阅读说明：本技术 基于集成超颖表面的宽带消色差透镜和波束偏折器 (Broadband achromatic lens and beam deflector based on integrated metasurfaces ) 是由 黄玲玲 陈屿丰 刘冰意 王涌天 于 2021-09-22 设计创作，主要内容包括：本发明涉及一种基于集成超颖表面的宽带消色差透镜和波束偏折器,属于微纳光学、光学设计、显示技术领域。该方法使用具有不同光谱响应的集成超颖原子构建宽带消色差超颖表面,所采用的集成超颖原子由相位板和纳米柱两部分组成,相位板的引入使得集成超颖表面在宽波段的相位调制能力较普通超颖表面得到提升,加之圆柱和环形柱结构的纳米柱天线阵列对相位进行更加细致的调控,使超颖表面在连续宽波段实现消色差功能。本发明提到的集成超颖表面可以被用于设计宽带消色差超透镜和宽带消色差波束偏折器等器件,所设计超透镜可以在宽波段范围内实现良好的消色差聚焦和成像,波束偏折器可以使宽波段入射光偏折相同角度出射,实现消色差波束偏折功能。(The invention relates to a broadband achromatic lens and a beam deflector based on an integrated metasurface, and belongs to the technical field of micro-nano optics, optical design and display. The method uses integrated metasoma with different spectral responses to construct a broadband achromatic metasurface, the adopted integrated metasoma consists of a phase plate and a nano-column, the phase modulation capability of the integrated metasoma in a wide band is improved compared with that of a common metasurface due to the introduction of the phase plate, and in addition, the nano-column antenna array with a cylindrical and annular column structure carries out finer regulation and control on the phase, so that the achromatic function of the metasurface in a continuous wide band is realized. The integrated metasurface can be used for designing devices such as a broadband achromatic superlens, a broadband achromatic beam deflector and the like, the designed superlens can realize good achromatic focusing and imaging in a broadband range, and the beam deflector can deflect incident light of the broadband to emit light at the same angle, so that the achromatic beam deflecting function is realized.)

1. A broadband achromatic lens and beam deflector based on integrated metasurfaces, comprising: the phase plate is integrated with the equal-height nano-column antenna of the common metasurface to realize wider-range phase modulation compared with the common metasurface, thereby realizing a large-size or large-numerical-aperture broadband achromatic metasurface.

2. An integrated metasurface-based broadband achromatic lens and beam deflector of claim 1, wherein: the nano-column antenna is a cylindrical nano-column antenna or an annular column nano-antenna, and the materials of the two nano-columns and the phase plate are both amorphous silicon.

3. The method for preparing the broadband achromatic lens and the beam deflector with the integrated metasurface is characterized by comprising the following steps of: the method comprises the following steps:

step one, constructing the metasoma integrated with the metasurface by using a phase plate and a nano-column, performing simulation calculation on phase response provided by the metasoma when the metasoma works in a wide waveband to obtain phase response of a metasoma library, and processing the phase response to construct a phase dispersion space;

changing the structural parameters of the metamaterial atoms, and performing simulation calculation on the phase response of the nano-columns to obtain a phase response A; calculating the phase response B of the phase plate by using the formula (1); the structural parameters include: when a cylindrical structure is used, the structural parameter is the radius; when the annular column structure is used, the structural parameter is the outer radius;

B＝ω(n-1)d/c (1)

where ω is the angular frequency of the incident light, n is the refractive index of the phase plate material for the frequency of the incident light, d is the thickness of the phase plate, and c is the speed of light

Adding the phase response A and the phase response B pairwise to obtain the phase response of the metasone library;

M_ij＝A_i+B_j (2)

taking the phase response of the minimum frequency light of the wave band required by design as a reference phase, and taking the difference value obtained by subtracting the phase response of the minimum frequency light from the phase response of the maximum frequency light as a phase compensation value, namely the dispersion value of the phase along with the frequency; each of the meta-atoms is described by two quantities, a reference phase and a phase dispersion value; introducing a plane rectangular coordinate system, wherein the horizontal axis and the vertical axis are respectively a reference phase and a phase dispersion value, all the metasoma are expressed by points in the coordinate system, and the set of the points covered by all the metasoma in the coordinate system is the phase dispersion space of the metasoma library;

step two, calculating a phase dispersion space actually required by the metasurface, comparing the phase and dispersion with the phase dispersion space of the metasurface library, selecting a structure required at each position of the metasurface, and arranging the selected structures to form a two-dimensional array, so as to obtain the integrated achromatic metasurface required by the design;

the phase distribution formula required by the design of the broadband achromatic superlens is

The phase distribution formula required by the design of the broadband achromatic beam deflector is as follows

Where ω is the angular frequency of the incident light, c is the speed of light, r₀F is the designed focal length of the super lens for the radius of the designed super lens, the designed focal length f is a determined value for a given super lens, and theta is the designed emergent light deflection angle. r is the distance from a certain point on the metasurface to the center of the designed superlens, namely the radius of the certain point on the lens, for the beam deflector designed by the formula (4), a straight line in the plane where the metasurface is located is selected as a datum line x which is 0, and x is the distance from the certain point on the beam deflector to the datum line.

The phase calculated by using the formula (3) is a function of two quantities of the position r and the frequency omega, the minimum frequency of a working wave band required by design is substituted into the formula (3), the distribution of the reference phase relative to the position r can be obtained, and the distribution of the phase dispersion relative to the position r can be obtained by subtracting the phase distribution of the maximum frequency and the phase distribution of the minimum frequency;

the phase calculated by using the formula (4) is a function of two quantities of the position x and the frequency omega, the minimum frequency of a working wave band required by design is substituted into the formula (4), the distribution of the reference phase relative to the position x can be obtained, and the distribution of the phase dispersion relative to the position x can be obtained by subtracting the phase distribution of the maximum frequency and the phase distribution of the minimum frequency;

and (3) the required reference phase and the phase dispersion at any position r or x on the metasurface are both expressed as a point in a phase dispersion space, the point of the metasone closest to the point in the phase dispersion space is searched, and the metasone represented by the point is selected as the required structure at the position on the metasurface. The operation of finding the desired metamaterial atoms is also performed for other positions on the metasurface. All the metasoms are arranged according to positions to complete the construction of the metasurface, and the metasurface can realize the functions of an achromatic lens or a beam deflector.

Technical Field

The invention relates to a broadband achromatic lens and a beam deflector based on an integrated metasurface, in particular to a design method of the broadband achromatic superlens and the broadband achromatic beam deflector, and belongs to the technical field of micro-nano optics, optical design and display.

Background

Chromatic aberration is aberration in an optical system, such as image quality degradation due to material dispersion of optical elements, and is usually corrected in a manner of stacking and optimizing a plurality of lenses in a conventional optical system design process, but this usually results in an increase in thickness and weight of the optical elements and an increase in the overall volume of the optical system. The metasurface is a new method for correcting chromatic aberration of an optical element, and generally consists of a metal or medium nano antenna array which is arranged periodically, quasiperiodically or randomly in sub-wavelength size, can be used for modulating the amplitude and the phase of an optical field in high resolution in the sub-wavelength size, and has great potential in the fields of information processing, beam shaping, micro-nano holography, polarization control and the like. The field of leading edge hot spots is to realize the lightness, thinness and miniaturization of optical elements by utilizing the metamaterial surface design and realizing the functions of optical elements such as lenses and the like to replace the traditional refractive elements. The metasurfaces provide new and more degrees of freedom for dispersion modulation of optical elements, and typically, the geometry, material properties, and spatial arrangement of the metasites all affect the phase and amplitude response of the metasurfaces to perform various functions as desired. By reasonably selecting and arranging the metamaterial atoms, different phase distributions can be provided for incident lights with different wavelengths, so that the effects of achromatic lens focusing, beam deflection and the like of the incident lights with wide wave bands are realized, and therefore, a new generation of optical elements based on the metamaterial surfaces has great potential in the aspects of chromatic dispersion regulation and chromatic aberration correction of an optical system.

Although the related technology of the existing metasurface dispersion regulation realizes functions of an achromatic superlens and the like in wave bands of visible light, near infrared, middle infrared, terahertz and the like, the achromatic superlens reported at present cannot realize the design of large diameter and large numerical aperture generally, as the metasurface is required to provide larger phase compensation for realizing the functions of the broadband achromatic superlens with large diameter and large numerical aperture, and if the metasurface is required to provide larger phase compensation, a unit structure of the metasurface needs a larger depth-to-width ratio, which brings great challenges to actual processing. Due to the limitation of processing conditions, the wide-band achromatic superlens with large diameter and large numerical aperture is difficult to realize all the time, which also causes obstruction to the practical application of the superlens. A new design scheme of the micro-nano structure is urgently needed, the depth-to-width ratio of the metamaterial atomic structure can be reduced, the processing difficulty is reduced, and actual processing is realized. In recent years, several new methods for designing achromatic flat optical elements based on micro-nano optics and diffraction optics have been proposed. The multi-order diffraction lens is a new design method of achromatic flat lens, the whole structure of the lens is concentric ring type, and is composed of a plurality of rings with different heights and classes, the achromatization function [1] Meem M, Banerji S, Majumder A, Pies C, Oberbiermann B, sensor-Rodrigz B, Menon R.Inverse-designed optically flat lens using imaging the optical fiber and NA is 0.3[ J ]. appl.Phys.Lett.2020,117,041101 can be approximately realized by optimizing the heights and widths of the rings, but the achromatization function can not be accurately designed. To provide more precise designs, the incorporation of metasurface nanostructures needs to be considered. In recent years, research has proposed the construction of three-dimensional Integrated metasurfaces for realizing the function of color holography, which are composed of two parts of a hologram nanostructure array and a microcavity array acting as a filter [2] Hu Y, Luo X, Chen Y, et al.3d-Integrated metasurfaces for full-color hologrAN _ SNhy [ J ] Light: Science & Applications,2019,8(1):86. The double-layer integrated structure provides a new solution for the design of the broadband achromatic metasurface.

Disclosure of Invention

The invention aims to solve the problem that an achromatic superlens cannot realize large diameter and large numerical aperture generally, and provides a broadband achromatic lens and a beam deflector based on an integrated metasurface; the lens and the beam deflector can realize the functions of an achromatic metasurface of a near-infrared broadband, and can realize the functions of an achromatic lens, an achromatic beam deflector and the like according to different structures.

The purpose of the invention is realized by the following technical scheme:

a broadband achromatic lens and a beam deflector based on an integrated metasurface integrates a phase plate with a high-altitude nano-column antenna of a common metasurface so as to realize wider-range phase modulation compared with the common metasurface and further realize a large-size or large-numerical-aperture broadband achromatic metasurface;

a method of making an integrated metasurface broadband achromatic lens and beam deflector, comprising the steps of:

step one, constructing the metasoma integrated with the metasurface by using a phase plate and a nano-column, performing simulation calculation on phase response provided by the metasoma when the metasoma works in a wide waveband to obtain phase response of a metasoma library, and processing the phase response to construct a phase dispersion space;

changing the structural parameters of the metamaterial atoms, and performing simulation calculation on the phase response of the nano-columns to obtain a phase response A; calculating the phase response B of the phase plate by using the formula (1); the structural parameters include: when a cylindrical structure is used, the structural parameter is the radius; when the annular column structure is used, the structural parameter is the outer radius;

B＝ω(n-1)d/c (1)

where ω is the angular frequency of the incident light, n is the refractive index of the phase plate material for the frequency of the incident light, d is the thickness of the phase plate, and c is the speed of light

Adding the phase response A and the phase response B pairwise to obtain the phase response of the metasone library;

M_ij＝A_i+B_j (2)

the A and the B are both phase responses of a working wave band, and for simplifying calculation, phases at two ends of the wave band are taken for calculation and design. Taking the phase response of the minimum frequency light of the wave band required by design as a reference phase, and taking the difference value obtained by subtracting the phase response of the minimum frequency light from the phase response of the maximum frequency light as a phase compensation value, namely the dispersion value of the phase along with the frequency; each of the meta-atoms is described by two quantities, a reference phase and a phase dispersion value; introducing a plane rectangular coordinate system, wherein the horizontal axis and the vertical axis are respectively a reference phase and a phase dispersion value, all the metasoma are expressed by points in the coordinate system, and the set of the points covered by all the metasoma in the coordinate system is the phase dispersion space of the metasoma library;

step two, calculating a phase dispersion space actually required by the metasurface, comparing the phase and dispersion with the phase dispersion space of the metasurface library, selecting a structure required at each position of the metasurface, and arranging the selected structures to form a two-dimensional array, so as to obtain the integrated achromatic metasurface required by the design;

the phase distribution formula required by the design of the broadband achromatic superlens is

The phase distribution formula required by the design of the broadband achromatic beam deflector is as follows

Where ω is the angular frequency of the incident light, c is the speed of light, r₀F is the designed focal length of the super lens for the radius of the designed super lens, the designed focal length f is a determined value for a given super lens, and theta is the designed emergent light deflection angle. r is the distance from a certain point on the metasurface to the center of the designed superlens, namely the radius of the certain point on the lens, for the beam deflector designed by the formula (4), a straight line in the plane where the metasurface is located is selected as a datum line x which is 0, and x is the distance from the certain point on the beam deflector to the datum line.

The phase calculated by using the formula (3) is a function of two quantities of the position r and the frequency omega, the minimum frequency of a working wave band required by design is substituted into the formula (3), the distribution of the reference phase relative to the position r can be obtained, and the distribution of the phase dispersion relative to the position r can be obtained by subtracting the phase distribution of the maximum frequency and the phase distribution of the minimum frequency;

the phase calculated by using the formula (4) is a function of two quantities of the position x and the frequency omega, the minimum frequency of a working wave band required by design is substituted into the formula (4), the distribution of the reference phase relative to the position x can be obtained, and the distribution of the phase dispersion relative to the position x can be obtained by subtracting the phase distribution of the maximum frequency and the phase distribution of the minimum frequency;

and (3) the required reference phase and the phase dispersion at any position r or x on the metasurface are both expressed as a point in a phase dispersion space, the point of the metasone closest to the point in the phase dispersion space is searched, and the metasone represented by the point is selected as the required structure at the position on the metasurface. The operation of finding the desired metamaterial atoms is also performed for other positions on the metasurface. All the metasoms are arranged according to positions to complete the construction of the metasurface, and the metasurface can realize the functions of an achromatic lens or a beam deflector.

The nano-column antenna is a cylindrical nano-column antenna or an annular column nano-antenna, and the materials of the two nano-columns and the phase plate are both amorphous silicon.

The various integrated nanoatoms described need to meet the following three requirements. First, the transmission phase response, i.e., the reference phase, of the various integrated meta-atoms at the minimum operating frequency must correspond to the phase required by the design. Second, the phase dispersion response of a variety of integrated meta-atoms must be compatible with the dispersion required for the meta-surface design. Thirdly, the wide-band phase response of various integrated metasoms during near-infrared work needs to provide continuously-changed phases, and the phases are approximately linearly changed along with the frequency, so that the designed metasurfaces can still realize the achromatization function at each frequency in the middle of the working band;

the specific method for modulating the phase by the phase modulation principle comprises the following steps: the nano-pillar structure provides phase response through a resonance phase, and the phase of the nano-pillar structure is related to factors such as the material and the specific structure of the nano-pillar, the incident light frequency and the like; the phase plate structure adjusts optical path difference by changing thickness, and then introduces a propagation phase value. The phase modulation provided by the nano-column and the phase plate are added to form the phase modulation generated by the integrated metamaterial atom.

Advantageous effects

1. The invention combines the nano-column antenna structure of the common metasurface with the phase plate structure, expands the coverage range of a metasoma library in a phase dispersion space, can provide larger phase compensation than the common metasurface without the phase plate, breaks through the situation that the existing metasurface is difficult to provide a large phase compensation value, is beneficial to the design of the achromatic super lens and the achromatic metasurface with large diameter or numerical aperture, plays a role in promoting the design of the large-area achromatic metasurface, further promotes the wider application of the metasurface, and has great potential in the fields of wide-band optical imaging, virtual reality and augmented reality, wide-band optical information processing and the like;

2. the invention can provide more accurate phase response by utilizing structures such as the nano-column, and is beneficial to realizing more ideal optical effect compared with a diffraction optical element and a micro-nano optical element which are similar in structure and are obtained by only depending on optimized phase design;

3. the integrated achromatic metasurface disclosed by the invention only consists of two structures, namely a phase plate and a nano-column used by a common metasurface, and the two structures are in a vertical cascade structural relationship, so that phases provided by the phase plate and the common metasurface can be processed in a simple addition mode in the design process, the structure is simple and clear, and the design is simple and easy to implement;

4. according to the integrated achromatic metasurface disclosed by the invention, the phase compensation value is increased by increasing the phase plate, the degree of freedom of the design of a common metasurface is increased, the current situation that the phase compensation is increased by only increasing the height of the nano-column on the common metasurface is changed, the depth-width ratio required by the nano-column can be ensured to be within a smaller range, and the practical processing of the structure of the nano-column is facilitated;

5. the integrated achromatic metasurface disclosed by the invention is formed by combining a phase plate and a nano column up and down, but the whole thickness of the integrated achromatic metasurface is still kept in a micron order, the characteristics of ultralightness and ultrathin of a micro-nano optical element similar to a common metasurface are kept, and the integrated achromatic metasurface is used for replacing a traditional achromatic optical element in an optical system, so that the integrated achromatic metasurface is beneficial to simplifying the whole structure of the optical system, realizing the light weight and the miniaturization of the optical system and promoting the development of the design of the optical system.

Drawings

FIG. 1 is a schematic diagram of an integrated broadband achromatic metasurface, including a schematic diagram of a superlens focus and a metasurface structure diagram, according to the present disclosure;

FIG. 2: fig. a shows two types of metasoma structures for constructing a metasurface in the integrated achromatic metasurface disclosed by the present invention, wherein cylindrical and annular cylindrical nano-antennas are respectively adopted at the upper parts of the two types of metasoma structures; graph (b) is the amplitude of the cylindrical nanoantenna; graph (c) is the amplitude of the circular cylindrical nanoantenna; graph (d) is the phase of the cylindrical nano-antenna; graph (e) is the phase of the circular cylindrical nanoantenna; graph (f) is the normalized magnetic field strength distribution of the cylindrical nanoantenna at 1200nm wavelength; graph (g) is the normalized magnetic field strength distribution of the circular cylindrical nanoantenna at 1200nm wavelength; plot (h) is the spatial range of phase dispersion covered by the nanoatoms;

FIG. 3 is a graph of the phase and phase dispersion profiles required for an integrated broadband achromatic superlens of example 1; graph (a) is the required phase of the lens at the minimum frequency; graph (b) shows the required phase dispersion for the lens; graph (c) is the lens required phase at maximum frequency; plot (d) is the phase provided by the nanopillars at the minimum frequency; plot (e) is the dispersion provided by the nanopillars; plot (f) is the phase provided by the nanopillars at the maximum frequency; plot (g) is the phase provided by the phase plate at the minimum frequency; plot (e) is the dispersion provided by the phase plate; plot (f) is the phase provided by the phase plate at the maximum frequency;

FIG. 4 is a graph of the simulated effect of the performance of the integrated broadband achromatic superlens designed in example 1; FIG. (a) is a schematic diagram of an integrated broadband achromatic superlens in example 1; FIG. b shows the calculated focal length and full width at half maximum of the superlens designed in example 1; FIG. (c) is a diagram of the simulated focusing effect of the integrated broadband achromatic superlens; FIG. d is a normalized light intensity distribution obtained by simulation on the superlens focal plane;

FIG. 5 is a diagram showing the object pattern and the imaging effect used in the imaging simulation in example 1; FIG. (a) is a capital letter "G" bi-color pattern for integrated broadband achromatic superlens imaging as used in the examples; the images (b-f) are images of the object by the superlens in the wide wavelength band range of 1100nm to 1500nm in example 1, and the five images are images of the superlens on the image plane under the incident light with the wavelengths of 1100nm, 1200nm, 1300nm, 1400nm and 1500nm in sequence.

FIG. 6: FIG. (a) is a schematic diagram of a broadband achromatic beam deflector designed in example 2; plot (b) the distribution in phase dispersion space of the phase and dispersion values provided for the different meta-atoms and the phase and dispersion values required for the beam deflector design; FIG. (c) is a simulation of the phase distribution at 1500nm for the metasurface designed in example 2; and (d) is the refraction angle of the beam deflector under the normal incidence of the light rays with different wavelengths obtained by simulation calculation.

Detailed Description

For a better understanding of the objects and advantages of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings and examples.

Example 1

Based on the integrated achromatic metasurface, an achromatic superlens working in a wide band of near infrared 1100nm to 1500nm is designed and realized, and a schematic diagram of the superlens is shown in fig. 1.

The embodiment comprises the following steps:

step one, constructing the metasoma integrated with the metasurface by using a phase plate and a nano-column, performing simulation calculation on phase response provided by the metasoma when the metasoma works in a wide waveband to obtain phase response of a metasoma library, and processing the phase response to construct a phase dispersion space;

the metasoma period is fixed to 400nm, the structure of the nano-pillar can adopt a cylindrical or annular pillar, as shown in fig. 2(a), the heights of the two pillars are fixed to 800nm, the radius of the cylinder is changed from 25nm to 154nm in the calculation process, the step length is 1nm, the inner radius of the annular pillar is fixed to 40nm, the outer radius is changed from 120nm to 160nm, the step length is 1nm, and the amplitude and phase responses of the two kinds of nano-pillars in the working wave band of 1100nm to 1500nm are calculated and obtained, as shown in fig. 2 (b-e). It can be seen that all cell structures have stable and high amplitude in the operating band and have continuous and nearly linear phase distribution. The cylindrical and toroidal column structures are based on the resonance phase principle, and the magnetic field intensity distributions thereof are shown in fig. 2(f) and fig. 2(g), respectively.

In order to simplify the structure, the nanopillar of the lens designed in this embodiment only adopts the above cylindrical structure, and the phase response is recorded as a₁-A₁₃₀；

B＝ω(n-1)d/c (5)

The phase response B of the phase plate is calculated by the formula (5), wherein omega is the angular frequency of the incident light, n is the refractive index of the phase plate material to the incident light with the frequency, d is the thickness of the phase plate, and c is the speed of light. d is given by formula (6).

In the formula (6), m is a natural number of 0 to 15, c is the speed of light, omega_minIs the minimum frequency of the incident light and,is the refractive index of amorphous silicon at this frequency.

And adding the phase response A and the phase response B pairwise to obtain the phase response of the metasoma library.

M_ij＝A_i+B_j (7)

Taking the phase response of the incident light with the minimum frequency as a reference phase, and taking the difference value obtained by subtracting the phase response of the light with the minimum frequency from the phase response of the light with the maximum frequency as a phase dispersion value; all the atoms of the metasoma are described by two quantities, the reference phase and the phase dispersion value; a plane rectangular coordinate system is introduced, the horizontal axis and the vertical axis are respectively a reference phase and a phase dispersion value, all the metasoma are expressed by points in the coordinate system, and the set of the points covered by all the metasoma in the coordinate system is the phase dispersion space of the metasoma library, as shown in fig. 2 (h).

And step two, calculating the actually required phase and dispersion of the metasurface, comparing the phase and dispersion with the phase dispersion space of the metasone library, selecting the structure required at each position of the metasone, and arranging the selected structures to form a two-dimensional array, so as to obtain the integrated achromatic metasurface required by design.

The phase distribution formula required by the design of the broadband achromatic superlens is

Where ω is the angular frequency of the incident light, c is the speed of light, r₀F is the designed focal length of the designed superlens, and r is the distance from a point on the superlens surface to the center of the designed superlens, i.e., the radius of a point on the lens.

The lens was designed to be square with side lengths of 32 μm, a focal length of 32 μm and a numerical aperture of about 0.577. The phase calculated by equation (8) is a function of two quantities, namely, the position r of each point on the lens and the incident light frequency ω, and the minimum frequency of the operating band required for design is substituted into equation (8), so that the distribution of the reference phase with respect to the position r is obtained, as shown in fig. 3 (a). The phase distribution of the maximum frequency is subtracted from the phase distribution of the minimum frequency to obtain a distribution of the phase dispersion with respect to the position r, as shown in fig. 3 (b). The maximum frequency required phase distribution is shown in fig. 3 (c).

The required reference phase and the phase dispersion at any position r on the metasurface are both expressed as a point in a phase dispersion space, the point of the metasone closest to the point in the phase dispersion space is searched, and the metasone represented by the point is selected as the required structure at the position on the metasurface. The operation of finding the desired metamaterial atoms is also performed for other positions on the metasurface. And arranging all the metamaterial atoms according to positions to complete the construction of the superlens. The phase and dispersion provided by the selected nanorod structures are shown in fig. 3(d-f), and the phase and dispersion provided by the phase plate are shown in fig. 3 (g-i).

And thirdly, focusing and imaging simulation are carried out on the designed achromatic superlens by adopting a finite difference time domain method (FDTD).

Step 3.1: and (5) focusing simulation. The super-lens focusing diagram is shown in fig. 4(a), the focal length and full width at half maximum are shown in fig. 4(b), and the focusing effect is shown in fig. 4 (c). Fig. 4(d) is a normalized intensity distribution on the focal plane. As can be seen from the figure, the designed superlens realizes good focusing effect in the working waveband, and the focal length is basically kept constant and is close to the designed focal length, so that good achromatic focusing effect is realized. When the wavelength is short, the simulated focal length is slightly short, which may be an error caused by a small lens diameter, and if a lens with a larger aperture is actually processed, the error can be reduced.

Step 3.2: and (5) imaging simulation. The capital letter "G" pattern etched by irradiating the gold film with a plane wave was used as an object, and the letter pattern was as shown in fig. 5 (a). The object was placed at 2 times the focal length of the superlens and the monitor was placed at 2 times the focal length of the other side of the superlens, and the simulation was performed, the results being shown in fig. 5 (b-f). As can be seen from the figure, in the working wave band, the lens forms a clear equal-size inverted real image on an object, and a good achromatic imaging effect is realized.

In summary, the present example provides an integrated metasurface-based broadband achromatic lens that enables achromatic focusing and imaging over a continuous broad wavelength band in the near-infrared 1100nm to 1500 nm. By combining the nano-antenna with the phase plate, the integrated achromatic superlens provides greater design freedom for designing the broadband achromatic superlens, and the integrated metamaterial atoms can provide greater phase dispersion compared with a single nano-antenna, so that the problems of large diameter, large numerical aperture and the like existing in the design of the superlens are solved.

The addition of the phase plate is beneficial to reducing the depth-to-width ratio of the nano antenna and provides certain convenience for processing. The integrated achromatic superlens keeps the characteristics of ultralightness and ultrathin of the superlens, is used for replacing the traditional elements in an optical system, and is helpful for simplifying the optical system and promoting the integrated development of the optical system. The integrated achromatic superlens is applied to AR/VR equipment and the like, so that the light-weight and portable development and chromatic aberration correction of the integrated achromatic superlens are facilitated, and the wider application of related fields is promoted. The integrated achromatic superlens is applied to imaging optical systems such as a telescope system and a microscope system, and is beneficial to light and small. The embodiment can be widely applied to an imaging optical system, and promotes the development of a novel broadband imaging device.

Example 2

An achromatic beam deflector working in a wide band of near-infrared 1100nm to 1500nm is designed and implemented based on an integrated achromatic metasurface, and fig. 6(a) is a schematic diagram of the beam deflector.

The embodiment comprises the following steps:

the method comprises the steps of firstly, constructing the metasoma integrated with the metasurface by using a phase plate and a nano column, carrying out simulation calculation on phase response provided by the metasoma when the metasoma works in a wide waveband, obtaining the phase response of a metasoma library, processing the phase response, and constructing a phase dispersion space.

The metasoma period is fixed to 400nm, the nanopillar structure can adopt a cylindrical nanopillar or a circular cylindrical nanopillar, as shown in fig. 2(a), the heights of the two nanopillars are 800nm, the radius of the cylinder is changed from 25nm to 154nm in the calculation process, the step length is 1nm, the inner radius of the circular nanopillar is fixed to 40nm, the outer radius is changed from 120nm to 160nm, and the step length is 1nm, and the amplitude and phase response of the two nanopillar structures in the working waveband are calculated. The phase response of the nano-column simulation calculation is recorded as A₁-A₁₇₁。

B＝ω(n-1)d/c (9)

The phase response B of the phase plate is calculated by the formula (9), wherein omega is the angular frequency of the incident light, n is the refractive index of the phase plate material to the incident light with the frequency, d is the thickness of the phase plate, and c is the speed of light. d is given by formula (10).

In the formula (10), m is a natural number of 0 to 31, c is the speed of light, omega_minIs the minimum frequency of the incident light and,is the refractive index of amorphous silicon at this frequency.

And adding the phase response A and the phase response B pairwise to obtain the phase response of the metasoma library.

M_ij＝A_i+B_j (11)

Taking the phase response of the incident light with the minimum frequency as a reference phase, and taking the difference value obtained by subtracting the phase response of the light with the minimum frequency from the phase response of the light with the maximum frequency as a phase dispersion value; all the atoms of the metasoma are described by two quantities, the reference phase and the phase dispersion value; a plane rectangular coordinate system is introduced, the horizontal axis and the vertical axis are respectively a reference phase and a phase dispersion value, all the metasoma are expressed by points in the coordinate system, and the set of the points covered by all the metasoma in the coordinate system is the phase dispersion space of the metasoma library, as shown in fig. 6 (b).

And step two, calculating the actually required phase and dispersion of the metasurface, comparing the phase and dispersion with the phase dispersion space of the metasone library, selecting the structure required at each position of the metasone, and arranging the selected structures to form a two-dimensional array, so as to obtain the integrated achromatic metasurface required by design.

The phase distribution formula required by the design of the broadband achromatic beam deflector is as follows

In the formula, omega is angular frequency, c is light speed, x is the distance between a certain point on the metasurface and a design selected datum line, and theta is a designed deflection angle, and emergent light can deflect the angle of theta when light with any wavelength in a wave band of 1100nm to 1500nm is vertically incident on the designed metasurface.

Designing theta to be 20 degrees, taking x within the range of-10 mu m to 10 mu m, calculating to obtain the phase and dispersion required at each position on the metasurface, comparing the phase and dispersion with the phase dispersion space of the metasone library in the step one, as shown in fig. 6(b), selecting the nearest metasone as the unit structure of each point on the metasone, and distributing the selected unit structures along the x direction to form the metasone required for designing.

And step three, performing simulation calculation on the designed broadband achromatic beam deflector through a Finite Difference Time Domain (FDTD) method, and verifying the beam deflection angle of the device.

As shown in fig. 6(c), the emitted light deflected by the metasurface is deflected and has a flat wave surface. As can be seen from the results of the far-field calculation in fig. 6(d), when the wavelength of the incident light is changed within the operating band of 1100nm to 1500nm, the deflection angle of the outgoing light is always maintained at a design angle close to 20 °, and the effect of deflecting the achromatic light beam is achieved.

In summary, the present embodiment provides an integrated metasurface-based broadband achromatic beam deflector, and the deflector method can deflect and emit incident light in a near-infrared broadband from 1100nm to 1500nm at the same angle, and generate the same deflection angle modulation on wavefronts of incident light with different frequencies, and can be widely applied to broadband imaging optical systems, and also applied to broadband modulation such as fiber end face integrated systems and on-chip integrated systems, so as to promote the development of micro-nano devices.

The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.