Observation of small group velocity in two-dimensional AlGaAs-based photonic crystal slabs

The characteristics of the small group velocity ${\nu }_g$ were experimentally studied with special concern to a flat band in AlGaAs-based two-dimensional photonic crystal slabs by using a time-of-flight method of a 200 fs light pulse. Two kinds of triangular air-rod samples, i.e., a deeply perforated waveguide and a perforated membrane suspended in air were used. For the former with the numbers of rod’s row N of 10, ${\nu }_g$ was found to vary from $0.17\times c$ at a wavelength far from the band edge to $0.03\times c$ at the edge; c is the light velocity in vacuum. For the latter with N of 26, ${\nu }_g$ was observed to be in a range of $(0.05\mathrm{}–0.07)\times c.\mathrm{}$ The significance of the result is discussed.