1. Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan
2. Department of Electrical and
Computer Engineering, University of California at Santa Barbara, Santa Barbara, California 93106, United States
3. Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan
4. Institute of Electronic Engineering, Cheng Shiu University, Kaohsiung 83347,
Taiwan