1. Centre for Optical and Electromagnetic Research, Academy of Advanced Optoelectronics, South China Normal University; Guangzhou 510006 China
2. Guangdong Peizheng College; Guangzhou 510830 China
3. Samsung Mobile R&D Center-Guangzhou; Guangzhou 510663 China
4. Department of Electromagnetic Engineering; Royal Institute of Technology; Stockholm S-100 44 Sweden