1. Department of Photonics Engineering, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
2. Center for Silicon Photonics for Optical Communication (SPOC), Technical University of Denmark, 2800 Kongens Lyngby, Denmark
3. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
4. Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
5. Center for Nano Optics and Danish Institute for Advanced Study, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
6. Center for Nanostructured Graphene (CNG), Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark