Dual-polarization Dirac cones in a simple 2D square lattice photonic crystal.

We report on dual-polarization Dirac cones in a simple square lattice two-dimensional (2D) photonic crystal (PC) based on transmission at accidental degeneracies centered at the $k = {0}$k=0 symmetry ($ \Gamma $Γ) point. Finite difference time domain simulations are used to identify the material and geometric parameters for Dirac-like dispersion. A configuration that produces a Dirac-like point for both transverse electric and transverse magnetic polarizations at the same frequency is presented. The PC dispersion shows the expected threefold degenerate linear branch crossings at the Dirac-like point. Full-field electromagnetic wave simulations exhibit some common behaviors of devices based on Dirac-like dispersion, such as cloaking and waveguiding. The configuration works for a considerable range of the parameter space, and thus is experimentally realizable with a wide range of materials.