Non-reciprocal electromagnetic wave transmission structure based on photo-excited graphene and transmission method thereof

Abstract

The application discloses an electromagnetic wave non-reciprocal transmission structure based on light-excited graphene and a transmission method thereof. The structure is composed of silicon rods with different widths placed on a silicon / silicon dioxide substrate, and large-area CVD graphene is transferred to the structure to form a graphene super surface structure. Due to the asymmetry of the structure and the excitation of the nonlinear Kerr effect, the transmission efficiency of electromagnetic waves is significantly related to the incident direction of signal light. By optimizing the structure parameters, the light-excited graphene super surface structure based on the light-excited graphene super surface structure shows a large positive and negative transmission ratio. The device structure is simple and compact, the required incident laser intensity is only 80kW / cm 2 , and is relatively easy to realize in experiments. By utilizing the optical adjustable function of graphene, the working frequency band of the non-reciprocal device can be effectively controlled, thereby flexibly realizing the optical isolation function.

Description

Technical Field

[0001] This invention belongs to the field of non-reciprocal electromagnetic wave technology, and particularly relates to the application of photoexcited graphene, specifically to a non-reciprocal electromagnetic wave transmission structure and transmission method based on photoexcited graphene. Background Technology

[0002] Realizing non-reciprocal optical transport is not only significant for fundamental scientific research but also plays an indispensable role in practical photonic applications, such as isolators, circulators, and directional amplifiers. Traditional methods generally utilize the Faraday rotation effect of magneto-optical crystals to break the Lorentz reciprocity theorem and achieve non-reciprocal transport. However, this method requires large magnets and high external magnetic fields, limiting the application of non-reciprocal devices in miniaturized and integrated systems. Another representative type of non-reciprocal device is realized through spatiotemporal dynamic modulation theory. This method does not require an external bias signal but demands sufficiently fast time modulation speeds, which presents experimental challenges. Another commonly used method utilizes the nonlinear response of materials, but this requires high laser incident intensity for excitation, breaking the Lorentz reciprocity theorem of the system.

[0003] Graphene, with its atomically thin honeycomb lattice structure, possesses unique charge carrier properties and excellent electrical performance. The conductivity of graphene can be dynamically tuned through electrostatic doping, enabling flexible design of graphene-based metasurface structures and the realization of various functional devices, including polarizers, invisibility cloaks, phase shifters, optical modulators, and absorbers. However, due to its single-atom thickness, graphene's light absorption is very weak, reducing the functional efficiency of graphene-based devices. Therefore, combining graphene with plasma structures to achieve graphene metasurface structures can effectively improve device power. Furthermore, sufficiently high laser intensity can induce a photoexcited graphene state, resulting in population inversion, where the emitted light power exceeds the absorbed light power, leading to increased optical gain.

[0004] This invention offers significant advantages in achieving optical non-reciprocity using photo-excited graphene. The design of the graphene metasurface structure eliminates the need for an external magnetic field. Due to the asymmetry of the structure and the excitation of the Kerr nonlinear effect, the electromagnetic wave transmission efficiency depends on the incident direction. By utilizing the adjustable conductivity of graphene, the operating wavelength of the structure can be dynamically controlled, achieving flexible tunability of the non-reciprocal device. Because of the use of photo-excited graphene, while maintaining zero reverse transmission efficiency, the forward transmittance can be significantly increased by enhancing the incident light intensity, achieving a high forward-to-reverse transmission ratio. Summary of the Invention

[0005] To overcome the above shortcomings and deficiencies, the present invention aims to provide a structure and method for realizing non-reciprocal transmission of electromagnetic waves based on photoexcited graphene, which can operate in the near-infrared band and achieve a high forward and reverse transmission ratio.

[0006] This invention is achieved through the following scheme:

[0007] The non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene includes a large-area graphene monolayer, an asymmetric silicon rod array, and a silicon / silicon dioxide substrate; the silicon rod array is an asymmetric design; the graphene is photoexcited graphene, which can be forged into a nanoscale controllable 3D shape by a pulsed laser beam, based on photoexcitation-induced local expansion of graphene.

[0008] The aforementioned non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene uses graphene in a novel photo-excited graphene state characterized by broadband electron population inversion, which can generate optical gain.

[0009] The non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene is theoretically based on the asymmetry of the structure and the excitation of the nonlinear Kerr effect of the material.

[0010] The aforementioned non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene exhibits the same forward and reverse transmission in a linear system, but different forward and reverse transmission in a nonlinear system.

[0011] The non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene has a refractive index of 3.5 for the silicon rod and silicon substrate, and a refractive index of 1.44 for silicon dioxide.

[0012] The non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene has a quasi-Fermi level of 50 meV.

[0013] The aforementioned non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene operates in the near-infrared band.

[0014] The non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene has a silicon rod thickness of t = 1.5 μm and a length of l = 8.5 μm. Because the silicon rod array is an asymmetric design, two adjacent silicon rods have different widths, w1 = 1.2 μm and w2 = 1.8 μm, respectively. The distance between the silicon rods is d = 2 μm, and the array period is p = 9 μm.

[0015] The aforementioned non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene has an incident laser intensity of I0 = 80 kW / cm². 2At that time, the forward transmittance was 1 and the reverse transmittance was only 0.01, achieving effective non-reciprocal transmission.

[0016] This invention also provides a method for transmitting non-reciprocal electromagnetic waves based on photoexcited graphene. This method is based on the above-mentioned non-reciprocal electromagnetic wave transmission structure and includes two steps: Step 1, performing an asymmetric design on the silicon rod array, finely adjusting the size and spacing of the silicon rods, determining the operating wavelength range of the structure, and operating in the near-infrared band; Step 2, introducing photoexcited graphene, optimizing the structural parameters to achieve the strongest non-reciprocal response.

[0017] Compared with existing technologies, the present invention has the following advantages: First, the present invention utilizes the asymmetry of the graphene metasurface structure and the nonlinear Kerr effect of the material to achieve non-reciprocal transmission of electromagnetic waves, requiring a relatively low laser intensity of only 80 kW / cm². 2 Firstly, it is easy to meet the experimental requirements; secondly, this invention effectively utilizes the optical gain effect of photoexcited graphene. While ensuring that the reverse transmittance is 0, the optical gain can significantly improve the efficiency of electromagnetic wave forward transmission, resulting in a large forward and reverse transmission ratio based on the photoexcited graphene structure. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a structure for achieving non-reciprocal electromagnetic wave transmission based on photoexcited graphene.

[0019] Figure 2 The graph shows the transmission spectra achievable by non-photoexcited graphene structures under linear and nonlinear conditions. In linear systems, the forward and reverse transmission are the same, as shown by the black line in the figure; in nonlinear systems, the forward and reverse transmission are different, as shown by the red and blue lines in the figure.

[0020] Figure 3 The transmission, reflection, and absorption spectra of photoexcited graphene metasurface structures under linear conditions.

[0021] Figure 4 In a nonlinear system, the laser intensity is 80 kW / cm². 2 At that time, the present invention is based on the highest forward and reverse transmittance that can be achieved by photoexcited graphene structure. Detailed Implementation

[0022] The invention will now be explained and described in further detail with reference to the accompanying drawings. However, the drawings are merely schematic diagrams of idealized embodiments of the invention, intended to clearly illustrate the physical structure of the device. As schematic diagrams, they should not be considered as strictly reflecting proportional geometric dimensions. Furthermore, the embodiments shown in the drawings should not be considered limited to the specific shapes of the areas depicted. In short, the drawings are illustrative and should not be considered as limiting the scope of the invention.

[0023] The technical solution of the present invention will be described in detail below with reference to several preferred embodiments and related drawings:

[0024] The structure for non-reciprocal electromagnetic wave propagation based on photoexcited graphene described in this invention is as follows: Figure 1 As shown, from top to bottom, it includes a single layer of large-area CVD graphene, a silicon rod array, and a silicon / silica substrate. The refractive index of the silicon rods and the silicon substrate is 3.5; the refractive index of the silicon dioxide is 1.44.

[0025] Achieving optical non-reciprocity based on photo-excited graphene involves two steps: Step one, optimizing the structure using non-photo-excited graphene. An asymmetric design is employed for the silicon rod array, with fine-tuning of the rod size and spacing. In a linear system, the structure exhibits identical forward and reverse transmission. Figure 2 As shown by the black line; in a nonlinear system, the forward and reverse transmissions of the structure are different, due to... Figure 2 As shown by the red and blue lines in the diagram.

[0026] Step two: Introduce photoexcited graphene. Figure 3 The transmission, reflection, and absorption spectra of photoexcited graphene metasurface structures under linear conditions are shown. Further structural optimization and tuning of the Fermi level of graphene are employed to maximize transmittance. Considering the nonlinear response of the material, a high forward and reverse transmittance ratio is obtained, such as... Figure 4 As shown, the required laser intensity is only 80 kW / cm². 2 hour.

[0027] The operating wavelength of this invention is in the near-infrared band, and is composed of... Figure 2 , Figure 3 and Figure 4 As can be seen.

[0028] The optimized non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene has the following dimensions for the silicon rod array: the thickness of the silicon rod is t = 1.5 μm, the length is l = 8.5 μm, the silicon rod array is an asymmetric design, so two adjacent silicon rods have different widths, w1 = 1.2 μm and w2 = 1.8 μm respectively, the distance between the silicon rods is d = 2 μm, and the array period is p = 9 μm.

[0029] The optimized Fermi level of graphene is E F =50meV.

[0030] This invention is based on a non-reciprocal electromagnetic wave transmission structure of photoexcited graphene, which can achieve a laser intensity of only 80 kW / cm². 2 It can achieve a high forward and reverse transmittance ratio, with a forward transmittance of 1 and a reverse transmittance of only 0.01, thus achieving effective non-reciprocal transmission.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A non-reciprocal electromagnetic wave transmission structure based on photoexcited graphene, characterized in that, Operating in the near-infrared band, this non-reciprocal electromagnetic wave transmission structure comprises, from top to bottom, a single-layer large-area CVD graphene, a silicon rod array, and a silicon / silicon dioxide substrate; the silicon rod array is an asymmetric design, and the graphene is photoexcited graphene; the graphene is in a new photoexcited graphene state characterized by broadband electron population inversion. In a linear system, the forward and reverse transmissions of the non-reciprocal electromagnetic wave transmission structure are the same; in a nonlinear system, the forward and reverse transmissions of the non-reciprocal electromagnetic wave transmission structure are different. The refractive index of the silicon rod and silicon substrate is 3.5; the refractive index of silicon dioxide is 1.

44. The quasi-Fermi level of the photo-induced graphene is 50 meV; The silicon rods in the array have a thickness of t = 1.5 μm and a length of l = 8.5 μm. Two adjacent silicon rods have different widths, w1 = 1.2 μm and w2 = 1.8 μm, respectively. The distance between the silicon rods is d = 2 μm. The array period is p=9um; The incident laser intensity is I0 = 80 kW / cm 2 At this time, the forward transmittance is 1 and the reverse transmittance is 0.01, achieving effective non-reciprocal transmission.

2. A method for transmitting non-reciprocal electromagnetic waves based on photoexcited graphene, characterized in that, The transmission method is based on the non-reciprocal electromagnetic wave transmission structure described in claim 1, and includes two steps: Step 1, the silicon rod array is designed asymmetrically, and the size and spacing of the silicon rods are finely adjusted to determine the operating wavelength range of the structure; Step 2, photo-excited graphene is introduced to optimize the structural parameters so that the achieved non-reciprocal response is the strongest.

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