A distributed feedback Bragg grating based on graphene array

Abstract

The present invention provides a distributed feedback Bragg grating based on a graphene array, which belongs to the field of optical technology. The composite structure includes two Bragg gratings, two first dielectric layers and one second dielectric layer; from the incident direction to the exit direction, the arrangement rule of the composite structure is: the first dielectric layer, the Bragg grating, the second dielectric layer, the Bragg grating, the first dielectric layer; the Bragg grating is composed of alternately arranged single-layer graphene and a third dielectric layer, and the incident surface and the exit surface of the Bragg grating are both single-layer graphene. The composite structure has the advantages of filtering function and the like.

Description

Technical Field

[0001] The invention belongs to the field of optical technology and relates to a distributed feedback Bragg grating based on a graphene array. Background Art

[0002] When the refractive index of a material changes periodically in space, a Bragg grating is formed. When two identical Bragg gratings are distributed at both ends of a layer of dielectric, a distributed feedback Bragg grating is formed. Distributed feedback Bragg gratings can be widely used in optical filters, wavelength selectors, fiber lasers, etc. Once the traditional distributed feedback Bragg grating is formed, the bandwidth of the optical filter and the central wavelength of the wavelength selector can only be adjusted by changing the refractive index of the defect layer. In practical applications, the electro-optic effect or acousto-optic effect is often used to change the refractive index of the material in the central defect layer to adjust the central wavelength of the filter. Is there another possibility to change the central wavelength of the filter by adjusting the Bragg gratings at both ends while keeping the refractive index of the material in the defect layer unchanged?

[0003] As a two-dimensional material, graphene has good electrical conductivity. If a single layer of graphene is embedded in a dielectric, a periodic arrangement is formed in space, which is a Bragg grating. Two Bragg gratings are placed on both sides of the dielectric to form a distributed feedback Bragg grating structure. The surface conductivity of graphene can be flexibly adjusted by chemical potential. In addition, graphene can be equivalent to a dielectric material with a certain thickness, and its equivalent refractive index can be controlled by the chemical potential of graphene.

[0004] The center wavelength and bandwidth of the optical filter and wavelength selector made by using the distributed feedback Bragg grating based on the graphene array can be flexibly controlled by the chemical potential of graphene. The chemical potential of graphene is related to the external gate voltage applied to the graphene, so the bandwidth and center wavelength of the optical filter can also be flexibly controlled by the external gate voltage. Summary of the invention

[0005] The purpose of the present invention is to provide a distributed feedback Bragg grating based on a 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 make the composite structure have a filtering function.

[0006] The object of the present invention can be achieved by the following technical solutions: A distributed feedback Bragg grating based on a graphene array, characterized in that it includes a composite structure consisting of two Bragg gratings, two first dielectric layers and one second dielectric layer; from the incident direction to the exit direction, the arrangement rule of the composite structure is: first dielectric layer, Bragg grating, second dielectric layer, Bragg grating, first dielectric layer;

[0007] The Bragg grating is composed of alternately arranged single-layer graphene and a third dielectric layer, and both the incident surface and the exit surface of the Bragg grating are single-layer graphene.

[0008] A single layer of graphene is embedded in a silicon dioxide matrix material to form a distributed feedback Bragg grating structure. The distributed Bragg grating consists of two Bragg gratings; the Bragg grating is formed by a single layer of graphene arranged periodically in space; the dielectric layer between the two Bragg gratings can be regarded as a defect layer of this periodic structure.

[0009] When the wavelength of the incident light wave is exactly equal to the defect mode, a resonance phenomenon will occur, and a resonance peak will appear on the transmittance curve, while the transmittance of other wavelengths will be suppressed. Therefore, this structure can be applied to optical filters and wavelength selectors. The central wavelength and bandwidth of the optical filter can be regulated by the chemical potential of graphene. In addition, the central wavelength of the optical filter and wavelength selector can also be adjusted by the thickness and refractive index of the defect layer.

[0010] Furthermore, the first dielectric layer, the second dielectric layer and the third dielectric layer are all made of light-transmitting silicon dioxide material. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the structure of a distributed feedback Bragg grating.

[0012] Figure 2 (a) Transmittance in a distributed feedback Bragg grating based on a graphene array; Figure 2 (b) Reflectivity in a distributed feedback Bragg grating based on a graphene array.

[0013] Figure 3 (a) is the transmittance corresponding to N = 40; Figure 3 (b) is the reflectivity corresponding to N=40.

[0014] Figure 4 (a) is the transmittance corresponding to d2 = 8 μm; Figure 4 (b) is the reflectivity corresponding to d2=8μm.

[0015] In the figure, σ, single-layer graphene; A, first dielectric layer; B, second dielectric layer; C, third dielectric layer; M, Bragg grating. 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] The single-layer graphene σ is embedded into the dielectric material to form a distributed feedback Bragg grating structure, such as Figure 1As shown. The distributed feedback Bragg grating consists of two Bragg gratings M. The single-layer graphene σ is arranged periodically in space to form a Bragg grating M. The first dielectric layer, the second dielectric layer and the third dielectric layer are made of the same material, which can be silicon dioxide. The thickness of the first dielectric layer A is d1, the thickness of the second dielectric layer B is d2, and the thickness of the third dielectric layer C is d3. Assuming N is the number of spatial periods of the Bragg grating, the entire structure can also be expressed as A(σC) N σBσ(Cσ) N A. The test was conducted under the following environment and conditions: the refractive index of the first dielectric layer A, the second dielectric layer B and the third dielectric layer C were all n = 1.449; the surface conductivity of the single-layer graphene σ is related to the temperature, chemical potential and input light wavelength, and the room temperature was taken as T = 23°C.

[0018] When the number of Bragg grating spatial periods is N = 20, Figure 2 (a) shows the transmittance in the distributed feedback Bragg grating based on graphene array. The ordinate T represents the transmittance, λ represents the wavelength, and the wavelength unit μm is micrometer. Here, d1=d2=4μm and d3=100nm are taken. The input wave is a transverse electric wave, and it is vertically incident. Ignoring the nonlinear effect, it can be seen that when the graphene chemical potential is μ=0.3eV, 0.4eV, and 0.5eV, different transmittance curves correspond. As the wavelength changes, a resonance peak, i.e., a transmission peak, will appear in the transmittance curve at the position of the dotted box. When the chemical potential of graphene increases, the peak value of the resonance peak will decrease, and the position of the resonance peak will blue shift. The greater the chemical potential of graphene, the narrower the transmittance resonance peak, indicating that the resonance is stronger; and the transmittance of the wavelengths on both sides of the resonance peak will decrease, indicating that the suppression of the transmission of these wavelengths is enhanced. The two Bragg gratings can be regarded as a graphene array, and the dielectric B sandwiched between the two gratings is the defect layer in this periodic graphene array. The transmission peak in the dashed box corresponds to the transmittance of the defect mode.

[0019] If the distributed feedback Bragg grating based on graphene array is applied to optical filter or wavelength selector, the wavelength size and wavelength selectivity of the transmitted light can be regulated by the chemical potential of graphene. The chemical potential of single-layer graphene can be adjusted by the gate voltage applied to graphene, so the central wavelength and bandwidth of the transmitted light can be flexibly regulated by the external gate voltage.

[0020] Figure 2 (b) shows the reflectivity in a single-period graphene array. The ordinate R represents the reflectivity. It can be seen that within the dotted box, each reflectivity curve has a trough, and the trough value is zero, that is, the reflectivity corresponding to the defect mode is zero, and the wavelengths on both sides of the defect mode can be well reflected back.

[0021] When the period number of the Bragg grating is increased from N = 20 to N = 40, Figure 3 (a) shows the transmittance curve. The chemical potential of graphene at this time is μ = 0.4 eV. It can be seen that: at the position of the asterisk ☆, there will be a transmission peak, which corresponds to the transmittance of the defect mode, and this transmittance is about 0.2; relative to the case of N = 20, the width of the resonance peak will become narrower and the intensity will become lower. This is because as the number of graphene periods increases, the resonance will increase and the wavelength selectivity will also increase. When light is transmitted in graphene, the greater the number of graphene, the greater the reflectivity.

[0022] Figure 3 (b) shows the reflectivity curve. As the wavelength changes, a reflectivity dip will appear at the asterisk ☆ position. The minimum value of the dip is the reflectivity of the defect mode, and the reflectivity at this time is not zero. This shows that increasing the period number of the Bragg grating will reduce the transmittance and increase the reflectivity. As the period number of the Bragg grating increases, the width of the transmission peak will become narrower, indicating that the wavelength selectivity is enhanced, and the monochromaticity of the transmitted wave is better.

[0023] As mentioned above, the wavelength of the defect mode can be changed by adjusting the chemical potential of graphene. However, this method has limited control over the wavelength, and the wavelength change is only carried out in a small range near the resonance peak. When the wavelength of the transmission mode needs to be changed significantly, the thickness or refractive index of the defect layer needs to be changed.

[0024] The thickness of the middle defect layer B is changed to d2 = 8 μm, Figure 4 (a) shows the transmittance curve. Keeping the period number of the Bragg grating unchanged from N = 20, the chemical potential of graphene is μ = 0.4 eV, and the thickness of dielectric A is d1 = 4 μm. It can be seen that: at the asterisk ☆, there is a resonance peak, and the maximum value of the resonance peak is the transmittance corresponding to the defect mode; relative to the case of d2 = 4 μm, the wavelength corresponding to the defect mode moves to the right from about 20 μm to slightly more than 30 μm. Figure 4 (b) shows the reflectivity curve. It can be seen that there is a dip at the asterisk ☆. The minimum value of the dip is the reflectivity corresponding to the defect mode, and the reflectivity of the defect mode is approximately 0. In addition, the wavelength of the transmission mode can be greatly adjusted by changing the refractive index of the defect layer.

[0025] In summary, when the distributed feedback Bragg grating based on graphene array is used in an optical filter or an optical frequency selector, the wavelength and wavelength selectivity of the transmitted light can be controlled by the chemical potential of graphene and the thickness and refractive index of the intermediate defect layer.

[0026] 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 distributed feedback Bragg grating based on a graphene array, characterized in that: A composite structure comprising two Bragg gratings (M), two first dielectric layers (A) and a second dielectric layer (B); from the incident direction to the exit direction, the arrangement of the composite structure is: the first dielectric layer (A), the Bragg grating (M), the second dielectric layer (B), the Bragg grating (M), the first dielectric layer (A); The Bragg grating (M) is composed of a single-layer graphene (σ) and a third dielectric layer (C) arranged alternately, and the incident surface and the exit surface of the Bragg grating (M) are both single-layer graphene (σ); The first dielectric layer (A), the second dielectric layer (B) and the third dielectric layer (C) are all made of light-transmitting silicon dioxide material.

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