Theoretical design and preparation of high performance MWiR notch filter
doi: 10.37188/CO.2022-0193
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摘要:
为了有效抑制4.3 μm CO2辐射对3 μm~5 μm中波红外目标信号的干扰，基于Needle随机插层优化算法，采用电子束蒸发方法，建立了石英晶振监控方式下多层超厚Ge/Al2O3薄膜生长误差的精确反演修正模型，实现了中波红外陷波滤光片的设计、精确反演与制备；同时，针对中波红外陷波滤光片存在的面型变化大的问题，采用预置基底面型方法，实现了中波红外陷波滤光片低面型调控。研究结果表明：随着镀膜时间的增加，高折射率Ge膜具有较好的生长稳定性，而低折射率Al2O3薄膜材料沉积比例因子变化高达11.9%，且呈规律性渐变趋势；所制备的中波红外陷波滤光片在4.2 μm~4.5 μm波段区间平均截止透过率小于0.3%；3.5 μm~4.05 μm及4.7 μm~5.0 μm波段的平均透过率大于95%，镀膜后的面型被有效控制在较小范围；膜层具有较好的复杂环境适应性，成功通过了GJB 2485-95中牢固性、高温、低温、湿热等环境试验考核。
Abstract:In order to effectively suppress the interference of CO2 radiation 4.3 μm on MWiR target signal with wavelength of 3 μm−5 μm, based on the Needle random intercalation optimization algorithm, an accurate inversion correction model for the growth error of multi-layer ultra-thick Ge/Al2O3 films under quartz crystal monitoring is established by the electron beam evaporation method, thus realizing the design, the accurate inversion and the accurate preparation of MWiR notch filter. In order to solve the problem that the surface profile of the MWiR notch filter changes greatly, the preset substrate surface method is used to realize the low surface profile regulation of MWiR notch filter. The results show that the high refractive index Ge film has good deposition stability with the increase of coating time, while the deposition scale factor of low refractive index Al2O3 thin film changes up to 11.9% in a regular gradual trend. For the prepared MWiR notch filter, the average cut-off transmittance is less than 0.3% in the wavelength range of 4.2 μm−4.5 μm, and the average transmittances are more than 95% in the wavelength range of 3.5 μm−4.05 μm and 4.7 μm−5.0 μm. The surface profile of the substrate after coating can be effectively controlled in a small range. The film has good adaptability to complex environment, and has successfully passed the environmental test of firmness, high temperature, low temperature and damp heat specified in GJB 2485-95.
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图 1 Ge和Al2O3薄膜折射率和消光系数变化曲线
Figure 1. Variation curves of refractive index and extinction coefficient of Ge and Al2O3 films
图 2 中波红外陷波滤光薄膜理论设计光谱曲线
Figure 2. Theoretical design spectral curve of MWiR notch filter
图 3 薄膜理论光谱透过率随入射角度的变化
Figure 3. Variation of theoretical spectral transmittance of films with incident angle
图 4 固定比例因子下，(LH)4L多层薄膜结构理论设计与实测光谱曲线
Figure 4. Theoretical design and measured spectral curves of (LH) 4L multilayer film structure under fixed scale factor
图 6 基于修正比例因子，获得的中波红外陷波滤光薄膜设计与实测光谱曲线
Figure 6. Design and measured spectral curves of MWiR notch filter film obtained based on the modified scale factor
图 7 双面镀膜后的实测透射光谱曲线
Figure 7. Measured transmission spectrum curve after double-sided coating
图 8 镀膜前(a)及镀膜后(b)表面形貌图
Figure 8. Surface morphology graphs before (a) and after (b) coating
图 9 基底无面型补偿情况下，镀膜前后的面型变化(a, b)；基底有面型补偿情况下，镀膜前后的面型变化(c, d)
Figure 9. Surface profile change before and after coating without surface profile compensation (a, b) and with surface profile compensation (c, d)
表 1 Deposition parameters of thin film
Table 1. Deposition parameters of thin film
Thin film Oxygen flow (sccm) Growth temperature (°C) Deposition rate (nm/s) Electron beam (mA) Ge − 200 0.35 250 Al2O3 20 200 0.30 320 
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