Ultrafast active plasmonics: transmission and control of femtosecond   plasmon signals
  We report that femtosecond surface plasmon polariton pulses can propagate along a metal-dielectric waveguide and that they can be modulated on the femtosecond timescale by direct ultrafast optical excitation of the metal, thereby offering unprecedented terahertz plasmonic bandwidth - a key missing component in the development of surface plasmons as information carriers for next generation nanophotonic devices. 
K. F. MacDonald, Z. L. Samson, M. I. Stockman, and N. I. Zheludev