1. Graduate
Institute of Photonics and Optoelectronics and Department of Electrical
Engineering, National Taiwan University, Taipei 106, Taiwan (R.O.C.)
2. National Synchrotron
Radiation Research Center, Hsinchu 307, Taiwan (R.O.C.)
3. Department
of Optoelectronic Engineering, National Dong Hwa University, Hualien 974, Taiwan (R.O.C.)