CN114706151B - Polarization-maintaining wide-spectrum focusing middle infrared super-structured lens based on bionic moth-eye structure - Google Patents
Polarization-maintaining wide-spectrum focusing middle infrared super-structured lens based on bionic moth-eye structure Download PDFInfo
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Abstract
The invention discloses a protection based on a bionic moth eye structureThe ultra-infrared super-structure lens comprises a substrate and a moth-eye type super-structure lens structure arranged on the same surface of the substrate, wherein the substrate can transmit the wide spectrum mid-infrared light with the wave band of 3.1-8.0 mu m, the moth-eye type super-structure lens structure consists of a plurality of bionic moth-eye type micro-nano structural units which are arranged at intervals in an array form, each bionic moth-eye type micro-nano structural unit is made of chalcogenide glass, and structural parameters of each bionic moth-eye type micro-nano structural unit consist of a top curvature radius R, a bottom diameter D and a height H, and R, D and H satisfy the following relation:
the super-structured lens can perform polarization-preserving emergent light and wide-spectrum focusing on middle-infrared wide-spectrum incident light with any polarization direction, can generate focusing effect under the condition of normal incidence and oblique incidence, has better focusing effect than the existing other super-structured lenses under the condition of oblique incidence, and lays a road for developing polarization-preserving, wide-spectrum and angle insensitive micro-optical devices and imaging systems.
Description
Technical Field
The invention relates to the field of lenses, in particular to a polarization-preserving wide-spectrum focusing middle infrared super-structure lens based on a bionic moth-eye structure.
Background
The lens is a basic optical element and plays a vital role in the scientific and industrial fields of imaging, precise measurement, optical communication and the like. The traditional optical lens is manufactured through a series of complex procedures such as cutting, polishing the surface, polishing, coating and the like. Generally, conventional lenses have disadvantages of large volume, high cost, and heavy weight. In recent years, super-structured lenses are emerging as technology, and the defects of the traditional lenses are overcome.
The super-structured lens is a micro-optical imaging device formed by a planar micro-nano structure, can flexibly regulate and control the polarization, amplitude and phase of incident light, and provides a promising platform for integrating optical devices. Compared with the heavy traditional optical lens, the super-structure lens has the advantages of planarization, small volume, low cost, easy integration and the like. Therefore, the super-structured lens has the potential of reducing the size and complexity of optical devices such as the existing camera and display, and has wide application prospect in the fields of augmented reality, virtual reality, medicine and the like. The working mechanism of the super-structured lens is mainly based on three phase regulation schemes, namely Bei Li phase (adv. Mate.27 (7), 1195-1200, 2015), resonance phase (Science 340 (6130), 331-334, 2013) and propagation phase (Science 352 (6290), 1190-1194, 2016). Bei Li phase, also called geometric phase, bei Li phase scheme is very simple and robust against manufacturing errors, but this scheme is only applicable to circularly polarized light and produces output light with opposite circular polarization. Resonant phase schemes have the ability to combine phase and amplitude modulation, but such schemes are only applicable to linearly polarized light and produce output light with cross polarization. Bei Li phase schemes and resonance phase schemes suffer from polarization sensitivity, low transmittance, and narrow spectrum modulation. In the propagation phase scheme, the phase modulation depends on the optical path difference, which makes the propagation phase scheme have the potential of wide-spectrum modulation, but the polarization characteristics of the output light have not been studied. Because of the polarization sensitivity of materials, polarization is critical for many optical applications, and it is important to explore polarization-preserving (i.e., the polarization direction of the exiting light is consistent with the polarization direction of the incident light) focusing at arbitrary polarization incidence.
The Mid-infrared (MIR) band (3.1-8.0 μm) covers the transparent region of the atmospheric window and the characteristic fingerprint spectrum of most molecules. The method has great application potential in aspects of biological sensing, high-precision thermal imaging, molecular detection and the like. However, little research has been done on the construction of microstructures for mid-infrared broad spectrum super-lenses. The prior researches show that the cylindrical super-structured lens (Nano Lett.16 (11)), 7229,2016) and the square super-structured lens (Nano Lett.17 (3)), 1819,2017) working in the propagation phase mode have better focusing effect on visible light, but the two structures are not reported for mid-infrared focusing. Meanwhile, the exploration of the middle infrared super-structure lens except the cylindrical super-structure lens and the square super-structure lens is also of great significance.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a polarization-preserving wide-spectrum focusing middle infrared super-structure lens based on a bionic moth-eye structure, which is used for solving the problems of polarization sensitivity, low transmittance and narrow-spectrum focusing of the traditional Bei Li phase super-structure lens and the traditional resonance phase super-structure lens, wherein the middle infrared wide-spectrum incident light can form focusing when passing through the surface of the super-structure lens, and the super-structure lens can perform polarization-preserving emergent and wide-spectrum focusing on the middle infrared wide-spectrum incident light with any polarization direction. In addition, the infrared super-structure lens can generate focusing effect under the condition of normal incidence and oblique incidence, has better focusing effect compared with the cylindrical super-structure lens and the square super-structure lens under the condition of oblique incidence, and lays a road for developing polarization-preserving, wide-spectrum and angle-insensitive micro-optical devices and imaging systems.
The technical scheme adopted for solving the technical problems is as follows: the utility model provides a polarization-preserving wide spectrum focusing middle infrared super-structure lens based on bionic moth-eye structure, includes the base plate and arranges the moth-eye super-structure lens structure of the same surface of base plate, the base plate can see through the wide spectrum mid-infrared light of 3.1 ~ 8.0 mu m wave band, moth-eye super-structure lens structure by a plurality of bionic moth-eye micro-nano structural unit that arrange with array form interval constitutes, every bionic moth-eye micro-nano structural unit be made by chalcogenide glass, every bionic moth-eye micro-nano structural unit's structural parameter by top radius of curvature R, bottom diameter D and high H constitute, R, D and H satisfy relational expression:
in nature, moth eyes have very fine micro/nano structures and have an anti-reflection function. According to the invention, the infrared super-structure lens utilizes the plurality of bionic moth-eye micro-nano structural units which are arranged at intervals in an array form, a moth-eye super-structure lens structure is formed on one surface of the substrate, the surfaces of the plurality of bionic moth-eye micro-nano structural units form the super-structure lens surface, and incident broad spectrum light can form focusing when passing through the super-structure lens surface. The moth-eye type super-structure lens structure of the infrared super-structure lens can carry out wave front shaping on the middle infrared broad spectrum incident light with any polarization direction entering from one side of the substrate, so that the emergent broad spectrum light generates focusing effect and keeps the polarization direction of the emergent light identical to that of the incident light. Compared with the existing cylindrical super-structured lens and square super-structured lens, the infrared super-structured lens can generate focusing effect under the condition of normal incidence and oblique incidence, and has better focusing effect under the condition of oblique incidence. The invention paves the way for developing polarization-preserving, broad-spectrum and angle-insensitive micro-optical devices and imaging systems.
Preferably, the moth-eye type super-structure lens structure is composed of a concentric circular super-structure array and a plurality of circular super-structure arrays, the circular super-structure arrays are sequentially arranged on the periphery of the circular super-structure array, the circular super-structure array and the circular super-structure arrays are respectively composed of a plurality of bionic moth-eye type micro-nano structure units, the structure parameters of the bionic moth-eye type micro-nano structure units in the circular super-structure array are completely the same, each circular super-structure array comprises a plurality of circles of bionic moth-eye type micro-nano structure units which are concentrically arranged, the circles of different circular super-structure arrays are different, the structure parameters of the bionic moth-eye type micro-nano structure units on the same circle are completely the same, the bottom diameters of the bionic moth-eye type micro-nano structure units on different circles radially outwards of the same circular super-structure array are sequentially reduced from the outermost circle of the circular super-structure array and radially outwards along the middle infrared super-structure lens, and in two adjacent circles: the number of the bionic moth eye type micro-nano structural units on the outer ring is greater than that on the inner ring, and the ratio of the number of the bionic moth eye type micro-nano structural units on the outer ring to the number of the bionic moth eye type micro-nano structural units on the inner ring is equal to the ratio of the circumference of the outer ring to the circumference of the inner ring.
Preferably, the number of the annular super-structure arrays is at least 4.
When the polarization-maintaining wide-spectrum focusing middle infrared super-structured lens based on the bionic moth-eye structure is designed, the array formed by the bionic moth-eye micro-nano structural units can realize the focusing of a wide-spectrum wave band as long as the focusing of the middle wavelength of the wide-spectrum wave band is met, namely, the focusing of 3.1-8.0 μm of the wide-spectrum wave band can be realized as long as the focusing of the middle wavelength of the wide-spectrum wave band is met. Preferably, the design method of the infrared super-structure lens in polarization-maintaining wide-spectrum focusing comprises the following steps: according to the target focal length of the infrared super-structured lens in the polarization-maintaining wide-spectrum focusing, the phase positions of the surface of the infrared super-structured lens at different spatial positions are determined, the range of the values of the phase positions is 0 to 2 pi, and the arrangement of the bionic moth-eye micro-nano structural units is determined according to the one-to-one correspondence relationship between the phase positions and the structural parameters and the arrangement period P of the bionic moth-eye micro-nano structural units, so that the moth-eye super-structured lens structure is formed.
Preferably, the one-to-one correspondence between each phase and the structural parameter and the arrangement period P of the bionic moth eye type micro-nano structure unit is calculated by adopting a finite element method and utilizing COMSOL Multiphysics software.
The waveguide effect of the incident light in the internal transmission process of the bionic moth-eye micro-nano structure unit of the infrared super-structured lens can generate corresponding phase accumulation, and the corresponding phase accumulation can be regulated and controlled by changing the structural parameters and the arrangement period of the bionic moth-eye micro-nano structure unit, so that the emergent light can be regulated and controlled in full phase within the range of 0 to 2 pi. Further, when the height H and the arrangement period P of the bionic moth-eye type micro-nano structure unit are determined, full-phase regulation and control in a range of 0 to 2 pi can be generated on emergent light by changing the bottom diameter D of the bionic moth-eye type micro-nano structure unit, and the expression of the waveguide type phase of the corresponding single bionic moth-eye type micro-nano structure unit is as follows:
wherein n is eff (D) Is the effective refractive index corresponding to the single bionic moth eye type micro-nano structure unit structure, and lambda is the incident wavelength.
Preferably, the substrate is made of MgF 2 The substrate is made, each bionic moth eye type micro-nano structure unit is made of As 2 Se 3 And sulfur-based glass. As As 2 Se 3 The chalcogenide glass has high transmissivity, high refractive index (2.88) and relatively low material hardness, and is a preferred material for manufacturing the bionic moth-eye type micro-nano structural unit.
Compared with the prior art, the invention has the following advantages: the moth-eye type super-structure lens structure of the infrared super-structure lens can carry out wave front shaping on the mid-infrared broad spectrum incident light with any polarization direction entering from one side of the substrate, so that the emergent broad spectrum light generates focusing effect and keeps the polarization direction of the emergent light identical to that of the incident light. By changing the structural parameters and the arrangement period of the bionic moth eye type micro-nano structural unit, the full-phase regulation and control of the emergent light within the range of 0 to 2 pi can be generated. Compared with the existing cylindrical super-structured lens and square super-structured lens, the infrared super-structured lens can generate focusing effect under the condition of normal incidence and oblique incidence, has better focusing effect under the condition of oblique incidence, and lays a road for developing polarization-preserving, wide-spectrum and angle-insensitive micro-optical devices and imaging systems.
Drawings
FIG. 1 is a schematic view of an infrared super-structure lens according to the present invention;
fig. 2a is a three-dimensional schematic diagram of a bionic moth-eye type micro-nano structure unit in an embodiment; FIG. 2b is a front view of a bionic moth eye type micro-nano structure unit in an embodiment;
FIG. 3a is a schematic diagram of eight biomimetic moth-eye micro-nano structural units for providing eight discrete phases that make up a mid-infrared super-structured lens in a broad spectrum focus in an embodiment; FIG. 3b is a graph showing the relationship between the bottom diameters of eight bionic moth-eye micro-nano structure units and the amplitude and phase of the emergent electric field; FIG. 3c shows the structural parameters and arrangement period P of eight bionic moth-eye micro-nano structural units;
FIG. 4a is a Stokes' parameters corresponding to eight bionic moth-eye micro-nano structure units under the action of x polarized incident light with a wavelength of 5.1 μm; FIG. 4b shows the amplitude and phase of the x-polarized and y-polarized electric fields emerging from eight bionic moth eye micro-nano structure units; FIG. 4c is a diagram of a beam deflector based on a biomimetic moth-eye structure in an embodiment; FIG. 4d is an x-polarization output electric field amplitude distribution of a beam deflector based on a biomimetic moth-eye structure under x-polarization incidence; FIG. 4e is a graph showing the amplitude distribution of the y-polarized output electric field of a beam deflector based on a bionic moth-eye structure under x-polarized incidence;
FIG. 5a is a schematic diagram of a discrete phase distribution of eight discrete phases for producing a focus with a focal length of 100 μm in an embodiment; FIG. 5b is a schematic top view and partial enlarged view of an infrared super-resolution lens in a polarization-preserving broad-spectrum focus in an embodiment; FIG. 5c is a graph showing the intensity distribution of the emergent electric field under x-polarized incidence; FIG. 5d is a schematic view of focusing at arbitrary polarization incidence;
FIG. 6 is a schematic diagram of polarization maintaining of an infrared super-resolution lens in polarization-preserving broad-spectrum focusing under arbitrary polarization incidence in an embodiment;
FIG. 7a is a schematic diagram showing the evolution of the intensity of the emergent electric field when the incident light with different x-polarization wavelengths irradiates the infrared super-structured lens in polarization-preserving broad-spectrum focusing; FIG. 7b is a graph showing the modulation efficiency and focusing efficiency of an IR super-resolution lens in polarization-maintaining broad-spectrum focusing as a function of wavelength;
fig. 8a, 8b and 8c are graphs of focusing effects of the infrared super-structure lens, the conventional cylindrical super-structure lens and the conventional square super-structure lens in the present invention under oblique incidence conditions, respectively.
Detailed Description
The invention is described in further detail below with reference to the embodiments of the drawings.
Embodiment one: a polarization-maintaining wide-spectrum focusing middle infrared super-structured lens based on bionic moth-eye structure, as shown in figure 1, comprises MgF 2 The substrate 1 made of the substrate 1 and the moth-eye type super-structure lens arranged on the same surface of the substrate 1, the substrate 1 can transmit the broad spectrum mid-infrared light with the wave band of 3.1-8.0 μm, the moth-eye type super-structure lens structure is composed of a plurality of bionic moth-eye type micro-nano structure units 2 which are arranged at intervals in an array form, each bionic moth-eye type micro-nano structure unit 2 is composed of As 2 Se 3 The structural parameters of each bionic moth-eye micro-nano structural unit 2 are composed of a top curvature radius R, a bottom diameter D and a height H, and R, D and H satisfy the relation:
in the first embodiment, the moth-eye type super-structure lens structure is composed of a concentric circular super-structure array 3 and a plurality of circular super-structure arrays 4 (3 circular super-structure arrays 4 are shown in fig. 1), the plurality of circular super-structure arrays 4 are sequentially arranged on the periphery of the circular super-structure array 3, the circular super-structure array 3 and the plurality of circular super-structure arrays 4 are respectively composed of a plurality of bionic moth-eye type micro-nano structure units 2, the structural parameters of the bionic moth-eye type micro-nano structure units 2 in the circular super-structure array 3 are completely the same, each circular super-structure array 4 comprises a plurality of circles of bionic moth-eye type micro-nano structure units 2 which are concentrically arranged, the circles of different circular super-structure arrays 4 are different, the structural parameters of the moth-eye type micro-nano structure units 2 on the same circle are completely the same, the bottom diameters of the moth-eye type micro-nano structure units 2 on different circles radially outwards of the same circular super-structure array 4 are sequentially reduced from the outermost circle of the circular super-structure array 3 to the adjacent circles outwards of the bionic moth-eye type micro-nano structure lens in the radial direction along the infrared super-structure lens in sequence: the number of the bionic moth eye type micro-nano structural units 2 on the outer ring is more than that of the bionic moth eye type micro-nano structural units 2 on the inner ring, and the ratio of the number of the bionic moth eye type micro-nano structural units 2 on the outer ring to the number of the bionic moth eye type micro-nano structural units 2 on the inner ring is equal to the ratio of the circumference of the outer ring to the circumference of the inner ring.
The design method of the polarization-maintaining wide-spectrum focusing middle infrared super-structure lens comprises the following steps: according to the target focal length of the infrared super-structured lens in the polarization-maintaining wide-spectrum focusing, the phase positions of the surface of the infrared super-structured lens at different spatial positions are determined, the range of the values of the phase positions is 0 to 2 pi, and the arrangement of the bionic moth-eye micro-nano structural units is determined according to the one-to-one correspondence relationship between the phase positions and the structural parameters and the arrangement period P of the bionic moth-eye micro-nano structural units, so that the moth-eye super-structured lens structure is formed. The one-to-one correspondence between each phase and the structural parameters and the arrangement period P of the bionic moth eye type micro-nano structural unit is calculated by adopting a finite element method and COMSOL Multiphysics software. Specifically, when the height H and the arrangement period P of the bionic moth-eye type micro-nano structure unit are determined, full-phase regulation and control in a range of 0 to 2 pi can be generated on emergent light by changing the bottom diameter D of the bionic moth-eye type micro-nano structure unit, and the expression of the waveguide type phase of the corresponding single bionic moth-eye type micro-nano structure unit is as follows:
wherein n is eff (D) Is the effective refractive index corresponding to the single bionic moth eye type micro-nano structure unit structure, and lambda is the incident wavelength.
When the broad spectrum incident light with arbitrary polarization irradiates the polarization-preserving broad spectrum focusing middle infrared super-structure lens based on the bionic moth-eye structure, the polarization state of the emergent light is kept consistent with the polarization state of the incident light, and a focusing effect is generated.
The relationship satisfied by R, D and H above
The derivation process of (2) is as follows:
as shown in fig. 2a, the three-dimensional bionic moth-eye micro-nano structure unit is formed by a space surrounded by a paraboloid of revolution (S) and a z=0 plane. The paraboloid of revolution (S) satisfies the following equation:
where (x, y) is the spatial coordinate. The equation of a two-dimensional parabola (s|y=0) formed by the intersection of a parabola of revolution (S) and a y=0 plane can be expressed as:
the two-dimensional parabola described by equation (2) is shown in fig. 2 b. The spatial coordinates of the top of the bionic moth eye type micro-nano structure unit are (0, H), and the curvature radius R at the position can be calculated as:
where z' and z "are the first and second derivatives of equation (2) over x. Taking equation (2) into equation (3) yields the radius of curvature R:
it should be noted that the radius of curvature R depends on D and H, however, three structural parameters D, H, R are essential when constructing a biomimetic moth-eye micro-nano structural unit using FDTD simulation software.
Taking the incident light with the wavelength of 5.1 mu m and the middle infrared polarization as an example, using COMSOL Multiphysics simulation software, adopting a finite element method to perform full-wave simulation on the emergent electric fields of the bionic moth-eye type micro-nano structural units with different parameters (D, H, P and R). By parametric scanning, we choose the period P to be 2.4 μm and the height H to be 3.7 μm in order to obtain a larger exit electric field strength. The waveguide effect of the incident light in the internal transmission process of the bionic moth-eye micro-nano structure unit can generate corresponding phase accumulation, so that the corresponding phase accumulation can be correspondingly regulated by changing the bottom diameter of the bionic moth-eye micro-nano structure unit, and then the emergent light is subjected to full-phase regulation and control within the range of 0 to 2 pi. When the height H of the bionic moth eye type micro-nano structure unit is 3.7 mu m and the arrangement period P is 2.4 mu m, the bottom diameter D of eight bionic moth eye type micro-nano structure units realizing 0, pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2 and 7 pi/4 discrete phase regulation and control are respectively 0.97P, 0.93P, 0.86P, 0.78P, 0.73P, 0.65P, 0.56P and 0.33P. Fig. 3a shows a schematic diagram of eight bionic moth-eye micro-nano structural units for providing eight discrete phases, which form a polarization-preserving broad-spectrum focusing mid-infrared super-structured lens, and the eight bionic moth-eye micro-nano structural units are respectively represented by numerals 1 to 8 from small to large in bottom diameter, so as to provide eight discrete phases: 0. pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2, 7 pi/4). Fig. 3b shows the amplitude and phase relationship between the bottom diameters of eight bionic moth-eye micro-nano structure units and the emergent electric field. Fig. 3c shows the structural parameters and the arrangement period P of eight bionic moth-eye type micro-nano structural units.
Embodiment two: the beam deflector is constructed by eight bionic moth eye type micro-nano structural units in the first embodiment, and specifically comprises:
fig. 4a is a stokes parameter corresponding to eight bionic moth-eye micro-nano structure units under the action of x polarized incident light with a wavelength of 5.1 μm, which is used for describing the polarization state of outgoing light regulated by the eight bionic moth-eye micro-nano structure units. Where we calculate stokes parameters (I, Q, U and V) of the outgoing light at the incidence of x-polarized light with a wavelength of 5.1 μm. I=1 is the normalized total outgoing light intensity; q is the light component along the x-polarization direction; u is the light component polarized at 45 ° to the x-axis; v is the right-handed circularly polarized light component. Then use the formula
The polarization degree P of the outgoing light can be calculated. P=1 means that the outgoing light belongs to fully polarized light. Thus, the total outgoing light can be separated into an x-polarized component and a y-polarized component. We extract the two orthogonal polarization components and then plot the amplitude and phase of the two polarization states in fig. 4 b. The result shows that the eight moth-eye micro-nano structural units generate 0-2 pi full-phase regulation on x polarized emergent light. Since the polarization degree p=1 of the outgoing light, we can define the modulation efficiency of the outgoing light as the ratio between the intensity of the target outgoing light (x-polarized outgoing light) and the total outgoing light intensity:
according to the data shown in equation (5) and fig. 4b, the regulation efficiency of the eight bionic moth-eye micro-nano structural units on x-polarized emergent light is 100%.
To verify the phase modulation and polarization maintaining properties of the biomimetic moth-eye micro-nano structural units, we constructed a beam deflector with a 15.4 degree angle with eight biomimetic moth-eye micro-nano structural units, as shown in fig. 4 c. We use the finite element method to pair slave mgfs 2 The output electric field excited by the x-polarized incident electric field at normal incidence to the substrate was subjected to full wave simulation. We theorize that the exit electric field of x-polarization (corresponding exit angle is 15 degrees) is extracted, as shown in fig. 4 d. The exit angle calculated by the numerical value is better matched with the theoretical exit angleThus, the phase modulation function of eight bionic moth eye type micro-nano structural units is demonstrated. To calculate the modulation efficiency of the beam deflector, we theorize that the exiting electric field of y polarization is extracted, as shown in fig. 4 e. The results show that the component of the y-polarized output electric field is 0. Combining the value of DOP (p=1) and the zero component of the y-polarized output electric field, we can derive that the exiting electric field of the beam deflector is x-polarized, which coincides with the polarization state of the incident light. Therefore, when the eight bionic moth-eye micro-nano structural units in the first embodiment are used for constructing the light beam deflector, the light beam deflector has polarization maintaining characteristics, and the regulating and controlling efficiency of the deflector is 100%.
Embodiment III: the polarization-preserving wide-spectrum focusing middle infrared super-structured lens based on the bionic moth-eye structure in the first embodiment is used for carrying out polarization-preserving focusing on incident light with arbitrary polarization, and specifically comprises the following steps:
in order to generate a focus of 100 μm for incident light in the mid-infrared band (5.1 μm), the required phase is
Can be written as:
where λ (λ=5.1 μm) is the incident wavelength and f is the focal length (f=100 μm). The continuous phase distribution calculated in equation (6) is subjected to discrete processing to determine a discrete phase distribution of eight discrete phases (0, pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2, 7 pi/4), as shown in fig. 5 a. The super-structured lens of the first embodiment is shown in fig. 5 b. The super-structure lens has 2828 bionic moth-eye type micro-nano structural units, and the size of each bionic moth-eye type micro-nano structural unit is 2.4x2.4mu m 2 。
And carrying out numerical calculation on the emergent electric field under the incidence of x polarization by using FDTD simulation software. The intensity distribution of the exiting electric field along the z-axis is shown on the left side of the first row in fig. 5c, where the dashed line is the intensity distribution at y=0 μm. The second row in fig. 5c shows the intensity distribution of the x and y polarized output electric fields at the surface of the super-structured lens. Using formula (5) and x and y polarizationsThe electric field intensity distribution, the modulation efficiency of numerical calculation is 92%, which is lower than the theoretical value of 100%. This is due to structural errors introduced during the construction of the super-structured lens. The electric field intensity distribution at the focal plane (z=100 μm) is shown on the right side of the first row in fig. 5c, where the two dashed lines represent the intensity distribution at x=0 μm and y=0 μm. From these two dashed lines, we calculated the full width at half maximum (FWHM, full Width at Half Maximum), about-4.8 μm (0.94 λ). We define the focusing efficiency as the diameter D at the focal plane 2 And the diameter of the super-structure lens surface is D 1 The ratio of the electric field intensity integral in the region of (2) can be written as:
wherein D is 1 Is the diameter of the super-structured lens, D 2 Equal to 3 times FWHM. The numerically calculated focusing efficiency is about 90% based on the above equation (7) and the electric field intensity distribution at the focal plane and the super-structured lens surface.
Focusing at any polarization incident is shown in fig. 5 d. The first three columns show the exit electric field intensity distribution at three different linear polarizations (LP, linearly Polarization) of incidence. The corresponding polarization angles are 30 degrees (lp_30), 60 degrees (lp_60) and 90 degrees (lp_90) with respect to the x-axis. The fourth and fifth columns are the exit electric field intensity distribution at right-hand circular polarization (RCP, right Circularly Polarization) and left-hand circular polarization (LCP, left Circularly Polarization), respectively, incidence. The last two columns show the output intensity evolution at right-hand elliptical polarization (REP, right Elliptically Polarization) and left-hand elliptical polarization (LEP, left Elliptically Polarization) incidence. Note that both REP and LEP discussed are composed of two perpendicular waves with an amplitude ratio of 1:2. The inset shows the electric field intensity distribution at the focal plane (z=100 μm). The results in fig. 5d show that the super-structured lens of the first embodiment can achieve the same focusing effect for any polarized incident light.
In order to verify the polarization-preserving emergent properties of the super-structured lens of the first embodiment on incident light with any polarization, we theoretically calculate the amplitudes and phases of the different polarization components of the emergent electric field of eight bionic moth-eye micro-nano structural units (lp_30, lp_60, lp_90, rcp, lcp, rep and LEP) under any polarization incidence, as shown in fig. 6. Wherein the thick dotted line represents the same emergent electric field as the incident polarization direction, and the thin dotted line represents the emergent electric field different from the incident polarization direction. The results show that the component of the outgoing electric field, which is different from the incoming polarization direction, is zero, that the component of the outgoing electric field, which is the same as the incoming polarization direction, is non-zero and can provide full phase modulation of 0 to 2 pi. This shows that the super-structured lens of the first embodiment can realize polarization-preserving emergent light and focusing under any polarized incidence.
Embodiment four: the polarization-maintaining wide-spectrum focusing middle infrared super-structure lens based on the bionic moth-eye structure in the first embodiment is used for focusing the middle infrared wide spectrum, and specifically comprises the following steps:
for the super-structured lens constructed in FIG. 5b, we numerically calculate the evolution of the exit electric field intensity under irradiation of different wavelengths of x-polarization (3.1 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm,5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm and 8.0 μm) as shown in FIG. 7 a. Although the focus intensities at the short and long wavelengths are smaller than at the intermediate wavelengths, a significant focusing effect occurs in the mid-infrared broad spectrum band of 3.1 μm to 8.0 μm. To quantify the effect of wavelength on the modulation efficiency and the focusing efficiency, we plotted the modulation efficiency and the focusing efficiency as a function of wavelength, as shown in fig. 7 b. In the mid-infrared band of 3.1 μm to 8.0 μm, the super-structured lens of embodiment one can achieve an average modulation efficiency of about 94%. The super-structured lens of example one has a maximum focusing efficiency of up to 90% at wavelengths of 5.0 μm and 5.1 μm.
Fifth embodiment: comparing the polarization-preserving wide-spectrum focusing middle infrared super-structure lens based on the bionic moth-eye structure in the first embodiment with the existing cylindrical super-structure lens (Nano Lett.16 (11), 7229,2016) and square super-structure lens (Nano Lett.17 (3), 1819,2017), the result shows that the infrared super-structure lens has better focusing effect in the oblique incidence focusing aspect, and the specific process is as follows:
in the first embodiment, a comparison graph of focusing effects of the polarization-preserving wide-spectrum focusing middle infrared super-structure lens based on the bionic moth-eye structure and the existing cylindrical super-structure lens and square super-structure lens under the oblique incidence condition is shown in fig. 8. Wherein the three super-lenses all provide the same phase modulation as shown in fig. 5 a. Taking 30-degree oblique incidence as an example, the intensity distribution of the emergent electric field under the action of polarized incident light with the wavelength of 5.1 mu mx is calculated by using FDTD simulation software. The schematic diagram of the bionic moth eye type micro-nano structural unit and the electric field intensity distribution of the emergent electric field and the structural parameters (D, H) corresponding to 8 discrete phases (0, pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2 and 7 pi/4) thereof are shown in fig. 8 a. The schematic diagram of the cylindrical micro-nano structural unit and the electric field intensity distribution of the emergent electric field and the structural parameters (D, H) corresponding to 8 discrete phases (0, pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2 and 7 pi/4) are shown in fig. 8 b. Schematic diagrams of square micro-nano structural units and electric field intensity distribution of emergent electric fields and corresponding structural parameters (L, H) of 8 discrete phases (0, pi/4, pi/2, 3 pi/4, pi, 5 pi/4, 3 pi/2 and 7 pi/4) are shown in fig. 8 c. The three focusing effects show that under the oblique incidence condition, the focusing effect of the mid-infrared super-structure lens is superior to that of the traditional cylindrical super-structure lens and square super-structure lens.
In summary, the invention relates to a polarization-preserving wide-spectrum focusing middle infrared super-structured lens based on a bionic moth-eye structure, which aims to realize polarization preservation and wide-spectrum focusing on incident light with arbitrary polarization in a middle infrared band (3.1-8.0 μm). We believe that the research of this patent makes a significant contribution in the relevant field, since ultra-structured lenses capable of maintaining polarization and broad spectrum focusing at arbitrary polarized incidence have not yet been studied. In addition, the polarization-preserving wide-spectrum focusing middle-infrared super-structure lens based on the bionic moth-eye structure has important potential application value, and high regulation and control efficiency and high focusing efficiency are realized. Moreover, the polarization-preserving wide-spectrum focusing middle-infrared super-structured lens based on the bionic moth-eye structure can work under normal incidence and oblique incidence. Compared with the super-structured lens (Nano Lett.16 (11), 7229,2016;Nano Lett.17 (3), 1819,2017), the super-structured lens based on the bionic moth-eye structure can show better focusing effect under the condition of oblique incidence, which ensures that the super-structured lens can effectively transmit light as the traditional lens. The invention paves the way for developing polarization-preserving, broad-spectrum and angle-insensitive micro-optical devices and imaging systems.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (6)
1. The polarization-maintaining wide-spectrum focusing middle infrared super-structure lens based on the bionic moth-eye structure is characterized by comprising a substrate and a moth-eye super-structure lens structure arranged on the same surface of the substrate, wherein the substrate can transmit wide-spectrum middle infrared light with a wave band of 3.1-8.0 mu m, the moth-eye super-structure lens structure is composed of a plurality of bionic moth-eye micro-nano structural units which are arranged at intervals in an array form, each bionic moth-eye micro-nano structural unit is made of chalcogenide glass, and structural parameters of each bionic moth-eye micro-nano structural unit are composed of a top curvature radius R, a bottom diameter D and a height H, and R, D and H satisfy the following relation:
the moth-eye type super-structure lens structure consists of a circular super-structure array and a plurality of circular super-structure arrays which are concentric, wherein the circular super-structure arrays are sequentially arranged on the periphery of the circular super-structure array, the circular super-structure array and the circular super-structure arrays respectively consist of a plurality of bionic moth-eye type micro-nano structure units, the structure parameters of the bionic moth-eye type micro-nano structure units in the circular super-structure array are completely the same, each circular super-structure array comprises a plurality of circles of bionic moth-eye type micro-nano structure units which are concentrically arranged, the circles of different circular super-structure arrays are different, the structure parameters of the bionic moth-eye type micro-nano structure units on the same circle are completely the same, the bottom diameters of the bionic moth-eye type micro-nano structure units on different circles outwards along the radial direction of the same circular super-structure array are sequentially reduced, and outwards along the radial direction of the infrared super-structure lens in two adjacent circles from the very outer circle of the circular super-structure array: the number of the bionic moth eye type micro-nano structural units on the outer ring is greater than that on the inner ring, and the ratio of the number of the bionic moth eye type micro-nano structural units on the outer ring to the number of the bionic moth eye type micro-nano structural units on the inner ring is equal to the ratio of the circumference of the outer ring to the circumference of the inner ring.
2. The polarization-preserving wide-spectrum focusing middle-infrared super-structure lens based on the bionic moth-eye structure according to claim 1, wherein the number of the circular super-structure arrays is at least 4.
3. The polarization maintaining wide spectrum focusing middle infrared super structure lens based on the bionic moth-eye structure according to any one of claims 1 to 2, wherein the design method of the polarization maintaining wide spectrum focusing middle infrared super structure lens is as follows: according to the target focal length of the infrared super-structured lens in the polarization-maintaining wide-spectrum focusing, the phase positions of the surface of the infrared super-structured lens at different spatial positions are determined, the range of the values of the phase positions is 0 to 2 pi, and the arrangement of the bionic moth-eye micro-nano structural units is determined according to the one-to-one correspondence relationship between the phase positions and the structural parameters and the arrangement period P of the bionic moth-eye micro-nano structural units, so that the moth-eye super-structured lens structure is formed.
4. The polarization-preserving wide-spectrum focusing middle-infrared super-structured lens based on the bionic moth-eye structure according to claim 3, wherein the one-to-one correspondence between each phase and the structural parameters and the arrangement period P of the bionic moth-eye micro-nano structural unit is calculated by adopting a finite element method and utilizing COMSOL Multiphysics software.
5. The polarization-maintaining wide-spectrum focusing mid-infrared super-structured lens based on a bionic moth-eye structure according to claim 3, wherein when the height H and the arrangement period P of the bionic moth-eye micro-nano structure unit are determined, the full-phase modulation in the range of 0 to 2 pi can be generated on emergent light by changing the bottom diameter D of the bionic moth-eye micro-nano structure unit, and the expression of the waveguide type phase of the corresponding single bionic moth-eye micro-nano structure unit is as follows:
wherein n is eff (D) Is the effective refractive index corresponding to the single bionic moth eye type micro-nano structure unit structure, and lambda is the incident wavelength.
6. The polarization-preserving wide-spectrum focusing middle-infrared super-structured lens based on the bionic moth-eye structure according to claim 1, wherein the substrate is made of MgF 2 The substrate is made, each bionic moth eye type micro-nano structure unit is made of As 2 Se 3 And sulfur-based glass.
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