1. Department of Electrical & Computer Engineering, The George Washington University, 800 22nd Street NW 5000 Science & Engineering Hall, Washington, D.C. 20052, United States
2. Physikalisches Institut, Universität Bonn, Nussallee 12, 53115 Bonn, Germany
3. Center for Nano Optics, University of Southern Denmark, DK-5230 Odense M, Denmark
4. Florida Semiconductor Institute, University of Florida, Gainesville, Florida 32603, United States
5. Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida 32603, United States