1. Laboratory for Optical Physics and Engineering, Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, USA
2. N. Holonyak, Jr. Micro and Nanotechnology Laboratory, University of Illinois, Urbana, Illinois 61801, USA
3. Cygnus Photonics, 60 Hazelwood Drive, Champaign, Illinois 61820, USA
4. Institute for Bioproducts and Paper Technology, Graz University of Technology, Inffeldgasse 23, 8010 Graz, Austria