1. Department of Photonics and Graduate Institute of Electro-Optical Engineering, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
2. Department of Electrical Engineering, National Central University, Taoyuan, Taiwan
3. Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan
4. Department of Photonics, Feng Chia University, Seatwen, Taichung, Taiwan
5. Philips Electronics Ltd., Shatin, Hong Kong, China