CN116953831A - An infrared and laser compatible stealth film structure based on DBR-metal - Google Patents

Abstract

This application relates to the technical field of optical selective reflection structures, specifically an infrared and laser-compatible stealth film structure based on DBR-metal. Its specific structure is a Ge-Al ₂ O ₃ -Ag type structure. The invention is based on distributed Bragg The working mechanism of the reflector (DBR) is used to design the photonic crystal film layer, so that the thin film structure with stealth function can achieve high reflectivity in the mid-far infrared and low reflectivity in the 10.6 micron band. The final film structure is obtained It can better achieve high reflectivity in the mid-far infrared, and achieves "spectral hole digging" low reflectivity at 10600nm, which can perfectly realize the stealth performance of mid-far infrared and 10600nm laser compatibility.

Description

An infrared and laser compatible stealth film structure based on DBR-metal

Technical field

This application relates to the technical field of optical selective reflection structures, specifically an infrared and laser compatible stealth film structure based on DBR-metal.

Background technique

As detection technology develops in the direction of multi-band composite detection, detected targets face dual threats or even multiple threats from infrared detection and laser detection. Single-band stealth technology can no longer adapt to its survival. In order to reduce the risk of targets being discovered by detectors, Probability, further research is needed on how to achieve compatible stealth performance in a multi-band environment.

(1) Infrared detection equipment is used to identify and track targets. 3 to 5 microns and 7 to 14 microns are the actual working bands of infrared detectors, that is, the mid-to-far infrared band. It is discovered by accepting the energy radiated by the target itself. Therefore, infrared stealth materials need to have high reflectivity to reduce surface radiation and achieve stealth; (2) The laser detector determines the target location based on the high reflectivity of the target, such as using CO with a wide operating wavelength of 10.6 microns. ₂ lasers. The principle of laser stealth is to reduce the target's reflection signal of the laser, absorb or diffract the electromagnetic waves from the target, so that the target's reflected wave is not received by the laser detector, thereby giving the target low detectability. The most fundamental requirement for laser stealth materials is to maintain low reflectivity within the laser working range.

In order to achieve both goals at the same time, on the one hand, it is necessary to ensure its high reflectivity in the mid-to-far infrared band, and on the other hand, it is necessary to maintain its low reflectivity at a specific laser wavelength, that is, 10.6 microns. Infrared stealth materials are usually Coating materials and laser stealth materials are divided into coating types and structural types. It is difficult for these materials in the conventional sense to meet the requirements of compatibility with both at the same time.

Distributed Bragg reflectors (DBRs) are mirrors used in waveguides and optical fibers that have extremely low losses at optical and infrared frequencies compared to ordinary metal mirrors. Its structure is formed from periodic thin layers of material alternating between high and low refractive index, with the first and last layers chosen to have a high refractive index. Therefore, how to design the photonic crystal film layer based on the working mechanism of distributed Bragg reflector (DBR), so that the thin film structure with stealth function can achieve high reflectivity in the mid-to-far infrared and low reflectivity in the 10.6 micron band. problems that need to be solved urgently in the field.

Contents of the invention

In order to solve the technical problem of preparing a reflective material that has high reflectivity in the mid-to-far infrared and low laser reflectivity in the 10.6 micron band, the present invention provides an infrared and laser-compatible stealth film structure based on DBR-metal.

In order to solve the above technical problems, the technical solution adopted by the present invention is: an infrared and laser compatible stealth film structure based on DBR-metal, which is a Ge-Al ₂ O ₃ -Ag type structure.

Specifically, an infrared and laser compatible stealth film structure based on DBR-metal has the structure: SUB|Ag/Ge(A)/Al ₂ O ₃ (B)/Ge(A ₁ )/Al ₂ O ₃ ( B ₁ )/Al ₂ O ₃ (B)/Ge(A)|AIR, this structure better meets the requirements of the present invention and perfectly realizes the stealth performance compatible with mid-far infrared and 10600nm laser.

The Ag thickness is 96nm-963nm.

Further, A and A ₁ can take values of 663nm and 1325nm respectively; B and B ₁ can take values of 3786nm and 7571nm respectively.

The optimized structure is SUB|Ag(963nm)/Ge(663nm)/Al ₂ O ₃ (3786nm)/Ge(1325nm)/Al ₂ O ₃ (7571nm)/Al ₂ O ₃ (3786nm)/Ge(663nm)| AIR.

This structure better meets the requirements of the present invention and perfectly realizes the stealth performance compatible with mid-far infrared and 10600nm laser.

This invention is based on the principle of distributed Bragg reflector (DBR) and uses COMSOL software for modeling and simulation. The model consists of a single domain of a substrate with a refractive index n _s = 1.5, the center wavelength is set to 10600 nm, and the incident wave is a plane wave. Outside the modeling domain is air with a refractive index n _a =1.0. A number of dielectric film features were added to represent alternating layers under the default material discontinuity boundary conditions at the substrate surface.

Based on a larger refractive index ratio, a wider photonic band gap can be obtained. Using a high refractive index ratio dielectric layer to form a DBR not only broadens the absorption spectrum, but also obtains high reflectivity. Two DBR structures are designed, among which, DBR-1 is composed of Ge and Al ₂ O ₃ , and DBR-2 is composed of AZO and CaF ₂ . Ge and AZO serve as high refractive index dielectric layers, and Al ₂ O ₃ and CaF ₂ serve as low refractive index dielectric layers. At a wavelength of 10600nm, in the DBR-1 structure, the refractive index of Ge is Al ₂ O ₃ refractive index In the DBR-2 structure, the refractive index of AZO/> The refractive index of CaF ₂

The DBR-1: Ge-Al ₂ O ₃ type DBR structure designed by the technical solution of the present invention is: SUB|ABA ₁ B ₁ BA|AIR, as shown in Figure 1(a), including a total of six layers of films, of which SUB is the base , AIR is air, A and A ₁ represent the thickness of the Ge layer, and B and B ₁ represent the thickness of Al ₂ O ₃ . The thickness of A is 663nm, that is The thickness of A ₁ is 1325nm, that is/> The thickness of B is 3786nm, that is/> The thickness of B ₁ is 7571nm, that is/>

The technical solution of the present invention is to design DBR-2: AZO-CaF ₂ type DBR structure: SUB|ABB ₁ A ₁ BA|AIR, as shown in Figure 1(b), which contains a total of six layers of films, in which SUB is the base and AIR is Air, A and A ₁ are AZO (aluminum-doped zinc oxide), and the thickness of A is That is 676nm. The thickness of A ₁ is/> That is 1352nm. B is a low refractive index material CaF ₂ , and the thickness of B is That is 4140nm. The thickness of B ₁ is/> That is 8281nm.

The present invention is based on the distributed Bragg principle (DBR) and designs two structures, namely the Ge-Al ₂ O ₃ type DBR structure and the AZO-CaF ₂ type DBR structure. Both are one-dimensional defects containing defects in the mid-far infrared band. DBR structural model of metal photonic crystal thin films.

The structure of Ge-Al ₂ O ₃ type DBR is: SUB|Ge(663nm)/Al ₂ O ₃ (3786nm)/Ge(1325nm)/Al ₂ O ₃ (7571nm)/Al ₂ O ₃ (3786nm)/Ge(663nm )|AIR, which successfully achieves high reflectivity in the mid-to-far infrared band and achieves "spectral hole digging" low reflectivity at 10600nm. In terms of the defect layer, when the thickness of the defect layer increases, the reflection valleys in the reflectance spectrum increase and the width of the defect state becomes narrower. In terms of period number, changing the period number changes the number of reflection valleys. As the period number increases, the reflection valley band gap characteristics intensify.

The structure of AZO-CaF ₂ type DBR is: SUB|AZO(676nm)/CaF ₂ (4140nm)/CaF ₂ (8281nm)/AZO(1352nm)/CaF ₂ (4140nm)/AZO(676nm)|AIR, which is in the mid-far infrared The band reaches high reflection and reaches low reflection at 10600nm. As for the defective layer, the thickness of the defective layer is reduced, and low reflection will not occur at 10600nm. As the thickness of the defect layer increases, the number of reflection valleys increases. The low reflection at 10600 nm remains unchanged and the reflectivity is 4%, but the width of the defect state becomes narrower here. The influence of periodicity, changing the period number, changes the number of reflection valleys. As the period number increases, the reflection valley band gap characteristics intensify.

By comparing and optimizing the above two structures, the Ge-type DBR structure was selected to be better, and its structure was further optimized. The optimization plan was based on the original structure, and a layer of metal was plated on the innermost layer of the structure close to the base. Silver, with a thickness of 963nm, improves the low reflectivity at 3600-4600nm to more than 90%, and does not affect the high reflection in the far infrared band and the low reflection in the 10600nm laser range, which better achieves the purpose of optimization. .

In summary, compared with the prior art, the present invention has the following beneficial effects: The Ge-Al ₂ O ₃ -Ag type DBR structure of the present invention: SUB|Ag (963nm)/Ge (663nm)/Al ₂ O ₃ (3786nm) /Ge(1325nm)/Al ₂ O ₃ (7571nm)/Al ₂ O ₃ (3786nm)/Ge(663nm)|AIR, this structure can better achieve high reflectivity in the mid-far infrared, and achieve "spectrum" at 10600nm Digging holes for low reflectivity.

Description of the drawings

Figure 1(a) is the structure diagram of Ge-Al ₂ O ₃ type DBR;

Figure 1(b) is the structure diagram of AZO-CaF type ₂ DBR;

Figure 2 shows the reflectance spectrum of the Ge-Al ₂ O ₃ type DBR structure at 3600-4800nm;

Figure 3 shows the reflectance spectrum of the Ge-Al ₂ O ₃ type DBR structure within 8000-12000nm;

Figure 4 shows the reflectance spectrum of the Ge-Al ₂ O ₃ type DBR structure within 10200-10800nm;

Figure 5 is the reflectance spectrum chart when the thickness of the defective layer _A1 decreases;

Figure 6 shows the reflectance spectrum chart of the defective layer _A1 when the thickness of the layer increases;

Figure 7(a) shows the reflectance spectrum when the thickness of the defective layer _B1 decreases;

Figure 7(b) shows the reflectance spectrum when the thickness of the defective layer _B1 increases;

Figure 8 shows the reflectance spectrum within 4000-12000nm;

Figure 9(a) shows the reflectance spectrum within 4620-4780nm;

Figure 9(b) shows the reflectance spectrum within 3400-3650nm;

Figure 9(c) is the reflectance spectrum at 10600nm;

Figure 9(d) shows the reflectance spectrum within 9600-11500nm;

Figure 9(e) shows the reflectance spectrum within 7700-7880nm;

Figure 10 shows the internal reflectance spectrum of AZO-CaF type ₂ DBR structure at 3600-4800nm;

Figure 11 shows the internal reflectance spectrum of the AZO-CaF ₂ type DBR structure at 8000-13000nm;

Figure 12 shows the internal reflectance spectrum of AZO-CaF type ₂ DBR structure at 9400-11600nm;

Figure 13(a) shows the reflectance spectrum when the thickness of defective layer _A1 decreases;

Figure 13(b) shows the reflectance spectrum when the thickness of the defective layer _A1 increases;

Figure 14 is the reflectance spectrum chart when the thickness of the defective layer _B1 decreases;

Figure 15 is the reflectance spectrum chart when the thickness of defective layer _B1 increases;

Figure 16 shows the reflectance spectrum within 4000-12000nm;

Figure 17(a) shows the reflectance spectrum within 8600-11800nm;

Figure 17(b) shows the reflectance spectrum within 3500-4000nm;

Figure 17(c) is the reflectance spectrum at 10600nm;

Figure 18 shows the refractive index data of four materials;

Figure 19 is the absorption diagram of AZO-CaF type ₂ DBR structure;

Figure 20 is the absorption diagram of the Ge-Al ₂ O ₃ type DBR structure;

Figure 21 shows the reflectance spectra when the thickness of the silver film is λ/n _k , λ/2n _k , λ/3n _k , and λ/4n _k ;

Figure 22 shows the reflectance spectra when the thickness of the silver film is λ/n _k , λ/5n _k , λ/6n _k , λ/7n _k , λ/8n _k , λ/9n _k , and λ/10n _k ;

Figure 23 is a schematic diagram of the DBR structure after silver plating;

Figure 24 shows the reflectance spectrum of the DBR structure at 3600-4600nm after silver plating;

Figure 25 shows the reflectance spectrum of the DBR structure after silver plating at 8000-12000nm;

Figure 26 shows the reflectance spectrum of the DBR structure after silver plating at 10000-10800nm;

Figure 27 is a comparison of the reflectance spectra of the DBR structure at 10600nm before and after coating.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not All embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

Embodiment 1. An infrared and laser compatible stealth film structure based on DBR-metal. The structure is: SUB|Ag/Ge(663nm)/Al ₂ O ₃ (3786nm)/Al ₂ O ₃ (7571nm)/Ge( 1325nm)/Al ₂ O ₃ (3786nm)/Ge (663nm)|AIR. Among them, SUB represents the basal layer and AIR represents the air layer. Ge and Al ₂ O ₃ represent the Ge layer and the Al ₂ O ₃ layer, and the following brackets represent the thickness of each layer. The film structure of this embodiment is obtained by alternately superimposing Ge layers and Al ₂ O ₃ layers.

The thickness of the Ag film is 963nm, and the structure is: SUB|Ge(663nm)/Al ₂ O ₃ (3786nm)/Al ₂ O ₃ (7571nm)/Ge(1325nm)/Al ₂ O ₃ (3786nm)/Ge(663nm) /Ag(963nm)|AIR.

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

Research and result analysis on structural performance of 1Ge-Al ₂ O ₃ type DBR

Research on the stealth performance of 1.1Ge-Al ₂ O ₃ type DBR structure

As shown in Figures 2, 3, and 4, they are the reflectance spectra of the Ge-Al ₂ O ₃ type DBR structure in the mid-to-far infrared range.

As can be seen from Figure 2, in the range of 3600-4500nm, the overall reflection state is high. Except for the 3900-4000nm band range, where the reflectivity drops to 98%, the rest of the reflectivity is 100%. The reflectance begins to show a downward trend after 4500nm. In the 4500-4800nm band, the decrease in reflectivity is relatively gentle. At 4800nm, the reflectivity drops to 88%. After 4800nm, the reflectivity decreases rapidly, and the trend is more severe until 5000nm. The reflectivity drops below 40% and the reflectivity value is low. However, the overall average reflectivity in the 3600-4800nm band reaches the requirement of high reflection, which can achieve mid-infrared stealth performance.

According to Figure 3, it can be seen that a high reflection band appears in the 8000-14000nm range. In addition to an obvious downward trend in the 10400-10800nm range, the reflectivity reaches 100% in the two bands of 8000-10400nm and 10800-14000nm. It achieves the high reflectivity required for far-infrared stealth and has better far-infrared stealth performance. At the same time, it can be clearly seen from Figure 4 that in the range of 10400-10800nm, the reflectance at 10600nm of the reflection spectrum is about 7%, forming an obvious reflection valley, showing a strong "spectral digging" characteristic, which is consistent with the ideal .

It can be seen from the above that the Ge-Al ₂ O ₃ type DBR structure designed in this embodiment can well achieve mid-far infrared and 10600 nm laser compatible stealth.

1.2 Effect of defect layer thickness on Ge-Al ₂ O ₃ type DBR structure

The Ge-Al ₂ O ₃ type DBR structure designed by the present invention is: SUB|ABA ₁ B ₁ BA|AIR.

If the defective layer is only located in the Ge layer, the structure at this time is recorded as: SUB|ABA ₁ BA|AIR. As shown in Figure 5, 6 is the thickness of layer _A1 given by Become/> The reflectance spectrum diagram.

As shown in Figure 5, the thickness of layer _A1 is given by Reduced to/> From the reflectivity diagram, it can be seen that when the thickness of the _A1 layer is reduced, low reflection will not appear at 10600nm.

As shown in Figure 6, the thickness of layer _A1 is given by sequentially increases to/> time reflectivity diagram, as can be seen from Figure 6, compared with the thickness of the defect layer/> The reflectance diagram when , the thickness of defective layer A ₁ increases to/> When , the width of the defect state at 10600nm becomes narrower. The thickness of defective layer A ₁ increases to/> When , the width of the defect state at 10600 nm narrowed and a new defect state appeared at 8565 nm, where the reflectance was 13.5%.

If the defect layer is located in the Al ₂ O ₃ layer: the structure at this time is recorded as: SUB|ABB ₁ BA|AIR. As shown in Figure 7, the thickness of layer _B1 is given by Become/> reflectivity map. As shown in Figure 7(a), the thickness of layer _B1 is given by/> Reduce to/> The reflectance spectrum chart shows that when the thickness of _B1 layer is reduced, low reflection will not appear at 10600nm. The thickness of B ₁ layer is given by/> Reduce to/> When, low reflection appears at 8966nm. The thickness of B ₁ layer is given by/> Reduce to/> When, low reflection appears at 8154nm.

As shown in Figure 7(b), the thickness of layer _B1 Increase to/> Time reflectance spectrum diagram, it can be seen from the figure that when the thickness of _B1 layer increases, the reflection valley increases. The width of the defect state becomes narrower. When the thickness of layer _B1 is given by/> Increase to/> When , there are two reflection valleys, located at 10600nm and 8055nm respectively, and the width of the reflection valley becomes narrower at 10600nm, and the reflectance at 8055nm is 7.2%. When the thickness of layer _B1 is given by/> Increase to/> When , there are two reflection valleys, located at 10600nm and 8877nm respectively, and the width of the reflection valley becomes narrower at 10600nm, and the reflectance at 8877nm is 7.8%.

1.3 Effect of cycle number on Ge-Al ₂ O ₃ type DBR structure

The structure of Ge-Al ₂ O ₃ type DBR is: SUB|ABA ₁ B ₁ BA|AIR. Change the period so that the period N _c =1, 2, 3, 4, 5. The reflectance spectrum in the band 4000-12000nm is obtained as shown in Figure 8.

Table 1. Reflection valley situation table under different period numbers

Figures 9(a) to 9(e) show the reflectance spectra of each band. It can be seen that when the period number is changed, as the period number increases, the reflection valley band gap characteristics intensify, and the increase in the number of reflection valleys is mainly concentrated at 3000nm. -5000nm, 9800nm-12000nm two bands. The specific performance is that the width of the defect state at 10600nm becomes narrower and narrower, but the minimum reflectance remains unchanged; the number of reflection valleys on both sides of the defect state at 10600nm increases.

Table 2. Reflection valley positions under different period numbers

Combining Tables 1 and 2, we can find the rules: when N _c =1, the reflection valley appears at 3531nm. When N _c =2, 3, 4, and 5, the reflection valley also appears at this position; when N _c =2 , a reflection valley appears at 3154 nm. Similarly, when N _c =2, 3, 4, and 5, a reflection valley also exists at this position. Under this period number, the two reflection valley positions of 4702 nm and 11261 nm also appear at the same time when N _c = 4 and 6, indicating that the two positions of 4702 nm and 11261 nm appear cyclically under even period numbers; N _c = At 3, the reflection valley at 3531 nm also appears at N _c = 4 and 5. At the same time, the 4007nm position that appears simultaneously when N _c = 3 also appears at the same time when N _c = 5, indicating that as the number of cycles increases, under odd number of cycles, the 4007nm reflection valley appears cyclically;

To sum up: as the number of cycles increases, the band gap characteristics of the reflection valleys intensify, the number of reflection valleys increases, and there is a cyclic pattern in the positions of the reflection valleys.

Comparative Example 2. A film structure with infrared and laser compatible stealth performance based on DBR-metal. The structure is: SUB|AZO(676nm)/CaF ₂ (4140nm)/CaF ₂ (8281nm)/AZO(1352nm)/CaF ₂ (4140nm)/AZO(676nm)|AIR.

Performance research and result analysis of 2AZO-CaF type ₂ DBR structure

2.1 Research on the Stealth Performance of AZO-CaF Type ₂ DBR Structure

Figures 10, 11, and 12 show the reflectance spectra of AZO and CaF ₂ -type DBR structures in the mid- and far-infrared range.

As shown in Figure 10, it is the internal reflectance spectrum of AZO and CaF ₂ type DBR structure at 3600-4800nm. It can be seen that within 3600-4500nm, it basically shows a high reflection state, with some small fluctuations, up and down, but the overall reflectivity is the same. Above 50%, after 4500nm, the reflectivity gradually decreases as the wavelength increases, finally reaching zero. Overall, the mid-infrared band achieves high reflection requirements and can achieve mid-infrared stealth performance.

According to Figure 11, it can be seen that the reflectivity of AZO and CaF ₂ type DBR structures within 8000-13000nm. In this band, the overall reflectivity is at least about 60% and can reach up to 100%, achieving the high required for far-infrared stealth. Reflectivity, good far-infrared stealth performance.

At the same time, it can be seen from Figure 12 that the reflectance spectrum at 10600nm has a reflectivity of about 4%, forming an obvious reflection valley, realizing a "spectral hole digging" structure. As a common laser wavelength, low reflection at 10600nm can be effectively achieved The purpose of laser stealth.

In summary, the AZO-CaF ₂ type DBR structure can achieve the purpose of laser stealth in the mid-far infrared and 10600nm.

2.2 Effect of defect layer thickness on AZO-CaF type ₂ DBR structure

The structure of the AZO-CaF ₂ type six-layer DBR designed by the present invention is: SUB|ABB ₁ A ₁ BA|AIR.

If the defective layer is only located in the AZO layer, the structure at this time is recorded as: SUB|ABA ₁ BA|AIR.

As shown in Figure 13(a)~13(b), the thickness of layer _A1 is given by Become/> When, the change diagram of reflectivity.

It can be seen from Figure 13(a) that the thickness of A ₁ layer Become/> When the thickness of the _A1 layer decreases, there will be no low reflection at 10600nm, and symmetrical reflection valleys will appear on both sides of 10600nm. The thickness of A ₁ layer is given by/> Become/> When , symmetrical reflection valleys appeared at 12480nm and 10480nm. The thickness of A ₁ layer is given by/> Become/> When , symmetrical reflection valleys appeared at 10230nm and 11860nm. The thickness of A ₁ layer is given by/> Become/> When , symmetrical reflection valleys appeared at 9780nm and 11480nm.

It can be seen from Figure 13(b) that the thickness of layer _A1 is given by Become/> When the thickness of the _A1 layer increases, the reflection valley increases in the reflectance spectrum, and the low reflectivity at 10600nm remains unchanged, with a reflectance of 4%, but the width of the defect state here becomes narrower. The thickness of A ₁ layer is given by/> Become/> When , there are three reflection valleys, the main reflection valley is 10600nm, and the remaining two are located on both sides of the main reflection valley, respectively 9230nm and 12500nm. The thickness of A ₁ layer is given by/> Become/> When , there are 4 reflection valleys, the main reflection valley is 10600nm, and the remaining three are located on both sides of the main reflection valley, which are 8250nm, 9620nm and 11800nm respectively.

If the defective layer is located in CaF ₂ layer: the structure at this time is recorded as: SUB|ABB ₁ BA|AIR.

As shown in Figure 14, the thickness of layer _B1 is given by Become/> Time reflectance spectrum diagram. Figure 15, the thickness of layer _B1 is given by/> Become/> Time reflectance spectrum diagram.

According to Figure 14, the thickness of _B1 layer is given by Become/> When the thickness of the B ₁ layer is reduced, low reflection will not appear at 10600nm.

The thickness of _B1 layer is given by Become/> When, low reflection appears at 9956nm.

The thickness of _B1 layer is given by Become/> When, low reflection appears at 9500nm.

The thickness of _B1 layer is given by Become/> When, low reflection appears at 9000nm.

According to Figure 15, the thickness of _B1 layer is given by Become/> When , the thickness of the B ₁ layer increases, the number of reflection valleys increases, the low reflection at 10600 nm remains unchanged, and the reflectivity is 4%, but the width of the defect state here becomes narrower.

The thickness of layer _B1 is When , there are two reflection valleys, located at 10600nm and 8620nm respectively.

The thickness of _B1 layer is given by Become/> When , there are 4 reflection valleys, and the main reflection valley is 10600nm. The rest are located on both sides of the main reflection valley, namely 8050nm, 9148nm and 12600nm.

The thickness of _B1 layer is given by Become/> When , there are 7 reflection valleys, the main reflection valley is 10600nm. The rest are located on both sides of the main reflection valley, namely 8000nm, 8520nm, 9118nm, 9804nm, 11538nm and 12660nm.

2.3 Effect of cycle number on AZO-CaF type ₂ DBR structure

The structure of AZO-CaF type ₂ DBR is: SUB|ABB ₁ A ₁ BA|AIR. Change the period and let Nc=1, 2, 3, 4, 5. The reflectance spectrum in the 4000-12000 nm band is obtained as shown in Figure 16.

Table 3. Reflection valley situation table under different period numbers

Figures 17(a) to 17(c) show the specific reflectance spectra of each band. It can be seen from the figure that when the period number is changed, as the period number increases, the reflection valley band gap characteristics intensify, and the increase in the number of reflection valleys is concentrated in the range of 3000nm-5000nm and 9000nm-12000nm. The specific performance is that the width of the defect state at 10600nm becomes narrower and narrower, but the minimum reflectance remains unchanged; the number of reflection valleys on both sides of the defect state at 10600nm increases.

Table 4. Reflection valley positions under different period numbers

According to Tables 3 and 4, the pattern is found: when N _c = 2, reflection valleys appear at 4460nm and 8710nm, and also appear at the same time when N _c = 4 and 6, indicating that the two positions 4460nm and 8710nm are under even period numbers. It appears cyclically; when N _c =3, the reflection valleys at 8850nm and 9780nm also appear at the same time when N _c =5, indicating that as the number of cycles increases, under odd number of cycles, the reflections at the two positions of 8850nm and 9780nm Valley cycles occur;

To sum up: as the number of cycles increases, the band gap characteristics of the reflection valleys intensify, the number of reflection valleys increases, and there is a cyclic pattern in the position of the reflection valleys.

3. Comparing the two structures in the embodiment, the present invention designs and calculates two DBR structures to achieve mid-far infrared and 10.6 micron laser stealth. They are Ge-Al ₂ O ₃ type DBR structure and AZO-CaF ₂ type DBR structure respectively.

As shown in Table 5, it is a comparative description of the two structures in terms of the number of film layers, film layer thickness, lowest point of reflectivity, lowest value of reflectivity, infrared absorption rate, number of defective layers, stealth range, etc.

Table 5. Comparison of the two structures

Combined with Table 5, comprehensive analysis shows that compared with the AZO-CaF _2- type DBR structure, the Ge-Al ₂ O _3- type DBR structure has a smaller film thickness, a higher reflectivity, can meet the requirements more perfectly, and has better performance. , successfully achieved high reflectivity in the mid- and far-infrared, and achieved "spectral hole digging" low reflectivity at 10600nm.

For structures designed using aluminum-doped zinc oxide AZO and calcium fluoride CaF ₂ , the resulting data are not ideal. Although there is a trough at 10600nm, there are also high and low peaks in other bands. The overall data The picture is not perfect. Analyzing the reason, it may be related to the fact that the refractive index of the material itself changes too much with the wavelength. The material AZO, in the infrared band, has a larger refractive index change with wavelength than the other three materials, as shown in Figure 18. Comparing Figure 19 and Figure 20, the Ge-Al ₂ O ₃ type photonic crystal structure has no absorption performance in the infrared band, while the AZO-CaF ₂ type photonic crystal structure has higher absorption in the infrared band. This factor affects its infrared performance. The band reflectivity does not reach the ideal value.

4. Optimize the Ge-Al ₂ O ₃ type DBR structure

The original structure of Ge-Al ₂ O ₃ type DBR: SUB|ABA ₁ B ₁ BA|AIR can achieve the requirements of mid-far infrared and 10.6 micron laser compatibility and stealth, but there is still room for optimization in the reflectivity of the 3600-4800nm band, based on The reflectivity of metallic silver in the mid- and far-infrared stage is as high as more than 90%. The present invention chooses to plate a layer of metallic silver on the innermost layer of the structure close to the base based on the original structure.

As shown in Figure 21, the reflectance spectrum diagram when the silver layer thickness is set to λ/n _k , λ/2n _k , λ/3n _k , λ/4n _k , that is, the thickness is 963nm, 482nm, 321nm, and 241nm. When the silver layer thickness is λ/n _k (963nm) and λ/2n _k (482nm), the reflection valley appears at 10600nm, which can meet the design requirements of the present invention; when the silver layer thickness is λ/3n _k (321nm), the reflection valley Appears at 10340nm; when the silver layer thickness is λ/4n _k (241nm), the reflection valley appears at 10064nm.

As shown in Figure 22, the thickness of the silver layer is set to λ/ _nk , λ/ _5nk , λ/ _6nk , λ/ _7nk , λ/ _8nk , λ/ _9nk , λ/ _10nk , that is, the thickness is 963nm, 193nm , reflectance spectra at 160nm, 138nm, 120nm, 107nm and 96nm. When the silver layer thickness is λ/5n _k (193nm), the reflection valley appears at 10983nm, and the reflectance is 29.1%; when the silver layer thickness is λ/6n _k (160nm), the reflection valley appears at 10884nm, At this time, the reflectance is 9.8%; when the silver layer thickness is λ/7n _k (138nm), the reflection valley appears at 10825nm, and the reflectance is 2.6; when the silver layer thickness is λ/8n _k (120nm), the reflection The reflection valley appears at 10790nm, with a reflectance of 0.5%; when the silver layer thickness is λ/9n _k (107nm), the reflection valley appears at 10762nm, with a reflectance of 0.3%; the silver layer thickness is λ/ At 10n _k (96nm), the reflection valley appears at 10742nm, and the reflectance is 0.2%. The following rules can be drawn: as the thickness of the silver layer decreases, the defect state position will move along the direction of short waves, and the minimum reflectivity value becomes smaller.

In summary, it can be concluded that when the silver layer thickness is set to λ/n _k , which is 963nm, and λ/2n _k , which is 482nm, both can meet the low reflection at 10600nm. However, when the film layer thickness is λ/2n _k , the mid-infrared reflectivity is relatively low. Low, so the selected silver layer thickness is λ/n _k , which is 963nm. Figure 23 shows a schematic diagram of the structure after coating.

Figure 24 shows the reflectance spectrum of the DBR structure at 3600-4600nm after coating with a layer of 963nm silver film. It can be seen from the figure that after coating, the original slight decrease in reflectivity around 4000nm improved to 100% at 4500nm. Finally, the reflectivity also tended to be perfect, reaching more than 90%, but there was a new band change, that is, a slight decrease around 3700nm, but the reflectivity still reached more than 95%. The original structure was indeed improved through coating. The defect problem in the infrared band can achieve the expected results.

According to Figure 25, it can be seen that a high reflection band appears in the 8000-12000nm range. In addition to an obvious downward trend in the 10400-10800nm range, the reflectivity reaches more than 97% in the two bands of 8000-10400nm and 10800-14000nm. , achieves the high reflectivity required for far-infrared stealth, and has better far-infrared stealth performance. At the same time, it can be clearly seen from Figure 26 that within the range of 10000-10800nm, the reflectance at 10600nm of the reflection spectrum is approximately 7%, forming an obvious reflection valley, showing a strong "spectral digging" characteristic, which is consistent with the ideal .

As shown in Figure 27, comparing the reflectivity of the DBR structure at 10600nm before and after coating, it can be seen that after coating the original DBR structure with a silver film, the position and depth of the defect state at 10600nm will not change, but the width of the defect state will. Narrow will widen the forbidden band width and achieve better stealth performance.

Therefore, by plating a silver film with a thickness of 963nm on the original structure of the Ge-Al ₂ O ₃ type DBR: SUB|ABA ₁ B ₁ BA|AIR, not only the shortcomings of the original structure in the mid-infrared band are better improved, but also The high reflection in the far infrared band and the low reflection in the laser range of 10600 nm have no impact. The coated structure can perfectly meet the requirements of the present invention, that is, it successfully achieves high reflectivity in the mid-far infrared and realizes "spectral mining" at 10600 nm. hole" low reflectivity.

In summary, the present invention finally selects the optimized structure, that is, the Ge-Al ₂ O ₃ -Ag type photonic crystal structure: SUB|Ag(963nm)/Ge(663nm)/Al ₂ O ₃ (3786nm)/Ge(1325nm) )/Al ₂ O ₃ (7571nm)/Al ₂ O ₃ (3786nm)/Ge (663nm)|AIR, this structure can better achieve high reflectivity in the mid-far infrared, and achieve low "spectral hole digging" at 10600nm Reflectivity.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not 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: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention. scope.

Claims (5)

1. An infrared and laser compatible stealth film system structure based on DBR-metal is characterized in that: the film system structure is Ge-Al ₂ O ₃ And an Ag layer is arranged near the basal layer in the film system structure.

2. According to claimThe DBR-metal based infrared and laser compatible stealth film system structure of claim 1, wherein the film system structure is: sub|Ag/Ge (A)/Al ₂ O ₃ (B)/Ge(A ₁ )/Al ₂ O ₃ (B ₁ )/Al ₂ O ₃ (B) Ge (A) |AIR, A and A1 represent the thickness of the corresponding Ge layer, B and B ₁ Representing corresponding Al ₂ O ₃ SUB represents the base layer and AIR represents the AIR layer.

3. The DBR-metal based infrared and laser compatible stealth film system structure of claim 2, wherein a has a value of 663nm, a ₁ The value is 1325nm; b takes on the value of 3786nm, B ₁ The value is 7571nm.

4. A DBR-metal based infrared and laser compatible stealth film system structure according to claim 2 wherein the Ag thickness is 96nm-963nm.

5. The DBR-metal based infrared and laser compatible stealth film system structure of claim 2, wherein the film system structure is: sub|Ag (963 nm)/Ge (663 nm)/Al ₂ O ₃ (3786nm)/Ge(1325nm)/Al ₂ O ₃ (7571nm)/Al ₂ O ₃ (3786nm)/Ge(663nm)|AIR。