Dispersion properties of photonic crystal waveguides with a low in-plane index contrast

We investigate dispersion properties of photonic crystal waveguides in a low-index material system. The modes above the light line, of a waveguide consisting of one row of missing holes (W1), exhibit high losses due to out-of-plane radiation. In contrast, the index-guided modes below the light line show moderate losses and we demonstrate both theoretically and experimentally that high dispersion is possible. Furthermore we investigate wider defect waveguides operated within the photonic band gap, where a mini-stopband with a very large suppression of transmission was found. The dispersion properties of these waveguides are discussed.