1. School of Physics and Materials Engineering, Dalian Nationalities University, Dalian, 116600 P. R. China
2. National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, Harbin, 150080, P. R. China
3. School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian, 116024, P. R. China