Interference supercell-based angle filtering stray light elimination superlens and design method thereof

Abstract

The application discloses an angle filtering stray light superlens based on interference supercells and a design method thereof, the superlens comprises a substrate and a plurality of supercells arranged on the substrate; the supercells are formed by alternately arranging two kinds of superatoms with similar transmission amplitudes and different lateral sizes, the light beams interfere at the top of the supercells, and the transmittance of the supercells decreases with the increase of the light beam incidence angle, so that the angle filtering is realized. The imaging system established based on the superlens can realize elimination of large-angle stray light in the imaging process and improve the image contrast.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optics, and in particular to angle-filtering stray light-eliminating metalenses based on interference supercells and their design methods. Background Technology

[0002] Stray light is one of the external factors limiting the imaging performance of optical systems. Large-angle stray light entering the imaging system can cover the effective imaging area, creating imaging glare and reducing image contrast. Traditional imaging systems often use mechanical apertures and light shields to limit the angle range of the light beam entering the system, but this undoubtedly increases the axial length of the system. With the development of micro-nano optics, the emergence of metalenses has enabled the continuous miniaturization of imaging systems; therefore, traditional mechanical light-shielding structures have significant limitations. Currently, emerging angle-selective optical devices can achieve this through mechanisms such as multilayer film structures, photonic crystals or guided mode resonance, and continuous-spectrum bound states. However, these devices have limited optical field manipulation dimensions, mainly handling angle-related transmittance control. If used for imaging, additional focusing lenses are needed to form a complex system. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide an angle-filtering stray light elimination meta-lens based on an interference supercell and its design method, which solves the problems of large volume, long axial length, and functional separation of independent angle filters and imaging lenses in traditional mechanical light-shielding structures.

[0004] Technical solution: The present invention provides an angle filtering and stray light elimination meta-lens based on interference supercells, comprising a substrate and a plurality of supercells disposed on the substrate; the supercells are formed by two types of superatoms with similar transmission amplitudes but different lateral dimensions arranged in an alternating pattern, the light beam interferes at the top of the supercells, and the transmittance of the supercells decreases as the incident angle of the light beam increases.

[0005] Furthermore, both types of metaatoms have the same height and a square cross-section.

[0006] Furthermore, both of the materials of the metaatoms are medium materials with high refractive index within the working wavelength range of the metalens.

[0007] The design method of the angle filtering and stray light elimination metalens based on the interference supercell described in this invention includes the following steps:

[0008] Determine the target phase distribution of the metalens, the first incident angle range to be suppressed, and the second incident angle range to be retained;

[0009] The initial parameters of the meta-atoms were determined and an initial supercell was established. The transmittance of the initial supercell was obtained by parameter scanning using a full-wave electromagnetic simulation method.

[0010] A phase library is established by selecting an initial supercell whose transmittance satisfies the target transmittance response; the target transmittance response is characterized by low transmittance within the first incident angle range and high transmittance within the second incident angle range.

[0011] Based on the target phase distribution of the metalens, an initial supercell that satisfies the target phase is selected from the phase library for each position of the metalens;

[0012] A metalens with angle filtering and stray light elimination is prepared by spatially arranging the initial supercells.

[0013] Furthermore, the transmittance and normal incident emission phase of the initial supercell are obtained by parameter scanning using the full-wave electromagnetic simulation method. A transmittance that satisfies the target transmittance response and an emission phase that covers the target is selected. The initial supercell is used to establish the phase library.

[0014] Furthermore, the finite-difference time-domain full-wave electromagnetic simulation method was adopted to perform parameter scanning on the structural dimensions of superatoms within the supercell using linearly polarized light as the incident light source, thereby obtaining the transmittance and emission phase of supercells with different structural dimensions at different incident angles.

[0015] Furthermore, the phase of the transmission field of the supercell is ,when hour For the positive incident exit phase of the supercell, select from the phase library for each position of the metalens. The initial supercell closest to the target phase, among which, and These represent the transmission field phases of the two metaatoms. The incident angle of the light beam is denoted as .

[0016] Furthermore, the metalens is fabricated using micro-nano fabrication techniques.

[0017] The interferometric supercell-based angle filtering stray light elimination metalens imaging system of the present invention includes the interferometric supercell-based angle filtering stray light elimination metalens and a CMOS imaging sensor.

[0018] The computer program product of the present invention includes a computer program that, when executed by a processor, implements the design method of the angle filtering and stray light elimination meta-lens based on interference supercell.

[0019] Beneficial effects: Compared with existing technologies, the advantages of this invention are as follows: This invention achieves different transmittances at different incident angles through the lateral interference of the supercell light field, and simultaneously introduces phase modulation, solving the problem of the single control dimension of traditional angle filtering methods. It also eliminates large-angle stray light during imaging, improving image contrast. Compared with traditional light-shielding solutions such as mechanical sleeves, this invention does not require the addition of centimeter-level axial light-shielding structures, can be directly integrated with imaging sensors such as CMOS, and is easy to manufacture. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the four-atom supercell structure according to an embodiment of the present invention.

[0021] Figure 2 This is a phase distribution diagram of the supercells within the phase library of an embodiment of the present invention.

[0022] Figure 3 The images show the light field focusing and light intensity distribution of a conventional metalens and an angle-filtering metalens according to embodiments of the present invention.

[0023] Figure 4 Optical micrographs, electron micrographs, focal spot characterization diagrams, and MTF curves of conventional filtering metalenses and angle filtering metalenses according to embodiments of the present invention.

[0024] Figure 5 This is a schematic diagram of the structure of the angle filtering stray light elimination meta-lens imaging system according to an embodiment of the present invention.

[0025] Figure 6 The images shown are the imaging results of the imaging systems built based on conventional filtering metalenses and angle filtering metalenses according to an embodiment of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0027] Example 1

[0028] The angle-filtering stray light elimination meta-lens based on interference supercells of the present invention includes a substrate and a plurality of supercells disposed on the substrate; the supercells are formed by two kinds of superatoms with similar transmission amplitudes but different lateral dimensions arranged in an alternating manner, the light beam interferes at the top of the supercells, and the transmittance of the supercells decreases as the incident angle of the light beam increases.

[0029] Specifically, each supercell is composed of two types of square-section nanopillars with different lateral dimensions but the same height and material, arranged in an alternating pattern, resulting in an overall structure exhibiting centrosymmetry. When the beam... When incident at an angle, the emitted light fields of the two metaatoms can be expressed as follows: and ,in, and These represent the transmission field amplitudes of the two metaatomic atoms, respectively. and Let represent the corresponding transmission field phases. Interference occurs near the top of the supercell. Assuming both superatoms have high transmittance, their transmission amplitude can be approximated as... The total output light field generated by collective interference can be expressed as:

[0030]

[0031] The normalized interference intensity of the supercell can be expressed as:

[0032]

[0033] Therefore, when the transmission amplitudes of the two metaatoms are at similar levels, the overall transmission intensity of the supercell mainly depends on the transmission phase difference between the two metaatoms. Since the structural parameters of the two metaatoms are different, their transmission phases also exhibit different trends with the incident angle. Thus, the transmission phase difference between the two metaatoms varies with the incident angle, and the normalized interference intensity of the supercell at different angles also changes accordingly (where I=1 for completely constructive interference and I=0 for completely destructive interference). That is, the supercell exhibits a transmittance that varies with the incident angle, thereby achieving angle filtering.

[0034] Based on this, it is possible to obtain supercell structures with different superatomic phase differences and different transmittances at different incident angles. According to the target phase distribution of the superlens, at various positions of the superlens... Determine a supercell with a specific lateral dimension for arrangement, and define the positive incident and exit phases of this supercell. Phase with target It has low transmittance when incident at close range and at large angles; thus, a metalens can be obtained to suppress stray light at large angles.

[0035] Example 2

[0036] The design method of the angle filtering and stray light elimination metalens based on the interference supercell described in this embodiment is used to design and fabricate the metalens described in Embodiment 1. The method includes the following steps.

[0037] Step 1: Determine the operating wavelength of the metalens and the range of incident angles to be retained and suppressed based on the actual application. For stray light elimination imaging, prioritize targets with high transmittance at small angles and low transmittance at large angles. That is, the light field undergoes approximately constructive interference at small angles and approximately destructive interference at large angles, achieving an angle low-pass filtering function. A metacell with angle high-pass filtering function can also be designed based on this interferometric method.

[0038] Determine the initial parameters, including the material of the meta-atom, the material of the substrate, the structural height, the supercell period, and the minimum linewidth. The meta-atom should preferably be a medium with a high refractive index in the design wavelength range.

[0039] Step 2 involves designing the metalens using a discrete phase-matching design method based on a structure library. First, a full-wave electromagnetic simulation is used to perform parameter scanning on the initial supercell structure, obtaining the transmittance of initial supercells with different lateral dimensions as a function of the incident angle and the exit phase for normal incidence. Supercells with the target transmittance response are selected, and further screening is conducted for initial supercells with different normal incidence and exit phases to establish a phase library for angle-filtered initial supercell structures covering the 0–2π phase range. Common phase libraries are of order eight and sixteen, containing information on the structural dimensions, phase, and transmittance of the initial supercells.

[0040] Step 3: Determine the target phase distribution of the metalens. Select the optimal structure for each position from the phase library to obtain the structural spatial arrangement of the metalens, i.e., select the phase response. Phase with target Arrange the closest supercells.

[0041] For a typical hyperbolic phase-focusing metalens, its planar position The target phase at that location can be expressed as:

[0042]

[0043] in, For the operating wavelength, Focal length and denoted as two-dimensional coordinates within the hyperlens plane.

[0044] The phase of the supercell is:

[0045]

[0046] in, and These represent the two types of superatoms at the incident angles. The phase of the transmitted field below.

[0047] Step 4: An angle-filtering meta-lens is fabricated using micro-nano fabrication processes such as thin film deposition, electron beam exposure, development, and etching.

[0048] Specifically, firstly, plasma vapor deposition is used to deposit on a fused silica substrate. Layer. Subsequently, electron beam photoresist and conductive polymer are spin-coated, and the desired pattern is formed using electron beam exposure. A chromium hard mask is prepared by a lift-off process, and then... and The gas is used for dry etching to transfer the pattern to the amorphous silicon layer. Finally, the chromium mask is removed to obtain the designed angle-filtering metalens.

[0049] The feasibility and effectiveness of the meta-lens and its design method described in this invention will be verified through a specific experiment below.

[0050] This experiment uses a near-infrared working wavelength of 980 nm as an example, and the substrate is fused silica ( The metaatomic atoms are made of amorphous silicon ( The medium has a superatomic height of 600 nm, a supercell period of P = 800 nm, and a minimum linewidth of 100 nm. The goal is to... Filter out beams other than those in the original beam and retain the original beam. Incident light within [a certain range].

[0051] like Figure 1 The study showcases a four-atom supercell structure, where each supercell is composed of two superatoms with different lateral dimensions arranged in an alternating pattern. The incident light is linearly polarized, and both superatoms employ a square structure with fourfold rotational symmetry. , To suppress polarization conversion, in which , and , These are the lateral dimensions of the two superatoms.

[0052] First, a finite-difference time-domain (FDTD) full-wave simulation method was used to perform parameter scanning on the structural dimensions of the superatoms within the supercell. The length and width scan range were set to 100 nm to 300 nm, with a y-polarized plane wave as the incident light source, and the incident angle varying within the xz plane. Bloch boundary conditions were applied in the simulation region in the x-direction, periodic boundary conditions in the y-direction, and perfectly matched layer boundary conditions in the z-direction. Through parameter scanning, the transmittance of supercells with different structural dimensions at different incident angles and the exit phase under normal incidence were obtained. During the FDTD software simulation, the transmittance and phase of the supercell could be directly read from the plane monitor and point monitor set at the exit surface, respectively. The specific solution method of the software is as follows: The electromagnetic field distribution of the supercell is obtained by solving Maxwell's equations, according to the formula: The emitted power and incident power are calculated separately, where E and H are the frequency-domain complex electric field and complex magnetic field at the exit surface, respectively, n is the unit normal vector along the emission direction, A is the monitor area, and the supercell transmittance is the ratio of emitted power to incident power. Then, the emitted electric field of the supercell is extracted, and the emitted phase of the supercell is calculated based on the reference electric field: .

[0053] Preliminary screening in Internal incidence has higher transmittance. A supercell structure with significantly reduced incident transmittance. (Since the supercell structure in this embodiment is symmetrical, its transmittance is symmetrically distributed with respect to positive and negative incident angles; therefore, only the relevant data for positive incident angles need to be calculated.) Based on this, the transmission phase is selected to cover the area at approximately uniform intervals. The eight supercells were used to obtain an eighth-order phase library with angular low-pass filtering function. Figure 2 (b) shows that all eight supercells in this phase library have high transmittance at small incident angles, and the transmittance gradually decreases as the incident angle increases, reaching an average of approximately It then dropped to a lower level.

[0054] To verify the effectiveness of the angle filtering function, this experiment further constructed a conventional metalens without angle filtering properties as a control. Its conventional phase library contains a supercell composed of four identical metaatoms, satisfying... This design achieves [something] through constructive interference. It exhibits high transmittance across the entire range. Furthermore, the conventional phase library and the angle-filtered phase library use the same supercell period to ensure consistent phase sampling intervals for both metalenses, thereby improving the rationality of subsequent imaging performance comparisons. Figure 2 In the figure, (a) represents the transmittance and phase of each supercell in the eighth-order conventional phase library as a function of angle.

[0055] Determine the target phase of the focusing metalens according to design requirements. At various positions of the metalens Select the normal incidence exit phase from the phase library. Phase with target The closest supercells were arranged to construct conventional and angle-filtered metalenses, respectively. The focusing characteristics of the two metalenses at multiple incident angles were analyzed using FDTD full-wave simulation. Both metalenses had the same diameter and focal length, 36 μm and 78 μm, respectively, and the incident angle of the light field was set to... , , , and ± . Figure 3 (a) in the figure shows the focusing of the light field of a conventional metalens under multi-angle incident light, calculated by simulation. Figure 3 (b) in the middle is along Figure 3 The normalized light intensity distribution map of the focal plane position extracted by the dashed line in (a) is shown. Figure 3 (c) in the figure shows the focusing of the light field of the angle-filtered metalens under multi-angle incident light, calculated by simulation. Figure 3 (d) in the middle is along Figure 3The normalized light intensity distribution at the focal plane position is extracted by the dashed line in (c). The comparison shows that the angle-filtered metalens, while maintaining the relative focusing ability of small-angle incident light, significantly weakens the relative focusing intensity of large-angle incident light, providing a basis for suppressing large-angle stray light.

[0056] In this experiment, conventional metalenses and angle-filtering metalenses were fabricated using micro-nano fabrication technology. Both types of lenses have a diameter of 300 μm and a designed focal length of 450 μm. Figure 4 Images (a) and (c) in the figure show optical microscope and scanning electron microscope images of a conventional metalens and an angle-filtered metalens, respectively. The electron microscope images show the arrangement of metaatoms within the supercell. Figure 4 Figures (b) and (d) show the measured focal spots and corresponding intensity distribution curves of a conventional metalens and an angle-filtered metalens under normal incidence conditions, respectively. Furthermore, the intensity distribution of the focal spot measured at the focal plane is used as the point spread function (PSF), and a Fourier transform is performed on it to obtain the modulation transfer functions (MTFs) of the two metalenses, as shown below. Figure 4 As shown in (e), the angle-filtering metalens exhibits a higher MTF across most of the spatial frequency range compared to conventional metalenses, indicating better imaging capabilities.

[0057] Example 3

[0058] The interferometric supercell-based angle filtering stray light elimination metalens imaging system of the present invention includes the metalens described in Example 1 and a CMOS imaging sensor. The metalens and the CMOS imaging sensor are directly integrated, and then the object is imaged under wide-angle LED light source illumination, and large-angle stray light within the suppression angle range is attenuated.

[0059] To verify the stray light suppression effect of the metalens imaging system of this invention in actual imaging, a near-infrared integrated imaging experimental system was constructed. A planar LED light source with a center wavelength of 980nm was used, and the emission angle of a single LED chip inside was approximately... A metalens is attached to the surface glass of a CMOS image sensor using optically transparent adhesive (OCA) to form a compact integrated imaging system, the structure of which is as follows: Figure 5 As shown, imaging systems were constructed using the conventional metalens and the angle-filtering metalens described in Example 2.

[0060] First, a reflection imaging experiment was conducted using a metal globe pendant as the imaging target. Figure 6(a) shows the imaging result of the imaging system based on a conventional metalens. Because the LED light source has a large divergence angle, some light that does not directly illuminate the target object may be reflected by other objects in the surrounding environment, entering the imaging system at a large incident angle, forming stray light superimposed on the target image, resulting in increased overall image brightness and decreased contrast. In contrast, under the same experimental conditions, the imaging result obtained by using an angle-filtered metalens to build the imaging system is as follows: Figure 6 As shown in (b) above, because the large-angle incident light is partially suppressed, stray light interference in the image is significantly reduced, the outline and details of the target object are clearer, and the imaging contrast is improved.

[0061] Furthermore, the human figure pattern was placed on the surface of a planar LED light source to conduct a transmissive imaging experiment. Figure 6 (c) shows the imaging result of an imaging system based on a conventional metalens, where some details of the figure are difficult to distinguish due to stray light interference. Figure 6 In the diagram, (d) shows the imaging results of the imaging system built based on the angle-filtered metalens under the same experimental conditions. Compared with conventional metalenses, the angle-filtered metalens can make the outline of the figure and some details clearer.

Claims

1. A stray light elimination metalens based on an interference supercell, characterized in that, The meta-lens includes a substrate and several supercells disposed on the substrate; the supercells are formed by two kinds of metaatoms with similar transmission amplitudes but different lateral dimensions arranged alternately, the light beam interferes at the top of the supercells, and the transmittance of the supercells decreases as the incident angle of the light beam increases.

2. The angle-filtering stray light-eliminating metalens based on an interference supercell according to claim 1, characterized in that, Both types of metaatoms have the same height and a square cross-section.

3. The angle-filtering stray light-eliminating metalens based on an interference supercell according to claim 1, characterized in that, Both of the materials used in the meta-atom are dielectric materials with high refractive index within the operating wavelength range of the meta-lens.

4. A design method for an angle-filtering stray light-eliminating metalens based on an interference supercell as described in any one of claims 1-3, characterized in that, Includes the following steps: Determine the target phase distribution of the metalens, the first incident angle range to be suppressed, and the second incident angle range to be retained; The initial parameters of the meta-atoms were determined and an initial supercell was established. The transmittance of the initial supercell was obtained by parameter scanning using the full-wave electromagnetic simulation method. A phase library is established by selecting an initial supercell whose transmittance satisfies the target transmittance response; the target transmittance response is characterized by low transmittance within the first incident angle range and high transmittance within the second incident angle range. Based on the target phase distribution of the metalens, an initial supercell that satisfies the target phase is selected from the phase library for each position of the metalens; A metalens with angle filtering and stray light elimination is prepared by spatially arranging the initial supercells.

5. The design method of the angle-filtering stray light elimination meta-lens according to claim 4, characterized in that, The transmittance and normal incident exit phase of the initial supercell were obtained by parameter scanning using the full-wave electromagnetic simulation method. The transmittance was selected to satisfy the target transmittance response and the exit phase coverage. The initial supercell is used to establish the phase library.

6. The design method of the angle-filtering stray light elimination meta-lens according to claim 5, characterized in that, Using the finite-difference time-domain full-wave electromagnetic simulation method, linearly polarized light is used as the incident light source to perform parameter scanning on the structural dimensions of superatoms within the supercell, obtaining the transmittance and emission phase of supercells with different structural dimensions at different incident angles.

7. The design method of the angle-filtering stray light elimination meta-lens according to claim 4, characterized in that, The phase of the transmission field of the supercell is ,when hour For the positive incident exit phase of the supercell, select from the phase library for each position of the metalens. The initial supercell closest to the target phase, among which, and These represent the transmission field phases of the two metaatoms. The incident angle of the light beam is denoted as .

8. The design method of the angle-filtering stray light elimination meta-lens according to claim 4, characterized in that, The metalens was fabricated using micro-nano fabrication technology.

9. A metalens imaging system based on interferometric supercells with angle filtering to eliminate stray light, characterized in that, Includes the angle-filtered stray light elimination meta-lens and CMOS imaging sensor based on any one of claims 1-3.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the design method of the angle filtering and stray light elimination meta-lens based on the interference supercell according to any one of claims 4-7.

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