1. Department of Electro-physics; National Chiao Tung University; 1001 University Road Hsinchu 30010 Taiwan
2. Green Energy & Environment Research Laboratories; Industrial Technology Research Institute; 195, Sec. 4, Chung Hsing Road Chutung Hsinchu 31040 Taiwan
3. School of Physics and Astronomy; University of Southampton; Southampton SO17 1BJ UK
4. Department of Photonic & Institute, of Electro-Optical Engineering; National Chiao Tung University; 1001 University Road Hsinchu 30010 Taiwan
5. Department of Physics; Chung Yuan University; 200 Chung Pei Road Chung Li Taoyuang 32023 Taiwan
6. School of Electronics and Computer Science; University of Southampton; SO17 1BJ Southampton UK
7. Department of Photonic Engineering; Yuan-Ze University; 135 Yuan-Tung Road Chung-Li Taoyuang 32003 Taiwan
8. Department of Electronic Engineering; Chang-Gung University; 259, Wen-Hwa 1 Road Kwei-Shan Taoyuang 33302 Taiwan
9. Cavendish Laboratory; University of Cambridge; Cambridge CB3 0HE UK
10. IESL-FORTH; PO Box 1527, 71110 Heraklion Crete Greece