A composite structure based on graphene array and dielectric

Abstract

The present invention provides a composite structure based on a graphene array and a dielectric, belonging to the field of all-optical communication technology. It includes a graphene array on one side close to the incident direction and a single layer on one side close to the outgoing direction. The graphene array is composed of a plurality of single layers of graphene and a first dielectric layer. The first dielectric layer and the single layer of graphene are arranged alternately, and the thickness of each first dielectric layer is the same. Both sides of the graphene array are single layers of graphene, and the single layer is a second dielectric layer with a thickness greater than the first dielectric layer. The threshold and threshold interval of the bistable state can be adjusted by adjusting the thickness of the second dielectric layer, and the thickness of the second dielectric layer can also be detected by the threshold and threshold interval. The upper and lower thresholds and threshold intervals of the optical bistable state and tristable state can be flexibly adjusted by the external gate voltage.

Description

Technical Field

[0001] The invention belongs to the technical field of all-optical communication and relates to a composite structure based on a graphene array and a dielectric. Background Art

[0002] Optical tristable means that one input light intensity corresponds to three stable output light intensities, that is, there can be three stable resonant states. Optical tristable is a nonlinear optical effect that can be widely used in all-optical switches, optical memories and optical logic devices.

[0003] In two adjacent optical bistable states, if the upper threshold of the first optical bistable state is between the upper and lower thresholds of the second optical bistable state, and at the same time, the lower threshold of the second optical bistable state is between the upper and lower thresholds of the first optical bistable state, then the two optical bistable states constitute an optical triptable state.

[0004] When the input light intensity is strong, the refractive index of the material will change with the input light intensity. The change in refractive index is directly proportional to the square of the local light intensity, which is the Kerr effect. When the incident light is strong enough, one input light intensity value can correspond to two or three different output light intensity values, forming a stable resonance, which is the optical bistable or tristable state.

[0005] The research on optical bistability or tristable states mainly focuses on how to use new materials and new structures to achieve these effects, as well as how to reduce the threshold of optical bistability or tristable states and increase the threshold interval. To this end, it is necessary to enhance the third-order nonlinear effect of the material. Currently, there are two aspects to start from: 1. Materials with large third-order nonlinear coefficients can be used to achieve low-threshold optical bistability, and 2. The local light field can be enhanced by optimizing the structure.

[0006] As an emerging two-dimensional material, graphene has a considerable third-order nonlinear coefficient, so it can be used as an ideal material for realizing optical bistability and tristability. On the one hand, the surface plasmon excited by graphene can be used to enhance the localized light field of graphene, thereby enhancing the third-order nonlinear effect of graphene.

[0007] In addition, defect photonic crystals can also be used to enhance the nonlinear effect of graphene. In defect photonic crystals, the transmittance of the defect mode is close to 1, so it is also called a transmission mode. The mode field energy of the defect mode is mainly distributed in the defect layer. Embedding graphene in the defect layer can greatly enhance the nonlinear effect of graphene.

[0008] Graphene is arranged periodically to form a graphene array, and a layer of dielectric is stacked on the right side of the array to form a composite structure. Light is transmitted in the structure to form a standing wave condition. The mode field distribution has a strong localization, so it can be used to enhance the third-order nonlinear effect of graphene, thereby realizing a low-threshold optical bistable or tristable state. The thickness of the dielectric layer on the right affects the standing wave condition and also affects the wavelength of the resonant wave. Therefore, the upper and lower thresholds and threshold intervals of the optical bistable and tristable states can be adjusted by changing the thickness of the dielectric. In addition, the conductivity of graphene is affected by the chemical potential of graphene, and the chemical formula can be regulated by the gate voltage applied to the graphene. Therefore, the upper and lower thresholds and threshold intervals of the optical bistable and tristable states can be flexibly adjusted by the external gate voltage. Summary of the invention

[0009] The purpose of the present invention is to provide a composite structure based on a graphene array and a dielectric in view of the above-mentioned problems existing in the prior art. The technical problem to be solved by the present invention is how to establish a corresponding relationship between the threshold and threshold interval of the optical tristable state and the composite structure.

[0010] The objective of the present invention can be achieved through the following technical solutions: a composite structure based on a graphene array and a dielectric, characterized in that it includes a graphene array on one side close to the incident direction and a single layer on one side close to the emitting direction, the graphene array is composed of a plurality of single layers of graphene and a first dielectric layer, the first dielectric layer and the single layer of graphene are arranged alternately, the thickness of each first dielectric layer is the same, both sides of the graphene array are single layers of graphene, and the single layer is a second dielectric layer with a thickness greater than that of the first dielectric layer; the threshold and threshold interval of the bistable state can be adjusted by adjusting the thickness of the second dielectric layer, and the thickness of the second dielectric layer can also be detected by the threshold and the threshold interval.

[0011] Furthermore, the first dielectric layer and the second dielectric layer are both made of silicon dioxide.

[0012] The graphene periodic array is compounded with a second dielectric layer near the emission direction to form a composite structure. When light is transmitted in the composite structure, a standing wave is formed, and the distribution of the light field changes alternately, thereby enhancing the third-order nonlinear effect of graphene, thereby realizing a low-threshold optical tristable state, and then applying the optical tristable state to all-optical switches, optical logic devices and optical storage.

[0013] The threshold and threshold interval of the optical tristable state are related to the chemical potential of graphene and the thickness of the second dielectric layer. The chemical potential of graphene can be regulated by an external gate voltage. Therefore, the on / off threshold and threshold interval of the all-optical switch based on the optical tristable state in the graphene array can be flexibly adjusted by the chemical potential of graphene. The upper and lower thresholds of the tristable state can also be adjusted by the thickness of the second dielectric layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a composite structure of graphene array and dielectric.

[0015] Figure 2 (a) is the linear transmission spectrum of the light wave; (b) is the relationship between the nonlinear transmittance and the input light intensity; (c) is the input-output light intensity change relationship.

[0016] Figure 3 is the effect of graphene chemical potential on the optical tripability.

[0017] Figure 4 It is a graph showing the relationship between output light intensity and input light intensity.

[0018] Figure 5 This is the output-input relationship diagram corresponding to different dielectric thicknesses.

[0019] In the figure, σ represents a single layer of graphene; A, the first dielectric layer; B, the second dielectric layer. DETAILED DESCRIPTION

[0020] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0021] The single-layer graphene and the first dielectric layer A are alternately arranged to form a graphene array, and then compounded with the second dielectric layer B so that the second dielectric layer B is located on one side of the emission direction. The structure formed is as follows: Figure 1 As shown. The symbol σ represents a single layer of graphene, and the first dielectric layer A and the second dielectric layer B are both silicon dioxide. The symbol d1 is the spatial period of the graphene array, that is, the thickness of the first dielectric layer A, and d2 is the thickness of the second dielectric layer B. i is the incident light, I o is the outgoing ray. This structure can also be written as (gA) N gB, where N represents the number of spatial periods. For example, if the number of spatial periods of graphene is N = 40, the spatial period of graphene is d1 = 100nm, and the refractive index of silicon dioxide is n a =1.449. The surface conductivity of graphene is related to temperature, chemical potential and input light wavelength, and the room temperature is taken as T = 23°C.

[0022] Figure 2(a) shows the relationship between the transmittance of the incident light and the wavelength. When the input wave is a transverse electric wave, ignoring the nonlinear effect, the chemical potential of graphene is μ = 0.4 eV (eV represents electron volts), and the thickness of the second dielectric layer B on the right is d2 = 4 μm. It can be seen that there are many resonance peaks in the transmission spectrum, corresponding to the resonance state. The mode field distribution of the resonance state will be concentrated on the interface of the dielectric, so the light field has a strong localization, that is, the local light field will become very strong. Graphene is located exactly on the interface of the dielectric, so this structure can be used to enhance the nonlinear effect of graphene.

[0023] Set the input wavelength to λ = 2.1μm. When the light intensity is strong, Figure 2 (b) shows the relationship between the nonlinear transmittance of the composite structure and the input light intensity. The horizontal axis unit is TW / cm 2 It represents terawatt per square centimeter. It can be seen that as the light intensity increases, the slope of the transmittance curve becomes negative, indicating that optical bistable, tristable or multistable phenomena may occur there.

[0024] Figure 2 (c) shows the input-output intensity variation relationship. When the light intensity increases to a certain value, the input-output relationship presents a three-curve relationship, i.e., an optical tristable state. When the input light intensity increases, the input-output curve changes along trajectory I. i =I u1 and I i =I u2 , the output light intensity jumps upward, and I u1 and I u2 It is called the upper threshold of the optical tristable state; when the input light intensity decreases, the input-output curve changes along trajectory II. i =I d1 and I i =I d2 , the output light intensity changes downward, and I d1 and I d2 It is called the lower threshold of the optical tristable state. The optical tristable state has two threshold intervals I u1 -I d1 and I u2 =I d2 The optical tripastable state consists of two optical bistable states. d2 <I i <I u1 When the input light intensity is between 1 and 2, one stable output corresponds to three stable outputs.

[0025] When the optical tristable in this structure is used as an all-optical switch, the on and off of two signals can be controlled at the same time. The upper and lower thresholds of the tristable correspond to the on and off thresholds of the all-optical switch, that is, when the light intensity is I i =Iu1 When the first optical switch is turned on, i =I d1 When the light intensity is I i =I u2 When the second optical switch is turned on, i =I d2 When , the second optical switch is turned off. In addition, the three bistability curves are also related to the incident wavelength and the chemical potential of graphene.

[0026] The transmission spectrum is also related to the thickness d2 of the second dielectric layer B at the right end. The optical tripod state with an appropriate threshold can be obtained by controlling the thickness of the second dielectric layer B. When μ = 0.45 eV, Figure 4 (a) Figure 4 (b) and Figure 4 (c) shows the transmission spectra corresponding to d2 = 4 μm, d2 = 8 μm and d2 = 12 μm. It can be seen that as the thickness of the second dielectric layer B increases, the interval between adjacent resonance peaks becomes smaller and the vibration frequency becomes larger. As the dielectric thickness increases, the parameters in the standing wave condition change, and the wavelength interval between adjacent standing waves becomes smaller.

[0027] Figure 5 The input-output relationship corresponding to different dielectric thicknesses is given. It can be seen that the thickness of the second dielectric layer B has a small effect on the lower threshold, but a large effect on the upper threshold. When the thickness is small, as the input light intensity increases, the threshold interval of the bistable state becomes larger and larger; and when the thickness is large, as the input light intensity increases, the threshold interval of the bistable state becomes smaller and smaller. Therefore, the threshold and threshold interval of the bistable state can be adjusted by the thickness, or the thickness of the second dielectric layer B can be detected by the threshold and threshold interval.

[0028] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A composite structure based on a graphene array and a dielectric, characterized in that: The invention comprises a graphene array on one side close to the incident direction and a single layer on one side close to the emitting direction, wherein the graphene array is composed of a plurality of single layers of graphene (σ) and a first dielectric layer (A), the first dielectric layer (A) and the single layers of graphene (σ) are arranged alternately, and the thickness of each first dielectric layer (A) is the same; both sides of the graphene array are single layers of graphene (σ), and the single layer is a second dielectric layer (B) with a thickness greater than that of the first dielectric layer (A); the threshold and threshold interval of the bistable state can be adjusted by adjusting the thickness of the second dielectric layer (B), and the thickness of the second dielectric layer (B) can also be detected by the threshold and the threshold interval.

2. A composite structure based on a graphene array and a dielectric according to claim 1, characterized in that: The first dielectric layer (A) and the second dielectric layer (B) are both made of silicon dioxide.

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