Gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna

Abstract

The application relates to an optical nano antenna, in particular to a multi-wavelength one-way scattering optical nano antenna based on a gallium phosphide arrowhead type, wherein the multi-wavelength one-way scattering optical nano antenna is an arrowhead type nano antenna, the material of the arrowhead type nano antenna is gallium phosphide, the included angle a of the arrowhead type nano antenna is 15 DEG, the length of two sides of the arrowhead G is 303 nm, the width of the arrow tail M is 40 nm, the length of the arrow tail L is 100 nm, the thickness H of the arrowhead type nano antenna is 420 nm, the background refractive index of the arrowhead type nano antenna is a constant 1, the incident light of the arrowhead type nano antenna is a plane wave, the wave vector is parallel to the z-axis direction, and the polarization is parallel to the x-axis direction. The nano antenna is composed of the arrowhead type of the high-refractive-index material gallium phosphide, under the excitation of the incident plane wave, the wave vector is parallel to the z-axis direction, and the polarization is parallel to the x-axis direction. The structure is a structure capable of supporting electric resonance and magnetic resonance.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical nanoantenna, in particular to a multi-wavelength unidirectional scattering optical nanoantenna based on a gallium phosphide arrowhead. BACKGROUND

[0002] Light scattering based on high refractive index medium nanoantennas has been a focus of many research fields such as optical communication, biophysics, astrophysics and material science. In previous studies, unidirectional light scattering phenomena of single structures such as nanodisks, nanospheres, nanoblocks, etc. have been reported. In addition, unidirectional light scattering has also been shown in some complex structures, such as double-metal plasmonic nanoantennas, plasmonic trimers and large-area plasmonic nanoparticles.

[0003] In recent years, high-dielectric nano-materials have attracted much attention because they can significantly reduce the loss of optical systems. However, they only involve the interaction between electric dipoles, magnetic dipoles and electric quadrupoles. In fact, the interference multipole that can cause unidirectional scattering has been extended from dipoles to high-order multipole and coupling between different multi-mode resonances.

[0004] Nanooptical antennas have wide application prospects in the fields of new light sources, high-density data storage, photolithography technology, solar cells, optical microscopes, etc. In the research of nanooptical antennas, the design of structural size and the optimization of performance are always an important challenge because the conversion and enhancement of light waves need to be realized at the subwavelength scale. Unidirectional nanoantennas can introduce directionality for any nondirectional light emitters such as micro-lasers, nano-lasers or spasers, even quantum dots. However, the multi-wavelength unidirectional scattering of nanoantennas has always been a great challenge. SUMMARY

[0005] The present application makes up for and improves the deficiencies of the prior art, and proposes a novel optical nanoantenna structure that can be used to adjust the direction of the far field. The nanoantenna is an arrowhead type composed of high refractive index material gallium phosphide. Under the excitation of an incident plane wave, the wave vector is parallel to the z-axis direction, and the polarization is parallel to the x-axis direction. This structure is a structure that can support both electric resonance and magnetic resonance.

[0006] The technical scheme adopted by the present application is as follows: a multi-wavelength unidirectional scattering optical nanoantenna based on a gallium phosphide arrowhead, the multi-wavelength unidirectional scattering optical nanoantenna is an arrowhead type nanoantenna, and the material of the arrowhead type nanoantenna is gallium phosphide; the included angle a of the arrowhead of the arrowhead type nanoantenna is 15°-60°, the two side lengths G of the arrowhead are 166nm-303nm, the width M of the arrow tail is 38-42nm, the length L of the arrow tail is 20nm-100nm, and the thickness H of the arrowhead type nanoantenna is 140nm-420nm.

[0007] Further, the arrowhead angle a of the arrowhead-shaped nanoantenna is 15°, the two side lengths G of the arrowhead are 303 nm, the width M of the arrow tail is 40 nm, the length L of the arrow tail is 100 nm, and the thickness H of the arrowhead-shaped nanoantenna is 420 nm.

[0008] Further, the arrowhead angle a of the arrowhead-shaped nanoantenna is 30°, the two side lengths G of the arrowhead are 219 nm, the width M of the arrow tail is 42 nm, the length L of the arrow tail is 60 nm, and the thickness H of the arrowhead-shaped nanoantenna is 280 nm.

[0009] Further, the arrowhead angle a of the arrowhead-shaped nanoantenna is 60°, the two side lengths G of the arrowhead are 166 nm, the width M of the arrow tail is 38 nm, the length L of the arrow tail is 20 nm, and the thickness H of the arrowhead-shaped nanoantenna is 140 nm.

[0010] Further, the background refractive index of the arrowhead-shaped nanoantenna is a constant 1, and the arrowhead-shaped nanoantenna produces a unidirectional scattering phenomenon under excitation of an external field.

[0011] Further, the incident light of the arrowhead-shaped nanoantenna is a plane wave, the wave vector is parallel to the z-axis direction, and the polarization is parallel to the x-axis direction.

[0012] Further, the gallium phosphide arrowhead-shaped optical nanoantenna occurs hybridization, and supports multiple resonance modes: ring dipole, magnetic dipole, magnetic quadrupole, and electric quadrupole resonance.

[0013] Further, the coupling effect of different resonance mode responses in the gallium phosphide arrowhead-shaped optical nanoantenna leads to the generation of electric and magnetic hot spots of the arrowhead structure of the high refractive index material gallium phosphide.

[0014] Further, the gallium phosphide arrowhead-shaped optical nanoantenna keeps the polarization of the incident light along the x-axis and the propagation direction along the +z-axis unchanged, introduces an electric dipole source, and explores its performance as an ED emitter by calculating the Purcell factor (PF).

[0015] Further, the gallium phosphide arrowhead-shaped optical nanoantenna keeps the polarization of the incident light along the x-axis and the propagation direction along the +z-axis unchanged, introduces a magnetic dipole source, and explores its performance as an MD emitter by calculating the Purcell factor (PF).

[0016] Further, the coupling of photons and electrons in the gallium phosphide arrowhead-shaped optical nanoantenna enhances the near-field intensity.

[0017] The beneficial effects of the present application: the present application provides a kind of based on gallium phosphide arrowhead type multi-wavelength unidirectional scattering optical nano antenna, gallium phosphide arrowhead type optical nano antenna structure can realize unidirectional scattering characteristics, backward far-field radiation energy is substantially completely inhibited, and the directionality of far-field scattering can be realized at multiple operating wavelengths, its continuous adjustable optical characteristics provide solid theoretical basis for nano antenna design;It can not only regulate the unidirectionality of far-field scattering, but also can regulate near-field performance, and its near-field characteristics are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a three-dimensional structure schematic diagram of arrowhead type nano antenna in embodiment one;

[0019] Figure 2 It is a three-dimensional far-field comparison schematic diagram of nano antenna in embodiment one at λ = 507nm, λ = 523nm and λ = 589nm wavelength;

[0020] Figure 3 It is a multipole expansion simulation diagram of nano antenna in embodiment one in different resonance modes;

[0021] Figure 4 It is a forward scattering, backward scattering and forward / backward scattering curve diagram of nano antenna in embodiment one;

[0022] Figure 5 It is a comparison diagram of electric field enhancement profile of nano antenna in embodiment one at wavelength 507nm, 523nm, 589nm;

[0023] Figure 6 It is a comparison diagram of magnetic field enhancement profile of nano antenna in embodiment one at wavelength 507nm, 523nm, 589nm;

[0024] Figure 7 It is a two-dimensional far-field diagram of nano antenna in embodiment one at wavelength 507nm;

[0025] Figure 8 It is a two-dimensional far-field diagram of nano antenna in embodiment one at wavelength 523nm;

[0026] Figure 9 It is a two-dimensional far-field diagram of nano antenna in embodiment one at wavelength 589nm;

[0027] Figure 10 It is a position marking diagram of nano antenna in embodiment one at five points of A, B, C, D, E, F;

[0028] Figure 11 It is Purcell factor of nano antenna in embodiment one under electric dipole excitation.

[0029] Figure 12 is the Purcell factor of the nano antenna in Example 1 under magnetic dipole excitation;

[0030] Figure 13 is the electric field contrast plot of the nano antenna in Example 1 at points A, B, C, D, E and F. Embodiment

[0031] Example

[0032] Referring to the drawings, a gallium phosphide arrowhead type multi-wavelength unidirectional scattering optical nano antenna, the multi-wavelength unidirectional scattering optical nano antenna is an arrowhead type nano antenna, and the material thereof is gallium phosphide; the included angle a of the arrowhead of the arrowhead type nano antenna is 15°, the two side lengths G of the arrowhead are 303 nm, the width M of the arrow tail is 40 nm, the length L of the arrow tail is 100 nm, and the thickness H of the arrowhead type nano antenna is 420 nm; the background refractive index of the arrowhead type nano antenna is a constant 1, and the arrowhead type nano antenna produces a unidirectional scattering phenomenon under the excitation of an external field; the incident light of the arrowhead type nano antenna is a plane wave, the wave vector is parallel to the z-axis direction, and the polarization is parallel to the x-axis direction.

[0033] The characteristics of the arrowhead type nano optical antenna are simulated and analyzed by the finite element method algorithm and the multipole decomposition theory. In the simulation, the excitation source adopts a plane wave, the electric field direction is parallel to the x-axis direction, the incident light direction is parallel to the z-axis direction, and the calculation wavelength range is 470 nm - 850 nm. In the calculation, the Gap (Gallium phosphide) - Palik material in the material library is used as a high refractive index material.

[0034] In order to explore the near-field and far-field characteristics of the nano antenna, different modes are usually applied for analysis. Under the excitation of incident light, when two or more modes cooperate with each other, different electromagnetic resonance modes can be activated. In the long wavelength approximation, in order to clarify the physical mechanism of the coupling between various modes, the multipole decomposition in the rectangular coordinate is adopted, including the electric dipole moment ED ), the magnetic dipole moment MD ), the electric quadrupole moment EQ ), and the magnetic quadrupole moment MQ ) to analyze the properties of the scattering cross section, and the formula is as follows:

[0035]

[0036]

[0037] ​​​​

[0038]

[0039]

[0040] where c denotes the speed of light, r and J denote the total distance vector and the total polarization current density excited in the antenna, respectively, denotes the triple integral over the distance vector r , 、 denotes the distance vector in different directions, α, β = x, y, z , , denotes the polarization current density excited in the antenna in different directions, α, β = x, y, z denotes the imaginary unit, Table i denotes the frequency, the Dirac function ω denotes the Taylor series expansion in different directions. α, β = x, y, z The formula for calculating the radiation power of various multipole moments is as follows:

[0041] I

[0042]

[0043] where denotes the dielectric constant in vacuum, ω and c denote the frequency and the speed of light, respectively, denotes taking the imaginary part of a complex number, denote the electric dipole moment ED, , the magnetic dipole moment MD , the electric quadrupole moment EQ , the magnetic quadrupole moment MQ , and the toroidal dipole moment TD , respectively.

[0044] In addition, the total scattering cross section should be mathematically represented by the following formula:

[0045]

[0046] where is the radiation power of the incident light.

[0047] In order to analyze the scattering characteristics of the nano antenna more carefully, Figure 2 ​​​The 3D far-field distributions of the GaP arrow-shaped optical nanoantenna at different FS / BS peak positions are given. It can be seen that when the working wavelength is 507 nm, 523 nm and 589 nm, the 3D (3D) far-field pattern shows unidirectional scattering, that is, the radiation towards the -z direction is almost completely canceled out, while the radiation towards the +z direction is further enhanced. This forward scattering can be explained by the redistribution of electric and magnetic fields.

[0048] In order to understand the origin of the electromagnetic resonance mode, Figure 3 The multipole decomposition of the nanoantenna in the wavelength range of 480 nm to 850 nm is shown. According to the figure, four different resonance peaks can be observed in the total scattering cross section, which occur at wavelengths λ = 485 nm, λ = 515 nm, λ = 523 nm and λ = 559 nm. These peaks can be explained by observing the contribution of each mode to explain the optical properties of the arrow-shaped nanoantenna. Specifically, for wavelengths of 485 nm and 559 nm, the resonance peaks are mainly caused by the joint coupling effect of TD, MD. Unlike the former, the resonance peaks at wavelengths of 515 nm and 532 nm are mainly the result of the joint coupling effect of TD, MD and MQ. Compared with other modes, ED is relatively weak and can be ignored. The total scattering cross section is dominated by TD. This result shows that high-order resonance modes (including TD) also play a key role in the far-field energy modulation of high-refractive-index medium nanoantennas.

[0049] In order to study the far-field scattering properties of the nanoantenna, the forward (FS), backward (BS) and forward / backward scattering (FS / BS) cross sections in the wavelength range of 470 nm to 650 nm are calculated, as Figure 4 shown. It is worth noting that the FS and BS cross sections of the structure can be determined by the integral of the Poynting vector in the half-space with Z coordinates <0 and Z coordinates >0. In addition, three different plasmonic resonance peaks are shown in the FS curve. The peak value of FS / BS occurs at wavelengths of 507 nm, 523 nm and 589 nm, and the corresponding ratio of their intensity is about 13.7, 15.5 and 11.9, respectively. This result shows that the designed arrow-shaped medium nanoantenna has strong directivity.

[0050] In order to obtain more information about the nanoantenna, Figure 5 The spatial distribution of its electric field at wavelengths of 507 nm, 523 nm and 589 nm is shown. For Figure 5 the electric field distribution in, the electric field of the arrow-shaped structure is almost always dispersed at the tip edge, and the current distribution is marked with red arrows. The displacement current in the dielectric, unlike the conduction current in free-electron metals, is produced by the oscillation of bound electrons caused by the field penetration and phase delay effects of particles. In addition,Figure 6 The magnetic fields at the locations of these three resonance peaks in the YOZ plane are given.

[0051] Intensity distribution. The magnetic hotspots are different at these different wavelengths. For a wavelength of λ = 507 nm, in

[0052] Two smaller magnetic hot spots can be seen at the edge of the structure. However, for wavelengths of λ = 523 nm and λ = 589 nm, the magnetic hot spots are mainly distributed in the center, and their intensity is significantly enhanced.

[0053] To clearly study the unidirectional scattering characteristics of gallium phosphide arrow-shaped optical nanoantennas, Figure 7 – Figure 9 The angular distribution of its two-dimensional (2D) far-field scattering intensity at the maximum wavelength of the FS / BS is shown. Significant suppression of backscattering and a strong enhancement of forward scattering are observed at the wavelengths of the FS / BS peak; unidirectional interference produces strong forward scattering at these wavelengths of the nanoantenna. Furthermore, the polarity attenuation of backscattering is closely related to the multipole decomposition of the nanoparticle scattering. Interference between multiple induction modes of the multipole-expanded electromagnetic field can also be used to explain the directivity. Directivity can also be explained by interference between different induction modes of the multipole expansion.

[0054] The effect of enhanced spontaneous emission, i.e., the ratio of the enhanced spontaneous emission rate to the spontaneous emission rate in vacuum, can be measured by the Purcell Factor (PF), and its formula is as follows:

[0055]

[0056]

[0057] In the formula, P0 is the power loss of MD without a resonator in a vacuum, and P is the power loss of an electric dipole emitter or a magnetic dipole emitter with a disk inside the resonator.

[0058] The Purcell value is a crucial parameter for evaluating the electric dipole emission performance of nanoantennas. In this invention, six points A, B, C, D, E, and F are marked on the xz plane along the positive y-axis of the nanoantenna. Figure 10 In this study, keeping the incident light's polarization along the x-axis and propagation direction along the +z-axis constant, the electric dipole source was placed at these six points, and its performance as an ED emitter was explored by calculating the Purcell factor (PF). Figure 11 As can be seen, the Purcell value of the electric dipole source located at point A is the largest, approximately 4.5 × 10⁻⁶. 9The highest PF values ​​are found at points C and F, while the PF values ​​at the other three points are almost zero. Similarly, magnetic dipole sources are placed at these six points to investigate their performance as MD emitters. Figure 12 It can be seen that the magnetic dipole source still has a maximum value at point A, which is 14 × 10⁻⁶. 17 In summary, the emission performance of both electric and magnetic dipole sources in gallium phosphide arrow-shaped optical nanoantennas is significantly enhanced, which has potential application value in fields such as quantum transmitters and fluorescence enhancement.

[0059] Finally, the electric field enhancement of the optical nanoantenna was analyzed. Six points on the optical nanoantenna were selected, and the electric field values ​​were calculated to verify whether electric field enhancement could be achieved. Figure 13 The lines in the graph show the electric field values ​​at these six points. The curves show that the electric field value at point F is the largest at 485 nm, reaching 21.69, while the electric field value at point D is the largest at 559 nm, with a value of 26.388. The data shows that enhanced coupling between photons and electrons can increase the near-field potential, thereby increasing the near-field intensity. Therefore, this optical nanoantenna can also be applied to surface enhancement and other applications.

[0060] Arrow-shaped structures excite different surface plasmon resonance modes: ring dipole, magnetic dipole, magnetic quadrupole, and electric quadrupole resonances. Using a multipole decomposition method, the influence of the responses of different resonance modes on the scattering characteristics of the nanoantenna was analyzed. The coupling effect of these resonance modes leads to the generation of electric and magnetic hot spots and far-field unidirectional scattering in the high-refractive-index gallium phosphide arrow-shaped optical nanoantenna. The electric field strength and Purcell coefficient under electric and magnetic dipole source excitation both indicate that the nanoantenna also exhibits excellent near-field performance. The influence of electric and magnetic dipole source radiation on the response characteristics of different resonance modes of the nanoantenna was demonstrated. This provides a solid theoretical foundation for realizing far-field unidirectional controllable nanoantennas. Example

[0061] The arrow-shaped nanoantenna has an included angle α of 30°, two sides G of 219 nm, a tail width M of 42 nm, a tail length L of 60 nm, and a thickness H of 280 nm. Example

[0062] The arrow-shaped nanoantenna has an included angle α of 60°, two sides G of 166 nm, a tail width M of 38 nm, a tail length L of 20 nm, and a thickness H of 140 nm.

[0063] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the invention to the specific implementations described above. Without departing from the overall concept and protection of the claims, several simple deductions or substitutions can be made, all of which should be considered within the scope of protection of the present invention.

Claims

1. A gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna, characterized in that: The multi-wavelength unidirectional scattering optical nanoantenna is an arrow-shaped nanoantenna made of gallium phosphide. The arrow-shaped nanoantenna has an included angle α of 15°-60°, two side lengths G of 166nm-303nm, tail width M of 38-42nm, tail length L of 20nm-100nm, and thickness H of 140nm-420nm.

2. The gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna according to claim 1, characterized in that: The arrow-shaped nanoantenna has an included angle α of 15°, two sides G of 303 nm, a tail width M of 40 nm, a tail length L of 100 nm, and a thickness H of 420 nm.

3. The gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna according to claim 1, characterized in that: The arrow-shaped nanoantenna has an included angle α of 30°, two sides G of 219 nm, a tail width M of 42 nm, a tail length L of 60 nm, and a thickness H of 280 nm.

4. The gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna according to claim 1, characterized in that: The arrow-shaped nanoantenna has an included angle α of 60°, two sides G of 166 nm, a tail width M of 38 nm, a tail length L of 20 nm, and a thickness H of 140 nm.

5. A gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna according to any one of claims 1-3, characterized in that: The background refractive index of the arrow-shaped nanoantenna is a constant 1.

6. A gallium phosphide arrowhead-shaped multi-wavelength unidirectional scattering optical nanoantenna according to any one of claims 1-3, characterized in that: The incident light of the arrow-shaped nanoantenna is a plane wave with the wave vector parallel to the z-axis and the polarization parallel to the x-axis.

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