极化控制的双波段宽带红外吸收器研究

红外吸收器在红外隐身、辐射制冷、红外探测、传感器等方面有重要的应用前景.一维光栅型吸收器由于其结构简单、易于加工的优势备受关注,然而其不足之处是频带很窄,且只对一种极化有效.本文提出了一种基于简单一维周期结构的双波段宽带吸收器,对横磁波和横电波都有效,且吸波频段随入射波的极化方式而改变.该结构的基本单元由八个梯度排列的子单元构成,每个子单元由两层金属-介质双层膜垂直层叠组成.全波仿真结果表明,在1.68—2μm波段,该结构对横磁波吸收超过90%,而对横电波吸收很小(小于6%);在3.8-3.9μm波段,该结构对横电波吸收超过90%,而对横磁波吸收很小(小于5%).另外,该结构具有宽角度吸收特性,当入射角增大到60°时仍然能够保持较高的吸收率和较宽的吸收频带.

Polarization-controlled dual-band broadband infrared absorber

As an important branch of metamaterial-based devices, metamaterial absorber (MA) has aroused great interest and made great progress in the past several years. By manipulating the magnetic resonance and the electric resonance simultaneously, the effective impedance of MA will match the free space impedance, thus resulting in a perfect absorption of incident waves. Due to the advantages of thin thickness, flexible design and tunable property, MA has been extensively studied at various frequencies, e. g. microwave frequency, THz, infrared frequency, and optical frequency. Infrared MA, having important applications in infrared stealth, infrared detection, radiative cooling, and sensors, receives more and more attention, especially for those absorbers based on easy-fabricated one-dimensional grating structure. However, such a grating-based absorber is usually workable in narrow band and effective only for transverse magnetic (TM) wave.
In this paper, a dual-band broadband absorber is proposed based on the easy-fabricated grating structure. The basic unit of the proposed absorber consists of eight gradient subunits, each of which is composed of vertically cascaded two pairs of metal-dielectric bilayers. The as-designed absorber has perfect absorption for both TM and transverse electric (TE) waves. More importantly, the absorption band is different for different polarized wave, which provides more choices and greater flexibility for application. Full-wave simulation shows that the absorption of TM wave is above 90% from 1.68 μm to 2 μm, while the absorption of TE wave is very small (no more than 6%). The absorption of TE wave is above 90% from 3.8 to 3.9 μm, while the absorption of TM wave is very small (no more than 5%). In order to reveal the working principle of the proposed absorber, the electric-field distributions of the whole structure are calculated at different frequency, which demonstrates that the broadband absorption is achieved by exciting multiple resonant coupling. Furthermore, we investigate the performance of the proposed absorber in oblique incidence, and find that the designed absorber can exhibit a good absorption within a broad incident angle ranging from 0 to 60 degrees. It is worth noting that there is an absorption fracture band in the absorption spectrum of TM waves, which is because no resonance occurs in all subunits, resulting in almost no absorption.
In conclusion, we have proposed a dual-band broadband absorber that demonstrates independent absorption of the TM waves and the waves in different bands, which has potential applications in thermal detectors and thermal emitters. The proposed scheme can be extended to microwave, THz, and even visible light band.