1. College of Optoelectronic Engineering, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
2. Key Laboratory of Optoelectronic Technology & Systems (Ministry of Education), College of Optoelectronic Engineering, Chongqing University, Chongqing 400044, China
3. School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China