Multifunctional nanometer antenna system

Abstract

The invention relates to a multifunctional nano antenna system which comprises a pair of asymmetric nano particles, the two nano particles are used for responding to light waves, each nano particle is a dielectric ball wrapped by a graphene layer with different Fermi levels, and the radius of each nano particle is far larger than the thickness of the graphene layer. According to the method, construction of the nano antenna system with asymmetry is achieved, the kinetic equation of the nano antenna system (a dimer system) is obtained through theoretical derivation, the kinetic equation is used for revealing the dynamic behavior of the nano antenna system, and the scattered field of the nano antenna system can be explored through the kinetic equation. In order to regulate and control the scattered field of the nanometer antenna system, the nanometer antenna system can be converted among different states by introducing additional dimensionless pulses to enter the nanometer antenna system, and the purpose of regulating and controlling the scattered field is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-antenna design, and in particular to a multifunctional nano-antenna system. Background Art

[0002] As an important nanophotonic device, nanoantennas can significantly enhance the interaction between light and matter and are widely used in ultrafast optical information processing, sensors, and dynamic scattering control. In recent years, the application of nonlinear optics has further broadened the potential of nanoantennas. In particular, under the action of plasmons, the multi-stable operation and dynamic response of nanoantennas can be significantly improved, making flexible control of scattering patterns possible. Compared with traditional linear systems, nonlinear optical effects can bring richer phenomena, especially in ultrafast optical switches, all-optical control, and fiber-optic sensors.

[0003] In this context, graphene, as a highly promising optoelectronic material, has attracted widespread attention in the field of nanoantennas due to its advantages such as high conductivity and high carrier mobility, controllable optoelectronic properties, wide spectral response (covering terahertz to visible light) and high chemical stability. Compared with traditional precious metal materials, graphene's low loss and high nonlinear response provide more abundant optical modulation possibilities. Graphene-based nanoantennas have the advantages of high sensitivity and high frequency response, and can be used to design efficient optical modulators, all-optical switches and sensors, etc.

[0004] Nonlinear metallic nanoantennas with tunable scattering patterns, consisting of two identical silver nanoparticles, are actively and dynamically controlled by using modulation instabilities. Such nanoantennas can operate at relatively low optical intensities, have wide scanning sectors and very short characteristic response times, allowing ultrafast modulation of the scattered field. This type of nanoantenna can be used in dynamic positioning systems for nanoscale targets (molecules, proteins, viruses) and as components of nanophotonic devices.

[0005] The disadvantages of the existing technology include:

[0006] First, the inherent high loss of metal materials (especially silver and gold) leads to low plasmon resonance efficiency and cannot achieve efficient operation in practical applications. In addition, the low adjustability of metal materials themselves makes it difficult to achieve flexible optical property adjustment, limiting their application potential in dynamic response.

[0007] Second, many current nanoantenna structures are composed of identical nanoparticles, with few parameters introduced, making it difficult to achieve multi-state regulation. This design lacks a wide range of multi-stable regions and cannot produce multiple periodic self-oscillation modes, which in turn limits the flexible control of different scattering modes. This system, with its simple structure and poor regulation capability, is difficult to meet the response requirements for nanoantennas in multiple scenarios.

[0008] Third, existing designs usually lack external excitation mechanisms and cannot achieve efficient switching between scattering modes. This means that the system is difficult to flexibly switch between different states, cannot cope with changing environmental requirements, and has low applicability in dynamic and real-time detection. Summary of the invention

[0009] To this end, the technical problem to be solved by the present invention is to overcome the problems in the prior art that the application of nanoantennas made of metal materials is greatly limited, the multi-state control capability of the symmetrical nanoantenna structure is poor, it is difficult to meet the response requirements for nanoantennas in multiple scenarios, and the nanoantenna lacks an external excitation mechanism, resulting in low applicability.

[0010] To solve the above technical problems, the present invention provides a multifunctional nanoantenna system, comprising a pair of asymmetric nanoparticles, the two nanoparticles are used to respond to light waves, and each nanoparticle is a BaF2 dielectric sphere wrapped by a graphene layer with different Fermi energy levels;

[0011] The graphene layer is characterized as a two-dimensional film with Kerr nonlinearity, and the conductivity of the two-dimensional film is σ = σ L +σ NL |E in | 2 , at room temperature is expressed as and represent the linear and Kerr nonlinear parts of the conductivity, respectively, where E in is the local electric field inside the graphene layer, i is the imaginary unit, ω is the frequency, n represents the nth nanoparticle, e is the electron charge, h is the reduced Planck constant, ξ is the relaxation time, and v F is the Fermi velocity, taken as ξ=0.3ps and v F ≈c / 300, c is the speed of light in vacuum, E Fn is the Fermi level of the nth nanoparticle.

[0012] In one embodiment of the present invention, the nanoantenna system is composed of a dimer system, and the dynamic behavior of the nanoantenna system is revealed by constructing a kinetic equation of the dimer system, and the method includes:

[0013] Assume that the electric dipole moment formula of two nanoparticles is:

[0014]

[0015] Among them, α n represents the electrical susceptibility of the two nanoparticles, E i =E0e i(kz-ωt) e y is the incident field polarized along the y-axis and propagating along the z-axis, E0 is the amplitude of the electric field, represents the dipole interaction between two nanoparticles, p m is the electric dipole moment, is the wave vector, ε h is the background dielectric constant;

[0016] Since the nonlinearity of the graphene layer in the nanoantenna system is weak, Decompose near the nanoparticle resonant frequency and keep only the first-order terms with time derivatives:

[0017]

[0018] Among them, Δω n =ω-ω n is the detuning amount, is the dipole resonance frequency of a single nanoparticle, ε0 is the vacuum dielectric constant;

[0019] Substituting formula (2) into formula (1) and performing dimensionless processing, the kinetic equation of the dimer system is obtained as follows:

[0020]

[0021] Among them, τ, Ω n , γ n , G, ν, P n and E represent dimensionless time, detuning parameter, loss, coupling coefficient, asymmetry coefficient, dipole moment and background field, respectively.

[0022] In one embodiment of the present invention, the detuning parameter Ω n , loss γ n , coupling coefficient G, asymmetry coefficient ν, dipole moment P n And the background E field are expressed as:

[0023]

[0024] In one embodiment of the present invention, P1 and P2 are calculated according to formula (3), and the dimensionless scattering intensity U is introduced. s , to characterize the scattering field of the nanoantenna system, the scattering field is used to analyze and optimize the optical response of the nanoantenna system under different conditions, wherein the formula of the scattering field is:

[0025]

[0026] Among them, θ and are the spherical polar angle and azimuth angle respectively, and ΔΨ represents the phase difference between P1(τ) and P2(τ).

[0027] In one embodiment of the present invention, in order to achieve the control of the scattering field of the nano-antenna system, an additional dimensionless pulse is introduced to the nano-antenna system, and its value is:

[0028]

[0029] Among them, E p , τ0, Δτ and ρ are the saturation value, start time, duration and edge sharpness respectively.

[0030] In one embodiment of the present invention, the radius a of each of the nanoparticles is 100 nm; and the center distance d between two of the nanoparticles is 300 nm.

[0031] In one embodiment of the present invention, the radius of each nanoparticle is greater than the thickness of the graphene layer.

[0032] The above technical solution of the present invention has the following advantages compared with the prior art:

[0033] The present invention realizes the construction of an asymmetric nanoantenna system, and theoretically derives a kinetic equation of the nanoantenna system (a dimer system), which is used to reveal the dynamic behavior of the nanoantenna system, and the scattering field of the nanoantenna system can also be explored through the kinetic equation;

[0034] The present invention increases the asymmetric degree of freedom for the nano-antenna system by regulating the Fermi energy level of the graphene layer, and does not need to change the physical structure of the nano-antenna system, but only changes the parameter size of the Fermi energy level;

[0035] In order to achieve the control of the scattering field of the nano-antenna system, the present invention introduces an additional dimensionless pulse (rectangular pulse) to be incident on the nano-antenna system, so as to realize the conversion of the nano-antenna system between different states and achieve the purpose of scattering field control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0037] Figure 1 is a schematic diagram of the structure of a nano-antenna system in an embodiment of the present invention;

[0038] Figure 2is a schematic diagram of scattering field control of a nanoantenna system in an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of an all-optical multi-stable switch in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0041] Embodiment 1

[0042] Reference Figure 1 As shown, the present invention relates to a multifunctional nanoantenna system, including a pair of asymmetric nanoparticles, the two nanoparticles are used to respond to light waves, each nanoparticle is a BaF2 dielectric sphere wrapped by a graphene layer with different Fermi energy levels; the radius of each nanoparticle is greater than the thickness of the graphene layer.

[0043] The following is a detailed introduction to this embodiment:

[0044] like Figure 1 As shown in the figure, a plane wave with a frequency of ω is incident on a nanoantenna system with a radius a of 100nm and a center spacing d of 300nm. This system consists of a pair of asymmetric nanoparticles, which are BaF2 (barium fluoride) dielectric spheres wrapped with graphene layers with different parameters. The external environment can be regarded as a vacuum.

[0045] (ε h =1). Since the radius of the dielectric particle is much larger than the thickness of graphene, the graphene layer can be characterized as a two-dimensional film with Kerr nonlinearity, and its conductivity is σ = σ L +σ NL |E in | 2 , at room temperature, can be expressed as and represent the linear and Kerr nonlinear parts of the conductivity, respectively, where E in is the local electric field inside the graphene layer, i is the imaginary unit, ω is the frequency, n represents the nth nanoparticle (n = 1, 2), e is the electron charge, h is the reduced Planck constant, ξ is the relaxation time, and v F is the Fermi velocity, taken as ξ=0.3ps and v F ≈c / 300, c is the speed of light in vacuum, E Fn is the Fermi level of the nth nanoparticle.

[0046] The nanoantenna system is composed of a dimer system. The dynamic behavior of the nanoantenna system is revealed by constructing the kinetic equation of the dimer system. The method includes:

[0047] The theoretical study of this embodiment will start from the electric dipole moments of the two nanoparticles, namely:

[0048]

[0049] In this formula, α n represents the electrical susceptibility of the two nanoparticles, E i =E0e i(kz-ωt) e y is the incident field polarized along the y-axis and propagating along the z-axis, E0 is the amplitude of the electric field, represents the dipole interaction between two nanoparticles, p m is the electric dipole moment, is the wave vector, ε h is the background dielectric constant. In addition, since the nonlinearity of the graphene layer in this dimer system is weak, The decomposition can be performed near the nanoparticle resonant frequency and only the first-order terms with time derivatives are retained:

[0050]

[0051] Among them, Δω n =ω-ω n is the detuning amount, and is the dipole resonance frequency of a single nanoparticle, and ε0 is the dielectric constant of vacuum.

[0052] Substituting formula (2) into formula (1) and performing dimensionless processing, the kinetic equation of the nonlinear coupled dimer system can be obtained as follows:

[0053]

[0054] Where τ, Ω n , γ n , G, ν, P n and E represent dimensionless time, detuning parameter, loss, coupling coefficient, asymmetry coefficient, dipole moment and background field, respectively. The detailed expressions of these parameters are as follows:

[0055]

[0056] In addition, this embodiment calculates P1 and P2 according to formula (3) and introduces the dimensionless scattering intensity U s , to characterize the scattering field of the nanoantenna system. The scattering field is used to analyze and optimize the optical response of the nanoantenna system under different conditions. The formula for the scattering field is:

[0057]

[0058] Among them, θ and are the spherical polar angle and azimuth angle respectively, and ΔΨ represents the phase difference between P1(τ) and P2(τ).

[0059] Finally, in order to control the scattering field of the nanoantenna system, an additional dimensionless pulse (i.e., the matrix pulse described below) is introduced into the nanoantenna system, and its value is:

[0060]

[0061] Among them, E p , τ0, Δτ and ρ are saturation value, start time, duration and edge sharpness respectively. For simplicity, this embodiment considers ρ = 1, and p and Δτ are modulated to control the switching of different states.

[0062] It should be noted that the E calculated by formula (6) ex Substituting the background field E into formula (3) changes formula (3). At this time, substituting P1 and P2 in formula (3) into formula (5) can obtain the change of the scattering field of the nanoantenna system.

[0063] In this embodiment, the asymmetry is controlled by adjusting the Fermi level of graphene in the nanoantenna. Here, the Fermi levels of graphene in the two nanoparticles are set to E F1 =0.9eV,E F2 =0.85eV, making the system asymmetric. When the background field is E=0.01 and the detuning parameter is Ω1=-0.1, due to the asymmetric nature of the nanoantenna system, energy can be transferred between the dipole moments, and two different periodic self-oscillation states appear at the same time, called period 1 and period 2, which is impossible in a symmetric system. Figure 2 As shown ( Figure 2 (a) is a rectangular pulse sequence (E p , Δτ); Figure 2 (b) is the corresponding forward scattering intensity Figure 2 (c) is the oscillation angle θ corresponding to the main lobe of the scattered field (Zoy cross section) max evolution over time; Figure 2 (d)-(g) Figure 2 The scattering mode corresponding to the dots in (c), the numbers represent the oscillation angles), the system is initially in a steady state, and when the first E p =0.008, Δτ=150, the system can be converted to periodic state 1 with a period of T=71.4. When a second E is applied at τ=3000, p= 0.01, Δτ = 100, the system switches to another periodic self-oscillation state 2, with a period of T = 78.3. Therefore, in order to further reveal the function of this nanoantenna, this embodiment Figure 2 (c) shows the oscillation angle θ max It should be noted that the angular scanning sector of the first cycle of the self-oscillation state is Δθ max ; 47.8°, much larger than the angular scanning sector Δθ of the second cycle self-oscillation state max ; 5.3°.

[0064] In practical applications, combined with the scanning characteristics of the periodic self-oscillation state, period 1 can be regarded as a fast search mode with a large scanning range, while period 2 can be used as a focusing mode with better directivity to enable continuous search after detecting a suspicious target. In addition, it is well known that the scattering pattern of a traditional antenna hardly changes, while in this asymmetric nanoantenna system, the periodic self-oscillation will also lead to ultrafast periodic changes in the scattering pattern. Therefore, it is feasible to modulate the scattering of the nanoantenna by external excitation.

[0065] When the background field is set to E = 0.014 in this embodiment, the other parameters are the same as Figure 2 At the same time, the scattering of the nanoantenna has three stable states at the same time. Although the tristable state also exists in the symmetric system, it needs to meet more stringent background field and detuning conditions. The asymmetry greatly expands the area where the tristable state exists, and even the quadri-stable state appears. The conversion of the all-optical multi-stable switch needs to be realized by adding pulses with different parameters. For example, this embodiment can add a pulse sequence containing six rectangular pulses to achieve Figure 3 Switching between the three states ( Figure 3 (a) is a rectangular pulse sequence (E p , Δτ): (0.01,55), (0.005,50), (0.027,15), (0.031,19), (0.008,50) and (0.048,14); Figure 3 (b) shows the switching of scattering between three stable states. Figure 3 As shown in (b), initially, the scattering is in the steady state S1. When stimulated by a series of pulses, the scattering switches to the S2, S3, S2, S1, S3 states in turn, and finally returns to the S1 state. After the last pulse ends, the scattering remains stable in the S1 state and no longer changes. Obviously, this tri-stable switch can switch between any two of the three states by modulating the pulse parameters. In this way, by encoding the pulse signal sequence, the expected multi-state conversion can be achieved very conveniently, which has great application potential in optical communications, computing, and quantum information processing.

[0066] In addition to the two feasible applications mentioned above, this asymmetric nanoantenna can also achieve more functions as needed by controlling the background field and pulse sequence.

[0067] The present invention designs an asymmetric nanoantenna system, and the asymmetry can be controlled by the Fermi level of the graphene layer wrapped on two dielectric spheres. The research results show that compared with the traditional symmetric nanoantenna system, the asymmetric structure can produce a variety of periodic self-oscillation states under the same background field, significantly broadening the multi-stable region of the system. In addition, using graphene as the wrapping layer not only has nonlinearity, but also reduces inherent losses.

[0068] The asymmetric multifunctional nanoantenna system constructed by the present invention can realize a variety of optical applications. Under the stimulation of a pulse sequence, the system can regulate the scattered field and realize the following functions: (1) regulate the self-oscillation periodic state and the scattered field to realize fast scanning and focusing search mode. (2) control the state transition of the all-optical multi-stable switch by encoding the pulse signal sequence.

[0069] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0070] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A multifunctional nano-antenna system, characterized in that: The invention comprises a pair of asymmetric nanoparticles, wherein the two nanoparticles are used to respond to light waves, and each nanoparticle is a BaF2 dielectric sphere wrapped by a graphene layer with a different Fermi energy level; The graphene layer is characterized as a two-dimensional film with Kerr nonlinearity, and the conductivity of the two-dimensional film is σ = σ L +σ NL |E in | 2 , at room temperature is expressed as and represent the linear and Kerr nonlinear parts of the conductivity, respectively, where E in is the local electric field inside the graphene layer, i is the imaginary unit, ω is the frequency, n represents the nth nanoparticle, e is the electron charge, h is the reduced Planck constant, ξ is the relaxation time, and v F is the Fermi velocity, taken as ξ=0.3ps and v F ≈c / 300, c is the speed of light in vacuum, E Fn is the Fermi level of the nth nanoparticle.

2. The multifunctional nano-antenna system according to claim 1, characterized in that: The nanoantenna system is composed of a dimer system, and the dynamic behavior of the nanoantenna system is revealed by constructing a kinetic equation of the dimer system. The method includes: Assume that the electric dipole moment formula of two nanoparticles is: Among them, α n represents the electrical susceptibility of the two nanoparticles, E i =E0e i(kz-ωt) e y is the incident field polarized along the y-axis and propagating along the z-axis, E0 is the amplitude of the electric field, represents the dipole interaction between two nanoparticles, p m is the electric dipole moment, is the wave vector, ε h is the background dielectric constant; Since the nonlinearity of the graphene layer in the nanoantenna system is weak, Decompose near the nanoparticle resonant frequency and keep only the first-order terms with time derivatives: Among them, Δω n =ω-ω n is the detuning amount, is the dipole resonance frequency of a single nanoparticle, ε0 is the vacuum dielectric constant; Substituting formula (2) into formula (1) and performing dimensionless processing, the kinetic equation of the dimer system is obtained as follows: Among them, τ, Ω n , γ n , G, ν, P n and E represent dimensionless time, detuning parameter, loss, coupling coefficient, asymmetry coefficient, dipole moment and background field, respectively.

3. The multifunctional nano-antenna system according to claim 2, characterized in that: The detuning parameter Ω n , loss γ n , coupling coefficient G, asymmetry coefficient ν, dipole moment P n And the background E field are expressed as:

4. The multifunctional nano-antenna system according to claim 2, characterized in that: P1 and P2 are calculated according to formula (3), and the dimensionless scattering intensity U is introduced s , to characterize the scattering field of the nanoantenna system, the scattering field is used to analyze and optimize the optical response of the nanoantenna system under different conditions, wherein the formula of the scattering field is: Among them, θ and are the spherical polar angle and azimuth angle respectively, and ΔΨ represents the phase difference between P1(τ) and P2(τ).

5. The multifunctional nano-antenna system according to claim 4, characterized in that: In order to control the scattering field of the nanoantenna system, an additional dimensionless pulse is introduced into the nanoantenna system, and its value is: Among them, E p , τ0, Δτ and ρ are the saturation value, start time, duration and edge sharpness respectively.

6. The multifunctional nano-antenna system according to claim 1, characterized in that: The radius a of each nanoparticle is 100 nm; the center distance d between two nanoparticles is 300 nm.

7. The multifunctional nano-antenna system according to claim 1, characterized in that: The radius of each nanoparticle is larger than the thickness of the graphene layer.

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