1. Institute of Electronic
Structure and Laser, Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece 71110
2. Department
of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576
3. Electronics
and Photonics Department, Institute of High Performance Computing, 1 Fusionopolis Way, Singapore 138632
4. Ames
Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, United States