Sub-wavelength antenna, wavelength-controllable superlens and superlens design method
Technical Field
The invention relates to the technical field of micro-nano photonics, in particular to a sub-wavelength antenna, a super lens with controllable wavelength and a super lens design method.
Background
The super surface, an ultra-thin plane composed of sub-wavelength optical scatterers, has the ability to manipulate the wavefront of electromagnetic waves at will, and has attracted great attention of researchers in the past few years. By spatially arranging sub-wavelength antennas of different structural parameters, various functional devices can be designed, such as beam deflectors, planar lenses, glass slides and super-surface holograms. The high resolution and high precision of the super-surface-based functional device enable the super-surface-based functional device to have wide application prospect in new generation wearable equipment and imaging/sensing thin optical systems. However, most super-surface functional devices are static and do not have dynamic tunability, and application scenes of the super-surface devices are greatly limited.
In recent years, researchers have proposed using different modulation techniques to design super-surface devices that implement dynamics, such as: mechanical deformation of elastomers, phase change materials or liquid crystals as embedding media, use of electro/photo diodes, etc. However, in most solutions, the super-surface is made of different materials, such as elastic materials, phase change materials or diode patch materials, and the complexity of the structure increases the difficulty of manufacturing the structure. Meanwhile, the weak light interacts with the substance to cause small refractive index changes, and the modulation depth of the dynamic super-surface is usually small. In 2020, the professor jennifera. dione, stanford university, usa, proposed to introduce fine periodic perturbations into Si nanorods, to improve the quality factor of the structural resonance mode (Q >5000), and to amplify the refractive index change. Then based on the nonlinear Kerr effect, a two-dimensional high Q superlens with dynamic focusing capability is realized. However, the ultra-small size (-50 nm) of the periodic notches in the Si nanorods is difficult to precisely manufacture, and the fine periodic perturbations are difficult to apply in the design of three-dimensional superlenses.
In view of the foregoing, there are still significant challenges to achieving a dynamic superlens with good performance that is easy to manufacture. In addition, dynamic hypersurfaces with wavelength (polarization or angle, etc.) dependent properties have not been reported.
Disclosure of Invention
The invention aims to solve the technical problem of providing a subwavelength antenna, a wavelength-controllable superlens and a superlens design method, wherein the subwavelength antenna (all-metal C-shaped antenna) with different structural parameters is spatially arranged to realize the dynamic switchable and zooming superlens of wavelength control.
The technical scheme adopted by the invention for solving the technical problems is as follows: the subwavelength antenna comprises a resonator and a metal substrate, wherein the resonator is arranged on the metal substrate and is a C-shaped ring provided with an opening.
The opening angle range of the C-shaped ring is 10-350 degrees.
The radius range of the C-shaped ring is 100 nm-180 nm.
The metal substrate is made of gold, silver or aluminum.
The technical scheme adopted by the invention for solving the technical problems is as follows: the super lens with the controllable wavelength comprises a plurality of sub-wavelength antennas, wherein the sub-wavelength antennas are arranged in space based on an amplitude-phase distribution physical model, and C-shaped rings of the sub-wavelength antennas have different opening angles and radiuses.
The formula of the physical model of amplitude and phase distribution is as follows:
wherein (x, y) is the spatial position coordinate of the super lens, n is the refractive index of the medium around the super lens, f is the focal length of the super lens, and lambda
0The vacuum wavelength of the incident light.
The technical scheme adopted by the invention for solving the technical problems is as follows: provided is a superlens design method, including:
step (1): constructing an amplitude phase distribution physical model of the superlens;
step (2): designing a plurality of the sub-wavelength antennas according to the amplitude-phase distribution physical model, wherein the C-shaped rings of the plurality of the sub-wavelength antennas have different opening angles and radii;
and (3): a plurality of sub-wavelength antennas with different structural parameters are arranged to form the super lens.
The formula of the amplitude and phase distribution physical model in the step (1) is as follows:
wherein (x, y) is the spatial position coordinate of the super lens, n is the refractive index of the medium around the super lens, f is the focal length of the super lens, and lambda
0The vacuum wavelength of the incident light.
The opening angle range of the C-shaped ring in the step (2) is 10-350 degrees.
The radius range of the C-shaped ring in the step (2) is 100 nm-180 nm.
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects: the sub-wavelength antenna (the all-metal C-shaped antenna) provided by the invention has low ohmic loss and high sensitivity, and the all-metal C-shaped antenna with different structural parameters is spatially arranged, so that the wavelength-controlled dynamically switchable and zooming super lens is realized; according to the invention, by changing the radius and the opening angle of the all-metal C-shaped antenna, the phase change of the cross polarization reflected light of the antenna can cover 0-2 pi; the all-metal C-shaped antenna greatly reduces the design difficulty of the adjustable super-surface device, increases the tunable freedom degree, and provides a new idea for realizing reconfigurable, multiplexed and multifunctional super-surface devices.
Drawings
FIG. 1 is a schematic diagram of a subwavelength antenna configuration according to an embodiment of the invention;
FIG. 2 is a top plan view of a subwavelength antenna according to an embodiment of the invention;
FIG. 3 is a schematic diagram of a superlens structure according to an embodiment of the present invention;
FIG. 4 shows an exemplary embodiment of the present invention where the incident light is λ0The focusing effect of the superlens at 950nm is shown schematically.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The embodiment of the invention relates to a subwavelength antenna, which comprises a resonator and a metal substrate, wherein the resonator is arranged on the metal substrate and is a C-shaped ring provided with an opening; therefore, the sub-wavelength antenna in this embodiment is an all-metal C-shaped antenna, and the all-metal C-shaped antenna supports a symmetric mode and an anti-symmetric mode with orthogonal polarizations. The metal substrate is made of gold, silver or aluminum, and due to the existence of the metal substrate, the electromagnetic field of the all-metal C-shaped antenna is mostly localized in the external environment (> 95%), and the antenna has low ohmic loss and high sensitivity. The all-metal C-shaped antenna adjacent medium can be switched from water to a micro bubble by using the laser-induced bubble effect, and the corresponding refractive index variation is-0.333, so that the wavelength shift (blue shift) of the antenna resonance mode is larger than 200 nm.
As shown in fig. 2, the resonator is disposed at a central position of the surface of the metal substrate, the opening angle θ of the C-shaped ring ranges from 10 ° to 350 °, the radius R of the C-shaped ring ranges from 100nm to 180nm, and the amplitude and phase of the cross-polarized reflected light of the antenna can be effectively controlled by changing the radius R and the opening angle θ of the all-metal C-shaped antenna, which is described in detail below by way of an example:
for example, when the radius R of the C-shaped ring is 150nm, the following phenomenon can be obtained by changing the antenna opening angle θ (100 ° to 280 °):
(1) when the wavelength of incident light is lambda0When the refractive index of the medium is n-1.0, the cross polarization reflection amplitude of the antenna is larger than that of the medium with the refractive index of n-1.333, the reflection phase can be changed to cover 0-2 pi when n-1.0, and the reflection phase is slightly changed to be less than 2 pi when n-1.333.
(2) When the wavelength of incident light is lambda0At 700nm, the reflection amplitude of the cross polarization of the antenna is basically equivalent under the conditions that the medium refractive index is n equal to 1.0 and n is 1.333, and the phase can cover 0-2π。
(3) When the wavelength of incident light is lambda0At 850nm, the cross polarization reflection amplitude of the antenna is larger at a medium refractive index n of 1.333 than at a medium refractive index n of 1.0, and the change in reflection phase at n of 1.333 can cover 0-2 pi, while the change in reflection phase at n of 1.0 cannot cover 0-2 pi.
In light of the wavelength-dependent properties described above, the present embodiments also provide a wavelength-controllable optical device including, but not limited to, superlenses, supersurface holograms, beam deflectors. The present embodiment takes a superlens as an example, the superlens includes several subwavelength antennas with different structural parameters (i.e. C-shaped rings with different opening angles and radii), and the several subwavelength antennas are spatially arranged to form the superlens.
The present embodiment also relates to a superlens design method, including:
step (1): an amplitude phase distribution physical model for the superlens is constructed.
The formula of the amplitude and phase distribution physical model in the step (1) is as follows:
wherein (x, y) is the spatial position coordinate of the super lens, n is the refractive index of the medium around the super lens, f is the focal length of the super lens, and lambda
0The vacuum wavelength of the incident light.
Step (2): and designing a plurality of sub-wavelength antennas with different structural parameters according to the amplitude and phase distribution physical model, namely, the C-shaped rings of the plurality of sub-wavelength antennas have different opening angles and radii so as to accurately match the amplitude and phase distribution in the physical model.
The opening angle range of the C-shaped ring in the step (2) is 10-350 degrees, and the radius range of the C-shaped ring is 100-180 nm.
And (3): a plurality of sub-wavelength antennas with different structural parameters are arranged to form the super lens.
Further, FIG. 4 is a graph of the intensity variation of the superlens along the x-axis at the center of the focal plane, particularly illustrating λ at the incident light0950nm time super lensThe full width at half maximum of the focused light spot can reach the diffraction limit (0.5 lambda)0and/NA). Therefore, when the refractive index of the medium around the superlens is changed from n to 1.333 to n to 1.0, the super surface structure designed by the present embodiment can be realized at λ0A broadband dynamic switchable lens with high modulation depth is achieved at incident light wavelengths in the range 850nm to 1000nm, 800nm dynamic zoom lens.
It should be noted that the sub-wavelength antenna in this embodiment can also be designed to implement a super-surface optical device with controllable wavelength in other band ranges (such as visible light band, infrared band, and terahertz band), and only the structural parameters of the sub-wavelength antenna need to be modified correspondingly.
Therefore, the sub-wavelength antenna (the all-metal C-shaped antenna) provided by the invention has low ohmic loss and high sensitivity, and the all-metal C-shaped antenna with different structural parameters (namely radius and opening angle) is spatially arranged, so that the wavelength-controlled dynamic switchable and zooming superlens is realized.