1. Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan
2. Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Hokkaido, Japan
3. Suzhou QiangMing Optoelectronics Co. Ltd., Suzhou 215-028, Jiangsu, China