1. School of Science Department of Optoelectronic Science Harbin Institute of Technology at Weihai Weihai 264209 P. R. China
2. Faculty of Physics and Center for Nanointegration (CENIDE) University of Duisburg‐Essen Lotharstr. 1 47057 Duisburg Germany
3. School of Marine Science and Technology Harbin Institute of Technology at Weihai Weihai Shandong 264209 P. R. China
4. Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 P. R. China
5. National Laboratory of Solid State Microstructures Nanjing University Nanjing 210093 China