1. Department of Electronics and Nanoengineering; Aalto University; Espoo 02150 Finland
2. MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, and Shaanxi Key Laboratory of Optical Information Technology; School of Science; Northwestern Polytechnical University; Xi'an 710072 China
3. VTT Technical Research Center of Finland; Espoo 02150 Finland
4. School of Information Science and Technology; Northwest University; Xi'an 710127 China
5. Nanobiophotonic Center; State Key Lab Incubation Base of Photoelectric Technology and Functional Materials; International Cooperation Base of Photoelectric Technology and Functional Materials, and Institute of Photonics and Photon-Technology; Northwest University; Xi'an 710069 China
6. Nanophotonics Research Division; CAS Center for Excellence in Nanoscience; National Center for Nanoscience and Technology; Beijing 100190 China
7. School of Electronic Science and Engineering; Nanjing University; Nanjing 210023 China
8. QTF Centre of Excellence; Department of Applied Physics; Aalto University; FI-00076 Aalto Finland