1. Hunan University, Key Laboratory for Micro-/Nano- Optoelectronic Devices of Ministry of Education, School of Physics and Electronics, Changsha 410082, China
2. Hunan University, Key Laboratory for Micro-/Nano- Optoelectronic Devices of Ministry of Education, School of Physics and Electronics, Changsha 410082, ChinabUniversity at Buffalo, The State University of New York, Institute for Lasers, Photonics and Bioph