Collimating emission from photonic crystals based on the quasi-zero-effective-index

Abstract

Transmission of light waves at the frequency near the edge of the band gap in two-dimensional square lattice photonic crystals is studied by using the plane wave expansion method (PWM) and finite difference in time domain (FDTD) method. It is found that, directional emission from two-dimensional photonic crystals can be realized if the effective refractive index is nearly zero. Moreover, the direction of the emitting beam is independent of the orientation of the crystal lattice, but dependent on the direction of the crystal surface. This is quite different from the self-collimation phenomenon in photonic crystals.