Infrared super lens with moth-eye-imitating anti-reflection nano structure
By fabricating a moth-eye-like antireflective nanostructure on the back of a superlens structure, the problem of high reflectivity in the infrared band of silicon-based optical devices was solved, achieving high transmittance and focusing effect, simplifying the process and improving light energy utilization efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-24
AI Technical Summary
The high refractive index of silicon-based optical devices in the infrared band results in high surface reflectivity at the interface with air or common media. Traditional antireflective films have problems such as wavelength sensitivity, limited material selection, increased risk of multilayer film, and poor mechanical and environmental stability in modern optical and photonic systems.
A single-layer double-sided metasurface structure is adopted. A moth-eye-inspired antireflective nanostructure is used to prepare subwavelength nanopillars on the back of the superlens structure, forming a structural layer with an equivalent refractive index between air and silicon. This reduces abrupt changes in refractive index, improves transmittance, and achieves a focusing effect by modulating the phase of incident light through the superlens structure.
It improves the transmittance and focusing efficiency of incident light, avoids thermal stability problems caused by different coefficients of thermal expansion of materials, achieves broadband performance and efficient light energy utilization, simplifies the process and is compatible with CMOS process.
Smart Images
Figure CN121721759A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a metasurface structure in the field of silicon-based photonics, specifically an infrared superlens with a moth-eye-inspired anti-reflection nanostructure. Background Technology
[0002] In recent years, an increasing number of researchers have been using superlens structures to replace traditional lenses in order to achieve lighter imaging systems. A superlens structure is essentially a two-dimensional plane micro / nanostructure. By precisely adjusting the micro / nanostructure (such as its shape, rotation direction, and height), various characteristics of incident light can be controlled. Compared to traditional lens arrays, superlens arrays offer numerous advantages, including: flexible phase design independent of surface shape, a vast parameter design space, and unique polarization multiplexing characteristics. These advantages enable superlens arrays to achieve rich functionality and superior performance on an extremely thin layer.
[0003] Silicon is one of the most commonly used and highly advantageous materials for designing and fabricating superlens structures. Its high refractive index in the infrared band allows it to strongly localize the light field within or near the nanostructure, greatly enhancing the interaction between light and matter. This enables complete phase coverage from 0 to 2π even using ultrathin silicon layers (typically < 600 nm), which is fundamental to achieving high-efficiency lenses. Furthermore, silicon has mature CMOS-compatible fabrication processes, and its nanofabrication techniques (such as photolithography, etching, and deposition) are extremely mature, standardized, and highly controllable (e.g., deep ultraviolet lithography (DUV), electron beam lithography (EBL), and reactive ion etching (RIE)).
[0004] However, silicon's high refractive index (n ≈ 3.4 - 3.6 in the visible to near-infrared range) directly results in high surface reflectivity at its interfaces with air or common media (such as silicon dioxide, n ≈ 1.5). This is a physical phenomenon determined by Fresnel's law of reflection, posing a significant challenge to the performance of silicon-based optical devices, such as transmission efficiency.
[0005] While traditional antireflective coatings are widely used, they have significant disadvantages in modern optical and photonic systems, especially in dealing with complex requirements. These disadvantages include severe wavelength sensitivity, limited material selection (ideal refractive index materials are scarce), the risk of increased multilayer film layers (stress mismatch risk, adhesion failure probability, scattering loss, poor mechanical and environmental stability, poor thermal stability (thermal stability issues due to different coefficients of thermal expansion of materials), and poor hydrophobicity, among other problems. Summary of the Invention
[0006] To address the problems existing in the background technology, the present invention aims to propose an infrared superlens with a moth-eye-inspired anti-reflection nanostructure. This superlens utilizes a monolithic double-sided metasurface structure. One side simulates a "moth-eye structure," with subwavelength nanopillars fabricated on the back side to form a structural layer with an equivalent refractive index between air and silicon. This reduces abrupt changes in refractive index, thereby increasing transmittance and significantly enhancing the intensity of incident light received by the other side of the superlens structure. The superlens structure further modulates the phase of the incident light to conform to a spherical wavefront profile, achieving a focusing effect. This achieves both anti-reflection and focusing effects at an extremely thin scale.
[0007] The technical solution adopted in this invention is as follows:
[0008] This invention discloses a superlens structure with a moth-eye-like anti-reflection structure for infrared imaging, comprising a substrate, a moth-eye-like anti-reflection structure located on the upper surface of the substrate, and a superlens structure located on the lower surface of the substrate. Both structures and the substrate are made of single-crystal silicon material.
[0009] As a further improvement, the moth-eye-like antireflective structure of the present invention is a micro-nano structure array of cylinders, frustums, or cones arranged periodically on the substrate surface.
[0010] As a further improvement, the micro-nano cylindrical structure array described in this invention has a rectangular outline with a length and width greater than 1 cm.
[0011] As a further improvement, the period of the micro-nano cylinder described in this invention remains unchanged and is less than 5µm. The radius and height of the cylinder are the same, with a radius of less than 2µm and a height of greater than 1µm. The number of micro-nano structures in the micro-nano structure array exceeds 4 million.
[0012] As a further improvement, the present invention uses an array of micro-nano cylindrical structures periodically arranged on the substrate surface to achieve light focusing.
[0013] As a further improvement, the superlens structure of the present invention is a circle with a diameter of at least 1 mm.
[0014] As a further improvement, the superlens structure of the present invention is composed of cylinders of different diameters. The period of the cylinders is less than 6µm and remains constant. The radius of the cylinders at different positions from the center of the contour circle varies according to design requirements, but is less than 2µm. The height of the cylinders is the same and exceeds 8µm. The number of cylinders exceeds 10,000.
[0015] As a further improvement, the moth-eye-like anti-reflection structure and the superlens structure described in this invention are located on opposite sides of the same substrate with a thickness of less than 1µm, achieving both anti-reflection and focusing effects using only one silicon wafer.
[0016] As a further improvement, the area of the superlens structure described in this invention is much smaller than the area of the moth-eye antireflective structure, and it is located approximately in the central region of the lower surface of the substrate, so alignment issues do not need to be considered.
[0017] The beneficial effects of this invention are:
[0018] 1) This invention uses the same material to prepare the moth-eye-like antireflective structure and the superlens structure on the substrate. Compared with the antireflective film, it can avoid the thermal stability problem caused by the different thermal expansion coefficients of the materials.
[0019] 2) The moth-eye-like anti-reflection structure effectively improves the transmittance of incident light, and when using micro-nano structures of frustum or cone, the gradual change of the equivalent refractive index along the height direction brings better broadband performance.
[0020] 3) For moth-eye-like anti-reflection arrays with a period of less than 5µm and a radius of less than 2µm, the incident anti-reflection in specific bands of long-wave infrared can be achieved by fine-tuning the period and radius. Furthermore, it is easy to process large areas using ultraviolet exposure, thereby achieving large-area anti-reflection with more than 4 million micro-nano structures.
[0021] 4) For superlens structures with a period of less than 6µm, a radius of less than 2µm, and a cylinder height of more than 8µm, it is possible to achieve 2π phase coverage while maintaining the radius at the micrometer scale, thereby modulating the phase of infrared light and achieving focusing.
[0022] 5) The total area of the superlens structure is much smaller than that of the moth-eye anti-reflective structure, which makes center alignment easier.
[0023] 6) The moth-eye antireflective structure and the superlens structure have similar micro-nano structures. During fabrication, they can be carried out on the same substrate using the same process steps, with step-by-step exposure and etching, which simplifies the process. Furthermore, because they adopt silicon-based structures, they are compatible with CMOS processes and are easy to manufacture.
[0024] 7) The present invention distributes a moth-eye-like anti-reflection array and a superlens array on both sides of the same silicon wafer, realizing anti-reflection and focusing at an extremely thin scale.
[0025] The superlens structure with moth-eye-like anti-reflection structure of the present invention directly fabricates the moth-eye-like anti-reflection structure on the back of the superlens structure, which improves the transmittance of incident light and enhances the utilization efficiency of incident light by the superlens structure. It has the characteristics of high energy utilization efficiency and low process difficulty, and is expected to promote the expansion of the application of superlens structure in the field of infrared imaging. Attached Figure Description
[0026] Figure 1 This is a cross-sectional view of a superlens structure with a moth-eye-like anti-reflective nanostructure, which is involved in this invention.
[0027] Figure 2 These are a top view and a magnified view of a part of the moth-eye-inspired antireflective nanostructure.
[0028] Figure 3 This is a morphological feature diagram of a nanostructure that mimics the straight sidewall of a moth's eye for enhanced transparency.
[0029] Figure 4 This is a morphological feature diagram of a nanostructure that mimics the oblique sidewall of a moth's eye for enhanced transparency.
[0030] Figure 5 These are top views and enlarged partial views of the superlens structure;
[0031] Figure 6 This is a topographic feature diagram of the superlens structure;
[0032] Figure 7 The figure shows the simulation results of the transmittance of the silicon interface as a function of wavelength, and compares the transmittance difference between the nanostructure without the moth-eye-like anti-reflection structure (dashed line) and the nanostructure with the moth-eye-like anti-reflection structure (solid line).
[0033] Figure 8 This is a simulation result of the far-field distribution of the emitted light from the superlens structure.
[0034] In the diagram: 1-Silicon layer, 2-Moth-eye-like anti-reflective structure, 3-Superlens structure. Detailed Implementation
[0035] The present invention will be further described below with reference to the accompanying drawings and examples.
[0036] This invention discloses a superlens structure 3 with a moth-eye-like anti-reflection structure 2 for infrared imaging, such as... Figure 1 As shown, it includes a substrate 1, a moth-eye-like anti-reflective structure 2 located on the upper surface of the substrate 1, and a superlens structure 3 located on the lower surface of the substrate 1. Both structures and the substrate 1 are made of single-crystal silicon material.
[0037] Both the superlens structure 3 and the substrate 1 are made of silicon substrate material, and the moth-eye anti-reflection structure 2 and the superlens structure 3 are located on the two surfaces of the substrate 1, respectively.
[0038] When incident light reaches the surface with the moth-eye-like anti-reflection nanostructure, it passes through the film layer formed by the moth-eye-like anti-reflection nanostructure, which has an equivalent refractive index between that of air and silicon, greatly reducing the reflectivity of the incident surface. Subsequently, the superlens structure 3 modulates the phase of the incident light, making it form a spherical wavefront profile to achieve focusing.
[0039] like Figure 2 , 3As shown in Figure 4, the moth-eye-like antireflective structure 2 is an array of micro / nano structures consisting of periodically arranged cylinders, frustums, or cones on the surface of substrate 1. In this embodiment, the moth-eye-like antireflective nanostructure is composed of periodically arranged micro / nano cylinders of the same radius. The structural scale is generally smaller than the working wavelength, making it impossible for the incident wave to distinguish the shape of the microstructure. Within the microstructure layer region, diffracted wave vectors of all orders are coupled to each other, resulting in the absence of higher-order diffraction in the reflection or transmission regions. That is, when the microstructure period is less than a specific value, all reflected and transmitted diffracted waves vanish instantly, leaving only zero-order diffraction. Therefore, it can be considered that the incident wave cannot distinguish the microstructure, and the microstructure layer can be regarded as an equivalent refractive index layer, eliminating the need to consider diffraction effects. For example, Figure 3 The cylindrical nanostructure shown can be considered as the equivalent refractive index layer of a single-layer film, while for... Figure 4 The frustum or cone nanostructure shown can be regarded as an equivalent graded refractive index layer of a multilayer film.
[0040] The micro-nano cylindrical structure array has a rectangular outline with a length and width greater than 1 cm. The period of the micro-nano cylinders remains constant and is less than 5 µm. The radius and height of the cylinders are the same, with a radius less than 2 µm and a height greater than 1 µm. The number of micro-nano structures in the array exceeds 4 million. Light focusing is achieved using the periodically arranged micro-nano cylindrical structure array on the surface of substrate 1.
[0041] like Figure 5 , 6 As shown, the superlens structure 3 is a circle with a diameter of at least 1 mm.
[0042] The superlens structure 3 consists of periodically arranged micro / nano cylinders with varying radii, which modulate the propagation phase. These micro / nano cylinders can be viewed as waveguide structures. Light propagates within them, resulting in phase accumulation. By altering the composition of the nano-cylinders, the superlens structure 3 is made up of cylinders with different diameters. The period of each cylinder is less than 6µm and remains constant. The radii of the cylinders at different locations from the center of the contour circle vary according to design requirements, but are all less than 2µm. The height of all cylinders is the same and exceeds 8µm, and the number of cylinders exceeds 10,000.
[0043] The cross-sectional dimensions can change the effective refractive index of the guided wave mode, thereby achieving different propagation phase modulations.
[0044] The large outline of the moth-eye-inspired anti-reflective nanostructure is rectangular, with an area larger than that of the back superlens structure 3 to achieve coverage of transmitted light. The large outline of the superlens structure 3 is circular to match the focusing phase profile of traditional lenses and avoid anisotropic aberrations (such as coma and astigmatism).
[0045] The moth-eye antireflective structure 2 and the superlens structure 3 are located on opposite sides of the same substrate 1 with a thickness of less than 1µm, achieving both antireflection and focusing effects using only a single silicon wafer. The area of the superlens structure 3 is much smaller than that of the moth-eye antireflective structure 2, and it is roughly located in the central region of the lower surface of the substrate 1, so alignment issues do not need to be considered.
[0046] like Figure 1 The cross-sectional structure of the present invention is shown. In terms of process, the superlens structure 3 can be first exposed and etched on one side of a silicon wafer, then the superlens structure 3 is protected with a photoresist coating, and then the other surface is photolithographically etched to prepare a moth-eye antireflection array. Afterwards, the protective coating is cleaned to obtain a superlens structure 3 with micro / nano structures on both sides.
[0047] The specific embodiments of the present invention and their implementation are as follows:
[0048] In this example, silicon was chosen as the substrate material 1, with a thickness of 500 μm, which is the thickness of commonly used commercial silicon wafers. The finite-difference time-domain (FDTD) method was used to simulate the design of the moth-eye antireflection array and the superlens structure 3. The target wavelength considered was 10.6 μm, which is the wavelength of CO2 lasers commonly used in the infrared band. At room temperature in this band, the refractive index of silicon is 3.4697.
[0049] A moth-eye-like anti-reflection array and a superlens structure array are arranged on two surfaces of a silicon wafer, respectively. The design parameters such as their period, column height, and cylinder diameter are as follows:
[0050] The moth-eye-inspired antireflection array employs a periodic array of straight-sidewall micro / nano cylinders. Transmittance simulations were performed on unit structures with different periods, radii, and cylinder heights. Based on the simulation results, the structure with the optimal transmittance at a wavelength of 10.6 μm was selected. Ultimately, a structure with a period of 3 μm, a radius of 1 μm for the micro / nano cylinders, and a height of 2 μm was chosen. Its morphological characteristics are as follows: Figure 3 As shown.
[0051] The outline of the moth-eye anti-reflective array is set to a rectangle, such as... Figure 2 As shown, the total area is 2*2mm to better cover the area where the superlens is located, avoiding the difficulty of double-sided alignment.
[0052] The transmittance of the moth-eye-like anti-reflection array as a function of wavelength, as obtained in FDTD simulation, is as follows: Figure 7 As shown, a transmittance of 94% was obtained at 10.6µm, which is about 23% higher than the surface transmittance without the moth-eye anti-reflection array, and the transmittance is improved by at least 15% in the far band of 8-12µm.
[0053] The superlens structure 3 utilizes the propagation phase for phase modulation design. In FDTD, simulations were performed to analyze the output phase and transmittance of unit structures with different periods, radii, and cylinder heights. Periods and cylinder heights with higher transmittance were selected, and under these period and height settings, a one-to-one mapping relationship between the radius and phase of different unit structures was established. Ultimately, a period of 5 μm, a micro-nano cylinder height of 10 μm, and a radius varying between 1 and 1.6 μm with a step size of 50 nm were chosen, covering a phase range of 2π. The designed superlens structure 3 has the following specifications: radius of 500 μm, focal length of 500 μm, and numerical aperture of 0.707. By designing and arranging the metasurface structures according to the focused phase (each location has a corresponding cylinder radius value for the required phase), the superlens structure 3 can be obtained, and its phase is represented as:
[0054]
[0055] Where f is the focal length of the lens, and R is the distance from a point on the lens to the center of the lens.
[0056] The far-field distribution of light rays obtained from the FDTD simulation of the superlens structure 3 is as follows: Figure 8 As shown, at the designed focal length of 500um, an extremely high light intensity peak was observed, the full width at half maximum (FWHM) was 10.5um, and the calculated focusing efficiency reached 31.0%.
[0057] Simulation results show that the embodiments based on the present invention have good performance in terms of transmittance and focusing effect, and have the potential for practical application.
[0058] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.
Claims
1. A superlens with a moth-eye-like anti-reflection structure for infrared imaging, characterized in that, It includes a substrate (1), a moth-eye-like anti-reflective structure (2) located on the upper surface of the substrate, and a superlens structure (3) located on the lower surface of the substrate. Both structures and the substrate are made of single-crystal silicon material.
2. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 1, characterized in that, The moth-eye-like antireflective structure (2) is a micro-nano structure array of cylinders, frustums or cones arranged periodically on the substrate surface.
3. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 2, characterized in that, The micro-nano cylindrical structure array has a rectangular outline with a length and width greater than 1 cm.
4. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 3, characterized in that, The period of the micro-nano cylinder remains constant and is less than 5µm. The radius and height of the cylinder are the same, with a radius of less than 2µm and a height of greater than 1µm. The number of micro-nano structures in the micro-nano structure array exceeds 4 million.
5. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 4, characterized in that, Light focusing is achieved using an array of micro / nano cylindrical structures arranged periodically on the substrate surface.
6. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 1, 2, 3, 4, or 5, characterized in that, The superlens structure (3) is a circle with a diameter of at least 1 mm.
7. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 6, characterized in that, The superlens structure (3) is composed of cylinders of different diameters. The period of the cylinders is less than 6µm and remains constant. The radius of the cylinders at different positions from the center of the contour circle varies according to the design requirements, but is less than 2µm. The height of the cylinders is the same and exceeds 8µm. The number of cylinders exceeds 10,000.
8. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 7, characterized in that, The moth-eye-like anti-reflective structure (2) and the superlens structure (3) are located on opposite sides of the same substrate with a thickness of less than 1µm, achieving both anti-reflective and focusing effects with only one silicon wafer.
9. The superlens with a moth-eye-like anti-reflection structure for infrared imaging according to claim 7 or 8, characterized in that, The area of the superlens structure is much smaller than that of the moth-eye antireflective structure, and it is roughly located in the central region of the lower surface of the substrate, so there is no need to consider alignment issues.