基于超表面的太赫兹与中长波红外高效分光器件

Metasurfaces based terahertz and mid- and long-wave infrared high-efficiency beam splitting devices

多模复合成像技术结合了不同传感器的优势,具有图像质量高、信息获取能力强、目标检测和识别能力高、对复杂环境的强适应能力、系统的稳定性和鲁棒性高等优点.其中,太赫兹和红外复合成像技术结合了太赫兹波段和红外波段的特点,具有宽频谱覆盖、高分辨率、穿透性强的优点,有广阔的应用前景.作为共口径复合成像系统的关键器件之一的太赫兹和红外波段的高效分光器目前仍然缺少,性能亟待提升.本文提出了一种结构简单、性能高效的双层金属加介质基底结构二向色超表面.作为分光器件使用,当入射角度为45°时,其在中心频率1.1 THz附近实现大于97%的透射系数,在中波红外3—5μm和长波红外8—14μm波长范围均实现大于98%的反射系数.该设计对层间结构错位、结构倒圆角、小倍率缩放等结构失配和加工误差都具有很好的鲁棒性,并且具有偏振不敏感特性.而当入射角度在0°—60°内变化时,器件依然保持优异的分光特性.基于巴比涅定理和等效电路模型,对该超表面的电磁响应特性进行理论分析,分析结果与模拟仿真结果相吻合.该研究结果证明了超表面作为分光器件应用于太赫兹与红外波段的多波长复合成像系统中的可行性,并为未来新型复合成像探测技术的研究提供了支撑.

The multi-mode composite imaging technology integrates the advantages of different sensors,and thus has the advantages of high image quality,strong information acquisition capability,high target detection and recognition ability,strong adaptability to complex environments,and high stability and robustness of the system.Among them,the terahertz and infrared composite imaging technology combines the characteristics of terahertz band and infrared band,has the advantages of wide spectrum coverage,high resolution and strong penetration,and has broad application prospects.As one of the key components of the common aperture composite imaging system,the efficient optical splitters in terahertz and infrared band are still lacking at present,and their performance needs to be improved urgently.In this paper,a kind of dichroic metasurface with a simple structure and high performance is proposed by combining simulation experiment and theoretical explanation.When used as a spectroscopic device at an incident angle of 45°,it achieves a transmission coefficient greater than 97% near the center frequency of 1.1 THz,and a reflection coefficient greater than 98%in a wavelength range of 35 μm for medium-wave infrared and 8-14 μm for long-wave infrared.The design has good robustness to structural mismatches and machining errors such as structural misalignment,structural fillet,small magnification scaling,and polarization insensitivity.When the incident angle changes in a range of0-60°,the device still maintains excellent spectral characteristics.In this paper,based on Babinet theorem and equivalent circuit model,the electromagnetic response characteristics of the metasurface are analyzed theoretically,and the analysis results are in agreement with the simulation results.The results of this study prove the feasibility of metasurface as a spectral device in the multiwavelength composite imaging system of terahertz and infrared bands,and provide support for future studying new composite imaging detection technology.In addition,the metasurface structure described in this paper has broad application prospects in many fields such as multi-band infrared stealth,laser and pump light separation in lasers,and provides a valuable reference for designing terahertz and infrared spectroscopy in various scenarios.In the following figure,for S wave and P wave at an incident angle of 45°,panel(a) shows the reflection coefficients varying with the wavelength of metasurface and panel(b) displays terahertz transmission coefficient changing with frequency.