1. Department of Physics, National Sun Yay-Sen University, Kaohsiung 804, Taiwan
2. Department of Physics, Military Academy, Kaohsiung 83059, Taiwan
3. Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
4. Department of Photonics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
5. Department of Institute of Electronics, National Yang Ming Chiao Tung University, Hsinchu, 300, Taiwan