1. Department of Electrical and Computer Engineering, University of Alberta, 9107-116 Street, Edmonton, Canada T6G 2V4
2. School of Material Science and Engineering, Jingdezhen Ceramic Institute (Xianghu Campus), Xianghu Road, Jingdezhen 333000, Jiangxi, P. R. China
3. School of Optoelectronics, Beijing Institute of Technology, No. 5 South Zhong Guan Cun Street, Beijing 100081, P. R. China