[1] Tampere Univ Technol, Opt Lab, FI-33101 Tampere, Finland
[2] Univ Roma Tre, NooEL Nonlinear Opt & OptoElect Lab, IT-00146 Rome, Italy
[3] Univ Southampton, Optoelect Res Ctr, Southampton SO17 1BJ, Hants, England
[4] Case Western Reserve Univ, Dept Phys, Cleveland, OH 44106 USA
[5] CNR Nanotec, I-87036 Arcavacata Di Rende, Italy
[6] Italian Inst Technol, I-16163 Genoa, Italy
[7] CNR ISC, Inst Complex Syst, IT-00185 Rome, Italy