A DBR-metal-based infrared and laser compatible stealth film system structure

Abstract

The application relates to the technical field of optical selective reflection structure, in particular to an infrared and laser compatible stealth film system structure based on DBR-metal, which has a specific structure of Ge-Al2O3-Ag type. The photonic crystal film layer is designed based on the working mechanism of a distributed Bragg reflector (DBR), so that the thin film structure of the stealth function has the purposes of achieving high reflectivity in the medium and far infrared and low reflectivity at a 10.6-micron wave band. The finally obtained film system structure better satisfies the purposes of achieving high reflectivity in the medium and far infrared and realizing "spectrum hole digging" low reflectivity at 10600 nm, and can perfectly realize the medium and far infrared and 10600-nm laser compatible stealth performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of optical selective reflection structure, in particular to an infrared and laser compatible stealth film system structure based on DBR-metal. BACKGROUND

[0002] With the development of detection technology towards multi-band composite detection, the detected target faces the dual threat of infrared detection and laser detection, even multiple threats. Single-band stealth technology has been unable to adapt to its survival. In order to reduce the probability of being discovered by the detector, it is necessary to further study how to realize the compatible stealth performance in the multi-band environment.

[0003] (1) Infrared detection equipment is applied to the identification and tracking of targets. The actual working waveband of the infrared detector is 3-5 microns and 7-14 microns, that is, the middle and far infrared waveband. It is discovered and identified by accepting the energy of the target itself. Therefore, the infrared stealth material needs to have high reflectivity to reduce the surface radiation and realize stealth. (2) The laser detector determines the target position based on the high reflectivity of the target. The widely used CO2 laser has a working wavelength of 10.6 microns. The principle of laser stealth is to reduce the reflection signal of the target to the laser, absorb or diffract the electromagnetic wave from the target, so that the reflection wave of the target is not received by the laser detector, thereby giving the target low detectability. The most fundamental requirement of laser stealth material is to maintain low reflectivity at the laser working range.

[0004] To realize the simultaneous realization of the two targets, on the one hand, it is necessary to ensure the high reflectivity in the middle and far infrared waveband, and on the other hand, it is necessary to maintain the low reflectivity at the specific laser wavelength, that is, 10.6 microns. The infrared stealth material is usually a coating material, and the laser stealth material is divided into coating type and structure type. These conventional materials are difficult to simultaneously meet the requirements of compatibility.

[0005] The distributed Bragg reflector (DBR) is a reflector used in waveguides and optical fibers. Compared with ordinary metal reflectors, the former has extremely low loss at optical and infrared frequencies. The structure is formed by periodic thin layers of high and low refractive index materials, in which the first layer and the last layer are selected to have high refractive index. Therefore, how to design the photonic crystal film layer based on the working mechanism of the distributed Bragg reflector (DBR) so that the stealth function thin film structure has high reflectivity in the middle and far infrared and low reflectivity at the 10.6 micron waveband is a problem to be solved in the field. SUMMARY

[0006] The application provides a DBR-metal-based infrared and laser compatible stealth film system structure to solve the technical problem of preparing a reflective material with high reflectivity in the middle and far infrared and low reflectivity at a 10.6-micron wave band.

[0007] To solve the above technical problems, the application adopts the technical scheme of a DBR-metal-based infrared and laser compatible stealth film system structure with a Ge-Al2O3-Ag type structure.

[0008] Specifically, the DBR-metal-based infrared and laser compatible stealth film system structure has a structure of SUB|Ag / Ge(A) / Al2O3(B) / Ge(A1) / Al2O3(B1) / Al2O3(B) / Ge(A)|AIR, which preferably meets the requirements of the application and perfectly realizes the middle and far infrared and 10600-nm laser compatible stealth performance.

[0009] The Ag thickness is 96nm-963nm.

[0010] Further, A and A1 can be 663nm and 1325nm respectively, and B and B1 can be 3786nm and 7571nm respectively.

[0011] The optimal structure is SUB|Ag(963nm) / Ge(663nm) / Al2O3(3786nm) / Ge(1325nm) / Al2O3(7571nm) / Al2O3(3786nm) / Ge(663nm)|AIR.

[0012] The structure preferably meets the requirements of the application and perfectly realizes the middle and far infrared and 10600-nm laser compatible stealth performance.

[0013] The application is based on the principle of a distributed Bragg reflector (DBR) and uses COMSOL software modeling simulation. s The model is composed of a single domain of a substrate with a refractive index n a =1.0. Under the default material discontinuous boundary condition of the substrate surface, many dielectric film features are added to represent the alternating layers.

[0014] Based on the larger refractive index ratio, a wider photonic band gap can be obtained, and the DBR structure with high refractive index ratio can not only expand the absorption spectrum, but also obtain high reflectivity. Two DBR structures are designed, wherein the DBR-1 is composed of Ge and Al2O3, and the DBR-2 is composed of AZO and CaF2. Ge and AZO are used as high refractive index medium layers, and Al2O3 and CaF2 are used as low refractive index medium layers. The refractive index of Al2O3 is In the DBR-2 structure, the refractive index of AZO is The refractive index of CaF2 is

[0015] The DBR-1: Ge-Al2O3 type DBR structure designed in the technical scheme of the application is: SUB|ABA1B1BA|AIR, as shown in FIG. 1(a), which contains six thin films in total, wherein SUB is a substrate, AIR is air, A and A1 represent the thickness of the Ge layer, and B and B1 represent the thickness of Al2O3. The thickness of A is 663 nm, that is, The thickness of A1 is 1325 nm, that is, The thickness of B is 3786 nm, that is, The thickness of B1 is 7571 nm, that is,

[0016] The DBR-2: AZO-CaF2 type DBR structure designed in the technical scheme of the application is: SUB|ABB1A1BA|AIR, as shown in FIG. 1(b), which contains six thin films in total, wherein SUB is a substrate, AIR is air, A and A1 are AZO (aluminum-doped zinc oxide), the thickness of A is That is, 676 nm. The thickness of A1 is That is, 1352 nm. B is a low refractive index material CaF2, the thickness of B is That is, 4140 nm. The thickness of B1 is That is, 8281 nm.

[0017] Based on the distributed Bragg principle (DBR), two structures are designed, which are Ge-Al2O3 type DBR structure and AZO-CaF2 type DBR structure, both of which are DBR structure models of one-dimensional metal photonic crystal thin films containing defects in the mid-infrared waveband.

[0018] The Ge-Al2O3 type DBR structure is SUB|Ge (663nm) / Al2O3 (3786nm) / Ge (1325nm) / Al2O3 (7571nm) / Al2O3 (3786nm) / Ge (663nm)|AIR, which successfully achieves high reflectivity in the middle and far infrared band, and achieves "spectrum hole digging" low reflectivity at 10600nm. In terms of defect layer, when the defect layer thickness increases, the number of reflection valleys in the reflectivity spectrum increases, and the width of the defect state becomes narrower. In terms of period number, the number of reflection valleys changes with the increase of the period number, and the reflection valley bandgap characteristics are intensified.

[0019] The AZO-CaF2 type DBR structure is SUB|AZO (676nm) / CaF2 (4140nm) / CaF2 (8281nm) / AZO (1352nm) / CaF2 (4140nm) / AZO (676nm)|AIR, which achieves high reflectivity in the middle and far infrared band, and achieves low reflectivity at 10600nm. In terms of defect layer, the defect layer thickness decreases, and low reflectivity will not appear at 10600nm. When the defect layer thickness increases, the number of reflection valleys increases, the low reflectivity at 10600nm remains unchanged, and the reflectivity is all 4%, but the defect state width at this point becomes narrower. The influence of periodicity, the number of reflection valleys changes with the change of the period number, and the reflection valley bandgap characteristics are intensified with the increase of the period number.

[0020] By comparing and optimizing the above two structures, the Ge type DBR structure is selected, and the structure is further optimized. The optimization scheme is to coat a layer of silver with a thickness of 963nm at the innermost layer of the original structure close to the substrate, which improves the low reflectivity at 3600-4600nm to more than 90% without affecting the high reflectivity in the far infrared band and the low reflectivity at 10600nm laser range, which better achieves the optimization purpose.

[0021] In summary, compared with the prior art, the Ge-Al2O3-Ag type DBR structure of the present application has the following beneficial effects: SUB|Ag (963nm) / Ge (663nm) / Al2O3 (3786nm) / Ge (1325nm) / Al2O3 (7571nm) / Al2O3 (3786nm) / Ge (663nm)|AIR, which better satisfies the high reflectivity in the middle and far infrared, and achieves "spectrum hole digging" low reflectivity at 10600nm. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1(a) is a Ge-Al2O3 type DBR structure diagram;

[0023] Fig. 1(b) is an AZO-CaF2 type DBR structure diagram;

[0024] Figure 2 Reflectivity spectrum for Ge-Al203 type DBR structure in 3600-4800 nm;

[0025] Figure 3 Reflectivity spectrum for Ge-Al203 type DBR structure in 8000-12000 nm;

[0026] Figure 4 Reflectivity spectrum for Ge-Al203 type DBR structure in 10200-10800 nm;

[0027] Figure 5 Reflectivity spectrum for defect layer Al with decreasing thickness;

[0028] Figure 6 Reflectivity spectrum for defect layer Al with increasing thickness;

[0029] Figure 7(a) is a reflectivity spectrum for defect layer Bl with decreasing thickness;

[0030] Figure 7(b) is a reflectivity spectrum for defect layer Bl with increasing thickness;

[0031] Figure 8 Reflectivity spectrum in 4000-12000 nm;

[0032] Figure 9(a) is a reflectivity spectrum in 4620-4780 nm;

[0033] Figure 9(b) is a reflectivity spectrum in 3400-3650 nm;

[0034] Figure 9(c) is a reflectivity spectrum at 10600 nm;

[0035] Figure 9(d) is a reflectivity spectrum in 9600-11500 nm;

[0036] Figure 9(e) is a reflectivity spectrum in 7700-7880 nm;

[0037] Figure 10 Reflectivity spectrum for AZO-CaF2 type DBR structure in 3600-4800 nm;

[0038] Figure 11 Reflectivity spectrum for AZO-CaF2 type DBR structure in 8000-13000 nm;

[0039] Figure 12 Reflectivity spectrum for AZO-CaF2 type DBR structure in 9400-11600 nm;

[0040] Figure 13(a) is a reflectivity spectrum for a decrease in the thickness of the defect layer Al;

[0041] Figure 13(b) is a reflectivity spectrum for an increase in the thickness of the defect layer Al;

[0042] Figure 14 Figure 14(a) is a reflectivity spectrum for a decrease in the thickness of the defect layer Bl;

[0043] Figure 15 Figure 14(b) is a reflectivity spectrum for an increase in the thickness of the defect layer Bl;

[0044] Figure 16 Figure 15 is a reflectivity spectrum over 4000-12000 nm;

[0045] Figure 17(a) is a reflectivity spectrum over 8600-11800 nm;

[0046] Figure 17(b) is a reflectivity spectrum over 3500-4000 nm;

[0047] Figure 17(c) is a reflectivity spectrum at 10600 nm;

[0048] Figure 18 Figure 18 is refractive index data for the four materials;

[0049] Figure 19 Figure 19 is an absorption graph for an AZO-CaF2 type DBR structure;

[0050] Figure 20 Figure 20 is an absorption graph for a Ge-Al2O3 type DBR structure;

[0051] Figure 21 Figure 21 is a reflectivity spectrum graph for a silver film thickness of λ / n k , λ / 2n k , λ / 3n k , λ / 4n k ;

[0052] Figure 22 Figure 22 is a reflectivity spectrum graph for a silver film thickness of λ / n k , λ / 5n k , λ / 6n k , λ / 7n k , λ / 8n k , λ / 9n k , λ / 10n k ;

[0053] Figure 23 Figure 23 is a schematic diagram of a DBR structure after silver plating;

[0054] Figure 24 Figure 24 is a reflectivity spectrum graph for a DBR structure after silver plating over 3600-4600 nm;

[0055] Figure 25 The reflectivity spectrum of the DBR structure after silver plating at 8000-12000nm;

[0056] Figure 26 The reflectivity spectrum of the DBR structure at 10000-10800nm after silver plating;

[0057] Figure 27 The reflectivity spectrum comparison chart of the DBR structure before and after film plating at 10600nm. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0059] Embodiment 1, an infrared and laser compatible stealth film system structure based on DBR-metal, the structure is: SUB|Ag / Ge(663nm) / Al2O3(3786nm) / Al2O3(7571nm) / Ge(1325nm) / Al2O3(3786nm) / Ge(663nm)|AIR. Wherein, SUB represents the substrate layer, AIR represents the air layer. Ge and Al2O3 represent the Ge layer and the Al2O3 layer, and the brackets behind represent the thickness of each layer. The film system structure of the present embodiment is obtained by alternately stacking the Ge layer and the Al2O3 layer.

[0060] Wherein the Ag thickness film layer is 963nm, and the structure is: SUB|Ge(663nm) / Al2O3(3786nm) / Al2O3(7571nm) / Ge(1325nm) / Al2O3(3786nm) / Ge(663nm) / Ag(963nm)|AIR.

[0061] The Ag thickness can also be 482nm, 321nm, 241nm, 193nm, 160nm, 138nm, 120nm, 107nm, 96nm.

[0062] 1 Ge-Al2O3 type DBR structure performance research and result analysis

[0063] 1.1 Stealth performance research of Ge-Al2O3 type DBR structure

[0064] As Figure 2 , 3, 4, as shown in the schematic, the reflectivity spectrum of Ge-Al2O3 type DBR structure in the middle and far infrared range.

[0065] From the above, Figure 2 It can be seen that in the range of 3600-4500nm, the overall presents a high reflection state, except that the reflectivity in the range of 3900-4000nm drops to 98%, the rest of the reflectivity is 100%. The reflectivity starts to present a downward trend after 4500nm, in the range of 4500-4800nm, the reflectivity decreases gently, at 4800nm, the reflectivity drops to 88%, after 4800nm, the reflectivity decreases rapidly, the trend is more intense, until 5000nm, the reflectivity drops to below 40%, the reflectivity value is low. But the overall average reflectivity in the range of 3600-4800nm band reaches the requirement of high reflection, and the middle infrared stealth performance can be realized.

[0066] According to the above, Figure 3 It can be seen that in the range of 8000-14000nm, a high reflection band appears, except that in the range of 10400-10800nm, a significant downward trend appears, in the range of 8000-10400nm and 10800-14000nm, the reflectivity reaches 100%, realizing the high reflectivity required by far infrared stealth, and having good far infrared stealth performance. At the same time, from Figure 4 It can be seen that in the range of 10400-10800nm, the reflectivity at 10600nm is about 7%, forming a significant reflection valley, showing strong "spectrum hole digging" characteristics, which is consistent with the ideal.

[0067] From the above, it can be seen that the Ge-Al2O3 type DBR structure designed in this embodiment can well realize the middle and far infrared and 10600nm laser compatible stealth.

[0068] 1.2 Influence of defect layer thickness on Ge-Al2O3 type DBR structure

[0069] The Ge-Al2O3 type DBR structure designed in the application is: SUB|ABA1B1BA|AIR.

[0070] If the defect layer is only located in the Ge layer, at this time the structure is recorded as: SUB|ABA1BA|AIR. As Figure 5 , 6 is the thickness of A1 layer, from to the reflectivity spectrum.

[0071] When Figure 5 , 6 is the thickness of A1 layer, from to , the reflectivity graph, it can be seen that when the thickness of A1 layer decreases, there will be no low reflection at 10600nm.

[0072] As Figure 6 the thickness of A1 layer increases from to , the reflectivity spectrum is shown in Fig. 6. It can be seen from Fig. 6 that the defect state width at 10600 nm becomes narrower when the thickness of A1 layer increases from Figure 6 to . When the thickness of A1 layer increases from to , the defect state width at 10600 nm becomes narrower and a new defect state appears at 8565 nm with a reflectivity of 13.5%.

[0073] If the defect layer is located in the Al2O3 layer, the structure is denoted as SUB|ABB1BA|AIR. The reflectivity spectrum is shown in Fig. 7 as the thickness of B1 layer increases from to . Fig. 7(a) is the reflectivity spectrum as the thickness of B1 layer decreases from to . It can be seen from Fig. 7(a) that there will be no low reflection at 10600 nm when the thickness of B1 layer decreases. When the thickness of B1 layer decreases from to , the low reflection appears at 8966 nm. When the thickness of B1 layer decreases from to , the low reflection appears at 8154 nm.

[0074] Fig. 7(b) is the reflectivity spectrum as the thickness of B1 layer increases from to . It can be seen from Fig. 7(b) that the number of reflection valleys increases when the thickness of B1 layer increases. The width of the defect state becomes narrower. When the thickness of B1 layer increases from to , there are two reflection valleys at 10600 nm and 8055 nm, respectively, and the width of the reflection valley at 10600 nm becomes narrower with a reflectivity of 7.2% at 8055 nm. When the thickness of B1 layer increases from to , there are two reflection valleys at 10600 nm and 8877 nm, respectively, and the width of the reflection valley at 10600 nm becomes narrower with a reflectivity of 7.8% at 8877 nm.

[0075] 1.3 Effect of the number of periods on the Ge-Al2O3 type DBR structure

[0076] The Ge-Al2O3 type DBR structure is SUB|ABA1B1BA|AIR. The number of periods N is changed to 1, 2, 3, 4 and 5. The reflectivity spectrum is shown in Fig. 8. c Figure 8 ​The reflectivity spectrum in the waveband 4000-12000 nm is shown.

[0077] Table 1. Table of reflection valley under different cycle numbers

[0078]

[0079] Figures 9(a) to 9(e) The reflectivity spectrum graph specific to each waveband is shown, and it can be seen that, with the increase of cycle number, the reflection valley band gap feature is intensified, and the number of reflection valleys increases, mainly concentrated in the two wavebands of 3000 nm-5000 nm and 9800 nm-12000 nm. The specific performance is that the defect state width at 10600 nm becomes narrower and narrower, but the minimum reflectivity does not change; the number of reflection valleys on both sides of the defect state at 10600 nm increases.

[0080] Table 2. Reflection valley position under different cycle numbers

[0081]

[0082] Combining Tables 1 and 2, the following rules can be found: N c = 1, the reflection valley appears at the position of 3531 nm, and in N c = 2, 3, 4, 5, the reflection valley also appears at this position; N c = 2, a reflection valley appears at 3154 nm, and similarly in N c = 2, 3, 4, 5, the reflection valley also exists at this position. And under this cycle number, the two reflection valley positions of 4702 nm and 11261 nm also appear at the same time in N c = 4, 6, indicating that the two positions of 4702 nm and 11261 nm are cyclically appearing under even cycle numbers; N c = 3, the reflection valley at 3531 nm also appears at the same time in N c = 4, 5. At the same time, the position of 4007 nm that appears at the same time in N c = 3 also appears at the same time in N c = 5, indicating that with the increase of cycle number, the reflection valley of 4007 nm cyclically appears under odd cycle numbers.

[0083] In summary: with the increase of cycle number, the reflection valley band gap feature is intensified, the number of reflection valleys increases, and the reflection valley position has a cyclic rule.

[0084] Comparative Example 2, an infrared and laser compatible stealth performance film system structure based on DBR-metal, the structure is: SUB|AZO(676nm) / CaF2(4140nm) / CaF2(8281nm) / AZO(1352nm) / CaF2(4140nm) / AZO(676nm)|AIR.

[0085] 2 Performance research and result analysis of AZO-CaF2 type DBR structure

[0086] 2.1 Stealth performance research of AZO-CaF2 type DBR structure

[0087] As Figure 10 , 11 , 12 is the reflectivity spectrum of AZO and CaF2 type DBR structure in the middle and far infrared range.

[0088] As Figure 10 , is the reflectivity spectrum of AZO and CaF2 type DBR structure in 3600-4800nm, it can be seen that in 3600-4500nm, it basically presents a high reflection state, there is a small fluctuation, up and down, but the overall reflectivity is above 50%, after 4500nm, with the increase of wavelength, the reflectivity gradually decreases, and finally reaches zero. Overall, it meets the requirement of high reflection in the middle infrared band, and can realize the middle infrared stealth performance.

[0089] According to Figure 11 , it can be seen that the reflectivity of AZO and CaF2 type DBR structure in 8000-13000nm, in this band, the overall reflectivity is about 60%, and the highest can reach 100%, realizing the high reflectivity required by far infrared stealth, and having good far infrared stealth performance.

[0090] At the same time, from Figure 12 , it can be seen that the reflectivity spectrum has a reflectivity of about 4% at 10600nm, forming a obvious reflection valley, realizing the "spectrum hole" structure, and the low reflection at 10600nm as the common laser wavelength can effectively achieve the purpose of laser stealth.

[0091] In summary, AZO-CaF2 type DBR structure can achieve the purpose of middle and far infrared and 10600nm laser stealth.

[0092] 2.2 Effect of defect layer thickness on AZO-CaF2 type DBR structure

[0093] The AZO-CaF2 type six-layer DBR structure designed by the application is: SUB|ABB1A1BA|AIR.

[0094] If the defect layer is located only in the AZO layer, the structure is denoted as: SUB|ABA1BA|AIR.

[0095] like Figures 13(a) to 13(b) The thickness of layer A1 is determined by... Become The graph shows the change in reflectance over time.

[0096] As shown in Figure 13(a), the thickness of layer A1 is... Become When the thickness of the A1 layer decreases, low reflection will no longer occur at 10600 nm, but symmetrical reflection valleys will appear on both sides around 10600 nm. The thickness of the A1 layer increases from... Become At that time, symmetrical reflection valleys appeared at 12480 nm and 10480 nm. The thickness of the A1 layer was... Become At that time, symmetrical reflection valleys appeared at 10230 nm and 11860 nm. The thickness of the A1 layer was... Become At that time, symmetrical reflection valleys appeared at 9780nm and 11480nm.

[0097] As shown in Figure 13(b), the thickness of layer A1 is... Become As the thickness of the A1 layer increases, the number of reflection valleys in the reflectance spectrum increases. The low reflectance at 10600 nm remains unchanged at 4%, but the width of the defect states at this point narrows. The thickness of the A1 layer increases from... Become At that time, there were three reflection valleys, with the main reflection valley at 10600 nm and the other two located on either side of the main reflection valley, at 9230 nm and 12500 nm respectively. The thickness of the A1 layer was determined by... Become There are four reflection valleys. The main reflection valley is 10600nm, and the other three are located on both sides of the main reflection valley, at 8250nm, 9620nm and 11800nm ​​respectively.

[0098] If the defect layer is located in the CaF2 layer: the structure is denoted as: SUB|ABB1BA|AIR.

[0099] like Figure 14 As shown, the thickness of layer B1 is... Become Time reflectance spectrum. Figure 15 The thickness of layer B1 is determined by... Become Time reflectance spectrum.

[0100] according to Figure 14 The thickness of layer B1 is determined by B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0101] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0102] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0103] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0104] According to the formula of Figure 15 , B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0105] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0106] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0107] B1 layer thickness is reduced, and low reflection will not occur at 10600 nm. B1 layer thickness is reduced, and low reflection will not occur at 10600 nm.

[0108] 2.3 Effect of period number on AZO-CaF2 type DBR structure

[0109] The AZO-CaF2 type DBR structure is: SUB | ABB1A1BA | AIR. Change the period, let Nc = 1, 2, 3, 4, 5. Get the reflectivity spectrum in the wavelength range of 4000-12000 nm as shown in Figure 16

[0110] Table 3. Reflection valley situation table under different period numbers

[0111] ​​​​​​​​

[0112] As shown in Figures 17(a) to 17(c) The reflectivity spectrum diagram specific to each waveband is shown. As can be seen from the figure, with the increase of the period number, the reflection valley band gap feature is intensified, and the number of reflection valleys increases and concentrates in the range of 3000nm-5000nm and 9000nm-12000nm. Specifically, the defect state width at 10600nm becomes increasingly narrow, but the minimum reflectivity remains unchanged; the number of reflection valleys on both sides of the defect state at 10600nm increases.

[0113] Table 4. Reflection valley position under different period numbers

[0114]

[0115] According to Tables 3 and 4, the following rules are found: N c = 2, reflection valleys appear at 4460nm and 8710nm, which also appear at N c = 4 and 6, indicating that the positions of 4460nm and 8710nm are cyclically present under even period numbers; N c = 3, reflection valleys at 8850nm and 9780nm also appear at N c = 5, indicating that with the increase of the period number, the reflection valleys at the positions of 8850nm and 9780nm cyclically appear under odd period numbers.

[0116] In summary: with the increase of the period number, the reflection valley band gap feature is intensified, the number of reflection valleys increases, and the reflection valley position has a cyclic rule.

[0117] 3. In the two structures of the comparative example, the two DBR structures are designed and calculated to realize the mid-infrared and 10.6-micron laser invisibility. The two DBR structures are Ge-Al2O3 type DBR structure and AZO-CaF2 type DBR structure.

[0118] As shown in Table 5, the two structures are compared in terms of film layer number, film layer thickness, reflectivity minimum point, reflectivity minimum value, infrared absorption rate, defect layer number, and invisibility range.

[0119] Table 5. Comparison of the two structures

[0120]

[0121] Compared with the AZO-CaF2 type DBR structure, the Ge-Al2O3 type DBR structure has smaller film layer thickness, higher reflectivity, better performance, and successfully achieves high reflectivity in the mid-infrared and low reflectivity at 10600nm.

[0122] The structures designed using aluminum-doped zinc oxide (AZO) and calcium fluoride (CaF2) yielded less than ideal results. While a trough was observed at 10600 nm, fluctuating peaks were also seen in other wavelength bands, resulting in an overall imperfect data graph. The reason for this may be related to the significant variation in refractive index of the materials with wavelength. In the infrared band, AZO exhibits a larger refractive index variation with wavelength compared to the other three materials, such as… Figure 18 As shown. Comparison Figure 19 and Figure 20 Ge-Al2O3 type photonic crystal structure has no absorption properties in the infrared band, while AZO-CaF2 type photonic crystal structure has high absorption in the infrared band. This factor affects its reflectivity in the infrared band, which does not reach the ideal value.

[0123] 4. Optimize the structure of Ge-Al2O3 type DBR

[0124] The original structure of Ge-Al2O3 type DBR, SUB|ABA1B1BA|AIR, can meet the requirements of stealth compatibility with mid- and far-infrared lasers and 10.6-micron lasers. However, there is still room for optimization in terms of reflectivity in the 3600-4800nm ​​band. Based on the fact that the reflectivity of metallic silver in the mid- and far-infrared stage is as high as 90%, this invention chooses to plate a layer of metallic silver on the innermost layer of the structure near the substrate, based on the original structure.

[0125] like Figure 21 Set the silver layer thickness to λ / n k , λ / 2n k , λ / 3n k , λ / 4n k This refers to the reflectance spectra at thicknesses of 963 nm, 482 nm, 321 nm, and 241 nm. The silver layer thickness is λ / n. k (963nm) and λ / 2n k At (482nm), a reflection valley appears at 10600nm, which meets the design requirements of this invention; the silver layer thickness is λ / 3n. k At (321nm), the reflection valley appears at 10340nm; the silver layer thickness is λ / 4n. k At (241nm), the reflection valley appears at 10064nm.

[0126] like Figure 22 Set the silver layer thickness to λ / n k , λ / 5n k , λ / 6n k , λ / 7n k , λ / 8n k ,λ / 9n k , λ / 10nk i.e. the reflectivity spectrum when the thickness of the silver layer is 963 nm, 193 nm, 160 nm, 138 nm, 120 nm, 107 nm and 96 nm. The thickness of the silver layer is λ / 5n k (193 nm), the reflection valley appears at 10983 nm, and the reflectivity is 29.1%; the thickness of the silver layer is λ / 6n k (160 nm), the reflection valley appears at 10884 nm, and the reflectivity is 9.8%; the thickness of the silver layer is λ / 7n k (138 nm), the reflection valley appears at 10825 nm, and the reflectivity is 2.6; the thickness of the silver layer is λ / 8n k (120 nm), the reflection valley appears at 10790 nm, and the reflectivity is 0.5%; the thickness of the silver layer is λ / 9n k (107 nm), the reflection valley appears at 10762 nm, and the reflectivity is 0.3%; the thickness of the silver layer is λ / 10n k (96 nm), the reflection valley appears at 10742 nm, and the reflectivity is 0.2%. The following rule can be obtained: with the decrease of the thickness of the silver layer, the position of the defect state will move in the direction of short wave, and the lowest reflectivity value will become smaller.

[0127] In summary, the thickness of the silver layer is set to λ / n k i.e. 963 nm and λ / 2n k i.e. 482 nm, the low reflection at 10600 nm can be met, but the thickness of the film layer is λ / 2n k , the mid-infrared reflectivity is low, so the thickness of the silver layer is set to λ / n k i.e. 963 nm. As shown in Figure 1, the structure diagram after plating. Figure 23

[0128] Figure 24 is the reflectivity spectrum of the DBR structure after plating a silver film of 963 nm at 3600-4600 nm. As can be seen from the figure, after plating, the slight decrease of the reflectivity at about 4000 nm is improved to 100%, and the reflectivity after 4500 nm also tends to be perfect, reaching more than 90%, but a new waveband change appears, i.e. a slight decrease at about 3700 nm, but the reflectivity is still above 95%. Through plating, the defect problem of the original structure in the mid-infrared waveband is indeed improved, and the expected result can be achieved.

[0129] According to Figure 25 ​It can be seen that high reflection band appears in the range of 8000-12000nm, except that the reflection rate decreases obviously in the range of 10400-10800nm, the reflection rate reaches more than 97% in the range of 8000-10400nm and 10800-14000nm, realizing high reflection rate required by far-infrared stealth, and having good far-infrared stealth performance. Figure 26 It can be obviously seen that in the range of 10000-10800nm, the reflection rate at 10600nm is about 7%, forming obvious reflection valley, and showing strong "spectrum hole digging" characteristics, which is consistent with the ideal.

[0130] As shown in Fig. 4, the reflection spectrum of the Ge-Al2O3-Ag type photonic crystal structure after silver film is plated on the Ge-Al2O3 type DBR structure is shown. Figure 27 Compared with the reflection rate of the DBR structure at 10600nm before and after plating, it can be seen that after the silver film is plated on the original DBR structure, the defect state position and depth at 10600nm do not change, but the width of the defect state becomes narrower, and the band gap width becomes wider, so that better stealth performance can be obtained.

[0131] Therefore, after the silver film with a thickness of 963nm is plated on the original Ge-Al2O3 type DBR structure: SUB|ABA1B1BA|AIR, the shortcomings of the original structure in the mid-infrared band are improved, and the high reflection in the far-infrared band and the low reflection at 10600nm in the laser range are not affected, and the structure after plating can perfectly meet the requirements of the present application, that is, high reflection rate is successfully achieved in the mid-infrared and far-infrared, and low reflection rate is achieved at 10600nm.

[0132] In summary, the finally selected optimized structure of the present application is the Ge-Al2O3-Ag type photonic crystal structure: SUB|Ag(963nm) / Ge(663nm) / Al2O3(3786nm) / Ge(1325nm) / Al2O3(7571nm) / Al2O3(3786nm) / Ge(663nm)|AIR, which can better meet the requirements of high reflection rate in the mid-infrared and far-infrared, and low reflection rate at 10600nm.

[0133] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An infrared and laser compatible stealth film structure based on DBR-metal, characterized in that, The membrane structure is: SUB|Ag / Ge(A) / Al2O3(B) / Ge(A1) / Al2O3(B1) / Al2O3(B) / Ge(A)|AIR, where A and A1 represent the thickness of the corresponding Ge layer, B and B1 represent the thickness of the corresponding Al2O3 layer, SUB represents the substrate layer, and AIR represents the air layer. The value of A1 is 1325 nm, and the value of B1 is 7571 nm.

2. The infrared and laser compatible stealth film structure based on DBR-metal according to claim 1, characterized in that, Value A is 663 nm; value B is 3786 nm.

3. The infrared and laser compatible stealth film structure based on DBR-metal according to claim 1, characterized in that, The Ag thickness is 96 nm-963 nm.

4. The infrared and laser compatible stealth film structure based on DBR-metal according to claim 1, characterized in that, The membrane structure is: SUB|Ag(963 nm) / Ge(663 nm) / Al2O3(3786 nm) / Ge(1325 nm) / Al2O3(7571 nm) / Al2O3(3786 nm) / Ge(663 nm)|AIR.

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