An optical non-reciprocal device based on graphene supersurface

Abstract

The application discloses an optical non-reciprocal device based on a graphene super surface, which is formed by splicing a plurality of unit structures, and the unit structure comprises single-layer graphene and a silicon super surface with asymmetric grooves on both sides. Due to the asymmetry of the structure, the structure itself can realize a non-reciprocal response of 76.05% in a reflection mode, and the non-reciprocal amplitude can reach 83.67% by considering the nonlinear effect of the material. The working wavelength of the structure can be controlled by changing the Fermi level of the graphene and the structure parameters, so that the dynamic adjustable characteristics of the device are realized. The device structure is simple, easy to realize in experiments, completely passive and low in operation power. The device based on the graphene super surface designed by the application can be applied to various fields such as optical isolation, excitation, modulation, sensing and detection, and plays an important role in the development of new photoelectric technology.

Description

Technical Field

[0001] This invention belongs to the field of optical non-reciprocity, specifically relating to an optical non-reciprocal device based on a graphene metasurface. Background Technology

[0002] Graphene's superior optical and electrical properties give it a unique advantage in applications such as tunable perfect absorbers, isolators, and filters. The Fermi level of graphene can be controlled using an applied voltage, and changes in the Fermi level alter its conductivity and loss characteristics. Therefore, by introducing graphene, more flexible and tunable devices operating at terahertz frequencies can be realized.

[0003] Reciprocity is a fundamental physical principle in fields such as electromagnetism, optics, and acoustics, stemming from time-reversal symmetry. According to the Lorentz reciprocity theorem, in a typical optical system, the received optical signal remains unchanged after exchanging the positions of the signal source and detector. In all-optical communication and quantum networks, it is necessary to effectively control the directional transmission of optical signals to avoid interference from reflected light and to separate opposing optical signals. Therefore, non-reciprocal devices that only allow unidirectional light transmission are required. There are three main methods to achieve non-reciprocity: using magneto-optical materials to break the Lorentz reciprocity theorem; temporally controlling the linear or angular momentum of waves propagating into the system to break the Lorentz reciprocity theorem; and using nonlinear materials to break the Lorentz reciprocity theorem. However, these methods all have some drawbacks that affect their applications. For example, magneto-optical materials require an external strong magnetic field, making it difficult to achieve small-scale integrated applications; temporal control requires dynamic modulation of the dielectric constant at different locations, which is difficult to achieve with ordinary switches or varactors due to their inability to achieve the required high modulation frequencies. The structure proposed in this invention utilizes graphene and silicon, two Kerr nonlinear materials, to achieve non-reciprocity. It possesses advantages such as being completely passive, requiring no bias, and easily achieving miniaturized integration. The structure designed in this invention is simple and easily implemented experimentally. Summary of the Invention

[0004] To address the challenges of existing technologies, this invention proposes an optical non-reciprocal device based on a graphene metasurface.

[0005] The technical solution adopted in this invention is as follows:

[0006] An optical non-reciprocal device based on a graphene metasurface is formed by periodically splicing together several sets of unit structures. Each unit structure includes a single layer of graphene and a silicon metasurface. The silicon metasurface has periodically arranged grooves of the same width but different depths on both the top and bottom sides, and the grooves are symmetrical on both sides. The single layer of graphene covers the silicon metasurface.

[0007] Preferably, the silicon metasurface is made of polycrystalline silicon with a refractive index of 3.4, a height of 100 nm, and a third-order nonlinear magnetic susceptibility of 2.8 × 10⁻⁶.-18 m 2 / V 2 .

[0008] Preferably, the graphene is coated on one side of the silicon metasurface to enhance the asymmetry of the structure.

[0009] Preferably, the groove has a depth of 3-7 nm on the side closest to the graphene, a depth of 18-22 nm on the other side, a width of 40 nm, and a period of 520 nm.

[0010] Preferably, the device operates in the near-infrared band and its dimensions are all smaller than the wavelength of light in the operating band.

[0011] Preferably, the present invention can achieve dynamically adjustable characteristics of the device by adjusting the operating wavelength of the structure by changing the Fermi level and groove structure parameters of the graphene in the optical non-reciprocal device.

[0012] Preferably, different non-reciprocal responses can be achieved by adjusting the intensity of the incident light.

[0013] Preferably, the device has a graphene Fermi level of 0.7 eV and an input light intensity of 70 kW / cm². 2 The best working effect is achieved at this time.

[0014] Compared with the prior art, the advantages of the present invention are: a large non-reciprocity can be achieved without external bias, and a reflection non-reciprocity amplitude of 83.67% can be achieved using 0.7 eV graphene; it is completely passive and easy to achieve small-scale integration; it has a simple structure and is easy to implement experimentally; and the non-reciprocity intensity can be dynamically tunable by adjusting the Fermi level of graphene. Attached Figure Description

[0015] Figure 1 These are schematic diagrams of the two-dimensional (a) and three-dimensional (b) structures of the optical non-reciprocal device based on graphene / silicon metasurface of this invention.

[0016] Figure 2 These are the reflection spectra of graphene metasurfaces under linear and nonlinear conditions.

[0017] Figure 3 a represents the graphene / silicon metasurface under input light intensities of 20, 70, and 120 kW / cm². 2 The reflection coefficients of the two ports are a function of the wavelength; Figure 3 b represents the input light intensity at a wavelength of 1.1626 μm, ranging from 0.1 to 200 kW / cm². 2 The reflection coefficients of the two ports within the range.

[0018] Figure 4'a' is the reflection coefficient of the two ports with graphene side groove depths of 7nm, 5nm, and 3nm as a function of wavelength. Figure 4 b is the reflection coefficient of the two ports on the other side with groove depths of 22nm, 20nm, and 18nm as a function of wavelength.

[0019] Figure 5 The variation of the non-reciprocal amplitude of reflection and the corresponding wavelength for different Fermi levels and maximum achievable values ​​in graphene. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0021] Figure 1 (a) and (b) are two-dimensional and three-dimensional schematic diagrams of a nonlinear metasurface based on a single layer of graphene integrated on a silicon metasurface, respectively.

[0022] The optical non-reciprocal device is formed by periodically splicing together several sets of unit structures. Each unit structure includes a single layer of graphene and a silicon metasurface. The operating wavelength is in the near-infrared band. The silicon metasurface has periodically arranged grooves of the same width but different depths on both sides, and the grooves are symmetrically positioned on both sides. The single layer of graphene covers the silicon metasurface. The side covered by the single layer of graphene is designated as port 1, and the other side is designated as port 2.

[0023] In this embodiment, the silicon height t = 100 nm is set, and periodic rectangular grooves are etched on the top and bottom sides of the silicon. The groove width w = 40 nm, the groove depth h1 on the port 1 side = 3 ~ 7 nm, the groove depth h2 on the port 2 side = 18 ~ 22 nm, and the period p = 520 nm; the refractive index of silicon is 3.4.

[0024] In the simulation calculations of the structure, since the length along the extension direction of the groove is arbitrary, a 2D model can be established to simulate the real structure. The incident light conditions at the port are used to excite the graphene structure. The reflection spectra of the graphene / silicon metasurface were fabricated under both linear and nonlinear conditions, and their curves are shown below. Figure 2 As shown.

[0025] By optimizing the structural parameters, the reflection coefficient of port 1 at the resonant wavelength reaches its maximum value (peak value) and the reflection coefficient of port 2 at the resonant wavelength reaches its minimum value (valley value) in a linear system.

[0026] Considering the nonlinear response of the material, the reflection spectra of ports 1 and 2 will exhibit a frequency shift. Theoretically, because the increase in electric field intensity at the resonant wavelength is smaller at port 1, the improvement in the effective dielectric constant of the structure is not significant, resulting in a smaller frequency shift; while the increase in electric field intensity at the resonant wavelength is larger at port 2, resulting in a significant frequency shift. By adjusting the intensity of the incident light, the difference in reflection coefficients at the resonant wavelength of the two ports can be maximized, i.e., the non-reciprocal response is strongest.

[0027] By adjusting the incident light intensity, different non-reciprocal responses can be achieved on the graphene / silicon metasurface at input light intensities of 20, 70, and 120 kW / cm². 2 The reflection coefficients of the two ports are distributed as a function of wavelength as follows: Figure 3 As shown in (a), the reflectance coefficients at the two ports of the graphene / silicon metasurface structure at a wavelength of 1.16261 μm change with the incident light intensity I0 as follows: Figure 3 As shown in (b).

[0028] Different non-reciprocal responses can be achieved by adjusting the groove depth dimensions on the sides of port 1 and port 2. Figure 4 (a) is the reflection coefficient of the two ports with groove depths of 7nm, 5nm, and 3nm on the graphene side as a function of wavelength. Figure 4 (b) is the reflection coefficient of the two ports on the other side with groove depths of 22nm, 20nm, and 18nm as a function of wavelength.

[0029] By changing the voltage applied to a single graphene layer, i.e., the Fermi level of graphene, the operating wavelength of the structure can be adjusted, and a corresponding non-reciprocal reflection response can be achieved. The variations in different graphene Fermi levels, the maximum achievable non-reciprocal reflection amplitude, and the corresponding wavelengths are shown below. Figure 5 As shown.

[0030] Graphene is a single-layer carbon atom surface material that can be simulated as a surface current: J = σ·E, where σ is the conductivity of graphene and E is the electric field intensity distribution along the graphene layer.

[0031] Under a nonlinear mechanism, graphene can be expressed as: J = σ·E + σ (3) ·E 3 , where σ (3) It is the third-order nonlinear conductivity of graphene.

[0032] The results show that, due to the asymmetry of the structure, the structure itself can achieve a non-reciprocal response of 76.05% in the reflection mode; at the graphene Fermi level of 0.7 eV, the input light intensity is 70 kW / cm². 2 The optimal working effect is achieved when the non-reciprocal amplitude reaches 83.67%.

[0033] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. An optical non-reciprocal device based on graphene and silicon supersurfaces, characterized in that: The optical non-reciprocal device has a non-reciprocal reflection response; the optical non-reciprocal device is formed by splicing a plurality of unit structure periods, the unit structure includes a single-layer graphene and a silicon super surface, the silicon super surface is provided with periodic grooves with the same width and different depths on the upper and lower sides, and the grooves are symmetrical on both sides; the single-layer graphene is covered on the silicon super surface; The silicon super surface adopts polycrystalline silicon, the refractive index of the polycrystalline silicon is 3.4, the height is 100nm, and the third-order nonlinear susceptibility of the polycrystalline silicon is 2.8*10 -18 m 2 / V 2 ; The graphene is only covered on one side of the silicon super surface and the side with shallow grooves.

2. An optical non-reciprocal device based on graphene and silicon supersurfaces as claimed in claim 1 characterized by: The width of the grooves is 40 nm, the depth of the grooves on the side with the graphene is 3-7 nm, the depth of the grooves on the other side is 18-22 nm, and the period of the groove structure is 520 nm.

3. An optical non-reciprocal device based on graphene and silicon supersurfaces as claimed in claim 1, wherein: The optical non-reciprocal device works in the near-infrared waveband, and the size of the single-layer graphene and the silicon super surface is smaller than the wavelength of light in the working waveband.

4. An optical non-reciprocal device based on graphene and silicon supersurfaces as claimed in claim 1, wherein: By changing the Fermi energy level of the single-layer graphene and the groove depth, the working wavelength of the non-reciprocal device is adjusted, and the non-reciprocal reflection response of the optical non-reciprocal device is adjusted.

5. An optical non-reciprocal device based on graphene and silicon supersurfaces as claimed in claim 1 or 4, wherein: By adjusting the incident light intensity, different non-reciprocal reflection responses can be achieved.

6. An optical non-reciprocal device based on graphene and silicon supersurfaces as claimed in claim 5, wherein: The maximum achievable reflection nonreciprocal amplitude can be achieved when the graphene Fermi level is 0.7 eV and the input light intensity is 70 kW / cm 2 2.

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