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 0.17xc at a wavelength far from the band edge to 0.03xc 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 (0.05-0.07)xc. The significance of the result is discussed.