二维正方晶格光子晶体平板的近场成像特性

Near-Field Imaging Properties of Two-Dimensional Square-Lattice Photonic Crystal Slabs

光子晶体是由两种或两种以上不同介电函数的材料周期性排列组成的一种人工晶体。由于介电函数的周期性分布对入射光的调制作用,使得特定频率区域的入射光在光子晶体中传播时的群速度方向和相速度方向相反,因而使得光子晶体平板表现出负折射特性。系统研究了介质柱的形状对二维正方晶格光子晶体近场成像特性的影响。通过对分别由正方形、三角形、椭圆形、长方形等形状介质柱组成的二维正方晶格光子晶体平板近场成像特性的理论分析,发现当介质柱形状的对称性降低到一定程度后可以实现光子晶体近场成像的纵向平移。进一步通过对相应等频率曲线形状的分析,明确了光子晶体近场成像是由于自准直效应和负折射效应的共同作用形成的。

Photonic crystals are man-made crystals consisting of two or more kinds of different dielectric materials arrayed periodically. Because of the collective modulation of the periodic dielectric distribution to the incident electromagnetic waves, the directions of the group velocity and the phase velocity can be opposite, a photonic crystal slab can work as a negative refractive-index material. In the letter we study the influence of the dielectric shape on the negative refraction and near-field imaging of the photonic crystal slab. By the analysis of near-field imaging properties of the two-dimensional square-lattice photonic crystals consisting of circular, square, triangular, elliptical and rectangular rods, respectively, we find that the image spot moves laterally with respective to the rectangular slab when the symmetry of the rods reduces for a certain degree. With the systemic analysis of the equifrequency-surface contours, we find that an excellent-quality near-field image of the photonic crystal slab can be formed mainly by the self-collimation and the negative-refraction effects.