Diffractionless propagation of light in a low-index photonic-crystal film

We experimentally demonstrate diffractionless propagation of light over 12 diffraction lengths in a two-dimensional photonic crystal film made of silicon nitride (SiNx). We show that self-guided beams may propagate for transverse electric (TE) and transverse magnetic (TM) polarized light but at slightly different frequencies. Three-dimensional calculations are used to optimize the structure for low loss and narrow beam operation in this low-index photonic crystals. Experimental and theoretical results are in good agreement.