A middle-long wave dual-band superlens and a design method thereof

Abstract

This invention relates to a mid-to-long-wavelength dual-band superlens and its design method. The superlens includes a substrate, on which a long-wavelength infrared superlens unit composed of multiple long-wavelength infrared superlens units is disposed. Each long-wavelength infrared superlens unit has a cuboid structure. An array of mid-wavelength infrared superlens units is disposed above each long-wavelength infrared superlens unit, and the array has a square matrix structure. This invention achieves confocal imaging across a wide optical band through a compact composite micro / nano structure. It also boasts a high degree of integration, enabling effective separation and precise control of focal lengths across multiple optical bands. The superlens achieves a transmittance of up to 78% under long-wavelength light field modulation and 45% under mid-wavelength light field modulation. The design method of this invention is simple and easy to implement, with a wide range of adjustable parameters, making it particularly suitable for large-scale industrial production design. It can be widely applied in optical infrared guidance technology.

Description

Technical Field

[0001] This invention belongs to the field of metasurface metalens imaging technology, specifically relating to a medium- and long-wavelength dual-band metalens and its design method. Background Technology

[0002] In fields such as infrared imaging detection and laser weapon guidance, existing metasurface lens designs are mainly focused on specific wavelengths, such as the visible or infrared bands. Such designs usually rely on the refractive index and dispersion characteristics of the unit material in a specific frequency band, which limits their applicability in different wavelength bands.

[0003] For dual-wavelength superlens design, the current approach is to use a dual-layer cascaded superlens, such as the dual-wavelength achromatic superlens designed by Yang Hui, Li Guanhai and others. The phase distribution of the 1μm and 1.55μm wavelengths is controlled by the two superlenses respectively, and then they are combined to achieve the overall focusing effect. However, this sacrifices transmittance and focusing efficiency, and the dual-layer cascaded structure is not integrated enough.

[0004] A recent paper by Cheng Guo, Zheng Zhishuai, and others, titled "Design and Analysis of Dual-Band Far-Field Superlenses," presents a method for designing far-field confocal superlenses at operating wavelengths of 632.8 nm and 1265.6 nm. This dual-band superlens utilizes two different nanorods to control the phase modulation of two wavelengths of light. These two nanorods are regularly arranged on the same plane, enabling dual-band far-field confocal focusing in both the visible and near-infrared bands. However, its band span is relatively small, only around 600 nm, making it difficult to meet the operating conditions in the mid-infrared and long-infrared bands and hindering the realization of large-span confocal imaging across different bands. Furthermore, the different heights of the two nanorods arranged on the same plane significantly increase the difficulty of fabrication, resulting in high manufacturing costs and hindering industrial production. Summary of the Invention

[0005] This invention provides a mid-to-long-wave dual-band superlens and its design method to solve the problem in the prior art that it is impossible to perform large-scale cross-band focusing imaging in the mid-to-long-infrared dual-band.

[0006] To achieve the objective of this invention, the technical solution is as follows: a large-span mid-to-long-wave dual-band superlens based on a composite micro / nano structure, comprising a substrate, wherein a long-wave infrared superlens composed of multiple long-wave infrared superlens units is disposed on the substrate, wherein the long-wave infrared superlens unit has a cuboid structure; and an array composed of mid-wave infrared superlens units is disposed on the upper part of the long-wave infrared superlens unit, wherein the array has a square matrix structure.

[0007] Furthermore, the aforementioned mid-wave infrared superlens units form a 3*3, 2*2, or 1*1 rectangular array.

[0008] Furthermore, the aforementioned mid-wave infrared superlens unit has a cylindrical structure.

[0009] Furthermore, the aforementioned cuboid structure has a height of 6.5 μm, a period of 2 μm, and a radius ranging from 0.63 to 1.8 μm; the cylindrical structure has a height of 6.6 μm, a period of 0.5 μm, and a radius ranging from 0.07 to 0.2 μm.

[0010] Furthermore, the substrate material is CaF2, and the materials of the long-wave infrared superlens unit and the mid-wave infrared superlens unit are Si.

[0011] Furthermore, the aforementioned design method for a mid-to-long-wave dual-band superlens involves selecting the material structure and then using the finite-difference time-domain method to simulate and optimize the performance parameters of the two-band units to ensure a phase delay of 2π. First, a long-wave infrared superlens unit array is constructed based on the wavefront reconstruction equation. After constructing the long-wave infrared superlens, the positions and sizes of all long-wave infrared superlens units are determined. Based on this data, the mid-wave infrared superlens unit matrix structure and the positions of each unit are designed to ensure that the mid-wave infrared superlens unit matrix structure can completely fall on the long-wave infrared superlens units. After one-to-one configuration, a mid-wave infrared superlens satisfying the wavefront reconstruction equation is constructed, thus completing the design of the mid-to-long-wave dual-band superlens.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] 1. The present invention adopts a three-layer stacking method. By superimposing long-wave infrared superlens units and mid-wave infrared superlens units, mid- and long-wave infrared dual-band confocal imaging is realized. When light waves pass through this structure, they are modulated by the unit structures of their respective bands. At the same time, through the compact composite micro-nano structure, a wide-span optical band confocal imaging is realized, and the degree of integration is high.

[0014] 2. This invention compactly superimposes unit structures of two wavebands to form a composite micro-nano structure. The superlens designed based on the composite micro-nano structure can freely match different wavelengths in the mid-wave infrared and long-wave infrared bands. By simply adjusting the parameters of the long-wave infrared superlens unit and the mid-wave infrared superlens unit, a wide-range cross-band focusing imaging can be achieved, and the effective separation and precise control of the focal length of multi-band optical waves can be realized.

[0015] 3. The medium- and long-wave dual-band superlens designed in this invention can achieve infrared dual-band common aperture focusing. When the long-wave light field is controlled, the superlens transmittance is as high as 78%, and when the medium-wave light field is controlled, the superlens transmittance reaches 45%.

[0016] 4. The design method of this invention is simple and easy to implement, and the parameter design has a wide range of adjustable parameters. It is particularly suitable for large-scale industrial production design and can be widely used in optical infrared guidance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention.

[0018] Figure 2 Diagram of an ultracompact superlens unit structure

[0019] Figure 3 Overall top view of the ultra-compact superlens structure

[0020] Figure 4 A diagram showing the mid-wave focusing effect of a dual-band superlens for medium and long waves.

[0021] Figure 5 Diagram showing the long-wave focusing effect of a dual-band superlens for medium and long waves.

[0022] in:

[0023] 2-Long-wave infrared superlens unit, 3-Mid-wave infrared superlens unit. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of specific embodiments of the present invention. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] See Figure 1 A large-span mid-to-long-wavelength dual-band superlens based on a composite micro / nano structure includes a substrate 1. A long-wavelength infrared superlens composed of multiple long-wavelength infrared superlens units 2 is disposed on the substrate 1. The long-wavelength infrared superlens unit 2 has a cuboid structure. In this embodiment, the aperture of the long-wavelength infrared superlens is 50μm. An array of mid-wavelength infrared superlens units 3 is disposed on the upper part of the long-wavelength infrared superlens unit 2. The array has a square matrix structure, wherein the specific number of units is determined according to the side length of the long-wavelength infrared superlens unit 2. The mid-wavelength infrared superlens unit 3 has a cylindrical structure.

[0026] The mid-wave infrared superlens unit 3 and the long-wave infrared superlens unit 2 together form a mid- and long-wave dual-band micro-nano ultra-compact structure. Multiple mid- and long-wave dual-band micro- and nano ultra-compact structures are arranged on the substrate to form a mid- and long-wave dual-band confocal superlens.

[0027] In this embodiment, the substrate 1 is a circle with a diameter of 60 μm. A long-wave infrared superlens array composed of multiple long-wave infrared superlens units 2 is disposed on the circular substrate 1. The long-wave infrared superlens unit 2 is a cuboid structure with a square cross-section, a side length ranging from 0.63 μm to 1.8 μm, and a period of 2 μm, forming a long-wave infrared superlens array. The upper part of each individual long-wave infrared superlens unit 2 is provided with a rectangular array of 3*3, 2*2, or 1*1 composed of 9, 4, or 1 mid-wave infrared superlens units 3, depending on its side length. The mid-wave infrared superlens unit 3 is a cylinder with a cross-sectional radius ranging from 0.07 to 0.2 μm and a period of 0.5 μm.

[0028] To facilitate manufacturing, both the mid-wave infrared superlens unit 3 and the long-wave infrared superlens unit 2, corresponding to the two wavebands, are made of Si as the unit structure material and CaF2 as the substrate material.

[0029] For the design of the long-wave infrared (10μm) superlens unit 2 structure, since the long-wave infrared (10μm) superlens unit 2 structure needs to serve as the substrate 1 of the mid-wave infrared (4.2μm) superlens unit 3 structure, a cuboid structure with a height h2 of 6.5μm and a period of 2μm is selected in this embodiment. Since the mid-wave infrared (4.2μm) superlens unit 3 structure should be as compactly integrated as possible onto the long-wave infrared superlens unit 2 structure, a cylindrical structure with a height h1 of 6.6μm and a period of 0.5μm is selected in this embodiment.

[0030] The basic principle of this invention is to use changes in the size of the metasurface unit structure to phase-modulate the incident light in the subwavelength scale. The phase to be modulated can be obtained from the optical path difference of the planar incident light from various points on the surface of the superlens device to the focal point, satisfying the wavefront reconstruction equation:

[0031]

[0032] r 2 =x 2 +y 2

[0033] Where λ is the incident light wavelength, f is the focal length, Δφ is the phase difference, and (x,y) are the coordinates of the superlens unit. In the calculation, the superlens surface is divided into several periods. To simplify the calculation, only the position of the center point in each period is substituted into the formula to calculate the phase value.

[0034] If all unit structures on the surface of a superlens can satisfy the above expression, then the superlens can achieve focusing at the focal point.

[0035] The fabrication process of this invention is as follows: After selecting the material structure, the performance parameters of the two-band units are optimized by finite difference time domain (FDTD) simulation to ensure that the phase delay reaches 2π. First, the long-wave infrared superlens unit 2 array is constructed according to the wavefront reconstruction equation. After the long-wave infrared superlens is constructed, the positions and unit structure sizes of all long-wave infrared superlens units 2 are obtained. Based on this data, the matrix structure of the mid-wave infrared superlens unit 3 and the positions of each unit are designed to ensure that the matrix structure of the mid-wave infrared superlens unit 3 can be completely placed on the long-wave infrared superlens unit 2. After ensuring that the one-to-one setting is completed, the mid-wave infrared superlens that satisfies the wavefront reconstruction equation is constructed, thus completing the design of the mid-wave and long-wave dual-band superlens.

[0036] See Figure 3 We can see the effect of the medium- and long-wavelength dual-band superlens on the modulation of their respective light waves.

[0037] See Figure 4 It can be seen that mid-wave infrared light achieves good focusing effect at a focal length of approximately 30μm.

[0038] See Figure 5 As can be seen, long-wave infrared light achieves good focusing effect at a focal length of 30μm.

[0039] The above description is a specific illustration of the present invention, and not a limitation thereof. Those skilled in the art can make various equivalent technical solutions without departing from the scope of the present invention; therefore, all equivalent technical solutions should fall within the patent protection scope of the present invention.

Claims

1. A middle-long wave dual-band superlens, characterized in that: Includes a substrate (1), on which a long-wave infrared superlens composed of multiple long-wave infrared superlens units (2) is disposed. The long-wave infrared superlens unit (2) has a cuboid structure with a square cross-section. An array composed of mid-wave infrared superlens units (3) is disposed on the upper part of the long-wave infrared superlens unit (2). The array has a square matrix structure.

2. The middle-long wave dual-band superlens according to claim 1, characterized in that: The mid-wave infrared superlens unit (3) forms a 3*3 or 2*2 rectangular array.

3. The middle-long wave dual-band superlens according to claim 2, characterized in that: The mid-wave infrared superlens unit (3) has a cylindrical structure.

4. The middle-long wave dual-band superlens according to claim 3, characterized in that: The cuboid structure has a height of 6.5 μm, a period of 2 μm, and the side length of the square cross-section of the cuboid structure ranges from 0.63 to 1.8 μm; the cylindrical structure has a height of 6.6 μm, a period of 0.5 μm, and a radius range of 0.07 to 0.2 μm.

5. The dual-band superlens according to claim 4, wherein: The material of the substrate (1) is The long-wave infrared superlens unit (2) and the mid-wave infrared superlens unit (3) are made of Si.

6. The design method of a medium-long wave dual-band superlens according to claim 1, characterized in that: After selecting the material structure, the performance parameters of the two-band units are optimized by finite difference time domain method to meet the requirement that the phase delay reaches 2π. First, the long-wave infrared superlens unit array is constructed according to the wavefront reconstruction equation. After the long-wave infrared superlens is constructed, the positions of all long-wave infrared superlens units (2) and the unit structure size are obtained. Based on this data, the mid-wave infrared superlens unit matrix structure and the position of each unit are designed to ensure that the mid-wave infrared superlens unit matrix structure can be completely placed on the long-wave infrared superlens unit (2). After the one-to-one setting is completed, the mid-wave infrared superlens unit that meets the wavefront reconstruction equation is constructed to complete the design of the mid-wave and long-wave dual-band superlens.

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