a bright-mode oscillator, while particle 2 is considered a dark-mode oscillator. In the simulation of electromagnetically induced transparency, particle 1 causes particle 2 to shift, just as in the electromagnetically induced transparent microstructure described above, where the electric field-coupled capacitor-inductor resonant structure excites the bright mode of the truncated structure.

[0036] Optical pumping refers to the excitation source that causes population inversion in the laser gain medium, generating stimulated emission. It uses light emitted from an external light source to irradiate the gain medium, achieving population inversion and maintaining the energy necessary for laser operation. This process of pumping atoms from a low-energy state to a high-energy state is called optical excitation. For solid-state and liquid laser gain media, there are generally strong absorption lines or bands in specific regions of the spectrum (such as the visible, near-infrared, or near-ultraviolet regions). When the external optical pumping is strong enough, population inversion and stimulated emission will occur between specific energy levels.

[0037] Optical pumping illuminates a silicon island by emitting an excitation beam of a specific wavelength and energy. Electrons in the silicon island absorb the photon energy and transition from a lower energy level to a higher energy level, forming non-equilibrium carriers (electron-hole pairs). This process alters the carrier concentration and distribution within the silicon island, thus affecting the silicon's conductivity. By adjusting the intensity (optical power) of the excitation beam, the conductivity of the silicon can be modulated. As terahertz waves pass through the silicon island, they are affected by the change in silicon conductivity, thereby altering their propagation characteristics (such as phase and amplitude), thus enabling control of the terahertz waves.

[0038] Based on the excitation state of the silicon island under different irradiation directions, it can be divided into four states, denoted as I.YY I YN I NY I NN The first letter of the subscript represents the excitation state when illuminated from the top polyimide dielectric substrate, the second letter represents the excitation state when illuminated from the bottom silicon backplane, "Y" indicates optical pumping excitation, and the silicon island conductivity is 6 × 10⁻⁶. 3 S / m, where "N" indicates no optical pumping excitation, and the silicon island conductivity is 2 × 10⁻⁶. 3 S / m. The maximum transmittance in the range of 1.1THz-1.3THz is taken as the output signal (the output is 1 when the transmittance is greater than 0.5 and 0 when it is less than 0.5). The excitation state in the front and rear illumination directions is taken as the input signal (the input is 1 when there is optical pumping excitation and 0 when there is no optical pumping excitation). The logic control table is shown in Table 1.

[0039] Table 1. Logical Control of Silicon-Gold Composite Electromagnetically Induced Transparent Microstructures

[0040]

[0041] For I YN I NY I NN In the three states, low conductivity leads to increased losses. Under the coupling effect, the bright mode fails to provide sufficient excitation for the dark mode, weakening the excitation of the bright mode on the truncated structure and causing the electromagnetically induced transparency effect to disappear. YY In the state of electromagnetic induction transparency, the transmittance reaches 0.87, indicating that the designed silicon-gold composite electromagnetic induction transparent microstructure can achieve AND gate logic control.

[0042] Example 3: Liquid Crystal Bandwidth Modulation

[0043] By arranging magnets in different orientations to alter the axial direction of liquid crystal molecules, the liquid crystal material acquires adjustable dielectric properties, enabling dynamic control of the operating frequency. The control scheme is as follows: Figure 7 As shown, a transmission array composed of multiple dielectric layers is placed in the middle, with the liquid crystal layer on the penultimate layer of the array. N-pole and S-pole magnets are placed at the left and right ends, respectively. By moving these magnets, the axial direction of the liquid crystal molecules is changed. The liquid crystal molecules are slowly deflected by the magnetic field between the magnets, eventually aligning with the direction of the magnetic field lines. Figure 8 As shown.

[0044] The relative permittivity ε of liquid crystal LC With respect to the refractive index n of liquid crystal LC The relationship between them is Therefore, refractive indices of 1.6, 1.7, 1.8, and 1.9 were chosen, corresponding to relative permittivity of 2.56, 2.89, 3.24, and 3.61. The simulated transmission spectra are shown below. Figure 9 As shown in Table 2, the control table shows that as the refractive index increases, the transmittance decreases from 0.87 to 0.83, and the operating frequency decreases from 1.18 THz to 1.07 THz. The AND gate logic control function is normal, realizing flexible control of the device's operating frequency band and widening the device's frequency band control range.

[0045] Table 2 LCD Bandwidth Control Table

[0046]

[0047] Example 4

[0048] A 100×100 transmission array is fabricated using standard ultraviolet lithography. This array is then placed as an intermediate control device in the communication link where terahertz waves require modulation. Through optical pumping and liquid crystal modulation, precise control over the on / off state and signal strength of terahertz waves at specific frequencies can be achieved. The frequency and amplitude information can be modulated or demodulated according to specific needs to encode and transmit information, thereby realizing ultra-high-speed terahertz wireless communication.

Claims

1. A terahertz electromagnetic induced transparency regulating device based on liquid crystal material, characterized in that, The control device consists of several transparent control units arranged in an array. The transparent control unit is composed of four parts from top to bottom: a dielectric substrate, an electromagnetically induced transparent microstructure, a liquid crystal layer, and a silicon backplate. The electromagnetically induced transparent microstructure includes a truncated line and a gold-plated electric field coupling capacitor-inductor resonant structure. A silicon island is introduced into the electric field coupling capacitor-inductor resonant structure to control the propagation of terahertz waves. The liquid crystal layer is used as an active modulation module; By using magnets arranged in different orientations to cause changes in the axial direction of liquid crystal molecules, the liquid crystal layer can be made to have adjustable dielectric properties, which can be used to achieve dynamic control of the operating frequency. The four excitation states are controlled by AND gate logic through optical pumping of the silicon island; The control device, acting as a transmission array, achieves precise control over the on / off state and signal strength of a terahertz wave at a specific frequency through optical pumping excitation and liquid crystal modulation.

2. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 1, characterized in that: The dielectric substrate is a 5μm thick polyimide dielectric substrate.

3. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 2, characterized in that: The dielectric substrate has a relative permittivity of 3.1 and a loss tangent of 0.

05.

4. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 1, characterized in that: The electromagnetically induced transparent microstructure has a thickness of 0.2 μm.

5. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 1, characterized in that: The relative permittivity of the liquid crystal layer is 2.56-3.

61.

6. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 1, characterized in that: The silicon backplane has a thickness of 5 μm and a relative permittivity of 11.

7.

7. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to any one of claims 1-6, characterized in that: The transparent control unit has a side length of The length of the transverse of the square. Width of the slit line Its electric field coupling capacitor-inductor structure has a wide cross-section. Silicon Island's length The spacing between the cut-off line and the electric field coupling capacitor-inductor structure The outer width of the electric field coupled capacitor-inductor structure The external length of the electric field coupled capacitor-inductor structure .

8. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 7, characterized in that: The control device consists of a transmission array composed of 100×100 transparent control units arranged in an array. The dielectric substrate, liquid crystal layer, and silicon backplate have dimensions of 10mm×10mm.

9. The application of a terahertz electromagnetically induced transparent control device based on liquid crystal material according to any one of claims 1-8 in terahertz wireless communication.

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