Polarization-independent waveguides based on the complete band gap of the two-dimensional photonic crystal slabs

Two-dimensional photonic crystal (PC) slabs exhibiting photonic band gaps (PBGs) in both TE and TM polarizations are of particular interest for a better control of light propagation and easy experimental fabrication. Through reducing the symmetry of the PC lattice, simultaneous realization of PBGs in both TE and TM polarizations within a certain frequency region can be achieved. Based on the air holes immersed in the silicon background, two kinds of two-dimensional PC slab structures are proposed. These are a honeycomb lattice of circular air holes with different sizes and larger circles, and smaller triangles alternately arranged, respectively. The light transmittances show that these two structures offer large complete band gaps. Different kinds of straight waveguides are designed, and their abilities of localizing the incident beam are studied by analysing the light transmittances and spatial field distributions, where the light energy is localized perfectly in the optimized waveguide structure. Our proposed PC slab waveguides are convenient for fabrication, and could be applied in future all-optical integrated circuits.