双层花瓣结构光学天线表面增强红外吸收特性研究

Study on Surface-Enhanced Infrared Absorption Characteristics of Double-Layer Petal-Structure Optical Antenna

设计了一种可用于中红外波段探测的双层花瓣结构光学天线,利用有限时域差分方法,分析了结构参数、入射光偏振方向对单层天线共振波长及尖端电场强度的影响。在优化单层结构的基础上,计算了双层天线层间距(h)介于0.1~0.8μm时,不同入射波长下上层天线尖端电场强度与入射光电场强度比值。为研究下层天线对于上层天线电场的增强机理,固定入射光波长,扩大天线层间距h (0.1~3.6μm),对有无上层天线两种结构,分析相同探测点电场强度比随h的变化。结果表明,h<1μm时,上层天线尖端电场增强主要来自于双层天线耦合增强,其中h<0.2μm时,上层天线尖端场强随着距离h的减小而降低,主要因为近场耦合导致上层天线尖端能量转移到层间;h>1μm时,上层天线尖端电场增强主要来自于下层天线反射光的干涉增强。

A double-layer petal-structure optical antenna for mid-infrared detection is presented in this paper. The finite-difference time-domain method is used to analyze the effects of structural parameters and polarization direction of incident light on the resonant wavelength of the antenna and intensity of the electric field at the tip of the antenna. Based on the optimization of a single-layer structure, the ratios of the intensity of the electric field at the tip of the upper antenna to the intensity of the incident light are calculated with different incident wavelengths when the gap(h) between the two antennas is 0. 1-0. 8 μm. To investigate the enhancing mechanism of the lower antenna on the electric field of the upper antenna,the variations of the electric-field intensity ratio of the same measured point with and without the upper antenna are analyzed under fixed incident wavelength and an enlarged gap h(0. 1-3. 6 μm). The results indicate that the enhancement of the electric field at the tip of the upper antenna is mainly attributed to the coupling effect of the double-layer antenna structure, with h being less than 1 μm. When h is less than 0. 2 μm, the electric-field intensity at the tip of the upper antenna reduces with decreasing h. This is because the energy at the tip of upper antenna is transferred to the interlayer region owing to near-field coupling. However, when h exceeds 1 μm, the enhancement of the electric field at the tip of the upper antenna is mainly ascribed to the interference effect of the reflected light from the lower antenna.