1. Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications Institute of Photonics Technology Jinan University Guangzhou 510632 China
2. Photonics Initiative Advanced Science Research Center City University of New York New York NY 10031 USA
3. School of Physics Nankai University Tianjin 300071 China
4. Physics Program, Graduate Center City University of New York New York NY 10016 USA