阅读说明：本技术 一种斐波那契序列电介质与石墨烯的复合结构 (Fibonacci sequence dielectric medium and graphene composite structure ) 是由 章普 于 2020-04-23 设计创作，主要内容包括：本发明提供了一种斐波那契序列电介质与石墨烯的复合结构,属于光电技术领域。本复合结构包括若干电介质层一、若干电介质层二和一个石墨烯层,复合结构由其一侧面至另一侧面的堆叠规律如下：电介质层二、电介质层一、电介质层二、电介质层二、电介质层一、电介质层二、电介质层一、电介质层二、电介质层二、电介质层一、电介质层二、电介质层二、电介质层一、石墨烯层、电介质层一、电介质层二、电介质层二、电介质层一、电介质层二、电介质层二、电介质层一、电介质层二、电介质层一、电介质层二、电介质层二、电介质层一、电介质层二；电介质层一的材料为MgF<Sub>2</Sub>晶体,电介质层二的材料为ZnS晶体。本发明具有提高缺陷模的反射率等优点。(The invention provides a composite structure of a Fibonacci sequence dielectric medium and graphene, and belongs to the technical field of photoelectricity. The composite structure comprises a plurality of first dielectric layers, a plurality of second dielectric layers and a graphene layer, and the stacking rule of the composite structure from one side surface to the other side surface is as follows: dielectric layer two, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer graphene layer, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer two; the first dielectric layer is made of MgF 2 The second dielectric layer is made of ZnS crystal. The invention is provided withImproving the reflectivity of the defect mode, and the like.)

1. The composite structure of the Fibonacci sequence dielectric medium and the graphene is characterized by comprising a plurality of first dielectric layers, a plurality of second dielectric layers and a graphene layer, wherein the composite structure is a multilayer structure formed by stacking the first dielectric layers, the second dielectric layers and the graphene layer, and the stacking rule of the composite structure from one side surface to the other side surface is as follows: dielectric layer two, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer graphene layer, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer two; the first dielectric layer is made of MgF₂And the second dielectric layer is made of ZnS crystals.

2. A process according to claim 1The Fibonacci sequence dielectric and graphene composite structure is characterized in that the refractive index of the first dielectric layer is n_a1.38, the refractive index of the second dielectric layer is n_b＝2.35。

3. The fibonacci sequence dielectric and graphene composite structure of claim 1, wherein the first dielectric layer has a thickness d_a＝λ₀/4n_a27.17 μm, and the thickness of the second dielectric layer is d_b＝λ₀/4n_b15.96 μm, where λ₀＝150μm。

4. A fibonacci sequence dielectric and graphene composite structure according to claim 1, 2 or 3, wherein the fibonacci sequence dielectric and graphene composite structure is applied to a sensor element sensitive to the wavelength of incident light.

5. A fibonacci sequence dielectric and graphene composite structure according to claim 1, 2 or 3, wherein the fibonacci sequence dielectric and graphene composite structure is applied to a sensor element sensitive to an angle of incident light.

Technical Field

The invention belongs to the technical field of photoelectricity, and relates to a composite structure of a Fibonacci sequence dielectric medium and graphene.

Background

Similar to the electronic band structure of semiconductors, photonic band structures exist in photonic crystals. The defect photonic crystal is provided with a defect mode, the defect mode is positioned in the middle of a photon energy band, and an electric field of the defect mode is mainly distributed in a defect layer. When the frequency of the input light is exactly equal to the defect mode, the light wave will pass through the photonic crystal without reflection, so the defect mode is also called the transmission mode. If there are weak losses in the photonic crystal and the incident wavelength is near the defect mode, the phase of the reflected beam will fluctuate dramatically as the angle of incidence, wavelength of incidence, or other parameters change. The lateral displacement of the reflected beam is proportional to the rate of change of the phase of the reflected beam, and therefore, a larger lateral displacement of the reflected beam can be achieved near the defective mode. The effect can be used for an optical switch and a high-sensitivity sensor, and the wavelength or angular displacement and the like are measured by utilizing the displacement change of a reflected light beam.

Two dielectrics with different refractive indexes are alternately arranged to form a quasi-photonic crystal structure. When the dielectric alignment satisfies the Fibonacci sequence type, the structure belongs to a quasi-photonic crystal. The rules that make up a fibonacci sequence are: f₁＝{B}，F₂= BA, and F_j＝{F_j-1F_j-2J is equal to or greater than 3. Two identical fibonacci sequence dielectrics of j-6 are multiplexed together to form a defect cavity, with the two dielectric sequences being symmetrically distributed about the center. Band structures are also present in quasi-photonic crystals, and band edge states can be enhanced by fibonacci sequence dielectrics. The band edge states in a fibonacci sequence dielectric are defect states whose mode fields are also distributed predominantly in the intermediate defect layer. Compared with a defect mode in a photonic crystal, the resonance of the energy band edge state in the Fibonacci sequence dielectric medium is stronger, and the mode field distribution is more concentrated. In addition, the reflectivity of the band edge states in the fibonacci sequence dielectric remains zero.

Disclosure of Invention

The invention aims to provide a composite structure of Fibonacci sequence dielectric and graphene, aiming at the problems in the prior art, and the technical problem to be solved by the invention is how to improve the reflectivity of a defect mode and realize large transverse displacement of a reflected light beam.

The purpose of the invention can be realized by the following technical scheme: the Fibonacci sequence dielectric and graphene composite structure is characterized by comprising a plurality of first dielectric layers, a plurality of second dielectric layers and a graphene layer, wherein the composite structure is a multilayer structure formed by stacking the first dielectric layers, the second dielectric layers and the graphene layer, and the composite structure is a structure formed by stacking the first dielectric layers, the second dielectric layers and the graphene layerThe stacking rule of the structure from one side surface to the other side surface is as follows: dielectric layer two, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer graphene layer, dielectric layer one, dielectric layer two, dielectric layer one, dielectric layer two; the first dielectric layer is made of MgF₂And the second dielectric layer is made of ZnS crystals.

In the above composite structure of a fibonacci sequence dielectric and graphene, the refractive index of the first dielectric layer is n_a1.38, the refractive index of the second dielectric layer is n_b＝2.35。

In the above composite structure of the fibonacci sequence dielectric and the graphene, the thickness of the first dielectric layer is d_a＝λ₀/4n_a27.17 μm, and the thickness of the second dielectric layer is d_b＝λ₀/4n_b15.96 μm, where λ₀＝150μm。

In the above composite structure of the fibonacci sequence dielectric and the graphene, the composite structure of the fibonacci sequence dielectric and the graphene is applied to a sensor element sensitive to the wavelength of incident light.

In the composite structure of the Fibonacci sequence dielectric medium and the graphene, the composite structure of the Fibonacci sequence dielectric medium and the graphene is applied to a sensing element sensitive to an incident light angle.

Since the light intensity is not large, there is no need to consider nonlinear effects, but only the other two effects of light: 1. a reflectivity enhancing effect. The reflectivity of the photonic band edge states is enhanced by embedding a single layer of graphene in the center of a quasicrystal composed of two fibonacci sequence dielectrics. The optical field is scattered back and forth by the dielectric and the graphene, and weak loss of the graphene can reduce the transmittance of the defect mode and enhance the reflectivity. 2. The large lateral displacement effect of the reflected beam. The weak loss of the graphene can cause the drastic change of the phase of the reflection coefficient, and the transverse displacement of the reflected light beam is in direct proportion to the change rate of the phase of the reflection coefficient, so that the transverse displacement of the reflected light beam can be relatively large. This lateral displacement is extremely sensitive to the incident angle and incident wavelength of the light beam, and therefore, the device can be used for a high-sensitivity sensor.

Drawings

Fig. 1 is a structural diagram of a graphene-inlaid fibonacci quasi-photonic crystal.

Fig. 2(a) is the reflectance of a fibonacci quasi-photonic crystal without graphene; (b) the reflectivity of a Fibonacci quasi-photonic crystal embedded with graphene; (c) is the phase of the reflection coefficient of a graphene-inlaid Fibonacci quasi-photonic crystal.

FIG. 3(a) is a graph showing the phase of the reflection coefficient as a function of the normalized frequency at different incident angles; (b) the lateral displacement of the reflected beam for several different angles of incidence varies with the normalized frequency.

Fig. 4 is a schematic diagram of a wavelength sensor based on the lateral displacement of the reflected beam.

In the figure, A, a dielectric layer I; B. a second dielectric layer; C. a graphene layer.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.

A fibonacci sequence type quasi-photonic crystal is formed by alternating dielectric A, B, G being a single layer of graphene, centered in the quasi-photonic crystal, as shown in fig. 1. Dielectric A is MgF₂And dielectric B is ZnS. Each having a refractive index of n_a＝1.38，n_bD is 2.35, the thickness of each_a＝λ₀/4n_aAnd d_b＝λ₀/4n_bWherein λ is₀150 μm. The incident ray is 1 and the reflected ray is 2. The transverse displacement of the reflected ray from the point of incidence is denoted D_y。

The graphene is embedded in the center of the defect layer, i.e., in the 0-point position of the z-axis. Graphene is considered to be a two-dimensional material without thickness, the surface conductivity of which satisfies the nonaberg formula (Kubo formula):

wherein f is_d＝1/(1+exp[(-μ_c)/(k_BT)]) Is a Fermi-Dirac statistic, is the particle energy, μ_cIs the chemical potential of graphene (also called the Fermi level E)_F) T is temperature, e is electron element charge, τ is momentum relaxation time, σ_gIs the surface conductivity of graphene, ω is the angular frequency of the input light,is a simple planck constant. Here we set the temperature to be 27 deg.c and the momentum relaxation time to be 0.15 eV.

As shown in fig. 1, the whole composite structure is a symmetrical dielectric stack structure, which can be represented as babbbabbababagabbabbabababbab, each letter represents a layer of dielectric, and the device is formed by stacking multiple layers of dielectric. Graphene can be considered as an equivalent dielectric with an equivalent thickness of 1nm and an equivalent dielectric constant of_g＝1+iσ_gη₀/(kd_g) Where k is the incident wave vector, η₀Is the vacuum impedance, i is the imaginary unit, d_gIs the thickness of the graphene. Incident light is assumed to be Transverse Magnetic (TM) polarized wave and propagates along the z-axis direction. The electromagnetic fields across each layer of dielectric may be related by a transmission matrix. For example, the relationship between the electromagnetic field across the first layer of dielectric and the transmission matrix is

Wherein M is_lA transmission matrix representing the l-th layer dielectric, wherein η_l＝_l(₀/μ₀)^1/2/(_l-sin²θ)^1/2，Theta is the incident angle of light, lambda is the incident wavelength, η_lRefers to the electrical impedance of the dielectric of the l-th layer, d_lIs the thickness of the dielectric of the l-th layer,_lis the dielectric permittivity of the l-th layer. E_l，H_lAnd E_l+1，H_l+1The electric field intensity and the magnetic field intensity at two ends of the first layer are respectively. M_lIs a shorthand for that matrix. The transmission matrix of the whole system is

Where N is the total number of layers of the structure, m_nRefers to each element in the resulting 2 × 2 matrix with a reflection coefficient of

η therein₁＝η_N+1＝(₀/μ₀)^1/2(1-sin²θ)^1/2The impedance of the incident end and the exit end is set to be in the air. The reflectivity can be expressed as R ═ rr, where the symbol indicates the complex conjugate operation. The photonic crystal has a band gap of omega_gap＝4ω₀arcsin│(n_b-n_a)/(n_b+n_a)│²N,/z, where ω₀＝2πc/λ₀，λ₀150 μm, and c is the speed of light in vacuum.

FIG. 2(a) is the reflectance R of a Fibonacci quasi-photonic crystal without graphene₁. Abscissa (ω - ω)₀)/ω_gapIs a normalized frequency. As can be seen from the reflection spectrum, a transmission band with small reflectivity is arranged in the middle, and the reflectivity is enhanced at the edge of the transmission band to form a recess with zero reflectivity. Respectively naming two reflection concave points at the leftmost end and the rightmost end as V₁₁And V₁₂Let us say that with a specific mark, the reflectivity of both points is zero.

Writing the reflection coefficient in the form of an indexWhereinIs the phase of the reflection coefficient. When the reflectivity is zero, there is uncertainty in the phase of the reflection coefficient, and therefore, the phase of the reflection coefficient changes drastically in the vicinity of the zero point of the reflectivity. The lateral displacement of the reflected beam being proportional to the rate of change of phase of the reflection coefficient, i.e.

Thus, the reflected beam may be at V₁₁And V₁₂There is a large lateral displacement nearby, however, due to V₁₁And V₁₂The reflectivities of the two points are zero, and the reflectivities near the two points are also low, so that the transverse moving effect of the reflected light beam is difficult to be implemented in experimental verification and practical application, wherein theta is the incident angle of light.

Fig. 2(a) reflectance of a fibonacci quasi-photonic crystal without graphene. (b) (c) phase of reflectivity and reflection coefficient of graphene-inlaid Fibonacci quasi-photonic crystal

In addition, V is seen from the reflection spectrum₁₁And V₁₂Is narrowest. V₁₁And V₁₂The mode field energy of the central defect mode respectively corresponding to the half wavelength and the 1/4 wavelength is mainly distributed in the central area. To increase V₁₁And V₁₂The reflectivity of the depressed part of the defect mode can be enhanced by embedding graphene in the Fibonacci quasi-photonic crystal, transmitting light in the quasi-photonic crystal, scattering the light by the graphene and utilizing the loss and the electric conductivity of the graphene, as shown in fig. 2 (b). V₂₁And V₂₂Has a reflectance of R₂At 0.17 and 0.05, it can be seen that the reflectivity has been significantly enhanced relative to that in the non-damascene graphene structure.

FIG. 2(c) shows the phase change of the reflection coefficient of a graphene-embedded Fibonacci quasi-photonic crystal as a function of normalized frequency, as can be seen at V₂₁And V₂₂In the vicinity, when the normalized frequency increases, the phase of the reflection coefficient changes very sharply. Thus, in a reflected beam, there may be a large lateral displacement, and this displacement is extremely sensitive to the wavelength of the incident light.

In a graphene-inlaid fibonacci quasi-photonic crystal, fig. 3(a) shows the phase of the reflection coefficient as a function of the normalized frequency at different incident angles. It can be seen that at V₂₁In the vicinity, the phase change of the reflection coefficient is relatively severe, that is, the phase change rate is relatively large. Several specific input angles are chosen for the purpose of illustrating the phase change characteristics. As can be seen from the figure, when θ is 18.5 °, the phase of the reflection coefficient changes continuously with the normalized frequency; when θ is 21.5 °, 24.5 ° and 27.5 °, a meaningless deep 2 pi dip pulse exists in the phase curve of the reflection coefficient, and therefore, it is considered that all the reflection coefficient phases are continuously varied with the normalized frequency.

Fig. 3(b) shows the variation of the lateral displacement of the reflected beam with the normalized frequency for several different incident angles, and the system is a graphene-embedded fibonacci quasi-photonic crystal. It can be seen that each curve has a peak of lateral displacement, and in order to make the observation more obvious, the interval of the selected incident angle parameters is larger, and if not, the peaks are closer. When the incident angle is constant, i.e. when the device is fixed and the light beam is incident on the quasi-photonic crystal from the same direction, the reflected light beam will have a lateral shift, changing the wavelength of the incident light and the lateral shift of the light beam will change. Therefore, the structure can be used for a wavelength sensor based on the transverse displacement of the reflected light beam, and can also fix the input wavelength to measure the size of the incident angle by detecting the transverse displacement of the reflected light beam.

Fig. 4 is a diagram illustrating detection of the wavelength of incident light by lateral displacement of a reflected light beam at an incident angle θ of 10 °. The incident light is 1, and when the central wavelength of the incident light beam is 197.8566 μmTransverse displacement of the reflected beam of D_y6.6147 λ, the reflected ray 2 shown in the figure; when the λ becomes 197.682 μm, the lateral displacement of the reflected light beam is D_y53.2907 λ, i.e., reflected ray 3. Therefore, the transverse displacement of the reflected light beam and the central wavelength of the incident light beam are in a functional relation, and the central wavelength of the incident light beam can be estimated by detecting the emergent position of the reflected light beam. In addition, when the incident angle of the light beam changes, the lateral displacement of the reflected light beam also changes, so that this structure can be used for a wavelength or angle displacement sensor based on the lateral displacement of the reflected light beam.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.