A composite structure of dielectric thin layer and graphene capable of realizing spatial displacement

Abstract

The present invention provides a composite structure of a dielectric thin layer and graphene that can realize spatial displacement, and belongs to the field of optical technology. It includes a non-Hermitian dielectric thin layer and two graphene monolayers, and the two graphene monolayers are respectively deposited on both sides of the non-Hermitian dielectric thin layer to form a three-layer structure; when a light wave passes through a certain graphene monolayer at a non-vertical incident angle, the reflectivity of the resonant state can be improved, and a large Goos-Hansen shift can be obtained near the resonant state. The present invention has the advantages of being able to improve the reflectivity of the resonant state of the composite structure and obtain a large Goos-Hansen shift near the resonant state.

Description

Technical Field

[0001] The invention belongs to the field of optical technology and relates to a composite structure of a dielectric thin layer and graphene capable of realizing spatial displacement. Background Art

[0002] When light is totally reflected at the interface between two different media, the reflected beam has a lateral displacement relative to the position predicted by geometric optics, namely the spatial Guth-Hansen ( Gus-Hansen shift can be widely used in sensing and detecting light wavelength, angle and material refractive index.

[0003] When light is totally reflected at the interface of a medium, part of the light wave will penetrate into the underlying medium, forming an evanescent wave. This effect is equivalent to moving the interface downward by a certain distance, causing the reflection point and the reflected light beam to move laterally relative to the incident point. The lateral displacement of the reflected light beam can be positive or negative. In fact, when the light waves of different wavelengths in the light beam are reflected at the interface, the relative phase shifts of the light waves of different frequencies are different, which leads to a lateral shift in the reflected light beam formed after superposition.

[0004] The Goos-Hansen shift was first measured experimentally by Goos and Hansen. However, because the spatial Goos-Hansen shift is only on the order of a few wavelengths, it was difficult to verify experimentally at first, and its application value was not easy to reflect in practice. Subsequent studies have shown that partially reflected light can also have a Goos-Hansen shift, and the magnitude can be further increased. In addition, the reflected light beam can also be deflected at an angle, which is an angular Goos-Hansen shift.

[0005] How to improve the magnitude of the Goos-Hansen shift and explore the potential application value of the Goos-Hansen shift are the directions that people have been working hard on. Studies have found that when there is weak loss in the material, a Goos-Hansen shift of several dozen times the wavelength can be induced; a large Goos-Hansen shift can also exist at the edge of the band gap of the photonic crystal; in addition, in the non-Hermitian photonic system (there is gain and loss, or one of the two in the system) near the exceptional points (EPs), a very large Goos-Hansen shift can occur. A common drawback in these three cases is that the reflectivity is very low, especially at the exceptional points, the reflectivity is zero, which brings great difficulties to actual detection and application.

[0006] As an emerging two-dimensional material, graphene has good electrical and mechanical properties and is widely used in scientific research and production practice. The weak loss in graphene can cause the phase of the reflection coefficient to change sharply, thereby obtaining a large Goos-Hansen shift; at the same time, the conductivity of graphene can be used to enhance the reflectivity of light. To this end, we composite graphene with a non-Hermitian dielectric thin layer to improve the reflectivity of the resonant state, and obtain a large Goos-Hansen shift near the resonant state. Summary of the invention

[0007] The purpose of the present invention is to provide a composite structure of a dielectric thin layer and graphene that can achieve spatial displacement in view of the above-mentioned problems existing in the prior art. The technical problem to be solved by the present invention is to improve the reflectivity of the resonant state of the composite structure and obtain a larger Goos-Hansen shift near the resonant state.

[0008] The objective of the present invention can be achieved through the following technical scheme: a composite structure of a dielectric thin layer and graphene capable of realizing spatial displacement, characterized in that it comprises a non-Hermitian dielectric thin layer and two graphene monolayers, wherein the two graphene monolayers are respectively deposited on both sides of the non-Hermitian dielectric thin layer to form a three-layer structure; when a light wave passes through a certain graphene monolayer at a non-vertical incident angle, the reflectivity of the resonant state can be improved, and a large Goos-Hansen shift can be obtained near the resonant state.

[0009] Furthermore, the material of the non-Hermitian dielectric thin layer is silicon dioxide, and the gain control of the non-Hermitian dielectric thin layer can be achieved by doping erbium ions, and the loss control of the non-Hermitian dielectric thin layer can be achieved by doping copper ions.

[0010] The advantages of the present invention are as follows: the non-Hermitian dielectric thin layer is compounded with graphene, which can greatly enhance the reflectivity of the resonant state compared with the case without graphene; it can also greatly improve the spatial Goos-Hansen shift of the reflected light beam; near the resonant state, the Goos-Hansen shift can be as high as 108 times the wavelength, and the shift is extremely sensitive to the incident angle, incident wavelength and dielectric constant, therefore, the structure can be used for high-sensitivity angle, wavelength and dielectric constant sensing and detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a layer structure diagram of this composite structure.

[0012] Figure 2 Figure (a) shows the dependence of transmittance on angle; Figure 2 Figure (b) shows the dependence of reflectivity on angle; Figure 2 Figure (c) shows the relationship between the reflection coefficient phase and angle; Figure 2 The middle figure (d) shows the relationship between the Guth-Hansen displacement and the angle.

[0013] Figure 3 Figure (a) shows the relationship between transmittance and wavelength; Figure 3 Figure (b) shows the relationship between reflectivity and wavelength.

[0014] Figure 4 Figure (a) shows the relationship between the reflection coefficient phase and wavelength; Figure 4 The middle figure (b) shows the relationship between the spatial Goos-Hansen shift and wavelength.

[0015] In the figure, σ, graphene monolayer; G, non-Hermitian dielectric thin layer. DETAILED DESCRIPTION

[0016] 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.

[0017] A graphene monolayer is deposited on the upper and lower surfaces of a non-Hermitian dielectric thin layer to form a sandwich structure, such as Figure 1 As shown. The thickness of the non-Hermitian dielectric thin layer is d = 18 μm (micrometers), and the non-Hermitian dielectric thin layer has gain or loss. The dielectric constant of the thin layer material is ε = ε r +iε i , where ε r =2 represents the real part of the dielectric constant, ε i represents the imaginary part of the dielectric constant, and i is the imaginary unit. A positive imaginary part represents a lossy medium; a negative imaginary part represents a gain medium. The letter σ represents a graphene monolayer, and G represents a non-Hermitian dielectric thin layer. The solid line 1 represents the incident light, the dotted line 2 represents the reflected light predicted by geometric optics, the solid line 3 represents the reflected light after a negative Goos-Hansen shift, the solid line 4 represents the reflected light after a positive Goos-Hansen shift, and the solid line 5 represents the transmitted light. The symbol +Δ represents a positive Goos-Hansen shift, and the symbol -Δ represents a negative Goos-Hansen shift. The letter θ represents the angle of incidence of the light. For a Goos-Hansen shift to occur, it must be obliquely incident.

[0018] The material of the non-Hermitian dielectric thin layer is silicon dioxide. The gain of the dielectric is controlled by doping impurities such as erbium ions, and the loss is controlled by doping copper ions. When the input wavelength is fixed, such as a transverse magnetic wave of λ = 10μm, the transmittance of the light wave can be obtained by changing the incident angle of the light, such as Figure 2 As shown in (a), the horizontal axis unit deg represents degree, that is, "°". The ambient temperature is set to room temperature T = 23 °C, and the chemical potential of graphene is set to μ c=0.15eV (eV stands for electron volt). Different imaginary parts of dielectric constants correspond to different transmittance curves. In each transmittance curve, there is a transmission peak, also called a resonance peak, which corresponds to the resonance state. It can be seen that the imaginary part of the dielectric constant basically does not affect the position of the resonance peak, and the incident angle corresponding to the resonance state is θ=57.8°. When ε i =-0.05, there is gain in the medium, and the maximum transmittance can be greater than 1; and when ε i = 0.05, corresponding to the lossy medium, the transmittance is less than 1. For lossless medium, that is, ε i = 0, and the maximum transmittance of the resonant state is 1. This phenomenon shows that under the action of graphene, the reflectivity of the resonant state can be greatly enhanced by modulating the gain and loss of the dielectric.

[0019] Figure 2 (b) is the reflectivity curve. It can be seen that there is a valley in the reflectivity curve at the resonance state. The inset shows the reflectivity near the resonance state. The figure shows that for lossless media, the reflectivity corresponding to the resonance state is 0; when it is a non-Hermitian medium, that is, when there is gain and loss, the reflectivity of the resonance state is not zero. Therefore, the reflectivity of the resonance state can be enhanced by modulating the gain and loss of the medium in the structure.

[0020] Figure 2 (c) shows the relationship between the phase of the reflection coefficient and the incident angle, and the vertical axis unit rad represents radians. It can be seen that when ε i = 0 and ε i When =0.05, there is a meaningless 2π phase jump near the resonance state. Therefore, ignoring this jump, the phase changes continuously with the incident angle. Near the resonance state, the rate of change of the curve is relatively large. Based on the fact that the spatial Goos-Hansen shift is proportional to the phase change rate of the reflection coefficient, it can be determined that there is a large Goos-Hansen shift near the resonance state.

[0021] Figure 2 (d) shows the dependence of the spatial Goos-Hansen shift of the reflected beam on the incident angle. Near the resonance state, the Goos-Hansen shift is large. When ε i = ±0.05, the maximum Goos-Hansen shift is of the order of several wavelengths, while when ε i = 0, the Goos-Hansen shift can be as high as several hundred wavelengths. This shows that by attaching graphene to a non-Hermitian thin layer, the magnitude of the Goos-Hansen shift can be greatly improved, and the shift is extremely sensitive to angle and dielectric constant. The structure can be used for high-sensitivity angle and dielectric constant sensing and detection.

[0022] When the transverse magnetic wave is incident on the composite structure at an incident angle of θ = 40°, Figure 3(a) shows the relationship between transmittance and incident wavelength. It can be seen that there are four resonance peaks on each transmission spectrum, which are marked with asterisks in sequence. The four resonance peaks from left to right represent four-wavelength, three-wavelength, two-wavelength and single-wavelength resonances. When there is gain in the medium, the transmittance of the resonant state will be greater than 1, and the transmittance of the multi-wavelength resonance is greater than that of the single-wavelength resonance. Figure 3 (b) shows the relationship between reflectivity and wavelength. It can be seen that in each reflectivity curve, the reflectivity of the resonant state is the smallest. Comparing the three types of dielectrics, in the gain medium, that is, ε i When <0, the reflectivity of the resonant state is the largest; in the lossy medium, that is, ε i When >0, the resonant state reflectivity is second; the resonant state reflectivity of the lossless medium is 0.

[0023] Figure 4 (a) shows the relationship between the phase of the reflection coefficient and the wavelength. The imaginary part of the dielectric constant is ε i =-0.00. The figure shows that: near the resonance state, the reflection coefficient phase changes dramatically with the increase of wavelength, and there is also a meaningless 2π phase jump in the curve; the phase change near the multi-wavelength resonance state is more dramatic than the phase change near the single-wavelength resonance state; the slope of the phase curve is positive and negative, which indicates that there are huge positive and negative Goos-Hansen shifts near the resonance state. Figure 4 (b) shows the response curve of the spatial Goos-Hansen shift to wavelength. Near the resonance state, the Goos-Hansen shift is very large and can also be negative. In order to observe the contour of the entire Goos-Hansen shift, the absolute value of the Goos-Hansen shift is taken and then the logarithm is calculated. It can be seen that the maximum Goos-Hansen shift is near the four-wavelength resonance state and can be as high as 108λ, which shows that the Goos-Hansen shift is extremely sensitive to the incident wavelength and can be used for high-sensitivity wavelength sensing and detection.

[0024] 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 of a dielectric thin layer and graphene capable of achieving spatial displacement, characterized in that: The invention comprises a non-Hermitian dielectric thin layer (G) and two graphene monolayers (σ), wherein the two graphene monolayers (σ) are respectively deposited on both sides of the non-Hermitian dielectric thin layer (G) to form a three-layer structure; when a light wave passes through a graphene monolayer (σ) at a non-vertical incident angle, the reflectivity of the resonant state can be improved, and a large Goos-Hansen shift can be obtained near the resonant state.

2. The composite structure of a dielectric thin layer and graphene capable of realizing spatial displacement according to claim 1, characterized in that: The material of the non-Hermitian dielectric thin layer (G) is silicon dioxide. The gain control of the non-Hermitian dielectric thin layer (G) is achieved by doping erbium ions, and the loss control of the non-Hermitian dielectric thin layer (G) is achieved by doping copper ions.

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