CN116908951A - Super-surface device capable of realizing multi-dimensional imaging and design method and application thereof - Google Patents
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Abstract
The invention belongs to the technical fields of micro-nano optics and optical imaging, and discloses a super-surface device capable of realizing multi-dimensional imaging, and a design method and application thereof. The invention adopts the super-surface design scheme of partition and lamination, realizes multi-parameter joint regulation and control of the spectrum, polarization and phase of the incident light, and can acquire multi-dimensional fusion information of an object in real time. The invention can greatly improve the information quantity obtained by optical detection, and provides a brand new technical approach for the multidimensional real-time imaging technology with precision, high efficiency, ultra compactness and high reliability.
Description
Technical Field
The invention belongs to the technical field of micro-nano optics and optical imaging, and particularly relates to a super-surface device capable of realizing multi-dimensional imaging, and a design method and application thereof.
Background
The polarization spectrum imaging technology is a multi-dimensional optical detection technology integrating polarization, spectrum and imaging functions, and can simultaneously acquire data hypercube containing polarization information, spectrum information and spatial information of a measured target. At present, although spectrum/polarization dimension imaging devices with two-by-two regulation and control of parameters such as spectrum, polarization state and phase are studied, multi-dimension super-surface imaging devices capable of simultaneously acquiring three-in-one information of spectrum, polarization and space image are not yet developed. The planar optical device based on the super surface has the outstanding advantages of ultra-thin, high efficiency, high reliability, multifunctional integration and the like, can flexibly and effectively regulate and control the amplitude, the phase, the polarization state and the like of an optical wave electromagnetic field in a sub-wavelength scale, and is a preferred technical path for developing an integrated multi-dimensional imaging optical system. Therefore, if spectrum, polarization and phase regulation can be organically combined through the super surface, a novel super surface original with a compact structure is hopeful to be developed, and a brand new technical approach is provided for a precise, efficient, ultra-compact and highly reliable multidimensional real-time imaging technology.
Disclosure of Invention
The invention aims to provide a super-surface device capable of realizing multi-dimensional imaging, a design method and application thereof, and aims to realize the joint regulation and control of multiple parameters of incident light and acquire three-in-one multi-dimensional fusion information of a spectrum, polarization and a space image of an object in real time.
In a first aspect, the present invention provides a method for designing a subsurface device capable of achieving multi-dimensional imaging, comprising the steps of:
step 1, constructing a basic structure of a super-surface device, wherein the basic structure sequentially comprises a lower reflecting layer, a microcavity, an upper reflecting layer, a substrate and a nano brick array from bottom to top; the lower reflecting layer, the microcavity and the upper reflecting layer form an FP cavity (Fabry-Perot resonant cavity), and the FP cavity is used for filtering; the substrate and the nano brick array form a nano structure, the nano brick array comprises a plurality of nano bricks which are periodically arranged and have the same height, the substrate is divided into a plurality of periodic substrate unit structures with the same size, each substrate unit structure and one nano brick positioned on the working surface form a nano unit structure, and the nano unit structure is used for carrying out geometric phase regulation;
step 2, performing functional partitioning on the basic structure based on a plurality of target working wavelengths and a plurality of target polarization states; through electromagnetic simulation, according to the target working wavelength and the target polarization state corresponding to each functional partition, the thickness of the lower reflecting layer, the thickness of the upper reflecting layer and the thickness of the microcavity corresponding to each functional partition of the FP cavity are optimally designed, the periodic size of the substrate and the height of the nano brick are optimally designed, and the length, the width and the azimuth angle of the nano brick contained in each functional partition are optimally designed, so that a super-surface device capable of realizing multi-dimensional imaging is obtained.
Preferably, the step 2 further includes: and aiming at reducing the Fano resonance between the FP cavity and the nanostructure, and optimally designing the thickness of the substrate.
Preferably, in the step 2, the thicknesses of the lower reflecting layer and the upper reflecting layer are the same, and the thickness of the reflecting layer is determined according to the half-width of the transmission line and the transmissivity; after the thickness of the reflecting layer is determined, the thickness of the microcavity corresponding to each functional partition is determined according to the target working wavelength of each functional partition.
Preferably, in the step 2, after the period size of the substrate and the height of the nano brick are determined, the length and the width of the nano brick are scanned under different target working wavelengths, and the length and the width of the nano brick under each target working wavelength are determined according to the polarization conversion efficiency obtained by scanning.
Preferably, in the step 2, the phase distribution of each functional partition is calculated, and the azimuth angles of all the nano bricks contained in each functional partition are arranged according to the phase distribution of each functional partition.
Preferably, each functional partition is used as a sub-lens, and the phase distribution of the sub-lens is obtained according to the arrangement calculation of the image, and the phase distribution calculation formula is as follows:
wherein ,is the phase adjustment quantity corresponding to the point with the coordinates of (x, y) on the ith sub-lens, lambda i For the target working wavelength corresponding to the ith sub-lens, f is the focal length, delta xi 、Δ yi The off-axis amounts of the ith sub-lens in the x-axis and y-axis directions respectively, (x) i ,y i ) The center coordinate of an image corresponding to the ith sub-lens, and β is the absolute value of the magnification of the sub-lens.
Preferably, the azimuth angle of the phase control amount and the nano brick satisfies the following formula:
wherein θ is the azimuth angle of the nanobrick;
the ultra-surface device capable of realizing multi-dimensional imaging focuses left-handed circularly polarized light and right-handed circularly polarized light under each target working wavelength respectively aiming at m target working wavelengths, the sign in the formula depends on the polarization state of incident light, and when the incident light is left-handed circularly polarized light or right-handed circularly polarized light, the phase regulation and control amounts are opposite numbers.
Preferably, the lower reflecting layer and the upper reflecting layer are silver layers, the medium in the microcavity is silicon dioxide, the material of the nano brick is titanium dioxide, and the material of the substrate is silicon dioxide.
In a second aspect, the present invention provides a subsurface device capable of implementing multi-dimensional imaging, which is obtained according to the above design method for a subsurface device capable of implementing multi-dimensional imaging.
In a third aspect, the present invention provides an application of a super-surface device capable of implementing multi-dimensional imaging, where the super-surface device capable of implementing multi-dimensional imaging is used to perform joint regulation and control on multiple parameters of incident light, so as to obtain multi-dimensional fusion information of an object in real time; the multiparameters include spectrum, polarization, and phase.
One or more technical schemes provided by the invention have at least the following technical effects or advantages:
the invention provides a super-surface device capable of realizing multi-dimensional imaging, which comprises a lower reflecting layer, a microcavity, an upper reflecting layer, a substrate and a nano-brick array, wherein the lower reflecting layer, the microcavity and the upper reflecting layer form an FP cavity for filtering, and the substrate and the nano-brick array form a nano-structure for regulating and controlling geometric phases; the invention carries out functional partitioning on the super-surface device based on a plurality of target working wavelengths and a plurality of target polarization states, and optimizes structural parameters through electromagnetic simulation to obtain the laminated super-surface of the 'FP cavity+nano structure' with multi-optical parameter regulation and control capability, and can realize independent control of light wave phases and spectrums without mutual influence. The invention adopts the super-surface design scheme of partition and lamination, realizes effective regulation and control of various optical parameters of incident light, and can acquire multi-dimensional fusion information of an object in real time. The design method based on the invention can greatly improve the information quantity obtained by optical detection, and provides a brand new technical approach for the multidimensional real-time imaging technology with precision, high efficiency, ultra compactness and high reliability.
Drawings
FIG. 1 is a schematic illustration of multi-layer media multi-beam interferometry;
FIG. 2 is a schematic diagram of a nano-cell structure in an embodiment of the invention;
FIG. 3 is a side view of a laminated cell structure in an embodiment of the invention;
FIG. 4 is a spectral response of 8 stacked cell structures designed for 8 wavelengths in an embodiment of the invention;
FIG. 5 is a schematic diagram of a subsurface device that can implement multi-dimensional imaging in accordance with an embodiment of the present invention;
FIG. 6 is a schematic diagram of functional partitioning of a subsurface device that can be imaged in multiple dimensions in an embodiment of the invention;
FIG. 7 is a phase layout of different functional areas of a subsurface device that can be imaged in multiple dimensions in an embodiment of the invention;
FIG. 8 is a schematic diagram of an optical path for polarization spectral imaging using a subsurface device capable of multi-dimensional imaging in an embodiment of the invention.
Detailed Description
In order to better understand the above technical solutions, the following detailed description will refer to the accompanying drawings and specific embodiments.
The embodiment provides a design method of a super-surface device capable of realizing multi-dimensional imaging, which comprises the following steps:
step 1, constructing a basic structure of a super-surface device, wherein the basic structure sequentially comprises a lower reflecting layer, a microcavity, an upper reflecting layer, a substrate and a nano brick array from bottom to top; the lower reflecting layer, the microcavity and the upper reflecting layer form an FP cavity, and the FP cavity is used for filtering; the substrate and the nano brick array form a nano structure, the nano brick array comprises a plurality of nano bricks which are periodically arranged and have the same height, the substrate is divided into a plurality of periodic substrate unit structures with the same size, each substrate unit structure and one nano brick positioned on the working surface form a nano unit structure, and the nano unit structure is used for carrying out geometric phase regulation.
Step 2, performing functional partitioning on the basic structure based on a plurality of target working wavelengths and a plurality of target polarization states; through electromagnetic simulation, according to the target working wavelength and the target polarization state corresponding to each functional partition, the thickness of the lower reflecting layer, the thickness of the upper reflecting layer and the thickness of the microcavity corresponding to each functional partition of the FP cavity are optimally designed, the periodic size of the substrate and the height of the nano brick are optimally designed, and the length, the width and the azimuth angle of the nano brick contained in each functional partition are optimally designed, so that a super-surface device capable of realizing multi-dimensional imaging is obtained.
In addition, the step 2 may further include: and aiming at reducing the Fano resonance between the FP cavity and the nanostructure, and optimally designing the thickness of the substrate.
The thickness of the lower reflecting layer is the same as that of the upper reflecting layer, and the thickness of the reflecting layer is determined according to the half-width and the transmissivity of the transmission spectrum line; after the thickness of the reflecting layer is determined, the thickness of the microcavity corresponding to each functional partition is determined according to the target working wavelength of each functional partition.
After the cycle size of the substrate and the height of the nano bricks are determined, the length and the width of the nano bricks are respectively scanned under different target working wavelengths, and the length and the width of the nano bricks under each target working wavelength are determined according to the polarization conversion efficiency obtained by scanning.
And calculating the phase distribution of each functional partition, and arranging azimuth angles of all the nano bricks contained in each functional partition according to the phase distribution of each functional partition. Specifically, each functional partition is used as a sub-lens, the phase distribution of the sub-lens is obtained according to the arrangement calculation of the image, and the phase distribution calculation formula is as follows:
wherein ,is the phase adjustment quantity corresponding to the point with the coordinates of (x, y) on the ith sub-lens, lambda i For the target working wavelength corresponding to the ith sub-lens, f is the focal length, delta xi 、Δ yi The off-axis amounts of the ith sub-lens in the x-axis and y-axis directions respectively, (x) i ,y i ) The center coordinate of an image corresponding to the ith sub-lens, and β is the absolute value of the magnification of the sub-lens.
The phase control quantity and the azimuth angle of the nano brick meet the following formula:
wherein θ is the azimuth angle of the nanobrick.
The ultra-surface device capable of realizing multi-dimensional imaging focuses left-handed circularly polarized light and right-handed circularly polarized light under each target working wavelength respectively aiming at m target working wavelengths, the sign in the formula depends on the polarization state of incident light, and when the incident light is left-handed circularly polarized light or right-handed circularly polarized light, the phase regulation and control amounts are opposite numbers.
The main design part of the present invention will be explained below.
1. The stacked unit of the FP cavity and the nano structure is optimally designed.
(1) The optimal design of the FP cavity.
And optimizing the design to obtain the FP cavity with the filtering function. The thickness of the upper and lower reflecting layers and the microcavity of the FP cavity is designed through electromagnetic simulation software. Regulating and controlling the transmission and reflection spectrum of the material, and comprehensively considering the half-width of the transmission spectrum and the filtering efficiency to determine the thickness of the upper and lower reflecting layers; and the micro-cavity thickness is reasonably selected to realize the FP cavity which can work at different wavelengths. For example, the FP cavity may be designed to operate at 8 wavelengths in the range of 480nm to 690nm, spaced 30nm apart.
Specifically, as shown in fig. 1 (a), when light waves are transmitted between different media, multiple back and forth reflections occur in a single-layer medium film wrapped by upper and lower medium materials, and finally multi-beam interference is formed, which affects the transmission and reflection coefficients, the transmission and reflection coefficients of outgoing light. T (ij) and r (ij) are defined as the transmission and reflection coefficients, respectively, at the interface from medium i to medium j. If the media i, j are adjacent and the refractive indices of both are already determined, then when a beam of light is incident normally, the following is satisfied:
while the light wave channelOver refractive index n 2 Thickness d 1 In view of light transmission, the outgoing light can be expressed asWhere k0=2pi/λ is the propagation constant. Thus, considering the multi-beam interference effect, the transmission and reflection coefficients of the medium film can be expressed as:
wherein ,t(13) and r(13) Respectively representing the transmission and reflection coefficients of incident light under the condition of incidence from the medium 1 end; t is t (31) and r(31) Respectively representing the transmission and reflection coefficients of the incident light upon the end of the medium 3.
Further, when a complex optical resonator is constructed from a multi-layer dielectric film, fabry-perot resonance will be formed, where the transmitted and reflected spectra of the emitted light tend to be wavelength selective. In order to study the light transmission characteristics of such a multilayered unit cell nanostructure, an analysis was made using the model shown in fig. 1 (b), and when all the media were composed of different media and had no anisotropy, multi-beam interference occurred in both the media 2 and 3 after light was incident from the medium 1, which means that the components of the outgoing light became complicated. The transmission and reflection coefficients of the emergent light can be calculated by adopting the thought of layer-by-layer analysis, and the whole thought is as follows: first, referring to the medium film model shown in fig. 1 (b), only the multi-beam interference effect in the medium 2 is considered, and the transmission and reflection coefficients t are calculated by adopting formulas (1) and (2) (13) 、r (13) 、t (31) and r(31) The method comprises the steps of carrying out a first treatment on the surface of the Secondly, ignoring the medium 2, only considering the multi-beam interference effect in the medium 3, and adopting the deformed formula (2) to analyze the total transmission and reflection coefficients of the light waves transmitted from the medium 1 to the medium 4 on the basis of the formula (1):
wherein ,d 2 is the thickness of the medium 3 in the model shown in fig. 1 (b). The simultaneous formulas (1), (2) and (3) can directly carry out theoretical analysis on the transmission and reflection characteristics of the multilayer common medium film. Based on the electromagnetic simulation software is adopted to perform electromagnetic simulation on the FP cavity, and the transmission and reflection coefficients and the wavelength selectivity of emergent light are related to the Fabry-Perot resonance in the medium film layer. Therefore, the Fabry-Perot resonance in the nanostructure is skillfully designed, and different emergent spectrums can be realized.
(2) And (3) optimizing the design of the nano unit structure.
The nano unit structure with the function of geometric phase regulation is designed. When the incident light passes through a single rectangular nano brick, a phase difference is generated between two linearly polarized lights with mutually perpendicular polarization directions, and the half-wave plate has the highest phase regulation efficiency when the phase difference of the fast and slow axes is pi, so that the incident circularly polarized light can be converted into circularly polarized light with opposite rotation directions, and a phase change amount with the size of +/-2 theta is added, wherein the sign depends on the rotation direction of the incident circularly polarized light. And optimizing the dimensional parameters of the nano unit structure through electromagnetic simulation soft simulation to respectively obtain the polarization-sensitive half-wave plate structure which works at 8 working wavelengths and can realize geometric phase regulation.
Specifically, the nano unit structure is formed by a substrate 202 and nano bricks 201 etched on the substrate, as shown in fig. 2, an xyz rectangular coordinate system is established, the length of the nano bricks 201 is L, the width is W, the height is H, the included angle between the long axis of the nano bricks 201 and the x-axis direction is azimuth angle, and is marked as θ, the side lengths of the substrate 202 in the x-direction and the y-direction are CS, that is, the period size of the substrate 202 is CS.
If Jones matrix isThe circularly polarized light of (2) is incident on an optical element with an azimuth angle θ, and the jones matrix of the output light is:
where G is the jones matrix of the optical element and R is the rotation matrix. The values of P and q are respectively:
as is clear from the formula (5), the output light includes two parts, one part is circularly polarized light having the same rotation direction as the incident light, and the other part is circularly polarized light having the opposite rotation direction to the incident light. When the optical element is isotropic, i.e. a=d and b= -C, the output light field does not contain reverse circularly polarized light with a phase modulation amount. Otherwise, as long as the optical element is anisotropic, the output light field always contains reverse circularly polarized light, and the absolute value of the phase regulating quantity of the reverse circularly polarized light is equal to twice of the azimuth angle of the optical element, and the specific relation is that:
the sign depends on the polarization state of the incident light, that is, when the incident light is left-handed circularly polarized or right-handed circularly polarized, the phase adjustment amounts are opposite to each other.
In addition, the co-polarized conversion efficiency |p| 2 And cross polarization conversion efficiency |q| 2 Depending on the complex transmission or reflection coefficient of the nanostructure. In particular, when the nanobrick is an ideal half-wave plate (a=1, d= -1, b=c=0), the cross polarization conversion efficiency is 1, i.e. all incident light is converted into reverse circular polarization with a phase retardation. Therefore, the size parameters of the nano unit structure are optimized through electromagnetic simulation software, so that the function of the high-efficiency half-wave plate is realized as much as possible.
(3) The stack units are jointly optimized.
The FP cavity and the nano-unit structure are stacked in the longitudinal direction to obtain a spectrum-polarization-phase multidimensional light wave regulation unit, see fig. 3, which includes a nano-brick 301, a substrate 302, an upper reflective layer 303, a microcavity 304, a lower reflective layer 305, and a substrate 306 that is convenient for preparing a super-surface device. In order to reduce the influence of the Fano resonance caused by the coupling between the FP cavity (comprising the upper reflective layer 303, microcavity 304, lower reflective layer 305) and the nano-unit structure (or nano-structure comprising the nano-brick 301, substrate 302) so that the spectral modulation function of the FP cavity and the geometric phase modulation function of the nano-unit structure do not interfere with each other, the thickness of the dielectric layer between the two is preferably also optimized, i.e. the thickness of the substrate is optimized.
Specifically, the FP cavity has a confinement effect on the light wave in the longitudinal direction, so that discrete optical modes exist therein, while the nanostructure has continuous light wave modes in the non-resonant region, and under certain conditions, the coupling of the two modes causes the generation of the farno resonance. In terms of the spectral filtering function of the stacked units, however, it is desirable that the spectral lines are smooth lorentz lines rather than asymmetric Fano lines. Therefore, in the structural design, the position of the Fano resonance can be changed by adjusting the size of the nano structure or adjusting the interval between the two systems in the longitudinal direction, so that the influence on the unit spectrum filtering function after the FP cavity and the nano structure are longitudinally stacked is reduced to the greatest extent.
2. Ultra-surface lens array optical design.
(1) And designing a super-surface lens array layout.
And performing functional partitioning on the super-surface device, and designing a super-surface lens array which works for different wavelengths and different polarization states. For 8 operating wavelengths, left-handed circularly polarized light and right-handed circularly polarized light at each wavelength are focused separately. For example, 8×2 functional partitions, i.e., 16 sub-lenses, may be designed.
(2) And designing the phase of the super-surface functional partition.
For each functional zone, the phase distribution of the focusing lens is designed for left-handed circularly polarized light and right-handed circularly polarized light at different wavelengths.
Taking 16 sub-lenses as an example, the whole super-surface device can be understood as being divided into 8 large areas (each large area corresponds to one working wavelength, and different large areas respectively focus light waves with different wavelengths), and each large area comprises 2 sub-lenses (respectively used for focusing left-handed circularly polarized light and right-handed circularly polarized light). Namely, when circularly polarized lights with the same wavelength and different directions of rotation are incident to the super-surface device, the positions of focusing light spots in the transmission space are different; when circularly polarized light of the same rotation direction and different wavelengths is incident on the super-surface device, the positions of the focusing light spots are also different. Thereby realizing the focusing with wavelength and polarization selectivity, and further acquiring the three-in-one information of the spectrum, polarization and space image of the measured object. The super-surface device provided by the invention can realize a phase modulation function with narrow-band spectral response and controlled by the polarization state of incident light, and can be used as a dimension imaging core device with spectral, polarization and space dimension imaging functions.
The phase design principle is described below with one sub-lens as an example. Assume that an object is placed at a distance L 'from the lens-L, which is a distance L' from the imaging plane. The object size is 2Y, the off-axis quantity of the sub-lenses is delta, and the caliber is D. From the geometrical optics law, the coordinates of two endpoints of the image of the object can be obtained as follows:
P 1′ ＝Δ+β(Δ-Y)
P 2′ ＝Δ+β(Δ+Y) (7)
where β= |l'/l| represents the absolute value of the lens magnification. As can be derived from the formula (7), the center coordinates of the image of the object are:
P＝Δ(β+1) (8)
assuming that the distribution of images of an object imaged by different sub-lenses is shown below the figure, the center coordinates of one of the images is (x i ,y i ) According to formula (8), the off-axis amounts of the corresponding sub-lenses in the x and y directions are respectively:
the phase distribution of each sub-lens can be calculated one by one according to the arrangement of the images:
wherein ,λi For the working wavelength of the sub-lens, f is the focal length, satisfying gaussian formula 1/f=1/L' -1/L.
In terms of preparation materials, silver is selected as a reflective layer material of the FP cavity, silicon dioxide is selected as a material of the microcavity, silicon dioxide is selected as a material of the substrate, and titanium dioxide is selected as a material of the nano brick, but the material is not limited to the material.
The invention will be further described with reference to specific parameters.
(1) The optimal design of the FP cavity.
Silver is used as the upper and lower reflecting layers, silicon dioxide is used as the medium in the cavity, and the transflective characteristic of the FP cavity is analyzed according to the formula (3). The upper and lower reflecting layers have the same thickness and are denoted as d mirror (corresponding to d in FIG. 3) uppermirror and dlowermirror ) The influence of the thickness of the silver reflecting layer on the FP cavity is simulated, the line width of the transmission spectrum is narrowed and the transmittance is reduced along with the increase of the thickness of the silver layer, and the half-width of the transmission line and the filtering efficiency are comprehensively considered, namely the transmittance of the transmission line with the half-width of less than 10nm is more than 40%, and the thickness of the silver reflecting layer is selected to be 45nm.
After the silver layer thickness is determined, the FP cavity is formed by varying the cavity length (corresponding to d in fig. 3 FP ) I.e. the position where its peak appears. Reasonable selection of the thickness d of the cavity FP FP cavity parameters operating at 8 wavelengths of 480nm, 510nm, 540nm, 570nm, 600nm, 630nm, 660nm and 690nm can be achieved, and the FP cavity lengths optimized at each wavelength are shown in table 1.
Table 1 cavity length of FP cavity at 8 wavelengths in the examples
(2) And (3) optimizing the design of the nano unit structure.
And modeling and simulating the single nano brick structure by adopting electromagnetic simulation software CST. For 8 wavelengths in the range of 480nm to 690nm, which are spaced at 30nm, half-wave plate structures operating at these wavelengths are optimized. The titanium dioxide material has low loss in the visible light wave band, so the titanium dioxide material is selected as the material of the nano brick. The working conditions under the respective wavelengths are comprehensively considered, and the cycle size CS of the substrate and the height of the nano bricks are respectively set to be 500nm and 800nm. The length and width of the nano brick are scanned, and the half-wave plate structure is optimized, so that the reverse polarization conversion efficiency is high, and the same-direction polarization conversion efficiency is inhibited. The nanostructure parameters and corresponding reverse polarization conversion efficiencies obtained by optimization at each wavelength are shown in table 2.
Table 2 nanostructure parameters at 8 wavelengths and corresponding reverse polarization conversion efficiencies in the examples
(3) The stack units are jointly optimized.
The FP cavity and the nano unit structure are stacked in the longitudinal direction to obtain the multi-dimensional light wave regulation and control unit, and the structural schematic diagram of the multi-dimensional light wave regulation and control unit is shown in figure 3. Taking the designed laminated unit structure parameter with the working wavelength of 690nm as an example to study the thickness d of the substrate 302 spacing The influence on the reverse polarization conversion efficiency spectrum is that no recess exists in the spectrum line in the independent simulation process of the FP cavity and the nano unit structure, but an asymmetric recess and protrusion can be observed in the transmission reverse polarization conversion spectrum in the integral simulation of the FP cavity and the nano unit structure, and the asymmetric recess and protrusion are along with d spacing Is gradually red-shifted. The thickness of the substrate 302 is chosen to be 280nm taking into account the spectral curves at each wavelength in combination so that asymmetric depressions and protrusions do not occur at the designed wavelength. Therefore, the spectrum regulation and control can be realized through the cavity length of the FP cavity, and the phase regulation and control are carried out through the azimuth angle of the nano structure, so that the two functions are hardly affected. Fig. 4 is a graph of the spectral response of a designed 8-stack cell structure, where the efficiency in the ordinate of fig. 4 is the reverse polarization conversion efficiency, here after longitudinally stacking the nanostructures and FP cavities.
(4) And designing a super-surface array layout.
Fig. 5 is a schematic diagram of a super-surface device, i.e., an "FP cavity + nanostructure" stack, comprising, from top to bottom, a nano-tile 501, a base 502, an upper reflective layer 503, a microcavity 504, a lower reflective layer 505, and a substrate 506 for use in preparing the super-surface device. And performing functional partitioning on the laminated super-surface, and designing super-surface lenses working for different wavelengths and different polarization states. Fig. 6 shows a functional layout of an optimal design, each distribution being labeled for polarization and wavelength, where |r > and |l > represent focusing of right-and left-circularly polarized light components, respectively. The lens array has dimensions of 2mm by 2mm and the number of functional zones is 16, i.e. the aperture size of each sub-lens is 500 μm by 500 μm.
(5) And designing the phase of the super-surface functional partition.
Considering imaging resolution:
let the resolution at 500nm reach 10 μm, design |L| to 8mm, let β take 0.5, then L' to 4mm, and the focal length of each lens to 8/3mm. The phase distribution of the lens array can be obtained according to the functional partition and formula (10) in fig. 6. Specifically, according to the geometric phase, the phase distribution of the lens array can be converted into the azimuth distribution of the nano-array, and the phase regulating quantity of reverse circularly polarized light is twice of the azimuth of the nano-brick. Considering the polarization dependence of geometric phases (i.e., the absolute value of the phase change is the same and opposite sign after the left and right circular polarization passes through the nanostructure with azimuth angle θ), one downward-rotating focusing lens is a diverging lens at the other downward-rotating. Therefore, when the phase distribution of the right-handed partition is designed, the opposite number is only needed to be taken on the basis of the formula (10). The resulting lens array phase distribution is shown in fig. 7.
The invention can realize the focusing with wavelength and polarization selectivity, and further acquire the three-in-one information of the spectrum, polarization and space image of the measured object. For example, a schematic of an optical path for polarization spectral imaging using a subsurface device (i.e., a subsurface lens array) is shown in fig. 8.
Finally, it should be noted that the above-mentioned embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications and equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and all such modifications and equivalents are intended to be encompassed in the scope of the claims of the present invention.
Claims (10)
1. A method of designing a subsurface device capable of achieving multi-dimensional imaging, comprising the steps of:
step 1, constructing a basic structure of a super-surface device, wherein the basic structure sequentially comprises a lower reflecting layer, a microcavity, an upper reflecting layer, a substrate and a nano brick array from bottom to top; the lower reflecting layer, the microcavity and the upper reflecting layer form an FP cavity, and the FP cavity is used for filtering; the substrate and the nano brick array form a nano structure, the nano brick array comprises a plurality of nano bricks which are periodically arranged and have the same height, the substrate is divided into a plurality of periodic substrate unit structures with the same size, each substrate unit structure and one nano brick positioned on the working surface form a nano unit structure, and the nano unit structure is used for carrying out geometric phase regulation;
step 2, performing functional partitioning on the basic structure based on a plurality of target working wavelengths and a plurality of target polarization states; through electromagnetic simulation, according to the target working wavelength and the target polarization state corresponding to each functional partition, the thickness of the lower reflecting layer, the thickness of the upper reflecting layer and the thickness of the microcavity corresponding to each functional partition of the FP cavity are optimally designed, the periodic size of the substrate and the height of the nano brick are optimally designed, and the length, the width and the azimuth angle of the nano brick contained in each functional partition are optimally designed, so that a super-surface device capable of realizing multi-dimensional imaging is obtained.
2. The method for designing a multi-dimensional imaging enabled subsurface device according to claim 1, wherein step 2 further comprises: and aiming at reducing the Fano resonance between the FP cavity and the nanostructure, and optimally designing the thickness of the substrate.
3. The method for designing a multi-dimensional imaging enabled subsurface device according to claim 1, wherein in said step 2, the thickness of said lower reflecting layer is the same as the thickness of said upper reflecting layer, and the thickness of the reflecting layer is determined according to the half-width of the transmission line and the transmittance; after the thickness of the reflecting layer is determined, the thickness of the microcavity corresponding to each functional partition is determined according to the target working wavelength of each functional partition.
4. The method for designing a multi-dimensional imaging super-surface device according to claim 1, wherein in the step 2, after the period size of the substrate and the height of the nano-bricks are determined, the length and the width of the nano-bricks are scanned respectively at different target working wavelengths, and the length and the width of the nano-bricks at each target working wavelength are determined according to the polarization conversion efficiency obtained by scanning.
5. The method for designing a multi-dimensional imaging enabled subsurface device according to claim 1, wherein in the step 2, phase distribution of each functional partition is calculated, and azimuth angles of all nano bricks included in each functional partition are arranged according to the phase distribution of the functional partition.
6. The method for designing a subsurface device capable of achieving multi-dimensional imaging according to claim 5, wherein each functional partition is used as a sub-lens, and the phase distribution of the sub-lenses is calculated according to the arrangement of the images, and the phase distribution calculation formula is as follows:
wherein ,is the phase adjustment quantity corresponding to the point with the coordinates of (x, y) on the ith sub-lens, lambda i For the target working wavelength corresponding to the ith sub-lens, f is the focal length, delta xi 、Δ yi The off-axis amounts of the ith sub-lens in the x-axis and y-axis directions respectively, (x) i ,y i ) The center coordinate of an image corresponding to the ith sub-lens, and β is the absolute value of the magnification of the sub-lens.
7. The method for designing a multi-dimensional imaging enabled subsurface device according to claim 6, wherein the phase adjustment and the azimuth angle of the nano-tile satisfy the following formula:
wherein θ is the azimuth angle of the nanobrick;
the ultra-surface device capable of realizing multi-dimensional imaging focuses left-handed circularly polarized light and right-handed circularly polarized light under each target working wavelength respectively aiming at m target working wavelengths, the sign in the formula depends on the polarization state of incident light, and when the incident light is left-handed circularly polarized light or right-handed circularly polarized light, the phase regulation and control amounts are opposite numbers.
8. The method for designing a multi-dimensional imaging super-surface device according to claim 1, wherein the lower reflecting layer and the upper reflecting layer are silver layers, the medium in the microcavity is silicon dioxide, the material of the nano brick is titanium dioxide, and the material of the substrate is silicon dioxide.
9. A multi-dimensional imaging enabled subsurface device, characterized in that it is obtained according to the design method of a multi-dimensional imaging enabled subsurface device according to any one of claims 1-8.
10. The application of the super-surface device capable of realizing multi-dimensional imaging is characterized in that the super-surface device capable of realizing multi-dimensional imaging as claimed in claim 9 is utilized to carry out joint regulation and control on multiple parameters of incident light, and multi-dimensional fusion information of an object is obtained in real time; the multiparameters include spectrum, polarization, and phase.
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| CN118011630A (en) * | 2024-04-09 | 2024-05-10 | 中国航天三江集团有限公司 | Optical element applied to common aperture detection and emission scheme and design method thereof |
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| CN117870883A (en) * | 2024-03-08 | 2024-04-12 | 中国航天三江集团有限公司 | Circular polarization Hartmann wave front detection design method based on geometric phase super surface |
| CN118011630A (en) * | 2024-04-09 | 2024-05-10 | 中国航天三江集团有限公司 | Optical element applied to common aperture detection and emission scheme and design method thereof |
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