1. Key Laboratory of Digital Medical Engineering of Hebei Province, Key Laboratory of Optoelectronic Information Materials of Hebei Province, College of Electron and Information Engineering, Hebei University, Baoding 071002, People's Republic of China
2. Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore 117576
3. Electrical and Computer Engineering Department, Southern Illinois University Carbondale, Illinois, 1230 Lincoln Drive, Carbondale, Illinois 62901, USA
4. College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210026, People's Republic of China