1. Department of Optoelectronic Engineering, Key Laboratory of Optoelectronic Technology and Systems Ministry of Education, Chongqing University, Chongqing 400044, P. R. China
2. Chongqing Key Laboratory of Laser Control & Precision Measurement, Chongqing University, Chongqing 400044, P. R. China
3. College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China