1. School of Sciences, Harbin Institute of Technology (Shenzhen), University Town, Shenzhen, Guangdong 518055, P. R. China
2. State Key Laboratory on Tunable Laser Technology, Ministry of Industry and Information Technology Key Laboratory of Micro-Nano Optoelectronic Information System, Harbin Institute of Technology (Shenzhen), University Town, Shenzhen, Guangdong 518055, P. R. China