1. Heilbronn University, Institute for Mechatronics, Optical Engineering Lab, Max-Planck-Str. 39, Heilbronn 74081, Germany
2. Hefei University of Technology, School of Computer and Information, Tunxi Road 193, Hefei, Anhui 230009, China
3. Hefei University of Technology, Department of Instrument Science and Opto-electronics Engineering, Tunxi Road 193, Hefei, Anhui 230009, China