Terahertz modulator based on optically modulated phonon plasma resonance splitting and its preparation method

Abstract

The present invention belongs to the field of terahertz technology, and discloses a terahertz modulator based on optically modulated phonon plasma resonance splitting and a preparation method thereof, comprising a quartz substrate and a plurality of metal units photoetched on the surface of the quartz substrate, wherein the plurality of metal units are arranged periodically; and a layer of semiconductor material thin film is covered on the surface of the metal unit. Compared with electrons in metal structures, phonons in dielectric materials of the present invention have lower losses and can replace metal structures. Compared with plasma-induced transparent terahertz modulation devices using metal structures, terahertz modulation devices using phonon plasma resonance splitting have their own unique advantages. Optical phonons usually have a lifetime three orders of magnitude lower than collective electron resonances in precious metals, showing significantly lower losses. Frequent scattering of phonons on the surface of nanostructures can significantly reduce heat conduction and can become an additional heat dissipation channel.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz technology, and in particular relates to a terahertz modulator based on light-tuned phonon plasma resonance splitting and a preparation method thereof. Background Art

[0002] At present, terahertz technology has a fascinating development prospect and has great potential in communication compared with light waves and electromagnetic waves. For lower electromagnetic waves, the radiation source is based on the control of classical electron transport and generates electricity. It is transparent to most dielectric materials, allowing radio signals to be received indoors, but the resolution of electromagnetic waves in imaging applications such as radar is usually limited to within a few centimeters; for higher frequency light waves, electromagnetic radiation usually propagates in free space, is opaque in many materials, and light radiation will be strongly scattered. For terahertz waves, which are between the two, they have the propagation characteristics of both. In some cases, terahertz wireless communication can also provide some advantages: compared with microwaves, terahertz communication has the potential to increase bandwidth capacity and is more directional; compared with infrared radiation, terahertz radiation has a lower attenuation rate and can provide longer links; terahertz waves can prevent channel interference and achieve "secure" communication links. Therefore, terahertz modulation technology, one of the core technologies of terahertz technology, has also received more and more attention.

[0003] According to the working principle, terahertz modulators can be roughly divided into electrically tuned terahertz modulators, thermally tuned terahertz modulators, optically tuned terahertz modulators, magnetically tuned terahertz modulators, etc. Metamaterial modulation devices: Metamaterials generally refer to composite materials that use traditional materials (such as metals) to form microstructure units and arrange them in a periodic manner. Their properties depend on the geometric size and arrangement of the structure. Usually, metamaterial structures use metal rods and split resonant rings (SRR). The terahertz wave is modulated by the plasma resonance of the metal rod and the LC resonance of the split resonant ring. In recent years, it has become increasingly mature to use the periodic arrangement between metamaterials and the mutual coupling of terahertz waves to adjust the amplitude, phase and other parameters of the terahertz wave. The terahertz metamaterial modulation devices currently used are inevitably electronically lost because they are composed of metal structures. The surface plasmon source is mediated by electrons. Tight localization is always accompanied by an increase in ohmic loss, resulting in considerable loss. Ohmic loss is often accompanied by thermal loss, which limits its development. It is very meaningful to find alternative low-loss materials.

[0004] Through the above analysis, the problems and defects of the prior art are as follows:

[0005] Existing terahertz metamaterial modulation devices are made of metal structures and have considerable losses. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a terahertz modulator based on light-tuned phonon plasma resonance splitting and a preparation method thereof.

[0007] The present invention is implemented as follows: a terahertz modulator based on optically modulated phonon plasma resonance splitting comprises:

[0008] A quartz substrate and a plurality of metal units photoetched on a surface of the quartz substrate;

[0009] Several metal units are arranged periodically, and are composed of n metal units arranged in sequence, where n ≥ 1;

[0010] The metal unit is composed of a square ring and an X-shaped bar located in the middle of the square ring, and the square ring has openings in the middle of the four sides;

[0011] The surface of the metal unit is covered with a semiconductor material film.

[0012] Furthermore, there is a spacing between adjacent metal units, and the spacing is equal.

[0013] Furthermore, the upper and lower periods of the metal unit are set to Px and Py, Px=Py=100 μm, the side length is set to a, a=45 μm, the opening gap is set to g, g=6.5 μm, and the width is set to w, w=5 μm.

[0014] Furthermore, the semiconductor material film is a film having a Lorentz parameter model, and the relative dielectric constant of the semiconductor material is calculated using a Drude response. Where γ represents the damping rate or scattering rate, ωp represents the plasma frequency, and the plasma frequency expression is: N represents the electron carrier concentration, e represents the electron charge, ε0 represents the vacuum dielectric constant, and m eff is the effective mass of the electron. At room temperature, when ω>ω p When the semiconductor is irradiated, the reflectivity decreases and it becomes transparent to the incident wave.

[0015] Furthermore, the semiconductor material film is a perovskite film.

[0016] Furthermore, the size parameter of the quartz substrate is 20*20*0.5 mm.

[0017] Another object of the present invention is to provide a method for preparing a terahertz modulator based on light-tuned phonon plasma resonance splitting, the method for preparing a terahertz modulator based on light-tuned phonon plasma resonance splitting comprising:

[0018] Step 1: Preparation of terahertz metamaterials: Use drawing software to draw the metamaterial structure pattern, prepare a mask plate based on the drawn pattern, use a photolithography machine to photolithography the pattern in the prepared mask plate onto a quartz substrate through a photolithography process, and use electron beam evaporation to deposit gold onto the film to obtain a metal unit;

[0019] Step 2, preparation of perovskite film: prepare MAPbI3 solution, spin-coat the MAPbI3 solution onto the surface of the metal unit, place it on a heating platform for annealing, and a bright perovskite film is formed on the surface of the substrate.

[0020] Furthermore, titanium / gold metal is selected for evaporation in step 1, and 20 nm thick titanium is first used as a buffer layer, and then 80 nm thick gold is adhered to the titanium buffer layer.

[0021] Furthermore, the concentration of the MAPbI3 solution in step 2 is 1 mol / L, and the preparation method of the MAPbI3 solution includes: weighing 159 mg of MAI powder and 461 mg of PbI2 powder into an empty solution bottle, and injecting 1 mL of DNF solution into the solution bottle containing the powder with a pipette to obtain a MAPbI3 solution.

[0022] Furthermore, in step 2, the temperature of the heating platform is 90° C., and the annealing is performed for 10 minutes.

[0023] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0024] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0025] The present invention is a terahertz modulator based on optically modulated phonon plasma resonance splitting. Compared with electrons in metal structures, phonons in dielectric materials have lower losses and can replace metal structures. Compared with plasma-induced transparent terahertz modulation devices using metal structures, terahertz modulation devices using phonon plasma resonance splitting have their own unique advantages. Optical phonons usually have a lifetime three orders of magnitude lower than the collective electron resonance in precious metals, showing significantly lower losses. The frequent scattering of phonons on the surface of nanostructures can significantly reduce thermal conduction and can become an additional heat dissipation channel.

[0026] The present invention can adjust the resonant frequency of the structure by changing the size of the structure and the size of the opening, so that the resonant frequency of the structure is close to the resonant frequency of the phonon, thereby achieving a coupling condition.

[0027] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0028] This technology regulates the device through external optical pumping, and absorbs the external light intensity to increase the conductivity and thus modulate the signal. This process will be accompanied by heat loss. During the operation of the device, the device temperature will increase with the working time. Since there is phonon resonance in the device, a heat conduction channel will exist in the device through the phonon resonance, thereby reducing the operating temperature of the device.

[0029] The amplitude of the modulation of the device of this technology is between 0.4 and 0.6, while the amplitude of the modulation device by structural resonance is between 0.1 and 0.4 due to the large initial loss.

[0030] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0031] The technical solution of the present invention fills the technical gap in the industry at home and abroad: before this, terahertz metamaterial optical modulation devices all used the coupling between structures to form a transparent window and modulate it through external laser pumping, and there has never been a transparent window formed by coupling dielectric materials and structures and modulated through external laser pumping. This fills the technical gap of coupling dielectric materials and metamaterials.

[0032] Does the technical solution of the present invention solve the technical problem that people have been eager to solve but have never succeeded in solving: the resonance of metamaterials is caused by the formation of surface plasmon excitation sources at the interface between metal and medium, but the surface plasmon excitation sources are the collective effect of electrons, which will lead to large losses, so it is hoped to find substitutes, while phonon excitation sources have low losses and can be replaced. This technical solution uses phonon excitation sources to replace surface plasmon excitation sources, thereby solving the loss problem of metamaterials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of a terahertz modulator based on optically modulated phonon plasma resonance splitting provided by an embodiment of the present invention;

[0034] Figure 2 is a structural effect diagram of a terahertz metamaterial provided by an embodiment of the present invention;

[0035] Figure 3 This is a unit structure effect diagram of the MAPbI3 / metamaterial / quartz sample provided in an embodiment of the present invention;

[0036] Figure 4 Schematic diagram of the measurement results of sample transmittance;

[0037] FIG5 is a schematic diagram of the modulation results of the sample. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] 1. Explanatory Examples In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an illustrative example that expands and describes the technical solution of the claims.

[0040] like Figure 1 As shown, the terahertz modulator based on optically tuned phonon plasma resonance splitting provided by the embodiment of the present invention includes a quartz substrate, a metal unit and a perovskite film. The quartz substrate is used as the substrate, and then the metal unit is photolithographically etched onto the surface of the quartz substrate. The metal unit structure layer is arranged periodically and is composed of n metal units arranged in sequence, where n≥1. The opening and structural dimensions of each metal unit are the same, and there is a spacing between adjacent metal units, and the spacing is equal. The structure of the designed metal unit is an electromagnetic resonance structure.

[0041] The metal unit is composed of a square ring with an opening in the middle of the four sides and an X-shaped strip, and then a layer of perovskite film is covered on the surface of the structure. The resonant frequency of the structure can be adjusted by changing the size of the structure and the size of the opening, so that the resonant frequency of the structure is close to the resonant frequency of the phonon, achieving the coupling condition.

[0042] The size and period parameters of the metal unit are maintained in order to make the resonance point of the metamaterial the same as the phonon resonance point, forming vacuum Rabi splitting, creating a transparent window, and playing a modulation role.

[0043] In electromagnetic simulation software, the simulation process of metal unit structure is as follows:

[0044] 1. First, make a metal structure composed of a square ring with an opening in the middle of the four sides and an "×" shape. The upper and lower periods of the metal structure are set to p x and p y , the side length of the structure is set to a, the opening gap is set to g, the width of the structure is set to w, and the various parameters are adjusted to determine the approximate range of the parameters so that S 21 The resonant frequency of the parameter is near the phonon resonance frequency. In the sub-wavelength range, the approximate range of the parameter can be obtained by adjusting the structural parameters. A thin film with a Lorentz parameter model is covered on the surface of the structure, and the structural parameters obtained in step 1 are slightly adjusted to obtain an optimal parameter, and the simulation phenomenon of phonon plasma resonance splitting occurs.

[0045] 2. The film selected for the sample is a semiconductor material. For semiconductor materials, the relative dielectric constant can be expressed using the Drude response. Where γ represents the damping rate or scattering rate, In the plasma frequency expression, N represents the electron carrier concentration, e represents the electron charge, ε0 represents the vacuum dielectric constant, and m eff is the effective mass of the electron. At room temperature, when ω>ω p When the semiconductor reflectivity decreases, it becomes transparent to the incident wave. By reducing the frequency of semiconductor material plasma, the semiconductor material can obtain a response in the terahertz band, that is, the concentration of photogenerated carriers in the semiconductor can be increased by external laser pumping to achieve modulation. Therefore, when achieving the modulation effect, the conductivity parameters of the film are changed to simulate the modulation of the structure by laser pumping.

[0046] 2. Application Examples: In order to prove the creativity and technical value of the technical solution of the present invention, this section provides examples of applying the technical solution of the claims to specific products or related technologies.

[0047] This technology mainly modulates terahertz signals. The strength of the signal can be seen from the transmittance curve. The higher the transmittance, the stronger the signal. The transmittance of the curve is adjusted by external optical pumping, thereby adjusting the signal strength and modulating the communication signal.

[0048] 3. Evidence of the effects of the embodiments. The embodiments of the present invention have achieved some positive effects during the development or use process, and indeed have great advantages over the prior art. The following content is described in conjunction with the data, charts, etc. of the test process.

[0049] This technology regulates the device through external optical pumping, and absorbs the external light intensity to increase the conductivity and thus modulate the signal. This process will be accompanied by heat loss. During the operation of the device, the device temperature will increase with the working time. Since there is phonon resonance in the device, a heat conduction channel will exist in the device through the phonon resonance, thereby reducing the operating temperature of the device.

[0050] The amplitude of the modulation of the device of this technology is between 0.4 and 0.6, while the amplitude of the modulation device by structural resonance is between 0.1 and 0.4 due to the large initial loss.

[0051] Implementation Cases:

[0052] Preparation of terahertz metamaterials: First, use drawing software to draw the metamaterial structure diagram, such as Figure 2As shown, the structural parameters are Px = Py = 100μm, a = b = 45μm, w = 5μm, g = 6.5μm. The mask is prepared by drawing the pattern, and the pattern in the prepared mask is photolithographically etched onto a quartz substrate using a photolithography machine. The quartz adopts the parameters of 20*20*0.5mm size. Electron beam evaporation is used to evaporate gold onto the film. Titanium / gold metal is used for evaporation. First, 20nm thick titanium is used as a buffer layer, and then 80nm thick gold is adhered to the titanium buffer layer to obtain a metal unit structure.

[0053] Preparation of perovskite film: First, prepare the solution. The experimental preparation is a MAPbI3 solution with a concentration of 1 mol / L. It requires 1 mmol of MAI and 1 mmol of PbI2 solvent, and 1 mL of DMF solution is also required. Weigh 159 mg of MAI powder and 461 mg of PbI2 powder into an empty solution bottle, and use a pipette to inject 1 mL of DNF solution into the solution bottle containing the powder to obtain a MAPbI3 solution. The solution is spin-coated onto the surface of the structure. Preparation of perovskite film: First, prepare the solution. The experimental preparation is a MAPbI3 solution with a concentration of 1 mol / L. It requires 1 mmol of MAI and 1 mmol of PbI2 solvent, and 1 mL of DMF solution is also required. Weigh 159 mg of MAI powder and 461 mg of PbI2 powder into an empty solution bottle, and use a pipette to inject 1 mL of DNF solution into the solution bottle containing the powder to obtain a MAPbI3 solution. The solution is spin-coated onto the surface of the structure and placed on a heating platform at 90°C for annealing for 10 minutes. A bright perovskite film is formed on the surface of the substrate. Figure 1 As shown, Figure 3 This is the unit structure of the MAPbI3 / metamaterial / quartz sample.

[0054] Figure 4 Figure 5 is a schematic diagram of the sample transmittance measurement results, and Figure 5 is a schematic diagram of the sample modulation results. Figure 5(a) is a sample transmittance curve calculated from the frequency domain data measured experimentally. The metal metamaterial resonates with the perovskite film phonons, and the anti-resonance splitting phenomenon appears a transparent window and two splitting peaks. The transmittance of the sample decreases with the increase of the pump light intensity; Figure 5(b) is a modulation depth curve of the sample at 0.84THz, 0.986THz and 1.11THz, which is specifically drawn according to the transmittance curve. The modulation depth of the sample is calculated by the formula |ΔT / T|=(T0-T p ) / T0, it is calculated that the modulation depth increases with the increase of pump light intensity, and reaches the maximum value of 27.179%, 25.332% and 18.425% respectively at 800mW.

[0055] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A terahertz modulator based on optically modulated phonon plasma resonance splitting, characterized in that: The terahertz modulator based on optically modulated phonon plasma resonance splitting comprises: A quartz substrate and a plurality of metal units photoetched on a surface of the quartz substrate; Several metal units are arranged periodically, and are composed of n metal units arranged in sequence, where n ≥ 1; The metal unit is composed of a square ring and an X-shaped bar located in the middle of the square ring, and the square ring has openings in the middle of the four sides; The surface of the metal unit is covered with a semiconductor material film.

2. The terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 1, characterized in that: There is spacing between adjacent metal units, and the spacing is equal.

3. The terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 1, characterized in that: The upper and lower periods of the metal unit are set to Px and Py, Px=Py=100 μm, the side length is set to a, a=45 μm, the opening gap is set to g, g=6.5 μm, and the width is set to w, w=5 μm.

4. The terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 1, characterized in that: The semiconductor material film is a film having a Lorentz parameter model, and the relative dielectric constant of the semiconductor material is expressed by a Drude response. Where γ represents the damping rate or scattering rate, ωp represents the plasma frequency, and the plasma frequency expression is: N represents the electron carrier concentration, e represents the charge of the electron, ε0 represents the vacuum dielectric constant, and m eff is the effective mass of the electron. At room temperature, when ω>ω p When the semiconductor is exposed to ultraviolet light, its reflectivity decreases and it becomes transparent to the incident wave.

5. The terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 1, characterized in that: The semiconductor material film is a perovskite film.

6. The terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 1, characterized in that: The size parameters of the quartz substrate are 20*20*0.5 mm.

7. A method for preparing a terahertz modulator based on optically modulated phonon plasma resonance splitting according to any one of claims 1 to 6, characterized in that: The method for preparing the terahertz modulator based on light-tuned phonon plasma resonance splitting comprises: Step 1: Preparation of terahertz metamaterials: Use drawing software to draw the metamaterial structure pattern, prepare a mask plate based on the drawn pattern, use a photolithography machine to photolithography the pattern in the prepared mask plate onto a quartz substrate through a photolithography process, and use electron beam evaporation to deposit gold onto the film to obtain a metal unit; Step 2, preparation of perovskite film: prepare MAPbI3 solution, spin-coat the MAPbI3 solution onto the surface of the metal unit, place it on a heating platform for annealing, and a bright perovskite film is formed on the surface of the substrate.

8. The method for preparing a terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 7, characterized in that: The evaporation in step 1 uses titanium / gold metal, first using 20nm thick titanium as a buffer layer, and then 80nm thick gold is adhered to the titanium buffer layer.

9. The method for preparing a terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 7, characterized in that: The concentration of the MAPbI3 solution in step 2 is 1 mol / L. The preparation method of the MAPbI3 solution includes: weighing 159 mg of MAI powder and 461 mg of PbI2 powder into an empty solution bottle, and injecting 1 mL of DNF solution into the solution bottle containing the powder with a pipette to obtain a MAPbI3 solution.

10. The method for preparing a terahertz modulator based on optically modulated phonon plasma resonance splitting according to claim 7, characterized in that: The temperature of the heating platform in step 2 is 90° C., and the annealing is performed for 10 minutes.

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