1. Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
2. Department of Electrophysics, National Yang-Ming Chaio-Tung University, Hsinchu 30010, Taiwan
3. Department of Photonics, National Yang-Ming Chaio-Tung University, Hsinchu 30010, Taiwan
4. Institute of NanoEngineering and MicroSystem, National Tsing-Hua University, Hsinchu 30013, Taiwan
5. Department of Physics and Astronomy, University of California at Irvine, Irvine, California 92697, United States
6. Department of Physics, National Tsing-Hua University, Hsinchu 30013, Taiwan