Extreme group index measured and calculated in 2D SOI-based photonic crystal waveguides

The paper reports on the measurement and evaluation of the group velocity (GV) dispersion in the proximity of the cutoff wavelength for the fundamental photonic bandgap mode in a 2D photonic crystal waveguide (PCW). The PCW is created by introducing a line defect in an otherwise perfect triangular lattice of air-holes in the 216-nm thick silicon layer in an SOI material. Experimental transmission spectra show a mode cut-off around 1562.5 nm for the fundamental photonic bandgap mode. In order to measure and model the group index of modes in the PCW, a time-of-flight (ToF) method is applied