1. Key Laboratory of Optoelectronic Technology and Systems of the Education Ministry of China, College of Optoelectronic Engineering, Chongqing University 1 , Chongqing 400044, China
2. School of Electromechannical and Automotive Engineering, Yantai University 2 , Yantai 264000, China
3. School of Energy and Power Engineering, Chongqing University 3 , Chongqing 400044, China
4. School of Optoelectronic Engineering, Chongqing University of Posts and Telecommunications 4 , Chongqing 400065, China