CN114815009B - Method for regulating focal length range of zoom superlens by introducing additional phase - Google Patents
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Abstract
The invention discloses a method for adjusting and controlling the focal length range of a zoom superlens by introducing additional phases, wherein the superlens comprises the following steps: two layers of glass as a base, and two layers of dielectric cylindrical layer arrays respectively arranged on a glass substrate; when the super lens works, incident light vertically irradiates on the lower surface of the first layer of glass substrate, phase modulation is obtained through glass transmission and the dielectric silicon nano-pillar array, focusing is carried out, the second layer of super surface is rotated, the focal length changes, and the focal length range can be regulated and controlled through additional deflection phase. The double-layer zoom super lens added with the deflection phase solves the contradiction between the large rotation angle and the efficiency of the traditional zoom lens; the invention adopts the micro-nano structure to improve the traditional zooming mode, reduces the volume and weight of the lens as much as possible, and accords with the trend of miniaturization and integrability of modern optical devices or photoelectric devices.
Description
Technical Field
The invention belongs to the field of optical zooming, and particularly relates to a method for adjusting and controlling the focal length range of a zooming superlens by introducing additional phases.
Background
Tunable optics, particularly tunable lenses with variable refractive power, have indispensable applications in many optical systems, such as imaging systems for simulating human eye functions, or for tunable illumination and beam control. However, these focusing methods require complex optical systems composed of many optical devices, which are bulky and disadvantageous for integration. The super surface is an ultra-thin two-dimensional artificial structure consisting of metallic or dielectric optical sub-wavelength antennas for wavefront modulation, which has attracted extensive research interest in recent years. The super surface can realize arbitrary control of the phase, amplitude and polarization state of incident light by designing a proper sub-wavelength structure. Structural designs have therefore proposed various subsurface-based devices such as holograms, deflectors, and waveplates. The super surface is used for solving the problems of the traditional geometrical optical element, such as chromatic aberration and monochromatic aberration, due to the advantages of small volume, good integration with semiconductor devices, high design freedom and the like. The super surface is also widely used in the focal length adjustment of lenses.
Currently, the main superlenses for realizing focusing are mainly divided into three types, namely thermal modulation, electric tuning and mechanical modulation. Thermal modulation of superlenses exploits the response to temperature by changing the complex refractive index affecting the phase shift and its phase distribution. A thermally tunable superlens uses a spiral gold heater to regulate the temperature rise; the refractive index varies with temperature and depends on the thermal coefficient dn/dT. Such tunable lenses that utilize both dielectric and thermally mediated phenomena are classified as electro-thermal optical systems. In an electrically tunable superlens, the phase shift is obtained by a bias voltage. The design of field effect induced tunable metallic materials takes advantage of the complex permittivity of meta-atoms' proportional increase with carrier concentration. A lens with tunable NA and focal length is proposed that exploits the variation of carrier density under the action of an electric field; the advantage of such a lens is that the change does not require a change in shape and the tuning speed is faster than a thermally tuned lens. Mechanical stimulation of the optical system may cause structural changes, affecting the position, size and shape of the focal spot. These stimuli include electrostatic actuation, rotation, and stretching. However, the manner of thermal modulation and electrical tuning requires an additional control system. In contrast, the mechanical modulation superlens device has fast tuning speed and simple modulation mode, and is more suitable for application in the imaging aspect of mobile electronic equipment. However, the polarization insensitive zoom superlens has low light utilization rate when the relative angle of the double-combined supersurface is large, so that the focusing efficiency is low.
Disclosure of Invention
The invention aims to provide a method for adjusting and controlling the focal length range of a zoom superlens by introducing additional phases.
The technical solution for realizing the purpose of the invention is as follows: the zoom superlens comprises two layers of glass serving as a substrate and two layers of dielectric cylindrical layer arrays arranged on the upper surface of the glass and used for adjusting phases, the zoom superlens constructs a supersurface according to the relationship between the structural radius of a micro-nano dielectric cylindrical unit and the phase change, a phase formula of the zoom superlens is formed by superposing the actual lens phase and the additional phase, and the additional phase is used for realizing the adjustment and control of the focusing range by adding a constant phase compensation.
Compared with the prior art, the invention has the remarkable advantages that: 1) The used zoom superlens is provided with the micro-nano dielectric cylindrical layer array arranged on the plane substrate so as to realize the function of the traditional zoom superlens, and the thickness of the zoom superlens can be reduced to the wavelength level to the greatest extent, so that the zoom superlens is easy to integrate into a complex system or a chip micro system; 2) The complex light beam modulation of the zoom superlens can be realized by a phase superposition principle, and the processing can simplify an optical system originally composed of a plurality of optical elements into a supersurface sheet, so that the volume of the optical system is further reduced; 3) The used zoom super lens has polarization insensitivity, and can realize the change of focal length for incident light with different polarization, thereby getting rid of the limit of the prior common geometric phase type super surface on the specific requirement of the polarization of the incident light, and effectively reducing the efficiency loss of the geometric phase type super surface caused by polarization conversion; 4) The invention can realize the zoom super lens with adjustable focal length and has better flexibility; 5) The focal length change is realized by rotating two super-surfaces, the method provides a direct wave front regulation method based on the super-surfaces for lens zooming, and provides a new possibility for application of structural beams; 6) The additional phase is added under the condition of ensuring the capability, so that the change of the focal distance regulating range can be realized, and the focal distance regulation is more flexible.
The invention is described in further detail below with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of an optical zoom superlens structure based on a polarization insensitive supersurface in one embodiment.
FIG. 2 is a schematic diagram of a subsurface unit structure in one embodiment.
FIG. 3 is a graph of normalized magnetic energy density for two adjacent nanopillars of 80nm radius in one embodiment, with white lines representing the boundaries of the structure.
FIG. 4 is a graph of the radius of the subsurface unit structure versus the amount of phase change and efficiency for x-polarization, y-polarization, left-handed circular polarization, and right-handed circular polarization obtained by performing a simulated scan of the subsurface unit structure of FIG. 2 in one embodiment.
Fig. 5 is a graph of simulation results after a round function is applied to an optical zoom superlens with a polarization insensitive supersurface in one embodiment, wherein fig. 5 (a) to (d) are respectively focus diagrams of 40 °, 80 °, 120 ° and 160 °, and fig. 5 (e) to (h) are respectively phase distribution diagrams thereof.
FIG. 6 is a graph of focus at different angles in one embodiment.
FIG. 7 is a schematic diagram of focal points for different polarizations in one embodiment. Fig. 7 (a) to (d) are graphs showing the results of the focal points after linear polarized light, X polarized light, Y polarized light, and circularly polarized light are used at 100 ° rotation angles, respectively.
Fig. 8 is a schematic diagram of the focal point and phase corresponding to the 4 angles of fig. 5, respectively, with the addition of 120 ° of additional phase in one embodiment. Fig. 8 (a) to (d) are focal point diagrams of-80 °, -40 °,0 ° and 40 °, respectively, and fig. 8 (e) to (h) are phase distribution diagrams thereof, respectively.
Fig. 9 is a schematic diagram of focusing efficiency, which is divided into 4 cases, including a round function and whether 120 ° additional phase is added, and a comparison diagram of the efficiency of each case under 17um,22um,33um three different focal lengths is taken.
Detailed Description
As shown in fig. 1, a method for adjusting the focal length range of a zoom superlens by introducing an additional phase, wherein the zoom superlens comprises two layers of glass serving as a substrate and two layers of dielectric cylindrical layer arrays arranged on the upper surface of the glass and used for adjusting the phase, and the zoom superlens is characterized in that the zoom superlens constructs a supersurface according to the relation between the structural radius of a micro-nano dielectric cylindrical unit and the phase change, and a phase formula of the zoom superlens is characterized in that the actual lens phase and the additional phase can be overlapped; the additional phase realizes the regulation and control of the focal distance range by adding a constant phase compensation, so that the focal length regulation and control is more flexible.
In one embodiment, the dielectric material used in the cylindrical structure should meet the condition that the real part of the refractive index is larger (reaching more than 1.5 times of the refractive index of the substrate) and the imaginary part is close to 0 in the working wavelength, and the curve relationship between the radius and the phase change and the transmittance can be obtained by FDTD simulation calculation of the micro-nano dielectric cylindrical unit structure.
In one embodiment, the micro-nano cylindrical structure layer is a nano cylindrical array with different radii, and in order to ensure high efficiency, the geometric parameters of the cylindrical unit structure (as shown in fig. 2) need to satisfy the following constraint conditions: according to the nyquist sampling law, the lattice constant p should be smaller than λ/2NA, λ being the wavelength and NA being the superlens numerical aperture, while at the same time, to ensure that there is only 0 th order diffraction at normal incidence, p should be smaller than the equivalent operating wavelength of the incident light in the substrate (λ/n L1) and larger than the diffraction condition (λ/2n L1),nL1 being the substrate refractive index).
In one embodiment, the minimum value of the radius r of the cylindrical cell structure depends on the manufacturing process, while the maximum value cannot be greater than half the lattice constant.
In one embodiment, the height h of the cylindrical cell structure should be greater than λ/(n M1-1),nM1) being the refractive index of the nanopillar material.
In one embodiment, the phase change should cover 0-2 pi when the radius of the cylindrical cell structure is changed within a certain range.
In one embodiment, the radius-phase variation obtained by scanning the radius and the radius-transmission efficiency variation curve of the cylindrical cell structure should have polarization insensitivity, i.e. the radius-phase variation curves measured at different polarizations should be identical and the radius-transmission efficiency variation curves measured at different polarizations should be identical.
The scattering of the varifocal superlens nanostructures should be a local effect, with no coupling between the nanostructures.
The zoom superlens has polarization insensitivity, i.e. for incident light of different polarization states, the zoom superlens can focus with unchanged focus position.
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It should be noted that, in the embodiment of the present invention, directional indications such as up, down, left, right, front, and rear … … are referred to merely for explaining a relative positional relationship, a movement condition, and the like between the components in a specific posture as shown in the drawings, and if the specific posture is changed, the directional indication is changed accordingly.
In addition, if there is a description of "first", "second", etc. in the embodiments of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention.
In one embodiment, in conjunction with fig. 1, a polarization insensitive zoom superlens based on a double layer supersurface is provided, the zoom superlens comprising double layer glass L1, L2 as a substrate, and two micro-nano dielectric cylinder layer arrays M1, M2 for adjusting phase disposed on the upper surface of the glass.
Here, the micro-nano dielectric cylindrical structural layers M1, M2 are used to realize a phase adjusting function, and are respectively disposed on the glasses L1, L2.
When the super lens works, incident light vertically irradiates on the lower surface of the first layer L2 glass substrate, phase modulation is obtained through glass transmission and the dielectric silicon nano-pillar array, focusing is carried out, the second layer L1 super surface is rotated, the focal length changes, and the focal length range can be regulated and controlled through additional deflection phase.
In one embodiment, tiO 2 is chosen as the cylindrical material because in the visible light range, tiO 2 has a large real part and negligible imaginary part of its refractive index, and thus has a high refractive index and almost negligible absorption loss. Preferably, the height h of the TiO 2 cylinder is 600nm, and the lattice constant p is 300nm.
Further, the relationship between the phase and transmission efficiency of the TiO 2 cylindrical unit structure and the radius of the TiO 2 cylinder can be obtained by performing FDTD simulation scanning on the TiO 2 cylindrical unit structure (shown in FIG. 2). Since the coupling between adjacent nanopillars is extremely weak (as shown in fig. 3), they can be considered to be independently phase-modulated, and thus the change in radius and transmission efficiency can be obtained by scanning the radius of the nanopillars. In the simulation, periodic boundary conditions are used in the x and y directions, and PML boundary conditions are used in the z direction. A point monitor is arranged at the position of 80 mu m on the upper surface of the substrate to obtain the change of the phase and the transmission efficiency, and the change relation of the phase, the transmission efficiency and the radius under the incidence of plane waves of x polarization, y polarization, left-hand circular polarization and right-hand circular polarization is measured as shown in figure 4. It can be seen that the phase, transmission efficiency and radius change are consistent for different polarizations, which illustrates that the cell structure has polarization insensitive properties. Meanwhile, when the nano-pillars are changed within the range of 40 nm-110 nm, the phase change amount covers 0-2 pi. In this range, the transmission efficiency is 80% or more. The results show that by changing the radius of the nano-pillar in the range of 40-110 nm, the high-efficiency phase regulation and control of any polarization can be realized.
Further, the super surface can be designed according to the phase formula by the method, wherein the formulas (1) and (2) respectively represent the transmission functions of the two phase plates, and the formula (3) is the transmission function of the phase plate corresponding to the formula (2) after being rotated by an angle theta. The formula (4) is the total transmission function after the two phase plates are overlapped, and the focal length of the designed zoom lens is obtained as formula (5) by comparing the standard spherical lens transmission function. It can be seen that the focal length f is a function of θ, and the focal length can be changed by changing the rotation angle of the second superlens, thereby realizing the zooming function. The equations (6) and (7) are transmission functions of two phase plates with additional phases added thereto, and the additional phase functions can be added. By adding a constant phase compensation, the contradiction between the focusing energy and the focusing range can be resolved, which can be kept highly efficient in the desired focal length range. Wherein Mo Erchao lens structures can be obtained by formulas (1), (2), (3) and (4), focal length can be obtained by formula (5), and Mo Erchao lens structures with additional phases added can be obtained by formulas (6) and (7).
Tcom＝T1(r,φ)T2,rot(r,φ)＝exp[iθround(ar2) (4)
f＝π/θaλ (5)
In the formula, λ represents the working wavelength, in this embodiment, r is the radius from any point to the center of the phase plate, Φ is the angle between the x-axis and the axis at the center of the point, f is the focal length, θ is the rotation angle of the lens, a and b are constants, limited by the resolution of the superlens, depending on the pixel size and the maximum radius of the superlens, C is the unit cell size of the nano-brick structure, and rmax is the radius of the GEMS. According to the corresponding phase formula, a superlens for zooming can be manufactured.
The manufacturing process of the optical zoom super lens based on the polarization insensitive super surface comprises the following steps: hexamethyldisilazane is coated on a flat silica surface to promote resist adhesion, and then an undiluted film of positive electron beam resist ZEP-520A is spin-coated to obtain a coating of resist material having a thickness of 600nm. The corrosion inhibitor was then baked at 180℃for 5 minutes. The sample was then coated with 10nm of chromium by electron beam evaporation to avoid charge effects during writing. The pattern was exposed to an accelerating voltage of 125kV and gently stirred in o-xylene for 60 seconds to visualize the pattern, and the inverted supersurface pattern was etched into the corrosion resistant coating. The system is then placed in a stream of N 2 and the film thickness resulting from the complete deposition of TiO 2,TiO2 by atomic layer deposition technique at 90 ℃ with tetra (dimethylamino) titanium as precursor should be greater than half the maximum feature size width, i.e. 600nm. Following reactive ion etching with a mixture of Cl 2 and BCl 3 ions, the top of the TiO 2 subsurface and residual corrosion inhibitor are exposed. Finally, exposing the sample to UV radiation and ozone, and immersing in a remover for 24 hours to obtain the final dielectric super surface.
In one embodiment, the FDTD simulation verification is carried out on the optical zoom superlens based on the polarization insensitive supersurface, and the flow is as follows:
1) Setting the parameters of the super-surface structure. The setting parameters are as follows: a silica glass layer with a specification of 20 μm by 20 μm and a thickness of 0.5 μm; analog wavelength 532nm; the thickness of the super surface unit cylinder is 0.6 μm, and the lattice constant is 0.3 μm.
2) And simulating the established model. The method comprises the steps of respectively arranging two different monitors by incidence of light in an x-polarization plane, and arranging one monitor on an xz plane to realize monitoring of phases; a monitor is arranged at a position 100nm away from the plane, so that the monitoring of the whole light field is realized. As can be seen from fig. 5, a schematic view of the focus and focusing effect at the focal plane at four different rotation angles θ. As expected, the focal length decreases with increasing angle. The phase distribution then characterizes the fresnel lens. Fig. 6 is a graph of rotation angle θ versus focal length f, both of which represent the relationship between theoretical and simulated focal points and rotation angle, respectively. It can be seen that as the angle increases, the focal length gradually decreases from infinity and gradually flattens. As the angle increases, the difference between the two curves gradually decreases. The reason for the difference is that the super surface size is limited.
3) Fig. 7 shows that the amplitude and phase distribution are substantially uniform with different polarization incidence, which indicates that the superlens has polarization insensitivity, and that the slight rotational asymmetry exhibited by it does not have a significant effect on the overall polarization insensitivity, based on which we have achieved focus and phase changes at different angles below using the supersurface, respectively.
4) Fig. 8 is a schematic of the focal point and phase with the addition of 120 ° of additional phase. It can be seen that the focus position and phase are not affected at the corresponding angles, but a large angle can be converted into a small angle to flexibly regulate the focus range.
5) Fig. 9 is a schematic diagram of focal length and focusing efficiency defined as total power in a circular area with a diameter of 2 xfwhm and total power in a circular area with a diameter of 1mm in the focal plane. The center of the two circular areas is the point of maximum intensity. It can be seen from fig. 9 that the additional phase has a certain effect on the focusing efficiency, which can be kept relatively high in the desired focal length range.
The optical zoom superlens used in the invention is a two-dimensional array supersurface of a micro-nano dielectric cylinder manufactured on a substrate, can regulate and control optical wave front under the sub-wavelength spatial resolution, and has perfect phase regulation function, thus realizing lens zooming. The polarization insensitive nature of the lens allows it to zoom the lens for any polarization of incident light, which is quite different from the previously common PB-phase based requirement of a specific polarization state of incident light. The designed zoom superlens has potential application in the field of super-resolution imaging. Such a polarization insensitive super surface based optical zoom super lens can be easily combined into a chip to form a composite device with extended functionality.
The foregoing has outlined and described the basic principles, 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, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. The method for regulating the focal length range of the zoom superlens by introducing additional phases is characterized in that the zoom superlens constructs a supersurface according to the structural radius and phase change relation of a micro-nano dielectric cylinder unit, a phase formula of the zoom superlens is overlapped by an actual lens phase and an additional phase, and the additional phase realizes the regulation of the focal length range by adding a constant phase compensation;
When incident light is incident, the incident light sequentially passes through the phase modulation of the first layer of super surface and the second layer of super surface, and finally is focused at a specific position;
When the second layer of super surface rotates relative to the first layer of super surface, the focusing effect of the super lens group on incident light is changed according to the change of the relative rotation angle;
An additional phase is introduced into the phase design of the two layers of super surfaces, so that the zoom range of the super lens group to incident light is enlarged;
the dielectric material used in the cylindrical structure meets the condition that the real part of the refractive index reaches more than 1.5 times of the refractive index of the substrate in the working wavelength, and the curve relation of radius, phase change and transmissivity is obtained through FDTD simulation calculation of the micro-nano dielectric cylindrical unit structure;
the phase distribution of the two super-surface layers is opposite, and the transmission functions respectively meet the following formulas:
wherein r is the distance from any point on the super surface layer to the center, Round is a rounding function, a is a constant, for the angle between the x-axis and the axis at the center;
When the second layer of subsurface rotates relative to the first layer of subsurface, its transmission function also changes:
wherein θ is the relative rotation angle of the second layer of supersurface and the first layer of supersurface;
The total transmission function after the superposition of the first layer of super surface and the rotated second layer of super surface is as follows:
after the second layer of super surface rotates, the relation between the focal length and the relative rotation angle of the zooming super lens group meets the following formula:
Wherein lambda is the working wavelength;
In order to increase the zoom range of the zoom superlens group, a constant compensation phase is introduced; the transmission functions of the final two super surface layers are respectively:
where ibr 2 is a constant compensation phase and b is a constant.
2. The method for adjusting focal length range of a zoom superlens by introducing additional phase according to claim 1, wherein the dielectric cylindrical layer array is a nano cylindrical array with different radiuses, and the geometric parameters of the cylindrical unit structure satisfy the following conditions: according to the nyquist sampling law, the lattice constant p should be smaller than λ/2NA, and at the same time, p should be smaller than the equivalent operating wavelength λ/n L1 of the incident light in the substrate, and larger than the diffraction condition λ/2n L1, where λ is the wavelength, NA is the superlens numerical aperture, and n L1 is the substrate refractive index.
3. The method of adjusting the focal length range of a zoom superlens by introducing additional phase as claimed in claim 2, wherein the maximum value of the radius of the cylindrical element structure is not more than half the lattice constant.
4. A method of adjusting the focal length range of a zoom superlens by introducing additional phases according to claim 3, wherein the phase change should cover 0-2 pi when the radius of the cylindrical element structure is changed within a certain range.
5. A method of adjusting the focal length range of a variable focus superlens by introducing additional phases according to claim 3, wherein the height h of the cylindrical cell structure is greater than λ/(n M1-1),nM1) being the refractive index of the nanopillar material.
6. A method of adjusting the focal length range of a zoom superlens by introducing additional phases according to claim 3, wherein the material of the cylindrical cell structure is TiO 2.
7. The method of adjusting a focal length range of a zoom superlens by introducing an additional phase according to claim 1, wherein a radius-phase variation curve obtained by scanning a radius of the cylindrical unit structure and a curve measured under different polarizations of the radius-transmission efficiency variation curve should be identical.
8. The method of claim 1, wherein the zoom superlens is capable of focus with a constant focal position for incident light of different polarization states by introducing additional phase modulation.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210503690.7A CN114815009B (en) | 2022-05-10 | 2022-05-10 | Method for regulating focal length range of zoom superlens by introducing additional phase |
| PCT/CN2022/116987 WO2023216472A1 (en) | 2022-05-10 | 2022-09-05 | Method for regulating focal length range of zoom super-lens by introducing additional phase |
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| CN114815009B (en) * | 2022-05-10 | 2024-06-07 | 南京理工大学 | Method for regulating focal length range of zoom superlens by introducing additional phase |
| CN115113308B (en) * | 2022-07-06 | 2024-05-14 | 重庆大学 | Super-resolution imaging lens with angle amplifying function |
| CN115283832A (en) * | 2022-08-10 | 2022-11-04 | 中国科学院西安光学精密机械研究所 | Processing system and processing method of anti-reflection micro-nano structure |
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| CN109212741A (en) * | 2018-10-31 | 2019-01-15 | 武汉邮电科学研究院有限公司 | A kind of continuous magnification lens and optical system |
| CN110161676A (en) * | 2019-05-31 | 2019-08-23 | 华中科技大学 | A kind of optical focal distance setting system surpassing surface based on two-layered medium |
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| CN114815009B (en) * | 2022-05-10 | 2024-06-07 | 南京理工大学 | Method for regulating focal length range of zoom superlens by introducing additional phase |
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| CN109212741A (en) * | 2018-10-31 | 2019-01-15 | 武汉邮电科学研究院有限公司 | A kind of continuous magnification lens and optical system |
| CN110161676A (en) * | 2019-05-31 | 2019-08-23 | 华中科技大学 | A kind of optical focal distance setting system surpassing surface based on two-layered medium |
| CN110376731A (en) * | 2019-07-13 | 2019-10-25 | 南京理工大学 | Construction method based on the super structure lens group of broadband achromatism that multilayer surpasses structure surface |
| CN111948805A (en) * | 2020-07-06 | 2020-11-17 | 中山大学 | Super-surface group capable of realizing coordinate transformation and preparation method of super-surface thereof |
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| CN114296155A (en) * | 2021-12-02 | 2022-04-08 | 华中科技大学 | Wide-spectrum optical zoom system based on double-layer medium super-surface |
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