作者机构:[1]Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
相关基金:Supported by the National Natural Science Foundation of China (No. 60502013) and by the National High-Tech Research and Development (863) Program of China (No. 2006AAO1Z115)Acknowledgements The authors are grateful to HUANG Zhen of Tsinghua University for his support.