1. School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China
2. Key Laboratory of Optoelectronics Information and Technology (Ministry of Education), Tianjin 300072, China
3. School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, United States
4. Mechanics Department, School of Mechanical Engineering, Tianjin University, Tianjin 300072, China