Positive–negative birefraction phenomenon for TM polarization in annular photoni

We propose a two-dimensional (2D) annular photonic crystal (APC) with dual equi-frequency contours (EFCs) in one band. The refractive behaviors of a Gaussian beam incident from air to the APC are analyzed by the EFC analysis and finite-difference time-domain (FDTD) method. The results show the posit