1. Department of Electronic Engineering, Dalian Neusoft University of Information, Dalian 116024, People's Republic of China
2. School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, People's Republic of China
3. The Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian University of Technology, Dalian 116024, People's Republic of China