Direct measurement of the group index of photonic crystal waveguides via Fourier transform spectral interferometry

The authors report a direct, single-shot measurement of the group index profile of photonic crystal waveguides, combining spectral interferometry with Fourier transform analysis. This technique’s versatility allows them to resolve subtle changes in dispersion and to quantify the “slow light” effect at the photonic crystal waveguide mode cutoff. For a waveguide 99μm long, they measure a group index up to 85, whereas for lengths of 397 and 695μm, they measure maximum values of 30 and 25, respectively. These results show the relationship between transmission characteristics and the maximum group delay observed in photonic crystals.