CN109270606B - Method for constructing dynamic multifocal super lens based on medium and graphene - Google Patents
Method for constructing dynamic multifocal super lens based on medium and graphene Download PDFInfo
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- CN109270606B CN109270606B CN201811165610.1A CN201811165610A CN109270606B CN 109270606 B CN109270606 B CN 109270606B CN 201811165610 A CN201811165610 A CN 201811165610A CN 109270606 B CN109270606 B CN 109270606B
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- G02B3/00—Simple or compound lenses
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Abstract
The invention discloses a method for constructing a dynamic multifocal superlens based on a medium and graphene. The method comprises the following steps: (1) calculating the phase gradient distribution on the super surface of the medium for incident light with different wavelengths in the infrared wavelength range of 0.7-500 um according to the position relation between the focus and the wavelength; (2) designing different periodic structures for each central wavelength, and determining a specific phase value by combining phase gradient distribution and Pancharatnam-Berry phase; (3) designing a columnar structure with determined height as a basic unit of the dielectric super-surface, and designing a corresponding specific implementation structure and a rotation direction; (4) a reflective focus lens is configured by using multilayer graphene at a base portion, and a position of a focus point is dynamically adjusted by changing a fermi level of the graphene. The invention realizes the effect of the dynamic multi-focus reflecting lens through the medium super surface and the multi-layer graphene structure, and has the advantages of high-efficiency focusing function, ultra wide band, dynamic adjustability, easy integration and the like.
Description
(I) technical field
The invention relates to a method for constructing a dynamic multifocal super lens based on a medium and graphene, and belongs to the fields of geometric optics and micro-nano optics.
(II) background of the invention
The super-surface, as a sub-wavelength structure arranged on a two-dimensional surface, is rapidly developed due to its special function of locally changing the amplitude, polarization and phase of an incident beam. Lenses based on a super-surface design have also attracted a lot of attention, unlike conventional lenses, which are based on optical nanomaterials and are therefore relatively lightweight. When the sub-wavelength nanostructures of the hypersurface form a specific repeating pattern, they can mimic the complex curvature of refracted rays, but are less bulky and have improved ability to focus rays with reduced distortion. However, most of these nanostructured devices are static, thus limiting their functionality. Based on the research on the lens, the invention provides a dynamic multi-focus reflecting lens based on the lens principle by utilizing a multi-layer graphene substrate.
Through the design calculation of the super-surface structure, the multi-focus dynamically adjustable dielectric reflection super-lens based on the multilayer graphene is designed by utilizing the fashionable super-surface technology, the defects of the traditional optical element are overcome, and the multi-focus dynamically adjustable dielectric reflection super-lens has the advantages of ultrathin and ultralight property, two-dimensional plane, simple structure, wide function, capability of controlling all incident energy during focusing, better improvement of spatial resolution and micron-order thickness. The multi-focus dynamic focusing function has very wide application prospect in an integrated optical system. The micro-nano reflecting lens overcomes the defect that the focus is fixed after the structural design is completed, and the practicability of the reflecting focusing lens is greatly improved by dynamically adjusting the focusing position through adjusting the Fermi level of the graphene substrate.
Disclosure of the invention
The invention aims to provide a method for constructing a dynamic multifocal reflective super lens based on a medium and multilayer graphene, which has the advantages of simple and compact structure, easiness in integration and strong practicability.
The purpose of the invention is realized as follows:
in the infrared wavelength working bandwidth of 0.7 um-500 um, firstly, according to the special regulation and control of the super surface to the light wave, the periodic super surface structure of the rotary oscillator responding to the incident light with different wavelengths is designed in a required period under different wavelengths;
step (2), for each central wavelength, calculating phase gradient distribution on the super surface of the medium according to a required focal point and a nano unit structure regulation phase mechanism, different focusing requirement formulas under different wavelengths and a lens aplanatism principle;
step (3), designing a columnar structure with determined height as a basic unit of the medium super surface, combining the obtained phase gradient distribution with a periodic structure of the medium super surface, and adjusting the spatial rotation angle of each unit structure according to the phase requirement of each basic unit and the Pancharatnam-Berry phase to obtain the required phase distribution;
step (4), reflecting incident light with high reflectivity by using multilayer graphene as a substrate, providing a required additional phase for the reflected light by changing the Fermi level of the graphene, realizing dynamic adjustment of the phase of the reflected light, and dynamically changing the focusing position of a focus under the condition of not changing the super-surface structure;
by reasonably designing the parameters of the unit structure, each columnar structure on the super-surface is equivalent to a half-wave phase shifter which can convert most of incident circularly polarized light into orthogonal polarization states thereof. After the left-handed circularly polarized incident electromagnetic wave interacts with the anisotropic super-structured surface structure, its reflected orthogonal polarization electromagnetic wave carries a converted phase portion (called Pancharatnam-Berry phase) containing the original spin phase without phase shift and with induced phase shift, this additional phase being ± 2 θ, where θ is the azimuth angle of the super-surface structure. Meanwhile, the multilayer graphene substrate also generates an additional phase for reflected light, and further tuning of the reflection phase of the original structure is realized.
The aplanatism principle of the lens in the step (2) is used for any focus F (x)1,y1,z1) The super-surface phase should satisfy:
One important point in the present invention that enables the planar beam to be focused after passing through the super-surface is that the reflected phase can contain a smooth change of 0-2 pi. The phase distribution is controlled by the rotation angle of the super-surface basic unit structure, so the key to focus or not is the analysis of the rotation angle of the unit structure.
Preferably, the method for constructing the dynamic multifocal superlens based on the medium and the graphene is characterized in that the wavelength range of the selected light wave is within an infrared wavelength range, the surface conductivity of the graphene is greatly influenced by chemical potential in the wavelength range according to the optical characteristics of the graphene, and when the chemical potential is increased, the surface conductivity is greatly increased, so that a larger reflectivity is provided for the reflection of electromagnetic waves.
Preferably, the method for constructing a dynamic multifocal superlens based on a medium and graphene is characterized in that the selected material of the columnar structure is characterized in that: the high dielectric constant and low loss in the working waveband include silicon nitride, phosphorized graft, titanium dioxide, silicon and the like.
Preferably, the method for constructing a dynamic multifocal superlens based on a medium and graphene is characterized in that the columnar structure in the step (3) includes a quadrilateral column, a triangular column, a hexagonal column, a column, an elliptic column and the like.
Has the advantages that: the invention makes full use of the different responses of the designed super-surface structure under different wave bands and the phase compensation characteristic of the high reflectivity of the substrate multi-layer graphene, so that under the condition of high transmission rate and high conversion rate of the super-surface, the light can be reflected out with high reflectivity when reaching the substrate, the problem of energy loss caused by using metal materials as the substrate of the prior reflection type focusing lens is solved, the conversion rate and the focusing efficiency of light waves are greatly improved, the focusing position of a focus can be dynamically adjusted by adjusting the Fermi level of graphene, thereby forming a high-reflectivity, wide-band, focus-adjustable multifocal reflective lens which can be used for distance measurement of multiple objects, clear images can be formed at different focal lengths under different Fermi energy levels of the multi-layer graphene, and the purpose of dynamic ranging is achieved.
(IV) description of the drawings
Fig. 1 is a schematic diagram of right-handed circularly polarized light (RCP) reflected after left-handed circularly polarized Light (LCP) is incident on a multifocal reflective lens.
FIG. 2 is a schematic view of a left-hand circularly polarized light ray entering and passing through a designed reflective lens to form multiple focal spots on the same side as the entering side.
Fig. 3 is a schematic plan view of an array of different structures on a multi-focus reflective lens, which respond to different wavelengths and correspond to different focuses, where w, l, and h respectively indicate the width, length, and height of the three structures.
Fig. 4 is a graph of simulated focal length values of graphene at different fermi levels at infrared wavelengths.
FIG. 5 is a schematic diagram of multi-focus two-dimensional and three-dimensional simulations formed after simulation of the overall structure using simulation software.
(V) detailed description of the preferred embodiments
The following further describes embodiments of the present invention with reference to the drawings.
A method for constructing a dynamic multifocal superlens based on a medium and graphene specifically comprises the following steps:
and (1) in the infrared wavelength working bandwidth of 0.7-500 um, according to the special modulation of the super-surface structure on the light wave, researching the super-surface structure and size capable of responding to different wave bands. Through the reasonable design of the unit structure, as shown in fig. 1, when left-handed circularly polarized waves (LCP) vertically enter a dielectric super-surface composed of a SiO2 dielectric layer, a multilayer graphene substrate and a unit structure with high dielectric constant and low loss at infrared wavelength, due to the polarization conversion characteristic and focusing characteristic of the designed super-surface structure and the high reflection characteristic of the multilayer graphene substrate, when light passes through the designed super-surface structure, light waves with two different polarization directions, namely right-handed circularly polarized waves (RCP) and left-handed circularly polarized waves (LCP), can be reflected and generated, and right-handed circularly polarized light opposite to the polarization state of the incident light is focused, and different focus points are generated for a plurality of wavelengths under the action of different periodic structures of the super-surface. The structures 1, 2, and 3 in fig. 3 form focuses in response to near-infrared, mid-infrared, and far-infrared bands, respectively. Responding to different bands means: the super-surface structures can respectively convert incident light into reflected light with the polarization state opposite to that of the incident light in different wavebands, each super-surface structure can only convert one waveband, and the mutual influence can be ignored.
And (2) calculating the phase distribution of the unit structure by utilizing the lens aplanatic principle according to the required focal position and arranging the unit structure according to the form of the figure 3. Each lens can produce a focus according to the focusing property of the lens, but when a plurality of sub-lenses are combined in one lens, each lens forms a focusing point corresponding to each wavelength, the geometric parameters of each lens structure are identical, but the spatial rotation angle is different, and each structure corresponds to one lens. The specific calculation of the phase-forming focal point for each structure on the lens is as follows:
firstly, the position of each focus point is determined, and then the aplanatism principle of the lens is applied
And calculating the phase distribution of the super-surface lens corresponding to each focus, namely the required rotation angle of each unit structure.
After determining the phases of the lenses corresponding to different wavelengths, the functions of the multifocal lens can be satisfied by only placing the three super-surface structures at corresponding positions and rotating the super-surface structures by corresponding angles, wherein Pancharatnam-Berry phases are utilized. Assuming that the electric field of incident circularly polarized light is expressed as:
wherein E is0And (r, theta) is the amplitude of the optical field, sigma is +/-1, and the sign represents left-handed and right-handed circularly polarized light. The output light field of the super-surface is:
we note that the output light field circular polarization handedness is reversed and an additional phase is obtained:
φPB＝2σθ (5)
the column with the variation of the pointing angle space theta or the complementary structure thereof is a typical unit structure for constructing a geometric phase type super-structured surface device. The structure has anisotropy for different polarization states, so when circularly polarized electromagnetic waves are incident on the surface of the structure, the electromagnetic waves transmitted after interaction with the structure can excite electromagnetic waves with orthogonal polarization states besides the main polarized electromagnetic waves. And the electromagnetic wave in the orthogonal polarization state generates a phase jump related to the structure pointing angle, and the phase jump value is 2 sigma theta (sigma is 1). The parameters of the columnar structure are reasonably designed, so that the homopolar reflected wave can be minimized, and the cross polarization reflected wave can be maximized.
The three different cylindrical structures of the super-surface proposed by the present design as shown in fig. 3 include three lenslets represented by rectangular blocks. Note that: the different rectangular structures here merely represent several different sub-lenses, and the composition of the lenses is explained here, and does not mean that the unit structure of the super-surface here is necessarily a rectangular block. The columnar structure comprises a quadrilateral columnar structure, a triangular columnar structure, a hexagonal columnar structure, a columnar structure, an elliptic columnar structure and the like.
A left-handed circularly polarized Light (LCP) beam is incident on the dielectric subsurface, and responds to different wavelengths through different structures of the subsurface, and at the same time, due to reflection of the multi-layer graphene, the incident light forms three different focuses on the same side of the dielectric subsurface, as shown in fig. 2, three independent reflective focusing focuses are formed in three defined bands, and the focus position can be dynamically adjusted by adjusting the fermi level of the multi-layer graphene, and the relationship of the focal length varying with the fermi level of the multi-layer graphene is shown in fig. 4.
When the designed super-surface is incident by using left-handed circularly polarized light of a certain waveband, the numerical simulation figure 5 shows that only one focus is generated in reflected light, and the number of simulated focuses corresponding to the number of the incident wavebands is increased gradually, so that the feasibility of the designed multifocal dynamically adjustable reflecting lens is demonstrated from the theoretical angle.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims.
Claims (6)
1. A method for constructing a dynamic multifocal super lens based on a medium and graphene, wherein the multifocal super lens is a multifocal super surface reflecting lens, and the multifocal super surface reflecting lens at least comprises a multi-layer graphene substrate and a plurality of super surface arrays with different periodic structures, and is characterized by comprising the following steps:
step (1), in the working bandwidth of infrared wavelength of 0.7 um-500 um, firstly, researching the optical characteristics of the super-surface structures with different shapes and sizes, and designing the periodic super-surface structure of the rotary oscillator responding to the incident light with different wavelengths in a required period under different wavelengths;
step (2), for each central wavelength, calculating phase gradient distribution on the super surface of the medium according to a required focal point and a nano unit structure regulation phase mechanism, different focusing requirement formulas under different wavelengths and a lens aplanatism principle;
step (3), designing a columnar structure with determined height as a basic unit of the medium super surface, combining the obtained phase gradient distribution with a periodic structure of the medium super surface, and adjusting the spatial rotation angle of each unit structure according to the phase requirement of each basic unit and the Pancharatnam-Berry phase to obtain the required phase distribution;
and (4) reflecting incident light with high reflectivity by using the multilayer graphene as a substrate, providing a required additional phase for the reflected light by changing the Fermi level of the graphene, realizing dynamic adjustment of the phase of the reflected light, and dynamically changing the focusing position of a focus under the condition of not changing the super-surface structure.
2. The method of claim 1, wherein each of the columnar structures on the super-surface is equivalent to a half-wave plate, which can convert most of incident circularly polarized light into its orthogonal polarization state, and after the left-handed circularly polarized incident electromagnetic wave interacts with the anisotropic super-surface structure, the reflected orthogonal polarization state electromagnetic wave contains an original spin phase without phase shift and a converted phase part with induced phase shift, and the additional phase is ± 2 θ, where θ is the azimuth angle of the super-surface unit structure, and the multi-layer graphene substrate also generates additional phase to the reflected light, thereby further tuning the reflection phase of the original structure.
3. The method of claim 1, wherein the method comprises constructing a dynamic multifocal superlens based on a medium and grapheneUsing the principle of lens aplanatism, i.e. for an arbitrary focus F (x)1,y1,z1) The super-surface phase should satisfy:
4. The method as claimed in claim 1, wherein the wavelength range of the selected light wave is in the infrared wavelength range, and according to the optical characteristics of graphene, the surface conductivity of graphene in the infrared wavelength range is influenced by chemical potential to be larger than that in other wavelength ranges, and when the chemical potential is increased, the surface conductivity is greatly increased, which provides a larger reflectivity for the reflection of electromagnetic waves compared with a conventional lens.
5. The method of claim 1, wherein the material characteristics of the columnar structures in step (3) are: the dielectric constant at the working wave band is high and the loss is low, and the material of the columnar structure can be silicon nitride, phosphorization graft, titanium dioxide and silicon.
6. The method according to claim 1, wherein the columnar structures in step (3) comprise a quadrilateral column, a triangular column, a hexagonal column, a cylinder and an elliptic column.
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| CN111913241A (en) * | 2019-05-07 | 2020-11-10 | 三星电子株式会社 | Superlens and optical device comprising a superlens |
| CN110133876B (en) * | 2019-06-18 | 2020-10-09 | 南开大学 | Terahertz graphene super-surface lens with adjustable focal length and design method |
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| CN110632684B (en) * | 2019-10-21 | 2021-06-01 | 中国科学院上海光学精密机械研究所 | Super-surface sparse aperture lens |
| CN112068228B (en) * | 2020-07-31 | 2022-04-26 | 国家纳米科学中心 | Plane focusing lens device based on phonon polarized waves |
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| CN113608282B (en) * | 2021-08-16 | 2023-04-25 | 合肥工业大学 | Six-pixel full-vector polarization information acquisition device based on full-medium super surface and application |
| CN113695748B (en) * | 2021-08-23 | 2022-10-25 | 西安交通大学 | Rapid preparation method of sharkskin surface structure based on spatial light modulator |
| CN114280707B (en) * | 2022-03-03 | 2022-06-03 | 季华实验室 | Full-polarization medium super-structured lens and use method thereof |
| CN115024695A (en) * | 2022-08-10 | 2022-09-09 | 杭州纳境科技有限公司 | Super lens subassembly, optical system and wearable equipment |
| CN115421227B (en) * | 2022-10-08 | 2023-06-13 | 桂林电子科技大学 | Bionic antireflection film structure |
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| CN108490509B (en) * | 2018-04-08 | 2019-10-11 | 武汉大学 | The super surfacing of dielectric geometric phase of low depth-to-width ratio and its structural optimization method |
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