A terahertz wave mixed mode waveguide structure based on three-dimensional dirac semimetal elliptical fiber

Abstract

The application relates to a terahertz hybrid mode waveguide structure based on an elliptical fiber of three-dimensional Dirac semimetal, which comprises a silicon medium bottom layer (1), a sample groove (2), an elliptical three-dimensional Dirac semimetal fiber (4) and a back electrode doped silicon layer (6); the sample groove (2) is located above the silicon medium bottom layer (1), the elliptical three-dimensional Dirac semimetal fiber (4) is located above the sample groove (2), and the back electrode doped silicon layer (6) is located on the side of the elliptical three-dimensional Dirac semimetal fiber (4). Compared with the prior art, the hybrid mode waveguide has the comprehensive advantages of large modulation depth and low loss. By changing the medium of the sample groove, the modulation depth of the propagation length can reach 69%. By adjusting the Fermi level (0.05-0.15eV) of the three-dimensional Dirac semimetal, the propagation length can reach 1.10*10 5 μm, the normalized mode area can reach 3.09*10 ‑3 , the optimization factor can exceed 5.0*10 3 , and the modulation depth of the propagation length can exceed 90%.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic materials and devices, specifically to a terahertz wave hybrid mode waveguide structure based on three-dimensional Dirac semimetallic elliptical fibers. Background Technology

[0002] Terahertz (THz, 1 THz = 10⁻⁶) 12 Terahertz waves (THz) refer to electromagnetic waves with frequencies between 0.1 and 10 THz and wavelengths between 0.03 and 3 mm, falling between millimeter waves and infrared light. Due to their superior characteristics such as low photon energy (1 THz = 4.1 meV), ultra-high transmission capacity, and strong penetration, THz waves have unique advantages and broad application prospects in fields such as secure wireless communication, biological sample detection, imaging, and material spectral analysis. For example, THz waves can provide data transmission rates of 10 Gbps for ultrafast future wireless communication systems, twice the current communication speed, thus providing a huge bandwidth for increasing data capacity. To advance the application and development of THz technology, higher requirements are placed on waveguide technology, necessitating effective manipulation of THz waves, which is currently one of the research hotspots and core research contents of THz technology. The lack of suitable waveguide transmission technologies and functional devices is a major reason restricting the further development of THz wave technology. Common waveguide transmission methods mainly include fiber optic waveguides, surface plasmon polariton waveguides, and photonic crystal waveguides.

[0003] Surface plasmons (SPs) are surface electromagnetic waves generated by the interaction of incident electromagnetic waves with free electrons on a metal surface, occurring at the interface of two media with opposite dielectric constants. SPs have attracted widespread attention due to their ability to overcome the diffraction limit. Common SP waveguides include metal wire, metal-dielectric-metal, dielectric-metal-dielectric, and metal V-groove waveguides. Traditional SP waveguides suffer from high losses, reducing the quality factor and propagation distance of the propagation modes, significantly limiting the development of functional devices. Hybrid-mode waveguides combine the advantages of SPs and dielectric fiber waveguides. Their principle utilizes the continuity of electric vectors at high- and low-dielectric-constant dielectric interfaces and the surface plasmon effect at the metal (semiconductor-dielectric interface) to form a "hybrid mode." This waveguide structure exhibits strong mode localization capabilities, low transmission loss, strong anti-interference capabilities, and is easier for chip integration and mass production.

[0004] Three-dimensional Dirac half-metals, a novel type of quantum material, can be considered as "three-dimensional graphene" due to the contact between their conduction and valence bands at the Dirac point and their linear dispersion relation in three-dimensional momentum space. Examples include quasicrystals such as Na3Bi, Cd3As2, and AlCuFe. The crystal symmetry protection results in ultra-high carrier mobility, reaching 9 × 10⁻⁶ at 5 K. 6 cm 2 V -1 s -1 It exhibits low inherent loss. Three-dimensional Dirac half-metals, as photosensitive materials, can demonstrate excellent optical properties and, as a bulk material, can interact more strongly with light to enhance responsiveness. More importantly, the dielectric properties of three-dimensional Dirac half-metals can be dynamically tuned by changing their Fermi level, making them a preferred control material for high-performance hybrid surface plasmon waveguides.

[0005] In 2020, H. Xiong et al. demonstrated a THz metamaterial absorber based on a three-dimensional Dirac semimetal and strontium titanate using electrical and temperature control methods. By adjusting the Fermi level of the three-dimensional Dirac semimetal pattern from 10 meV to 80 meV, the peak absorption rate could be continuously tuned from 70% to 99.9%, and the absorption frequency point could be shifted from 3.26 THz to 4.82 THz. The absorption peak could be dynamically controlled between 2.66 THz and 3.69 THz by varying the temperature of the strontium titanate metamaterial between 200 K and 300 K.

[0006] Regarding patent applications, patent CN106772733A disclosed in 2017 a three-dimensional Dirac semi-metallic diffraction grating. This grating operates in the infrared region covering wavelengths of 2-6 μm. By precisely controlling the growth time, rate, and temperature of the material, the thickness of the functional layer of this diffraction grating is designed and adjusted, thereby obtaining an infrared optical switching device with a modulation depth adjustable in the range of 0.5-50%. Patent CN108063364A disclosed in 2018 a semiconductor external cavity mode-locked laser based on cadmium arsenide saturable absorber material, which can directly achieve ultrafast, highly stable, and wavelength-tunable mode-locked pulse output in the mid-infrared band. Although there is some research on three-dimensional Dirac devices both domestically and internationally, it mainly focuses on mid-infrared lasers and converters, with a lack of research on terahertz tunable device design. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a terahertz hybrid mode waveguide structure based on three-dimensional Dirac semimetal elliptical fibers with large modulation depth, low loss and strong confinement capability.

[0008] This invention achieves effective modulation of incident THz waves by altering the Fermi level of a three-dimensional Dirac half-metal through the magnitude of a bias voltage. This objective can be achieved through the following technical solution:

[0009] A terahertz hybrid mode waveguide structure based on a three-dimensional Dirac semimetal elliptical fiber, the structure comprising a silicon dielectric substrate, a sample groove, an elliptical three-dimensional Dirac semimetal fiber, and a silicon-doped back electrode layer.

[0010] The sample cell is located above the silicon dielectric substrate, the elliptical three-dimensional Dirac semimetal fiber is located above the sample cell, and the back electrode doped silicon layer is located to the side of the elliptical three-dimensional Dirac semimetal fiber.

[0011] The propagation length of this invention can reach 1.16 × 10⁻⁶. 5 μm, corresponding normalized mode area A m / A0 is 3.09×10 -3 Breaking the diffraction limit area (A0=λ) 2 The optimization factor can reach 5.29×10⁻⁴, which is 323 times that of / 4). 3 The modulation depth of the propagation length exceeds 90%.

[0012] Furthermore, a polyethylene medium layer is provided on both sides of the sample tank.

[0013] Furthermore, the sample cell is made of polyethylene, TNT, or HMX. The thickness ratio of the sample cell and the polyethylene dielectric layer to the thickness of the silicon dielectric substrate is (0.1-20):20.

[0014] Furthermore, a silicon dioxide insulating layer is provided between the elliptical three-dimensional Dirac semimetal fiber and the back electrode doped silicon layer.

[0015] Furthermore, the silicon dielectric substrate is made of intrinsic silicon.

[0016] Furthermore, the elliptical three-dimensional Dirac semi-metallic fiber is made of cadmium arsenide (Cd3As2).

[0017] Furthermore, the back electrode doped silicon layer has a carrier doping concentration of (0.8-1.2)×10⁻⁶. 15 cm -3 n-type doped silicon materials.

[0018] Furthermore, the ellipticity ratio a of the elliptical three-dimensional Dirac semimetallic fiber is... x / a y The range is 1-10.24.

[0019] Furthermore, the ellipticity ratio a of the elliptical three-dimensional Dirac semimetallic fiber is... x / ay It ranges from 2.56 to 6.25.

[0020] In other words, the semi-major axis of the three-dimensional Dirac semi-metallic elliptical fiber along the x-direction is 16-64 μm, preferably 45-50 μm. The semi-major axis of the three-dimensional Dirac semi-metallic elliptical fiber along the y-direction is 6.25-25 μm, preferably 6-8 μm.

[0021] The minor axis of the three-dimensional Dirac semimetallic elliptical fiber is parallel to the polarization direction of the incident wave: compared to circular fibers (a x / a y =1), with the elliptic ratio (a x / a y As the amplitude of α increases, more mixed modes are confined to the sample slot, resulting in reduced loss of the mixed waveguide modes and increased propagation length. For example, at 1 THz, α x / a y As the value increases from 1 to 6.25, the propagation length increases from 9.58 × 10⁻⁶. 3 μm changed to 1.52×10 4 μm, the corresponding optimization factor changes from 562 to 832. However, when a x / a y Too large, that is, a y When the size is too small, the elliptical fiber along the y-direction cannot provide good pattern constraints, leading to an increase in the normalized pattern area and a decrease in the optimization factor. x / a y =6.25(a) x =50μm,a y =8μm) is the optimal elliptic ratio.

[0022] Furthermore, the structure also includes an electronic control unit for tuning the Fermi level of the elliptical three-dimensional Dirac semimetal fiber. This electronic control unit is connected between the back electrode doped silicon layer and the elliptical three-dimensional Dirac semimetal fiber. The Fermi level varies from 0.05 to 0.10 eV, and the modulation depth of the propagation length and optimization factor can exceed 90%.

[0023] Compared to circular fibers, this invention utilizes elliptical fibers, which achieve lower losses and stronger mode confinement. By altering the Fermi level (0.05-0.15 eV) of the three-dimensional Dirac half-metal through a bias voltage, effective modulation of THz waves is achieved, with propagation lengths increasing from 6.28 × 10⁻⁶ eV. 3 μm changed to 1.16×10 5 μm, with a corresponding modulation depth exceeding 90% for the propagation length.

[0024] This invention uses a three-dimensional Dirac half-metal instead of a metal to support surface plasmon resonances. A hybrid-mode waveguide composed of a three-dimensional Dirac half-metal elliptical fiber-sample groove-silicon dielectric substrate achieves strong mode confinement while maintaining a considerably long propagation length. Electrical control of the waveguide is achieved by adjusting the bias voltage across the three-dimensional Dirac half-metal. The maximum propagation length reaches 1.16 × 10⁻⁶ eV when the Fermi level varies from 0.05 to 0.15 eV. 5 The modulation depth of the propagation length exceeds 90% at μm. The three-dimensional Dirac semi-metallic hybrid mode structure proposed in this invention can be used to develop various terahertz wave functional devices, such as lasers, modulators, and resonators.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) This invention utilizes a hybrid-mode plasmon waveguide composed of a three-dimensional Dirac semimetallic elliptical fiber-sample slot-silicon dielectric structure, which exhibits strong mode confinement and a considerably long propagation length in the terahertz band. The maximum propagation length can reach 1.16 × 10⁻⁶. 5 μm, corresponding normalized mode area A m / A0 reached 3.09×10 -3 It can break through the diffraction limit area (A0=λ) 2 323 times that of / 4);

[0027] (2) This invention is based on a three-dimensional Dirac semimetal elliptical fiber tunable hybrid-mode waveguide for terahertz waves. The Fermi level of the three-dimensional Dirac semimetal can be changed by bias voltage, thereby achieving effective control of THz waves. When the Fermi level varies from 0.05 to 0.15 eV, the propagation length increases from 6.28 × 10⁻⁶ eV. 3 μm changed to 1.16×10 5 μm, with a corresponding modulation depth exceeding 90% for the propagation length. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the waveguide structure in Example 1;

[0029] Figure 2 For the waveguide structure in Example 1, different elliptic ratios a x / a y The following diagram illustrates the situation;

[0030] Figure 3 The diagram shows the waveguide structure in Example 1 with different dielectric gap thicknesses.

[0031] Figure 4 The diagram shows the waveguide structure in Example 1 as it changes with different samples at different operating frequencies.

[0032] The numbers in the figure indicate: 1. Silicon dielectric substrate; 2. Sample cell; 3. Polyethylene dielectric layer; 4. Elliptical three-dimensional Dirac semi-metallic fiber; 5. Silicon dioxide insulating layer; 6. Back electrode doped silicon layer. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] Example 1

[0035] A terahertz hybrid-mode waveguide structure based on a three-dimensional Dirac semimetal elliptical fiber includes: a silicon dielectric substrate 1; a sample groove 2 located at the center of the surface of the silicon dielectric substrate 1; a polyethylene dielectric layer 3 located above the silicon dielectric substrate 1 and on both sides of the sample groove 2; an elliptical three-dimensional Dirac semimetal fiber 4 grown above the sample groove 2; a silicon dioxide insulating layer 5 grown on the left side of the three-dimensional Dirac semimetal elliptical fiber 4 and above the polyethylene dielectric layer 3; and a back electrode doped silicon layer 6 grown above the polyethylene dielectric layer 3 and on the left side of the silicon dioxide insulating layer 5. The hybrid-mode waveguide also includes an electrical control unit for tuning the Fermi level of the three-dimensional Dirac semimetal fiber. The thickness of the silicon dielectric substrate 1 is 20 μm. The cross-sectional area of ​​the three-dimensional Dirac semimetal elliptical fiber 4 is fixed at 400 μm. 2 The silicon dioxide insulating layer 5 has a thickness of 100 nm. Sample cell 2 is a dielectric. The back electrode doped silicon layer 6 has a thickness of 2 μm and a carrier doping concentration of 1 × 10⁻⁶. 15 cm -3 The research design method is as follows:

[0036] 1. The radio frequency module of COMSOL Multiphysics software was used for the study, and the partial differential equations were solved based on the finite element method. The steps were: model building, material setting, mesh generation, and study. For thinner directions, the mesh size along the minor axis (y-axis) of the elliptical fiber was smaller, less than 0.02 wavelengths. Figure 1 The diagram shows the 3D structure of the hybrid mode waveguide (a) and the variation of the electric field intensity y component along the y-axis (b).

[0037] 2. The influence of the shape of the three-dimensional Dirac semimetallic fiber on waveguide performance. As the ellipticity ratio (a) increases... x / a y As the a value increases, the loss of this hybrid waveguide mode decreases, and the propagation length increases. At 1 THz, a x / a y The propagation length increased from 8.91 × 10⁻⁵ as the value increased from 0.64 to 6.25. 3 μm changed to 1.52×10 4μm, the diffraction limit area was increased from 61 times to 67 times, and the optimization factor changed from 465 to 832. Figure 2 For hybrid mode waveguides with different three-dimensional Dirac semimetal elliptic ratios (a x / a y The real part (a), propagation length (b), normalized mode area (c), and optimization factor (d) of the effective mode index under ) are compared with those of three-dimensional Dirac semimetal circular fibers (a) x / a y =1), three-dimensional Dirac semimetallic elliptical fiber (a x / a y >1) Shows lower losses and stronger mode limitations.

[0038] 3. The effect of the sample cell medium on waveguide performance. As the sample refractive index increases, the loss decreases and the propagation length increases. At 0.3 THz, the propagation length increases from 4.07 × 10⁻⁶. 3 μm changed to 1.34×10 4 μm, the optimization factor changed from 155 to 617, the propagation length and the modulation depth of the optimization factor were 69.63% and 74.87%, respectively. Figure 4 The real part (a), propagation length (b), normalized mode area (c), and optimization factor (d) of the effective mode exponent at different operating frequencies are given for the hybrid-mode waveguide under different samples. At 0.3 THz, the propagation length increases from 4.07 × 10⁻⁶. 3 μm changed to 1.34×10 4 μm, corresponding to a modulation depth of 69.63%.

[0039] 4. By adding an electronic control unit—that is, by applying a bias voltage to the three-dimensional Dirac elliptical fiber, with the positive terminal connected to the three-dimensional Dirac semimetal elliptical fiber and the negative terminal connected to the doped silicon layer—the Fermi level can be modulated. By changing the bias voltage across the three-dimensional Dirac semimetal, its Fermi level (0.05-0.15 eV) is altered, thereby changing its photoelectric properties and ultimately achieving modulation of the THz wave, increasing the propagation length from 6.28 × 10⁻⁶ eV. 3 μm changed to 1.16×10 5 μm, optimization factor from 2.83×10 2 It changed to 5.29×10 3 The propagation length and the modulation depth of the optimization factor both exceed 90%. Figure 3 The real part (a), propagation length (b), normalized mode area (c), and optimization factor (d) of the effective mode exponent for a hybrid-mode waveguide in different three-dimensional Dirac half-metals are given by varying dielectric gap thickness. I represents the near-field region, and II represents the dissipation region. The critical thickness of the near-field region decreases with increasing Fermi level.

[0040] 5. Based on the three-dimensional Dirac semimetal elliptical fiber terahertz wave tunable hybrid mode waveguide, this hybrid mode waveguide structure can be fabricated by methods such as molecular beam growth, thermal evaporation, chemical vapor deposition and ultraviolet lithography, on the basis of existing semiconductor process technology.

[0041] In summary, the hybrid-mode waveguide of this invention possesses the combined advantages of large modulation depth and low loss. By changing the medium of the sample slot, the modulation depth of the propagation length can reach 69%. By adjusting the Fermi level (0.05-0.15 eV) of the three-dimensional Dirac half-metal, the propagation length can reach 1.10 × 10⁻⁶ eV. 5 μm, the normalized model area can reach 3.09 × 10 μm. -3 The optimization factor can exceed 5.0 × 10⁻⁶. 3 The modulation depth of the propagation length can exceed 90%.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A terahertz wave hybrid mode waveguide structure based on three-dimensional Dirac semimetallic elliptical fibers, characterized in that, The structure includes a silicon dielectric substrate (1), a sample groove (2), an elliptical three-dimensional Dirac semimetal fiber (4), a back electrode doped silicon layer (6), and an electrical control unit; The sample groove (2) is located above the silicon dielectric bottom layer (1), the elliptical three-dimensional Dirac semi-metallic fiber (4) is located above the sample groove (2), and the back electrode doped silicon layer (6) is located to the side of the elliptical three-dimensional Dirac semi-metallic fiber (4). The material of the sample in the sample cell (2) includes air, polyethylene, TNT or HMX; The electronic control unit is connected between the back electrode doped silicon layer (6) and the elliptical three-dimensional Dirac semimetal fiber (4) to regulate the Fermi level of the elliptical three-dimensional Dirac semimetal fiber (4); The silicon dielectric substrate (1) is made of intrinsic silicon; the elliptical three-dimensional Dirac semimetal fiber (4) is made of cadmium arsenide; the ellipticity ratio of the elliptical three-dimensional Dirac semimetal fiber (4) is a x / a y The value is 2.56-6.25; Wherein, y-direction: perpendicular to the silicon dielectric substrate upwards; x-direction: the horizontal direction within the waveguide cross-section, perpendicular to the y-direction; z-direction: perpendicular to the xy-plane, according to the right-hand coordinate system. Parallel to the length direction of the elliptical three-dimensional Dirac semimetallic fiber (4); a x : The semi-major axis of the ellipse along the x-direction; a y : The semi-major axis of the ellipse along the y-direction.

2. The terahertz wave hybrid mode waveguide structure based on three-dimensional Dirac semimetallic elliptical fibers according to claim 1, characterized in that, The sample tank (2) is also provided with polyethylene medium layers (3) on both sides.

3. The terahertz wave hybrid mode waveguide structure based on three-dimensional Dirac semimetallic elliptical fibers according to claim 1, characterized in that, A silicon dioxide insulating layer (5) is provided between the elliptical three-dimensional Dirac semi-metallic fiber (4) and the back electrode doped silicon layer (6).

4. The terahertz wave hybrid mode waveguide structure based on three-dimensional Dirac semimetallic elliptical fibers according to claim 1, characterized in that, The back electrode doped silicon layer (6) has a carrier doping concentration of (0.8-1.2)×10⁻⁶. 15 cm -3 n-type doped silicon materials.

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