1. Institute of Microscale optoelectronics and College of Electronics and Information EngineeringShenzhen University Shenzhen 518060 P. R. China
2. Department of PhysicsThe Chinese University of Hong Kong Hong Kong 999077 P. R. China
3. College of Optoelectronic EngineeringShenzhen University Shenzhen 518060 P. R. China
4. Institute for Advanced StudyShenzhen University Shenzhen 518060 P. R. China
5. Department of Applied PhysicsThe Hong Kong Polytechnic University Hong Kong 999077 P. R. China