Terahertz electromagnetic induction transparency regulation and control device based on liquid crystal material and application

Abstract

The invention discloses a liquid crystal material-based terahertz electromagnetically-induced transparency regulation and control device and application, the regulation and control device is composed of transparent regulation and control units arranged according to an array, and each transparent regulation and control unit is composed of a dielectric substrate, an electromagnetically-induced transparent microstructure, a liquid crystal layer and a silicon backboard in sequence from top to bottom; the electromagnetic induction transparent microstructure comprises a section line and a gold-plated electric field coupling capacitance inductance resonance structure, and a silicon island is introduced into the electric field coupling capacitance inductance resonance structure and used for controlling propagation of terahertz waves; the liquid crystal layer is used as an active modulation module. Logic regulation and control based on the electromagnetic induction transparent effect are achieved through the silicon-gold composite electromagnetic induction transparent microstructure, regulation and control of the working frequency band of the device are achieved by filling the liquid crystal material, and the designed regulation and control device meets the terahertz regulation and control requirements of wide regulation and control frequency band range, simple structure and multi-frequency-band continuous regulation and control. And the application range of the liquid crystal material in the field of terahertz wave regulation and control is widened.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz control devices, and relates to a terahertz electromagnetically induced transparent control device based on liquid crystal materials and applications thereof. Background Art

[0002] Terahertz control devices are devices that can precisely control and manipulate electromagnetic waves in the terahertz frequency band. Terahertz waves, located between microwaves and infrared rays, have many unique physical properties, such as strong penetration and large amount of information they carry. Therefore, they have broad application prospects in wireless communications, imaging technology, materials science and other fields.

[0003] In order to realize these applications, terahertz control devices need to have characteristics such as high sensitivity, fast response, and wide-band control. These devices usually use advanced materials, precise processes, and innovative structural designs to achieve flexible control of parameters such as the amplitude, phase, and polarization of terahertz waves.

[0004] Among many control technologies, the electromagnetically induced transparency effect has been widely used in refractive index sensing, optical switching, optical modulation, optical filtering, slow light devices, etc. due to its advantages of strong dispersion and enhanced transmission window. The electromagnetically induced transparency effect refers to the phenomenon that due to the destructive interference between two quantum transition paths in a three-level atomic system, an abnormal transmission peak and a large group delay appear in a wide absorption spectrum, accompanied by a significant attenuation of the group velocity. However, the realization of a typical electromagnetically induced transparency effect requires ultra-low temperature and high energy conditions. Circuits, plasma structures, microcavities, photonic crystal waveguides and metamaterials can realize the electromagnetically induced effect at room temperature.

[0005] Terahertz electromagnetically induced transparent control devices use the electromagnetically induced transparency effect to achieve a higher transmission peak within a narrow bandwidth at a certain frequency point, and produce higher dispersion and group delay around the transmission peak. At least two types of resonators are required to achieve the electromagnetically induced transparency effect in a single frequency band, and the electromagnetically induced effect in multiple frequency bands requires three or more resonators. In the terahertz frequency band, multiple types of resonators make the structure of electromagnetically induced transparent control devices complicated and difficult to process, thereby increasing the manufacturing cost.

[0006] As a metamaterial with adjustable dielectric properties, the molecular pointing axis of liquid crystal material is strongly dependent on surface effects and ambient temperature. Its adjustable properties are particularly sensitive to changes in external fields (such as electric fields, magnetic fields, light fields, etc.). It has continuous adjustability, low loss and high linearity. In fact, the adjustable dielectric constant property of liquid crystal material can be maintained over a wide frequency range, from direct current to visible light, including microwave and terahertz bands.

[0007] How to use a simple structure to achieve the electromagnetically induced transparent effect while broadening the range of the control frequency band is a difficult problem that terahertz control devices need to solve. In order to solve this problem, liquid crystal materials are used as controllable metamaterials to design a terahertz electromagnetically induced transparent control device, which uses the electromagnetically induced effect to achieve terahertz multi-band continuous control. Summary of the invention

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

[0009] (1) Design transparent control units and arrays to achieve terahertz wave transmission;

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

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

[0012] The technical solution of the present invention is:

[0013] A terahertz electromagnetically induced transparent control device based on liquid crystal material, the control device is composed of transparent control units arranged in an array, and 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 backplane. Among them: the top is a 5μm thick polyimide dielectric substrate with a relative dielectric constant 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, a stub and an electric field coupling capacitor inductor resonant structure are gold-plated, and a silicon island is introduced into the electric field coupling capacitor inductor resonant structure to control the propagation of terahertz waves. The relative dielectric constant of silicon is 11.7, and the conductivity of gold is 4.56×10 4 S / m; the third layer is a 5μm thick liquid crystal layer, used as an active modulation module, and its relative dielectric constant is 2.56-3.61; the fourth layer is a 5μm thick silicon backplane, and its relative dielectric constant is 11.7.

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

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

[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, the device, as a transmission array, has the ability to actively modulate the operating frequency and is placed in a communication link that requires terahertz wave regulation. Through optical pump excitation and liquid crystal regulation, it can achieve precise control of the on / off state and signal strength of terahertz waves of a specific frequency. This regulation capability enables the device to modulate and demodulate terahertz signals as needed, achieve information encoding and transmission, and thus support ultra-high-speed terahertz wireless communications.

[0018] The beneficial effects of the present invention include:

[0019] The present invention realizes terahertz wave transmission through reasonable unit structure design, realizes logical regulation based on electromagnetically induced transparent effect through silicon-gold composite electromagnetically induced transparent microstructure, realizes regulation of device working frequency band through filling liquid crystal material, and the designed regulation device meets the terahertz regulation requirements of wide regulation frequency band range, simple structure, and multi-band continuous regulation, thus broadening the application scope of liquid crystal materials in the field of terahertz wave regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : Diagram of the structure of the transparent control unit, where: 1-dielectric substrate, 2-electromagnetically induced transparent microstructure, 3-liquid crystal layer, 4-silicon backplane.

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

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

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

[0024] Figure 5 : Transmission spectrum.

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

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

[0027] Figure 8 : Schematic diagram of the axial deflection of liquid crystal molecules. Fig. 9 : Simulated transmission spectra of different relative dielectric constants. DETAILED DESCRIPTION

[0028] Example 1

[0029] 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: dielectric substrate 1, electromagnetically induced transparent microstructure 2, liquid crystal layer 3, and silicon backplane 4. The top is a 5μm thick polyimide dielectric substrate 1, whose relative dielectric constant is 3.1 and loss tangent is 0.05. The second layer is a 0.2μm thick silicon-gold composite electromagnetically induced transparent microstructure 2. A stub and an electric field coupling capacitor inductor resonant structure are gold-plated. Silicon islands are introduced into the electric field coupling capacitor inductor resonant structure to control the propagation of terahertz waves. The relative dielectric constant of silicon is 11.7, and the conductivity of gold is 4.56×10 4 The third layer is a 5 μm thick liquid crystal layer 3, which is used as an active modulation module and has a relative dielectric constant of 2.56-3.61. The fourth layer is a 5 μm thick silicon backplane 4, which has a relative dielectric constant of 11.7.

[0030] Silicon-gold composite electromagnetically induced transparent microstructures such as Figure 3 As shown, the unit is a square with a side length of a=100μm, the length of the section b=58μm, the width of the section d=5μm, the cross-sectional width d=5μm of the electric field coupling capacitor inductor structure, the length e=17.5μm of the silicon island, the spacing f=21μm between the section and the electric field coupling capacitor inductor structure, the outer width w=47μm of the electric field coupling capacitor inductor structure, and the outer length l=76.5μm of the electric field coupling capacitor inductor structure.

[0031] The unit structure forms 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, and the dimensions of the dielectric substrate 1, the liquid crystal layer 3, and the silicon backplane 4 are 10 mm×10 mm (length×width).

[0032] Example 2: Logical Control Design

[0033] The electromagnetic simulation software is used to solve the electromagnetically induced transparent microstructure with only the stub structure, only the electric field coupling capacitor and inductor resonant structure and their combination in the frequency domain of 0.5-1.5THz to obtain the transmission spectrum, such as Figure 5 As shown, the conductivity of the silicon island is 6×10 3S / m, the relative dielectric constant of liquid crystal is 2.56. For only the cut-line, a sudden drop in transmittance in the range of about 0.3 THz occurs at 1.15 THz due to high radiation loss, indicating that the cut-line is opaque to the incident terahertz wave at around 1.15 THz. On the contrary, only the electric field coupling capacitor inductor resonant structure shows good transmission characteristics in the range of 0.5-1.5 THz, indicating that the electric field coupling capacitor inductor resonant structure is transparent to the incident terahertz wave. The combined electromagnetically induced transparent microstructure presents an obvious "W"-shaped curve. Compared with the cut-line structure, a transparent window with a transmittance of 0.87 opens around 1.18 THz, indicating that the terahertz wave frequency band that was originally opaque in the cut-line structure becomes transparent in the combined electromagnetically induced transparent microstructure, showing typical electromagnetically induced transparent characteristics.

[0034] The dual oscillator model is used to explain the above electromagnetically induced transparency features, 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. Particle 1 on the left is subjected to a harmonic force to the right. Particle 1 is acted upon by force F(t), and is considered to be an oscillator in the bright mode, while particle 2 is considered to be an oscillator in the dark mode. In the simulation of the electromagnetically induced transparency effect, particle 1 drives particle 2 to move, just as in the electromagnetically induced transparent microstructure combined above, the electric field coupled capacitor-inductor resonant structure excites the bright mode of the stub structure.

[0035] Optical pumping refers to an exciting light source that causes a particle population inversion in the laser working material and produces stimulated radiation. It uses light from an external light source to irradiate the working material to achieve a particle population inversion in order to maintain 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 and liquid laser working materials, there are generally relatively strong absorption lines or absorption bands in specific regions of the spectrum (such as the visible region, near-infrared region, or near-ultraviolet region). When the external optical pumping effect is strong enough, a particle population inversion and stimulated emission will be achieved between specific energy levels.

[0036] The optical pump emits an excitation beam of a certain wavelength and energy to the silicon island. The electrons in the silicon island absorb the photon energy and jump from the low energy level to the high energy level to form non-equilibrium carriers (i.e., electron-hole pairs). This process changes the carrier concentration and distribution inside the silicon island, thereby affecting the conductivity of silicon. The conductivity of silicon is modulated by adjusting the intensity of the excitation beam of the optical pump (i.e., optical power). When the terahertz wave passes through the silicon island, it will be affected by the change in the conductivity of silicon, thereby changing its propagation characteristics (such as phase, amplitude, etc.), thereby achieving control of the terahertz wave.

[0037] According to the excitation state of the silicon island in different irradiation directions, it can be divided into four states, represented by IYY ,I YN ,I NY ,I NN The first letter of the subscript represents the excited state illuminated from the top polyimide dielectric substrate, the second letter represents the excited state illuminated from the bottom silicon backplane, and "Y" represents the excited state with optical pump. The conductivity of the silicon island is 6×10 3 S / m, “N” means no optical pump excitation, the conductivity of the silicon island is 2×10 3 The maximum transmittance in the range of 1.1THz-1.3THz is taken as the output signal (when the transmittance is greater than 0.5, the output is 1, and when it is less than 0.5, the output is 0), and the excitation state in the front and rear irradiation directions is taken as the input signal (when there is optical pump excitation, the input is 1, and when there is no optical pump excitation, the input is 0), and the logic control table is shown in Table 1.

[0038] Table 1 Logic control table of silicon-gold composite electromagnetically induced transparent microstructure

[0039]

[0040] For I YN ,I NY ,I NN In the three states, low conductivity leads to increased loss. 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, resulting in the disappearance of the electromagnetically induced transparency effect. YY state, due to the electromagnetic induced transparency effect, the transmittance reaches 0.87, indicating that the designed silicon-gold composite electromagnetic induced transparent microstructure can realize AND gate logic control.

[0041] Example 3: Liquid crystal band control

[0042] The magnets arranged in different directions cause the axial direction of the liquid crystal molecules to change, so that the liquid crystal material has adjustable dielectric properties, which can realize dynamic control of the operating frequency. Figure 7 As shown in the figure, a transmission array composed of multiple layers of dielectrics is placed in the middle, and the liquid crystal layer is the penultimate layer of the transmission array. N-pole and S-pole magnets are placed at the left and right ends respectively. By moving the magnets at both ends, the axial direction of the liquid crystal molecules is changed. The axial direction of the liquid crystal molecules is slowly deflected by the magnetic field between the magnets, and finally the axial direction of the liquid crystal molecules will be along the direction of the magnetic field line, as shown in the figure below. Figure 8 shown.

[0043] The relative dielectric constant ε of liquid crystal LC The refractive index n of the liquid crystal LC The relationship between Therefore, the refractive index is taken as 1.6, 1.7, 1.8, and 1.9 respectively, that is, the relative dielectric constant is taken as 2.56, 2.89, 3.24, and 3.61 respectively. The transmission spectrum obtained by simulation is as follows Fig. 9 The control table is shown in Table 2. As the refractive index increases, the transmittance decreases from 0.87 to 0.83, the operating frequency decreases from 1.18 THz to 1.07 THz, and the AND gate logic control function is normal, which realizes the flexible control of the device's operating frequency band and broadens the device's frequency band control range.

[0044] Table 2 LCD frequency band control table

[0045]

[0046] Example 4

[0047] A 100×100 transmission array is processed by standard ultraviolet lithography technology, and the transmission array is placed as an intermediate control device in the communication link that needs to control the terahertz wave. Through optical pump excitation and liquid crystal control, the on-off state and signal strength of the terahertz wave of a specific frequency can be precisely controlled. The regulated frequency information and amplitude information can be used to modulate or demodulate the terahertz signal according to specific needs, realize information encoding and transmission, and thus realize ultra-high-speed terahertz wireless communication.

Claims

1. A terahertz electromagnetically induced transparent control device based on liquid crystal material, characterized in that: The control device is composed of a plurality of transparent control units arranged in an array, wherein 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 backplane; The electromagnetically induced transparent microstructure includes a stub and a gold-plated electric field coupling capacitor-inductor resonant structure, in which a silicon island is introduced to control the propagation of terahertz waves; The liquid crystal layer serves as an active modulation module.

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 5 μm 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 relative dielectric constant of the dielectric substrate is 3.1 and the loss tangent is 0.

05.

4. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to claim 1, characterized in that: The thickness of the electromagnetically induced transparent microstructure is 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 dielectric constant 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 thickness of the silicon back plate is 5 μm, and its relative dielectric constant is 11.

7.

7. The terahertz electromagnetically induced transparent control device based on liquid crystal material according to any one of claims 1 to 6, characterized in that: The transparent control unit is a square with a side length a=100μm, a length b=58μm of its section, a width d=5μm of the section, a cross-sectional width d=5μm of its electric field coupling capacitor inductor structure, a length e=17.5μm of the silicon island, a spacing f=21μm between the section and the electric field coupling capacitor inductor structure, an outer width w=47μm of the electric field coupling capacitor inductor structure, and an outer length l=76.5μm of the electric field coupling 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 is composed of 100×100 transparent control units arranged in an array to form a transmission array, and the length and width dimensions of the dielectric substrate, liquid crystal layer, and silicon backplane are 10mm×10mm.

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

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