High-contrast modulation of light with light by control of surface   plasmon polariton wave coupling
  We have demonstrated a new mechanism for modulating light with light by controlling the efficiency with which light is coupled into a plasmon polariton wave. An optical fluence of 15 mJ/cm^2 in the control channel is sufficient to achieve nearly a 10-fold intensity modulation of the signal beam reflected from a Glass/MgF_2/Ga structure. The mechanism depends on a nanoscale light-induced structural transformation in the gallium layer and has transient switching times of the order of a few tens of nanoseconds. It offers high modulation contrast for signals in the visible and near infrared spectral ranges. 
A. V. Krasavin, A. V. Zayats, K. F. MacDonald, N. I. Zheludev