A dual-band adjustable lidar absorber

Abstract

The present invention provides a dual-band adjustable lidar absorber, which comprises a metal layer, a dielectric layer and a metal fractal layer arranged in sequence from bottom to top. The metal fractal layer comprises multi-stage self-similar polygonal metals, and the vertices of adjacent two-stage polygonal metals are connected to each other. A slit cavity is formed in the metal layer. The dual-band adjustable lidar absorber provided by the present invention has a simple structure and can achieve perfect absorption of lidar at two working wavelengths of 1.06 μm and 10.6 μm simultaneously.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser detection absorbers, and particularly relates to a dual-band adjustable lidar absorber. Background Art

[0002] As an active detection signal, laser has many advantages, such as high brightness, good directivity, good monochromaticity, and good coherence. With the continuous development of laser technology, its role on the battlefield is becoming more and more important. Weapon systems using laser detection and guidance technologies have high precision. Once a target is tracked by a weapon using laser detection and guidance technologies, the probability of survival will be extremely small. Therefore, the development of laser detection technology has great strategic significance.

[0003] Lidar is an important device in radar applications and plays an important role in the field of target detection. At present, the two frequency bands of 1.06μm and 10.6μm are the main frequency bands of lidar. To maintain the invisibility in front of the laser, a dual-frequency absorber with corresponding response is required. However, the frequency ratio of the above two central points of 1.06μm and 10.6μm differs by as much as 10 times, making it impossible for a broadband to cover these two target points simultaneously. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an adjustable lidar absorber with a simple structure, which can achieve perfect absorption at two working wavelengths of 1.06μm and 10.6μm in the amorphous state of Ge2Sb2Te5, and the absorption difference between the amorphous state and the crystalline state at the same wavelength is preferably as large as possible.

[0005] To achieve the above object, the technical solution of the present invention is as follows. A dual-band adjustable lidar absorber includes a metal layer, a dielectric layer, and a metal fractal layer arranged in sequence from bottom to top. The metal fractal layer includes multi-stage self-similar polygon metals, and the vertices of adjacent two-stage polygon metals are connected to each other. A slit cavity is formed on the metal layer.

[0006] Preferably, the metal fractal layer includes a first-stage square metal, a second-stage square metal, and a third-stage square metal. The similarity ratio of the second-stage square metal to the first-stage square metal is 2 / 3, and the similarity ratio of the third-stage square metal to the first-stage square metal is 1 / 3.

[0007] Preferably, the dielectric layer includes a first dielectric layer, a second dielectric layer, and a third dielectric layer arranged in sequence from bottom to top.

[0008] Preferably, the first dielectric layer is silicon, the second dielectric layer is Ge2Sb2Te5, and the third dielectric layer is alumina.

[0009] Preferably, the two slit cavities are arranged perpendicular to each other.

[0010] Preferably, the slit cavity includes a slit and a box. The slit is formed on the top surface of the metal layer, and the bottom of the slit communicates with the top of the box. Both the slit and the box are filled with the same material as the first dielectric layer.

[0011] Preferably, the thickness of the first dielectric layer is 20 - 25 nm, the thickness of the second dielectric layer is 15 - 20 nm, and the thickness of the third dielectric layer is 25 - 30 nm.

[0012] Preferably, both the metal layer and the dielectric layer are squares with side lengths of 1100 - 1200 nm, and the side length of the first - order square metal is 155 - 165 nm.

[0013] Preferably, the thickness of the metal layer is 290 - 310 nm, the thickness of the metal fractal layer is 8 - 12 nm, the width of the slit is 85 - 100 nm, the height is 35 - 45 nm, the width of the box is 420 - 470 nm, and the height is 220 - 250 nm.

[0014] Preferably, the centers of the metal layer, the dielectric layer, the metal fractal layer, and the slit cavity are located on the same straight line.

[0015] The beneficial effects of the present invention are as follows: The structure is simple. Utilizing the characteristics of multi - scale self - similarity of fractal geometry, the first - order polygon fractal continuously evolves into the N - th order polygon, generating multiple resonance peaks from the same element structure. A slit cavity 4 is formed on the metal layer 1 to form a Helmholtz resonance cavity, and then the Helmholtz resonance cavity is used to actively select the required frequency band. Due to its symmetric structure, it has wide - angle absorption characteristics and polarization - insensitive characteristics, and can achieve perfect absorption at the resonance frequency points of 1.06 μm and 10.6 μm, and can solve the problem that the frequency ratio of the two central points of 1.06 μm and 10.6 μm differs by 10 times. The designed ideal absorber metal fractal layer has potential application value in the fields of laser detection, lidar, and infrared stealth. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of one embodiment of the present invention.

[0017] Figure 2 is Figure 1 an exploded view of the shown embodiment.

[0018] Figure 3 is Figure 1 a schematic structural diagram of the shown metal fractal layer; wherein, Figure 3a is a schematic diagram of the first - order metal fractal structure, Figure 3b is a schematic diagram of the second - order metal fractal structure, Figure 3c is a schematic diagram of the third - order metal fractal structure.

[0019] Figure 4 is Figure 1 The structural schematic diagram of the metal fractal layer shown

[0020] Figure 5 is Figure 1 The structural schematic diagram of the dielectric layer shown

[0021] Figure 6 is Figure 1 The structural schematic diagram of the slit cavity shown

[0022] Figure 7 is the diagram of the first - level fractal wavelength absorption of this embodiment

[0023] Figure 8 is the diagram of the second - level fractal wavelength absorption of this embodiment

[0024] Figure 9 is the diagram of the third - level fractal wavelength absorption of this embodiment

[0025] In the figure, 1 is the metal layer; 2 is the dielectric layer; 21 is the first dielectric layer; 22 is the second dielectric layer; 23 is the third dielectric layer; 3 is the metal fractal layer; 31 is the first - level square metal; 32 is the second - level square metal; 33 is the third - level square metal; 4 is the slit cavity; 41 is the slit; 42 is the box Specific embodiments

[0026] The technical solutions of the present invention will be further specifically described below in conjunction with the accompanying drawings and specific embodiments

[0027] Please refer to Figures 1-5 , the dual - band tunable lidar absorber provided in this embodiment includes a metal layer 1, a dielectric layer 2, and a metal fractal layer 3 arranged in sequence from bottom to top. The metal fractal layer 3 includes multi - level self - similar polygonal metals, and the vertices of adjacent two - level polygonal metals are connected to each other. A slit cavity 4 is opened on the metal layer 1

[0028] Utilizing the characteristics of multi - scale self - similarity of fractal geometry, the first - level polygonal fractal continuously evolves into the N - th level polygon, generating multiple resonance peaks from the same element structure. A slit cavity 4 is opened on the metal layer 1 to form a Helmholtz resonance cavity, and then the Helmholtz resonance cavity is used to actively select the required frequency band. The structure is simple and can achieve perfect absorption at the resonance frequency points in the two frequency bands of 1.06μm and 10.6μm, and can solve the problem that the frequency ratio of the two center points of 1.06μm and 10.6μm differs by 10 times

[0029] More specifically, the metal fractal layer 3 includes a first-level square metal 31, a second-level square metal 32, and a third-level square metal 33. The similarity ratio of the second-level square metal 32 to the first-level square metal 31 is 2 / 3, and the similarity ratio of the third-level square metal 33 to the first-level square metal 31 is 1 / 3. Starting from the first-level square metal 31 with a side length of L, continuous fractalization is carried out. The secondary fractal adds a self-similar shape on the 2 / 3L ratio of the first-level fractal square metal, and the tertiary fractal continues to add on the 1 / 3L ratio of the first-level fractal square metal, thus forming a 1-3 level fractal structure formed by continuous branching. The absorber is arranged in a periodic structure. All units have the same size, arrangement direction, and the same geometric shape, and are in the same plane, reducing the difficulty of later process manufacturing. By combining the fractal technology and electromagnetic theory, the self-similarity and space-filling properties of fractal geometry are used to achieve the multi-band and miniaturization of the antenna.

[0030] More specifically, the dielectric layer 2 includes a first dielectric layer 21, a second dielectric layer 22, and a third dielectric layer 23 arranged in sequence from bottom to top. The first dielectric layer 21, the second dielectric layer 22, and the third dielectric layer 23 are made of different materials.

[0031] More specifically, both the metal layer 1 and the metal fractal layer 3 are Au. The first dielectric layer 21 is silicon, the second dielectric layer 22 is Ge2Sb2Te5, and the third dielectric layer 23 is alumina; the Ge2Sb2Te5 material can achieve adjustable absorption between the crystalline state and the amorphous state, and the absorption exceeds 99% in the amorphous state of Ge2Sb2Te5.

[0032] The first dielectric layer 21 is Si: The Si layer is the bottom layer of the entire structure. Since Si is a transparent medium in the infrared band (1000 - 14000nm), its main function is to serve as a substrate and form the lowest Helmholtz resonance cavity in combination with Au. At the same time, due to the characteristics of this target band of Si, it can be extended to subsequent etching work and the substrate design of superlenses or metasurfaces.

[0033] The second dielectric layer 22 is made of Ge2Sb2Te5 material: In other fractal devices and Helmholtz structures at home and abroad, only perfect absorption and camouflage in a single band or a single function can often be achieved. In our model, a phase change material Ge2Sb2Te5 (GST) is utilized, which has two states: crystalline state and amorphous state. In the amorphous state, the atomic arrangement of Ge2Sb2Te5 is very chaotic, while in the crystalline state, it is very orderly. The different atomic arrangement methods result in Ge2Sb2Te5 having completely different optical properties in the infrared band: the extinction coefficient of amorphous Ge2Sb2Te5 is 0 in the mid-infrared band, so it is a transparent medium in the mid-infrared band. When Ge2Sb2Te5 changes from the amorphous state to the crystalline state, at this time, the refractive index will increase significantly, and the extinction coefficient also appears from zero, making crystalline Ge2Sb2Te5 an infrared absorption material in the mid-infrared band. And we can calculate the absorption rates of the crystalline state, amorphous state, and intermediate state for the infrared band through the atomic doping rate of Ge2Sb2Te5. Due to the unique properties of Ge2Sb2Te5, with the change of temperature, the change of absorption rates in the same structure can be realized, so as to realize the controllable adjustment change of the absorption rate.

[0034] The third dielectric layer 23 is alumina: In our design model, an alumina gap with a T6 height is used to excite the gap plasmon mode of infrared wavelengths. While the top metal array fractal device couples the nano-gap resonance, the electric field therein is tightly trapped in the ultra-thin alumina gap, so as to generate two obvious absorption peaks in the thermal radiation spectrum in combination with the bottom Helmholtz resonance cavity, and they are located at 1.06μm and 10.6μm respectively.

[0035] More specifically, the two slit cavities 4 are arranged perpendicular to each other and cross in a cross shape; compared with other Helmholtz resonance cavities, the range is wider. Due to the introduction of the structure of the metal fractal device, the designed absorption peaks in our absorber can be affected. The appearance of this model also solves the problem that the frequency ratio (a difference of 10 times) between the two central points (1.06μm and 10.6μm) is too large.

[0036] More specifically, the slit cavity 4 includes a slit 41 and a box 42. The slit 41 is opened on the top surface of the metal layer 1, and the bottom of the slit 41 communicates with the top of the box 42. Both the slit 41 and the box 42 are filled with the same material as the first dielectric layer 21 to form the Helmholtz resonance cavity to actively select the required frequency band.

[0037] More specifically, the thickness of the first dielectric layer 21 is 20 - 25nm, the thickness of the second dielectric layer 22 is 15 - 20nm, and the thickness of the third dielectric layer 23 is 25 - 30nm.

[0038] More specifically, both the metal layer 1 and the dielectric layer 2 are squares with a side length of 1100 - 1200 nm, and the side length of the first - level square metal 31 is 155 - 165 nm.

[0039] More specifically, the thickness of the metal layer 1 is 290 - 310 nm, the thickness of the metal fractal layer 3 is 8 - 12 nm, the width of the slit 41 is 85 - 100 nm, the height is 36 - 45 nm, the width of the box 42 is 420 - 470 nm, and the height is 220 - 250 nm.

[0040] More specifically, the centers of the metal layer 1, the dielectric layer 2, the metal fractal layer 3, and the slit cavity 4 are located on the same straight line. Due to its symmetric structure, it has wide - angle absorption characteristics and polarization - insensitive characteristics.

[0041] In specific implementation, both the metal layer 1 and the dielectric layer 2 are squares with a side length Q of 1150 nm, the thickness T1 of the metal layer 1 is 300 nm, the thickness of the metal fractal layer T7 is 10 nm, the width W1 of the box 42 is 450 nm, the height T2 is 235 nm, the width W2 of the slit 41 is 90 nm, the height T3 is 40 nm, the side length L of the first - level square metal 31 is 160 nm, the thickness T4 of the first dielectric layer 21 is 22 nm, the thickness T5 of the second dielectric layer 22 is 18 nm, and the thickness T6 of the third dielectric layer 23 is 28 nm.

[0042] From Figure 7 it can be seen that the metal fractal layer 3 is a first - level metal fractal structure. When Ge2Sb2Te5 is in the amorphous state, the absorption rate at a wavelength of 1.06 μm is 99.104%, and the absorption rate at a wavelength of 10.6 μm is 94.363%. When Ge2Sb2Te5 is in the crystalline state, the absorption rate at a wavelength of 1.06 μm is 58.575%, and the absorption rate at a wavelength of 10.6 μm is 86.603%. From Figure 8 it can be seen that the metal fractal layer 3 is a second - level metal fractal structure. When Ge2Sb2Te5 is in the amorphous state, the absorption rate at a wavelength of 1.06 μm is 99.212%, and the absorption rate at a wavelength of 10.6 μm is 97.919%. When Ge2Sb2Te5 is in the crystalline state, the absorption rate at a wavelength of 1.06 μm is 59.100%, and the absorption rate at a wavelength of 10.6 μm is 82.574%. From Figure 9As can be seen, the metal fractal layer 3 is a three-level metal fractal structure. When Ge2Sb2Te5 is in the amorphous state, the absorption rate at a wavelength of 1.06 μm is 99.110%, and the absorption rate at a wavelength of 10.6 μm is 99.475%, showing a perfect absorption effect. When Ge2Sb2Te5 is in the crystalline state, the absorption rate at a wavelength of 1.06 μm is 60.124%, and the absorption rate at a wavelength of 10.6 μm is 78.314%. It can be seen that with the increase in the grading of the metal fractal layer 3, when Ge2Sb2Te5 is in the amorphous state, the change in the absorption rate at a wavelength of 1.06 μm is small, while the absorption rate at a wavelength of 10.6 μm is significantly improved. When Ge2Sb2Te5 is in the crystalline state, the change in the absorption rate at a wavelength of 1.06 μm is small, while the absorption rate at a wavelength of 10.6 μm is significantly decreased. Therefore, it is possible to adjust the absorption rate of the absorber at different wavelengths by changing the crystallization state of Ge2Sb2Te5, achieving perfect absorption at two working wavelengths of 1.06 μm and 10.6 μm in the amorphous state of Ge2Sb2Te5, and having a larger absorption difference between the two different states of Ge2Sb2Te5 at the same wavelength, thus realizing a tunable lidar absorber.

[0043] The dual-band tunable lidar absorber provided by the present invention has a simple structure. Utilizing the characteristics of multi-scale self-similarity of fractal geometry, the first-level polygon fractal continuously evolves into the N-level polygon, generating multiple resonance peaks from the same element structure. Due to its symmetric structure, it has wide-angle absorption characteristics and polarization-insensitive characteristics. The numerical simulation results show that when the absorber has a three-level metal fractal structure, it achieves perfect absorption with an absorption exceeding 99% at two target wavelengths of 1.06 μm and 10.6 μm, and there is almost no absorption / emission at 3 - 8 μm. After adding the Ge2Sb2Te5 material, it realizes tunability between the crystalline and amorphous states. When Ge2Sb2Te5 is in the amorphous state, the absorption exceeds 99%, and there is a large absorption gap between the crystalline and amorphous states at the same frequency of the three-level fractal. The designed ideal absorber metal fractal layer has potential application value in the fields of laser detection, lidar, and infrared stealth.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-band adjustable lidar absorber, characterized in that: It includes a metal layer (1), a dielectric layer (2), and a metal fractal layer (3) arranged successively from bottom to top. The metal fractal layer (3) includes multi-level self-similar polygonal metals, and adjacent two levels of the polygonal metals are connected to each other through vertices. A slit cavity (4) is formed on the metal layer (1). The metal fractal layer (3) includes a first-level square metal (31), a second-level square metal (32), and a third-level square metal (33). The similarity ratio of the second-level square metal (32) to the first-level square metal (31) is 2 / 3, and the similarity ratio of the third-level square metal (33) to the first-level square metal (31) is 1 / 3. The dielectric layer (2) includes a first dielectric layer (21), a second dielectric layer (22), and a third dielectric layer (23) arranged successively from bottom to top. The first dielectric layer (21) is silicon, the second dielectric layer (22) is Ge2Sb2Te5, and the third dielectric layer (23) is alumina.

2. The dual-band adjustable lidar absorber according to claim 1, characterized in that: The two slit cavities (4) are arranged perpendicular to each other.

3. The dual-band adjustable lidar absorber according to claim 2, characterized in that: The slit cavity (4) includes a slit (41) and a box (42). The slit (41) is formed on the top surface of the metal layer (1), and the bottom of the slit (41) communicates with the top of the box (42). Both the slit (41) and the box (42) are filled with the same material as the first dielectric layer (21).

4. The dual-band adjustable lidar absorber according to claim 1, wherein: The thickness of the first dielectric layer (21) is 20 - 25 nm, the thickness of the second dielectric layer (22) is 15 - 20 nm, and the thickness of the third dielectric layer (23) is 25 - 30 nm.

5. The dual-band adjustable lidar absorber according to claim 4, wherein: Both the metal layer (1) and the dielectric layer (2) are squares with side lengths of 1100 - 1200 nm, and the side length of the first-level square metal (31) is 155 - 165 nm.

6. The dual-band adjustable lidar absorber according to claim 5, wherein: The thickness of the metal layer (1) is 290 - 310 nm, the thickness of the metal fractal layer (3) is 8 - 12 nm, the width of the slit (41) is 85 - 100 nm, the height is 35 - 45 nm, the width of the box (42) is 420 - 470 nm, and the height is 220 - 250 nm.

7. The dual-band adjustable lidar absorber according to claim 1, characterized in that: The centers of the metal layer (1), the dielectric layer (2), the metal fractal layer (3), and the slit cavity (4) are located on the same straight line.

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