A composite structure based on a double-periodic graphene array

Abstract

The present invention provides a composite structure based on a double-periodic graphene array, which belongs to the field of all-optical communication technology. It includes a plurality of periodic composite units, each of which includes a first dielectric layer, a second dielectric layer and a single-layer graphene. The composite units are arranged in the following manner: a single-layer graphene, a first dielectric layer, a single-layer graphene, and a second dielectric layer are sequentially arranged from one side of the incident direction of the composite structure to the other side; the thickness of the first dielectric layer is less than that of the second dielectric layer; and a layer of graphene is arranged on the exit side. The present invention has the advantages of strong resonance of the resonant state and the like.

Description

Technical Field

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

[0002] All-optical switches are important components in all-optical communication systems and can be widely used in optical logic devices and optical storage devices. At present, research on all-optical switches based on optical bistable states mainly focuses on how to use new materials and new structures to reduce the upper and lower thresholds of the bistable state and increase the threshold interval. When the bistable state is used in all-optical switches, the upper and lower thresholds of the bistable state correspond to the on and off thresholds of the all-optical switch, respectively.

[0003] Optical bistability is a third-order nonlinear effect based on the change of the material's refractive index with the local light intensity. One input light intensity can correspond to two different resonant states.

[0004] When the light field is strong enough, the refractive index of the material is proportional to the third-order nonlinear coefficient of the material and the local light field intensity. Therefore, in order to enhance the third-order nonlinear effect of the material, on the one hand, nonlinear materials with larger third-order nonlinear coefficients can be found, and on the other hand, new structures can be constructed to enhance the local light field intensity.

[0005] Graphene has a considerable third-order nonlinear coefficient, and its surface conductivity can be flexibly adjusted by chemical potential. The nonlinear effect of graphene can be enhanced by using surface plasmons and defect photonic crystals excited by graphene. In addition, a periodic array composed of single-layer graphene can be regarded as a one-dimensional photonic crystal. If a resonant cavity is formed between two adjacent graphene sheets, the entire array constitutes a multi-resonant cavity.

[0006] When light propagates in a graphene array, a standing wave condition is formed. Light waves that meet the standing wave condition will resonate. The mode field distribution of the resonant state is highly localized, so the resonant state can be used to enhance the third-order nonlinear effect of graphene.

[0007] If graphene is arranged into a double-periodic array, two different periodic arrays will form different standing wave conditions. When the two periods are in multiples, the resonance will be enhanced. Compared with a single period, the double-periodic graphene array has a stronger resonance and stronger electric field localization, thus further improving the nonlinear effect of graphene. Summary of the invention

[0008] The purpose of the present invention is to provide a composite structure based on a double-periodic graphene array 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 enhance the resonance of the resonant state of the graphene multilayer structure, thereby further improving the third-order nonlinear effect of graphene and realizing a low-threshold optical bistability.

[0009] The objective of the present invention can be achieved through the following technical solutions: a composite structure based on a double-periodic graphene array, characterized in that it comprises a plurality of periodic composite units, each of which comprises a first dielectric layer, a second dielectric layer and a single-layer graphene, and each of which is arranged in the following manner: a single-layer graphene, a first dielectric layer, a single-layer graphene, and a second dielectric layer are sequentially arranged from one side of the incident direction of the composite structure to the other side; the thickness of the first dielectric layer is smaller than that of the second dielectric layer; and a layer of graphene is arranged on the side of the structured light exiting.

[0010] Furthermore, the first dielectric layer and the second dielectric layer are both made of a light-transmitting material such as silicon dioxide.

[0011] Furthermore, the thickness of the second dielectric layer is four times the thickness of the first dielectric layer.

[0012] A single layer of graphene is embedded between the first dielectric layer and the second dielectric layer of different thicknesses to form a double-periodic array of graphene. Compared with a single-periodic array, the resonant state in the double-periodic array of graphene is more resonant and has a stronger localization to the light field, thereby further improving the third-order nonlinear effect of graphene, thereby achieving low-threshold optical bistability, and then applying the optical bistability to all-optical switches, optical logic devices and optical storage.

[0013] The upper and lower thresholds of the optical bistability are related to the chemical potential of graphene and the wavelength of the input wave. The chemical potential of graphene can be controlled by the external gate voltage applied to graphene. Therefore, the on / off thresholds and threshold intervals of the all-optical switch based on the optical bistability in the dual-period graphene array can be flexibly adjusted by the chemical potential of graphene and the wavelength of the incident wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the layered structure of the composite structure.

[0015] Figure 2 (a) is the transmission and reflection spectra in a single-period graphene array; Figure 2 (b) is the transmission and reflection spectra in the double-periodic graphene array; Figure 2 (c) is the relationship between the transmittance and the input light intensity in the double-periodic graphene array; Figure 2 (d) is the input-output light intensity relationship in the double-periodic graphene array.

[0016] Figure 3 These are the optical bistability curves corresponding to different graphene chemical potentials.

[0017] Figure 4 It is the input-output light intensity relationship corresponding to different incident wavelengths.

[0018] In the figure, g, single-layer graphene; A, first dielectric layer; B, second dielectric layer. DETAILED DESCRIPTION

[0019] 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.

[0020] The single-layer graphene g is embedded into the dielectric material to form a double-periodic array composite structure, such as Figure 1 Symbol d 1 and d 2 Respectively represent the thickness of the first dielectric layer and the second dielectric layer, that is, the two spatial periods of the graphene array. The first dielectric layer A and the second dielectric layer B are made of the same material, and silicon dioxide is used as an example here. The thickness of the first dielectric layer A is d 1 , the thickness of the second dielectric layer B is d 2 The number 1 represents the incident light and the number 2 represents the transmitted light. This structure can also be written as (gAgB) N g, where N represents the number of spatial periods. Here we take the number of spatial periods of graphene as N = 40, 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.

[0021] Figure 2 (a) shows the transmission and reflection spectra of a single-period graphene array. The ordinate T represents the transmittance, and R represents the reflectance. Here, d 1 =d 2 =200nm (nm means nanometer), the array is a single period. Assume that the input wave is a transverse electric wave, incident vertically. When the light intensity is relatively weak, the nonlinear effect is ignored. The chemical potential of graphene is μ=0.50eV. The horizontal axis λ represents the input wavelength, and the unit μm represents micrometer. It can be seen that with the increase of the input wavelength, 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 the resonance state of the structure can be used to enhance the nonlinear effect of graphene. It can be seen that the reflectivity is relatively low, the maximum reflectivity is about 0.1, and most of the light intensity is transmitted.

[0022] Figure 2 (b) shows the transmission and reflection spectra of the double-periodic graphene array. 1 =200nm,d 2=800nm. The chemical potential of graphene is μ=0.50eV. There are also many resonant states in the transmission spectrum. Compared with the single-period graphene array, the interval between adjacent resonant states in the double-period graphene array becomes smaller. The resonance peak becomes narrower and steeper, indicating that the resonance is enhanced, and the localization of the electric field is enhanced accordingly. Therefore, the use of a double-period graphene array can enhance the nonlinear effect of graphene more than a single-period graphene array, thereby further reducing the threshold of the optical bistability. Moreover, the reflectivity at the position of the asterisk symbol ☆ is enhanced, and this structure can be used to improve the reflectivity of light waves. The maximum reflectivity can reach about 0.3.

[0023] When the input light is strong enough, the effect of light intensity on the conductivity of graphene needs to be considered. Therefore, changes in light intensity will inevitably cause changes in transmittance. In the double-periodic graphene array, Figure 2 (c) shows the relationship between transmittance and input light intensity. The chemical potential of graphene is μ = 0.40 eV. The input wavelength is a fixed value of λ = 2.2 μm. The horizontal axis I i Indicates input light intensity, unit TW / cm 2 It represents terawatts per square centimeter. It can be seen that as the light intensity increases, the slope of the transmittance curve becomes negative, indicating that optical bistability can occur there.

[0024] Figure 2 (d) shows the output-input light intensity relationship in the double-periodic graphene array. Symbol I o Represents the input light intensity. When the input light intensity increases to a certain value, the input-output light intensity relationship presents a hyperbolic relationship, which is the optical bistability. As can be seen from the illustration, when the input light intensity increases, the input-output curve changes along the trajectory I. i =I u At this point, the output light intensity changes upward, and I u It is called the upper threshold of optical bistability; when the input light intensity decreases, the input-output curve changes along trajectory II. i =I d , the output light intensity changes downward, and I d It is called the lower threshold of optical bistable state. The difference between the upper and lower thresholds is I u -I d When the optical bistable in this structure is used as an all-optical switch, the upper and lower thresholds of the bistable state correspond to the on and off thresholds of the all-optical switch, that is, when the light intensity is I i =I u When the optical switch is turned on, i =I d When the input light intensity is between the upper and lower thresholds, that is, I d <I i <Iu , corresponding to two output light intensities, which is the so-called optical bistability.

[0025] Figure 3 The optical bistability curves corresponding to different graphene chemical potentials are given. The wavelength of the incident light wave is λ = 2.2μm. It can be seen that with the increase of graphene chemical potential, the upper and lower thresholds of the optical bistability will increase, and the upper and lower threshold intervals will also increase. The chemical potential of graphene can be adjusted by the external gate voltage applied to graphene, so the upper and lower thresholds and threshold intervals of the optical bistability can be flexibly controlled by the gate voltage. When the optical bistability is applied to an all-optical switch, the upper and lower thresholds of the optical bistability correspond to the on and off thresholds of the all-optical switch, and the on and off thresholds and threshold intervals of the all-optical switch can be controlled by the external gate voltage.

[0026] The chemical potential of graphene is μ = 0.40 eV. Figure 4 The input-output light intensity relationship corresponding to different incident wavelengths is given. It can be seen that different incident wavelengths correspond to different bistable curves, and the upper and lower thresholds of the bistable state are also different. When the incident wavelength increases, the upper and lower thresholds of the optical bistable state increase. Therefore, the threshold of the optical bistable state can also be regulated by the wavelength of the incident wave, and even the formation of the optical bistable state can be regulated.

[0027] 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 double periodic graphene array, It is characterized in that The invention comprises a plurality of periodic composite units, wherein the composite unit comprises a first dielectric layer (A), a second dielectric layer (B) and a single-layer graphene (g), and the composite unit is arranged in the following manner: a single-layer graphene (g), a first dielectric layer (A), a single-layer graphene (g), and a second dielectric layer (B) are sequentially arranged from one side of the incident direction of the composite structure to the other side; the thickness of the first dielectric layer (A) is smaller than that of the second dielectric layer (B); the output side of the composite unit is graphene (g); as the input wavelength increases, there are many resonance peaks on the transmission spectrum, corresponding to the resonance state, and the mode field distribution of the resonance state will be concentrated on the interface of the dielectric, so the light field is localized, and the single-layer graphene (g) is just located on the interface of the first dielectric layer (A) or the second dielectric layer (B), and the resonance state of the structure is used to enhance the nonlinear effect of graphene, thereby obtaining a low-threshold optical bistability; The first dielectric layer (A) and the second dielectric layer (B) are both made of a light-transmitting material such as silicon dioxide; The thickness of the second dielectric layer (B) is four times the thickness of the first dielectric layer (A).

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