1. Unit of Measurements and Biomedical Instrumentation, Università Campus Bio-Medico di Roma, Rome, Italy
2. Physics Department, i3N, University of Aveiro, Aveiro, Portugal
3. Neurorobotics Group, Newcastle University, Newcastle Upon Tyne, U.K.
4. Photonics Micro and Nanostructures Laboratory, ENEA, Frascati, Italy