Experimental demonstration of wideband dispersion-compensated slow light by a chirped photonic crystal directional coupler.

We report on the fabrication and evaluation of a directional coupler consisting of two different chirped photonic crystal (PC) waveguides that can generate wideband, low dispersion slow light. The directional coupler was fabricated from a silicon-on-insulator PC slab with airhole diameter chirping. For both waveguides, we observed a group index of 60-80 near the photonic band edge and opposite dispersion characteristics. In the directional coupler, we evaluated a group index of 30-40 in a wavelength bandwidth of 32 nm. The experimental results agree with the theoretical relation between the group index and bandwidth.