1. Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan
2. Department of Photonics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
3. Chunghwa Telecom Company, Ltd., Taoyuan city, Taiwan
4. Department of Electrical and Computer Engineering, Princeton School of Engineering and Applied Science, New Jersey, NJ, USA