Band gap characteristics of anisotropic photonic crystals

The band gap characteristics of one-dimensional and two-dimensional photonic crystals made of uniaxial anisotropic materials were analyzed with a focus on the band gap characteristics as a function of optical axis orientation in the aniostropic material. For one-dimensional case, with optical axis normal to periodicity axis, the two polarization of on axis light will experience different refractive indexes and thus the degeneracy in photonic band will disappear. Theoretically we show that in some nonlinear materials, with presence of certain symmetry, the band lines correspond to two polarizations will degenerate under a high electric field. It is also shown that the gap position and size varies as the position of the optical axis varies and the range is limited by the birefringence of the anisotropic material. In two dimensional photonic crystal, we showed that, changing the position of optical axis in the propagation plane is simply change of symmetry in photonic band structure. If the position of the optical axis is varied in the transversal direction, we can open or close the band gap. The characteristic of anisotropic material, the direction dependant refractive index can be used to improve the band structure of conventional isotropic photonic crystal.