1. University of Oulu, Optoelectronics and Measurement Techniques Laboratory, P.O. Box 4500, 90014 Oulu, Finland
2. National Yang-Ming University, Biophotonics and Molecular Imaging Research Center (BMIRC), Taipei 11221, TaiwancNational Dong-Hwa University, Department of Physics, Hualien 97401, Taiwan