Investigation on slow light of nonuniform photonic crystal fiber Bragg gratings

Based on the coupled-mode theory and transmission matrix method, the influences of Gaussian apodization coefficient and linear chirp coefficient on group velocity of photonic crystal fiber Bragg gratings are demonstrated. The results indicate that the minimum value of group velocity first decreases and then increases with the increase of apodization coefficient when the ‘dc’ index change value is big enough, which means that the minimum value of group velocity can be optimized at a certain apodization coefficient. But when the ‘dc’ index change value is very small, the minimum value of group velocity increases with the increase of apodization coefficient. A good linear area of the group velocity can be obtained by linear chirp and the linear area can be broadened by increasing the absolute value of chirp coefficient.