1. Measurement Technology & Instrumentation; Key Lab of Hebei Province; Institute of Electrical Engineering; Yanshan University; Hebei 066004 China
2. Centre for Disruptive Photonic Technologies; Nanyang Technological University; 21 Nanyang Link 637371 Singapore
3. Institute of Materials Research and Engineering; Agency for Science; Technology and Research (A*STAR); 3 Research Link 117602 Singapore
4. College of Information Science and Engineering; Northeastern University; Shenyang 110004 China