1. Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30013, Taiwan
3. Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA
4. Frontier Research Center on Fundamental and Applied Science of Matters, Hsinchu 30013, Taiwan