Slow light propagation in photonic crystal waveguides with ring-shaped holes

We use a single-defect photonic crystal waveguide with ring-shaped holes to achieve a small group velocity with relatively low group velocity dispersion. We show theoretically that a group index larger than 20 with a nearly constant group velocity dispersion parameter of 4.2 ps nm(-1) mm(-1) over a wavelength range of 5 nm can be achieved. We manufactured a photonic crystal waveguide with ring-shaped holes onto silicon-on-insulator substrate. From the Fabry-Perot oscillations in the transmission spectrum, we deduced the group index in the waveguides as a function of the wavelength. We recorded group index values as large as 22.