二维空气环型光子晶体的负折射成像特性

Focusing property of two-dimensional photonic crystals with ring-shaped air holes

采用平面波展开法和时域有限差分法研究了由空气环组成的二维三角晶格光子晶体平板的负折射成像特性.研究结果表明对于外半径为0.4a,内半径0—0.13a的空气环型光子晶体,第二能带中归一化频率为0.3的电磁波可以实现有效折射率为-1的负折射成像.通过光子晶体有效折射率的计算,得到了有效折射率为-1的电磁波频率随空气环内径由0—0.2a变化的规律,并由对应等频曲线的变化解释了结构参数对光子晶体平板成像的影响.

Imaging properties of two-dimensional photonic crystal slab lens consisting of a triangular lattice of ring-shaped air holes in a high-refraction-index dielectric medium have been studied. The results calculated by the plane wave expansion method （PWE） and the finite-difference time-domain method （FDTD） show that the effective index n=-1 can be realized in this structure. A perfect image can be obtained by increasing the inner radius of ring-shaped holes from 0 to 0.13a with the outer radius 0.4a at the normalized frequency 0.3（a/λ）. Based on the result of normalized frequency with effective refraction index -1 versus inner radius of ring-shaped holes we theoretically analyzed the effects of structure parameters to equifrequency contours of respective normalized frequency and imaging properties.