Research On The Bandgap Properties Of Two-dimensional Double-layer Photonic Crystals

Photonic crystal(PC) is a new artificial dielectric material, which was proposed in the late 1980 s. It has a periodic arrangement of dielectric or metallic materials. PC has a wide use of optoelectronic applications due to two unique characters of it, i.e., bandgaps(PBG) and photon localization. It is possible to obtain integrated optical circuits with more superior integration density and performance, if the photonic devices produced by PC could replace the existing photovoltaic devices.In recent years, basic research on the theory of PCs has been analyzing, and the design of photonic crystal devices with special functions becomes the focus of research.In this context, 2D double-layer PC, which can achieve the larger PBG, and the defect mode of it are studied. The primary research and achievement are as follows:1、Using the plane wave expansion method, the PBG properties of two-dimensional double-layer PC in square lattice and hexagonal lattice are studied in this paper. Four common kinds of dielectric cylinders in air are considered, namely, elliptical, circular,rectangular and square, respectively. The results show that the maximum PBGs of four kinds of dielectric cylinder are more than 14.7%. Especially for elliptical cylinder in hexagonal lattice structure, the PBG of it reaches 27.3%.2 、 In order to further understand the PBG characteristics of two-dimensional double-layer PC with different kinds of dielectric cylinders, the variation of lattice constant, thickness of outer dielectric rings and orientation angle of dielectric cylinders are also studied. The calculation results present that the lattice constant has almost no effects on the PBG, but the PBG varies with the variation of outer dielectric ring’s thickness. Because of the adjustment of the orientation angle reduces the symmetry of the entire structure, the variation of the orientation angle ? improves the PBG greatly and the maximum PBG is 33.2%.3、The paper also studied the PBG properties of two-dimensional double-layer PC with point defect. The point defect is introduced by removing the outer dielectric ring.In square lattice structure, a defect mode exists in the PBG and it moves to the low-frequency area gradually with the increment of radius. And the variation between PBG and the refractive of defect cylinder is similar with the variation between PBG andradius. The PBG has a number of defect modes within it in hexagonal lattice structure,and the number of defect modes decreases to two with the increment of radius/refractive of defect cylinder, respectively. Among the defect modes, the first and second defect modes remain unchanged, while the third and forth defect mode move to the low-frequency area. The results also show that both in square and hexagonal lattice structure, the variation of the elliptical defect cylinder’s orientation angle can not affect the amount and location of defect modes.