1. Department of Photonics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
3. Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan, Taiwan
4. Industrial Technology Research Institute, 195, Sec. 4, Chung Hsing Rd., Hsinchu 31040, Taiwan