Swamping of circular Bragg phenomenon and shaping of videopulses
  We studied the durations and average speeds of videopulses transmitted through chiral sculptured thin films using a finite-difference algorithm. The chiral STF was either linear or possessed an intensity-dependent permittivity. Videopulse durations tended to decrease with increasing carrier wavelength and to increase, for given carrier wavelength and polarization state, when the chiral STF was nonlinear with intensity-dependent permittivity. The rate of decrease in durations with wavelength was less than that for longer-duration pulses. The effect of the circular Bragg phenomenon was swamped by the wide bandwidth possessed by videopulses. Two measures of videopulse average speed did not change much with carrier wavelength, and decreased slightly, for a given carrier wavelength and polarization state, in the nonlinear case. The other measure of average speed tended to increase with increasing carrier wavelength, and decrease, for a given carrier wavelength and polarization state, in the nonlinear case. 
Joseph B. Geddes III and Akhlesh Lakhtakia